What size and number of screws are recommended for fixation of a syndesmotic injury?

Syndesmotic Injury Screw Fixation

For acute syndesmotic injuries requiring surgical fixation, use one 3.5-mm tricortical screw placed 2-4 cm above the tibial plafond, as this provides equivalent biomechanical stability to larger screws while allowing earlier weight-bearing without routine removal. 1, 2, 3

Screw Size Selection

• A 3.5-mm cortical screw is the optimal choice for syndesmotic fixation, as biomechanical testing demonstrates no advantage of 4.5-mm screws over 3.5-mm screws in terms of stiffness or syndesmotic reduction 2
• The 3.5-mm screw actually failed at a greater external rotation angle (38.9° vs 32.0°) compared to 4.5-mm screws, suggesting superior performance under torsional stress 2
• The 3.5-mm screw is the most commonly used size in clinical practice, with 81.2% of surgeons preferring this diameter for syndesmotic stabilization 4

Number of Screws

• One screw is sufficient for most syndesmotic injuries, particularly in Weber-B ankle fractures where 81.2% of surgeons use a single screw 4
• Two screws are typically reserved for more severe injuries such as Maisonneuve fractures with proximal fibular involvement 4
• A single tricortical 3.5-mm screw represents the most dynamic fixation option, which may better accommodate physiologic ankle motion during healing 1

Cortical Purchase: Three vs Four Cortices

• Either three or four cortices of fixation provide equivalent clinical outcomes, with no statistical difference in loss of reduction (p=0.871), screw breakage (p=0.689), or need for hardware removal (p=0.731) 3
• Tricortical fixation (three cortices) had an 8% hardware failure rate with three patients experiencing loss of reduction, while quadricortical fixation (four cortices) had a 7% hardware failure rate with no loss of reduction 3
• Three-cortex fixation is preferred as it allows more physiologic motion and reduces the risk of tibiofibular synostosis, which occurred in 0% of patients with dynamic fixation versus 5% with rigid four-cortex fixation 1
• The trend toward higher loss of reduction with tricortical fixation only occurred when weight-bearing restrictions were violated, emphasizing the importance of postoperative protocols 3

Screw Placement Location

• Position the screw 2.1-4.0 cm (approximately 2-4 cm) above the tibial plafond, as this is the most commonly used location and provides optimal biomechanical stability 4
• Placement too close to the joint line risks intra-articular penetration, while placement too proximal may not adequately stabilize the syndesmosis 4

Alternative: Suture Button Devices

• Suture button devices (such as TightRope) demonstrate significantly lower malreduction rates (15%) compared to two-screw fixation (39%, p=0.028) 5
• However, suture button fixation results in greater anterior fibular translation (5.4 mm vs 4.3 mm contralateral, p<0.01) and increased syndesmotic diastasis (4.1 mm vs 3.3 mm contralateral, p<0.01) 5
• Functional outcomes at 12 months are equivalent between suture button and screw fixation (Foot and Ankle Disability Index: 93±9 vs 90±14, p>0.2) 1, 5
• The reoperation rate is dramatically lower with suture button devices (4%) compared to screw fixation (30%, p=0.02), primarily due to elimination of routine hardware removal 5
• A single tricortical 3.5-mm screw provides similar 2-year outcomes to suture button fixation and represents an inexpensive alternative 1

Screw Removal Considerations

• Routine screw removal is not necessary, as retained syndesmotic screws—even with mechanical failure—do not cause clinical problems 3
• Despite this evidence, 87% of surgeons still routinely remove syndesmotic screws, typically between 6-8 weeks postoperatively 4
• Screw breakage occurs in approximately 7-8% of cases but is typically asymptomatic and does not require removal 3
• Weight-bearing can be safely allowed at 6-10 weeks without routine screw removal 3

Critical Technical Points

• Perform open reduction of the syndesmosis in all cases to ensure anatomic restoration of the tibiofibular relationship 5
• Use the "Hook test" intraoperatively to assess syndesmotic stability after fibular fixation 4
• Verify reduction with fluoroscopy in both anteroposterior and lateral views before screw placement 5
• Consider bilateral ankle CT scanning at 3 months postoperatively to assess reduction quality, as malreduction rates can be substantial (15-39%) even with modern techniques 5