Reverse Total Shoulder Arthroplasty for Glenohumeral Osteoarthritis



Reverse Total Shoulder Arthroplasty for Glenohumeral Osteoarthritis


Michael P. Kucharik

Austin F. Smith

Mark A. Frankle





INDICATIONS AND CONTRAINDICATIONS

Rotator cuff arthropathy and irreparable rotator cuff tears have historically been the most common indications for reverse total shoulder arthroplasty (RTSA).1 In the absence of a mechanically effective rotator cuff, the force vector generated by contraction of the deltoid causes superior migration of the humeral head rather than abduction. Clinically, this phenomenon is termed pseudoparalysis, which can be effectively addressed with RTSA. While these were the original indications for RTSA, indications have expanded to include acute three-part or four-part proximal humerus fractures, revision of a failed fracture fixation or failed arthroplasty, and rheumatoid arthritis.1 In addition, RTSA has become an increasingly popular procedure for glenohumeral osteoarthritis (GHOA), which predominantly has traditionally been treated by total shoulder arthroplasty (TSA).2

An impetus for this evolving indication was the publication of long-term studies that revealed the leading cause for TSA failure: loosening of the glenoid component.3 The etiology of glenoid loosening in the setting of TSA is multifactorial but ultimately derives from the inability of the glenoid component to withstand repeated eccentric loads and glenohumeral translation, which eventually results in loss of fixation at the glenoid component-bone interface.4 This phenomenon was found to be much more prevalent in patients with significant preoperative glenoid deformity, such as eccentric glenoid wear, glenoid retroversion, static posterior humeral head subluxation, or poor glenoid bone stock.5,6

While the utilization of bone graft and development of augmented glenoid components have addressed some of these issues, RTSA has become a popular choice for surgeons due to its inherent biomechanical advantages that confer joint stability.7 Specifically, the biomechanical position of the reverse total shoulder prosthesis provides for a stable fulcrum by most mechanically efficiently neutralizing the destabilizing superior-directed force of the deltoid.8 This ability to steady the unbalanced muscular forces with the reverse articulation allows for asymmetric forces to be better balanced. Thus, it is important to consider preoperative bony morphology and rotator cuff function to anticipate how contact forces will be distributed if one were to employ a TSA prosthesis. Even in patients with mild rotator cuff deficiency without chronic rotator cuff arthropathy, TSA may lead to what is known as the “rocking horse phenomenon”, which occurs when subluxation of the humeral head component in the anterior-posterior direction creates a lifting effect of the glenoid component.9

Contraindications for RTSA include deltoid muscle or axillary nerve dysfunction, as patients without a fully functional and innervated deltoid are unlikely to experience a significant functional improvement and are at high risk for recurrent instability.1 Other contraindications include active infection, neuropathic glenohumeral joint, and glenoid vault deficiency that would preclude baseplate fixation. Adequate glenoid bone stock and bone quality are other considerations when planning for RTSA. While a certain degree of bone loss can be overcome by augmented implants or autologous bone graft, there remains a minimum amount of bone stock and quality to secure fixation of the glenoid component.10 For example, patients with severe osteoporosis of the glenoid may not be
able to achieve adequate fixation of the glenosphere baseplate. Computed tomography (CT) is the gold standard for preoperative imaging of the glenoid vault. Using the CT scan as a guide, three-dimensional planning software is often utilized to provide surgeons with templates to determine the feasibility of a reverse total shoulder prosthesis.10


PREOPERATIVE PREPARATION

When first examining a patient with suspected shoulder pathology, it is important to divide the patient’s evaluation into three parts: history, physical examination, and imaging. Once a clinical history is obtained, it is important to have the patient provide a subjective shoulder value of both shoulders, which is a subjective measurement of how the patient perceives how functional their shoulder is out of 100%.11 This establishes a quantifiable baseline, which can then be followed by more nuanced questions, such as chronicity, comparison with prior episodes of shoulder dysfunction, and how their shoulder pain limits their activities of daily living. Patients will often provide context to their shoulder pain, such as, “I can no longer extend for objects on the top shelf” or “I have trouble reaching for the seatbelt when I drive.” Having a detailed conversation about how their shoulder pain limits them and what their goals are with respect to treatment is crucial, as this helps one determine the best treatment modality for patients and whether their goals are attainable with surgical intervention.

A thorough physical examination begins with observation and palpation to assess for any specific areas of concern or atrophy. Then, one should evaluate active and passive range of motion in abduction, forward flexion, external rotation, and internal rotation. Starting with the contralateral shoulder provides the surgeon with reference values to compare. After examining the patient’s neurovascular status, special physical examination tests of the shoulder are other tools in a shoulder surgeon’s armamentarium to identify potential sources of shoulder dysfunction. These include arthritis, rotator cuff pathology, instability, fracture, and cervical radiculopathy.12 Patients with primary osteoarthritis will most often present with palpable crepitus of the glenohumeral joint and limited range of motion in the plane of external rotation due to contraction of the anterior capsule.

Imaging in the form of plain radiographs, CT, or magnetic resonance imaging (MRI) will then be scrutinized for evidence of abnormalities that may be responsible for the patient’s shoulder pain and dysfunction. Plain radiographs are often sufficient when diagnosing patients with primary GHOA.13 Commonly, these radiographs will feature narrowing of the glenohumeral joint space, osteophyte formation along the humeral neck, asymmetric posterior bone loss of the glenoid, and a normal acromiohumeral interval, which indicates an absence of rotator cuff arthropathy. CT can also be helpful in patients with GHOA and is especially useful when it comes to analyzing bony pathology, such as the shape of the glenoid, extent of osteophyte formation, and resting position of the humeral head in relation to the glenoid. While potentially superfluous in the setting of primary GHOA, MRI can also be used to assess the integrity of the rotator cuff, which can help surgeons decide between TSA and RTSA.

Finally, one must analyze the patient’s history, physical examination, and imaging and determine if these elements align in a coherent manner with a specific diagnosis. If these are inconsistent, it is important to reassess prior to providing the patient with a definitive diagnosis and treatment plan. If the patient’s history, physical examination, and imaging are consistent with a uniform diagnosis, then one can advance to the next step and treat the pathology with confidence. Surgical intervention for specifically primary glenohumeral osteoarthritis is considered once the patient’s shoulder pain and dysfunction have significantly hampered their ability to perform activities of daily living and they have exhausted nonoperative treatments.

Once the decision is made to proceed with operative intervention, a preoperative planning software can be utilized to help develop an operative plan that will guide implant size, position, and orientation. Often, this software can template both TSA and RTSA using a patient’s CT scan, which is another tool that can help surgeons decide between the two prostheses. We typically start by analyzing the patient’s current pathologic glenoid inclination and version and compare that with their premorbid anatomy (Figure 49-1A and B).







We then place the glenosphere implant at the middle of the glenoid, centered in both the anterior-posterior and superior-inferior directions, with neutral inclination. Then, we adjust the glenosphere accordingly by analyzing several factors including percentage of backside coverage, approximate screw length, and impingement-free range of motion. Ideally, our prostheses will have at least 70% backside coverage. For screw length, we prefer our center screw to be at least 26 to 30 mm and two or more of the four peripheral screws to be minimum 22 mm. The impingement-free range of motion will be based on a variety of factors including presence of osteophytes, glenosphere size, glenosphere offset, and depth of reaming. The humeral component can be adjusted in a similar manner and should ultimately be positioned in the plane of the anatomical neck with the depth of the socket below the projected osteotomy, which will allow for the component to lie inset. This will most likely be positioned so that the superior aspect of the implant is just medial to the footprint of the supraspinatus (Figure 49-2A-C). The goal is to develop a plan that allows to us position the implants in such a way to restore the premorbid anatomy and position of the muscle-tendon units, which will maximize stability and impingement-free range of motion.








TECHNIQUE

Once the patient is marked and transported to the operating room, they will undergo general anesthesia and endotracheal intubation before being placed upright in the beach chair position. When utilizing the beach chair position, attention should be paid to the position of the patient’s neck to ensure it remains neutral. The beach chair position also allows for the sterile drapes to form a barrier between the anesthesiologist and operative field. These drapes should be sufficiently under tension to ensure that the barrier is maintained throughout the procedure. Moreover, tension of the drapes provides the
operating surgeon the ability to use blunt towel clips on the drapes to hold retractors throughout the procedure. Following sterile prepping and draping of the operative extremity, we employ a sterile, padded Mayo stand to support the arm. We prefer to use a padded Mayo stand, as this can be easily raised or lowered throughout the case to help adduct or abduct the arm.


Deltopectoral Approach

The natural outline of the deltoid can be seen in its extension from the clavicle to the distal insertion, and this is utilized to mark the incision. The proximal portion of the incision will be at the level of the clavicle, approximately three fingerbreadths or about 5 cm medial to the acromioclavicular joint, while the distal extent will be at the deltoid tuberosity of the humerus. Utilizing the full length of this incision allows for mobilization of the deltoid with minimal trauma during retraction throughout the case. Moreover, the incision is positioned along the deltopectoral groove, which is a centered position to easily address the humerus and the glenoid throughout the procedure.

The skin incision is started along the length of the ordained line with a 10-blade scalpel. Electrocautery is utilized to dissect through deep cutaneous tissue and subcutaneous fat with the assistance of Gelpi reactors to spread subcutaneous tissue as needed. Long, steady strokes in the center plane over the deltopectoral groove are preferred. The goal is to dissect enough subcutaneous fat until you can identify the infraclavicular fat pad on the medial border of the deltoid at the proximal aspect of the deltopectoral interval (Figure 49-3). Once this is identified, electrocautery along the deltoid side of the infraclavicular fat pad will allow the cephalic vein to fall medially with the pectoralis major. Be careful to avoid the coracoacromial ligament, as this will be intact in patients with primary glenohumeral osteoarthritis and its preservation will prevent postoperative superior escape.






The operating surgeon should progress with deep dissection distally along the deltopectoral groove. We find it helpful to use army-navy retractors to tension the deltoid within the groove laterally as we progress distally. Being cognizant of neighboring vasculature and achieving adequate hemostasis are key elements of the deltopectoral approach. During deep dissection, one may encounter the deltoid branch of the thoracoacromial artery, which courses along the pectoralis minor and lateral to the cephalic vein. The cephalic vein also has lateral perforating tributaries into the deltoid that will inevitably be cauterized during deep dissection. We prefer to let the cephalic vein fall medially with the pectoralis major because once the cephalic vein is completely dissected from the deltoid, it will stay away from the surgical field for the remainder of the surgical procedure. If the cephalic vein is left laterally with the deltoid, one must be constantly aware of the vein when manipulating the deltoid laterally with retractors.

Once deep dissection of the deltopectoral interval with adequate hemostasis is achieved, the operating surgeon should perform the subdeltoid release. Raising the Mayo stand places the humerus in abduction, which will take tension off the deltoid. As previously mentioned, adhesions in the subdeltoid space should be minimal in patients with primary osteoarthritis compared with those with rotator cuff arthropathy and/or prior shoulder surgery. Next, electrocautery is used to release subdeltoid adhesions (Figure 49-4A and B). The goal is to adequately visualize the clavicle proximally and deltoid insertion distally. Failure to mobilize the deltoid from the clavicle to the deltoid
tuberosity may result in injury to the deltoid with lateral retraction during the following steps in the procedure. Placement of a Brown retractor proximally between the deltoid and rotator cuff at the level of the greater tuberosity under minimal tension can serve as a barometer for optimal deltoid release (Figure 49-4C). One should avoid placing the Brown retractor distally under the deltoid, as retraction in this location may place stress on the axillary nerve. Once the Brown retractor is in place in the subdeltoid space, one should adduct the arm prior to the next step.







Biceps Tenotomy and Subscapularis Peel

Once the deltopectoral interval is established, the next steps involve biceps tenotomy and subscapularis peel to expose the humeral head. However, one must be conscious of the anterior humeral circumflex artery and two venae comitantes (colloquially termed the “three sisters”), which can be found at the bicipital groove at the base of the subscapularis tendon and converge at the arcuate artery. While some surgeons prefer to tie off the vessels with suture ligate, our preference is to cauterize these bleeding vessels before the subscapularis peel, as well as the vessel that is left behind once the subscapularis peel is completed.

The operating surgeon should locate the biceps tendon in the bicipital groove. Electrocautery through the overlying capsule will expose the tendon, which can be further uncovered by using a still clamp to poke through the sheath. We prefer to track the tendon proximally to the level of the rotator interval adjacent to its insertion point on the supraglenoid tubercle. Next, the operating surgeon should incise and release the biceps tendon. We prefer to release the biceps as proximally as possible without violating the coracoacromial ligament, as the remaining biceps tendon tissue can be used to estimate the ideal subscapularis approximation after component placement and be incorporated
into our future subscapularis repair. Cutting the biceps tendon is preferred to tearing or ripping, as aggressive manipulation of the tendon will compromise the vinculae and soft tissue.

At the superior aspect of the glenohumeral joint, which is adjacent to where the biceps tendon was incised, the operating surgeon should place a small, sharp Hohmann retractor to initiate the subscapularis peel. Using electrocautery, peel the subscapularis from the lesser tuberosity from proximal to distal. Placing the arm in progressive adduction and external rotation during the peel with assistance of an intra-articular sharp Hohmann retractor will effectively tension the subscapularis and anterior capsular tissues to facilitate the peel (Figure 49-5A). Switching the small, sharp Hohmann retractor for a large, sharp Hohmann retractor as the peel progresses will also make the subscapularis easier to dissect under tension. In the setting of primary osteoarthritis, there may be intra-articular loose bodies that become evident during the subscapularis peel, which should be removed. Once the operating surgeon reaches the inferior aspect of the subscapularis, another small Hohmann retractor can be placed at a 90° angle to the initial Hohmann retractor (Figure 49-5B).