Preoperative patellofemoral anatomy affects failure rate after isolated patellofemoral inlay arthroplasty

Purpose To analyze whether preoperative patellofemoral anatomy is associated with clinical improvement and failure rate after isolated patellofemoral arthroplasty (PFA) using a modern inlay-type trochlear implant. Methods Prospectively collected 24 months data of patients treated with isolated inlay PFA (HemiCAP ® Wave, Arthrosurface, Franklin, MA, USA) between 2009 and 2016, and available digitalized preoperative imaging (plain radiographs in three planes and MRI) were retrospectively analyzed. All patients were evaluated using the WOMAC score, Lysholm score, and VAS pain. Patients revised to TKA or not achieving the minimal clinically important difference (MCID) for the total WOMAC score or VAS pain were considered failures. Preoperative imaging was analyzed regarding the following aspects: Tibiofemoral OA, patellofemoral OA, trochlear dysplasia (Dejour classification), patellar height (Insall–Salvati index [ISI]; Patellotrochlear index [PTI]), and position of the tibial tuberosity (TT–TG and TT–PCL distance). Results A total of 41 patients (61% female) with a mean age of 48 ± 13 years could be included. Fifteen patients (37%) were considered failures, with 5 patients (12%) revised to TKA and 10 patients (24%) not achieving MCID for WOMAC total or VAS pain. Failures had a significantly higher ISI, and a significantly lower PTI. Furthermore, the proportion of patients with a pathologic ISI (> 1.2), a pathologic PTI ( 1.2 and PTI 21 mm). Concomitant procedures such as tibial tuberosity transfer may, therefore, be considered in such patients. Level of evidence Level III, retrospective analysis of prospectively collected data.