Purpose of the study: Acetabular bone loss and loosening after total hip arthroplasty has been evaluated on plain x-rays (Vives, 1988; D’Antonio, 1989; Paprosky, 1994). Experience has proven that intraoperative assessment of bone loss is more important than previously thought. Our main objective was to quantify, intraoperatively, the real volume of bone loss. A secondary objective was to measure, independently of the observer, the course of acetabular loosening.
Material and method: This was a prospective series of acetabular loosenings (10 female, 4 male, mean age 68 years). Plain x-rays and computed tomography (CT) were obtained. A special image analysis software was used for the CT images after manual segmentation of the prosthetic acetabulum: automatic 3D volume and periprosthetic bone density were noted.
Results: Bone loss was divided into three stages. At stage 1, the volume lost was from 10 to 20 cm3; at stage 2, the volume loss was 20 to 40 cm3; and at stage 3 the loss was greater than 40 cm3. At six months, two hips exhibited early stage acetabular loosening with 5% lucency. The corresponding volumes between the stages observed on the plain x-rays and those measured on the CT scan did not correlate significantly.
Discussion: Compared with conventional x-ray methods for volume assessment, this computed tomography method is precise. The segmentation preparation was semi-automatic and took about 30 minutes. The prosthetic material did not hinder the image analysis. Results were produced automatically. The 3D representation enabled the operator to visualize intraopera-tively the acetabular zones the most affected, helpful for planning the procedure and choosing the implant. The density analysis gave the quality of the bone and the limit between healthy tissue, pathological tissue and the cement, increasing the volume of the bone loss.
Conclusion: These automatic measurement tools reduce analysis time. The precision of the measurements is a supplementary factor for determining the stage of the bone loss and the amount of graft tissue or bone substitute needed. This method can be used for all joints.
