Abstract
In this article, the authors retrospectively reviewed the clinical and radiological performance of a short cementless tapered wedge stem design (Taperloc Complete Microplasty stem) in 257 primary total hip arthroplasty (THA) for patients with the pre-operative diagnosis of developmental dysplasia of hip (DDH). The success of cementless short femoral stems in selected patients has been published in the past. 1,2 However THA in DDH patients is technically more challenging because of the distorted anatomy and altered hip biomechanics. 3 The post-operatively complication rate is higher and patients’ satisfaction may be compromised. 4
It is worth noting that among 461 THAs performed in the authors’ centre during 5 years period, 311 (67.5%) were diagnosed with DDH, which was exceptionally high. The diagnostic criterion used for DDH was ‘superolateral subluxation of femoral head’ in pre-operative X-ray. In other reports on the indication for primary THA in Asian patients, DDH is usually not on the top of the list. 5 Primary hip OA or secondary OA due to other pathologies with osteophytes formation at the acetabular floor can also cause superolateral subluxation of femoral head. These patients usually don’t have dysplastic femur, i.e. excessive anteversion and narrow canal. Stem fixation in these patients is easier and safer. The authors did not elaborate on the Crowe’s classification of their patients. Theoretically in Crowe’s III and IV femora, subtrochanteric osteotomy may be indicated in order to restore the anatomical hip centre. A short stem may not be able to achieve adequate distal fixation.
The authors reported excellent clinical and radiological outcomes at minimum 2-year follow-up, with 100% bone ingrowth and 0% loosening/changing in position on the X-rays. The clinical score (JOA) improved significantly. There was one peri-operative fracture of the greater trochanter, one early dislocation and one early infection. CT scan images of 44 hips were analysed to evaluate the change in femoral anteversion. The authors demonstrated a reduced variability in femoral anteversion from 13–58 degrees pre-operatively to 17–46 degrees post-operatively. The mean post-operative anteversion was 31 degrees, which is still high compared to the generally acceptable value of 15 degrees. This is due to the monoblock nature of the stem, which gives very little freedom in intra-operative adjustment of the femoral anteversion. Excessive femoral anteversion may predispose to dislocation after THA. 6 If surgeons cannot achieve satisfactory stem anteversion, they may need to adjust the anteversion of the acetabular component instead to reduce such risk.
One known complication after a short tapered wedge stem is peri-operative fracture of the femur. 7 The authors described their technique to avoid such complication. They suggested careful broaching and lateralization of the broach when entering the calcar region. The authors reported one post-op fracture of the greater trochanter. It could be the result of excessive lateralization of the broach during insertion. Because of the risk of fracture, significant change of anteversion is not advisable with such a stem design.
It is of utmost importance to restore the normal hip anatomy and biomechanics after THA. A versatile stem that allows intra-op adjustment of offset, anteversion, leg length, and same time achieves stable initial fixation and long-term bone ingrowth is ideal in clinical practice. In patients with Crowe I and II DDH, a short tapered wedge stem could provide good radiological and clinical outcome if performed properly. In patients with Crowe III and IV DDH, a modular stem may offer additional advantage.
