Abstract
Background:
We studied the effect of posterior condylar offset on maximum knee flexion after a posterior stabilised total knee arthroplasty. We also looked at gender difference and the post-operative change in posterior condylar offset.
Methods:
Eighty consecutive computer navigated posterior stabilised total knee replacements were prospectively assessed intra-operatively for maximum knee flexion. The flexion angle was measured and recorded with an imageless computer navigation system (Brainlab) before and after implantation of the prosthesis. This was correlated with a radiological review of the posterior condylar offset pre- and post-operatively, as defined by posterior condylar offset ratio (PCOR) originally described by Soda (2007) and modified by the Bristol Knee Group (2010).
Results:
No relationship could be found between change in posterior femoral offset ratio and the change in knee flexion before and after implantation of the prosthesis (p = 0.46.)This was especially true for female subjects (p = 0.87.)For male patients there was a trend towards an inverse relationship demonstrating decreasing flexion with an increase in PCOR (p = 0.16.) PCOR increased in 91 % of cases and overall increased from an average of 0.44 pre-operatively to 0.49 post-operatively. The increase in PCOR was smaller where a large pre-operative PCOR was present (p = 0.0006.)Pre-operative flexion correlated significantly with postoperative flexion (p = 0.00.)There was no difference in PCOR between male and female patients.
Conclusion:
Knee flexion is not influenced by a change in posterior condylar offset in posterior stabilised knees. The increase in posterior condylar offset with a posterior stabilised TKA could by explained a larger increase in the flexion gap than in the extension gap, when sectioning the posterior cruciate ligament. The PCOR increases in cases with smaller pre-operative posterior condylar offset. Pre-operative flexion is a significant predictor of postoperative flexion.
