Naiquan Zheng

Effects of technique variations on knee biomechanics during the squat and leg press

PURPOSE The specific aim of this project was to quantify knee forces and muscle activity while performing squat and leg press exercises with technique variations. METHODS Ten experienced male lifters performed the squat, a high foot placement leg press (LPH), and a low foot placement leg press (LPL) employing a wide stance (WS), narrow stance (NS), and two foot angle positions (feet straight and feet turned out 30 degrees ). RESULTS No differences were found in muscle activity or knee forces between foot angle variations. The squat generated greater quadriceps and hamstrings activity than the LPH and LPL, the WS-LPH generated greater hamstrings activity than the NS-LPH, whereas the NS squat produced greater gastrocnemius activity than the WS squat. No ACL forces were produced for any exercise variation. Tibiofemoral (TF) compressive forces, PCL tensile forces, and patellofemoral (PF) compressive forces were generally greater in the squat than the LPH and LPL, and there were no differences in knee forces between the LPH and LPL. For all exercises, the WS generated greater PCL tensile forces than the NS, the NS produced greater TF and PF compressive forces than the WS during the LPH and LPL, whereas the WS generated greater TF and PF compressive forces than the NS during the squat. For all exercises, muscle activity and knee forces were generally greater in the knee extending phase than the knee flexing phase. CONCLUSIONS The greater muscle activity and knee forces in the squat compared with the LPL and LPH implies the squat may be more effective in muscle development but should be used cautiously in those with PCL and PF disorders, especially at greater knee flexion angles. Because all forces increased with knee flexion, training within the functional 0-50 degrees range may be efficacious for those whose goal is to minimize knee forces. The lack of ACL forces implies that all exercises may be effective during ACL rehabilitation.

Pitching Biomechanics as a Pitcher Approaches Muscular Fatigue During a Simulated Baseball Game

Background The effects of approaching muscular fatigue on pitching biomechanics are currently unknown. As a pitcher fatigues, pitching mechanics may change, leading to a decrease in performance and an increased risk of injury. Hypothesis As a pitcher approaches muscular fatigue, select pitching biomechanical variables will be significantly different than they were before muscular fatigue. Study Design Controlled laboratory study. Methods Ten collegiate baseball pitchers threw 15 pitches per inning for 7 to 9 innings off an indoor throwing mound during a simulated baseball game. A pitching session ended when each pitcher felt he could no longer continue owing to a subjective perception of muscular fatigue. A 6-camera 3D automatic digitizing system collected 200-Hz video data. Twenty kinematic and 11 kinetic variables were calculated throughout 4 phases of the pitch. A repeated-measure analysis of variance (P < .01) was used to compare biomechanical variables between innings. Results Compared with the initial 2 innings, as a pitcher approached muscular fatigue during the final 2 innings he was able to pitch, there was a significant decrease in ball velocity, and the trunk was significantly closer to a vertical position. There were no other significant differences in kinematics or kinetics variables. Conclusion The relatively few differences observed imply that pitching biomechanics remained remarkably similar between collegiate starting pitchers who threw between 105 and 135 pitches for 7 to 9 innings and approached muscular fatigue. Clinical Relevance This study did not support the idea that there is an increase in shoulder and elbow forces and torques as muscular fatigue is approached. It is possible that if a pitcher remained in a fatigued state for a longer period of time, additional changes in pitching mechanics may occur and the risk of injury may increase.

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.

Failure Analysis of Rotator Cuff Repair: A Comparison of Three Double-Row Techniques

BACKGROUND The use of suture anchors has made arthroscopic repair of the torn rotator cuff possible. However, objective evaluations have demonstrated high failure rates. The goal of this study was to compare the modes and rates of failure of two double-row arthroscopic repair techniques and the mini-open double-row technique. METHODS Thirty pairs of fresh-frozen human shoulders were used in this study. The specimens were prepared to simulate a cuff defect, which was then repaired. The repairs were done with three different lateral row techniques (Mason-Allen sutures passed through transosseous tunnels, the knotless anchor method, and the corkscrew suture anchor method) with the same medial row technique (corkscrew suture anchors). Cyclic tests were conducted at 33 mm/s with a cyclic force of 10 to 180 N. Specimens were cycled to 5000 cycles or to failure as defined as formation of a 10-mm gap at the repair. Failure rates and failure modes of the suture, tendon, and bone-anchor interface were compared for the medial and lateral rows and among the three techniques. RESULTS Fourteen of the twenty repairs made with the transosseous technique, fifteen of the twenty repairs made with the knotless anchor technique, and ten of the twenty repairs made with the corkscrew anchor technique survived 5000 cycles. The failure rates for the medial row were not significantly different among the three repair techniques. For the lateral row, there was a significant difference (p < 0.01) in the rate of failure among individual transosseous tunnel-suture complexes (32%), knotless anchor-suture complexes (48%), and corkscrew anchor-suture complexes (75%), with a similar suture-tendon failure rate for all three techniques. The tendon and repair complexes with corkscrew suture anchors had the smallest displacement both at the first and the 5000th cycle. CONCLUSIONS Although repairs made with the anchor techniques had higher individual failure rates, the survival rates for the anchor techniques at the 5000th cycle were similar to that for the transosseous technique during cyclic tests. Suture failure was the main failure mode for the transosseous technique, whereas failure at the anchor-bone interface was the main failure mode for the anchor techniques.

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.

The effects of thermal capsulorrhaphy of medial parapatellar capsule on patellar lateral displacement

BackgroundThe effectiveness of thermal shrinkage on the medial parapatellar capsule for treating recurrent patellar dislocation is controversial. One of reasons why it is still controversial is that the effectiveness is still qualitatively measured. The purpose of this study was to quantitatively determine the immediate effectiveness of the medial parapatellar capsule shrinkage as in clinical setting.MethodsNine cadaveric knees were used to collect lateral displacement data before and after medial shrinkage or open surgery. The force and displacement were recorded while a physician pressed the patella from the medial side to mimic the physical exam used in clinic. Ten healthy subjects were used to test the feasibility of the technique on patients and establish normal range of lateral displacement of the patella under a medial force. The force applied, the resulting displacement and the ratio of force over displacement were compared among four data groups (normal knees, cadaveric knees before medial shrinkage, after shrinkage and after open surgery).ResultsDisplacements of the cadaveric knees both before and after thermal modification were similar to normal subjects, and the applied forces were significantly higher. No significant differences were found between before and after thermal modification groups. After open surgery, displacements were reduced significantly while applied forces were significantly higher.ConclusionNo immediate difference was found after thermal shrinkage of the medial parapatellar capsule. Open surgery immediately improved of the lateral stiffness of the knee capsule.