Hirotaka Kawano

Purpose: Bone and soft tissue sarcomas are rare, heterogeneous malignancies presenting major diagnostic and therapeutic challenges. Over the past century, Japanese orthopaedic surgeons have occupied a unique position as both primary surgeons and comprehensive oncologists. On the occasion of the Centennial of the Japanese Orthopaedic Association (JOA), this review synthesizes the key historical milestones and future prospects of Japanese orthopaedic oncology. Methods: A narrative synthesis was structured across five consolidated domains: (1) Surgical Innovation; (2) Advanced Basic Research and Novel Therapeutics; (3) The Japan Bone and Soft Tissue Tumor Registry (JBSTTR); (4) Nationwide Collaborative Research Groups and Multidisciplinary Platforms; and (5) Onco-Orthopaedics and Future Musculoskeletal Care. Results: Japanese orthopaedic oncologists established quantitative surgical margin concepts, pioneered Total En Bloc Spondylectomy (TES) for spinal tumours, and developed recycled treated autografts (freezing, pasteurization, and irradiation). Translational research milestones encompass caffeine-potentiated chemotherapy, peptide-based immunotherapy, oncolytic viral therapies, Japan’s first investigator-initiated clinical trial in oncology, and carbon-ion radiotherapy. Furthermore, a robust nationwide infrastructure has been forged through six decades of the JBSTTR alongside collaborative research engines—the Japanese Musculoskeletal Oncology Group (JMOG), the Japan Clinical Oncology Group Bone and Soft Tissue Tumor Study Group (JCOG-BSTTSG), and the Japan Ewing Sarcoma Study Group (JESS)—and the multidisciplinary platform Japanese Association of Sarcoma Treatment and Research (JSTAR). Expanding beyond primary sarcoma care, the conceptual framework of Onco-Orthopaedics has pioneered a holistic paradigm for managing locomotive syndrome in cancer patients "Cancer Locomo". Conclusion: The surgeon-led collaborative ecosystem in Japan bridges surgical precision, translational science, and nationwide multidisciplinary platforms, offering a sustainable model for advancing musculoskeletal oncology.

Early functional rehabilitation after acute Achilles tendon rupture is increasingly used in nonoperative protocols, but the definition of “early” remains highly heterogeneous across the literature and no standardized timing threshold has been established. This narrative review clarifies the conceptual and operational definitions of early rehabilitation and examines the unresolved timing-threshold problem. Existing evidence supports early functional rehabilitation without a demonstrated increase in rerupture risk compared with delayed immobilization. Early rehabilitation may improve short-term functional recovery; however, clear long-term superiority over more delayed strategies has not been demonstrated. Substantial heterogeneity persists in the initiation of weightbearing and range of motion and in orthosis duration. Although weightbearing within four weeks is commonly used as an operational definition of early rehabilitation for evidence synthesis, it is not a biologically or clinically validated threshold. The literature also lacks granular evidence defining a timing–response relationship or an optimal initiation window. Current evidence therefore supports early functional rehabilitation as a reasonable strategy, but future research should identify validated timing–response relationships and patient-specific strategies.

Background: The Japanese Orthopaedic Association (JOA), founded in 1926, celebrates its centennial in 2026 as one of the world’s largest national orthopaedic societies. Methods: This article reviews the historical development of the JOA during its first century and highlights major scientific, clinical, educational, and public health achievements of Japanese orthopaedics. Results: The JOA has played a central role in the development of Japanese orthopaedics through specialist education, clinical practice guidelines, nationwide registries, and the promotion of basic and clinical research. Japanese orthopaedic surgeons have contributed to modern orthopaedics through pioneering surgical techniques, technological innovations, and international academic exchange. These developments have expanded the role of orthopaedics beyond the treatment of musculoskeletal disorders to encompass broader public health challenges associated with population aging and the maintenance of mobility and quality of life. Conclusions: Over the past century, Japanese orthopaedics has evolved from a small academic discipline into an internationally recognized field, alongside profound demographic and epidemiological changes, particularly the emergence of a super-aged society.

Background: Chronic insertional rupture of the tibialis anterior tendon is uncommon and presents substantial reconstructive challenges, particularly when associated with large tendon defects and distal degeneration. Primary repair is often not feasible in such cases, and conventional reconstructive techniques frequently require prolonged postoperative immobilization, delaying functional recovery. Case presentation: We report a case of chronic insertional tibialis anterior tendon rupture in a 64-year-old Japanese male recreational weightlifter, treated with reconstruction using an ipsilateral semitendinosus autograft. A modified side-locking loop suture technique was employed for proximal fixation, and anatomical distal fixation was achieved using multiple all-suture anchors. This construct was designed to provide sufficient initial biomechanical stability to permit early postoperative rehabilitation. Postoperatively, the ankle was immobilized for 2 weeks, followed by initiation of active range of motion exercises and progressive weight-bearing. At the 2-year follow-up, the patient demonstrated complete pain relief, normal gait, and excellent functional recovery. Isokinetic testing revealed dorsiflexion strength exceeding 95% of the contralateral side, and magnetic resonance imaging confirmed continuity and favorable remodeling of the reconstructed tendon. Conclusions: This case demonstrates that reconstruction of chronic insertional tibialis anterior tendon rupture using a semitendinosus autograft combined with a modified side-locking loop suture and multi-anchor fixation can provide sufficient stability to allow early functional rehabilitation. This approach may represent a viable treatment option for active patients with large tendon defects.

Background: Iatrogenic ulnar nerve (UN) injury is a serious complication of percutaneous medial pinning for pediatric supracondylar humeral fractures, particularly when deep elbow flexion is required for reduction. However, the flexion angle at which the nerve becomes unstable and patient characteristics predisposing to displacement remain unclear. This study aimed to determine the elbow flexion angle at which UN instability occurs in healthy children and to identify independent risk factors for anterior displacement. Methods: A cross-sectional study of 74 healthy, asymptomatic children (144 elbows) aged 7 to 12 years was conducted. Dynamic ultrasonography was performed at 5 static flexion angles (0°, 30°, 60°, 90°, and 120°), with nerve position classified as normal, subluxated, or dislocated relative to the medial epicondyle. Multivariate logistic regression analysis identified independent predictors of instability (subluxation or dislocation) at deep flexion (≥90°), evaluating age, sex, body mass index, handedness, and generalized joint laxity. Results: UN instability increased progressively with elbow flexion. At 0° and 30°, the nerve remained stable in >97% of elbows. A marked increase in instability was observed at ≥90°: 60.4% demonstrated instability (50.0% subluxation, 10.4% dislocation) at 90°, rising to 94.4% (54.2% subluxation, 40.3% dislocation) at 120°. Multivariate analysis identified female sex (odds ratio 3.61; 95% confidence interval 1.50-8.67) and generalized joint laxity (odds ratio 2.61; 95% confidence interval, 1.03-6.61) as independent risk factors. Age, body mass index, and handedness were not significantly associated with displacement. Conclusions: In healthy children, the UN demonstrated a pronounced angle-dependent pattern, with marked anterior displacement at ≥90° of flexion. Female sex and generalized joint laxity were associated with higher odds of sonographic instability. These findings characterize the anatomical behavior of the UN during elbow flexion and provide context for future investigation in surgical populations. Level of Evidence: Level III . See Instructions for Authors for a complete description of levels of evidence.

Retrospective observational study. To determine whether preoperative ligamentum flavum (LF) thickness at the cranial adjacent level predicts postoperative LF hypertrophy progression at the same level 1 year after posterior lumbar interbody fusion (PLIF), and whether preoperative LF thickness at L2/3 also predicts this progression. Adjacent segment disease (ASD) is a recognized complication of PLIF. LF hypertrophy at adjacent levels contributes to symptomatic ASD; however, it remains unclear whether preoperative LF thickness predicts postoperative hypertrophy progression. This retrospective study included 51 patients with lumbar spinal stenosis who underwent PLIF and had preoperative and 1-year postoperative computed tomography scans. LF thickness was measured at the cranial adjacent level and at L2/3. Additional preoperative radiographic and clinical variables were also assessed. Patients were classified into progression and nonprogression groups based on the median change in LF thickness at the adjacent level, and intergroup comparisons were performed. Correlation analysis and linear regression with backward elimination were performed to identify predictors of LF hypertrophy progression. Sensitivity analyses using ridge and least absolute shrinkage and selection operator regression were conducted to confirm robustness. LF thickness at the cranial adjacent level increased from 3.4 mm preoperatively to 4.0 mm at 1 year (p<0.001). In univariate analysis, preoperative LF thickness at the cranial adjacent level, LF thickness at L2/3, and facet joint degeneration were associated with postoperative LF thickening. In multivariable regression, only LF thickness at L2/3 (coefficient=0.37, p<0.001) and cranial adjacent facet joint degeneration (coefficient=0.32, p=0.030) remained predictors (adjusted R2=0.27). No other preoperative variable showed an association. Preoperative LF thickness at L2/3 and cranial adjacent facet degeneration predicted postoperative LF hypertrophy progression after PLIF. Both inherent predisposition and mechanical stress may contribute to adjacent-level LF thickening.

Aims: Extendable endoprostheses are utilized to reconstruct segmental defects following resection of bone sarcomas in skeletally immature children. However, there remains a paucity of data regarding long-term functional and quality of life outcomes.Methods: We conducted a retrospective, multicentre study and reviewed 45 children who underwent cementless minimally invasive extendable endoprosthetic replacement. Anatomical sites included the distal femur (n = 29), proximal femur (n = 4), proximal tibia (n = 11), and total femur (n = 1). The mean follow-up period was 12 years. The mean age at extendable endoprosthetic replacement was ten years (5 to 15). Most patients (96%, 43/45) had reached skeletal maturity at the final follow-up.Results: The ten-year endoprosthetic failure-free survival rate was 60%. Of the 45 patients, 25 (56%) had 42 complications which were frequently related to structural failure (45%, 19/42), with extension mechanism jamming being the most common (n = 7, 17%). Excluding lengthening procedures, 20 patients (44%) underwent additional surgery with a mean of two surgeries per patient. The mean limb-length discrepancy at the final follow-up was 2.3 cm. Limb salvage was achieved in 44 (98%) patients. The mean Musculoskeletal Tumor Society (MSTS) scores, Toronto Extremity Salvage Score (TESS), and EuroQol five-dimension five-level questionnaire (EQ-5D-5L) were 78%, 92%, and 92% at the last follow-up, respectively. Multiple additional surgeries (≥ 2 times) for complications were associated with worse MSTS scores compared with those without multiple additional surgeries (p = 0.009). Moreover, limb-length discrepancy > 3 cm showed significantly worse MSTS scores compared with those ≤ 3 cm (p = 0.019).Conclusion: Extendable endoprostheses were associated with a high complication rate and need for additional surgeries over time, especially for structural-related complications. Despite this, successful limb salvage with reasonable function/quality of life and small limb-length discrepancy were achievable in the long term. Patients’ function in the long term depended on the experience of postoperative complications and limb-length discrepancy.Cite this article: Bone Jt Open 2025;6(8):954–963.

Objectives: Hamstring strain injuries are common in elite athletes and affect return-to-sport timelines. Although magnetic resonance imaging (MRI) is the gold-standard method for assessing injury severity, ultrasonography (US) is a more accessible and cost-effective alternative. This study aimed to evaluate the agreement between US and MRI in the diagnosis of hamstring injuries and their prognostic value in predicting recovery. Methods: This retrospective study included elite athletes who sustained acute first-time hamstring strains and underwent both MRI and US within five days after injury. The injuries were classified according to location (muscle belly, musculotendinous junction, or tendon) and severity (modified Peetron’s classification). The agreement between the imaging findings and return-to-sports timelines was analyzed. Results: US demonstrated a 70% agreement with MRI in identifying injury locations, showing the highest concordance for muscle belly injuries (90%), followed by musculotendinous junction (80%) injuries, but a lower accuracy for tendon injuries (60%). Recovery times differed significantly by location and severity (p < 0.01), with tendon grade 3 injuries requiring the longest recovery (383 days) and muscle belly injuries requiring the shortest recovery (16 days). Musculotendinous junction grade 2, tendon grade 1, and tendon grade 2 injuries had similar recovery durations (57–65 days). Conclusions: High-resolution US is a reliable diagnostic tool for muscle belly and musculotendinous junction injuries. However, MRI remains essential for high-grade tendon injuries. US serves as the first-line imaging modality, with MRI reserved for cases that require a detailed prognostic assessment. These findings provide guidance for optimizing imaging strategies for hamstring injury management.

Background/Objectives: Hamstring strain injuries are common in elite athletes and affect return-to-sport timeline. Although magnetic resonance imaging (MRI) is the gold standard for assessing injury severity, ultrasonography (US) is a more accessible and cost-effective alternative. This study aimed to evaluate the agreement between US and MRI in the diagnosis of hamstring injuries and their prognostic value in predicting recovery. Methods: This retrospective study included elite athletes with acute first-time hamstring strains who underwent both MRI and US within five days after injury. The injuries were classified according to location (muscle belly, musculotendi-nous junction, or tendon) and severity (modified Peetrons classification). The agree-ment between imaging findings and return-to-sport timelines was analyzed. Results: US demonstrated 70% agreement with MRI in identifying injury locations, with the highest concordance for muscle belly (90%) and musculotendinous junction (80%) in-juries but lower accuracy for tendons (60%). Recovery times differed significantly by location and severity (p < 0.01), with tendon grade 3 injuries requiring the longest re-covery (383 days), while muscle belly injuries had the shortest recovery (16 days). Musculotendinous junction grade 2, tendon grade 1, and tendon grade 2 injuries had similar recovery durations (57–65 days). Conclusions: High-resolution US is a reliable diagnostic tool for muscle belly and musculotendinous junction injuries; however, MRI remains essential for high-grade tendon injuries. US serves as a first-line imaging mo-dality, with MRI reserved for cases that require a detailed prognostic assessment. These findings provide guidance for optimizing imaging strategies for hamstring inju-ry management.