Blood flow to the extensor carpi radialis brevis muscle following adrenaline infusion in patients with lateral epicondylitis.

PURPOSE: Based on previous evidence of muscle fiber injury and decreased blood flow in the extensor carpi radialis brevis (ECRB) muscle in lateral epicondylitis (LE), we hypothesized that there would also be an abnormal (vasoconstrictive) vascular response to adrenaline in the ECRB muscle in LE. METHODS: In a case-control study, we measured skeletal muscle blood flow in 8 patients with LE and in 8 healthy controls in response to a 30-minute intravenous infusion of adrenaline. We used local clearance of technetium-99m in the main portion of the ECRB muscle to calculate muscle blood flow. RESULTS: In support of the hypothesis, the blood flow response to the adrenaline infusion was markedly different in the 2 study groups. Whereas the continuous decrease in technetium-99m clearance rate over time was interrupted by the adrenaline-induced vasodilatory effect in the control group, we detected no such effect in the patient group. CONCLUSIONS: In the ECRB muscle in LE, there is a shift in the balance of vasodilatory and vasoconstrictory influences of adrenaline, leading to vasoconstriction during low-dose adrenaline infusion. The adverse adrenaline effect is similar to what was previously observed after minor muscle injury. Whether the vasoregulatory change, by causing relative muscle ischemia, represents the primary etiology in LE or results from muscle injury cannot be determined, but it is likely to contribute to the development and continuation of chronic muscle pain in LE. New ways of thinking about the condition may be required, and pharmacological treatment might be an option to improve the blood supply and avoid further damage to the affected ECRB muscle-tendon unit.

Evidence of wrist proprioceptive reflexes elicited after stimulation of the scapholunate interosseous ligament.

PURPOSE: Recent publications on the sensory innervation of wrist ligaments have challenged our understanding of ligaments as mere passive restraints in wrist stability. Mechanoreceptors in ligaments have a role in signaling joint perturbations, in which the afferent information is believed to influence periarticular muscles. The scapholunate interosseous ligament is one of the most richly innervated ligaments in the wrist. The purpose of our study was to investigate the possible existence of a wrist proprioceptive reflex, by which afferent information elicited in the scapholunate interosseous ligament was hypothesized to influence the muscles moving the wrist joint. METHODS: Nine volunteers (4 women and 5 men; mean age, 26 years; range, 21-28 years) participated in this study. Using ultrasound guidance, a fine-wire electrode was inserted into the dorsal scapholunate interosseous ligament and stimulated with four 1-ms pulses at 200 Hz. Electromyographic activities in extensor carpi radialis brevis, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris muscles were recorded using surface electrodes with the wrist actively positioned in isometric extension, flexion, and radial and ulnar deviation. The average EMGs from 30 consecutive stimulations were rectified and analyzed using the Student's t-test to compare the prestimulus (t(1)) and poststimulus (t(2)) EMG activities. RESULTS: Statistically significant changes in poststimulus EMG activity (t(1)- t(2)) were observed at various time intervals. Within 20 ms, an excitation was seen in the flexor carpi radialis and flexor carpi ulnaris in extension, radial and ulnar deviation, and in extensor carpi radialis brevis in flexion. Co-contractions between agonist and antagonist muscles were observed, with peaks around 150 ms after stimulus. CONCLUSIONS: We present evidence of wrist ligamento-muscular reactions. The early-onset reactions may serve in a joint-protective manner, and later co-contractions indicate a supraspinal control of wrist neuromuscular stability. These findings contribute new information to the physiologic functions of the wrist joint, which may further our understanding of dynamic wrist stability and serve as a foundation for future studies on proprioceptive dysfunctions after wrist ligament injuries.

Immunohistochemical analysis of wrist ligament innervation in relation to their structural composition.

PURPOSE: To analyze ligament innervation and the structural composition of wrist ligaments to investigate the potential differences in sensory and biomechanical functions. METHODS: The ligaments analyzed were the dorsal radiocarpal, dorsal intercarpal, scaphotriquetral, dorsal scapholunate interosseous, scaphotrapeziotrapezoid, radioscaphoid, scaphocapitate, radioscaphocapitate, long radiolunate, short radiolunate, ulnolunate, palmar lunotriquetral interosseous, triquetrocapitate, and triquetrohamate ligaments. The ligaments were harvested from 5 cadaveric, fresh-frozen specimens. By using the immunohistochemical markers p75, Protein Gene Product 9.5, and S-100 protein, the mechanoreceptors and nerve fibers could be identified. RESULTS: The innervation pattern in the ligaments was found to vary distinctly, with a pronounced innervation in the dorsal wrist ligaments (dorsal radiocarpal, dorsal intercarpal, scaphotriquetral, dorsal scapholunate interosseous), an intermediate innervation in the volar triquetral ligaments (palmar lunotriquetral interosseous, triquetrocapitate, triquetrohamate), and only limited/occasional innervation in the remaining volar wrist ligaments. The innervation pattern also was reflected in the structural differences between the ligaments. When present, mechanoreceptors and nerve fibers were consistently found in the loose connective tissue in the outer region (epifascicular region) of the ligament. Hence, ligaments with abundant innervation had a large epifascicular region, as compared with the ligaments with limited innervation, which consisted mostly of densely packed collagen fibers. CONCLUSIONS: The results of our study suggest that wrist ligaments vary with regard to sensory and biomechanical functions. Rather, based on the differences found in structural composition and innervation, wrist ligaments are regarded as either mechanically important ligaments or sensory important ligaments. The mechanically important ligaments are ligaments with densely packed collagen bundles and limited innervation. They are located primarily in the radial, force-bearing column of the wrist. The sensory important ligaments, by contrast, are richly innervated although less dense in connective tissue composition and are related to the triquetrum. The triquetrum and its ligamentous attachments are regarded as key elements in the generation of the proprioceptive information necessary for adequate neuromuscular wrist stabilization.

Differences in the presence of mechanoreceptors and nerve structures between wrist ligaments may imply differential roles in wrist stabilization.

The purpose of this study was to analyze human wrist ligaments with regard to presence of general innervation and mechanoreceptors. The ligaments studied were: dorsal radiocarpal (DRC), dorsal intercarpal (DIC), long radiolunate (LRL), radioscaphocapitate (RSC), ulnocarpal (UC), scapholunate interosseous (SLI) and lunotriquetral interosseous (LTI) ligaments. Specific immunohistochemical markers were used to target neural/perineurial structures. Both Ruffini and Pacini-like mechanoreceptors (sensory corpuscles) as well as nerve fascicles/free nerve fibers were identified. Ruffini corpuscles were primarily identified via their dendritic intracapsular nerve endings, whereas the Pacini-like corpuscles were identified through their thick perineurial capsules with marked p75 immunoreaction. The wrist ligaments were found to vary in innervation, the DIC, DRC and SLI being richly innervated, whereas the LRL being almost without innervation. The difference in innervation between the ligaments might reflect differential function. Ligaments without innervation might act as structures of passive restraint, whereas ligaments with rich innervation are proposed to also provide proprioceptive information. Wrist ligament injuries should, therefore, be regarded as a disturbance not only of the intrinsic carpal kinematics, but also of the coordination and proprioception of the entire wrist joint.

General innervation pattern and sensory corpuscles in the scapholunate interosseous ligament.

The scapholunate interosseous ligament (SLIL) is biomechanically important in maintaining wrist motion and grip strength in the hand, but its possible sensory role in the dynamic muscular stability of the wrist joint has not been examined. The aim of this study was to use immunohistochemical methods to analyze the general innervation and the possible existence of sensory corpuscles in the SLIL. The ligament was excised in its entirety from 9 patients. Antibodies against the low-affinity p75 neurotrophic receptor (p75) were used to reveal sensory corpuscles as well as general innervation. Furthermore, antibodies against the general nerve marker protein gene product 9.5 (PGP 9.5) and the glial marker S-100 were used to additionally depict innervation and corpuscular structures. Blood vessels occurred in areas interspersed throughout the homogeneous collagenous structure. In these vascularized areas, the SLIL was found to be supplied with nerve fascicles and sensory corpuscles of both the Ruffini and lamellated type. p75 immunoreactivity (IR) was detected in association with the nerve fascicles and the corpuscles, particularly in their capsule. S-100 IR was found in the Schwann cells in the central regions of the corpuscle, and PGP 9.5 IR marked the axonal structures in the corpuscles. New information on neurotrophin receptor distribution in ligaments has been obtained here. The presence of nerve fascicles and particularly sensory corpuscles in the SLIL suggests that the ligament has a proprioceptive role in the stability of the wrist. The marked p75 IR further indicates that neurotrophins play a part in a proprioceptive system in the ligament, given the importance of neurotrophins in maintaining sensory function.

Neurokinin 1-receptors and sensory neuropeptides in tendon insertions at the medial and lateral epicondyles of the humerus. Studies on tennis elbow and medial epicondylalgia.

There is no information on the sensory innervation at the flexor muscle origin at the medial epicondyle of the humerus and it is not known if substance P receptors (Neurokinin 1-receptors, NK1-R) are present in tendon insertions in general. In the present investigation, we have studied the muscle origin in patients suffering from medial epicondylalgia and tennis elbow. Immunohistochemistry and antibodies to substance P (SP) and CGRP as well as the general nerve marker PGP 9.5 were used. Specific immunoreactions were observed in nerve bundles and as free nerve fibers. The immunoreactive structures were partly seen in association with some of the blood vessels. The observations constitute a morphological correlate for the occurrence of nerve mediated effects in this region. By using immunohistochemistry and antibodies to NK1-R, the distribution of this receptor was studied at the insertion of the proximal tendon of the extensor carpi radialis brevis muscle at the lateral epicondyle. Specific immunoreactions were seen as varicose fibers occurring as single fibers or grouped into bundles, indicating that SP has effects in the nerves in this region. The results give further evidence for a possible neurogenic involvement in the pathophysiology of tennis elbow and in medial epicondylalgia.