Joon Soon Kang, et al. Complications The postoperative complications included two cases of hip dislocation. No further recurrence was noted following man- ual reduction. Partial palsy of the sciatic nerve was observed in one case, but this recovered to normal level at ten months post-operation. Intraoperatively, periprosthetic fracture on the proximal femur occurred in one case. Stable fixation was obtained by cerclage wiring. Infected cup loosening developed in one case at three years post-operation. This case was treated with revision surgery. At three year post- operation, this case showed a good clinical outcome with no recurrent episodes of infection. DISCUSSION The terminal point of the natural course of hip dysplasia is secondary degenerative arthritis. Acetabular dysplasia exerts an excessive amount of stress to the articular cartilage at the weight-bearing portion. Patients who complain of pain and functional disturbance and who are refractory to conserva- tive treatment are indicated for total hip arthroplasty. Arthroplasty becomes problematic in cases in which growth failure of the hip is concurrently present, due to devel- opmental dysplasia of the hip joint or pediatric hip diseases, because of the deformities of the anatomical structures around the hip joint, including limb shortening, deformed acetabu- lum, deformed femur, and muscle atrophy around the hip joint. In particular, because femoral deformity shortens the femoral neck, the greater trochanter is located superiorly to the femoral head and the anteverion angle is increased. The narrow canal of the bone marrow cavity in the femur poses difficulty when selecting appropriate joint prostheses.2,3,5,12,13 A proximal modular femoral stem (S-ROM stem) is com- posed mainly of three parts: the stem, sleeve and head. Each stem and sleeve are available to select the optimal type and size. It is known that 10,398 combinations of the type and size are available on a theoretical basis.14,15 Due to these ad- vantages, the S-ROM modular stem is highly advantageous for total hip arthroplasty in patients with arthritis and who concurrently have anatomical deformities. Particularly in cases with developmental dysplasia of the hip joint in which the anterior and posterior diameters on the left and right side of the proximal femur are small, the degree of curva- ture is low and the bone marrow cavity is narrow, the S- ROM stem can provide the maximum correction force be- cause it forms maximum filling to the deformed proximal femur at the initial phase. The S-ROM modular stem is also advantageous in that it can be easily used for correcting the femoral anteversion angle and leg length discrepancy and for offset correction during the surgery. It has been reported that the clinical outcomes of total hip arthroplasty using the S-ROM modular stem showed no dif- ference from or that they were more excellent than the con- ventional type of total hip arthroplasty.16,17 Cameron16 report- ed that the clinical outcomes were more than ‘Good’ in 97.9% of the total patients. Park, et al.17,18 also reported that the clinical outcomes were 92.25 points at 2-year follow-up and 95.90 points at 5-year follow-up. Also in our series, the Harris hip score improved from 52.5 points preoperative to 85.5 points postoperative. At the final follow-up, the clinical outcomes were more than ‘Good’ in 41 cases (91.9%). On the other hand, thigh pain following cementless total hip ar- throplasty has been reported to have a relatively lower inci- dence. Presumably, this might be true because flexibility of the femoral bone marrow cavity could be generated because of the decrease in comparison with the cylindrical stem with the same diameter due to the presence of a slot with a tubular shape in the distal area.19 In the current study, thigh pain de- veloped in three cases. Of these, two cases had a radiolucent line detected around the femoral stem. In all three cases, the thigh pain disappeared two years post-operation. The S-ROM modular stem was designed to generate maximal contact between the stem and the endosteum in the metaphysis and the diaphysis. In the proximal part, ca- nal filling could be maximized with the use of a sleeve. In the distal part, the S-ROM modular stem has a flute-like shape and therefore tolerates torsional force. For inserting the femoral stem into the bone marrow cavity, the contact surface between the stem and the proximal femur can be maximized and the stability can also be maximized. Thus, the anterior length of the stem can be stabilized. Also in the current study, the femoral stem showed stable fixation in all cases. According to Cameron,20 the distal flute- like shape of the S-ROM modular stem can provide the fix- ation effect in cases in which the degree of curvature of the proximal femur was excessive or when shortening osteoto- my was performed. In the current study, shortening osteoto- my of the femur was performed in five cases. This was effec- tive in securing the initial fixation force in the distal femur. Accordingly, early rehabilitation was possible for these cases. With regards to the change in the proximal femur due to stress shielding following a cementless total hip arthroplas- ty, Rosenthall, et al.21 compared the bone loss using a Dexa 658 Yonsei Med J http://www.eymj.org Volume 52 Number 4 July 2011