Effects of Radial Extracorporeal Shockwave Therapy on Piriformis Syndrome: A Single-Case Experimental Design.

The effects of radial extracorporeal shockwave therapy (rESWT) on piriformis syndrome were investigated using a single-case study design. This study used an AB single case with a follow-up phase design. The baseline phase consisted of general physical therapy, including piriformis stretching, while the experimental phase consisted of rESWT in addition to general physical therapy. A man in his 70s diagnosed with piriformis syndrome participated in the study. The Numerical Rating Scale (NRS) score, piriformis hardness, and cross-sectional area of the sciatic nerve were measured to determine the effectiveness of the intervention. The baseline and experimental phases were compared using a binomial distribution based on the celeration line. The NRS score, piriformis hardness, and cross-sectional area of the sciatic nerve were significantly decreased in the experimental phase compared to the baseline phase (NRS, p<0.001; piriformis hardness, p<0.001; cross-sectional area of the sciatic nerve, p<0.001). This effect was carried over to the follow-up phase for all variables. rESWT for piriformis syndrome improved the clinical symptoms, piriformis hardness, and cross-sectional area of the sciatic nerve. However, these results are exploratory and require further validation in future clinical trials.

Assessment of the ulnar nerve stiffness during valgus stress of the elbow using shear wave elastography: an observational cross-sectional study.

BACKGROUND: Identification of the relationship between valgus stress in the medial elbow and ulnar nerve strain during maximum external rotation of the shoulder is pivotal for the prevention and management of ulnar neuropathies. In this observational cross-sectional study, we aimed to determine the changes in ulnar nerve stiffness under valgus stress at different nerve entrapment sites. METHODS: Twenty healthy baseball players participated in the study. The stiffness of the ulnar nerve on the throwing side was assessed at two sites, the arcade of Struthers and the Osborne's ligament, at 0°, 60°, and 90° flexion by shear wave elastography using a 10-MHz linear transducer. The arcade of Struthers was defined as the proximal site and the Osborne's ligament as the distal site. Valgus stress was applied to the medial elbow at 0, 30, 50, and 70 N using a Telos stress device, and the stiffness caused by valgus stress was measured. RESULTS: At all elbow flexion angles, the stiffness of the ulnar nerve under 70 N valgus stress was higher than that under 30 N stress. The stiffness of the ulnar nerve at the proximal site was significantly higher than that at the distal site. CONCLUSION: Valgus stress increases ulnar nerve stiffness. In addition, the stiffness of the proximal site increases.

Effect of isometric quadriceps exercise on local microcirculation of the infrapatellar fat pad in female patients with knee osteoarthritis.

OBJECTIVE: To elucidate the local microcirculation of the infrapatellar fat pad (IFP) in patients with knee osteoarthritis (KOA) by determining the changes in IFP hardness and hemoglobin concentration during isometric quadriceps exercise (IQE). DESIGN: In this observational cross-sectional study, patients diagnosed with bilateral KOA were included in the KOA group (30 knees), healthy older adults in the control group (20 knees), and younger adults in the young group (20 knees). Ultrasonography was performed at rest and during IQE to measure IFP hardness based on shear wave velocity. Near-infrared spectroscopy was performed to measure oxygenated hemoglobin (O2Hb), deoxygenated hemoglobin (HHb), and total hemoglobin (cHb) in the IFP before (Baseline), during (IQE task), and after IQE (Post). IFP hardness and O2Hb, HHb, and cHb concentration were analyzed using a linear mixed model for the groups and measurement points. RESULTS: During IQE, IFP hardness changes were significantly less in the KOA group than in the other groups (KOA: 95 % confidence intervals (CIs) [-0.854, 0.028]; control: 95 % CI [-0.941, -0.341]; and young: 95 % CI [-2.305, -1.706]). In the KOA group, O2Hb concentration exhibited no significant changes at Post compared with Baseline; however, significant changes were observed in the other groups (KOA: 95 % CI [-1.176, 0.423]; control: 95 % CI [-1.452, -0.276]; and young: 95 % CI [-4.062, -2.102]). CONCLUSIONS: During IQE, changes in hardness and hemoglobin concentration in the IFP were not significant in the KOA group, suggesting impaired local microcirculation of the IFP.

Capsular attachment on the anterosuperior femoral head-neck junction: A hypothesis about femoroacetabular impingement.

Femoroacetabular impingement (FAI), characterized by a pathological contact between the proximal femur and acetabulum, is a common precursor of hip osteoarthritis. Cam morphology is a bony prominence that causes FAI and frequently forms on the anterosuperior femoral head-neck junction. Despite anatomical consensus regarding the femoral head-neck junction as a boundary area covered by the articular cartilage and joint capsule, it remains unclear whether the joint capsule is continuous with the anterosuperior articular cartilage. For the anatomical consideration of cam morphology formation, this study aimed to investigate the histological characteristics of the capsular attachment on the anterosuperior femoral head-neck junction, particularly focusing on the presence or absence of continuity of the joint capsule to the articular cartilage. A total of 21 anterosuperior regions (seven hips each for the 12:00, 1:30, and 3:00 positions) from seven hips (three males and four females; mean age at death, 68.7 years) were histologically analyzed in this study for quantitative evaluation of the capsular thickness using histological sections stained with Masson's trichrome, as well as qualitative evaluation of the capsular attachment. The present study showed that the joint capsule, which folded proximally to the femoral head-neck junction from the recess, exhibited a blend of the fibrous and synovial regions. Notably, it not only continued with the superficial layer of the articular cartilage, but also attached to the articular cartilage via the fibrocartilage. This continuous region was relatively fibrous with dense connective tissue running in the longitudinal direction. The capsular thickness at the recess point (mean, 1.7 ± 0.9 mm) and those at the distal end of the articular cartilage (0.35 ± 0.16 mm) were significantly greater than the control value for the most superficial layer thickness of the articular cartilage (0.019 ± 0.003 mm) (Dunnett's T3, both p-value <0.001). Based on the fibrous continuity between the joint capsule and articular cartilage and its thickness, this study suggests the anatomical possibility that some mechanical stress can be transmitted from the joint capsule to the articular cartilage at the frequent sites of cam morphology.

Proposals for talonavicular joint assessment using ultrasound imaging and its reliability and validity.

[Purpose] We aimed to develop a noninvasive specific ultrasonographic assessment of the talonavicular joint during loading to facilitate the analysis of treatment of flatfoot. [Participants and Methods] Sixty healthy participants underwent ultrasound imaging of the talonavicular joint while sitting and standing. The talonavicular angle was defined as the intersection of the line connecting the navicular and talar heads and the line connecting the talar head and sustentaculum tali. Talonavicular coverage was assessed using X-ray images of 15 participants. [Results] Ultrasonographic assessment of the talonavicular joint showed a lateral shift of the navicular relative to the head of the talus from sitting to standing. The talonavicular angle was significantly larger when standing than in the sitting position. The difference in talonavicular angle values between sitting and standing significantly correlated with the differences in the talonavicular coverage values. [Conclusion] We showed that ultrasonographic talonavicular angle assessment has good reliability and moderate validity for detecting significant alignment changes in the talonavicular joints due to loading. In the future, this evaluation method should be performed before and after exercise therapy to assess and develop appropriate exercise therapy for flatfoot.

Contribution of the complex comprising the masticatory fascia, disc, and capsule to temporomandibular joint stabilization: An anatomical study.

BACKGROUND: Anterior displacement of the temporomandibular joint (TMJ) disc is the most typical pathological condition of TMJ disorders. Structures attached to the articular disc may support the disc in various directions and contribute to stabilizing the TMJ. However, the relationship between the articular disc, capsule, and masticatory muscles remains unclear. Therefore, this study aimed to clarify the relationship between the masticatory muscles, related masticatory fascia, articular disc, and capsule. METHODS: We examined 10 halves from adult Japanese cadavers, with five halves macroscopically analyzed and the remaining five histologically analyzed. The TMJ was dissected from the lateral aspect for gross anatomical analysis. For histological analysis, the relationship between the temporal and masseteric fasciae and the articular capsule was observed in the coronal section. Additionally, we evaluated relationships among the disc, capsule, temporal fascia, and masseteric fascia in 10 living and healthy volunteers using magnetic resonance imaging. RESULTS: The articular disc was attached to the capsule without a clear border. The capsule continued into the masseteric and temporal fasciae. Consequently, the articular disc, capsule, masseteric, and temporal fasciae were considered a single complex. CONCLUSIONS: The single complex of the temporalis, masseter, capsule, masticatory fascia, and disc may antagonize the force in the posterolateral direction through the fascia.

Morphological differences between the dorsal and palmar septa of the first extensor compartment in relation to the brachioradialis and pronator quadratus.

BACKGROUND: The first extensor compartment of the wrist is known as a frequent site of stenosing tenosynovitis, referred to as de Quervain's disease. De Quervain's disease occurs more frequently in the dorsal part of the first extensor compartment than in the palmar part; however, the anatomical reason why the dorsal part is worse remains poorly elucidated. This study clarified the morphological differences between the dorsal and palmar parts by examining their relationship with the surrounding structures. METHODS: In this study, a total of 35 wrists from 23 Japanese cadavers were used. Twenty-five wrists were randomly assigned for macroscopic analysis, and the remaining 10 wrists were used for histological analysis. RESULTS: The palmar septum of the first extensor compartment was connected to the brachioradialis tendon and superficial head of the pronator quadratus and was histologically stout compared to the dorsal septum. Despite several anatomical variations, such as the septum between the abductor pollicis longus/extensor pollicis brevis and the multiple tendons of these muscles, the aforementioned characteristics of the fibrous sheath in the first extensor compartment were identical in all specimens. CONCLUSION: In contrast to the fragile structure of the dorsal septum, the stout structure of the palmar septum could be related to the low occurrence of symptoms of de Quervain's disease. The present results could play a role in revealing the pathogeny and establish the precise treatment for de Quervain's disease and provide an anatomical basis for kinesiological/biomechanical studies.

In vivo interrelationships between the gluteus minimus and hip joint capsule in the hip internal rotation position with flexion.

BACKGROUND: The flexion adduction internal rotation (FADIR) test is performed by the combined motions of hip flexion (with knee flexion), adduction, and internal rotation, and can often reproduce anterior hip pain consistent with an individual's presenting pain. Since it has high sensitivity for intraarticular pathology diagnosis but low specificity, understanding the extraarticular pathology that can induce anterior hip pain in the FADIR test may also be essential. This study hypothesized that the interrelationships between the joint capsule and gluteus minimus differ in individuals with and without FADIR-positive pain and aimed to elucidate the in vivo interrelationships at hip internal rotation in 90°-flexion, which is also often restricted in individuals with FADIR-positive pain. METHODS: Ten hips were included in the FADIR-positive group, and ten hips without hip pain in the FADIR test were included in a control group. Based on the ultrasound images at the four hip rotation conditions (20° and 10° external rotations, 0° external/internal rotation, and 10° internal rotation), orientation measurements of the gluteus minimus (muscle belly portion) and joint capsule were performed and quantitatively compared between the FADIR-positive and control groups. Additionally, 3 hips of 3 participants were randomly selected from each of the control and FADIR-positive groups for magnetic resonance imaging analysis. RESULTS: At 0°-external/internal and 10°-internal rotation, on ultrasound images, fibers of the gluteus minimus and joint capsule in the FADIR-positive group were significantly more oriented in the same direction than those in the control group. Magnetic resonance imaging showed that the loose connective tissue between the gluteus minimus and joint capsule was prominent at 10°-internal rotation in the control group, although this was not apparent in the FADIR-positive group. CONCLUSIONS: At hip internal rotation in 90° flexion, the muscular belly portion of the gluteus minimus and joint capsule were oriented in the same direction to a greater extent in the FADIR-positive group than in the control group owing to a morphological change in the loose connective tissue between them. The pathological changes in the loose connective tissue may inhibit smooth movement of the gluteus minimus relative to the joint capsule in individuals with FADIR-positive pain.

Effects of short foot exercises with ultrasound bio-feedback on motor learning and foot alignment: A double blinded randomized control trial.

BACKGROUND: Short foot exercises (SFE) take a long time to master and require a feedback tool to improve motor learning. OBJECTIVE: This study aimed to investigate the effect of bio-feedback of talonavicular joint movements in learning SFE with ultrasound (US) imaging. METHODS: This study included thirty-one healthy volunteers and was designed as a double-blind randomized control trial. Subjects were randomly assigned to one of two groups: the control group, which performed SFE under verbal instruction, and the US bio-feedback (USBF) group, which performed SFE with real-time bio-feedback of the talonavicular joint alignment. All subjects underwent two sessions of 5 minutes each, and SFE was performed as a self-exercise, between sessions, for one week. The difference in foot length and navicular height were assessed at baseline, after Session 1, before Session 2, and one week after Session 2. These differences were compared between the two groups using the Mann-Whitney U test. RESULTS: In terms of navicular height change, the USBF group (7.5 ± 4.3 mm) was significantly higher than the control group (4.2 ± 3.3 mm) one week after session 2 (p= 0.04, effect size = 0.86). CONCLUSION: SFE with USBF is an effective intervention for performing SFE.

Effects of Compression Intervention on the Thigh Using Elastic Bandage on Lateral Femoral Pain After Trochanteric Fractures: A Multicenter Randomized Controlled Trial.

A trochanteric fracture is one type of hip fracture. Management of postoperative pain after trochanteric fracture that is caused by decreased gliding between tissues in the lateral thigh is not established. The aim of this study was to examine the effect of compression of the thigh using an elastic bandage on trochanteric fracture after surgery. Multicenter randomized controlled trial was conducted in collaboration with the Comprehensive Rehabilitation Unit (sub-acute rehabilitation Unit) in two hospitals. Eligible volunteers (n = 34) with trochanteric fractures after surgery were randomly assigned to two groups. In the treatment group, participants practiced standing and walking under compression of the thigh with an elastic bandage. The control group was blinded to the intervention and practiced standing and walking under non-compression of the thigh with an elastic bandage. Both groups underwent a standard physical therapy program 2 times a day, daily. Two-way repeated measures of ANOVA showed significant main effect between the groups for gliding between tissue (p < .001), lateral femoral pain (p < .001), subcutaneous tissue thickness (p = .044). Compression of the thigh with an elastic bandage significantly improved subcutaneous tissue thickness, gliding between tissues, lateral thigh pain. Gait velocity improved with these functional improvements.

Elevated levels of interleukin-9 in the serum of bullous pemphigoid: possible association with the pathogenicity of bullous pemphigoid.

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease (sAIBD). In addition to disease causing autoantibodies, several leukocyte subsets, including mast cells and eosinophils, play key roles in mediating skin inflammation. Detailed immunophenotyping and, more recently, the therapeutic effects of interleukin-4 (IL-4) receptor alpha inhibition in BP pointed to a prominent role of T helper 2 (Th2) cells. Among other cell types, IL-9 is expressed by Th2 and mast cells and potentially drives allergic, Th2-dominated inflammation. Although cytokines in BP have been relatively well investigated, the role of IL-9 has remained enigmatic. This study aimed to evaluate the effect of IL-9 in BP. Serum IL-9 levels were significantly elevated in patients with BP and decreased upon induction of remission. Serum IL-9 levels were not elevated in epidermolysis bullosa acquisita, another sAIBD. The time-course analysis using serum sets from four patients with BP revealed that serum IL-9 was a sensitive biomarker of BP. IL-9-positive cells infiltrated dominantly in BP lesions, especially in the blister fluid, and Th9 cells were abundant. Therefore, IL-9 was elevated in the serum and lesions of BP, which could be a biomarker of BP.

Automatic Identification of Ultrasound Images of the Tibial Nerve in Different Ankle Positions Using Deep Learning.

Peripheral nerve tension is known to be related to the pathophysiology of neuropathy; however, assessing this tension is difficult in a clinical setting. In this study, we aimed to develop a deep learning algorithm for the automatic assessment of tibial nerve tension using B-mode ultrasound imaging. To develop the algorithm, we used 204 ultrasound images of the tibial nerve in three positions: the maximum dorsiflexion position and -10° and -20° plantar flexion from maximum dorsiflexion. The images were taken of 68 healthy volunteers who did not have any abnormalities in the lower limbs at the time of testing. The tibial nerve was manually segmented in all images, and 163 cases were automatically extracted as the training dataset using U-Net. Additionally, convolutional neural network (CNN)-based classification was performed to determine each ankle position. The automatic classification was validated using five-fold cross-validation from the testing data composed of 41 data points. The highest mean accuracy (0.92) was achieved using manual segmentation. The mean accuracy of the full auto-classification of the tibial nerve at each ankle position was more than 0.77 using five-fold cross-validation. Thus, the tension of the tibial nerve can be accurately assessed with different dorsiflexion angles using an ultrasound imaging analysis with U-Net and a CNN.

Posteromedial capsular anatomy of the tibia for consideration of the medial meniscal support structure using a multidimensional analysis.

Medial meniscal extrusion (MME) is a structural abnormality that leads to early knee osteoarthritis; however, its formation remains debated. For anatomical consideration of the mechanism underlying MME formation, we examined the capsular attachment on the posteromedial tibia and its layered association with the semimembranosus. Fourteen knees of eight body donors were analyzed in this study; six knees were grouped for macroscopic analysis, whereas four knees each were grouped for histological and phosphotungstic acid-enhanced micro-computed tomography analyses. The capsular attachment varied in width according to location and was not distant from the articular cartilage and posterior root. A portion of the posteromedial joint capsule formed the semimembranosus tendinous sheath. The dense fibrous membrane superficial to the semimembranosus, which was continuous from its tendinous sheath, existed as one of the layers of the joint capsule. The aforementioned findings were confirmed in all specimens. Based on the capsular attachment and its layered association with the semimembranosus, the conventional posteromedial knee ligaments may be only a part of the joint capsule divided into two layers by the semimembranosus. If the coordinated action of the joint capsule and semimembranosus partially contributes to the medial meniscus stability, such a structural problem may affect MME formation.

Tibial nerve dynamics during ankle dorsiflexion: The relationship between stiffness and excursion of the tibial nerve.

Peripheral nerves extend with a gradual increase in stiffness and also with excursion, namely reduction of fiber bundle waviness, to adapt to joint movements. Although the close relationships between the tibial nerve (TN) excursion and stiffness during ankle dorsiflexion in cadaver studies, the precise in vivo their relationships remain unclear. We hypothesized that the excursion of the TN can be estimated from its stiffness in vivo using shear-wave elastography. This study aimed to analyze the relationships between the TN stiffness at the plantarflexion and dorsiflexion and TN excursion during dorsiflexion using ultrasonography. Twenty-one healthy adults participated in constant-velocity movements of the ankle joint with a 20° range from the maximum dorsiflexion, and the TN was imaged using an ultrasound imaging system. The maximum flow velocity value and the TN excursion distance per dorsiflexion were then calculated as indexes of excursion using the application software Flow PIV. The shear wave velocities of the TN at plantarflexion and dorsiflexion were also measured. Based on our single linear regression, the shear wave velocities of the TN at the plantarflexion had the strongest effect on the excursion indexes, followed by the those at dorsiflexion. Ultrasonographic shear wave velocity could predict the TN excursion if measured under mild plantarflexion of the ankle joint, and might have a close biomechanical relation to the total waviness of the TN.

Origin, course, and distribution of the posterior femoral cutaneous nerve and the spatial relationship among its branches.

This study aimed to elucidate the origin, course, and distribution of the branches of the posterior femoral cutaneous nerve, considering the segmental and dorsoventral compositions of the sacral plexus, including the pudendal nerve. The buttocks and thighs of five cadavers were analyzed bilaterally. The branches emerged from the sacral plexus, which was divided dorsally to ventrally into the superior gluteal, inferior gluteal, common peroneal, tibial, and pudendal nerves. It descended lateral to the ischial tuberosity and comprised the thigh, gluteal, and perineal branches. As for the thigh and gluteal branches, the dorsoventral order of those originating from the sacral plexus corresponded to the lateromedial order of their distribution. However, the dorsoventral boundary was displaced at the inferior margin of the gluteus maximus between the thigh and gluteal branches. The perineal branch originated from the ventral branch of the nerve roots. In addition, the pudendal nerve branches, which ran medially to the ischial tuberosity, were distributed in the medial part of the inferior gluteal region. These branches should be distinguished from the gluteal branches; the former should be classified as the medial inferior cluneal nerves and the latter as the lateral ones. Finally, the medial part of the inferior gluteal region was distributed by branches of the dorsal sacral rami, which may correspond to the medial cluneal nerves. Thus, the composition of the posterior femoral cutaneous nerve is considered necessary when considering the dorsoventral relationships of the sacral plexus and boundaries of the dorsal and ventral rami.

Evaluation of morphological features of palatopharyngeus insertion into the thyroid cartilage.

The attachment of the palatopharyngeus extended from the posterior end of the thyroid cartilage to the posterior margin of the inferior constrictor attachment that might contribute to successive swallowing movements. Laryngeal elevation is essential for proper swallowing and breathing. Recently, clinical research has demonstrated that the palatopharyngeus, a longitudinal muscle of the pharynx, is involved in the elevation of the larynx. However, the morphological relationship between the larynx and palatopharyngeus remains unclear. In the present study, we analyzed the attachment site and characteristics of the palatopharyngeus in the thyroid cartilage. We evaluated 14 halves of seven heads from Japanese cadavers (average age: 76.4 years); 12 halves, anatomically and two halves histologically. A part of the palatopharyngeus, which originated from the inferior aspect of the palatine aponeurosis, was attached to the inner and outer surfaces of the thyroid cartilage through collagen fibers. The attachment area extends from the posterior end of the thyroid cartilage to the posterior margin of the attachment site of the inferior constrictor. The palatopharyngeus may elevate the larynx with the suprahyoid muscles and contribute to successive movements of swallowing with surrounding muscles. Based on our findings and previous studies, palatopharyngeus with various muscle bundle directions may be essential for the coordination of continuous swallowing events.

Subcorneal pustular dermatosis-type IgA pemphigus associated with multiple myeloma: A case report and literature review.

Immunoglobulin A (IgA) pemphigus, also known as intercellular IgA dermatosis, is a rare autoimmune bullous disease presenting with IgA anti-keratinocyte cell surface autoantibodies. Concomitant lymphoproliferative disorders have been reported in IgA pemphigus, including IgA monoclonal gammopathy of undetermined significance and IgA type multiple myeloma (MM). A 35-year-old Japanese woman with a 3-year history of pruritic papulovesicles on her lower legs and trunk was referred to our department. Histopathological examination revealed acantholytic blisters, and results of both direct and indirect immunofluorescence were negative. Direct and indirect immunofluorescence were still negative 3 years and 7 months later. Approximately 7 years after her first visit, the patient was re-referred to us because of disease exacerbation. Histopathological findings revealed subcorneal blistering with acantholysis, in which neutrophil-dominant inflammatory cells were present. Indirect immunofluorescence was positive for IgA on the epidermal cell surface and both desmoglein (Dsg) 1/3 and (Dsc) desmocollin 1-3 enzyme-linked immunosorbent assays (ELISAs) for IgA were positive. The histological findings and positive Dsc1 IgA ELISA led to the diagnosis of subcorneal pustular dermatosis (SPD)-type IgA pemphigus. Further examination revealed hyper-IgA globulinemia, increased serum IgA-κ protein, and increased plasma cells in the bone marrow, enabling the diagnosis of IgA type MM. Daratumumab, lenalidomide, and dexamethasone (DLd) therapy was effective for both the MM and the skin lesions, resulting in negative results on Dsg1/3 and Dsc1-3 IgA ELISAs. The association between IgA pemphigus and IgA type multiple myeloma remains unclear, and only seven cases including the present case have been reported. Literature review revealed associations between SPD-type and IgA κ chain in IgA pemphigus and MM, and that in most cases the onset or diagnosis of MM was simultaneous or occurred after the diagnosis of IgA pemphigus. Therefore, clinicians should be aware of the development of multiple myeloma during the clinical course of patients with SPD-type IgA pemphigus.

Carcinoma showing thymus-like differentiation of the parotid gland: The brief report of cytomorphology and review of the literature.

Here, we report an extremely rare case of carcinoma with thymus-like differentiation (CASTLE) of the parotid gland. CASTLE is a rare malignant epithelial tumor with thymic epithelial differentiation that arises in the thyroid gland or perithyroidal soft tissue. CASTLE of salivary gland origin is rare, with only nine published case reports to date (reported as "CASTLE" or "thymic carcinoma"). It is critical to diagnose salivary gland tumors using fine needle aspiration cytology. However, this tumor is rare, and there have been few studies on its cytomorphological features. Therefore, it is important to understand the cytological diagnostic characteristics of CASTLE. Herein, we review the cytological features and diagnostic characteristics of salivary gland CASTLE. We also report the genotype results obtained using targeted exome sequencing, which we analyzed with DNA extracted from formalin-fixed paraffin-embedded tissue.

Anatomical study for elucidating the stabilization mechanism in the trapeziometacarpal joint.

To determine the pathogenesis of trapeziometacarpal (TMC) joint instability, which leads to osteoarthritis, we investigated the anatomical relationships among the surrounding ligaments, muscles (first dorsal interosseous [FDI] and opponens pollicis [OPP]), and joint capsule. We examined the bone morphology and cortical bone thickening in 25 cadaveric thumbs using micro-computed tomography and performed macroscopic and histological analyses. The dorsal trapezium had a tubercle with cortical bone thickening, corresponding to the attachment of the FDI aponeurosis intermingled with the joint capsule. Radially, the thin joint capsule was observed to underlie the muscular part of the OPP. Therefore, the dorsal ligaments, which have been previously considered static stabilizers, could be interpreted as parts of the capsuloaponeurotic complex consisting of the FDI aponeurosis and joint capsule. In the radial aspect, muscular OPP activation may be essential for TMC joint stabilization. Our findings may contribute to the appropriate management of TMC osteoarthritis.