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This study was designed to observe the effect of the nonsteroidal antiinflammatory piroxicam on a controlled muscle strain injury in the rabbit model. The tibialis an terior tendons of 90 New Zealand White rabbits were detached at their distal insertions, and the right tendon was stretched to the yield point of the deformation curve. One group of 50 rabbits received piroxicam treat ment and the others received no treatment. At 1, 2, 4, and 7 days the parameters of muscle function, tensile strength, and histology were examined. Muscle con tractile force was significantly greater in the piroxicam- treated group at Day 1, but no difference was noted at any other time period. Tensile strength was not signifi cantly different at any time period in either group. His tology revealed delayed degradation of damaged tissue and slowed regeneration of muscle tissue at the injury site in the piroxicam-treated group.Piroxicam and other antiinflammatories are fre quently given to athletes being treated for muscle strain injuries to control pain through their effect on the in flammatory process. This study demonstrates that pi roxicam does not adversely influence the recovery of contractile and tensile strength in a followup period of 1 week. Therefore, antiinflammatory treatment may be beneficial early in the course of muscle injury.

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 biomechanical 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.

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°C and the contralateral leg at 40°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 de pendent 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 unstimu lated ones. Stimulated extensor digitorum longus mus cles 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 im provement in athletic performance.

Pentoxifylline improves microvascular blood flow in conditions of vascular insufficiency. The clinical benefits of pentoxifylline have been attributed to its effects on the cellular elements of whole blood, although a few studies suggest it may also be a vasodilator. The purpose of this study was to determine whether pentoxifylline has a vasodilator effect on the luminal diameter of small arteries preconstricted with norepinephrine and on resting small arteries in the rat cre master muscle.Intravital videomicroscopy was used in order to observe directly the vasodi lator capacity of topically applied pentoxifylline. The results reveal that pentox ifylline (100 μM and more) can significantly dilate small arteries preconstricted with norepinephrine. Pentoxifylline had no effect on the diameter of resting small arteries.These results suggest that vasodilation may play a role in the ability of pen toxifylline to improve arterial blood flow.

This study is an attempt to provide biomechanical sup port for the athletic practice of warming up prior to an exercise task to reduce the incidence of injury. Tears in isometrically preconditioned (stimulated before stretching) muscle were compared to tears in control (nonstimulated) muscle by examining four parameters: 1) force and 2) change of length required to tear the muscle, 3) site of failure, and 4) length-tension defor mation. The tibialis anterior (TA), the extensor digitorum longus (EDL), and flexor digitorum longus (EDL) mus cles from both hindlimbs of rabbits comprised our ex perimental model. Isometrically preconditioned TA (P < 0.001), EDL (P < 0.005), and FDL (P < 0.01) muscles required more force to fail than their contralateral controls. Precondi tioned TA (P < 0.05), EDL (P < 0.001), and FDL (P < 0.01) muscles also stretched to a greater length from rest before failing than their nonpreconditioned con trols. The site of failure in all of the muscles was the musculotendinous junction; thus, the site of failure was not altered by condition. The length-tension deforma tion curves for all three muscle types showed that in every case the preconditioned muscles attained a lesser force at each given increase in length before failure, showing a relative increase in elasticity, although only the EDL showed a statistically significant differ ence. From our data, it may be inferred that physiologic warming (isometric preconditioning) is of benefit in pre venting muscular injury by increasing the and length to failure and elasticity of the muscle-tendon unit.

In recent years much effort has been devoted to finding a satisfactory replacement for the injured ACL. None of the reconstruction techniques used in the past can be considered ideal because of their inability to dupli cate the complex geometry, structure, and function of the ligament. Current advances in allograft transplan tation and cryopreservation have led us to design and implement an experimental model for testing the feasi bility of cryopreserved ACL allotransplantation. Groups of dogs were used to evaluate the effect of cryopreservation on ligament strength and to compare the relative performance of both autograft and allograft ACL transplants up to 18 months after implantation. The ligaments were examined mechanically, histologi cally, and microangiographically. The cryopreservation process and duration of stor age had no effect on the biomechanical or structural properties of the ligament. The mechanical integrity of the allografts was similar to that of the autografts, with both achieving nearly 90% of control ligament strength by 36 weeks. Revascularization approached normal by 24 weeks in both autograft and allograft. No evidence of structural degradation or immunological reaction was seen. Based on these results, we believe that a cryopre served ACL allograft can provide the ideal material for ACL reconstruction. We have outlined a surgical tech nique for harvesting and implanting this graft clinically.

We compared the biomechanical properties of passive and stimulated muscle rapidly lengthened to failure in an experimental animal model. The mechanical param eters compared were force to tear, change in length to tear, site of failure, and energy absorbed by the muscle- tendon unit before failure. Paired comparisons were made between 1) muscles stimulated at 64 Hz (tetanic stimulation) and passive (no stimulation) muscles, 2) muscles stimulated at 16 Hz (wave-summated stimu lation) and passive muscles, and 3) muscles stimulated at 64 Hz and at 16 Hz.Both tetanically stimulated and wave-summation con tracted muscles required a greater force to tear (at 64 Hz, 12.86 N more, P < 0.0004; and at 16 Hz, 17.79 N more, P < 0.003) than their nonstimulated controls, while there was no statistical difference in failure force between muscles stimulated at 16 Hz and 64 Hz. The energy absorbed was statistically greater for the stim ulated muscles than for the passive muscles in Groups 1 and 2 (at 64 Hz, 100% more, P < 0.0003; and 16 Hz, 88% more, P < 0.0002). In Group 3, the tetanically contracted muscle-tendon units absorbed 18% more energy than the wave-summated stimulated muscles (P < 0.01). All muscles tore at the distal musculotendi nous junction, and there was no difference in the length increase at tear between muscles in each group. These findings may lead to enhanced understanding of the mechanism and physiology of muscle strain injuries.