CT scans superior to radiographs for assessing hindfoot arthrodesis

Poor images hurt predictions of clinical outcomes.

A radiograph of the hindfoot showing the subtalar joint. The orthopedist read it as fused. The radiologist read it as 100% healed.

A coronal CT scan of the posterior facet of the subtalar joint. The radiologist read it as 59% healed.

COURTESY JERRY GRIMES

Radiographs have traditionally been the preferred means of assessing bone healing and fusion following foot and ankle surgery. However, a recent study showed a tenuous connection between the clinical and radiographic results of hindfoot arthrodesis surgery.

Jerry Speight Grimes, MD, and his co-authors, Michael J. Coughlin, MD, and Carroll Jones, MD, did a prospective one-year study involving 15 patients who underwent hindfoot fusion and then compared radiographs to CT scans in evaluating fusion results.

The researchers selected six patients who had undergone subtalar arthrodesis and nine who had triple arthrodesis and prospectively evaluated the patients with the preoperative AOFAS ankle and hindfoot scale, Visual Analog Scale pain Scale, SF-12 and body mass index.

The surgeries involved identical exposure and internal fixation. Surgeons used autografts from the ipsilateral tibia; all patients wore nonweight-bearing casts for six weeks and weight-bearing casts for six more weeks after surgery, Grimes said. Surgeons took anterior/posterior, lateral and Broden radiographs at three, six, 12 and 24 weeks after surgery. They took axial and coronal CT scans at six, 12 and 24 weeks. An objective, certified radiologist read the X-rays and CT scans, he said.

The researchers then measured healing of the calcaneocuboid, talonavicular, sinus tarsi, middle and posterior facets of the subtalar joint. Metal components obscured portions of the joint on radiography. Thus, researchers did not use the obscured joint surfaces to determine the percentage of arthrodesis achieved. However, they considered bridging trabeculae as evidence of arthrodesis.

Patients took AOFAS, VAS and SF-12 surveys six months after surgery. A six-month CT scan showed that the percentage of the joint fused across the posterior facet of the subtalar joint ranged from 40 to 97%, Grimes said.

“There appeared to be no correlation between the plain films and the CT scan data,” he said.

Researchers compared the clinical results of AOFAS, VAS and SF-12 scores to the percentage of arthrodesis shown on CT scans, Grimes said, in his presentation at the American Orthopaedic Foot and Ankle Society 21st Annual Summer Meeting in Boston. “Clinical results appeared to be independent of radiographic results.”

For more information:

Coughlin M.J., Jones C., Grimes J.S. Comparison of radiographs and CT scans in evaluating healing of hindfoot arthrodesis. Presented at the American Orthopaedic Foot and Ankle Society 21st Annual Summer Meeting. July 14-17, 2005. Boston.