Search Results (179)

Background and Clinical Significance: Multiligamentous knee injuries (MLKIs) are uncommon but severe injuries associated with instability, neurovascular compromise, and long-term functional impairment. Irreducible knee dislocations are a distinct subgroup requiring urgent intervention because soft-tissue interposition may prevent closed reduction and place the limb at risk of skin necrosis and vascular compromise. This report reviews current concepts in MLKI management and presents a complex KD-IV irreducible knee dislocation treated with a staged surgical strategy. Case Presentation: A 56-year-old woman presented 24 h after a skiing injury with a grossly deformed knee, multidirectional instability, and an anteromedial “pucker sign”. Magnetic resonance imaging demonstrated a KD-IV injury with complete rupture of the anterior cruciate ligament, posterior cruciate ligament, and medial collateral ligament, associated with capsular disruption and intra-articular soft-tissue interposition causing irreducibility. Urgent open reduction was performed. The first stage included reduction of the incarcerated capsule, capsular repair, and reconstruction of the posteromedial corner and medial collateral ligament using a semitendinosus autograft. Delayed reassessment at 6 months demonstrated satisfactory stability, minimal residual anterior laxity, and no subjective instability; therefore, anterior cruciate ligament reconstruction was not performed. At final follow-up, the patient had near-full range of motion, no significant valgus instability, and no arthrofibrosis or vascular complications. Conclusions: Management of MLKIs should be individualized according to reducibility, soft-tissue condition, neurovascular status, and functional demands. Irreducible KD-IV dislocations with a pucker sign require urgent open reduction. In selected patients, staged reconstruction may reduce postoperative stiffness and allow selective omission of cruciate ligament reconstruction when satisfactory functional stability is achieved. Full article

Compliant mechanisms have contributed to many advances in soft robotics, and there is strong motivation to translate these ideas to assistive devices where adaptive motion at the human interface is required. This work presents novel reconfigurable compliant joints (RCJs) as a parameterized joint element for functional biomimicry in lower-extremity joints for prosthetic knees and ankle–foot orthoses, with concepts that extend to other limb joints. The RCJ uses a rigid hub and outer ring joined by an array of flexible links with centerlines defined by cubic Bézier curves. Link shapes are organized into four Bézier classes (A–D), with base types using 10, 12, or 14 uniformly distributed link slots and variants generated by modifying active-link count and distribution, forming a structured morphology space of 12 configurations for machine design. Dual-extrusion 3D-printed prototypes are characterized by a custom testing apparatus using a 2.2 kN load cell at 25 mm/s over a 0–90° rotation range across six recorded load cycles to measure torque–angle curves and stiffness under large deformations. Angle-dependent stiffness is evaluated over three fixed intervals (0–30°, 30–60°, and 60–90°) to quantify multi-stage behavior. A 2-dimensional corotational frame model and a Simscape Multibody model, including a rolling-contact knee configuration, use the same parameterization to relate geometry, nonlinear mechanics, and system-level motion. Experiments and simulations show multi-stage torque–angle profiles and predictable stiffness modulation across all configurations, with both magnitude and transition angle tunable through Bézier class and active-link distribution, positioning the RCJ as a CAD/CAE-compatible joint architecture for assistive devices or wearable robotic systems and a basis for advancing functional biomimicry in compliant mechanism design. Full article

Background: Multibody models are essential for studying knee joint mechanics, but their reliability and subsequent clinical utility are limited by uncertainties in ligament and contact parameters. Currently, no consensus exists on which parameters to prioritize or which statistical distributions best establish model credibility. Objectives: This scoping review aims to systematize reported uncertainty values for ligament and contact parameters in multibody models of the natural knee to identify trends and research gaps. Methods: Following PRISMA-ScR guidelines, a systematic search was conducted across PubMed, Scopus, and Web of Science. Methodological quality was assessed using a customized 13-item checklist, and the data were synthesized via a narrative approach by charting parameter types, quantification methods, and model structures. Results: In total, 19 articles were included (out of 494 identified), showing a wide variability in uncertain parameter types, values, and modeling approaches. Ligaments were typically represented as deformable cables with quadratic–linear behavior, while articular contact utilized elastic foundation formulations or mechanisms. Standard deviations of 30% of the mean for ligament stiffness and 0.02 for reference strain (typically modeled within Gaussian distributions) were the most frequently quantified uncertain parameters. Geometric uncertainties for ligament attachment points varied widely, ranging from 1.0 to 5.0 mm. Idealized contact geometry also varied within 2.5 mm for linear coordinates and 15° for angular coordinates. Conclusions: Wide variability and inconsistent reports highlight a need for standardized definitions of parameter uncertainty in multibody knee modeling to improve reproducibility of musculoskeletal knee simulations and ensure a reliable transition of these models into clinical practice. Full article

Background and Objectives: Medial unicompartmental knee arthroplasty (UKA) has emerged as an effective surgical option for isolated medial compartment osteoarthritis (OA), offering advantages in bone preservation, knee kinematics, and postoperative recovery compared with total knee arthroplasty (TKA). Although numerous studies have evaluated the mid- to long-term outcomes of UKA, reports focusing on cohorts with follow-up periods exceeding 10 years remain relatively limited. The purpose of this study was to analyze the long-term clinical and radiological results of medial fixed-bearing UKA using the Miller-Galante prosthesis. Methods: Sixty-eight patients who underwent UKA at a single institution with at least 10 years of follow-up were retrospectively reviewed. Clinical outcomes were assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score and knee range of motion (ROM). Radiological parameters including the hip-knee-ankle axis angle (HKA) and osteoarthritis (OA) grade using the Kellgren-Lawrence (K-L) grading system were evaluated. Implant survivorship was evaluated using Kaplan–Meier survival analysis. Results: A total of 68 patients were included with a mean age of 56.8 ± 7.5 years at surgery and a mean follow-up of 170.9 ± 37.3 months. Significant improvement in the WOMAC score was observed from 48.9 ± 17.2 preoperatively to 23.8 ± 27.7 at final follow-up (p = 0.002). The cumulative survival rates were 97.1% at 10 years and 84.8% at 15 years with conversion to total knee arthroplasty as the endpoint. Significant improvement in the HKA was observed from 172.5° ± 4.4° to 174.3° ± 4.8° postoperatively (p = 0.002), though residual varus alignment persisted. Progressive OA was observed in the lateral tibiofemoral and patellofemoral compartments (both p < 0.001) but showed no correlation with the WOMAC score. The failure group showed trends toward higher body mass index (BMI) and smaller preoperative HKA angle compared to the non-failure group. Conclusions: The long-term outcomes of medial fixed-bearing UKA using the Miller–Galante prosthesis were generally favorable, with significant functional improvement and acceptable implant survivorship. Although overall varus alignment was corrected, some residual varus deformity remained, and OA progression was observed in the lateral tibiofemoral and patellofemoral compartments over time. However, given the retrospective design and limited sample size, these findings should be interpreted with caution. Full article

Tibial torsion significantly influences knee biomechanics, yet its interaction with ACL reconstruction history in elite alpine skiers remains under-investigated. In this cross-sectional observational study, we analyzed 20 elite alpine skiers (7 ACL-reconstructed, 13 non-injured) using a markerless motion capture system during dynamic tasks (Squat, Single-Leg Squat, Lunge). Static tibial torsion was assessed via the Transmalleolar Axis and Thigh–Foot Angle. The results revealed a critical divergence in biomechanical strategies based on tibial alignment (p < 0.05). Skiers with rotational deformity adopted a pattern we describe as a “Stiffness Strategy”, characterized by suppressed knee valgus and hip rotation, but relied on excessive ankle dorsiflexion (39.5°)—a compensatory mechanism that may become limited when constrained by rigid ski boots. In contrast, ACL-reconstructed skiers with normal alignment exhibited what we term an “Instability Strategy”, showing dynamic valgus collapse and persistent asymmetry. These findings suggest that “one-size-fits-all” rehabilitation may be insufficient. We propose that injury prevention protocols may benefit from incorporating anatomical screening, focusing on decoupling mobility for skiers with tibial torsion and enhancing dynamic stability for those with normal alignment. Full article

Background: Revision total knee arthroplasty (rTKA) is a technically demanding procedure that, when performed using mechanically aligned strategies, frequently relies on stems, augments, metaphyseal cones and constrained implants to restore knee alignment and stability. In carefully selected cases with preserved metaphyseal bone stock and competent collateral ligaments, robotic assistance allows a bone-preserving strategy in which alignment, joint line height, and soft-tissue balance are restored using conventional posterior-stabilized components with short cemented stems rather than higher invasive and constrained constructs. Methods: This technical note describes a step-by-step surgical workflow using the Mako robotic system (Stryker) to revise failed primary TKA associated with minimal metaphyseal bone loss to rTKA with conventional posterior-stabilized components and short cemented stems within a functional alignment framework. Results: The workflow integrates CT-based three-dimensional planning, registration on in situ implants, real-time gap assessment, and precise robotic bone preparation to correct deformity and to restore stability while minimizing additional bone resection. In this setting, limited tibial metaphyseal defects are managed with impacted autologous cancellous graft, and stable fixation is achieved with short cemented stems. Conclusions: This robotic-assisted approach is intended as a bone-preserving option for selected rTKA cases associated with minimal bone loss and as a conceptual bridge between robotic-assisted primary and conventional revision TKAs performed with mechanical techniques and alignments. Full article

Background/Objectives: The anterior cruciate ligament (ACL) plays a key role in knee stability, biomechanics, and proprioception, and is one of the most frequently injured and reconstructed ligaments in both athletes and the general population. The anatomical placement of femoral and tibial tunnels close to the native ACL insertion sites is critical for long-term clinical outcomes and graft survival. This study aimed to define sagittal and coronal ACL alignment and tibial footprint morphology on magnetic resonance imaging (MRI) in healthy knees, to explore sex- and side-related differences, and to provide population-specific reference values. Methods: In this retrospective cross-sectional study, knee MRIs acquired between 2018 and 2021 were screened, and knees with an intact ACL and without deformity or joint pathology that could alter alignment were included. After applying inclusion and exclusion criteria, 636 knees (320 right, 316 left) from 545 individuals (338 women, 298 men; 15–80 years, mean age 34.87 ± 11.65 years) were analyzed. On sagittal images, the sagittal ACL angle (S-ANGLE) was measured on the slice where the ligament appeared maximally visualized. The midpoints of the ACL were identified on two adjacent sagittal slices, and a line drawn through these midpoints was used to represent the central axis of the ligament; the angle between this line and the tibial plateau was recorded as the S-ANGLE. For anteroposterior localization of the tibial footprint, an anteroposterior reference distance (S-long) was defined as the length measured parallel to the tibial plateau, extending from the midpoint of the tibial tuberosity (corresponding to the insertion site of the patellar ligament and used as a topographic anterior landmark) toward the posterior aspect of the proximal tibia. A perpendicular line was drawn from the anterior end of S-long to establish the anterior reference boundary. The distance from this anterior reference line to the midpoint of the ACL tibial footprint along the same anteroposterior axis was defined as S-short. The sagittal footprint percentage (S-PERCENTAGE) was calculated as (S-short/S-long) × 100, representing the size-normalized sagittal anteroposterior position of the ACL tibial footprint midpoint. On coronal images, the ACL–tibial plateau angle (C-ANGLE), mediolateral tibial length (C-LONG), and distance from the medial edge to the ACL insertion (C-short) were obtained; C-PERCENTAGE was calculated analogously. Medial mechanical proximal tibial angle (mMPTA) was used to confirm physiological coronal alignment. Non-parametric tests were applied, with p < 0.05 considered statistically significant. Results: Women had significantly greater sagittal ACL angles than men, whereas anteroposterior distances measured from the midpoint of the tibial tuberosity (used as an anterior topographic landmark) and oriented parallel to the tibial plateau (S-LONG) and mediolateral tibial lengths (C-LONG) and absolute distances to the ACL tibial footprint were larger in men. In contrast, normalized sagittal and coronal footprint percentages (S-PERCENTAGE, C-PERCENTAGE) did not differ meaningfully between sexes, indicating the preservation of the relative ACL tibial insertion site despite size differences. Small but statistically significant side-to-side differences were observed in some coronal parameters; however, absolute differences were small and did not substantially modify the overall alignment pattern. Conclusions: This study provides large-sample, population-specific reference values for ACL orientation and tibial footprint location in both sagittal and coronal planes in healthy knees. The combination of higher sagittal ACL angles and shorter anteroposterior distances reference measured from the midpoint of the tibial tuberosity and oriented parallel to the tibial plateau (S-LONG) in women may represent a structural substrate contributing to the higher ACL injury rates reported in females. The morphometric data presented here may assist in individualized ACL reconstruction planning, MRI-based assessment of tibial tunnel position, and the design of knee-related biomedical implants and devices. Full article

Objectives: Medial open-wedge high tibial osteotomy (MOWHTO) is a surgical procedure used to treat medial compartment osteoarthritis of the knee with varus deformity. The aim of this study was to examine whether a larger correction angle in medial open wedge high tibial osteotomy (MOWHTO) leads to greater changes in postoperative patellar height (PH) and posterior tibial slope (PTS). Methods: Data from 83 patients who underwent MOWHTO were retrospectively analyzed. Lower limb alignment was evaluated using the hip–knee–ankle angle (HKAA). The PH was assessed using the Insall–Salvati index (ISI), the Blackburne–Peel index (BPI), the Caton–Deschamps index (CDI), the modified Miura–Kawamura index (MKI), and the plateau–patella angle (PPA). The PTS was determined using the Moore–Harvey method. Results: The median correction of HKAA was 8°. A decrease in PH was observed in the majority of cases across all methods, with the highest frequency of postoperative patella infera detected using the MKI. PTS most frequently increased, with a median increase of 3°. A significant association between the magnitude of HKAA correction and patellar height in the overall cohort was observed only for the MKI, whereas in patients with an HKAA correction ≥ 10°, significant associations were found for both the MKI and CDI. No significant association was found between the magnitude of HKAA correction and changes in posterior tibial slope in the overall cohort, while a significant negative correlation was observed in patients with an HKAA correction ≥ 10°. Conclusions: Assessment using the MKI demonstrated greater sensitivity in detecting postoperative PH decrease, particularly in identifying patella infera. The magnitude of HKAA correction was significantly associated with greater changes in PTS and PH in patients with a coronal plane correction of ≥10°. Full article

Objectives: This study aimed to evaluate longitudinal changes in knee muscle strength following open wedge high tibial osteotomy (OWHTO) for medial compartment knee osteoarthritis with varus deformity, with particular emphasis on differences between the operated and non-operated knees. Methods: This retrospective study included 78 patients who underwent OWHTO. All patients followed a standardized rehabilitation protocol consisting of protected weight-bearing for six weeks, followed by closed kinetic chain exercises and subsequent open kinetic chain exercises from three months postoperatively. Isokinetic knee extension and flexion strength were assessed preoperatively and at 3, 6, and 12 months postoperatively using a Biodex System IV dynamometer at angular velocities of 60°/s and 180°/s. Absolute muscle strength values and inter-limb strength deficits were analyzed. Statistical analyses were performed using the Shapiro–Wilk, Friedman, and Wilcoxon signed-rank tests, with significance set at p ≤ 0.05. Results: At 60°/s, knee extensor and flexor strength deficits significantly increased after surgery, peaking at three months postoperatively, and gradually improved; however, deficits remained significantly greater than preoperative values at one year (p < 0.05). Similar trends were observed at 180°/s, although they did not reach statistical significance. These deficits were primarily attributable to reduced muscle strength in the operated knee, while strength in the non-operated knee remained unchanged throughout follow-up. Conclusions: Knee muscle strength in the operated limb markedly declined during the first three months following OWHTO, particularly in maximal power, and generally required more than six months to recover toward preoperative levels. These findings emphasize the importance of targeted postoperative rehabilitation strategies focusing on early muscle power recovery after OWHTO. Full article

Background: The PITX1 gene encodes a transcription factor that plays a crucial role in the development of the lower limbs, pelvis, and structures derived from the first branchial arch. Pathogenic variants in PITX1 are associated with a limited spectrum of rare disorders, including congenital talipes equinovarus with or without long bone anomalies and/or mirror-image polydactyly, and Liebenberg syndrome. In 2020, a novel clinical phenotype, Mandibular–Pelvic–Patellar (MPP) syndrome, resulting PITX1 missense variants, was proposed. Case presentation: We report the fourth documented case of MPP syndrome worldwide, identified in a 17-year-old female patient presenting with congenital lower limb deformities, patellar aplasia, and micrognathia. Whole-genome sequencing revealed a heterozygous PITX1 missense variant NM_002653.5: c.412A>C, p.(Lys138Gln). The clinical phenotype included knee flexion contractures and severe equinovarus and planovalgus foot deformities requiring multiple staged reconstructive surgical procedures. Conclusions: This case supports recognition of MPP syndrome as a clinically and genetically distinct PITX1-related disorder. Our findings expand the phenotypic spectrum of MPP syndrome and suggest that severe congenital foot deformities represent a consistent and clinically relevant feature of this condition. Full article

This work provides an overview of the mechanics of lithium-ion batteries, both from the aging and diagnostics perspective. Battery diagnostics based on mechanical measurements exploit the strong correlation between electrode lithiation and its deformation, resulting in macroscopic cell deformation. Macroscopic deformation is then a proxy for lithium concentration, enabling estimation of state of charge (SOC) and degradation indicators such as loss of active material and lithium inventory. The results demonstrate that SOC estimation algorithms based on deformation measurements are more robust than voltage-based methods, which are sensitive to temperature and aging, requiring constant updates of the algorithm parameters. Moreover, the health of the battery can be assessed through the differential expansion method even under high-current operation, providing results consistent with the traditional differential voltage method but applicable to real-world industrial applications. Mechanics plays a crucial role also in battery degradation. This work presents the application of POLIDEMO, an advanced battery aging model that explicitly accounts for mechanical degradation phenomena, providing a physics-based framework describing the coupled electrochemical–mechanical aging processes in lithium-ion batteries. It enables the prediction of key degradation indicators, including capacity fade—capturing the characteristic knee-point behavior—and the irreversible battery thickness increase associated with long-term aging. The model is validated with multiple aging datasets, demonstrating that parameters calibrated under a single operating condition can accurately predict degradation across diverse aging scenarios. Full article

Background and Clinical Significance: With increasing demand for total knee arthroplasty (TKA), the incidence of post-operative instability has also risen. Although fracture of the polyethylene tibial post in posterior-stabilized (PS) prostheses is relatively uncommon, it should not be overlooked because delayed recognition may lead to severe late sequelae. Case Presentation: Between April 2008 and January 2020, 132 revision TKAs were performed at our institution due to suspected instability with or without component loosening. Among these, three patients were identified as having instability associated with fracture of the polyethylene tibial post in PS implants. All three patients presented late, with a mean interval of 49.66 months (range 34–74) after the index TKA. At presentation, all demonstrated multiplanar global instability, and two showed recurvatum deformity. Pre-operatively, revision surgery was indicated due to progressive global instability. Although tibial post fracture was suspected as a possible underlying cause, the diagnosis could not be definitively established until intraoperative inspection, which confirmed polyethylene tibial post fracture in all cases. Each patient underwent revision TKA using a semi-constrained prosthesis with an increased polyethylene insert height. At final follow-up (12–18 months), all patients achieved complete resolution of clinical instability and demonstrated meaningful improvement in the Hospital for Special Surgery (HSS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores. Conclusions: Although rare, polyethylene tibial post fracture should be considered in the differential diagnosis of post-operative knee instability following PS TKA. Early recognition may allow management with isolated polyethylene exchange, whereas delayed diagnosis can result in progressive ligamentous insufficiency and global multiplanar instability, ultimately necessitating revision using a semi-constrained implant. Full article

Background and Objectives: Coronal plane deformities of the knee, particularly genu valgum and varum, represent common indications for guided growth in pediatric orthopedics. This study evaluates the clinical and radiographic outcomes of temporary hemiepiphysiodesis using tension-band plates in skeletally immature patients and identifies factors associated with successful correction. Materials and Methods: A retrospective review was conducted on patients treated with tension-band plate hemiepiphysiodesis for knee valgus or varus deformities between 2012 and 2023. Inclusion required open physes, pre- and postoperative full-length radiographs, and follow-up until implant removal or skeletal maturity. Mechanical axis parameters (mLDFA, mMPTA) were compared pre- and postoperatively, and correction rates were calculated. Idiopathic cases were analyzed separately from those with neurological or osteological disorders. Results: Sixty-six limbs were included (51 valgus, 15 varus). In the idiopathic subgroup, significant correction was achieved, with mLDFA improving by +5.19° and mMPTA by −1.88°, corresponding to annual correction rates of 4.75°/year and −1.74°/year, respectively (p < 0.001). Regression analysis showed no significant predictive value of age or treatment duration for total correction. Patients with pathological physes demonstrated inconsistent outcomes, often requiring additional procedures. No major complications occurred. Conclusions: Temporary hemiepiphysiodesis using tension-band plates is a safe, minimally invasive, and highly effective method for correcting idiopathic valgus deformities in growing children, with correction rates comparable to the existing literature. Outcomes in patients with neurological or osteological comorbidities remain less predictable, underscoring the need for individualized planning and close follow-up. Full article

Background/Objectives: This study introduces and evaluates a novel surgical technique for total knee arthroplasty (TKA) that uses the trochlear groove bisector (TGB) as an anatomical landmark to achieve kinematic alignment of the femoral component in the coronal plane. The aim of the present retrospective observational analysis was to assess the reproducibility and accuracy of this approach and to report preliminary clinical outcomes. Methods: Twenty-eight TKA procedures were performed using the TGB-guided alignment technique. Preoperative planning and postoperative assessments were conducted on long-leg weight-bearing radiographs to measure the agreement between planned and achieved alignment, analysed using Bland–Altman statistics. Functional outcomes were evaluated at 12 months with the Knee Society Score (KSS), Forgotten Joint Score (FJS), and patient satisfaction. Results: The mean difference between planned and post-operative mLDFA was −0.3° ± 0.65°, with a root mean square error (RMSE) of 0.7°, demonstrating high accuracy and reproducibility. Postoperative outcomes showed mean KSS (knee = 89.6, function = 91.4), FJS = 69.6 ± 12, mean flexion = 124.6°, and mean HKA = 178°. Ninety percent of patients reported being satisfied or very satisfied at 12 months. Conclusions: The TGB-based technique offers a reliable, easily applicable method for restoring native femoral alignment in TKA using standard instrumentation. It allows accurate prediction of postoperative alignment and achieves favourable early functional outcomes. While currently limited to moderate varus deformities, future developments integrating 3D or CT-based planning may extend its applicability to more complex cases. Full article

Introduction: Medial compartment knee osteoarthritis (OA) is characterized by varus deformity. A medial open-wedge high tibial osteotomy (MOWHTO), frequently invoked in the treatment of this deformity, affects the knee as well as the ankle joints. This study aims to evaluate the radiological and clinical effects of a MOWHTO on the ankle joint. Materials and Methods: A retrospective analysis was conducted with data from 110 patients (mean age: 52 years; 74.5% female) who underwent a MOWHTO between 2020 and 2023. Radiographic assessments were conducted both preoperatively and one year after surgery using full-length weight-bearing radiographs. The measurements included several alignment parameters such as the hip–knee–ankle angle (HKA), medial proximal tibial angle (MPTA), joint line convergence angle (JLCA), lateral distal tibial angle (LDTA), and talar tilt. Clinical outcomes were assessed using the Lysholm knee score and the American Orthopedic Foot and Ankle Society (AOFAS) ankle score. Results: While changes in the LDTA demonstrated a small effect size (d = 0.225), moderate-to-large effect sizes were observed in key alignment parameters (MPTA (d = 0.838), the JLCA (d = 0.798), and talar tilt (d = 0.752)), all of which showed statistically significant differences indicative of a correction in the joint alignment of potential clinical significance. Median Lysholm and AOFAS scores at one year were 90 and 100, respectively, indicating favorable clinical outcomes. No significant difference in outcomes was observed based on the amount of correction. Conclusions: An MOWHTO not only restores knee alignment but also significantly improves ankle alignment in the coronal plane. These findings suggest that an MOWHTO is associated with the restoration of knee alignment and with improvements in ankle alignment in the coronal plane. Full article