Knee Deformities

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Osteochondromas in the upper fibula may lead to a valgus knee deformity (knock knees). To correct this, we will perform an osteotomy of the tibia. The osteochondroma often tethers or envelops the peroneal nerve. The peroneal nerve is very important and is responsible for controlling the muscles of the foot. Injury to the peroneal nerve results in foot drop (inability to pull up the foot). In order to safely perform the tibial osteotomy, we must first decompress the peroneal nerve around the neck of the fibula.

Once the peroneal nerve has been safely accounted for, we can remove the osteochondroma and perform the osteotomy. If the upper growth plate of the fibula is damaged beyond recovery, we will remove a segment of fibula so that the two ends do not reconnect and re-tether to the tibia.

The valgus deformity can be corrected either acutely (all at once) or gradually. Acute correction involves the removal of a wedge-shaped piece of bone and closing of the wedge to straighten the tibia. This alignment is then fixed in place with a metal plate or an external fixator.

There are two approaches to gradual correction: external fixation and hemi-epiphysiodesis. An external fixator can be used to gradually straighten the tibia. An osteotomy of the tibia is performed and a specialized external fixator, the Taylor spatial frame (TSF) is applied. The TSF slowly corrects the deformity by moving the severed bones into place. The advantage of this technique is that the TSF can lengthen the bone simultaneous with three-dimensional correction. This is the preferred correction technique for patients who have a limb length discrepancy.

Another method of gradual correction is a hemi-epiphysiodesis. This is the least invasive technique, however, it can only be performed on younger patients who have not yet reached skeletal maturity. The procedure involves the insertion of small metal staples to one side of the growth plate of the upper tibia. This impedes growth on that side but allows growth on the other side. This will induce a slow correction as the patient grows. This is a very slow process and may take several years. Once the tibia is aligned, the staples can be removed and normal growth will resume. This method does not result in increased bone length; therefore the TSF is preferred in patients who have a limb length discrepancy.

Patients with MHE may also have a knee flexion deformity. This is caused by osteochondromas tethering the soft tissues surrounding the knee joint. This causes the knee to “catch” and reduces the range of motion (ROM). We correct this by removing the osteochondromas and lengthening the hamstrings tendons.