Evidence of trochlear dysplasia in patellofemoral arthroplasty designs

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. 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 (0A degrees, 15A degrees, 30A degrees and 45A degrees) to deduce the following variables: sulcus angle, height of lateral facet and trochlear groove orientation. Four specimens had sulcus angle > 144A degrees in the 45A degrees of flexion, and all five specimens had sulcus angle > 143A degrees in 30A degrees of flexion. Three specimens had a facet < 5 mm high through the entire range of early flexion (0A degrees-30A degrees), and two specimens had a facet < 5 mm high beyond early flexion (30A degrees-45A degrees). The trochlear groove was oriented laterally in all specimens (range 1.6A degrees-13.5A degrees). 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.