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Biomedical subjects

P A Renstrom

Publications and source records attributed to P A Renstrom.

11 recordsLinked to original sources
PubMed2006

Calcitonin gene related peptide and neuropeptide Y in skeletal muscle after eccentric exercise: a microdialysis study.

OBJECTIVES: To detect neuropeptides in human skeletal muscle at rest and after eccentric exercise. METHOD: Eight healthy subjects participated in the study. Microdialysis of the distal part of the vastus lateralis of the quadriceps muscle and pain evaluation were performed immediately after eccentric exercise, after two days, and at rest. Calcitonin gene related peptide (CGRP) and neuropeptide Y (NPY), representatives of the sensory and autonomic nervous system, were analysed by radioimmunoassay. RESULTS: Overall, the measured concentrations were low, some even below the limit of detection. At rest, CGRP was detected in two of seven samples, but after eccentric exercise it was detected in 27 of 30 samples. At rest, all NPY concentrations were below the limit of detection, but after exercise it was found in six of 30 samples. CONCLUSION: The significant increase in detectability of CGRP after eccentric exercise may be related to the increased experience of pain. Therefore the occurrence of CGRP after heavy eccentric exercise may be associated with the regulation of delayed onset muscle soreness and possibly also the stimulation of tissue regeneration.

Adult↗
PubMed2001

The effect of weightbearing and external loading on anterior cruciate ligament strain.

A force balance between the ligaments, articular contact, muscles and body weight maintains knee joint stability. Thus, it is important to study anterior cruciate ligament (ACL) biomechanics, in vivo, under weightbearing conditions. Our objective was to compare the ACL strain response under weightbearing and non-weightbearing conditions and in combination with three externally applied loadings: (1) anterior-posterior shear forces, (2) internal-external torques, and (3) varus-valgus moments. A strain transducer was implanted on the ACL of 11 subjects. All joint loadings were performed with the knee at 20 degrees of flexion. A significant increase in ACL strain was observed as the knee made the transition from non-weightbearing to weightbearing. During anterior shear loading, the strain values produced during weightbearing were greater than those of the non-weightbearing knee (shear loads <40N). At higher shear loads, the strain values became equal. During axial torsion, an internal torque of 10Nm strained the ACL when the knee was non-weightbearing while an equivalent external torque did not. Weightbearing significantly increased ACL strain values in comparison to non-weightbearing with the application of external torques and low internal torques (<3Nm). The strains became equal for higher internal torques. For V-V loading, the ACL was not strained in the non-weightbearing knee. However, weightbearing increased the ACL strain values over the range of moments tested. These data have important clinical ramifications in the development of rehabilitation protocols following ACL reconstruction since weightbearing has been previously thought to provide a protective mechanism to the healing graft.

Adult↗
PubMed2001

The gastrocnemius muscle is an antagonist of the anterior cruciate ligament.

Since the proximal tendon of the gastrocnemius muscle wraps around the posterior aspect of the tibia, its contraction could potentially strain the anterior cruciate ligament (ACL) by pushing the tibia anteriorly. However, the relationship between contraction of the gastrocnemius muscle and ACL strain has not been studied in vivo. The objectives of this study were to evaluate the ACL strain response due to isolated contractions of the gastrocnemius muscle and to determine how these strains are affected by cocontraction with the hamstrings and quadriceps muscles. Six subjects with normal ACLs participated in the study; they underwent spinal anesthesia to ensure that their leg musculature was relaxed. Transcutaneous electrical muscle stimulation (TEMS) was used to induce contractions of the gastrocnemius, quadriceps and hamstrings muscles while the strains in the anteromedial bundle of the ACL were measured using a differential variable reluctance transducer. The ACL strain values produced by contraction of the gastrocnemius muscle were dependent on the magnitude of the ankle torque and knee flexion angle. Strains of 2.8% and 3.5% were produced at 5 degrees and 15 degrees of knee flexion, respectively. The ACL was not strained at 30 degrees and 45 degrees. Changes in ankle angle did not significantly affect these strain values. Co-contraction of the gastrocnemius and quadriceps muscles produced ACL strain values that were greater than those produced by isolated activation of either muscle group when the knee was at 15 degrees and 30 degrees. Co-contraction of the gastrocnemius and hamstrings muscles produced strains that were higher than those produced by the isolated contraction of the hamstrings muscles. At 15 degrees and 30 degrees of knee flexion. the co-contraction strain values were less than those produced by stimulation of the gastrocnemius muscle alone. This study verified that the gastrocnemius muscle is an antagonist of the ACL. Since the gastrocnemius is a flexor of the knee, this finding may have important clinical ramifications in ACL rehabilitation since flexor torques are generally thought to be protective of a healing ACL graft.

Adult↗
PubMed1999

The strain behavior of the anterior cruciate ligament during stair climbing: an in vivo study.

Stair climbing is a closed kinetic chain exercise that is thought to be useful for knee rehabilitation following anterior cruciate ligament (ACL) reconstruction while protecting the graft from excessive strain. The objectives of this study were to measure the strain produced in the anteromedial band (AMB) of the normal ACL during stair climbing in vivo. We have previously shown that the normal AMB strain pattern during knee passive flexion-extension motion is similar to that of an ACL graft immediately after graft fixation. We successfully tested five subjects with normal ACLs, who were candidates for arthroscopic meniscectomy under local anesthesia. AMB strain was measured in vivo using the Differential Variable Reluctance Transducer (MicroStrain, Burlington, VT). The stair climbing activities were performed on a StairMaster 4000PT (Randall Sports Medicine, Kirkland, WA). Two different climbing cadences were evaluated; 80 and 112 steps per minute. Consistent with our previous studies of ACL biomechanics, strain values increased as the knee was moved from a flexed to an extended position. The mean peak AMB strain values for the 80 and 112 steps per minute conditions were 2.69% (+/-2.89&) and 2.76% (+/-2.68%), respectively. These values were not significantly different. Compared with other rehabilitation activities previously tested in the same manner, the AMB strain values produced during stair climbing were highly variable across subjects. High strain values were observed in some patients but not in others.

Anterior Cruciate Ligament↗
PubMed1991

Chronic lateral ankle instability.

Chronic lateral ankle instability may be present in as many as 10% to 30% of people suffering from acute lateral ankle ligament injuries. Ankle instability has been referred to as either functional instability or mechanical instability. Management options consist of either nonoperative or operative treatment, with the majority of the literature emphasizing operative management for chronic instability. Long-term studies assessing the different types of available operative repairs have now been published. This review article discusses chronic lateral ankle ligament instability from a functional, anatomical point of view. The indications for treatment, nonoperative and operative treatment, as well as the biomechanical information available regarding these methods of treatment are considered. The major emphasis of this review is discussion and analysis of the many different surgical treatment options. Following this review, we presently recommend anatomical repair to the bone of both the anterior talofibular ligament and the calcaneofibular ligament, together with imbrication of the ligaments. In patients with hypermobility, long-standing instability, or arthritis, reconstruction using the Chrisman-Snook technique is recommended.

Ankle Joint↗
PubMedDate not supplied

The benefit of a single-leg strength training program for the muscles around the untrained ankle.

Severe ankle injuries can require extended periods of immobilization that adversely affect the strength of the ankle muscles. We have investigated a single-leg strength training program of the muscles surrounding the ankle to determine if it produces a crossover benefit for the contralateral ankle muscles. Twenty subjects without any history of ankle injuries were randomly divided into a control and a training group. Both groups underwent isokinetic testing of the ankle muscles at the beginning and end of an 8-week period. The control group maintained normal activities between the tests. Half of the training group trained the dominant leg only and the other half trained the nondominant leg only for the 8-week period, three times per week. The subjects who trained the dominant leg improved peak torque values by 8.5% in the trained leg and 1.5% in the untrained leg. Similarly, the subjects who trained the nondominant leg improved peak torque values by 9.3% in the trained leg and 3.5% in the untrained leg. In contrast, the control group showed no significant change in peak torque, power, or endurance between the initial and final tests. With improvements in peak torque as high as 40% in the trained leg and a crossover benefit of 19% in the untrained leg in eccentric inversion, this strength training technique deserves further investigation in an injured population where the benefits may be more substantial.

Adolescent↗
PubMedDate not supplied

The influence of functional knee bracing on the anterior cruciate ligament strain biomechanics in weightbearing and nonweightbearing knees.

Functional knee braces are commonly prescribed after anterior cruciate ligament injury or reconstruction; however, their ability to protect the ligament, or graft, remains unclear. Our objective was to evaluate the anterior cruciate ligament strain response in braced and unbraced knees during weightbearing and nonweightbearing in combination with three externally applied loads: 1) anterior-posterior shear forces, 2) internal-external torques, and 3) varus-valgus moments. The Legend brace was tested. All external loads were applied to the tibia with the knee flexed to 20 degrees. Reproducible data were obtained from 11 subjects. For anterior shear loads up to 130 N, the brace significantly reduced strain values compared with the unbraced knee during nonweightbearing and weightbearing conditions. For internal torques of the tibia (up to 9 N x m), strain in the braced knee was significantly less than in the unbraced knee when the knee was nonweightbearing only. The brace did not reduce strain values when the knee was subjected to external torques (9 N x m) or varus-valgus moments (10 N x m) in weightbearing and nonweightbearing knees. These data indicate that a functional knee brace can protect the anterior cruciate ligament during anterior-posterior shear loading in the nonweightbearing and weightbearing knee and during internal torques in the nonweightbearing knee.

Adult↗
PubMedDate not supplied

Electromyographic latency changes in the ankle musculature during inversion moments.

Ten uninjured subjects (ages 18 to 30 years) had electromyographic testing of the peroneus longus, peroneus brevis, and tibialis anterior muscles in response to inversion moments at two speeds (50 and 200 deg/sec) and two joint angles (neutral and 20 degrees of plantar flexion) using a hydraulically controlled tilt platform. Subjects underwent 10 trials of each type of inversion moment on Day 1 testing, which included both legs. On Day 2, subjects again underwent 10 trials of each type of inversion moment, but only on one leg. Reliability was assessed by comparing left and right leg data within muscle groups for Day 1 testing. Repeatability was assessed by comparing Day 1 with Day 2 data. The latency measurements (the time between the beginning of the inversion moment and the onset of first motor response) for the peroneus brevis and tibialis anterior muscles were found to be reliable and repeatable with no significant differences between the same muscle groups. The peroneus longus muscle had a significant difference between legs but was found to be highly repeatable. Speed of inversion moment and plantar flexion angle both caused significant changes in latency response of the peroneus muscles, with increased speed producing a shorter latency response and increased angle causing a longer latency response. Our results indicate a loss of protective reflexes with increasing plantar flexion.

Adolescent↗
PubMedDate not supplied

The effect of functional knee bracing on the anterior cruciate ligament in the weightbearing and nonweightbearing knee.

We investigated the effect of functional bracing on anterior cruciate ligament strain in humans by arthroscopic implantation of a differential variable reluctance transducer on the ligament and measurement of its strain behavior. Strains were measured while "injury mechanism" loads were applied to the weightbearing and nonweightbearing knees for both braced and unbraced conditions. For the unbraced knee, there was a significant increase in ligament strain values when subjects went from a seated position (minimal shear and compressive loads across the knee) to a standing posture (substantial shear and compressive loads across the knee). Similar strain values were found between these same seated and standing postures when a 140-N anterior-directed load was applied to the tibia. This indicates that the ligament is strained during weightbearing and demonstrates that the compressive load across the knee produced during weightbearing does not significantly reduce ligament strain values in comparison with the unweighted joint with relaxed muscles for the 140-N load limit of our anterior shear test. Bracing produced a protective effect on the ligament by significantly reducing the strain values for anterior-directed loading of the tibia up to 140 N with the knee in both weightbearing and nonweightbearing conditions. Likewise, bracing produced a protective effect on the ligament by significantly reducing strain values in response to internal-external torque of the tibia up to 6 N-m with the knee nonweightbearing. The brace strap that contacts the tibia just distal to the insertion of the patellar tendon was instrumented with a load sensor, allowing us to measure the posterior-directed loads applied by the brace to the tibia. Adjustment of strap tension between low and high settings did not modulate the protective effect of the brace on the ligament.

Adult↗
PubMedDate not supplied

The strain behavior of the anterior cruciate ligament during bicycling. An in vivo study.

Stationary bicycling is commonly prescribed after anterior cruciate ligament injury or reconstruction; however, the strains on the ligament or ligament graft during stationary bicycling remain unknown. In this study we measured ligament strain on eight patients who were candidates for arthroscopic meniscectomy under local anesthesia. Six different riding conditions were evaluated: three power levels (75, 125, and 175 W), each of which was performed at two cadences (60 and 90 rpm). The peak ligament strain values ranged from 1.2% for the 175-W, 90-rpm, condition to 2.1% for the 125-W, 60-rpm, condition. No significant differences were found in peak strain values due to changes in power level or cadence. Thus, the strain values were pooled across the six riding conditions tested. The mean peak strain value was 1.7%, a value that is relatively low compared with other rehabilitation activities previously tested. These data suggest that knee rehabilitation programs can be designed to include this selection of power and cadence levels without significantly changing ligament strain values. Thus, stationary bicycling is a rehabilitation exercise that permits the patient to increase muscle activity by increasing the power level or decreasing the cadence without subjecting the ligament or ligament graft to higher strain values.

Adult↗