REPORT-PFP: a consensus from the International Patellofemoral Research Network to improve REPORTing of quantitative PatelloFemoral Pain studies.

Patellofemoral pain is a common and often debilitating musculoskeletal condition. Clinical translation and evidence synthesis of patellofemoral pain research are compromised by heterogenous and often inadequately reported study details. This consensus statement and associated checklist provides standards for REPORTing of quantitative PatelloFemoral Pain (REPORT-PFP) research to enhance clinical translation and evidence synthesis, and support clinician engagement with research and data collection. A three-stage Delphi process was initiated at the 2015 International Patellofemoral Research Network (iPFRN) retreat. An initial e-Delphi activity (n=24) generated topics and items, which were refined at the 2017 iPFRN retreat, and voted on prior to and following the 2019 iPFRN retreat (n=51 current and past retreat participants). Voting criteria included 'strongly recommended' (essential), 'recommended' (encouraged) and uncertain/unsure. An item was included in the checklist if ≥70% respondents voted 'recommended'. Items receiving ≥70% votes for 'strongly recommended' were labelled as such. The final REPORT-PFP checklist includes 31 items (11 strongly recommended, 20 recommended), covering (i) demographics (n=2,4); (ii) baseline symptoms and previous treatments (n=3,7); (iii) outcome measures (2,4); (iv) outcomes measure description (n=1,2); (v) clinical trial methodology (0,3) and (vi) reporting study results (n=3,0). The REPORT-PFP checklist is ready to be used by researchers and clinicians. Strong stakeholder engagement from clinical academics during development means consistent application by the international patellofemoral pain research community is likely. Checklist adherence will improve research accessibility for clinicians and enhance future evidence synthesis.

Clinical Estimation of the Use of the Hip and Knee Extensors During Athletic Movements Using 2D Video.

Given that increased use of the knee extensors relative to the hip extensors may contribute to various knee injuries, there is a need for a practical method to characterize movement behavior indicative of how individuals utilize the hip and knee extensors during dynamic tasks. The purpose of the current study was to determine whether the difference between sagittal plane trunk and tibia orientations obtained from 2D video (2D trunk-tibia) could be used to predict the average hip/knee extensor moment ratio during athletic movements. Thirty-nine healthy athletes (15 males and 24 females) performed 6 tasks (step down, drop jump, lateral shuffle, deceleration, triple hop, and side-step-cut). Lower-extremity kinetics (3D) and sagittal plane video (2D) were collected simultaneously. Linear regression analysis was performed to determine if the 2D trunk-tibia angle at peak knee flexion predicted the average hip/knee extensor moment ratio during the deceleration phase of each task. For each task, an increase in the 2D trunk-tibia angle predicted an increase in the average hip/knee extensor moment ratio when adjusted for body mass (all P < .013, R2 = .17-.77). The 2D trunk-tibia angle represents a practical method to characterize movement behavior that is indicative of how individuals utilize the hip and knee extensors during dynamic tasks.

Hip Abductor Rate of Torque Development as Opposed to Isometric Strength Predicts Peak Knee Valgus During Landing: Implications for Anterior Cruciate Ligament Injury.

Peak knee valgus has been shown to predict anterior cruciate ligament injury. The purpose of the current study was to compare peak rate of torque development (RTD) to peak isometric torque as a predictor of peak knee valgus during landing. Twenty-three healthy females participated. Hip abductor muscle performance was quantified using 2 types of isometric contractions: sustained and rapid. Peak isometric torque was calculated from the sustained isometric contraction. Peak RTD was calculated from the rapid isometric contraction (0-50 and 0-200 ms after force initiation). Kinematic data were collected during the deceleration phase of a double-leg drop jump task. Linear regression was used to assess the ability of hip abductor muscle performance variables to predict peak knee valgus. Increased peak RTD during the 0 to 50 milliseconds window after force initiation was found to significantly predict lower peak knee valgus (P = .011, R2 = .32). In contrast, neither peak RTD from 0 to 200 milliseconds after force initiation window (P = .45, R2 = .03) nor peak isometric torque (P = .49, R2 = .03) predicted peak knee valgus. The inability of the hip abductors to rapidly generate muscular force may be more indicative of "at-risk" movement behavior in females than measures of maximum strength.

Trunk Inclination During Squatting is a Better Predictor of the Knee-Extensor Moment Than Shank Inclination.

CONTEXT: A limitation of previous studies on squatting mechanics is that the influence of trunk and shank inclination on the knee-extensor moment (KEM) has been studied in isolation. OBJECTIVE: The purpose of the current study was to determine the influence of segment orientation on the KEM during freestanding barbell squatting. DESIGN: Repeated-measures cross sectional. SETTING: University research laboratory. PARTICIPANTS: Sixteen healthy individuals (8 males and 8 females). INTERVENTION: Each participant performed 8 squat conditions in which shank and trunk inclinations were manipulated. MAIN OUTCOME MEASURES: 3D kinematic and kinetic data were collected at 250 and 1500 Hz, respectively. Regression analysis was conducted to identify the individual relationships between the KEM and the trunk and shank inclination at 60° and 90° of knee flexion. To identify the best predictor(s) of the KEM, stepwise regression was implemented. RESULTS: Increased shank inclination increased the KEM (P < .001, R2 = .21-.25). Conversely, increased trunk inclination decreased the KEM (P < .001, R2 = .49-.50). For the stepwise regression, trunk inclination entered first and explained the greatest variance in the KEM (all P < .001, R2 = .49-.50). Shank inclination entered second (all P < .010, R2 = .53-.54) and explained an additional 3% to 5% of the variance. CONCLUSIONS: Our results confirm that inclination of the trunk and shank have an opposing relationship with the KEM. Increased forward shank posture increases the KEM, while increased forward trunk posture decreases the KEM. However, when viewed in combination, the trunk was the superior predictor of the KEM, highlighting the fact that increased quadriceps demand created by a forward shank can be offset by trunk inclination.

2018 Consensus statement on exercise therapy and physical interventions (orthoses, taping and manual therapy) to treat patellofemoral pain: recommendations from the 5th International Patellofemoral Pain Research Retreat, Gold Coast, Australia, 2017.

Patellofemoral pain affects a large proportion of the population, from adolescents to older adults, and carries a substantial personal and societal burden. An international group of scientists and clinicians meets biennially at the International Patellofemoral Research Retreat to share research findings related to patellofemoral pain conditions and develop consensus statements using best practice methods. This consensus statement, from the 5th International Patellofemoral Research Retreat held in Australia in July 2017, focuses on exercise therapy and physical interventions (eg, orthoses, taping and manual therapy) for patellofemoral pain. Literature searches were conducted to identify new systematic reviews and randomised controlled trials (RCTs) published since the 2016 Consensus Statement. The methodological quality of included systematic reviews and RCTs was graded using AMSTAR and PEDro, respectively. Evidence-based statements were developed from included papers and presented to a panel of 41 patellofemoral pain experts for consensus discussion and voting. Recommendations from the expert panel support the use of exercise therapy (especially the combination of hip-focused and knee-focused exercises), combined interventions and foot orthoses to improve pain and/or function in people with patellofemoral pain. The use of patellofemoral, knee or lumbar mobilisations in isolation, or electrophysical agents, is not recommended. There is uncertainty regarding the use of patellar taping/bracing, acupuncture/dry needling, manual soft tissue techniques, blood flow restriction training and gait retraining in patients with patellofemoral pain. In 2017, we launched the International Patellofemoral Research Network (www.ipfrn.org) to consolidate and grow our patellofemoral research community, facilitate collaboration and disseminate patellofemoral pain knowledge to clinicians and the general public. The 6th International Patellofemoral Research Retreat will be held in Milwaukee, Wisconsin, USA, in October 2019.

Runners With Patellofemoral Pain Exhibit Greater Peak Patella Cartilage Stress Compared With Pain-Free Runners.

The primary purpose of this study is to determine whether recreational runners with patellofemoral pain (PFP) exhibit greater peak patella cartilage stress compared with pain-free runners. A secondary purpose was to determine the kinematic and/or kinetic predictors of peak patella cartilage stress during running. A total of 22 female recreational runners (12 with PFP and 10 pain-free controls) participated in this study. Patella cartilage stress profiles were quantified using subject-specific finite element models simulating the maximum knee flexion angle during the stance phase of running. Input parameters to the finite element model included subject-specific patellofemoral joint geometry, quadriceps muscle forces, and lower-extremity kinematics in the frontal and transverse planes. Tibiofemoral joint kinematics and kinetics were quantified to determine the best predictor of stress using stepwise regression analysis. Compared with the pain-free runners, those with PFP exhibited greater peak hydrostatic pressure (PFP vs control: 21.2 [5.6] MPa vs 16.5 [4.6] MPa) and maximum shear stress (PFP vs control: 11.3 [4.6] MPa vs 8.7 [2.3] MPa). Knee external rotation was the best predictor of peak hydrostatic pressure and peak maximum shear stress (38% and 25% of variances, respectively), followed by the knee extensor moment (21% and 25% of variances, respectively). Runners with PFP exhibit greater peak patella cartilage stress during running compared with pain-free individuals. The combination of knee external rotation and a high knee extensor moment best predicted the elevated peak stress during running.

The Influence of Squat Kinematics and Cam Morphology on Acetabular Stress.

PURPOSE: To evaluate the effect of varying degrees of simulated cam morphology on acetabular stress magnitude and location using a finite element model with 1 subject that incorporates population-specific hip/pelvis kinematics during a squat task. METHODS: A reference model of the hip joint was created from magnetic resonance images obtained from 1 asymptomatic 28-year-old man without femoroacetabular impingement (FAI) morphology or hip dysplasia (alpha angle 41.9°, lateral center edge angle 34.0°, neck-shaft angle 137°, and no visible articular cartilage lesions or bone marrow edema on magnetic resonance). The femoral head/neck geometry was manipulated to mimic different cam morphology severities as reported in a previous study (minimum, moderate, and large). Peak hip and pelvis squat kinematics from healthy individuals (hip flexion 112.6°, abduction 10.5°, internal rotation 14.8°) and persons with FAI (hip flexion 106.3°, abduction 10.5°, internal rotation 8.9°) were applied to the control and cam models. Relative acetabular joint stress values and location of contact were the variables of interest. RESULTS: Average von Mises stress values for control, minimum, moderate, and large cam models were 9.64, 9.27, 11.36, and 28.43 MPa, respectively. Contact in the control and minimum cam models occurred within the acetabular cup. In the moderate and large cam models, contact shifted anterosuperiorly within the acetabular cup and to anterosuperior acetabular rim, respectively. CONCLUSIONS: Despite simulating lower degrees of hip flexion and internal rotation, increased stress and a shift in contact location were observed in the simulated models of FAI. This finding suggests that decreased hip internal rotation in this population during functional tasks may be the result of bony abutment. CLINICAL RELEVANCE: Clinicians should be cautious about prescribing deep squats for persons with cam morphology. Performing squat exercises with neutral or external hip rotation may limit bony abutment at high hip flexion angles.

Increasing hip and knee flexion during a drop-jump task reduces tibiofemoral shear and compressive forces: implications for ACL injury prevention training.

Although most ACL injury prevention programmes encourage greater hip and knee flexion during landing, it remains unknown how this technique influences tibiofemoral joint forces. We examined whether a landing strategy utilising greater hip and knee flexion decreases tibiofemoral anterior shear and compression. Twelve healthy women (25.9 ± 3.5 years) performed a drop-jump task before and after a training session (10-15 min) that emphasised greater hip and knee flexion. Peak tibiofemoral anterior shear and compressive forces were calculated using an electromyography (EMG)-driven knee model that incorporated joint kinematics, EMG and participant-specific muscle volumes and patella tendon orientation measured using magnetic resonance imaging (MRI). Participants demonstrated a decrease in peak anterior tibial shear forces (11.1 ± 3.3 vs. 9.6 ± 2.7 N · kg-1; P = 0.008) and peak tibiofemoral compressive forces (68.4 ± 7.6 vs. 62.0 ± 5.5 N · kg-1; P = 0.015) post-training. The decreased peak anterior tibial shear was accompanied by a decrease in the quadriceps anterior shear force, while the decreased peak compressive force was accompanied by decreased ground reaction force and hamstring forces. Our data provide justification for injury prevention programmes that encourage greater hip and knee flexion during landing to reduce tibiofemoral joint loading.

Does Patella Tendon Tenodesis Improve Tibial Tubercle Distalization in Treating Patella Alta? A Computational Study.

BACKGROUND: Patellofemoral malalignment associated with patella alta may cause pain and arthritis; because of this, the condition sometimes is treated surgically. Two common procedures are tibial tubercle distalization with or without patellar tendon tenodesis. However, the biomechanical consequences of these interventions for patella alta are not clearly understood. QUESTIONS/PURPOSES: We evaluated changes in patellofemoral joint contact mechanics after tibial tubercle distalization and tibial tubercle distalization combined with patella tendon tenodesis. Specifically, we asked: (1) Are there biomechanical differences between these two types of procedures? (2) Is there an ideal range to distalize the patella? METHODS: Subject-specific finite-element models were created for 10 individuals with patella alta (mean Insall-Salvati ratio of 1.34 ± 0.05). Input parameters for the finite-element models included subject-specific joint geometry, quadriceps muscle forces, and weightbearing patellofemoral joint kinematics. Virtual operations were conducted to simulate the two procedures. For distalization, the tibial tubercle and patella were displaced distally 4 mm to 20 mm in 4-mm increments based on the original model. At each level of distalization, the patella tendon was attached back to its original insertion to simulate the additional tenodesis procedure. Cartilage stress, contact area, and contact forces were quantified and compared between procedures and distalization levels. RESULTS: Distalization and distalization + tenodesis reduced patellofemoral joint stress compared with the baseline of 1.02 ± 0.11 MPa. Distalization led to lower cartilage stress than distalization + tenodesis, and the effect size was relatively large (0.88 ± 0.10 MPa vs 0.92 ± 0.10 MPa; mean difference, 0.04 MPa [95% CI, 0.02 MPa-0.05 MPa], p < 0.01; effect size of 1.64 [Cohen's d], with Insall-Salvati ratio decreased to 0.95). For both procedures, the trend of stress reduction plateaued when the Install-Salvati ratio approached 0.95. CONCLUSIONS: Cartilage stress appears lower using distalization as opposed to distalization + tenodesis in this finite-element analysis simulation. An Insall-Salvati ratio of 0.95 may be an ideal level for distalization; further distalization does not show additional benefits. CLINICAL RELEVANCE: This study suggests that distalization may result in less stress than distalization + tenodesis, therefore future clinical research might be preferentially directed toward evaluating isolated distalization procedures.

Pressure-controlled treadmill training in chronic stroke: a case study with AlterG.

BACKGROUND AND PURPOSE: Body-weight-supported treadmill training has been shown to be an effective intervention to improve walking characteristics for individuals who have experienced a stroke. A pressure-controlled treadmill utilizes a sealed chamber in which air pressure can be altered in a controlled manner to counteract the effects of gravity. The focus of this case study was to assess the immediate and short-term impact of a pressure-controlled treadmill to improve gait parameters, reduce fall risk, improve participation, and reduce the self-perceived negative impact of stroke in an individual with chronic stroke. CASE DESCRIPTION: The subject was an 81-year-old man (14.5 months poststroke). He had slow walking speed, poor endurance, and multiple gait deviations. INTERVENTION: The subject trained 4 times per week for 4 weeks (40 minutes per session) on a pressure-controlled treadmill (AlterG M320) to counter the influence of gravity on the lower extremities. OUTCOMES: Following training, self-selected gait speed increased from 0.50 m/s to 0.96 m/s, as measured by the 10-meter walk test. Stride length increased from 0.58 m to 0.95 m after training and to 1.00 m at 1-month follow-up. Peak hip flexion increased from 3.7° to 24.6° after training and to 19.4° at 1-month follow-up. Peak knee flexion increased from 19.4° to 34.3° after training and to 42.7° at 1-month follow-up. Measures of endurance, fall risk, and percentage of perceived recovery also were found to improve posttraining. DISCUSSION: Training with a pressure-controlled treadmill may be a viable alternative to traditional body-weight-supported treadmill training for persons poststroke. Additional studies with larger sample sizes are needed to elucidate the role of pressure-controlled treadmill training in this population. Video abstract available for more insights from the authors (see Supplemental Digital Content 1, http://links.lww.com/JNPT/A97).

Comparison of three-dimensional patellofemoral joint reaction forces in persons with and without patellofemoral pain.

The purpose of this study was to determine if persons with patellofemoral pain (PFP) exhibit differences in patellofemoral joint reaction forces (PFJRFs) during functional activities. Forty females (20 PFP, 20 controls) underwent two phases of data collection: (1) magnetic resonance imaging (MRI) and (2) biomechanical analysis during walking, running, stair ascent, and stair descent. A previously described three-dimensional model was used to estimate PFJRFs. Resultant PFJRFs and the orthogonal components were reported. The PFP group demonstrated lower peak resultant PFJRFs and posterior component and superior component of the PFJRFs compared with the control group across all conditions. However, the PFP group had a higher peak lateral component of the PFJRF in three out of the four conditions evaluated. The lower resultant PFJRFs suggested that individuals with PFP may employ strategies to minimize patellofemoral joint loading, but it did not result in diminished lateral forces acting on the patella.

A Biomechanical Review of the Squat Exercise: Implications for Clinical Practice.

The squat is one of the most frequently prescribed exercises in the rehabilitative setting. Performance of the squat can be modified by changing parameters such as stance width, foot rotation, trunk position, tibia position, and depth. An understanding of how the various squatting techniques can influence joint loading and muscular demands is important for the proper prescription of this exercise for various clinical conditions. The purpose of this clinical commentary is to discuss how the biomechanical demands of the squat can be influenced by various modifiable parameters. General recommendations for specific clinical conditions are presented. Level of Evidence: 5.

Reliability of a method to assess corticomotor excitability of lower limb muscles using a normalized EMG motor thresholding procedure.

Given the importance of determining intervention-induced neuroplastic changes with lower extremity functional tasks, a reliable transcranial magnetic stimulation (TMS) methodology for proximal lower extremity muscles is needed. A pre-set fixed voltage value is typically used as the criterion for identifying a motor evoked potential (MEP) during the motor thresholding procedure. However, the fixed voltage value becomes problematic when the procedure is applied to proximal lower extremity muscles where active contractions are required. We sought to establish the reliability of a method measuring corticomotor excitability of gluteus maximus and vastus lateralis using normalized electromyography (EMG) as the criterion for identifying MEPs during the motor thresholding procedure. The active motor threshold for each muscle was determined using the lowest stimulator intensity required to elicit 5 MEPs that exceeded 20% maximal voluntary isometric contraction from 10 stimulations. TMS data were obtained from 10 participants on 2 separate days and compared using random-effect intra-class correlation coefficients (ICCs). Slopes from two input-output curve fitting methods as well as the maximum MEP of gluteus maximus and vastus lateralis were found to exhibit good to excellent reliability (ICCs ranging from 0.75 to 0.99). The described TMS method using EMG-normalized criteria for motor thresholding produced reliable results utilizing a relatively low number of TMS pulses.

Measuring bone mineral density with fat-water MRI: comparison with computed tomography.

PURPOSE: To develop a method for measuring bone mineral density (BMD) with MRI, and to validate this method against quantitative computed tomography (QCT). MATERIALS AND METHODS: A mathematical relationship between signal intensities from proton-density-weighted in-phase images generated by multi-fat-peak T2*-IDEAL MRI and BMD was derived using a set of calibration standards constructed from various concentrations of hydroxyapatite in water. Using these standards, the relationship between hydroxyapatite concentration and MRI signal intensity was examined. A T2*-IDEAL protocol was performed on the patella of 5 volunteers and the signal model was used to compute BMD of all voxels of the patella. The BMD data were validated by obtaining QCT scans of the same patella, computing QCT BMD of all voxels, and comparing the MRI and QCT BMD data by performing linear regression analysis on a voxel-by-voxel basis. RESULTS: A strong linear correlation between hydroxyapatite concentration of the calibration standards and MRI signal intensities was observed (r = 0.98; P < 0.01). In the patella, BMD measurements (N = 28796 voxels) from the MRI signal model were significantly correlated with those from QCT (r = 0.82; P < 0.001; slope = 1.02; and intercept = -0.26). CONCLUSION: A standardized phantom consisting of hydroxyapatite and water can be used to accurately quantify BMD in vivo using MRI.

Association between measures of patella height, morphologic features of the trochlea, and patellofemoral joint alignment: the MOST study.

BACKGROUND: Patellofemoral joint (PFJ) malalignment (lateral patella displacement and tilt) has been proposed as a cause of patellofemoral pain. Patella height and/or the morphologic features of the femoral trochlea may predispose one to patella malalignment. QUESTIONS/PURPOSES: The purposes of our study were to assess the associations among patella height, morphologic features of the trochlea, and measures of PFJ alignment and to determine which measures of patella height and morphologic features of the trochlea were the best predictors of PFJ alignment. METHODS: Measures of patella height (Insall-Salvati ratio and modified Insall-Salvati ratio), morphologic features of the trochlea (sulcus angle, trochlear angle, lateral trochlear inclination, medial trochlear inclination), and PFJ alignment (bisect offset and patella tilt angle) were assessed in 566 knees from the Multicenter Osteoarthritis Study. RESULTS: Bisect offset was correlated with the Insall-Salvati ratio (r = 0.25) and lateral trochlear inclination (r = -0.38). Patella tilt angle correlated with the trochlear angle (-0.27) and lateral trochlear inclination (-0.32). Linear regression models including the Insall-Salvati ratio and lateral trochlear inclination explained 20% and 11% of the variance in bisect offset and patella tilt angle, respectively. CONCLUSIONS: Of the variables measured in the current study, the Insall-Salvati ratio and lateral trochlear inclination were the best predictors of lateral patella displacement and lateral tilt. This knowledge will aid clinicians in the identification of anatomic risk factors for PFJ malalignment and/or PFJ dysfunction.

Quantification of tibiofemoral shear and compressive loads using a MRI-based EMG-driven knee model.

The purpose of this study is to describe an MRI-based EMG-driven knee model to quantify tibiofemoral compressive and shear forces. Twelve healthy females participated. Subjects underwent 2 phases of data collection: (1) MRI assessment of the lower extremity to quantify muscle volumes and patella tendon orientation and (2) biomechanical evaluation of a drop-jump task. A subject-specific EMG-driven knee model that incorporated lower extremity kinematics, EMG, and muscle volumes and patella tendon orientation estimated from MRI was developed to quantify tibiofemoral shear and compressive forces. A resultant anterior tibial shear force generated from the ground reaction force (GRF) and muscle forces was observed during the first 30% of the stance phase of the drop-jump task. All of the muscle forces and GRF resulted in tibiofemoral compression, with the quadriceps force being the primary contributor. Acquiring subject-specific muscle volumes and patella tendon orientation for use in an EMG-driven knee model may be useful to quantify tibiofemoral forces in persons with altered patella position or muscle atrophy following knee injury or pathology.

Is muscular strength a predictor for primary or secondary ACL injury? A scoping review of prospective studies.

OBJECTIVE: To identify strength-related risk factors of ACL injury by conducting a scoping review of the peer-reviewed literature. METHODS: PubMed and EBSCO host (CINAHL Complete, MEDLINE Complete, SPORTDiscus) were searched from inception to August 2022. Prospective studies that examined strength strength-related risk factors for ACL injury (primary and secondary) were included. PRISMA Extension for Scoping Reviews guided data charting/extraction. RESULTS: 17 studies were included (eight primary ACL injury, nine secondary ACL injury). Knee flexor strength was the most studied predictor (10 studies), followed by hip abductor strength (9 studies). Across studies, measures of muscle performance were inconsistent. Significant strength-related risk factors were reported in seven of 17 studies. Potential strength-related risk factors of primary ACL injury included measures of hip strength (abductor or external rotator) and knee strength (knee flexor/extensor ratio and knee extensor strength symmetry) for secondary ACL injury. Limited/conflicting evidence was found for all strength-related risk factors. CONCLUSION: Measures of muscle strength appear to be predictive of primary and secondary ACL injury in a subset of identified studies. The heterogeneity of study designs and lack of standardization related to strength testing make it difficult to determine the overall impact of strength in predicting ACL injury.

The influence of isolated femur and tibia rotations on patellar tendon stress: A sensitivity analysis using finite element analysis.

The purpose of this study was to determine the influence of frontal and transverse plane rotations of the femur and tibia on peak maximum principal stress in the patellar tendon. Using finite element modeling, patellar tendon stress profiles of eight healthy individuals were obtained during a simulated squatting task (45° of knee flexion). The femur and tibia of each model were rotated 10° (in 2° increments) along their respective axes beyond that of the natural degree of rotation. This process was repeated for the transverse plane (internal and external rotation) and frontal plane (adduction and abduction). Quasi-static loading simulations were performed to quantify peak maximum principal stress in patellar tendon. Internal and external rotations of the femur and tibia that exceeded 4° beyond that of the natural rotation resulted in progressively greater patellar tendon stress (p < 0.05). Incremental femur and tibia adduction and abduction resulted in an increase in patellar tendon stress, but only at the end range of motions evaluated. These results suggest that tibiofemoral rotations in the frontal and transverse planes have the potential to influence patellar tendon stress. In particular, patellar tendon stress is highly sensitive to small degrees of tibia and/or femur motions in the transverse plane.

Comparison of electromyographic activity of the gluteal muscles and tensor fascia lata in persons with patellofemoral pain: evaluation of selected, hip-targeted exercises using indwelling fine-wire electrodes.

INTRODUCTION: Excessive hip adduction and internal rotation are common movement impairments associated with patellofemoral pain (PFP). As such, strengthening of the hip abductors and external rotators commonly is recommended. Because tensor fascia latae (TFL) is a hip internal rotator in addition to being an abductor, it is important to select exercises that target the superior gluteus maximus (SUP-GMAX) and gluteus medius (GMED) while minimizing activation of the TFL. OBJECTIVE: To identify hip-targeted exercises resulting in greater activation of the SUP-GMAX and GMED relative to the TFL in persons with PFP. METHODS: Twelve individuals with PFP participated. Electromyographic (EMG) signals were obtained from the GMED, SUP-GMAX, and TFL using fine-wire electrodes while participants performed 11 hip-targeted exercises. Normalized EMG of GMED and SUP-GMAX was compared to that of the TFL for each exercise using repeated measures ANOVAs and descriptive statistics. RESULTS: Of the 11 hip exercises evaluated, only the clam exercise with elastic resistance resulted in significantly greater activity of both gluteal muscles (SUP-GMAX = 24.2 ± 14.4%MVIC, p = .05; GMED = 37.2 ± 19.7%MVIC, p = .008) relative to the TFL (12.5 ± 11.7%MVIC). Five exercises exhibited significantly lower activation of SUP-GMAX relative to TFL: 1) unilateral bridge: SUP-GMAX = 17.7 ± 9.8%MVIC, TFL = 34.0 ± 17.7%MVIC, p = .01; 2) bilateral bridge: SUP-GMAX = 10.0 ± 6.9%MVIC, TFL = 14.0 ± 7.5%MVIC, p = .04; 3) abduction: SUP-GMAX = 14.2 ± 11.1%MVIC, TFL = 33.0 ± 11.9%MVIC, p = .001; 4) hip hike: SUP-GMAX = 14.8 ± 12.8%MVIC, TFL = 46.8 ± 33.7%MVIC, p = .008; and 5) step-up: SUP-GMAX = 15.0 ± 5.4%MVIC, TFL = 31.7 ± 19.9 %MVIC, p = .02). No differences in gluteal activation relative to TFL were found for the remaining 6 exercises (all p > .05). CONCLUSION: The clam with elastic resistance exercise was effective at activating the SUP-GMAX and GMED greater than TFL. No other exercises achieved a similar level of muscular recruitment. When attempting to strengthen the gluteal muscles in persons with PFP, care should be taken in assuming that common hip-targeted exercises result in the desired recruitment patterns.

Persons with Patellar Tendinopathy Exhibit Greater Patellar Tendon Stress during a Single-Leg Landing Task.

PURPOSE: This study aimed to compare peak maximum principal stress in the patellar tendon between persons with and without patellar tendinopathy during a simulated single-leg landing task. A secondary purpose was to determine the biomechanical predictor(s) of peak maximum principal stress in the patellar tendon. METHODS: Using finite element (FE) modeling, patellar tendon stress profiles of 28 individuals (14 with patellar tendinopathy and 14 pain-free controls) were created at the time of the peak knee extensor moment during single-leg landing. Input parameters to the FE model included subject-specific knee joint geometry and kinematics, and quadriceps muscle forces. Independent t -tests were used to compare the peak maximum principal stress in the patellar tendon and biomechanical variables used as input variables to the FE model (knee flexion, knee rotation in the frontal and transverse planes and the peak knee extensor moment) between groups. A stepwise regression model was used to determine the biomechanical predictor(s) of peak maximum principal stress in the patellar tendon for both groups combined. RESULTS: Compared with the control group, persons with patellar tendinopathy exhibited greater peak maximum principal stress in the patellar tendon (77.4 ± 25.0 vs 60.6 ± 13.6 MPa, P = 0.04) and greater tibiofemoral joint internal rotation (4.6° ± 4.6° vs 1.1° ± 4.2°, P = 0.04). Transverse plane rotation of the tibiofemoral joint was the best predictor of peak maximum principal stress in the patellar tendon ( r = 0.51, P = 0.01). CONCLUSIONS: Persons with patellar tendinopathy exhibit greater peak patellar tendon stress compared with pain-free individuals during single-leg landing. The magnitude of peak patellar tendon stress seems to be influenced by the amount of tibiofemoral rotation in the transverse plane.