Hip arthroplasty – All problems solved or still place for improvement?

Total hip arthroplasty was popularised by Sir Charnley since the late 1950s of the last century. Over the following decades, some evolutions had been made, one of them regarding the implant fixation, leading to a high rate of cementless implants since the 1970s. Today, in Germany and central Europe, the majority of total hips are fixed cementless. Another evolution was the increasing size of femoral heads, so that a 22 mm large head is only used in very small cup sizes these days in Europe. By this increasing head diameter, the problem of hip instability and dislocation could be reduced to numbers of less than 2–5%. Another part of improvement was related to the approach. By introducing different minimal invasive approaches, muscle damage became less and recovery faster.

With all those innovations, hip arthroplasty became extremely successful over the last years. For example, comparing total hips and total knees, hips deliver a far higher number of very happy patients; however, there are still some percentages for improvements left. The revision rate within the first year in Germany, for example, is still 4%. The reasons for early and for late revision are multiple. While predominantly infection and luxation are early failure modes, polyethylene wear and loosening are late failure reasons. Minor forms of instability may not lead to a complete luxation; however, it can lead to a bony or implant related impingement syndrome. This can finally accelerate polyethylene wear and by that loosening. Relevant parameters for hip biomechanics and by that also for a good clinical and functional outcome are leg length, lateral and posterior offset, cup and stem position. An increased inclination angle of the cup, as well as changes of the anteversion can cause instability from the cup side. Therefore, Lewinnek defined the safe zone as goal for cup placement. Various studies could show that this zone is only reached in 26–57% of cases. An insufficient restoration of the lateral offset as well of the leg length can induce instability from the stem side. However, the overall offset is influenced by the cup position too.

The individual anatomy of the proximal femur can be influenced by the various hip pathologies (e.g. dysplasia, other secondary arthritis forms), also by previous surgeries and ethnic origin. It could be shown that pre-op planning and templating is mandatory to restore the anatomy. In these days, planning should be performed on digital X-rays (Fig. 1).