Irreducible Ankle Fracture Dislocation Because of Tibialis Posterior and Flexor Digitorum Longus Tendon Entrapment in the Interosseous Membrane: A Case Report.

CASE: We describe the case of a 63-year-old man with anterior ankle dislocation and fracture confirmed by x-ray. Postreduction x-ray and computed tomography (CT) revealed Arbeitsgemeinschaft für Osteosynthesefragen/Orthopaedic Trauma Association (AO/OTA) type 44C3 and Lauge-Hansen pronation-external rotation-type ankle fractures. CONCLUSION: This was a rare case of ankle fracture dislocation because of entrapment of the tibialis posterior and flexor digitorum longus tendons in the interosseous membrane. Tendon entrapment should be suspected in cases of high-energy injuries, Weber type C fractures, Lauge-Hansen pronation-external rotation fractures, syndesmosis widening, and irreducible fractures using manual closed reduction. Fractures and soft tissues should be evaluated by changing the CT settings.

Investigation of the Characteristics and Mechanism of Interosseous Membrane Injuries in Typical Maisonneuve Fracture.

OBJECTIVES: Previous studies on the mechanism and scope of interosseous membrane injury in Maisonneuve fractures have been inconsistent. In order to better guide clinical treatment, the characteristics and mechanism of interosseous membrane injuries and proximal 1/3 fibular fracture in typical Maisonneuve fracture were investigated. METHODS: The study comprised 15 patients between January 2019 and June 2021 with Maisonneuve fracture. All patients received X-ray and MRI examination of the calf and ankle joint, and CT scanning of the ankle joint. The injuries of medial structure, inferior tibiofibular syndesmosis, fibula, posterior malleolus, and interosseous membrane were evaluated. RESULTS: MR images of the calf showed that the injury of interosseous membrane (IOM) was from the syndesmosis to the proximal fibular fracture site in two patients, with a range of 32.3 and 29.8 cm, respectively. In the other 13 patients, the IOM rupture was not only confined to the distal third of the calf, but also close to the fibula fracture, and the IOM was intact between the two fracture sites. The range of distal IOM rupture was 3.7-12.2 cm, with an average of 8.06 ± 2.35 cm. The proximal IOM was completely ruptured from the fibular side at the site of the fibular fracture and the range was 4.1-9.1 (average: 6.75 ± 1.64) cm. The average length of the integrate middle segment of the IOM was 14.55 ± 4.11 (5.6-20.3) cm. MR images of the calf also showed partial rupture of the posterior tibial muscle at the ending point on the fibula in 15 cases, partial rupture of soleus muscle and flexor hallucis longus in seven cases. CONCLUSIONS: The rupture of the IOM was caused by a combination of abduction and external rotation violence. It was manifested in two forms, most of which was not only distal end but also near fibular fracture site ruptures with the middle part intact, and a few were ruptures of the IOM from the ankle to the near fibular fracture site. The tibialis posterior muscle may be related to the location of the fibular fracture.

A Cadaveric Limb Analysis of the Posterior Tibial Musculotendinous Junction to determine the feasibility of Interosseous Membrane Tendon Transfer.

The transfer of the posterior tibial tendon through the interosseous membrane is potentially an effective treatment to correct the deformity of the foot and ankle. Our study aimed to evaluate the anatomical feasibility of anterior transfer of the posterior tibial tendon through the interosseous membrane route using the musculotendinous junction (MTJ). Eighteen adult cadavers were used. The width and thickness of the tibial posterior MTJ, width of the interosseous membrane at the corresponding level, and the window size of the interosseous membrane were measured. Additionally, the distance between the distal end of the MTJ and the tip of the medial malleolus were recorded. The mean length of the posterior tibial tendon was 83.60 mm, the mean distance of the posterior tibial MTJ to medial malleolus tip was 45.48 mm and the mean length of MTJ was 31.74 mm. The mean width of distal end of MTJ was 7.76 mm, thickness of distal end of MTJ was 4.07 mm and the mean width of the interosseous membrane at the distal end of MTJ was 4.76 mm. We found the mean width of the proximal end of MTJ was 20.68 mm, the mean thickness of proximal end of MTJ was 5.52 mm, and mean width of interosseous membrane at the proximal end of MTJ was 8.76 mm. Our study has demonstrated that a 31 mm length incision made at approximately 45 mm from the proximal end of the medial malleolus can safely reach the MTJ. We recommend an opening length of the interosseous membrane of at least 20 mm.

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.

Treatment of acute distal radioulnar joint instability with distal oblique bundle augmentation of the interosseous membrane by suture-button suspension: A case series.

The stability of distal radioulnar joints is afforded by bony radioulnar articulation and peripheral soft-tissue stabilizers. The primary soft-tissue stabilizers are structures that surround the distal radioulnar joint and are collectively referred to as the triangular fibrocartilaginous complex. Among the stabilizers, the volar and dorsal radioulnar ligaments contribute the most to the stability of distal radioulnar joints. For acute traumatic distal radioulnar joint instability accompanied by purely ligamentous injury, traditional surgical treatments involve the repair or reconstruction of the distal radioulnar ligament; however, these intra-articular procedures are highly invasive and difficult. The extra-articular reconstruction of the secondary stabilizer such as the distal oblique bundle of the interosseous membrane has attracted significant attention in recent years; however, most studies have only conducted cadaveric or laboratory modelbased investigations. In this article, we present three patients who suffered from acute dorsal wrist pain after a trauma event. Radiographic and physical examinations revealed distal radioulnar joint instability. All patients were treated with minimally invasive suture-button suspension augmentation in the direction of distal oblique bundle of the interosseous membrane. The instability was resolved after the surgical procedure, but two patients developed ulnar wrist pain and one patient underwent implant removal. All patients have been continually followed at our outpatient department and exhibited stable wrists, despite mild limitation in the range of motion after the procedure. In conclusion, acute traumatic distal radioulnar joint instability may be sufficiently treated with suture-button suspension for augmentation of the distal oblique bundle; however, some obstacles impede the in vivo adoption of this treatment.

Biomechanical assessment of the central band of the interosseous membrane using shear wave elastography: reliability and reproducibility.

The interosseous membrane of the forearm is an essential structure for the stability of the forearm skeleton, the most important part being the central band. The purpose of this study was to determine if shear wave elastography, a non-invasive ultrasound technique, can be used to measure shear wave speed in the central band and quantify stiffness. Fifteen healthy adult subjects were included (30 forearms). The participants forearms were positioned on an articulated plate, with their hand in neutral, pronated and then supinated positions of 30°, 60° and 90°. The shear wave speed was highest in 90° pronation (4.4 m/s (SD 0.3)) and 90° supination (4.4 m/s (SD 0.27)) indicating maximum stiffness in these positions. Its minimum value was in the neutral position, and either in 30° pronation or supination (3.5 m/s (SD 0.3)). Intra- and interobserver agreement was excellent, regardless of probe positioning or forearm mobilization. This study presents a reliable shear wave elastography measurement protocol to describe the physiological function of the central band of the interosseous membrane in healthy adults.Level of evidence: IV.

Simultaneous Reconstruction of the Distal Radioulnar Joint Ligaments and Interosseous Membrane Combined with Ulna Shortening Osteotomy for Chronic Essex-Lopresti Injury.

The Essex-Lopresti pattern of injury comprises radial head fracture, distal radioulnar joint (DRUJ) dislocation and disruption of the interosseus membrane (IOM). Diagnosis is often delayed, and reconstruction remains a management dilemma, with several proposed techniques addressing the radial head via either replacement or fixation; reconstruction of the DRUJ ligaments via anatomic or non-anatomic methods; and IOM reconstruction with synthetic grafts, allograft or autograft. We present a 26-year-old man with a chronic Essex-Lopresti injury who underwent revision ulnar shortening osteotomy (USO), IOM reconstruction using a brachioradialis graft and an Adams-Berger ligament reconstruction of the DRUJ ligaments following a three-year course of increasing pain and instability following radial head dislocation. This case demonstrates the feasibility of a single-stage reconstruction of a chronic Essex-Lopresti injury using a brachioradialis and a palmaris longus autograft. Level of Evidence: Level V (Therapeutic).

Traumatic rupture of the midportion of the interosseous membrane: a rare cause of acute lower leg pain in two soccer players kicked in the anterior shin.

The interosseous membrane (IOM) of the leg is a component of the tibiofibular syndesmosis that serves an important role in stabilization, as well as transferring forces to the fibula during weight-bearing. We present two separate cases of acute traumatic rupture of the midportion of the interosseous membrane in high school soccer players with blunt trauma to the anterior shin with MRI and ultrasound confirmation.

Clinical relationship between distal interosseous membrane thickness measured through magnetic resonance imaging and distal radioulnar joint stability: A retrospective study.

BACKGROUND: Cadaveric studies suggest that a thick part of the distal interosseous membrane (DIOM), known as the distal oblique bundle (DOB), contributes to the distal radioulnar joint (DRUJ)'s stability. We hypothesized that the DIOM thickness, measured through magnetic resonance imaging (MRI), has a clinically significant association with DRUJ stability. METHODS: We retrospectively reviewed patients, from February 2018 to April 2019, who underwent wrist MRI examination with physical examination for DRUJ stability. We evaluated the correlation between their MRI findings (i.e., triangular fibrocartilage complex [TFCC] tears and presence of the DOB) and DRUJ instability. RESULTS: Out of 85 patients with an average age of 42 years, 45 (53%) had foveal TFCC tears, 29 (34%) had a DOB, and 38 patients (45%) had clinical DRUJ instability. Patients with DRUJ instability had a significantly higher incidence of foveal TFCC tears (30/38, vs 15/47, p < 0.001), while DOB was absent (36/38 vs. 20/47, p < 0.001). Among 45 patients with foveal TFCC tears, only 1 out of 13 patients with a DOB had DRUJ instability, whereas 29 out of 32 patients without a DOB had DRUJ instability (p < 0.001). The odds ratio for DRUJ instability was 11.7 (95% CI 2.9-47.5, p = 0.001) for foveal TFCC tear and 54.2 (95% CI 8.2-358.2, p < 0.001) for the absent DOB. CONCLUSIONS: Clinical DRUJ instability was less common when the DOB is present in patients with foveal TFCC tears, which supports DOB's role as a secondary DRUJ stabilizer.

Distal-Ulna Stump Stability: The Role of Distal Interosseous Membrane: Myth or Reality? Anatomical Research.

BACKGROUND: Distal-ulna stump (DUS) instability often occurs when performing a distal radioulnar joint (DRUJ) arthroplasty. Recent studies suggest that the distal interosseous membrane (DIOM) reinforces the triangular fibrocartilage complex, providing additional stability to the DRUJ. The aim of this study was to determine whether the DIOM stabilizes the ulnar stump. METHODS: Twenty fresh-frozen random forearms were dissected. The presence of a distal oblique bundle (DOB) was recorded and measured. The radius was fixed to a vise and the ulna kept free. The DRUJ was fixed with a lag screw. A bone slice was removed by transverse ulna osteotomies 10 and 15 mm proximal to the DRUJ. A 10-N force was applied to the ulna in dorsal and volar directions. Displacements were measured. The DIOM was then transected, and maneuvers and measurements were repeated and compared. RESULTS: A distinct distal membrane was present in 70% and a cord-like DOB in 30%. The mean length was 29 mm. Its origin was proximal to the sigmoid notch; its insertion was on the distal third of the ulna, at its lateral border. This attachment is comprised between 39 and 48 mm proximal to the ulnocarpal joint. Initial displacements averaged 22 mm dorsally and 13 mm volarly. After DIOM transection, ulnar translocation increased to 31 mm dorsally and 19 mm volarly. CONCLUSION: In DRUJ arthroplasties, the DIOM does not appear to be a stabilizer of the DUS beneath a useful threshold. Its retaining effect occurs only after an initial 22-mm dorsal displacement, which we consider not clinically admissible. Therefore, in DRUJ arthroplasties, some augmentation might be advisable.

Role of the interosseous membrane in post-traumatic forearm instability: instructional review.

PURPOSE: In the last two decades, a strong interest on the interosseous membrane (IOM) has developed. METHODS: The authors present a review of the new concepts regarding the understanding of forearm physiology and pathology, with current trends in the surgical management of these rare and debilitating injuries. RESULTS: Anatomical and biomechanical studies have clarified the anatomy of forearm constrains and their role in forearm longitudinal and transverse stability. The radial pull test, a new intraoperative test, has been developed that might increase the detection on IOM injuries. The forearm is now considered a "functional unit" and, consequently, a new classification has been proposed. Uncommon variants and rare patterns of forearm fracture dislocations have been reported in the literature and could not be classified to those commonly referred to using eponyms (Monteggia, Galeazzi, Essex-Lopresti). The new Artiaco et al. classification includes all injury patterns, thus avoids confusion in the nomenclature, and helps surgeon with detection of lesions and guiding surgical treatment. CONCLUSION: Based on the new classification and after current literature review, authors propose a management flowchart for treatment of forearm instability injuries.

Coexistence of two accessory flexor pollicis longus heads or coexistence of two-headed flexor pollicis longus with an unrecognized anatomical structure?

The flexor pollicis longus (FPL) is located in the anterior compartment of the forearm. It is morphologically variable in both point of origin and insertion. An additional head of the FPL can lead to anterior interosseous syndrome. This report presents a morphological variation of the FPL (additional head in proximal attachment and bifurcated tendinous insertion in distal attachment) and an unrecognized structure that has not so far been described in the literature. This structure originates in six heads (attached to the FPL or interosseous membrane) that merge together, and inserts on to the FPL. All the variations noted have clinical significance, ranging from potential nerve compression to prevention of tendon rupture.

Forearm Interosseous Membrane Maintains the Stability of Proximal Radioulnar Joint.

OBJECTIVE: To evaluate the effect of the proximal and central bundles of the interosseous membrane on the stability of proximal radioulnar joint. METHODS: Twenty fresh samples of human forearm provided by the anatomy room of the Department of Human Anatomy of Nanjing Medical University were included in this study. They were used to explore the effect of proximal interosseous membrane bundle on the stability of proximal radioulnar joint. The proximal bundle was reconstructed along the original attachment point. The reconstructions of central bundle were divided into the reconstruction of original attachment point on radius-midpoint of the ulnar original attachment point (reconstruction A) and original attachment point reconstruction (reconstruction B). The loads of the proximal radioulnar joint in different positions were measured. The load of the proximal radioulnar joint was analyzed in neutral, pronation, and supination positions. RESULTS: After resection of proximal and central fascicles, the loads of proximal radioulnar joint in neutral, pronation, and supination positions were significantly lower than those before resection (P < 0.05). After reconstruction, the loads of proximal radioulnar joint in neutral and supination positions were higher than those after resection (P < 0.05). After reconstruction, the loads of proximal radioulnar joint in neutral and supination positions were higher than those after resection (P < 0.05), and that after reconstruction B in pronation position was higher than that after resection (P < 0.05), while there was no significant difference between reconstruction A and after resection (P > 0.05). In supination position, the load of reconstruction B was higher than that of reconstruction A (P < 0.05). After reconstruction of the proximal and central bundles, the proximal radioulnar joint could not reached the same load as it could before resection (P < 0.05). CONCLUSION: The stability of proximal radioulnar joint is affected by central bundle and proximal bundle. Reconstruction can increase the stability of proximal radioulnar joint.

Fracture-dislocations of the forearm joint: a systematic review of the literature and a comprehensive locker-based classification system.

BACKGROUND: Monteggia, Galeazzi, and Essex-Lopresti injuries are the most common types of fracture-dislocation of the forearm. Uncommon variants and rare traumatic patterns of forearm fracture-dislocations have sometimes been reported in literature. In this study we systematically review the literature to identify and classify all cases of forearm joint injury pattern according to the forearm joint and three-locker concepts. METHODS: A comprehensive search of the PubMed database was performed based on major pathological conditions involving fracture-dislocation of the forearm. Essex-Lopresti injury, Monteggia and Galeazzi fracture-dislocations, and proximal and/or distal radioulnar joint dislocations were sought. After article retrieval, the types of forearm lesion were classified using the following numerical algorithm: proximal forearm joint 1 [including proximal radioulnar joint (PRUJ) dislocation with or without radial head fractures], middle radioulnar joint 2, if concomitant radial fracture R, if concomitant interosseous membrane rupture I, if concomitant ulnar fracture U, and distal radioulnar joint 3 [including distal radioulnar joint (DRUJ) dislocation with or without distal radial fractures]. RESULTS: Eighty hundred eighty-four articles were identified through PubMed, and after bibliographic research, duplication removal, and study screening, 462 articles were selected. According to exclusion criteria, 44 full-text articles describing atypical forearm fracture-dislocation were included. Three historical reviews were added separately to the process. We detected rare patterns of two-locker injuries, sometimes referred to using improper terms of variant or equivalent types of Monteggia and Galeazzi injuries. Furthermore, we identified a group of three-locker injuries, other than Essex-Lopresti, associated with ulnar and/or radial shaft fracture causing longitudinal instability. In addition to fracture-dislocations commonly referred to using historical eponyms (Monteggia, Galeazzi, and Essex-Lopresti), our classification system, to the best of the authors' knowledge, allowed us to include all types of dislocation and fracture-dislocation of the forearm joint reported in literature. According to this classification, and similarly to that of the elbow, we could distinguish between simple dislocations and complex dislocations (fracture-dislocations) of the forearm joint. CONCLUSIONS: All injury patterns may be previously identified using an alphanumeric code. This might avoid confusion in forearm fracture-dislocations nomenclature and help surgeons with detection of lesions, guiding surgical treatment. LEVEL OF EVIDENCE: V.

Naringin increases osteoprotegerin expression in fibroblasts from periprosthetic membrane by the Wnt/ß-catenin signaling pathway.

BACKGROUND: The osteoclast bone resorption is critical in aseptic loosening after joint replacement. The balance between activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG) is considered to play a central role in osteoclast maturation. Fibroblasts from the periprosthetic membrane express RANKL and promote osteoclast formation. Studies have demonstrated that naringin inhibited osteoclastogenesis and wear particle-induced osteolysis. In this study, the naringin-induced OPG/RANKL effects and its underlying mechanism were studied in fibroblasts from periprosthetic membrane. METHODS: Fibroblasts were isolated from the periprosthetic membrane during hip arthroplasty for revision due to aseptic loosening. Fibroblasts were cultured and treated with or without naringin and DKK-1 (the classical inhibitor of Wnt/ß-catenin signaling pathway). OPG and RANKL mRNA and protein levels, gene expression of ß-catenin, and cyclin D1, which participate in the Wnt signaling pathway, were examined by real-time polymerase chain reaction and enzyme-linked immunosorbent assay. RESULTS: The mRNA and protein levels of OPG were enhanced by naringin in a dose-dependent manner compared to that of the non-treated control. In contrast, naringin did not affect the expression of RANKL. Importantly, DKK-1 attenuated OPG expression in fibroblasts under naringin treatment. Moreover, naringin stimulated the gene expression of ß-catenin and cyclin D1 in fibroblasts, and the effect could be inhibited by DKK-1. CONCLUSION: The results indicated that naringin enhanced OPG expression through Wnt/ß-catenin signaling pathway in fibroblasts from periprosthetic membrane, which may be useful to inhibit periprosthetic osteolysis during aseptic loosening after total joint arthroplasty.

Epidermal growth factor or platelet-rich plasma combined with induced membrane technique in the treatment of segmental femur defects: an experimental study.

OBJECTIVE: Extensive bone defects remain a therapeutic challenge necessitating alternative surgical approaches with better outcomes. Can increase the effectiveness of PRP or EGF treatment in surgical treatment of large bone defects with Masquelet technique? Aim of this study examined potential therapeutic benefits of the Masquelet technique with induced membranes in combination with platelet-rich plasma (PRP) or epidermal growth factor (EGF) in a rat model of segmental femur defect. METHODS: Three groups each consisting of 20 Sprague-Dawley rats were defined as follows: EGF group, PRP group, and control group. A femoral bone defect was created and filled with antibiotic embedded polymethyl methacrylate. Half of the animals in each group were sacrificed at week 6 and the pseudo-membranes formed were analyzed. In the remaining half, the cement was removed and the space was filled with autograft. After another 6 weeks, the structures formed were examined radiologically, histologically, and biochemically. RESULTS: At week 6, both PRP and EGF groups had significantly higher membrane CD31, TGF-beta, and VEGF levels than controls. At week 12, when compared to controls, PRP and EGF groups had significantly higher membrane CD31 levels and the PRP group had significantly higher membrane TGF levels. Regarding bone tissue levels, PRP and EGF groups had significantly higher VEGF levels and the EGF group had significantly higher BMP levels. In addition, PRP and EGF groups had higher radiological scores than controls. However, the two experimental groups did not differ with respect to any parameter tested in this study. CONCLUSION: Both PRP and EGF seem to be associated with histological, biochemical, and radiological improvements in experimental rat model of Masquelet technique, warranting in further clinical studies. LEVEL OF EVIDENCE: Level 5.

Stabilization of the distal radioulnar joint by reconstructing the interosseous membrane's distal oblique bundle: Cadaver study.

INTRODUCTION: The distal radioulnar (DRU) ligaments play a key role in stabilizing the DRU joint. Ligament reconstruction in this area is an accepted treatment. However, another structure may also be a significant DRUJ stabilizer-the distal oblique bundle (DOB) of the interosseous membrane (IOM). Recent studies have described DOB reconstruction methods, which should be compared to DRU ligament reconstruction. METHODS: Twelve upper limbs were used. First, a descriptive anatomy study was done to determine the prevalence and features of the DOB (insertions, thickness, and relationship with DRU ligaments). Second, biomechanical testing was done with the wrist in neutral position, supination, and pronation. Distal radius translation was evaluated first on an intact wrist then evaluated again after creating bidirectional instability. Lastly, the same tests were repeated after DRU reconstruction using the Adams-Berger technique and DOB reconstruction using the Riggenbach technique. RESULTS: The DOB was present in 50% of specimens and was bilateral. Reconstructing the DOB stabilized the wrist to the same degree as the Adams-Berger technique in neutral and pronation (8% residual major instability). Stability was harder to achieve in supination (25% major instability). It was better at controlling posterior radial translation than anterior translation (3% versus 14% major instability). CONCLUSION: DOB reconstruction appears to be a reliable and less invasive treatment option for DRUJ instability since it is extra-articular. However, the wrist's position and the direction of radial translation seem to alter the stabilization's effectiveness. LEVEL OF EVIDENCE: IV; Cadaver study.

The Essex-Lopresti Injury:: Evaluation and Treatment Considerations.

This article describes evaluation and treatment considerations for Essex-Lopresti injuries. Specific information about pattern recognition and treatment options is provided.

Structural topography of the interosseous membrane of the human forearm.

The aim of this study was to evaluate the morphology of the six different parts of the interosseous membrane (IOM) in 11 human cadaver forearms, including 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). Hematoxylin-eosin and Elastica van Gieson stained slices were used to investigate the tissue morphology. The DOB and DOAC were absent in one IOM and the POB in two IOMs, respectively. The CB and DAB were longer than all other structures except for each other. The DOAC was longer than the DOB. The DAB, CB, and PAB, were broader than the DOB, DOAC, and POC. No significant differences were observed regarding structure thickness. All structures were found to consist of densely packed parallel collagen fiber arrangement. The DOB and POC had a higher amount of elastic fibers in the fascicular collagen tissue than the other structures. Elastic fibers were more often equally distributed throughout the structures than condensed epifascicular or at the insertion into bone. The tight parallel collagen composition within the different structures reflects the central stabilizing role of the IOM in the forearm. The higher amount of elastic fibers within the DOB and POC can be attributed to their location close to the distal and proximal radioulnar joints, respectively. Here elastic fibers allow adaption to forearm rotation, whereas the structures of the central part of IOM have less elasticity reflecting the predominant stabilizing function.