Background
Posterior osteophytes are commonly encountered during total knee arthroplasty (TKA), but in many workflows they are accessed only after balancing and planned resections have been made. We hypothesised that posterior osteophytes act as mechanical blocks to extension, tighten the
extension gap more than the flexion gap, and that these effects are related to osteophyte volume.
Methods
A paired intraoperative study was performed in 61 robotic-assisted TKAs with large posterior osteophytes. For each knee, medial and lateral gaps in extension and flexion, together with range of motion, were measured twice with trial components in situ: first with posterior osteophytes intact, and again after posterior osteophyte resection. Preoperative computed tomography (CT) scans were analysed using Digital Imaging Processing Software (DIPS) to quantify posterior osteophyte volume. The association between combined posterior osteophyte volume and improvement in extension was assessed with Pearson correlation.
Results
Posterior osteophyte resection increased both extension and flexion gaps, with a much larger effect in extension. Mean medial and lateral extension gap opening was 0.79 mm (95% confidence interval [CI] 0.60 to 0.98; p<0.001) and 0.60 mm (95% CI 0.42 to 0.77; p<0.001), respectively. Mean medial and lateral flexion gap opening was 0.38 mm (95% CI 0.21 to 0.55;
p<0.001) and 0.30 mm (95% CI 0.08 to 0.52; p=0.007). Medial extension gap opening occurred in 51/61 knees (83.6%) and lateral extension gap opening in 41/61 knees (67.2%). Extension improved by 4.01° (95% CI 3.34 to 4.68; p<0.001), with mean extension changing from 4.64° flexion pre-resection to 0.63° flexion post-resection. Flexion improved by 2.67° (95% CI 1.91 to 3.43; p<0.001), and overall range of motion increased by 6.68° (95% CI 5.54 to 7.82; p<0.001). Combined posterior osteophyte volume showed a modest positive correlation with improvement in extension (r=0.40, p=0.0014).
Conclusion
Posterior osteophytes have a measurable effect on balance and motion during robotic TKA, particularly in extension. Their resection commonly opens the extension gap and improves extension towards neutral. Larger posterior osteophytes are associated with greater improvement in extension, supporting the concept that they are clinically relevant mechanical blocks during balancing. This may inform pre-resection planning in workflows where posterior osteophytes are accessed late.
