Original Article
Anterior Cruciate Ligament Soft Tissue Graft Fixation in the Elderly: Is There a Reason to Use Interference Screws? A Human Cadaver Study

https://doi.org/10.1016/j.arthro.2017.03.017Get rights and content

Purpose

To analyze the ultimate failure load, yield load, stiffness, and cyclic resistance of different anterior cruciate ligament (ACL) soft tissue graft fixation techniques in osteopenic bone.

Methods

In this study, 24 fresh-frozen human cadaveric tibiae (mean age 82.6 years; range 56-96; 6 male and 6 female donors) were used. Quantitative computed tomography was performed to match bone density. Looped porcine flexor tendon grafts were chosen as ACL graft substitutes for tibial graft fixation techniques (n = 8 each): (1) hybrid fixation with an interference screw and extracortical button fixation; (2) extracortical button fixation; and (3) interference screw fixation. In single cycle mode, constructs were loaded to failure to evaluate stiffness, yield load, and maximum load. In cyclic testing, 2,000 cycles (25-100 N) were applied followed by loading to failure. A 1-way analysis of variance was performed with significance set at P = .05.

Results

Hybrid fixation resulted in significantly higher yield load (283.4 ± 86.19 N; P = .0037) and maximum load (407.9 ± 102.3 N; P = .0026) than interference screw fixation (yield load 176.4 ± 26.03, max load 231.8 ± 94.06 N) in elderly bone. Yield load after extracortical button fixation (252.9 ± 41.97 N; P = .0286) was also higher than that after interference screw fixation, but stiffness (18.98 ± 9.154 N/mm; P = .0041) was less than that after hybrid fixation (37.28 ± 13.53 N/mm). Of 8 specimens in the interference screw group, 7 did not survive 2,000 cycles and failed by graft slippage, whereas all other specimens in both other groups survived.

Conclusions

Tibial hybrid fixation of ACL soft tissue grafts provides less vertical graft movement than extracortical button fixation and higher primary failure loads than interference screw fixation in elderly bone.

Clinical Relevance

In this elderly human joint in vitro model, tibial hybrid fixation provides biomechanical advantages over other techniques. Graft fixation with only an interference screw should be avoided in osteopenic bone.

Section snippets

Specimens/Preparation

For biomechanical testing, 24 fresh-frozen human cadaveric knees (12 pairs) that had been stored at −20°C before testing were used. The mean age of the donors was 82.6 years (range: 56-96; 6 male and 6 female donors). Inclusion criteria were female specimens from 55 years and male specimens from 65 years and older with macroscopically osteopenic trabecular bone structure. Exclusion criteria were severe post-traumatic changes of anatomy or arthroplasty. None of the included 24 specimens had to

Trabecular Bone Quality

All human cadaveric specimens showed signs of osteopenic bone quality with an increased porosity of trabecular bone and thinning of cortical bone. The average density of the medial ROI was 224 ± 80 HU (mean ± SD), and that of the lateral ROI was 168 ± 78 HU. The variation of BMD of each matching group, containing 3 ranked specimens each, was <9 HU between the highest and lowest ranked specimen.

Single Cycle Load

Hybrid fixation resulted in a significantly higher yield load (283.4 ± 86.19 N; P = .0037) and a

Discussion

The results of the current study support our initial hypotheses: first, in the elderly human tibial bone, hybrid fixation of ACL soft tissue grafts provides less vertical graft movement (higher stiffness) compared with extracortical button fixation. Secondly, hybrid fixation results in increased primary strength (maximum load) compared with interference screw fixation. Failure of 7 of 8 specimens in the interference screw fixation group during cyclic testing suggests that this intramedullary

Conclusions

Tibial hybrid fixation of ACL soft tissue grafts provides less vertical graft movement than extracortical button fixation and higher primary failure loads than interference screw fixation in elderly bone.

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      Those fixators include the cross-pins (Bio-transfix, Arthrex, Germany), interference screws (Milagro, Johnson & Johnson Medical Limited, United Kingdom), double cross-pins, cortical buttons and staples [3]. At the tibial fixation area, the interference screw has been widely used in securing the graft inside the bone tunnel to replace the torn ACL as shown in previous studies [4], where it demonstrated higher pull-out stiffness as compared to the cortical button in a previous experiment work by Fogel et al. [5]. Meanwhile, a suspension device such as the cross-pin was superior to the interference screw [6] and cortical button [7] as a femoral graft fixation, since it exerted lower displacement with higher load failure.

    • A Comparison of Two-Year Anterior Cruciate Ligament Reconstruction Clinical Outcomes Using All-Soft Tissue Quadriceps Tendon Autograft With Femoral/Tibial Cortical Suspensory Fixation Versus Tibial Interference Screw Fixation

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      According to a recent systematic review by Crum et al.,19 suspensory fixation warrants further consideration due to literature demonstrating greater IKDC scores, decreased anterior laxity, and postoperative pain with successful short-term outcomes when compared to aperture fixation. Other reasons favoring suspensory over aperture fixation include reported greater biomechanical graft durability, greater preservation of flexion strength, improved arthrometric stability, theorized potential improvement when used in osteopenic bone, and the lack of potential for screw migration and subsequent tunnel widening leading to graft migration or cyst formation within the tunnels.29,44-48 In fact, multiple studies have found that interference screw fixation can pose a greater risk to tibial tunnel widening or increased tibial tunnel diameter size up to 2 years or longer postoperatively compared with TFSF,49-52 although these findings are dependent on the method of tibial tunnel measurement used and remain largely focused on hamstring autografts.53

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    C.D. and M.H. contributed equally to this work.

    The authors report the following potential conflicts of interest or sources of funding: M.H. receives support from Karl Storz, Mathys, and Conmed Linvatec. M.J.R. receives support from Depuy Synthes, MSD, Marquardt, Nexilis, and Implantcast. B.S. receives support from Mathys (Switzerland). W.P. receives support from Karl Storz and Otto Bock.

    See commentary on page 1701

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