Mechanoreceptors in the palmar wrist ligaments

Immunofluorescence analysis of sensory nerve endings in the periarticular tissue of the human elbow joint

INTRODUCTION

To investigate the dynamic aspects of elbow stability, we aimed to analyze sensory nerve endings in the ligaments and the capsule of elbow joints.

MATERIALS AND METHODS

The capsule with its anterior (AJC) and posterior (PJC) parts, the radial collateral ligament (RCL), the annular ligament (AL), and the ulnar collateral ligament with its posterior (PUCL), transverse (TUCL) and anterior parts (AUCL) were dissected from eleven human cadaver elbow joints. Sensory nerve endings were analyzed in two levels per specimen as total cell amount/ cm² after immunofluorescence staining with low-affinity neurotrophin receptor p75, protein gene product 9.5, S-100 protein and 4',6-Diamidin-2-phenylindol, Carbonic anhydrase II and choline acetyltransferase on an Apotome microscope according to Freeman and Wyke's classification.

RESULTS

Free nerve endings were the predominant mechanoreceptor in all seven structures followed by Ruffini, unclassifiable, Golgi-like, and Pacini corpuscles (p ≤ 0.00001, respectively). Free nerve endings were observed significant more often in the AJC than in the RCL (p < 0.00002). A higher density of Ruffini endings than Golgi-like endings was observed in the PJC (p = 0.004). The RCL contained significant more Ruffini endings than Pacini corpuscles (p = 0.004). Carbonic anhydrase II was significantly more frequently positively immunoreactive than choline acetyltransferase in all sensory nerve endings (p < 0.05). Sensory nerve endings were significant more often epifascicular distributed in all structures (p < 0.006, respectively) except for the AJC, which had a pronounced equal distribution (p < 0.00005).

CONCLUSION

The high density of free nerve endings in the joint capsule indicates that it has pronounced nociceptive functions. Joint position sense is mainly detected by the RCL, AUCL, PUCL, and the PJC. Proprioceptive control of the elbow joint is mainly monitored by the joint capsule and the UCL, respectively. However, the extreme range of motion is primarily controlled by the RCL mediated by Golgi-like endings.

Scapholunate interosseous ligament dysfunction as a source of elbow pain syndromes: Possible mechanisms and implications for hand surgeons and therapists

Elbow pain syndromes are common upper extremity musculoskeletal disorders, and they are usually associated with repetitive occupational exposure. Ligaments are often one of the sources of musculoskeletal disorders because of their mechanical and neurological properties. The wrist ligaments are some of the ligaments most vulnerable to occupational exposure. Since most occupational tasks require wrist extension for handling tools and loading, the scapholunate interosseous ligament (SLIL) bears greater strain during loading, which results in creep deformation and hysteresis. Ligamentous creep may result in diminished ability to detect signal changes during joint movements, which impairs neuromuscular control established by ligamentomuscular reflex arcs elicited from mechanoreceptors in the ligaments. Changes in muscle activation patterns of forearm muscles due to diminished ligamentomuscular reflexes may initiate a positive feedback loop, leading to musculoskeletal pain syndromes. The relationship between elbow pain syndromes and SLIL injury will be presented through two hypotheses and relevant pain mechanisms: 1. Repetitive tasks may cause creep deformation of the SLIL, which then impairs ligamentomuscular reflexes, leading to elbow pain disorders. 2. Lateral epicondylalgia may increase the risk of SLIL injury through the compensation of the lower extensor carpi radialis muscle activity by higher extensor carpi ulnaris muscle activity, which may alter carpal kinematics, leading to SLIL degeneration over time. The differential diagnosis is usually complicated in musculoskeletal pain disorders. The failure of treatment methods is one of the issues of concern for many researchers. A key element in developing treatment strategies is to understand the source of the disorder and the nature of the injury. We proposed that the differential diagnosis include SLIL injuries when describing elbow pain syndromes, particularly, lateral epicondylalgia.

El papel de la rehabilitación tras las reparaciones de las inestabilidades de muñeca

De las patologías de muñeca más frecuentes en la consulta del cirujano de la mano, las inestabilidades carpianas ocupan un lugar importante junto con el dolor en la vertiente ulnocarpiana cuya causa más frecuente son las lesiones del complejo fibrocartílago triangular, que en ocasiones van a condicionar una inestabilidad de la articulación radiocubital distal. Analizando los datos anatómicos y biomecánicos que diponemos de la muñeca y tomando como punto de partida los escasos protocolos rehabilitadores de las inestabilidades escafolunares y lunopiramidales que existen en la bibliografía, se exponen los programas rehabilitadores específicos para cada una de ellas. Se describen también los protocolos existentes para la rehabilitación tras las reparaciones del complejo fibrocartílago triangular y exponemos los protocolos con los que trabajamos en la actualidad.

Definimos también la importancia de la reeducación propioceptiva en este tipo de lesiones y describimos un programa detallado de introducción progresiva de determinados ejercicios encaminados a ello.

Patient-rated long-term results after complete denervation of the wrist

The aim of this study was to examine the long-term results after the denervation of the wrist. Between 1977 and 2001, we treated 375 patients in our clinic. The mean age was 43.5 years; 81% were male and 19% female. The long-term results were assessed by a questionnaire assessing pain on a visual analog scale and patient satisfaction and by the DASH questionnaire. After a mean follow-up of 12.23 years, we found an overall pain reduction of 52.1%. In 67.7% of the patients, we found a relief of pain: of these, 44% are free of pain until today and 56% were temporarily asymptomatic. Patients with a painful osteoarthritic condition without dynamic instability and good range of motion are ideal candidates to benefit from the denervation. The complete denervation of the wrist is an effective treatment option in patients with painful wrist conditions to reduce pain and improve the overall function.

Role of muscles in the stabilization of ligament-deficient wrists

This article reviews the results of a series of cadaver investigations aimed at clarifying the role of muscles in the stabilization of ligament-deficient wrists. According to these studies, isometric contraction of some forearm muscles induces midcarpal (MC) supination (ie, the abductor pollicis longus, extensor carpi radialis longus, and flexor carpi ulnaris), whereas other muscles induce MC pronation (ie, the extensor carpi ulnaris). Because MC supination implies tightening of the volar scaphoid-distal row ligaments, the MC supination muscles are likely to prevent scaphoid collapse of wrists with scapholunate ligament insufficiency. MC pronator muscles, by contrast, would be beneficial in stabilizing wrists with ulnar-sided ligament deficiencies owing to their ability to tighten the triquetrum-distal row ligaments. Should these laboratory findings be validated by additional clinical research, proprioceptive reeducation of selected muscles could become an important tool for the treatment of dynamic carpal instabilities.

Robot-Aided Mapping of Wrist Proprioceptive Acuity across a 3D Workspace

Proprioceptive signals from peripheral mechanoreceptors form the basis for bodily perception and are known to be essential for motor control. However we still have an incomplete understanding of how proprioception differs between joints, whether it differs among the various degrees-of-freedom (DoFs) within a particular joint, and how such differences affect motor control and learning. We here introduce a robot-aided method to objectively measure proprioceptive function: specifically, we systematically mapped wrist proprioceptive acuity across the three DoFs of the wrist/hand complex with the aim to characterize the wrist position sense. Thirty healthy young adults performed an ipsilateral active joint position matching task with their dominant wrist using a haptic robotic exoskeleton. Our results indicate that the active wrist position sense acuity is anisotropic across the joint, with the abduction/adduction DoF having the highest acuity (the error of acuity for flexion/extension is 4.64 ± 0.24°; abduction/adduction: 3.68 ± 0.32°; supination/pronation: 5.15 ± 0.37°) and they also revealed that proprioceptive acuity decreases for smaller joint displacements. We believe this knowledge is imperative in a clinical scenario when assessing proprioceptive deficits and for understanding how such sensory deficits relate to observable motor impairments.

The role of proprioception and neuromuscular stability in carpal instabilities

Carpal stability has traditionally been defined as dependent on the articular congruity of joint surfaces, the static stability maintained by intact ligaments, and the dynamic stability caused by muscle contractions resulting in a compression of joint surfaces. In the past decade, a fourth factor in carpal stability has been proposed, involving the neuromuscular and proprioceptive control of joints. The proprioception of the wrist originates from afferent signals elicited by sensory end organs (mechanoreceptors) in ligaments and joint capsules that elicit spinal reflexes for immediate joint stability, as well as higher order neuromuscular influx to the cerebellum and sensorimotor cortices for planning and executing joint control. The aim of this review is to provide an understanding of the role of proprioception and neuromuscular control in carpal instabilities by delineating the sensory innervation and the neuromuscular control of the carpus, as well as descriptions of clinical applications of proprioception in carpal instabilities.

Altered Innervation Pattern in Ligaments of Patients with Basal Thumb Arthritis

Purpose The population of mechanoreceptors in patients with osteoarthritis (OA) lacks detailed characterization. In this study, we examined the distribution and type of mechanoreceptors of two principal ligaments in surgical subjects with OA of the first carpometacarpal joint (CMC1). Methods We harvested two ligaments from the CMC1 of eleven subjects undergoing complete trapeziectomy and suspension arthroplasty: the anterior oblique (AOL) and dorsal radial ligament (DRL). Ligaments were divided into proximal and distal portions, paraffin-sectioned, and analyzed using immunoflourescent triple staining microscopy. We performed statistical analyses using the Wilcoxon Rank Sum test and ANOVA with post-hoc Bonferroni and Tamhane adjustments. Results The most prevalent nerve endings in the AOL and DRL of subjects with OA were unclassifiable mechanoreceptors, which do not currently fit into a defined morphological scheme. These were found in 11/11 (100%) DRLs and 7/11 (63.6%) AOLs. No significant difference existed with respect to location within the ligament (proximal versus distal) of mechanoreceptors in OA subjects. Conclusion The distribution and type of mechanoreceptors in cadavers with no to mild OA differ from those in surgical patients with OA. Where Ruffini endings predominate in cadavers with no to mild OA, unclassifiable corpuscles predominate in surgical patients with OA. These findings suggest an alteration of the mechanoreceptor population and distribution that accompanies the development of OA. Clinical Relevance Identification of a unique type and distribution of mechanoreceptors in the CMC1 of symptomatic subjects provides preliminary evidence of altered proprioception in OA.

Anticipatory and Reactive Response to Falls: Muscle Synergy Activation of Forearm Muscles

We investigated the surface electromyogram response of six forearm muscles to falls onto the outstretched hand. The extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, abductor pollicis longus, flexor carpi radialis and flexor carpi ulnaris muscles were sampled from eight volunteers who underwent ten self-initiated falls. All muscles initiated prior to impact. Co-contraction is the most obvious surface electromyogram feature. The predominant response is in the radial deviators. The surface electromyogram timing we recorded would appear to be a complex anticipatory response to falling modified by the effect on the forearm muscles following impact. The mitigation of the force of impact is probably more importantly through shoulder abduction and extension and elbow flexion rather than action of the forearm muscles.

[Carpal dynamic stability mechanisms. Experimental study]

OBJECTIVE

To evaluate, experimentally in cadavers, the effect of the motor muscles in the wrist in the kinetic behaviour of the carpal, under axial load, and the wrist in a neutral position.

MATERIAL AND METHOD

The changes in the spatial orientation of the carpal bones were recorded with a movement trajectory gauge that functions with electromagnetic fields. A total of 30 fresh cadaver wrists were used, in which the principal motor tendons were isolated and subjected to loads proportional to the area of the physiological section of each muscle. The experiment was performed under isometric load conditions of all the tendons, and separately from each tendon.

RESULTS

The simultaneous load of all the tendons studied caused a three-dimensional change of the carpal bones. The flexor carpi radialis led to supination of the scaphoids and pronation of the pyramidal. Conversely, the isolated load of the flexor carpi ulnaris, abductor pollicis longus and the extensor carpi radialis longus, caused a supination movement of the 2 carpal rows. Only the extensor carpi ulnaris led to a marked pronation of the carpal.

COMMENTS AND CONCLUSIONS

The forearm muscles, as well as the movements of the wrist, cause pronation/supination/supination, flexion/extension and radial/cubital inclination movements. It is proposed that the most important movements in the dynamic stabilisation of the carpal are the intercarpal pronation and supination movements provoked by these muscles. Depending on the carpal injury mechanism or instability, the stimulating of one muscle group or the other may be beneficial.

Effects of forearm muscles on carpal stability

Thirty cadaveric forearms were tested using a wrist testing apparatus specifically designed to investigate the mechanisms of muscle stabilization of the wrist. The specimens were set in a jig allowing the distal row to migrate proximally and to rotate around the pronosupination forearm axis. Five wrist motor tendons (FCR, FCU, ECU, ECRL and APL) were loaded with specific weights. Reactive rotations of the scaphoid, triquetrum and capitate were measured by an electromagnetic motion tracking device. When all five tendons were loaded simultaneously, the capitate supinated and the proximal row predominantly supinated and flexed. By contrast, when the ECU was loaded in isolation, it caused pronation to both proximal and distal rows. The FCR exhibited a mixed effect pronating the capitate and triquetrum, whilst supinating the scaphoid. Based on this, a hypothesis is proposed linking wrist stability to the balance of wrist pronators (ECU and FCR) and supinators (FCU, ECRL and APL).

Immunofluorescent triple-staining technique to identify sensory nerve endings in human thumb ligaments

Ligament innervation purportedly plays a critical role in stability, proprioception and pathology of joints with minimal bony constraints. The human thumb carpometacarpal (CMC) joint is such a joint: with a complex saddle configuration and wide circumduction, its constraint is primarily ligamentous and it is prone to osteoarthritis. CMC reconstruction is the most commonly performed arthritis surgery in the upper extremity. Little, however, is known about CMC ligament innervation. We describe a novel triple-staining immunofluorescence technique using the markers for low-affinity neurotrophin receptor p75, the pan-neuronal marker protein gene product (PGP) 9.5 and 4',6'-diamidino-2-phenylindole (DAPI) to simultaneously detect and differentiate between specific sensory nerve endings: the Pacini corpuscles, the Ruffini endings and nerve fascicles. Five primary CMC ligaments (dorsal radial, dorsal central, posterior oblique, anterior oblique and ulnar collateral ligaments) were harvested from 10 fresh-frozen human cadaver hands. Following paraffin sectioning, each ligament was stained using a triple-stain technique and imaged with fluorescence microscopy. Multidimensional acquisition permitted simultaneous capture of images at different wavelengths. Pacini corpuscles were distinguished by their distinct p75 immunoreactive capsules, and Ruffini endings by their overlapping p75 and PGP9.5 immunoreactive dendritic nerve endings. Simultaneous use of PGP9.5, p75 and DAPI immunofluorescence to analyze innervation patterns in human ligaments provides descriptive analysis of staining patterns and receptor structure as well as clues as to the proprioceptive function of CMC ligaments and the joint as a whole. Our novel findings of CMC ligament innervation augment the study of normal and pathological joint mechanics in this joint so prone to osteoarthritis.

Time dependent spine stability: the wise old man and the six blind elephants

Spine stability of the behaving human in health or disorder is a complex, multi-factorial and time variable index. The major components of stability are the properties of the external load, passive viscoelastic tissues (ligaments, discs, facet capsules and dorso-lumbar fascia) combined with the properties of the active tissues (muscles and their sensory-motor control, co-activation and associated intra-abdominal pressure) as well as the pro-inflammatory status of the tissues. Each of the many components' contribution is time variable with dependence on the dose-duration of the work stimulus and the associated rest. Interaction of many variables is also dominant. A call is issued to focus research efforts on the development of a multi-factorial description of spine stability while representing the contribution of all relevant components as time variable functions. An example is provided, using models of four components described as functions of time derived from real data obtained simultaneously from the in-vivo feline. The example elucidates the potential errors made when using single components to assess stability and the insight gained when stability is introduced as a time dependent index. It is expected that such time variable stability assessment will provide uniform and insightful estimation that will have valuable applications in occupational, sports and rehabilitation fields as well as the leisure lifestyles required for maintaining a healthy spine.

The role of the flexor carpi radialis muscle in scapholunate instability

PURPOSE

The flexor carpi radialis (FCR) muscle has been suggested to act as a dynamic scaphoid stabilizer. Because the FCR tendon uses the scaphoid tuberosity as a pulley to reach its distal insertion onto the second metacarpal, it has been hypothesized that FCR muscle contraction generates a dorsally directed vector that resists the scaphoid from rotating into flexion. The purpose of the present study was to validate that hypothesis and clarify the role of the FCR as a dynamic scaphoid stabilizer.

METHODS

Ten fresh cadaver wrist specimens were tested. A custom-designed testing apparatus was used to hold the forearm and wrist vertically, in neutral forearm rotation. A 6-degree-of-freedom, electromagnetic motion-tracking device, with sensors attached to the scaphoid, triquetrum, capitate, and radius, was used to monitor spatial changes in carpal alignment as a result of isometrically loading the FCR in 5 different wrist positions.

RESULTS

In all specimens and all wrist positions, the scaphoid consistently rotated into flexion when the FCR was loaded. It also exhibited variable degrees of pronation or supination, depending on whether the wrist was in flexion or extension. When the wrist was loaded in neutral position, the scaphoid consistently supinated and the triquetrum pronated, these differences being statistically significant (p < .05).

CONCLUSIONS

The scaphoid consistently rotated into flexion and supination when the FCR was loaded, while the triquetrum rotated in flexion and pronation. The positive effects of FCR muscle re-education in dynamic scapholunate instabilities can be explained not by this muscle's capability of extending the scaphoid, as has often been hypothesized, but by its ability to induce supination to the scaphoid and pronation to the triquetrum. Such opposite rotations are likely to result in a dorsal coaptation of the scapholunate joint with relaxation of the dorsal scapholunate ligament.

Desensitizing the posterior interosseous nerve alters wrist proprioceptive reflexes

PURPOSE

The presence of wrist proprioceptive reflexes after stimulation of the dorsal scapholunate interosseous ligament has previously been described. Because this ligament is primarily innervated by the posterior interosseous nerve (PIN) we hypothesized altered ligamento-muscular reflex patterns following desensitization of the PIN.

METHODS

Eight volunteers (3 women, 5 men; mean age, 26 y; range 21-28 y) participated in the study. In the first study on wrist proprioceptive reflexes (study 1), the scapholunate interosseous ligament was stimulated through a fine-wire electrode with 4 1-ms bipolar pulses at 200 Hz, 30 times consecutively, while EMG activity was recorded from the extensor carpi radialis brevis, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris, with the wrist in extension, flexion, radial deviation, and ulnar deviation. After completion of study 1, the PIN was anesthetized in the radial aspect of the fourth extensor compartment using 2-mL lidocaine (10 mg/mL) infiltration anesthesia. Ten minutes after desensitization, the experiment was repeated as in study 1. The average EMG results from the 30 consecutive stimulations were rectified and analyzed using Student's t-test. Statistically significant changes in EMG amplitude were plotted along time lines so that the results of study 1 and 2 could be compared.

RESULTS

Dramatic alterations in reflex patterns were observed in wrist flexion, radial deviation, and ulnar deviation following desensitization of the PIN, with an average of 72% reduction in excitatory reactions. In ulnar deviation, the inhibitory reactions of the extensor carpi ulnaris were entirely eliminated. In wrist extension, no differences in the reflex patterns were observed.

CONCLUSIONS

Wrist proprioception through the scapholunate ligament in flexion, radial deviation, and ulnar deviation depends on an intact PIN function. The unchanged reflex patterns in wrist extension suggest an alternate proprioceptive pathway for this position. Routine excision of the PIN during wrist surgical procedures should be avoided, as it alters the proprioceptive function of the wrist.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Proprioception of the wrist joint: a review of current concepts and possible implications on the rehabilitation of the wrist

STUDY DESIGN

Narrative review. Recent years have brought new research findings on the subject of wrist joint proprioception, which entails an understanding of the wrist as part of a sensorimotor system where afferent information from nerve endings in the wrist joint affects the neuromuscular control of the joint. An understanding of proprioception is also essential to adequately rehabilitate patients after wrist injuries. The aim of this narrative review was to give the reader a background of proprioception as it relates to neuromuscular control and joint stability, what is presently known in relation to the wrist joint and how these findings may be applied to the field of wrist rehabilitation.

LEVEL OF EVIDENCE

5.

Immunohistochemical study of mechanoreceptors in the tibial remnant of the ruptured anterior cruciate ligament in human knees

This study was performed to identify the mechanoreceptors in the tibial remnants of ruptured human anterior cruciate ligaments (ACL) by immunohistochemical staining. Thirty-six specimens of tibial ACL remnants were obtained from patients with ACL ruptures during arthroscopic ACL reconstruction. As control, two normal ACL specimens were taken from healthy knee amputated at thigh level due to trauma. The specimen was serially sectioned at 40 mum. In control group, the average number of sections per specimen was 132, and a total of 264 slices were available. In remnant group, the average number of sections per specimen was 90, and a total of 3,251 slices were available. Immunohistochemical staining was performed to detect the neural element of mechanoreceptors. Histologic examinations were performed under a light microscope and interpreted by a pathologist. Nineteen (8 Ruffini, 11 Golgi) mechanoreceptors were identified in the two normal ACLs, which were evenly distributed at both tibial and femoral attachments. In the remnant group, mechanoreceptors were observed in 12 out of 36 cases (33%), and a total of 17 (6 Ruffini and 11 Golgi) mechanoreceptors observed. No significant differences in the harvest volume, number of sections, age, or time between injury to surgery was observed between the 12 mechanoreceptor-present and the 24 mechanoreceptor-absent ones. The presence of mechanoreceptor at the tibial remnants of torn ACLs was verified. The immunohistochemical staining methodology proved useful, but requires further refinement. Although the mechanoreceptors were detected relatively less frequently than expected, the authors consider that it does not negate the necessity of remnant-preserving ACL reconstruction.

Fluorescence immunohistochemistry and confocal scanning laser microscopyA protocol for studies of joint innervation

We have developed a reliable technique for labeling and examining neural structures in soft tissues associated with articular joints and have tested it in human wrist joints under various specimen-related conditions. The labeling protocol employs an immunohistochemical process with a panneuronal marker (PGP 9.5) as the primary antibody and Alexa Fluor 488 as the fluorescing secondary antibody. Imaging was done using a confocal laser scanning microscope, which produced exceptionally detailed three-dimensional images of nerve endings and transiting nerve fibers from thick sections of wrist joint ligaments obtained from human cadavers. The protocol provided a practical postmortem window for specimen acquisition and processing without significant apparent worsening of image quality. The images produced are resistant to fading with repeated exposure to a fluorescent light source, which gives many opportunities for observation. Background staining is minimal, producing high contrast labeling of target tissues, which, in turn, enhances image analysis.

Ligaments: a source of musculoskeletal disorders

The mechanical and neurological properties of ligaments are reviewed and updated with recent development from the perspective which evaluates their role as a source of neuromusculoskeletal disorders resulting from exposure to sports and occupational activities. Creep, tension-relaxation, hysteresis, sensitivity to strain rate and strain/load frequency were shown to result not only in mechanical functional degradation but also in the development of sensory-motor disorders with short- and long-term implication on function and disability. The recently exposed relationships between collagen fibers, applied mechanical stimuli, tissue micro-damage, acute and chronic inflammation and neuromuscular disorders are delineated with special reference to sports and occupational stressors such as load duration, rest duration, work/rest ratio, number of repetitions of activity and velocity of movement.

Distribution of nerve endings in the human dorsal radiocarpal ligament

PURPOSE

The purpose of this investigation was to evaluate the nerve-ending apparatus populations within a large number of adult human dorsal radiocarpal (DRC) ligaments to test the hypothesis that the majority of nerve endings could be grouped into established classifications and that the nerve endings could be found in predictable locations within the substance of the ligament.

METHODS

The DRC ligaments were harvested from 20 wrists of 10 fresh cadavers with an average age of 75.6 years within 12 to 18 hours of death. Before the tissues were harvested, radiographs were taken to exclude any arthritic conditions of the wrists. Tissues were fixed, sectioned with a cryostat, and serial sections were collected on glass slides. Slides were processed for fluorescence immunohistochemistry using antibody to protein gene product 9.5 and a secondary antibody conjugated to a fluorescent tag (Alexa Fluor 488). The sections were evaluated with an LSM-510 confocal laser microscope and a Kontron KS 400 image analyzer. Labeled nerve endings were counted, mapped, and reconstructed.

RESULTS

The average number of nerve endings in each DRC ligament was 10.1+/-4.7. More than 76% of the nerve endings were found in the 2 ends of the ligament with 23.3% in the central third and approximately 80% distributed in the superficial layer. More than 80% of the nerve endings were discovered in the epiligamentous sheath rather than in the perifascicular spaces.

CONCLUSIONS

The distribution of the nerve endings follows a consistent pattern. These results will provide a foundation of morphologic information useful in understanding normal and abnormal neural control of wrist joint mechanics.

Sensory – Motor control of ligaments and associated neuromuscular disorders

The ligaments were considered, over several centuries, as the major restraints of the joints, keeping the associated bones in position and preventing instability, e.g. their separation from each other and/or mal-alignment. This project, conducted over 25 years, presents the following hypothesis: 1. Ligaments are also major sensory organs, capable of monitoring relevant kinesthetic and proprioceptive data. 2. Excitatory and inhibitory reflex arcs from sensory organs within the ligaments recruit/de-recruit the musculature to participate in maintaining joint stability as needed by the movement type performed. 3. The synergy of the ligament and associated musculature allocates prominent role for muscles in maintaining joint stability. 4. The viscoelastic properties of ligaments and their classical responses to static and cyclic loads or movements such as creep, tension-relaxation, hysteresis and strain rate dependence decreases their effectiveness as joint restraint and stabilizers and as sensory organs and exposes the joint to injury. 5. Long-term exposure of ligaments to static or cyclic loads/movements in a certain dose-duration paradigms consisting of high loads, long loading duration, high number of load repetitions, high frequency or rate of loading and short rest periods develops acute inflammatory responses which require long rest periods to resolve. These inflammatory responses are associated with a temporary (acute) neuromuscular disorder and during such period high exposure to injury is present. 6. Continued exposure of an inflamed ligament to static or cyclic load may result in a chronic inflammation and the associated chronic neuromuscular disorder known as cumulative trauma disorder (CTD). 7. The knowledge gained from basic and applied research on the sensory - motor function of ligaments can be used as infrastructure for translational research; mostly for the development of "smart orthotic" systems for ligament deficient patients. Three such "smart orthosis", for the knee and lumbar spine are described. 8. The knowledge gained from the basic and applied research manifests in new physiotherapy modalities for ligament deficient patients. Ligaments, therefore, are important structures with significant impact on motor control and a strong influence on the quality of movement, safety/stability of the joint and potential disorders that impact the safety and health of workers and athletes.

The Pathomechanics of Plantar Fasciitis

Plantar fasciitis is a musculoskeletal disorder primarily affecting the fascial enthesis. Although poorly understood, the development of plantar fasciitis is thought to have a mechanical origin. In particular, pes planus foot types and lower-limb biomechanics that result in a lowered medial longitudinal arch are thought to create excessive tensile strain within the fascia, producing microscopic tears and chronic inflammation. However, contrary to clinical doctrine, histological evidence does not support this concept, with inflammation rarely observed in chronic plantar fasciitis. Similarly, scientific support for the role of arch mechanics in the development of plantar fasciitis is equivocal, despite an abundance of anecdotal evidence indicating a causal link between arch function and heel pain. This may, in part, reflect the difficulty in measuring arch mechanics in vivo. However, it may also indicate that tensile failure is not a predominant feature in the pathomechanics of plantar fasciitis. Alternative mechanisms including 'stress-shielding', vascular and metabolic disturbances, the formation of free radicals, hyperthermia and genetic factors have also been linked to degenerative change in connective tissues. Further research is needed to ascertain the importance of such factors in the development of plantar fasciitis.

Innervation of the wrist joint and surgical perspectives of denervation

PURPOSE

Because our experience with the techniques used in denervation surgery of the wrist joint often has proven insufficient in treating chronic pain we conducted an anatomic study to clarify the exact contributions of the nerves supplying the wrist joint. Our goal was to reveal all periosteal and capsular nerve connections and if necessary adjust our technique used in denervation surgery.

METHODS

Innervation of the wrist joint was investigated by microdissection and histologic examination of 18 human wrists. An acetylcholinesterase method was used to identify the nerves, both in whole-mount preparations and in sections.

RESULTS

We found that the main innervation to the wrist capsule and periosteal nerve network came from the anterior interosseous nerve, lateral antebrachial cutaneous nerve, and posterior interosseous nerve. The palmar cutaneous branch of the median nerve, the deep branch of the ulnar nerve, the superficial branch of the radial nerve, and the dorsal branch of the ulnar nerve also were found to have connections with the capsule. The periosteal nerve branches did not appear to play a major role in the innervation of the capsule and ligaments; here the specific articular nerve branches proved more important. The posterior and medial antebrachial cutaneous nerves did not connect to the wrist capsule or periosteum but rather terminated in the extensor and flexor retinaculum.

CONCLUSIONS

Based on our findings we propose to denervate the wrist by making 2 incisions. With one palmar and one dorsal incision it should be possible to disconnect the periosteum from the capsule and interrupt the majority of the capsular nerve branches.

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.

Neuromuscular response to cyclic loading of the anterior cruciate ligament

BACKGROUND

Cyclic load applied to various joints during occupational and sports activities is epidemiologically linked to higher risk of neuromuscular disorder development.

HYPOTHESIS

Passive cyclic loading of the knee will develop laxity and creep in the anterior cruciate ligament, and these may elicit a neuromuscular disorder in the quadriceps and hamstrings. Women may be more susceptible to the disorder.

STUDY DESIGN

Controlled laboratory study.

METHODS

Male and female groups were subjected to 10 minutes of passive cyclic loading (0.1 Hz) of the knee at a mild load (150-200 N) and at 35 degrees and 90 degrees flexion. Anterior tibial displacement and electromyogram from the quadriceps and hamstrings were monitored during cyclic loading. Maximal voluntary contraction of knee extension and flexion was assessed before and after cyclic loading. The effect of gender and angle on maximal voluntary contraction and quadriceps/hamstrings electromyogram was tested by a 2-way analysis of variance. Differences between the preload and postload data were tested by a paired t test.

RESULTS

At a knee angle of 90 degrees, after cyclic loading, a decrease in maximal voluntary contraction during extension was present in men and women, with an associated decrease in quadriceps electromyogram activity. At 35 degrees, a decrease in maximal voluntary contraction in extension was noted in women and men. Electromyogram spasms were present in the quadriceps and hamstrings during the 10-minute cyclic loading in 51.7% of subjects. Analysis of variance demonstrated that ligament creep was significantly greater in women than in men at both knee angles.

CONCLUSIONS

Even a mild cyclic loading of the anterior cruciate ligament, for a relatively short period, can elicit substantial creep, laxity, and a neuromuscular disorder. The disorder is composed of spasms and attenuated muscular function that may together create a condition that exposes the knee to injury. Women seem to be more susceptible than men.

CLINICAL RELEVANCE

Cyclic actions performed at high frequencies and high-load magnitudes may lead to the occurrence of increased knee laxity and changes in neuromuscular function that, together with fatigue and changes in proprioception, may increase the risk of injury.

Short rest periods after static lumbar flexion are a risk factor for cumulative low back disorder

The objective of this work was to study the effect of rest periods of various durations applied between six 10-min sessions of static flexion on the development of cumulative low back disorder (CLBD). Three experimental groups of a feline model were used, and the rest duration between sequential static load periods was set to 5, 10, and 20 min, with a corresponding load-to-rest ratio of 2:1, 1:1 and 1:2, respectively. The reflex electromyographic (EMG) activity from the multifidus muscles and supraspinous ligament displacement (creep) were recorded during the flexion periods and over 7 h of rest following the load-rest cycles. It was found that a minor disorder developed in all the groups whereas a severe neuromuscular disorder including a delayed hyperexcitability was observed only in the group subjected to 5 min rest. The two-way ANOVA showed a significant effect of time post loading (p<0.001) and rest duration (p<0.001) on the Normalized Integrated EMG (NIEMG) recovery data; a significant effect of time post loading on the Displacement data (p<0.001) was observed as well. The post hoc Fisher test performed on the NIEMG data during the recovery phase showed a significant difference between the group subjected to 5 min rest and the other two groups (p<0.001). These results suggest that while a short rest period of 2:1 load-to-rest ratio leads to CLBD, longer rest at 1:1 and 1:2 load-to-rest ratio are more favorable for preventing or attenuating the development of CLBD. Short rest periods between sessions of static lumbar flexion, therefore, are a risk factor for the development of CLBD.

Adipose tissue at entheses: the rheumatological implications of its distribution. A potential site of pain and stress dissipation?

OBJECTIVES

To describe the distribution of adipose tissue within and adjacent to entheses in order to assess its functional significance at attachment sites.

METHODS

Entheses were removed from 29 different sites in the limbs of formalin fixed, elderly, dissecting room cadavers and the samples prepared for paraffin and/or methylmethacrylate histology. Entheses from four young volunteers with no history of significant musculoskeletal injury were examined by magnetic resonance imaging using T(1) weighted sequences.

RESULTS

Adipose tissue was present at several different sites at numerous entheses. Many tendons/ligaments lay on a bed of well vascularised, highly innervated, "insertional angle fat". Endotenon fat was striking between fascicles, where entheses flared out at their attachments. It was also characteristic of the epitenon, where it occurred in conjunction with lamellated and Pacinian corpuscles. Fat filled, meniscoid folds often protruded into joint cavities, immediately adjacent to attachment sites.

CONCLUSION

Adipose tissue is a common feature of normal entheses and should not be regarded as a sign of degeneration. It contributes to the increase in surface area of attachment sites, promotes movement between tendon/ligament and bone, and forms part of an enthesis organ that dissipates stress. The presence of numerous nerve endings in fat at attachment sites suggests that it has a mechanosensory role and this could account for the rich innervation of many entheses. Because damage to fat is known to lead to considerable joint pain, our findings may be important for understanding the site of pain in enthesopathies.

Ligaments: a source of work-related musculoskeletal disorders

The mechanical and neurological properties of ligaments are reviewed and updated with recent development from the perspective which evaluates their role as a source of neuromusculoskeletal disorders resulting from exposure to occupational activities. Creep, tension-relaxation, hysteresis, sensitivity to strain rate and strain/load frequency were shown to result not only in mechanical functional degradation but also in the development of sensory-motor disorders with short- and long-term implication on function and disability. The recently exposed relationships between collagen fibers, applied mechanical stimuli, tissue microdamage, acute and chronic inflammation and neuromuscular disorders is delineated with special reference to occupational stressors.

Muscular dysfunction elicited by creep of lumbar viscoelastic tissue

The biomechanics, histology and electromyography of the lumbar viscoelastic tissues and multifidus muscles of the in vivo feline were investigated during 20 min of static as well as cyclic flexion under load control and during 7 h of rest following the flexion. It was shown that the creep developed in the viscoelastic tissues during the 20 min of static or cyclic flexion did not fully recover over the 7 h of following rest. It was further seen that a neuromuscular disorder with five distinct components developed during and after the static and cyclic flexion. The neuromuscular disorder consisted of a decreasing magnitude of reflexive EMG from the multifidus upon flexion as well as of superimposed spasms. The recovery period was characterized by an initial muscle hyperexcitability, a slowly increasing reflexive EMG and a delayed hyperexcitability. Histological data from the supraspinous ligament demonstrate significant increase (x 10) in neutrophil density in the ligament 2 h into the recovery and even larger increase (x 100) 6 h into the recovery from the 20 min flexion, indicating an acute soft tissue inflammation. It was concluded that sustained static or cyclic loading of lumbar viscoelastic tissues may cause micro-damage in the collagen structure, which in turn reflexively elicit spasms in the multifidus as well as hyperexcitability early in the recovery when the majority of the creep recovers. The micro-damage, however, results in the time dependent development of inflammation. In all cases, the spasms, initial and delayed hyperexcitabilities represent increased muscular forces applied across the intervertebral joints in an attempt to limit the range of motion and unload the viscoelastic tissues in order to prevent further damage and to promote healing. It is suggested that a significant insight is gained as to the development and implications of a common idiopathic low back disorder as well as to the development of cumulative trauma disorders.

Neuromuscular dysfunction elicited by cyclic lumbar flexion

An attempt was made to develop an in vivo model that could explain the neurophysiological and biomechanical processes active in the development of the idiopathic low back disorder common in workers who perform repetitive lifting tasks in industry. Passive cyclic flexion of the feline lumbar spine at 0.1 HZ for 20 min resulted in creep of the supraspinous ligament and other lumbar viscoelastic tissues as well as spasms superimposed on a decreasing electromyogram (EMG) elicited reflexly from the multifidus muscles. Rest for 7 h did not allow full recovery of the viscoelastic creep; the multifidus EMG gradually increased with initial and delayed hyperexcitability. Increasing the peak load of the cyclic flexion resulted in larger creep in the passive tissues and required a longer time for recovery of reflex EMG activity and longer delayed hyperexcitability, but development of spasms and hyperexcitability was unaffected. It is conceivable that damage to the viscoelastic tissues elicits an inflammatory process that in turn triggers a transient neuromuscular disorder. The present findings provide a biomechanical and neurophysiological explanation for a common idiopathic low back disorder as well as for the development of a cumulative trauma disorder often seen in workers engaged in repetitive lumbar flexion.

Physical characteristics of the axial interosseous ligament of the human sacroiliac joint

BACKGROUND CONTEXT

Although the sacroiliac joint has occupied a place in medical literature since at least the eighteenth century, its role in normal function and dysfunction of the back and hip remains controversial. The controversy persists, because there is still no suitable method to study the role of stability and mobility at the sacroiliac joints in vivo. One cost-effective approach to understanding such complex, deeply placed structures is biomechanical modeling. Unfortunately, very few data on the mechanical properties of tissues in this region are currently available to modelers.

PURPOSE

The objective of this preliminary project was to determine some mechanical properties of the axial interosseous ligament (AIL), and to investigate the histology of the ligament.

STUDY DESIGN/SETTING

A modified split plot design was used in conjunction with descriptive statistics to identify AIL characteristics.

PATIENT SAMPLE

This was a cadaveric study.

OUTCOME MEASURES

The study used descriptive statistics to categorize the ultimate failure strength of the AIL, and to describe the macro-constituents of the ligament.

METHODS

Eighteen sacroiliac joints were harvested from nine fresh female cadavers (age range, 54 to 92). Data from 10 joints submitted to mechanical testing are reported. The eight remaining joints were used for histologic analysis of the AIL by light microscopy.

RESULTS

The AIL proved to be relatively weak, with a mean failure load of 381 N (SD 43.7N) and a peak stress of 1.73 MPa (SD 0.99 MPa). Histologically, the AIL contained significantly less collagen than most other "typical" ligaments.

CONCLUSIONS

The AIL failure loads are just slightly higher than those for the ligamentum flavum in the spine, a tissue composed mainly of elastic fibers. In contrast, the AIL has negligible elastin content. Because the AIL represents about 14% of the total area of interosseous sacroiliac ligaments, its mechanical properties should be useful to modelers of the joint. In addition, it appears that injury to the AIL would do little to compromise the mechanical integrity of the sacroiliac joint. Further study of this ligament seems warranted.

Neuromuscular neutral zones sensitivity to lumbar displacement rate

OBJECTIVES

To determine the displacement and tension thresholds (developed during anterior lumbar flexion) which trigger reflexive muscular activity in the multifidus muscles; their variability with the velocity of flexion; and the pattern of threshold variability across the lumbar spine.Design. An in-vivo study of the feline during passive lumbar flexion applied via the L-4/5 supraspinous ligament.

METHOD

EMG from six pairs of intramuscular electrodes inserted in the L-1/2 to L-6/7 multifidus muscles was recorded while the lumbar spine was passively flexed to 75% of the physiological strain of the supraspinous ligament at rates of 17-100%/s. Three-dimensional models of tension threshold, flexion rate and lumbar levels were developed from the experimental data.

RESULTS

Displacement and tension thresholds were the lowest at the fastest flexion rate and gradually increased as flexion rates decreased. Electromyographic activity was detected at low thresholds at the center of the flexion and at gradually increasing thresholds at higher and lower lumbar segments.

CONCLUSION

Multifidus reflexive muscular activity, which stabilize the spine, is triggered at a displacement and tension thresholds of 5-15% of the physiological range. Earlier activation of muscular activity occurs as the velocity of flexion increases. Earlier activation also occurs near the center of flexion.

RELEVANCE

Sensory-motor neurological feedback maintains spine stability and is responsive to the velocity of lumbar motion. A neuromuscular silence exists in small lumbar movements in which spine stability is not protected by the musculature. Spine models constructed to predict risk factors could benefit from incorporating this new information.

Biomechanics of increased exposure to lumbar injury caused by cyclic loading: Part 1. Loss of reflexive muscular stabilization

STUDY DESIGN

The recording of electromyographic responses from the in vivo lumbar multifidus of the cat, obtained while cyclic loading was applied as in occupational bending/lifting motion over time.

OBJECTIVES

To determine whether the effectiveness of stabilizing reflexive muscular activity diminishes during prolonged cyclic activity; the recovery of lost muscle activity by a 10-minute rest; and whether such diminished muscular activity is caused by fatigue, neurologic habituation, or desensitization of mechanoreceptors in spinal viscoelastic tissues resulting from its laxity.

SUMMARY OF BACKGROUND DATA

The literature repeatedly confirms observation that cyclic occupational functions expose workers to a 10-fold increase in episodes of low back injury and pain. The biomechanical evidence indicates that creep in the viscoelastic tissues of the spine causes increased laxity in the intervertebral joints. The impact of cyclic activity on the function of the muscles, which are the major stabilizing structures of the spine, is not known.

METHODS

Electromyography was performed from the L1 to L7 in vivo multifidus muscles of the cat, while cyclic passive loading of 0.25 Hz was applied to L4-L5. Cyclic loading was applied for 50 minutes, followed by 10 minutes rest and a second 50-minute cyclic loading session. A third 50-minute cyclic loading period also was applied after the preload was reset to 0.5 N to offset the effect of laxity.

RESULTS

Reflexive muscular activity was recorded from the multifidus muscles of all lumbar levels at the initiation of the first 50 minutes of cyclic loading. Activity recorded on electromyography quickly diminished with each cycle during the first 8 minutes of loading to 15% of its initial value. A slower decrease in muscular activity was evident throughout the remaining period, settling at 5% to 10% of its initial level by the end of 50 minutes. A 10-minute rest provided a 20% to 25% recovery of the electromyographic activity, but that was lost within the first minute of cycling. Offsetting the laxity in the spine resulted in full restoration of the electromyographic activity at all lumbar levels.

CONCLUSIONS

The creep induced in the viscoelastic tissues of the spine as a result of cyclic loading desensitizes the mechanoreceptors within, which is manifest in dramatically diminished muscular activity, allowing full exposure to instability and injury, even before fatigue of the musculature sets in.