Structural topography of the interosseous membrane of the human forearm

Biomechanical characterization of the central fibrous region of the forearm interosseous Membrane: Implications for finite element modeling

The interosseous membrane (IOM) of the forearm plays a crucial role in facilitating forearm function and mechanical load transmission between the radius and ulna. Accurate characterization of its biomechanical properties is essential for developing realistic finite element models of the forearm. This study aimed to investigate the mechanical behavior and material properties of the central fibrous regions of the IOM using fresh frozen cadavers. Ten forearms from five cadavers were dissected, preserving the IOM and identifying the distal accessory band (DAB), central band (CB), and proximal accessory band (PAB). Bone-ligament-bone specimens were prepared and subjected to uniaxial tensile testing, with the loading direction aligned with the fiber orientation. Force-displacement curves were obtained and converted to force-strain and stress-strain curves using premeasured fiber lengths and cross-sectional areas. The results demonstrated distinct mechanical responses among the IOM regions, with the PAB exhibiting significantly lower force-strain behavior compared to the DAB and CB. The derived force-strain and stress-strain relationships provide valuable insights into the regional variations in stiffness and strength of the IOM, highlighting the importance of considering these differences when modeling the IOM in finite element analysis. In conclusion, this study establishes a foundation for the development of advanced finite element models of the forearm that accurately capture the biomechanical behavior of the IOM.

Periarticular Proprioception: Analyzing the Three-Dimensional Structure of Corpuscular Mechanosensors in the Dorsal Part of the Scapholunate Ligament

INTRODUCTION

Sensory nerve endings transmit mechanical stimuli into afferent neural signals and form the basis of proprioception, giving rise to the self-perception of dynamic stability of joints. We aimed to analyze the three-dimensional structure of periarticular corpuscular sensory nerve endings in a carpal ligament to enhance our understanding of their microstructure.

METHODS

Two dorsal parts of the scapholunate ligament were excised from two human cadaveric wrist specimens. Consecutive cryosections were stained with immunofluorescence markers protein S100B, neurotrophin receptor p75, protein gene product 9.5 (PGP 9.5), and 4',6-diamidino-2-phenylindole. Three-dimensional images of sensory nerve endings were obtained using confocal laser scanning microscopy, and subsequent analysis was performed using Imaris software.

RESULTS

Ruffini endings were characterized by a PGP 9.5-positive central axon, with a median diameter of 4.63 μm and a median of 25 cells. The p75-positive capsule had a range in thickness of 0.94 μm and 15.5 μm, consisting of single to three layers of lamellar cells. Ruffini endings were significantly smaller in volume than Pacini corpuscles or Golgi-like endings. The latter contained a median of three intracorpuscular structures. Ruffini endings and Golgi-like endings presented a similar structural composition of their capsule and subscapular space. The central axon of Pacini corpuscles was surrounded by S100-positive cells forming the inner core which was significantly smaller than the outer core, which was immunoreactive for p75 and PGP 9.5.

CONCLUSION

This study reports new data regarding the intricate outer and intracorpuscular three-dimensional morphology of periarticular sensory nerve endings, including the volume, number of cells, and structural composition. These results may form a basis to differ between normal and pathological morphological changes in periarticular sensory nerve endings in future studies.

The Distal Oblique Bundle in the Distal Forearm: From Anatomical Features to Clinical Implementation

Background and objective The distal oblique bundle (DOB) is nowadays recognized as the thickest component of the distal interosseous membrane (DIOM). It is neither thought to be a clear-cut ligament, and nor does it follow the typical configuration of the rest of the DIOM. It is not always present and some studies have raised disputes about its prevalence and a few anatomical features. In this study, we aimed to provide data on the prevalence and anatomical features of the DOB, which are of great importance at this early stage of research into the topic. Our findings have been correlated with current knowledge and are expected to contribute to clinical implementation. Materials and methods Twenty-eight fresh-frozen forearms were utilized for measurements. Specifically, mean length, width, distance from the middle of the bundle's insertion to the ulna to the tip of the styloid process of the ulna, as well as the distance from the midpoint of its insertion to the radius to the tip of the radiuses' styloid process were calculated. The prevalence was described with a cutoff thickness point of 0.5 mm. Early results based on three cases of DOB reconstruction with the "Riggenbach" technique due to distal radioulnar joint (DRUJ) instability were documented. Results Eleven DOBs were reported out of the 28 specimens, suggesting a prevalence of 39.3%. The mean thickness was 0.88 mm (range: 0.6-1.3 mm), the mean width was 5.22 mm (range: 2.2-8.4 mm), and the mean length was 25.68 mm (range: 22.7-29.2 mm). Proximally, the mean distance from the bundle's ulnar insertion to the tip of the styloid process of the ulna was 51.02 mm (range: 45.5-55.6 mm) while distally, the mean distance from the bundle's insertion to the radius to the tip of the styloid process of the radius was 34.5 mm (range: 31.3-37.7 mm). After a follow-up of at least six months, improvement was evident in all measured areas in the three patients who underwent surgery. Additionally, they reported satisfaction and accomplishment of their preoperative goals. Conclusions Discrepancies in measurements in some anatomic features between studies are probably due to variations in specimen types, measurement methods, and sites. Efforts must continue to be made on a more extensive scale and in a more standardized manner for more factual results and conclusions. "Reconstruction-recreation" or "original construction-creation" procedures yield promising results in a fast, simple, and less invasive manner than traditional methods of DRUJ stabilization.

Malunion deformity of the forearm: Three-dimensional length variation of interosseous membrane and bone collision

It remains unclear to what extent the interosseous membrane (IOM) is affected through the whole range of motion (ROM) in posttraumatic deformities of the forearm. The purpose of this study is to describe the ligament- and bone-related factors involved in rotational deficit of the forearm. Through three-dimensional (3D) kinematic simulations on one cadaveric forearm, angular deformities of 5° in four directions (flexion, extension, valgus, varus) were produced at two locations of the radius and the ulna (proximal and distal third). The occurrence of bone collision in pronation and the linear length variation of six parts of the IOM through the whole ROM were compared between the 32 types of forearm deformities. Similar patterns could be observed among four groups: 12 types of deformity presented increased bone collision in pronation, 8 presented an improvement of bone collision with an increase of the mean linear lengthening of the IOM in neutral rotation, 6 had an increased linear lengthening of the IOM in supination with nearly unchanged bone collision in pronation and 6 types presented nearly unchanged bone collision in pronation with a shortening of the mean linear length of IOM in supination or neutral rotation. This kinematic analysis provides a better understanding of the ligament- and bone-related factors expected to cause rotational deficit in forearm deformity and may help to refine the surgical indications of patient-specific corrective osteotomy.

Alteration of Ligamento-Muscular Reflex Patterns After Cutaneous and Periarticular Desensitization of the Basal Thumb Joint: An Electromyographic Study

PURPOSE

Stimulation of the dorsoradial ligament (DRL) of the first carpometacarpal joint (CMC-1) has shown a ligamento-muscular reflex pathway between the DRL and CMC-1 stabilizing muscles in healthy volunteers. However, it remains unclear how this ligamento-muscular reflex pattern is altered after anesthetizing sensory skin receptors and administering a further periarticular block around the CMC-1 joint, which may influence the dynamic aspects of joint stability.

METHODS

Ligamento-muscular reflexes were obtained from the extensor pollicis longus, abductor pollicis longus, abductor pollicis brevis, and the first dorsal interosseous muscles in 10 healthy participants after establishing superficial anesthesia of the skin around the CMC-1. The DRL was stimulated with a fine wire electrode while EMG activities were recorded during isometric tip, key, and palmar pinch. The measurements were repeated after an additional periarticular CMC-1 block using 5 ml of 1% lidocaine. Average EMG values were analyzed to compare the prestimulus and poststimulus activity.

RESULTS

Statistically significant changes in poststimulus EMG activity were observed in all 4 muscles and all 3 tested thumb positions. A markedly reduced activity in all 4 muscles was observed in the palmar position, followed by the tip and key pinch positions. Almost no reactions were observed in the first 20 ms poststimulus for all muscles in all positions.

CONCLUSIONS

Superficial skin anesthesia and an additional periarticular CMC-1 block anesthesia resulted in a reduced ligamento-muscular reflex pattern in all 4 muscles.

CLINICAL RELEVANCE

Ligamento-muscular reflexes play an important role in dynamic CMC-1 joint stability. The elimination of early reactions, those considered joint-protective reflexes, is a potential risk factor for developing osteoarthritis or injury because it results in an inability to adequately protect and stabilize the joint in sudden movements.

Creation of 3D anatomical models illustrating an intact and centrally torn triangular fibrocartilage complex for patient education prior treatment

BACKGROUND

The triangular fibrocartilage complex (TFCC) is a composite structure located in the human wrist and is made up from fibrocartilage and ligaments. It consists of eight distinct structures, with the ligamentous structures acting as the major stabilizer of the distal radioulnar joint and with the articular disc acting as a shock absorber at the ulnocarpal joint. The articular disc can be called the triangular fibrocartilage (TFC). Thus, traumatic injuries of the TFCC ligamentous structures cause instability of the joint and a centrally torn TFC disc causes ulnar sided wrist pain. TFCC pathologies can be difficult for patients to understand in clinic, due to their complex three-dimensional (3D) nature. The purpose of this study was to produce 3D anatomical models illustrating the normal anatomy of the wrist joint with the TFCC structure and a pathological model with a centrally torn TFC. These models would be used in a hand clinic to aid explanation of this complex three-dimensional anatomical structure and their injury to patients and trainee doctors.

MATERIALS

Three fresh frozen forearm and hand specimens were dissected, 3D scanned, 3D printed and painted. These models were introduced into a hand clinic to aid explanation of the complex anatomical structures, with the first 50 patients being asked, on a visual analog scale of 0-10, to state how much the models helped their understanding of the condition.

RESULTS

Three 3D printed anatomical models were produced to illustrate the (1) forearm muscles and wrist tendons, (2) an intact TFC and (3) a centrally torn TFC. 48 of 50 patients surveyed completed the scale, with an average rating of 8.7 increase in understanding with the models.

CONCLUSION

Patient education and understanding is crucial as it enhances decision making between surgeon and patient. These 3D anatomical models were shown to increase patient's understanding of the pathology. This should consequentially improve discussions on corresponding treatment options during consultation.