Ankle arthroscopy, peroneal tendon inspections more effective

Study data presented by Patrick J. O’Neill, MD, at the recent Annual Summer Meeting of the American Orthopaedic Foot & Ankle Society (AOFAS), revealed that preoperative magnetic resonance imaging (MRI) may miss a substantial number of associated lesions in patients with chronic ankle instability.

Patients with lateral ankle ligament instability commonly have associated ankle pathology. The role of routine concurrent arthroscopy to assess the joint at the time of ligament reconstruction remains under debate, and the efficacy of using MRI as a proxy for intra-articular surgical examination is unclear.

“MRI is often used to identify lesions, and in the foot and ankle it is usually used to confirm suspected lesions,” Dr. O’Neill said.

The purpose of this study was to assess the accuracy of diagnostic MRI for identifying lesions around the ankle in patients with ankle instability warranting surgery.

Patient population
The retrospective study included 157 consecutive patients who received lateral ankle ligament reconstructions between 2003 and 2008. Patients with neuromuscular disease, revision procedures, or other major concomitant deformity correction, those with radiographic evidence of osteochondral lesions, and those unable to obtain an MRI due to insurance, timing, or claustrophobia were excluded, leaving 133 patients—95 females and 38 males, with a mean age of 29. All patients had surgery for lateral ankle ligament reconstruction and had received both a preoperative MRI and ankle arthroscopy. The MRIs were read by a radiologist and the attending foot and ankle surgeon.

“Most of the MRIs were read independently,” said Dr. O’Neill, “although that wasn’t a requirement of the study.”

MRIs lack sensitivity
Seventy-two associated lesions were found during 66 surgeries: 38 chondral injuries, 18 peroneus brevis tears, 7 loose bodies, 4 os trigonum injuries, 1 talar exostosis, 1 lateral malleolus stress fracture, 1 medial malleolus stress fracture, 1 posterior tibial tendon tear, and 1 impinging posterior talar process.

Comparison of MRI findings versus intraoperative findings revealed radiologists missed 61 percent of the chondral injuries, 44 percent of the brevis tears, 43 percent of loose bodies, and 29 percent of the other pathologies. Similarly, when surgeons read the MRIs, they missed 53 percent of the chondral injuries, 11 percent of the brevis tears, and 29 percent of the loose bodies (Table 1). MRI sensitivity for detecting any significant lesion was 65 percent.

“Superficial cartilage lesions won’t show up on MRI, and it may be difficult to see a more subtle tear in the peroneals,” Dr. O’Neill explained. “Physicians may still want to order an MRI for documentation or to identify other lesions, but it’s important to counsel patients that just because the preop MRI is negative, that doesn’t mean everything else is normal,” he added.

As a result, study findings support routine ankle arthroscopy and inspection of the peroneal tendons in patients undergoing ligament reconstruction for ankle instability (Fig. 1).

“Most experts recommend routine arthroscopy because the rate of associated lesions is high. The question of whether to address an asymptomatic lesion found on arthroscopy is unclear. Most surgeons, however, would likely treat a full-thickness cartilage lesion or a peroneal tear to prevent the possibility of surgery down the road,” Dr. O’Neill said.

Additional authors of “Comparison of Operative Findings and Preoperative MRI in Patients with Ankle Instability” include Scott E. Van Aman, MD, and Gregory P. Guyton, MD.

Dr. Guyton reports no conflicts of interest; disclosure information for Drs. O’Neill and Van Aman is not available.

Maureen Leahy is assistant managing editor for AAOS Now. She can be reached at leahy@aaos.org