Hybrid Bone-Tendon Grafts for Enhanced Tendon Healing
Abstract
This proposal addresses the Surgical Care Focus Area of Soft Tissue Trauma. Bone-tendon interface is a mechanically, compositionally graded, and structurally continuous tissue that is maintained by multiple musculoskeletal cells, including bone formation cells, fibrocartilage cells, and tendon cells. The native rotator cuff bone-to-tendon interface (enthesis) consists of bone, mineralized fibrocartilage, unmineralized fibrocartilage, and tendon regions. This gradually progresses from soft tendon to hard bone, spanning 0.10 mm to 1.0 mm in length, which minimizes stress concentrations during physiological motion. Rotator cuff injuries in the active military present unique challenges because traumatic or repetitive overhead injuries are inherent with the job description. Additionally, active duty personnel have basic physical demands that include overhead work activities and physical fitness requirements. In addition, over 200,000 rotator cuff surgeries are performed annually in the United States alone, with an estimated cost of $3.44 billion USD. Presently, the clinical management of rotator cuff injuries involves physical therapy, surgical intervention or a combination thereof. During surgical repair, medical devices known as suture anchors are affixed to bone, allowing either suture alone or a combination of suture and a tendon-like graft to be secured to the injured tendon. These current treatments lead to mechanically inferior scar tissue after healing instead of native enthesis. Failures usually occur along the suture-tendon interface. High re-tear rates ranging from 20% for small tears to 94% for large tears have been reported. With massive tears, the tendon may actually be irreparable. As such, research efforts to pursue more consistent tendon-to-bone healing will enable active duty personnel to reliably return to full military Service. Although natural and synthetic tendon grafts are commercially available, they are not commonly used due to poor clinical outcomes. For example, rotator cuff patches have been employed as bridging grafts but their rapid degradation within 3 to 6 months were associated with failed repairs and patient complications. Although alternative treatments exist, tendon transfers are associated with donor site morbidity and typically suitable for young patients with minimal glenohumeral arthritis while total shoulder arthroplasty, due to its highly invasive nature, results in high morbidity. While the underlying reasons for this lack of efficacy vary, materials and devices that mimic the features of native tissues are expected to improve clinical outcomes. Research efforts have focused primarily on the development of materials to sustain physiological loading and the administration of biochemical cues to direct healing. Efforts on material development include engineering non-graded materials as tendon substitutes or engineering mechanically graded materials to mimic the bone-tendon interface. Applications of biologic materials have included the use of platelet-rich plasma, bone- and tendon-promoting growth factors and extracellular matrix, stem cell delivery, and genetic engineering to try to improve healing. However, there has been a paucity of literature in re-establishing native bone to tendon interface and multi-tissue continuity. No previous studies have simultaneously demonstrated approximation of bone and tendon mechanical properties, spatial control of musculoskeletal differentiation, and physicochemical features for structural continuity and integrity. Most recently, we have demonstrated promising results in hybrid bone-tendon (Hybt) graft development and rotator cuff repair: (1) novel polymers approximated the mechanical properties of bone and tendon tissue by varying ultraviolet light exposure, (2) a structurally-continuous, mechanically-graded Hybt graft was fabricated, (3) gently-graded interfaces offset stress concentrations compared to steeply-graded ones, (4) growth fac
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 29, 2021
- Source ID
- W81XWH2010343
Entities
People
- Yunzhi Peter Yang
Organizations
- Stanford University
- United States Army