To establish an automated, landmark-based patellar coordinate system for standardized alignment, develop a patellar statistical shape model (SSM), and quantify 3D morphological variations associated with patellar dislocation (PD). Patellar surface models were reconstructed from CT/MRI scans of 54 participants (33 PD, 21 controls). An automated coordinate system was established and quantitatively validated. Demographic/morphometric risk factors were assessed using logistic regression. An SSM was built for the entire cohort, and principal component analysis (PCA) was used to extract major 3D shape modes. Between-group differences in PC scores were evaluated with multiple-testing control and covariate adjustment. A logistic regression classifier based on shape modes and demographics was evaluated using stratified 10-fold cross-validation. The automated coordinate system showed high repeatability. Patellar linear dimensions and centroid size did not differ between groups and were not independent predictors. Two robust shape modes differentiated PD from controls: PC4 (thickness/facet morphology) and PC7 (facet-edge morphology). A cross-validated classifier showed good in-cohort discrimination (mean AUC ≈ 0.91). In this cohort, PD was associated with localized 3D articular-surface shape patterns, characterized by a prominent medial facet, a flattened posterolateral facet, and accentuated facet margins, without corresponding differences in linear dimensions. The automated coordinate system and SSM provide a reproducible approach for quantitative patellar phenotyping. These shape modes may deepen understanding of PD pathomechanics and provide a quantitative basis for future, externally validated risk modeling in diverse populations.

This study aimed to investigate the kinematic and kinetic characteristics of the lower limbs during the Y-Balance Test (YBT) between male badminton athletes with patellofemoral pain syndrome (PFPS) and healthy controls. A cross-sectional study was conducted involving forty university male badminton athletes with PFPS (n = 20) and healthy controls (n = 20). Reach distance, electromyographic signals, kinematic data, and ground reaction forces were collected during YBT performance. Joint angles, joint moments, and muscle forces at the point of maximum reach distance were calculated using OpenSim and statistically analyzed. PFPS participants exhibited a greater hip internal rotation angle in the anterior reach direction (p = 0.032). Weaker gluteus maximus activation was observed in the anterior and posterolateral directions (p = 0.045, p = 0.038), while reduced hamstring and quadriceps forces were identified in the posteromedial direction (p = 0.010, p = 0.025). A lower vastus medialis-to-vastus lateralis ratio was detected in the anterior and posteromedial directions (p = 0.023), whereas a higher hamstring-to-quadriceps ratio was found in the anterior test (p = 0.029). In the PFPS group, the anterior reach distance was negatively correlated with hip internal rotation angle (r = − 0.651, p = 0.009) and positively correlated with gluteus maximus (r = 0.591, p = 0.037), gluteus medius (r = 0.612, p = 0.024), and the vastus medialis-to-vastus lateralis ratio (r = 0.778, p = 0.016). In the posteromedial direction, reach distance showed strong positive correlations with hip external rotation angle (r = 0.768, p = 0.043), hamstring force (r = 0.771, p = 0.021), and quadriceps force (r = 0.592, p = 0.016). The results of the current study indicate that the reductions in YBT performance are closely associated with hip internal rotation angle, weak hip muscle force, and abnormal knee muscle force ratios, which may serve as potential diagnosis indicators for screening and preventing PFPS in male athlete populations. Data derived from healthy athletes may provide valuable reference benchmarks to guide clinicians in the rehabilitation management of individuals with PFPS.

Early viscoelastic deterioration of anterior cruciate ligament (ACL) reconstruction grafts impairs knee biomechanics and elevates osteoarthritis risk, with unclear mechanisms. We established a knee viscoelastic finite element model, set graft parameters at postoperative day 0 and 30 from animal data, and calculated joint stress under multiple loadings. By day 30, graft peak axial force dropped by 50%, causing abnormal stress redistribution. This study fills related research gaps and informs clinical rehabilitation and graft preparation.

The aim of this study is to evaluate and compare the performance of three non-rigid registration methods—coherent point drift (CPD), non-rigid iterative closest point (NRICP), and spherical parameterization—in building statistical shape models (SSMs) of femurs for identifying morphological features in patients with knee osteoarthritis (OA). A simplified femur template was selected. Non-rigid registration algorithms (CPD, NRICP, spherical parameterization) were applied to align the template surface to all other femur samples. The registration methods were assessed using multiple evaluation criteria: root mean square error (RMSE), Hausdorff distance (HD), computational efficiency, local deformation capability, outlier sensitivity, compactness, generalization, and specificity. The results showed that all deformable algorithms exhibited reasonable registration results. Among them, CPD performed best in RMSE, HD, local deformation, and specificity. Spherical parameterization balanced all these metrics but was unsuitable for handling abnormal structures and could occasionally result in severe reconstruction errors in complex anatomical structures. NRICP was the fastest technique with the lowest generalization reconstruction error but achieved the lowest registration accuracy. CPD is the most suitable method for accurate femur registration in SSMs, especially for detecting OA-related morphological variations. Spherical parameterization is a promising approach if it can mitigate extreme errors. NRICP favors efficiency over accuracy, suitable for real-time tasks.

The elasticity and viscosity of the grafts are both crucial for joint stability, yet the changes trend in short-term following anterior cruciate ligament reconstruction (ACLR) remains unclear. The purpose of this study was to evaluate the short-term variations in graft elasticity and viscosity following ACLR. Sixteen male rabbits underwent ACLR using Achilles tendon graft. Animals were randomly euthanized 15 and 30 days following ACLR. The Young’s modulus and viscosity coefficient of the grafts were measured through uniaxial tensile and creep experiments. The cross-sectional area of the graft decreased mainly between day 15 and day 30 with no significant. The Young’s modulus decreased significantly between day 0 and day 15. while the decrease in viscosity coefficient significantly between day 0 and day 30. The average of uniaxial tensile Young’s moduli at day 0, 15, and 30 were 293.11 ± 42.58 MPa, 23.75 ± 6.62 MPa, and 9.02 ± 3.46 MPa, respectively, compared with 37.52 ± 6.12 MPa for the native ACL. The average of viscosity coefficients at 0, 15, and 30 days were 255.00 ± 55.06 MPa∙s, 205.56 ± 68 MPa∙s, and 58.06 ± 11.04 MPa∙s, compared with 159.54 ± 22.61 MPa∙s for the native ACL. Even the cross-sectional area, elasticity, and viscosity of grafts showed nonlinear decreasing trends in the short term after ACLR, but the patterns of decrease differ. These findings may serve as a reference for preoperative planning and postoperative rehabilitation.

Precise execution of preoperative 3D planning is critical in total knee arthroplasty (TKA), but current verification methods—postoperative imaging, navigation, robotics—have limitations: they often assess alignment indirectly or fail to directly compare planned and actual osteotomy surfaces. An in vivo method to quantitatively evaluate plan-execution discrepancies on resected surfaces is lacking. This study aimed to introduce a novel technique for acquiring the TKA osteotomy surface using intraoperative CT, and subsequently comparing it with the preoperative plan to accurately evaluate the precision of osteotomy. Furthermore, this technique was utilized to assess the reliability of osteotomy accuracy in patient-specific instrumentation (PSI) assisted TKA procedures. In this case series study, intraoperative CT scans were acquired immediately after bone resection in 80 TKAs. 3D models of the resected surfaces were created and precisely superimposed onto the preoperative 3D planning models. Angular discrepancies between planned and achieved osteotomy planes (coronal, sagittal, axial) for femur and tibia were quantified. Outliers (> 3°) were assessed. Excellent inter- and intra-observer reliability was confirmed, with Intra-class Correlation Coefficient (ICC) ranging from 0.807 to 0.959. Intraoperative CT verification demonstrated femoral deviations of 0.91° ± 0.71° (coronal plane, 2.5

The purpose of this study was to investigate continuous knee passive stiffness and its fatigue responses. Knee osteoarthritis is a clinically degenerative disease that mostly cause sustained stiff knee, hence, there is an urgent need to evaluate continuous knee passive stiffness, which corresponded to the stiffness of various angles during actual continuous knee rotation. However, how to measure this kind of stiffness is yet to reach an agreement. This is a study incorporating 36 individuals, in which the fatigue protocol consisted of three bouts of multiple quadriceps voluntary isometric contractions of their dominant legs. Angle and passive torque were measured before and after each fatigue intervention cycle. Continuous knee passive stiffness of various angles and rate of stiffness under fatigue were both calculated. We derived the continuous knee passive stiffness data appeared as an asymmetric U-shaped curve. The passive stiffness (Nm/°) of the initial angle (0°) is 0.249 (0.159–0.285), while that of the other endpoint angle (91°) is 0.156 (0.130–0.354). The responses of continuous knee passive stiffness following fatigue interventions revealed a significant decrease in the knee angle from 10 to 36° (p = 0.02–0.05). This renew study experimentally develop a novel approach to expand upon the existing methods of knee passive stiffness measurements. The intrinsic continuous knee passive stiffness and its fatigue responses both vary at specific knee angles. Our findings may provide stiffness assessment for knee osteoarthritis patients, complete fatigue intervention program, and optimize the artificial prosthesis design.

Abstract Purpose Long-leg-radiography (LLR) is commonly used for the measurement of lower limb alignment. However, limb rotations during radiography may interfere with the alignment measurement. This study examines the effect of limb rotation on the accuracy of measurements based on the mechanical and anatomical axes of the femur and tibia, with variations in knee flexion and coronal deformity. Methods Forty-five lower limbs of 30 patients were scanned with CT. Virtual LLRs simulating five rotational positions (neutral, ± 10 $$^{\circ }$$ ∘ , and ± 20 $$^{\circ }$$ ∘ internal rotation) were generated from the CT images. Changes in the hip–knee–ankle angle (HKA) and the femorotibial angle (FTA) were measured on each image with respect to neutral values. These changes were related to knee flexion and coronal deformity under both weight- and non-weight-bearing conditions. Results The measurement errors of the HKA and FTA derived from limb rotation were up to 4.84 ± 0.66 $$^{\circ }$$ ∘ and 7.35 ± 0.88 $$^{\circ }$$ ∘ , respectively, and were correlated with knee flexion (p < 0.001) and severe coronal deformity (p < 0.001). Compared with the non-weight-bearing position, the coronal deformity measured in the weight-bearing condition was 2.62 $$^{\circ }$$ ∘ greater, the correlation coefficients between the coronal deformity and the deviation ranges of HKA and FTA were also greater. Conclusions Flexion and severe coronal deformity have a significant influence on the measurement error of lower limb alignment. Errors can be amplified in the weight-bearing condition compared with the non-weight-bearing condition. When using HKA and FTA to represent the mechanical axis and the anatomical axis on LLR, limb rotation impacts the anatomic axis more than the mechanical axis in patients with severe deformities. Considering LLR as the gold standard image modality, attention should be paid to the measurement of knee alignment. Especially for the possible errors derived from weight-bearing long-leg radiographs of patients with severe knee deformities.

Purpose. Bony resection is the primary step during total knee arthroplasty. The accuracy of bony resection was highly addressed because it was deemed to have a good relationship with mechanical line. Patient-specific instruments (PSI) were invented to copy the bony resection references from the preoperative surgical plan during a total knee arthroplasty (TKA); however, the accuracy still remains controversial. This study was aimed at finding out the accuracy of the bony resection during PSI-assisted TKA. Methods. Forty-two PSI-assisted TKAs (based on full-length leg CT images) were analyzed retrospectively. Resected bones of every patient were given a CT scan, and three-dimensional radiographs were reconstructed. The thickness of each bony resection was measured with the three-dimensional radiographs and recorded. The saw blade thickness (1.27 mm) was added to the measurements, and the results represented intraoperative bone resection thickness. A comparison between intraoperative bone resection thickness and preoperatively planned thickness was conducted. The differences were calculated, and the outliers were defined as >3 mm. Results. The distal femoral condyle had the most accurate bone cuts with the smallest difference (median, 1.0 mm at the distal medial femoral condyle and 0.8 mm at the distal lateral femoral condyle) and the least outliers (none at the distal medial femoral condyle and 1 (2.4%) at the distal lateral femoral condyle). The tibial plateau came in second (median difference, 0.8 mm at the medial tibial plateau and 1.4 mm at the lateral tibial plateau; outliers, none at the medial tibial plateau and 1 (2.6%) at the lateral tibial plateau). Regardless of whether the threshold was set to >2 mm (14 (17.9%) at the tibial plateau vs. 12 (14.6%) at the distal femoral condyle, p>0.05) or >3 mm (1 (1.3%) at the tibial plateau vs. 1 (1.2%) at the distal femoral condyle, p>0.05), the accuracy of tibial plateau osteotomy was similar to that of the distal femoral condyle. Osteotomy accuracy at the posterior femoral condyle and the anterior femoral condyle were the worst. Outliers were up to 6 (15.0%) at the posterior medial femoral condyle, 5 (12.2%) at the posterior lateral femoral condyle, and 6 (15.8%) at the anterior femoral condyle. The percentages of overcut and undercut tended to 50% in most parts except the lateral tibial plateau. At the lateral tibial plateau, the undercut percentage was twice that of the overcut. Conclusion. The tibial plateau and the distal femoral condyle share a similar accuracy of osteotomy with PSI. PSI have a generally good accuracy during the femur and tibia bone resection in TKA. PSI could be a kind of user-friendly tool which can simplify TKA with good accuracy. Level of Evidence. This is a Level IV case series with no comparison group.