Reversed shoulder prothesis in irreparable rotator cuff tears
In some cases, tears of the rotator cuff of the shoulder cannot be surgically repaired, particularly in older persons. This is due to the poor quality of the tissue, retraction of the tendon and fatty transformation of the muscle. In these cases, a reversed shoulder prothesis should be discussed.
In the images below, you can see the MRI and standard x-rays of 79-year-old man, who has pain in his shoulder, and cannot raise his right arm actively without the help of his other hand.
On the left, the arrow points to the torn remnants of the rotator cuff;
On the right, the arrow shows the pointed tip of the acromion, apart from the shoulder blade which has, over the years, caused the progressive degeneration and rupture of the cuff.
When the rotator cuff is torn beyond repair, the deltoid muscle, which can be seen as forming the outer contour of the shoulder, is unable to raise the patient's arm actively, because the rotator cuff is no longer there to help it. Patients have to help with their good arm to raise and lower the affected shoulder.
The head of the humerus is no longer maintained in a relatively low position, and moves upward and impinges against the acromion, as can be seen below:
This phenomenon causes pain and loss of motion.
The reversed prosthesis changes the anatomy of the shoulder, in order to allow the deltoid muscle to "act alone" without the help of the rotator cuff: below, left, the normal anatomic situation with an intact rotator cuff. The lever arm for the deltoid is relatively small, but thanks to the cuff, the deltoid can operate normally.
In the reversed prosthesis, on the right, the original "ball" formed by the humeral head is replaced by a "socket", and the original socket of the shoulder blade, the glenoid, is replaced by a ball, in fact a hemisphere. The center of rotation of the joint has been moved internally towards the midline of the body, thereby increasing the deltoid lever arm. This muscle is able again to function without the cuff.
On the x-ray picture below, you can see the base-plate fixed on the shoulder blade with two screws, and the humeral part which is wedged in the medullary cavity of the humerus. The hemisphere affixed onto the base-plate is not visible, because it is made of polyethylene (high-quality plastic), which is transparent to x-rays.
The surgery is done in the semi-sitting position, under general anesthetic, through a lateral incision of approximately 7 cm:
The surgery time is approximately 2 hours. Rehabilitation by a physical therapist begins on the next day, and is ar first entirely passive (no active motion from the patient). A side effect of the operation is a small dent in the shoulder contour on the front (above, right), where the humeral head used to be.
Hospital stay ranges from 3 to 7 days, after which physical therapy continues during 2 to 3 months on an outpatient basis.
Conclusion: the reversed shoulder prosthesis greatly allievates pain and restores a useful range of motion in patients with irreparable rotator cuff tears.
