Do osteoarthritic subchondral bone cysts spontaneously consolidate after total hip replacement?

During total hip replacement (THR), subchondral acetabular bone cysts are either left alone or treated by filling with autologous bone graft. We hypothesized that subchondral cysts would consolidate spontaneously over time without compromising the midterm survival of the implant.

We retrospectively screened the anteroposterior hip radiographs of 731 consecutive patients who underwent primary THR between January 2006 and April 2009. Patients were included in the current study if they had acetabular subchondral bone cysts visible radiographically that had been left alone during THR.

52 patients (54 hips) matched the inclusion criteria, with mean age of 66 ± 11 years at surgery, and a mean follow-up of 6.3 years (range 5–9 years). Among the 52 patients, there were 88 cysts, with 1.6 ± 0.83 cysts per patient and a mean cyst size of 9.3 ± 10 mm² (range 0.9–57 mm²). Among the 88 cysts, 71 cysts (38 hips) had disappeared by the final follow-up, whereas 17 cysts (16 hips) were still visible. Most of these persistent cysts were located in Charnley zone I and were significantly smaller at the follow-up than before surgery (p = 0.015). Overall, most cysts decreased in size (p = 0.04). All cups survived and none showed radiological signs of loosening.

After THR, most neglected subchondral cysts spontaneously consolidate or decrease in size. Larger cysts may persist without affecting the surgical outcome. No radiological signs of loosening or other adverse effects were observed when acetabular bone cysts are neglected during primary THR.