Patellar tendon shortening following patellofemoral joint replacement.

PURPOSE: Patellar tendon shortening may occur following patellofemoral joint replacement (PFJR). We hypothesized that patellar tendon shortening results in unfavourable patient-reported outcomes (PROs). The aim of this study was to determine the effect of patellar tendon shortening following PFJR on PROs.

METHODS: In this substudy of a prospective cohort study, a total of 108 patients with isolated patellofemoral osteoarthritis underwent 124 patellofemoral joint replacements. We measured both patellar tendon length and length of the patella on pre-operative radiographs, and on radiographs acquired at eight weeks and at one year post-operative. More than 10% decrease in patellar tendon length relative to the pre-operative patellar tendon length was defined as patellar tendon shortening. Clinical outcomes were assessed using the knee-specific KOOS questionnaire (Knee Injury and Osteoarthritis Outcome Score). Repeated measures ANOVA was used to analyze for differences in change from baseline KOOS subscales between patients with and patients without patellar tendon shortening.

RESULTS: A complete series of standardized pre-operative, eight weeks and one year post-operative radiographs was available for 87 knees in 82 patients. At eight weeks, 16 of 87 knees (18%) showed patellar tendon length shortening, and 27 of 87 knees (31%) at one year. We found no statistically significant relation between patellar tendon length shortening and change from baseline KOOS subscales at one year follow-up (pain p = 0.29, symptoms p = 0.56, ADL p = 0.23, sport or recreation p = 0.22, knee-related quality of life (QOL) p = 0.15).

CONCLUSIONS: Patellar tendon length shortening following PFJR occurs in 31% of knees at one year, and does not result in inferior PROs.