As the number of aging, physically active Americans increases, so does the prevalence of surgeries for symptomatic rotator cuff tears. Approximately one quarter of U.S. adults will experience a rotator cuff tear at some point in their lives, with the incidence increasing to near 50 percent in adults older than age 70. As a result, nearly 300,000 rotator cuff surgeries are performed every year in the United States, with a combined cost to the healthcare system of about $3 billion annually. Unfortunately, rotator cuff repair surgery has a fairly high rate of recurrent tearing—from 20 percent up to 70 percent. This is especially true for older patients.
These suboptimal clinical outcomes for older patients may be the result of diminished healing potential for the rotator cuff tendons and/or deficiencies in the overall healing capability in the elderly patient population—a subject that has not been well studied. With a 2011 Orthopaedic Research and Education Foundation (OREF) Resident Clinician Scientist Training Grant, Sandeep Mannava, MD, PhD, used an animal model to investigate the effects of age on tendon-to-bone healing in the surgically repaired rotator cuff. The study’s findings were recently published in The American Journal of Sports Medicine (April 2014).
“Identifying the pathophysiology of tendon-to-bone healing in the aged is essential for improving outcomes after rotator cuff repair surgery,” said Dr. Mannava, a resident/physician scientist in the department of orthopaedic surgery at Wake Forest University in Winston-Salem, N.C. “By unraveling the biologic mechanisms that underlie rotator cuff tendon healing, we have the potential to improve our understanding of tendon-to-bone healing, which may eventually lead to age-specific interventions for the management of rotator cuff tears,” he added.
Do older shoulders heal differently?
Dr. Mannava employed a small-animal model to study the rat rotator cuff, which shares remarkable similarities with the anatomy of the human shoulder. For the purpose of these experiments, a 10-month-old rat is considered middle-aged and a 28-month-old rat is considered old. A total of 56 rats underwent rotator cuff repair surgery during which a rotator cuff tear was artificially created and then surgically repaired. The shoulders were harvested and studied, with the following two main objectives:
- histologic evaluation of the rotator cuff tendon-to-bone structure after lesion repair in both age groups
- quantification and comparison of the effect of age on the biomechanical properties of the repaired rotator cuff tendons in both age groups
“We learned that aged individuals heal differently than younger individuals,” said Dr. Mannava. “Our hypothesis was that the middle-aged rats would have increased healing potential and show more extensive remodeling and biomechanical integration of the repaired rotator cuff tendon after surgery when compared to the older rats. Our data seem to support this experimental hypothesis.
“Further,” he added, “we saw greater organization and structural biomechanical recovery of the tendon-to-bone morphology in the middle-aged group. Now that we have established that differences in the aged healing environment exist, future studies can begin to examine what factors make the healing response less robust in aged individuals.”
Future molecular studies will examine in vivo osteointegration, tendon remodeling, and muscle healing to better define the cell signaling pathways and growth factor expressions that underlie rotator cuff healing. If these factors can be confirmed, it is likely new treatment methods can be developed for older patients, whether by modifying surgical techniques or augmenting them with growth factors to improve bone-tendon healing.
Improved outcomes for older patients
“The OREF grant is incredibly important in moving this research forward,” said Dr. Mannava. “This is a highly understudied area of orthopaedic research. Although we know clinically it’s a problem of aging, many animal models for rotator cuff tears don’t account for age; we don’t see many basic scientists looking at the role of aging and its influence in the rotator cuff. I think this particular study is quite novel, and it was made possible by the grant funding from OREF.”
Dr. Mannava is optimistic that the results will have important implications for improving the outcome of rotator-cuff surgeries in older patients. “Ultimately, I hope that this advanced knowledge will improve patient outcomes, with expedited return to independent living and recreational activities for elderly patients who have undergone rotator cuff surgery,” he said.
Mark Crawford is a contributing writer for OREF. He can be reached at email@example.com