No Impact of Contact Between the Medial Collar of a Hydroxyapatite-Coated Triple-Tapered Stem and the Femoral Neck on Periprosthetic Bone Mineral Density.

Background: Hydroxyapatite-coated, triple-tapered, shorter-length stems with a medial collar have been reported with good results for a few years. We investigated whether contact between the medial collar and femoral neck affects clinical outcomes and changes in bone mineral density (BMD) in patients who have this type of stem in their total hip arthroplasty construct.

Methods: This was a retrospective, single-center study involving 62 patients scheduled for unilateral total hip arthroplasty using a hydroxyapatite-coated, triple-tapered, shorter-length stem who were followed for at least 1 year postoperatively. All patients had a Dorr type B femoral canal shape. Contact between the medial collar and the femoral neck was evaluated by computed tomography at the third postoperative month, and patients were classified into 2 groups. Postoperative clinical outcomes were investigated by the Western Ontario and McMaster Universities Arthritis Index and the Japanese Orthopaedic Association scores; radiological evaluation included stem fixation, spot welds and cortical hypertrophy, postoperative 3-dimensional stem alignment, and periprosthetic BMD changes.

Results: There were 51 patients in the Contact + group (collar and neck contact) and 11 in the Contact-group (no contact). There were no differences between the 2 groups in the improvement of Western Ontario and McMaster Universities Arthritis Index and Japanese Orthopaedic Association scores, stem fixation, occurrence of cortical hypertrophy, or 3-dimensional stem alignment. Radiolucent lines were present in zones 3, 4, and 5 in 6 patients (12%) in the Contact + group only, who had no statistical difference between the 2 groups. Bone mineral density (BMD) decreased most in zone 7 in both groups, with no difference between the 2 groups.

Conclusions: The presence or absence of contact between the medial collar and femoral neck did not affect postoperative BMD changes or radiological or clinical results.

Level Of Evidence: Therapeutic Level III.