• Hip and knee surgery

Introduction Hip-revision surgery is frequently complicated by unexpected periacetabular osteolysis. Preoperative x-rays normally do not reveal sufficient information about the amount of osteolysis, but in the course of the operation, huge localized osteolytic lesions in the pelvic bone may appear. X-ray examinations often underestimate the extent of osteolysis, and CT-scans have not yet overcome the metal artifacts and high radiation doses to evolve into a useful tool in this matter. Wear-particles from polyethylene are suspected to play a role in the development of osteolysis. HA-coating of implants seems to reduce the risk by sealing off the bone-implant interface. DEXA-scanning has proven a sensitive tool in the assessment of bone mineral changes around femoral stems, and tibial plateaus. However, only few studies have focused on the bone mineral changes around acetabular components. The aim of the present studies was to utilize DEXA-scanning as a simple tool to determine periacetabular osteolysis and to quantify the extent of osteolysis, including estimation of precision and accuracy of such a measure. Furthermore, a randomized controlled trial was conducted in order to study the effect of HA coating on bone mineral density changes around cementless acetabular components. Material and Methods To test reproducibility and accuracy of a certain scanning model and to elucidate how a difference in patient posture affected the result; we conducted a study with ten patients in each of three groups. We scanned to assess the influence of time since surgery, the difference between scanning in AP direction and the 45-degree iliac-oblique position, and finally the influence of controlled pelvic tilt. To quantify the amount of bone loss in a controlled experimental cadaver model we performed a study comprising of 10 pelvic specimens. Finally, we performed a clinical consecutive controlled randomized study. One hundred patients were operated with press-fit hemispherical cups +/- hydroxyapatite coating. Frequent DEXA-scans during the 3-year follow-up period were analyzed in order to analyze the pattern of bone remodeling around press-fit cups in the two groups. Results The study of different scanning positions revealed that DEXA-scanning in the AP position gave the best reproducibility. Pelvic tilt of more than 10 degrees affected reproducibility, and the intra observer variation was very low. DEXA-scanning of the pelvic specimens before and after removal of bone corresponded very significantly with the amount of removed bone in all regions. After 3 years, we neither found any differences between HA-coated cups and the standard cups, clinically nor measured by BMD. However, in one region, we found significantly better bone regeneration in the overweight and obese groups, compared to the normal weight patients; and the tendency was similar in the other regions. Conclusion DEXA-scanning has a high reproducibility, and has the ability to detect and quantify even small osteolytic lesion with high precision. In a controlled randomized trial, it proved reliable in the description of bone remodeling around prosthesis. We found no difference in bone remodeling between hydroxyapatite-coated and porous-coated cups.

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