Better short-term knee function with lateral MIS

Early data on new technique shows great Knee Society scores but a highcomplication rate.

Issue: June 2005

A new lateral mini technique may provide less pain, better short-term results and quadriceps protection. But, researchers caution that, at this time, this total knee approach also carries a high complication rate.

In a comparison study of 77 knees, researchers found that 90% of lateral patients performed straight leg raises on the day of surgery vs. one-third of traditional TKA patients. “At the early time points, these [mini lateral knees] do much better,” said Michael A. Mont, MD, the director for joint preservation and reconstruction at the Rubin Institute for Advanced Orthopaedics, during his presentation at the American Academy of Orthopaedic Surgeons 72nd Annual Meeting.

At three-month follow-up, the lateral minimally invasive group demonstrated a mean objective Knee Society score of 97 points compared to 91 points in the standard cohort, Mont told Orthopedics Today. Six months after surgery, the Knee Society scores in both groups were similar, he said during his presentation. “Now, [this] sounds really good, but I’m going to tell you the picture is not all good, and I’m very cautious and selective about doing these procedures because we’ve had a number of complications.”

One lateral mini patient developed peroneal nerve palsy after a tibial device was placed in extension, Mont said. The case required revision and nerve decompression, the researchers wrote in their study. Another patient with a history of peroneal nerve palsy had the condition worsen after surgery. A third, 270-pound patient needed a revision when the tibial component loosened five months postoperatively. “Another patient has had recurrent effusions and is a laborer with Knee Society Scores fluctuating from 60 to 100 points,” researchers wrote in their study.

“So, I’m going to urge tremendous caution for anybody here trying these types of procedures,” Mont said. “We still have a lot to learn. We have a lot to develop.”

Surgical technique

The multicenter study compared 30 mini lateral knees (average patient age, 63) to 47 knees that received standard TKA. Researchers also used a third comparison group of mini medial TKA patients, they wrote in their study.

In the lateral group, surgeons made lateral incisions and cut through the iliotibial band, Mont said. In this quad-sparing technique, the initial incisions measure 8 cm and then expand to 10 cm to 11 cm at the end of surgery. Surgeons do not need to perform whole bone cuts at once.

“You can start your cuts, finish it up three-quarters, then … you use the bony platforms to finish your cuts,” Mont said.

The procedure offers minimal patella eversion. Surgeons used navigation in some cases, but it is not required, he said. The surgery is also performed without lateral releases and intramedullary guides, researchers wrote in their study.

“You just have to do a different way of doing a knee where you’re bending the knee, you’re flexing or extending the knee to expose different parts of the knee,” Mont said. Similar to other minimally invasive surgeries, the lateral operation uses downsized instruments, he said.

Preliminary outcomes

Postoperatively, 27 of the 30 lateral patients performed straight leg raises in the recovery room, Mont said. “Surgeons can do knee replacements without cutting much muscle or any muscle whatsoever,” Mont told Orthopedics Today. “So they’re almost back to full functional ability rather quickly.”

Results from peroneal nerve releases inspired the lateral minimally invasive procedure. Researchers noted that these patients did not report any postoperative pain. “Maybe the sensory afferents are different on the lateral side of the knee. They go home the same day. So why don’t we try incisions for knee replacements there?” Mont said.

They noted similar results with the lateral procedure. “In this approach, the patient is bending their knee with the front of the knee not affected: thus, there is no problem when you bend your knee and the incision is placed on the side of your knee,” researchers wrote in their study. The patients also reported less analgesic use, researchers wrote in their abstract.

In the standard group, one patient demonstrated a 90° range of motion and recurrent effusion occurred in another patient, three months after surgery. Mont noted that no complications occurred in the traditional TKA patients.

The lateral mini approach demonstrates a high complication rate and surgeons remain in the early part of the learning curve, Mont said. “The main thing that has to be done with all these techniques is get further refinements in instrumentation and surgical technique and perhaps modifications in prosthetic design, and that’s occurring with all of the companies right now,” he said.

Dr. Mont is a consultant to Stryker Howmedica Osteonics.

For more information:

Mont MA, Bezwada H, Ragland P, et al. Minimally invasive lateral approach to total knee arthroplasty. #71. Presented at the American Academy of Orthopaedic Surgeons 72nd Annual Meeting. Feb. 23-27, 2005. Washington.