Short stems have been developed for some years for preservation of femoral bone stock and achieve physiological proximal loading. Shortening stem length is a merit for bone stock preservation. However, it might lead to reduction of primary stability. We investigated relationship between stem length and primary stability by patient specific finite element analysis (FEA). Thirty-one hips in 31 patients were performed total hip arthroplasty with standard length tapered wedge-shaped (TW) cementless stem (CTi-II: Corin, Cirencester, UK). There were 6 males and 25 females. The average age at operation was 69 years old. The average body mass index was 23.9 kg/m2. Primary diagnoses were secondary osteoarthritis due to developmental dysplasia of the hip in 29 hips. Femoral canal shapes were normal in 21, stovepipe in 6 and champagne-flute in 4 hips. Bone qualities were type A in 6, B in 19 and C in 6 hips. The patients underwent computed tomography (CT) preoperatively and postoperatively. We constructed preoperative three dimensional (3D) femur surface models from preoperative CT data with individual bone mineral density (BMD) mapping. The postoperative 3D femur and rough stem surface models were obtained from postoperative CT data. The coordinates of the postoperative femur were transformed to fit the preoperative femur model. A precise stem model constructed using computer-assisted design data was matched to the transformed rough stem model using the iterative closest point algorithm. We obtained a patient-specific model with the proximal bone geometry, allocation of BMD and stem alignment. We estimated the average of axial and rotational micromotion (MM) at stem-bone interface and the ratio of area (MM � 40 micrometers) on the porous surface in order to analyze primary stability of TW stem with several lengths (standard (100 %), 75 %, 50 %, 40 % and 30 % length).Introduction
Materials and Methods
Short tapered wedge-shaped cementless (TW) stems have been widely used for several years. The concept of fixation of TW stem is wedge-fit fixation in the proximal metaphysis. Developmental dysplasia of the hip (DDH) has anatomical abnormality, such as excessive femoral anteversion, short femoral neck length, narrow femoral cavity, or proximal-distal mismatching of the femoral canal. Therefore, Mismatching between stem and bone might be occurred in DDH. We evaluated intramedullary matching of short TW stem for DDH by three dimensional (3D) digital template in order to clarify whether mismatching between stem and bone is seen in DDH implanted short TW stem. One hundred hips (92 patients) with DDH were performed preoperative simulation for total hip arthroplasty by 3D digital template system (ZedHip: Lexi, Tokyo, Japan). The average age was 63.5 years old. There were 12 males and 80 females. The average bone mass index was 21.5 kg/m2. Femoral canal shape was normal in 71, champagne-flute in 16 and stovepipe in 13 hips. Bone quality was classified into type A in 23, type B in 74 and type C in 3 hips. Preoperative computed tomography data were used for 3D digital template and reconstructed to 3D femoral model. Short TW stem (Taperloc Complete Microplasty: Biomet, Warsaw, IN) model constructed from computer-assisted design was matched to the reconstructed femoral model. Short TW stem model was in principle implanted according to the femoral neck anteversion with neutral alignment (varus and valgus < 2 degrees, flexion and extension < 2 degrees) at the coronal and sagittal plane of the femur. Stem size was determined in order to obtain the largest intramedullary matching at the coronal plane. Area of stem fitting with the cortical bone was investigated at 10 mm intervals above and below of mid minor trochanter. Intramedullary matching pattern was classified into proximal mediolateral metaphyseal fit, proximal flare fit and diaphyseal fit at multiple reconstructed planes of the 3D femoral model according to stem fitting area.[Introduction]
[Materials and Methods]
The occurrence of impingement can lead to instability, accelerated wear, and unexplained pain after THA. While implant and bony impingement were widely investigated, importance of soft tissue impingement was unclear. In the THA through posterior approach, it is known that posterior soft tissue repair can decrease the risk of dislocation. However, it is not known whether anterior soft tissue impingement by anterior hip capsule will influence hip ROM. The purpose of this study is to quantitatively measure the effect of anterior capsule resection on hip ROM in vivo during posterior approach THA using hip navigation system. From June 2011, 26 hips (25 patients) that underwent primary THA using Stryker CT-based hip navigation system were the subjects. All were female osteoarthritis patients and the average age at the operation was 59 (47–76) years. Intraoperatively, acetabular cup and femoral stem placement were performed through posterior approach under the navigation system. After reduction of the joint, we measured hip ROM using the same navigation system. We measured them before and after the resection of anterior hip capsule and compared the difference. After the resection of anterior hip capsule, the average increases of ROM were 0.7±3.5 degrees for flexion, 2.3±2.3 degrees for extension, 1.1±2.3 degrees for abduction and 2.1±2.9 degrees for external rotation at flexion 0 degree compared with ROM before the resection. However, it significantly increased 7.5±5.1 degrees for internal rotation at flexion 90 degree (range; −3–20, paired t-test p<0.001) and 6.1±5.5 degrees for internal rotation at flexion 45 degree (range; −4–18, p<0.001). In this study, we used navigation system for assessment of soft tissue impingement. We found that during posterior approach THA, resection of anterior hip capsule brought about significant increase of ROM, especially in the direction of flexion with internal rotation. We also found that this procedure did not change ROM of flexion, extension, abduction and external rotation. These results indicated that, during THA through posterior approach, resection of anterior hip capsule could reduce the risk of posterior instability without increasing the risk of anterior instability.
We developed a custom-made template for corrective femoral osteotomy during THA in a patient with a previous Schanz osteotomy. A seventy-year-old woman presented to our clinic with a chief complaint of right hip, left knee and left ankle pain with marked limp. She had undergone Schanz osteotomy of the left femur because of high dislocation of the left hip when she was 20 years old. After right THA was performed, we decided to perform left THA with corrective femoral osteotomy. A custom-made osteotomy template was designed and manufactured with use of CT data. During surgery, we placed the template on the bone surface, cut the bone through a slit on the template, and corrected the deformity as preoperatively simulated. Two years after surgery, she had no pain in any joints, could walk more than one hour without limp. Japanese Orthopedic Association hip score were 100 points for both hips. THA in patients with previous Schanz osteotomy was reported to be technically demanding and the rate of complications was high. In 2008, Murase T et al. developed a system, including a 3D computer simulation program and a custom-made template to corrective osteotomy of malunited fractures of the upper extremity. We applied the system to corrective femoral osteotomy during THA in a patient with a previous Schanz osteotomy. The surgical procedure was technically easy and accurate osteotomy brought the patient to acquire good alignment of lower extremities with good clinical results.
