Aims

The aim of this study was to evaluate the effects of using a portable, accelerometer-based surgical navigation system (KneeAlign2) in total knee arthroplasty (TKA) on the alignment of the femoral component, and blood loss.

INTRODUCTION

Although the most commonly used method of femoral component alignment in total knee arthroplasty (TKA) is an intramedullary (IM) guides, this method demonstrated a limited degree of accuracy. The purpose of this study was to assess whether a portable, accelerometer-based surgical navigation system (Knee Align 2 system; Orth Align, Inc, Aliso Viejo, Calif) improve accuracy of the post-operative radiographic femoral component alignment compared to conventional IM alignment guide.

INTRODUCTION

Rotational alignment of the femoral and tibial component in total knee arthroplasty (TKA) are separately determined based on the anatomy of each bone. Popular references are the transepicondylar axis (TEA) for femoral component, and medial one-third of the tibial tubercle for the tibial component. It was reported that these references are not in accordance with each other in osteoarthritic (OA) knees and rotational mismatch could occur even when the components were accurately aligned. There has been, however, a paucity of data as for the rotational mismatch after TKA for OA knees. The purpose of this study was to evaluate the rotational mismatch between the femoral and tibial component after TKA for OA knees.

INTRODUCTION:

It has been reported that rotational deformity is present in varus osteoarthritis (OA) of the knee and the tibia rotates externally as the varus deformity progresses. Although many studies addressed the rotational alignment of the femoral and tibial component in total knee arthroplasty (TKA), the pre-and postoperative changes of the rotational alignment in varus OA knee has not been evaluated. The purpose of this study was to quantitatively analyze the alteration of rotational deformity after TKA for the varus OA knee.

Over the past decade, there has been an increase in the number of total knee arthropalsty (TKA). Demand of TKA for the young patients who often have high physical demands is also increasing. However, the revision rate in such young patients is much higher due to polyethylene (PE) wear and instability (Julin J, Acta Orthop 2010). Therefore, next generation total knee prostheses are expected to decrease PE wear and to provide stability.

Although in vitro study such as wear simulator test provides important information about PE wear, we have often encountered the discrepancy between the in vitro results and in vivo results. Thus we have performed in vivo PE wear particle analysis, and showed that in vivo PE wear was affected by the design of articulating surface and the materials of femoral component and PE insert (Minoda Y, JBJS Am 2009). Medial pivot design, ceramic femoral component, and highly cross-linked PE decreased in vivo PE wear particle generation.

Patients who underwent bilateral staged TKAs were more likely to prefer medial pivot prosthesis or ACL-PCL retaining prosthesis than the other types of prostheses, because they feels “more stable overall” (Pritchett JW, J Arthroplasty 2011). In vivo fluoroscopic 3D analysis showed that medical pivot and bi-cruciate substituting designs restored physiological knee motion and provided higher reproducibility (Mueller J. Komistek RD, Trans ORS 2009, Iwakiri K, Trans ORS 2007).

The excellent mid-term clinical results of those newly introduced total knee prosthesis, such as alumina medial pivot TKA (Iida T, ORS 2008), medial pivot TKA (Mannan K, JBJS Br 2009, Kakachalions T, Knee 2009), ACL-PCL retaining TKA (Clouter JM, JBJS Am 1999), and highly cross-linked PE (Hodrick JT, CORR 2008), have been reported.

From the point of view of in vivo PE wear, in vivo stability, and the mid-term clinical results, we suspect that medial pivot prosthesis is one of the prostheses which meet the demand in future especially for young active patients.

Several anatomical landmarks are preferable in order to achieve the precise decision of femoral component rotation in order to achieve a satisfying result in total knee arthroplasty (TKA). The posterior condylar axis (PCA) is apparent and allows minimization of interobserver error compared with the transepicondylar axis or anterior-posterior axis. The rotation angle based on PCA observed during surgery differs from the angle measured on pre-and postoperative epicondylar view, because X-rays do not reflect the posterior condylar cartilage. We investigated the influence of the posterior condylar cartilage on setting the rotation angle of the femoral component in 184 knees in 112 patients with varus osteoarthritis undergoing TKA.

Medial and lateral thickness of the resected posterior femoral condyle was measured before and after removing the cartilage to determine its thickness. The amount of rotation angle influenced by the cartilage is expressed as an inverse trigonometric function (arctangent) of the distance between the posterior condylar surfaces and the difference in thickness between the medial and lateral cartilage.

Average thickness of the lateral and medial cartilage turned out to be 2.1±0.7mm and 0.7±0.7mm, respectively. The average rotation angle influenced by this difference was calculated to be 1.7±1.3°. These findings suggest that using PCA as a guide to determine the rotation angle of the femoral component results in approximately 1.5–2.0° of excess external rotation in varus osteoarthritis. Because of significant individual variability in condylar twist angle, formed by the intersection of the clinical epicondylar axis with the PCA, preoperative CT or epicondylar view is recommended in order to calculate this angle in each subject. Thickness of the posterior condylar cartilage should be taken into consideration when finalizing the rotation angle of the femoral component by PCA in addition to transepicondylar and anterior-posterior axis.

Achieving deep flexion of knee after total knee arthroplasty (TKA) is particularly desirable in some Asian and Middle Eastern who have daily or religious customs typically use full knee flexion. After TKA, some patients complained about anterior knee pain during deep knee flexion. We evaluated the efficacy of arthroscopic fat pad resection in a series of patients suffering from anterior knee pain associated with high flexion achievement after TKA.

The efficacy of fat pad resection via arthroscopy for treating anterior knee pain associated with high flexion angle (average = 133.1°) was evaluated in eight knees of eight patients among 207 knees performed between 1996 and 1999. The mean age of patients was 71.1 years when the primary TKA was performed. All implatants were posterior stabilized type (IB-II, Nexgen PS and LPS). The symptom of anterior knee pain during deep knee flexion developed within one year after TKA in all cases. In addition to pain in eight knees, two patients have crepitation as the knee was flexed and extended and three patients had hydrarthrosis. Impingement and fibrosis of fat pad were confirmed, and fibrous structures were removed by arthroscopy.

Before arthroscopy, the symptom obviously subsided after injection of local anesthesia into infrapatellar fat pad. Patellar clunk syndrome is also soft tissue impingement and suprapatellar fibrous nodule becomes entrapped intercondylar notch on the femoral component during knee flexion. On this point, these cases does not cause by patellar clunk syndrome. After fat pad resection, the symptom disappeared, and keeps symptom-free after a mean follow-up of six years five months in all cases. Any complications following fat pad resection, such as patella baja and necrosis, were not experienced.

Those cases achieving higher flexion angle tended to experience severe pain and shorter time interval between TKA and arthroscopic surgery, suggesting impingement of the infrapatellar fat pad is closely related to deep flexion after TKA. These results demonstrate that the anterior knee pain due to repetitive infrapatellar fat pad impingement is one of the complications during deep knee flexion after TKA, and the arthroscopic fat pad resection is useful to relief the anterior knee pain. Because of our experience with patients encountering anterior knee pain, we have begun to remove 70 to 80% of the fat pad during the primary TKA procedure since 1999, and until today, none developed anterior knee pain thought to be associated with fat pad impingement, patellar baja nor patellar necrosis. We suggest that fat pad resection is necessary to prevent the anterior knee pain due to fat pad impingement during deep flexion in TKA.

To make rectangular flexion and extension gap is an important goal in total knee arthroplasty (TKA). The purpose of this study was to determine the AP and rotational position of the femora component to obtain rectangular flexion with reference to the anatomical landmarks.

One hundred and twenty seven varus osteoarthritic knees (87 patients) undergoing TKA from June 2004 to March 2006 were included (72 women and 15 men, mean age 74.4 years). All operations were performed with Vanguard PS, Biomet (Warsaw, IN U.S.A.). The position of femoral component was determined using a modified Ranawat block (Equiflex^™) to obtain the rectangular flexion gap equal to extension gap. This instrument uses the balanced soft tissue sleeve in extension as a guide to create a balanced flexion gap. The flexion gap asymmetry after TKA was evaluated as the angle between the posterior condylar axis (PCA) and the tibial cutting line (TCL) by axial radiography of the distal femur. (Tokuhara et. al., JBJS (88-B), 2006). Briefly, axial radiography of the distal femur of flexed knee was obtained with a 1.5kg distraction force in ankle joint. This technique led to clear visualization of the asymmetry of the flexion gap. Femoral component rotation was evaluated using pre- and post-operative axial radiography of the distal femur (Kanekasu et. al., CORR (434), 2005). Condylar twist angle (CTA) is the angle between the CEA and the PCA. The rotational position femoral component relative to the PCA was calculated by subtracting post-operative CTA from pre-operative CTA. In addition, the thicknesses of resected bone from the lateral and medial posterior femoral condyles were measured.

The asymmetry of the flexion gap was 1.6±2.4° with slight laxity in the lateral side. The average amount of external rotation of the femoral component relative PCA was on 6.2 ±2.5°. The thickness of resected bone from the posterior lateral and medial condyles were 4.7 ± 2.1 mm and 8.6 ±2.1 mm respectively.

The results of this study have shown that, for a well-balanced flexion gap, femoral component should be excessively rotated by 3 degrees compared to current recommendation (Parallel to SEA) As for the AP position, the average amount of medial bone resection is equal to the implant thickness (9 mm). This information is useful for the modification of measured resection technique to obtain rectangular flexion gap.

The shape of the flexion gap in 20 normal knees was evaluated by axial radiography of the distal femur, and the results compared with those obtained in a previous study by MRI. The observed asymmetry was reduced by 29% using radiography, with a mean value of 3.6° (1.5° to 6.3°) compared with that obtained by MRI of 5.1° (2.6° to 9.5°), a mean discrepancy of 1.49°. The results obtained by radiography and MRI showed a strong correlation (r = 0.78).

Axial radiography is acceptable for the evaluation of the flexion gap and is less expensive and more comfortable to perform than MRI. Additionally, no metallic artefact occurs when the radiological method is used for assessment after arthroplasty.

Varus and valgus joint laxity of the normal living knee in flexion was assessed using MRI. Twenty knees were flexed to 90° and were imaged in neutral and under a varus-valgus stress in an open MRI system. The configuration of the tibiofemoral joint gap was studied in slices which crossed the epicondyles of the femur.

When a varus stress was applied, the lateral joint gap opened by 6.7 ± 1.9 mm (mean ± sd; 2.1 to 9.2) whereas the medial joint gap opened by only by a mean of 2.1 ± 1.1 mm (0.2 to 4.2). These discrepancies indicate that the tibiofemoral flexion gap in the normal knee is not rectangular and that the lateral joint gap is significantly lax. These results may be useful for adequate soft-tissue balancing and bone resection in total knee arthroplasty and reconstruction surgery on ligaments.

Introduction: Recently, highly cross-linked polyethylene has been highlighted in THAs, which is thought to reduce wear. However, little is known about an accurate nature of cross-linked polyethylene particles and long term wear in vivo. One of the authors implanted all polyethylene cups irradiated by 100 Mrad in 1970’s. Recently, we performed two revisions with this cup. In the present study, we extracted polyethylene particles and analyzed them.

Methods: Case1 was revised for a stem fracture and ace-tabular loosening at 25 years postoperatively and case2 for acetabular loosening at 27 years postoperatively. There was no osteolysis on X rays. We extracted polyethylene particles using a tiussue digestion and iamge analysis using computed iamge analyzer developed by Cambell.

Results: Equivalent circle diameter (ECD) was 0.73mm, roundness was 0.69, aspect ratio (AR) was 1.4 and number of particles was 6.0x108/g wet tissue in case1. ECD was 0.57mm, roundness was 0.62, AR was 1.54 and number of particles was 5.8x108/g in case2. SEM showed that granule or globular shapes were abundant and fibril shapes were rare.

Discussion and conclusion: Cross-linked polyethylene particles were less, a little smaller and much rounder in compared with our previous result of conventional polyethylene particles in peri-implant tissue after more than 25 years postoperatively in vivo.

Impaction allografting is one of the techniques for reconstruction of femur during revision total hip arthroplasties. The initial stability of the stem fixed with impacted morsellized allogtafts and cement depends on multiple factors. The aim of this study was to investigate the stability of stem in reference to the size of bone chips, femoral bone defect and implant design.

Morsellized grafts of human femoral heads were prepared using a reciprocating type bone mill or a rotating type bone mill. Femoral bone defect was created at proximal medial cortex. Two types of polished stem were tested; CPT stem and VerSys CT stem (Zimmer Inc.). The cross section of the stem was relatively rectangular in CPT stem, while round in VerSys CT stem. Morsellized grafts were impacted into an over-reamed plastic bone and the stem was fixed with PMMA bone cement. Cyclic compression test and torsional test were performed using an Instron type machanical tester. Bone chips prepared by a reciprocating type bone mill contained large chips with broad size distribution, which represented high stiffness in compression test and high maximum torque in torsional test. Femoral bone defect and implant geometry did not affect the axial stability of stem, while large bone defect and round shape stem showed significantly lower maximum torque.

These results indicated that the size of bone chips, femoral bone defect and implant geometry affected the initial stability of the stem. Impaction grafting seems to be a technically demanding procedure, however several factors can be controlled to obtain secure implant stability.

As for the number of patients who requires total knee arthroplasty (TKA), Asian-Pacific countries will be the most important market. However, due to the paucity of anthropometric data on the proximal tibia in this population, many prostheses designed for Caucasian knees have been introduced without specific modification.The aim of the current study was to analyze the geometry of the proximal tibia to design the optimum component for the Japanese population.

Anthropometric data on the proximal tibia of 100 knees in 80 patients undergoing TKA was obtained. Briefly, anterior-posterior (AP) and medial-lateral (ML) lengths were measured with a combination of two different methods, namely on the computed tomography (CT) images obtained preoperatively and intraoperative direct measurement on tibial resection surface. Reproducible measurement was possible only when the intraoperative measurement was combined with the corresponding CT images while the direction of measurements being aligned to the epicondylar axis of the femur.

It was shown that smaller components with an ML of around 60 mm were rarely required. Tibial component size variation should focus on an ML length of 65 to 75 mm because 76 of 100 knees (76 %) fell into this size range. When the subjects were confined to women, 70 of 77 knees (91%) were included in this size range. The intraoperative AP to ML ratio had a negative correlation with the ML length (r = −0.412, P < 0.0001) indicating that bigger knees were shallower in the AP direction. The size variation of currently popular pros-theses were not in accordance with the geometry of the tibial resection surface shown in this study.

The results of this study applied to a cross-section of the Japanese population can be used by manufacturers to create a prosthesis suitable for most of the Asian-Pacific population.

Aim: In alumina-on-alumina (Al/Al) THA, microsepa-ration is reported to accelerate wear and to be a risk factor of alumina cup fracture. While microseparation after THA is detected during walking, microseparation also occurs in relation to the hip position. Using Al/Al THA with cemented polyethylene-back alumina cup, the microseparation is clearly visible on plain roentgen-ograms. The aim of this study is to investigate the factors that affect hip position related microseparation. Materials and Methods: We performed 65 primary Al/Al THA. An average age at operation was 61.1 years and an average follow-up period was 29.5 months. Roentgenograms were taken in hip neutral position, abduction, adduction, external rotation and internal rotation. Results: Microseparation was observed in 15 hips (23.1%); 10 hips with hip external rotation and 5 hips with hip abduction. An average abduction angle of the cup was 33.5±9.8 degrees with microseparation and 36.6±7.3 degrees without microseparation. An average anteversion of the cup was 9.7±6.7 degrees and 7.8±5.8 degrees, respectively. The factors that brought about microseparation were postoperative muscle weakness in 3 hips, impingement in 9, cup malposition (abduction angle: 19, 23 degrees) in 2, and short off-set stem in one. Discussion and Conclusions: It should be noted that microseparation is not a rare phenomenon and it occurs in hip particular position even if it can not be detected on routine roentgenograms.

The benefit of mobile-bearing mechanism in total knee arthroplasty (TKA) has been controversial. The aim of this paper is to analyse the rotation of polyethylene (PE) and its effect on the range of motion (ROM) in mobile-bearing, posterior stabilised TKA (LPS-Flex™, Zimmer Co. Ltd.).

Thirty-four consecutive PS-Flex™ TKAs (28 patients) were analysed. Three tantalum markers were inserted in the PE and the tibia (one for medial side and two for lateral side; total six markers). The rotation of the PE and the tibia was analysed in fluoroscopically-controlled radiograph taken at one years in full extension, 90 degrees flexion and passive maximum flexion. The markers in the tibia were identifiable in 19 knees and the analysis was based on these knees.

The tibia rotated internally relative to the femur by 7.1± 5.2 degrees (mean ± SD, range −1 to 20 degrees). The amount of tibial rotation has no correlation to ROM. The rotation of the PE relative to the femur was unpredictable showing three knees with external rotation and four knees without rotation (Average; 4.0 ± 4.5 degrees internal rotation). The rotation of the PE on the tibia was 4.2± 5.2 degrees and seven knees (37 %) showed no rotation and 12 knees (63 %) showed less than 5 degrees rotation. There was a positive correlation between the amount of PE rotation on the tibia and ROM, which approached to statistical significance (p = 0.0684).

This study has demonstrated that the rotation of the PE on the tibial tray is generally small (< 5 degrees). Because not tibial internal rotation but PE movement on the tibia correlated to ROM, the essential benefit of the mobile-bearing mechanism could be to compensate the rotational mismatch between the components rather than to reproduce normal knee kinematics.

The new 3-Dimensional (3D) polyethylene wear measurement software GAWDI (Genetic Algorithm for Wear Detect Instrument) was developed to evaluate in vivo movement of the femoral head into the polyethylene liner. It enabled to detect 3D position of femoral head against polyethylene socket from two radiographs. Inter observer error of this system was 0.09 mm, intra observer error was 0.08 mm. Fifteen patients after THA was taken anterior-posterior (AP) and semi-lateral radiographs in both standing and supine position one year post operation. The difference of the 3D position of the femoral head was not observed between standing and supine position. However 8.1 degrees (mean) and 0.2 to 16.5 degrees (range) pelvic tilt was observed between these positions. 0.8 mm (mean) difference was observed by 2-Dimensional measurement system although no difference was observed by 3D system. Small separation between head and socket was observed in a few patients. However the influence of pelvic tilt was main origin of the difference between 2D and 3D measurement methods.

The role of posterior cruciate ligament (PCL) in total knee replacement (TKR) has been a matter of debate for long time and remains controversial. In this study, the effect of posterior cruciate ligament (PCL) sacrifice on the tibiofemoral joint gap was analysed in 30 varus osteoarthritic knees undergoing posterior stabilized total knee replacement. Medial soft tissue was released and bone cut was made without preserving the bone segment of tibial PCL insertion. Then the medial and lateral joint gaps in full extension and 90□& lsaquo; flexion were measured before and after PCL sacrifice using a tensioning device (V-STAT tensor(tm), Zimmer). After PCL sacrifice, the flexion gap significantly increased both in medial and lateral side (4.8 □} 0.4 and 4.5 □} 0.4 mm respectively, mean □} SE) compared to those seen in the extension gap (0.9 □} 0.2 and 0.8 □} 0.2 mm, p < 0.001 ANOVA). There was no significant difference between the changes in the medial and lateral gap (p = 0.493). In conclusion, results of this intraoperative measurement showed that PCL sacrifice leads to a selective increase in the size of flexion gap by an average of 4.7 mm whereas it had little impact on the correction of varus deformity. These findings provided insights as for the role and necessity of PCL sacrifice in the correction of varus and flexion deformity. Because the flexion gap surpassed the unchanged extension gap during PCL sacrifice, PCL release could be used as a surgical technique to balance the gaps without additional bone cut.

The purpose of this study was to investigate the bone anatomy in determining the rotational alignment in total knee arthroplasty (TKA) using CT scan. Axial CT images of eighty-four varus osteoarthritic knees undergoing TKA were analysed. On the images of the distal femur and the proximal tibia, base line for anterior-posterior axis of each component was drawn based on the epicondylar axis for the femur and medial one-third of the tibial tuberosity for the tibia. Angle between these two lines was analysed as the rotational mismatch between the components when they were determined based on the anatomical landmark of each bone. Thirty-eight knees (45%) showed more than 5-degree mismatch and seven knees (8.3%) showed the mismatch more than 10-degree. There was a tendency to put the tibial component in external rotation relative to the femoral component when they were aligned to medial one-third of the tibial tuberosity. The results have indicated that the landmark of each bone was the intrinsic cause of the rotational mismatch between the components. The surgeons performing TKA surgery should aware of this fact and should align the tibial component in a compromised position, if necessary, to have overall satisfactory clinical outcome.

We studied active flexion from 90° to 133° and passive flexion to 162° using MRI in 20 unloaded knees in Japanese subjects. Flexion over this arc is accompanied by backward movement of the medial femoral condyle of 4.0 mm and by backward movement laterally of 15 mm, i.e., by internal rotation of the tibia. At 162° the lateral femoral condyle lies posterior to the tibia.

Our aim was to analyse the influence of the size, shape and number of particles on the pathogenesis of osteolysis. We obtained peri-implant tissues from 18 patients having revision surgery for aseptically loosened Freeman total knee replacements (10), Charnley total hip replacements (3) and Imperial College/London Hospital double-cup surface hip replacements (5). The size and shape of the polyethylene particles were characterised using SEM and their concentration was calculated. The results were analysed with reference to the presence of radiological osteolysis.

The concentration of polyethylene particles in 6 areas with osteolysis was significantly higher than that in 12 areas without osteolysis. There were no significant differences between the size and shape of the particles in these two groups.

We conclude that the most critical factor in the pathogenesis of osteolysis is the concentration of polyethylene particles accumulated in the tissue.