Evidence of trochlear dysplasia in patellofemoral arthroplasty designs.

Purpose: The design of the trochlear compartment is crucial in patellofemoral arthroplasty (PFA), because 78 % of patients with isolated patellofemoral arthritis present concomitant trochlear dysplasia with patellar maltracking and therefore remain predisposed to post-operative patellar subluxation and dislocation. The study investigated whether current PFA implants are designed with anatomic trochlear parameters such as the sulcus angle, lateral facet height and groove orientation. Methods: Five trochlear components of commercially available PFA implants were scanned, and the generated three-dimensional surfaces were measured using engineering design software. The mediolateral trochlear profiles were plotted at various flexion angles (0°, 15°, 30° and 45°) to deduce the following variables: sulcus angle, height of lateral facet and trochlear groove orientation. Results: Four specimens had sulcus angle >144° in the 45° of flexion, and all five specimens had sulcus angle >143° in 30° of flexion. Three specimens had a facet <5 mm high through the entire range of early flexion (0°-30°), and two specimens had a facet <5 mm high beyond early flexion (30°-45°). The trochlear groove was oriented laterally in all specimens (range 1.6°-13.5°). Conclusion: Current PFA trochlear components are not always designed with anatomic parameters, and some models exhibit characteristics of trochlear dysplasia. Surgeons are therefore advised to implant components with a deep sulcus, particularly in patients with history of patellofemoral disorders, and to adapt the surgical technique and extensor mechanism if the component implanted has a shallow sulcus, to ensure normal patellar tracking. Level of evidence: III. [ABSTRACT FROM AUTHOR]