Deficit in human muscle strength with cast immobilization: contribution of inorganic phosphate

Sensitivity to change and responsiveness of the Segmental Assessment of Trunk Control (SATCo) in children with spinal cord injury

PURPOSE

The purpose of this study was to assess the sensitivity and responsiveness of the Segmental Assessment of Trunk Control (SATCo) for evaluating trunk control in children with spinal cord injury (SCI) receiving activity-based locomotor training (AB-LT).

METHODS

Prospective study of nine outcomes for consecutively enrolled children in outpatient AB-LT. To evaluate sensitivity to change, linear-mixed models were constructed and adjusted for covariates: age at and time since SCI. To evaluate responsiveness, standardized response means and 95% confidence intervals were estimated per outcome.

RESULTS

SATCo scores increased significantly (p < 0.05) regardless of chronicity, initial score, and injury level. The SATCo was the most responsive measure and the only outcome demonstrating a large effect size after 3 months of therapy.

CONCLUSIONS

Children with SCI receiving AB-LT improved trunk control regardless of chronicity, initial impairment, or prior experience. SATCo sensitivity and responsiveness support its usefulness in measuring trunk control in children with SCI.

Effects of immobilization and whole-body vibration on rat serum Type I collagen turnover

Objective

The aim of this study was to investigate the effects of short-term, high-magnitude whole-body vibration (WBV) on serum type I collagen turnover in immobilized rats.

Materials and Methods

Thirty Wistar albino rats were randomly divided into the following 5 groups: immobilization (IS), immobilization + remobilization (IR), immobilization + WBV (IV), control (C), and WBV control (CV). Immobilization was achieved by casting from the crista iliaca anterior superior to the lower part of the foot for 2 weeks. The applied WBV protocol involved a frequency of 45 Hz and amplitude of 3 mm for 7 days starting a day after the end of the immobilization period. Serum type I collagen turnover markers were measured by using ELISA kits.

Results

Serum NH2-terminal propeptide of type I collagen (PINP) levels were significantly lower in the immobilization groups (p < 0.02) compared with the control groups. Although WBV improved PINP levels in the control groups, there were no differences in PINP levels among the immobilization groups. Similarly, serum COOH-terminal telopeptide of type I collagen (CTX) levels were higher in the WBV controls than their own controls (p < 0,05). Immobilization led to deterioration of tendon tissue, as observed by histopathological analysis with a transmission electron microscope.

Conclusion

Although 1 week of WBV had a positive effect on type I collagen turnover in controls, it is not an efficient method for repairing tissue damage in the early stage following immobilization.

In vivo (31)P NMR spectroscopy assessment of skeletal muscle bioenergetics after spinal cord contusion in rats

PURPOSE

Muscle paralysis after spinal cord injury leads to muscle atrophy, enhanced muscle fatigue, and increased energy demands for functional activities. Phosphorus magnetic resonance spectroscopy ((31)P-MRS) offers a unique non-invasive alternative of measuring energy metabolism in skeletal muscle and is especially suitable for longitudinal investigations. We determined the impact of spinal cord contusion on in vivo muscle bioenergetics of the rat hind limb muscle using (31)P-MRS.

METHODS

A moderate spinal cord contusion injury (cSCI) was induced at the T8-T10 thoracic spinal segments. (31)P-MRS measurements were performed weekly in the rat hind limb muscles for 3 weeks. Spectra were acquired in a Bruker 11 T/470 MHz spectrometer using a 31P surface coil. The sciatic nerve was electrically stimulated by subcutaneous needle electrodes. Spectra were acquired at rest (5 min), during stimulation (6 min), and recovery (20 min). Phosphocreatine (PCr) depletion rates and the pseudo first-order rate constant for PCr recovery (k PCr) were determined. The maximal rate of PCr resynthesis, the in vivo maximum oxidative capacity (V max) and oxidative adenosine triphosphate (ATP) synthesis rate (Q max) were subsequently calculated.

RESULTS

One week after cSCI, there was a decline in the resting total creatine of the paralyzed muscle. There was a significant reduction (~24 %) in k PCr measures of the paralyzed muscle, maximum in vivo mitochondrial capacity (V max) and the maximum oxidative ATP synthesis rate (Q max) at 1 week post-cSCI. During exercise, the PCr depletion rates in the paralyzed muscle one week after injury were rapid and to a greater extent than in a healthy muscle.

CONCLUSIONS

Using in vivo MRS assessments, we reveal an acute oxidative metabolic defect in the paralyzed hind limb muscle. These altered muscle bioenergetics might contribute to the host of motor dysfunctions seen after cSCI.

Magnetic resonance imaging: the underlying principles

The creation of a magnetic resonance image (MRI) and its inherent contrast are controlled by a variety of anatomical structure- and sequence-dependent parameters. While these may seem confusing to the uninitiated, they provide MRI with great flexibility and make it a powerful clinical tool. This article describes the principles of basic physics behind magnetic resonance spectroscopy (MRS) and imaging, including a basic description of the properties of magnetic resonance compatible nuclei, how a radiofrequency (RF) pulse produces a signal, and how this signal can be spatially encoded to produce an image. The relaxation properties of the MRI signal depend on biological tissue type and can provide information on tissue composition, environment, and pathological changes. The contrast properties within an image can be manipulated based on the relaxation properties of the anatomical sample and the nature of the imaging sequence. The benefits of T1- and T2-weighted images in musculoskeletal imaging and the common sequences used (including turbo spin echo [TSE], fat suppression sequences such as STIR, and rapid breath-hold sequences such as HASTE and FISP) are discussed. The principles behind contrast agents and diffusion-weighted imaging and how they can be applied in the body are considered.

Removal of a below knee plaster cast worn for 28 months: a case report

Introduction

An unusual situation in which a below knee cast was removed after 28 months is reported. To the best of our knowledge no similar cases have been reported in the literature.

Case presentation

The cast was removed from the leg of a 45-year-old Caucasian woman. Significant muscle atrophy and dense skin scales were present but the underlying skin surface was relatively healthy with only small pitted 1-2 mm ulcers. No pathogenic organisms were cultured from this environment.

Conclusion

It seems likely that skin can tolerate cast immobilization for prolonged duration.

Desequilíbrios musculares entre flexores dorsais e plantares do tornozelo após tratamento conservador e acelerado da ruptura do tendão calcâneo

A ruptura do tendão calcâneo (TC) reduz a sobrecarga mecânica dos flexores plantares (FP) do tornozelo. Essa alteração muda o equilíbrio natural entre os FP e flexores dorsais (FD) do tornozelo. O objetivo do estudo foi avaliar as razões isocinéticas concêntricas convencionais de torque de pacientes submetidos a tratamento cirúrgico de ruptura aguda do TC após dois protocolos diferentes de reabilitação. Após procedimento cirúrgico para reconstrução do TC, a amostra foi dividida de forma intencional em dois grupos: conservador (GC, 11 homens, 41,3±7,9 anos) e grupo acelerado (GA, 13 homens, 43,5±13,7 anos). O GC permaneceu com imobilização gessada no tornozelo por seis semanas (tratamento tradicional), enquanto o GA usou uma órtese robofoot em posição neutra e, após duas semanas, iniciou mobilização e apoio precoce do tornozelo, com reabilitação por seis semanas. Após 3 meses de pós-operatório, a razão do torque concêntrico máximo dos FD pelos FP do tornozelo foi avaliada por dinamômetro isocinético. As razões de torque do lado operado se mantiveram superiores às do lado saudável mesmo após 3 meses de pós-operatório (p<0,05). Não foi encontrada diferença no equilíbrio muscular entre os grupos. Pode-se concluir que os dois grupos requerem um período mais longo de reabilitação para recuperar o equilíbrio natural do tornozelo no lado operado.

The influence of training status on the drop in muscle strength after acute exercise

Skeletal muscles fatigue after exercise, and reductions in maximal force appear. A difference in training status between the legs was introduced by unilateral immobilization of the calf muscles for 2 weeks in young men, who were randomly assigned to two groups, either a RUN group (n = 8) that was exposed to prolonged exercise (1-h running: individual pace) or a REST group (n = 12) that did no exercise after immobilization. Cross-sectional area (CSA) of the triceps-surae muscles was calculated by magnetic resonance imaging (MRI), and maximal voluntary contraction (MVC) force of the plantar flexors was measured before and after immobilization and after the running protocol. The CSA of triceps-surae muscles decreased significantly with a 7% reduction in both groups. A significant drop in the MVC of the triceps-surae muscle (10%; P < 0.05) was observed in response to immobilization. When subjected to running exercise immediately after immobilization, the muscle strength of the triceps-surae muscles dropped even further, but just in the immobilized leg (41%; P < 0.05). The present study highlights the importance of determining the muscle endurance when evaluating the effect of immobilization on muscle parameters.

Short-term immobilization and recovery affect skeletal muscle but not collagen tissue turnover in humans

Not much is known about the effects of immobilization and subsequent recovery on tendon connective tissue. In the present study, healthy young men had their nondominant leg immobilized for a 2-wk period, followed by a recovery period of the same length. Immobilization resulted in a mean decrease of 6% (5,413 to 5,077 mm(2)) in cross-sectional area (CSA) of the triceps surae muscles and a mean decrease of 9% (261 to 238 N.m) in strength of the immobilized calf muscles. Two weeks of recovery resulted in a 6% increased in CSA (to 5,367 mm(2)), whereas strength remained suppressed (240 N.m). No difference in Achilles tendon CSA was detected between the two legs at any time point. Local tendon collagen synthesis, measured as the peritendinous concentrations of PINP (NH(2)-terminal propeptide of type I collagen; indirect marker for collagen synthesis), was unchanged after 2 wk of immobilization. However, peritendinous levels of PINP were significantly elevated in the immobilized leg (15 to 139 ng/ml) following 2 wk of remobilization compared with preimmobilization levels. In contradiction hereto, systemic concentrations of PINP remained unchanged throughout the study. Immobilization reduced muscle size and strength, while tendon size and collagen turnover were unchanged. While recovery resulted in an increase in muscle size, strength was unchanged. No significant difference in tendon size could be detected between the two legs after 2 wk of recovery, although collagen synthesis was increased in the previously immobilized leg. Thus 2 wk of immobilization are sufficient to induce significant changes in muscle tissue, whereas tendon tissue seems to be more resistant to short-term immobilization.

Effects of long-term immobilization and recovery on human triceps surae and collagen turnover in the Achilles tendon in patients with healing ankle fracture

The aim of the present study was to analyze how human tendon connective tissue responds to an approximately 7-wk period of immobilization and a remobilization period of a similar length, in patients with unilateral ankle fracture, which is currently unknown. Calf muscle cross-sectional area (CSA) decreased by 15% (5,316 to 4,517 mm2) and strength by 54% (239 to 110 N.m) in the immobilized leg after 7 wk. During the 7-wk remobilization, the CSA increased by 9% (to 4,943 mm2) and strength by 37% (to 176 Nm). Achilles tendon CSA did not change significantly during either immobilization or remobilization. Local collagen turnover was measured as the peritendinous concentrations of NH2-terminal propeptide of type I collagen (PINP) and COOH-terminal telopeptide region of type I collagen (ICTP), markers thought to be indexes of type I collagen synthesis and degradation, respectively. Both markers were increased (PINP: 257 vs. 56 ng/ml; ICTP: 9.8 vs. 2.1 microg/l) in the immobilized leg compared with the control leg after the 7 wk of immobilization, and levels decreased again in the immobilized leg during the recovery period (PINP: 103 vs. 44 ng/ml; ICTP: 4.2 vs. 1.9 microg/l). A significant reduction in calf muscle CSA and strength was found in relation to 7 wk of immobilization. Immobilization increased both collagen synthesis and degradation in tendon near tissue. However, it cannot be excluded that the facture of the ankle in close proximity could have affected these data. Remobilization increased muscle size and strength and tendon synthesis and degradation decreased to baseline levels. These dynamic changes in tendon connective tissue turnover were not associated with macroscopic changes in tendon size.

Alterations in inorganic phosphate in mouse hindlimb muscles during limb disuse

Muscle disuse induces a wide array of structural, biochemical, and neural adaptations in skeletal muscle, which can affect its function. We recently demonstrated in patients with an orthopedic injury that cast immobilization alters the resting P(i) content of skeletal muscle, which may contribute to loss of specific force. The goal of this study was to determine the direct effect of disuse on the basal phosphate content in skeletal muscle in an animal model, avoiding the confounding effects of injury/surgery. (31)P and (1)H MRS data were acquired from the gastrocnemius muscle of young adult mice (C57BL6 female, n = 8), at rest and during a reversible ischemia experiment, before and after 2 weeks of cast immobilization. Cast immobilization resulted in an increase in resting P(i) content (75%; p < 0.001) and the P(i) to phosphocreatine (PCr) ratio (P(i)/PCr; 80%, p < 0.001). The resting concentrations of ATP, PCr and total creatine (PCr + creatine) and the intracellular pH were not significantly different after immobilization. During ischemia (30 min), PCr concentrations decreased to 54 +/- 2% and 52 +/- 6% of the resting values in pre-immobilized and immobilized muscles, respectively, but there were no detectable differences in the rates of P(i) increase or PCr depletion (0.55 +/- 0.01 mM min(-1) and 0.52 +/- 0.03 mM min(-1) before and after immobilization, respectively; p = 0.78). At the end of ischemia, immobilized muscles had a twofold higher phosphorylation potential ([ADP][P(i)]/[ATP]) and intracellular buffering capacity (3.38 +/- 0.54 slykes vs 6.18 +/- 0.57 slykes). However, the rate of PCr resynthesis (k(PCr)) after ischemia, a measure of in vivo mitochondrial function, was significantly lower in the immobilized muscles (0.31 +/- 0.04 min(-1)) than in pre-immobilized muscles (0.43 +/- 0.04 min(-1)). In conclusion, our findings indicate that 2 weeks of cast immobilization, independent of injury-related alterations, leads to a significant increase in the resting P(i) content of mouse skeletal muscle. The increase in P(i) with muscle disuse has a significant effect on the cytosolic phosphorylation potential during transient ischemia and increases the intracellular buffering capacity of skeletal muscle.