Abstract
INTRODUCTION
Recently, short shaped stem becomes popular in total hip arthroplasty (THA). Advantages of the short stem are preserving femoral bone stock, thought to be less thigh pain, suitable for minimally invasive THA. However, bony reaction around the short stem has not been well known. The purpose of this study was to compare the two years difference of radiographic change around the standard tapered round stem with the shorter tapered round stem.
MATERIALS AND METHODS
Evaluation was performed in 96 patients (100 joints) who underwent primary THA. Standard tapered round stem (Bicontact D stem) was used in 44 patients from January 2011 to May 2013. Shorter stem (Bicontact E stem) was used in 56 patients from May 2015 to March 2016. The proximal shapes of these two stems are almost the same curvature. The mean age at surgery was 64 years. The mean BMI at surgery was 24.0 kg/m2. Eighty-six patients had osteoarthrosis and 10 patients had osteonecrosis. Evaluation was performed 2 years after surgery with standard AP radiographs. The OrthoPilot imageless navigation system was used during surgery. Evaluation of the stem fixation, stress shielding, and cortical hypertrophy were carried out.
RESULTS
There were no differences of patient characteristics between the standard D stem group and the shorter E stem group. All 100 stems showed bony stable fixation two years after surgery. No subsidence was observed in both groups. No clear zone was observed around the stems in both groups. Cortical hypertrophy was observed 19 patients (43.2%) with the standard D stem group and 13 patients (23.2%) with the shorter E stem group. The standard D stem group showed higher incidence of cortical hypertrophy. Stress shielding was observed 35 patients (80%) with the standard D stem group and 42 patients (75%) with the shorter E stem group. The number of grade 1 and grade 2 stress shielding cases were 13 and 22 with the standard D stem group and 10 and 32 with the shorter E stem group, respectively. There were no grade 3 stress shielding case in both groups. Regarding the incidence of stress shielding, there was no difference between the two groups.
DISCUSSION
This study demonstrated that the shorter stem showed less incidence of cortical hypertrophy compared to the standard stem. With radiographic evaluation, both standard and shorter stem showed good fixation. The meaning of cortical hypertrophy, whether it is a good reaction for the femur or not, has not been clarified yet. Less bony reaction around the shorter stem may suggest the potential for better clinical performance of the shorter stem compare to the standard stem.
