Aims

The aim of this study was to estimate the clinical and economic burden of dislocation following primary total hip arthroplasty (THA) in England.

Aims

The aim of this modified Delphi process was to create a structured Revision Hip Complexity Classification (RHCC) which can be used as a tool to help direct multidisciplinary team (MDT) discussions of complex cases in local or regional revision networks.

Aims

This study uses prospective registry data to compare early patient outcomes following arthroscopic repair or debridement of the acetabular labrum.

Aim: To identify the microbiology of infected knee arthroplasty, emerging patterns of resistance over the last decade, and suggest appropriate empirical treatment.

Methods: A retrospective analysis was conducted of 121 patients with microbiologically proven infection, who underwent revision TKA between 1994–2008. The causative organism was identified from microbiological samples and the corresponding sensitivities recorded. The data was then collated to determine the most common causative organisms, changing patterns of antibiotic resistance over the time frame, and the antibiotics currently most effective at treating deep infection. A theoretical model combining gentamicin with other antibiotics was used to determine the most effective antibiotics for use as empirical treatments.

Results: Coagulase negative Staphylococcus (CNS) was the most common causative organism (49%). Staphylococcus aureus (SA) accounted for 13% of cases. The prevalence of CNS appears to be increasing, while that of SA and other organisms is decreasing. Vancomycin and teicoplanin were the most effective antibiotics with overall sensitivity rates of 100% and 96% respectively. Levels of resistance were significantly higher among the antibiotics more commonly used in the community. Antimicrobial resistance was higher when the causative organism was CNS, suggesting that multi-drug resistant CNS is becoming a problem in knee arthroplasty. Our theoretical model showed that gentamicin combined with vancomycin would be the most effective empirical treatment.

Conclusion: Understanding the microbiology of deep infection of the knee allows surgeons to treat this complication as effectively as possible. Vancomycin and teicoplanin appear to be the most effective antimicrobials, with relative invulnerability to the development of resistance. Given the effectiveness of these antibiotics, the use of vancomycin in gentamicin bone cement, combined with IV teicoplanin potentially allows for infected knee arthoplasties to be treated with a one-stage procedure. The rational use of antibiotics may help limit the amount of antibiotic resistance which develops in the future.

Introduction: Stiffness is a disabling problem following TKR surgery. The overall incidence is 1–3%. Though multiple factors have been implicated in development of stiffness, it still remains an incompletely understood condition. Furthermore, opinion is divided about the efficacy, timing and the number of MUA’s post TKR surgery, as there are no definitive guidelines.

Aims & Objectives: The aim of this study was to assess the predisposing factors for stiffness following TKR surgery, to determine the efficacy of single and multiple manipulations and to investigate the most appropriate timing for manipulation.

Material & Methods: We retrospectively reviewed 86 patients who underwent manipulation for stiffness post-primary TKR surgery with at least one-year follow up. The number of manipulations, predisposing factors, the flexion gain at different intervals, final gain in flexion and range of movement was noted till the end of 1 year.

Results: Results were assessed by timing and number of MUA’s performed. Sixty five patients underwent single MUA and 21 had multiple MUA. At the end of one year the single MUA group showed 310 of sustained gain in flexion and in the multiple MUA group only 90 flexion gain was noted (p=0.003). MUA within 20 weeks of primary surgery showed 300 of flexion gain, whereas only 70 of flexion gain was seen when MUA was undertaken after 20 weeks (p=0.004). Patients on warfarin (9.5%) and with previous major surgeries to the knee prior to TKR (11.5%) had increase incidence of stiffness and poor flexion gain.

Conclusion: The timing of the 1st MUA is crucial, with better results achieved in MUA performed less than 20 weeks (particularly between 12–14 weeks) from primary surgery. Age, sex and type of disease do not influence the severity of stiffness in this study. There appears to be no added benefit in re-manipulation.

Aims & Objectives: To assess whether the incidence of infection in Primary Total knee Arthroplasty is increased as a result of previous steroid infiltration into the knee joint.

Introduction: Steroid injection into the arthritic joint is a well-known modality of treatment of the arthritic joints. Its efficacy is well documented. Increased incidence of Infection secondary to steroid injection as compared to uninjected joints is reported in recent literature.

Material & Methods: 440 patients underwent Total Knee replacement (PFC SIGMA-Depuy) by senior author during 1997–2005 at Wrightington hospital. 90 patients had intraarticular steroid injection prior to surgery of which 45 patients had injection with in 1 year prior to surgery. All patients had at least one year follow up. Infection rate was assessed by case note, x-rays and microbiology review till last follow up.180 patients of a matched cohort who had total knee replacement without steroid injection were compared for infection rate.

Results: 2 cases of superficial infection were noted in Injection group and 5 cases of superficial infection in Non Injection group. No cases of Deep infection noted in either group. Stastical analysis showed no significant difference in incidence of infection in either group.

Conclusion: Steroids are useful adjuncts in the management of patients with arthritic joints. This study shows no increased incidence of infection in patients given steroid injection prior to arthroplasty.

Introduction: Movement of the limb during computer aided arthroplasty may cause soft tissue impingement on the reference marker(RM) and consequently alter the spatial relationship between RM and bone with resulting inaccuracies in navigation. The purpose of this study was to investigate the effect of different degrees of soft tissue dissection on the stability of reference markers during limb movement.

Methods: The stability of both one- and two-pin RM systems inserted using three different levels of soft-tissue dissection was analysed in relation to a super-stable RM in fresh cadaver lower limbs. The spatial relationship of the two RMs was analysed using the VectorVision^® system (BrainLAB, Germany) during multiple repetitions of four predefined limb movements. All tests were done with RMs inserted in both the distal-anterior femur and distal-lateral femur.

Results: Analysis of movements of the test RM in relation to the super-stable RM showed that rotations of less than 0.15^o and translations of less than 0.4mm occurred in most test combinations. The combination that showed the greatest instability was when a stab incision was used to insert a pin in the distal/lateral femur (translation 0.73mm+/−0.05, rotation 0.25^o+/− 0.05)(p< 0.001). This instability occurred in both single and double pin RMs(p=0.21).

Conclusions: RM pins can be placed in the anterior distal femur through simple stab incisions without resulting in significant soft tissue impingement during limb movement. If pins are placed in the lateral distal femur through stab incisions, impingement may occur from the fascia lata. Release of the fascia lata 1cm either side of the pin prevents significant impingement. Wide skin incision is unnecessary in any location.

Introduction: Hip resurfacing arthroplasty is increasing in popularity, particularly in young and active patients. One unique advantage is retention of upper femoral bone stock with the hypothesis of easy revision should the resurfacing fail. The pupose of this study was to document the complexity or otherwise of our early experience with failed hip resurfacing.

Methods: We retrospectively reviewed all the patients who had revision surgery for failed hip resurfacing arthroplasty at our institution.

Results: Eleven patients with mean age of 52.8 years underwent revision of resurfacing at a mean time of 21.2 months following primary surgery. Revision was performed for deep infection in 4, cup loosening in 4 and 1 patient each for femoral neck fracture, avascular necrosis, and femoral loosening. For the 4 patients with cup loosening, the acetabular component was revised in 3 using a dysplasia Birmingham cup while 1 patient had both components revised. Of the 4 patients with deep infection, 3 had both components revised as one-stage revision with cemented components and 1 patient had a pseudarthosis. For the 3 cases with femoral loosening, neck fracture or avascular necrosis only the femoral component was revised using a cemented stem. Bone grafting was performed in 1 patient who had revision for loosening of acetabular cup with protrusio.

Conclusion: Acetabular failure appears to be equally common as femoral failure in resurfacing arthroplasty. Revision of both aseptic and septic failure appears to be relatively straightforward with primary implants used in all cases.

In computer assisted orthopaedic surgery, rigid fixation of the Reference Marker (RM) system is essential for reliable computer guidance. A minimum shift of the RM can lead to substantial registration errors and inaccuracies in the navigation process. Various types of RM systems are available but there is little information regarding the relative stabilities of these systems. The aim of this study was to test the rotational stability of three commonly used RM systems.

One hundred and thirty Synbones and 15 cadavers were used to test the rotational stability of three different RM systems (Schanz’ screw, Brain-Lab MIRA and Stryker adjustment system). Using a specially developed testing device, the peak torque sustained by each RM system was assessed in various anatomical sites.

Comparison of means for Synbone showed that the BrainLab MIRATM system was the most stable (mean peak torque 5.60+/− 1.21 Nm) followed by the Stryker systemTM (2.53+/− 0.53 Nm) and the Schanz screw(0.77+/− 0.39 Nm)(p< 0.01). The order of stability in relation to anatomical site was femoral shaft, distal femur, tibial shaft, proximal tibia, anterior superior iliac spine, iliac crest and talus. Results from the cadaver experiments showed similar results. Bi-cortical fixation was superior to mono-cortical fixation in the femur(p< 0.01) but not the tibia(p=0.22).

The RM system is the vital link between bone and computer and as such the stability of the RM is paramount to the accuracy of the navigation process. In choosing RM systems for computer navigated surgery surgeons should be aware of their relative stability. Anatomical site of RM placement also affect the stability. Mono-cortical fixation is generally less stable than bi-cortical.

Introduction: The success of impaction-grafting depends on mechanical stability and adequate bony incorporation of the graft. Full incorporation of this type of graft has been demonstrated histologically and depends on many factors including the biological activity of the graft. Bone morphogenic proteins (BMPs) are known to play a central role in bone formation and their presence reflects the biological activity of a graft material. The aim of this study was to determine the activity of fresh frozen femoral head (FFH) grafts by analysing BMP-7 release after milling and during strain imposed by the impaction process.

Methods: 10mm cancellous bone cubes were cut from 5 samples of FFH. The cubes were washed, centrifuged and washed again to remove the marrow contents. Specimens from each femoral head were allocated to five groups and subjected to strains of 0%, 20%, 40%, 60% and 80% with a material testing machine. The cubes were washed again and the wash fluid analysed for bmp-7 activity using a commercially available elisa kit. Additionally, samples of bone were taken after standard milling of FFH, washed and the fluid analysed for bmp-7 activity.

Results: bmp-7 activity was found to be present in all groups. Release of bmp-7 was found to increase with increasing strain in a linear relationship. At 80% strain the mean concentration of bmp-7 released (2.2 ng/g bone) was approximately double that released at 20% strain.

Discussion: activity of bmp-7 in FFH has not previously been demonstrated. This study shows that the freezing and storage of femoral heads allows some maintainance of biological activity. Furthermore we have shown that bmp-7 may be released from FFH cancellous bone in proportion to the strain applied to the bone. This may go some way to explaining the full bony incorporation often seen after impaction-grafting.

Fine-wire fixators are a powerful tool in the management of acute fractures, non-unions, mal-unions and limb lengthening. The tension in the wires is very important in achieving stiffness of the whole fixator construct and current guidelines suggests tensioning wires to 900-1275N. There is evidence that during long term use the tension in the wires can reduce significantly. The effects of a reduction in tension on the fixator stiffness has been well characterised however the effect on the stresses imparted on the bone at the interface with the wire remain unknown. The main aim of this study was to identify any relationship between wire tension and wire-bone interface pressure.

An experimental system utilizing artificial cancellous bone mounted on a tensioned 2mm wire and then loaded by a material testing machine was employed. Pressure sensitive film allowed determination of interface stresses. The experiment was repeated at wire tensions of 600, 900 and 1200N. All other variables were kept the same during testing.

The highest pressures were found closest to the wire. At 1200N the peak pressures were 6-8 MPa, at 900N of tension the pressures rose to 8-10 MPa and at 600N pressures up to 14 MPa were observed. Deeper in the bone the pressures observed at 600N tension were double that seen at 1200N.

This is the first characterisation of the relationship between interface pressure and wire tension in fine-wire fixators. At 1200N the highest pressures are less than the compressive yield strength of cancellous bone whereas at both 600 and 900N pressures are greater than the yield which may lead to loosening. We therefore conclude that a tension of 1200N be employed when applying fine-wire fixators and during long term treatments the tensions should be regularly monitored to prevent loss of tension.

Fine-wire fixator systems have been used successfully for the treatment of fractures, malunions and for limb lengthening for many years. There has been much research investigating the biomechanical properties of these systems but this has been almost entirely centred on the mechanical properties of the fixator as a whole. Our knowledge of the interactions occurring at the interface between wire and bone remains sparse. To this end we devised an experimental model to analyse the distribution of pressure in cancellous bone surrounding a tensioned wire under loading conditions. The Sawbones cancellous bone material (type 1522-11) was cut into 65x30x40 mm blocks. A 2 mm olive wire was inserted into each block, parallel to the surface and along the 65 mm dimension. The distance from the wire to the surface was variable, from 0.5mm to 5mm in a 0.5mm increment. The wire was mounted on a 150 mm ring and tensioned to 1200 N against a load cell. The ring was rigidly mounted on a material testing machine and a second bone block was incorporated into the testing machine crosshead with a universal joint. Three grades of pressure-sensitive films (Low, Superlow and Ultralow) were sandwiched in turn between the testing block and cross head. The force applied was 175 N for 5 s. The developed film was scanned into a computer and a Matlab program was developed to analyse the pressure image. The results show three phases of pressure distribution. Very close to the wire there is a polar distribution of pressure that is, the pressure is concentrated towards the entry and exit points of the wire. At a depth of 1.5mm away from the wire the pressure becomes evenly distributed along the path of the wire in a beam-loading manner. At a distance of greater than 4mm from the wire there is even distribution of pressure throughout the bone. The peak pressures (6–8 MPa) were found closest to the wire. Most of the pressure measured was less than 1 MPa, which is less than the yield strength of cancellous bone (2–7 MPa, Li and Aspden, 1997). In contrast a similar analysis using threaded half pins under the same conditions showed far higher peak pressures (20 MPa), which were present deeper in the bone specimen. The pressure was concentrated toward the pin entry site and was not well distributed throughout the pin-bone interface. These results allow us to explain why ring fixators are superior to half pin fixators when used in metaphyseal bone.