The assessment of Charnley acetabular cup malposition.

Technical errors are the commonest cause of dislocation of hip prostheses (Hamblen 1984). An excessively anteverted or retroverted acetabular component is often responsible. The deleterious effects of such malposition have been documented by Ackland, Bourne and Uhthoff (1986), Fackler and Poss (1980) and Lewinnek et ab (1978). These workers were abbe to measure anteversion or retroversion by utilising the marginal wire markers in the prostheses they studied. Unfortunately, the Charnley backwards ; in fact it is more distorted than in Figure 1, so the cup is not retroverted. The third radiograph is taken with the X-ray tube angulated 20#{176} towards the patient’s feet. Figure 3 shows a more hemispherical appearance of the wire marker indicating an excessively anteverted position of the cup. Discussion. The information obtained from this technique can be used to anticipate early postoperative dislocation and to manage later recurrent dislocation. If an early