Bone-to-bone fixation enhances functional healing of the porcine anterior cruciate ligament using a collagen-platelet composite

Abstract

Purpose: The purpose of this study was to determine whether providing bony stabilization between the tibia and femur improves the structural properties of an "enhanced" anterior cruciate ligament (ACL) repair using a collagen-platelet composite when compared with the traditional (Marshall) suture technique.

Methods: Twelve pigs underwent unilateral ACL transection and were treated with sutures connecting the bony femoral ACL attachment site to the distal ACL stump (ligament group) or to the tibia through a bone tunnel (tibia group). A collagen-platelet composite was placed around the sutures to enhance the biological repair in both groups. Anteroposterior knee laxity and the graft structural properties were measured after 15 weeks of healing in both the ACL-repaired and contralateral, ACL-intact joints.

Results: Enhanced ACL repair with bone-to-bone fixation significantly improved yield load and linear stiffness of the ACL repairs (P < .05) after 15 weeks of healing. However, laxity values of the knees were similar in both groups of repaired knees (P > .10).

Conclusions: Using an enhanced ACL suture repair technique that includes bone-to-bone fixation to protect the repair in the initial healing stages resulted in an ACL with improved structural properties after 15 weeks in the porcine model.

Clinical relevance: The healing response of an ACL suture repair by use of a collagen-platelet composite can be enhanced by providing bony stabilization between the tibia and femur to protect the graft during the initial healing process in a translational model.

Fig. 1

Schematic of the enhancement of the suture repair using the collagen-platelet composite (CPC) for the LIGAMENT group (A) and the TIBIA group (B). For the pigs in the LIGAMENT group, the two #1 Vicryl sutures (green) were secured in the distal ACL stump using a modified Kessler stitch. A suture anchor was placed into the bony femoral ACL insertion site. The collagen-platelet composite was threaded onto the sutures exiting the anchor and passed into the notch (Insert). The sutures from the anchor were then tied to the Vicryl sutures in the distal ACL stump with maximum manual tension. For the pigs in the TIBIA group, the femoral anchor and collagen-platelet scaffold were placed in the same manner, and after the collagen-platelet composite was threaded onto the femoral sutures, the sutures were passed through the through the tibia tunnel (B) and tied over a delrin button at the anteromedial tibial cortex with the knee in 60° of flexion

Fig. 2

Schematic of the load-displacement curve from the mechanical testing demonstrating the key mechanical parameters used to evaluate the function of the repair groups. The slack region is designated as the displacement from 5N of compression on the joint to 5N of tension. The linear stiffness is calculated as the slope of the load-displacement curve between the points corresponding to 20% and 80% of the yield load. Yield load is defined as the point where the load-displacement curve becomes non-linear and failure load is the maximum load supported by the sample before failure. Figure used with permission.

Fig. 3

Shown is an anterior (left) and sagittal (right) view of a enhanced ACL repair from the TIBIA group after 15 weeks of healing.

Fig. 4

Bar graph of AP laxity at 30°, 60° and 90° of flexion for both types of repair (LIGAMENT and TIBIA) and the INTACT group. The AP laxities of the repaired knees were similar in both groups (Table 1). However, the AP laxities of all of the treated knees (LIGAMENT and TIBIA) were significantly greater than their intact contralateral controls at fifteen weeks (p<0.0001 for all angles).

Fig. 5

Mean load-displacement curves for TIBIA, LIGAMENT and INTACT groups where the curve starts at 5N of tension showing the highest linear stiffness and yield load in the INTACT group, with the enhanced repair group with bony fixation (TIBIA) comparing favorably to the LIGAMENT group in terms of replicating the INTACT ligament behavior at low load conditions. Error bars represent one standard error. For statistical analyses, the failure properties were normalized to the contralateral INTACT knee (Table 1).