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Minimally invasive TKA: Surgeons debate whether it is helpful or a hindrance
Benefits of less pain and quick recovery may be offset by malrotations and possible loosening.
While proponents of minimally invasive total knee arthroplasty tout the advantages of rapid recovery and less postoperative pain, others cite increased surgical difficulty.
"Patients with MIS have less pain, get their motion back faster [and] get [back to] their activities more rapidly," Richard S. Laskin, MD, said during a debate at the 23rd Annual Current Concepts in Joint Replacement Winter 2006 Meeting. "We've shown that we can do it with good positioning of the implants and good balancing and really not extend the surgical time."
In a study comparing patients who underwent MIS total knee arthroplasty (TKA) with those who received conventional arthroplasty, Laskin found that the MIS-treated group required less medication during hospitalization and only a few additional minutes of tourniquet time.
Another study also revealed a faster return to function after MIS, but no significant difference in blood loss, he said.
"We found no decrease in blood loss, because I think it has nothing to do with the capsular incision and so on," Laskin noted. "I think that the blood loss is from the bone cuts and the pin holes."
Postoperative examinations for knee stability and patient X-rays showed no significant differences in outliers or tibial component malpositioning with MIS compared to conventional TKA.
"[We have] excellent knee scores at 2 years, and we're now up to 4 years looking at these [with] excellent stability in these groups," Laskin said.
More good findings
The results of a soon-to-be published prospective study also indicate good results with the procedure, he said. During a 2-year follow-up of 200 patients who underwent either TKA with patella eversion or mini midvastus TKA without eversion, Laskin found that significantly more patients in the everted group had patella baja.
"Everting the patella the way most people do it on a standard incision increases the prevalence of patella baja," Laskin said. "And more importantly than just having patella baja is what patella baja causes. Patella baja has a direct correlation with decreased flexion postop, and I think that's what MIS has taught us. We don't have to flip the patella."
He also cited recent research from Japan. Investigators there found that MIS-treated patients had a more rapid return of quadriceps muscle strength and a faster postoperative walking cadence.
No long-term advantages yet
Laskin said he found no long-term benefit of MIS over conventional TKA in his patients.
"After a year in our study, they looked the same," he said. "But, the [MIS] patients got there with less pain and more rapid return [of function]."
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Image: Laskin R |
While some may counter that longer follow-up on MIS-treated patients will reveal higher failure rates, Laskin said that this assumption is unwarranted.
"TKRs fail because the implants are malpositioned, knees are not balanced, patients get infected or the polyethylene wears out," he said. "In our published studies, they weren't malpositioned, they were balanced, they didn't get infected and we used the same implant for other operations as well, so there is no reason to think it should fail in an MIS situation."
More revisions
Yet, some surgeons contend that MIS TKA can create more surgical difficulties.
"The credo of all doctors is 'primum non nocere', which means first, do no harm," countered Hugh U. Cameron, MBChB, FRCS.
"So, do [minimally invasive surgery] if you can, but caveat emptor — that means let the buyer beware." Cameron said that many of the problems with MIS stem from a combination of minor errors, which typically result in malrotations and maltranslations. Surgeons may encounter an outward-facing foot, which is a sign of tibial torsion.
"If there's more than 35° of external tibial torsion, it should be corrected by a derotation osteotomy above the level of the tibial tubercle prior to a total knee replacement," Cameron said. "An osteotomy done at the time of total knee replacement risks avascular necrosis, nonunion and stiffness of the knee."
In cases with less than 35° of tibial torsion, an osteotomy is not required and surgeons can leave up to 15° of torsion. "You must use a high central post knee and, under no circumstances in these cases, should you use a rotating platform knee," Cameron said. He warned that using a cruciate-retaining implant can lead to dislocation.
Lateral ligament releases
Surgeons performing minimally invasive surgery may also have difficulty with extensive lateral ligament releases best done by releasing the lateral epicondyle. In cases where there is an intact proximal periosteum, screw refixation may not be necessary, Cameron pointed out. Surgeons should use a high central-post knee as an internal splint while healing occurs. "I have at least 2 nonunions, but that doesn't seem to bother the patient," he said.
Cameron noted that uncorrected tibial torsion cannot be radiologically diagnosed and that physicians must examine the entire leg — not just the knee — to identify the condition. Many cases also require revision, which is may be difficult.
"Iatrogenic tibial torsion is due to the pull of the patella tendon," Cameron said. "During exposure, the tibia will rotate. If you don't recognize that, the tibial component will be placed in internal rotation and you have the same problem. This is potentially a problem with MIS. A revision is often fairly easy, but the ligaments may have tightened up."
Valgus knees
Valgus knees can also present problems when treated with MIS TKA. Many have dysplasia of the lateral femoral condyle. The entry points using intramedullary guidance systems is medial. Inserting the rod centrally can create a valgus femoral component.
The posterior reference will also internally rotate the implant. Therefore, surgeons must use Whiteside's line, he said. "If you put the component in an internal rotation, it results in patella maltracking leading to edge wear and even dislocation," Cameron said. "This is not a patella tracking problem; this is a femoral rotation problem."
Taken together, the tiny mistakes can have a huge impact.
"It's often quite difficult to see these minor problems, and I don't think that doing it through a key hole makes it any easier," Cameron said. "Perhaps if you just opened the door the first time, there wouldn't be so many revisions to do."
MIS may exacerbate the existing problems of conventional TKA, such as loosening and wear, Cameron said. "In fact, the loosening rate's liable to go up because stems can't be used on the tibia, polyethylene wear might go up because of edge loading, and infection may go up because of tissue trauma," he said.
For more information:
- Cameron H. The MIS TKA: Bopkis (of little or no value) — Affirms. #77. Laskin R. The MIS TKA: Bopkis (of little or no value) — Opposes. #78. Both presented in Session XVII, Orthopaedic Crossfire III: Controversies in knee arthroplasty at the 23rd Annual Current Concepts in Joint Replacement Winter 2006 Meeting. Dec. 13-16, 2006. Orlando, Fla.
- Hugh U. Cameron, MBChB, FRCS, Sunnybrook Health Sciences Centre, Holland Orthopedic & Arthritic Centre, 43 Wellesley Street East, Suite 318, Toronto, ON, M4Y 1H1; 416-967-8734; hugh.cameron@sunnybrook.ca. He receives teaching and speaking funding from DePuy, a Johnson & Johnson Company. Richard S. Laskin, MD, Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021; 212-606-1041; laskinr@hss.edu. He receives consulting, membership on advisory committee or review panels and teaching and speaking funding from Smith& Nephew Orthopedics.