Biology and augmentation of tendon-bone insertion repair

Abstract

Surgical reattachment of tendon and bone such as in rotator cuff repair, patellar-patella tendon repair and anterior cruciate ligament (ACL) reconstruction often fails due to the failure of regeneration of the specialized tissue ("enthesis") which connects tendon to bone. Tendon-to-bone healing taking place between inhomogenous tissues is a slow process compared to healing within homogenous tissue, such as tendon to tendon or bone to bone healing. Therefore special attention must be paid to augment tendon to bone insertion (TBI) healing. Apart from surgical fixation, biological and biophysical interventions have been studied aiming at regeneration of TBI healing complex, especially the regeneration of interpositioned fibrocartilage and new bone at the healing junction. This paper described the biology and the factors influencing TBI healing using patella-patellar tendon (PPT) healing and tendon graft to bone tunnel healing in ACL reconstruction as examples. Recent development in the improvement of TBI healing and directions for future studies were also reviewed and discussed.

Figure 1

Photomicrographs showing the (a) Safrainin-O staining; (b) H&E staining and (c) polarized microscopic image of the direct tendon-to-bone insertion. Note the gradual transition of the four zone at the direct tendon-to-bone insertion. Magnification: 20×; B: bone; CFC: calcified fibrocartilage; UFC: uncalcified fibrocartilage; T: tendon.

Figure 2

ACL surgical operation procedures. (a) Expose knee joint; (b) Isolation of semitendinous graft; (c) Tide graft with holding suture; (d) Record the length and diameter of the graft; (e) Dislocate the parapatellar and remove the fat pad; (f) Identification and dissection of ACL; (g) Drilling of bone tunnel; (h) Pull the tendon graft into the tunnel; (i) Tide the femoral and tibial ends of graft to periosteum with knots at tension at 30° knee flexion; (j) Re-locate parapatellar; (k) Parapetaller wound closure; (l) skin wound closure.

Figure 3

A schematic diagram showing the contribution of mechanical and biological factors to the sub-optimal healing in ACL reconstruction.

Figure 4

Photographs showing the presence of chondrocytes at the interface between tendon-bone were associated with better Sharpey's fiber formation and better tendon osteointegration. (a) H&E staining; (b) SO: Safrainin O staining of corresponding H&E images; (c) Polarized: polarized images of corresponding H&E images of exit segment of femoral tunnel at week 6 after ACL reconstruction in a rabbit model. Magnification: 200×. B: Bone; dark arrowhead: chondrocytes; G: tendon graft; white arrowhead: Sharpey's fibers.

Figure 5

Approaches for Tendon-Bone Insertion Repair.

Figure 6

Diagram summarizing TBI injury treatment options currently available.