Biomedical subjects

T M Best

Publications and source records attributed to T M Best.

33 records · Page 2Linked to original sources

PubMed1995

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.

Animals↗

PubMed1995

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.

Adolescent↗

PubMed1994

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.

Achilles Tendon↗

PubMed1994

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.

Animals↗

PubMed1993

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↗

PubMed1993

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.

Achilles Tendon↗

PubMed1993

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)

Animals↗

PubMed1992

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)

Achilles Tendon↗

PubMedDate not supplied

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.

Adolescent↗

PubMedDate not supplied

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.

Animals↗

PubMedDate not supplied

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.

Animals↗

PubMedDate not supplied

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.

Analysis of Variance↗

PubMedDate not supplied

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.

Athletic Injuries↗

PubMedDate not supplied

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.

Adolescent↗

PubMedDate not supplied

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.

Animals↗