Cheng-Chung Lin

Accurate femoral tunnel placement in canine cranial cruciate ligament (CrCL) reconstruction is challenging because of small joint anatomy and limited dedicated instrumentation. This study evaluated an adjustable femoral tunnel aiming device combined with patient-specific preoperative planning. Thirteen surgeons (six experienced and seven novices) performed simulated tunnel positioning using the device and a freehand technique. Outcomes included aperture positional error, measured as Euclidean distance (ED), angular deviation (AD), positioning time, and intra- and intersurgeon variability. Device-guided positioning reduced EDs (4.1–4.7 mm vs. 5.1–6.2 mm; p = 0.0275) and ADs (6.4–8.2° vs. 10.7–12.6°; p = 0.0038). Neither surgeon experience nor its interaction with technique significantly affected EDs or ADs. The device significantly reduced intrasurgeon variability in both outcomes and intersurgeon ADs variability among experienced surgeons. However, systematic distal bias (3.1–3.4 mm; p < 0.001) was observed with device-guided positioning. These findings support improved positioning accuracy and consistency with the device in simulated canine CrCL reconstruction. Further device refinement and hands-on practice may help address systematic deviations, while additional cadaveric and clinical validation is required before clinical application.

Accurate subject-specific bone geometry and ligament attachment sites are important for biomechanical analysis and surgical planning of the canine stifle joint. This study developed and validated a dual-plane X-ray–based 2D–3D reconstruction framework for simultaneous estimation of subject-specific bone geometry and ligament footprint locations. A footprint-embedded deformable shape template was constructed by integrating ligament footprint outlines into femoral and tibial statistical shape models derived from CT datasets. Bone reconstruction was performed using an alternating two-stage optimization combining point-to-plane correspondence–based pose estimation and silhouette-based shape refinement. The framework was validated using 12 canine hindlimb specimens with CT-derived models as ground truth. X-ray fluoroscopic images were acquired sequentially at different viewing angles and paired to form dual-plane X-ray configurations with angular separations of 90°, 60°, and 30° for evaluation. The root-mean-square errors for the reconstructed distal femur and proximal tibia ranged from 0.4 to 0.5 mm. The 90° and 60° configurations achieved significantly higher reconstruction accuracy than the 30° configuration. Mean ligament footprint centroid errors ranged from 1.6 to 3.1 mm across the ligaments and insertion sites. In conclusion, the proposed framework achieved submillimetre bone shape reconstruction errors with concurrent ligament footprint estimation under the evaluated ex vivo conditions when dual-plane X-rays were acquired with larger angular separations.

Objective: To evaluate whether femoral head diameter and head-to-neck ratio (HNR) influence prosthetic impingement-free motion (IFM) in canine total hip replacement (THR) using a press-fit cementless hip system in silico. Methods: This was a descriptive study conducted from January through June 2025. Twenty-eight head-neck combinations were assembled using 3-D stereolithographic files of cementless THR implants (Universal Hip System; BioMedtrix). For each implant combination, IFM was evaluated using a custom-built computer simulation software program around 3 orthogonal axes: abduction-adduction, flexion-extension, and internal-external rotation. Impingement-free motion was also evaluated in 3-D, characterized as the envelope where the femoral neck axis has IFM. Head diameter, neck diameter, and HNR were calculated, and their effects on IFM were analyzed. Results: Larger femoral head diameters were associated with increased IFM in all directions. Each increase in head size corresponded to a 16% to 33% gain in IFM. The presence of a head collar reduced 3-D IFM by 10% to 36%. The IFM loss was larger for smaller head sizes. Higher HNRs were strongly and positively associated with 3-D IFM. The IFM in internal and external rotation occurred beyond estimated physiologic hip motion when HNR was larger than 1.6. Conclusions: Femoral head size and HNR are key determinants of IFM in the simulated canine THR model. The use of larger heads without collars improves prosthetic mobility and may reduce in vivo prosthetic impingement. Clinical Relevance: The risk of postoperative prosthetic luxation in canine THR may be reduced through proper implant selection and maximizing IFM.

Accurate femoral tunnel placement is essential for successful anatomical intra-articular reconstruction of the cranial cruciate ligament (CrCL), a standard treatment for anterior cruciate ligament disease in humans. Surgical outcomes are influenced by multiple factors related to tunnel placement, including ligament footprint restoration, tunnel length, and graft bending angle (GBA), among others. However, no consensus has been reached regarding the optimal placement of the femoral tunnel for CrCL reconstruction in dogs. This study aimed to investigate the effects of various femoral tunnel entry (FTE) points on these key parameters to determine favourable tunnel locations for canine CrCL reconstruction. The influences of various FTE points were evaluated based on six parameters: footprint coverage, footprint overhang, footprint similarity, tunnel length, tunnel‐face angle, and GBA. Three‐dimensional femoral models reconstructed from CT scans of 25 canine cadaveric hindlimbs were used to simulate tunnel placement. In addition, tibiofemoral kinematic data from 13 client-owned dogs during treadmill gait were analysed to quantify the GBA associated with each simulated tunnel. A more proximal extracapsular tunnel aperture relative to Blumensaat's line provided greater footprint coverage, improved similarity, and longer tunnel length. However, along the cranial-caudal axis, a trade-off emerged between these factors and GBA, suggesting that a mid-range position may offer the most balanced compromise. Placing the FTE point proximally is preferable, while a mid-range cranial-caudal position may best balance key factors affecting postoperative outcomes in dogs.

Model-based 3D/2D image registration using single-plane fluoroscopy is a common setup to determine knee joint kinematics, owing to its markerless aspect. However, the approach was subjected to lower accuracies in the determination of out-of-plane motion components. Introducing additional kinematic constraints with an appropriate anatomical representation may help ameliorate the reduced accuracy of single-plane image registration. Therefore, this study aimed to develop and evaluate a multibody model-based tracking (MbMBT) scheme, embedding a personalized kinematic model of the tibiofemoral joint for the measurement of tibiofemoral kinematics. The kinematic model was consisted of three ligaments and an articular contact mechanism. The knee joint activities in six volunteers during isolated knee flexion, lunging, and sit-to-stand motions were recorded with a biplane X-ray imaging system. The tibiofemoral kinematics determined with the MbMBT and mediolateral view fluoroscopic images were compared against those determined using biplane fluoroscopic images. The MbMBT was demonstrated to yield tibiofemoral kinematics with precision values in the range from 0.1 mm to 1.1 mm for translations and from 0.2° to 1.3° for rotations. The constraints provided by the kinematic model were shown to effectively amend the nonphysiological tibiofemoral motion and not compromise the image registration accuracy with the proposed MbMBT scheme.

Objectives: To measure in vivo three-dimensional kinematics of the mandible and associated end-point trajectories and to quantify their relationships during temporomandibular joint activities using 3D fluoroscopy. Methods: A novel fluoroscopy-based 3D measurement method was used to measure motions of the mandible and the associated end points (i.e. incisors and lateral poles of both condyles) during open close, lateral gliding and protrusion-retraction movements in healthy young individuals. The contributions of each of the rotational and translational components of the mandible to the end-point trajectories were quantified through experiment-based computer simulations. Results: The mandibular rotation was found to account for 91% of the maximal mouth-opening-capacity and 73% of the maximal lateral incisor movement, while the condylar translation contributed to 99% of the anterior protrusion distance. Incisor trajectories were nearly vertical within the first 60% of the maximal opening during the open-close movement. Conclusions: Similar condylar downward rotation paths but with bilaterally asymmetrical ranges were used to perform basic mandibular movements of different targeted TI trajectories in three dimensions, that is, open-close, lateral-gliding and protrusion-retraction. Mandibular rotations contributed to the majority of the principal displacement components of the incisor, that is, vertical during open-close and towards the working-side-during lateral-gliding, while mandibular translation contributed mainly to the forward movement of the incisor during protrusion-retraction. Owing to the anatomical constraints, the freedom of mandibular translation is limited and mainly in the anteroposterior direction, which is considered helpful for the control and stability of the TMJ during oral activities.

Model-based tracking of the movement of the tibiofemoral joint via a biplane X-ray imaging system has been commonly used to reproduce its accurate, three-dimensional kinematics. To accommodate the approaches to existing clinical asynchronous biplane fluoroscopy systems and achieve comparable accuracy, this study proposed an automated model-based interleaved biplane fluoroscopy image tracking scheme (MIBFT) by incorporating information of adjacent image frames. The MIBFT was evaluated with a cadaveric study conducted on a knee specimen. The MIBFT reproduced skeletal poses and tibiofemoral kinematics that were in good agreement with the standard reference kinematics provided by an optical motion capture system, in which the root-mean-squared (Rms) errors of the skeletal pose parameters ranged from 0.11 to 0.35 mm in translation and 0.18 to 0.49° in rotation. The influences of rotation speed on the pose errors were below 0.23 mm and 0.26°. The MIBFT-determined bias, precision, and Rms error were comparable to those of the reported model-based tracking techniques using custom-made synchronous biplane fluoroscopy. The results suggested that the further use of the clinical imaging system is feasible for the noninvasive and precise examination of dynamic joint functions and kinematics in clinical practice and biomechanical research.

Background: Soft tissue artifacts (STAs) are a source of error in marker-based gait analysis in dogs. While some studies have revealed the existence of STAs in the canine hindlimb, STAs and their influence on kinematic gait analysis remain unclear. Methods: Thirteen healthy Taiwan dogs affixed with twenty skin markers on the thigh and crus were recruited. Soft tissue artifacts and their influence on the determination of segment poses and stifle angles were assessed by simultaneously measuring marker trajectories and kinematics of the underlying bones via a model-based fluoroscopic analysis method. Results: Markers on the thigh showed higher STAs than those on the crus, with root-mean-square amplitudes up to 15.5 mm. None of the tested marker clusters were able to accurately reproduce the skeletal poses, in which the maximum root-mean-square deviations ranged from 3.4° to 8.1°. The use of markers resulted in overestimated stifle flexion during 40–60% of the gait cycle and underestimated stifle flexion during 80–90% of the gait cycle. Conclusions: Considerable magnitudes and effects of STAs on the marker-based 3D gait analysis of dogs were demonstrated. The results indicate that the development of error-compensation techniques based on knowledge regarding STAs is warranted for more accurate gait analysis.

Skin marker‐based motion analysis has been widely used to evaluate the functional performance of canine gait and posture. However, the interference of soft tissues between markers and the underlying bones (soft tissue artefacts, STAs) may lead to errors in kinematics measurements. Currently, no optimal marker attachment sites and cluster compositions are recommended for canine gait analysis. The current study aims to evaluate cluster‐level STAs and the effects of cluster compositions on the computed stifle kinematics. Ten mixed‐breed healthy dogs affixed with 19 retroreflective markers on the thigh and shank were enrolled. During isolated stifle passive extension, the marker trajectories were acquired with a motion capture system, and the skeletal poses were determined by integrating fluoroscopic and CT images of the bones. The cluster‐level STAs were assessed, and clusters were paired to calculate the stifle kinematics. A selection of cluster compositions was useful for deriving accurate sagittal and frontal plane stifle kinematics with flexion angles below 50 per cent of the range of motion. The findings contribute to improved knowledge of canine STAs and their influence on motion measurements. The marker composition with the smallest error in describing joint kinematics is recommended for future applications and study in dogs during dynamic gait assessment.