The influence of screw geometry on hamstring tendon interference fit fixation

Area of Science:

• Orthopedic surgery
• Biomedical engineering
• Sports medicine

Background:

• Anterior cruciate ligament (ACL) reconstruction often utilizes hamstring tendon grafts.
• Achieving robust graft fixation, particularly at the tibial site, is critical for successful outcomes.
• Interference screw fixation is a common method, but optimal screw geometry requires further investigation.

Purpose of the Study:

• To evaluate the effect of biodegradable interference screw diameter and length on hamstring tendon graft fixation strength.
• To determine whether screw diameter or screw length has a greater impact on tibial fixation in ACL reconstruction.

Main Methods:

• A standardized calf tibial bone model was used.
• Three-stranded semitendinosus tendon grafts were fixed with biodegradable poly-(L-lactide) screws of varying diameters (7, 8, 9 mm) and lengths (23, 28 mm).
• Pull-out forces were measured for three experimental groups comparing screw diameter and length configurations.

Main Results:

• Mean pull-out forces were 367.2 N (Group 1), 479.1 N (Group 2), and 537.4 N (Group 3).
• Groups with larger diameter screws (Group 2) and longer screws (Group 3) demonstrated significantly higher pull-out forces compared to the control group (Group 1).
• Increasing screw length resulted in a greater improvement in fixation strength than increasing screw diameter.

Conclusions:

• Screw geometry significantly influences the interference fit fixation of hamstring tendon grafts.
• Increasing screw length is more effective than oversizing screw diameter for enhancing tibial fixation strength in ACL reconstruction.
• These findings are important for optimizing tibial graft fixation, addressing a known weak point in ACL reconstruction.