Correcting for Bone Deficiency and Deformity in Shoulder ReplacementIf you had a perfectly shaped shoulder with good bone stock, you probably wouldn't need a shoulder replacement. But the long-term effects of osteoarthritis (the number one reason for joint replacement) alter joint shape and biomechanics. And if those changes are not corrected during joint replacement, the chance of implant failure increases dramatically.
Surgeons performing shoulder replacements are often faced with challenging joint deformities. There can be areas of uneven or increased points of joint contact, defects in the bone, and twists or torsions of the bone structures. Poor bone quality can make it difficult for the implant to have the support it needs to function properly and last for a long time.
The authors of this review article help other surgeons appreciate the technical difficulty of correcting shoulder joint deformities. These modifications must be done during shoulder replacement surgery but before inserting the new joint (called a prosthesis or implant).
Eccentric reaming, posterior bone graft, augmented glenoid component, and surgical resurfacing are four surgical techniques described and discussed when facing glenoid bone loss. Glenoid tells us we are specifically dealing with the socket side of the joint.
Let's take a look at each of these options. First, what is eccentric reaming? It's a way to restore normal, even contact between the round head of the humerus (upper arm bone) and the glenoid fossa (shoulder socket).
The surgeon uses a shaver to reshape the curvature of the shallow socket and make it the same depth from front to back. Proper reaming is required for the implant to sit inside the socket and move with even contact and force between the two parts of the prosthesis. If there is more than 15 degrees of retroversion (backward twist), then eccentric reaming cannot be used effectively. Anything more than that requires the second treatment option: bone grafting.
When there isn't enough bone to work with, then the surgeon turns to bone grafting to smooth out uneven wear. There are many advantages to this approach and a few disadvantages. On the positive side, the bone lasts a long time and is considered a permanent solution. The surgeon can use the patient's own bone by using the removed humeral head.
Using bone graft material also gives the surgeon a chance to restore a more normal joint line. This effect prevents altered joint motion, which could lead to implant failure. On the downside, bone grafts can break down and dissolve or fail to bond with the natural bone. Using bone graft does require a certain skill level on the part of the surgeon to contour the joint properly.
The third solution (augmented glenoid component) refers to the use of plastic liners to help restore a normal joint line and build up areas of thin or deficient bone. Long-term studies to show results with this solution are not yet available.
And finally, the surgeon may turn to the use of joint resurfacing. Shoulder resurfacing that makes it possible to get a "new" shoulder without losing much bone and without replacing the whole thing. Instead the damaged surfaces of the joint are covered with a resurfacing prosthesis or implant.
In addition to saving bone there are many other advantages to the resurfacing technique. For example, the patient's normal anatomy is preserved. The prosthesis can be fit to the patient instead of the other way around.
The natural angle of the humeral (upper arm) bone is maintained. The cap that fits over the round humeral head has a peg that sets down into a hole drilled in the bone. The bits of bone taken from the hole are used to patch defects under the humeral cup. This means that the joint surface can be smoothed out and no bone is lost.
Joint resurfacing is most likely an option when there is still some joint surface left to work with. At least 60 per cent of the joint surface must be present. The rest can be treated with bone graft or bone graft substitute.
In summary, when choosing from among each of these surgical procedures, the surgeon must evaluate each patient individually to determine all possibilities. Every effort is made to avoid implant loosening or failure for any reason. The surgeon takes into consideration the amount and severity of bone loss and the type of deformities present. Eccentric reaming works well for mild bone loss or minor joint changes. More severe problems may require more extensive surgery (e.g., augmentation, bone graft, or joint resurfacing).
Benjamin W. Sears, MD, et al. Glenoid Bone Loss in Primary Total Shoulder Arthroplasty. In Journal of the American Academy of Orthopaedic Surgeons. September 2012. Vol. 20. No. 9. Pp. 604-613.
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