Minimally Invasive THA: Where Are We Now and Where Are We Heading?

Commentary Total hip arthroplasty (THA) is a well-documented and highly successful surgical procedure. Minimally invasive (MIS) THA was developed to improve early functional outcomes of THA by minimizing soft-tissue damage during surgery. What was known about MIS THA before the current study? First, the MIS approach may lead to very modest early functional advantages that typically last for only a few weeks after surgery1. Second, an increased risk of early postoperative complications has been reported after MIS THA2. Third, the impact of the MIS approach on the long-term outcome and implant survivorship after THA is not known. The aim of this study was to address these unanswered questions. Stevenson et al. launched a prospective randomized controlled trial (RCT) in 2003 to assess whether MIS THA through a posterior approach would improve functional outcomes as compared with those of a standard posterior approach3. Their initial study was planned and powered to be a superiority trial with the hypothesis that MIS THA would result in lower blood loss and less postoperative pain and would allow earlier mobilization and discharge from the hospital with no increase in the rate of intraoperative or early postoperative complications. The results of the original study showed that MIS THA performed through a single-incision posterior approach by a high-volume hip surgeon is a safe and reproducible procedure. However, it did not result in any early benefits in terms of functional outcome, early walking ability, or length of hospital stay. The current study was of the 10-year clinical and radiographic outcomes as well as the long-term implant survivorship in the same patient cohort. The authors did not find any significant differences in any of the above-mentioned outcome measures between THAs performed through an MIS posterior approach and those done through a standard posterior approach. It must be noted that the results of the study can be generalized only to patients operated on through the posterior approach. Furthermore, the results clearly represent a best-case scenario; similar good long-term outcomes may not be achieved by lower-volume surgeons. It also seems obvious that this study was underpowered to reveal any clinically relevant differences in the long-term implant survivorship. However, it is evident that the MIS posterior approach with a predetermined short (≤10-cm) skin incision does not provide any benefits over the standard approach in either the short or the long term. There is still heterogeneity in the literature on MIS THA approaches and their effect on clinical outcome. In a recent RCT, Greidanus et al. found no differences in clinical outcome among MIS anterior, posterior, and direct lateral approaches at 2 years postoperatively4. More research is still warranted to assess both cost-effectiveness and long-term implant survivorship of the MIS anterior approach compared with other commonly used approaches. Cost-effectiveness should be addressed with a sufficiently powered RCT, whereas nationwide arthroplasty registers will most probably play a big role settling the issue of long-term implant survivorship5. As the authors highlight in the discussion, patients’ top priorities are a long-lasting joint replacement and a low complication rate. Many of the claimed benefits of MIS THA, such as earlier mobilization without restrictions as well as accelerated recovery and discharge, have already been reached with fast-track-type protocols irrespective of the incision used. As surgeons, we should thus concentrate on using well-documented implants, optimizing component positioning, and using atraumatic surgical technique. In the big picture, the length of the skin incision is certainly peripheral. The bottom line here is that we should use common sense and apply the smallest possible incision—rather than a predetermined maximal length of skin incision—that allows easy visualization and implant insertion and causes the least possible surgical trauma to the patient.