Shoulder and Elbow Arthroplasty

History

The earliest known report of shoulder arthroplasty dates back to 1893, when a French surgeon, Péan, substituted a platinum and rubber implant for a glenohumeral joint destroyed by tuberculosis. In the early 1950s, Neer introduced a humeral head prosthesis that he planned to use for complex shoulder fractures. In 1951, he reported his initial results of replacement of the humeral head with an unconstrained cobalt-chromium alloy (Vitallium) prosthesis. In 1974, the Neer II humeral prosthesis, which was modified to articulate with a glenoid component, was introduced. In the early 1990s, Paul Grammont introduced an improved design of a semiconstrained shoulder replacement using a metal sphere implanted into the glenoid and a polyethylene liner and stem into the humerus: the reverse total shoulder arthroplasty. Although implant design factors continue to evolve, the primary features of this prosthesis are retained in current iterations of reverse arthroplasty.

Glenoid components for anatomic total shoulder arthroplasty were initially designed for cementless fixation using screws and porous coating on metal backing with a polyethylene shell. But long-term studies have shown an unacceptably high complication rate, and as such these implants have been largely abandoned. Subsequently, more emphasis was placed on restoring normal kinematics with anatomic location and orientation of the glenoid joint surface, advanced soft-tissue balancing techniques, and physiologic stabilization of the joint. Most current glenoid implants are polyethylene and use cement for fixation with either a pegged or keeled configuration on the backside of the component. Use of anchor-pegged devices to improve glenoid fixation and encourage bony ingrowth also has become a popular implant design.

Anatomy and Biomechanics

The anatomy of the shoulder joint permits more mobility than any other joint in the body. Although it often is described as a ball-and-socket joint, the large humeral head articulates against and not within the small glenoid cavity. The glenohumeral joint depends on the static and dynamic stabilizers for movement and stability, especially the rotator cuff, which not only stabilizes the glenohumeral joint while allowing greater freedom of motion but also fixes the fulcrum of the upper extremity against which the deltoid can contract and elevate the humerus. The rotator cuff must act simultaneously and synergistically, however, with the deltoid muscle for normal function.

Restoration of glenohumeral anatomy is essential for a good functional outcome in shoulder replacement. Anatomic studies have defined the humeral geometry further and suggested applications to shoulder arthroplasty prosthesis design and surgical techniques ( Fig. 12.1 and Table 12.1 ). The articular surface of the humeral head is essentially spherical, with an arc of approximately 160 degrees covered by articular cartilage. The radius of curvature is approximately 25 mm and is slightly larger in men than in women. The glenoid articular surface radius of curvature is 2 to 3 mm larger than that of the humeral head. The average neck-shaft angle is 45 degrees (±5 degrees), with a range of 30 to 50 degrees. Murthi et al. found that arthritic shoulders have a flatter neck-shaft angle close to 50 degrees. CT studies found that the normal position of the glenoid surface in relation to the axis of the scapular body ranged from 2 degrees of anteversion to 7 degrees of retroversion.

The superior margin of the humeral head articular surface normally is superior to the top of the greater tuberosity by 8 to 10 mm ( Fig. 12.2 ). Restoring the center of rotation for the humeral head in relation to the axis of the humeral diaphysis may play a role in prolonging glenoid fixation and decreasing polyethylene wear. The distance from the lateral base of the coracoid process to the lateral margin of the greater tuberosity is called the lateral humeral offset. Maintaining this distance is important because a significant decrease reduces the lever arms for the deltoid and supraspinatus muscles, which weakens abduction and impairs function. A significant increase causes excessive tension on the soft tissues (“overstuffing” of the joint), which results in loss of motion and also likely accelerates polyethylene wear. A biomechanical cadaver study determined that humeral articular malposition of more than 4 mm led to increased subacromial contact and that offset of 8 mm in any direction significantly decreased passive range of motion. The authors suggested that anatomic reconstruction of the humeral head/humeral shaft offset should be within 4 mm of normal to minimize subacromial contact and maximize glenohumeral motion.

Based on the clinical success of the Neer II implant, numerous modular designs were developed to improve implant fixation and durability. Detailed studies of shoulder anatomy found not only that normal shoulder anatomy aligned differently than the commonly used prostheses, but also that normal anatomy varied greatly among individuals. Modularity allows a better fit for individual patients because various stem and head sizes can be “mixed and matched” to an individual’s anatomy. Biomechanical studies also showed that shoulder biomechanics are adversely affected by the use of a prosthetic head that is too thick, too thin, or shifted too far from its original position along the plane of the anatomic humeral neck. Other characteristics of shoulder anatomy that are important in prosthesis design are retroversion, head-shaft angle, offset, radius of curvature, and humeral head height. Proximal humeral retroversion is highly variable, ranging from 0 to 55 degrees, depending on the method used for measurement. The proximal and the distal axes used to define retroversion have various definitions. For the proximal reference axis, the plane of the articular surface, a line connecting the center of rotation and the central point of the articular surface, and a line from the greater tuberosity to the central point of the articular surface have been used. For the distal reference axis, the trochlear axis, a line between epicondyles, and the forearm itself have been used. The inclination of the proximal humeral articular surface relative to the humeral shaft is the neck-shaft angle; it ranges from 30 to 55 degrees, depending on the method of measurement. The humeral offset defines the position of the proximal humeral articular surface relative to the humeral shaft; it is measured as the distance from the center of rotation of the proximal humeral articular surface to the central axis of the humeral canal. The medial offset (coronal plane) ranges from 4 to 14 mm, and the anteroposterior offset (transverse plane) ranges from −2 to 10 mm. Reported values for the radius of curvature of the proximal humeral articular surface range from 20 to 30 mm; smaller radii typically are reported in women, and some authors have reported that the radius of curvature is larger in the coronal plane than in the sagittal plane.

Prosthesis Design

Most current systems are modular with varying humeral head diameters and neck lengths to allow more accurate coverage of the cut surface of the humeral neck and improve the ability to establish correct position of the joint line and rotator cuff tension. Some designs allow independent sizing of head thickness and head diameter to make soft-tissue balancing easier. Most stems are made of cobalt-chrome or titanium alloy and have proximal porous ingrowth coating to allow insertion without cement.

In an effort to match the proximal humeral anatomy as closely as possible, several implant systems offer concentric and offset humeral heads. In an anatomic dissection study, Boileau and Walch found that the center of the humeral head was 2.6 mm posterior and 6.9 mm medial to the center of the humeral shaft, and Robertson et al., using CT, noted similar measurements of 2.2 and 7.4 mm.

Anatomic positioning of the humeral head prosthesis is best done with an eccentric locking position of the Morse taper, which allows adjustments to the variable medial offset and any posterior offset. Curiously, postoperative kinematics after total shoulder arthroplasty do not mimic those of the native shoulder. Massimini et al. found that the posterosuperior quadrant of the glenoid is the primary contact location and that the replaced shoulder is not subject to traditional kinematic conceptions. Nevertheless, positioning the head too far superiorly puts additional tension on the overlying supraspinatus tendon and can cause impingement between the head and the acromion. Positioning the head too far inferiorly may cause abutment of the greater tuberosity on the acromion or internal impingement on the rim of the glenoid. Positioning the head too far anteriorly or posteriorly can result in abutment of the uncovered humeral neck on the corresponding glenoid rim and excessive tension on the overlying subscapularis or posterior rotator cuff tendons. Most current systems offer humeral heads that are offset by 3 or 4 mm; some allow several discrete positions, and some allow free rotation around the taper.

Most stems can be inserted with a press-fit or cemented technique. In a cadaver study, micromotion was found to be significantly less with proximal cement than with press-fit; no difference was found between proximal cementation and full cementation, and full cementation did not increase rotational stability over proximal cementation. One study found a very low rate of radiolucencies around proximal porous-coated stems and no clinical signs of loosening. Clinically significant loosening of the humeral component in the absence of infection is uncommon regardless of fixation methods. Due to improved design concepts and ingrowth technology, the use of shorter stems and stemless implants to preserve proximal humeral bone also has become more popular.

Cemented all-polyethylene components remain the gold standard for glenoid component fixation, but designs remain in evolution. Both inlay and onlay glenoid components are available, and many systems now employ bone ingrowth technology to reduce reliance on the bone-cement-implant interface. Regardless of these design features, most components now have an increased radius of curvature (i.e., nonconforming glenoid components ) compared with the humeral head (2 to 6 mm larger) to allow translation during movement and to decrease edge loading. Several studies have shown that translation accompanies glenohumeral rotation after total shoulder arthroplasty. Such translation in a perfectly congruent or conforming joint may have a potential for localized wear and loosening (rocking-horse effect); however, increased loosening and polyethylene wear have not been reported to occur when the radii of curvature of the glenoid component and the humeral head are matched within 2 mm. In a multicenter study of 319 total shoulder arthroplasties using the same type of prosthesis, Walch et al. noted fewer radiolucencies with mismatches between the glenoid and humeral head diameters of more than 5.5 mm (6 to 10 mm). Current opinion seems to suggest that a nonconforming glenoid with a radius curvature of 2 to 4 mm larger than the humeral head allows normal translation during rotation without rim loading or risk of loosening ( Fig. 12.3 ).

A larger glenoid component results in an increased risk for volumetric polyethylene wear similar to what is seen in hip and knee arthroplasty, but this risk has not been substantiated clinically. However, larger components have been linked with improved stability. In a biomechanical study, Tammachote et al. demonstrated improved stability with increasing sizes of glenoid components. Specifically, transverse plane stability improved 17% between the small and medium components and then improved 10% between the medium and large components.

All-polyethylene glenoid components generally are cemented into place. A biomechanical study found that cemented all-polyethylene designs had an overall stress pattern closer to that of an intact glenoid than did uncemented metal-backed components. In a report of 408 shoulder arthroplasties using a standard glenoid component and followed for more than 2 years, Neer reported that only three (0.07%) required reoperation because of glenoid loosening. More recently, Hopkins et al. found that bone quality was important in achieving solid glenoid component fixation. They also stressed the importance of proper implant positioning.

Polyethylene glenoid components generally have a central keel or multiple peripheral pegs for fixation into the glenoid vault. The preponderance of biomechanical evidence suggests an advantage to pegged designs, however. Lacroix et al., using a three-dimensional model and finite element analysis, found that bone stresses were not much affected by prosthesis design except at the tip of the central peg or keel. They did conclude, however, that pegged prostheses were better for normal bone. As understanding of glenoid deformities has improved, augmented glenoid components also have been developed to accommodate commonly seen glenoid wear patterns. Although long-term studies are not yet available, short-term outcomes have been promising.

The biomechanics of reverse total shoulder arthroplasty revolve around recruitment of the deltoid to restore active motion in a rotator cuff-deficient shoulder. All reverse arthroplasty designs medialize the center of rotation to some degree and generally lengthen the deltoid to increase its lever arm to power forward elevation. The original Grammont style reverse total shoulder arthroplasty design medialized the center of rotation at the glenoid face and used a valgus neck-shaft angle of 155 degrees in the humeral component to provide straight line vertical pull of the deltoid. Although this implant improved loosening rates over prior designs and was reliable for the restoration of forward elevation, the return of external rotation was less reliable, and concerns developed over impingement between the polyethylene humeral bearing surface and glenoid neck with resultant scapular notching. Therefore, implant designers turned toward developing “lateralized” (i.e., less-medialized) components in which the center of glenohumeral rotation is placed lateral to the glenoid face. This can be done through the glenosphere or with bone graft (so-called medial humerus-lateral glenoid constructs) or the humeral bearing surface (lateral humerus-medial glenoid constructs). Because most current systems employ modular design concepts that often allow conversion between anatomic total shoulder arthroplasty and reverse total shoulder arthroplasty, constructs that employ a lateral humerus and lateral glenoid design are available, but uncommonly used. Nevertheless, these convertible systems offer an advantage in the revision setting because they often allow preservation of the humeral stem without the need for removal.

The biomechanical data on lateralization in reverse total shoulder arthroplasty suggest an improvement in remaining rotator cuff torque, which may be helpful for restoration of internal and external rotation. In addition, a systematic review concluded that lateralized constructs reduce scapular notching rates as well as improve external rotation. In general, larger glenospheres are thought to improve range of motion and decrease scapular notching as well. Additional investigation has focused on the position of the humeral component in reverse total shoulder arthroplasty. Placing the humeral stem in neutral version demonstrated the least amount of intraarticular and extraarticular impingement, but stems placed in 40 degrees of retroversion allowed the greatest range of motion in a simulator study. To balance these two priorities, most authorities recommend placing the humeral stem in 20 to 30 degrees of retroversion for reverse total shoulder arthroplasty.

Clinical Presentation and Radiographic Evaluation

The clinical appearance of advanced glenohumeral degeneration was initially described by Neer. Patients typically present with global pain about the shoulder with difficulty performing overhead activities and, often, activities of daily living. On physical examination, diminished active and passive range of motion may be observed, and patients may have previously been diagnosed with adhesive capsulitis. In patients with intact rotator cuff tendons, strength is often preserved but may be diminished secondary to pain. Palpable crepitus often can be elicited with passive internal and external rotation of the glenohumeral joint and/or with strength testing. The acromioclavicular joint and biceps tendon should be carefully evaluated because symptomatic acromioclavicular degeneration and/or biceps tendinitis may also be present.

Standard radiographs include anteroposterior views with a 40-degree posterior oblique view in neutral position and internal and external rotation and an axillary lateral view. Radiographs of the opposite, uninvolved shoulder and humerus are helpful in unusual situations, such as when a custom implant is indicated for large humeral or glenoid deficiencies.

The radiographic appearance varies with the patient’s pathologic process. Those with osteoarthritis reliably demonstrate subchondral sclerosis and a large osteophyte on the inferior aspect of the humeral head ( Fig. 12.4 ). This so-called “goat’s beard” is pathognomonic of advanced glenohumeral degeneration. These osteophytes can enlarge the humeral head to twice its normal size, resulting in capsular distention ( Fig. 12.5 ). Joint space narrowing, which is so reliably seen in hip and knee osteoarthritis, is not commonly seen in the shoulder until very late in the disease process owing to the non-weight-bearing position of the shoulder under standard radiography. Axillary lateral radiographs typically demonstrate posterior subluxation of the humeral head on the glenoid, and a wear pattern in the posterior glenoid may be present ( Fig. 12.6 ). Patients with capsulorrhaphy arthropathy have a similar radiographic appearance except that loose bodies and osteophytes tend to be more common and numerous ( Fig. 12.7 ) than in standard osteoarthritis.

Malunions of proximal humeral fractures can make shoulder arthroplasty more difficult. A varus malunion between the head and shaft can complicate positioning of components, but osteotomy usually is unnecessary as newer short-stem and stemless designs allow accommodation of these deformities. Patients with inflammatory arthritis often do not have an inferior osteophyte on radiographs and, instead, demonstrate a more symmetrical pattern of joint space narrowing with periarticular osteopenia. The wear pattern is more commonly central in the glenoid, and posterior subluxation of the humeral head is less common. Cystic change is also common. Rotator cuff tears are more common in patients with rheumatoid arthritis than in patients with osteoarthritis: full-thickness rotator cuff tears have been identified in 25% to 50% of patients undergoing shoulder arthroplasty. Most of these tears are in the superior rotator cuff.

MRI can be a useful preoperative planning tool in this population. In patients with strength deficits that could be caused by either arthritic pain or a torn rotator cuff, MRI can help determine the status of the tendons. Whereas rotator cuff tendinopathy is common in this setting, full-thickness tears are uncommon and are seen in only about 10% of patients. MRI also typically demonstrates advanced cartilage degeneration and may show numerous other findings, including thinning of the subscapularis and degenerative changes in the biceps tendon. Increased capsular volume posteriorly and capsular contraction anteriorly are usual changes as well. Finally, in patients with precollapse osteonecrosis, MRI is useful for visualizing the area of dead bone and is often the best tool to make the diagnosis ( Fig. 12.8 ).

CT is also a valuable asset in the evaluation and preoperative planning for patients with advanced glenohumeral degeneration. The scans give an excellent picture of the patient’s glenoid bone stock and the pattern of glenoid wear, which is essential for determining if standard glenoid components can be used or if a bone graft will be needed. Loose bodies may be seen in the axillary or subscapularis recess or attached to the synovium. In the case of malunions or nonunions, three-dimensional reconstruction helps to precisely show the bony deformities and defects before surgery. CT arthrography often is useful to evaluate both the bony architecture of the shoulder and the rotator cuff in patients with contraindications to MRI.

Preoperative Planning

Once the patient is determined to have advanced glenohumeral degeneration and has consented to a shoulder arthroplasty, preoperative planning includes careful evaluation of the radiographs and the CT scans, if obtained. As noted earlier, CT gives a clear view of the glenoid bone stock and wear pattern. Viewing these changes preoperatively allows the surgeon to prepare for the possibility that glenoid bone grafting, augmented components, or glenoid recontouring procedures may be necessary to correct the deformity. The role of preoperative planning based on three-dimensional CT scans to optimize implant position, size, and range of motion is an evolving area of investigation. Most reports have concluded that preoperative planning software using CT scans results in more accurate glenoid component placement with either conventional or patient-specific implants. In particular, shoulders with significant posterior glenoid erosion tend to benefit from implant reaming and targeting systems.

In patients who have had previous shoulder surgery, infection can be evaluated by laboratory tests including erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and complete blood cell count. Aspiration and culture of glenohumeral joint fluid, holding the culture for at least 14 days to isolate Cutibacterium acnes ( formerly Propionibacterium acnes) , is essential if infection is suspected. Electromyography and nerve conduction studies should be obtained preoperatively in patients with suspected deficits. Finally, preoperative medical clearance often is warranted in this typically elderly population.

Hemiarthroplasty

Surgical Technique

The goal of hemiarthroplasty is restoration of the humeral articular surface to its normal location and configuration. Because the glenoid is not replaced, the size, radius, and orientation of the prosthetic joint surface must duplicate that of the original biologic humeral head. Radiographs of the contralateral shoulder can provide information about a patient’s normal humeral head anatomy. Care should be taken to avoid a “big head” humeral prosthesis that can “overstuff” the joint ( Fig. 12.9 ).

Hemiarthroplasty

Technique 12.1

• ▪

  Place the patient in the beach chair position to allow positioning of the patient at the top and edge of the table ( Fig. 12.10A ). Pad all bony prominences. The medial border of the scapula should be free and off the table, allowing full adduction to gain access to the intramedullary canal.

  

• ▪

  Secure the patient’s head to the headrest, holding the head in a position that avoids hyperextension or tilting of the neck, which can cause compression of the cervical roots.

• ▪

  Prepare the arm and drape it widely. We recommend using occlusive dressings to cover the entire surgical field.

• ▪

  Make an incision anteriorly, approximately one third to halfway between the coracoid and the lateral aspect of the acromion ( Fig. 12.10B ). Carry dissection down to the deltoid and raise medial and lateral flaps to mobilize the deltoid.

• ▪

  Open the deltopectoral interval and allow the cephalic vein to fall medially.

• ▪

  Perform subdeltoid, subcoracoid, and subacromial releases to release the proximal humerus. In the subcoracoid space, locate the axillary nerve by passing the volar surface of the index finger down along the anterior surface of the subscapularis muscle ( Fig. 12.10C ). If scarring and adhesions make identification of the nerve difficult, pass an elevator along the anterior surface of the subscapular muscle to create an interval between the muscle and the nerve. Great care must be taken in this step to avoid plunging into the brachial plexus. After the axillary nerve is identified, carefully retract and hold it out of the way, especially during the crucial steps of releasing the anteroinferior capsule.

• ▪

  We prefer to perform a biceps tenodesis before incising the subscapularis. A figure-of-eight stitch is placed between the biceps and pectoralis major tendons. The biceps is then divided, and the proximal portion is later resected before making the humeral head osteotomy.

• ▪

  Incise the subscapularis 1 cm medial to the lesser tuberosity. Place two retention sutures in the subscapularis to be used as traction sutures when freeing the rest of the tendon from the underlying capsule and scar tissue. Some authors prefer either a lesser tuberosity osteotomy or a release of the subscapularis directly off of bone. If external rotation is markedly limited, the subscapularis also can be reattached to the proximal humerus more medially to allow increased external rotation. Alternatively, the tendon can be lengthened with a coronal Z-plasty technique.

• ▪

  Incise the rotator interval, directing the cut medially toward the glenoid. Typically, a large amount of synovial fluid escapes as the joint is entered.

• ▪

  Release the anteroinferior capsule from the humerus and externally rotate the arm to bring the inferior aspect of the shoulder capsule into view. Take care to stay directly on bone so as not to injure the axillary nerve during the capsular release. The importance of the inferior capsule release cannot be overstated and must be thoroughly carried out to at least the 7 o’clock position to dislocate the humeral head and gain access to the glenoid.

• ▪

  Once the capsule is adequately released, place a large Darrach retractor in the joint and gently externally rotate, adduct, and extend the arm to deliver the humeral head up and out of the glenoid fossa ( Fig. 12.10D ). If the humeral head cannot be delivered in this fashion, the inferior capsule must be released further.

• ▪

  Prepare the humeral canal, using the humeral axis to reference the osteotomy. Initially, open the canal with a high-speed burr at the base of the rotator cuff footprint and ream it to a size where appropriate fit is felt. Do not use motorized equipment for reaming, and be careful not to overream the canal, which could create a stress riser or cause a fracture.

• ▪

  We prefer to use a cutting guide that employs extramedullary referencing, using the axis of the forearm as the reference point, with the cutting guide pinned into position at 30 degrees of retroversion. Other surgeons may prefer a free-hand, anatomic neck-cutting technique. Regardless of the cutting technique, care must be taken to avoid violating the rotator cuff.

• ▪

  Complete the osteotomy with an oscillating saw. If any inferior humeral head osteophyte remains, remove it with a rongeur.

• ▪

  After the head cut, broach the humeral canal to the same size as the reamed canal. It is imperative to confirm proper position of the broaches in 30 degrees of retroversion during this step to prevent component malposition.

• ▪

  Inspect the glenoid to confirm there is enough glenoid cartilage to provide an adequate bearing surface for the metal humeral head. After this inspection, check the humeral trial stem to ensure it is seated securely within the humeral canal. If so, tap the component stem into position, taking care to keep the stem in 30 degrees of retroversion.

• ▪

  If cementing is deemed necessary because of a previous surgical procedure, fracture, osteoporosis, rheumatoid arthritis, or degenerative cysts, place a cement restrictor or a cortical bone plug from the resected humeral head 2 cm inferior to the tip of the prosthesis.

• ▪

  Place a trial humeral head and reduce the glenohumeral joint using internal rotation and gentle traction. With the arm in neutral rotation, check the height of the humeral head to confirm anatomic reconstruction. As a rule of thumb, the most superior aspect of the humeral head should be 1 cm superior to the greater tuberosity.

• ▪

  Also check the version to confirm that the humeral head rests directly across from the glenoid. With a thumb on the lesser tuberosity, push the humeral head posteriorly and then release it: 50% posterior excursion with immediate “bounce back” of the humeral head is optimal. Evaluate forward elevation and internal rotation.

• ▪

  Once the checks have been performed, thoroughly clean the Morse taper, impact the humeral head into position, and reduce the joint for the final time.

• ▪

  Perform a tight closure of the rotator interval and the subscapularis with heavy nonabsorbable suture. Both transosseous and tendon-to-tendon repair techniques are reasonable. If the tendon was divided or lengthened, repair and secure it with heavy nonabsorbable sutures to allow immediate passive movement beginning the day after surgery. If a lesser tuberosity osteotomy is preferred, robust fixation of the bone back to the humeral shaft is critical. Place a drain in the deltopectoral interval and close it with No. 0 sutures. Close the skin in standard fashion and place the arm in a soft sterile dressing and a sling while the patient is still upright and before being aroused from anesthesia.

Postoperative Care

Patients are instructed in a gentle home exercise program with passive forward elevation to 90 degrees and passive external rotation to neutral. Patients typically are discharged from the hospital on the morning after surgery and are encouraged to use a pillow behind the elbow while recumbent in the sling to support the extremity. Full-time sling immobilization continues for 6 weeks, followed by 6 weeks of sling use only in unprotected environments. Therapy progresses to full passive range of motion by 6 to 12 weeks and to isometric strengthening at 10 weeks.

Total Shoulder Arthroplasty

Total shoulder arthroplasty is a well-established procedure with an excellent long-term track record of pain relief and functional improvements. Long-term results have been reported that are equivalent to those after replacement of the knee and hip. In a meta-analysis of series that included 646 shoulder arthroplasties done for osteoarthritis, Wilde found that 89% had complete or nearly complete relief of pain; 91% of patients with rheumatoid arthritis reported satisfactory relief.

Reverse Total Shoulder Arthroplasty

In 1983, Neer, Craig, and Fukuda described “cuff-tear arthropathy” as a distinct form of osteoarthritis associated with a massive chronic tear of the rotator cuff. Clinically, rotator cuff arthropathy is characterized by pain, poor active motion, near-normal passive motion, crepitus, weakness, and occasionally significant fluid buildup under the deltoid. Radiographic changes include elevation of the humeral head, formation of an acromiohumeral pseudoarticulation, and loss of joint space at the glenohumeral joint. The radiographic pattern of degenerative changes can vary, and not all patients with rotator cuff arthropathy have pain or limited motion.

The glenohumeral instability resulting from this condition is manifested as proximal migration of the humerus relative to the glenoid, resulting in erosion of the superior glenoid and the caudal surface of the acromion. Rotator cuff tears have been implicated in early glenoid component loosening in total shoulder replacements, and irreparable tears are a contraindication to traditional glenoid resurfacing. Until the introduction of reverse total shoulder arthroplasty, patients with cuff tear arthropathy were generally treated with hemiarthroplasty, which was a durable, if imperfect, solution that provided adequate pain relief but did not restore forward elevation.

Surgical Technique

Biomechanically, the reverse prosthesis works by reestablishing a fulcrum around which the deltoid muscle can power shoulder motion. With standard prostheses, absence of the rotator cuff allows the humeral head to subluxate superiorly during deltoid muscle contraction. The reverse prosthesis corrects this by moving the center of rotation of the shoulder medially and distally and reestablishing a semiconstrained fulcrum around that fixed point ( Fig. 12.15 ).

Because the reverse prosthesis places high shear stresses across the glenoid, several investigators have sought to define the factors most important in maximizing glenoid fixation. Parsons et al. stressed that proper orientation of the baseplate and placement of the screws in optimal position were important for fixation. Others have found that the inferior screw faces the highest shear stress and is key to prevent loosening, whereas others have recommended screw placement in areas with the highest quality bone: the coracoid base, the scapular spine, or the inferior pillar. A device with a lateralized center of rotation was shown to obtain adequate fixation despite a 69% greater moment at the baseplate-glenoid interface.

Glenoid wear is common in rotator cuff-deficient conditions. Frankle et al. (2009) studied 216 glenoids with plain radiographs and CT scans before operative intervention and found that 37.5% of the glenoids had abnormal morphology. They classified the wear patterns as posterior (17.6%), superior (9.3%), global (6.5%), and anterior (4.2%). These wear patterns were found to affect surgical technique, often requiring placement of the center screw along an alternate center line along the scapular spine. In a later follow-up study of 143 of these patients, all 56 shoulders with abnormal glenoids had center screw placement along the alternative center line, and 22 had bone grafting procedures; larger glenospheres also were used more often than in shoulders with normal glenoids. Outcomes were not significantly different between the two groups. Augmented glenoid components and bone grafting procedures also are available to treat glenoid deficiency.

Reverse Total Shoulder Arthroplasty

Technique 12.3

• ▪

  Approach the proximal humerus and prepare it for stem implantation as described in Technique 12.1. Some authors recommend a superior approach, but we prefer the deltopectoral approach because of its versatility and easily extensive nature. However, there are some important differences in humeral preparation from a total shoulder arthroplasty or hemiarthroplasty. First, because of the common superior subluxation deformity of rotator cuff-deficient shoulders, a larger humeral head cut is often required. Second, some authors advocate placing the stem in less retroversion (∼20 degrees) to prevent impingement and maximize rotation; however, we believe that stem placement in 30 degrees of retroversion is not only acceptable but also preferable to prevent the more common instability in adduction and extension seen with the reverse prosthesis. Although stems were initially cemented in reverse total shoulder arthroplasty, the use of uncemented and shorter stems has been reported with clinical success. Once the glenoid vault is adequately debrided and all four borders are visible, identify the centering point. Move the starting point inferiorly 1 to 2 mm to allow inferior placement of the baseplate to prevent scapular notching. Most authors recommend placing the baseplate with the inferior aspect flush with the inferior surface of the bony glenoid.

• ▪

  Place a guide pin through this centering hole using a guide. Take care to place the guide pin in 10 to 15 degrees of inferior tilt, again to prevent scapular notching.

• ▪

  Ream the glenoid until the “smiley face” is achieved, with bleeding cancellous bone inferiorly and hard sclerotic bone superiorly ( Fig. 12.16 ). This confirms adequate inferior tilt of the baseplate.

  

• ▪

  Impact the baseplate and secure it with screws. The peripheral screws are ideally placed in the “pillars” of densest cortical bone—the coracoid base, inferior pillar, and scapular spine. We have found screw placement to be inconsistent in the scapular spine; however, fixed-angle locking screws can be reliably positioned in the coracoid base and inferior pillar by internally rotating a circular baseplate approximately 10 degrees.

• ▪

  Dry the Morse taper and impact the glenosphere into position.

• ▪

  Place the humeral stem as described in Technique 12.1, using trial components to test for stability and motion. Reduction and dislocation of the glenohumeral joint typically are more difficult than with standard shoulder arthroplasty. Reduction involves a combination of longitudinal traction and forward elevation on the arm. The deltoid tension should be slightly greater than before joint relocation, but take care not to overlengthen the deltoid, which can result in dehiscence and/or acromial fracture. There can be 2 to 3 mm of gapping in the glenohumeral articulation once the joint is reduced without loss of stability.

• ▪

  To dislocate the glenohumeral joint, place the dislocation instrument between the bearing surface and glenosphere to disrupt the articulation. Then pull the humerus anteriorly (shoulder extension) to deliver the bearing surface.

• ▪

  Once the proper bearing surface is chosen, dry the Morse taper and impact it into position. Reduce the glenohumeral joint for a final time. Close the wound as described in Technique 12.1. The importance of subscapularis repair after reverse total shoulder arthroplasty remains controversial. One study found no correlation between subscapularis integrity and outcome. Another large study found that outcomes were not inferior when the subscapularis was left free compared to when it was repaired. However, closure of the subscapularis has been found to correlate with improved stability in traditional Grammont style prostheses but is likely less important for lateralized designs.See also Video 12.2 .

Postoperative Care

Postoperative care is as described for Technique 12.1.