UC San Diego

Background

First-time patellar dislocation with an associated chondral or osteochondral loose body is typically treated operatively to address the loose fragment. The incidence of recurrent instability in this patient population if the medial patellofemoral ligament (MPFL) is not reconstructed is unknown.

Purpose

To determine the recurrent instability rate in patients undergoing surgery for patellar instability with chondral or osteochondral loose bodies, as well as to identify and stratify risk factors for recurrent instability.

Study design

Case series; Level of evidence, 4.

Methods

This was a retrospective analysis of adolescent patients treated operatively for acute patellar dislocation with associated chondral or osteochondral loose bodies between 2010 and 2016 at a single pediatric level I trauma center with minimum 2-year follow-up. Potential demographic, injury-related, radiographic, and surgical risk factors were recorded. The primary outcome variable was recurrent subluxation and/or dislocation. Secondary outcome variables included need for additional procedures, Kujala score, Single Assessment Numerical Evaluation (SANE) score, and patient satisfaction.

Results

Forty-one patients were included. In total, 61% experienced recurrent instability at a mean follow-up of 4.1 years and 39% required subsequent MPFL reconstruction. Tibial tubercle-trochlear groove (TT-TG) distance greater than 15 mm was a risk factor for recurrent instability ( P = .03). Patients with TT-TG distance greater than 15 mm and greater than 20 mm had recurrent instability rates of 75% and 86%, respectively. MPFL repair did not reduce the rate of recurrent instability ( P = .87). Recurrent instability was associated with significantly worse mean Kujala (93.9 vs 83.0; P = .01), SANE (88.9 vs 73.1; P = .01), and patient satisfaction scores (9.4 vs 7.3; P = .002).

Conclusion

If the MPFL is not reconstructed during index loose body treatment, children have a 61% recurrent instability rate. Patients with TT-TG distance greater than 15 mm, and particularly greater than 20 mm, are at highest risk for recurrent instability.