Abstract
Category:
Ankle Arthritis
Introduction/Purpose:
During internal fixation of ankle fusions, besides the standard crossed screw fixation pattern, the use of a percutaneously placed augmenting screw, directed from the posterolateral tibial metaphysis proximally across the ankle into the talar neck (“ankle fusion home run screw”), is a widely used technique. The placement of this screw is technically demanding and multiple attempts under fluoroscopy guidance are frequently needed to achieve a perfect positioning of the implant. Injuries to local neurovascular and tendinous structures might happen. The objective of this cadaver study was to identify the number of attempts necessary for a perfect positioning of the ankle fusion home run screw and the neurovascular and tendinous structures at risk.
Methods:
Eleven fresh frozen cadaver limbs were used. Guide wires (3.2 mm) from the Stryker (Selzach, Switzerland) 7.0-mm headless cannulated set were percutaneously placed into the distal posterolateral aspect of the leg, under fluoroscopic guidance, with the ankle held in neutral position. Mal positioned pins were not removed and served as guidance for the following pins. The number of guide wires needed to achieve an acceptable positioning of the implant was noted. After a layered dissection from the skin to the tibia, we evaluated neurovascular and tendinous injuries, and measured the shortest distance between the closest guide pin and the soft tissue structures, using a precision digital caliper.
Results:
The mean number of guide wires needed to achieve and acceptable positioning of the implant was 2.09 (SD 0.83, range 1- 4). The mean distances between the closest guide pin and the soft tissue structures of interest were: Achilles tendon 6.90 mm (SD 3.74 mm); peroneal tendons 9.65 mm (SD 3.99 mm); sural neurovascular bundle 0.97 mm (SD 1.93 mm); posteromedial neurovascular bundle 14.26 mm (SD 4.56 mm). Sural bundle was in contact with the guide pin in 5/11 specimens (45.5%) and transected in 3/11 specimens (27.3%).
Conclusion:
The placement of percutaneous ankle fusion home run screws is technically demanding and multiple guide pins are needed. Our cadaveric study showed that important tendinous and neurovascular structures are in close proximity with the guide pins and that the sural bundle is injured in approximately 73% of the cases. Caution should be taken during percutaneous placing of screws and an appropriate approach and surgical dissection to bone is advised.