Session I - Tibia

*Neurovascular Risk Associated with Submuscular Fixation of the Proximal Tibia: A Cadaveric Study

Philip J. Kregor, MD; Ron Christensen, DVM, MBA; Deborah Nemecek, BS; Steve Gilbert, BS; Peter A. Cole, MD, University of Mississippi Medical Center, Jackson, MS (all authors ­ a-Synthes USA)

Introduction: The Less Invasive Stabilization System (LISS) has gained popularity and shown efficacy in the treatment of proximal tibial plateau and shaft fractures. The purpose of this study was to investigate potential injury to neurovascular and/or musculotendinous structures during submuscular tibial LISS fixation in a cadaveric dissection.

Methods: Twenty-six fresh frozen whole-leg intact cadaveric specimens were used in an operating-room environment with standard fluoroscopic equipment. Tibial LISS fixators were placed on the proximal tibia by a single surgeon experienced in submuscular fixation. A standard anterolateral curvilinear incision was made over the proximal aspect of the tibia. The anterior compartment fascia was incised and reflected posteriorly, and a 13-hole tibial LISS fixator was slid submuscularly into the anterior compartment. Two screws were then placed in the proximal aspect of the tibia after confirmation of the appropriate placement of the fixator by a fluoroscopic examination. Drill sleeves for holes 7 to 13 were then placed through standard 1.0-cm incisions using the outrigger device of the LISS system. Dissection around the drill sleeves was performed while the drill sleeves were in place to investigate: 1) the relationship of the drill sleeves to anterior compartment musculature and tendons, 2) the distance between the anterior tibial artery and vein and the deep peroneal nerve, 3) the distance between the superficial peroneal nerve and the drill sleeves, and 4) any injury to neurovascular and/or tendinous structures. All measurements were made with calipers.

Results: In 13 of 26 cases, the distal aspect of the fixator tented the anterior tibial artery and/or vein and the deep peroneal nerve and was in direct contact with the end of the fixator. In three additional cases, the anterior tibial artery and/or vein was transected or injured. The superficial peroneal nerve was injured in 3 of 26 cases. The extensor hallucis longus tendon was injured in one case. The distance of the anterior compartment neurovascular bundle from the drill sleeve averaged: hole 13, 0 mm; hole 12, 3 mm; hole 11, 6 mm; hole 10, 8 mm; and hole 9, 9 mm. The distance from the posterior aspect of the drill sleeve to the superficial peroneal nerve averaged: hole 13, 7 mm; hole 12, 6 mm; hole 11, 9 mm; hole 10, 12 mm; and hole 9, 13 mm. No injuries to musculotendinous and/or neurovascular structures were seen from drill sleeves 1 through 9.

Discussion: Submuscular fixation of distal femur fractures is currently undergoing clinical trials. The risk of injury from femoral percutaneous screw placement is low because of the paucity of neurovascular structures on the lateral aspect of the femur. Submuscular fixation of proximal tibial fractures is inherently potentially injurious to neurovascular structures. An unacceptable 12% injury rate to the anterior tibial artery and a 12% injury rate to the superficial peroneal nerve were observed with use of standard percutaneous methods. There is a significant risk of injury to the anterior tibial artery and/or vein, deep peroneal nerve, superficial peroneal nerve, and anterior compartment tendons during insertion of a longer (13-hole) tibial LISS fixator in the ideal model (intact tibia). The study was limited by the variation in tibial lengths and in the surgical variation in fixator placement. However, on the basis of these results, a limited distal full-length incision of approximately 4 to 5 cm is proposed. The superficial peroneal nerve, if present, is then protected. The anterior tibial muscles and tendon may then be reflected anteriorly with the extensor digitorum longus and extensor hallucis longus muscles reflected posteriorly. The anterior compartment neurovascular bundle is also thus protected.

Conclusion: Standard percutaneous screw placement for submuscular fixation of proximal tibial fractures was associated with a 24% incidence of significant neurovascular injury in an intact cadaveric proximal tibial model. Therefore, a formal approach to the distal tibia should be considered when placing distal tibial submuscular screws.