Differential knee joint loading patterns during gait for individuals with tibiofemoral and patellofemoral articular cartilage defects in the knee

OBJECTIVE

To determine compartment-specific loading patterns during gait, quantified as joint reaction forces (JRF), of individuals with knee articular cartilage defects (ACD) compared to healthy controls (HC).

METHODS

Individuals with ACDs and HC participated. Individuals with ACDs were divided into groups according to ACD location: PF (only a patellofemoral ACD), TF (only a tibiofemoral ACD), and MIX (both PF and TF ACDs). Participants underwent three-dimensional gait analysis at self-selected speed. TF joint reaction force (TF-JRF) was calculated using inverse dynamics. PF joint reaction force (PF-JRF) was derived from estimated quadriceps force (F_QUAD) and knee flexion angle. Primary variables of interest were the PF- and TF-JRF peaks (body weight [×BW]). Related secondary variables (gait speed, quadriceps strength, knee function, activity level) were evaluated as covariates.

RESULTS

First peak PF-JRF and TF-JRF were similar in the TF and MIX groups (0.75-1.0 ×BW, P = 0.6-0.9). Both peaks were also similar in the PF and HC groups (1.1-1.3 ×BW, P = 0.7-0.8), and higher than the TF and MIX groups (P = 0.004-0.02). For the second peak PF-JRF, only the HC group was higher than the TF group (P = 0.02). The PF group walked at a similar speed as the HC group; both groups walked faster than the TF and MIX groups (P < 0.001). With gait speed and quadriceps strength as covariates, no differences were observed in JRF peaks.

CONCLUSIONS

The results suggest the presence of a TF ACD (TF and MIX groups), but not a PF ACD (PF group), may affect joint loading patterns during walking. Walking slower may be a protective gait modification to reduce load.

Biological and physiological role of reactive oxygen species--the good, the bad and the ugly

Reactive oxygen species (ROS) are chemically reactive molecules that are naturally produced within biological systems. Research has focused extensively on revealing the multi-faceted and complex roles that ROS play in living tissues. In regard to the good side of ROS, this article explores the effects of ROS on signalling, immune response and other physiological responses. To review the potentially bad side of ROS, we explain the consequences of high concentrations of molecules that lead to the disruption of redox homeostasis, which induces oxidative stress damaging intracellular components. The ugly effects of ROS can be observed in devastating cardiac, pulmonary, neurodegenerative and other disorders. Furthermore, this article covers the regulatory enzymes that mitigate the effects of ROS. Glutathione peroxidase, superoxide dismutase and catalase are discussed in particular detail. The current understanding of ROS is incomplete, and it is imperative that future research be performed to understand the implications of ROS in various therapeutic interventions.

Characterization of reactive oxygen species in diaphragm

Reactive oxygen species (ROS) exist as natural mediators of metabolism to maintain cellular homeostasis. However, ROS production may significantly increase in response to environmental stressors, resulting in extensive cellular damage. Although several potential sources of increased ROS have been proposed, exact mechanisms of their generation have not been completely elucidated. This is particularly true for diaphragmatic skeletal muscle, the key muscle used for respiration. Several experimental models have focused on detection of ROS generation in rodent diaphragm tissue under stressful conditions, including hypoxia, exercise, and heat, as well as ROS formation in single myofibres. Identification methods include direct detection of ROS with confocal or fluorescent microscopy and indirect detection of ROS through end product analysis. This article explores implications of ROS generation and oxidative stress, and also evaluates potential mechanisms of cellular ROS formation in diaphragmatic skeletal muscle.

Mesenchymal stem-cell potential in cartilage repair: an update

Articular cartilage damage and subsequent degeneration are a frequent occurrence in synovial joints. Treatment of these lesions is a challenge because this tissue is incapable of quality repair and/or regeneration to its native state. Non-operative treatments endeavour to control symptoms and include anti-inflammatory medications, viscosupplementation, bracing, orthotics and activity modification. Classical surgical techniques for articular cartilage lesions are frequently insufficient in restoring normal anatomy and function and in many cases, it has not been possible to achieve the desired results. Consequently, researchers and clinicians are focusing on alternative methods for cartilage preservation and repair. Recently, cell-based therapy has become a key focus of tissue engineering research to achieve functional replacement of articular cartilage. The present manuscript is a brief review of stem cells and their potential in the treatment of early OA (i.e. articular cartilage pathology) and recent progress in the field.

The role of muscle strength & activation patterns in patellofemoral pain

BACKGROUND

To investigate the extent to which quadriceps muscle activation and strength are responsible for patellofemoral pain.

METHODS

A pain on-off switch system synchronized with a force transducer and surface electromyography was utilized on 32 volunteer patellofemoral pain patients during maximal isometric and squat exercises.

FINDINGS

There were 26 patients out of the 32 tested who complained of pain during the squat or isometric test, of these 20 subjects presented a significant advantage for the vastus lateralis compared to the vastus medialis obliquis activation and 12 patients had decreased quadriceps strength of the symptomatic compared to the non symptomatic leg. All patients who demonstrated weak vastus medialis obliquis activation during the isometric exercise possessed the same symptoms during the squat. On the other hand, 9 patients who showed diminished vastus medialis obliquis activation during the squat displayed equal activation between the vastus medialis obliquis and the vastus lateralis during the isometric task. With regard to the timing for the onset of muscle activation, there were only 4 patients who had a difference (P=0.03) between the symptomatic (0.042 s) and non-symptomatic legs (0.011 s).

INTERPRETATION

Causes for patellofemoral pain vary and are not necessarily a result of quadriceps strength deficit or vastus medialis obliquis activation weakness. Patellofemoral pain patients who possess lower vastus medialis obliquis activation compared to the vastus lateralis do not necessarily have quadriceps weakness while patients presenting with quadriceps strength deficits do not always have an imbalance between vastus medialis obliquis and vastus lateralis activation.

A systematic review of four injection therapies for lateral epicondylosis: prolotherapy, polidocanol, whole blood and platelet-rich plasma

OBJECTIVE

To appraise existing evidence for prolotherapy, polidocanol, autologous whole blood and platelet-rich plasma injection therapies for lateral epicondylosis (LE).

DESIGN

Systematic review.

DATA SOURCES

Medline, Embase, CINAHL, Cochrane Central Register of Controlled Trials, Allied and Complementary Medicine.

SEARCH STRATEGY

names and descriptors of the therapies and LE.

STUDY SELECTION

All human studies assessing the four therapies for LE.

MAIN RESULTS

Results of five prospective case series and four controlled trials (three prolotherapy, two polidocanol, three autologous whole blood and one platelet-rich plasma) suggest each of the four therapies is effective for LE. In follow-up periods ranging from 9 to 108 weeks, studies reported sustained, statistically significant (p<0.05) improvement in visual analogue scale primary outcome pain score measures and disease-specific questionnaires; relative effect sizes ranged from 51% to 94%; Cohen's d ranged from 0.68 to 6.68. Secondary outcomes also improved, including biomechanical elbow function assessment (polidocanol and prolotherapy), presence of abnormalities and increased vascularity on ultrasound (autologous whole blood and polidocanol). Subjects reported satisfaction with therapies on single-item assessments. All studies were limited by small sample size.

CONCLUSIONS

There is strong pilot-level evidence supporting the use of prolotherapy, polidocanol, autologous whole blood and platelet-rich plasma injections in the treatment of LE. Rigorous studies of sufficient sample size, assessing these injection therapies using validated clinical, radiological and biomechanical measures, and tissue injury/healing-responsive biomarkers, are needed to determine long-term effectiveness and safety, and whether these techniques can play a definitive role in the management of LE and other tendinopathies.

Where tendons and ligaments meet bone: attachment sites ('entheses') in relation to exercise and/or mechanical load

Entheses (insertion sites, osteotendinous junctions, osteoligamentous junctions) are sites of stress concentration at the region where tendons and ligaments attach to bone. Consequently, they are commonly subject to overuse injuries (enthesopathies) that are well documented in a number of sports. In this review, we focus on the structure-function correlations of entheses on both the hard and the soft tissue sides of the junction. Particular attention is paid to mechanical factors that influence form and function and thus to exploring the relationship between entheses and exercise. The molecular parameters indicative of adaptation to mechanical stress are evaluated, and the basis on which entheses are classified is explained. The application of the 'enthesis organ' concept (a collection of tissues adjacent to the enthesis itself, which jointly serve the common function of stress dissipation) to understanding enthesopathies is considered and novel roles of adipose tissue at entheses are reviewed. A distinction is made between different locations of fat at entheses, and possible functions include space-filling and proprioception. The basic anchorage role of entheses is considered in detail and comparisons are explored between entheses and other biological 'anchorage' sites. The ability of entheses for self-repair is emphasized and a range of enthesopathies common in sport are reviewed (e.g. tennis elbow, golfer's elbow, jumper's knee, plantar fasciitis and Achilles insertional tendinopathies). Attention is drawn to the degenerative, rather than inflammatory, nature of most enthesopathies in sport. The biomechanical factors contributing to the development of enthesopathies are reviewed and the importance of considering the muscle-tendon-bone unit as a whole is recognized. Bony spur formation is assessed in relation to other changes at entheses which parallel those in osteoarthritic synovial joints.

Hyperbaric oxygen therapy for delayed onset muscle soreness and closed soft tissue injury

BACKGROUND

Soft tissue injuries (including muscle damage after unaccustomed exercise) are common and are often associated with athletic activity. Hyperbaric oxygen therapy (HBOT) is the therapeutic administration of 100% oxygen at environmental pressures greater than one atmosphere.

OBJECTIVES

To assess the benefits and harms of HBOT for treating soft tissue injury, including delayed onset muscle soreness (DOMS).

SEARCH STRATEGY

We searched the following in July 2004: CENTRAL, MEDLINE, EMBASE, CINAHL, DORCTIHM and reference lists from relevant articles. Relevant journals were handsearched and researchers in the field contacted.

SELECTION CRITERIA

Randomised trials comparing the effect on closed soft tissue injury (including DOMS) of therapeutic regimens which include HBOT with those that exclude HBOT (with or without sham therapy).

DATA COLLECTION AND ANALYSIS

Four reviewers independently evaluated study quality and extracted data. Most of the data presented in the review were extracted from graphs in the trial reports.

MAIN RESULTS

Nine small trials involving 219 participants were included. Two trials compared HBOT versus sham therapy on acute closed soft tissue injuries (ankle sprain and medial collateral knee ligament injury respectively). The other seven trials examined the effect of HBOT on DOMS following eccentric exercise in unconditioned volunteers. All 32 participants of the ankle sprain trial returned to their normal activities. There were no significant differences between the two groups in time to recovery, functional outcomes, pain, or swelling. There was no difference between the two groups in knee function scores in the second acute injury trial; however, intention-to-treat analysis was not possible for this trial. Pooling of data from the seven DOMS trials showed significantly and consistently higher pain at 48 and 72 hours in the HBOT group (mean difference in pain score at 48 hours [0 to 10 worst pain] 0.88, 95% CI 0.09 to 1.67, P = 0.03) in trials where HBOT was started immediately. There were no differences between the two groups in longer-term pain scores or in any measures of swelling or muscle strength. No trial reported complications of HBOT but careful selection of participants was evident in most trials.

AUTHORS' CONCLUSIONS

There was insufficient evidence from comparisons tested within randomised controlled trials to establish the effects of HBOT on ankle sprain or acute knee ligament injury, or on experimentally induced DOMS. There was some evidence that HBOT may increase interim pain in DOMS. Any future use of HBOT for these injuries would need to have been preceded by carefully conducted randomised controlled trials which have demonstrated effectiveness.

Effects of eccentric phase velocity of plyometric training on the vertical jump

The aim of this study was to compare the effects of plyometric training performed with rapid or slow stretch contraction on jump performance and muscle properties. Thirty males between the ages of 19 and 22 volunteered for the 8-week experiment. Subjects were divided into the following three groups: training group 1 (TG1), training group 2 (TG2), and control group (CG). Each of the two experimental groups underwent a unique training regimen. For the first group (TG1, n = 12): from a standing position the subject flexed his knees to a 90 degrees angle with velocity standardized and controlled at 0.4 m/s and immediately performed a leg extension as quickly as possible. For the second group (TG2, n = 12): from a standing position, the subject flexed his knees to a 90 degrees angle with velocity standardized at 0.2 m/s and then performed a leg extension as quickly as possible. Each exercise consisted of six sets of ten repetitions with a barbell on the shoulders at 70 % of the maximal isometric force (1 RM). The 70 % load was modified at two-week intervals by evaluating a new 1 RM. Exercises were performed four times a week over the eight-week period. The third group (CG, n = 6), served as the control group. Maximal isometric force (MVC), maximal concentric force, squat jump (SJ) and counter movement jump (CMJ) exercises were performed before and after the training program. Subjects were filmed (100 Hz) and each jump was divided into three phases: eccentric phase (ECC), transition phase (TR) and concentric phase (CON). Surface EMG was used to determine the changes in the electromyographic (EMG) activity before and after the training program. There was an increase in leg extension force, velocity and electrical activity for SJ and CMJ for the two training groups (p < 0.05). However, TG1 showed a significant advantage in CMJ performance as well as a significant decrease in TR compared to the TG2 (p < 0.05). The results of this study show that when plyometric training is performed with rapid stretch contraction the CMJ jump height increases and the TR decreases.

M1/70 attenuates blood-borne neutrophil oxidants, activation, and myofiber damage following stretch injury

The purpose of this study was to determine the role of the CD11b-dependent respiratory burst in neutrophil oxidant generation and activation, interleukin-8 (IL-8) production, and myofiber damage after muscle stretch injury by using the monoclonal antibody M1/70 to block this pathway. Twelve male New Zealand White rabbits were randomly assigned to a treatment group: M1/70 (n = 6), IgG isotype control (n = 3), or saline control (n = 3). After intravenous injection of the assigned agent under gas anesthesia, a standardized single-stretch injury was created in the right tibialis anterior, whereas the left tibialis anterior underwent a sham surgery. Blood-borne neutrophil oxidant generation and CD11b receptor density and plasma IL-8 levels were measured pre- and 24 h postinjury. Damage was assessed histologically at the hematoma site by counting torn myofibers. M1/70 group demonstrated decreased blood-borne neutrophil oxidant generation (P < 0.05) and CD11b receptor density (P < 0.05), an increase in plasma IL-8 concentration (P < 0.01), and less torn myofibers (P < 0.01) compared with IgG isotype or saline control groups. These data indicate that 1). CD11b-dependent respiratory burst is a major source of oxidants produced by the neutrophil, and that treatment with M1/70 2). attenuates neutrophil activation status, 3). increases plasma IL-8 concentration, and 4). minimizes myofiber damage 24 h postmuscle stretch injury.

The inflammatory response: friend or enemy for muscle injury?

Limiting certain aspects of inflammation may be a useful new treatment for sport related muscle injury.

Oxidant production and immune response after stretch injury in skeletal muscle

PURPOSE

This study investigated oxidant production and associated immune response after acute muscle stretch injury.

METHODS

A standardized single stretch injury was performed on the tibialis anterior (TA) muscle of 36 male New Zealand white rabbits while contralateral control limbs underwent a sham surgery. Animals were sacrificed 0, 4, 12, 24, 48, and 72 h after injury. Potential sites of oxidant production, measured with a dichlorofluorescein (DCF) probe, were evaluated using two separate buffers.

RESULTS

Nonmitochondrial oxidant production measured under basal buffer conditions (0.1 M potassium phosphate) was increased in both injured and control limbs at 24 h (P < 0.01) and was greater in the injured limb at 12 and 48 h (P < 0.01). There was also an interaction of time and injury (P < 0.05). Maximum oxidant production by neutrophils and macrophages, stimulated by the induced buffer (including 1.7 mM ADP, 0.1 mM NADPH, 0.1 mM FeCl3), was increased in both injured and control limbs at 4 h (P < 0.01) and was greater in the injured limb at 48 h (P < 0.01). Myeloperoxidase (MPO) activity, indicating the presence of activated neutrophils, was higher in the injured limb at 4 and 48 h (P < 0.01). The activities of superoxide radical producing and quenching enzymes, xanthine oxidase (XO) and superoxide dismutase (SOD), were elevated at 24 (P < 0.01) and 4 h (P < 0.05), respectively, but showed no difference between injured and control limbs.

CONCLUSION

We conclude that acute muscle stretch injury and the required surgeries to generate the injury result in a biphasic increase in oxidant production in both injured and control limbs, suggesting a systemic immune response. The increase in oxidant production at 4 h may be caused by an increase in activated neutrophils, whereas XO activity may contribute to oxidant generation at 24 h.

Analysis of changes in mRNA levels of myoblast- and fibroblast-derived gene products in healing skeletal muscle using quantitative reverse transcription-polymerase chain reaction

Changes in expression of type III alpha1-collagen and myosin II heavy chains were characterized in rabbit skeletal muscle following single stretch injury using quantitative reverse transcription-polymerase chain reaction. Collagen III expression was highly elevated in the injured leg compared with the control limb both at the myotendinous junction and in the distal muscle belly. While upregulation of collagen III expression at the myotendinous junction was maximal on day 1, collagen III expression in the distal muscle belly was unchanged on day 1 but highly elevated by day 3. Over the initial 7-day period, there was on average a 94% increase in collagen III expression at the myotendinous junction and a 42% increase in the distal muscle belly. On the other hand, there was little difference, in fact, slightly less expression of myosin II isoforms, in the injured leg compared with the control side. Immunohistochemical analysis of injured muscle showed significant collagen III deposition at the myotendinous junction beginning at day 3 post-injury and still evident by day 14. Focal deposits of type I and III collagen were first apparent in the distal muscle belly by day 3 and striking by day 7. Taken together, the data suggest the formation of connective tissue scar at the injury site and the absence of significant muscle regeneration following muscle stretch. Furthermore, microinjuries distant to the primary site of injury may result in more general muscle fibrosis and scarring.

The painful shoulder: part II. Acute and chronic disorders

Fractures of the humerus, scapula and clavicle usually result from a direct blow or a fall onto an outstretched hand. Most can be treated by immobilization. Dislocation of the humerus, strain or sprain of the acromioclavicular and sternoclavicular joints, and rotator cuff injury often can be managed conservatively. Recurrence is a problem with humerus dislocation, and surgical management may be indicated if conservative treatment fails. Rotator cuff tears are often hard to diagnose because of muscle atrophy that impairs the patient's ability to perform diagnostic maneuvers. Chronic shoulder problems usually fall into one of several categories, which include impingement syndrome, frozen shoulder and biceps tendonitis. Other causes of chronic shoulder pain are labral injury, osteoarthritis of the glenohumeral or acromioclavicular joint and, rarely, osteolysis of the distal clavicle.

The painful shoulder: part I. Clinical evaluation

Family physicians need to understand diagnostic and treatment strategies for common causes of shoulder pain. We review key elements of the history and physical examination and describe maneuvers that can be used to reach an appropriate diagnosis. Examination of the shoulder should include inspection, palpation, evaluation of range of motion and provocative testing. In addition, a thorough sensorimotor examination of the upper extremity should be performed, and the neck and elbow should be evaluated.

Muscle injury and repair

Muscle injury triggers a sequence of events that begin with a host inflammatory response that is followed by muscle fiber regeneration and new collagen synthesis. The inflammatory response involves at least three types of cells, including neutrophils, ED1+ macrophages, and ED2+ macrophages. A host of growth factors and cytokines appear to play a role in the inflammatory process and repair of the damaged tissue. Satellite cells play an integral role in normal development of skeletal muscle by providing a source for postmitotic myonuclei. In addition, the satellite cell is essential to the repair of injured muscle by serving as a source of myoblasts for fiber regeneration. At the same time muscle fiber regeneration is occurring, there is expression of types I and III collagen that under certain circumstances can lead to scarring and fibrosis. Current studies of treatment of muscle injury often incorporate investigations of basic principles of injury and repair together with clinical experience and principles in an effort to coordinate basic science and outcome studies.

MR imaging of the distribution and location of acute hamstring injuries in athletes

OBJECTIVE

Although hamstring injuries are common in athletes, the distribution and location of such injuries have not been well defined. We used MR imaging to determine the frequency of injury by muscle, involvement of one or more muscles, and location of injuries within the musculotendinous unit.

SUBJECTS AND METHODS

We performed MR imaging on 15 consecutive college athletes with clinically diagnosed acute hamstring injuries. A hamstring injury was diagnosed and located on MR imaging by identifying high signal intensity within the muscle on T2-weighted images.

RESULTS

We found that 10 athletes had injuries of a single muscle with six injuries of the biceps femoris, three of the semitendinosus, and one of the semimembranosus. In an additional five athletes, we found primary injuries of the biceps femoris and secondary injuries of the semitendinosus. The injuries occurred in diverse locations within the muscles including five injuries at the proximal musculotendinous junction, two at the distal musculotendinous junction, four within the proximal half of the muscle belly, and four in the distal half. All eight intramuscular injuries were located at the musculotendinous junction within the muscle.

CONCLUSION

The biceps femoris is the most commonly injured hamstring muscle and the semitendinosus is the second most commonly injured. Although hamstring injuries often involve one muscle injured proximally, multiple muscles were involved in 33% of athletes (5/15) and the injuries were distal in 40% of athletes (6/15). All intramuscular injuries occurred at the musculotendinous junction, either at the ends of the muscle or within the muscle belly.

Free radical activity, antioxidant enzyme, and glutathione changes with muscle stretch injury in rabbits

The present study investigated changes in rate of free radical production, antioxidant enzyme activity, and glutathione status immediately after and 24 h after acute muscle stretch injury in 18 male New Zealand White rabbits. There was no change in free radical production in injured muscles, compared with noninjured controls, immediately after injury (time 0; P = 0.782). However, at 24 h postinjury, there was a 25% increase in free radical production in the injured muscles. Overall, there was an interaction (time and treatment) effect (P = 0.005) for free radical production. Antioxidant enzyme activity demonstrated a treatment (injured vs. control) and interaction effect for both glutathione peroxidase (P = 0.015) and glutathione reductase (P = 0.041). There was no evidence of lipid peroxidation damage, as measured by muscle malondialdehyde content. An interaction effect occurred for both reduced glutathione (P = 0.008) and total glutathione (P = 0.015). Morphological analysis (hematoxylin and eosin staining) showed significant polymorphonuclear cell infiltration of the damaged region at 24 h postinjury. We conclude that acute mechanical muscle stretch injury results in increased free radical production within 24 h after injury. Antioxidant enzyme and glutathione systems also appear to be affected during this early postinjury period.

Nitric oxide donors, sodium nitroprusside and S-nitroso-N-acetylpencillamine, stimulate myoblast proliferation in vitro

Nitric oxide (NO) is an inter- and intracellular messenger involved in a variety of physiologic and pathophysiologic conditions. The effect of two NO donors, sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) and their effect on myoblast proliferation was examined. Both donors stimulated an increase in myoblast cell number over a range (1-10 microM) of donor concentrations. However, 50 microM SNAP inhibited myoblast proliferation. Cell numbers from cultures treated with degraded 10 microM SNAP were equivalent to the control. Therefore, it appears NO can stimulate as well as inhibit myoblast proliferation.

Anthropometric and performance measures for high school basketball players

OBJECTIVE

To determine possible anthropometric and performance sex differences in a population of high school basketball players.

DESIGN AND SETTING

Measurements were collected during the first week of basketball practice before the 1995-1996 season. Varsity basketball players from 4 high schools were tested on a battery of measures chosen to detect possible anthropometric and performance sex differences.

SUBJECTS

Fifty-four female and sixty-one male subjects, from varsity basketball teams at high schools enrolled in the athletic training outreach program at the University of Wisconsin Hospital Sports Medicine Center in Madison, WI, volunteered to take part in this study.

MEASUREMENTS

We took anthropometric measurements on each of the 115 subjects. These included height, weight, body composition, ankle range of motion, and medial longitudinal arch type in weightbearing. Performance measures included the vertical jump, 22.86-m (25-yd) shuttle run, 18.29-m (20-yd) sprint, and single-limb balance time.

RESULTS

We compared anthropometric and performance characteristics using a 2-sample t test. The only exception to this was for medial longitudinal arch type, where the 2 groups were compared using a 2-tailed Fisher's exact test. The male subjects were significantly taller and heavier, while the females had a significantly higher percentage of body fat. There were no significant differences found for ankle plantar flexion and dorsiflexion, but the females had significantly more inversion and eversion range of motion. Analysis of medial longitudinal arch type found females to have a higher percentage of pronated arches and males to have a higher percentage of supinated arches. Performance testing revealed that the males were able to jump significantly higher and run the 22.86-m (25-yard) shuttle run and 18.29-m (20-yard) sprint significantly faster than the female subjects. There was no significant difference between the groups for single-limb balance time.

CONCLUSIONS

We found significant anthropometric and performance sex differences in a cohort of high school basketball players. Further study of these measures is necessary to determine if these differences can predict the risk for ankle injuries in this particular population.

Hyperbaric oxygen in the treatment of acute muscle stretch injuries. Results in an animal model

Hyperbaric oxygen therapy is an established therapy in several areas of clinical medicine. However, studies have produced conflicting results regarding its efficacy for sports-related soft tissue injuries. This study examines the use of hyperbaric oxygen therapy after an acute muscle stretch injury in an animal model. Two groups of rabbits (nine in each group) were subjected to a partial stretch injury to the tibialis anterior muscle-tendon unit. For all 18 animals, the injuries were induced in the left limb, and the uninjured right limb served as a sham-operated control. In group 1, the animals were exposed to hyperbaric oxygen (> 95% O2 at 2.5 atm) for 60 minutes daily for 5 days. Treatment began 24 hours after injury. Group 2 animals were not exposed to hyperbaric oxygen. Evaluation 7 days after injury demonstrated a functional deficit (percent ankle isometric torque; injured side versus uninjured side) of 14.9% +/- 5.5% (mean +/- SD) for the treated group and 47.5% +/- 5.4% for the untreated group, representing a statistical difference using the Behrens-Fisher version of the t test (P = 0.001). Morphologic studies revealed more complete healing in the treated group. This study suggests that hyperbaric oxygen therapy may play a role in accelerating recovery after acute muscle stretch injury. Further studies are needed before definitive conclusions and treatment recommendations can be made.

Evaluation of a new method to create a standardized muscle stretch injury

Herein we describe a new test system to produce a standardized partial muscle-tendon junction (MTJ) stretch injury. In anesthetized rabbits the tibialis anterior (TA) muscle-tendon unit is unilaterally shortened using a custom designed clamp roller system. An angular displacement (average velocity of 450 degrees x s[-1]) is applied about the foot to plantarflex the ankle 90 degrees while the lower extremity is fixed. During ankle rotation the TA muscle is tetanically stimulated to generate an eccentric stretch injury at the MTJ. Forty-eight hours after injury, isometric torque deficit (injured/sham) was measured. Two groups of animals (N = 6 in each group) were tested with the only difference between the two groups being the initial tendon shortening. In Group 1 (tendon shortening = 1.2 cm. N = 6) the torque deficit was 36.7+/-5.9% (mean+/-SD). In Group 2 (tendon shortening = 1.5 cm. N = 6) the torque deficit was 58.7+/-7.4% (mean+/-SD). No order effect was suggested by the data (P = 0.6062), but the difference in torque deficit between the two groups was highly significant (P = 0.0001). For all tests in which the tendon was temporarily shortened before muscle stimulation and stretch (N = 12) there was a visible hematoma at the MTJ similar to the injury that is common in athletic injuries. Histological evaluation 48 h after injury revealed both fiber tearing and inflammation at the MTJ. In addition, there was focal fiber damage in the muscle belly for both groups. The damage and inflammatory process, however, were more severe in the group with greater initial tendon shortening.

The influence of strain rate on the passive and stimulated engineering stress--large strain behavior of the rabbit tibialis anterior muscle

The passive and stimulated engineering stress-large strain mechanical properties of skeletal muscle were measured at the midbelly of the rabbit tibialis anterior. The purpose of these experiments was to provide previously unavailable constitutive information based on the true geometry of the muscle and to determine the effect of strain rate on these responses. An apparatus including an ultrasound imager, high-speed digital imager, and a servohydraulic linear actuator was used to apply constant velocity deformations to the tibialis anterior of an anesthetized neurovascularly intact rabbit. The average isometric tetanic stress prior to elongation was 0.44 +/- 0.15 MPa. During elongation the average stimulated modulus was 0.97 +/- 0.34 MPa and was insensitive to rate of loading. The passive stress-strain responses showed a nonlinear stiffening response typical of biologic soft tissue. Both the passive and stimulated stress-strain responses were sensitive to strain rate over the range of strain rates (1 to 25 s-1). Smaller changes in average strain rate (1 to 10, and 10 to 25 s-1) did not produce statistically significant changes in these responses, particularly in the stimulated responses, which were less sensitive to average strain rate than the passive responses. This relative insensitivity to strain rate suggests that pseudoelastic functions generated from an appropriate strain rate test may be suitable for the characterization of the responses of muscle over a narrow range of strain rates, particularly in stimulated muscle.

Soft-tissue injuries and muscle tears

Soft-tissue injuries and muscle tears occur frequently in athletes. The mainstay of treatment in most cases is nonoperative management and aggressive rehabilitation. Most injuries result from direct trauma or contusion or indirect stretch injury. It is important to keep in mind the possibility of other potentially more serious conditions, such as compartment syndrome. More research is needed to define optimal treatment patterns and potential strategies for injury prevention.

Hamstring strains: expediting return to play

Strains to the hamstring muscle group are prevalent and, unfortunately, often recurrent, with prolonged rehabilitation and persistent disability. Most hamstring injuries are of a single muscle near the muscle-tendon junction. Rarely, the hamstring muscle group may avulse from the ischial tuberosity. The diagnosis can usually be made by history and physical exam, but MRI can be used to help pinpoint the extent and location of the injury. Initial treatment typically consists of rest, ice, compression, elevation, and pain relief. There is no consensus on optimal rehabilitation, but functional exercises with stretching and strengthening have been emphasized.

Experimental impact injury to the cervical spine: relating motion of the head and the mechanism of injury

The purpose of this study was to analyze, with use of an impact model, the relationships among motion of the head, local deformations of the cervical spine, and the mechanisms of injury; the model consisted of the head and neck of a cadaver. Traditionally, the mechanisms of injury to the cervical spine have been associated with flexion and extension motions of the head and neck. However, the classification of the mechanisms is not always in agreement with the patient's account of the injury or with lacerations and contusions of the scalp, which indicate the site of the impact of the head. Eleven specimens were dropped in an inverted posture with the head and neck in an anatomically neutral position. Forces, moments, and accelerations were recorded, and the impacts were imaged at 1000 frames per second. The velocity at the time of impact was on the order of 3.2 meters per second. The angle and the padding of the impact surface varied. Observable motion of the head did not correspond to the mechanism of the injury to the cervical spine. Injury occurred 2.2 to 18.8 milliseconds after impact and before noticeable motion of the head. However, the classification of the mechanism of the injuries was descriptive of the local deformations of the cervical spine at the time of the injury. Accordingly, it is a useful tool in describing the local mechanism of injury. Buckling of the cervical spine, involving extension between the third and sixth cervical vertebrae and flexion between the seventh and eight cervical vertebrae, was observed. Other, more complex, buckling deformations were also seen, suggesting that the deformations that occur during impact are so complex that they can give rise to a number of different mechanisms of injury.

Axial strain measurements in skeletal muscle at various strain rates

A noncontact optical system using high speed image analysis to measure local tissue deformations and axial strains along skeletal muscle is described. The spatial resolution of the system was 20 pixels/cm and the accuracy was +/- 0.125 mm. In order to minimize the error associated with discrete data used to characterize a continuous strain field, the displacement data were fitted with a third order polynomial and the fitted data differentiated to measure surface strains using a Lagrangian finite strain formulation. The distribution of axial strain along the muscle-tendon unit was nonuniform and rate dependent. Despite a variation in local strain distribution with strain rate, the maximum axial strain, Exx = 0.614 +/- 0.045 mm/mm, was rate insensitive and occurred at the failure site for all tests. The frequency response of the video system (1000 Hz) and the measurement of a continuous strain field along the entire length of the structure improve upon previous noncontact optical systems for measurement of surface strains in soft tissues.

Incomplete, intrasubstance strain injuries of the rectus femoris muscle

Rectus femoris muscle strain injuries commonly occur at the distal muscle-tendon junction of the quadriceps tendon. However, we have recently recognized a pattern of strain injury that consists of an incomplete intrasubstance tear at the muscle-tendon junction formed by the deep tendon of the muscle's indirect head and those muscle fibers originating from this tendon. These injuries are found more proximally within the thigh than the "classic" distal rectus femoris muscle strain. We reviewed 10 athletes with these intrasubstance tears, all of whom had diagnostic imaging performed using computed tomography or magnetic resonance imaging or both. Two of these patients required surgical intervention. The mechanism of injury usually involved kicking or sprinting. All patients had chronic thigh pain or an anterior thigh mass or both. Physical examination revealed thigh asymmetry and a nontender to mildly tender intrasubstance muscle mass. Magnetic resonance imaging demonstrated abnormal signal intensity centered about the intramuscular tendon of the indirect head of the muscle. Surgical findings included a mass of fibrous scar and fatty tissue encasing the deep tendon. Surgical removal of this fibrous mass appears curative. We contrast this injury from distal strains of the rectus femoris muscle, as well as from soft tissue neoplasms.

An explanation for various rectus femoris strain injuries using previously undescribed muscle architecture

We performed cadaveric dissection of the rectus femoris muscle to correlate the various lesions of strain injury seen with imaging studies to the muscular anatomy. The proximal tendon is composed of a superficial, anterior portion from the direct head, and a deep intramuscular portion from the indirect head. The muscle fibers arising from the anterior superficial tendon of the direct head travel in a posterior and distal direction to insert on the posterior tendon of insertion, giving the proximal muscle a unipennate architecture. Muscle fibers from the intramuscular tendon of the indirect head originate on both the medial and lateral sides of the tendon and insert on the distal posterior tendon to create its bipennate structure. Three chronic strain injuries involving the midmuscle belly substance were explored grossly and microscopically. It appears that one type of acute strain injury occurs in the midmuscle belly with disruption of the muscle-tendon junction of the intramuscular tendon resulting in local hemorrhage and edema. More chronically, this hematoma organizes into a fatty, loose connective tissue encasement of the deep intramuscular proximal tendon. Serous fluid from the hematoma may remain within the connective tissue sheath, creating a pseudocyst with the deep intramuscular tendon of the indirect head at its center. The muscle's anatomy helps to explain a different rectus femoris strain injury.

Muscle-tendon injuries in young athletes

The pediatric athlete with open physeal plates is more susceptible to growth plate injuries and avulsion fractures rather than ligament and muscle-tendon injuries that most often occur in adults. In general, the pediatric athlete is able to return to full activity quicker than the adult athlete because of a more rapid healing response. There has been a recent interest in the study of the pathophysiology of muscle-tendon injuries and treatment strategies based on these studies have changed. Laboratory studies have several implications regarding the prevention of muscle-tendon injuries. Clinical studies to confirm their efficacy are needed. Complications of re-injury include more serious injury and conditions such as myositis ossificans. Injury prevention has focused on the use of protective equipment and an emphasis on stretching and strengthening programs.

A threshold and continuum of injury during active stretch of rabbit skeletal muscle

Previous studies of acute muscle injury with active stretch used cyclic stretching or stretching the muscle to complete muscle-tendon dissociation. This study tried to determine minimal force required for skeletal muscle injury with one active stretch to establish an injury "threshold." Tibialis anterior and extensor digitorum longus rabbit muscles were actively stretched at 10 cm/sec to 60%, 70%, 80%, or 90% of the force required to passively fail tibialis anterior and extensor digitorum longus muscles of the control (contralateral) limb. Maximal isometric contractile force, tensile properties, histology, and electromyography were measures of injury. Both muscles of the 60% group showed no abnormalities in maximal isometric contractile force, tensile properties, histology, or electromyographic activity; 70%, 80%, and 90% groups showed diminished maximal isometric contractile force, muscle fiber disruption, edema, hemorrhage, and decreased electromyographic maximal voltage amplitude. The 90% group also showed alterations in tensile properties at failure along with connective tissue damage. Injury site included fiber disruption both at the distal myotendinous junction and muscle belly, with injury noted initially at the distal myotendinous junction in the 70% group. Electromyographic studies showed maximal isometric contractile force and maximal voltage correlated well as indices of damage. This study shows that a threshold and continuum for active stretch-induced injury exist, with muscle fiber disruption occurring initially and connective tissue disruption occurring only with larger muscle displacements.

Effects of immobilization on Achilles tendon healing in a rat model

The aim of this study was to evaluate the effects of immobilization and mobilization on the functional and biomechanical recovery of injured Achilles tendons. Male Sprague-Dawley rats were allocated randomly into four groups: (a) sham operation, (b) division only (surgical transection of the Achilles tendon without immobilization), (c) "dummy" external fixation (division of the Achilles tendon and application of Kirschner wires), and (d) rigid external fixation (division of the Achilles tendon and immobilization with Kirschner wires connected by two triangular frames). All procedures were performed on the right lower limb; the left, uninjured, lower limb served as an internal control. Kirschner wires and external fixators were removed on day 12. Functional performance was determined from measurements of hind pawprints of rats walking preoperatively and on postoperative days 1, 3, 5, 7, 9, 11, 13, and 15. On day 15, the animals were killed and biomechanical evaluations were performed on both the injured and the uninjured Achilles tendon constructs. No functional or mechanical deficits were observed in the sham-operation group. Animals subjected to division of the Achilles tendon had an initial functional deficit that returned to near normal by day 15. The application of Kirschner wires was associated with an impairment of the functional performance of the rat as well as of the mechanical properties of the tendon-bone constructs. Immobilization by connection of the Kirschner wires to an external frame had an additional, highly significant (p < 0.001) detrimental effect on the functional and mechanical recovery of Achilles tendon-calcaneal complexes.

Characterization of the passive responses of live skeletal muscle using the quasi-linear theory of viscoelasticity

The tensile viscoelastic responses of live, innervated rabbit skeletal muscle were measured and characterized using the quasi-linear model of viscoelasticity. The tibialis anterior (TA) and extensor digitorum longus (EDL) muscles of anesthetized New Zealand white rabbits were surgically exposed and tested under in vivo conditions. Rate sensitivity of the force-time history was observed in response to constant velocity testing at rates from 0.01 to 2.0 Hz. Average hysteresis energy, expressed as a percentage of maximum stored strain energy, was 39.3 +/- 5.4% and was insensitive to deformation rate. The quasi-linear model, with constants derived from relaxation testing, was able to describe and predict these responses with correlation exceeding the 99% confidence interval for the 132 constant velocity tests performed (rmean = 0.9263 +/- 0.0373). The predictive ability of this model was improved when compressive loading effects on the muscle were neglected, rmean = 0.9306 +/- 0.0324. The rate insensitivity of hysteresis energy was predicted by the model; however, the absolute value of the hysteresis was underestimated (30.2 +/- 4.0%). Both muscles demonstrated strikingly different elastic functions. Geometric normalization of these responses (stress and strain) did not result in a single elastic function capable of describing both muscles. Based on these results, the quasi-linear model is recommended for the characterization of the structural responses of muscle; however, further investigation is required to determine the influence of muscle geometry and fiber architecture on the elastic function.

Identification of a threshold for skeletal muscle injury

This study was designed to detect the first evidence of injury to muscle induced by passive stretching. Rabbit extensor digitorum longus and tibialis anterior skeletal muscles were subjected to passive stretching at set force levels of 20% or 30% of load to failure. Both tibialis anterior and extensor digitorum longus muscles that were stretched to 30% exhibited no difference in the three tensile parameters when compared with their contralateral control specimens. Maximum contractile force was decreased after stretching. Tibialis anterior and extensor digitorum muscles that were stretched to 20% of control failure force showed no decrement in the tensile parameters or maximum contractile force. Histology of the extensor digitorum longus muscles stretched to 30% of failure force showed small focal areas of muscle fiber rupture and hemorrhage near the distal myotendinous junction. Tibialis anterior and extensor digitorum longus muscle-tendon units stretched to 30% of failure force suffered functional injury as their contractile ability decreased after stretching. In contrast, muscle-tendon units stretched to 20% of failure force suffered no decrement in contractile ability; therefore, a threshold for passive muscle stretch injury has been found. Furthermore, changes in contractile properties and histologic assessment appear to be more sensitive predictors of injury than measurement of structural failure properties.

Achilles tendon healing: a correlation between functional and mechanical performance in the rat

The pathogenesis and treatment of rupture of the Achilles tendon remain a source of controversy. This study presents the results of a biomechanical, functional, and morphological evaluation of a group of rats that had division and repair of the Achilles tendon. A total of 46 rats were used: 18 for biomechanical testing, 18 for functional evaluation, and 10 for histology. Morphological examination revealed an early inflammatory response with loose connective tissue formation that was replaced gradually by fibroblasts and a collagenous matrix. The functional evaluation (Achilles functional index [AFI]) was made from measurements of the hind pawprints of walking rats. Division and repair of the Achilles tendon produced a significant functional impairment (mean [+/- SEM] AFI = -87 +/- 8; p < 0.001), which gradually improved with healing time. The load to failure for the repaired tendons consistently improved with healing time, in a manner similar to the functional recovery. The average deformation (repair/control) varied considerably and was not related to healing time. The stiffness of the repaired tendons increased with healing time and was 60% of the corresponding control side by day 15. The major finding of this study was a strong correlation between the AFI and the failure load of the healing tendon-bone constructs (250-300 g group, r = 0.97, p < 0.001; 325-375 g group, r = 0.96, p < 0.001).

Achilles tendon injuries: a comparison of surgical repair versus no repair in a rat model

Controversy exists regarding the treatment of Achilles tendon ruptures. The aim of this study was to determine whether surgical repair of the rat Achilles tendon offered any biomechanical, functional, or morphological advantage over no repair. Thirty-two male Sprague-Dawley rats were randomly allocated into four groups: (1) sham operated (skin incision only), (2) no repair (complete division of the Achilles tendon and plantaris tendon without repair), (3) internal splint (plantaris left intact), and (4) Achilles repair (with a modified Kessler-type suture). Functional performance was determined from the measurements of hindpaw prints utilizing the Achilles Functional Index. On day 15, the animals were killed, and biochemical and histological evaluations were performed on both the injured and uninjured Achilles tendon constructs. All groups subjected to Achilles tendon division had a significant initial functional impairment that gradually improved so that by day 15 there were no functional or failure load impairments in any group. The injured tendons in all three groups subjected to Achilles tendon division had a 13-fold increase in the cross-sectional area and were less stiff and more deformable than uninjured and sham-operated tendons on day 15 (P < .001). The magnitude of the biomechanical and morphological changes at postoperative day 15 and the initial impairment and rate of functional recovery were similar for no repair, internal splint, and Achilles repair groups. In summary, this study demonstrates that surgical repair of the Achilles tendon in the rat does not offer any advantage over nonoperative management.

Thermal effects on skeletal muscle tensile behavior

The effect of temperature on the mechanical failure properties of rabbit skeletal muscle (tibialis anterior and extensor digitorum longus) was examined. For all tests, one leg was maintained at 25 degrees C and the contralateral leg at 40 degrees C. Muscles were pulled to failure according to assignment into one of three groups: 1) passive failure at 10 cm/sec, 2) passive failure at 1 cm/sec, or 3) active (muscle is stimulated to contract as it is pulled) failure at 10 cm/sec. Load to failure was higher in the cold muscle for all groups tested. Total deformation was the same except in Group 1, when the warm muscle had a greater deformation. Energy absorbed before failure was greater in the cold muscle in Groups 2 and 3. Stiffness was higher in cold muscles for all muscles except the extensor digitorum longus in Group 1. In this study, temperature had a significant effect on the tensile properties; these thermal effects were dependent on both loading rate and contractile state. Comparing loading rates, warm muscle tested at 10 cm/sec had higher failure loads than that tested at 1 cm/sec. Comparing stimulated versus unstimulated muscle (Group 1 versus Group 3), the stimulated tibialis anterior muscle absorbed more energy than unstimulated ones. Stimulated extensor digitorum longus muscles had higher failure loads, absorbed more energy, and were stiffer than nonstimulated muscles. This study offers experimental data to support the theory that warming muscles can aid in injury prevention and improvement in athletic performance.

Restriction of the injury response following an acute muscle strain

Indirect skeletal muscle injuries have been found to occur exclusively near the myotendinous junction (MTJ). Although muscle cells are syncytial and extend far into the muscle belly, the response to this injury has been shown to be limited to a focal area near the MTJ. This study examined single muscle fibers near their site of rupture in order to document structural changes that may help to explain this limited injury response. A partial, nondisruptive strain injury was created in a New Zealand white rabbit extensor digitorum longus muscle. The muscles were left in vivo for 60 min or 6 h before harvesting. The specimens were divided into four groups of single fibers: ruptured fibers (60 min) attached to muscle belly (group I); ruptured fibers (60 min) attached to tendon (group II); ruptured fibers (6 h) attached to muscle belly (group III); and normal, unstretched fibers (60 min) at the MTJ (group IV) (N = 10 for each group). Sarcomeres closest to the site of fiber rupture in the three injured groups (I, II, and III) were hypercontracted, with lengths well below the physiologic range (I: 0.86 +/- 0.08 microns, II: 0.96 +/- 0.09 microns, III: 0.96 +/- 0.21 microns). There was a progressive increase in sarcomere length, which became normal by 300-500 microns away from the site of rupture (I: 2.17 +/- 0.48 microns, II: 2.69 +/- 0.42 microns, III: 2.08 +/- 0.48 microns). The 6-h fibers in group III showed evidence of necrosis before the transition to normal sarcomere spacing occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

The Achilles Functional Index

The literature regarding the management of spontaneous rupture of the Achilles tendon is controversial and confusing. The relative infrequency of the condition in any one center prohibits the completion of well-designed clinical studies. Many of the disputes could be addressed and innovations tested if an appropriate animal model were available. We present a method for evaluating Achilles tendon function from measurements of the prints, preserved in bromphenol-blue-impregnated photocopying paper, of the hindfeet of walking rats. The stimulus for this study was derived from de Medinaceli's method for assessing the functional condition of rat sciatic nerves (de Medinaceli L, Freed WJ, Wyatt RJ: An index of the functional condition of rat sciatic nerve based on measurements made from walking tracks. Exp Neurol 77:634-643, 1982). Four variables were measured from these walking tracks, and comparisons between the damaged (experimental) and intact (normal) side were converted to proportional deficits. The relative contribution of each parameter to the overall deficit was determined by multiple linear regression analysis, and the variables were weighted accordingly to obtain an "Achilles Functional Index" (AFI). A sham operation produced no functional deficit, whereas animals subjected to a 0.5-cm midsubstance Achilles tendon defect demonstrated a markedly impaired AFI. Animals with repaired transected Achilles tendons also demonstrated a significant, but less severely impaired AFI. The functional deficit in this repair group returned to control values by postoperative day 15, whereas animals with a defect remained impaired at day 15. Furthermore, an excellent correlation was found between the functional recovery and biomechanical properties (ultimate failure load) of the healing tendon (r = 0.94; p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Posterior cruciate ligament reconstruction by transfer of the medial gastrocnemius tendon

A retrospective study to determine the efficacy of medial gastrocnemius tendon transfer for symptomatic PCL instability is presented. Results from a group of 31 patients undergoing this procedure were compared with a group of 8 patients managed conservatively while awaiting surgery. The mean injury to follow-up interval was 82 months in the operated group and 104 months in the nonoperated group. The mean surgery to follow-up interval was 53 months. Sixty-nine percent of surgical patients were subjectively improved; however, 29 (91%) continued to have pain and 19 (59%) continued to experience giving way. Thirteen patients from the operated group who had associated procedures performed were significantly better subjectively than those with no associated procedures (P less than 0.05). Physical examination demonstrated no difference in clinical laxity between the operated and nonoperated groups. Medial gastrocnemius transfer did not result in any significant reduction in anterior-posterior translation (KT-1000 assessment) when reconstructed knees were compared with control posterior cruciate deficient knees. Surgery, combined with subsequent immobilization, may have also been responsible for the significant reduction in lower limb function observed in the reconstructed patients. We do not recommend this procedure as a primary PCL reconstruction.