Forearm compartment pressures and grip strength in elite motorbike racers with chronic exertional compartment syndrome

Background Remarkably little research has been published on chronic exertional compartment syndrome (CECS) of the forearm. This study investigated forearm flexor compartment pressure pre- and post-exercise in elite motorbike racers clinically diagnosed with CECS and assessed their grip strength before and after arm pump exercise. Methods Elite motorbike riders with a clinical diagnosis of CECS of the right forearm when racing were recruited during the opening rounds of a British Superbike season. Their grip strength and forearm flexor compartment pressures were measured before and after a set exercise programme. Results Of the 11 riders recruited to the study, 10 completed the full testing regime. The mean pre-exercise forearm compartment pressures [11.7 mmHg (range 7–17 mmHg)] significantly increased post-exercise [30.5 mmHg (range 15–45 mmHg)], with a mean increase of 18.80 mmHg (P < 0.0001). The mean pre-exercise grip strength [50.61 mmHg (range 37–66.7 mmHg)] decreased post-exercise to [35.62 mmHg (range 17.1–52.5 mmHg)], a mean decrease of 14.99 mmHg (P < 0.0001). Conclusion There is a statistically significant increase in the forearm flexor compartment pressures in elite motorbike racers with CECS, but with marked variability of these values. Grip strength decreases statistically significantly following onset of symptoms of CECS of the forearm.

Biceps, Brachialis, and Triceps

Tendon injuries at the elbow affect mostly the distal biceps and can progressively degenerate over time or rupture in an acute event. The degree of retraction may depend on the integrity of the lacertus fibrosus, a fibrous expansion that merges with the forearm flexor fascia. Biceps disorders are frequently associated with fluid or synovitis of the adjacent bicipital bursa; primary bursal disorders (primary inflammatory synovitis) can also be observed. Distal triceps is less frequently injured than the distal biceps, and tears usually manifest as distal ruptures with avulsion of a small flake of bone from the tip of the olecranon. Brachialis injuries are uncommon and the consequence of sudden muscle stretching during forced elbow hyperextension, as in posterior elbow luxation.

Adolescent Pitcher Fatigue: Ulnar Collateral Ligament Stress, Flexor-Pronator Mass Energy Depletion, and Correlation to Pitch Count

Objectives: There has been a rise in elbow ulnar collateral ligament (UCL) injuries in youth pitchers over recent years. With forearm flexor-pronator mass fatigue, the dynamic stability provided could be diminished placing greater stress on the UCL. Pitch count limits have been instituted in an attempt to help curtail this rise in throwing injuries, especially in youth athletes. In order to provide more objective data regarding current pitch count limits for youth pitchers, the purpose of this pilot study was to evaluate for potential fatigue of the flexor-pronator mass by assessing changes in medial elbow laxity, noninvasively characterizing changes in muscle glycogen storage within the forearm flexor-pronator mass, and evaluating changes in subjective fatigue, strength, range of motion (ROM), pitching velocity, and accuracy with increasing number of pitches thrown by 10-year-old pitchers up to their recommended 75 pitch count limit. Methods: After appropriate power analysis, male pitchers 10 years of age were recruited for the study (n=22). Pitchers threw a total of 75 pitches divided into sets of 25 pitches, with standardized periods of rest in between throws and sets to best simulate a game. Bilateral medial elbow laxity was measured by applying 10 decanewtons of valgus force with a standardized stress device and utilizing ultrasound imaging (Figures 1A-B) prior to pitching and after each pitching set. The change in medial ulnohumeral joint distance (Figure 1C) after stress was applied was calculated from baseline without stress. Relative changes in muscle glycogen storage, detected as changes in echogenicity, within the flexor carpi radialis (FCR) and the flexor digitorum superficialis (FDS)/flexor carpi ulnaris (FCU) muscles were measured non-invasively with ultrasound-based software (Figures 1D-E) and recorded as fuel percentile. Repeated measures analysis of variance and post-hoc testing were used to determine statistical significance (alpha=0.05). Results: There were no significant differences in medial elbow laxity between arms or time points. There was a trend for similar decline in FCR fuel percentile values between each arm, indicating relative decreases in glycogen storage bilaterally. However, only the throwing arm demonstrated a statistically significant decline in fuel percentile from baseline to after 75 pitches (p=0.05). There were no statistically significant differences across time points for FDS/FCU fuel percentile values. Fatigue measurements for both arms were significantly higher at all time points compared to baseline (p≤0.03). Grip strength of the dominant arm after 75 pitches was significantly decreased compared to after 25 pitches (p=0.02). There were no statistically significant changes in other strength measurements, ROM, velocity, or accuracy between all time points. Conclusions: By the recommended 75 pitch count limit in 10-year-olds, subjective fatigue and a decrease in grip strength had occurred. Furthermore, relative glycogen storage of the flexor-pronator mass of the throwing arm decreased between pitching 50 to 75 pitches, but without an increase in medial elbow gapping. This study provides a foundation and raises questions for further objective testing of physiologic changes that occur throughout increasing pitching to better guide pitch count limits and ensure the safety of young athletes

A Re-evaluation of Whether Non-monosynaptic Homonymous H Reflex Facilitation Tests Propriospinal Circuits

The C3–C4 propriospinal system is an important pathway mediating movement in cats; it contributes to movements in primates (including humans), and may have a role in recovery after lesion. Validated clinical tests of this system would find many applications, therefore we sought to test whether non-monosynaptic homonymous facilitation of the forearm flexor H reflex is mediated solely via a C3–C4 propriospinal pathway. In one anesthetized macaque monkey, median nerve stimulation elicited an H reflex in the flexor carpi radialis (FCR). Median nerve conditioning stimuli at sub-threshold intensities facilitated the H reflex, for inter-stimulus intervals up to 30 ms. Successive spinal surgical hemisections were then made. C2 lesion left the homonymous facilitation intact, suggesting mediation by spinal, not supraspinal pathways. Facilitation also remained after a second lesion at C5, indicating a major role for segmental (C7–C8) rather than propriospinal (C3–C4) interneurons. In separate experiments in five healthy human subjects, a threshold tracking approach assessed changes in peripheral axon excitability after conditioning stimulation. This was found to be enhanced up to 20 ms after the conditioning stimulus, and could partly, although not completely, underlie the H reflex facilitation seen. We conclude that homonymous facilitation of the H reflex in FCR can be produced by segmental spinal mechanisms, as well as by a supranormal period of nerve excitability. Unfortunately, this straightforward test cannot therefore be used for selective assessment of propriospinal circuits.

Modulation of Muscle Pain Is Not Somatotopically Restricted: An Experimental Model Using Concurrent Hypertonic-Normal Saline Infusions in Humans

We have previously shown that during muscle pain induced by infusion of hypertonic saline (HS), concurrent application of vibration and gentle brushing to overlying and adjacent skin regions increases the overall pain. In the current study, we focused on muscle-muscle interactions and tested whether HS-induced muscle pain can be modulated by innocuous/sub-perceptual stimulation of adjacent, contralateral, and remote muscles. Psychophysical observations were made in 23 healthy participants. HS (5%) was infused into a forearm muscle (flexor carpi ulnaris) to produce a stable baseline pain. In separate experiments, in each of the three test locations (n = 10 per site)—ipsilateral hand (abductor digiti minimi), contralateral forearm (flexor carpi ulnaris), and contralateral leg (tibialis anterior)—50 μl of 0.9% normal saline (NS) was infused (in triplicate) before, during, and upon cessation of HS-induced muscle pain in the forearm. In the absence of background pain, the infusion of NS was imperceptible to all participants. In the presence of HS-induced pain in the forearm, the concurrent infusion of NS into the ipsilateral hand, contralateral forearm, and contralateral leg increased the overall pain by 16, 12, and 15%, respectively. These effects were significant, reproducible, and time-locked to NS infusions. Further, the NS-evoked increase in pain was almost always ascribed to the forearm where HS was infused with no discernible percept attributed to the sites of NS infusion. Based on these observations, we conclude that intramuscular infusion of HS results in muscle hyperalgesia to sub-perceptual stimulation of muscle afferents in a somatotopically unrestricted manner, indicating the involvement of a central (likely supra-spinal) mechanism.

Association between forearm cortical bone properties and handgrip strength in women with distal radius fractures: A cross-sectional study

Objectives Mechanical and biochemical bone properties are influenced by muscles. However, the muscle-bone interaction has not been fully elucidated regarding the upper extremities. The objective of the present study was to evaluate the mechanical muscle-bone interaction at the forearm by evaluating the relationship between the properties of three-dimensional (3D) forearm cortical bone models derived from conventional computed tomography (CT) images and handgrip strength (HGS). Methods A total of 108 women (mean age, 75.2 ± 9.4 years; range, 62–101 years) with a distal radius fracture who took conventional CT scans for the assessment of the fracture were included in this study. Distal radius 3D models were reconstructed and the average cortical bone density (Cd) and thickness (Ct) of the region of interest (ROI), which might be affected by the forearm flexor muscles, were calculated using a 3D modeling software. Clinical parameters including HGS, lumbar and hip bone mineral densities (BMDs), and other demographic factors were also obtained. A multivariate linear regression analysis was performed to identify relevant factors associated with HGS. Results HGS was found to be independently associated with height and Cd, but no significant difference was found between HGS and Ct, age, weight, as well as lumber and hip BMDs. Conclusions Cortical bone density might be associated with HGS, which is generated by the forearm flexor muscles. Hence, the mechanical muscle-bone interaction in the upper extremities could be supported by the present study.