Minimally Invasive (MIS) Total Knee Replacement &
CAS – Computer Assisted Surgical Techniques

Better Mobility and Less Manipulation with MIS

Surgeons manipulated 2% of mini knees vs. 14% with standard total knee arthroplasty.

By Gina Brockenbrough
ORTHOPEDICS TODAY 2005; 25:8

June 2005

WASHINGTON — While previous research indicates minimally invasive procedures offer less operating time, hospitalization and pain, a new study also cites less stiffness and manipulation.

In a study examining the effect of patella eversion, researchers found that non-everting mini surgeries required 12% less manipulation compared to standard TKA. They also discovered better short-term postoperative motion in the mini group (P=<.05), researchers wrote in their abstract. “Stiffness is a problem after total knee replacement and that’s been seen in multiple different studies,” said Craig M. McAllister, MD, an orthopedist with the Evergreen Orthopedic Center in Kirkland, Washington. “And our traditional group basically experienced the same experiences as … these studies in terms of stiffness, pain and the need for manipulation,” he said during his presentation at the American Academy of Orthopaedic Surgeons 72nd Annual Meeting. The Evergreen Hospital and Stryker Orthopaedics supported the research.

McAllister performed all 200 consecutive total knees on osteoarthritis patients with similar demographics. Half of the patients received standard operations while the rest had minimally invasive surgery. The same implants were used in both groups. To decrease study bias, patients and staff were blinded to treatment.

MIS vs. Standard Operation

In the minimally invasive surgeries (MIS), the surgeons focused on preventing patella eversion. “We did not evert the patella, except when the knee was in extension and only loosely,” McAllister said. They also showed caution with tibial positioning. “If we did subluxate the tibia, it was only after the osteotomies and after soft tissue relaxation maneuvers,” he said. They were able to use smaller exposures by using downsized Duracon (Stryker Corp.) instruments and using the incision as a mobile window, McAllister said, who is also a Stryker consultant.

In the standard group, surgeons made traditional anterior cuts and performed medial para-patellar arthrotomies, McAllister said. They flexed knees during medial releases and used conventional Duracon instruments, he said.

“In order to accommodate these instruments, we did a medial patella eversion, putting the knee back into flexion,” McAllister said. Unlike mini procedures, surgeons often subluxated tibias, he said.

During all procedures, investigators verified gap balance. “We did a distal cut first technique,” McAllister said. “We used the balancer method to quantify the flexion and extension spaces in both the traditional and MIS groups,” he said. They assessed femoral component rotation, sizing and flexion gaps by adding an AP sizer to balancers. They then calculated gaps at 30-foot pounds of tension, he said. Post surgery, all patients received identical rehab and medication. Researchers also manipulated knees that did not flex 90° six to 12 weeks post-operation.

Motion, Manipulation

Investigators examined patients at two, six, 12, 24 and 52 weeks. They X-rayed participants at six weeks, six months and one-year postoperatively. At one year, researchers also assessed Lysholm and Knee Society scores, McAllister said. Unlike other studies evaluating MIS, the investigator in this study observed no increase in complications among the MIS patients.

Using standard AP and lateral X-rays, they noted no difference between the traditional MIS groups in component position other than 1° difference in tibial slope. Similar to other comparison studies, the MIS group also demonstrated less postoperative pain, shorter tourniquet time and smaller incisions.

McAllister emphasized that unlike other MIS reports, in this series very little attention was devoted to decreasing the incision size. The incision size decreased from 20 cm in the traditional group to 14 cm in the MIS group as a natural consequence of the MIS technique and downsized instruments.

The traditional group lost 8° of extension compared to only a 2° loss in the MIS group. A significant difference in extension persisted until six months postoperatively. A similar trend was seen in flexion. While the preoperative flexion was no different between the two groups, the traditional group lost more flexion than the MIS group. The traditional group took 52 weeks to regain their postoperative flexion, whereas the MIS group regained their preoperative flexion by three months.

Researchers noticed significant differences in manipulation rates. “Our manipulation rate dropped precipitously as we moved from a traditional to an MIS technique,” he said. Just 2% of the mini group needed manipulation compared to 14% of the standard cohort. “Manipulation after knee replacement is still a part of traditional total knee replacement surgery, but it must be considered a complication because it requires a return to the operating room,” McAllister said.

McAllister and colleagues believe that everting the patella, placing the patellar tendon on stretch, and leaving the extensor mechanism in this everted position for prolonged periods of time may contribute to soft tissue injury and to postoperative stiffness. This study shows that total knee replacement can be done safely and accurately without patellar eversion.

For More Information

McAllister CM, Stepanian J. Minimally invasive total knee replacement: The impact of patellar eversion on recovery. #72. Presented at the American Academy of Orthopaedic Surgeons 72nd Annual Meeting. Feb. 23-27, 2005. Washington.

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