Objective: Patellofemoral pain has high recurrence rates and minimal long-term treatment success. Central sensitization refers to dysfunctional pain modulation that occurs when nociceptive neurons become hyper responsive. Research in this area in PFP has been increasingly productive in the past decade. The aim of this review is to determine whether evidence supports manifestations of central sensitization in individuals with PFP. Data sources: MeSH terms for quantitative sensory testing (QST) pressure pain thresholds, conditioned pain modulation, temporal summation, sensitization, hyperalgesia, and anterior knee pain or PFP were searched in PubMed, SportDiscus, CINAHL, Academic Search Complete, and Ebscohost. Study Selection: Peer reviewed studies written in English, published between 2005–2020 which investigated QST and/or pain mapping in a sample with PFP were included in this review. Data Extraction: The initial search yielded 140 articles. After duplicates were removed, 78 article abstracts were reviewed. Full-text review of 21 studies occurred, with 11 studies included in the meta-analysis and eight studies included in the systematic review. Data Synthesis: A random-effects meta-analysis was conducted for four QST variables (local pressure pain thresholds, remote pressure pain thresholds, conditioned pain modulation, temporal summation). Strong evidence supports lower local and remote pressure pain thresholds, impaired conditioned pain modulation, and facilitated temporal summation in individuals with PFP compared to pain-free individuals. Conflicting evidence is presented for heat and cold pain thresholds. Pain mapping demonstrated expanding pain patterns associated with long PFP symptom duration. Conclusions: Signs of central sensitization are present in individuals with PFP, indicating altered pain modulation. PFP etiological and treatment models should reflect the current body of evidence regarding central sensitization. Signs of central sensitization should be monitored clinically and treatments with central effects should be considered as part of a multi-modal plan of care. Registration Number: This review is registered with Prospero (CRD42019127548) Registration URL: https://www.crd.york.ac.uk/PROSPERO Key Points:

Purpose: Altered hip strength is a risk factor for lower extremity injury but its relationship to biomechanical dysfunction is debated. Hip strength assessment methods are criticized for using unidirectional, non-weight-bearing positions which may not be representative of athletic activity and may affect comparison to biomechanical analysis of athletic tasks. A weight-bearing task may better represent hip muscle function during these movements. The aim of this study was to identify EMG and force differences for a clinical weight-bearing method of hip strength (the squat-hold) to traditional non-weight-bearing maximal voluntary isometric contractions (MVICs) for hip abduction, extension, and external rotation. Methods: Twenty-nine healthy volunteers (23 female, 6 male; 23.3±5.8 years) performed the squat-hold, sidelying abduction, prone extension, and seated hip external rotation MVICs. The squat-hold was performed by exerting a bilateral, maximal force against a rigid strap encircling both knees in a semi-squatted position. Surface electromyography (EMG) recorded peak activation of the gluteus medius (GMed), gluteus maximus (Gmax), and tensor fascia lata (TFL) and a handheld dynamometer simultaneously measured force during all tasks. Peak activation was compared between the squat-hold and each MVIC using paired t-tests. Force was compared across tasks using a one-way ANOVA. Results: Greater force was observed during the squat-hold than the external rotation MVIC, but abduction and extension MVICs yielded greater force than the squat-hold. GMax activation was higher during the squat-hold than the external rotation task. TFL activation was higher during the abduction MVIC than the squat-hold but GMed activation was similar across tasks. Peak GMax activation was similar between the extension MVIC and squat-hold. Conclusions: Squat-hold force may have been reduced due to altered gluteal moment arms, which affected the length-tension relationship. Clinicians should consider the squat-hold as an alternative assessment of external rotation force, but should continue to assess abduction and extension force with MVICs. Researchers should examine positions optimizing length-tension relationships to better relate motor function and movement patterns.

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