Is there a new learning curve with transition to a new resurfacing system?

Metal-on-metal hip resurfacing has been proven to be a successful option for treating hip osteoarthritis in young, active patients. However, compared to a standard primary hip arthroplasty, hip resurfacing has a higher degree of technical difficulty. While all resurfacing systems utilize similar principles, there can be some variation in surgical technique. The purpose of this study was to determine if there was a second learning curve when a surgeon transitioned from one hip resurfacing system to another.

In 2007, the senior investigator (MAM) transitioned from using one resurfacing system for a majority of his patients to a different system. The records of 200 resurfacings were reviewed, including the last 150 patients who underwent this procedure prior to the switch, and who were then compared with the first 50 patients using a newer system. The mean age and mean body mass index (BMI) of the patients in the prior 150-patient group was 53 years and 28 kg/m2, respectively, compared to a mean age of 51 years and a mean BMI of 29 kg/m2 in the newer system group. The mean follow-up for the prior 150 patients was 45 months (range, 40 to 50 months), compared to 31 months (range, 25 to 37 months) for the first 50 receiving the new system. Clinical survivorship and complications were monitored, and clinical outcomes were evaluated using Harris hip scores.

The implant survival rate of the last 150 patients regarding the first resurfacing system was 97.3 (146/150), compared to 100% survival with the second system. The mean Harris hip score improved from 61 points (range, 40 to 76 points) to 93 points (range, 50 to 100 points) in the first group and from 52 points (range, 31 to 83 points) to 97 points (range, 86 to 100 points) in the latter group. There were four revisions: three for femoral neck fractures and one for unexplained groin pain; two revisions were in the postoperative period, and one was 1-year postoperative and the other 2-years postoperative. Of these four revisions, all had femoral component sizes smaller than 48 mm and were revised to total hip arthroplasty; all are doing well at the most recent follow-up (Harris hip scores greater than 80 points).

This study illustrates that there is no additional learning curve when transitioning from one re-surfacing system to another for an experienced surgeon. It also reinforces the previously established criteria that only well-selected patients should have a hip resurfacing arthroplasty performed in order to minimize the likelihood of postoperative complications such as femoral neck fracture. The learning curve appears to be a phenomenon that only occurs once for resurfacing and is not related to the specific implant manufacturer, but rather to the nature of the operation itself.