How to Delay That Knee Replacement

Patients with malalignment of the knee that leads to arthritis face some unique challenges. The alignment problems usually mean one side of the knee wears out faster than the other. They can't just have a knee replacement -- or even a unicompartmental procedure. Unicompartmental means just the side that's arthritic is replaced.

And why not? Because the cause of the arthritis is the way the bones fit together to form the knee. In most cases, there is too much pressure on the medial compartment (that's the side of the knee closest to the other knee). Replacing the joint (or the medial half of the joint) doesn't change the alignment issues. That's where a procedure called tibial osteotomy comes in handy.

In this operation, the surgeon removes a wedge- or pie-shaped piece of bone from one side of the tibia<>/i (lower leg bone). The purpose of the osteotomy is to correct the malalignment and take pressure off the medial compartment. There are two ways to do this surgery. Both remove bone from the upper tibia near the knee. The medical term for this type of osteotomy is high tibial osteotomy (HTO).

The first way to do the high tibial osteotomy is called a medial opening wedge tibial osteotomy. Bone is removed from the medial side of the tibia, shifting the weight off the medial compartment and more toward the midline. The two edges of remaining bone are held open with a metal plate or special device called a fixator.

The second method is a lateral closing wedge osteotomy. In this type of osteotomy, bone is taken from the lateral side of the tibia (side away from the other knee). The two edges of the bone are then allowed to shift closer together. The effect is the same as the opening wedge osteotomy: to take pressure off the damaged medial compartment.

There are advantages and disadvantages to each type of osteotomy. Many surgeons prefer the medial open wedge osteotomy because there's less chance of causing shortening of the leg and fewer complications with nerve injuries.

In this study, 106 medial opening wedge high-tibial osteotomies were done for patients who had malalignment leading to arthritis of the medial knee joint. The size of the osteotomy (determined by the amount of bone removed) depended on the overall condition of the knee.

For example, the surgeon looked at the other side of the knee during surgery to see what kind of arthritic changes might have been present there. Most of the time, they tried to correct the alignment to neutral but sometimes it was necessary to overcorrect, shifting weight past the middle to the other side.

The patients were active and interested in delaying joint replacement for as long as possible. In addition to the osteotomy, they also had a microfracture procedure. Microfracture involves drilling tiny holes in the damaged joint surface down to the first level of bone (subchondral bone). Blood seeping into the joint through the holes helps the healing process and aids in restoring joint cartilage.

Patients were followed for up to seven years after the surgery to see how well the knee held up and whether or not joint replacement was required. The term used to describe osteotomies that lasted and delayed the need for joint replacement was survivorship. Failure was defined as anyone who had a joint replacement after the microfracture and osteotomy procedures. The length of time to failure/time to joint replacement was also calculated.

They found that almost all the patients (97 per cent) were active and satisfied with the results five years later. Survivorship remained high (91 per cent) seven years later. Patients who had a failed result were those who had damage to the meniscus (knee joint cartilage) along with arthritic changes of the joint surface. Age and sex (male vs. female) did not seem to have any bearing on which osteotomies survived or failed.

There aren't too many studies looking at the results of microfracture with medial opening wedge high-tibial osteotomy for painful unicompartmental (medial) knee arthritis. The good-to-excellent survivorship reported in this study will be of interest to surgeons and their patients who want to avoid knee replacement due to activity level or personal preference.

Reference: 

William I. Sterett, MD, et al. Chondral Resurfacing and High Tibial Osteotomy in the Varus Knee. In The American Journal of Sports Medicine. July 2010. Vol. 38. No. 7. Pp. 1420-1424.

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