Screw oversizing for anterior cruciate ligament graft fixation in primary and enlarged tibial tunnels: A biomechanical study in a porcine model

Smaller diameter femoral tunnel biocomposite interference screws provide adequate fixation strength in anterior cruciate ligament reconstruction

PURPOSE

The purpose of this study was to evaluate the effect of bioabsorbable interference screw diameter on the pullout strength and failure mode for femoral tunnel fixation in primary anterior cruciate ligament reconstruction (ACLR) at time zero fixation using bone-patellar tendon-bone (BTB) autograft in a cadaveric model.

METHODS

Twenty-four fresh-frozen cadaveric knees were obtained from 17 different donors. Specimens were allocated to three different treatment groups (n = 8 per group) based on interference screw diameter: 6 mm, 7 mm, or 8 mm biocomposite interference screw. All specimens underwent dual energy X-ray absorptiometry (DEXA) scanning prior to allocation to ensure no difference in bone mineral density among groups (n.s.). All specimens underwent femoral-sided ACLR with BTB autograft. Specimens subsequently underwent mechanical testing under monotonic loading conditions to failure. The load to failure and failure mechanism were recorded.

RESULTS

The mean pullout force (N) at time zero for each group was 309 ± 213 N, 518 ± 313 N, and 541 ± 267 N for 6 mm, 7 mm, and 8 mm biocomposite interference screw diameter, respectively (n.s.). One specimen in the 6 mm group, two specimens in the 7 mm group, and one specimen in the 8 mm group failed by screw pullout. The remainder in each group failed by graft failure (n.s.).

CONCLUSION

Biocomposite interference screw diameter did not have a significant influence on fixation pullout strength or failure mode following femoral tunnel fixation using BTB autograft at time zero. A 6 mm interference screw can improve preservation of native bone stock, increase potential for biologic healing, and decrease the risk of damage to the graft during insertion without significantly compromising fixation strength. This study supports the use of smaller 6 mm interference screw diameter options for femoral tunnel fixation in ACLR.

Functional results of multiple revision anterior cruciate ligament with anterolateral tibial tunnel associated with anterolateral ligament reconstruction

Background

Revision anterior cruciate ligament (ACL) reconstructions are usually complex owing to previous tunnels. The objective of this study is to report the results of a revision ACL reconstruction technique with a tibial tunnel performed from the anterolateral plateau associated with an anterolateral ligament (ALL) reconstruction.

Methods

Patients with at least two ACL reconstructions that failed and who had significant enlargement and confluence of tunnels in the medial tibial plateau and underwent revision ACL reconstruction associated with ALL reconstruction with the tibial tunnel for the ACL performed from the lateral plateau between 2017 and 2019 were evaluated. All patients were evaluated by physical examination, International Knee Documentation Committee (IKDC), and Lysholm functional scales.

Results

Six patients who underwent this surgical procedure were evaluated. All patients were sports practitioners and presented a grade 3 pivot shift. The mean age was 28.5 ± 8.2 years, and the mean follow-up time was 34.1 ± 12.8 months. No patient had a new graft rupture, but three (50%) had grade 1 pivot shift. Four patients had minor complications with no clinical impact on the final result. All except one patient were able to return to pre-injury type of sports, at a mean time of 14.6 ± 2.3 months after surgery.

Conclusion

The anterolateral tibial tunnel technique using an Achilles tendon allograft for revision ACL reconstruction after multiple failures associated with an ALL reconstruction showed good results and no major complications. The anterolateral tunnel can be considered a good alternative in cases of medial tibial confluence or significant enlargement of the medial tunnels in re-revision procedures.

Effect of Geometry on the Fixation Strength of Anterior Cruciate Ligament Reconstruction Using BASHTI Technique

The goal of this study is to investigate the effects of tendon and cannulated drill bit diameter on the strength of the bone and site hold tendon inside (BASHTI) fixation technique for an anterior cruciate ligament (ACL) reconstruction. Bovine digital tendons and Sawbones blocks were used to mimic the ACL reconstruction. Mechanical strength of the specimens was measured using a cyclic loading continued by a single cycle pullout load until failure to simulate the real postsurgical loading conditions. Finally, failure modes of specimens and ultimate failure load were recorded. The maximum possible tendon surface strain (i.e., tendon compression [TC]) for tendon diameters of 6, 7, 8, and 9 mm were 0.73, 0.8, 0.7, and 0.65, respectively. Eighty per cent of the specimens with tendon diameter of 6 mm and 20% of specimens with tendon diameter of 7 mm failed on the torn tendon. All samples with larger tendon diameters (i.e., 8 and 9 mm) failed on the fixation slippage. The maximum fixation strength according to the most suitable core bones for 6, 7, 8, and 9 mm tendons were 148 ± 47 N (core 9.5 mm), 258 ± 66 N (core 9.5 mm), 386 ± 128 N (core 8.5 mm), and 348 ± 146 N (core 8.5 mm), respectively. The mode of tendon failure was significantly influenced by the tendon diameter. Also, an increase in TC raised the fixation strength for all tendon diameters; however, tendon over compression decreased the fixation strength for the 8 mm tendon group. Finally, an empirical equation was proposed to predict BASHTI fixation strength.