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Medial Compartment Knee Biomechanics

During normal daily activities, a load of two to four times body weight crosses the knee joint.  In the normal knee, approximately two-thirds of this load passes through the medial compartment.

The degree of varus (bowing) present in a knee joint is a combination of the geometric alignment of the femur and tibial (congenital), and the degree of narrowing in the medial compartment (due to loss of cartilage and/or bone), and/or widening of the other joint space compartments (due to ligament laxity or injury to other soft tissue structures).

These alterations in the joint alignment may result from injury, surgical removal of the medial meniscus and /or degenerative changes, and, if the knee is predisposed, will accelerate the development of arthritis of the medial knee joint. The greater the degree of varus alignment, the greater the load across the medial compartment and the greater the potential for the development of degenerative changes. 

The presence of medial compartment arthritis will further alter the knee alignment and redistribute the weight-bearing load to the affected compartment. This may accelerate the degenerative process, and cause pain.

Varus knee alignments in the presence of painful medial compartment arthritis have been treated by high tibial osteotomy orthopaedic surgical procedures, where the tibial is cut and re-aligned to help take weight off the medical compartment of the knee. Results as high as 80% satisfactory outcomes at 10 years post-op have been reported.

Complications include inadequate correction or recurrence of the varus deformity, osteonecrosis (bone death) of the proximal fragment and non-union of the fragments.  Delayed or non-union occurs in 1 - 3 % of patients and is treated by bone grafting or a repeat osteotomy.

If a high tibial osteotomy procedure fails, a subsequent total knee replacement is technically more difficult.  In one study of 45 knees, only half of such patients had an excellent result and 29% a good result. These results are roughly comparable to those of revision total knee surgery (when knee joint replacement surgery has to be re-done)

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