The neuromuscular compartments of the flexor carpi ulnaris

Learning Objectives: After studying this article, the participant should be able to: 1. Report on the vascular supply and innervation pattern of the flexor carpi ulnaris. 2. Describe the muscle architecture of the flexor carpi ulnaris, including the physiological cross-sectional area and fiber length. 3. State the uses of the flexor carpi ulnaris both for resurfacing defects in the vicinity of the elbow and in local functional tendon transfers. 4. Understand the principles of splitting skeletal muscles based on neurovascular supply to enhance its utilization in reconstructive procedures. The aim of this study was to describe the intramuscular innervation and vascular supply of the human flexor carpi ulnaris, with confirmation of findings by a similar study in the primate. Two distinct intramuscular nerve branches running parallel to each other, on either side of a central tendon, from the proximal quarter of the muscle belly to its insertion were found. The muscle could then be split into a humeral and an ulnar compartment, each with its own primary nerve branch. Perfusion studies confirmed the adequacy of circulation to the two compartments. In the primate flexor carpi ulnaris, electrical stimulation of the respective branches revealed independent contraction of each compartment. This study provides useful information for enabling the local transfer of the muscle as a whole, both for resurfacing in the vicinity of the elbow and for functional tendon transfers. It will also enable the transfer of the muscle as one or two separate compartments (for resurfacing, in tendon transfers for muscle paralysis, congenital defects, and muscle defects resulting from trauma, and after resections for neoplasm and infection).     

Assessment of Flexor carpi ulnaris function for tendon transfer surgery

Active and passive length-force curves of spastic flexor carpi ulnaris (FCU) muscles were intra-operatively measured in 10 patients with cerebral palsy to study the variability in FCU muscle function. Maximum active FCU force was in general situated near the neutral position of the wrist and varied between 40 and 135 N. Passive forces varied between 1 and 8 N at maximum active force. The potential active excursion varied between 4 and 7 cm, while patients moved their wrists from flexion to extension along different parts of the active length-force curve. We measured a large inter-individual variety of spastic FCU muscle function in this group of patients. Thus, tailoring the surgical technique of tendon transfer to the specific needs of the desired function requires the assessment of muscle-specific data for each individual patient.     

Contraction properties and motor nucleus morphology of the two heads of the cat flexor carpi ulnaris muscle

Previous studies have examined the isometric contraction properties of the two heads of the cat flexor carpi ulnaris acting as a single unit. In this study, the contraction properties and fiber architecture of each head of the flexor carpi ulnaris were determined separately and related to previous reports on the histochemical characteristics of this muscle. The morphology of retrograde-labeled motor nuclei for the two heads of the muscle was also examined. The humeral head had a significantly longer contraction time (48 msec) than the ulnar head (36 msec) as well as a significantly lower tetanic fusion frequency (28 Hz vs. 35 Hz). The maximum tetanic tension per gram of muscle tissue was 71% greater in the ulnar head. Motoneurons of the flexor carpi ulnaris formed a column 12 mm long and 0.5 mm wide in the center of the ventral grey in spinal segments C8 and T1. The ulnar head had alpha-motoneurons with greater soma diameters than those in the humeral head. The smaller soma diameter, slower contraction time, and weaker contraction in the humeral head correlate with the preponderance of oxidative-metabolic muscle fiber types found in the humeral head by other workers. These correlations suggest that the humeral head plays a major role in maintaining a sustained antigravity tension that prevents the wrist from buckling during standing.     

Clinical anatomy of the m. flexor carpi radialis tendon sheath

At the transitional zone from the forearm to the hand the insertion tendon of the m.flexor carpi radialis (FCR) glides on a fibrous and fatty cushion, which is connected dorsally with the joint capsule of the radiocarpal articulation. The tendon distally crosses the palmar side of the scaphoid tubercle and enters the dorsally curved rim of the trapezoid tubercle. At the level of the wrist joint the narrow tendon sheath begins, which extends to the insertion at the metacarpus. Immediately after entering the gliding tunnel the tendon branches off radially as a rule with an accessory fibre strand 8 mm in width to the scaphoid, trapezium and the joint capsule between these two bones. The insertion tendon regularly is attached to the palmar and radial surfaces of the second and third metacarpal bones. The wall of the osteofibrous gliding tunnel can be prominent following trauma, inflammation or arthrosis deformans in the trapezio-scaphoideal joint and may irritate the tendon (tendovaginosis stenosans). Against resistance forces pain will occur in the wrist joint during palmar flexion. The typical point of tenderness is situated at the entering of the tendon in the thenar region. Operative decompression will be effective by opening the radial wall of the tendon sheath from the carpal tunnel.     

Morphological and histochemical organization of the flexor carpi radialis muscle in the cat.

Most studies concerning the structure and function of skeletal muscle have utilized the hind limb of the experimental animal. However, it has been shown that the number of behavioral tasks performed by the cat's forelimb is greater than that of the hind limb. In addition, the forelimb muscles exhibit a functional complexity not observed in hind-limb musculature. The purpose of this study was to investigate the distribution of fast-twitch and slow-twitch muscle fibers and muscle spindles in the flexor carpi radialis muscle (FCR) and to correlate the distributional patterns in these structures with muscle tendon architecture and muscle function. It was found that the FCR, a wrist flexor, contains 37% slow-twitch fibers and 63% fast-twitch fibers. However, the slow-twitch fibers were concentrated in the deep region located between the tendons of origin and insertion, while the fast-twitch-glycolytic fibers were concentrated more peripherally. Muscle spindles were associated with the slow-twitch region and were never found in the region containing high concentrations of fast-twitch-glycolytic fibers. Fast-twitch-oxidative-glycolytic fibers were uniformly distributed throughout the muscle. It is proposed that the association of muscle spindles with slow-twitch fibers and the differential distribution of muscle fibers into slow-twitch and fast-twitch regions might allow these regions to function independently of one another when called upon to perform complex behavioral tasks.     

Distribution of sensory receptors in the flexor carpi radialis muscle of the cat

The structures and distribution of encapsulated muscle receptors were examined in serial transverse sections of flexor carpi radialis in the adult cat. Four types of receptors (muscle spindles, Golgi tendon organs, paciniform, and Pacinian corpuscles) were identified. Their structures resembled those encountered in other limb muscles. Pacinian corpuscles were rare and occurred only in the external fascial coat of the muscle near its origin. The other three receptor types were distributed in an uneven but consistent pattern throughout the muscle. As noted previously (Gonyea and Ericson, '77), spindles were largely confined to a deep muscle region comprising less than 20% of the muscle volume, located directly between the long tendon of origin and the tendon of insertion. This region contains the largest proportion of type SO muscle fibers (Gonyea and Ericson, '77). Tendon organs and paciniform corpuscles were concentrated along the tendons that lined the spindle-rich muscle region. This region appeared to be composed of extrafusal fibers that were shorter and of more oblique pinnation than those in other regions. The localization of muscle receptors to the "oxidative" core of the muscle in its direct line of pull may have functional implications for afferent input to the spinal cord which are discussed. In addition, the possibility is raised that there are more paciniform corpuscles in flexor carpi radialis (and possibly other muscles) than previously thought.     

Whole-body vibration increases upper and lower body muscle activity in older adults: potential use of vibration accessories

The current study examined the effects of whole-body vibration (WBV) on upper and lower body muscle activity during static muscle contractions (squat and bicep curls). The use of WBV accessories such as hand straps attached to the platform and a soft surface mat were also evaluated. Surface electromyography (sEMG) was measured for the medial gastrocnemius (MG), vastus lateralis (VL), and biceps brachii (BB) muscles in fourteen healthy older adults (74.8±4.5 years; mean±SD) with a WBV stimulus at an acceleration of 40 m s(-2) (30 Hz High, 2.5 mm or 46 Hz Low, 1.1 mm). WBV increased lower body (VL and MG) sEMG vs baseline (no WBV) though this was decreased with the use of the soft mat. The addition of the bicep curl with hand straps had no effect on lower body sEMG. WBV also increased BB sEMG vs baseline which was further increased when using the hand straps. There was no upper body effect of the soft mat. This study demonstrates WBV increases both lower and upper body muscle activity in healthy older adults. Moreover, WBV accessories such as hand straps attached to the platform or a soft surface mat may be used to alter exercise intensity.     

Activation level of extensor carpi ulnaris affects wrist and elbow acceleration responses following simulated forward falls

The main objective of this study was to measure the acceleration response at the wrist and elbow as a function of different levels of isometric forearm muscle activation during the impact phase of a simulated forward fall.A seated human pendulum was designed to impact the hands of 28 participants while maintaining one of four levels of isometric muscle activation (12%, 24%, 36% and 48% maximal voluntary exertion (MVE)) in the extensor carpi ulnaris muscles. The acceleration responses including peak acceleration (PA), acceleration slope (AS) and time to peak acceleration (TPA) were measured at the wrist and elbow along two axes (axial and off-axis) with two low mass surface mounted accelerometers.At the wrist, significant muscle activation effects were found for PA_off, AS_axial, AS_off, such that they increased as muscle activation increased from baseline to 48% MVE. At the elbow, a similar response was noted, with the acceleration variables increasing as muscle activation level increased, except for AS_off.The results suggest that increases in muscle activation from 12% to 48% MVE stiffen the forearm complex and increase the transmissibility of the impact reaction force shock waves through the forearm.     

Measurement of muscle and tendon stiffness in man

Human first dorsal interosseous muscle was stimulated tetanically using several levels of percutaneous electrical current which produced forces in the muscle-tendon complex of between 30% and 100% of maximum. During the tetanus the muscle was subjected to a small fast stretch. The ratio of the force response to the displacement of the muscle-tendon complex gave a measure of the stiffness of the total complex. An adaptation of the method of Morgan (1977) allowed the stiffness to be separated into two components the stiffness of the muscle fibres and the stiffness of the tendon. The results showed that at full activation the stiffness of the muscle fibres and the tendon are approximately the same. The normalised stiffness values obtained in the experiments compared well with animal data.     

Dystrophin deficiency compromises force production of the extensor carpi ulnaris muscle in the canine model of duchenne muscular dystrophy

Loss of muscle force is a salient feature of Duchenne muscular dystrophy (DMD), a fatal disease caused by dystrophin deficiency. Assessment of force production from a single intact muscle has been considered as the gold standard for studying physiological consequences in murine models of DMD. Unfortunately, equivalent assays have not been established in dystrophic dogs. To fill the gap, we developed a novel in situ protocol to measure force generated by the extensor carpi ulnaris (ECU) muscle of a dog. We also determined the muscle length to fiber length ratio and the pennation angle of the ECU muscle. Muscle pathology and contractility were compared between normal and affected dogs. Absence of dystrophin resulted in marked histological damage in the ECU muscle of affected dogs. Central nucleation was significantly increased and myofiber size distribution was altered in the dystrophic ECU muscle. Muscle weight and physiological cross sectional area (PCSA) showed a trend of reduction in affected dogs although the difference did not reach statistical significance. Force measurement revealed a significant decrease of absolute force, and the PCSA or muscle weight normalized specific forces. To further characterize the physiological defect in affected dog muscle, we conducted eccentric contraction. Dystrophin-null dogs showed a significantly greater force loss following eccentric contraction damage. To our knowledge, this is the first convincing demonstration of force deficit in a single intact muscle in the canine DMD model. The method described here will be of great value to study physiological outcomes following innovative gene and/or cell therapies.     

A cause of wrist pain: non-specific tenosynovitis involving the flexor carpi radialis

We describe 4 patients who complained of pain over the course of the flexor carpi radialis tendon at the wrist, and who presented with point tenderness there. These 4 patients presented a spectrum of non-specific tenosynovitis involving the flexor carpi radialis tendon at the wrist, ranging from slight tenderness and swelling to complete disruption of the tendon. Their clinical course and treatment is presented.     

Habitual loading results in tendon hypertrophy and increased stiffness of the human patellar tendon.

The purpose of this study was to examine patellar tendon (PT) size and mechanical properties in subjects with a side-to-side strength difference of >/=15% due to sport-induced loading. Seven elite fencers and badminton players were included. Cross-sectional area (CSA) of the PT obtained from MRI and ultrasonography-based measurement of tibial and patellar movement together with PT force during isometric contractions were used to estimate mechanical properties of the PT bilaterally. We found that distal tendon and PT, but not mid-tendon, CSA were greater on the lead extremity compared with the nonlead extremity (distal: 139 +/- 11 vs. 116 +/- 7 mm(2); mid-tendon: 85 +/- 5 vs. 77 +/- 3 mm(2); proximal: 106 +/- 7 vs. 83 +/- 4 mm(2); P < 0.05). Distal tendon CSA was greater than proximal and mid-tendon CSA on both the lead and nonlead extremity (P < 0.05). For a given common force, stress was lower on the lead extremity (52.9 +/- 4.8 MPa) compared with the nonlead extremity (66.0 +/- 8.0 MPa; P < 0.05). PT stiffness was also higher in the lead extremity (4,766 +/- 716 N/mm) compared with the nonlead extremity (3,494 +/- 446 N/mm) (P < 0.05), whereas the modulus did not differ (lead 2.27 +/- 0.27 GPa vs. nonlead 2.16 +/- 0.28 GPa) at a common force. These data show that a habitual loading is associated with a significant increase in PT size and mechanical properties.     

Examining the reliability of the flexor carpi radialis V-wave at different levels of muscle contraction

This study examined the reliability and scaling of the flexor carpi radialis (FCR) V-wave during submaximal and maximal voluntary muscle contractions (MVC). 23 participants were tested on three separate sessions. For each session, participants performed isometric wrist flexions at five contraction levels (20, 40, 60, 80 and 100 %MVC). When the target contraction level was reached, a supramaximal electrical stimulus was applied to the median nerve in order to elicit an FCR V-wave. Across all participants, the FCR V-wave amplitude, normalized to its superimposed M-wave amplitude, increased from 0.030 ± 0.001 to 0.143 ± 0.015 (P < 0.001) as the muscle contraction increased from 20 to 100 %MVC. Contraction level did not influence the reliability of evoking the FCR V-wave, as the V-wave demonstrated both stability and consistency. With the exception of a single day main effect during the 20 %MVC condition, V:M_sup was not different across days or trials (P > 0.05) indicating measurement stability. High reliability co-efficients (0.827–0.913) at each contraction level signified measurement consistency. This study establishes that FCR V-waves can be reliably evoked during both submaximal and maximal muscle contractions and suggests the possibility for FCR V-wave recordings to be used to document neuromuscular adaptations associated with factors such as training or fatigue.