Toran D. MacLeod

Estimation of Ligament Loading and Anterior Tibial Translation in Healthy and ACL-Deficient Knees During Gait and the Influence of Increasing Tibial Slope Using EMG-Driven Approach

The purpose of this study was to develop a biomechanical model to estimate anterior tibial translation (ATT), anterior shear forces, and ligament loading in the healthy and anterior cruciate ligament (ACL)-deficient knee joint during gait. This model used electromyography (EMG), joint position, and force plate data as inputs to calculate ligament loading during stance phase. First, an EMG-driven model was used to calculate forces for the major muscles crossing the knee joint. The calculated muscle forces were used as inputs to a knee model that incorporated a knee–ligament model in order to solve for ATT and ligament forces. The model took advantage of using EMGs as inputs, and could account for the abnormal muscle activation patterns of ACL-deficient gait. We validated our model by comparing the calculated results with previous in vitro, in vivo, and numerical studies of healthy and ACL-deficient knees, and this gave us confidence on the accuracy of our model calculations. Our model predicted that ATT increased throughout stance phase for the ACL-deficient knee compared with the healthy knee. The medial collateral ligament functioned as the main passive restraint to anterior shear force in the ACL-deficient knee. Although strong co-contraction of knee flexors was found to help restrain ATT in the ACL-deficient knee, it did not counteract the effect of ACL rupture. Posterior inclination angle of the tibial plateau was found to be a crucial parameter in determining knee mechanics, and increasing the tibial slope inclination in our model would increase the resulting ATT and ligament forces in both healthy and ACL-deficient knees.

Effects of Statins on Skeletal Muscle: A Perspective for Physical Therapists

Hyperlipidemia, also known as high blood cholesterol, is a cardiovascular health risk that affects more than one third of adults in the United States. Statins are commonly prescribed and successful lipid-lowering medications that reduce the risks associated with cardiovascular disease. The side effects most commonly associated with statin use involve muscle cramping, soreness, fatigue, weakness, and, in rare cases, rapid muscle breakdown that can lead to death. Often, these side effects can become apparent during or after strenuous bouts of exercise. Although the mechanisms by which statins affect muscle performance are not entirely understood, recent research has identified some common causative factors. As musculoskeletal and exercise specialists, physical therapists have a unique opportunity to identify adverse effects related to statin use. The purposes of this perspective article are: (1) to review the metabolism and mechanisms of actions of statins, (2) to discuss the effects of statins on skeletal muscle function, (3) to detail the clinical presentation of statin-induced myopathies, (4) to outline the testing used to diagnose statin-induced myopathies, and (5) to introduce a role for the physical therapist for the screening and detection of suspected statin-induced skeletal muscle myopathy.

Patellofemoral joint force and stress during the wall squat and one-leg squat.

PURPOSE To compare patellofemoral compressive force and stress during the one-leg squat and two variations of the wall squat. METHODS Eighteen subjects used their 12 repetition maximum (12 RM) weight while performing the wall squat with the feet closer to the wall (wall squat short), the wall squat with the feet farther away from the wall (wall squat long), and the one-leg squat. EMG, force platform, and kinematic variables were input into a biomechanical model to calculate patellofemoral compressive force and stress as a function of knee angle. To asses differences among exercises, a one-factor repeated-measure ANOVA (P = 0.0025) was used. RESULTS During the squat ascent, there were significant differences in patellofemoral force and stress among the three squat exercises at 90 degrees knee angle (P = 0.002), 80 degrees knee angle (P = 0.002), 70 degrees knee angle (P < 0.001), and 60 degrees knee angle (P = 0.001). Patellofemoral force and stress were significantly greater at 90 degrees knee angle in the wall squat short compared with wall squat long and one-leg squat, significantly greater at 70 degrees and 80 degrees knee angles in the wall squat short and long compared with the one-leg squat and significantly greater at 60 degrees knee angle in the wall squat long compared with the wall squat short and one-leg squat. CONCLUSIONS Except at 60 degrees and 90 degrees knee angles, patellofemoral compressive force and stress were similar between the wall squat short and the wall squat long. Between 60 degrees and 90 degrees knee angles, wall squat exercises generally produced greater patellofemoral compressive force and stress compared with the one-leg squat. When the goal is to minimize patellofemoral compressive force and stress, it may be prudent to use a smaller knee angle range between 0 degrees and 50 degrees compared with a larger knee angle range between 60 degrees and 90 degrees .

Cruciate ligament force during the wall squat and the one-leg squat.

PURPOSE To compare cruciate ligament forces during wall squat and one-leg squat exercises. METHODS Eighteen subjects performed the wall squat with feet closer to the wall (wall squat short), the wall squat with feet farther from the wall (wall squat long), and the one-leg squat. EMG, force, and kinematic variables were input into a biomechanical model using optimization. A three-factor repeated-measure ANOVA (P < 0.05) with planned comparisons was used. RESULTS Mean posterior cruciate ligament (PCL) forces were significantly greater in 1) wall squat long compared with wall squat short (0 degrees -80 degrees knee angles) and one-leg squat (0 degrees -90 degrees knee angles); 2) wall squat short compared with one-leg squat between 0 degrees -20 degrees and 90 degrees knee angles; 3) wall squat long compared with wall squat short (70 degrees -0 degrees knee angles) and one-leg squat (90 degrees -60 degrees and 20 degrees -0 degrees knee angles); and 4) wall squat short compared with one-leg squat between 90 degrees -70 degrees and 0 degrees knee angles. Peak PCL force magnitudes occurred between 80 degrees and 90 degrees knee angles and were 723 +/- 127 N for wall squat long, 786 +/- 197 N for wall squat short, and 414 +/- 133 N for one-leg squat. Anterior cruciate ligament (ACL) forces during one-leg squat occurred between 0 degrees and 40 degrees knee angles, with a peak magnitude of 59 +/- 52 N at 30 degrees knee angle. Quadriceps force ranged approximately between 30 and 720 N, whereas hamstring force ranged approximately between 15 and 190 N. CONCLUSIONS Throughout the 0 degrees -90 degrees knee angles, the wall squat long generally exhibited significantly greater PCL forces compared with the wall squat short and one-leg squat. PCL forces were similar between the wall squat short and the one-leg squat. ACL forces were generated only in the one-leg squat. All exercises appear to load the ACL and the PCL within a safe range in healthy individuals.

Quadriceps intramuscular fat fraction rather than muscle size is associated with knee osteoarthritis

OBJECTIVES To compare thigh muscle intramuscular fat (intraMF) fractions and area between people with and without knee radiographic osteoarthritis (ROA); and to evaluate the relationships of quadriceps adiposity and area with strength, function and knee magnetic resonance imaging (MRI) lesions. METHODS Ninety six subjects (ROA: Kellgren-Lawrence (KL) > 1; n = 30, control: KL = 0, 1; n = 66) underwent 3-T MRI of the thigh muscles using chemical shift-based water/fat MRI (fat fractions) and the knee (clinical grading). Subjects were assessed for isometric/isokinetic quadriceps/hamstrings strength, function Knee injury and Osteoarthritis Outcome Score (KOOS), stair climbing test (SCT), and 6-minute walk test (6MWT). Thigh muscle intraMF fractions, muscle area and strength, and function were compared between controls and ROA subjects, adjusting for age. Relationships between measures of muscle fat/area with strength, function, KL and lesion scores were assessed using regression and correlational analyses. RESULTS The ROA group had worse KOOS scores but SCT and 6MWT were not different. The ROA group had greater quadriceps intraMF fraction but not for other muscles. Quadriceps strength was lower in ROA group but the area was not different. Quadriceps intraMF fraction but not area predicted self-reported disability. Aging, worse KL, and cartilage and meniscus lesions were associated with higher quadriceps intraMF fraction. CONCLUSION Quadriceps intraMF is higher in people with knee OA and is related to symptomatic and structural severity of knee OA, whereas the quadriceps area is not. Quadriceps fat fraction from chemical shift-based water/fat MR imaging may have utility as a marker of structural and symptomatic severity of knee OA disease process.

Patellofemoral compressive force and stress during the forward and side lunges with and without a stride.

BACKGROUND Although weight bearing lunge exercises are frequently employed during patellofemoral rehabilitation, patellofemoral compressive force and stress are currently unknown for these exercises. METHODS Eighteen subjects used their 12 repetition maximum weight while performing forward and side lunges with and without a stride. EMG, force platform, and kinematic variables were input into a biomechanical model, and patellofemoral compressive force and stress were calculated as a function of knee angle. FINDINGS Patellofemoral force and stress progressively decreased as knee flexion increased and progressively increased as knee flexion decreased. Patellofemoral force and stress were greater in the side lunge compared to the forward lunge between 80 degrees and 90 degrees knee angles, and greater with a stride compared to without a stride between 10 degrees and 50 degrees knee angles. There were no significant interactions between lunge variations and stride variations. INTERPRETATION A more functional knee flexion range between 0 degrees and 50 degrees may be appropriate during the early phases of patellofemoral rehabilitation due to lower patellofemoral compressive force and stress during this range compared to higher knee angles between 60 degrees and 90 degrees. Moreover, when the goal is to minimize patellofemoral compressive force and stress, it may be prudent to employ forward and side lunges without a stride compared to with a stride, especially at lower knee angles between 0 degrees and 50 degrees. Understanding differences in patellofemoral compressive force and stress among lunge variations may help clinicians prescribe safer and more effective exercise interventions.

Patellofemoral Joint Force and Stress Between a Short- and Long-Step Forward Lunge

STUDY DESIGN Controlled laboratory biomechanics study using a repeated-measures, counterbalanced design. OBJECTIVES To compare patellofemoral joint force and stress between a short- and long-step forward lunge both with and without a stride. BACKGROUND Although weight-bearing forward-lunge exercises are frequently employed during rehabilitation for individuals with patellofemoral joint syndrome, patellofemoral joint force and stress and how they change with variations of the lunge exercise are currently unknown. METHODS AND MEASURES Eighteen subjects used their 12-repetition maximum weight while performing a short- and long-step forward lunge both with and without a stride. Electromyography, ground reaction force, and kinematic variables were put into a biomechanical optimization model, and patellofemoral joint force and stress were calculated as a function of knee angle. RESULTS Visual observation of the data show that during the forward lunge, patellofemoral joint force and stress increased progressively as knee flexion increased, and decreased progressively as knee flexion decreased. Between 70 degrees and 90 degrees of knee flexion, patellofemoral joint force and stress were significantly greater when performing a forward lunge with a short step compared to a long step (P<.025). Between 10 degrees and 40 degrees of knee flexion, patellofemoral joint force and stress were significantly greater when performing a forward lunge with a stride compared to without a stride (P<.025). CONCLUSIONS When the goal is to minimize patellofemoral joint force and stress during the forward lunge performed between 0 degrees to 90 degrees knee angles, it may be prudent to perform the lunge with a long step compared to a short step and without a stride compared to with a stride, because patellofemoral joint force and stress magnitudes were greater with a short step compared to a long step at higher knee flexion angles and were greater with a stride compared to without a stride at lower knee flexion angles.

Cruciate ligament forces between short-step and long-step forward lunge.

PURPOSE The purpose of this study was to compare cruciate ligament forces between the forward lunge with a short step (forward lunge short) and the forward lunge with a long step (forward lunge long). METHODS Eighteen subjects used their 12-repetition maximum weight while performing the forward lunge short and long with and without a stride. EMG, force, and kinematic variables were input into a biomechanical model using optimization, and cruciate ligament forces were calculated as a function of knee angle. A two-factor repeated-measure ANOVA was used with a Bonferroni adjustment (P < 0.0025) to assess differences in cruciate forces between lunging techniques. RESULTS Mean posterior cruciate ligament (PCL) forces (69-765 N range) were significantly greater (P < 0.001) in the forward lunge long compared with the forward lunge short between 0 degrees and 80 degrees knee flexion angles. Mean PCL forces (86-691 N range) were significantly greater (P < 0.001) without a stride compared with those with a stride between 0 degrees and 20 degrees knee flexion angles. Mean anterior cruciate ligament (ACL) forces were generated (0-50 N range between 0 degrees and 10 degrees knee flexion angles) only in the forward lunge short with stride. CONCLUSIONS All lunge variations appear appropriate and safe during ACL rehabilitation because of minimal ACL loading. ACL loading occurred only in the forward lunge short with stride. Clinicians should be cautious in prescribing forward lunge exercises during early phases of PCL rehabilitation, especially at higher knee flexion angles and during the forward lunge long, which generated the highest PCL forces. Understanding how varying lunging techniques affect cruciate ligament loading may help clinicians prescribe lunging exercises in a safe manner during ACL and PCL rehabilitation.

Cruciate ligament tensile forces during the forward and side lunge

BACKGROUND Although weight bearing lunge exercises are frequently employed during anterior cruciate ligament and posterior cruciate ligament rehabilitation, cruciate ligament tensile forces are currently unknown while performing forward and side lunge exercises with and without a stride. METHODS Eighteen subjects used their 12 repetition maximum weight while performing a forward lunge and side lunge with and without a stride. A motion analysis system and biomechanical model were used to estimate cruciate ligament forces during lunging as a function of 0-90 degrees knee angles. FINDINGS Comparing the forward lunge to the side lunge across stride variations, mean posterior cruciate ligament forces ranged between 205 and 765N and were significantly greater (P<0.0025) in the forward lunge long at 40 degrees , 50 degrees , 60 degrees , 70 degrees , and 80 degrees knee angles of the descent phase and at 80 degrees , 70 degrees , 60 degrees knee angles of the ascent phase. There were no significant differences (P<0.0025) in mean posterior cruciate ligament forces between with and without stride differences across lunging variations. There were no anterior cruciate ligament forces quantified while performing forward and side lunge exercises. INTERPRETATION Clinicians should be cautious in prescribing forward and side lunge exercises during early phases of posterior cruciate ligament rehabilitation due to relatively high posterior cruciate ligament forces that are generated, especially during the forward lunge at knee angles between 40 degrees and 90 degrees knee angles. Both the forward and side lunges appear appropriate during all phases of anterior cruciate ligament rehabilitation. Understanding how forward and side lunging affect cruciate ligament loading over varying knee angles may help clinicians better prescribe lunging exercises in a safe manner during anterior cruciate ligament and posterior cruciate ligament rehabilitation.

Higher Knee Flexion Moment During the Second Half of the Stance Phase of Gait Is Associated With the Progression of Osteoarthritis of the Patellofemoral Joint on Magnetic Resonance Imaging

STUDY DESIGN Controlled laboratory study, longitudinal design. OBJECTIVE To examine whether baseline knee flexion moment or impulse during walking is associated with the progression of osteoarthritis (OA) with magnetic resonance imaging of the patellofemoral joint (PFJ) at 1 year. BACKGROUND Patellofemoral joint OA is highly prevalent and a major source of pain and dysfunction. The biomechanical factors associated with the progression of PFJ OA remain unclear. METHODS Three-dimensional gait analyses were performed at baseline. Magnetic resonance imaging of the knee (high-resolution, 3-D, fast spin-echo sequence) was used to identify PFJ cartilage and bone marrow edema-like lesions at baseline and a 1-year follow-up. The severity of PFJ OA progression was defined using the modified Whole-Organ Magnetic Resonance Imaging Score when new or increased cartilage or bone marrow edema-like lesions were observed at 1 year. Peak external knee flexion moment and flexion moment impulse during the first and second halves of the stance phase of gait were compared between progressors and nonprogressors, and used to predict progression after adjusting for age, sex, body mass index, and presence of baseline PFJ OA. RESULTS Sixty-one participants with no knee OA or isolated PFJ OA were included. Patellofemoral joint OA progressors (n = 10) demonstrated significantly higher peak knee flexion moment (P = .01) and flexion moment impulse (P = .04) during the second half of stance at baseline compared to nonprogressors. Logistic regression showed that higher peak knee flexion moment during the second half of the stance phase was significantly associated with progression at 1 year (adjusted odds ratio = 3.3, P = .01). CONCLUSION Peak knee flexion moment and flexion moment impulse during the second half of stance are related to the progression of PFJ OA and may need to be considered when treating individuals who are at risk of or who have PFJ OA.