Association and impact of patellofemoral dysplasia on patellofemoral arthropathy and arthroplasty

Background: The association of patellar and trochlear anomalies resulting in isolated patellofemoral osteoarthritis has often been postulated but rarely studied. The purpose of this study was to examine the association of patellofemoral dysplasia, specifically trochlear anomalies, which are a cause for degenerative disease and may result in a worse outcome after arthroplasty for isolated patellofemoral arthritis. Methods: Eighteen consecutive patients who underwent robotic image-based patellofemoral arthroplasty were compared with an age and sex-matched group of patients who underwent medial unicompartmental arthroplasty using the same image-based navigation system and had no patellofemoral, lateral disease or malalignment.The compared parameters were the patellofemoral-trochlear angle and Dejour score in the preoperative radiographs and patellofemoral-trochlear angle and internal rotation of the trochlea compared to the intercondylar line in the proximal, middle and distal trochlea. Results: Significantly higher rates of patella alta (T=5, P=0.0001) and trochlear dysplasia (6% vs. 55%) were found, as manifested by an increase in the trochlear angle and Dejour score. Furthermore, the trochlea was found to have a higher degree of internal rotation in patients with isolated patellofemoral arthritis compared to the control group. Conclusions: In conclusion, patellofemoral anomalies such as patella alta and trochlear dysplasia are present in association with isolated patellofemoral arthritis. Isolated patellofemoral arthritis is also associated with higher rates of trochlear internal rotation. Correction of this internal rotation is essential in the success of arthroplasty in patients with patellofemoral disease. Level of evidence: Level III study, It is a case control study.