Total Hip Arthroplasty Using S-ROM Prosthesis for Dysplastic Hip RESULTS Clinical assessment The preoperative Harris hip score was 52.2 points on aver- age. At the final follow-up, the mean Harris hip score was 85.5 points. Of all the cases, 21 cases were assessed as ‘Ex- cellent’, 20 cases were ‘Good’, 4 cases were ‘Fair’ and none of the cases were ‘Poor’. Overall, clinical findings of more than ‘Good’ were presented at the final follow-up for 41 cases (91.9%). Three cases of thigh pain were presented, and two cases of these had a radiolucent line around the femoral stem. In all three cases, the thigh pain disappeared after two years post-operation and the radiolucent lines around the stem did not progress. Radiological assessment In two cases, there were progressive radiolucent lines and loosening around the acetabular cup. Of these, one case un- derwent monitoring of the clinical course and the other case was diagnosed as the loosening of an infected cup. The latter case was treated with revision surgery. Excluding these two cases, the remaining 43 cases showed stable fixation. There were no findings that were suggestive of osteolysis of the acetabular cup. In all cases, the femoral stem showed stable fixation (Figs. 1 and 2). The initial degree of the femoral fix- ation was also measured in accordance with the classifica- tion system proposed by Engh and Bobyn.8 This showed that 41 cases had canal filling of >90% and four cases had canal filling ranging from 80% to 90%. These findings indi- cate that all cases had satisfactory canal filling. The stability of the femoral stem was assessed based on the classification system proposed by Engh, et al.9 This showed that 37 cases had bony stability and eight cases had fibrous stability. There were no cases of instability. Fibrous fixation was defined in the cases in which the reactive radiolucent line was observed in Gruen zones II and VI until postoperative year 2. There- after, the radiolucent line did not progress further, but rather was stabilized. In ten cases, a reactive radiolucent line was observed in Zone I around the femoral stem. Yet it was as- sumed that these lines were local reactive lines that did not extend to the areas below the sleeve. Upon final follow-up, radiolucency of the calca femorale was observed in 16 cas- es (35.5%). Progressive bone loss of the proximal femur due to stress shielding was not shown. In accordance with the classification system proposed by Brooker, et al.,11 Types I and II heteotopic ossification were A B Fig. 1. (A) Radiography of a 40-year-old female shows Crowe’s type III dys- plasia of the left hip. (B) The follow-up radiograph after 7 years shows a stable femoral stem and cup. A B Fig. 2. (A) Radiography of a 38-year-old female patient shows Crowe’s type IV dysplasia of the right hip. (B) Total hip arthroplasty with femoral shorten- ing osteotomy was performed. The radiograph at five years post operation shows stable cup fixation in the true acetabulum. identified in four cases. However, their clinical outcomes were all determined to be ‘Excellent’. A hard bearing sur- face was used in all cases. Measuring the wear of the artic- ular surface at the final follow-up radiography was impossi- ble. There were no problems found associated with the articular surface. Yonsei Med J http://www.eymj.org Volume 52 Number 4 July 2011 657