Collagen-platelet composite enhances biomechanical and histologic healing of the porcine anterior cruciate ligament

Abstract

Background: The anterior cruciate ligament (ACL) fails to heal after traumatic rupture. Furthermore, large-animal models have recently shown that 1-month functional ACL healing is augmented after suture repair when a bioactive scaffold is placed in the tear site.

Hypothesis: At the time of suture repair, placement of a bioactive scaffold in the ACL wound site would improve the structural properties of the tissue.

Study design: Controlled laboratory study.

Methods: Twenty-seven knees in immature pigs underwent ACL transection and suture repair. A collagen-platelet composite (CPC) was used to supplement the repair in 14 knees. Knees were harvested at 4 weeks, 6 weeks, and 3 months. Mechanical testing and histologic analysis were performed.

Results: The addition of a CPC to a suture repair resulted in improvements in yield load and linear stiffness of the repair tissue at 3 months, as well as a significant increase in cell density. A reduction in yield load and stiffness occurred at the 6-week time point in both groups, a phase when revascularization was noted.

Conclusion: The addition of a CPC to a suture repair enhanced the structural properties of the ACL, and the improvement was associated with increased cellularity within the healing ligament.

Clinical relevance: The addition of a bioactive scaffold to the wound site improved the functional healing of the ACL after suture repair. The decreased repair strength during revascularization may indicate a need to protect the repair site through this period.

Conflict of interest statement

One or more authors has declared a potential conflict of interest: Dr Murray is a paid consultant, founder, and stockholder in Connective Orthopaedics. Dr Fleming is a paid consultant for Connective Orthopaedics.

Figures

Figure 1

Schematic representation of the suture (A) and collagen-platelet composite (B) techniques. The sutures (arrows) are fixed proximally with a suture anchor and attached to a second set of sutures placed in a variable depth fashion in the tibial stump. The collagen-platelet composite is threaded on the proximal sutures before the sutures are tied. Figure 1B used with permission from John Wiley and Sons.

Figure 2

Scar mass between treatment groups at 4 weeks after surgery: A, suture repair–only group; B, collagen platelet composite group. Ligaments treated with collagen platelet composites had larger scar masses at 4 weeks.

Figure 3

Scar mass between treatment groups at 3 months after surgery: A, suture repair–only group; B, collagen platelet composite group. Ligaments treated with collagen platelet composites have a larger and more organized scar mass at 3 months, with a gross appearance closer to that of an intact porcine ACL. Both photographs are taken with the knee in 90° of flexion.

Figure 4

Changes in suture and CPC groups over time. Blood vessels are noted as the ringlike structures staining positive for α-SMA (arrow points to example). Notice the change in cellularity from ovoid cells in both groups at 4 weeks to spheroid cells in the suture group and fusiform cells in the CPC group at 3 months; note also the increase in blood vessels in both groups at 6 weeks. The arrows in 64× H&E polarized indicate bundles of collagen, which are more consistent in the CPC-treated ligaments at 3 months. The size bar for 160× H&E is 10 microns; for 20× α-SMA, 100 microns; for 64× H&E polarized, 100 microns. CPC, collagen-platelet composite; H&E, hematoxylin and eosin; α-SMA, α–smooth muscle actin, where red is a positive stain.

Figure 5

The relationship among mechanical properties, cellularity, and vascularity over the 3-month healing period. Cellularity of the wound site peaks at 4 weeks; vascular density peaks at 6 weeks. Yield load of the healing ligament does not start to significantly increase until after the cellularity and vascularity peaks, at 3 months.