A single dislocation after total hip arthroplasty may not be a problem, once it becomes recurrent it rapidly undermines patients’ confidence. With an increasing number of revisions the problem of dislocations is likely to increase. The study and development of methods of prevention and management must proceed in pace with revision surgery.

We have designed a new cup: the angle-bore cup – to simulate both the structure and the function of the natural acetabulum with freedom of flexion, adduction, internal rotation and stability in the opposite direction. In its manufacture the centre of the hemisphere of the plastic is approached at an acute, less than 90 degrees angle, to the face of the cup creating a chamfer anteriorly and a recess postero-superiorly. The cup is side specific and cannot be reversed.

The angle-core cup was used in conjunction with a 22.225mm diameter head of the Charnley design with the exposure by trochanteric osteotomy. One thousand and thirty nine revisions were carried out: 505 were males and 534 females, mean age 65 (22.2 – 93.3): 66% were referred from other units. The indications for revision were: loose and worn cup 740, loose stem 553, deep infection 212, dislocation 65, fractured stem 51, bent stem 3, unexplained pain 17. There were 30 post-operative dislocations 2.9%; 22 (2.1%) had to be revised for recurrent dislocation. Of the 65 cases where dislocation was the original indication for revision 7 (10.8%) had to have further revision for dislocation.

(In 2330 primary Charnley low frictional torque arthroplasty with 22.225 mm diameter head and the angle-bore cup, there were 17 dislocations (0.73%); seven having to have revision for dislocation – a revision rate of 0.3% with a mean follow-up of 6.2 years.)

Full exposure, preservation of soft tissues, correct placement of components ensures stability in primary total hip arthroplasty. The same principles apply to revisions where the first attempt produces best results.

Dislocation after revision of 2.9% and re-revision for dislocation of 2.1% has been achieved with the 22.225 mm head and angle-bore cup. Advantages of the low-frictional torque can be maintained and low rate of dislocation achieved, even in revision surgery, using a 22.225 mm diameter head and the angle-bore cup.