The Use of Highly Variable Angle Screws Increased Compression in Orthopaedic Plating
Authors: Adams Samuel B. , Gross Christopher E. , King Shannon , Filicette Taylor , Johnson James , Safranski David 
Published: December 2024

Category:

Basic Sciences/Biologics; Midfoot/Forefoot

Introduction/Purpose:

Interfragmentary stability and compression are ideal for bone healing in fracture repair and arthrodesis procedures. The primary purpose of orthopaedic plate and screw hardware is to provide interfragmentary stability with a lesser focus on interfragmentary compression as this is typically achieved with lag screw fixation outside of the plate, before plate application. Modern plates afford variable screw angulation with the intended purposes to capture bony fragments or avoid other hardware but not for compression. We hypothesized that variable angle technology can be used to pull bony fragments together, thereby optimizing interfragmentary compression and contact area. However, there is no data to support this rationale. This study aimed to elucidate the impact of “highly-angled” screw angulation to optimize interfragmentary compression and contact area for bony healing.

Methods:

Interfragmentary fixation was simulated using interlocking orthopedic plates on simulated fractures in foam bone models (SawBones). To ensure findings were not specific to plate model, two orthopedic plate models were tested (Plate 1 = 4-hole plate, Max Screw Angle=15°, Plate 2 = 4-hole plate, Max Screw Angle=30°). Plates were applied to the bone fragments according to manufacturer instructions FigA. Screws were inserted (1) perpendicular to the plate (0°), (2) angled 15° away from fracture line, or (3) angled 30° away from fracture line (Plate 2 only as this exceeds max angulation of Plate 1). Interfragmentary compression and contact area were measured following application of all screws using pressure sensing film (TekScan Evolution). Data were analyzed using a two-way ANOVA with plate model and screw angle as main effects.

Results:

Interfragmentary compression markedly and significantly increased with increasing screw angle (p< 0.001,Fig1B). Specifically, mean interfragmentary compression across both plate groups increased by 470% in the 15° screw angle group as compared to the 0° group. When screws were applied at 30° offset from fracture plane, compression was increased by 956% as compared to the 0° group. The Plate 2 group demonstrated significantly increased compression across all screw angles as compared to the Plate 1 group (p=0.045,FigB). Contact area increased significantly with increased screw angle (p< 0.001, FigC). No significant differences in contact area were noted between plate groups (p=0.81, FigC).

Conclusion:

Our findings underscore the critical role of screw angulation in achieving optimal interfragmentary compression and contact area. Specifically, even a modest 15° screw angle significantly enhanced interfragmentary compression and contact area by 470% and 212%, respectively. Importantly, these data highlight that maximum allowable screw angulation provided by plate models is a key factor in enhancing fixation quality. Surgeons should consider utilizing plates offering greater that offer maximum angulation flexibility to optimize fixation quality. This approach not only affords improved compression but also allows for improved adaptation to the anatomical and intraoperative challenges, offering a substantial advancement in fracture stabilization techniques.