Joon Soon Kang, et al. are very challenging when performing total hip replacement surgery using a standard femoral stem. Various methods have been attempted to solve these problems,2-4 and one of them is the use of a proximal modular femoral stem. We analyzed the clinical and radiological outcomes of to- tal hip arthroplasty using the S-ROM proximal modular femoral stem (DePuy Johnson and Johnson Co., Warsaw, IN, USA). MATERIALS AND METHODS Materials Among all patients who underwent total hip arthroplasty using the S-ROM stem at our medical institution between January 2001 and March 2004, 42 patients (45 hips) were enrolled in the current study. For these patients, the mean follow-up period was 80 months (range: 60 to 96 months). The mean age was 48.5 years (range: 21 to 65 years). There were 28 women and 14 men. The inclusion criteria for this study were cases with a dysplastic hip or deformed femur due to previous hip disease. Hips with normal proximal fem- oral geometry were excluded. The preoperative diagnoses were classified based on the preoperative radiological find- ings of the hip joint and the patient histories, which includ- ed 26 cases of developmental dysplastic hip, 13 cases of the sequelae of LCP disease, two cases of slipped capital femo- ral epiphysis, three cases of sequelae of pyogenic arthritis and one case of congenital coxa vara. In accordance with Crowe’s classification5 system based on the severity of femo- ral subluxation, there were 13 cases of type 1, 16 cases of type 2, 10 cases of type 3, and 6 cases of type 4. The surgery was performed through a posterolateral ap- proach. Femoral shortening osteotomy was concomitantly performed in five cases. The insertion of the acetabular cup in the proper anatomical location was the primary goal of the surgery. Yet in two cases, the acetabular cup was insert- ed more superiorly. The fixation of the acetabular cup was performed compressively by under-reaming it to 1 to 2 mm smaller than its actual size. Variable sizes of acetabular cup were used, and the mean value was 50.2 mm (range: 42 to 58 mm). The femoral stems used herein include 20 cases with a 13 mm stem, 12 cases with a 15 mm stem, ten cases with an 11 mm stem and three cases with a 9 mm stem. The articular surface used herein was metal-metal articula- tion in 22 cases and ceramic-ceramic articulation in 23 cas- es. A 28 mm head was used in all cases. Clinical assessment Clinical assessment was performed based on the preopera- tive and postoperative Harris hip scores.6 Scores of >90 points were assessed as ‘Excellent’; scores of 80-90 points were assessed as ‘Good’; scores of 70-80 points were as- sessed as ‘Fair’; and scores of <70 points were assessed as ‘Poor’. The presence of thigh pain was confirmed. This clini- cal study was approved by the Institutional Review Board of Inha University Hospital. Radiological assessment For radiological assessment, radiography was taken with a certain method and attempts were made to minimize error. Changes in radiological findings around the acetabular cup and femoral stem were monitored on radiography that was performed immediately after surgery, six months post-opera- tion, and thereafter on a yearly basis. The osteolysis seen around the acetabular cup was analyzed based on three ar- eas that were classified by DeLee and Charnley.7 Vertical migration of the acetabular cup was defined as the measure- ment of the vertical distance between the inferior border and that of the ipsilateral tear drop. The horizontal migra- tion was defined as the horizontal distance between the cen- ter of the lateral border and Kohler’s line. The cases in which the acetabular cup had migrated by more than a 5-degree angle or more than 2 mm were assessed as unsta- ble fixation. The initial degree of fixation of the femoral stem was de- termined by measuring the ratio between the femoral pros- thesis and the intramedullary canal in the upper part of the lesser trochanter and the distal part of the implant on the an- terior and posterior view, which were taken postoperatively in accordance with the classification system recommended by Engh and Bobyn.8 Based on these criteria, the cases in which the degree of canal filling exceeded 80% in the bone marrow cavity in the proximal area and those in which the contact between the cortical bone of the femur and the im- plant was achieved within a 1 mm distance were deter- mined to be ‘Fair’. The final degree of femoral fixation was determined based on the methods of Engh, et al.9 To do this, the stabilization scores were measured. This led to the assessment of stability based on such parameters as stable bone ingrowth, stable fibrous ingrowth and unstable fixa- tion. The locations of osteolysis and radiolucent lines were analyzed in accordance with the classification system pro- posed by Gruen.10 656 Yonsei Med J http://www.eymj.org Volume 52 Number 4 July 2011