Decreased Femoral Trochlear Length Associated With Increased Anterior Knee Pain Following Total Knee Arthroplasty: A New Anatomical Perspective.

Background: Anterior knee pain (AKP) and patello-femoral crepitus (PFCr) continue to plague total knee arthroplasty patients despite advances and modifications to implant design and surgical techniques. We present our study of the femoral trochlear length measurement preimplantation and postimplantation and its association with AKP/PFCr and clinical scores.

Methods: Using computer navigation, we obtained several measurements in 263 total knee arthroplasty (posterior-stabilized) patients, which included femoral native trochlear measurement (NTM) and difference in trochlear length between implant and native trochlea. We report their association with Knee Society Score, Western Ontario McMaster University Arthritic Index, and AKP/PFCr at 1 year postoperatively.

Results: Mean Knee Society Score and Western Ontario McMaster University Arthritic Index scores were significantly worse in patients who had AKP (P = .005 and P = .002 respectively). Receiver operating characteristic curve showed a statistically significant association between NTM and AKP (Area under the curve = 0.609, P = .014). Lower the NTM, greater was the incidence of AKP. Analysis of the receiver operating characteristic curve identified the cutoff value of NTM to be ≤25.5 with sensitivity of 76.7(95% confidence interval - 57.7 - 90.1) and specificity of 46.9 (95% confidence interval - 41.9 - 55.1). Patients who had NTM of ≤25.5 had an odds ratio of 3.09 to have AKP. The difference in trochlear length ranged from 7.4 to 32.1 millimeters, indicating that postimplantation there was lengthwise overstuffing along the trochlea in every patient.

Conclusion: We found that the shorter the native femoral trochlea and greater the difference between implanted and native trochlea, the higher was the occurrence of AKP. A mismatch in trochlear measurement preimplantation and postimplantation resulted in lengthwise overstuffing in the anterior knee causing AKP and PFCr.