Minimally invasive total knee arthroplasty compared with traditional total knee arthroplasty. Assessment of the learning curve and the postoperative recuperative period.

BACKGROUND: There is disagreement about whether so-called minimally invasive approaches result in faster recovery following total knee arthroplasty. It is also unknown whether patients are exposed to excess risk during the surgeon's learning curve. We hypothesized that a minimally invasive quadriceps-sparing approach to total knee arthroplasty would allow earlier clinical recovery but would require longer operative times and compromise component alignment during the learning period compared with a traditional medial parapatellar approach.

METHODS: The first 100 minimally invasive total knee arthroplasties done by a single high-volume arthroplasty surgeon were compared with his previous fifty procedures performed through a medial parapatellar approach, with respect to operative times, implant alignment, and clinical outcomes. Radiographic end points and operative times for the minimally invasive group were evaluated against increasing surgical experience, in order to characterize the learning curve.

RESULTS: Overall, the minimally invasive approach took significantly longer to perform, on the average, than a medial parapatellar approach (86.3 and 78.9 minutes, respectively; p=0.01); this was the result of especially long operative times in the first twenty-five patients in the minimally invasive group (mean, 102.5 minutes). After the first twenty-five minimally invasive operations, no significant difference in the operative times was detected between the groups. The first twenty-five minimally invasive procedures had significantly less patellar resection accuracy (p<0.001) and significantly more patellar tilt than the last twenty-five (p=0.006). Other end points for implant alignment, including the frequency of radiographic outliers, were not different between the minimally invasive and traditional groups. The patients who had the minimally invasive approach demonstrated significantly better clinical outcomes with respect to the length of hospital stay (p<0.0001), need for inpatient rehabilitation after discharge (p<0.001), narcotic usage at two and six weeks postoperatively (p=0.001 and p=0.01, respectively), and the need for assistive devices to walk at two weeks postoperatively (p=0.025).

CONCLUSIONS: A quadriceps-sparing minimally invasive approach seems to facilitate recovery, but a substantial learning curve (fifty procedures in the hands of a high-volume arthroplasty surgeon) may be required. If this experience is typical, the learning curve may be unacceptably long for a low-volume arthroplasty surgeon.