Biomechanical comparison of stimulated and nonstimulated skeletal muscle pulled to failure.

We compared the biomechanical properties of passive and stimulated muscle rapidly lengthened to failure in an experimental animal model. The mechanical parameters 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 stimulation) and passive muscles, and 3) muscles stimulated at 64 Hz and at 16 Hz. Both tetanically stimulated and wave-summation contracted muscles required a greater force to tear (at 64 Hz, 12.86 N more, P less than 0.0004; and at 16 Hz, 17.79 N more, P less than 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 stimulated muscles than for the passive muscles in Groups 1 and 2 (at 64 Hz, 100% more, P less than 0.0003; and 16 Hz, 88% more, P less than 0.0002). In Group 3, the tetanically contracted muscle-tendon units absorbed 18% more energy than the wave-summated stimulated muscles (P less than 0.01). All muscles tore at the distal musculotendinous 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.

The role of warmup in muscular injury prevention.

This study is an attempt to provide biomechanical support 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 deformation. The tibialis anterior (TA), the extensor digitorum longus (EDL), and flexor digitorum longus (EDL) muscles from both hindlimbs of rabbits comprised our experimental model. Isometrically preconditioned TA (P less than 0.001), EDL (P less than 0.005), and FDL (P less than 0.01) muscles required more force to fail than their contralateral controls. Preconditioned TA (P less than 0.05), EDL (P less than 0.001), and FDL (P less than 0.01) muscles also stretched to a greater length from rest before failing than their nonpreconditioned controls. 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 deformation 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 difference. From our data, it may be inferred that physiologic warming (isometric preconditioning) is of benefit in preventing muscular injury by increasing the and length to failure and elasticity of the muscle-tendon unit.

The effect of muscle architecture on the biomechanical failure properties of skeletal muscle under passive extension.

This study investigates the biomechanical failure properties of five architecturally different skeletal muscles and examines the role muscle structure plays in the passive extension characteristics of musculotendinous units. The muscles used in this study fall into four morphologic categories: fusiform, unipennate, bipennate, and multipennate. Each muscle was pulled to failure at three different rates of strain (1, 10, and 100 cm/min). Specimens of fusiform, unipennate, and bipennate muscles were pulled from their proximal as well as distal attachments. The relationship of elongation to failure of the entire musculotendinous unit to resting muscle fiber length was examined to determine the effect of angle of pennation and fiber length on the failure properties. Our results demonstrate that all four muscle types tested show injury and rupture at the musculotendinous junction whether pulled from proximal or distal attachment, regardless of muscle structure and rate of strain. There was a statistically significant difference (P less than 0.005) in the degree of elongation to failure relative to resting muscle fiber length, with a tendency to greater elongation relative to fiber length for muscles with more pennate structure (tibialis anterior, 72.7% +/- 1.0%; extensor digitorum longus, 113.1% +/- 3.5%; rectus femoris, 225.5% +/- 3.7% elongation in percent resting fiber length).

Anterior cruciate ligament allograft transplantation. Long-term function, histology, revascularization, and operative technique.

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 duplicate the complex geometry, structure, and function of the ligament. Current advances in allograft transplantation and cryopreservation have led us to design and implement an experimental model for testing the feasibility 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, histologically, and microangiographically. The cryopreservation process and duration of storage 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 cryopreserved ACL allograft can provide the ideal material for ACL reconstruction. We have outlined a surgical technique for harvesting and implanting this graft clinically.

Biomechanical and histologic assessment of a controlled muscle strain injury treated with piroxicam.

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 anterior 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 treatment 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 contractile 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 significantly different at any time period in either group. Histology revealed delayed degradation of damaged tissue and slowed regeneration of muscle tissue at the injury site in the piroxicam-treated group. Piroxicam and other anti-inflammatories are frequently given to athletes being treated for muscle strain injuries to control pain through their effect on the inflammatory process. This study demonstrates that piroxicam 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.

Respiratory effects of spinal immobilization in children.

STUDY OBJECTIVE: To assess the restrictive effects of two spinal immobilization strapping techniques on the respiratory capacity of normal, healthy children. DESIGN: Prospective study with each subject serving as his own control. PARTICIPANTS: Fifty-one healthy children 6 to 15 years old. INTERVENTIONS: Participants' forced vital capacity (FVC) measurements were first obtained with children standing and lying supine and then in full spinal immobilization using two different strapping configurations, cross straps and lateral straps. Straps were tightened to allow one hand to fit snugly between the strap and child. MEASUREMENTS AND MAIN RESULTS: Supine FVC was less than upright FVC (P less than .001). FVC in spinal immobilization ranged from 41% to 96% of supine FVC (80 +/- 9%). There was no difference in FVCs between strapping techniques (P = .83). CONCLUSION: Spinal immobilization significantly reduced respiratory capacity as measured by FVC in healthy patients 6 to 15 years old. There is no significant benefit of one strapping technique over the other.

Injury surveillance: a method for recording E codes for injured emergency department patients.

STUDY PURPOSE: Little information exists on the cause of injury for patients who are treated and discharged from emergency departments; these patients comprise approximately 90% of all injured patients requiring medical care. A method is described to assign external cause of injury codes (E codes) prospectively to all injured patients seen in a large-volume ED. METHODS: E code assignment was performed by the ED triage nurses on entrance to the ED. A checklist was used that contained frequently occurring codes as identified in a pilot study. E codes were entered into the patients' records on the hospital mainframe computer by a medical records technician. These were acquired for a nine-month period to determine feasibility, accuracy, and ease of use. Accuracy was verified retrospectively. RESULTS: During the nine-month period, 67,495 patients were treated. Acute injury accounted for 16,186 of the visits, and 2,085 were return visits for a previously treated injury. The majority of patients with any injury type were treated and discharged and would not have been included in traditional data sets of injured patients. Overall admission rate for injury was 13%. Accuracy of prospectively assigned E codes was 98%, and this method of assigning E codes resulted in no additional effort by the triage nurse. CONCLUSION: E coding is a valuable method for injury surveillance, easily performed in EDs with high volume. Its value is essential for injury prevention research on injuries from any cause.

Immediate and delayed neurorrhaphy in a rabbit model: a functional, histologic, and biochemical comparison.

The effect of timing of neurorrhaphy on neuromuscular function was studied. The extensor digitorum longus neuromuscular units of 51 rabbits were used, with repairs performed immediately, 3 weeks, 3 months, and 6 months after nerve transection. Neuromuscular function was assessed 3 months after nerve repair, as was histology, histochemistry, and muscle hydroxyproline content. Force generated by immediately repaired units was 93% of unoperated controls. All functional delayed repairs produced approximately 50% of control force. Mild endomysial and perimysial fibrosis was present in the immediate neurorrhaphy group. Fibrosis was mild to moderate in the functional delayed repairs and moderate to severe in the nonfunctional repairs. Total and regional hydroxyproline content correlated to both function and timing of nerve repair. The data demonstrate that immediate repair of peripheral nerve lacerations gives the best functional recovery in this rabbit model. If immediate repairs are not performed in the rabbit, approximately 50% to 75% of normal function can be obtained when repairs are delayed for periods of 3 weeks to 6 months.