BACKGROUND:Injury to the popliteal artery (PA) is a severe complication during total knee arthroplasty (TKA). Current information on the anatomical proximity of the PA to the posterior tibial cortex is mostly derived from imaging studies, which may not accurately represent surgical conditions. Additionally, anatomical differences between sexes remain unclear. This cadaver study aimed to determine the anatomical relationship between the PA and tibial landmarks at clinically relevant tibial resection levels during TKA, emphasizing potential sex-based differences. METHODS:Overall, 102 knees from 51 formalin-embalmed cadavers (24 men and 27 women) were dissected. An Akagi line-based coordinate system defined the tibial landmarks, and three standard tibial resection levels employed in TKA (joint line, 10 mm distal, and 15 mm distal) were evaluated. The posterior, lateral, and shortest distances from the posterior tibial cortex to the PA were measured. Multivariate linear regression analyses that adjusted for lower leg length were used to assess sex-based anatomical differences. RESULTS:The PA progressively approached the posterior tibial cortex distally; the median shortest distances significantly decreased from 10.0 mm (joint line) to 5.0 mm (15 mm distal). After adjusting for lower leg length, multivariate linear regression analysis revealed men as independently associated with greater posterior (P = 0.043) and shortest (P = 0.045) distances only at the joint level. However, these sex-based differences were no longer significant at deeper resection levels. CONCLUSIONS:During TKA, the anatomical risk of PA injury significantly increases at deeper tibial resection levels. Although there are sex-based anatomical differences at the joint line, they disappear at clinically relevant distal resection levels, highlighting the need for careful surgical vigilance regardless of the patient's sex.

Peroneal tendon dislocation is a rare and often overlooked condition, particularly when coexisting with Achilles tendon rupture. It can lead to persistent pain and instability if overlooked. Therefore, an accurate diagnosis in the acute phase is crucial. Both injuries share a similar mechanism, making simultaneous occurrence possible, but difficult to diagnose. This set of patient cases is based on two older male patients that had chronic Achilles tendon rupture and peroneal tendon dislocation following low-energy trauma. Owing to the gait disturbance caused by the Achilles tendon rupture, a peroneal tendon dislocation was overlooked. Sonography provided critical diagnostic information and identified tendon instabilities that magnetic resonance imaging (MRI) could not detect. This case series emphasizes the value of dynamic sonography, in evaluating peroneal tendon instability, especially when symptoms persist or when MRI findings are inconclusive. Clinicians should have a high index of suspicion for combined injuries, even after minor trauma, to ensure accurate diagnosis and appropriate surgical intervention.

Study Design.A retrospective registry-based study.Objective.To elucidate the nationwide epidemiology, treatment patterns, and prognosis of primary malignant spine tumors (PMST) using the Japanese Orthopaedic Association's Bone and Soft Tissue Tumor (BSTT) Registry.Summary of Background Data.PMSTs are rare, comprising a small proportion of primary malignant bone tumors. The surrounding anatomical structures make complete resection challenging, leading to poor prognoses. Studies using the Surveillance, Epidemiology, and End Results database have provided valuable epidemiological insights; however, limitations in the granularity and diversity of histologic subtypes persist, leaving detailed knowledge of PMSTs insufficiently clarified.Methods.We analyzed 288 PMST cases from the BSTT Registry (2006-2019), evaluating patient demographics, tumor characteristics, treatment details, and prognostic outcomes. Kaplan-Meier methods estimated disease-specific survival (DSS), and Cox proportional hazards models identified prognostic factors.Results.PMSTs accounted for 3.3% of primary malignant bone tumors. Common histologic subtypes included osteosarcoma (21.9%), chondrosarcoma (16.3%), chordoma (13.9%), and undifferentiated pleomorphic sarcoma (13.9%). Surgery was performed in 46.2% of cases, with intralesional margins in 54.1%. Chemotherapy and radiotherapy were administered in 42.0% and 54.9% of cases, respectively. The 5-year DSS was 47.5%. Adjusted analysis revealed favorable prognoses for chondrosarcoma [hazard ratio (HR): 0.23, 95% CI: 0.06-0.87, P=0.031], chordoma (HR: 0.27, 95% CI: 0.09-0.84, P=0.024), and Ewing sarcoma (HR: 0.42, 95% CI: 0.18-0.98, P=0.044) compared with osteosarcoma. Adults (40-64 yr) had better outcomes than the elderly (>= 65 yr; HR: 0.43, 95% CI: 0.24-0.76, P=0.015). Advanced TNM stage (IVA + IVB) was an adverse prognostic factor (HR: 7.60, 95% CI: 1.85-31.18, P=0.005).Conclusions.PMSTs are rare and present diverse histologic subtypes with poor prognoses. This study emphasizes the need for further investigations to optimize PMST management and improve prognoses.Level of Evidence:Level IIb.

BACKGROUND CONTEXT:Lumbar segmental instability is an important factor in determining surgical strategies for degenerative lumbar spine disorders. Although dynamic slip comparing extension and flexion radiographs (DSEF) is commonly used, dynamic slip comparing upright and supine positions (DSUS) has been proposed as an alternative measure. PURPOSE:To examine the association between DSUS and postoperative outcomes after lumbar decompression surgery without fusion and to identify a DSUS threshold predictive of reoperation. STUDY DESIGN:Multicenter retrospective cohort study. PATIENT SAMPLE:A total of 188 patients who underwent initial single-level lumbar decompression surgery and were followed for at least 3 years. OUTCOME MEASURES:Symptomatic reoperation, Oswestry Disability Index (ODI), visual analogue scale (VAS) scores, and radiographic parameters. METHODS:DSUS and DSEF were measured using standing-supine imaging and flexion-extension radiographs. Patients were classified as DSUS-positive (≥3 mm) or DSUS-negative (<3 mm). Clinical and radiographic outcomes were compared longitudinally. Time-to-event outcomes were assessed using Kaplan-Meier and Cox proportional hazards models. Receiver operating characteristic (ROC) analyses were performed. RESULTS:DSUS and DSEF showed moderate correlation (r=0.37) with frequent discordance. A total of 33 patients (17.6%) were DSUS-positive. DSUS-positive patients had significantly higher reoperation rates, worse postoperative ODI and VAS scores, and greater postoperative slip progression. In Cox models, DSUS independently predicted reoperation after adjustment for key covariates. ROC analysis identified 3.0 mm as the optimal cutoff (area under the curve 0.90). CONCLUSIONS:DSUS is associated with poorer postoperative outcomes and increased reoperation risk after lumbar decompression surgery.

Introduction:Impaction bone grafting (IBG) with cemented stems in revision total hip arthroplasty (THA) is a well-established method, but reports using cementless stems are scarce. The purpose of this study is to report short-term outcomes of six revision THAs using the IBG technique with a collared fully hydroxyapatite (HA)-coated stem. Materials and Methods:From 2014 to 2021, six joints (median age 64.3 years; median follow-up 4.5 years) were revised for aseptic loosening (n = 5) or septic loosening (n = 1). All cases used the IBG technique with a collared fully HA-coated stem (CORAIL or UNIVERSIA). Full weight-bearing was allowed post-operative day 1. Outcomes included the Japanese Orthopedic Association Score, stem subsidence, and radiographic remodeling. Results:Median surgical time was 127 min; blood loss was 855 mL. No complications (infection, polyethylene wear, loosening, or dislocation) occurred. The JOA score improved from 63 (preoperatively) to 95 (final follow-up). Median stem subsidence was 1.4 mm (1-3 mm), with no case >5 mm. Radiographs showed no radiolucent lines and remodeling in all cases. Computed tomography (CT) images of one case confirmed bone ingrowth between the stem and the compressed allograft. Conclusion:Short-term outcomes of revision THA with IBG using a collared fully HA-coated stem are favorable. This technique, supported by radiographic and CT evidence of bone ingrowth, is a useful and effective treatment option for femoral component revision.

BACKGROUND:Mobility decline increases risks of falls, long-term care, and mortality, yet it may start in midlife. We examined lifestyle-related factors for the incident mobility decline in middle-aged adults. METHODS:We conducted a 7-year cohort study using a health checkup database from an urban area of Japan (2016-2023). Participants without baseline mobility limitation were included; those without 2023 follow-up or with missing data were excluded. Mobility was assessed at baseline and follow-up using locomotive syndrome (LS) risk tests, including two-step and stand-up tests and the Geriatric Locomotive Function Scale-25. Baseline lifestyle habits and lifestyle-related conditions were collected. The main outcome was incident LS at follow-up. Multivariable logistic regression assessed associations between baseline factors and LS development. RESULTS:Among 10,445 participants (median age 47 years [interquartile range 42-53]; 3949 [38%] female), 1205 (12%) developed LS over 7 years, mainly due to deterioration in the stand-up test (681, 6%) and Geriatric Locomotive Function Scale-25 (566, 6%). In analyses stratified jointly by age group and sex, high waist circumference was associated with incident LS in women across all age groups and in men aged 40-49 and 50-59 years. Diabetes was associated with incident LS in men aged 40-49 and 50-59 years. However, interaction analyses did not provide statistical evidence that these associations differed across age-sex subgroups. CONCLUSIONS:High waist circumference and diabetes in midlife were associated with incident LS over 7 years, although residual confounding factors and potential informative censoring due to loss to follow-up may have influenced these associations.

Giant cell tumor of bone (GCTB) is a locally aggressive osteolytic bone tumor characterized by recurrent mutation in the H3-3A gene. Although surgical resection remains the mainstay of treatment, a considerable proportion of patients experience local recurrence or pulmonary metastasis, and effective systemic therapy has not yet been established. Given the inherent clinicopathological heterogeneity of GCTB, we established a novel patient-derived cell line, NCC-GCTB16-C1, from the primary tumor of a patient with GCTB to expand the experimental resources available for translational research. The cells exhibited stable proliferation over a 3-month period, retained the characteristic H3-3A mutation, and formed spheroids with variable morphologies under three-dimensional conditions. They also demonstrated invasive and migratory behavior consistent with the biological properties of GCTB. Proteomic analysis revealed that NCC-GCTB16-C1 exhibited properties similar to those of the original tumor tissue. Thus, NCC-GCTB16-C1 provides an in vitro model that faithfully reflects the molecular and phenotypic features of GCTB, offering a valuable tool for mechanistic studies and preclinical drug evaluation.

BACKGROUND:Forearm diaphyseal fixation requires a mechanical environment appropriate for healing, but effects of residual gaps and cortical contact patterns remain unclear. This study used finite element analysis to quantify how gap size and contact pattern affect fracture-site strain and plate stress and to inform fixation strategy. METHODS:Computed tomography scans from uninjured contralateral forearms of five adults with forearm diaphyseal fractures were used to create subject-specific models of the central 4/6 radius fixed with a small-fragment Ti-6Al-7Nb low-contact locking compression plate. We modeled simple transverse fractures with 0-2.0 mm gaps, partial-contact constructs with opposite-cortex contact or plate-side contact, and a comminuted configuration with two intermediate fragments. Coulomb friction (μ = 0.1) was used. A dorsal load up to 40 N was applied under cantilever conditions. Outcomes were plate equivalent stress, cortical-edge equivalent stress, and minimum principal strain within the gap. FINDINGS:Full cortical contact minimized plate stress and maintained cortical load sharing. Residual gaps increased plate stress and altered cortical load transfer; small gaps generated the largest compressive interfragmentary strain. Opposite-cortex contact reduced plate stress and interfragmentary strain compared with plate-side contact. In comminution, intermediate fragments redistributed load and reduced average strain at the main fracture. INTERPRETATION:Bone-to-bone contact and gap minimization improve the initial mechanical environment in simple fracture configurations. When only partial apposition is possible, opposite-cortex contact is mechanically preferable to plate-side contact. In comminution, bridge constructs may promote load sharing favorable to secondary healing.

Objectives:This study examined the feasibility, short-term safety, and changes in objective mobility measures associated with initiating gait training between postoperative day (POD) 2 and POD 4 and completing it by POD 14 following surgery for thoracic myelopathy. Methods:This retrospective, single-arm cohort study included 11 patients with thoracic myelopathy and preoperative gait impairments. Individualized gait training combined recumbent cycling and treadmill walking (~40 min/session, 3-5 times/week) at a "somewhat hard" intensity on the modified Borg scale (rating: 6). Primary outcomes were walking speed and step length on the 10-m Walk Test. Secondary outcomes included time and step count from the Timed Up-and-Go Test (TUG), the Japan Orthopaedic Association lower-extremity motor function score (JOA-LE), static balance, muscle strength, and sensory function. Assessments were performed preoperatively and on POD 14. Results:Walking speed (median change 0.25 m/s, P = 0.029) and step length (median change 0.05 m, P = 0.009) improved significantly. TUG results also improved for completion time (median change -3.03 s, P = 0.007) and step count (median change -3 steps, P = 0.046). Standing balance improved, with nine patients achieving independence in the Romberg position with eyes closed (P = 0.029). No notable changes were observed in JOA-LE, muscle strength, or sensory function. No adverse events occurred. Conclusions:Early, device-assisted gait training initiated within POD 4 was feasible and safe, and it was associated with short-term improvements in objective mobility measures. Controlled trials are warranted to confirm these findings.

Background: Extracorporeal shock wave therapy (ESWT) and platelet-rich plasma (PRP) therapy are effective treatments for tendinopathy; however, in some cases, these monotherapies are ineffective, leading to a delayed return to competition for athletes or the need for surgical intervention in middle-aged and older patients, creating challenges in clinical practice. Purpose/Hypothesis: Few clinical reports have examined the synergistic therapeutic effects of combined ESWT and PRP therapy in fields other than tendinopathy, such as pseudarthrosis. The authors hypothesized that the combined use of ESWT and PRP would exert a synergistic therapeutic effect on tendon disorders. Consequently, when compared with monotherapy, the effects would be observed earlier, promoting pain relief and tendon healing. This study aimed to evaluate the therapeutic efficacy of combined ESWT and PRP therapy in a rat model of acute Achilles tendinopathy. Study Design: Controlled laboratory study. Methods: Fifty male Sprague-Dawley rats (10 weeks old) were randomly assigned to control, sham, ESWT, PRP, and combined treatment (E+P) groups. Collagenase-induced Achilles tendinopathy was established only in the left hindlimb of all mice, except those in the control group, on day −7. The ESWT, PRP, and E+P groups were administered ESWT on day 0 or injected with PRP on day 1 (stored at −30°C before injection). The load ratios between the injured and healthy hindlimbs were measured on days 0, 7, 14, 21, and 28. Pathologic evaluation and Achilles tendon scoring were performed on day 28. Results: On day 0, the load ratios of the injured limbs were significantly decreased in all groups, except the control group. On day 7, the ESWT and PRP groups demonstrated significant improvements in the ratios as compared with the sham group. The E+P group showed significantly superior improvement when compared with both groups. Pathologic analysis revealed remarkable tendon healing in the E+P group, which significantly outperformed ESWT and PRP monotherapy. Conclusion: ESWT combined with PRP administration produces a synergistic effect, resulting in earlier pain relief and better tendon repair than monotherapy alone. Clinical Relevance: The combined use of ESWT and PRP may offer an enhanced therapeutic strategy for tendinopathies in clinical settings.

BACKGROUND:The original Gruen classification is widely used for radiographic assessment of femoral stems in total hip arthroplasty (THA). However, when stems of different lengths are compared, the same zones may not correspond to equivalent anatomical regions, limiting interpretation of regional fixation patterns. This study proposed a complementary modified Gruen classification for comparing short and conventional Zweymüller-type stems and evaluated its utility using three-dimensional computed tomography (3D CT). METHODS:We retrospectively reviewed 519 primary THAs performed through the direct anterior approach between 2013 and 2021. After propensity score matching, 91 hips with a MIRFY short stem and 91 with a Profemur Z conventional stem were included. Stem-cortex contact was assessed on postoperative 3D CT. In addition to the original Gruen classification, a modified classification based on reproducible femoral landmarks was used to divide the femur into proximal, middle, and distal regions. Contact was defined as the proportion of the stem surface in each region that contacted cortical bone. Radiographic bone reactions and thigh pain were also evaluated at 2 years postoperatively. RESULTS:With the original Gruen classification, the short stem appeared to show greater contact in distal zones. In contrast, the modified classification reassigned these contacts to more anatomically proximal regions, suggesting that the original classification may distort regional interpretation when stems of different lengths are compared. Under the modified classification, the MIRFY stem showed a more proximal contact distribution than the conventional stem. Radiographic bone reactions at 2 years were similar between groups, whereas thigh pain was less frequent in the MIRFY group. CONCLUSIONS:The modified Gruen classification may serve as a complementary framework for comparing femoral stems of different lengths. This approach may allow more anatomically appropriate interpretation of regional stem-cortex contact when stems of different lengths are compared.

BACKGROUND:Surgical smoke is a gaseous intraoperative byproduct that contains numerous toxic compounds, including fine particles with a diameter of ≤2.5 µm (PM2.5). However, intraoperative exposure during joint arthroplasty has not been well characterized. In this study, we aimed to quantify PM2.5 exposure during arthroplasty and to determine, by procedure and approach, how often it reached potentially harmful levels. METHODS:We conducted a single-center prospective study of 83 primary arthroplasties (20 bipolar hemiarthroplasties [BHAs] via a direct lateral approach, 35 total hip arthroplasties [THAs] via a direct anterior approach, and 28 total knee arthroplasties [TKAs]). Intraoperative PM2.5 concentrations were measured using a portable monitor and were mapped to Air Quality Index (AQI) categories. Summary metrics, including maximum and cumulative PM2.5 exposure, were calculated by procedure. Logistic regression was used to estimate odds ratios (ORs) for exceeding AQI thresholds. RESULTS:In BHA and TKA, PM2.5 concentrations increased sharply during field development, whereas they remained low throughout THA. The median maximum PM2.5 concentrations were 129.50 µg/m 3 (interquartile range [IQR], 85.44 to 275.28 µg/m 3 ) for BHA, 6.14 µg/m 3 (IQR, 2.54 to 23.94 µg/m 3 ) for THA, and 118.80 µg/m 3 (IQR, 56.23 to 208.04 µg/m 3 ) for TKA. The concentrations were significantly higher in BHA and TKA (both adjusted p < 0.001) than in THA. At 25% of the normalized surgical time, 80% of BHA cases and 71% of TKA cases reached an AQI of Unhealthy or worse, whereas most THA cases remained within the Good or Moderate categories. The adjusted ORs for reaching an AQI of Unhealthy or worse were 34.280 (95% confidence interval [CI], 7.479 to 215.044; p < 0.001) for BHA and 21.971 (95% CI, 6.011 to 101.814; p < 0.001) for TKA compared with THA. CONCLUSIONS:BHA via a direct lateral approach and TKA generated substantially higher intraoperative PM2.5 concentrations than THA via a direct anterior approach, and many cases reached an AQI of Unhealthy or worse. Procedure and approach are not readily modifiable determinants of surgical smoke exposure, underscoring the need for comprehensive control strategies, including smoke evacuation and high-efficiency masks, in arthroplasty practice. CLINICAL RELEVANCE:Operating room teams may be exposed to potentially harmful levels of surgical smoke during arthroplasty. Understanding the characteristics of this exposure may help to guide strategies to optimize the operating room environment.

Objective Walking speed is an important indicator of physical function and is associated with adverse outcomes such as falls and mortality. This study aimed to examine the associations between walking speed and sagittal spinal alignment, osteoporotic vertebral fracture (OVF), and handgrip strength in female patients aged 60 years or older attending osteoporosis outpatient clinics. Methods This exploratory cross-sectional study included 102 female patients aged ≥60 years with confirmed osteoporosis who attended osteoporosis outpatient clinics. Walking speed, sagittal vertical axis (SVA), OVF, handgrip strength, age, BMI, and lumbar bone mineral density (BMD) were assessed. Multiple linear regression analysis was performed using data from all 102 participants, with walking speed as the dependent variable. Results In the multivariable model, OVF (B = -0.1484, p < 0.001), SVA (B = -0.00307, p < 0.001), and handgrip strength (B = 0.0178, p = 0.002) were significantly associated with walking speed, whereas BMI, age, and lumbar BMD were not. The model had an R² of 0.478 and an adjusted R² of 0.446. Conclusion Walking speed in female patients aged 60 years or older attending osteoporosis outpatient clinics was associated with sagittal spinal alignment, OVF, and handgrip strength. These findings suggest that sagittal spinal alignment, vertebral fracture, and handgrip strength may be relevant factors to consider when interpreting reduced walking speed in this population.

Background Postoperative reduction loss remains a major concern after arthroscopic coracoclavicular ligament (CCL) reconstruction. Although bone tunnel position has been suggested as a contributing factor, most previous studies have relied on plain radiographs, which are limited in evaluating three-dimensional positioning. The purpose of this study was to evaluate clavicular and coracoid bone tunnel positions using computed tomography (CT) and to investigate their association with postoperative reduction loss. Methods This retrospective, single-center study included 22 patients who underwent arthroscopic CCL reconstruction for acute acromioclavicular joint dislocation or distal clavicle fracture with CCL rupture. Postoperative CT with multiplanar reconstruction was used to assess the anteroposterior (AP) and mediolateral (ML) positions of the clavicular and coracoid tunnels. Reduction loss was defined as the percentage increase in coracoclavicular distance at final follow-up relative to the immediate postoperative value. Correlation analyses were performed between tunnel positions and reduction loss. Redisplacement was defined as ≥25% compared with the contralateral side, and clinical outcomes (ASES, Constant score, and SSV) were compared between groups. Results The ML position of the clavicular tunnel showed a moderate correlation with reduction loss, whereas the AP position of the clavicular tunnel and both ML and AP positions of the coracoid tunnel showed weak or no significant correlation. The overcorrection rate demonstrated a strong correlation with reduction loss, whereas the preoperative displacement rate showed no significant association. Redisplacement occurred in 7 of 22 patients (31.8%) but was not associated with clinical outcomes. Conclusion The ML position of clavicular tunnel plays an important role in postoperative stability following arthroscopic CCL reconstruction. In contrast, AP tunnel position and coracoid tunnel position appear to have less influence on reduction loss. Although redisplacement was not associated with clinical outcomes, its relatively high incidence (31.8%) remains a concern. Accordingly, preventing redisplacement remains important, and particular attention should be paid to the ML position of the clavicular tunnel during arthroscopic CCL reconstruction. Level of Evidence Level IV, Case Series, Prognosis Study

BACKGROUND:Hindfoot compensation for coronal knee deformity is recognized in end-stage osteoarthritis (OA), but evidence in non-surgical populations is limited. This study aimed to clarify the independent association between knee and hindfoot coronal alignment and to identify factors related to hindfoot compensation in community-dwelling adults. METHODS:In this cross-sectional study, adults aged ≥40 years underwent bilateral hip-to-calcaneus radiography. Knee varus angle, hindfoot valgus angle, medial distal tibial angle, and talar tilt angle were measured. Knee OA was defined as Kellgren-Lawrence grade ≥2. Simple linear regression evaluated univariate associations between the hindfoot valgus angle and the knee varus angle. Generalized linear mixed models assessed independent associations, adjusting for other radiographic parameters and participant characteristics. RESULTS:We analyzed 1006 legs from 509 participants (66% female; median age, 71 years). Median knee varus and hindfoot valgus were 2.3° and 1.3°, respectively. Knee OA was observed in 526 (52%) legs. Knee varus angle was positively associated with hindfoot valgus angle in both univariate (β = 0.26, P < 0.001) and multivariate analyses (β = 0.19, P < 0.001). Varus knee OA (β = 1.03, P < 0.001) was also independently associated with increased hindfoot valgus angle. Approximately 30% of varus knee OA cases exhibited varus hindfoot, indicating absent compensation. CONCLUSIONS:In community-dwelling older adults, hindfoot valgus increased with increasing knee varus, supporting the physiological coronal-plane compensation, although substantial individual variability was observed. Knee OA was independently associated with hindfoot valgus. These findings provide data for clinical assessment in patients with knee OA.

Retrospective, single-center, observational study. To evaluate the diagnostic reliability of magnetic resonance (MR) Bone Imaging in stage classification of adolescent lumbar spondylolysis, assessing its clinical applicability as an alternative to computed tomography (CT). The diagnosis of adolescent lumbar spondylolysis typically requires CT; however, concerns regarding medical radiation exposure have been raised. With recent advancements in magnetic resonance imaging (MRI) technology, MR bone imaging has been developed, enabling the acquisition of CT-like images. This study included 116 adolescent patients diagnosed with lumbar spondylolysis between August 2022 and April 2024. In addition to conventional MRI, MR Bone Imaging and CT scans were performed on the affected vertebrae. Two independent raters assessed sagittal images and classified the fractures using the Oba classification system. MRI examinations were performed using either a 1.5T or 3T scanners. For statistical analysis, CT classification was used as the reference standard. Inter-rater and inter-modality agreements for both CT and MR Bone Imaging were evaluated using the weighted kappa coefficient (linear weights). Among the 116 patients, 70 cases (140 pars) underwent 3T MRI, while 46 cases (92 pars) underwent 1.5T MRI. In the 3T MRI group, the inter-rater agreement was κ=0.98 for CT and κ=0.91 for MR Bone Imaging, while inter-modality agreement was κ=0.89 for Rater A and κ=0.83 for Rater B. In the 1.5T MRI group, inter-rater agreement was κ=0.94 for CT and κ=0.92 for MR Bone Imaging, while inter-modality agreement was κ=0.83 for Rater A and κ=0.84 for Rater B. These results indicate that MR Bone Imaging provides stage classification accuracy comparable to that of CT in the evaluation of adolescent lumbar spondylolysis. Furthermore, similar findings were observed for both 1.5T and 3T MRI.

Restoration of the hip center of rotation (COR) is a primary goal in total hip arthroplasty (THA). Although the teardrop has been widely used as a reference for acetabular cup positioning, its effect on offsets remains uncertain. We conducted a computed tomography-based simulation study of 60 hips (30 osteoarthritis, 30 osteonecrosis of the femoral head) undergoing THA. The contralateral, unaffected hip served as the control. The acetabular cup was positioned just lateral to the teardrop, aligned with the true floor of the acetabulum using preoperative templating software. Acetabular, femoral, and vertical offsets (AO, FO, and VO) were measured bilaterally, and the horizontal and vertical displacements of the COR were evaluated. Compared to the contralateral unaffected side, AO and FO significantly decreased and VO significantly increased on the surgical side (p < 0.01). The COR shifted medially and superiorly in both OA and ONFH groups (average: 2.7-2.8 mm medial, 2.0-2.8 mm superior). In the OA group, global offset (GO), the sum of AO and FO, decreased by 4.7 mm due to a significant reduction in FO. Teardrop-based positioning of the acetabular cup results in medial and superior displacement of the COR, consequently reducing AO and GO. In patients with osteoarthritis, a decreased FO further compromises GO, making femoral component adjustment essential for biomechanical restoration. Further investigation into the clinical ramifications of these offset changes is warranted.