Summary

The study sets MOI thresholds for different PROM, thus correlating patient- and surgeon-defined satisfactory outcomes after isolated MPFL-R.

Abstract

Objective

The primary aim of the study was to define the threshold value of maximal outcome improvement (MOI) for previously validated PROM associated with surgeon-defined satisfactory postoperative outcomes after isolated Medial Patellofemoral Ligament Reconstruction (MPFL-R) for patellar instability. The secondary aim was to identify the most effective PROM in predicting these outcomes and to evaluate the factors associated with it.

Methods

As part of the JUPITER (Justifying Patellar Instability Treatment by Results) multi-center study, a retrospective review of the prospectively maintained database was performed to identify patients who underwent isolated MPFL-R from January 2018 to December 2021. Inclusion criteria for the current study were patients with at least one year of follow-up and exclusion criteria included revision MPFL-R, concomitant bony procedures such as tibial tubercle osteotomy, and those missing follow-up PROMs. PROM including the Banff Patellofemoral Instability (BPII 2.0) Instrument, International Knee Documentation Committee (pedi-IKDC), Knee Injury and Osteoarthritis Outcome Score (KOOS) and Kujala were collected at baseline and at 1-year, 2-year and 5-year follow-up. From a surgeon standpoint, satisfactory outcomes were defined as the ability to return to sports at same or higher level compared to pre-injury state, no episodes of further patellar subluxation or dislocation, and not having undergone any additional surgery for patellar instability. MOI was calculated as a percentage of the maximum potential improvement that could be achieved from the preoperative state. Receiver operating characteristic curve analyses were performed to determine threshold values for percentages of MOI for PROM associated with satisfactory outcomes. Multivariate analyses were performed to determine preoperative, intraoperative, and radiographic factors (patellar height, patellar tilt, tibial tubercle lateralization and trochlear dysplasia) that were associated with satisfactory outcomes after isolated MPFL-R

Results

284 patients were included in the analysis.183 (66.9%) patients had satisfactory outcomes. For MOI, achieving an improvement in the BPII 2.0 score greater than 65.86%, in the Pedi-IKDC score greater than 62.96%, in the KOOS score greater than 61.65%, and in the Kujala score greater than 85.18% of the maximum possible improvement from the preoperative state was associated with a satisfactory outcome (Table 1). BPII 2.0 had the highest AUC amongst the others indicating better discriminating ability of the score, while Kujala had the least AUC with statistically significant difference between the two measures (Table 2, Fig 1). Multiple Logistic regression analysis showed that patients with recurrent patellar dislocation had higher odds of satisfactory outcomes (OR 4.09, P = 0.0015) compared to first-time dislocation. Amongst those with recurrent patellar dislocation, having 10 or more dislocations significantly decreased the odds of achieving satisfactory outcomes (OR 0.12, P = 0.0012) (Table 3).

Conclusion

The study sets MOI thresholds for different PROM, thus correlating patient- and surgeon-defined satisfactory outcomes after isolated MPFL-R. BPII 2.0 had superior discriminating ability compared to other scores while Kujala had the worst. The study identifies that isolated MPFL-R after first-time dislocation and after having 10 or more dislocations are associated with decreased odds of satisfactory outcomes.