Multi-plane, multi-joint lower extremity support moments during a rapid deceleration task: Implications for knee loading.

The principle of lower limb support, and the contribution of hip, knee and ankle moments to an overall limb support strategy for an impact-like, rapid deceleration movement may help explain individual moment magnitude changes, thereby providing insight into how injury might occur or be avoided. Twenty subjects performed single limb, impact-like, deceleration landings at three different knee flexion angles in the range of 0-25, 25-50 and 50-75°. Kinematic and kinetic measures identified hip, knee and ankle moment contribution to limb support moments (LSMs) in three planes. Repeated measures ANOVA compared LSMs and the contribution of individual joint moments at initial contact (IC) and 50 ms after. There were no significant differences in the overall LSMs at IC in any plane when the deeper knee flexion landings (25-50° and 50-75°) were compared to the 0-25° landing position but there were significant changes in the 50 ms period after IC. There were greater overall extensor LSMs, less resistance to medial opening of the knee and decreased support against internal tibia rotation when landing in greater knee flexion. The role of individual joint moments changed rapidly in the 50 ms period after initial landing; and, the relative contribution of the hip and ankle moments depended on the degree of limb flexion at landing. Analyses of individual joint moments emphasized the critical role that the hip joint moments have in balancing potentially injurious knee moments in all three planes for all three landing conditions.

The effect of augmented somatosensory feedback on standing postural sway.

Impaired balance resulting from reduced postural control occurs with aging and various medical conditions. Sensory input for balance control is provided by the visual, vestibular and somatosensory systems. Previous research suggests that increased proprioceptive feedback from various lower extremity devices improves balance. Mixed results have been reported with the use of orthoses such as ankle foot orthoses (AFOs). In this study, 20 healthy subjects wore footplates in their shoes or straps around their lower legs in order to imitate the somatosensory feedback produced by wearing AFOs, but without providing ankle restriction. Subjects' standing balance was assessed using force plates and computerized dynamic posturography (the sensory organization test-SOT) to determine if either the footplates or the lower-leg straps would affect standing balance. The results revealed no significant difference with the use of the footplates, however, wearing the straps resulted in reduced postural sway for conditions when visual cue deprivation was combined with manipulation of somatosensory or vestibular feedback. This effect was more pronounced in participants with the poorest baseline measures of balance. These findings suggest that lower extremity devices, such as AFOs, may augment somatosensory feedback that could improve balance during challenging sensory deprivation conditions, independent of orthotic support at the ankle.

The effect of firefighter protective garments, self-contained breathing apparatus and exertion in the heat on postural sway.

Fire suppression wearing thermal protective clothing (TPC) and self-contained breathing apparatus (SCBA) challenges a firefighter's balance and may explain firefighter falls. Postural control based on force plate centre of pressure (COP) was compared for healthy subjects wearing TPC and SCBA before and after 20 min of heavy physical exertion in hot conditions. Baseline measures with and without TPC and SCBA (two different SCBA cylinder masses) were compared before and after exertion that included elements of fire suppression activities in an environmental chamber. COP excursion and variability increased with exertion for TPC and SCBA conditions compared to non-stressed conditions. The two different cylinder masses had no significant effect. Wearing TPC and SCBA when physically stressed in a hot environment increases postural sway and exacerbates postural control. Subjects compensated for the extra mass and adjusted to control postural sway with the addition of TPC and SCBA, but the stress protocol amplified these adjustments. Practitioner Summary: Firefighters wear thermal protective clothing (TPC) and self-contained breathing apparatus (SCBA) when heat-stressed and fatigued. Wearing TPC and SCBA was found to negatively impact balance when stressed, but not for non-stressed or two different sized SCBA tanks. Simulating fire-ground conditions wearing TPC and SCBA should be considered for improving balance.

Posterior glenohumeral thermal capsulorraphy, capsular imbrication and labral repair with complication of adhesive capsulitis: a modified rehabilitation approach.

BACKGROUND: Isolated atraumatic posterior glenohumeral instability is rare. Use of thermal capsulorraphy for glenohumeral instability is considered controversial. This case study describes a modified rehabilitation protocol for a patient who underwent a multistep arthroscopic procedure for isolated posterior glenohumeral instability with a postoperative complication of adhesive capsulitis. CASE DESCRIPTION: A 30-y-old man with a 15-y history of bilateral posterior glenohumeral instability related to generalized hypermobility underwent right-shoulder arthroscopy consisting of a combined posterior labral repair, capsular imbrication, and thermal capsulorraphy. A gunslinger orthosis was prescribed for 6 wk of immobilization. Adhesive capsulitis was diagnosed at the 5-wk postoperative visit and immobilization was discontinued. A modified treatment protocol was devised to address both the surgical procedures performed and the adhesive capsulitis. Residual symptoms resolved with release of an adhesion while stretching 10 months postoperatively. OUTCOMES: Scores of 5 shoulder-assessment tools improved from poor to excellent/good with subjective report of a very good outcome. DISCUSSION: The complication of adhesive capsulitis required an individualized treatment protocol. In contrast to the standard protocol, our modified approach allowed more time to be spent in each phase of the program, was aggressive with restoring range of motion (ROM) without excessively stressing the posterior capsule, and allowed the patient to progress to activities that were tolerated regardless of protocol phase. Shoulder stiffness or frank adhesive capsulitis after stabilization, as in this case, requires a more aggressive modification to prevent permanent ROM limitations. Conversely, patients with early rapid gains in ROM must be protected from overstretching the repaired tissue with a program that allows functional motion to be incorporated over a longer time frame. This study indicates the use of thermal capsulorraphy as a viable surgical modality when it is used judiciously with the proper postoperative restrictions and rehabilitation.

Effect of knee flexion angle on ground reaction forces, knee moments and muscle co-contraction during an impact-like deceleration landing: implications for the non-contact mechanism of ACL injury.

Investigating landing kinetics and neuromuscular control strategies during rapid deceleration movements is a prerequisite to understanding the non-contact mechanism of ACL injury. The purpose of this study was to quantify the effect of knee flexion angle on ground reaction forces, net knee joint moments, muscle co-contraction and lower extremity muscles during an impact-like, deceleration task. Ground reaction forces and knee joint moments were determined from video and force plate records of 10 healthy male subjects performing rapid deceleration single leg landings from a 10.5 cm height with different degrees of knee flexion at landing. Muscle co-contraction was based on muscle moments calculated from an EMG-to-moment processing model. Ground reaction forces and co-contraction indices decreased while knee extensor moments increased significantly with increased degrees of knee flexion at landing (all p<0.005). Higher ground reaction forces when landing in an extended knee position suggests they are a contributing factor in non-contact ACL injuries. Increased knee extensor moments and less co-contraction with flexed knee landings suggest that quadriceps overload may not be the primary cause of non-contact ACL injuries. The results bring into question the counterbalancing role of the hamstrings during dynamic movements. The soleus may be a valuable synergist stabilizing the tibia against anterior translation at landing. Movement strategies that lessen the propagation of reaction forces up the kinetic chain may help prevent non-contact ACL injuries. The relative interaction of all involved thigh and lower leg muscles, not just the quadriceps and hamstrings should be considered when interpreting non-contact ACL injury mechanisms.

Skeletal muscle fiber types in the ghost crab, Ocypode quadrata: implications for running performance.

Ghost crabs possess rapid running capabilities, which make them good candidates for comparing invertebrate exercise physiology with that of more extensively studied vertebrates. While a number of studies have examined various aspects of running physiology and biomechanics in terrestrial crabs, none to date have defined the basic skeletal muscle fiber types that power locomotion. In the current study, we investigated skeletal muscle fiber types comprising the extensor and flexor carpopodite muscles in relation to running performance in the ghost crab. We used kinematic analyses to determine stride frequency and muscle shortening velocity and found that both parameters are similar to those of comparably sized mammals but slower than those observed in running lizards. Using several complementary methods, we found that the muscles are divided into two primary fiber types: those of the proximal and distal regions possess long sarcomeres (6.2+/-2.3 microm) observed in crustacean slow fibers and have characteristics of aerobic fibers whereas those of the muscle mid-region have short sarcomeres (3.5+/-0.4 microm) characteristic of fast fibers and appear to be glycolytic. Each fiber type is characterized by several different myofibrillar protein isoforms including multiple isoforms of myosin heavy chain (MHC), troponin I (TnI), troponin T (TnT) and a crustacean fast muscle protein, P75. Three different isoforms of MHC are differentially expressed in the muscles, with fibers of the mid-region always co-expressing two isoforms at a 1:1 ratio within single fibers. Based on our analyses, we propose that these muscles are functionally divided into a two-geared system, with the aerobic fibers used for slow sustained activities and the glycolytic mid-region fibers being reserved for explosive sprints. Finally, we identified subtle differences in myofibrillar isoform expression correlated with crab body size, which changes by several orders of magnitude during an animal's lifetime.

Altering asymmetric limb loading after hip arthroplasty using real-time dynamic feedback when walking.

OBJECTIVE: To evaluate a walking program incorporating real-time biofeedback to reduce asymmetric limb loading after total hip arthroplasty (THA). DESIGN: Within-subject clinical intervention. SETTING: Biomechanics laboratory. PARTICIPANTS: Volunteers were screened for confounding disorders that could affect their gait other than unilateral THA. Participants included 28 subjects who were evaluated a minimum of 2 months after surgery and ambulatory without assistive devices. INTERVENTIONS: THA subjects were assigned to a feedback, no-feedback, or control group. The feedback group walked on a treadmill 15 minutes, 3 times a week for 8 weeks while matching step-to-step reaction forces. Subjects walking without feedback had equal time. The control group did not train. MAIN OUTCOME MEASURES: Symmetry indices for peak limb-loading force, rate of rise of loading force, and impulse calculated from vertical foot-ground forces. Symmetry index changes were evaluated using 2-factor, repeated-measures analyses of variance with a Tukey post hoc test. RESULTS: Loading rate and impulse equalization improved for the feedback group (P<.01). Loading rate equalization improved for the no-feedback group (P=.01). There were no changes for the control group. CONCLUSIONS: This preliminary study suggests that a treadmill walking program may help persons with a THA achieve a more symmetric gait. Additional investigation of the potential benefits of a rehabilitation program incorporating treadmill walking with and without biofeedback is recommended.

Differences in peak knee valgus angles between individuals with high and low Q-angles during a single limb squat.

BACKGROUND: Differences in anatomical alignment between genders have been suggested as causes of the disparity in anterior cruciate ligament injury rates. A larger Q-angle may be associated with increased knee valgus during movement resulting in anterior cruciate ligament strain. This study investigated whether healthy college-aged subjects with a large Q-angle display greater peak knee valgus during a single limb squat compared to those with a small Q-angle. The study also determined whether the high and low Q-angle groups displayed differences in other select anatomical variables, and whether these anatomical variables were related to knee valgus. METHODS: Twenty subjects, categorized as having a "high Q-angle" (> or = 17 degrees) or a "low Q-angle" (< or = 8 degrees) were videotaped during the performance of a single leg squat. The peak valgus angles for the right knee were calculated. One-tailed independent measures t-tests were used to determine whether individuals with a large Q-angle exhibit (1) significantly greater peak knee valgus during a single leg squat compared to those with a small Q-angle and, (2) greater pelvic width to femoral length ratios and greater static knee valgus than subjects with a small Q-angle. The Pearson product-moment correlation was used to establish the relationships between pelvic width to femoral length ratios and static knee valgus, pelvic width to femoral length ratios and dynamic knee valgus, and static knee valgus and dynamic knee valgus. FINDINGS: Peak knee valgus during the single leg squat, and static knee valgus were not significant greater in the high Q-angle group compared to the low Q-angle group (P=0.09; P=0.31). Subjects with a larger Q-angle, however, had a significantly greater pelvic width to femoral length ratios (P=0.015) compared to subjects with a small Q-angle. Pelvic width to femoral length ratios was related to both static and dynamic knee valgus (r=0.47, P=0.02; r=0.48, P=0.02), but static knee valgus was not related to dynamic knee valgus. INTERPRETATION: The findings suggest that pelvic width to femoral length ratios, rather than Q-angle, may be a better structural predictor of knee valgus during dynamic movement.

Kinetic changes with fatigue and relationship to injury in female runners.

PURPOSE: This research examined how ground reaction forces (GRF) changed with fatigue induced by an exhaustive treadmill run in female runners. A separate retrospective and prospective analysis correlated initial magnitude of GRF and fatigue-induced changes in GRF with lower-extremity injury. METHODS: Ninety adult female runners had vertical GRF measured before and after an exhaustive treadmill run. Subjects initially were questioned about previous running injuries, and were contacted during the following year and asked to report any additional running injuries. RESULTS: Fatigue induced by the exhaustive treadmill run resulted in decreased impact peak and loading rates in all runners by an average of 6 and 11%, respectively. The changes in GRF were attributed to altered running cadence, step length, and lower-extremity joint kinematics. It is unclear whether these changes were attempts by the runners to minimize impact forces and protect against injury, or represented a fatigue-induced loss of optimal performance capabilities. An interaction between injury in the previous year and change in impact loading rate with fatigue was observed, suggesting previously injured runners are exposed to relatively higher impact forces over time. CONCLUSION: Habitual female runners appear to adapt their running style with fatigue, resulting in altered GRF. Changes in GRF with fatigue may be associated with lower-extremity running injuries.

Asymmetric limb loading with true or simulated leg-length differences.

Unequal leg lengths result in asymmetric limb loading but opinions vary on the size of the difference inducing abnormal loading, and which limb sustains the greater load. Our study compared limb-loading asymmetries during walking for subjects with anatomic leg-length discrepancies between 1.0 and 3 cm, subjects without length discrepancies, and for subjects with a simulated a 1.31-cm leg-length discrepancy. Symmetry indices were calculated for peak ground reaction force during weight acceptance, rate of change of weight acceptance force, peak push-off force, and rate of change of push-off force. All symmetry measures were significantly different from normal for the simulated leg-length discrepancy. The shorter limb sustained a greater proportion of the load and loading rate. The anatomic leg-length discrepancy group showed the same trend with the exception of the push-off force rate. There were equivalent size-effect differences for both leg-length discrepancy conditions; however, for the anatomic leg-length discrepancy group, only the weight acceptance force symmetry value was statistically different from normal. The shorter limb sustains a greater proportion of load and loading rates; therefore, equalizing leg lengths should be considered even with bilateral differences less than 3 cm.