[Show abstract][Hide abstract] ABSTRACT: Synthetic femurs were used to assess the initial bone-implant interface stability of three total hip systems: Wright Medical Technology's Infinity smooth trochanteric module (S-TM), Infinity porous-coated trochanteric module (PC-TM), and Johnson and Johnson S-ROM with a porous surface. The hips were implanted into synthetic femurs, rigidly fixed, and subjected to internal rotation and cyclic, axial compressive loads. The results showed that all three implants achieved good initial implant stability and would be expected to permit bone ingrowth. The porous-coated implants showed greater initial implant stability with less axial micromotion compared with the smooth implants. This finding suggests that surface texture plays a role in initial stability of uncemented prostheses if the bone behaves similar to the material used in this study.
[Show abstract][Hide abstract] ABSTRACT: Thirty-six patellae were used to geometrically assess anatomically based patellar resection criteria for total knee arthroplasty. The plane of resection was defined in the coronal plane by three distinct anatomic landmarks on the undersurface of the patella: the medial and lateral edges of the quadriceps tendon insertion and the lateral edge of the patellar ligament insertion. The depth of the resection plane is defined by the anatomic landmark points approximately 1 mm posterior to the posterior aspect of the superior and inferior ligament insertions. Following resection, the resected patellae were geometrically characterized using two dimensional rectangular Cartesian coordinate system. The anatomically based patellar resection yielded a simple, consistent, and reliable method for patellar resection for total knee arthroplasty. The proportionate geometric characteristics of both the remaining anterior piece and the resected posterior piece were remarkably uniform. Following resection, the remaining patellar thickness was 65.6+/-5.3% (mean+/-SD) of the original thickness. The maximum width to height ratio of the resected surface was approximately 1:1. The thickness to diameter ratio of the resected portion of the patella was approximately 1:5. The apex of the patella was slightly off to the medial-distal quadrant from the geometric center of the resected surface. The results of this study indicate that anatomically based patellar resection criteria may help reduce the surgical variations associated with patellar resurfacing in total knee arthroplasties with dome-shaped prostheses.
No preview · Article · Feb 1998 · The American journal of knee surgery
[Show abstract][Hide abstract] ABSTRACT: Patellofemoral joint kinematics, contact areas, and contact pressures were measured concomitantly before and after total knee arthroplasty in 10 fresh frozen human cadaver knees using an Instron machine, a custom patellofemoral joint testing jig, axial bone markers, a continuous video digitizing system, and Fuji pressure sensitive film. The implant used in this study was the Kirschner Performance Knee System with an all polyethylene, domed patellar component. For all tests, the patella was aligned in its anatomically neutral position. Patellofemoral joint contact areas decreased as much as 19-fold after total knee arthroplasty. Mean patellofemoral joint contact pressures increased as much as 32-fold, and peak patellofemoral joint contact pressures increased as much as 22-fold after total knee arthroplasty. No statistically significant differences between preoperative and postoperative specimens were observed with respect to the patellofemoral, patellotibial, or patellar tilt angles from 30 degrees to 120 degrees knee flexion. Thus, the elevated patellofemoral joint contact pressures observed after total knee arthroplasty in vitro are not a primary consequence of iatrogenically altered patellofemoral kinematics.
No preview · Article · Aug 1997 · Clinical Orthopaedics and Related Research
[Show abstract][Hide abstract] ABSTRACT: The stress and deformation characteristics of the proximal femur are very complex due to its intricate geometry that allows the femur to accommodate wide range of loading configurations. In laboratory bench testing, the complex physiological loading scheme is simplified so that the cause and effect of loading on the femur can be determined effectively. In this study, five human cadaveric femora were used to determine the regional deformation characteristics of the proximal half of the femur at adduction angles of neutral, 10, 20 and 30 degrees. The entire femur was cleaned of all soft tissues and fixed in to a steel cylinder using eight fixation pins and then potted with dental stone up to the mid-diaphysis level. Small reflective markers were then placed on the anterior and medial surface of the femur for the characterization of regional deformation. The cylinder is bolted on to a custom jig that is mounted onto the Instron machine and cyclic compressive loads ranging from 250 N to 2750 N were applied for ten cycles. The load application on the femoral head was via an X-Y translator so that the femur was being loaded in an unconstrained manner in the proximal region. The regional deformation characteristics were determined using a motion analysis system which provides non-contact measurement of the displacement of multiple reflective markers at 60 Hz. The results show that at neutral adduction angle, the greatest deformation was observed at the femoral neck region. With increasing adduction angle of the femur, the maximum deformation region shifts to the diaphyseal region. The quantitation of the regional deformation of the femur under various loading schemes is necessary in order to effectively evaluate the structural integrity of the femur and hip systems.
[Show abstract][Hide abstract] ABSTRACT: The quantitative characterization of anatomical geometry of the human cadaveric femur is essential for assessing the structural integrity of the femur and the hip system. Three dimensional geometric characteristics of the femur were determined using a Motion Analysis System which provides non-contact position measurement of multiple reflective markers in two dimensions. The basic concept is that by using two dimensional position measurements of the reflective markers placed at strategic locations on the femur, the three dimensional geometric characteristics of the human femur can be calculated using the measurements obtained from the three orthogonal views. Using this technique, the internal orientational geometry of the femur is determined in addition to periosteal dimensions. Twenty human cadaveric femora were used. The measurement of anteversion, neck angle and neck length were made to compare with the radiographic and conventional measurements using calipers. Additional measurement of femoral head diameter and the diameter at the isthmus and mid-lesser trochanter level of the diaphysis were determined from both the anterior and medial views. The diaphyseal curvature of the femur was also determined. The anatomical dimensions determined from this study were similar to that of the previously published results. In our comparison of femoral neck angle and neck length however, there was a consistent difference between the three dimensional measurement and the two dimensional radiographic and conventional measurements. The differences were due to the limitation of two dimensions in the radiographic and conventional measurement method.