Purpose of the study: We have tried to produce a new acetabular ring in order to obtain an early stability of cemented cup for acetabular protrusion in R.A. In this presentation, we intend to introduce this new support ring and report these results.
Materials and methods: The new support ring with double-hook we produced was made of pure titanium, and has eight screw holes in medial side and two screw holes in superolateral side. Size variation of this ring comprises 40mm, 42mm, 46mm, 48mm and 50mm in inner diameter. Width of the hook is 10.05mm and its thickness is 1.19mm. Hook length is 33.5mm. After the remaining bone defect is packed with morselizd and mushed allograft bone, proper support ring with double hook is selected. Straight portions of double hook are bent in order to fit to acetabular shape after bone grafts. If good fitting is achieved, this support ring was fixed to the acetabulum with three to five screws. Total hip arthroplasty with this support ring was performed in ten patients with eleven hips. Three cases were in male and seven in female. The age at surgery ranged from 46 to 73 years old with an average of 59.8 years.
Results: Setting angle of support ring ranged from 40 to 50 degrees with an average of 43.7 degrees. Follow-up period was from one year to three years with an average of two years one month. No loosening was encountered and no migration of support ring and cup was visualized on radiological findings. JOA(Japanese Orthopaedic Association) hip score which was adopted for clinical evaluation was 31.3+/−10.2 before surgery and 70.1+/−8.5 after surgery.
Discussion: Various types of reinforcement ring have been used with or without bone grafts for acetabular protrusion. I had prefered Ganz ring among them. Bending a hook of Ganz ring, however, is not easy as its hook portion is slightly thick. Accordingly, setting angle of the ring is often apt to be acute as it must be fitted to acetablualr shape. In superior cortical defect of the acetabulum, hook length is often insufficient because a hip center of the ring is in high position. Therefore, it is sometimes impossible to hook acetabular notch. We produced a new support ring with double-hook in order to solve these problems. As the hook was thinner in the new ring than in Ganz ring, it was easier to bend the hook. As the hook of of the new ring was longer than that of Ganz ring, it was possible to hook acetabular notch in spite of high hip center. Setting angle of the new rings was less than 50 degrees. Radiological findings and clinical results were good though follow-up period was short.
