A Swiss study of obese patients who underwent total ankle replacement (TAR) found that survivorship of prosthesis components at midterm follow-up was comparable to results obtained in nonobese patients. The investigators also observed that approximately 12 percent of the patients had lost weight 1 year after surgery.

These findings were reported in a paper by Alexej Barg, MD, and associates, which was presented at the 2011 annual meeting of the American Orthopaedic Foot & Ankle Society. The paper won the International Federation of Foot and Ankle Societies award for best clinical study.

Obesity has been linked to poor outcomes after total knee or hip replacement, but no data are available for TAR in overweight patients. This study also sought to determine intra- and perioperative complication rates and midterm functional outcomes (range of motion and patient satisfaction).

Study description
A single surgeon performed 123 TAR procedures in 118 obese patients (body mass index [BMI] ≥ 30 kg/m2) between 2000 and 2008. The 61 male and 57 female patients had a mean age of 59.8 years (range 25.4–79.4); 83.1 percent (98) were classified as grade I obesity (BMI of 30 kg/m2 to 34.9 kg/m2), 16.1 percent (19) were grade 2 obese (35 kg/m2 –39.9 kg/m2), and 1 patient was grade III obese (40 kg/m2 or higher).

Posttraumatic osteoarthritis was the most common diagnosis (81.3 percent), followed by rheumatoid arthritis (10.6 percent) and miscellaneous ailments including osteoarthritis related to gout, hemophilia, or hereditary hemochromatosis. One fourth of the patients had at least one comorbidity.

The prosthesis used in the study was the mobile-bearing Hintegra (Newdeal SA, Lyon, France), which is not approved for use in the United States.

All patients followed the same postoperative protocol, which included the initial use of a padded short leg splint to hold the foot in a neutral position, followed by a short leg walking cast, and a stable 7 walker. Full weight-bearing was allowed as tolerated. A 4-month rehabilitation program included walking exercises, stretching and strengthening of the triceps, and training in ankle motion and balance/proprioception.

Complications and outcomes
Intraoperative complications occurred in 9 ankles (7 patients sustained a medial malleolar fracture and 2 sustained flexor hallucis longus laceration). Postoperative complications included delayed wound healing in 8 patients and systemic deep vein thrombosis that developed in 12 patients at a mean postoperative time of 5.7 days.

Prosthesis metallic component survival was 93 percent at 6 years. One or both components failed in six ankles; revision arthroplasty was performed in two, and ankle fusion in the other four. In all ankles, the revision was secondary to aseptic loosening. In another 17 ankles (13.8 percent), a secondary surgery was performed at a mean of 1.9 years after the primary TAR.

The mean preoperative BMI for the entire patient cohort was 32.9 kg/m2 (range, 30.0 kg/m2–40.0 kg/m2). This dropped to 32.4 kg/m2 at 1-year follow-up and to 32.2 kg/m2 at 2-year follow-up.

Using a 5 percent change from the preoperative weight as the cut-off point, researchers found that 14 patients had lost weight, 101 remained constant, and 3 had gained weight 1 year after the surgery. Weight loss could not be predicted by age or postoperative sport activity.

The average VAS pain score decreased significantly, and 33 patients were completely pain-free at the time of the latest follow-up. The average range of motion increased significantly, although the improvement was less than 10° in almost half of the ankles and 10 percent experienced a slight decrease in range of motion.

More patients were able to participate in sports activities after TAR; the number of patients who reported moderate participation rose from 23 to 61, and the number who reported normal participation nearly doubled—from 15 to 29.

At the time of final follow-up, 107 patients were either very satisfied or satisfied, 9 patients were “satisfied with reservations,” and 2 patients were dissatisfied with the results of TAR.

Cautions
The authors note that the 93 percent midterm survivorship rate of the prosthesis and the degree of pain relief experience by patients is comparable to that observed in other TAR studies. No other studies have documented weight loss after TAR.

The low number of intraoperative complications was due in part to the familiarity of the operating surgeon and senior author, Beat Hintermann, MD, with the implant technique. “Our results should not be generalized to orthopaedic surgeons who do not have much experience with foot and ankle surgery, especially with TAR,” the authors write.

Another limitation is Dr. Hintermann’s involvement in the development of the prosthesis, which raises conflict-of-interest issues; clinical and radiographic evaluations, however, were performed by two nonconflicted reviewers.

Co-authors of “Total Ankle Replacement in Obese Patients: Component Stability, Weight Change, and Functional Outcome in 118 Consecutive Patients” are Markus Knupp, MD; Andrew E. Anderson, MD; and Beat Hintermann, MD.

Disclosure information: Dr. Knupp—Integra, Mathys Ltd, Foot and Ankle International; Dr. Hintermann—Integra. The other authors reported no conflicts.

Terry Stanton is senior science writer for AAOS Now. He can be reached at tstanton@aaos.org

Bottom Line

• In a group of obese patients undergoing TAR, implant survivorship was similar to that of findings in nonobese patients.
• Among the obese patients in the study, 12 percent had significant weight loss after TAR.
• The VAS pain scores for the studied patients decreased significantly, and the AOFAS-Hindfoot score increased significantly.
• One-third of the patients were pain-free at follow-up.
• Intraoperative complications included medial malleolar fractures and flexor hallucis longus lacerations; posteroperative complications included delayed wound healing and deep vein thrombosis.
• Surgeon skill and familiarity with the TAR procedure and device are important factors in outcomes.