Christopher M Powers’s research while affiliated with University of Southern California and other places

Individuals who undergo anterior cruciate ligament reconstruction are at elevated risk for developing early‐onset patellofemoral joint osteoarthritis. Our objective was to use K‐means clustering to ascertain whether individuals at risk for patellofemoral joint osteoarthritis could be identified as determined by the presence of multiple co‐existing anatomical and patella alignment risk factors. Forty participants (20 after anterior cruciate ligament reconstruction, 20 healthy controls) underwent magnetic resonance imaging assessment of the patellofemoral joint. Measures of hypothesized risk factors for patellofemoral joint osteoarthritis were obtained including patella alignment (lateral patella displacement and tilt), trochlear morphology (sulcus angle, lateral inclination angle), patella height (Insall‐Salvati ratio and patella articulating overlap), and patellofemoral joint contact area. K‐means clustering ( k = 2) was used to ascertain whether a high‐risk group could be identified. Following clustering, two distinct groups were detected. Participants assigned to cluster 1 exhibited features consistent with patellofemoral joint osteoarthritis including greater lateral patellar displacement and tilt, flatter trochlear grooves and lower lateral trochlear inclination, less patella articulating overlap, and reduced contact area. The proportion of females after anterior cruciate ligament reconstruction assigned to cluster 1 was 75% ( N = 15) compared to 25% of healthy females ( N = 5). K‐means clustering was capable of characterizing individuals at elevated risk for patellofemoral joint osteoarthritis based on the presence of multiple co‐existing anatomical and patella alignment risk factors. The fact that a significant percentage of females were assigned to the high‐risk cluster supports the clinical observation that these individuals may be at higher risk of early‐onset patellofemoral joint osteoarthritis.

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

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.

Although reactive arm motions are important in recovering from a slip event, the biomechanical influences of upper extremity motions during slipping are not clear. The purpose of the current study was to determine whether reactive arm motions during slip recovery leads to increased margins of stability (MoS), and decreased center of mass (CoM) velocity and excursion. Thirty-two participants were randomized into 2 conditions: arms free and arms constrained. Participants traversed a 10-meter walkway and were exposed to an unexpected slip while wearing a protective harness. Anterior-posterior and medial-lateral MoS, as well as the CoM excursion and velocity during the slip perturbation was quantified using a three-dimensional motion capture system. In the frontal plane, individuals with their arms unconstrained demonstrated greater MoS (0.06 ± 0.03 vs -0.01 ± 0.02 m, p < 0.01), decreased CoM excursion (0.05 ± 0.02 vs 0.08 ± 0.01 m, p = 0.015), and a reduced CoM velocity (0.07 ± 0.03 vs. 0.14 ± 0.02 m/s, p < 0.01) compared to individuals with their arms constrained. In the sagittal plane, individuals with their arms unconstrained demonstrated, decreased CoM excursion (0.83 ± 0.13 vs 1.14 ± 0.20 m, p < 0.01) reduced CoM velocity (1.71 ± 0.08 vs. 1.79 ± 0.07 m/s, p = 0.02), but no differences in margins of stability (0.89 ± 0.13 vs 0.94 ± 0.10 m, p = 0.32). Our findings demonstrate that arm motions during a slip perturbation act to restore balance by minimizing displacement and velocity of the body CoM during a slip event in the frontal plane.