Stable fixation of the ulnar component in the Kudo elbow prosthesis. A radiostereometric (RSA) study of 13 prostheses with 2-year follow-up

Background?Concern has been expressed about the large number of radiolucent lines around the ulnar component of the Kudo elbow prosthesis in medium-term follow-up.

Patients and methods?We studied the metal-backed cemented ulnar component in 13 Kudo elbow prostheses (type 5) using radiostereometric analysis (RSA). All patients had rheumatoid arthritis. There were 2 men and 9 women with a mean age of 55 years. 2 were operated bilaterally. The metal-backed ulnar component was marked with three 0.8 mm tantalum spheres and the proximal ulna with 5 spheres of 0.8 or 1.0 mm diameter. The initial RSA examination was performed during the first week after the operation. Further examinations were done at 4, 12 and 24 months. Conventional radiographs were taken during the first week postoperatively, and at 12 and 24 months.

Results?Translations (medial/lateral, antero/poste-rior and proximal/distal) were less than 0.5 mm in all but 1 patient who had a maximal translation of 3.4 mm distally. The mean rotations around all three axes were less than 0.4 degrees. The patient who had a translation of 3.4 mm also had varus angulation exceeding 4 degrees. This patient also had progressive circumferential radiolucent lines on conventional radiographs. The Mayo elbow score increased from 40 (25-65) before surgery to 92 (45-100) at 2 years.

Interpretation?The fixation of the metal-backed ulnar component of the Kudo elbow prosthesis at 2 years is good.