Papers - Iwamoto, Takuji

Enhanced nerve regeneration after transplantation of NCAM-positive neural crest-like cells derived from human iPSC

Amemiya T., Ouchi T., Kimura H., Okuyama K., Phan T.Q., Iwamoto T., Nakagawa T., Matsumoto M., Nakamura M., Okano H., Nagoshi N., Shibata S.

Inflammation and Regeneration 46 ( 1 )  2026.12

ISSN  18809693

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Background: Peripheral nerve injuries often cause persistent sensory and motor deficits, and autologous nerve grafting, the current standard, is limited by donor site morbidity and tissue availability. Human induced pluripotent stem cells (hiPSCs)-derived neural crest-like cells (NCLCs) have shown potential for nerve regeneration, but achieving high purity and safety remains a challenge. Methods: Using a mouse model of large sciatic nerve defects, we evaluated the efficacy of transplanting NCLCs triple-positive for low-affinity nerve growth factor receptor (LNGFR), thymocyte antigen 1 (THY-1), and neural cell adhesion molecule (NCAM). Purified triple-positive cells induced from hiPSC-derived neural crest lineage were seeded in the conduit with collagen gel in the transplantation group and compared the regeneration with the autograft group and the negative control group without cells. Results: NCAM-positive NCLCs promoted robust angiogenesis and recruited host Schwann cells, thereby establishing a supportive regenerative microenvironment. This facilitated axonal regrowth, thick myelination, and organized nerve architecture comparable to that of autografts. Functional recovery, assessed by electrophysiological conduction and motor performance, eventually matched autografts, with earlier improvement observed in the transplantation group. No tumor formation was detected, and the proliferative activity of transplanted cells declined over time. Selective marker-based purification likely contributed to the favorable safety profile. Conclusion: NCAM-positive NCLCs derived from hiPSCs enhance peripheral nerve regeneration through vascularization and Schwann cell-mediated remyelination, resulting in structural and functional recovery equivalent to autografts. This strategy offers a safe, scalable alternative to donor nerve harvest, and integration with bioengineered conduits could further expand clinical applicability in peripheral nerve reconstruction.

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Anatomical Reconstruction of the Terminal Tendon and Lateral Band for Severe Chronic Tendon Mallet Injury

Suzuki T., Kiyota Y., Matsumura N., Sato K., Nakamura M., Iwamoto T.

Journal of Hand Surgery 51 ( 1 ) 92 - 92.e7 2026.01

ISSN  03635023

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Purpose This study aimed to evaluate the clinical outcomes of surgical treatment for chronic mallet injury with severe extension lag using an anatomic reconstruction of the terminal tendon and lateral band with a palmaris longus (PL) tendon graft. Methods Eleven patients with a mean age of 52 years (range, 24–82 years) who underwent surgical reconstruction for chronic tendon mallet injuries using the PL tendon were included. The harvested PL tendon was either folded longitudinally or divided into two slips. The graft was secured to the distal phalanx using a bone anchor and sutured to the soft tissues and remnants of the original terminal tendon distal to the distal interphalangeal (DIP) joint. Each half-slip tendon was passed under the transverse retinacular ligament and sutured side-to-side to the lateral band at approximately the midpoint of the proximal phalanx. The active range of motion of the affected finger was evaluated before and after surgery, and any complications were recorded. Results Before surgery, the extension of the DIP joint averaged −49.5° (range, −40° to −60°). The postoperative mean lag of the DIP joint improved to −7.8° (range, −20° to +20°). According to the Miller classification, four patients had excellent results, four had good results, and three had fair results. Two patients who underwent folded-PL tendon grafting developed superficial dorsal skin infections on the little finger that resolved with oral antibiotics or removal of the sutures. Conclusions Anatomical reconstruction of the terminal tendon and lateral bands using a PL tendon graft yielded satisfactory outcomes in chronic tendon mallet injuries. Dividing the PL tendon into two slips is recommended to reduce the risk of postoperative infection. Type of study/level of evidence Therapeutic IV.

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Platelet-like cells differentiated from adipose-derived mesenchymal stem cells inhibit acute inflammation of tendinopathy in rats

Torii A., Yamada Y., Ono-Uruga Y., Sato Y., Kaneko Y., Nakamura S., Iwamoto T., Matsubara Y., Matsumoto M., Nakamura M., Sato K., Miyamoto T.

Journal of Bone and Mineral Metabolism 44 ( 1 ) 18 - 27 2026.01

ISSN  09148779

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Introduction: Tendinopathy, a disease that causes inflammation and pain and limits patients’ activities of daily living, is considered particularly important to treat during the acute inflammatory phase to prevent the transition to chronic degeneration. Recently, platelet-rich plasma (PRP) has been used to treat tendinopathy; however, it is not clear whether platelets themselves, which are the active component of PRP, could be effective in treating tendinopathy. Materials and Methods: We made rat Achilles tendinopathy models by incision of the calcaneal attachment and administrated platelet-like cells derived from adipose-derived mesenchymal stem cells (ASCL-PLCs) to the injury site and investigated the anti-inflammatory effect. Results: ASCL-PLCs significantly inhibits the inflammatory cytokine expression and inflammatory cell infiltration in acute tendonitis in a rat Achilles tendon injury model in vivo. Interestingly, we observed no xeno-reaction when human-derived ASCL-PLCs were administered to wild-type rats in vivo. Moreover, IL-6 expression and phosphorylation seen in NIH3T3 fibroblasts treated with IL-6 plus soluble IL-6 receptor were both significantly suppressed by ASCL-PLCs in vitro. Conclusion: ASCL-PLC has advantages over existing PRP therapies, including the ability to be cryopreserved after quality checks, and homogeneous populations of ASCL-PLCs can be prepared in large quantity. We conclude that in the future ASCL-PLCs may serve as an allogeneic transplant effective to treat tendinopathy.

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Delayed diagnosis of psoriatic arthritis presenting with infection-like finger inflammation: A case report

Takahashi S., Kiyota Y., Iwamoto T., Torii A., Oki S., Suzuki T., Matsumura N., Nakamura M.

Modern Rheumatology Case Reports 10 ( 1 )  2026

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Psoriatic arthritis is a chronic inflammatory disease associated with psoriasis, and its diagnosis can be challenging owing to nonspecific symptoms, absence of reliable biomarkers, and occasional delay in skin manifestations. Herein, we report a case of psoriatic arthritis that initially presented as an acute finger inflammation mimicking infection. A 46-year-old woman developed sudden swelling and pain in the left ring finger during chemotherapy for cervical cancer. Based on the results of the physical examination, laboratory tests, and magnetic resonance imaging, pyogenic flexor tenosynovitis was suspected, and synovectomy was performed; however, bacterial and mycobacterial cultures yielded negative results. Despite the administration of antibiotics, the inflammation persisted, and she was referred to the Rheumatology Department, where she was diagnosed with reactive arthritis secondary to Chlamydia infection. Although the inflammation improved after antimicrobial therapy, the finger swelling persisted. Follow-up magnetic resonance imaging and serological testing were performed, and the patient was diagnosed with seronegative rheumatoid arthritis. Four years after onset, erythematous skin lesions appeared, and dermatological evaluation confirmed plaque psoriasis; thus, a definitive diagnosis of psoriatic arthritis was established. Disease-modifying antirheumatic drug adjustments improved symptoms, but residual ‘pencil-in-cup’ deformity and limited finger motion remained. This case highlights the difficulty in diagnosing psoriatic arthritis when arthritis precedes skin lesions. Clinicians should consider psoriatic arthritis in persistent or refractory arthritis and carefully monitor skin and nail changes to achieve an earlier diagnosis and prevent irreversible joint damage.

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Accuracy of Implant Placement Using Augmented Reality–assisted Technique in Total Wrist Arthroplasty

Watanabe S., Iwamoto T., Tanji A., Kiyota Y., Suzuki T., Nagura T., Nakamura M.

Journal of Hand Surgery 51 ( 4 ) 371 - 381 2026

ISSN  03635023

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Purpose The study aimed to evaluate the accuracy of augmented reality–assisted total wrist arthroplasty (AR-TWA) in a cadaveric model using a three-point registration method. The hypothesis is that AR-assisted surgery can enable surgeons to achieve accurate implant placement comparable with surgeries performed under specialist guidance. Methods Fourteen fresh-frozen upper extremities from seven cadavers were used for TWA. Computed tomography data were imported into three-dimensional image analysis software for surgical planning. On one side, AR-TWA was performed by a board-certified orthpaedic surgeon with no clinical experience in TWA, and on the contralateral side, non–AR-TWA was performed by the same surgeon under the guidance of an experienced hand surgeon. The accuracy of implant placement was assessed by comparing preoperative and postoperative computed tomography scans and measuring deviations and angular errors between the planned and actual component positions. Results For both the radial and carpal components, four of six parameters demonstrated smaller errors in the AR-TWA. Although certain parameters favored the non–AR-TWA, overall variability was lower with AR. When classified as acceptable or outlier, all seven radial cases in the AR-TWA were acceptable for deviation, and six were acceptable for angular error, indicating better consistency than the non–AR-TWA. On the carpal side, AR-TWA demonstrated higher accuracy than non–AR-TWA, but more outliers were observed, suggesting relatively greater variability in this region. Conclusions Augmented reality–assisted TWA using a three-point registration method improved the accuracy of implant placement, even when performed by a less experienced surgeon. Clinical relevance Augmented reality technology may assist less experienced surgeons in performing technically demanding procedures, such as TWA, with improved accuracy.

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Peripheral nerve regeneration using a bioresorbable silk fibroin-based artificial nerve conduit fabricated via a novel freeze–thaw process

Matsuo T., Kimura H., Nishijima T., Kiyota Y., Suzuki T., Nagoshi N., Shibata S., Shindo T., Moritoki N., Sasaki M., Noguchi S., Tamada Y., Nakamura M., Iwamoto T.

Scientific Reports 15 ( 1 ) 3797 2025.12

ISSN  2045-2322

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While silk fibroin (SF) obtained from silkworm cocoons is expected to become a next-generation natural polymer, a fabrication method for SF-based artificial nerve conduits (SFCs) has not yet been established. Here, we report a bioresorbable SFC, fabricated using a novel freeze–thaw process, which ensures biosafety by avoiding any harmful chemical additives. The SFC demonstrated favorable biocompatibility (high hydrophilicity and porosity with a water content of > 90%), structural stability (stiffness, toughness, and elasticity), and biodegradability, making it an ideal candidate for nerve regeneration. We evaluated the nerve-regenerative effects of the SFC in a rat sciatic-nerve-defect model, including its motor and sensory function recovery as well as histological regeneration. We found that SFC transplantation significantly promoted functional recovery and nerve regeneration compared to silicone tubes and was almost equally effective as autologous nerve transplantation. Histological analyses indicated that vascularization and M2 macrophage recruitment were pronounced inside the SFC. These results suggest that the unique properties of the SFC further enhanced the peripheral nerve regeneration mechanism. As no SFC has been applied in clinical practice, the SFC reported herein may be a promising candidate for repairing extensive peripheral nerve defects.

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Mid-term clinical outcomes of the unlinked type K-NOW total elbow arthroplasty

Matsuo T., Iwamoto T., Kiyota Y., Suzuki T., Matsumura N., Sato K., Ikegami H.

Bone and Joint Journal 107 B ( 11 ) 1203 - 1211 2025.11

ISSN  20494394

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Aims This study aimed to evaluate the mid-term clinical outcomes, complications, and survival rates of the unlinked K-NOW (Teijin Nakashima Medical, Japan) total elbow arthroplasty (TEA), focusing on the use of cementless fixation. Methods This retrospective study included 41 elbows in 37 patients who underwent primary TEA using unlinked K-NOW between April 2012 and March 2021, with a minimum follow-up of two years. Surgical approaches included the lateral paraolecranon (LPO) and triceps-off approaches. Clinical evaluations included range of motion (ROM) and Mayo Elbow Performance Score (MEPS). Complications were recorded, and Kaplan-Meier survival analysis was performed, with aseptic loosening and revision surgery as endpoints. Results The mean patient age was 68.4 years (SD 11.6), and the mean follow-up period was 4.7 years (2.1 to 10.1). The LPO approach was used in 35 elbows (85.4%), and cementless fixation was applied to 41 humeral components (100%) and 35 ulnar components (85.4%). Among patients with ≥ five years of follow-up (n = 16), significant improvements were observed in ROM (extension, from -38° to -19°; flexion, from 107° to 130°; pronation, from 55° to 72°; supination, from 62° to 73°; p < 0.001), and MEPS (from 48 to 93 points; p < 0.001) at five years postoperatively. Complications occurred in six elbows (14.6%): three elbows (7.3%) with aseptic loosening and three elbows (7.3%) with periprosthetic fractures; no postoperative dislocation was observed. Revision surgeries were required in two elbows (4.9%). Kaplan-Meier survival rates were 92.7% (95% CI 84.7 to 100) at five years for loosening, and 97.1% (95% CI 91.4 to 100) at five years for revision. All aseptic loosening occurred within three months postoperatively. Conclusion The unlinked K-NOW with cementless fixation, mostly using the LPO approach, demonstrated favourable outcomes with improved ROM and MEPS, a low complication rate, and promising survival. In cases with severe osteoporosis or bone-implant instability, cemented fixation or a triceps-off approach may help reduce the risk of early complications.

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Three-Dimensional Magnetic Resonance Imaging of Median Nerve Volume for Assessing Carpal Tunnel Syndrome Severity

Hayakawa K., Suzuki T., Hayakawa K., Kawano Y., Iwamoto T., Fujita N.

Muscle and Nerve 72 ( 5 ) 1117 - 1121 2025.11

ISSN  0148639X

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Introduction/Aims: 3D magnetic resonance imaging (MRI) is a tool for visualizing and quantifying the volume of the median nerve; however, the diagnostic value of the volume of the median nerve for assessing CTS severity is unclear. This study aimed to evaluate the utility of 3T MRI combined with three-dimensional (3D) imaging to assess the cross-sectional volume (CSV) of the median nerve for diagnosing carpal tunnel syndrome (CTS) and determining its severity. Methods: We used MRI to measure the CSV of the median nerve in 95 patients with CTS and 26 healthy controls. CTS severity was graded according to the Padua classification, and differences in CSV according to severity were analyzed. Results: The mean CSVs for the severity groups were as follows: control, 22.4 mm³; minimal, 28.8 mm³; moderate, 34.4 mm³; severe, 53.6 mm³; and extreme, 48.3 mm³. CSV increased with CTS severity, with significantly higher values in the severe and extreme groups compared with the moderate, minimal, and control groups. Discussion: This study showed that the CSV of the median nerve increased with disease severity, both visually and in three dimensions. This helps to visually understand the severity of CTS, and the association between morphology and disease severity may contribute to a better understanding of the pathophysiology of CTS.

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Optimizing surgical instrument and implant utilization in orthopedic procedures: A lean methodology approach to cost reduction and efficiency improvement

Watanabe K., Iwamoto T., Nakayama R., Kobayashi S., Oya A., Matsumoto M., Nakamura M.

Journal of Orthopaedic Science 30 ( 6 ) 1199 - 1205 2025.11

ISSN  09492658

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Background: Operating rooms (ORs) are among the most resource-intensive areas in hospitals, and optimizing surgical efficiency is crucial for cost reduction. A key contributor to inefficiency is the overstocking of surgical instrument trays and implants, leading to increased sterilization costs, longer processing times, and workflow inefficiencies. Despite its impact, instrument tray optimization has received limited attention in orthopedic surgery. Methods: This single-center prospective observational study analyzed the utilization rates of surgical instruments and implants in total knee arthroplasty (TKA), total hip arthroplasty (THA), anterior cruciate ligament (ACL) reconstruction, and posterior spinal fusion (PSF) surgeries. Using Lean methodology, unnecessary instruments and implants were identified and removed from standard trays. The effectiveness of this optimization was assessed through comparisons of instrument utilization rates, sterilization costs, and OR preparation times before and after implementation. Results: A total of 162 procedures were analyzed. Prior to optimization, mean instrument tray utilization rates were low across all procedures (58–65 %), and implant utilization was particularly poor (5–11 %). Post-optimization, significant reductions were observed in the mean number of instrument trays and implants brought into the OR, leading to improved utilization rates (PSF: 67 %, THA: 75 %, ACL: 67 %) and cost savings of up to 1374 JPY per case. The mean intraoperative times unchanged after optimization, while in THA, a notable decrease in intraoperative time was observed (p = 0.022). Conclusion: Lean-based surgical instrument tray optimization effectively reduces unnecessary material use, lowers sterilization costs up to 1374 JPY per case, without compromising intraoperative times. The estimated annual cost savings for the hospital amounted to 729,575 JPY. Further research on long-term impact is warranted to maximize cost savings and enhance standardization in orthopedic surgeries.

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シリコンインプラントを用いたMP関節形成術後に重度の骨融解を生じた1例

菊地 啓士朗, 岩本 卓士, 清田 康弘, 鈴木 拓, 松村 昇, 中村 雅也

日本手外科学会雑誌 ((一社)日本手外科学会)  42 ( 2 ) 246 - 246 2025.09

ISSN  2185-4092

Steindler変法による肘屈曲再建と腕橈骨筋re-routingによる前腕回外再建を行った前腕回外再建を行った腕神経叢損傷の1例

沖 智碩, 清田 康弘, 木村 洋朗, 鈴木 拓, 松村 昇, 岩本 卓士, 佐藤 和毅, 中村 雅也

日本手外科学会雑誌 ((一社)日本手外科学会)  42 ( 2 ) 240 - 240 2025.09

ISSN  2185-4092

鎖骨下動脈盗血症候群を合併した胸郭出口症候群の1例

影山 瑛大, 鈴木 拓, 清田 康弘, 松村 昇, 岩本 卓士, 中村 雅也

日本手外科学会雑誌 ((一社)日本手外科学会)  42 ( 2 ) 138 - 138 2025.09

ISSN  2185-4092

伸筋腱断裂を伴うKienbock病に対して人工月状骨置換術を施行した1例

早川 賀津野, 鈴木 拓, 古旗 了伍, 木村 洋朗, 松村 昇, 岩本 卓士, 中村 雅也

日本手外科学会雑誌 ((一社)日本手外科学会)  42 ( 2 ) 61 - 61 2025.09

ISSN  2185-4092

新型コロナウイルス感染症(COVID-19)のワクチン接種後に胸郭出口症候群をきたした1例

古旗 了伍, 鈴木 拓, 木村 洋朗, 松村 昇, 佐藤 和毅, 岩本 卓士

日本手外科学会雑誌 ((一社)日本手外科学会)  42 ( 2 ) 170 - 170 2025.09

ISSN  2185-4092

尺骨神経の解剖学的変異により生じた手関節尺側部痛の1例

名久井 龍成, 岩本 卓士, 木村 洋朗, 鈴木 拓, 松村 昇, 中村 雅也

日本手外科学会雑誌 ((一社)日本手外科学会)  42 ( 2 ) 148 - 148 2025.09

ISSN  2185-4092

尺側側索の過形成が原因で中指MP関節に弾発症状をきたした1例

中西 杏奈, 鈴木 拓, 木村 洋朗, 松村 昇, 岩本 卓士, 中村 雅也

日本手外科学会雑誌 ((一社)日本手外科学会)  42 ( 2 ) 162 - 162 2025.09

ISSN  2185-4092

外科的治療により胸部症状が改善した胸郭出口症候群の1例

牧田 修太朗, 鈴木 拓, 清田 康弘, 松村 昇, 岩本 卓士, 中村 雅也

日本手外科学会雑誌 ((一社)日本手外科学会)  42 ( 2 ) 235 - 235 2025.09

ISSN  2185-4092

副甲状腺癌に伴う原発性副甲状腺機能亢進症により橈骨骨折をきたした1例

早川 賀津野, 鈴木 拓, 清田 康弘, 松村 昇, 佐藤 和毅, 岩本 卓士

日本手外科学会雑誌 ((一社)日本手外科学会)  42 ( 2 ) 135 - 135 2025.09

ISSN  2185-4092

内視鏡補助下鎖骨下アプローチを用いて第1肋骨奇形を切除した胸郭出口症候群の1例

麓 政人, 鈴木 拓, 清田 康弘, 松村 昇, 岩本 卓士, 中村 雅也

日本手外科学会雑誌 ((一社)日本手外科学会)  42 ( 2 ) 74 - 74 2025.09

ISSN  2185-4092

【手指の変形性PIP関節症(ブシャール結節)に対する保存治療と外科治療:Knowledge Update】クリニカルクエスチョン　変形性PIP関節症に対する人工関節置換術の効果と合併症は?

岩本 卓士

Loco Cure ((株)先端医学社)  11 ( 3 ) 240 - 242 2025.08

ISSN  2189-4221