Histologic changes during healing with autologous fascia lata graft after superior capsule reconstruction in rabbit model

Superior capsule reconstruction (SCR) has been developed to improve shoulder function and relieve pain in the treatment of irreparable rotator cuff tears. Previous studies have reported that graft healing can enhance favorable outcomes after SCR. On the other hand, graft tears often lead to less desirable outcomes and sometimes require additional surgical procedures. However, the healing process underlying this remains unclear. In this study, we aimed to investigate histologic changes occurring during the healing process associated with autologous fascia lata graft after SCR in vivo. We hypothesized that (1) autologous fascia lata graft can regenerate the fibrocartilaginous insertion into both the greater tuberosity and superior glenoid and (2) the midsubstance of the grafted fascia gradually remodels into tendon- and/or ligament-like tissue after SCR. Irreparable supraspinatus tendon defects were created in 24 mature Japanese white rabbits (age, 6 months; mean weight, 3.2 kg). Four weeks after creation of the defects, the right shoulders were subjected to SCR using autologous fascia lata grafts. The left shoulders were left untreated. Samples from the shoulders were harvested at 4, 8, 12, and 16 weeks after surgery to undergo histologic and immunohistochemical examinations. Macroscopically, we did not observe graft tears after SCR in our experiments. Histologically, the number of chondrocyte-like cells gradually increased, and the extracellular matrices around those cells contained glycosaminoglycan at the fascia-bone junction after SCR. The unmineralized fibrocartilage, mineralized fibrocartilage, and tidemark were observed 16 weeks after SCR. The distribution of type II collagen presented a pattern similar to that of a normal tendon and ligament insertion. The cells and collagen fiber gradually oriented parallelly to the long axis in the midsubstance of the grafted fascia lata. Additionally, type III collagen was replaced with type I collagen in the midsubstance of the grafted fascia lata after SCR. SCR using fascia lata autograft regenerated the fibrocartilaginous insertion at both the greater tuberosity and superior glenoid. The midsubstance of the grafted fascia gradually remodeled into tendon- and/or ligament-like tissue. These results suggest that the fascia lata autograft has the capacity for graft-to-bone healing and remodeling after SCR.