Monday, May 25, 2015

The rotator cuff deficient shoulder, superior instability, and rocking horse loosening

Like the normal shoulder, the anatomic shoulder arthroplasty is stabilized by concavity compression: the action of the rotator cuff compressing the humeral head into the glenoid concavity as well as by the articulation of the cuff-covered head against the coracoacromial arch. In some cases this stabilizing mechanism remains functional even though the cuff is not completely intact . However, in the absence of a sufficiently functional cuff, the humeral head is not stabilized in the socket so that contraction of the deltoid pulls the humerus superiorly. This superior displacement can compromise the effectiveness of the superior lip of the glenoid concavity. Over time this process can lead to rounding of the humeral tuberosities - which we have named ‘femoralization’ - along with the creation of a socket that includes the acromion, coracoacromial arch and upper glenoid – which we have named ‘actetabularization’.

The combination of a deficient rotator cuff and shoulder arthritis is referred to as cuff tear arthropathy. Instability from cuff deficiency also arises when the cuff tendons fail after shoulder arthroplasty and when tuberosity fractures have compromised the ability of the cuff to insert securely into the humerus. In the absence of the normal stabilizing effect of the rotator cuff, the coracoacromial arch may provide secondary stabilization of the humeral head in the glenoid unless the arch has been compromised by acromioplasty or wear.  When the head is superiorly displaced relative to the glenoid, , an anatomic total shoulder often unsuccessful. As the examples below demonstrate, superior displacement of the humeral head relative to the glenoid places an anatomic prosthetic glenoid component at risk for rocking horse loosening from eccentric loading, one of the most common findings of failed total shoulders that have been referred to us.



In evaluating a shoulder with major cuff deficiency, it is important to document any history of prior injury, surgery, or infection. Physical examination includes evaluation of the skin and prior incisions, passive range of motion, active range of motion, strength of the deltoid, subscapularis and infraspinatus, and the function of all peripheral nerves. The combination of good passive motion, inability to actively elevate the arm in the presence of intact deltoid function is known as pseudoparalysis. Anterosuperior escape refers to the superior displacement of the humeral head on attempted active elevation of the arm. Standardized x-rays are needed to evaluate the integrity of the humeral and glenoid bone. While a number of different approaches have been used to classify the various degrees of pathology seen with cuff tear arthropathy, our approach to rotator cuff tear arthropathy is based primarily on the history, the physical examination, standardized plain radiographs and the characteristics and needs of the patient.

In considering treatment, one must not overlook the potential value of non-operative management. We have been referred many patients for consideration of reverse total shoulder arthroplasty whose primary problem was shoulder stiffness or weakness from disuse. A gentle progressive range of motion and strengthening program can substantially increase the comfort and function of shoulders with large cuff tears, in spite of the presence of a degree of arthritis. Even if these exercises do not sufficiently improve the condition of the shoulder, they can facilitate both the surgery and the post-surgical recovery. Before proceeding to surgery, a detailed discussion with the patient is needed to understand his or her functional goals as well as the risks of falling, especially if Parkinson’s disease or other issues with balance are present. Because individuals with cuff deficient shoulders are often older and debilitated, careful planning is necessary to minimize the risk of surgery as well as to optimize their post hospital support and recovery.

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