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Improvements in Surgery for Unicompartmental Knee Osteoarthritis

Sometimes osteoarthritis of the knee only affects one side of the joint. When that happens, it's called unicompartmental knee arthritis. Although either side of the joint can be involved, the medial joint (side closest to the other knee) is affected most often.

Surgical treatment for this problem could be with a tibial osteotomy. During this procedure, the surgeon removes or adds a pie- or wedge-shaped piece of bone. The osteotomy may be an opening wedge tibial osteotomy or a closing wedge.

Open wedge is used to create distance between the two sides of the bone. The result is to shift the weight away from the side of the osteotomy. In an opening wedge osteotomy, the surgeon cuts though the tibia (lower leg bone) on the medial side and opens a wedge, adding a bit of bone graft to hold the wedge open. The bone graft is usually taken from pelvc bone. The bone graft is held in position with a metal plate or pins.

In a closing wedge osteotomy, the surgeon cuts though the tibia on the lateral side (side of the leg away from the other leg). A pie-shape or wedge of bone is removed. Pins or a metal plate and pins are used to close the open edges back together. Closed wedge collapses the two edges of bone, thus shifting the weight toward the side of the osteotomy.

In either procedure, care is taken to protect the nerves and blood vessels that travel across the knee joint. The surgeon uses either X-rays or a fluoroscope, a special kind of X-ray machine to make sure the wedge is the right size and is placed correctly.

There are pros and cons with either technique. The goal is to shift the mechanical weight-bearing load away from the medial joint line and move the weight distribution more toward the middle of the joint. The intended result is to decrease joint pain and improve function.

The authors share the result of their experience performing the tibial osteotomy procedure on patients over the years. When they first started doing tibial osteotomies, they used a horizontal cut just above the point at which the patellar tendon attaches to the tibia (lower leg bone).

But they noticed that with this technique, the patella (knee cap) slipped down too far. This condition is called patella baja. The patella acts as a fulcrum or lever for the quadriceps muscle during knee motion. Without good alignment after tibial osteotomy, the result can be compromised.

So, the surgeons switched to using an oblique (cut at an angle) osteotomy right at the level of the patellar tendon insertion. The hope was that the change in technique would provide a possible solution to the patella baja.

Before and after X-rays were used to compare the results between using the higher horizontal wedge cut and the lower angled osteotomy. Patellar height, slope of the tibia when viewed from the side, and the weight-bearing line seen on X-rays were used as measures of results.

A detailed description of each surgical procedure is provided along with schematic diagrams to show what was done. The effect on alignment was demonstrated using photographs of the X-rays. The postoperative films were taken at least one year after the surgery to get a better idea of the long-term results.

There was no difference between the two groups in terms of size of osteotomy needed to treat the unicompartmental osteoarthritis. Patient demographics were similar except for age. Demographics refer to age, sex, education, etc.).

The group having the oblique osteotomy was younger. By the time they switched from a horizontal cut to an oblique osteotomy, other things had changed in how patients with unicompartmental osteoarthritis were treated. Older, less active patients can now have a partial knee joint replacement. Just the worn down side is replaced. Younger, more active patients have the tibial osteotomy instead. The osteotomy preserves bone and makes it possible to have a unicompartmental joint replacement later if needed.

The surgeons found there were many advantages to the oblique osteotomy. Because the cut was made lower down on the tibia, there was less disruption of the patellar tendon. The patella was also less likely to slip down. And this approach prevented unintentional damage to the nearby nerves and blood vessels.

Some things in the knee alignment didn't improve with the change in location (lower) osteotomy. They speculate that using fluoroscopy to guide the surgery may help enhance their ability to correct angle deformities.

Loss of correction and delayed bone healing were two concerns after surgery. But the change in level of osteotomy didn't seem to result in either of these problems. Perhaps the younger age of patients having the oblique osteotomy was a factor. The authors weren't really sure the exact influence of age on final outcomes.

After all the X-ray measurements were taken of knee angles, alignment, and patellar position, it looks like the oblique tibial osteotomy with its lower angle is safer and more effective than the horizontal approach.

References: Wadith Y. Matar, MD, MSc, FRCSC, et al. Open Wedge High Tibial Osteotomy. In American Journal of Sports Medicine. April 2009. Vol. 37. No. 4. Pp. 735-742.

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