A numerous of hip-preserving surgeries were performed in young patients with hip dysplasia or ONFH [2, 13,14,15]. When these patients developed arthritis, the residual deformity would pose severe challenges to following THA . The surgical strategy of THA varies along with the severity and position of femoral deformity . As one uncommon type of femoral deformity, the severe valgus deformity of trochanter is critical for prosthetic morphology and surgical technique.
The concurrent arthroplasty with femoral osteotomy was a technically demanding procedure which had high risk of complications [1, 5]. Some surgeons suggested that customized prosthesis may provide one effective solution for severe femoral deformity [18,19,20]. However, the economic cost of customized prosthesis limited its wide application.
According to the design of S-ROM, the angle between sleeve and femoral stem can be adjusted freely, but it is seldom beyond 90 degree in clinical practice. The opposite direction of sleeve (180 degree) described in this study have never been reported previously.
In this study, no aseptic loosening or revision of femoral stem was found in the case series with a mean follow-up period of 6 years. There was the significant increase of HHS in all patients. The high revision rate of complex osteotomy or cemented THA was avoided. Better function and less complication indicated the safety and effectiveness of this technique in patients who had severe TVD. Cone has such advantages as easier bone preparation, less bone loss and less stress shielding. It was considered when an osteotomy is not planned, because the anti-rotation stability would be weakened by osteotomy [21, 22]. In the meanwhile, the risk of subsidence cannot be ignored in cone or fully-coated cylindrical stem [22, 23].
Although the method has produced satisfying clinical outcomes, we can’t neglect its technical flaws. Firstly, it can’t go through all kind of trochanter valgus deformities. Some special deformities still need osteotomy to facilitate offset and straighten medullary cavity. Secondly, since the valgus greater trochanter is not corrected, the increased joint offset would increase the risk of the greater trochanteric bursitis. Two patients reported lateral thigh pain after surgery, which was probably related to the bursitis. Thirdly, the manual work of implanting sleeve and malformed medullary cavity increased the risk of proximal femoral fractures. In this study, two patients had intra-operative fractures. Burs or other certain tools should be standing by for bone preparation. Fourthly, leg length might be influenced by residual deformity. While the equal leg length could be achieved by proper neck length and femoral head.
The clear indication of this special sleeve-implanting method was equal important. The medial support and lateral cover are two essential aspects of sleeve ingrowth. Once the medial cortex of proximal femur is destroyed, patients can’t meet the requirement of this special method. We can make basic predictions though measuring G/L ratio and TVA. In this study, compared with controls, the G/L ratio and TVA of 12 patients had significant differences, which indicated that their anatomies of proximal femur were characteristic. When G/L ratio was larger than 1.50, it can be regarded as one good indicator for the method.
Nowadays, an angular osteotomy on proximal femur is not suggested in hip-preserving surgeries. But this specific deformity was still occasionally met in conversion DDH for THA, which accounted for significant challenge. Although we introduced one alternative, it is necessary to remind the surgeons who are still performing angular osteotomy on proximal femurs of its potentially serious consequences.
This study has several limitations. Firstly, given that hip arthritis combining with trochanter valgus deformity were relative rare (12 cases in 9 years), suitable control cases could hardly be found to conduct case-control study. No comparison to other prostheses or other surgical methods would inevitably affect the persuasiveness of this study on technical notes. Secondly, because it was a retrospective case-series study, we don’t need the prospective ethics approval. In the future, multicenter randomized controlled trial will be performed to further evaluate its safety and effectiveness. Thirdly, this study was conducted over a long period of time. Changes in surgical personnel and related technical details might influence the final evaluation. Fourthly, study population be made up of various primary etiologies. The heterogeneity also had some impact on this method’s universality.