Reduction of Broach Rotation for Versys Fibermetal Tapered Stem during the Femoral Canal Shaping / 대한정형외과연구학회지

PURPOSE: Inaccurate femoral canal shaping can result in post-operative complications in hip arthroplasty. We addressed the amount of broach rotation during shaping of the femoral canal and compared it with respect to newly designed broaches which were modified to minimize the rotation. MATERIALS AND METHOD: we designed the broaches that had canal guide which restricts the broach motion such that it is always aligned with the femoral axis while the broach machines the metaphyseal bone. Conventional broaches and the modified broach applied to 5 pair of fresh-frozen cadaver femurs and its spatial motion was measured with motion tracker. Rotations in coronal, saggital and frontal plane during the final 10 mm of broach advance were measured. RESULTS: 2.4..of axial rotation was occurred during final 10 mm advance of broach in the conventional method, which was the largest component of the rotation. Rotation of the broach during machining was decreased to 37% (p=0.075) and 25% (p=0.042) in the sagittal plane and coronal plane, respectively, by proposed method. CONCLUSION: The canal guide in the proposed method significantly reduced the rotation of the broach without any extra incision or measurement devices, resulting in increased accuracy in the femoral canal shaping.

Hip Resurfacing with Buffered Fixation Method / 대한정형외과연구학회지

PURPOSE: Interface between bone and implant is one of the crucial factors that influence the implant longevity. We proposed an implant fixation method that could induce osseointegration. MATERIALS AND METHODS: Buffer which had polished inner surface and roughed outer one was inserted between femoral head and femoral cup. To verify the effect of proposed fixation method, we made buffered implant with composite femur, applied normal walking force with universal test machine and measured principle strain at the medial region of femoral head. Also we estimated contact stress and compared mechanical characteristics to conventional fixation method by FEM. RESULTS: Experimental results showed compressive stress at the medial region was occurred and maintained. Contact stress was estimated to 0.9 MPa by FEM. As using buffer, tensile stress regions were reduced from 10% to 4.5% and after osseointegration to 6.7%. The regions that had micromotion less than 28 micrometer were about 95%. Fracture risks at the interface and inside the buffer were low. CONCLUSION: We found that the fixation method we proposed reduced tensile stresses and micromotion which separate implant from bone, so that osseointegration at the interface would be possible.

Retrieval Study of Total Hip Arthroplasty with Use of a Cemented Polyethylene Cup and a Non-cemented Polyethylene Liner in Combination with Zirconia Ceramic Femoral Head: Report of 2 Cases / 대한정형외과학회잡지

Catastrophic failure of a zirconia head with Hylamer acetabular component and early failure due to the phase transformation of zirconia ceramic head after total hip arthroplasty have been indebted issues. We report two cases who had failure of the zirconia ceramic head with polyethylene articulations shortly after total hip arthroplasty. Revision retrieval studies were performed subsequently.

Total Hip Arthroplasties with High Dislocation in Tuberculous Hip and Developmental Dysplasia of the Hip / 대한정형외과학회잡지

PURPOSE: To confirm the effect of the frog leg lateral radiographs for determining the clinical indication of total hip arthroplasty for high riding dislocation and to discuss its theoretical background. MATERIALS AND METHODS: A consequent series of reconstructive THA were studied in 28 recent tuberculous hips. Twenty-three hips (17patients) with developmental dysplastic hip were compared. Preoperatively, frog-leg lateral radiographs were performed in all the patients, which were enhanced using a 2-dimensional computer model to predict the reattachment of the greater trochanter. RESULTS: The modified scores of Merle d'aubigne and Postel improved from a mean of 2.6 points preoperatively to a mean of 5.1 points. Sciatic nerve palsies occurred in three cases. In two cases, they fully recovered, but in one case, it did not. We confirmed that old high dislocation of the hip could be adopted in type 1 and 2 categories of frog leg lateral position. The reconstruction of hip was relatively simple in type 3, however, further study is necessary in type 5 due to unsuitable abduction contracture. CONCLUSION: We confirm that frog leg lateral radiography is effective for determining the operative indication of high riding dislocation. However irreducible frog leg lateral position is absolutely contraindirated for total hip arthroplasty.

CT-Free Registration Method for Finding Accurate Orientation of Acetabular-Cup in Total Hip Replacement Surgery / 대한정형외과연구학회지

PURPOSE: This paper is proposing an improved CT-free registration method which may provide us an accurate and reliable placement of acetabular cup without CT/MRI images. DESIGN AND METHODS: The proposed method employs a T-bar shaped gauge placed on the anatomical landmarks of the pelvis for the registration. The T-bar shaped gauge has its own LED markers and the position of the gauge is obtained through OPTOTRAK3020 system. These landmark points are the anterior superior iliac spines and the symphysis pubis defining anterior pelvic plane. Two subjects were tested to compare the landmark based registration and the proposed T-bar based registration. RESULTS: The measurement deviations of the pelvic obliquity in the frontal plane, tilt in the sagittal plane, and rotation in the transverse plane were 2.08, 1.41, and 2.51 degrees respectively in the point based registration. The T-bar based registration produced 40% smaller deviations(p<0.05): the pelvic obliquity in the frontal plane, tilt in the sagittal plane, and rotation in the transverse plane were 0.84, 0.81, and 1.17 degrees respectively in the T-bar based registration. There was no outlier exceeding 5 degrees in measurement deviation by the T-bar based registration while the outliers were found by the landmark based registration. CONCLUSIONS: We found that T-bar based CT free registration method is more reliable and accurate than the landmark based registration for the acetabular cup navigation. Also, the new method produced more precise registration(p<0.05). We are expecting some offset error of the new registration method due to the skin thickness existing between the T-bar frame and the bony pelvic frame, which may be compensated if we may accumulate sufficient database of the offset.

Cadaveric Study of Robotic Femoral Canal Preparation by Gauge Based Registration in Total Hip Arthroplasty / 대한정형외과연구학회지

PURPOSE: To propose a method providing an accurate femoral shaping for cementless total hip arthroplasty to maximize bone contact without femoral bone breakage and make secure correct position of the implant by eliminating the manual broach process MATERIALS AND METHODS: 5-cadaver specimens were tested with this system. A reamer-shaped registration gauge is inserted into the femoral canal. This gauge defines the position of the implant to be inserted. Then, the base frame is attached to the femur and the position of the gauge with respect to the base frame is measured. After removing the gauge, a mini robot is mounted on the frame and shapes the femoral canal. After the milling operation, model implant is inserted and its position and gap are measured. RESULTS: Anteversion angle error was 0.9degrees(S.D.1.7) and Varus/Valgus alignment error was 1.1degrees(S.D.1.5). 95%(S.D. 3.2) of contact surface had less than 0.3mm gap error. CONCLUSIONS: Proposed THA surgery system increased the accuracy of stem position and fitness compared with manual operation. Our mini robot THA surgery provides most of the benefits RobodocR does while operating procedure is much more simplified and economic.

Axisymmetric Contact Stress analysis of an Artificial Hip Joint of the Conical Fitting Type / 대한정형외과학회잡지

The purpose of this study is to investigate the effect of the ball-cone contact interface variation on the ceramic ball stress which is the dominant factor of the design of the moldular artificial hip joint. A contact stress analysis problem is formulated using the optimization principle and finite element analysis technique on the ball-cone system of three dimensional axi-symmetrical model, Numerical procedure is employed to get the solution for varying angles of cones and angular mismatches between the ball and cone interfaces. There is a fair amount of friction in the interface and included in the analysis model.