Abstract
Introduction Satisfactory patellar tracking is important following total knee arthroplasty. A lateral retinacular release may be required to correct patellar maltracking but can be complicated by damage to the skin, soft tissues or patella.
Aim The aim of this study was to determine if, when using the LCS prosthesis, the rate of lateral patellar release was reduced by centering the finishing guide on Whiteside’s line as opposed to the mid-point of the femoral condyles.
Patients and Methods One hundred and ten consecutive patients (64 female, 46 male) undergoing primary total knee arthroplasty were prospectively studied. At the time of performing the champher cuts, the finishing guide was first centered on the mid-point of the femoral condyles and a mark placed on the trochlea using the needle diathermy. The finishing guide was then finally centered on the previously marked Whiteside’s line. The distance between the two marks was measured using a caliper. Following component insertion patellar tracking was checked. If required a lateral release was performed allowing the patella to track with its medial facet in contact with the medial femoral condyle.
Results Centralization of the femoral component on Whiteside’s line instead of the mid-point of the femoral condyles lateralized the component by an average of 2.7mm (range, x–ymm). This parameter was termed the patellofemoral offset (PFO). When compared to a sample of patients where the finishing guide was centered on the mid-point of the femoral condyles, the lateral patellar release rate was reduced from 25% to 18%.
The magnitude of PFO increased with age however there was no significant difference in PFO between males and females. The PFO was significantly greater for knees with a preoperative valgus deformity (p=0.006).
Conclusion Centering the femoral component on White-side’s line leads to a reduction in lateral patellar release rate during TKA.
Correspondence should be addressed to Roger Smith, Honorary Secretary, BASK c/o Royal College of Surgeons, 35 – 43 Lincoln’s Inn Fields, London WC2A 3PN
