The Effect of Screw Position and Number on the Time to Union of Arthroscopic Ankle Arthrodesis

Purpose: This study aimed to investigate the factors that influence the time to union after arthroscopic ankle arthrodesis. Methods: From June 2005 to October 2010, 46 patients (50 ankles) underwent arthroscopic ankle arthrodesis with 6.0-mm cannulated cancellous screws. There were 22 men and 24 women (mean age, 63 years). Medical records and radiographs were retrospectively reviewed. Screw configurations used were as follows: 3 transmedial and translateral malleolar screws (ML3) in 12 ankles (24%), 2 transmedial and translateral malleolar screws (ML2) in 4 ankles (8%), 3 transmedial malleolar screws (M3) in 23 ankles (46%), and 2 transmedial malleolar screws (M2) in 11 ankles (22%). Results: Radiographic fusion was achieved in 46 (92%) of the 50 ankles. The mean time to fusion was 11.0 +/- 4.5 weeks for ML3, 13.1 +/- 3.3 weeks for ML2, 9.7 +/- 2.7 weeks for M3, and 12.5 +/- 3.5 weeks for M2 (P < .05). The mean American Orthopaedic Foot & Ankle Society scores were 81.3 +/- 2.2 for ML3, 83.5 +/- 4.4 for ML2, 88.3 +/- 1.5 for M3, and 85.3 +/- 2.2 for M2. The mean time until radiographic fusion was 10.2 +/- 3.4 weeks for correction angles of less than 10 degrees and 13.2 +/- 3.4 weeks for angles of 10 degrees or greater (P < .01). In obese patients a significant difference in ankle fusion time was observed (12.6 +/- 3.5 weeks for patients with body mass index >= 25 v 9.4 +/- 2.9 weeks for patients with body mass index <25, P < .01). Conclusions: Overall, this study showed that arthroscopic ankle arthrodesis achieves a high rate of union, with fastest union achieved with 3 parallel screws placed medially from the distal tibia into the talus. Care should be taken when one is designing treatment strategies for obese patients and/or patients with large correction angles. Level of Evidence: Level IV, retrospective case series.