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Case of the Month - March 2020

Isolated knee arthritis (osteochondral defect) and bow leggedness (genu varum)

Case: 38 year old otherwise healthy and active female with symptomatic zone of arthritis (cartilage defect to the medial femoral condyle) after failed previous microfracture procedure by another surgeon. Continued pain after surgery. Diagnostic arthroscopy revealed large grade 4 (full-thickness) oblong cartilage defect with healthy opposing cartilage, intact medial meniscus and ligamentously stable knee. She was also in genu varum (bow legged) alignment putting more weight through her medial compartment compounding her problem. She underwent an osteochondral allograft transplant using cadaver tissue to treat her cartilage defect and simultaneous proximal tibial osteotomy to treat her bow leggedness. At 3 months post-op, near complete relief of symptoms that had been plaguing her for over 5 years!

Intraoperative photos from first stage diagnostic knee arthroscopy showing large cartilage defect of the medial femoral condyle.

Preoperative full length mechanical axis X-ray (left) showing genu varum alignment (bow leggedness). Because of this alignment, the patient put more of her weight through the symptomatic side of her knee causing pain even when walking. Symptoms improved with use of an unloader brace confirming her diagnosis. Measurements on X-ray (right) used in planning for the second stage surgery, which included osteotomy.

What is an Osteochondral Allograft (OCA)?

Articular cartilage is a unique tissue in our joints that is constantly subjected to stress and is very vulnerable to traumatic injury or degenerative conditions. This is especially true in large weight-bearing joints such as the knee. When someone has a localized area of a full thickness cartilage or a full thickness cartilage and bone defect, this represents a localized area of osteoarthritis. When there is no bone to minimal bone involvement, microfracture (poking holes into the bone to stimulate new cartilage formation) can work in some cases, however, the failure rate is high. In patients with large defects, or in defects involving the bone, a more effective treatment for the cartilage deficiency is a fresh osteoarticular allograft. These allografts are obtained from young donors who had the same size knee as the affected patient. While this procedure is not felt to be a cure for arthritis, many patients can achieve 10 years or more of significant symptom improvement with this surgery. In effect, this is a “biologic resurfacing” procedure and it is important to recognize that not all patients can return back to full impact activities after the surgery.

Second stage surgery showing large osteochondral allograft transplant from donor specimen (left) and simultaneously performed proximal tibial osteotomy to correct varus alignment (right)

What is a Proximal Tibial Osteotomy?

Proximal tibial osteotomies, also known as high tibial osteotomies, involve correcting bow-leggedness. This involves creating a surgical fracture on the medial (inside) aspect of the tibia (shin bone) and wedging it open to allow the leg alignment to swing over. A plate and screws are then used to hold it in place and bone graft is inserted into the opening created. In younger patients (under 50 years old), a proximal tibial osteotomy can allow patients to still participate in high-level activities, such as climbing, hiking, and hunting, without fear of having the metal and plastic from a knee replacement wear out. We certainly do not advocate that patients go back to high-impact activities, such as long distance running, because they run the risk of having their knee wear out sooner. It is generally felt that a medial meniscus transplant or cartilage resurfacing procedure are at greater risk of failure if the patient is bow-legged. Thus, a proximal tibial osteotomy either concurrently with or prior to a cartilage resurfacing procedure and/or meniscal transplant is sometimes indicated. Most patients reach their maximal improvement after an osteotomy, assuming that strength is regained, at about 6 months postoperatively. The outcomes of proximal tibial osteotomies in delaying the need for a total knee replacement are approximately 75% to 80% at 10 years with some studies reporting that 65% of patients up to 20 years having continued relief of their knee pain.

Three month postoperative X-rays showing complete healing of the osteochondral allograft and proximal tibial osteotomy site.

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