Introduction: Several techniques have been described for revision of acetabulum associated with severe superior bony defects. An Oblong cup inserted without bone cement has the advantage of restoration of the centre of hip rotation and maintenance of bone stock. The aim of this study was to analyse the medium-term results of acetabular revision using Oblong cup for severe superior bony defects.

Methods: Thirty-five acetabular revisions using porous coated Oblong cups (S-Rom, Depuy) in 34 patients were performed by the senior author between 1998–2001. All patients were followed-up clinically and thirty-one hips were analysed radiologically for a mean duration of 39.6 months (range 18 to 60). The clinical assessment was performed using Harris hip score and subjective patient’s satisfaction. The acetabular defects were classified according to the method described by Paprosky et al. The position of the acetabular implant, restoration of the centre of hip rotation and the extent of osseo-integration of the acetabular shell were assessed in the post-operative radiographs.

Results: The mean Harris hip score has improved from a preoperative value of 40.6 to 69.4 post-operatively. According to the Leprosy’s method, two acetabula were classified as type 2B, 12 as type 3A and 17 as 3B. The post-operative radiographs showed a mean abduction angle of the Oblong cups of 54.2 degrees (range 40–80). Osseointegration was achieved in 29(94%) of cups. Three cups showed early migration, of which two eventually stabilised and osseointegrated by 12 months. The centre of rotation of hip improved from a mean lateral migration of 8.3 mm and superior migration of 23.5 mm in the pre-operative radiographs to 2.8 mm and 4.3 mm respectively post-operatively.

Discussion: Acetabular revision using porous coated oblong cup for severe superior acetabular defects provides satisfactory medium-term results with predictable restoration of hip centre of rotation.

Results in revision Hip surgery are compromised where there is extensive bony destruction or significant bone loss. While restoration of bone stock and a return to normal anatomy is the gold standard this is not always possible and may not be required in those patients with lower functional demands and other co-morbidities. The senior authors designed a new hip prosthesis as an aid to revision Arthroplasty and to allow them to bypass defects in the proximal femur. This was a titanium modular cemented prosthesis of varying lengths (from 140mm to 220mm) with a distal flange to transmit compressive loads. It used cement to obtain fixation in the remaining bone, had a short offset designed to reduce torsional loading and a standard (12/14mm) trunion to allow the use of a variety of modular heads.

Operative technique: A transfemoral approach was used allowing easy removal of the old prosthesis, cement and other debris. This also gives an excellent view of the acetabulum if this is also to be revised. The distal femur is sectioned transversely and an appropriately sized component selected, the remaining femur is reamed to 14mm and cemented in place. The proximal femur is then closed over the prosthesis and held with cerclage bands. Full weight bearing was allowed once quadriceps function had been regained.

Results: 48 proximal femoral replacements were performed in 47 patients between December 1992 and June 1997. 12 patients died and 6 declined follow up. The remaining patients were seen in clinic and radiographs of the femur were performed. There was a significant reduction in the postoperative pain score (p< 0.01), and improvement in the Harris hip score. 7 patients suffered dislocations, 4 responding to conservative measures after a single episode. There were 5 implants revised, 3 to total femoral replacements and 1 to a calcar replacing prosthesis. Most patients were satisfied with their result, and all but 1 walk with minimal walking aids. Despite its high complication rate we continue to use this prosthesis as we feel that it remains as a useful alternative in the management of selected low demand patients.

Individual components of a total hip replacement are difficult to evaluate and quantify. We have studied the assessment of the acetabular component, and conclude that the measurement of migration allows the comparison of implants, although there is no established link between migration and significant loosening. A method of measurement based on clinical radiographs has been developed, and its limitations estimated. The accuracy of the technique was calculated to be +/- 3 mm.

Torsional instability of femoral components has not received much attention, and is difficult to detect in conventional radiographs. To test this we designed a system to apply a load in an anteroposterior direction to the head of a femoral component, implanted into a cadaveric femur. Rotation within the bone was measured, using a purpose built transducer, with and without preservation of the neck, with and without cement, and with longitudinal ridges but no cement. The results show that torsional instability may be a problem in uncemented replacement. Preservation of the femoral neck and the use of a ridged prosthesis increases resistance to rotation. Rotational movements occurring in vivo during such activities as climbing stairs and rising from the seated position may contribute to mechanical loosening.

The Ring plastic-on-metal total hip replacement was introduced with the intention of combining the advantages of the cemented low-friction arthroplasty with those of a cementless system. Fourteen hundred and eighty-eight of these procedures have been reviewed. The results of a two to seven-year follow-up, and of a group which has completed at least five years are presented. There was an excellent clinical result in 93% of the whole series, and in 87% of the five-year group. When graded on the Charnley scale there was an average score of 5.86 for pain, 5.96 for function and 5.9 for range of movement, which compares favourably with cemented replacements. The deep infection rate was zero, and the revision rate 1.5% for the whole series. Erosive problems occurred with the smaller acetabular components and the reasons are discussed. The ease and success of exchange have been maintained.

The results of using the Ring uncemented polyethylene-to-metal (UPM) prosthesis in patients with protrusio acetabuli or dysplasia are reported. Fifty-four cases of protrusio were analysed and a modified method of measuring the deformity is described; after operation, remodelling of the medial wall had improved, on average, by 29.6%. For the dysplastic acetabulum the main difficulty is the lack of lateral support for the cup. In order to test the hypothesis that this support improves with an uncemented prosthesis, 38 hips with an average follow-up of 31 months were studied. Lateral support, measured radiographically, showed an average increase of 21%. The remodelling effect may be attributed to the biomechanical design of the prosthesis.