MONOBLOCK TRABECULAR METAL ACETABULAR CUPS IN TOTAL HIP REPLACEMENT IN PATIENTS WITH DEVELOPMENTAL DYSPLASIA OF THE HIP

Abstract

Aim: We present the surgical technique and early functional and radiological results of cementless acetabular reconstruction with Monoblock Trabecular Metal (MTM) (Zimmer Warsaw, Indiana) cups in patients with Developmental Dysplasia of the Hip (DDH).

Materials and Methods: From 1997 to 2004, 70 hips (57 patients) with DDH were received an MTM acetabular component. There where 7 men and 49 women. Average age was 50 years (range 35 to 77). According to the classification of Hartofilakidis et al there where 14 hips with high dislocation, 15 with low type I, 16 with low type II, 8 with low type III dislocation and 17 with hip dysplasia. In all patients a MTM cup was implanted in the true acetabulum through a standard posterior approach. Morselized graft was used in 6 cases and a structural graft only in one. Diameter of the cup was ranging from 42 to 56 mm with 54 out of 70 cups being smaller than 50 mm. Screws where used in 12 out of 70 cases A femoral shortening osteotomy was utilized in only two high dislocation cases.

All patients where followed up prospectively and evaluated clinically and radiologicaly at three, six months at one year and yearly thereafter. The clinical outcome was assessed with the Harris Hip score (HHS) and Oxford Score (OS).

Results: Average follow up was 50 months (range 103 to 24). There were no revisions for aseptic loosening, radiologic loosening or cup migration during last evaluation. Two patients developed non-progressive radiolucencies in zone one.

There were four dislocations in this group. One required open reduction and head replacement while another one needed cup revision due to mal orientation. There were five femoral fractures treated intraoperatively with wires, two patients developed transient sciatic nerve palsy and two non fatal PE.

Harris Hip Score was 91 (range 69 to 97) compared with 48 (range 24 to 58) before surgery. The outcome was excellent in 59 hips, very good in 8, good in two and fair in one. Leg length discrepancy more than 2 cm was evident in five unilateral cases (range 2 to 4.5). Trendelebourgh sign was evident in four patients.

Conclusion: MTM acetabular component achieved adequate initial stability in this demanding group of patients and they have excellent radiological and clinical results. Posterior approach without femoral osteotomy provided adequate exposure in almost all cases.