麻豆传媒

Shoulder bursal tissue is often removed during rotator cuff repair, but that might not be such a good idea, researchers said.

Studies with human bursa samples and in rats with tendon injuries showed that the subacromial bursa helped protect intact structures and promoted inflammatory responses in injured tendons associated with healing, according to Stavros Thomopoulos, PhD, a biomechanical engineer of Columbia University in New York City, and colleagues.

Moreover, the researchers found that dexamethasone-containing microspheres could be injected into the rat bursa, with the steroid's slow release diminishing harmful inflammation in tendons that were healing.

"Our findings indicate that the subacromial bursa contributes to healing in underlying tissues of the shoulder joint, suggesting that its removal during rotator cuff surgery should be reconsidered," Thomopoulos and colleagues wrote .

The researchers pointed to high failure rates for rotator cuff repair procedures -- as high as 94% in older people with substantial damage -- as a reason to explore ways to improve outcomes.

"Surgical repair or reconstruction of the damaged rotator cuff tendon is typically accompanied by decompression of the subacromial space by debriding the overlying bone (acromion) and removing the subacromial bursa," they explained. The bursa can block the surgeon's view of the damaged structures, and there has been a belief that the decompression helps to speed healing. However, the researchers noted, evidence to support the latter rationale is lacking.

Traditionally, the squishy bursa was believed to play a purely passive mechanical role, as a cushion between the acromion bone and rotator cuff tendons. But studies over the past couple decades have shown that it's more complicated than that, housing blood vessels and mesenchymal stromal cells. It also seems to be involved in inflammatory responses to damage in the adjoining tendons.

All of this, Thomopoulos and colleagues argued, supports "a biological role for this tissue in addition to its previously described mechanical role."

The group also hypothesized that the bursa could provide an ideal point for depositing drugs that could promote local tendon healing. "The bursa is largely composed of adipose tissue, making it a potential endogenous reservoir for lipophilic drug delivery systems," they wrote.

Thomopoulos and colleagues analyzed bursa and tendon samples from nine patients with rotator cuff tears under the microscope and with proteomic techniques. These studies showed distinct changes to both the bursal and tendon proteomes that varied with the presence of a tendon tear and, in the case of the tendon proteome, to the tear size. The findings were consistent with "a molecular response in the adjacent bursa" when a tendon was damaged. Moreover, these responses varied within the bursa, depending on the tissue subtype involved (fatty, fibrous, or vascular).

Further studies were conducted in Sprague-Dawley rats, whose shoulder anatomy is sufficiently like that of humans to serve as a "clinically relevant model," the researchers said. These animals had their supraspinatus tendon cut surgically to simulate rotator cuff tear. After 8 weeks, it was apparent that the bursa had morphed, from primarily fatty to a greater proportion of vascular and fibrous tissue. Gene expression profiles in the bursa also changed markedly in comparison with tissues from uninjured rats, suggestive of new infiltration by immune cells and also of processes associated with wound healing.

Another important finding was that, following supraspinatus tendon rupture in the rats, the infraspinatus tendon and humeral head remained relatively healthy 8 weeks later when the bursa was kept in place, but were less so when the bursa had been removed. In a slightly different experiment, it appeared that healing occurred faster without bursectomy.

Lastly, injection of slow-release dexamethasone microspheres into the bursa at the time of tenotomy led to reduced interleukin-1 and interleukin-6 expression in the severed tendon, suggesting a benefit to healing.

Thomopoulos and colleagues noted that inflammation isn't always unhealthy. In their study, the results suggested that inflammation "may incite infiltration of key cellular players that are essential to the healing process." Of course, it can also interfere with healing, which is why the researchers were pleased that the dexamethasone microsphere treatment appeared to limit expression of pro-inflammatory cytokines.

The study's most important limitation was its conduct in rats. However, while the use of dexamethasone microspheres will require more research before trying it clinically, surgeons are free to consider leaving the bursa intact during routine rotator cuff repair, given the shaky rationale for the bursectomy tradition.

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