Cognitive effects of one season of head impacts in a cohort of collegiate contact sport athletes.

OBJECTIVE: To determine whether exposure to repetitive head impacts over a single season negatively affects cognitive performance in collegiate contact sport athletes. METHODS: This is a prospective cohort study at 3 Division I National Collegiate Athletic Association athletic programs. Participants were 214 Division I college varsity football and ice hockey players who wore instrumented helmets that recorded the acceleration-time history of the head following impact, and 45 noncontact sport athletes. All athletes were assessed prior to and shortly after the season with a cognitive screening battery (ImPACT) and a subgroup of athletes also were assessed with 7 measures from a neuropsychological test battery. RESULTS: Few cognitive differences were found between the athlete groups at the preseason or postseason assessments. However, a higher percentage of the contact sport athletes performed more poorly than predicted postseason on a measure of new learning (California Verbal Learning Test) compared to the noncontact athletes (24% vs 3.6%; p < 0.006). On 2 postseason cognitive measures (ImPACT Reaction Time and Trails 4/B), poorer performance was significantly associated with higher scores on several head impact exposure metrics. CONCLUSION: Repetitive head impacts over the course of a single season may negatively impact learning in some collegiate athletes. Further work is needed to assess whether such effects are short term or persistent.

Ankle biomechanics during impact landings on uneven surfaces.

Inversion sprains of the lateral ligaments of the ankle are one of the most common of all sporting injuries. While the strains in the anterior talofibular (ATFL) and calcaneofibular (CFL) ligaments have been measured in quasi-static conditions, the dynamic strains during an actual traumatic event have not been determined. The present investigation determined the strains and strain rates in the ATFL and CFL during an in vitro inversion sprain. The ATFL tended to have higher strain and strain rate values than the CFL, which may explain why it is more often injured than the CFL.

A biomechanical analysis of a medial unloading brace for osteoarthritis in the knee.

OBJECTIVES: The goals of the study were to measure the force applied to the lateral side of the knee by a valgus loading brace designed for patients with medial compartment osteoarthritis (OA) and to compare the varus moment at the knee during level gait with and without the brace. METHODS: Five subjects diagnosed with medial compartment OA were fitted with a custom Monarch valgus loading knee brace. A 3-dimensional videobased motion analysis system and force plate information were used to calculate forces and moments at the knee. An instrumented condylar bladder was used to determine the force applied to the knee by the brace. The varus moments for the braced and unbraced trials were compared during gait at 15%, 20%, 25%, and 30% of stance. RESULTS: The Monarch brace significantly reduced the varus moment at 20% and 25% of stance. The valgus force measured with the custom condylar bladder remained fairly constant throughout the first 80% of the stance phase. CONCLUSIONS: The reduced various moment observed for the braced condition demonstrates the biomechanical function of the brace in 5 subjects and may contribute to a reduction of pain for patients with medial compartment OA.

Dynamic impact response of human cadaveric forearms using a wrist brace.

The purpose of this study was to compare the dynamic impact response of braced and unbraced cadaveric wrists using a commercially available wrist guard. Twelve arms were harvested from six cadavers. Each pair of forearms, one with and one without a brace, were impacted using a modified guillotine-type drop fixture placed over a force platform. Using a piece-wise linear regression analysis, we identified four phases of dynamic loading in the vertical force profile before fracture. These phases included an initial linear loading phase starting at impact, followed by a nonlinear phase, a second rapid linear loading phase, and a final nonlinear loading phase to failure. Three transition points were identified that defined the boundaries of the linear loading phases. Vertical force and impulse were significantly higher (P < 0.01) at each transition point and at failure in all braced specimens compared with unbraced specimens. However, the most noticeable differences were found during the initial two loading phases. Time to each transition point and to failure was not significantly different (P > 0.27) between the braced and unbraced wrists. The results of this study differ from those obtained under more quasistatic loading conditions. Dynamic impact testing suggests that wrist guards may have a prophylactic effect during low-energy dynamic impact situations.

Muscle activity in the slalom turn of alpine skiing and in-line skating.

The electromyographic (EMG) activity of seven muscles of the trunk and lower extremity in five male masters level ski racers during a slalom turn in both alpine skiing and in-line skating was recorded using a telemetry system. Measurements were made on separate testing days using slopes commonly used in each activity (24 slope alpine skiing, 5 in-line skating). Qualitative video recorded at 60 Hz was analyzed to partition the turning cycle in both slalom skiing and in-line skating into initiation and turning phases. The EMG data from each turning cycle were normalized to standard isometric contractions (SIC's) for each muscle in order to quantitatively compare the amplitude characteristics of each phase of the turning cycle in both slalom skiing and in-line skating. The turning phase of in-line skating was found to be significantly longer (55%) than in slalom skiing, most likely due to significantly lower subject velocities recorded during in-line skating (8.5 m/s vs 10.2 m/s). All muscles were active at moderate to high levels (48-172% of SIC) during each phase of the turning cycle in both slalom skiing and in-line skating. The EMG amplitude characteristics were similar for six of the muscles in both slalom skiing and in-line skating for each of the turning phases. Only the erector spinae displayed significantly higher average and peak amplitudes in slalom skiing for both phases. It is concluded that the muscle activity patterns associated with the slalom turn of in-line skating are similar but notably more quasi-static than in slalom skiing.

New surgical technique for treatment of extraarticular knee ankylosis.

Laboratory and clinical studies were conducted to evaluate a treatment regimen for extraarticular ankylosis of the knee. The study evaluated the use of a porcine biomembrane to prevent quadriceps adhesions. A canine model was studied to determine the cellular response to the membrane by evaluating biopsies at 3, 7, 14, and 21 days after surgery using light and scanning electron microscopy. The results showed that there was nonspecific inflammatory cell infiltration into the base (rough) layer of the biomembrane during the first few days, although fibroblasts were the dominant cellular response 7 days later. No significant tissue ingrowth was seen on the smooth (muscular interface) surface of the membrane. The clinical study applied the information gained from the canine model to a series of 23 patients who suffered from extraarticular knee ankylosis and who were treated with a surgical procedure in which the released interface between the femur and the muscle groups was protected with a piece of porcine biomembrane. Subjects were observed from 16 to 30 months (mean, 26 months) after surgery. An average increase in knee range of motion of 86 degrees was documented, and a 100% patient satisfaction rate was noted. The technique yields satisfactory results in terms of cost, range of motion, and postoperative pain.

The influence of baseball modulus and mass on head and chest impacts: a theoretical study.

Although not common, injuries that result in death do occur in youth baseball. Specifically, in the 5- to 14-year old age group a total of 68 deaths between 1973 and 1995 have been directly attributed to impacts from baseballs to the head and chest. The purpose of this work was to determine the effect of lowering ball modulus and ball mass on the likelihood of reducing impact injury. A theoretical model, based upon the assumption of ideal elastic behavior, was used to calculate the impact response of the head. At a constant ball velocity, lowering both modulus and mass had the greatest influence in decreasing peak head acceleration, Gadd Severity Index, and Head Injury Criterion. Independently lowering the modulus or the mass decreased the impact variables and the estimates of injury, but the decreases varied with the specific impact variable and injury criterion. To study the impact response of the ball and chest, an existing viscoelastic lumped-element model of the chest was used. Lowering ball modulus and mass had various effects, e.g., lowering ball modulus did not affect peak sternal displacement, but it did decrease peak sternal velocity. These theoretical models aid in illustrating that impact response depends upon ball modulus and mass, the physical properties of the target, and the specific impact variable studied. This theoretical model suggests that a softer and lighter than traditional baseball would be the most likely ball model to minimize impact injuries because this ball consistently reduced all impact response variables studied. Since impact injury criteria for youths are presently not validated, the degree to which impact injuries may be reduced remains uncertain.

A comparison of the effect of ski sidecut on three-dimensional knee joint kinematics during a ski run.

The popularity of alpine skis with large sidecuts has increased dramatically in the last few years. However, little scientific data exists regarding the effect of these skis on certain human factors. The purpose of this study was to compare three-dimensional knee joint motions during entire ski runs while skiing on two skis with a large difference in sidecut (Elan SCX and Elan RP90). Five, expert male skiers performed three runs on each ski. Three-dimensional knee joint motion was collected throughout each run using a portable, magnetic motion tracking system. Twenty-four turns from each run were analyzed for joint motion characteristics. The results indicated that no statistically significant differences in knee joint range of motion or angular velocities were found to exist between the Elan SCX and Elan RP90 during normal skiing maneuvers. Further research is needed on the effect of ski sidecut on knee joint kinematics while skiing on varied terrain and/or with different skiing styles. In addition, similar studies comparing the effect of ski sidecut on metabolic cost and effect on injury rates are also needed.

A biomechanical and clinical evaluation of a patellofemoral knee brace.

A clinical and biomechanical evaluation of a patellofemoral knee brace was conducted to determine subjectively and objectively if the brace was effective in controlling knee motion and relieving patellofemoral pain symptoms. The subjective results indicated that the patellofemoral brace was able to significantly improve the level of perceived knee stability and decrease the level of pain experienced by all the subjects during their daily living and athletic activities. The objective results showed that the patellofemoral brace had no effect on knee flexion angle during gait or level walking, stair ascent, or stair descent for 2 groups of subjects (patellofemoral patients and controls). Joint pain and stability are affected by factors other than knee flexion angle.