TROCHLEAR LENGTH: ANATOMICAL AND CLINICAL IMPLICATIONS IN MODERN TOTAL KNEE ARTHROPLASTY

Introduction The aim of our study was to study a) the native host trochlear cartilage length and b)the relationship of host trochlear cartilage length on anterior knee pain (AKP) and clinical outcomes post primary total knee arthroplasty (TKA). Methods We prospectively recruited 251 patients who underwent primary TKA at a single tertiary care centre. Patients received one of two modern patella friendly femoral designs with patella resurfacing. Intraoperatively, we recorded: a) Host trochlear length (HTL)- length from the cut distal femoral surface to the proximal most point of the host trochlear cartilage (HTL) after the distal femoral cut, b) Overstuffing- difference between length of the trochlea of the corresponding implant used (ITL) and the HTL (Overstuffing = ITL-HTL), and c) HTL/ML ratio- ratio between the HTL and mediolateral width of the trochlea at the anterior femoral cortex at the level of the cut surface after the distal femoral cut. At 1 year, we categorized patients as having mild AKP if Visual analogue scale(VAS) ≤3 and severe AKP if VAS >3. Results The mean HTL was 25.4 mm(range 8.5 – 45). All patients had lengthwise overstuffing ranging from 6.1 mm to 37mm(mean 21.3 mm). The mean HTL/ML ratio was 0.57(range 0.17 to 1.30). At 1 year post TKA, 19.7% had mild AKP, while 14.2% had severe AKP. Patients having severe AKP had significantly lower (p<0.001) HSS Patella Score, WOMAC Score, Oxford Knee Score and Forgotten Joint Score. On logistic regression analysis, female sex and posterior stabilized femoral components were significant predictors (p<0.05) of lower HSS patella scores. Conclusion Patients undergoing primary TKA with modern femoral components continue to have a high incidence (33.9%) of AKP with 14.2% having severe AKP at 1 year post surgery. The trochlea was overstuffed lengthwise in all patients. However, the effect of this overstuffing on clinical outcomes needs further research.