Paul S. Weinhold

The Effects of Strength Training on the Lower Extremity Biomechanics of Female Recreational Athletes During a Stop-Jump Task

Background Strength training is considered a strategy for anterior cruciate ligament injury prevention. Little is known about the contribution of strength training to knee and hip biomechanics. Hypothesis Lower extremity muscle strength training alters knee and hip biomechanics during a stop-jump task. Study Design Controlled laboratory study. Methods Knee and hip 3-dimensional kinematic and kinetic data were collected for 66 female recreational athletes (33 intervention and 33 control) while performing 3 stop-jump tasks before and after completing a 9-week strength-training program targeting the quadriceps, hamstrings, gluteus medius, and gluteus maximus (intervention) or a 9-week period of no strength training (control). Maximum voluntary isometric contraction strength data were also collected for each subject before the stop-jump tasks in each data collection session. Knee and hip joint angles as well as resultant forces and moments were calculated. Results The intervention group increased in strength (P < .001 for all muscles). No significant differences were observed in knee and hip kinematics and kinetics between groups before and after the strength-training protocol. Conclusions Strength training alone does not alter knee and hip kinematics and kinetics in female recreational athletes. Further research is needed to determine the effect of strength training in combination with other intervention methods on lower extremity biomechanics. Clinical Relevance Strength training as a single intervention method may not be sufficient to reduce the risk of noncontact anterior cruciate ligament injury in female recreational athletes.

The effects of feedback with and without strength training on lower extremity biomechanics

Background Feedback instruction is a proven modality for the alteration of motion patterns. There are no existing data on the contribution of strength training, when combined with feedback instruction, to the altering of lower extremity biomechanics. Hypothesis Lower extremity muscle strength training provides an increased capacity to alter knee and hip biomechanics during a stop-jump task in response to a feedback protocol. Study Design Controlled laboratory study. Methods Knee and hip 3-dimensional kinematic and kinetic data were collected for 58 female recreational athletes while performing 3 stop-jump tasks after completing a 9-week strength training program (ST-FB; n = 29) or a 9-week period of no strength training (FB; n = 29). Data were then collected for both groups after completing a jump-landing feedback instruction protocol. Knee and hip joint angles, as well as resultant forces and moments, were calculated. Results Across all participants, there were decreased peak vertical ground-reaction forces (P < .001) and increased knee flexion (P = .050), hip flexion (P < .001), and hip abduction (P = .032) angles, subsequent to the feedback protocol. Hip abduction angle (P < .001) increased in the ST-FB group but not the FB group, and peak knee anterior shear force (P = .015) decreased in the ST-FB group but increased in the FB group (P = .009). Conclusion The results indicate that strength training, when used in conjunction with video-assisted feedback, may provide an increased capacity for the alteration of knee and hip biomechanics. Clinical Relevance Programs that include both strength training and movement education through feedback may be necessary to increase the effectiveness of anterior cruciate ligament prevention programs. Strength training may provide an increased capacity for athletes to respond to other intervention modalities used in anterior cruciate ligament injury prevention programs.

The Effects of Common Anti-Inflammatory Drugs on the Healing Rat Patellar Tendon

Background Tendon injuries that occur at the osteotendinous junction are commonly seen in clinical practice and range from acute strain to rupture. Nonsteroidal anti-inflammatory drugs are often prescribed in the treatment of these conditions, but the effect that these agents may have on the healing response at the bone-tendon junction is unclear. Hypothesis In response to an acute injury at the osteotendinous junction, the healing patellar tendon will have inferior biomechanical properties with administration of anti-inflammatory drugs as compared with acetaminophen and control. Study Design Controlled laboratory study. Methods A total of 215 Sprague-Dawley rats underwent transection of the patellar tendon at the inferior pole of the patella, which was subsequently stabilized with a cerclage suture. The animals were then randomized into 7 groups and administered 1 of the following analgesics for 14 days ibuprofen, acetaminophen, naproxen, piroxicam, celecoxib, valdecoxib, or control. At 14 days, all animals were sacrificed, and the extensor mechanism was isolated and loaded to failure. Biochemical analysis of the repair site tissue was performed. Animal activity throughout the study was monitored using a photoelectric sensor system. Results The control group demonstrated greater maximum load compared with the celecoxib, valdecoxib, and piroxicam groups (P < .05). The acetaminophen and ibuprofen groups were also significantly stronger than the celecoxib group (P < .05) but not statistically different than the control group. A total of 23 specimens had failure of the cerclage suture with the following distribution control (0/23), ibuprofen (0/23), acetaminophen (0/24), naproxen (3/24), piroxicam (4/24), celecoxib (6/22), and valdecoxib (10/24). The difference in distribution of the failures was significant (P < .001). Conclusions Anti-inflammatory drugs, with the exception of ibuprofen, had a detrimental effect on healing strength at the bone-tendon junction as demonstrated by decreased failure loads and increased failures of the cerclage suture. Acetaminophen had no effect on healing strength. The biomechanical properties paralleled closely with the total collagen content at the injury site, suggesting that these agents may alter healing strength by decreasing collagen content. Clinical Relevance Selective and nonselective cyclooxygenase (COX) inhibitors should be used judiciously in the acute period after injury or surgical repair at the bone-tendon junction.

Gap junctions regulate responses of tendon cells ex vivo to mechanical loading.

Avian digital flexor tendons were used with a device to apply load ex vivo to study the effects on deoxyribonucleic acid and collagen synthesis when cell to cell communication is blocked. Flexor digitorum profundus tendons from the middle toe of 52-day-old White Leghorn chickens were excised and used as nonloaded controls, or clamped in the jaws of a displacement controlled tissue loading device and mechanically loaded for 3 days at a nominal 0.65% elongation at 1 Hz for 8 hours per day with 16 hours rest. Tendon samples were radiolabeled during the last 16 hours with 3H-thymidine to monitor deoxyribonucleic acid synthesis or with 3H-proline to radiolabel newly synthesized collagen. Cyclic loading of whole avian flexor tendons stimulated deoxyribonucleic acid and collagen synthesis, which could be blocked with octanol, a reversible gap junction blocker. Cells from human digital flexor tendon were used to populate a rectangular, three-dimensional, porous, polyester foam that could be deformed cyclically in vitro. Together, these results support the hypothesis that tendon cells must communicate to sustain growth and matrix expression and that an engineered three-dimensional construct can be used to study responses to mechanical load in vitro.

An in vivo model of degenerative disc disease.

Although the precise etiology of low back pain is disputed, degeneration of the intervertebral disc is believed to play an important role. Many animal models have been described which reproduce the changes found in degenerative disc disease, but none allow for efficient, large‐scale testing of purported therapeutic agents. The purpose of this study was to develop a simple animal model resembling degenerative disc disease using the intervertebral discs found in the tails of rats. The proximal two intervertebral discs in the tails of 20 rats were injected with either chondroitinase ABC or control (phosphate buffered saline, PBS). The tails were harvested at 2 weeks, and measurements were made of intervertebral disc height (measured radiographically and histologically), biomechanics (stiffness, hysteresis, and residual deformation), and histologic appearance. Treatment with chondroitinase ABC resulted in a significant loss in intervertebral disc height (radiographic intervertebral disc height, p < 0.001; histologic intervertebral disc height, p < 0.001) and significant increases in all biomechanical parameters (stiffness, p < 0.001; hysteresis, p < 0.006; residual deformation, p < 0.004) compared to PBS controls. Intervertebral discs treated with chondroitinase ABC had significantly lower histologic grades for each grading category (nucleus pulposus (NP), annulus fibrosus, and proteoglycan staining) compared to controls. The results of injury with chondroitinase ABC were similar to the findings in degenerative disc disease: reduced intervertebral disc height, diminished proteoglycan content, loss of NP cells, and increased stiffness of the disc. Thus, the model appears to be a reasonable tool for the preliminary in vivo evaluation of proposed treatments for degenerative disc disease.

A Cyclooxygenase-2 Inhibitor Impairs Ligament Healing in the Rat

Celecoxib was the first of a new class of nonsteroidal antiinflammatory drugs, the cyclooxygenase-2 (COX-2) specific inhibitors, marketed as having the same antiinflammatory efficacy as other nonsteroidal antiinflammatory drugs without their increased risk of gastrointestinal ulceration. Among the widest uses of nonsteroidal antiinflammatory drugs is in the treatment of acute soft tissue injuries. Although the benefits of celecoxib have been shown when used for rheumatoid arthritis and osteoarthritis, we are unaware of any studies concerning its effect on soft tissues. We used the surgically incised medial collateral ligament of male Sprague-Dawley rats as an experimental model for acute ligament injuries to investigate the effects of celecoxib on ligament healing. Fifty rats underwent surgical transection of the right medial collateral ligament. Postoperatively, half were given celecoxib for the first 6 days of recovery, the other half were not. The animals were sacrificed 14 days after the operation, and both the injured and uninjured medial collateral ligaments were mechanically tested to failure in tension. Celecoxib-treated/injured ligaments were found to have a 32% lower load to failure than untreated/ injured ligaments. The results of this study do not support use of cyclooxygenase-2 specific inhibitors in the treatment of ligament injuries.

Fixed-angle plate fixation in simulated fractures of the proximal humerus: a biomechanical study of a new device.

This study was performed to evaluate the biomechanical properties of a new device for displaced fractures of the proximal humerus. The device is a low-profile, fixed-angle plate specially designed for percutaneous application. With the use of embalmed cadaveric humeri, we simulated both noncomminuted and comminuted 2-part surgical neck fractures of the proximal humerus. Each humerus of a pair was then randomly fixed with either the new experimental device or the Association for the Study of Internal Fixation (ASIF) T-plate and mechanically tested to failure in an axial shear-loading model. The two fixation devices were evaluated in paired humeri with regard to mode of failure, stiffness, displacement at physiologic loads, and displacement, load, and energy at the point of ultimate load before failure. In the noncomminuted fracture trials the experimental device exhibited significantly greater stiffness (P <.001; P =.002 for normalized values) and ultimate load before failure (P =.015) and significantly less displacement at higher physiologic loads (P =.031). In the comminuted fracture trials the experimental device exhibited significantly greater stiffness (P =.048), ultimate load (P <.001) and energy absorbed (P =.048) before failure, and significantly less displacement at higher (P =.004) and lower physiologic loads (P =.011). The study demonstrates improved biomechanical properties for the new experimental device over the T-plate in simulated fractures of the proximal humerus. We extrapolate that these improved biomechanical properties may prove advantageous in future clinical investigation.

Compression etiology in tendinopathy

Recent studies have emphasized that the etiology of tendinopathy is not as simple as was once thought. The etiology is likely to be multifactorial. Etiologic factors may include some of the traditional factors such as overuse, inflexibility, and equipment problems; however, other factors need to be considered as well, such as age-related tendon degeneration and biomechanical considerations as outlined in this article. More research is needed to determine the significance of stress-shielding and compression in tendinopathy. If they are confirmed to play a role, this finding may significantly alter our approach in both prevention and in treatment through exercise therapy. The current biomechanical studies indicate that certain joint positions are more likely to place tensile stress on the area of the tendon commonly affected by tendinopathy. These joint positions seem to be different than the traditional positions for stretching exercises used for prevention and rehabilitation of tendinopathic conditions. Incorporation of different joint positions during stretching exercises may exert more uniform, controlled tensile stress on these affected areas of the tendon and avoid stresshielding. These exercises may be able to better maintain the mechanical strength of that region of the tendon and thereby avoid injury. Alternatively, they could more uniformly stress a healing area of the tendon in a controlled manner, and thereby stimulate healing once an injury has occurred. Additional work will have to prove if a change in rehabilitation exercises is more efficacious that current techniques.

Strain patterns in the patellar tendon and the implications for patellar tendinopathy

This study investigated the strain pattern in human patellar tendon in an area of the tendon where changes commonly associated with patellar tendinitis are found. Eight fresh frozen human knees were instrumented with strain gauges on both the anterior and posterior side of the proximal patellar tendon. Both static and dynamic measurements were carried out in a range from 0° to 60° of flexion. We found uniform tensile strain in the tendon with the knee in full extension. However, as the knee was brought into flexion, the tensile strain increased on the anterior side but decreased on the posterior side in the central, proximal location of the tendon. The posterior side of the proximal patellar tendon is most commonly affected in patellar tendinopathy. This study indicates that this area of the tendon may not subjected to the highest tensile loads in the functional flexion range. It is possible that stress shielding is more important etiological factor in insertional tendinopathy as opposed to repetitive tensile loads.

Strain Behavior of the Distal Achilles Tendon Implications for Insertional Achilles Tendinopathy

Background The changes associated with Achilles insertional tendinopathy (AIT) are seen in the anterior portion of the Achilles tendon near its calcaneal insertion. Strain behavior of this portion of the tendon was evaluated. Hypothesis The highest strains are in the anterior portion of the tendon. Study Design Controlled laboratory study. Methods Six cadaveric legs were tested. While moving through a functional range of ankle motion, strains in five different regions of the tendon insertion were tested. First, the load on the tendon was increased from 30 to 170 N in the starting, plantar flexed position. Then, the ankle was moved from a plantar flexed position into dorsiflexion. Results Strains in the posterior sites increased significantly (P < 0.001) as the movement into dorsiflexion occurred. This was significantly (P < 0.01) different than the anterior sites, which showed a trend toward decreasing strain. Conclusions Although the anterior portion of the Achilles tendon is generally affected in AIT, relative strain shielding is seen in this portion of the tendon. These findings suggest that the role of repetitive tensile loads in the causation of AIT is more complex than often described. Clinical Relevance These findings may explain the variable therapeutic response following measures aimed at decreasing tensile loads on the tendon.