Of all the musculoskeletal conditions that affect both professional and weekend athletes, complete tears of the rotator cuff tendon(s) remain one of the most significant therapeutic challenges to the orthopedic surgeon. Rotator cuff tears affect more than four million people annually in the U.S. and are the most common source of shoulder pain and disability. There is a well-recognized need for a better solution to treat the condition.
Even with technological advances in fixation devices (i.e. suture anchors) and arthroscopic surgical techniques, repairs of full-thickness rotator cuff tears still result in a high rate of re-tears and impaired function. Part of the problem is that these advances fail to address the underlying problem. Consider that trying to fix the rotator cuff is often like trying to sew together fabric with lots of holes. Improving the quality of the “thread” will only get us so far. What we really need to focus on is improving the quality of the underlying tissue – the “fabric” in this analogy.
The challenges associated with poor tissue quality at the time of surgery have led to an influx of collagen ‘patches’ designed to biomechanically augment the repair by providing increased tissue strength and stiffness at the time of surgery. However, because these patches are often chemically treated to increase their strength and stiffness, they do not allow normal incorporation or remodeling in the host. Ultimately, these patch augmentations cannot overcome the significant tissue loss associated with massive rotator tears and surgical results are not significantly improved.
One potential solution to the problem of rotator cuff repair may lie in earlier intervention. Partial-thickness tears of the supraspinatus tendon comprise a complex and significant pathological process that is increasing in prevalence as the population ages. These partial thickness tears are known to progress over time with up to a third becoming full-thickness tears. The ability to treat partial thickness cuff tears earlier may offer a ‘window of opportunity’ to restore normal tissue structure and function. Currently, a variety of treatments are utilized, including strengthening exercises, debridement, acromioplasty, in situ repair, and completing the tear so as to allow for a conventional surgical repair. However, the literature suggests that none of these approaches have produced consistent clinical outcomes.
An innovative approach to treating partial thickness tears may lie in ‘leveraging’ the body’s own repair mechanisms to create a more favorable environment for the healing process. Studies suggest that partial thickness tears may result from differential shear strains in a rotator cuff tendon causing a portion of the tendon fibers to rupture. This, in turn, increases the strain at the tear site and adjacent tendon tissues, which can disrupt the normal healing response. By simply increasing the thickness of the rotator cuff tendon over a partial thickness tear site, this strain could be reduced over 40%, thus significantly improving the biomechanical healing environment of the tissue.
The ability to induce the formation of a tendon-like tissue which increases the cross sectional area of the normal rotator cuff tendon could represent a novel, early intervention, treatment option for rotator cuff pathologies. However, two important design criteria need to be met:
- The creation of a bioactive scaffold to induce the formation of a functional, tendon-like tissue
- The ability to deliver and implant this bioactive scaffold arthroscopically
While previous collagen patches, derived from human dermis or animal dermis, small intestine submucosa, or pericardium, were designed to immediately augment the strength of a rotator cuff repair, they necessitated a mini-open approach for insertion by all but the most accomplished arthroscopic surgeons. In addition, the mechanical properties (i.e. stiffness) and collagen orientation of theses patches did not always favor the creation of a functionally-oriented, tendon-like tissue. Because some scaffolds were chemically treated so as to add strength and stiffness to the construct, they were never fully incorporated into the host and were often walled off with remnants of the scaffold still present several years after implantation. Finally, increased levels of residual donor DNA in these allografts/xenografts were a source of concern.
To address these issues, Rotation Medical investigated many scaffold designs and materials before settling on a highly oriented and highly porous (85-90% porosity) collagen scaffold. This scaffold was not designed to immediately augment the initial mechanical environment of the rotator cuff but rather to ‘partner’ with the body’s inherent healing capabilities to induce the formation of new tendon-like tissue. This new tissue then serves to optimize the healing environment of partial tear lesions by decreasing intra-tendinous strain. Preclinical animal studies have confirmed the biocompatibility as well as tissue induction and conductions attributes of this bioscaffold. The rapid induction of an oriented, collagen-based extracellular matrix in the absence of any inflammatory or foreign-body response was consistently observed as was the disappearance of the collagen scaffold by six months. These results provided the basic science foundation for a first in man study.
As noted previously, another design challenge is the ability to easily and accurately implant the bioscaffold arthroscopically. This important issue has been addressed through an iterative design process by which a complete surgical ‘system’ was created to allow for precise arthroscopic implantation. This concept of coupled ‘implant and instrumentation’ has served the total joint world well and its application to rotator cuff repair represents a new and innovative approach to this surgery.
This early interventional, biological approach to the treatment of rotator cuff pathology advocated by Rotation Medical represents a significant change in the therapeutic paradigm. The ability to enhance the inherent biological healing mechanisms of an individual to regenerate a more normal tendon before significant pathological changes occur which may preclude complete recovery is an exciting concept in regenerative therapy. While initial clinical data has shown excellent results, additional analysis and clinical experience will better define the clinical potential for this regenerative therapy concept.