Although the incidence of total hip dislocation has decreased, it still remains a major problem particularly if recurrent. The actual incidence is around 1–2% but it has been documented as the leading cause for hip revision in the United States. In patients with recurrent hip dislocation, technical issues of leg length inequality, incorrect offset, and poor implant position should be addressed surgically and the abnormality corrected. In patients with recurrent hip dislocation, the articulation is preferably converted to a more stable articulation, with constrained sockets and dual mobility being the choices.

In my experience, dual mobility articulations remain an excellent option for recurrent hip dislocation and its use is increasing significantly. It provides improved hip stability and data have demonstrated good success with recurrent hip dislocation. However, with use of the modular variety of dual mobility which is needed for acetabular cup fixation with screw augmentation, dissimilar metals are placed in contact (titanium socket and cobalt chrome liner insert) which potentially can pose a fretting or corrosion problem in longer term outcomes. Constrained sockets of the tripolar configuration provide another option which is useful in those patients with severe abductor dysfunction or insufficiency. Constrained sockets can also be cemented into the existing shell in cases where there is a well-fixed cup and cup removal may lead to significant bone loss and a need for complex acetabular reconstruction. It is important to remember that there are two types of constrained sockets, tripolar and focal constraint. Results with the tripolar constrained socket have been significantly better than the focal constraint variety which adds a polyethylene rim piece to the liner. In a mid-term follow up (2–9 years) of 116 constrained tripolar sockets, recurrent dislocation was only 3.3%. In papers reporting on focal constrained sockets, recurrent dislocation was in the 9–29% range. There continues to be a role for constrained sockets and selection of implant type has made a difference in ultimate outcome.

Bone loss in total knee replacement has different configurations and most condylar and plateau deficits are well managed with prosthetic augmentation. Cones are rarely, if ever, necessary for these deficits and when entire femoral condyles are absent distal segmental replacement has worked well. In the setting of severe intramedullary bone loss on the tibial or femoral side cones may be used to support deficit bone. This is the one indication for the use of cones.

The negative side of cones is that additional bone may be removed to fit a cone adequately. Many of the lesser areas of bone deficiency can be managed by the use of larger diameter stems for fixation. In a paper from Sandford et al. from the Vancouver group allograft results at 5 −10 year follow up had a similar success rate to cones. Rohl in a paper looking at cones and hybrid stems for bone loss in revision TKR found no difference in results at 3.5 years.

Cones cost $4,000–6,000 each and their utilization has been increasing greatly. At Hospital for Special Surgery in 2015 18 cones were used, this has increased to over 150 in 2017 at a cost of $800,000. The overutilization of cones adds considerably to the cost of a revision procedure. Cones have a place in revision TKR for bone loss but it is limited and they should be used in the most extreme cases where bone augmentation is required for structural stability.

Although the incidence of total hip dislocation has decreased, it still remains a major problem particularly if recurrent. The actual incidence is around 1–2% but it has been documented as the leading cause for hip revision in the United States. In patients with recurrent hip dislocation, technical issues of leg length inequality, incorrect offset, and poor implant position should be addressed surgically and the abnormality corrected. In patients with recurrent hip dislocation, the articulation is preferably converted to a more stable articulation, with constrained sockets and dual mobility being the choices.

In my experience, dual mobility articulations remain an excellent option for recurrent hip dislocation and its use is increasing significantly. It provides improved hip stability and data have demonstrated good success with recurrent hip dislocation. However, with use of the modular variety of dual mobility which is needed for acetabular cup fixation with screw augmentation, dissimilar metals are placed in contact (titanium socket and cobalt chrome liner insert) which potentially can pose a fretting or corrosion problem in longer term outcomes. Constrained sockets of the tripolar configuration provide another option which is useful in those patients with severe abductor dysfunction or insufficiency. Constrained sockets can also be cemented into the existing shell in cases where there is a well-fixed cup and cup removal may lead to significant bone loss and need for complex acetabular reconstruction. It is important to remember that there are two types of constrained sockets, tripolar and focal constraint. Results with the tripolar constrained socket have been significantly better than the focal constraint variety which adds a polyethylene rim piece to the liner. In a mid-term follow up (2–9 years) of 116 constrained tripolar sockets, recurrent dislocation was only 3.3%. In papers reporting on focal constrained sockets, recurrent dislocation was in the 9–29% range. There continues to be a role for constrained sockets and selection of implant type has made a difference in ultimate outcome.

Stiffness after total knee replacement remains a significant factor in a suboptimal result after total knee arthroplasty. Interference with function including stair climbing, arising from a seated position, driving and return to activities of daily living and recreational sports are all compromised when stiffness results after knee replacement. The key indicator for resultant range of motion after knee replacement remains knee motion prior to surgery. A knee with limited motion prior to surgery will rarely achieve the same motion as a fully mobile knee and the patient should be counseled to this ultimate result. Patients with prior knee surgery, post-traumatic knee arthritis also tend to be stiffer after knee replacement. If a knee is stiff after replacement it is key to determine if there is a mechanical impediment to motion (e.g. implant sizing problem, overstuffing of the patellofemoral joint) and revision knee replacement to address this problem will be necessary and is best done when recognised.

When referring to a stiff knee after replacement flexion less than 90 degrees is generally accepted. Management of the knee with limited motion after knee replacement should first be treated with manipulation of the knee under anesthesia. Timing of manipulation is key to its success and if a patient is not progressing after 4–6 weeks manipulation is generally indicated. Manipulation can be performed up to 6–12 months after replacement but ultimate motion is negatively impacted by delay as scar tissue becomes more indurated and fixed.

Arthroscopic lysis of adhesions can be performed in the recalcitrant knee but in my experience will generally improve motion in the 10- to 15-degree range, if at all. In patients with persistent and disabling stiffness, open resection with radical scar excision can be performed and if there is not an implant sizing issue this may improve motion. It is important to rapidly mobilise these patients after surgery with early flexion to beyond 90 degrees with use of optimal analgesia to allow vigorous early motion. At time of open lysis of adhesions revision of components should be performed if there is any question of need to do this to improve range of motion.

The selection of an acetabular component for primary hip arthroplasty has narrowed significantly over the past 10 years. Although monoblock components demonstrated excellent long-term success the difficulty with insertion and failure to fully appreciate full coaptation of contact with the acetabular floor has led to almost complete elimination of its utilization. Modular acetabular components usually with titanium shells and highly crosslinked polyethylene are by far the most utilised today. This is particularly true with mid-term results demonstrating excellent wear rates and extremely low failure rates and the concern of possible mechanical failure of highly crosslinked polyethylene not being a clinical problem. Ceramic liners are also used but problems with squeaking articulations and liner chipping have made highly crosslinked polyethylene the preferred liner material. Metal-on-metal except in surface replacement arthroplasty is rarely used in primary hip arthroplasty.

With instability in total hip replacement still being a significant and the leading cause of revision hip replacement the dual mobility articulation has emerged as an increasingly used acetabular component. This is composed of either a monoblock cobalt chrome socket articulating with a large polyethylene liner into which the femoral head is constrained. The polyethylene liner becomes essentially a larger femoral head articulation and hip stability is significantly improved. A modular dual mobility can also be utilised with a titanium shell and a cobalt chrome liner inserted into the shell and then a dual mobility articulation. In a recent series of 182 dual mobility cups, all monoblock ADM, in high risk patients undergoing primary total hip replacement there was 1 interprosthetic dislocation which occurred during reduction of a dislocation. Average follow up was 4.4 years with a range of 2–6.6 years.

Instability continues to be a troublesome complication after THA and has been reported to be the main indication for revision in the United States, accounting for 22.5% of revisions. Risk factors associated with dislocation include: age of 75 years or older, body mass index (BMI) of 30 kg/m2 or greater, alcohol abuse, and neuro-degenerative diseases such as multiple sclerosis or Parkinson's disease. Dual-mobility articulations have become an increasingly popular option for these “at risk” primary THAs. Few studies have assessed their use in this complex patient population. The purpose of this study was to assess dislocation rate, radiographic outcomes and complications of the dual-mobility articulation in the setting of primary THA for patients at high risk for dislocation at a minimum follow up of 2 years.

We retrospectively reviewed 151 dual mobility acetabular components, that had been performed using a single design (ADM Stryker, Mahwah, NJ) between 2010 and 2014 at a single institution by a single surgeon. The mean age at time of index surgery was 82 years (range, 73–95), 114 patients were female, and mean BMI was 26.2 kg/m2 (range, 16.1–60.9). Dislocation rate and complications associated with dual mobility cups were reviewed, along with the radiographic outcomes after an average follow-up period of 3.6 years (range, 1.9–6.1 years).

The indication for hip replacement was osteoarthritis in all cases. We had one traumatic dislocation which required component revision after intraprosthetic dislocation following an attempt of closed reduction. There were no further dislocations in this cohort. No progressive radiolucencies or component positional changes were seen on radiographic assessment.

At short-term follow-up dual mobility provides a stable reconstruction in patients at high risk of dislocation with excellent radiographic results. Longer follow-up is needed to confirm the durability of these reconstructions.

Periprosthetic infection after total joint replacement is a catastrophic complication. Current rates of infection have been decreasing and in most centers now are in the range of 0.1–1%. Peri-operative intravenous antibiotic therapy is used routinely in total hip arthroplasty patients at this time. With rates this low and mixed evidence that antibiotics in bone cement for routine total hip replacement are beneficial at reducing joint infection, routine use of this practice seems unnecessary and has potential disadvantages. Cost of antibiotics being added to cement on a routine basis will increase the cost of the arthroplasty $300–$500. Although small addition of bone cement also has a negative effect on the mechanical properties of the cement. The major disadvantage remains the danger of resistant bacterial strains from excessive use of antibiotics particularly vancomycin resistant organisms when it is used routinely. Although rare with the aminoglycosides, allergic reactions may occur if cephalosporins are used as prophylaxis. Use of antibiotics in bone cement should be considered in high risk patients for infection undergoing total hip replacement but not routinely because of cost, emergence of resistant organism and possible allergic reaction.

Bilateral one stage total knee replacement (TKR) has a number of advantages. There is one operative procedure and anesthetic and overall recovery time is significantly reduced. It is a more cost-effective procedure in that acute hospital stay is less and although rehabilitation time is greater in the short term, overall it is less. Additionally, if there is a bilateral flexion contracture present there is an inevitable loss of extension if a single knee is operated upon as this knee will assume the position of the unoperated knee. Patients greatly prefer having both knees corrected at one operative setting rather than having to have the inconvenience and pain associated with a second operative procedure at three to six months after the first one.

There are potential disadvantages to a one stage procedure. One concern has been that there is more peri-operative morbidity associated with one stage bilateral total knee replacement. In a review of 501 patients undergoing bilateral one stage total knee replacement at the Hospital for Special Surgery (HSS) there were no peri-operative deaths, myocardial infarctions or cerebrovascular accidents. There were arrhythmias present in 5% of patients. Fat emboli were present in 3% and 2 patients (0.4%) had pulmonary emboli. The average transfusion requirement was 2.6 units and allogeneic blood was required in 42%. There were 2 deep infections, 3 hematomas and 5 patients with delayed wound healing There was an increased incidence of major complications in patients with ASA classification 3 and with increasing age over 70 years.

New data indicates peri-operative administration of hydrocortisone may mitigate lung injury as demonstrated by reduction in cytokine and desmosine levels in a randomised trial. There was also a trend toward less need for narcotic medication and better range of motion in the steroid treated group

Patient selection is important and all patients are screened pre-operatively by an internist and anesthesiologist. In over 3000 bilateral TKRs at HSS infection rate and mortality were lower than in the unilateral total knee replacement patients. Much of this is due to patient selection criteria. All patients underwent the procedure with epidural anesthesia with post-operative epidural PCA for 48 hours. All patients are discharged on warfarin and spend the operative night in the recovery room. The procedure has acceptable morbidity and great advantage in properly selected patients.

Background

Tranexamic acid (TXA) and fibrin sealants have gained widespread use in total knee arthroplasty. They can decrease bleeding, drainage volume, hematoma formation, and incidence of blood transfusion. However, they are costly and carry a theoretical risk of infection transmission and thrombosis. This study compares the two pharmacologic interventions to preoperative autologous blood donation as well as no intervention.

Instability after total hip arthroplasty is the most common indication for revision arthroplasty and can be difficult to treat. The purpose of this study is to evaluate the outcomes associated with the use of a constrained acetabular component as a treatment for instability after hip arthroplasty. We reviewed the clinical and radiographic outcomes of 149 arthroplasties, that had been performed with use of a single design of constrained acetabular component between 2007 and 2012 at a single institution. Patient demographics and case specific data were collected The Mann-Whitney U test was used to assess continuous variables. Categorical variables were examined using the Chi-square test and Fisher's exact test when appropriate. Survival probability was calculated using the Kaplan-Meier method.

The mean age at time of index surgery was 70 years, 65% were female, and mean BMI was 26.3. The average number of previous surgeries was 3.6. The constrained liner was cemented into a well-fixed cup in 40 hips (20%). In eighty-two (55%) hips the constrained component was implanted for the treatment of recurrent instability, and in sixty-seven (45%) hips it was implanted because the hips demonstrate instability during revision surgery. At an average duration of follow-up of 4.2 (2–7) years the overall revision rate was 10.6 % The constrained acetabular device eliminated or prevented hip instability in all patients except five; 3.3% had a new dislocation and six (4.0%) had failure of the retentive ring. Three revisions (2%) were performed for deep infection, and 2 (1.3%) for acetabular component loosening. Radiographic analysis revealed a non-progressive radiolucent line around the cup in 19 hips (12.7%). When stratified by patient age, survivorship for patients less than 65 years of age versus those greater than 65 years was similar.

This study correlates with results of other papers in the literature looking at outcome of constrained tripolar type sockets. The focal constraint socket with a metal ring type design has a much greater failure rate (9–29%). Constrained liners remain an excellent option for hip instability in early to mid- term follow up.

Bilateral one stage total knee replacement has a number of advantages. There is one operative procedure and anesthetic and overall recovery time is significantly reduced. It is a more cost effective procedure in that acute hospital stay is less and although rehabilitation time is greater in the short term overall it is less. Additionally if there is a bilateral flexion contracture present there is an inevitable loss of extension if a single knee is operated upon as this knee will assume the position of the unoperated knee. Patients greatly prefer having both knees corrected at one operative setting rather than having to have the inconvenience and pain associated with a second operative procedure at three to six months after the first one.

There are potential disadvantages to a one stage procedure. One concern has been that there is more peri-operative morbidity associated with one stage bilateral total knee replacement. In a review of 501 patients undergoing bilateral one stage total knee replacement at the Hospital for Special Surgery there were no peri-operative deaths, myocardial infarctions or cerebrovascular accidents. There were arrhythmias present in 5% of patients. Fat emboli were present in 3% and 2 patients (0.4%) had pulmonary emboli. The average transfusion requirement was 2.6 units and allogeneic blood was required in 42%. There were 2 deep infections, 3 hematomas and 5 patients with delayed wound healing. There was an increased incidence of major complications in patients with ASA classification 3 and with increasing age over 70 years.

New data indicates peri-operative administration of hydrocortisone my mitigate lung injury as demonstrated by reduction in cytokine and desmosine levels in a randomised trial. There was also a trend toward less need for narcotic medication and better range of motion in the steroid treated group

Patient selection is important and all patients are screened pre-operatively by an internist and anesthesiologist. In over 3000 bilateral TKR at HSS infection rate and mortality were lower than in the unilateral total knee replacement patients. Much of this has is due to patient selection criteria. All patients underwent the procedure with epidural anesthesia with post-operative epidural PCA for 48 hours. All patients are discharged on warfarin and spend the operative night in the recovery room. The procedure has acceptable morbidity and great advantage in properly selected patients.

Introduction

Successful cementless acetabular designs require sufficient initial stability between implant and bone (with interfacial motions <150 μm) and close opposition between the porous coating and the reamed bony surface of the acetabulum to obtaining bone ingrowth and secondary stability. While prior generations of cementless components showed good clinical results for long term fixation, modern designs continue to trend toward increased porosity and improved frictional characteristics to further enhance cup stability.

For most complex primary total knee replacement there is associated soft tissue and bone loss. A constrained condylar implant can be useful in improving the stability of the knee after revision. Augmentation is commonly used to deal with bone loss on the femoral and tibial side of the joint. Stems are known to reduce the load at the interface of the femoral and tibial component and transfer the load into the medullary canals. There are problems with using stems in the complex primary knee setting however, which include: (1) increased cost, (2) difficulty with removal should further revision be necessary, (3) violation of the intramedullary canals if infection occurs, (4) increased operating time. For these reasons a CCK implant was developed without stems in 1998. The use of this device must be very selective and it is primarily used for severe valgus deformity in elderly patients. In a revision setting where there is good preservation of femoral and/or tibial bone but the need for increased constraint is present (e.g. unicompartmental, cruciate retaining knee) a CCK without stems can be used with good results. We retrospectively reviewed 36 primary constrained condylar knee implants without stem extensions from 1998 to 2000 in 31 patients with knees in 15 degrees valgus or greater. All patients were followed up for a minimum 10 years (range, 10 to 12 years). One patient had aseptic loosening and needed to be revised with stemmed components at 9 years post surgery. Wear was found in two patients. One patient, with severe rheumatoid arthritis, had infection and required a two-stage re-implantation procedure. Patients who are very active or heavy body weight where stresses may be excessive at the implant bone interface should have stems utilised.

Dislocation is a particular problem after total hip replacement in femoral neck fractures and elderly, especially female, patients. The increased rate of dislocation in this population is probably due to significant ligamentous laxity in these patients and poor coordination and proprioception. Another population of patients with increased propensity for dislocation is the revision hip replacement patient. Current dislocation rates in these patients can approach 10% with conventional implant systems.

The Dual Mobility total hip system is composed of a cobalt chrome acetabular shell that has a grit blasted, beaded and/or hydroxyapatite coating to improve bone ingrowth. The polyethylene liner is highly crosslinked polyethylene and fits congruently into the cobalt chrome shell and acts like a large femoral head (usually > 40 mm). The femoral head attached to the trunnion is usually 28 mm. The femoral head snaps into the polyethylene liner to acts as a second protection against dislocation.

Indications for the Dual Mobility socket are in the high risk for dislocation patient and particularly in elderly, female patients. It is also indicated in patients with neuromuscular disease who are at more risk to dislocate. To date 237 dual mobility cups have been performed with an average age of 79 and 207 of the procedures in women. The follow up extends to 5.6 years with an average of 3.5. There has been 1 dislocation which occurred after a traumatic event. There have been no mechanical failures, no infections and no other revisions in this series. Interprosthetic dislocation has been reported in long term follow up and there was, in this series, when reduction was performed on the only liner dislocation. Pain relief has been no different than conventional hip replacement and range of motion is unchanged as well.

Osteoarthritis of the knee is commonly a disease which afflicts more than one compartment of the knee so medial compartment arthritis is almost always associated with patellofemoral and or lateral compartment disease to a lesser extent. In a review of 250 consecutive osteoarthritic knees strictly unicompartmental involvement occurred in less than 15% of affected knees. To segmentally replace one compartment when more than one is involved may lead to a suboptimal result from the compartmental replacement as well as lead to pain and failure with mid- to long-term follow up. The long term results with tricompartmental replacement continue to show success rates in the order of 90–95% at 15–20 year follow-up with multiple designs and fixation types. Additionally failure to replace the patella, although popular in Europe, has led to increased anterior knee pain in studies in North America. The disadvantage of tricompartmental knee replacement is the extent of surgical trauma compared to compartmental replacement although newer less invasive approaches may lead to similar recovery to compartmental replacement.

For most revision total knee replacement there is associated soft tissue and bone loss. A constrained condylar implant can be useful in improving the stability of the knee after revision. Augmentation is commonly used to deal with bone loss on the femoral and tibial side of the joint. Stems are known to reduce the load at the interface of the femoral and tibial component and transfer the load into the medullary canals. There are problems with using stems in the revision setting however, which include: (1) increased cost, (2) difficulty with removal should further revision be necessary, (3) violation of the intramedullary canals if infection occurs, (4) increased operating time. For these reasons a CCK implant was developed without stems in 1998. The use of this device must be very selective and it is primarily used for severe valgus deformity in elderly patients. In a revision setting where there is good preservation of femoral and/or tibial bone but the need for increased constraint is present (e.g. unicompartmental, cruciate retaining knee) a CCK without stems can be used with good results. We retrospectively reviewed 36 primary constrained condylar knee implants without stem extensions from 1998 to 2000 in 31 patients with knees in 15 degrees valgus or greater. All patients were followed up for a minimum 10 years (range, 10 to 12 years). One patient had aseptic loosening and needed to be revised with stemmed components at 9 years post-surgery. Wear was found in two patients. One patient, with severe rheumatoid arthritis, had infection and required a two-stage re-implantation procedure. Patients who are very active or heavy body weight where stresses may be excessive at the implant bone interface should have stems utilised.

There are many types and articulating surfaces in acetabular cups. Most of the designs currently available are modular, the liner snapping into a locking mechanism of some type. These modular inserts may be polyethylene, usually highly crosslinked polyethylene, or ceramic. Metal shells used in metal-on-metal devices are usually of a monoblock design.

The elliptical monoblock design has been available for 20 years and was originally made of Titanium with a compression molded polyethylene liner. Tantalum (trabecular metal) was used as the shell material in the more recent designs and the polyethylene is actually molded directly into the tantalum framework. Monoblock acetabular components have a number of advantages. They do not allow access to the ilium because there are no holes in the socket shell with the monoblock construct. They require no locking mechanism which may increase metallic debris. No back surface liner wear can occur because all motion is eliminated at the liner/shell interface. However, because of this absence of screw holes there is an inability to visualise the floor of the acetabulum and perfect coaptation between the shell and the acetabular floor may not occur. The presence of dome gaps of greater than 1.5 mm have been noted in 5% of these components but these have not compromised implant stability and in a review of over 600 cups there has been no change in implant position.

Results with over 258 monoblock cups with a minimum of 10-year follow-up (10–15 years) have been excellent. (Poultsides, et al) The incidence of pelvic osteolysis was not seen in any patient in this series. There were 3 revisions for instability but none for mechanical failure. There were 3 femoral revisions for loosening but the cup was intact and not revised in these patients. Utilizing the Livermore measurement method polyethylene wear averages 0.08 mm per year (0.06 – 0.13 mm) and there have been no revisions for wear. Radiographic evaluation demonstrates stable bony interface in all patients. At minimum 10- year follow-up the monoblock acetabular component with compression molded polyethylene confirms the theoretical advantages of this design and results have been excellent. Moen et al have demonstrated no osteolysis in CT scans in tantalum monoblock cups at a follow up of 10.3 years.

Bilateral one-stage total knee replacement has a number of advantages. There is one operative procedure and anesthetic and overall recovery time is significantly reduced. It is a more cost effective procedure in that acute hospital stay is less and although rehabilitation time is greater in the short term overall it is less. Additionally if there is a bilateral flexion contracture present there is an inevitable loss of extension if a single knee is operated upon as this knee will assume the position of the unoperated knee. Patients greatly prefer having both knees corrected at one operative setting rather than having to have the inconvenience and pain associated with a second operative procedure at three to six months after the first one.

There are potential disadvantages to a one-stage procedure. One concern has been that there is more peri-operative morbidity associated with one-stage bilateral total knee replacement. In a review of 501 patients undergoing bilateral one-stage total knee replacement at the Hospital for Special Surgery there were no peri-operative deaths, myocardial infarctions or cerebrovascular accidents. There were arrhythmias present in 5% of patients. Fat emboli were present in 3% and 2 patients (0.4%) had pulmonary emboli. The average transfusion requirement was 2.6 units and allogeneic blood was required in 42%. There were 2 deep infections, 3 hematomas and 5 patients with delayed wound healing. Average hospital stay was 7.2 days but this had decreased in the more recent patients. There was an increased incidence of major complications in patients with ASA classification 3 and with increasing age over 70 years.

New data indicates peri-operative administration of hydrocortisone may mitigate lung injury as demonstrated by reduction in cytokine and desmosine levels in a randomised trial.

Patient selection is important and all patients are screened pre-operatively by an internist and anesthesiologist. All patients underwent the procedure with epidural anesthesia with post-operative epidural PCA for 48 hours. All patients are discharged on warfarin and spend the operative night in the recovery room. The procedure has acceptable morbidity and great advantage in properly selected patients.

There are many types and articulating surfaces in acetabular cups. Most of the designs currently available are modular, the liner snapping into a locking mechanism of some type. These modular inserts may be polyethylene, usually highly crosslinked polyethylene, or ceramic. Metal shells used in metal on metal devices are usually of a monoblock design.

The elliptical monoblock design has been available for 20 years and was originally made of Titanium with a compression molded polyethylene liner. Tantalum (trabecular metal) was used as the shell material in the more recent designs and the polyethylene is actually molded directly into the tantalum framework. Monoblock acetabular components have a number of advantages. They do not allow access to the ilium because there are no holes in the socket shell with the monoblock construct. They require no locking mechanism which may increase metallic debris. No back surface liner wear can occur because all motion is eliminated at the liner/shell interface. However, because of this absence of screw holes there is an inability to visualise the floor of the acetabulum and perfect coaptation between the shell and the acetabular floor may not occur. The presence of dome gaps of greater than 1.5mm have been noted in 5% of these components but these have not compromised implant stability and in a review of over 600 cups there has been no change in implant position. The elliptical shape of the cup makes the mouth of the acetabular component 2mm greater than the dome so that an exceptionally strong acetabular rim fit results.

Results with over 258 monoblock cups with a minimum of 10-year follow up (10–15 years) have been excellent (Poultsides, et al.). The incidence of pelvic osteolysis was not seen in any patient in this series. There were 3 revisions for instability but none for mechanical failure. There were three femoral revisions for loosening but the cup was intact and not revised in these patients. Utilising the Livermore measurement method polyethylene wear averages 0.08mm per year (0.06mm-0.13mm) and there have been no revisions for wear. Radiographic evaluation demonstrates stable bony interface in all patients. At minimum 10-year follow up the monoblock acetabular component with compression molded polyethylene confirms the theoretical advantages of this design and results have been excellent. Moen et al. have demonstrated no osteolysis in CT scans in tantalum monoblock cups at a follow up of 10.3 years.

Total hip replacement can be performed through multiple surgical approaches including anterior, anterolateral, lateral, transtrochanteric, posterolateral, posterior and the two incision technique. The overwhelming majority of hip replacement surgery today is performed through a posterolateral approach and this approach certainly has many advantages. The posterolateral approach can be extended without difficulty, it is expeditious, has reduced blood loss, there is little muscle damage and recovery is rapid. The major disadvantage of the approach that has been cited is its increased dislocation rate which has become less of a problem with the advent of larger femoral heads and dual mobility acetabular components.

The less invasive posterolateral approach is performed through an incision of 8–10 centimeters and is suitable for patients with BMI index of less than 35. Deep dissection is less radical and the gluteus maximus tendon is not released and only the upper 1/4 of the quadratus femoris insertion is released. Full visualisation of the acetabulum must be accomplished with this approach and soft tissue releases of the labrum and anterior capsule must be performed to accomplish this. Similarly exposure of the entire proximal osteotomised femoral neck must be effected so that reaming and broaching can be performed safely. Special retractors have been developed to facilitate these techniques. Ongoing review of this procedure in almost 1500 patients operated on by me has yielded excellent radiographic and functional results. Complications have included a dislocation rate of 1.2%, femoral fracture 0.3% and sciatic neuropraxia of 0.3% all but one which resolved.

Rapid recovery from total hip replacement is multifactorial with current accelerated rehabilitation programs and improved pain management playing a role as well as surgical approach. The need for external support during ambulation with the mini-posterior approach rarely is greater than 3–4 weeks in the vast majority of patients. Hip precautions are used for a 4 week period. Hospital stay is 2–3 days and could be accelerated further in young, active patients.

There are many excellent approaches to the hip each of which has its advantages and disadvantages. The anterior approach is an excellent approach but requires advanced training, experience, a specialised table, longer surgical time, more difficultly with exposure with no evidence of advantage in outcome.

New technology in joint replacement design and materials adds cost which must be documented by improved outcomes. This is not always the case as the recent metal/metal data has shown. The current economics of arthroplasty surgery have put increasing financial pressure on hospitals and will progress under new health care legislation. New technology must be cost effective and this will be increasingly difficult in an era of outstanding long term results with current designs. Cost may necessitate less expensive alternatives, e.g. generic implants, in arthroplasty patients.

Joint replacement surgery has evolved over the past four decades into a highly successful surgical procedure. Earlier designs and materials which demonstrated inferior functional and long term results have disappeared in a Darwinian fashion. Through this evolutionary process many of the current designs have proven efficacy and durability. Current outcome data indicates that hip and knee designs demonstrate 90–95% success rates at 15 year follow-up. Technologic advances are necessary to improve implant design and materials, however, in an environment of reduced reimbursement to hospitals can the increase cost be justified.

The rationale that technology in medicine would be expensive at the outset yet be cost effective eventually has in many areas not been the case. Currently about one half of the rapid increase in health care costs in relation to GNP may be attributed to technology. Uwe Reinhardt, an economist at Princeton University, in referring to new technology has stated that the health care system provides misaligned incentives that create over-utilisation or misutilisation of everything that is new. It is now common knowledge among health care economists that if the cost of health care is to be controlled the growth of technology must be constrained.

Increasingly as new technology emerges the question will be: what is the cost-benefit analysis. A new era of comparative effectiveness research is being launched and will become predominant in medicine and arthroplasty surgery in the future. What is the newest may not always be the best. According to Reinhardt there is a need for comparative effectiveness studies of emerging and existing technology so that the new can be priced in a way that reflects its incremental value. New technology must demonstrate its benefit to justify its cost, often in arthroplasty there is little data available to document these better outcomes.

In a recent study by Bozic the cost effectiveness of new technologies were evaluated. Based on the authors' findings for an alternative bearing with an incremental cost of $2000 to be cost saving for a 50 year old there would have to be a 19% reduction in 20 year failure rates. The likelihood of cost savings for these alternate bearings in patients 63 or older is highly unlikely at current costs. Newer biomaterials (metal/metal, ceramic/ceramic, highly cross linked polyethylene) also have limited outcome analysis in patients beyond short to mid-term follow-up evaluation and all of these technologies add significant cost to the implant. With diminishing reimbursement careful analysis of utilisation of these newer technologies must be weighed if hospitals are to maintain economic viability.

The pharmaceutical, airline, and food industries have all moved toward generic products which are less costly and this will be the trend in the future in prosthetic implants as well. Newer technologies must demonstrate their efficacy in long term follow-up and be clearly superior to conventional implants. This is not always the case as new data on metal-metal implants is demonstrating. Change is not always progress.

For most revision total knee replacement there is associated soft tissue and bone loss. A constrained condylar implant can be useful in improving the stability of the knee after revision. Augmentation is commonly used to deal with bone loss on the femoral and tibial side of the joint. Stems are known to reduce the load at the interface of the femoral and tibial component and transfer the load into the medullary canals. There are problems with using stems in the revision setting, however, which include: (1) increased cost, (2) difficulty with removal should further revision be necessary, (3) violation of the intramedullary canals if infection occurs, (4) increased operating time. For these reasons a CCK implant was developed without stems in 1998. The use of this device must be very selective and it is primarily used for severe valgus deformity in elderly patients. In a revision setting where there is good preservation of femoral and/or tibial bone but the need for increased constraint is present (e.g. unicompartmental, cruciate retaining knee) a CCK without stems can be used with good results. We retrospectively reviewed 36 primary constrained condylar knee implants without stem extensions from 1998 to 2000 in 31 patients with knees in 15° valgus or greater. All patients were followed up for a minimum 10 years (range, 10 to 12 years). One patient had aseptic loosening and needed to be revised with stemmed components at nine years post-surgery. Wear was found in two patients. One patient, with severe rheumatoid arthritis, had infection and required a two-stage re-implantation procedure. Patients who are very active or heavy body weight where stresses may be excessive at the implant bone interface should have stems utilised.

Background: A navigated 8 in 1 femoral cutting guide for TKA that does not require primary fixation or intramedullary guides was developed. The hypothesis of our study were twofold: 1) the navigation system allows for precise alignment and adjustment of a new femoral 8 in 1 cutting guide with negligible variance in the initially planned vs. achieved implant position; 2) resulting femoral cuts are very accurate without relevant cutting errors.

Material and Methods: We demonstrate our approach with the Universal Knee Instrument (UKI, Precimed Inc. USA), a versatile 8 in 1 TKA guide designed to perform all femoral cuts with a single jig. We integrated an array of “adjustable constraints” into the UKI by machining four threaded holes directly through the template. Adaptation to a navigation system has been performed by integrating the adjustable constraints protocol on the open platform Surgetics Station (PRAXIM-medivision, France), which uses image-free BoneMorphing technology. Based on navigated bone morphing the required preadjustment of the guide was done mechanically, with depth control by mini screws. Testings on 10 cadavers compared the planned vs. achieved positions of the jig before, after fixation, final implant position and planned vs. achieved cutting procedures.

Results: Results revealed for valgus/varus deviations before fixation −0.1°±0.7°, after 0.0°±0.8° (p=0.51), final implant position 0.9°±1.7° (p=0.93). For flexion before fixation −0.3°±1.3° after −0.3°±1.8° (p=0.44), final position 2.9°±2.5° (p=0.65). Distal cut height before fixation 0.0°±0.4°, after 0.1°±0.3° (p=0.61), final position 0.3°±1.0° (p=0.1). Axial rotation before −0.3°±1.1°, after fixation 0.2°±1.4° (p=0.57), final implant position 0.8°±2.7° (p=0.89). Anterior-posterior positions before fixation 0.7°±1.4°, after 1.0°±1.6° (p=0.27), final position 3.4°±1.3° (p=0.13). Highest deviations in the planned vs. actual cut position was found for the posterior cut −3.1°±2.4° in sagittal and anterior cut 0.8°±1.9° in the coronal plane. The highest mean errors in the final implant position where on the order of 3 degrees/mm in flexion and anterior-posterior positioning.

Conclusion: A novel ‘CAS-enabled 8 in 1 jig’ has been developed and validated. The system allows for direct execution of a complex, multi-planar CAS plan with single navigated device. The instrumentation is considerably simplified and eliminates the problems associated with sequential jigs.

Particles generated at the non articulating surface (backside) of modular acetabular components have been implicated in the development of periprosthetic osteolysis after total hip arthroplasty. Several design changes have been introduced in modern uncemented acetabular cups in an attempt to reduce backside wear, including the use of so called “non-modular cups”. We compared the backside wear of retrieved cementless non-modular cups, with modular cups of first and second generation designs.

Nine retrieved non-modular cups (Implex) were match paired for time in situ, patient age and weight, with 9 retrieved Trilogy cups, 9 Harris-Galante 1, and 9 Harris-Galante 2. The average time in situ was 2.5 years (1 to 7). The backside was divided in quadrants and each rated utilizing a score with a value from 0 (absence of wear) to 3 (severe backside wear) for a total ranging from 0 to 12. The score was validated for intra and inter observer reproducibility.

Among 36 quadrants in the HG1 group there were 3 rated 1, 23 rated 2, and 10 rated 3. In the HG2 group, there was 1 quadrant rated 0, 16 rated 1, 14 rated 2, and 5 rated 3. In the Trilogy group, there were 6 quadrants rated 0, 27 rated 1, and 3 rated 2. In the Implex group, there were 15 quadrants rated 0, 21 rated 1. The average total backside wear score and 95%CI were 8.4 (7.6–9.3); 7.3 (5.5–9.1); 3.7 (3.2–4.1); and 2.3 (1.3–3.4) respectively. The HG1 and HG2 groups demonstrated similar backside wear scores (p=0.3). The HG1 and HG2 designs demonstrated significantly more backside wear than the Trilogy and Implex (p< 0.01). The differences between the Trilogy and the Implex were not significant in this cohort.

A comparison of the “in vivo” backside wear of first generation and modern acetabular cups has not been published to date. Despite the limitations imposed by the small sample studied, the presence of multiple screw holes in the HG retrievals, and sub-optimal matching for sex, height, and varied indication for revision, we detected significant reduction in the backside wear of modern modular and non-modular acetabular cups when compared to first generation modular designs.

Particles generated at the non articulating surface (backside) of modular acetabular components have been implicated in the development of periprosthetic osteolysis after THA. Several design changes have been introduced in modern acetabular cups in an attempt to reduce backside wear, including the use of “non-modular cups”. We compared the backside wear of retrieved cementless non-modular cups, with modular cups of first and second generation designs. Nine retrieved non-modular cups (Implex) were match-paired for time-in-situ, patient age and weight, with 9 retrieved Trilogy cups, 9 Harris-Galante 1, and 9 Harris-Galante 2. The average time in situ was 2.5 years (1–7). The backside was divided in quadrants and each rated with a value from 0 (absence of wear) to 3 (severe backside wear) for a total ranging from 0 to 12. This new score was validated for intra and inter observer reproducibility. Among 36 quadrants in the HG1 group there were 3 rated 1, 23 rated 2, and 10 rated 3. In the HG2 group, 1 quadrant was rated 0, 16 rated 1, 14 rated 2, and 5 rated 3. In the Trilogy group, 6 quadrants were rated 0, 27 rated 1, and 3 rated 2. In the Implex group, 15 quadrants were rated 0, 21 rated 1. The average backside wear score and 95%CI were 8.4 (7.6–9.3); 7.3 (5.5–9.1); 3.7 (3.2–4.1); and 2.3 (1.3–3.4) respectively. The HG cups demonstrated more severe backside wear than the Trilogy and Implex (p< 0.02). There was a tendency towards less backside wear in the Implex cup when compared to the Trilogy (p=0.04). The difference between the HG1 and HG2 was not significant. We detected significant reduction in the backside wear of modern modular and non-modular acetabular cups when compared to first generation modular designs.

Introduction: Patello-femoral complications are a major problem after total knee arthroplasty (TKA). Purpose of the present study was to analyze patello-femoral complications and function after two different posterior-stabilized TKA designs (Optetrak 913 vs IB-II).

Materials and Methods: This study was performed in two consecutive phases. In the first phase 1410 TKA’s performed by the senior author between 1994 and 1998 were considered for chart review. Within this period, the last 300 IB-II and the first 300 913 performed were analyzed for patello-femoral complication rate. In the second phase, of the 600 charts analyzed, two matched groups (50 patients each of IB-II and 913), were selected for a clinical (Knee Society score), functional (HSS Patellar score) and radiological assessment (AP, Lateral, Merchant, modified-wb Merchant views).

Results: A lateral retinacular release was performed in 30% for the IB-II and 16% for the 913 (p=0.02). The following patello-femoral complications were encountered (phase-1):

IB-II 913

Patellar clunk 3.5% 0.3%

Dislocation 0% 0.3%

Fracture 0% 0.3%

Loosening 0% 0%

Clinical results at follow-up (phase-2) did not show any significant difference between the two matched groups in terms of Knee and Function scores (p=0.7). Patellar score showed a higher rate of excellent and good results in the 913 group (88% vs 81%: p=.043). Anterior knee pain was only mild and activity related in 26% of the IB-II and 14% of the 913 (p=.025). In a multivariate regression analysis, radiographic patellar tilt, subluxation, and height, did not correlate with clinical outcomes, whilst bone-implant contact showed a trend towards a higher incidence of pain, particularly when associated with asymmetric patellar resection.

Discussion: At an intermediate follow-up, the Optetrak 913 prostheses showed fewer complications and an improved patello-femoral function compared to the IB-II prosthesis.

Introduction: Patello-femoral evaluation after total knee arthroplasty (TKA) is not addressed by most knee scoring systems. Patellar radiographic assessment after TKA is obtained with static, unloaded views that may not reproduce the in-vivo patello-femoral kinematics. The purpose of this study was to develop and validate new reliable and reproducible clinical and radiographic assessment tools for analysis of the patello-femoral joint in TKA.

Materials and Methods: The existing axial Merchant view was modified by positioning the standing patient in the semi-squatted position with the knees at 45°. Relationship between X-ray source, the angle of incidence on the joint, and the cassette position, were kept unchanged from the original view. The standing position and consequent muscle involvement were the only differences. The quality of the view was confirmed on a cadaveric knee model with multiple markers. Safety, reproducibility and clinical reliability were obtained in 100 posterior-stabilized TKA’s. These patients were assessed by a new Patella Scoring System (0–100 points). This system considers anterior knee pain, crepitus, stair performance and quadriceps strength. Radiographic abnormalities are calculated as deductions. Intra- and inter-observer variability were obtained comparing the results of two different investigators.

Results: The modified Merchant view showed significant patello-femoral tracking changes in 68% of patients. Twenty-one cases of bone-implant contact were observed when load was applied. Correlation between excellent-good clinical outcome and excellent patello-femoral performance was significantly higher for the Patellar Score compared to Knee Society Clinic or Function scores (p=.022, p=.014). Multivariate regression analysis of radiographic tilt, subluxation, and height, did not correlate with clinical outcomes, whilst bone-implant contact showed higher incidence of pain, particularly when associated with asymmetric patellar resection.

Conclusion: These new patello-femoral clinical and radiological assessment methods employed in the study represent additional valuable tools for the comprehensive evaluation of results in TKA.

We evaluated the safety and efficacy of a multimodal approach for prophylaxis of thromboembolism after THA, which includes preoperative autologous blood donation; hypotensive epidural anesthesia; intravenous administration of heparin during surgery, before femoral preparation when the thrombogenesis is maximally activated; expeditious surgery, minimizing femoral vein occlusion and blood loss; pneumatic compression; and early mobilization after surgery. 1946 consecutive, non-selected patients (2016 THAs) who received multimodal thromboembolic prophylaxis were followed prospectively for 3 months. Only patients with history of thrombocytopenia (platelet count < 100.000) or adverse reaction to heparin were excluded. The average age was 65 years (14 to 93), ASA classification was 1 in 14%, 2 in 48%, 3 in 37% and 4 in 1% of patients. There was a history of DVT in 86 patients and PE in 35. After surgery, the patients also received pharmacologic prophylaxis for 6 weeks (aspirin 83%; warfarin 17%). The incidence of asymptomatic DVT assessed by ultrasound in the first 198 consecutive patients was 7.1% (14 of 198). The incidence of clinical DVT in the subsequent 1748 patients was 1.8% (32 of 1748). Symptomatic PE occurred in 0.56% (11 of 1946), none of them fatal. The rate of PE in patients receiving aspirin was 0.49% (8 of 1615) and warfarin 0.9% (3 of 331). There was 1 PE among 95 patients with a prior history of PE or DVT (1%). One morbidly obese patient died of a cardiac arrhythmia confirmed by autopsy. There was only one major bleeding complication: one patient with a history of coagulopathy developed hematuria requiring a bladder flush and five units of blood, with an uneventful recovery. No patients developed epidural hematoma following administration of intraoperative heparin. A multimodal approach to prevent thromboembolic disease, showed results that compare favorably with the literature, and with our historic control of 2592 THRs without intraoperative heparin (PE rate of 1%; 0.04% fatal). This multimodal approach appears safe and efficacious as thromboembolic prophylaxis. Our low rate of PE does not support routine anticoagulation prophylaxis with drugs with a significant risk of bleeding.

Introduction and Aims: Retroacetabular osteolysis is a common cause of failure of hip replacements. Polyethylene wear particles from the joint are often present in osteolytic lesions. We investigate three theories that describe how fluid and debris could be pumped from the joint space through the holes in the shell to the retroacetabular bone.

Method: We report three experiments that investigate this question. We performed an in vivo study where we measured pressures in the hip joint and in the osteolytic lesion while cyclically loading the hip in 10 patients. We performed a series of biomechanical studies, where we model diaphragm pumping and piston pumping of the polyethylene liner within the metal shell in the laboratory. We also carried out a finite element analysis showing how loading of the hip affects the size of an osteolytic lesion and the pressure of fluid within an osteolytic lesion.

Results: In the in vivo study, loading of the hip produced a pressure increase in each of the four contained osteolytic lesions (mean 68mmHg), but not in the six uncontained osteolytic lesions. This pressure rise was independent of hip joint pressure, demonstrating that there is a pumping mechanism in the artificial hip joint that is independent of hip joint pressure. In the diaphragm pumping experiment, the pressure produced by the non-congruent liners (4030 ±1250mmHg) was six times the pressure produced by the congruent liners (670 ±240mmHg). In the piston pumping experiment, the pressure produced by the pistoning liners (5140 ±330mmHg) was eight times the pressure produced without pistoning (650 ±300mmHg). FEA demonstrates that loading of the hip may reduce the volume and, therefore, increase pressure in a contained osteolytic lesion.

Conclusion: The prosthetic hip contains a complex system of pumps transporting fluid and particles and generating pressures. The importance of each pumping mechanism varies with patient activity and with implant design features. These pumping mechanisms may contribute to the pathogenesis of osteolysis.

The major failure mode of cemented or non-cemented acetabular fixation is osteolysis produced by polyethylene debris and biologic reaction to this material. A monoblock acetabular non-cemented component offers advantages in reducing the failure mechanism of acetabular cups. First, because the polyethylene is fixed to the metal shell there is no motion between the shell and the liner as is seen with modular components. Therefore extra-articular polyethylene wear debris is not generated. Secondly, there is no need for a locking mechanism which may fail and from which metallic debris may be produced. Thirdly, no screw holes are present on the back of the monoblock cup increasing the surface area for ingrowth and eliminating an entrance point for wear debris to access the floor of the acetabulum. Avoidance of the use of screws also prevents the possibility of neurovascular injury during screw insertion. Fourthly, by adding an elliptical configuration to a monoblock cup the dome of the shell is the same dimension as the reamed diameter allowing for improved coaptation of shell to acetabular floor. By increasing the diameter at the rim secure press fit is achieved without sacrificing contact at the dome.

There are disadvantages to a monoblock cup and these include the need for a revision liner mechanism should there be a need to replace the polyethylene liner. Additionally, if secure stabilisation is not achieved, the cup cannot be converted to screw fixation.

In a radiologic review of 661 acetabular components, 5.1% of cups were noted to have a polar dome acetabular gap of greater than 1.5 mm on the immediate postoperative radiograph. These patients were followed for a minimum of two years and there was noted shift in implant position in only one patient. Gaps tended to lessen in degree and fill in with bone in almost all cases. The clinical result was not compromised by the presence of a dome gap.

In a short-term follow-up of 6 years, 1843 elliptical monoblock acetabular cups have been inserted with greater than two-year follow-up in 972 hips. There have been no mechanical failures requiring revision. Two patients have been revised for instability and one for infection. The need to convert to a cup with screw fixation because of poor press fit is less than 2%.

Inciting events leading to deep vein thrombosis occur primarily intraoperatively. Therefore, if at all possible, intervention should be performed at the time of the operative procedure. It has been demonstrated in hip replacement surgery that DVT is significantly reduced with epidural hypotensive anaesthesia, which may or not be augmented with intraoperative small doses of heparin (500–1000 units). Reduction of extreme limb position with occlusion of the femoral vein during hip replacement surgery reduces the stasis effect, which promotes clotting. In the hip, overall DVT rates have been reduced to 7% and proximal DVT rates to 2% using these intraoperative techniques.

Mechanical devices work by a myriad of mechanisms: 1.) venous turbulence is created in valve pocket areas and this reduces clot formation; 2.) there is an increase release of endothelial relaxing factor (EDRF) which inhibits platelet aggregation; 3.) intermittent compression stimulates fibrinolysis by inducing release of urokinase and tissue plasminogen from the venous endothelium. Randomised trials have demonstrated a reduction in DVT to levels similar to pharmacologic agents (20–27%) without the risk of postoperative haemorrhage. However, compliance with use of these devices is crucia1, as a positive relationship has been demonstrated between time of use and DVT rates. Although plantar pump devices tend to be well tolerated with occasional complaints of foot and skin irritation, calf compression devices with or without sequential foot compression applying at least 50 mmHg of external pressure at a frequency of at least once per minute and an inflation rate of less than 1 second tend to be the ideal device for DVT prophylaxis.

The indications for unicompartmental replacement are quite specific. Overall there should be involvement of one tibiofemoral compartment, mild malalignment, and ligamentous stability. In a review of 250 osteoarthritic knees these pathologic findings were present in 9% of patients. If the average orthopaedic surgeon performs 25 total knee replacements per year only 2–3 patients will be ideally suited for this procedure. Technique, despite improvement in instrumentation, is still more demanding than tricompartmental knee replacement and therefore failure to achieve an optimal arthroplasty is higher. Overall results with unicompartmental replacement in the literature have been inferior to tricompartmental replacement (82% versus 97%). The concept that unicompartmental replacement is a temporising procedure is not a valid one in that the patient has to undergo another arthroplasty with all the risks of revision arthroplasty surgery. Tibial osteotomy remains the procedure of choice in the younger, active patient with unicompartmental replacement and tricompartmental replacement in the older, lower demand patient.

A multi-centre clinical trial of ICLH (Freeman-Swanson) arthroplasty has been in progress since 1971. In this paper the results up to two years after operation are reported in seventy-one knees displaying at least 30 degrees of fixed flexion, 25 degrees of valgus or 20 degrees of varus, before operation. It has been found that knees displaying 70 degrees of fixed flexion, 70 degrees of valgus, 30 degrees of varus or 50 degrees of valgus/varus instability can be satisfactorily aligned and stabilised with acceptable function. Three knees required revision. The other complications are listed and were unremarkable in nature. These results depend upon the prosthesis and upon the operative technique. The latter avoids damage to healthy bone but does involve the replacement of the tissues in the midline of the knee.