Comparison of Short-Term Results of Total Hip Arthroplasty with Polarstem by Dorr Type

The use of cementless stems in patients with stovepipe-type femoral morphology (Dorr type C) remains controversial. Limited data are available on the clinical and radiological outcomes of cementless total hip arthroplasty using the Polarstem, particularly with proximal femoral bone morphology. This study compared clinical and radiological outcomes following Polarstem total hip arthroplasty (THA) based on medullary canal morphology, with a secondary aim of evaluating short-term findings.

This retrospective study included 101 consecutive patients who underwent Polarstem THA. Inclusion criteria required a minimum 2-year postoperative follow-up. We excluded patients with incomplete clinical data, pathological fractures, or severe comorbidities. Resulting in 95 patients (112 hips) for final analysis. Radiographic findings and Japanese Orthopaedic Association (JOA) hip scores were compared among the three Dorr-type classifications.

Postoperative JOA scores showed significant improvement compared to preoperative values (p < 0.001). No significant differences were observed among Dorr types preoperative and postoperative JOA scores, subsidence incidence, or cortical hypertrophy (p = 0.199, 0.061, 0.623, and 0.384, respectively). No cases exhibited radiolucent lines. Pedestal formation occurred in 64 hips, with significantly higher occurrence in Dorr type C (p < 0.009). Stress shielding was observed in 47 hips, with significantly higher grade 2 incidence in Dorr type A and lower incidence type B (p < 0.001).

The Polarstem demonstrated favorable short-term clinical outcomes regardless of proximal femoral morphology. However, grade 2 stress shielding occurred more frequently in Dorr type A femurs, suggesting that medullary canal morphology should be considered when selecting this stem design.