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 and lunotriquetral joint dynamic stabilizers and their role in wrist neuromuscular control and proprioception.

BACKGROUND: Recent research interest has grown in exploring the role of muscles, isometric contraction, proprioception, and neuromuscular control in addressing dynamic scapholunate and lunotriquetral joint instability, marking a shift in the understanding of wrist stability. PURPOSE: To present a comprehensive review of the carpal ligaments anatomy and wrist biomechanics, with a particular focus on the role of proprioception in dynamic carpal stability and their role in managing scapholunate (SL) and lunotriquetral (LTq) dynamic instabilities. STUDY DESIGN: We conducted a systematic search of the literature and review of the most relevant papers published and indexed in pubmed, related to wrist biomechanics, proprioception and its contribution to carpal dynamic stability. METHODS: The study involved a comprehensive review of neuromuscular mechanisms in dynamic stabilization of the carpus, based on cadaver studies. The 3D position of the scaphoid, triquetrum, and capitate was monitored before and after tendon loading. RESULTS: The extensor carpi ulnaris (ECU) and the flexor carpi radialis (FCR) are identified as the primary pronators of the midcarpal joint. The ECU's pronation effect can potentially strain the scapholunate ligament, while the supinator muscles, the abductor pollicis longus (APL), the extensor carpi radialis longus (ECRL), and the flexor carpi ulnaris (FCU), have a protective role, particularly in cases of scapholunate ligament dysfunctions. The FCR, despite being a pronator of the distal row, has a beneficial effect as it provokes supination of the scaphoid. CONCLUSIONS: Comprehending carpal dysfunctions and instabilities hinges on understanding carpal anatomy and normal biomechanics. Proprioception, encompassing joint position sensation and neuromuscular control, is pivotal for stability. Biomechanical research informs tailored muscle strengthening for specific carpal issues. Supinator muscles should be strengthened for SL injuries, and ECU-focused strengthening and proprioceptive training are key for dynamic LTq instabilities. Ongoing research should delve into the intricate relationship between carpal ligaments, muscles, and proprioception to enhance wrist stability.

Influence of forearm rotation on the kinetic stabilizing efficiency of the muscles that control the scapholunate joint. Clinical application in proprioceptive and neuromuscular rehabilitation programs.

BACKGROUND: This study focuses on the relationship between forearm muscles, carpal ligaments, and their impact on scapholunate joint stability across varying forearm rotations. This is crucial for optimizing pre and postoperative rehabilitation strategies for scapholunate joint dysfunction. PURPOSE: Our study aims to understand the kinetic influence of forearm muscles on scapholunate joint instability. We emphasize the significance of forearm rotation to enhance treatment efficacy. STUDY DESIGN: We conducted an experimental study to understand how forearm muscles contribute to the stability of the scapholunate joint during different degrees of forearm rotation and we focused on the joint effect of muscle groups rather than individual muscles for treatment protocols. RESULTS: Our findings shed light on the conservative treatment of dynamic scapholunate instability and the postoperative rehabilitation of scapholunate ligament repair. We found that the effect of forearm muscles significantly contributes to preserve stability in the scapholunate joint across various forearm rotational positions. These insights have practical implications for hand therapists, offering innovative strategies to enhance clinical practice. CONCLUSIONS: This research underscores the importance of considering forearm rotation when developing rehabilitation protocols for scapholunate joint instability and provides a valuable perspective in line with current rehabilitation principles.

Bilateral Ulnar Deviation Supination Stress Test to Assess Dynamic Scapholunate Instability.

PURPOSE: We describe a new radiologic test to assess the integrity of the scapholunate ligament in dynamic scapholunate dysfunction. METHODS: A bilateral forearm-holding device was designed to perform a comparative radiographic assessment of the scapholunate joint gap during resisted isometric contraction of the extensor carpi ulnaris muscle with full supination of the forearm. The concept is based on the known scaphoid pronation effect of this muscle. Clinical data from 12 patients were collected retrospectively and used to analyze the patients' symptomatic and asymptomatic (contralateral) wrists with a newly developed test called the Bilateral Ulnar Deviation Supination (BUDS) test. A wrist arthroscopy was performed in all cases as a reference standard for the radiologic test. RESULTS: The test was positive in 7 patients, with a mean scapholunate joint gap of 4.8 mm. The mean differences in the scapholunate joint gaps between both wrists were 2.6 mm in BUDS-positive patients and 0.2 mm in BUDS-negative patients. A Geissler stage III or IV scapholunate ligament rupture was confirmed in all BUDS-positive patients; by contrast, BUDS-negative patients exhibited either no lesion or a Geissler stage I injury. CONCLUSIONS: The BUDS test is a new radiologic test based on proven biomechanical effects that is able to accurately assess dynamic scapholunate dysfunctions. The analysis carried out found a correlation between radiographic and arthroscopic findings. Further research is needed to confirm the validity and reliability of the test. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic III.

Immunofluorescence analysis of sensory nerve endings in the interosseous membrane of the forearm.

The human interosseous membrane (IOM) is a fundamental stabilizer during forearm rotation. To investigate the dynamic aspects of forearm stability, we analyzed sensory nerve endings in the IOM. The distal oblique bundle (DOB), the distal accessory band (DAB), the central band (CB), the proximal accessory band (PAB), the dorsal oblique accessory cord (DOAC) and the proximal oblique cord (POC) were dissected from 11 human cadaver forearms. Sensory nerve endings were analyzed at two levels per specimen as total cell amount/mm2 after immunofluorescence staining with low-affinity neurotrophin receptor p75, protein gene product 9.5, S-100 protein and 4',6-diamidino-2-phenylindole on an Apotome microscope, according to Freeman and Wyke's classification. Sensory nerve endings were significantly more commonly found to be equally distributed throughout the structures, rather than being epifascicular, interstitial, or close to the insertion into bone (P ≤ 0.001, respectively). Free nerve endings were the predominant mechanoreceptor in all six structures, with highest density in the DOB, followed by the POC (P ≤ 0.0001, respectively). The DOB had the highest density of Pacini corpuscles. The DOAC and CB had the lowest amounts of sensory innervation. The high density of sensory corpuscles in the DOB, PAB and POC indicate that proprioceptive control of the compressive and directional muscular forces acting on the distal and proximal radioulnar joints is monitored by the DOB, PAB and POC, respectively, due to their closed proximity to both joints, whereas the central parts of the IOM act as structures of passive restraint.

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.

The use of artificial intelligence (AI) to enhance academic communication, education and research: a balanced approach.

Much has been written about the concerns surrounding artificial intelligence (AI). This article looks positively at how AI can enhance communication and academic skills, including teaching and research. The article explains what AI, Generative Pre-trained Transformer (GPT), and chat-GPT are and highlights a few AI-based tools that are currently in use to improve communication and academic skills. It also mentions potential AI problems, such as a lack of personalization, societal biases, and privacy concerns. The future lies in the training of hand surgeons to master the skill of precise communication and academia using AI tools.

Kienböck's disease: preventing disease progression in early-stage disease.

Currently Kienböck's disease remains an 'unsolved' problem in hand surgery. Different factors have been associated with the avascular necrosis of the lunate. Mechanical, vascular and biological factors, alone or in combination, may have an influence in the aetiopathogenesis and determine the progress of the disease and even the results of the treatment. This is especially relevant in the early stages, in which conservative or surgical treatment may modify the natural history of the disease, maintaining the lunate structure and thus preserving the joint surfaces. There are multiple surgical treatments for Kienböck's disease in the early stages, before lunate collapse; each one is based on one of the possible factors that can cause avascular necrosis of the lunate. The objective is not only to treat symptoms but to prevent progression. This article is a review of the most frequent treatments used in the early stages and a personal view of the authors.Level of evidence: V.

Ligaments and muscles stabilizing the radio-ulno-carpal joint.

The technical simplicity of the Darrach procedure may explain why it has been so popular. Excising the distal ulna, however, may have potentially undesired consequences to the biomechanics in two areas: the distal radioulnar and the ulno-carpal joints. These conjointly define the radio-ulno-carpal joint (RUCJ). The RUCJ is not a small and irrelevant articulation that can be removed without possibly paying a functional penalty. It is an important link of the antebrachial frame that provides stability to the distal forearm and the carpus. This article revisits the mechanisms by which some ligaments and muscles ensure that all forces about and within the RUCJ are dealt with efficiently.

Kinetic dysfunction of the wrist with chronic scapholunate dissociation. A cadaver study.

BACKGROUND: Most laboratory studies investigating scapholunate dissociations are based on normal cadaver arms with serially sectioned ligaments. It is assumed that the kinetic behavior of a ligament-sectioned wrist is similar to a scapholunate dissociation. We tested five cadaver wrists with real injuries. The goal of this research was to evaluate the biomechanical behavior of scapholunate advanced collapse wrists compared to an experimental group with simulated injuries. METHODS: Using a magnetic 6-degree of freedom motion tracking device, changes in scaphoid alignment induced by isometric loading 5 wrist motor tendons in two groups of specimens were monitored. Twelve fresh cadaver wrists in which scapholunate injury was simulated by sectioning the scapholunate ligament were compared to 5 arms with chronic scapholunate dissociation. FINDINGS: The behavior of the scaphoid is the same in both groups, but the magnitude of displacement is greater in chronic scapholunate dissociation wrists, although not statistically significant. The extensor carpi ulnaris is the only muscle that provokes scaphoid pronation; all other muscles induce its supination. INTERPRETATION: Different factors may play a role in the amount of scaphoid rotation observed in wrists with chronic scapholunate dissociation. Ligament sectioning alone in the experimental setup can only partially replicate the behavior of real scapholunate dissociations. The extensor carpi ulnaris has a major role in destabilizing scapholunate advanced collapse wrists; therefore, isometric contraction of this muscle should be avoided in the conservative treatment. The experimental setup designed is useful to evaluate the biomechanical behavior of the carpus under traction load.

Trapeziometacarpal Ligaments Biomechanical Study: Implications in Arthroscopy.

Purpose In the presence of early osteoarthritis, changes to the trapeziometacarpal joint (TMJ) often result in pain and is associated with joint instability and a tendency of dorsoradial subluxation. In these instances, arthroscopy may be indicated to: (1) assess the extent of cartilage disease and the laxity of ligaments and to (2) treat TMJ instability. The purpose of our study was to biomechanically analyze which ligaments are the primary stabilizers of the TMJ. Methods Overall, 11 fresh-frozen human cadaver specimens were dissected and attached to a testing device with the thumb positioned in neutral abduction, neutral flexion, and neutral opposition. The four extrinsic and five intrinsic muscle tendons acting on the TMJ were simultaneously loaded with weights proportional to their physiological cross-sectional area. The dorsal, volar, and ulnar groups of ligaments were dissected. A motion-tracking device, FasTrak (Polhemus Inc., Colchester, VT), was used to study the spatial position of the base of the first metacarpal bone (MC1), before and after random sectioning of each of the ligaments. Statistical analysis of the MC1 translation along the transverse XY plane was performed using one-way analysis of variance and a paired t-test, with a significance level of p < 0.05. Results After isolated sectioning of the volar or the ulnar ligaments, the MC1 moved dorsoradially with an average of 0.150 mm (standard deviation [SD]: 0.072) and 0.064 mm (SD: 0.301), respectively. By contrast, the destabilization of the MC1 after sectioning of the dorsal ligaments was substantially larger (0.523 mm; SD: 0.0512; p = 0.004). Conclusion Sectioning of the dorsal ligament group resulted in the greatest dorsoradial translation of the MC1. Consequently, the dorsal ligaments may be regarded as the primary TMJ stabilizers. Clinical Relevance This study suggests that stabilizing arthroscopic shrinkage of the TMJ should be targeted toward the dorsal TMJ ligaments.

How to Avoid Ulnar Nerve Injury When Setting the 6U Wrist Arthroscopy Portal.

The dorsal sensory branch of the ulnar nerve (DSBUN) is at risk in setting the 6U wrist arthroscopy portal. Although surgeons know the risk and are careful when they set the 6U portal, DSBUN injuries still occur. The purpose of the present anatomical study was to evaluate the possibility that DSBUN undergoes dynamic anatomical variations in its location during wrist arthroscopy. The goal of the study was to clarify (1) whether the nerve-to-portal (NTP) distance changes with flexion/extension wrist and/or hand/forearm rotation, and (2) whether there is any particular combination of flexion-extension/hand-forearm rotation where the NTP distance is maximal. Six fresh cadaver arms were suspended in a traction tower with forearm rotation locked, the skin and subcutaneous tissue around the ulnar head was removed, and the NTP distance measured in three predetermined loading/positional conditions. Of all options, the one that consistently showed the longest and safest NTP distance involved wrist flexion and radiocarpal supination when forearm rotation is limited. In conclusion, when an arthroscopic traction device restricts the forearm rotation, the 6U portal should not be set under traction with the hand passively pronated. Failure to observe this precaution can result in serious neuropathic pain.

Extensor mechanism of the fingers: MR imaging-anatomic correlation.

Extension of the fingers is a complex function carried out by simultaneous action of extrinsic and intrinsic muscles, as well as retinacular structures in the dorsum of the wrist, hand, and fingers that support and coordinate the action of the muscles. The extensor mechanism of the fingers is divided into topographic zones, which extend from the forearm to the distal phalanx. Magnetic resonance (MR) imaging shows in detail the musculotendinous and retinacular structures of the extensor apparatus. In the different extensor zones, MR imaging findings are similar to those seen macroscopically in anatomic sections. Understanding of and familiarity with the extensor anatomy of the hand and fingers by the radiologist is crucial for better assessment of pathologic conditions with MR imaging and optimization of this modality as a diagnostic tool. Extensor tendon injuries and tenosynovitis represent clinical situations in which knowledge of this anatomy is useful for the clinical radiologist.

MR imaging of ligament and tendon injuries of the fingers.

Magnetic resonance (MR) imaging can provide important information for diagnosis and evaluation of soft-tissue trauma in the fingers. An optimal imaging technique should include proper positioning, dedicated surface coils, and specific protocols for the suspected abnormalities. Familiarity with the fine anatomy of the normal finger is crucial for identifying pathologic entities. MR imaging is a powerful method for evaluating acute and chronic lesions of the stabilizing articular elements (volar plate and collateral ligaments) of the fingers and thumbs, particularly in the frequently affected proximal interphalangeal and metacarpophalangeal joints. As in other body regions, MR imaging is also useful for depicting traumatic conditions of the extensor and flexor tendons, including injuries to the pulley system. In general, normal ligaments and tendons have low signal intensity on MR images, whereas disruption manifests as increased signal intensity. Radiologists need to understand the full spectrum of finger abnormalities and associated MR imaging findings.