Summary

Substantial cartilage injuries are present in 56% of patients who undergo primary isolated MPFL reconstruction, with medial patellar lesions being the most common. Increased age at surgery is associated with an increased risk of substantial cartilage damage.

Abstract

Introduction

Recurrent patellar instability is a debilitating condition that is often managed surgically with reconstruction of the medial patellofemoral ligament (MPFL) among other procedures. Damage to the articular cartilage of the patella and trochlea can occur with these injuries and recent work has demonstrated poorer outcomes of MPFL reconstruction in patients with articular cartilage damage. The goals of this study are to quantify the prevalence and location of articular cartilage injuries in patients treated for patellar instability with MPFL reconstruction and to identify factors associated with cartilage damage.

Methods

199 patients undergoing isolated MPFL reconstruction at 6 centers on 5 continents between 2016 and 2020 were prospectively enrolled. All procedures were performed for recurrent patellar instability. Patients treated with bony procedures (tibial tubercle osteotomy, trochleoplasty, or other osteotomy) were not included. Indications for bony procedures were the presence of a jumping j-sign on examination, unloadable chondral defects, patellar alta with a Caton-Deschamps index (CDI) greater than 1.30, or severe trochlear dysplasia that the surgeon felt warranted a trochleoplasty. Patient history (age at surgery, number of prior dislocations, time from injury to surgery) and demographic (age, sex, BMI, Beighton score) variables were collected at enrollment and imaging measurements were collected from plain films (CDI) and MRI (trochlear sulcus angle and depth, patellotrochlear index [PTI] tibial tubercle-trochlear groove [TT-TG] distance, Dejour calssification). All patients underwent a diagnostic arthroscopy and articular cartilage of the patellofemoral joint was assessed according to the International Cartilage Restoration Society (ICRS) system. Cartilage damage location on the patella was recorded. Patients with articular cartilage damage of ICRS grade 2 or greater in the patellofemoral joint were defined as having substantial cartilage damage. Patient and injury factors were compared based on the presence or absence of cartilage damage and a multiple logistic regression model was created to identify predictors of cartilage damage.

Results

111 patients (56%) were noted to have substantial patellofemoral articular cartilage injury (72 grade 2, 27 grade 3, 12 grade 4). Most of these patients (106) had patellar cartilage damage, with trochlear damage less common (19 patients). Sixty-nine of the 106 patients with patellar cartilage damage (65%) had medial patellar damage. The cartilage damage group demonstrated significantly increased age at surgery (p = 0.022) and trends toward higher BMI (p = 0.059), lower Beigton score (0.059), more severe trochlear dysplasia (p = 0.16), higher patellotrochlear index (p = 0.20), and a higher incidence of contact injury (p = 0.16). Logistic regression demonstrated that increased age at surgery (OR = 1.079, p = 0.010) was the only significant predictor of substantial cartilage injury. Each one year increase in patient age was associated with a 7.9% increase in the odds of having substantial cartilage injury.

Conclusion

Substantial cartilage injuries are present in 56% of patients who undergo primary isolated MPFL reconstruction, with medial patellar lesions being the most common. Increased age at surgery is associated with an increased risk of substantial cartilage damage.