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Prognosis for Coxa Vara After Surgery

Posted on: 09/18/2008
The angle of the femur (thigh bone) as it supports the femoral head in the hip socket is important. If there's too much (or not enough) angulation in one direction or another, it can cause a problem in the growing child. Coxa vara is one of these problems and the subject of this study.

The normal femoral neck angle is about 150 degrees at birth. As the bones grow and develop, the shape changes. By the time we are adults, this angle is about 125 degrees. Less than 110-degrees creates this condition of coxa vara.

Congenital (present at birth) coxa vara is often seen in children who have other deformities or congenital conditions. In this study, children with osteochondrodysplasia (including coxa vara) were treated surgically. Osteochondrodysplasia is a general term for a disorder in the development (dysplasia) of bone (osteo) and cartilage (chondro).

The purpose of the study was to see what kind of results are possible after surgery to correct the hip deformity. Children from age four to 13 were followed for up to 24 years. At first, the authors used arthrography under general anesthesia to assess the hip, especially the cartilaginous structures.

An arthrogram is a series of X-rays of a joint after injection of a dye. A special X-ray called fluoroscopy is used to guide the needle into the correct place in the joint. The joint can be seen from many angles in real time using this method. Early in the study, they realized that arthrograms were not necessary. Only plain X-rays were needed to measure femoral neck angles.

There were two groups of patients based on the condition of the bone and cartilage. Group one had coxa vara with a nonintact epiphysis (round femoral head). The femoral head was fragmented in pieces and had not ossified or solidified into one smooth, round bony structure.

This condition was referred to as coxa vara with fragmented or nonossifying epiphysis. It is the result of a genetic mutation affecting collagen. Collagen is the basic building block of soft tissue and bone structures. The children with this type of disorder often have severe deformities of the spine and limbs. Their growth is delayed or stunted.

Group two had coxa vara but with a normally shaped and developed femoral head. Group two (hips with a regular epiphysis or femoral head) was further classified into two separate subgroups (IIa and IIb) based on the exact location of the angular deformity.

The actual surgical procedure done varied depending on the deformity present. The goal of surgery was to stop slippage of the growth plate, improve hip motion, and reduce pain. Limping or other abnormalities when standing and walking were also addressed.

The most common surgical procedure was an osteotomy. A wedge- or pie-shaped piece of bone was removed. It may be reinserted on the other side to further change the angulation. In a few cases, the osteotomy was accompanied by a derotation procedure.

In those patients, the femur was actually twisted or turned during surgery to further improve angulation and hip stability. There were patients with other osteochondrodysplasia deformities requiring additional surgeries.

Everyone was placed in a spica cast for six to eight weeks. This type of cast goes from the waist down to the toes on the involved side and from the waist down to just above the knee on the uninvolved side. Sometimes, bilateral coxa vara is present requiring surgery on both hips and a full spica cast on both sides.

The results of surgery for group one with fragmented or nonossifying femoral head were very poor. This was especially true for children operated on early (age four). The patients in this group ended up with hip pain and stiffness. Despite improved femoral head and neck angles, joint motion throughout the entire range was not improved. Degenerative arthritis requiring joint replacement was common in the early adult years for this group.

Group two (subgroup IIa) had quite a few cases (60 per cent) of recurrence. The authors suggest this might be caused by the young age of the children at the time of surgery. With so much growth still remaining, the hip could not be kept stable. Over time, some children in this group also developed a leg-length difference.

Children in subgroup IIb had better results because the deformity was mild-to-moderate and didn't require surgery. When surgery was done in this group, the results were good with lasting benefits.

Overall, recurrence of hip instability after reconstructive surgery for coxa vara linked with osteochondrodysplasia was common. In this study, the prognosis for most patients did not change with treatment. This was especially true when surgery was performed at a young age (before growth is complete).

Surgeons are encouraged to delay surgery until an HEA is greater than 60 degrees. HEA refers to a measurement made on X-rays called the Hilgenreiner epiphyseal angle. The authors also suggested that bracing to hold the hips in place may be helpful until surgery is done. This type of treatment was not done in their patients.

Bracing may make it possible to change mechanical and anatomic factors affecting the hip. Placing stress and strain on the skeleton with special immobilizers and/or braces may help stabilize the femoral head before surgery. More studies are needed to clarify this.

References:
Moez Trigui, MD, et al. Coxa Vara in Chondrodysplasia. In Journal of Pediatric Orthopaedics. September 2008. Vol. 28. No. 6. Pp. 599-606.

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