Columbia University Irving Medical Center
A common practice by shoulder surgeons may be harming the success of rotator cuff surgery, suggests a new study by orthopedic scientists and biomedical engineers at Columbia University. The work is published in the journal Science Translational Medicine .
The subacromial bursa modulates tendon healing after rotator cuff injury in rats
Publisher’s summary
Rotator cuff tendon surgery frequently includes removal of the subacromial bursa ; However, the biological role of this fatty tissue in tendon injury and repair remains unclear. Marshall et al. report that the bursa is not a bystander tissue but actively participates in the inflammatory and repair processes after tendon injury. In clinical biopsies and in a rodent model of supraspinatus tendon injury, the bursa responded to nearby tendon injury by upregulating genes associated with inflammation and healing. Removal of the bursa in the rat altered the expression of inflammatory cytokines and had a detrimental effect on the intact adjacent infraspinatus tendon and humeral head. These results suggest that bursa removal during rotator cuff surgery should be further evaluated. —Molly Ogle
Summary
Rotator cuff injuries result in more than 500,000 surgeries annually in the United States, many of which fail . These surgeries typically involve repair of the injured tendon and removal of the subacromial bursa , a synovial-like tissue found between the rotator cuff and the acromion. The subacromial bursa has been implicated in the pathogenesis and healing of the rotator cuff.
Using proteomic profiles of bursa samples from nine patients with rotator cuff injury, we show that the bursa responds to injury to the underlying tendon. In a rat supraspinatus tenotomy model, we evaluated the effect of the bag on the injured supraspinatus tendon, the uninjured infraspinatus tendon, and the underlying humeral head. The bursa protected the intact infraspinatus tendon adjacent to the injured supraspinatus tendon by maintaining its mechanical properties and protected the underlying humeral head by maintaining bone morphometry. The bursa promoted an inflammatory response in the injured rat tendon, initiating the expression of genes associated with wound healing, including Cox2 and Il6.
These results were confirmed in rat pouch organ cultures. To evaluate the potential of the pouch as a therapeutic target, dexamethasone-loaded polymer microspheres were administered into the intact pouches of rats after tenotomy. Dexamethasone released from the bursa reduced Il1b expression in the injured rat supraspinatus tendon, suggesting that the bursa could be used for drug delivery to reduce inflammation in the healing tendon.
Our findings indicate that the subacromial bursa contributes to the healing of the underlying tissues of the shoulder joint , suggesting that its removal during rotator cuff surgery should be reconsidered.
The subacromial bursa modulates tendon healing after rotator cuff injury in rats
Figure: Anatomy of the rotator cuff. The bursa is a thin, fluid-filled sac that was originally thought to protect the rotator cuff tendons by providing a cushion between the tendons and adjacent bones. While repairing injuries to the rotator cuff tendons, surgeons often remove the bursa because they suspect it is a source of inflammation and pain in the shoulder. Credit: Stavros Thomopoulos.
During surgery, surgeons typically remove tissue called the subacromial bursa while repairing torn tendons in the shoulder joint, but the study suggests the small tissue plays a role in helping the shoulder heal.
"It is common to remove the bursa during shoulder surgery, even for the simple purpose of visualizing the rotator cuff," says Stavros Thomopoulos, Ph.D., senior author of the study and professor at the Robert E. Carroll and Jane Chace Carroll Laboratories. . Orthopedic Surgery at Columbia University Vagelos College of Physicians and Surgeons.
"But we don’t really know the role of the bursa in rotator cuff disease, so we don’t know all the implications of removing it," Thomopoulos says. "Our findings in an animal model indicate that surgeons should not remove the bursa without carefully considering the consequences."
The challenge of rotator cuff surgery
Most damage to rotator cuff tendons comes from wear and tear that accumulates over years of repetitive motion. Among people over 65, about half have experienced a rotator cuff tear, which can make simple daily tasks like combing your hair difficult and painful.
More than 500,000 rotator cuff surgeries are performed each year in the United States to repair these injuries, restore range of motion, and relieve pain, but they frequently fail, from one in five surgeries in young patients to up to 94% in older people with large tears.
Rotator cuff repairs usually fail due to poor healing between the tendon and bone, where the tendon reattaches to the bone.
Bursa: Friend or Foe?
The bursa is a thin, fluid-filled sac that was originally thought to protect the tendons by providing a cushion between the tendons and adjacent bones.
The bursa often becomes inflamed, sometimes at the same time, when underlying tendons are injured, and surgeons often remove the tissue because they suspect it is a source of inflammation and pain in the shoulder. But recent studies suggest that the tissue may be performing other biological functions besides mechanical cushioning, including promoting the healing of shoulder tendon injuries .
To explore the role of the bursa in rotator cuff disease, Thomopoulos and graduate student Brittany Marshall examined rats with repaired rotator cuff injuries, with and without removal of the bursa.
Removal of the bursa damages uninjured tendons
After rats underwent repair of a rotator cuff injury, the researchers measured the mechanical properties of the repaired tendon and an adjacent undamaged tendon, the quality of the underlying bone, and changes in protein and gene expression.
The researchers found that the presence of the bursa protected the undamaged tendon by maintaining its mechanical properties and protected the bone by maintaining its morphometry. When the bursa was removed, the strength of the undamaged tendon deteriorated and the quality of the bone deteriorated.
"The loss of mechanical integrity in the uninjured tendon in the absence of the bursa was surprising," says Thomopoulos. Uninjured tendons of the shoulder often degenerate over time after the initial injury, and "animal data imply that retaining the bursa may prevent or delay the progression of this pathology."
In the damaged tendon, the researchers found that the bursa promoted an inflammatory response and activated wound healing genes, but no changes were observed in the mechanical properties of the repaired tendon two months after the repair. Differences in mechanical properties may be detected after a longer curing period, says Thomopoulos, something the research team is currently investigating.
"Overall, what we are seeing is a beneficial role of the bursa for rotator cuff health, in contrast to the historical view that the inflamed bursa is detrimental," says Thomopoulos.
The researchers documented similar changes in cells and proteins in bursa samples from patients who underwent surgery to repair rotator cuff injuries, suggesting that comparable processes may occur in people.
The bursa as a drug delivery depot
If the bursa is not removed, the tissue could be used to deliver medications to the repaired tendon to improve healing.
Thomopoulos and Marshall explored this possibility by injecting corticosteroid microspheres into the bursa of their rat model after tendon injury. Steroids are often used to treat musculoskeletal injuries and reduce inflammation.
"The treatment results are somewhat preliminary and require additional time points and mechanical characterization before we can draw solid conclusions," says Thomopoulos, "but our initial data support the idea that the pouch can be therapeutically targeted to improve healing of the rotator cuff".
