Summary

A two subscale composite KOOS score that includes sport and recreation and quality of life subscales is an improved option for measuring patient related outcomes for patellofemoral instability patients, with the full 42-item KOOS having limited applicability.

Abstract

Background

Various knee-related patient reported outcome measures (PROMs) have been used for patients who undergo surgical treatment for patellofemoral instability. There has been limited evaluation of their suitability and no agreement as to an optimal set of measures.

Purpose

To evaluate the original Knee injury and Osteoarthritis Outcome Score (KOOS) and other published shorter versions of the KOOS to determine their suitability for use in patients with patellofemoral instability.

Methods

This cohort involved patients enrolled in an international multi-centre study, who underwent surgical stabilization with medial patellar ligament reconstruction (MPFL-R) for recurrent lateral patellar dislocations. The full KOOS was administered at pre-operative baseline, and at the 6-, 12- and 24-month time points following the index surgery. Four short form versions were then calculated: KOOS-12, KOOS-Physical Function, KOOS-Joint Replacement and KOOS-Global. For each measure, floor and ceiling effects were determined (threshold >15%). Individual items were evaluated to identify those that had >67% of patients with preoperative responses of “moderate” or greater (demonstrating item relevance). The standardized response mean (SRM) was calculated to assess responsiveness from baseline to each postoperative assessment time, as well as between postoperative assessments.

Results

289 patients completed the full KOOS at least once. No ceiling effects were present at any time point for the Quality of Life (QoL) or Symptoms subscales, and KOOS-12 and KOOS-Global short forms. Only 11 of the 42 KOOS items passed the >67% threshold for item relevance. These included all the Sport/Recreation items (SR) and QoL items as well as one item (knee stiffness after sitting/ resting later in the day) from the Symptom subscale and one item (pain frequency) from the Pain subscale. Given these individual item results, a two subscale ‘composite’ score was calculated that included the 9 items of the KOOS Sport/Recreation (SR) and Quality of Life (QoL) subscales (KOOS-SR+QoL). Excellent responsiveness was seen for all preoperative to post operative comparisons, especially the composite SR+QoL measure (SRM >1). Between 6- and 12-month the composite SR+QoL score was also shown to be the most responsive measure.

Conclusion

The composite KOOS SR+QoL score may be an improved option for measuring patient related outcomes in this younger, more active population, as it focuses on sports and recreation as well as quality of life which were shown to be the most relevant constructs for this patient group. The full 42-item KOOS was shown to have limited applicability.