Abstract
Summary Statement
This study examined the fixation stiffness of 13 tibial and 12 femoral Salter-Harris fracture fixation methods, and determined that screws and screws+ k-wires methods provided the highest stability. In situations where k-wire use is unavoidable, threaded k-wires are preferable.
Introduction
Salter-Harris fractures of the proximal tibia and distal femur are common in pediatric patients that present to orthopedic surgeons. Salter-Harris type I fractures are characterised by breaks that extend only through the physis while Salter-Harris II fractures are the most common, accounting for 85% of Salter-Harris fractures, and extend past the growth plate, exiting through the metaphyseal bone. Fixation of these fracture types can be accomplished using a variety of methods including the use of Kirschner wires, cannulated screws, and a combination of both materials. Stability of fracture fixation is of utmost importance as persistent motion at the fracture margin leads to deformity. The purpose of this study is to analyze the biomechanical efficacy of various fixation methods used to stabilise Salter-Harris I and II fracture patterns in both the proximal tibia and distal femur. Stiffness, the primary gauge of efficacy, will be tested in flexion and extension, varus and valgus movement, and internal and external rotation and will be compared to determine the optimal fixation method.
Materials and Methods
This study utilised 39 tibia and 36 femur 4th generation synthetic bones (Model 3401 and 3403, Pacific Research Laboratories Inc.) The synthetic bones were fractured and fixated to model Salter-Harris fractures and common fixation methods. Fixation methods used employed 6.5mm cannulated screws, 4.5mm cannulated screws, 2mm smooth K-wires, and 2mm threaded K-wires. Tibias were fractured according to Salter-Harris I, valgus Salter-Harris II, and flexion Salter-Harris II patterns with 13 different fixation methods. Femurs were fractured according to Salter-Harris I and Salter-Harris II patterns with 12 different fixation methods. Testing was performed in three orientations, flexion/extension, varus/valgus, and internal/external rotation, on a materials testing machine (Model 8874, Instron, Norwood, MA) and cyclic displacement tests were performed using Wavematrix software. These displacement tests recorded the torque required to reach an angulation of ±5° for 10 cycles. From this data, the rotational stiffness of the loading phases for each cycle was determined. Statistical analysis was performed to compare construct stiffness and differences between groups using analysis of variance.
Results
Results show superior fixation for threaded k-wires in both femoral and tibial Salter-Harris I fractures. Methods utilizing transverse screws were least optimal for the fixation of femoral Salter-Harris II fractures, while a combination of k-wires and screws or the use of oblique screws was more effective. Fixation utilizing a combination of k-wires and screws yielded greater stiffness in valgus and flexion tibial Salter-Harris II fractures. Internal and external rotational stiffness values were low for all fixation methods and no significant variance existed for internal and external rotational stiffnesses in most fracture patterns.
Discussion/Conclusion
Based on the results and statistical analysis, we believe that significant variance exists between most of the studied fixation methods for each fracture type. Fixation methods utilizing screws and a combination of screws and k-wires would provide optimal stability. In situations where the use of k-wires is unavoidable, threaded k-wires are preferable.
