Soft tissue graft interference fit fixation: observations on graft insertion site healing and tunnel remodeling 2 years after ACL reconstruction in sheep

Abstract

Using soft tissue grafts for anterior cruciate ligament (ACL) reconstruction, insertion site healing plays a crucial role in the long-term fate of the graft. It has been shown in an experimental animal study that using a soft tissue graft and anatomic graft fixation, a direct ligamentous insertion alike the native ACL developed 24 weeks postoperatively. Yet there are no reports on the long-term insertion site healing of anatomically fixed soft tissue grafts. The objective of this study was to evaluate graft insertion site healing, the intra-tunnel fate of the graft and its osseous replacement 2 years after ACL reconstruction in sheep. The left ACLs of six sheep were replaced by an autologous flexor tendon split graft and anatomically fixed with biodegradable poly-(D, L-lactide) interference screws. Animals received polychromic sequential labeling at different points in time to determine bone apposition per period. For evaluation of the insertion site healing and intra-tunnel changes, MRI scans were taken in vivo. Following sacrifice, radiographic imaging, conventional histology and fluorescence microscopy was undertaken. Most of the specimens showed a wide direct ligamentous insertion. It showed patterns alike the direct ligament insertion seen in intact ACLs. The intra-tunnel part of the graft had completely lost its tendon-like structure and in two cases, it was separated from the graft insertion by a thick bony layer. The biodegradable interference screw was fully degraded in all specimens. Ossification of the former drill tunnels was intense, showing only partial-length tunnel remnants in one femoral and three tibial specimens. As the graft heals to the joint surface and the aperture site is closed with soft tissue, mechanical stress of the intra-tunnel part of the graft is eliminated and the bone tunnel is protected from synovial fluid, resulting in osseous bridging of the tunnel aperture site, accelerated intra-tunnel graft resorption and its osseous replacement.

Graft healing in anterior cruciate ligament reconstruction

“…They also suggested that once the surface healing has been established, the intratunnel healing is stress shielded, and that portion of the graft is reabsorbed. These findings were confirmed in a 2-year study using the same animal model [48]. While the findings are important in understanding the healing process of soft-tissue graft using a direct type of fixation, no comparative group with different fixation device in these studies was used.…”

Graft-dependent differences in the ligamentization process of anterior cruciate ligament grafts in a sheep trial

“…Similar observations were made by Weiler et al [41]. After 12 weeks, the load to failure of the flexor tendon was in the range of most other studies [12,34,41,44]. However, the load to failure achieved by the patellar tendon graft was almost twice as high.…”

“…At what time the definitive stability of the anterior cruciate ligament grafts is reached in sheep is not quite clear. It is probable that no further substantial increase in load capacity occurs after one year [12,13]. Like the present study, no other sheep trials have shown that more than 66% of the biomechanical structural properties of a healthy anterior cruciate ligament are achieved by an anterior cruciate ligament graft [11,12,34,41].…”

“…It is probable that no further substantial increase in load capacity occurs after one year [12,13]. Like the present study, no other sheep trials have shown that more than 66% of the biomechanical structural properties of a healthy anterior cruciate ligament are achieved by an anterior cruciate ligament graft [11,12,34,41]. Johnson et al also suspects a different remodeling of the hamstring in humans compared with the patellar tendon autograft, since hamstrings are transplanted with the synovialized paratenon and the individual strands are smaller in diameter [16].…”

A watertight construct in arthroscopic rotator cuff repair

“…35,37,40,41,44,45,50 Synovial fluid has been shown to contain various matrix metalloproteinases that can impede tendonebone healing. 9,15,18,29 These cytokines and matrix metalloproteinases are elevated in the setting of rotator cuff tears. 49 In addition, the subacromial bursa in patients with rotator cuff tears contains a high level of expression of proinflammatory cytokines, proteinases, and cyclooxygenase enzymes, which are known to produce a catabolic environment.…”