Collagen-platelet composites improve the biomechanical properties of healing anterior cruciate ligament grafts in a porcine model

Abstract

Background: The outcome of anterior cruciate ligament (ACL) reconstruction is variable, and many patients have increased joint laxity postoperatively.

Hypothesis: Placement of a collagen-platelet composite (CPC) around the graft at the time of ACL reconstruction decreases postoperative knee laxity and improves the structural properties of the graft compared with standard ACL reconstruction.

Study design: Controlled laboratory study.

Methods: Thirteen immature pigs underwent unilateral ACL reconstruction with a bone-patellar tendon-bone allograft. In 6 pigs, a standard allograft was used to reconstruct the ACL. In 7 pigs, a CPC was placed around the allograft. After 15 weeks of healing, the animals were euthanized, and the anterior-posterior (AP) knee laxity and structural properties of the graft were measured. Qualitative histology of the grafts was also performed.

Results: The AP laxity values of the reconstructed knees, normalized to the contralateral control, were significantly reduced by 28% and 57% at 60 degrees and 90 degrees of knee flexion, respectively, with the addition of CPC (P < .001). Significant improvements in the graft structural properties were also found; the normalized yield (P = .044) and maximum failure loads (P = .025) of the CPC group were 60% higher than the standard ACL-reconstructed group. Although cellular and vessel infiltration were observed in the grafts of both groups, regions of necrosis were present only in the standard ACL-reconstructed group.

Conclusion: These data demonstrate that the application of CPC at the time of ACL reconstruction improves the structural properties of the graft and reduces early AP knee laxity in the porcine model after 15 weeks of healing.

Clinical relevance: Application of a CPC to an ACL graft at the time of surgery decreased knee laxity and increased the structural properties of the graft after 15 weeks of healing.

Figure 1

Schematic of standard ACL reconstruction (ACLR; Top) and enhanced ACL reconstruction with the CPC (E-ACLR; Bottom) is shown. A collagen sleeve was threaded over the graft and infiltrated with autologous 5X platelet-rich plasma to form the CPC.

Figure 2

Schematics of the test fixtures used for AP laxity and tensile failure testing. For AP laxity testing (A), the knee flexion angle was prescribed, axial tibial rotation was constrained in the neutral position, and the translations in the coronal plane were unconstrained while the AP loads were prescribed. Figure 2A used with permission. For tensile testing (B), the knee flexion angle was initially set at 30°. The tibia was mounted to the base of the MTS via a sliding X-Y platform while the femur was unconstrained to rotations so that the specimen could seek its own position to ensure that the load was distributed over the entire graft cross section.

Figure 3

Load-displacement behavior of ACL-intact, ACL reconstruction enhanced with a CPC (E-ACLR) and standard ACL reconstruction (ACLR) groups demonstrating the improvement of the E-ACL graft, particularly in the functional loading region of the load-displacement curve. The error bars represent one standard error of the mean.

Figure 4

E-ACLR produced yield and maximum failure loads that were closer to that of the ACL. The structural properties are expressed as a percent of the ACL-intact contralateral control. A value of 100% indicates that the property is equal to that of the control. The error bars represent one standard deviation.

Figure 5

Histology of the ACLR (A, C) and E-ACLR (B, D) groups. Cellular repopulation of the allografts is seen in both the (5A) ACLR and (5B) E-ACLR groups, with vessels seen in both groups of grafts (black arrow, 5B). Central necrosis was found in the ACLR group (5C) but not in the E-ACLR grafts. A thick, vascular epiligamentous tissue was seen around the E-ACLR grafts, and vessels were actually noted to be extending from the hypercellular and hypervascular epiligamentous tissue into the graft substance (white arrow, 5D).