Small stem Exeter total hip replacement: clinical and radiological follow-up over a minimum of 2.5 years

Journal of Orthopaedic Surgery, Dec 2003 by Sivananthan, S, Arif, M, Choon, D S K

ABSTRACT

Purpose. To evaluate the clinical and radiological outcome in patients undergoing small stem Exeter total hip replacement.

Methods. A total of 46 small stem Exeter total hip replacements were performed on 44 consecutive patients (18 men and 26 women) attending the University of Malaya Medical Centre. The mean age at the time of operation was 58 years (range, 24-81 years). Of the 46 procedures performed, 35 were primary total hip replacements and 11 were revision operations, with aseptic loosening of the original implant being the main indication for revision. The main indications for surgery in primary cases were avascular necrosis and rheumatoid arthritis. Clinical and radiographic outcomes were assessed at 6 weeks', 12 weeks', 6 months' follow-up, and annually thereafter. Postoperative cementing technique was also assessed.

Results. The mean follow-up period was 4 years. The mean Oxford Hip Score improved from 46 points preoperatively to 17 points at the final follow-up examination. There were no revision operations, no implant breakages, and no excessive migration of the implants. The potential complications of implant failure due to smaller implant size and increased patient activity were not observed.

Conclusion. Due to the smaller size of Asian femora, the small stem Exeter implant is a very useful development. This study suggests that it will perform as well as its larger counterparts.

Key words: prosthesis implantation; total hip replacement; treatment outcome

INTRODUCTION

The Exeter total hip replacement prosthesis was first implanted in the autumn of 1970. In 1976, design modifications were made whereby the anteroposterior (AP) section of the stem was increased slightly, and 5 sizes were introduced with a 44 mm offset, together with 4 having a 37.5 mm offset. Three sizes were made with a 22 mm head for cases of congenital dislocation of the hip (CDH). At the same time, the original polished surface was changed to a matt finish, a step later found to be retrograde and this was reversed at the beginning of 1986.1,2 Until 1986, all stems were made of 316L stainless steel. At the beginning of 1986, Orthinox, a high strength, low corrosion stainless steel was introduced.3 Throughout these design modifications, the fundamental stem geometry remained unchanged. The double-tapered, collarless design allows distal subsidence of the stem within the cement mantle and therefore, more uniform transmission of load into the cement, and dynamic ongoing pressurisation. The Exeter implant has had 30-year follow-up with good results. We report our experience with the small stem Exeter total hip implant, which has been used in Malaysia since 1995.

These smaller implants were introduced to the East Asian market in the mid-90's to cater for the smaller build of the Asian population. Initially, the small CDH stem with a 35.5 mm offset was used. For some patients, this was still too large. Later the newly manufactured small stem Exeter total hip replacement implant was used. This implant is shorter and therefore, the angle of taper is altered. It is available with offsets of 30 mm, 33 mm and 35.5 mm (Fig. 1).

PATIENTS AND METHODS

From 1995 through 1999, 46 consecutive total hip arthroplasty (THA) procedures were performed on 44 consecutive patients at the University of Malaya Medical Centre, using the small stem Exeter total hip replacement implant (Stryker Inc, Warsaw, US). Stems with offsets of 30 mm, 33 mm and 35.5 mm were used (Table 1). The head size was 26 mm in all cases. Preoperative templating was performed in all cases.

The last author carried out all the procedures, using the anterolateral approach to the hip in all cases. Second generation cementing techniques were used, including cement restrictor, pressurised lavage, retrograde introduction of cement with a cement gun, and a proximal femoral cement pressuriser. Simplex P radiopaque bone cement (Stryker Inc, Warsaw, US) was used in all cases. Patients were mobilised and fully weightbearing as soon after the operation as possible. There were 18 male and 26 female patients. The mean age at surgery was 58 years (range, 24-81 years). The mean weight was 58 kg (range, 38-82 kg) and the mean height was 157 cm (range, 143-175 cm). There was a range of indications for surgery (Table 2), with a broad spread across the 3 Charnley categories4 (Table 3).

Clinical outcomes were assessed using the Oxford Hip Score5 and radiological outcomes were assessed from AP radiographs of the pelvis, and lateral views of the affected hips. Stem failure was classified according to the criteria described by Gruen et al.,6 and the classification of cup failure by DeLee and Charnley7 was used for the acetabular component. Cementing technique was assessed using the criteria described by Barrack et al.8 Subsidence was meas -ured using a modification of the method described by Fowler et al.3 All immediate postoperative and latest follow-up radiographs were digitised in black and white and stored in jpeg (DSC-F55V; Sony Corporation, Tokyo, Japan), using a 3.3-megapixel Sony Cybershot camera. Osiris Imaging Software (version 4; University Hospital of Geneva, Geneva, Switzerland) was then used to measure alignment and subsidence of the implant.9