Development of a musculoskeletal shoulder model considering anatomic joint structures and soft-tissue deformation for dynamic simulation.

The shoulder joint has a high degree of freedom and an extremely complex and unstable kinematic mechanism. Coordinated contraction of the rotator cuff muscles that stop around the humeral head and the deltoid muscles and the extensibility of soft tissues, such as the joint capsule, labrum, and ligaments, contribute to shoulder-joint stability. Understanding the mechanics of shoulder-joint movement, including soft-tissue characteristics, is important for disease prevention and the development of a device for disease treatment. This study aimed to create a musculoskeletal shoulder model to represent the realistic behavior of joint movement and soft-tissue deformation as a dynamic simulation using a rigid-body model for bones and a soft-body model for soft tissues via a spring-damper-mass system. To reproduce the muscle-contraction properties of organisms, we used a muscle-expansion representation and Hill's mechanical muscle model. Shoulder motion, including the movement of the center of rotation in joints, was reproduced, and the strain in the joint capsule during dynamic shoulder movement was quantified. Furthermore, we investigated narrowing of the acromiohumeral distance in several situations to induce tissue damage due to rotator cuff impingement at the anterior-subacromial border during shoulder abduction. Given that the model can analyze exercises under disease conditions, such as muscle and tendon injuries and impingement syndrome, the proposed model is expected to help elucidate disease mechanisms and develop treatment guidelines.

Neglected Sprengel's deformity in an 80-year-old female cadaver: a case report.

BACKGROUND: Sprengel's deformity is a congenital abnormality of the shoulder girdle. Because scapular retraction, such as the Green procedure, is usually performed during childhood to improve esthetics and shoulder function, Sprengel's deformity is rarely found in older patients. CASE PRESENTATION: We presented a unique case of a Japanese female cadaver with Sprengel's deformity at the age of 80 years. Anatomical dissection and radiological imaging revealed musculoskeletal anomalies associated with Sprengel's deformity, including Klippel-Feil syndrome, presence of an omovertebral bone, and absence of the trapezius muscle. In addition, bilateral cervical ribs were in contact with the brachial plexus. These anomalies may lead to numbness, pain, and limited range of motion of the neck and upper girdle with aging. CONCLUSIONS: Because most adult patients with Sprengel's deformity experience neck pain and limited movement of the shoulder, the presented case is a rare case of neglected Sprengel's deformity in an 80-year-old cadaver.

A rat model for acute limb ischemia using microsized gelatin beads.

OBJECTIVE: Acute limb ischemia (ALI) is a rapid decrease in lower limb blood flow due to acute occlusion of peripheral arteries or bypass grafts. This study aimed to establish an ALI model using microsized gelatin beads and to investigate the pathophysiological conditions. METHODS: Male Sprague-Dawley rats were anesthetized, and a low or high dose of microsized gelatin beads was administered into the left femoral artery on days 0 and 7. A control, that is, normal saline (NS) group in which NS was administered in the left femoral artery, a femoral artery cut (FAC) group in which the left femoral artery was cut, and a sciatic nerve cut (SNC) group in which the left sciatic nerve was cut were prepared. After 21 days, the temperature changes and the muscle weights in the lower limbs were measured. To assess nerve damage, the L1-6 sympathetic ganglia were immunostained with activating transcription factor 3 (ATF3) antibody. RESULTS: In the Low-dose, High-dose, and FAC groups, a decrease in temperature was predominantly observed in the left limb. In the High-dose and SNC groups, the weight of the soleus muscle and extensor digitorum longus in the left limb decreased; however, no weight changes were observed in the Low-dose and FAC groups. Conversely, the weight of the gastrocnemius muscle significantly decreased in the Low-dose, High-dose, FAC, and SNC groups. In the High-dose and SNC groups, the number of ATF3-positive cells in the sympathetic ganglia significantly increased, and in the Low-dose, a small number of ATF3-positive cells were observed. However, ATF3-positive cells were rarely observed in the FAC and NS groups. CONCLUSION: We established an ALI rat model using microsized gelatin beads. The results of this study suggest that autonomic neuropathy in ALI is related to both muscle damage and peripheral neuropathy.

Role of endothelial hyaluronan in peritoneal membrane transport and disease conditions during peritoneal dialysis.

Peritoneal membrane dysfunction in peritoneal dialysis (PD) is primarily attributed to angiogenesis; however, the integrity of vascular endothelial cells can affect peritoneal permeability. Hyaluronan, a component of the endothelial glycocalyx, is reportedly involved in preventing proteinuria in the normal glomerulus. One hypothesis suggests that development of encapsulating peritoneal sclerosis (EPS) is triggered by protein leakage due to vascular endothelial injury. We therefore investigated the effect of hyaluronan in the glycocalyx on peritoneal permeability and disease conditions. After hyaluronidase-mediated degradation of hyaluronan on the endothelial cells of mice, macromolecules, including albumin and ß2 microglobulin, leaked into the dialysate. However, peritoneal transport of small solute molecules was not affected. Pathologically, hyaluronan expression was diminished; however, expression of vascular endothelial cadherin and heparan sulfate, a core protein of the glycocalyx, was preserved. Hyaluronan expression on endothelial cells was studied using 254 human peritoneal membrane samples. Hyaluronan expression decreased in patients undergoing long-term PD treatment and EPS patients treated with conventional solutions. Furthermore, the extent of hyaluronan loss correlated with the severity of vasculopathy. Hyaluronan on endothelial cells is involved in the peritoneal transport of macromolecules. Treatment strategies that preserve hyaluronan in the glycocalyx could prevent the leakage of macromolecules and subsequent related complications.

Intimal growth on the luminal surface of arteriovenous grafts in rats.

BACKGROUND: Endothelial cells are known to grow on the luminal surface of arteriovenous grafts (AVGs) used in hemodialysis. Although endothelial cells are important for preventing infection, a detailed growth of endothelial cells in AVGs is unknown. This study sought to create a simpler animal model of AVGs and to investigate how endothelial cells form on the luminal surface. METHODS: Polyethylene grafts were placed between the cervical artery and vein of Wistar rats. The grafts were removed at 6 h, 24 h, 3 days, or 7 days after placement. The luminal surface was observed under optical and polarizing microscopy and stained with endothelial cell markers (LEL, CD31), the progenitor cell marker CD34, and the macrophage marker ED-1. RESULTS: Microscopy demonstrated many diffuse vascular endothelial cells on the luminal surface of AVGs after placement. While there was no difference in the number of LEL-positive cells between the arterial side (AS) and venous side (VS) at 6 h or 7 days, there were significantly more of these cells on the VS at both 24 h and 3 days (p < 0.05). Analysis at 24 h showed some CD31-positive cells and few CD34-positive cells. CONCLUSIONS: This was the first study to use a simple rat model of AVG placement. Endothelial cell formation was initially more active on the VS than on the AS, but these cells subsequently increased in number across the luminal surface. Future clinical studies might contribute clinically by confirming whether AS versus VS puncture results in different infection rates.

Relationship between attachment site of tibialis anterior muscle and shape of tibia: anatomical study of cadavers.

BACKGROUND: Tibialis anterior (TA) muscle is the largest dorsiflexor of the ankle joint and plays an important role during gait movement. However, descriptions of the TA attachment site are inconsistent even among major anatomy textbooks, and its origin, especially the attachment site for the tibia, has not been reported in detail. This study is the first experimental attempt to investigate the origin of the TA in detail, paying particular attention to the relationship with the shape of the tibia, including sex differences. METHODS: Forty legs (20 males, 20 females) from twenty Japanese cadavers were examined. Gross anatomical examination of the TA's attachment site to the tibia and the tibia's shape was performed. RESULTS: The location of the distal end of the TA's attachment on tibia was significantly more distal in males than in females (p < 0.01). The anterior border of the tibia had a gentle S-like curve, with a medially convex curve in the proximal region and a laterally convex curve in the distal region in frontal plane. The most protruding point of the distal curve of the anterior border located significantly more proximal in females than in males (p = 0.02). CONCLUSIONS: There were sex differences in the distal end of the attachment site on tibia of the TA and the shape of the tibia. Consequently, the variations in the attachment site of TA were considered to provide for differences in function of TA. In males, the TA may enable advantageous power exertion, whereas in females it may work efficiently for dorsiflexion of ankle, respectively. Sex differences in TA's attachment site and the shape of the tibia may be involved in gait movement as well as frequency of lower leg disorders such as chronic exertional compartment syndrome.

Short-term high-fat and high-carbohydrate diets increase susceptibility to liver injury by inducing hepatic procoagulant and proinflammatory conditions with different balances.

OBJECTIVES: High-fat diet (HFD) and high-carbohydrate diet (HCD) are strongly linked to nonalcoholic fatty liver disease, a hepatic manifestation of metabolic syndrome. The mechanism of pathologic progression from nonalcoholic fatty liver disease to nonalcoholic steatohepatitis, which is a more severe form associated with inflammation and fibrosis, remains poorly understood. Thus, the aim of this study was to investigate and compare the inflammatory and coagulative state of the liver in short-term HFD- or HCD-fed mice with acute liver injury induced by concanavalin A (Con A). METHODS: Histopathologic evaluation, real-time polymerase chain reaction, and immunohistochemical evaluation were performed on the liver of mice fed HFDs and HCDs for 4 d before and after Con A administration. RESULTS: The liver of the HFD-fed mice had larger fibrinogen/fibrin depositions than those fed the HCD. HCD induced the expression of the proinflammatory cytokine tumor necrosis factor-α in the liver. Moreover, the expression of proinflammatory cytokines and chemokines was further enhanced after Con A stimulation in HCD (e.g., interleukin-1α, interleukin-6 at 1 h), with a strong tendency for inflammatory cell infiltration also found (24 h). CONCLUSIONS: Short-term HCD and HFD increased susceptibility to liver injury. HCD tended to induce more intense inflammation, whereas HFD tended to induce more intense hypercoagulation, suggesting that HCD and HFD may have different mechanisms of pathologic progression to nonalcoholic steatohepatitis.

Nerve branches to the anterior tibial artery: Clinical application.

Arteries receive vascular branches (VBs) from peripheral nerves. VBs are thought to be involved in arterial constriction. Although the anterior tibial artery (ATA) receives VBs, information on their branching patterns and distribution areas remains limited. The aim of this study was to investigate the anatomical structures of the VBs reaching the ATA. Forty cadaver limbs were examined to assess the branching patterns and distribution areas of the VBs reaching the ATA. The VBs reaching the ATA ramified from the deep fibular nerve (DFN), and the ATA received two or three VBs in each limb. The following mean distances from the head of fibula to the points at which the VBs reached the ATA were measured: all the VBs, 1st VB, 2nd VB and 3rd VB. The measurements were 51.5 ± 23.2 mm, 33.3 ± 3.7 mm, 53.3 ± 18.6 mm, and 72.2 ± 24.5 mm, respectively. In all limbs, the DFN and the ATA converged after the DFN branched into the 1st VB. The 2nd VB in 38 of 40 limbs and the 3rd VB in 20 of 32 limbs were distributed in the ATA proximal to the convergence point of the ATA and the DFN. These findings revealed that all VBs reaching the ATA ramified from the DFN in all limbs. The ATA received two or three VBs, and all the 1st VBs distributed to the ATA proximal to the convergence point.

Comparison of the decompressive effect of different surgical procedures for dysthyroid optic neuropathy using 3D printed models.

PURPOSE: To compare the decompressive effect around the optic nerve canal among 3 different decompression procedures (medial, balanced, and inferomedial) using 3D printed models. METHODS: In this experimental study, based on data obtained from 9 patients (18 sides) with dysthyroid optic neuropathy, a preoperative control model and 3 plaster decompression models were created using a 3D printer (total, 72 sides of 36 models). A pressure sensor was placed at the optic foramen, and the orbital space was filled with silicone. The surface of the silicone was pushed down directly, and changes in pressure were recorded at 2-mm increments of pushing. RESULTS: At 10 mm of pushing, there was significantly lower pressure in the medial (19,782.2 ± 4319.9 Pa, P = 0.001), balanced (19,448.3 ± 3767.4 Pa, P = 0.003), and inferomedial (15,855.8 ± 4000.7 Pa, P < 0.001) decompression models than in the control model (25,217.8 ± 6087.5 Pa). Overall, the statistical results for each 2-mm push were similar among the models up to 10 mm of pushing (P < 0.050). At each push, inferomedial decompression caused the greatest reduction in pressure (P < 0.050), whereas there was no significant difference in pressure between the medial and balanced decompression models (P > 0.050). CONCLUSION: All 3 commonly performed decompression procedures significantly reduced retrobulbar pressure. Because inferomedial decompression models obtained the greatest reduction in pressure on the optic nerve canal, inferomedial decompression should be considered the most reliable procedure for rescuing vision in dysthyroid optic neuropathy.

Efficacy of urea solution reperfusion to a formalin-embalmed cadaver for surgical skills training.

Formaldehyde has been traditionally used for embalming human cadavers for gross anatomy education and surgical skills training. However, exposure to formaldehyde negatively affects human health. This study aimed to assess the efficacy of reperfusing urea solution to a formalin-embalmed cadaver for surgical skills training and then investigate the cadaver's tissue elasticity alteration after being soaked into the urea solution. Twelve surgeons evaluated the similarity of tissue characteristics between the cadaver (embalmed by formalin solution and reperfused by urea solution) and a living human body. Furthermore, the tissue formaldehyde content and mechanical properties of the formalin-fixated femoral skin and artery specimens with or without soaking into urea solution were measured. Results showed that the tactile assessment, skin incision, vessel ligation and suture, and decollement were better and more useful in the cadaver reperfused by urea solution than in the cadaver merely fixated by formalin solution. In the urea-reperfused cadaver, the volatilized, or tissue formaldehyde levels declined. The stiffness and Young's modulus of the femoral skin and artery were also lower in the specimen than in the mere formalin-fixated specimen. In conclusion, reperfusion of urea solution to the formalin-fixated cadaver makes anatomical education and surgical skills training more efficient with fewer requirements for cadaver management.

The effect of simulation-based education before a cadaver dissection course.

Although the methods for medical education continue to evolve due to the development of medicines, the cadaver dissection course still plays a fundamental role. The cadaver dissection course allows students to learn to handle instruments correctly while actively exploring three-dimensional anatomy. However, dissection comes with the risk of accidental injury. In recent years, the number of classes offered for the cadaver dissection course has decreased while the amount of knowledge required in clinical medicine has increased. Simulation-based education (SBE) has been proven to be an effective educational method that enhances the development of practical skills by integrating learners' knowledge and skills. This study aimed to investigate the effect of SBE as a preparatory education course when taken prior to a medical student's enrollment in the cadaver dissection course. In the present study, an SBE assuming practical cadaver dissection course was performed in the Clinical Simulation Center. The frequency of injury rates per 1000 h of cadaver dissection course was significantly less in 2017 and 2018 compared to that in 2016. Two years after the implementation of the SBE, average student self-efficacy scores and written examination scores significantly increased, whereas self-contentment scores were relatively unchanged. The results showed that the implementation of SBE decreased the incidence of injuries and improved students' overall self-efficacy scores and increased acquisition of knowledge evident on written examination score. Therefore, SBE as a preparatory education course may effectively promote the combined development of dissection skills and anatomical knowledge in the subsequent fundamental cadaver dissection course.

Anorectal Transplantation: The First Long-term Success in a Canine Model.

OBJECTIVE: Anorectal transplantation is a challenging procedure but a promising option for patients with weakened or completely absent anorectal function. SUMMARY BACKGROUND DATA: We constructed a canine model of anorectal transplantation, evaluated the long-term outcomes, and controlled rejection and infection in allotransplantation. METHODS: In the pudendal nerve function study, 6 dogs were randomly divided into 2 groups, transection and anastomosis, and were compared with a control using anorectal manometry, electromyography, and histological examination. In the anorectal transplantation model, 4 dogs were assigned to 4 groups: autotransplant, allotransplant with immunosuppression, allotransplant without immunosuppression, and normal control. Long-term function was evaluated by defecography, videography, and histological examination. RESULTS: In the pudendal nerve function study, anorectal manometry indicated that the anastomosis group recovered partial function 6 months postoperatively. Microscopically, the pudendal nerve and the sphincter muscle regenerated in the anastomosis group. Anorectal transplantation was technically successful with a 3-stage operation: colostomy preparation, anorectal transplantation, and stoma closure. The dog who underwent allotransplantation and immunosuppression had 2 episodes of mild rejection, which were reversed with methylprednisolone and tacrolimus. The dog who underwent allotransplantation without immunosuppression had a severe acute rejection that resulted in graft necrosis. Successful dogs had full defecation control at the end of the study. CONCLUSIONS: We describe the critical role of the pudendal nerve in anorectal function and the first long-term success with anorectal transplantation in a canine model. This report is a proof-of-concept study for anorectal transplantation as a treatment for patients with an ostomy because of anorectal dysfunction.

Roles of glomerular endothelial hyaluronan in the development of proteinuria.

Vascular endothelial cells are covered with glycocalyx comprising heparan sulfate, hyaluronan, chondroitin sulfate, and associated proteins. Glomerular endothelial glycocalyx is involved in protecting against induction of proteinuria and structural damage, but the specific components in glycocalyx that represent therapeutic targets remain unclear. Anti-vascular endothelial growth factor (VEGF) therapy is associated with an increased risk of glomerular endothelial injury. This study investigated whether hyaluronan could provide a therapeutic target to protect against proteinuria. We conducted ex vivo and in vivo experiments to explore the effects of degrading glomerular hyaluronan by administering hyaluronidase and of supplementation with hyaluronan. We investigated hyaluronan expression using biotin-labeled hyaluronan-binding protein (HABP) in human kidney specimens or serum hyaluronan in endothelial injuries under inhibition of VEGF signaling. We directly demonstrated hyaluronan in glomerular endothelial layers using HABP staining. Ex vivo and in vivo experiments showed the development of proteinuria after digestion of hyaluronan in glomerular capillaries. Supplementation with hyaluronan after hyaluronidase treatment suppressed proteinuria. Mice in the in vivo study developed albuminuria after intraperitoneal injection of hyaluronidase with decreased glomerular hyaluronan and increased serum hyaluronan. In human kidneys with endothelial cell dysfunction and proteinuria due to inhibition of VEGF, glomerular expression of hyaluronan was reduced even in normal-appearing glomeruli. Serum hyaluronan levels were elevated in patients with pre-eclampsia with VEGF signaling inhibition. Our data suggest that hyaluronan itself plays crucial roles in preventing proteinuria and preserving the integrity of endothelial cells. Hyaluronan could provide a therapeutic target for preventing glomerular endothelial glycocalyx damage, including VEGF signaling inhibition.

Heat shock protein A4L is a potent autoantigen for testicular autoimmunity in mice.

Experimental autoimmune orchitis (EAO) may be used as a model to investigate immunological infertility in men. Murine EAO is induced via immunization with auto-immunogenic antigens (AIAgs) from testicular germ cells (TGCs). CD4 + T cells play a crucial role in EAO induction. However, whether AIAgs induce an immune response remains unclear. We aimed to identify self-antigens that induce EAO by screening a phage display library of random TGC peptides using IgG from EAO-induced A/J mice. Twenty TGC-specific AIAgs were detected, and G protein-coupled receptor kinase 2 interacting protein-1 (GIT1) and heat shock protein A4L (HSPA4L) were identified as candidate AIAgs that induce EAO. Immunization with GIT1 or HSPA4L, emulsified in complete Freund's adjuvant, resulted in 66 % or 100 % incidence of EAO, respectively, indicating that HSPA4L is a most potent AIAg that induces EAO in mice. These findings may expectedly help improve the diagnostic procedures and treatment of immunological infertility in men.

A rare third head of the biceps femoris in the posterior thigh.

The occurrence of a third head of the biceps femoris is very rare. We encountered the case of a 90-year-old Japanese male cadaver with a third head of the biceps femoris in the posterior aspect of the thigh during dissection at Aichi Medical University in 2016. It originated from the proximal part of the femur and fused with the muscle belly between the long and short heads of the biceps femoris. Additionally, three muscle tendons were connected to the gluteus maximus. To the best of our knowledge, this is the first report on the third head of the biceps femoris demonstrating two origins, i.e., the proximal part of the femur and the insertion tendon of the gluteus maximus. Moreover, the third head, as well as the short head, of the biceps femoris was innervated by the muscular branch of the common peroneal nerve. Based on the origin and innervation, it can be believed that the third head of the biceps femoris is analogous to its short head and is related to the tenuissimus, a phylogenetic remnant. Therefore, we concluded that this third head is an intermediate muscle type of the tenuissimus and short head of the biceps femoris.

Cardioprotection via Metabolism for Rat Heart Preservation Using the High-Pressure Gaseous Mixture of Carbon Monoxide and Oxygen.

The high-pressure gas (HPG) method with carbon monoxide (CO) and oxygen (O2) mixture maintains the preserved rat heart function. The metabolites of rat hearts preserved using the HPG method (HPG group) and cold storage (CS) method (CS group) by immersion in a stock solution for 24 h were assessed to confirm CO and O2 effects. Lactic acid was significantly lower and citric acid was significantly higher in the HPG group than in the CS group. Moreover, adenosine triphosphate (ATP) levels as well as some pentose phosphate pathway (PPP) metabolites and reduced nicotinamide adenine dinucleotide phosphate (NADPH) were significantly higher in the HPG group than in the CS group. Additionally, reduced glutathione (GSH), which protects cells from oxidative stress, was also significantly higher in the HPG group than in the CS group. These results indicated that each gas, CO and O2, induced the shift from anaerobic to aerobic metabolism, maintaining the energy of ischemic preserved organs, shifting the glucose utilization from glycolysis toward PPP, and reducing oxidative stress. Both CO and O2 in the HPG method have important effects on the ATP supply and decrease oxidative stress for preventing ischemic injury. The HPG method may be useful for clinical application.

A Part of the Medial Branch of the Deep Peroneal Nerve Distributes the Dorsal Pedis Artery and Its Distribution Area is Close to the Acupuncture Point LR3 (Taichong).

Cutaneous nerves have vascular branches (VBs) that reach the arteries and are thought to be involved in arterial constriction. We aimed to examine the anatomical and histological relationship between the VBs of a cutaneous nerve in the foot and the acupuncture point LR3 (Taichong), which is a depression between the base of the first and second metatarsal bones on the dorsum of the foot and is a source point of the foot. We examined 40 cadaver feet to assess the distribution areas of the VBs of the medial branch of the deep peroneal nerve (MBDPN). MBDPNs were distally followed to identify the point where the VBs reached the arteries. The distance between the point and LR3 was measured. Sympathetic fibers in the VBs were histologically observed using tyrosine hydroxylase (TH) immunostaining. The VBs of the MBDPNs reaching the dorsal pedis arteries were observed in all specimens (100%). The mean distance between LR3 and the point where the VBs of the MBDPN reached the arteries was 3.2 ± 2.6 mm. Among the VBs, 70% were distributed proximal to LR3. Moreover, TH-positive fibers were present in the VBs. These findings revealed that a part of the MBDPN distributed the dorsal pedis artery and contained sympathetic fibers. We also found that the distribution area of the VBs was close to LR3. Our study provides anatomical evidence that LR3 is a specific area and its stimulation would be useful for treating peripheral circulatory failure.

Developing spray-freeze-dried particles containing a hyaluronic acid-coated liposome-protamine-DNA complex for pulmonary inhalation.

The liposome-protamine-DNA complex (LPD) is an effective cationic carrier of various nucleic acid constructs such as plasmid DNA and small interfering RNA (siRNA). Hyaluronic acid coated on LPD (LPDH) reduces cytotoxicity and maintains the silencing effect of LPD-encapsulated siRNA. Herein, we aim to develop LPD- or LPDH-containing spray-freeze-dried particles (SFDPs) for therapeutic delivery of siRNA to the lungs. LPD- or LPDH-containing SFDPs (LPD- or LPDH-SFDPs) were synthesized and their structure and function as gene carriers were evaluated using physical and biological methods. The particle size of LPDH, but not of LPD, was constant after re-dispersal from the SFDPs and the amount of siRNA encapsulated in LPDH was larger than that in LPD after re-dispersal from the SFDPs. The in vitro pulmonary inhalation properties of LPDH-SFDPs and LPD-SFDPs were almost the same. The cytotoxicity of LPDH-SFDPs in human umbilical vein endothelial cells (HUVEC) was greatly decreased compared with that of LPD-SFDPs. In addition, Bcl-2 siRNA in LPDH-SFDPs had a significant gene silencing effect in human lung cancer cells (A549), whereas Bcl-2 siRNA in LPD-SFDPs had little effect. These results indicate that compared with LPD, LPDH is more useful for developing SFDPs for siRNA pulmonary inhalation.

Anatomical relationship between the sagittal band and extensor tendon of the thumb: a focus on variations of the extensor pollicis brevis tendon insertion.

The sagittal band of the finger is an aponeurosis-like structure surrounding the metacarpophalangeal joint. Sagittal band rupture causes extensor tendon dislocation from the dorsal side of the metacarpophalangeal joint. The thumb has two extensor tendons: extensor pollicis longus and extensor pollicis brevis tendons. Multiple studies have reported variations of extensor pollicis brevis tendon insertion. However, it remains unclear how the thumb sagittal band envelopes the extensor pollicis longus and extensor pollicis brevis tendons. This study investigated the anatomical relationship between the sagittal band and the two extensor tendons of the thumb. One hundred hands (47 right, 53 left) from 54 cadavers were examined to assess the detailed structure of the thumb sagittal band and extensor pollicis longus and extensor pollicis brevis tendons. We found that the thumb sagittal band enveloped both the tendons either separately (type I) or collectively (type II). Thirty-four cases (34.0%) were type I and 66 cases (66.0%) were type II. The extensor pollicis longus and extensor pollicis brevis tendons enveloped in the type I thumb sagittal band were inserted on different sites, respectively, whereas those tendons enveloped in the type II thumb sagittal band were inserted on the same sites. This study demonstrated that differences in the type of thumb sagittal band are closely associated with variations in extensor pollicis brevis tendon insertion. We predicted that these differences contribute to the sliding distance between the extensor pollicis brevis and extensor pollicis longus tendons and affect the pathophysiology of extensor tendon dislocation.

Evaluation of the pressure on the dorsal surface of the distal radius using a cadaveric and computational model: clinical considerations in intersection syndrome and Colles' fracture.

The fibers of the abductor pollicis longus (APL) and extensor pollicis brevis (EPB) muscles intersect the distal radius. This anatomical structure puts pressure on the dorsal surface of the distal radius when various wrist positions are adopted. An increase in this pressure is associated with the risk of intersection syndrome and with immobilization after Colles' fracture. However, the relationship between the pressure on the distal radius and various wrist positions remains unclear. This study was established to provide quantitative data on the mechanical effect of the pressure exerted by the APL and EPB. Ten cadaveric wrist models containing a force sensor were prepared and used to record pressure levels at various wrist positions, such as pronation, supination, flexion and dorsiflexion, and radial and ulnar deviation. A three-dimensional simulation model comprising four bones, one muscle, one tendon, and one tendon sheath was constructed and analyzed in detail using the finite element method. The contribution of the APL and EPB to the pressure exerted on the distal radius was quantified by dissecting muscles while measuring pressure. The position (pronation and ulnar deviation without flexion/dorsiflexion) associated with a strong force being exerted on the distal radius was determined by measuring and analyzing the mechanical effect. We concluded that this position increases the risk of intersection syndrome but provides effective immobilization after Colles' fracture. The cadaveric and computational method presented herein is the first to identify the anatomical relationship between the pressure on the distal radius and various wrist positions.