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Biomechanical Comparison of 4- and 6-Strand All-Inside Anterior Cruciate Ligament Reconstruction Grafts: The Value of
Julian André1, Asheesh Bedi2, Patrick A Smith3
1Arthrex Research Department, Munich, Germany.
Background:
Data comparing primary fixation of hamstring tendon (HT) grafts for all-inside anterior cruciate ligament reconstruction (ACLR) using direct ripstop (RS) suturing of free graft limbs with the adjustable loop device (ALD) versus standard grafts are lacking.
Purpose:
To evaluate the biomechanical effect of direct RS suturing backup fixation of free graft limbs to the adjustable loop in 4- and 6-strand HT grafts compared with standard cerclage sutured grafts in all-inside ACLR.
Study Design:
Controlled laboratory study.
Methods:
Four different HT groups (n = 8 per group) with 9-mm graft diameter were prepared: 4- and 6-strand grafts with standard cerclage suturing (4HT/6HT) and additional direct RS suturing (4HT-RS/ 6HT-RS) of the free graft limbs to the ALD. Each construct was preconditioned with graft retensioning (250 N) followed by a total of 3000 cycles. This included 1 position-controlled and 2 force-controlled load blocks (1000 cycles each), with a constant valley (10 N) and 2 different peak loads (250 N, 400 N). Residual graft force, dynamic elongation, and stiffness were analyzed. The ultimate strength was evaluated during pull to failure (50 mm/min). One-way analysis of variance and Holm-Sidak post hoc tests were used as statistical methods.
Results:
The maintenance of residual graft force of RS suturing groups (4HT-RS, 68.3% ± 2.8%; 6HT-RS, 72.1% ± 4.9%) was higher (P≤ .002) than both controls (4HT, 6HT) (≤61.0% ± 3.1%). The control groups showed lower dynamic stiffness (250 N: 125.2 ± 5.4 N/mm vs 139.4 ± 7.4 N/mm, 124.8 ± 6.9 N/mm vs 145.3 ± 10.9 N/mm; 400 N: 140.1 ± 5.3 N/mm vs 154.1 ± 8.3 N/mm, 139.4 ± 6.4 N/mm vs 162.1 ± 13.1 N/mm; P≤ .04) and higher dynamic elongation (each P < .001) at each peak load, resulting in higher total elongation (4.4 ± 0.4 mm vs 2.9 ± 0.5 mm, 3.9 ± 0.6 mm vs 2.3 ± 0.4 mm; P≤ .001) compared with both RS suturing groups. The ultimate stiffness of 4HT (162.4 ± 13.7 N/mm) was lower (P≤ .02) than in both RS groups (4HT-RS: 181.9 ± 9.2 N/mm; 6HT-RS: 185.4 ± 17.3 N/mm). The ultimate load of 6HT-RS (1133.4 ± 67.9 N) was higher (P≤ .003) than for other groups. The predominant failure mode was suture rupture of the ALD.
Conclusion:
This study demonstrated that direct RS suturing of free graft limbs to the adjustable loop significantly decreased graft tension loss, increased construct stiffness, and reduced cyclic elongation in 4- and 6-strand all-inside HT grafts compared with standard grafts with cerclage suturing. Improved primary fixation may ensure more homogeneous load distribution across the graft limbs and reduce the risk of early clinical failure.
Clinical Relevance:
Direct RS suturing of the free graft ends to the ALD improved primary construct stability in all-inside ACLR, but future studies will determine if the improved time-zero biomechanics translate into favorable clinical outcomes.
