Elevated Instability Resolution Angle Predicts Inferior Patient-Reported Outcomes in Isolated Medial Patellofemoral Ligament Reconstruction.

Purpose: To investigate the prognostic utility of an examination under anesthesia (EUA) by evaluating the patient-reported outcome scores (PROs) and failure rates of patients undergoing primary, isolated medial patellofemoral ligament reconstruction (MPFLR) relative to their EUA findings.

Methods: A retrospective review was performed on patients who underwent primary, isolated MPFLR between August 2015 and August 2021. During the EUA the instability resolution angle (IRA) was identified by applying a lateral force on the patella through increasing knee flexion and defined by the degree of flexion the patella ceased lateral translation. PROs, including International Knee Documentation Committee (IKDC), Knee Injury and Osteoarthritis Outcome Score Jr, and Kujala, were collected at 1-year and 2-year minimum after surgery. In addition, MPFLR failure was recorded and defined by patellar redislocation.

Results: In total, 94 patients met inclusion criteria, with 42 patients having an IRA <60° and 52 patients with an IRA ≥60° of knee flexion. At 2-year minimum follow-up, IKDC and Kujala PROs were significantly lower in patients with IRA ≥60° compared with patients with IRA <60° for both final and delta PROs. Mean tibial tubercle-trochlear groove distance examined on preoperative magnetic resonance imaging was 17.21 ± 5.00 mm for the IRA ≥60° cohort and 14.36 ± 4.89 mm for the IRA <60° cohort ( .01). Four patients redislocated their patella, and all 4 had an IRA ≥60° ( .07).

Conclusions: Patients who underwent isolated MPFLR with an IRA ≥60° had significantly lower IKDC and Kujala scores than similar patients with IRA <60° of knee flexion at 2-year minimum follow-up. Four (7.7%) patients with IRA ≥60° redislocated their patella, whereas zero patients with IRA <60° experienced redislocation.

Level Of Evidence: Level III, retrospective cohort study.