Patellar dislocation is associated with increased tibial but not femoral rotational asymmetry.

PURPOSE: Patellar dislocation is associated with a range of anatomical abnormalities affecting the trochlea, extensor mechanism and the tibia. The relationship between patellofemoral instability and rotational abnormalities of the posterior condyles, trochlear groove and proximal tibia has not been adequately determined. This study aimed to identify the frequency and severity of anatomical risk factors to determine their relative contribution to patellofemoral instability. METHODS: A retrospective morphological study was undertaken comparing multiple anatomical measurements with magnetic resonance imaging of 50 patients with patellofemoral instability to an age- and gender-matched Control group (n = 50). Several techniques were assessed measuring both femoral and tibial axial asymmetry. A new measurement, tibial rotational asymmetry, comparing a line between the midpoints of the collateral ligaments to the axis between the patellar tendon and posterior cruciate ligament, was assessed for its association with patellofemoral instability. RESULTS: Compared to the controls, the patellofemoral instability group demonstrated a significant difference in tibial rotational asymmetry, with a mean of 2.9° (SD 3.2°) externally rotated vs - 1.6° (SD 2.2°) in the control group. Significant differences were also demonstrated regarding the sulcus angle, tibial tubercle-trochlear groove distance, tibial tubercle-posterior cruciate ligament distance, patellar size and the Insall-Salvati ratio. There were no differences between groups regarding the lengths of the posterior condyles, the heights of the trochlear ridges or lateralisation of the trochlear groove. Further analysis of the patellofemoral instability group revealed a subgroup of males with normal anatomy (7/50) and a subgroup of females with isolated patella alta (7/50). CONCLUSION: Patellofemoral instability is associated with tibial rotational asymmetry due to lateralisation of the tibial tubercle. It is also associated with patella alta and reduced trochlear groove depth. The femoral axial shape is otherwise unchanged. LEVEL OF EVIDENCE: III.

Modular Total Femur Replacement for Staged Total Femur Replacement.

As the numbers of arthroplasties performed worldwide increase, so do complications such as prosthetic joint infection. Cases that require a two-stage revision of a total femur replacement in the femur pose an ongoing challenge to the modern orthopedic surgeon. Unlike antibiotic spacers in hip and knee arthroplasty, there lacks a commercially available cement spacer for use in total femur replacements. We describe a novel technique for the intraoperative fabrication of a total femur spacer which uses modular components. As such, our technique is unique as it is modular and, therefore, highly customisable to each individual patient. Individual components can be made by different members of the team simultaneously and then assembled to make the final construct, thereby minimizing operative time. Furthermore, the inherent stability of the spacer allows immediate partial weightbearing and functional rehabilitation while patients are waiting for their second-stage procedure.

Averaging rotational landmarks during total knee arthroplasty reduces component malrotation caused by femoral asymmetry.

BACKGROUND: Femoral component malrotation is a common cause of patient dissatisfaction after total knee arthroplasty. The sulcus line (SL) is more accurate than Whiteside's line as it corrects for variation in the coronal orientation of the groove. The hypothesis is that averaging the SL and posterior condylar axis (PCA) will reduce femoral malrotation. METHODS: The component was inserted at a position between the SL and PCA in 91 patients. An intraoperative photograph was taken showing the landmarks. These were compared to the component position achieved relative to the surgical epicondylar axis (SEA) on a postoperative CT scan. The component position was compared to the position achieved using the individual landmarks. RESULTS: Relative to the SEA, the final component position was 0.6° (SD 1.4°, range -3.8° to +4.0°), the coronally corrected SL position was -0.7° (SD 2.3°, -5.5° to +4.6°), the PCA position was 0.9° (SD 1.9°, -6.1° to +5.0°). Averaging the landmarks significantly decreased the variance of the component position compared to using the SL and PCA individually. The number of outliers (>3° from SEA) was also significantly less (p < 0.05) for the average position (2/84) when each was compared to the SL (16/84) and PCA (14/84) individually. In 21/84 (25%) of cases, there was more than 4° of divergence between the SL and PCA. CONCLUSIONS: Averaging the SL and the PCA decreases femoral component malrotation. Femora are frequently asymmetrical in the axial plane. Referencing posterior condyles alone to set rotation is likely to cause high rates of patellofemoral malalignment.