What Is the Best Surgical Treatment for Cuff Tear Arthropathy?

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Chapter 19 What Is the Best Surgical Treatment for Cuff Tear Arthropathy?

ROBERT H. HAWKINS, MD, FRCS(C)

HISTORICAL OVERVIEW

Cuff tear arthropathy (CTA) is the term Neer ^1,² originally proposed to describe a form of shoulder arthritis in association with long-standing rotator cuff deficiency. It is distinct clinically and radiographically from other forms of shoulder arthropathy in which joint destruction coexists with cuff deficiency such as rheumatoid arthritis or osteoarthritis with traumatically acquired cuff tear. The causative factor was first attributed to a crystal-mediated synovitis (the Milwaukee shoulder),^3,⁴ and it is still recognized that there is a correlation between large rotator cuff tears and high levels of calcium phosphate crystals in synovial fluid.⁵ It is now generally agreed that this unique pattern of joint destruction occurs because of, not simply in association with, rotator cuff deficiency. Mechanical and nutritional factors associated with progressive upward humeral head migration from loss of cuff integrity are its causes. This combination of pain, glenohumeral joint destruction, and a nonfunctioning rotator cuff present treatment challenges that stand apart from other forms of shoulder arthropathy.

PATHOMECHANICS

An understanding of shoulder biomechanics is necessary to appreciate surgical treatment options. The fact that shoulder muscles function as force couples in the coronal plane was first appreciated by Inman and colleagues ⁶ and expanded subsequently by Burkhart,⁷ who described a transverse force couple as well. Applying this theory to explain why full shoulder elevation is still possible in some shoulders with massive cuff tears and not in others, Burkhart⁸ identified three groups of fulcrum kinematics. Despite major cuff tearing, transverse and coronal force couples may remain intact and the fulcrum is stable; the humeral head is contained within the glenoid socket, and full elevation is possible. When force couples are destroyed by cuff tearing, the humeral head rises out of the socket on attempted arm elevation; that is, the fulcrum is unstable, and so-called pseudoparalysis of elevation results. In some cases, the humeral head may restabilize in a superiorly subluxated position under an intact coracoacromial arch, the so-called captured fulcrum, again allowing arm elevation (Fig. 19-1).

FIGURE 19-1 Swollen shoulder of an elderly woman with cuff tear arthropathy.

The dynamic action of muscle forces including those of the rotator cuff, together with other capsuloligamentous restraints, stabilize the humeral head through the concavity compression mechanism. As explained by Matsen and coauthors ⁹ and in the biomechanical analysis of De Wilde and coworkers,¹⁰ a loss of any of the normal osseous, capsuloligamentous, or muscular constraints leads to glenohumeral instability. Superior instability results from loss of the compression of the rotator cuff and spacer effect of the normal supraspinatus. Upward displacement of the humerus slackens the deltoid, making it less effective in humeral elevation and weakness, or even pseudoparalysis is the result. The coracoacromial arch is then the only remaining barrier to further upward migration. When this barrier has been compromised by frictional wear or aggressive surgical acromioplasty, anterosuperior escape of the humeral head occurs, further compounding pseudoparalysis.

CLINICAL PRESENTATION

CTA is the end stage of a continuum which begins with a simple cuff tear. The incidence of CTA is estimated to be anywhere from 4% to 20% of cuff tears.^11,¹² Patients with CTA typically present with pain and weakness of the shoulder and glenohumeral joint destruction on radiographs. Jensen and investigators¹³ collected clinical data on 104 cases from 10 different published reports and found the majority were elderly women (average age, 77.5 years), and almost 50% had bilateral involvement. Neer and researchers² describe the findings in 26 cases averaging 69 years of which 75% were women. No history of trauma was reported in 75%. The shoulders typically were swollen (Fig. 19-2), muscles were atrophic, and the long head of biceps ruptured. Passive motion was limited to an average of 90-degree elevation and 20-degree external rotation. Only 2 of 26 were able to actively elevate greater than 90 degrees. Positive lag signs for cuff deficiency¹⁴ are frequently seen. These include the lift-off test for subscapularis,^15,¹⁶ the external rotation lag sign for supraspinatus and infraspinatus, and the drop sign for infraspinatus. In the presence of a normal deltoid, the drop-arm sign is indicative of a massive posterosuperior cuff tear with loss of the ability to create a stable fulcrum. The term pseudoparalysis¹⁷ is also used when active shoulder elevation is less than 90 degrees in the presence of free anterior elevation with an intact deltoid.

FIGURE 19-2 Radiograph of a shoulder with advanced cuff tear arthropathy.

RADIOGRAPHIC FEATURES

Radiographic indicators of major cuff deficiency such as acromiohumeral narrowing and superior migration of the humeral head represent the earliest phases in a continuum that eventually leads to the joint destruction characteristic of true CTA.¹⁸ Chronic wear of the superiorly displaced humeral head sculpts the undersurface of the coracoacromial arch and glenoid, termed acetabularization. Rounding off of the tuberosities leads to femoralization of the humerus (Fig. 19-3). In advanced cases, there may be collapse of the humeral head.²

FIGURE 19-3 Force couples of the shoulder.

Seebauer ¹⁹ has proposed a classification of CTA (Fig. 19-4) that combines radiographic features with an appreciation of the altered fulcrum mechanics that Burkhart⁸ described. The four distinct groups are distinguished by the degree of superior migration from the center of rotation and the amount of instability at the center of rotation. In the most advanced category, IIB, the humeral head has escaped superiorly, removing any remaining fulcrum stability.

FIGURE 19-4 Seebauer’s radiographic and biomechanical classification of cuff tear arthropathy.

DIFFERENTIAL DIAGNOSIS

It is important to identify other forms of destructive arthopathy that resemble CTA but may require different treatment. Advanced rheumatoid arthritis of the shoulder often includes major cuff deficiency but typically is polyarticular in distribution. Osteoarthritis with incidental cuff tear lacks the characteristic component of vertical instability. Neuropathic arthropathy or Charcot shoulder presents radiographically with significant joint destruction but not of the coracoacromial arch.

TREATMENT

Medical management of CTA is based on specific needs and symptoms. When pain is minor and function remains good, mild analgesics and a gentle maintenance exercise program may be all that is necessary. Intra-articular steroid injections may give short-term relief, but repeated use is to be discouraged for fear of iatrogenic infection.

Quantifying Treatment Results in Cuff Tear Arthropathy

Many grading systems have become popular for clinical assessment of shoulder outcomes. Neer and researchers ²⁰ recognized the need for a “limited goals” category in the case of patients with poorly functioning cuff musculature. This acknowledges that a result can still be considered successful if there is good pain relief and “useful” shoulder function even if the rigid criteria of success in those with intact cuff muscles are not met. Here, a result is considered successful if no significant pain is felt, the patient is pleased with the procedure, the patient remains independent for activities of daily living, and the patient has at least 90 degrees of arm elevation and 20-degree external rotation.

Surgical Management

Arthroscopic Debridement.

Arthroscopic irrigation to remove activated enzymes and crystals offers only limited short-term relief ²¹ (Level IV). Any surgical violation of the coracoacromial arch, if still intact, is to be vigorously discouraged for fear of further destabilizing the humeral head.¹³

Arthrodesis.

Glenohumeral arthrodesis has the potential to stabilize the glenohumeral joint and relieve pain but at the cost of reduced motion and function. However, most patients with CTA are unsuitable for arthrodesis because they are older, intolerant of prolonged immobilization, and frequently have bilateral disease.² Furthermore, osteoporosis in these typically elderly women presents problems with internal fixation. Arthrodesis is best reserved for younger high-demand patients disabled by an irreparable cuff tear, often with a nonfunctioning deltoid, and who require a strong stable shoulder girdle ²² (Level V). It may also have a place in other instances of massive irreparable cuff tear with deltoid dysfunction.

Unconstrained Shoulder Replacement.

Shoulder prostheses with no built-in constraint rely on an intact and functioning rotator cuff to stabilize the humeral head within the socket. Although it is agreed that small cuff tears, regardless of whether they are repaired, have no effect on the outcome of total shoulder arthroplasty ²³ (Level III); the same is not true for cases of major cuff deficiency. Franklin and coauthors²⁴ report a direct association between superior migration of the humeral component and a deficient rotator cuff (Level IV). They called the eccentric superior loading of the glenoid component the “rocking horse” phenomenon that leads to loosening and superior tilt. Therefore, unconstrained prostheses are not recommended for cuff tear arthroplasty.

Semiconstrained Shoulder Replacement.

Semiconstrained glenoid components have also been used to give resistance to ascent of the humeral head in cuff deficient shoulders. Neer and researchers ² experimented with 200% and 600% glenoid components for CTA in 11 cases followed for an average of 30 months, but they soon abandoned such designs because of the greater risk for failure and the difficulty of closing residual cuff defects²⁵ (Level IV). Amstutz and colleagues²⁶ and Gristina and investigators²⁷ have described the use of hooded glenoid components for use with nonconstrained systems but reported only short-term results (Level IV). It has been shown by finite element analysis²⁸ that the superior constraints of the component intending to prevent humeral head ascent increase stresses and may cause earlier loosening than with unconstrained designs.

Bipolar Shoulder Replacement.

Bipolar hemiarthroplasty was introduced by Swanson and coworkers ²⁹ for the treatment of advanced glenohumeral arthritis associated with superior migration of the humeral head and loss of rotator cuff function. It uses a larger diameter mobile shell around the head in an attempt to gain several advantages: increased mobility because of the lateralization of the center of rotation and the increase in the muscle lever arm; increased stability of the prosthetic shoulder; and reduced glenoid and acromial wear in contact with the prosthetic head.³⁰ Few published³¹^–³³ and unpublished studies³⁴ exist that detail results but in general these indicate that even if pain relief is achieved, function remains low after the procedure (Level IV). Noting the better results reported with simple hemiarthroplasty particularly about mobility, Duranthon and investigators³³ conclude that the deltoid lever arm was being increased at the expense of overstretching capsular and residual cuff tissues, and that it was better to use a head size closer to normal anatomy. In addition to this overstuffing effect, concerns have been raised regarding rupture of the subscapularis tendon because of the vertical orientation of the component and the potential for excessive polyethylene wear.³⁵