Isolated subtalar arthrodesis

Background The purposes of this retrospective study were to review the resu lts of isolated subtalar arthrodesis in adults and to identify factors infl uencing the union rate. The hypotheses were that (1) the overall outcome is acceptable but is not as favorable as previously reported, (2) complicatio n rates, especially the nonunion rate, are higher than previously reported, and (3) factors contributing to a less favorable union rate can be identif ied. Methods: Between January 1988 and July 1995, 184 consecutive isolated subta lar arthrodeses were performed in 174 adults (115 men and fifty-nine women) whose average age was forty-three years (range, eighteen to seventy-nine y ears). Eighty patients (46 percent) were smokers. The indications for the p rocedure included posttraumatic arthritis after a fracture of the calcaneus (109 feet), a fracture of the talus (thirteen feet), or a subtalar disloca tion (thirteen feet); primary subtalar arthritis (thirteen feet); failure o f a previous subtalar arthrodesis (twenty-eight feet); and residual congeni tal deformity (eight feet). Rigid internal fixation with one or two screws was used for all feet. Bone graft was used in 145 feet; the types of graft material included cancellous autograft (ninety-four feet), structural autog raft (twenty-nine feet), cancellous autograft (seventeen feet), and structu ral allograft (five feet). Bone graft was not used in the remaining thirty- nine feet. Results Clinical and radiographic follow-up examinations were performed for 148 (80 percent) of the 184 feet at an average of fifty-one months (range, twenty-four to 130 months) postoperatively. The average ankle-hindfoot sco re according to the modified scale of the American Orthopaedic Foot and Ank le Society (maximum possible score, 94 points) improved from 24 points preo peratively to 70 points at follow-up. Thirty feet had clinical evidence of nonunion. The union rate was 84 percent (154 of 184) overall, 86 percent (1 34 of 156) after primary arthrodesis, and 71 percent (twenty of twenty-eigh t) after revision arthrodesis. The union rate was 92 percent (ninety-three of 101 feet) for nonsmokers and 73 percent (sixty-one of eighty-three feet) for smokers (p < 0.05). Intraoperative inspection revealed that 42 percent (seventy-eight) of the 184 feet had evidence of more than two millimeters of avascular bone at the subtalar joint; all thirty nonunions occurred in t his group (p < 0.05). A nonunion occurred in three of the five feet that ha d been treated with structural allograft and in two of the six feet in whic h the subtalar arthrodesis had been performed adjacent to the site of a pre vious ankle arthrodesis. After elimination of the subgroups of feet in pati ents who smoked, those that had had a failure of a previous subtalar arthro desis, those that had been treated with a structural graft, and those that had had the subtalar arthrodesis adjacent to the site of a previous ankle a rthrodesis the union rate improved to 96 percent (seventy-three of seventy- six). Complications other than nonunion included prominent hardware requiri ng screw removal (thirty-six of 184 feet; 20 percent), lateral impingement (fifteen of 148 feet; 10 percent), symptomatic valgus malalignment (five of 148 feet; 3 percent), symptomatic varus malalignment (four of 148 feet; 3 percent), and infection (five of 184 feet; 3 percent). Conclusions To the best of our knowledge, the present study includes the la rgest reported series of isolated subtalar arthrodeses in adults. Our resul ts suggest that the outcome following isolated subtalar arthrodesis is not as favorable as has been reported in previous studies. The rate of union wa s significantly diminished by smoking, the presence of more than two millim eters of avascular bone at the arthrodesis site, and the failure of a previ ous subtalar arthrodesis (p < 0.05 for all). Other factors that probably af fect the union rate include the use of structural allograft and performance of the arthrodesis adjacent to the site of a previous ankle arthrodesis.