Aim
Patellofemoral complications remain a leading cause of patient dissatisfaction after TKA. Intraoperative patella tracking has traditionally relied on subjective assessment, limiting meaningful outcome correlation. This study leverages objective robotic tracking data to examine whether coronal or sagittal patella track influences early patient reported outcome measures (PROMs).
Methods
A prospective cohort of 94 patients (103 knees; 47 male, 56 female) undergoing primary robotic TKA using the CORI system (Smith & Nephew) was analysed. Mean age was 71.4 years (SD 6.9). Intraoperative patella tracking was captured pre- and post-implantation using the system's point capture function, generating coronal and sagittal track profiles reviewed by two independent assessors. Coronal tracks were classified relative to Whiteside's line as retained or unretained. Sagittal tracks were subjectively and objectively classified as understuffed, neutral, or overstuffed across four zones (overall, proximal, middle, distal), with further stratification across six objective zones. Anterior and distal femoral resection depths provided objective validation. PROs — normality, pain, and satisfaction — were collected at 3 months via the Sydney Orthopaedic Research Institute survey.
Results
PROM scores were skewed: median normality 80 (IQR 30.0), pain 21.5 (IQR 32.5), and satisfaction 79.2 (IQR 20.8). Post-implantation coronal tracking shifted significantly medially (McNemar p<0.001), driven predominantly by conversion of pre-operative lateral tracks (lateral→medial, p<0.001). Despite this shift, neither pre- nor post-operative coronal track classification, nor track retention status (47 retained vs 40 unretained), demonstrated any association with normality, pain, or satisfaction scores (Kruskal-Wallis and Mann-Whitney U, all p>0.2).
For sagittal patella tracking analysis, understuffing was the predominant finding — occurring in 39% overall, 59% proximally, 39% in the middle zone, and 24% distally. A clinically meaningful association was identified between sagittal track and pain outcomes: neutral middle-zone tracking was associated with significantly lower median pain scores compared to understuffed tracks (median 10 vs 25; DSCF p=0.028), with a consistent pattern observed in the overall sagittal track (p=0.024). No other zones or PROM domains reached significance. Objective sagittal tracking across all six zones showed no association with any PRO (Kruskal-Wallis, all p>0.14), and Spearman correlation of raw sagittal offset values confirmed no relationship with outcomes across any zone. Notably, anterior lateral femoral resection depth demonstrated a significant positive correlation with pain scores (Spearman r=+0.31, p=0.009), suggesting that technical decisions around this resection may have downstream symptomatic consequences.
Conclusion
Sagittal patella understuffing — particularly in the middle zone — is associated with increased early post-operative pain following robotic TKA. Coronal track pattern and retention did not influence PROMs. These findings highlight the clinical importance of optimising sagittal patella position during TKA, and suggest that anterior lateral resection depth warrants particular intraoperative attention. Robotic platforms provide objective, reproducible intraoperative tracking data that may help guide surgical technique and ultimately improve patient outcomes.
