Recurrent patellar instability is a common, disabling condition. Isolated MPFL reconstruction (MPFLr) and, concomitant MPFL reconstruction with tibial tubercle osteotomy (MPFLr + TTO) are common corrective operations for recurrent patellar instability. However, there is a lack of consensus surrounding the exact indications for the addition of a TTO in the recurrent patellar instability population. This study assessed the post-operative outcomes in either procedure across a patient population with varying radiographic and demographic factors to determine indications for either surgery.
This study was a retrospective cohort study. Patients from a large orthopaedic clinic who underwent a MPFLr +/- TTO between 2006 to 2020 were contacted after a minimum of 12 months post-op to report their clinical and functional outcomes by reporting return to sport, further dislocations, ongoing discomfort and completing Kujala and Norwich Patellar Instability questionnaires. Radiographic measurements of IS ratio, Caton-Deschamps index (CDI), Blackburne-Peele ratio, sulcus angle, TT-TG and skeletal maturity were assessed from pre-op MRIs by two independent reviewers. Radiographic measurements were compared between groups using an independent t-test. Logistic regressions were used to compare post-operative outcomes between groups. A chi square test and ordinal regression was used to compare return to sport between-groups. A significance level of 5% was used throughout.
97 patients with a total of 104 operated knees responded, consisting of 56 isolated MPFLr’s, and 48 MPFLr + TTO’s. Both cohorts had a high incidence of pre-operative patellar alta, trochlear dysplasia and patella tilt. Between groups, patients with an additional TTO procedure had a greater patellar height as measured by CDI and an increased sulcus angle compared to the MPFLr cohort (p<0.05). There was no difference in post-operative outcome measures, return to sport or reported discomfort between MPFLr versus MPFLr + TTO cohorts. Time since operation was also not a predictor for pain or instability indicating a quick recovery of patient reported outcomes to long-term baseline at twelve months post-op. Older age and female sex were statistically significant (p<0.05), but not clinically significant, predictors of poorer pain outcomes in both groups. There were no predictors of instability outcomes in either group.
While an additional TTO is established in the literature to incur an increased risk of post-operative morbidity, both MPFLr and MPFLr + TTO cohorts had similar post-operative outcomes. This suggests successful patient selection with patients with greater patellar height as measured by CDI (p<0.05) and an increased sulcus angle benefitted from an additional TTO. While further prospective investigation is required, in this cohort, radiographic features of patellar alta and trochlear dysplasia were consistent criteria for the addition of a TTO to the MPFLr.