This prospective randomized multicenter trial from five European sites compares the clinical and radiographic outcomes of total knee arthroplasty, utilizing two separate techniques. This study is registered on ClinicalTrials.gov (NCT00853398) and is sponsored by Smith and Nephew (Memphis, Tennessee) for evaluation of the Genesis II minimally invasive total knee system. For this study, a minimally invasive approach was defined by an incision of <15 cm with use of instrumentation specifically designed for minimally invasive surgery. A standard technique was defined by separate instrumentation and an incision of >15 cm.
Clinical outcomes for both the minimally invasive and standard cohorts were determined with use of Knee Society scores and visual analog pain scores. Radiographic measurements included coronal and sagittal alignment measurements as well as a mechanical axis measurement. This study was originally designed to include two years of follow-up, but the authors terminated the study after one year, citing no expected change in outcomes after an additional year.
The authors were unable to show a statistical difference between the two techniques in any utilized measurement of outcome. All clinical evaluations followed the expected course, improving with time postoperatively. Mean radiographic measurements were also reassuring, with both cohorts reporting appropriate implant positioning. The minimally invasive technique was associated with an average increase in surgical time of 5.6 minutes and a mean of only 17 mL less blood loss than that associated with standard techniques. There were seven adverse events in each group.
This study was underpowered, resulting in a greater than 20% probability that their resulting conclusion (i.e., that there was no difference in the results between these two techniques) represents a type-II error. The authors did not perform a pre-enrollment calculation to determine the appropriate sample size. Recalculation of the sample size on the basis of the observed outcomes suggests that they would need more than twice the number of enrolled patients per group for adequate statistical power to draw the conclusions that they did, though it is unlikely that a difference would be determined even with the necessary numbers. Also, other quality-of-life outcomes, including length of hospital stay, total narcotic usage, and inpatient rehabilitation requirements, were not addressed.
This study confirms previous reports that similar, if not equal, results can be obtained with either technique for total knee arthroplasty1. Although this study was industry sponsored, there appears to be minimal financial gain for Smith and Nephew with these outcomes. Certainly, the initial excitement of minimally invasive techniques continues to fade as priority is appropriately being placed on implant position and patient outcomes instead of incision length. This study also confirms that blood loss may be related more to a surgeon's technique below the incision as opposed to the length of the incision itself. Patients with a body mass index of >35 kg/m2 were excluded from this study; the performance of a minimally invasive procedure on such patients would certainly have been difficult.
It is reassuring to note that both groups had excellent alignment on mean radiographic evaluation, confirming an improvement in minimally invasive techniques from some earlier reports2. Neither technique in this study involved computer navigation, which is certainly being advocated by program developers more than by orthopaedic surgeons. We will have to decide if navigation systems are a good use of health-care dollars, and clinical outcomes similar to those presented in this study should justify our answer—one way or the other. The authors make an excellent concluding statement in advising surgeons to carefully weigh the theoretical advantages of minimally invasive surgery against those of standard techniques before deciding on an appropriate technique—essentially substantiating the use of an appropriate-length incision and appropriate instrumentation to perform a well-placed total knee arthroplasty.