Comparison of the Frontal Plane Projection Angle and the Dynamic Valgus Index to Identify Movement Dysfunction in Females with Patellofemoral Pain.

Background: Clinicians typically measure the knee frontal plane projection angle (FPPA) during a single-leg squat to identify females with patellofemoral pain (PFP). A limitation of this measure is minimal attention to movement of the pelvis on the femur that can create knee valgus loading. The dynamic valgus index (DVI) may be a better assessment. Hypothesis/Purpose: The purpose of this study was to compare the knee FPPA and DVI between females with and without PFP and determine if the DVI better identified females with PFP than the knee FPPA. Study Design: Case-control. Methods: Sixteen females with and 16 without PFP underwent 2-dimensional motion analysis when performing five trials of a single-leg squat. The average peak knee FPPA and peak DVI were analyzed. Independent t-tests determined between-group peak knee FPPA and peak DVI differences. Receiver operating characteristic (ROC) curves determined the area under the curve (AUC) scores for sensitivity and 1 - specificity of each measure. Paired-sample area difference under the ROC curves was conducted to determine differences in the AUC for the knee FPPA and DVI. Positive likelihood ratios were calculated for each measure. The significance level was p < 0.05. Results: Females with PFP exhibited a higher knee FPPA (p = 0.001) and DVI (p = 0.015) than controls. AUC scores were .85 (p = 0.001) and .76 (p = 0.012) for the knee FPPA and DVI, respectively. Paired-sample area difference under the ROC curves showed a similar (p = 0.10) AUC for the knee FPPA and DVI. The knee FPPA had 87.5% sensitivity and 68.8% specificity; the DVI had 81.3% sensitivity and 81.0% specificity. Positive likelihood ratios for the knee FPPA and DVI were 2.8 and 4.3, respectively. Conclusion: The DVI during a single-leg squat may be another useful tool for discriminating between females with and without PFP. Level of Evidence: 3a.

Patient-Reported Outcome Measures for Adults and Adolescents With Patellofemoral Pain: A Systematic Review of Construct Validity, Reliability, Responsiveness, and Interpretability Using the COSMIN Methodology.

OBJECTIVE: We aimed to appraise the construct validity, reliability, responsiveness, and interpretability of patient-reported outcome measures (PROMs) used to assess function and pain in adults and adolescents with patellofemoral pain (PFP). DESIGN: Systematic review of measurement properties LITERATURE SEARCH: We searched the PubMed, CINAHL, Scopus, SPORTDiscus, and Cochrane Library databases from inception to January 6, 2022. STUDY SELECTION CRITERIA: We included studies that assessed the measurement properties of English-language PROMs for PFP and their cultural adaptations and translations. DATA SYNTHESIS: Using the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) methodology, we determined overall ratings and quality of evidence for construct validity, internal consistency, reliability, measurement error, and responsiveness. We extracted data related to interpretability for clinical use. RESULTS: After screening 7066 titles, 61 studies for 33 PROMs were included. Only 2 PROMs had evidence of "sufficient" or "indeterminate" quality for all measurement properties. The Knee injury and Osteoarthritis Outcome Score patellofemoral subscale (KOOS-PF) had "low" to "high" quality evidence for a rating of "sufficient" for 4 measurement properties. The Lower Extremity Functional Scale (LEFS) had very low-quality evidence for a "sufficient" rating for 4 measurement properties. The KOOS-PF and LEFS were rated "indeterminate" for structural validity and internal consistency. The KOOS-PF had the best interpretability with reported minimal important change and 0% ceiling and floor effects. No studies examined cross-cultural validity. CONCLUSION: The KOOS-PF and LEFS had the strongest measurement properties among PROMs used for PFP. More research is needed, particularly regarding structural validity and interpretability of PROMs. J Orthop Sports Phys Ther 2023;53(8):1-20. Epub: 20 June 2023. doi:10.2519/jospt.2023.11730.

Patient-Reported Outcome Measures for Adults and Adolescents with Patellofemoral Pain: A Systematic Review of Content Validity and Feasibility Using the COSMIN Methodology.

OBJECTIVE: To assess the content validity and feasibility of patient-reported outcome measures (PROMs) used to assess pain and function in adults and adolescents with patellofemoral pain (PFP). DESIGN: Systematic review. LITERATURE SEARCH: We searched the databases PubMed, CINAHL, Scopus, SPORTDiscus, and the Cochrane Library from inception to January 6, 2022. STUDY SELECTION CRITERIA: We included studies that described the development or evaluation of the content validity of English-language PROMs for PFP, as well as their translations and cultural adaptations to different languages. DATA SYNTHESIS: Using the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) methodology, we determined overall ratings and quality of evidence for the relevance, comprehensiveness, and comprehensibility of PROMs. We extracted data related to feasibility for clinical use (eg, administration time and scoring ease). RESULTS: Forty-three studies for 33 PROMs were included. The overall quality of most studies was "inadequate" due to failure to engage stakeholders and/or ensure adherence to rigorous qualitative research procedures. Of all PROMs evaluated, the Knee injury and Osteoarthritis Outcome Score-Patellofemoral subscale (KOOS-PF), was the only PROM with sufficient content validity components. Quality of evidence for content validity of the KOOS-PF was low. Most PROMs were rated feasible for clinical and research purposes. CONCLUSION: Most PROMs used to measure pain and function in patients with PFP have inadequate content validity. The KOOS-PF had the highest overall content validity. We recommend the KOOS-PF for evaluating pain and function (in research and clinical practice) in adults and adolescents with PFP. J Orthop Sports Phys Ther 2023;53(1):23-39. Epub: 18 October 2022. doi:10.2519/jospt.2022.11317.

Reliability of the scapular dyskinesis test yes-no classification in asymptomatic individuals between students and expert physical therapists.

BACKGROUND: Scapular dyskinesis is considered a risk factor for the shoulder pain that may warrant screening for prevention. Clinicians of all experience screen scapular dyskinesis using the scapular dyskinesis test yes-no classification (Y-N), yet its reliability in asymptomatic individuals is unknown. We aimed to establish Y-N's intra- and inter-reliability between students and expert physical therapists. METHODS: We utilized a cross-sectional design using consecutive asymptomatic subjects. Six students and two experts rated 100 subjects using the Y-N. Cohen's kappa (κ) and Krippendorff's alpha (K-α) were calculated to determine intra- and inter-rater reliability. RESULTS: Intra- and inter-rater values for experts were κ=0.92 (95% confidence interval [CI], 0.91-0.93) and 0.85 (95% CI, 0.84-0.87) respectively; students were κ=0.77 (95% CI, 0.75-0.78) and K-α=0.63 (95% CI, 0.58-0.67). CONCLUSIONS: The Y-N is reliable in detecting scapular dyskinesis in asymptomatic individuals regardless of experience.

Survey of confidence and knowledge to manage patellofemoral pain in readers versus nonreaders of the physical therapy clinical practice guideline.

OBJECTIVES: To compare beliefs of physical therapists (PTs) who read the clinical practice guideline (CPG) for the management of individuals with patellofemoral pain (PFP) to those who have not read the CPG. DESIGN: Cross-sectional study. SETTING: Online survey. PARTICIPANTS: 494 currently licensed/registered PTs or physiotherapists. MAIN OUTCOME MEASURES: Respondents answered Likert-based or open-ended questions regarding the diagnosis, prognosis, risk factors, and management of individuals with PFP, as well as confidence for managing individuals with PFP, especially the ability to identify beneficial and non-beneficial interventions. We dichotomized responses into participants who read (READERS) and did not read (NonREADERS) the CPG. RESULTS: Most respondents held inaccurate beliefs about risk factors and prognosis; however, READERS' beliefs better aligned with the CPG than NonREADERS (P < 0.01). Most respondents correctly agreed that hip and knee exercise was the recommended treatment strategy; yet NonREADERS believed in implementing unsupported passive treatments (P < 0.01). READERS reported greater confidence in managing individuals with PFP, delivering evidence-based interventions, identifying less beneficial treatments, and locating evidence-based resources than NonREADERS (P < 0.01). CONCLUSION: While READERS and NonREADERS held accurate beliefs for exercise-based treatment for PFP, greater knowledge translation is needed to counter inaccurate beliefs regarding risk factors, prognostic factors, and passive treatments.

Hamstring Strain Injury in Athletes.

Hamstring strain injury (HSI) may result in considerable impairment, activity limitation, and participation restriction, including time lost from competitive sports. This CPG includes sports-related overloading and overstretching injuries to myofascial or musculotendinous structures in any combination of the 3 hamstring muscles (the semitendinosus, semimembranosus, and biceps femoris). J Orthop Sports Phys Ther 2022;52(3):CPG1-CPG44. doi:10.2519/jospt.2022.0301.

Patellofemoral Pain.

Patellofemoral pain (PFP) is a common musculoskeletal-related condition that is characterized by insidious onset of poorly defined pain, localized to the anterior retropatellar and/or peripatellar region of the knee. The onset of symptoms can be slow or acutely develop with a worsening of pain accompanying lower-limb loading activities (eg, squatting, prolonged sitting, ascending/descending stairs, jumping, or running). Symptoms can restrict participation in physical activity, sports, and work, as well as recur and persist for years. This clinical practice guideline will allow physical therapists and other rehabilitation specialists to stay up to date with evolving PFP knowledge and practices, and help them to make evidence-based treatment decisions. J Orthop Sports Phys Ther. 2019;49(9):CPG1-CPG95. doi:10.2519/jospt.2019.0302.

COMPARISON OF PATELLA ALIGNMENT AND CARTILAGE BIOMARKERS IN YOUNG ADULT FEMALES WITH AND WITHOUT PATELLOFEMORAL PAIN: A PILOT STUDY.

BACKGROUND: Evidence suggests that individuals with patellofemoral pain (PFP) may develop patellofemoral joint osteoarthritis (PFJOA). Limited data exist regarding an absolute association between PFP and PFJOA. Understanding this relationship will support the need for early interventions to manage PFP. HYPOTHESIS/PURPOSE: This study was conducted to determine if females with PFP have a patella position and cartilage biomarkers similar to individuals with PFJOA. It was hypothesized that females with PFP and excessive patella lateralization would have higher cartilage biomarker levels than controls. It also was hypothesized that a significant association would exist between pain and cartilage biomarker levels in subjects with excessive patella lateralization. STUDY DESIGN: Single-occasion, cross-sectional, observational. METHODS: Pain was assessed using a 10-cm visual analog scale (VAS) for activity pain over the previous week. Patella offset position (RAB angle) was measured using diagnostic ultrasound. Urine was collected and cartilage biomarkers quantified by analyzing C-telopeptide fragments of type II collagen (uCTX-II). Independent t-tests were used to determine between-group differences for RAB angle and uCTX-II. Bivariate correlations were used to determine associations between VAS and uCTX-II for females with PFP. RESULTS: Subjects (age range 20 to 30 years) had similar RAB angles (p = 0.21) and uCTX-II (p = 0.91). A significant association only existed between VAS scores and uCTX-II for females with PFP who had a RAB angle > 13 ° (r = 0.86; p = 0.003). Comparison of uCTX-II in the 25-to-30-year-old females with PFP and excessive patella lateralization in the current study to published normative data showed that this cohort had elevated biomarkers. CONCLUSION: These findings support that a certain cohort of individuals with PFP have features similar to individuals with confirmed PFJOA (patella lateralization and elevated biomarkers). Additional studies are needed to determine if interventions can reverse not only pain but biomarker levels. LEVEL OF EVIDENCE: 2b (diagnosis).

National Athletic Trainers' Association Position Statement: Management of Individuals With Patellofemoral Pain.

OBJECTIVE:: To present recommendations for athletic trainers and other health care providers regarding the identification of risk factors for and management of individuals with patellofemoral pain (PFP). BACKGROUND:: Patellofemoral pain is one of the most common knee diagnoses; however, this condition continues to be one of the most challenging to manage. Recent evidence has suggested that certain risk factors may contribute to the development of PFP. Early identification of risk factors may allow clinicians to develop and implement programs aimed at reducing the incidence of this condition. To date, clinicians have used various treatment strategies that have not necessarily benefitted all patients. Suboptimal outcomes may reflect the need to integrate clinical practice with scientific evidence to facilitate clinical decision making. RECOMMENDATIONS:: The recommendations are based on the best available evidence. They are intended to give athletic trainers and other health care professionals a framework for identifying risk factors for and managing patients with PFP.

Treatment Success of Hip and Core or Knee Strengthening for Patellofemoral Pain: Development of Clinical Prediction Rules.

CONTEXT: Patellofemoral pain (PFP) is a common injury that interferes with quality of life and physical activity. Clinical subgroups of patients may exist, one of which is caused by proximal muscle dysfunction. OBJECTIVES: To develop clinical prediction rules that predict a positive outcome after either a hip and core- or knee-focused strengthening program for individuals with PFP. DESIGN: Secondary analysis of data from a randomized control trial. SETTING: Four university laboratories. PATIENTS OR OTHER PARTICIPANTS: A total of 199 participants with PFP. INTERVENTION(S): Participants were randomly allocated to either a hip and core-focused (n = 111) or knee-focused (n = 88) rehabilitation group for a 6-week program. MAIN OUTCOME MEASURE(S): Demographics, self-reported knee pain (visual analog scale) and function (Anterior Knee Pain Scale), hip strength, abdominal muscle endurance, and hip range of motion were evaluated at baseline. Treatment success was defined as a decrease in visual analog scale score by ≥2 cm or an increase in the Anterior Knee Pain Scale score by ≥8 points or both. Bivariate relationships between the outcome (treatment success) and the predictor variables were explored, followed by a forward stepwise logistic regression to predict a successful outcome. RESULTS: Patients with more pain, better function, greater lateral core endurance, and less anterior core endurance were more likely to have a successful outcome after hip and core strengthening (88% sensitivity and 54% specificity). Patients with lower weight, weaker hip internal rotation, stronger hip extension, and greater trunk-extension endurance were more likely to have success after knee strengthening (82% sensitivity and 58% specificity). CONCLUSION: The patients with PFP who have more baseline pain and yet maintain a high level of function may experience additional benefit from hip and core strengthening. The clinical prediction rules from this study remain in the developmental phase and should be applied with caution until externally validated.

Trunk and hip muscle activation during yoga poses: Do sex-differences exist?

OBJECTIVE: To compare core activation during yoga between males and females. METHODS: Surface electromyography was used to quantify rectus abdominis (RA), abdominal obliques (AO), lumbar extensors (LE), and gluteus maximus (GMX) activation during four yoga poses. Data were expressed as 100% of a maximum voluntary isometric contraction. Mixed-model 2 × 2 analyses of variance with repeated measures were used to determine between-sex differences in muscle activity. RESULTS: Females generated greater RA activity than males during the High Plank (P < 0.0001) and Dominant-Side Warrior 1 (P = 0.017). They generated greater AO (P < 0.0001) and GMX (P = 0.004) activity during the High Plank (P < 0.0001). No between-sex EMG activity differences existed for the Chair and Upward Facing Dog. CONCLUSION: Findings have provided preliminary evidence for between-sex differences in muscle activation during yoga poses. Clinicians should consider such differences when prescribing yoga to improve muscle strength and endurance.

PAIN, FUNCTION, AND STRENGTH OUTCOMES FOR MALES AND FEMALES WITH PATELLOFEMORAL PAIN WHO PARTICIPATE IN EITHER A HIP/CORE- OR KNEE-BASED REHABILITATION PROGRAM.

BACKGROUND: Hip exercise has been recommended for females with patellofemoral pain (PFP). It is unknown if males with PFP will benefit from a similar treatment strategy. HYPOTHESES/PURPOSE: The purpose of this study was to compare improvements in pain, function, and strength between males and females with PFP who participated in either a hip/core or knee rehabilitation program. The directional hypothesis was that females would respond more favorably to the hip/core rehabilitation program and males to the knee program. STUDY DESIGN: Randomized-controlled clinical trial. METHODS: Patients were randomly assigned to a six-week hip/core or knee rehabilitation program. Visual analog scale (VAS), Anterior Knee Pain Scale (AKPS), and hip and knee isometric strength were collected before and after subjects completed the rehabilitation program. Data were analyzed using an intention-to-treat basis. Separate mixed-model analyses of variance (ANOVA) with repeated measures were used to determine changes in VAS and AKPS and strength changes for subjects classified as treatment responders (successful outcome) and non-responders (unsuccessful outcome). RESULTS: Regardless of sex or rehabilitation group, VAS (F1,181=206.5; p<.0001) and AKPS (F1,181 = 160.4; p < 0.0001) scores improved. All treatment responders demonstrated improved hip abductor (F1,122 = 6.6; p = 0.007), hip extensor (F1,122 = 19.3; p < 0.0001), and knee extensor (F1,122 = 16.0; p < 0.0001) strength. A trend (F1,122 = 3.6; p = 0.06) existed for an effect of sex on hip external rotator strength change. Males demonstrated a 15.4% increase compared to a 5.0% increase for females. All treatment non-responders had minimal and non-significant (p > 0.05) strength changes. CONCLUSION: On average, males and females with PFP benefitted from either a hip/core or knee rehabilitation program. Subjects with successful outcomes likely had hip and knee weakness that responded well to the intervention. These males and females had similar and meaningful improvements in hip extensor and knee extensor strength. Only males had relevant changes in hip external rotator strength. Clinicians should consider a subgroup of males who may benefit from hip extensor and external rotator exercise and females who may benefit from hip extensor exercise. LEVEL OF EVIDENCE: 2b.

Relative electromyographic activity in trunk, hip, and knee muscles during unilateral weight bearing exercises: Implications for rehabilitation.

BACKGROUND: Clinicians routinely prescribe unilateral weight bearing exercises to strengthen the lower extremity. Researchers have primarily examined thigh muscle activation with minimal attention to the hip and trunk muscles. The purpose of this study was to quantify trunk, hip, and thigh muscle activation during these types of exercises. METHODS: Electromyographic (EMG) activity was collected for the abdominal obliques (AO), lumbar extensors (LE), gluteus maximus (GMX), gluteus medius (GM), and vastus medialis (VM) as subjects performed four unilateral weight bearing exercises. Data were expressed as 100% of a maximum voluntary isometric contraction (% MVIC). Separate analyses of variance with repeated measures were used to identify muscle activity differences across exercise. The sequentially-rejective Bonferroni test was used for all post-hoc analyses. RESULTS: EMG activity for the AO, LE, and GMX was low (5.7-18.9% MVIC) during all the exercises. The GM activity was moderate (21.4-26.5% MVIC) while VM activity was high (40.0-45.2% MVIC). CONCLUSION: Lower AO and LE activation most likely resulted from subjects maintaining a vertical trunk position over the stance limb during each exercise. The fact that the exercises required greater frontal plane control (from balancing on a single limb) most likely accounted for lower GMX activity. The exercises would provide little, if any, benefit for individuals with AO, LE, or GMX weakness. The unilateral weight bearing exercises would be beneficial for GM neuromuscular re-education and endurance and VM strengthening.

Comparison of hip and knee strength in males with and without patellofemoral pain.

OBJECTIVES: The primary purpose of this study was to compare hip strength in males with and without patellofemoral pain (PFP). The secondary purpose was to compare knee strength in males with and without PFP. DESIGN: Secondary analysis of cross-sectional data for males with and without PFP from a larger randomized controlled trial examining hip and core versus knee-muscle strengthening for the treatment of PFP. SETTING: Laboratory setting. PARTICIPANTS: Sixty-six males with PFP and 36 controls. MAIN OUTCOME MEASURES: Peak isometric force for the hip abductors, external rotators, internal rotators, extensors, and knee extensors expressed as a percentage of body mass (%BM). RESULTS: No differences existed with respect to any of the hip strength measures (P > .05). Males with PFP demonstrated almost 17% less knee extensor strength than controls (mean difference = 7.3 %BM; 95% confidence interval, 1.3-13.4 %BM; t = 2.41; P = .02). CONCLUSIONS: Unlike females, males with PFP did not demonstrate hip muscle weakness. However, differences did exist with knee extensor strength. These data provide preliminary evidence for the potential need for sex-specific interventions for individuals with PFP.

Patellofemoral pain: proximal, distal, and local factors, 2nd International Research Retreat.

Patellofemoral pain (PFP) is one of the most common lower extremity conditions seen in orthopaedic practice. The mission of the second International Patellofemoral Pain Research Retreat was to bring together scientists and clinicians from around the world who are conducting research aimed at understanding the factors that contribute to the development and, consequently, the treatment of PFP. The format of the 2.5-day retreat included 2 keynote presentations, interspersed with 6 podium and 4 poster sessions. An important element of the retreat was the development of consensus statements that summarized the state of the research in each of the 4 presentation categories. In this supplement, you will find the consensus documents from the meeting, as well as the keynote addresses, schedule, and platform and poster presentation abstracts.

A literature review of studies evaluating gluteus maximus and gluteus medius activation during rehabilitation exercises.

Recently, clinicians have focused much attention on the importance of hip strength for the rehabilitation of not only patients with low back pain but also lower extremity pathology. Properly designing a rehabilitation program for the gluteal muscles requires careful consideration of biomechanical principles, such as length of the external moment arm, gravity, and subject positioning. Understanding the anatomy and function of these muscles also is essential. Electromyography (EMG) provides a useful means to determine muscle activation levels during specific exercises. Descriptions of specific exercises, as they relate to the gluteal muscles, are described. The specific performance of these exercises, the reliability of such EMG measures, and descriptive figures are also detailed. Of utmost importance to practicing clinicians is the interpretation of such data and how it can be best used in exercise prescription when formulating a treatment plan.

Comparison of hip and knee strength and neuromuscular activity in subjects with and without patellofemoral pain syndrome.

PURPOSE/BACKGROUND: Historically, patellofemoral pain syndrome (PFPS) has been viewed exclusively as a knee problem. Recent findings have suggested an association between hip muscle weakness and PFPS. Altered neuromuscular activity about the hip also may contribute to PFPS; however, more limited data exist regarding this aspect. Most prior investigations also have not concurrently examined hip and knee strength and neuromuscular activity in this patient population. Additional knowledge regarding the interaction between hip and knee muscle function may enhance the current understanding of PFPS. The purpose of this study was to compare hip and knee strength and electromyographic (EMG) activity in subjects with and without PFPS. METHODS: Eighteen females with PFPS and 18 matched controls participated in this study. First, surface EMG electrodes were donned on the gluteus medius, vastus medialis, and vastus lateralis. Strength measures then were taken for the hip abductors, hip external rotators, and knee extensors. Subjects completed a standardized stair-stepping task to quantify muscle activation amplitudes during the loading response, single leg stance, and preswing intervals of stair descent as well as to determine muscle onset timing differences between the gluteus medius and vastii muscles and between the vastus medialis and vastus lateralis at the beginning of stair descent. RESULTS: Females with PFPS demonstrated less strength of the hip muscles. They also generated greater EMG activity of the gluteus medius and vastus medialis during the loading response and single leg stance intervals of stair descent. No differences existed with respect to onset activation of the vastus medialis and vastus lateralis. All subjects had a similar delay in gluteus medius onset activation relative to the vastii muscles. CONCLUSION: Rehabilitation should focus on quadriceps and hip strengthening. Although clinicians have incorporated gluteus medius exercise in rehabilitation programs, additional attention to the external rotators may be useful. LEVEL OF EVIDENCE: 4.

An update for the conservative management of patellofemoral pain syndrome: a systematic review of the literature from 2000 to 2010.

PURPOSE/BACKGROUND: Patellofemoral pain syndrome (PFPS) is one of the most common and clinically challenging knee pathologies. Historically, clinicians have used a myriad of interventions, many of which have benefited some but not all patients. Suboptimal outcomes may reflect the need for an evidence-based approach for the treatment of PFPS. The authors believe that integrating clinical expertise with the most current scientific data will enhance clinical practice. The purpose of this systematic review is to provide an update on the evidence for the conservative treatment of PFPS. METHODS: The PubMed, CINAHL, and SPORTDiscus databases were searched for studies published between January 1, 2000 and December 31, 2010. Studies used were any that utilized interventions lasting a minimum of 4 weeks for subjects with PFPS. Data were examined for subject sample, intervention duration, intervention type, and pain outcomes. RESULTS: General quadriceps strengthening continues to reduce pain in patients with PFPS. Data are inconclusive regarding the use of patellar taping, patellar bracing, knee bracing, and foot orthosis. Although emerging data suggest the importance of hip strengthening exercise, ongoing investigations are needed to better understand its effect on PFPS. CONCLUSIONS: Current evidence supports the continued use of quadriceps exercise for the conservative management of PFPS. However, inconsistent or limited data regarding the other interventions precluded the authors' ability to make conclusive recommendations about their use. Future investigations should focus on identifying cohorts of patients with PFPS who may benefit from the other treatment approaches included in this systematic review.

Reliability of electromyographic methods used for assessing hip and knee neuromuscular activity in females diagnosed with patellofemoral pain syndrome.

Patellofemoral pain syndrome (PFPS) is one of the most common, yet misunderstood, knee pathologies. PFPS is thought to result from abnormal patella tracking caused from altered neuromuscular control. Researchers have investigated neuromuscular influences from the gluteus medius (GM), vastus medialis (VM), and vastus lateralis (VL) but with inconsistent findings. A reason for these discrepancies may be from varying methodology. The purpose of this study was to determine the reliability of electromyographic (EMG) methods used to assess amplitudes and timing differences of the GM, VM, and VL in subjects with PFPS. Seven females with PFPS participated. GM, VM, and VL activity was assessed during the stance phase of a stair descent task on two separate occasions. Amplitudes during the different intervals of stance were recorded and expressed as a percent of each muscle's maximum voluntary isometric contraction. Muscle onsets at the beginning of stair descent were also determined. VM-GM, VL-GM, and VL-VM onset timing differences were quantified. Intraclass correlation coefficients (ICCs) and standard errors of measurement (SEMs) were calculated to assess between-day reliability. Most EMG measures had acceptable reliability (ICC(3,5)>or=0.70). Although some measures had moderate reliability (ICC<0.70), they had low SEMs, which suggested high measurement precision. These findings support using these methods for examining neuromuscular activity in subjects with PFPS.