Suspended-leg technique may help surgeons better perform MIS total kneereplacement

At three years, results proved comparable to those attained with standardand other MIS approaches.

Issue: June 2005

In response to the growing trend toward minimally invasive knee replacements, surgeons have developed a suspended-leg minimally invasive total knee arthroplasty technique and produced similar results to standard and other less invasive approaches.

The new technique capitalizes on the gravitational effects from suspending the leg to achieve good joint distraction, they said.

“The results appear to be similar to our standard or to our minimally invasive (MIS) approaches without any significant increase in morbidity, so it might be a viable approach,” said Peter M. Bonutti, MD, director of the Bonutti Clinic in Effingham, Ill.

He presented three-year results from a small study involving patients treated with the technique at the American Academy of Orthopaedic Surgeons 72nd Annual Meeting. Those patients’ results were compared to those of two other groups of patients: ones whose total knee replacements (TKR) were done standardly and another group operated on with MIS TKR techniques.

Minimally invasive TKR

The suspended leg MIS total knee replacement technique studied uses downsized incisions and instruments. It allows gravity to gradually open up the knee joint for good distraction.

Courtesy of Peter M. Bonutti

For the suspended-leg TKR, surgeons hung the patient’s leg in a bolster or holder with the hip in slight hyperflexion. “Gravity distracts the joint to stretch out the soft tissues, so it allows body weight to open the knee up and the skin and tissue are stretched and moved by progressively flexing and hanging and extending the joint,” Bonutti said. Investigators developed a special aseptic draping system for these procedures, which created what he described as a “mobile sterile field.” The surgeon was draped to the patient and to the assistant, which Bonutti said was effective.

Surgeons incorporated MIS TKR features into the new technique, which were downsized incisions (less than 12 cm), smaller instruments, and using a 2 cm vastus medialis origin (VMO) snip and other quadriceps sparing techniques. They did not evert the patella.

They made their bone cuts in such as way as to avoid dislocating the tibiofemoral joint in the process and used symbiotic retractors to improve exposure, according to Bonutti. “You make your cuts first and then slide the tibia against the femur so each bone cut opens up the next space.”

Gentle to soft tissues

Intraoperatively, surgeons rocked the patient’s knee joint back and forth on the edge of the operating table with the trial implant in place in a rocker test. This helped them determine how much soft tissue balancing was needed based on the status of the collateral ligaments.

“You can perform this MIS technique without any undue trauma to the VMO and to the soft tissue if you progressively extend and flex the joints,” he said.

In the comparative study, investigators tried to directly match the 16 patients (20 TKRs) across the three surgical groups, according to age, type of implant and rehabilitation, keeping the surgical technique used relatively consistent within each group. They also limited the hospitalization length of stay to about four days, which was fairly standard for 2001 and 2002, when the surgeries were done.

Rapid functional return

When they analyzed the three groups, most surgical elements such as tourniquet time, blood loss and range of motion were highly similar, as were the pre- and postop Knee Society scores. A few patients in each group, however, needed a lateral release; there was one manipulation in each group.

The main difference: functional return. “By two weeks in the standard group, 65% of patients were still using a walker, but in the MIS and the MIS suspended leg [group] a much lower percentage used a walker. And what was really interesting is the independent ambulation, again in my hands, was quicker with the suspended leg and MIS approaches. So clearly the results appear to be similar in all groups — clinical, radiographic, complications … and the MIS techniques may have had a faster recovery. … Clearly, we need more evaluation.”

For more information:

Bonutti PM, McMahon M, Mont MA. The use of the suspended leg minimally invasive technique for total knee arthroplasty. #73. Presented at the American Academy of Orthopaedic Surgeons 72nd Annual Meeting. Feb. 23-27, 2005. Washington.