Ossification of the posterior longitudinal ligament (OPLL) is a heterotopic ossification that may cause spinal cord compression. With the recent development of computed tomography (CT) imaging, it is known that patients with OPLL often have complications related to ossification of other spinal ligaments, and OPLL is now considered part of ossification of the spinal ligaments (OSL). OSL is known to be a multifactorial disease with associated genetic and environmental factors, but its pathophysiology has not been clearly elucidated. To elucidate the pathophysiology of OSL and develop novel therapeutic strategies, clinically relevant and validated animal models are needed. In this review, we focus on animal models that have been reported to date and discuss their pathophysiology and clinical relevance. The purpose of this review is to summarize the usefulness and problems of existing animal models and to help further the development of basic research on OSL.

Aims: Nonunion occurs when a fracture fails to heal permanently, often necessitating surgical intervention to stimulate the bone healing response. Current animal models of long-bone nonunion do not adequately replicate human pathological conditions. This study was intended as a preliminary investigation of a novel rat nonunion model using a two-stage surgical intervention, and to evaluate the efficacy of a selective prostaglandin E2 receptor 4 agonist (AKDS001) as a novel nonunion therapeutic agent compared with existing treatments.Methods: Initially, Sprague-Dawley rats underwent intramedullary Kirschner wire (K-wire) fixation of a femoral fracture with the interposition of a 2 mm-thick silicon disc. After three weeks, the silicon disc was removed, and the intramedullary K-wire was replaced with plate fixation while maintaining the 2 mm defect. Contrary to the control group (1) that received no treatment, the following therapeutic interventions were performed at injury sites after freshening: (2) freshening group: no grafting; (3) iliac bone (IB) group: IB grafting; (4) AKDS group: AKDS001-loaded microspheres (MS) combined with IB (0.75 mg/ml); and (5) bone morphogenetic protein (BMP) group: grafting of a BMP-2-loaded collagen sponge (10 μg; 0.10 mg/ml). After six weeks, micro-CT (μCT) and histological analysis was performed.Results: In the control group, the radiological union rate was 0%, and histological findings showed that fracture sites comprised fibrous scar tissue, resembling the histology of human nonunion. The union rates in the freshening, IB, AKDS, and BMP groups were 16.7%, 0%, 62.5%, and 50.0%, respectively. The AKDS group demonstrated a significantly higher union rate than the IB group (p = 0.026). μCT and histological analysis indicated that the quality of newly formed bone was superior in the AKDS group than in the BMP group.Conclusion: We developed a novel long-bone nonunion model. The co-therapy of AKDS001-MS and IB grafting presents a promising new treatment for nonunion.Cite this article: Bone Joint Res 2025;14(3):166–175.

Foraminal stenosis in patients with L5/S1 adjacent segment disease (ASD) presents a significant clinical challenge, as conventional treatment often requires fusion extension surgery. This approach sacrifices spinal mobility and is associated with considerable surgical morbidity. This video article describes a motion-preserving surgical alternative, namely, transforaminal full-endoscopic foraminotomy performed under local anesthesia, detailing a step-by-step protocol to navigate the challenges of these revision cases. The technique utilizes a posterolateral corridor, avoiding prior surgical scarring. Key procedural steps include meticulous preoperative trajectory planning, foraminoplasty via resection of the superior articular process (SAP), and partial resection of the inferior articular process to fully expose the ligamentum flavum (LF). A specific "detach" technique is then demonstrated, involving undercutting the ventral rim of the S1 SAP to release the LF before its removal. Representative results demonstrate successful osseous decompression confirmed by postoperative computed tomography. The procedure resulted in immediate improvement in radicular pain and motor weakness, with the patient's visual analog scale score decreasing from 9/10 to 1/10 at the one-month follow-up. This minimally invasive technique provides effective neural decompression and facilitates rapid recovery, offering a valuable alternative to more extensive surgery for this challenging patient population.

Background Symptomatic small-sized lumbar disc herniation (small LDH) presents a significant challenge in elite athletes, where rapid return to competition is paramount. This study aimed to characterize the clinical and imaging features of small LDH in this population and to evaluate the efficacy of transforaminal endoscopic lumbar discectomy (TELD) under local anesthesia. Methods We retrospectively reviewed the medical records of 11 elite athletes (12 discs) who underwent TELD for small LDH, defined as a herniation not exceeding 25% of the spinal canal’s anteroposterior diameter on magnetic resonance imaging. Preoperative assessments included neurological status and magnetic resonance imaging findings, focusing on T2 hyperintensity within or posterior to the posterior longitudinal ligament (PLL). Outcomes were time to return to sport, recurrence, and patient-reported outcomes by modified MacNab criteria at final follow-up. Results All athletes presented with function-limiting radiculopathy despite radiographically small herniations (mean anteroposterior diameter, 3.3 ± 1.0 mm; mean canal occupancy ratio, 16.7% ± 6.6%). T2 hyperintensity in or behind the PLL was present in all 12 discs. Following TELD, all athletes returned to unrestricted competition at a median of 2.0 months (range, 1.5–5.0). At a median final follow-up of 26.0 months, modified MacNab outcomes were excellent in 63.6% and good in 36.4%. No recurrences requiring reoperation occurred. Conclusions Symptomatic small LDH with associated T2 hyperintensity in the PLL is a distinct clinical entity in elite athletes. TELD under local anesthesia is a safe and effective intervention that facilitates a rapid and reliable return to sport with favorable mid-term outcomes. Clinical Relevance This study provides evidence that TELD under local anesthesia is an effective treatment for elite athletes with symptomatic small LDH, facilitating a predictable and rapid return to high-level competition. The identification of T2 hyperintensity in the PLL as a key imaging marker may help guide surgical decision-making in this specific patient population. Level of Evidence 4. ijss;8858v1/VISUALABSTRACT1 F1 visualabstract1

Retrospective case-control study. To determine whether maximal facet tropism (FT) is an independent risk factor for lumbar disk herniation (LDH) in young athletes and establish a data-driven, quantitative cutoff value. The role of FT in LDH remains debated because previous studies have focused on level-specific prevalence without defining a clinically significant threshold for maximal asymmetry, particularly in athletes. Axial magnetic resonance images from L3 to S1 in 43 athletes were compared with LDH and 11 symptomatic nonherniated athletes. The primary variable was maximal FT, the single greatest asymmetry across the measured levels. Risk was assessed using multivariable logistic regression, and a cutoff was determined by receiver-operating characteristic (ROC) curve analysis. The LDH group exhibited significantly greater maximal FT (11.8°±5.9° vs. 7.6°±3.0°, p=0.028) and was confirmed to be an independent predictor of LDH (with odds ratio of 1.23 per increment of 1°; p=0.041). ROC curve analysis identified an optimal 10.8° cutoff (area under the ROC curve, 0.727), yielding 55.8% sensitivity and 90.9% specificity. Although severe FT (>10°) was most prevalent at L5/S1 in the LDH group (p=0.024), maximal FT values were not significantly different between the L4/5 and L5/S1 groups (p=0.353) in an analysis stratified by herniation level. Maximal FT is an independent risk factor for LDH in young athletes. The magnitude of maximal asymmetry in the lower lumbar spine, rather than its specific spinal level, appears to be the primary contributor to this risk, and an angle >10.8° serves as a preliminary threshold for identifying high-risk athletes.

Background Thoracic disc herniation extruding into the dorsal epidural space is exceptionally rare and is frequently mistaken for an epidural tumor, abscess, or hematoma. We aimed to characterize its clinicoradiological features, identify imaging features that may favor a disc fragment over a neoplasm, and report surgical outcomes. Methods We retrospectively present 2 histologically confirmed cases treated by posterior decompression at our institution. To contextualize these cases, a focused literature review was performed, limited to thoracic-only cases, excluding cervical, lumbar, and other epidural pathologies that mimic this condition. The primary outcome (neurological recovery) was prespecified using the modified Frankel grade, with “complete recovery” defined as full motor strength (5/5) plus the patient’s preinjury independent ambulation. Results The pooled cohort comprised 16 patients (14 men, 2 women; median age 56.5 years; T10–T11 most common, 38%). All presented with thoracic myelopathy, most with rapid neurological deterioration. In this highly selected cohort, posterior decompression was followed by neurological improvement in all reported cases, with no major complications. Documented complete recovery was identified in 5 of 16 patients (31%), using a conservative proxy definition, at a median follow-up of 4.5 months (range 0.1–30 months). Contrast enhancement (rim, peripheral, or diffuse) did not reliably distinguish disc fragments from tumor; features favoring a disc fragment were continuity with a degenerated disc space, absence of a dural tail, and absence of a homogeneous markedly high T2 signal. Conclusions Dorsal thoracic disc extrusion should be considered when a posterior thoracic epidural mass causes acute or rapidly progressive myelopathy. In the reported thoracic cases, posterior decompression was followed by neurological improvement in all patients, but complete recovery was documented in only 31% under a conservative proxy definition. These findings remain limited by short follow-up, small sample size, level 4 evidence, and significant publication and selection bias. Clinical Relevance A high index of suspicion for dorsal disc extrusion is warranted whenever a posterior thoracic epidural mass is encountered, even when imaging suggests neoplasm. Continuity with a degenerated disc space, absence of a dural tail, and absence of homogeneous markedly high T2 signal are clues that may support early surgical decompression when the clinical presentation is consistent with compressive myelopathy. Level of Evidence 4.