Is outcome observed in performance of clinical tests associated with patient-reported outcome measures after patellofemoral pain treatment? Secondary analysis of data from a randomized clinical trial.
Eliane de Morais Machado, Mark Matthews, Michael Skovdal Rathleff and 2 others
Among 157 people with patellofemoral pain, step-up repetitions were the clinical test most strongly linked to patient-reported improvements, though the relationship was modest.
Step-down showed a weaker association; squat showed none. These tests explain only part of what drives a patient's perceived change.
Key findings
1Change in step-up repetitions was significantly associated with improvement in KOOS Symptoms, KOOS Pain, KOOS Sport & Recreation, and KOOS Quality of Life, but was not significantly associated with the Kujala scale or the KOOS Activities of Daily Living subscale.
2Change in step-down repetitions was significantly associated with Kujala and KOOS Sport & Recreation improvement; change in squat repetitions was not significantly associated with any of the six patient-reported outcomes.
3The regression models explained between 11.2% and 29.6% of the variation in patient-reported outcomes, meaning the functional tests capture only a portion of what drives a patient's perceived change.
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What it does not show
This is a secondary, exploratory analysis of an RCT whose primary question was treatment comparison, not the association between tests and PROMs. 61 of 218 participants (about 28%) were excluded because they hit the 25-repetition ceiling on all tests at both timepoints, mostly on step-up; their potentially larger improvements were not captured. The associations are weak to moderate: the best model (KOOS Sport & Recreation) explained 29.6% of variance, the worst (KOOS Symptoms) only 11.2%. Knee flexion angle was not measured, so the actual joint load and pain threshold varied between participants. Psychological factors known to influence PFP outcomes (kinesiophobia, self-efficacy, catastrophizing, anxiety) were not assessed. Step-up was performed first in the fixed test order, so fatigue or pain from that test could have influenced the subsequent step-down and squat scores. The step-up test may not be sufficiently challenging for higher-functioning individuals, limiting its ability to detect change at the upper end of performance.
Declared interests
The authors declare no competing interests. The research did not receive specific funding from public, commercial, or not-for-profit sectors.
The easy way to misread this
Do not read the step-up association as proof that the step-up test is a reliable standalone measure of treatment success. Each individual association explains only 4–11% of the change in a given patient-reported outcome, the squat test showed no association with any outcome, and this is a secondary analysis rather than a primary hypothesis test. A patient who improves by five step-up repetitions may still feel no better, because psychological factors, self-efficacy, and other unmeasured variables also drive perceived change.
Summarised by AI from the full paper, without a clinician reviewing it. Check it against the source before it changes what you do. Read it on PubMed →