Physical Activity Variability in Patellofemoral Pain: Relationships with Clinical and Psychological Outcomes.

OBJECTIVES: To (1) compare physical activity variability between individuals with patellofemoral pain (PFP) and pain-free individuals and (2) evaluate the relationships of physical activity variability with pain severity, symptom duration, disability, and pain catastrophizing in PFP cohorts. DESIGN: Cross-sectional case-control study. SETTING: University research laboratory. PARTICIPANTS: Individuals with PFP (N=34) and pain-free individuals (N=34) aged 18 to 40 years. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: We assessed physical activity (daily steps and moderate-to-vigorous physical activity [MVPA]) over a period of 14 consecutive days using a triaxial accelerometer. Variability (coefficient of variation) for daily steps and MVPA was calculated, where higher CV values indicate greater physical activity variability. We evaluated pain severity (numeric pain rating scale), symptom duration (months), disability (Knee Injury and Osteoarthritis Outcome Score-Patellofemoral subscale), and pain catastrophizing (Pain Catastrophizing Scale). Independent t-tests or Mann-Whitney U tests evaluated group differences in physical activity variability. Spearman ρ correlation coefficients were calculated to determine the relationships of physical activity variability with pain severity, symptom duration, disability, and pain catastrophizing in PFP cohorts. Correlation coefficients were interpreted as weak (<0.40), moderate (0.40-0.70), and strong (>0.70). RESULTS: Age, height, and mass did not differ between individuals with PFP and pain-free individuals (P>.05). Individuals with PFP displayed greater variability in daily steps (P<.001) and MVPA (P=.001) compared to pain-free individuals. In individuals with PFP, greater variability in daily steps was moderately related to higher pain severity (ρ=0.41, P=.016), while greater variability in MVPA was weakly related to higher pain severity (ρ=0.36, P=.037). CONCLUSIONS: Individuals with PFP demonstrated greater physical activity variability compared to pain-free individuals, which positively related to more severe pain. Future PFP research may explore the underlying factors contributing to increased physical activity variability and their potential implications for pain management.

Knee joint pathology and efferent pathway dysfunction: Mapping muscle inhibition from motor cortex to muscle force.

BACKGROUND: Dysfunction in efferent pathways after knee pathology is tied to long-term impairments in quadriceps and hamstrings muscle performance, daily function, and health-related quality of life. Understanding the underlying etiology is crucial for effective treatment and prevention of poor outcomes, such as post-traumatic osteoarthritis or joint replacement. OBJECTIVES: To synthesize recent evidence of efferent pathway dysfunction (i.e., motor cortex, motor units) among individuals with knee pathology. DESIGN: Commentary. METHOD: We summarize the current literature investigating the motor cortex, corticospinal tract, and motoneuron pool in individuals with three common knee pathologies: anterior cruciate ligament (ACL) injury, anterior knee pain (AKP), and knee osteoarthritis (OA). To offer a complete perspective, we draw from studies applying a range of neuroimaging and neurophysiologic techniques. RESULTS: Adaptations within the motor cortices, corticospinal tract, and motoneuron pool are present in those with knee pathology and underline impairments in quadriceps and hamstrings muscle function. Each pathology has evidence of altered motor system excitability and reduced volitional muscle activation and force-generating capacity, but few impairments were common across ACL injury, AKP, and OA studies. These findings underscore the central role of the motor cortex and motor unit behavior in the long-term outcomes of individuals with knee pathology. CONCLUSIONS: Adaptations in the efferent pathways underlie persistent muscle dysfunction across three common knee pathologies. This review provides an overview of these changes and summarizes key findings from neurophysiology and neuroimaging studies, offering direction for future research and clinical application in the rehabilitation of joint injuries.

Upper extremity neuromuscular function can distinguish between individuals with and without glenohumeral labral repair.

The purpose of this study was to determine whether common measures of neuromuscular function could distinguish injury status indicated by group membership (glenohumeral labral repair, uninjured controls). 16 individuals with glenohumeral labral repair (24.1 ± 5.0 years, 36.7 ± 33.3 months after surgery) and 14 uninjured controls (23.8 ± 2.7 years) volunteered. We measured mass-normalized shoulder abduction and wrist flexion maximal voluntary isometric contraction torque (Nm/kg), motoneuron pool excitability of the flexor carpi radialis (Hoffmann reflex), corticospinal excitability of the upper trapezius, middle deltoid, and flexor carpi radialis (active motor threshold [%]) bilaterally. Receiver operator characteristic curve analyses were performed to determine if each outcome could distinguish injury status along with their outcome thresholds. Binary logistic regression was used to determine the accuracy of classification for each outcome. Our results suggest shoulder abduction torque symmetry (≤95.5 %) and corticospinal excitability for the upper trapezius (≥41.0 %) demonstrated excellent diagnostic utility. Shoulder abduction torque (≤0.71 Nm/kg) and motoneuron pool excitability (≤0.23) demonstrated acceptable diagnostic utility. Shoulder abduction torque symmetry alone was the strongest indicator, and classified injury status with 90.0 % accuracy (p < 0.01). Overall, symmetric shoulder abduction strength most accurately distinguished individuals' injury status, suggesting the utility of bilateral assessment in this population.

Influence of unilateral versus bilateral patellofemoral pain on physical activity, pain self-efficacy, and disability.

BACKGROUND: Patellofemoral pain (PFP) affects physical and psychosocial health; however, it is unclear if unilateral and bilateral PFP induce similar levels of impairments. OBJECTIVES: We aimed to compare physical activity (PA), pain self-efficacy, and disability between individuals with unilateral and bilateral PFP, and to compare these groups against pain-free controls. DESIGN: Cross-sectional case-control. METHOD: Sixty-two individuals with PFP (25 unilateral and 37 bilateral) and 20 pain-free controls completed the PA assessment using an accelerometer by daily steps, light PA, and moderate-to-vigorous PA (MVPA). We also calculated variability in each PA variable. Pain self-efficacy and disability were measured using the Pain Self-Efficacy Questionnaire and Anterior Knee Pain Scale, respectively. RESULTS: Individuals with bilateral PFP took fewer daily steps compared to pain-free controls (9568.1 ± 3827.0 vs. 12,285.8 ± 2821.2 steps/day; P = 0.018, Cohen d = 0.79), whereas individuals with unilateral PFP did not (11,099.2 ± 3547.1 steps/day; P = 0.503, Cohen d = 0.37). Individuals with bilateral PFP showed greater variability in MVPA compared to individuals with unilateral PFP (42.9 ± 23.1 vs. 29.0 ± 15.9; P = 0.011, Cohen d = 0.91) and pain-free controls (42.9 ± 23.1 vs. 17.6 ± 6.1; P < 0.001, Cohen d = 1.21). Individuals with unilateral and bilateral PFP similarly exhibited less time spent in MVPA, greater variability in daily steps, lower pain self-efficacy, and greater disability compared to pain-free controls (P < 0.001, Cohen d = 1.14-3.89). CONCLUSIONS: Versus pain-free controls, individuals with bilateral PFP displayed greater variability in MVPA than individuals with unilateral PFP. However, it is important to note that unilateral PFP influenced time spent in MVPA, variability in daily steps, pain self-efficacy, and disability at similar levels to bilateral PFP.

Reliability and validity of belt-stabilized and tension dynamometry for assessing hip strength and power in uninjured adults.

OBJECTIVES: To investigate the intra-rater reliability and validity of belt-stabilized and tension dynamometry to assess hip muscle strength and power. DESIGN: Repeated measures. SETTING: Biomechanics laboratory. PARTICIPANTS: Seventeen uninjured adults (age = 22.0 ± 2.3y; 13 females). MAIN OUTCOMES MEASURES: Peak torque (strength) and rate of torque development (RTD; power) were measured for hip abduction, internal rotation, external rotation and extension using an isokinetic dynamometer, and belt-stabilized and tension dynamometry. RESULTS: For peak torque assessment, belt-stabilized and tension dynamometry showed good (Intraclass Correlation Coefficient [ICC] = 0.848-0.899) and good-to-excellent (ICC = 0.848-0.942) reliability, respectively. For RTD, belt-stabilized dynamometry showed fair reliability for abduction (ICC = 0.524) and good reliability for hip internal rotation, external rotation, and extension (ICC = 0.702-0.899). Tension dynamometry showed good reliability for all motions when measuring RTD (ICC = 0.737-0.897). Compared to isokinetic dynamometry, belt-stabilized and tension dynamometry showed good-to-excellent correlations for peak torque assessment (r = 0.503-0.870), and fair-to-good correlations for RTD (r = 0.438-0.674). Bland-Altman analysis showed that measures from belt-stabilized and tension dynamometry had clinically meaningful disagreement with isokinetic dynamometry. CONCLUSION: Tension dynamometry is reliable for assessing hip strength and power in all assessed motions. Belt-stabilized dynamometry is reliable for assessing internal rotation, external rotation, and extension. Validity of both methods is questionable, considering the lack of agreement with isokinetic dynamometry.

Physical Activity Levels in Persons With Patellofemoral Pain: A Systematic Review and Meta-analysis.

CONTEXT: Pain and symptoms of patellofemoral pain (PFP) are often exacerbated during daily activities, which may result in reduced overall physical activity levels. OBJECTIVE: To summarize the evidence for physical activity levels among persons with PFP compared with pain-free controls. DATA SOURCES: PubMed, Embase, CINHAL, Cochrane Library, and SPORTDiscus were searched from January 1, 2000 to February 22, 2024. STUDY SELECTION: Peer-reviewed studies published in English that measured physical activity subjectively or objectively in persons with PFP and pain-free controls. STUDY DESIGN: Systematic review with meta-analysis. LEVEL OF EVIDENCE: Level 1. DATA EXTRACTION: Standardized mean difference (SMD) with 95% CI are reported based on Hedges' g effect sizes. RESULTS: From 23,745 records, 41 studies met the eligibility criteria. There was high-to-moderate-certainty evidence that persons with PFP reported higher physical activity levels compared with pain-free controls using the International Physical Activity Questionnaire (SMD, 0.27; 95% CI 0.03, 0.51), whereas lower physical activity levels compared with pain-free controls using the Tegner Activity Scale (SMD, -0.31; 95% CI -0.57, -0.04). There was low-to-moderate-certainty evidence that there was no group difference in physical activity levels using the Baecke Physical Activity Questionnaire (SMD, 0.17; 95% CI -0.09, 0.44) or self-reported sports participation duration (SMD, -0.46; 95% CI -0.98, 0.05). There was high-certainty evidence that runners with PFP reported shorter running distances compared with pain-free runners (SMD, -0.36, 95% CI -0.57, -0.14). No data pooling was possible for objectively measured physical activity levels due to device heterogeneity (ie, different algorithms used to quantify the intensity of physical activity). CONCLUSION: Self-reported physical activity levels among persons with PFP were inconsistent depending on the physical activity measurement tool used or which specific physical activity was measured. Clinicians should integrate multiple physical activity assessment tools to determine the extent to which PFP influences physical activity levels. TRIAL REGISTRATION: PROSPERO #CRD42022314598.

The Influence of Psychological Factors on Physical Activity in Individuals With Patellofemoral Pain.

CONTEXT: Patellofemoral pain (PFP) is a prevalent chronic condition characterized by retropatellar or peripatellar pain exacerbated by various knee flexion-based activities. Previous research has highlighted the impact of psychological constructs on pain and function in chronic musculoskeletal pain conditions, yet their influence on physical activity in PFP cohorts remains unexplored. We aimed to evaluate whether pain self-efficacy and pain catastrophizing predict variations in steps per day and moderate to vigorous physical activity (MVPA) among individuals with PFP. DESIGN: Cross-sectional observational study. METHODS: Thirty-nine participants (11 males) with PFP were included. Dependent variables were steps per day and minutes of MVPA. Independent variables were pain self-efficacy and pain catastrophizing, measured by the pain self-efficacy questionnaire and the pain catastrophizing scale. Participants were given an ActiGraph wGT3X-BT for 7 days to assess physical activity. Correlations were assessed between psychological measures and physical activity, and a simple linear regression was performed on psychological variables that correlated with physical activity. Alpha was set a priori at P < .05. RESULTS: Pain self-efficacy scores displayed a moderate association with steps per day (rho = .45, P = .004) and a weak association with MVPA (rho = .38, P = .014). Pain catastrophizing scores exhibited no significant associations with physical activity (P < .05). Regression models affirmed pain self-efficacy scores as significant predictors of both steps per day (F1,37 = 10.30, P = .002) and MVPA (F1,37 = 8.98, P = .004). CONCLUSIONS: Psychological measures continue to demonstrate value to clinicians treating PFP. Pain self-efficacy scores were moderately associated with steps per day and weakly associated with MVPA, explaining nearly a fifth of the variation in physical activity. Clinicians should prioritize the assessment of pain self-efficacy when treating individuals with PFP, potentially employing psychological interventions to improve physical activity in the PFP population.

Hip rate of torque development, but not strength, is associated with single-leg squat kinematics in individuals with patellofemoral pain.

INTRODUCTION: Isometric hip strength seems to have limited association with frontal plane kinematics in individuals with patellofemoral pain (PFP), but little is known about the association with hip rate of torque development (RTD). OBJECTIVE: To explore the association of hip strength and RTD with trunk, pelvis, hip, and knee kinematics during a single-leg squat (SLS) in individuals with PFP. METHODS: Twenty individuals with PFP participated in this study. Hip abductor and extensor strength and RTD (early phase and late phase) were assessed using a hand-held dynamometer. Lateral trunk motion, pelvic drop, hip frontal plane projection angle (HFPPA), and knee frontal plane projection angle (KFPPA) were evaluated during a SLS using a two-dimensional motion analysis. RESULTS: Lower early and late phase hip abductor RTD were moderately associated with greater HFPPA (early phase: r = -0.501, p = .025; late phase: r = -0.580, p = .007) and KFPPA (early phase: r = -0.536, p = .015; late phase: r = -0.554, p = .011). Lower early phase hip extensor RTD was moderately associated with greater pelvic drop (r = 0.571, p = .009), HFPPA (r = -0.548, p = .012), and KFPPA (r = -0.530, p = .016). Hip abductor and extensor strength were not associated with any kinematic variables (p > .05). CONCLUSION: Lower hip RTD, but not strength, was associated with greater frontal plane kinematics during a SLS in individuals with PFP, indicating that the ability to produce torque rapidly may be important for kinematic control during functional tasks.

Changes in Hip and Knee Strength Are Not Associated With Improved Clinical Outcomes After Rehabilitation in Individuals With Patellofemoral Pain: A Critically Appraised Topic.

CLINICAL SCENARIO: Patellofemoral pain (PFP) is a widespread knee disorder encountered in clinical practice. Clinicians have often focused on strengthening hip and knee musculature to improve pain and disability, which are the ultimate clinical goals of PFP treatment. However, PFP literature has shown improvement in pain and disability without concurrent changes in lower-extremity strength after rehabilitation. Although some researchers have achieved a significant increase in strength after rehabilitation in PFP cohorts, there was no association with improved pain and disability. The inconsistent improvements in strength and the lack of association with clinical outcomes call for a critical appraisal of the available evidence to better understand the association between changes in hip and knee strength and improved clinical outcomes in individuals with PFP. CLINICAL QUESTION: Are changes in hip and knee strength associated with improved pain and disability after rehabilitation in individuals with PFP? SUMMARY OF KEY FINDINGS: Four studies met the inclusion criteria and were included in the appraisal. Following rehabilitation, one study achieved strength improvements in knee extension. One study achieved strength improvements in knee extension, but not in hip external rotation and hip abduction. Two studies did not achieve strength improvements in hip external rotation, hip abduction, hip extension, or knee extension. All included studies achieved improvements in pain or disability after rehabilitation. None of the studies found a significant association between changes in hip and knee strength (either improved or not) and improved pain and disability. CLINICAL BOTTOM LINE: There is consistent evidence that changes in hip and knee strength are not associated with improved clinical outcomes after rehabilitation in adults with PFP. STRENGTH OF RECOMMENDATION: Collectively, the body of evidence included is to answer the clinical question aligns with the strength of recommendation of B based on the Strength of Recommendation Taxonomy.

Sex Differences in Knee Extensor Neuromuscular Function in Individuals With and Without Patellofemoral Pain.

BACKGROUND: Impaired knee extensor neuromuscular function has been frequently observed in individuals with patellofemoral pain (PFP); however, few researchers have aimed to understand the influence of sex on knee extensor neuromuscular function in this pathological population. The authors aimed to determine whether there are differences in knee extensor neuromuscular function between sexes in individuals with and without PFP. HYPOTHESIS: Women with PFP would exhibit greater deficits in knee extensor neuromuscular function than men with PFP, compared with sex-matched individuals without PFP. STUDY DESIGN: Cross-sectional, case-control study. LEVEL OF EVIDENCE: Level 4. METHODS: A total of 110 individuals were classified into 4 groups: women with PFP (n = 25); men with PFP (n = 30); women without PFP (n = 25); and men without PFP (n = 30). Knee extensor strength (isometric peak torque [PT]), activation (central activation ratio), early, late, and total phase rate of torque development (RTD0-100, RTD100-200, and RTD20-80%), and endurance (isokinetic average PT) were assessed using an isokinetic dynamometer. Group differences were assessed using a 2-way multivariate analysis of variance (sex by PFP). RESULTS: Both women and men with PFP exhibited lower knee extensor strength, activation, early, late, and total phase RTD, and endurance versus sex-matched individuals without PFP (P < 0.05 for all comparisons). Women with PFP exhibited lower early phase (7.91 ± 2.02 versus 9.78 ± 2.43 N·m/s/kg; P < 0.01; Cohen d = 0.83), late phase (5.34 ± 1.02 versus 7.28±2.28 N·m/s/kg; P < 0.01; Cohen d = 1.37), and total phase (7.40 ± 2.57 versus 8.72 ± 2.57 N·m/s/kg; P = 0.03; Cohen d = 0.51) RTD than men with PFP. CONCLUSION: Compared with sex-matched pain-free individuals, women with PFP displayed lower RTD than men with PFP. Clinicians should note that among individuals with PFP, women are more likely to experience a greater impairment in their knee extensor torque-generating capacity than men. CLINICAL RELEVANCE: Additional treatment strategies that effectively improve the ability to rapidly generate torque should be developed and implemented, especially when treating women with PFP.

Lower Extremity Muscle Volume in Unilateral and Bilateral Patellofemoral Pain: A Cross-Sectional Exploratory Study Including Superficial and Deep Muscles Authors.

CONTEXT: Existing patellofemoral pain (PFP) literature has primarily focused on quadriceps muscle volume, with limited attention given to the lower limbs deep and superficial muscle volumes in individuals with unilateral and bilateral PFP. This research aims to fill this gap. OBJECTIVE: To explore superficial and deep lower extremity muscle volume in women with unilateral and bilateral PFP compared to a normative database of pain-free women. DESIGN: Cross-sectional study. SETTING: University imaging research center. PATIENTS OR OTHER PARTICIPANTS: Twenty women with PFP (10 unilateral and 10 bilateral) and 8 pain-free women. MAIN OUTCOME MEASURE(S): We quantified lower extremity muscle volume via 3.0 Tesla magnetic resonance imaging. Two separate one-way analyses of variance were performed: (1) unilateral PFP (painful vs. non-painful limb) vs. pain-free control and (2) bilateral PFP (more painful vs. less painful limb) vs. pain-free control. RESULTS: There were no differences in age and body mass index across groups (P >.05). Compared to pain-free women, both women with unilateral and bilateral PFP had bilaterally smaller volumes of the anterior (iliacus: P ≤ .0004, d = 2.12-2.65), medial (adductor brevis, adductor longus, gracilis, and pectineus: P ≤ .02, d = 1.25-2.24), posterior (obturator externus, obturator internus, and quadratus femoris: P < .05, d = 1.17-4.82), and lateral (gluteus minimus: P ≤ .03, d = 1.16-2.09) hip muscles, and knee extensors (rectus femoris: P ≤.003, d = 1.67-2.16) and flexors (biceps femoris: long and short head: P ≤ .01, d = 1.56-1.93). CONCLUSIONS: Both women with unilateral and bilateral PFP 25 displayed decreased volume of multiple superficial and deep muscles of the bilateral hips and knees compared with pain-free women. Interventions should bilaterally target lower limb muscles when treating PFP, and hypertrophy exercises for specific muscles should be explored to enhance interventional choices.

Can Clinicians Trust Objective Measures of Hip Muscle Strength From Portable Dynamometers? A Systematic Review With Meta-analysis and Evidence Gap Map of 107 Studies of Reliability and Criterion Validity Using the COSMIN Methodology.

OBJECTIVE: To summarize the evidence on reliability and criterion validity of hip muscle strength testing using portable dynamometers. DESIGN: Systematic review with meta-analysis. LITERATURE SEARCH: Five databases were searched from inception to March 2023. STUDY SELECTION CRITERIA: We included studies investigating reliability or criterion validity of hip flexor, extensor, abductor, adductor, or internal/external rotator strength testing with portable dynamometers in injury-free individuals or those with pelvic/lower limb musculoskeletal disorders. DATA SYNTHESIS: We performed meta-analyses for each muscle group, position, and method of fixation. We rated pooled results as sufficient (>75% of studies with correlations ≥0.70), insufficient (>75% of studies with correlations <0.70), or inconsistent (sufficient/insufficient results). We assessed the quality of evidence, created evidence gap maps, and made clinical recommendations. RESULTS: We included a total of 107 studies (reliability 103, validity 14). The intrarater and interrater reliability for hip muscle strength testing across different positions and methods of fixation was sufficient (intraclass correlation coefficient = 0.78-0.96) with low- to high-quality evidence. Criterion validity was less investigated and mostly inconsistent (very low-to moderate-quality evidence) with a wide range of correlations (r = 0.40-0.93). CONCLUSION: Hip muscle strength testing using portable dynamometers is reliable. The use of portable dynamometers as clinical surrogates for measuring strength using an isokinetic dynamometer requires further investigation. Clinicians testing hip muscle strength with portable dynamometers should use external fixation seated for hip flexors, prone or supine for hip extensors, side-lying or supine for abductors and adductors, and prone and seated for internal and external rotators. J Orthop Sports Phys Ther 2023;53(11):655-672. Epub 3 October 2023. doi:10.2519/jospt.2023.12045.

Exercise-induced fatigue affects knee proprioceptive acuity and quadriceps neuromuscular function more in patients with ACL reconstruction or meniscus surgery than in healthy individuals.

PURPOSE: To observe how knee proprioceptive acuity and quadriceps neuromuscular function change during and after repeated isokinetic knee-extension exercise in patients with anterior cruciate ligament reconstruction (ACLR) or meniscus surgery. METHODS: Patients with ACLR or meniscus surgery and matched controls (n = 19 in each group) performed knee-flexion replication at 15° and 75°, and quadriceps peak torque (PT), central activation ratio (CAR) and rate of torque development (RTD) at baseline and immediately after every five sets of isokinetic knee-extension exercise (times 1-5). RESULTS: Compared to the baseline, the ACLR and control groups displayed errors in knee-flexion replication at 75° only at time 5 (115.9-155.6%; p ≤ 0.04, d ≥ 0.97), whereas the meniscus surgery group exhibited errors at all time points (142.5-265.6%; p ≤ 0.0003, d ≥ 1.4). Significant percentage reductions in quadriceps CAR were observed between times 4 and 5 in the ACLR group (-5.8%; p = 0.0002, d = 0.96), but not in the meniscus surgery (-1.4%; n.s.) and control (0.1%; n.s.) groups. Significant percentage reductions in quadriceps RTD were observed between times 4 and 5 in the ACLR (-24.2%; p = 0.007, d = 0.99) and meniscus surgery (-23.0%; p = 0.01, d = 0.85) groups, but not in the control group (-0.2%; n.s.). CONCLUSION: Patients with ACLR or meniscus surgery displayed a greater loss in knee proprioceptive acuity and quadriceps neuromuscular function during and after exercise than healthy individuals. Evidence-based interventions to enhance exercise-induced fatigue resistance should be implemented following ACLR or meniscus surgery, aiming to prevent proprioceptive and neuromuscular changes within the knee joint and quadriceps. LEVEL OF EVIDENCE: III.

There is more to the knee joint than just the quadriceps: A systematic review with meta-analysis and evidence gap map of hamstring strength, flexibility, and morphology in individuals with gradual-onset knee disorders.

BACKGROUND: Impairments in hamstring strength, flexibility, and morphology have been associated with altered knee biomechanics, pain, and function. Determining the presence of these impairments in individuals with gradual-onset knee disorders is important and may indicate targets for assessment and rehabilitation. This systematic review aimed to synthesize the literature to determine the presence of impairments in hamstring strength, flexibility, and morphology in individuals with gradual-onset knee disorders. METHODS: Five databases ((MEDLINE, Embase, CINAHL, SPORTDiscus, and Web of Science) were searched from inception to September 2022. Only studies comparing hamstring outcomes (e.g., strength, flexibility, and/or morphology) between individuals with gradual-onset knee disorders and their unaffected limbs or pain-free controls were included. Meta-analyses for each knee disorder were performed. Outcome-level certainty was assessed using the Grading of Recommendations Assessment, Development, and Evaluation, and evidence gap maps were created. RESULTS: Seventy-nine studies across 4 different gradual-onset knee disorders (i.e., knee osteoarthritis (OA), patellofemoral pain (PFP), chondromalacia patellae, and patellar tendinopathy) were included. Individuals with knee OA presented with reduced hamstring strength compared to pain-free controls during isometric (standard mean difference (SMD) = -0.76, 95% confidence interval (95%CI) : -1.32 to -0.21) and concentric contractions (SMD = -0.97, 95%CI : -1.49 to -0.45). Individuals with PFP presented with reduced hamstring strength compared to pain-free controls during isometric (SMD = -0.48, 95%CI : -0.82 to -0.14), concentric (SMD = -1.07, 95%CI : -2.08 to -0.06), and eccentric contractions (SMD = -0.59, 95%CI : -0.97 to -0.21). No differences were observed in individuals with patellar tendinopathy. Individuals with PFP presented with reduced hamstring flexibility when compared to pain-free controls (SMD = -0.76, 95%CI : -1.15 to -0.36). Evidence gap maps identified insufficient evidence for chondromalacia patellae and hamstring morphology across all gradual-onset knee disorders. CONCLUSION: Our findings suggest that assessing and targeting impairments in hamstring strength and flexibility during rehabilitation may be recommended for individuals with knee OA or PFP.

Influence of self-perceived disability on squatting kinematics in individuals with patellofemoral pain.

BACKGROUND: Individuals with patellofemoral pain have a heterogeneous presentation of symptoms during functional tasks; however, biomechanical data often negates self-reported disability. The single leg squat is common in patellofemoral pain literature but may not be a pain provoking task for all individuals. Therefore, our study examined the influence of self-perceived squatting disability in individuals with patellofemoral pain on lower extremity squatting kinematics. METHODS: We analyzed two-dimensional hip frontal plane projection angle, knee frontal plane projection angle, lateral trunk movement, and pelvic drop in 100 participants, 82 with patellofemoral pain and 18 pain-free controls. Participants with patellofemoral pain were dichotomized based on the level of disability reported during squatting on the anterior knee pain scale. An analysis of variance with post hoc testing was used to compare differences in lower extremity and trunk kinematics between groups, p < 0.05. FINDINGS: Participants who reported only being able to squat with partial weight bearing had greater hip frontal plane projection angles than those who reported squatting painful each time (p = 0.017). The partial weight bearing group had greater knee frontal plane projection angles compared those who reported pain with repeated squatting and the pain-free group, (p < 0.034). We found no significant differences in lateral trunk motion or pelvic drop between groups. INTERPRETATION: Individuals with patellofemoral pain who self-reported worse squatting disability had greater hip and knee frontal plane motion compared to individuals with less disability and pain-free controls. Clinicians and researchers should consider specific pain provoking tasks when evaluating and treating patients with patellofemoral pain.

Lower extremity muscle volume in females with patellofemoral pain and its relationships to hip and knee torque: A cross-sectional study.

OBJECTIVES: Compare lower extremity muscle volume in females with patellofemoral pain (PFP) to a cohort of pain-free females and investigate the relationship between thigh and hip muscle volume and torque. DESIGN: Cross-sectional. PARTICIPANTS: Twenty-one females, 13 with PFP and 8 pain-free controls. MAIN OUTCOME MEASURES: We quantified normalized lower extremity muscle volume (cm3/kg*m) via magnetic resonance imaging and isometric hip and thigh torque (Nm/kg) via a multimodal dynamometer. RESULTS: Versus pain-free individuals, females with PFP had smaller muscle volume of the anterior hip (P < 0.019; d = 0.97-2.42), deep external rotators (P < 0.006; d = 1.0-3.93), hamstrings (P < 0.009; d = 1.09-2.12), rectus femoris (P < 0.001; d = 1.79), and vastus intermedius (P < 0.001; d = 1.88). There was no difference in muscle volume of the gluteus maximus (P = 0.311; d = 0.22), gluteus medius (P = 0.087; d = 0.87), vastus lateralis (P = 0.22; d = 0.39), and vastus medialis (P = 0.47; d = 0.04). Gluteus maximus volume was moderately correlated to hip abduction torque (r = 0.60; P = 0.03). Vasti muscles and semitendinosus volume were moderately correlated to knee extension (r = 0.57-0.69; P < 0.05) and flexion (r = 0.66; P = 0.01) torque, respectively. CONCLUSION: Females with PFP present with lesser thigh and hip muscle volumes, with variability in volumetric profiles across participants. Lower extremity knee extension and hip abduction strength are moderately associated with the vasti and gluteus maximus muscle volume, respectively.

The Comparison of Psychological Barriers Between Individuals with a History of Anterior Knee Pain, Anterior Cruciate Ligament Reconstruction, and Healthy Individuals.

Background: Psychological barriers due to anterior knee pain (AKP) and anterior cruciate ligament reconstruction (ACLR) may have a direct impact on an individual's return to physical activity. A comprehensive understanding of these psychological barriers in individuals with AKP and ACLR may help clinicians to develop and implement better treatment strategies to address deficits that may exist in these individuals. Hypothesis/Purpose: The primary purpose of this study was to evaluate fear-avoidance, kinesiophobia, and pain catastrophizing in individuals with AKP and ACLR compared with healthy individuals. The secondary purpose was to directly compare psychological characteristics between the AKP and ACLR groups. It was hypothesized that 1) individuals with AKP and ACLR would self-report worse psychosocial function than healthy individuals and 2) the extent of the psychosocial impairments between the two knee pathologies would be similar. Study Design: Cross-sectional study. Methods: Eighty-three participants (28 AKP, 26 ACLR, and 29 healthy individuals) were analyzed in this study. Fear avoidance belief questionnaire (FABQ) with the physical activity (FABQ-PA) and sport (FABQ-S) subscales, Tampa scale of Kinesiophobia (TSK-11) and pain catastrophizing scale (PCS) assessed psychological characteristics. Kruskal-Wallis tests were used to compare the FABQ-PA, FABQ-S, TSK-11, and PCS scores across the three groups. Mann-Whitney U tests were performed to determine where group differences occurred. Effect sizes (ES) were calculated with the Mann-Whitney U z-score divided by the square root of the sample size. Results: Individuals with AKP or ACLR had significantly worse psychological barriers compared to the healthy individuals for all questionnaires (FABQ-PA, FABQ-S, TSK-11, and PCS) (p<0.001, ES>0.86). There were no differences between the AKP and ACLR groups (p≥0.67), with a medium ES (-0.33) in the FABQ-S between AKP and ACLR groups. Conclusion: Greater psychological scores indicate impaired psychological readiness to perform physical activity. Clinicians should be aware of fear-related beliefs following knee-related injuries and are encouraged to measure psychological factors during the rehabilitation process. Level of Evidence: 2.

Strength Training Rehabilitation Incorporating Power Exercises (STRIPE) for individuals with patellofemoral pain: a randomised controlled trial protocol.

Patellofemoral pain (PFP) is a chronic condition that presents with patellar pain during various daily and recreational activities. Individuals with PFP have a wide range of impairments that result in long-term disability and reduced quality of life. Current interventions target hip muscle weakness with strength-based exercises, but recurrence rates are as high as 90%. A single feasibility study demonstrated success with power-based exercises; however, there is limited evidence evaluating pain or self-reported function in larger cohorts, and no study has assessed recurrence rates. This protocol details a study evaluating a strength-based rehabilitation programme compared with a strength-based programme incorporating power-based exercises in individuals with PFP. This single-blinded randomised controlled trial will evaluate 88 participants with PFP, aged 18-40 years old. Participants will be recruited from three universities, the surrounding community and sports medicine clinics. Participants will receive three telemedicine rehabilitation sessions a week for 6 weeks. The rehabilitation programme will consist of either strength-based exercises or a combination of power and strength-based exercises. Pain, subjective function and recurrence rates will be assessed at baseline, immediately after the intervention and at four follow-up time points: 6-month, 12-month, 18-month and 24-month postintervention. We will also assess neuromuscular function of the hips and global rating of change at each postintervention time point. Trial registration number NCT05403944.

Whole-body vibration reduces hamstrings neuromuscular function in uninjured individuals.

OBJECTIVES: Despite the growing use of whole-body vibration (WBV) to enhance quadriceps neuromuscular function, the hamstrings-specific response is unclear among those without neuromuscular impairment, which is important to inform performance-based recommendations. Our objective was to determine the immediate and prolonged effects of WBV on hamstrings and quadriceps neuromuscular function in uninjured individuals. DESIGN: Crossover. SETTING: Laboratory. PARTICIPANTS: Nineteen, recreationally active individuals performed WBV and control exercise protocols, consisting of six 1-min repetitions of isometric squats, on separate days in a randomized order. MAIN OUTCOME MEASURES: Electromyographic (EMG) amplitude, antagonist-to-agonist co-activation, rate of torque development, and peak torque of the hamstrings and quadriceps were measured pre-, immediately post-, and 20 min post-condition. Percentage change scores were calculated from baseline to each post-measurement. RESULTS: A condition main effect indicated that WBV reduced agonist semitendinosus EMG amplitudes more than the control (-12.1% vs. -1.5%, p < .001). Antagonist vastus medialis EMG amplitudes were reduced immediately, but not 20 min following WBV (-7.1% vs. 3.5%, p < .001). CONCLUSIONS: WBV induced an inhibitory effect on medial hamstrings activity during knee flexion contraction in a majority of our sample, yet this response was not uniformly observed and its functional relevance remains unclear in an uninjured population.

Quadriceps Neuromuscular Function During and After Exercise-Induced Fatigue in Patients With Patellofemoral Pain.

CONTEXT: Exercise-induced fatigue reduces muscle force production and motoneuron pool excitability. However, it is unclear if patients with patellofemoral pain (PFP) experience further loss in quadriceps neuromuscular function due to fatigue during exercise and postexercise. OBJECTIVE: To observe how quadriceps maximal strength, activation, and force-generating capacity change during and after repetitive bouts of isokinetic knee-extension exercise in patients with PFP. DESIGN: Cross-sectional study. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty-two patients with PFP (visual analog scale mean pain severity = 4.2 of 10 cm, mean symptom duration = 38.6 months) and 19 healthy control individuals matched on age and body mass index. MAIN OUTCOME MEASURE(S): Quadriceps peak torque (PT), central activation ratio (CAR), and rate of torque development (RTD) were assessed at baseline and immediately after every 5 sets of knee-extension exercise (times 1-5). Participants continued knee-extension exercises until the baseline quadriceps PT dropped below 50% for 3 consecutive contractions. RESULTS: No group-by-time interaction was observed for quadriceps PT (F5,195 = 1.03, P = .40). However, group-by-time interactions were detected for quadriceps CAR (F5,195 = 2.63, P= .03) and RTD (F5,195 = 3.85, P = .002). Quadriceps CAR (-3.6%, P = .04, Cohen d = 0.53) and RTD (-18.9%, P = .0008, Cohen d = 1.02) decreased between baseline and time 1 in patients with PFP but not in their healthy counterparts (CAR -1.9%, P = .86; RTD -9.8%, P = .22). Quadriceps RTD also decreased between times 4 and 5 in patients with PFP (-24.9%, P = .002, Cohen d = 0.89) but not in the healthy group (-0.9%, P = .99). CONCLUSIONS: Patients with PFP appeared to experience an additional reduction in quadriceps activation, force-generating capacity, or both during the early and late stages of exercise compared with healthy individuals. Clinicians should be aware of such possible acute changes during exercise and postexercise and use fatigue-resistant rehabilitation programs for patients with PFP.