Objective: to measure cartilage and bone acetabular erosion in patients treated with a bipolar hip hemiarthroplasty because of a femoral neck fracture.

Material and methods:

- 34 patients, 31 female. average age 72.9 +/− 7.1 years (56–90)

- Level of activity previous to fracture: 82.4% level III, 14.6% level II

- Displaced (Garden III and IV) fracture of femoral neck excluding pathologic fractures

- Hip hemiartrhoplasty with a JRI Furlong bipolar head (22.25 mm inner head), 30 patients with a Furlong HAP-coated uncemented stem and 4 patients with an auto-blocking-type Surgival cemented stem

- Follow-up: minimum 2 years, average 2.9 years (2–5)

- Clinical evaluation: Merle-DAubigne-Postel six-point scale for pain and for function

- Radiological evaluation: measure of joint line width at superior-lateral quadrant (weight bearing area), perpendicular distance from prosthesis head to Kohler line

- Statistical analysis: Kolmogorov-Smirnov, ANOVA, Bonferroni, Pearson, and Spearman tests

Results – Pain: average score 4.5 +/− 1.3 after 1 year, 4.7 +/− 1.3 after 2 years, 4.6 +/− 1.4 after 3 years

- Function: average score 4.7 +/− 1.1 after 1 year, 4.7 +/− 1.4 after 2 years, 4.8 +/− 1.3 after 3 years

- Radiological joint line: disappeared in 13 patients (38.2%) after 1 year, in 14 (41.2%) after 2 years, in 54.5% of patients after 3 years. Average joint line width in the other patients: 0.9 mm (0.6–1.3) immediately after surgery, 0.6 mm (0.4–0.8) after 1 year, 0.5 mm (0.3–0.7) after 2 years, 0.5 mm (0.2–0.7) after 3 years (p< 0.05)

- Distance from head to Kohler line: 5.7 +/− 3.8 mm (4.6–6.8) immediately after surgery, 4.6 +/− 3.7 mm (3.6–5.6) after 1 year, 4.3 +/− 2.9 mm (3.3–5.3) after 2 years, 4.0 +/− 3.3 mm (2.5–5.5) after 3 years (p< 0.05). There were 2 cases of acetabular protrusion.

Conclusions 1. Bipolar heads in hemiarthroplasty do not avoid acetabular erosion. 2. The radiological progressive erosion does not correlate with clinical worsening of the patients.