Sunday, May 22, 2011

Ream and Run for Shoulder Arthritis - healing of the reamed bone - research foundation 2

Our May 16 post illustrated some long-forgotten work on the hip, showing that after reaming the bone of the hip socket, the surface of the bone could heal over with a smooth layer of soft tissue. My colleagues John Clark and John Sidles along with Kristi Gibbs and Tony Norman performed an in vivo lab study of the healing response of the canine socket in response to glenoid reaming followed by a period of articulation with a metal humeral implant. The full text of the article can be seen here. The normal canine socket in cross section is shown below. Note the reddish staining cartilage on the surface and the blue bone beneath.

The surface of the glenoid was then reamed using a specially designed reamer, shown below.

The smooth reamed surface is shown below.

A cross section after reaming is shown below. Note that the glenoid has a new contour different than that of the normal socket and that all of the cartilage has been removed. The many small bone plates (trabeculae) that previously supported the surface cartilage have been fractured by the reaming. We suspect that these many small fractures along with the accompanying bleeding bring stem cells and growth factors to the reamed surface to instigate the healing response.

The humeral head (ball side of the shoulder's ball and socket joint), was replaced with a special humeral prosthesis.

This is shown in place on a post-operative x-ray.
After 10 weeks of use, the cross-section of the glenoid shows substantial, but incomplete healing of the reamed surface by red-staining soft tissue.

On closer look, buds of regenerating soft tissue (red) can be seen pushing up from the reamed bony surface (blue-green) indicated by the arrow. The black dots in the soft tissue represent living cells. It is of note that this regenerative surface is powerful, pushing up against the resistance of the metal ball articulating with the reamed glenoid surface. This reminds me of the power of tree roots growing beneath the sidewalk.
At 26 weeks, a cross section of the glenoid shows complete healing with red soft tissue covering the reamed glenoid surface.

The regenerated soft tissue is firmly bonded to the underlying bone by arching strands of fibrous tissue. This type of fixation could not be accomplished with a plastic socket or by interposing a graft of capsule or meniscus between the humeral head and glenoid. Note also that the red soft tissue contains living cartilagenous cells, confirming that fibrocartilage has regenerated on the surface.

While this surface covering is not the same as the hyaline cartilage that covers normal joints, it appears to provide a smooth and durable covering for bone articulating with a metal ball. In contrast to an artificial surface that deteriorates over time, this living, smooth joint surface firmly bonded to the underlying bone has the potential to remodel continuously with use.


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