In total knee arthroplasty (TKA), the patella is significantly associated with range of motion and gait performance. Currently, no highly accurate methods are available that can measure the 3D in vivo behavior of the TKA patellar component, as the component is made of x-ray-permeable ultra-high molecular weight polyethylene. Previously, we developed a computer simulation that matches CT scan and unidirectional radiographic images using image correlations, and applied it to kinematic studies of natural and TKA knees. The examination of the measurement accuracy for the patellar bone of a fresh-frozen pig knee joint yielded a root mean square error of 0.2 mm in translation and 0.2˚in rotation. In this study, we recruited four patients who had a TKA and investigated 3D movements of the patellar component during squatting. We could visualize the patellar component using the position of the holes drilled for the component peg, and estimated and visualized the contact points between the patellar and femoral components. The principles and the utility of the simulation method are reported. This analytical method is useful for evaluating the pathologies and post-surgical conditions of the knee and other joints. Total knee arthroplasty (TKA) is a reliable surgical procedure for reconstructing severely impaired knee joints. TKA can improve pain relief, functional mobility, weight-bearing capability, and patient quality of life.1 The widespread use of TKA promoted studies on TKA kinematics, particularly of the femorotibial joint.2,3 TKA knee kinematics, including range of motion (ROM) and physical performance, are also influenced by the biomechanical properties of the patella. Surgeons sometimes report post-TKA complications involving the patellofemoral articulation, for example, anterior knee pain, patellofemoral impingement and instability.4,5 Therefore, it is important to examine whether the implanted total knee prosthesis is functioning as designed. However, conventional imaging techniques cannot analyze the biomechanical characteristics of the patellofemoral joint accurately enough because of the small volume of patella bone and the overlapping of patellar and femoral silhouettes on scan images. In TKA, the patella is commonly resurfaced, which further reduces its volume, and the radiopaque metal femoral component is often superimposed on the patellar component on 2D images. In addition, the patellar component is made of radiolucent ultra-high molecular weight polyethylene. Therefore, it is impossible to determine radiographically the external contour of the patellar component precisely. Because of these technical limitations, no methods have been established to track the dynamic in vivo trajectory of the patella.Previously, we developed a unique computerassisted image matching procedure to analyze the kinematics of natural and TKA knees by applying an image window-based analytical method to serial unidirectional x-ray scans. [6][7][8][9][10] In this study, we aimed to visualize the patellar component and iden...

BackgroundIn periacetabular osteotomy for the treatment of developmental dysplasia of the hip, impairments in ADL due to limitations in hip flexion can occur when anterior displacement is added to lateral displacement in order to obtain sufficient femoral head coverage. This study was conducted to determine, by the range of motion (ROM) simulation based on CT images, the minimum angle of hip flexion and internal rotation at 90° of flexion that is necessary to avoid ADL impairments after eccentric rotational acetabular osteotomy (ERAO) and to estimate the angles of anterior femoral head coverage on plain radiography that enable the above flexion.MethodsOf 47 hips treated with ERAO at our hospital from December 2007 to May 2012, 27 hips without progressive osteoarthritis which could be CT scanned were examined and included. The mean age at the time of surgery was 40.7 years (SD 1.8). The postoperative follow-up period was 30.2 months (SD 3.6). Two hips were in male patients and 25 hips were in female patients. The disease stage prior to surgery was pre-osteoarthritis in 5 hips, early in 11 hips, and progressive in 11 hips. We checked whether the patients were capable of activities that require deep hip flexion for the evaluation of postoperative ADL. Radiographic examination was performed before and one year after surgery to calculate LCE angle, Sharp angle, AHI, and VCA angle. The angle at which impingement of the displaced fragment of the bone and the femur appeared was measured using 3D CAD software, and the relationship between this angle and the physical findings, ADL impairment, or radiographic findings, were also examined.Results22 out of 27 hips that were capable of 116° or more of flexion or 42° or more of internal rotation at 90° of flexion in ROM simulation showed the absence of ADL impairment and a postoperative VCA angle ≤42°, whereas 5 hips with 110° or less of flexion or 40° or less of internal rotation at 90° of flexion in ROM simulation had ADL impairments associated with limitations in hip flexion and a postoperative VCA angle ≥46°.ConclusionsAnterior and lateral coverage requires a postoperative VCA angle of ≥20° to achieve anterior structural stability and an LCE angle of >25° to obtain adequate superior lateral coverage of the femoral head. A VCA angle ≤42° is required to avoid impingement during deep flexion. A VCA angle ≥46° is a probable risk factor for pincer FAI syndrome after ERAO.

BCS-TKA stabilized varus-valgus laxity to better than preoperative levels at midflexion range.

In biomechanics of the knee joints, the definition of the cruciate ligament adhesion areas is discussed for the cruciate ligament reconstruction. Effective information can be expected to be fed back to the cruciate ligament reconstruction if accurate movement of the natural knee joints can be analyzed. Therefore, this study performed in vivo six-degree-of-freedom (6-DOF) motion analysis for the natural knee joints with high precision using an image matching technique. The image matching technique was performed determining the strength of correlation between the X-ray images from a single-plane flat panel detector (FPD) and the computational simulated image from three-dimensional gray-scale model reconstructed using computed tomography (CT). Average root mean square errors of this technique were 0.84 mm for the in-plane translation, 0.17 mm for the out-of-plane translation, and 0.29 degrees for the rotation.We report analysis results for the natural knee joints in squat activity using this technique. Subjects were the natural knee joints of four healthy men. We assessed the four items for the motion pattern and the functionality of cruciate ligament. The roll-back motion of subluxation in high-flexion, and the importance of anteromedial (AM) bundle and posterolateral (PL) bundle in the anterior cruciate ligament (ACL) could be confirmed from the results. From these, this highly accurate technique can be expected to become a valuable tool for the medical device development and the diagnostic in field of orthopedics.

IntroductionMidflexion stability can potentially improve the outcome of total knee arthroplasty (TKA). The purpose of this study was to evaluate the correlation between varus–valgus stability at 0° of extension and 90° of flexion and that at the midflexion range in posterior-stabilized (PS)-TKA.Materials and methodsForty-three knees that underwent PS-TKA were evaluated. Manual mild passive varus–valgus stress was applied to the knees, and the postoperative maximum varus–valgus stability was measured every 10° throughout range of motion, using a navigation system. Correlations between the stability at 0°, 90° of flexion, and that at each midflexion angle were evaluated using Spearman’s correlation coefficients.ResultsThe stability of 0° modestly correlated with that of 10°–20°, but it did not significantly correlate with that of 30°–80°. However, the stability of 90° strongly correlated with that of 60°–80°, modestly correlated with that of 40°–50°, weakly correlated with that of 20°–30°, and did not correlate with that of 10°.ConclusionsThe present study confirmed the importance of acquiring stability at 90° flexion to achieve midflexion stability in PS-TKA. However, initial flexion stability did not strongly correlate with the stability at either 0° or 90°. Our findings can provide useful information for understanding varus–valgus stability throughout the range of motion in PS-TKA. Attention to soft tissue balancing is necessary to stabilize a knee at the initial flexion range in PS-TKA.