Q: I had a very large rotator cuff tear repaired but it didn't hold. The surgeon said it was both a mechanical and a biologic failure.  Can you explain it?

A: Massive (very large) rotator cuff tears are at great risk of retears. Studies show a retear rate as high as 94 per cent. Not all of those retears are symptomatic but that is still not a very successful outcome.
Retears are considered "failures" that fall into one of two categories: mechanical and biologic.

Mechanical failure refers more to the technical aspects of the surgery. Perhaps the type of sutures used or the way the stitches are put in place contributes to mechanical failure. Some studies have pointed to the way the soft tissue attachment is prepared at the start of surgery. This area is called the footprint -- the place where the rotator cuff pulls away from the bone.

Biologic failures occur when your soft tissue just don't heal or hold as hoped. This has more to do with the tendon healing where it is repaired or reattached to the bone. There is some thought that if the healing tendon can be protected long enough from stress, strain, and overload, then the patient is much less likely to retear the repair.

Tears that occur while the patient is still in a sling are more likely to be mechanical failures. The person has not even started moving the arm or seeing the physiotherapistyet. This points to the strong possibility of the repair itself being the problem (a mechanical failure where the suture and tendon interface).

There aren't as many tears after six months, which supports the idea that once the repair is healed, unless there is a biologic weakness in the repair, the surgery should hold up quite well. Using serial ultrasound studies, the surgeons can see how the tendons are healing and that helps them know if the failure is mechanical, biologic, or both.

Studies have shown that the strength of the repair is superior when surgeons use suture anchors with a double-row fixation technique. Mechanical failures are more likely when holes are drilled through the bone and the tendons are reattached by threading them through the tunnels. The suspicion that where the tendon is stitched back to the bone (tendon-bone interface) is part of the problem or the "weak link" is another mechanical possibility under investigation.

Ultrasound images showing sutures in the gap between the tendon and the bone is an indication that the tendon has pulled away from the bone leaving the suture behind. The fact that the suture anchor is still in place and hasn't shifted further confirms mechanical failure as the cause of early retears.

In cases where the failure didn't occur until three months after rotator cuff repair, there may be a different story. There simply isn't enough tendon-bone healing to hold the repair. This is more of a biologic failure. And that raises a whole new set of questions.

For example, are there some other biologic or patient factors to explain this result? Does it have to do with the patient's age, general health, medications being taken, or the presence of other problems (e.g., diabetes, heart disease, cancer)? Some other studies have shown that the use of antiinflammatory drugs may have a negative impact on where the tendon is reattached to the bone.

Surgeons are actively studying the problem of rotator cuff retears looking for ways to improve the surgical technique. By recognizing there can be mechanical failures, biologic failures, or both it will eventually be possible to reduce and even eliminate factors contributing to any and all types of failures.

Reference: Bruce S. Miller, MD, MS, et al. When Do Rotator Cuff Repairs Fail? In The American Journal of Sports Medicine. October 2011. Vol. 39. No. 10. Pp. 2064-2070.