Cuff Tear Arthropathy Humeral Head Replacement: When More Is Better
When confronted with the diagnosis of shoulder arthritis, it is incumbent on the treating physician to discern the complete nature of the pathology. Arthritic processes about the shoulder predictably involve disease both to the bony elements and to the soft tissues about the joint. While there are many options available for the surgical management of shoulder arthritis, the exact type of shoulder replacement depends on both the bone issues and the soft tissue issues as well. For the patient with a massive and irreparable rotator cuff tear, a cuff tear arthropathy (CTA) head may be most appropriate. Indications for humeral head replacement with the CTA head depend on specific anatomic and physiologic factors. For the patient with a massive and irreparable cuff tear who retains an intact coracoacromial arch, this type of prosthetic replacement provides predictable relief of pain while allowing significant improvement in function. Recovery of function requires a structured muscle re-education program.
Each implant designed for the shoulder has specific indications for its use. Because pathologic processes in the shoulder can include classic arthritis of the humeral head and glenoid in addition to degenerative processes of the rotator cuff, implants have been designed to address the various combinations of these clinical conditions. This paper will review and discuss the design rationale and specific indications for the cuff tear arthropathy (CTA) humeral head replacement (Fig. 1).
Figure 1. Photograph of the CTA head design. Note that the articular arc spans more than 180°. This allows the lateral portion to articulate with the acromion when there is no rotator cuff.
The ability to elevate the arm overhead requires a functional fulcrum for the deltoid muscle. In normal physiology, the rotator cuff functions as a dynamic fulcrum by locking the humeral head in the glenoid during arm elevation (Fig. 2). It is only by the combined action of the cuff and deltoid that shoulder elevation is accomplished. When the cuff is deficient and nonfunctional, as occurs in chronic cuff tears, this dynamic fulcrum is impaired and patients develop weakness and an ultimate inability to elevate their arm (Fig. 3). In some patients, the coracoacromial ligament will function as a static fulcrum and permit some ability to elevate the arm even in the face of a large and chronic rotator cuff tear. For this reason, preservation of the coracoacromial ligament has come to be understood as an important part of rotator cuff repair.1 For decades, it was thought that the coracoacromial ligament was little more than a vestigial structure, only present to provoke shoulder pain.2 And for decades, it was thought that it should be released or excised when shoulder impingement syndrome developed. However, current study and contemporary understanding recognize its critical importance in protecting against cuff tear arthropathy and superior shoulder escape3 (Fig. 4). Indeed, the presence or absence of a functional coracoacromial ligament will dictate whether a CTA head is appropriate or whether a reverse shoulder replacement is the better choice. The CTA head requires a functional “contained” head within the acromial arch, either through passive mechanisms (intact coracoacromial ligament) or by dynamic means (functional rotator cuff force couple).
Figure 2. The physiologic action of the rotator cuff is to lock the humeral head into the glenoid. The rotator cuff muscle contraction creates a dynamic fulcrum at the glenoid surface as noted by the black circle. The resultant force of the cuff muscles results in a medial and downward force on the humeral head. The resultant deltoid force vector then elevates the arm.
Figure 3. When the rotator cuff is deficient, there is no dynamically created medial fulcrum at the joint surface (open circle). The fulcrum is now moved superiorly (dark circle) and the resultant deltoid vector force only results in superior displacement of the humerus. Rotation and elevation of the arm are not possible.
Figure 4. This postoperative radiograph demonstrates what can occur when there is incompetence of the coracoacromial arch. This is referred to as “superior escape.” The arrow shows where the normal coracoacromial ligament should be. The humeral head replacement has migrated well superior to that line.
When the rotator cuff tears–typically through degenerative processes–there are both mechanical and physiologic sequelae that can lead to cuff tear arthropathy.4 Mechanically, the glenohumeral joint becomes unstable within the glenoid fossa. Because the cuff does not provide balanced compressive loads between the humeral head and glenoid, shear forces develop and ultimately there is mechanical failure of the articular cartilage resulting in “classic” glenohumeral arthritis. But much more occurs physiologically (Fig. 5). To some degree, the presence of the synovial fluid is important in the nutrition of the articular cartilage. As a rotator cuff tear becomes larger, the hydrodynamics of the fluid become altered and the nutritional and perhaps reparative status of the cartilage becomes impaired. This cycle becomes self-generating and progressive and extensive destruction of both the soft tissues and joint surfaces ensues. This leads to the classic presentation of the elderly patient with painful inability to elevate their arm—and the potential indication for the CTA shoulder replacement (Fig. 6).
Figure 5. Many physiologic sequelae arise from a massive rotator cuff tear. When the synovial fluid dynamics are disrupted, the articular cartilage becomes thin and atrophic and the head ascends, which results in mechanical abrasion of the tuberosity on the acromion. This causes formation of bone spurs and joint incongruity—ultimately resulting in cuff tear arthropathy.
Figure 6. This is a classic clinical photograph of a patient trying to elevate his arm in the presence of a massive rotator cuff tear with an inadequate dynamic fulcrum for the deltoid muscle.
Clinical Presentation
The classic patient with cuff tear arthropathy is a female in the seventh to eighth decade of life. While the condition may develop in a younger patient, the most common clinical scenario is one of a 70-year-old female with a slowly progressive inability to elevate her arm together with increasing pain. Rarely, if ever, does the condition begin acutely, even in the face of a traumatic event. Much more commonly, the patient will relate a pattern of increasing pain and weakness spanning many years. In some cases, the patient may have had a prior cuff repair in the distant past, which included division or resection of the coracoacromial ligament. Over time, with further degeneration and tearing of the rotator cuff, now without the benefit of a coracoacromial ligament to act as a passive restraint, cuff tear arthropathy develops.
Besides the obvious inability for the patient to elevate their arm, patients will have remarkable atrophy evident in their supraspinatus and infraspinatus fossae (Fig. 7). A fluid sign is a common clinical manifestation of the condition as well (Fig. 8). Because the synovial fluid is no longer contained by an intact rotator cuff, the clinical manifestation is usually unmistakable.
Figure 7. A clinical photograph demonstrating the extensive atrophy of the supraspinatus and infraspinatus muscles. Note the prominence of the scapular spines.
Figure 8. This patient has a massive cuff tear and cuff tear arthropathy. The large and bulbous appearance of the shoulder is caused by uncontained synovial fluid. This is called a “fluid sign.”
The massive cuff tear will result in weakness of both elevation and external rotation at a minimum. If the subscapularis muscle is also torn or nonfunctional, the patient will exhibit even less ability to elevate their arm while in a supine position. The combination of these muscle deficiencies result in the classic presentation of a patient unable to reach their mouth while keeping their elbow at their side as they eat.
In deciding the appropriate prosthetic device to implant in a patient with painful cuff tear arthropathy, it is critically important to ascertain the functionality of the coracoacromial arch. If a patient is unable to elevate their arm against the force of gravity, the physician must determine whether that inability is caused by pain alone or whether the inability of elevation is caused by absence of a functional coracoacromial arch and fulcrum for the muscle to act against. An important diagnostic test to consider involves injecting the joint (which is contiguous with the subacromial space in the presence of a large cuff tear) with a local anesthetic. If the patient is able to elevate their arm against gravity in the presence of the local anesthetic, a CTA humeral head replacement is the appropriate choice. This test suggests that the inability to elevate their arm is a result of pain. With pain, the patient is either unable or unwilling to contract muscles in an effort to elevate their arm. The fact that they can elevate the arm in the presence of a local anesthetic indicates that there is muscle power present in sufficient amount to lift the arm when that action does not cause pain. The CTA shoulder replacement diminishes the joint pain enough to act as a “permanent” local anesthetic (Fig. 9). Conversely, if the patient remains unable to elevate their arm in the presence of the local anesthetic, implying poor functional mechanics, a reverse shoulder arthroplasty becomes the better choice (Fig. 10).
Figure 10. A reverse shoulder replacement is indicated when, even in the face of a local anesthetic, the patient cannot elevate the arm, suggesting an incompetent dynamic deltoid fulcrum.
While plain radiographs alone will clearly demonstrate findings characteristic of a chronic massive cuff tear with superior migration and destruction of the articular surfaces, it is the clinical examination that provides the critical information for determining the appropriate surgical procedure. We must remember the wisdom that states: “We treat patients, not X-rays.” Nowhere is this more critical than in the condition known as cuff tear arthropathy.
References
1. 1Lee TQ, Black AD, Tibone JE, et al.Release of the coracoacromial ligament can lead to glenohumeral laxity: a biomechanical study. J Shoulder Elbow Surg. 2001;10:68–72. Abstract | Full Text |
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2. 2Neer CS. Anterior acromioplasty for the chronic impingement syndrome in the shoulder. J Bone Joint Surg Am. 2005;87:1399;(Original reference: J Bone Joint Surg 54:41-50, 1971). MEDLINE
3. 3Williams GR, Rockwood CA, Bigliani LU, et al.Rotator cuff tears: why do we repair them?. J Bone Joint Surg. 2004;86:2764–2776.
4. 4Neer CS, Craig EV, Fakuda H. Cuff-tear arthropathy. J Bone Joint Surg. 1983;65:1232–1244. MEDLINE
Department of Orthopaedic Surgery, Cleveland Clinic Foundation, Euclid, OH.
Address reprint requests to John J. Brems, MD, Department of Orthopaedic Surgery, Cleveland Clinic Foundation, 99 Northline Circle Dr., Suite 100. Euclid, OH 44119.
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