Precision of Targeting Device for Subtalar Screw Placement

Background: When performing subtalar arthrodesis, proper screw placement is fundamental to provide primary stability and to help ensure bone healing. In inexperienced hands this step can be time-consuming and exposes surgeons and patients to radiation. By means of a targeting device these potential drawbacks and dangers could be reduced. It was hypothesized that a specifically designed targeting device would reduce radiation exposure while improving screw placement when compared with the conventional "free-hand" method. Methods: Twenty matched-pairs of cadaveric hindfoot specimens (Thiel fixation) were prepared for the purpose of the study. The specimens were randomly assigned into two groups consisting of 10 specimens each: in Group 1 screw placement was performed with the targeting device and in Group 2 screw placement was performed under fluoroscopic control. Screw placement was radiographically judged to be optimal, suboptimal and poor. An experienced, fellowship-trained foot and ankle surgeon and a resident, who had never done subtalar fusions performed the screw placements. Exposure to radiation was assessed by means of the dose area product given by the fluoroscope. Results: Optimal screw positioning was achieved in both groups in ten out of 20 specimens (Group 1, n = 5; Group 2, n = 5). Suboptimal screw placement was found in eight cases (Group I, n = 4; Group 2, n = 4). There were two failures which occurred in fusions performed by the resident (Group 1, n = I; Group 2, n = 1). Exposure to radiation was significantly reduced in Group 1 when compared with Group 2 (4.1cGy*cm(2) versus 8.1cGy*cm(2); p = 0.012). No lesion of neurovascular structures due to aiming device placement occurred in Group 1. Conclusion: A target-device for screw-placement did not provide a significant technical advantage but did result in less radiation exposure.