Operative Technique Using an Onlay Humeral Component



Operative Technique Using an Onlay Humeral Component


Kaveh R. Sajadi, MD



The reverse total shoulder arthroplasty (RTSA) designed in the 1980s by Dr. Paul Grammont medialized the center of rotation of the shoulder by moving it to the face of the glenoid. His design had three primary criteria—a medialized center of rotation, lengthening of the deltoid by lowering the humerus, and a convex glenoid (bearing side) with a concave supported humerus side. This design revolutionized the management of rotator cuff tear arthropathy. Problems with the design, however, began to appear with follow-up. The most common concerns with the original Grammont design have been scapular notching and instability. Scapular notching rates have been reported as high as 96%.1 Though initially felt to be of unclear significance, numerous studies have associated notching with inferior clinical outcomes.2,3,4,5 Instability, another common concern in RTSA, has been reported to occur at a rate between 1.5% and 31%.6 Several modifications of Grammont’s original design have been developed since, with most systems falling into three design categories, as described by Routman et al.7 A prosthesis with the center of rotation 5 mm or less from the glenoid face was defined as a medialized glenoid, and those with the center of rotation more than 5 mm from the glenoid face were classified as lateralized glenoid (even with lateralized glenoids, the center of rotation is medial to a native shoulder). The three design categories are medialized glenoid and medialized humerus (original Grammont design); lateralized glenoid and medialized humerus; and medialized glenoid and lateralized humerus.

The medialized glenoid/lateralized humerus design offers several advantages. By medializing the glenoid, the center of rotation is placed on the face of the glenoid—allowing medialization of the center of rotation while minimizing glenoid shear forces, reducing the risk of loosening of the glenoid implant. By lateralizing the humerus, deltoid tension is optimized via the deltoid wrap angle. Deltoid wrapping refers to the wrapping of the middle deltoid around the greater tuberosity (FIGURE 23.1), resulting in increased humeral compression into the glenoid. This theoretically decreases the deltoid force needed to abduct the arm.8 Humeral lateralization has also been shown in a cadaveric study to improve joint and muscle loading, by decreasing the amount of deltoid force required for active abduction9 while also improving tension on the remaining rotator cuff muscles, particularly with regard to external rotation. Humeral lateralization improves stability10 as well as decreases scapular notching11 and is achieved by decreasing the humeral neck angle from the Grammont design of 155° to a more anatomic humeral neck angle (145°). This allows an anatomic, bone-preserving osteotomy to be performed at the anatomic neck. Furthermore, an onlay design has a greater effect on humeral lateralization than modifying the humeral neck angle.12 With use of an onlay prosthesis design, proximal humeral bone is preserved and lengthening of the humerus is achieved. In addition, with an onlay prosthesis, the glenosphere size is not limited to fitting within the proximal humerus as it is in an inlay system. Use of an onlay design makes a platform system ideal as well, making convertibility in a revision setting easier. In summary, an onlay, lateralized humerus design reverse system decreases scapular notching, improves stability, preserves proximal humeral bone, and allows for a platform stem while optimizing deltoid wrap, decreasing the deltoid force required to lift the arm, and maximizing tension on the remaining rotator cuff muscles (VIDEO 23.1).


EXPOSURE

Optimizing exposure does not start in the operating room. Preoperative factors to consider begin with the history and physical examination. Factors that make
exposure more difficult or challenging include previous surgeries and scarring, altered postsurgical anatomy, and patient size. Previous operative reports should be reviewed for factors that could influence exposure. Truncal obesity can make adducting the arm difficult. Muscular patients can be challenging as well due to difficulty retracting the large, often noncompliant muscles.











Preoperative imaging should begin with standard radiographs, including an anteroposterior (AP) Grashey, a scapula lateral (Y or outlet view), and an axillary lateral/truth view (FIGURE 23.2). At the discretion of the surgeon, a computed tomography (CT) scan in the plane of the scapula with 1 mm or less cuts with three-dimensional (3D) reconstruction can be beneficial, as it not only provides details of glenoid version and inclination but also allows assessment of bone stock and presence of bony defects or cysts which may require grafting. CT scan is also beneficial for templating and preoperative planning and/or navigation. Magnetic resonance imaging (MRI) can be beneficial to evaluate the rotator cuff preoperatively (FIGURE 23.3) but is not routinely ordered by the author. Routine laboratory studies are ordered, including hemoglobin A1c in diabetic patients. In addition, patients are given a preoperative prescription for topical benzoyl peroxide.

Operating room setup is critical for success. The operating table should be positioned such that the operative shoulder is rotated to the center of the room, allowing all surgical lights to be centered on the field. Adequate space for back table setup and position of assistants is essential (FIGURE 23.4). Multiple commercial beach chair attachments are available, though not necessary. The head and neck must be positioned in neutral alignment, avoiding hyperextension or tilting of the neck, which may cause cervical nerve root compression. The patient is positioned in the beach chair position with their head/torso elevated approximately 30° and the
lower extremities flexed at the hips and with a pillow under their knees to alleviate strain on the lumbar spine (FIGURE 23.5). Using a Trendelenburg position, elevation of the head/torso, and flexion of the legs create a deep “V” which cradles the body and prevents sliding. If the patient is morbidly obese or has a large body habitus, the torso is elevated to a higher angle to ease positioning of the arm. A bolster may be placed under the medial scapula for support, and the arm should be completely free. It is essential to be able to extend, adduct, and externally rotate the humerus to allow vertical orientation of the humerus during humeral preparation and stem insertion. A body support or bolster placed on the operative side should be against the hip if possible so as not to impede adduction/extension of the arm. Before prepping, the arm should be examined under anesthesia for range of motion and to ensure it can be positioned as necessary during the procedure. The entire arm should be prepped and draped. A pneumatic arm holder is helpful for positioning during the procedure, particularly if the surgeon has a limited number of surgical assistants. These arm holders, though expensive, have the advantage of not fatiguing and will also minimize crowding. When adequate assistants are present, the author prefers to use a padded Mayo stand, which should be draped to rest the arm upon during initial approach as well as glenoid exposure (FIGURE 23.6).





















Numerous skin preparation solutions are available. Patients are given a preoperative prescription for benzoyl peroxide to use for 3 to 5 days prior to the surgery.13 On the day of surgery, the surgical area is shaved with electric clippers in the preoperative area. A chlorhexidine wipe is also administered to clean the surgical area. Anesthesia then performs the regional anesthetic. An indwelling interscalene catheter is utilized unless otherwise contraindicated. Once positioned in the operating room, the operative shoulder, axilla, and arm are wiped down with ethyl alcohol and then dried prior to prepping with chlorhexidine prep sticks. Recent studies suggest that the addition of hydrogen peroxide prior to chlorhexidine may reduce the Cutibacterium acnes load, though studies of the safety and efficacy of combinations of different preparation solutions are limited. Preoperative antibiotics are administered. The author’s preference is appropriate weight-based first-generation cephalosporin followed by vancomycin to provide improved coverage
of C. acnes. Prior to placement of surgical drapes, the indwelling interscalene nerve catheter is covered with a sterile blue towel to prevent drapes from adhering to it and causing it to be dislodged at the conclusion of the procedure. Draping should provide exposure from the area superior to the clavicle to several centimeters medial to the coracoid process anteriorly and allow posterior exposure to the medial edge of the scapula and full access to the arm. An iodine-impregnated drape is used to seal off the surgical field and to seal off the axilla.

The surgery can be performed with either general or regional anesthesia with sedation. The author’s preferred technique is either general or sedation along with an indwelling interscalene catheter. Although paralytic agents may allow easier exposure, the author does not routinely use them but has anesthesia prepared to administer them, if necessary, in complicated or difficult exposures where complete muscle relaxation may be helpful.

The two most commonly performed surgical approaches are the superior approach and the deltopectoral approach. The superior approach, similar to an open rotator cuff approach, does allow for more direct glenoid exposure and potentially better stability through preservation of the subscapularis tendon if it is intact. However, it is not extensile and requires takedown and repair of the deltoid, which may compromise the deltoid if healing is impaired. The deltopectoral approach is the author’s preferred approach for multiple reasons. First, it is more familiar to most orthopedic surgeons, especially with open rotator cuff repairs no longer routinely performed. Second, the approach is versatile, extensile, and revision friendly. Third, it does not compromise the deltoid origin or insertion, which is vital to the outcome of a reverse arthroplasty. Finally, if adjunctive muscle transfers are planned, they can be performed through the same incision.

The skin incision is made beginning at the lateral margin of the coracoid process and extends distally toward the deltoid insertion and 1 to 2 cm lateral to the axillary crease (FIGURE 23.7). If extended, the incision should be on a path along the lateral edge of the biceps muscle, in line with the anterolateral approach to the humerus. Subcutaneous flaps are developed to create approximately 1.5 cm flaps on either side of the fat stripe (FIGURE 23.8). The fat stripe may or may not contain or cover the cephalic vein due to variable anatomy. If the incision is made too lateral, one may be fooled by the fat stripe/raphe between the anterior and middle thirds of the deltoid. The correct fat stripe when followed proximally will lead to a trapezoidal area of fatty connective tissue that overlies the coracoid process. This location should be confirmed by palpation of the coracoid process, which has been referred to as the “lighthouse of the shoulder.”14 If the surgeon is having difficulty identifying the interval, it is best to begin at the coracoid process and progress distally. Additionally, the deltoid and pectoralis muscles can be differentiated based on the direction of their muscle fibers, which can be accentuated by external rotation of the arm. The cephalic vein is exposed both to confirm its location and to protect it. It is then retracted either medially or laterally. Medial retraction has a decreased risk of injury as it crosses the interval proximally but
requires more ligation of branches as there are more branches entering from the deltoid side. The vein actually often overlies the deltoid muscle and is not directly over the interval. This lends itself to mobilizing the vein laterally with the deltoid, which is the author’s preferred approach. The deltopectoral interval is then developed by gentle dissection using Metzenbaum scissors with a gentle snipping technique to advance through the adventitial tissue separating the deltoid and pectoralis. Using this more precise method allows clearer differentiation of the interval with less muscular damage. A blunt elevator, such as a Cobb or Darrach (FIGURE 23.9), is placed under the deltoid and over the proximal humerus. The subdeltoid and subpectoral spaces are bluntly developed to free adhesions. This mobilization is critical for improving mobility and for deep exposure to allow adequate mobilization of the humerus for later glenoid exposure. If a previous rotator cuff repair has been performed, particularly an open repair, extensive adhesions of the deltoid to the bursal tissue or proximal humerus may be present. Careful release of these adhesions is necessary for exposure and mobilization of the humerus. A blunt (Kolbel type) self-retaining retractor is placed under the deltoid and pectoralis muscles. Alternatively, a Browne deltoid retractor can be placed laterally under the deltoid, and a Richardson-type retractor is placed medially under the pectoralis muscle. Next, the clavipectoral fascia is opened on the lateral margin of the conjoined tendon. Often, a thin strip of muscle lies lateral to the tendon, and the fascia should be opened just lateral to this to preserve the muscle (FIGURE 23.10). The fascia is opened proximally until reaching the coracoacromial (CA) ligament. It is the author’s preference to preserve the CA ligament if possible. The Darrach or Cobb elevator is passed first over the supraspinatus fossa and then over the infraspinatus fossa to release adhesions. It is then repositioned under the CA ligament, and the Kolbel retractor is then repositioned with the medial blade/retractor positioned deep to the conjoined tendon. Avoid excessive tension as this risks injury to the musculocutaneous nerve.





















Next, the proximal 1/2 to 1 cm of pectoralis major tendon is released just medial to the long head of the biceps tendon. Pectoralis release allows exposure of the long head of the biceps and also facilitates posterior subluxation of the humerus during glenoid exposure. The biceps is then tenotomized or tenodesed based on surgeon preference. The author’s preferred technique is soft-tissue tenodesis to the lateral edge of the pectoralis tendon using one to two figure-of-eight sutures with #2 braided nonabsorbable suture. If there is significant proximal migration of the humeral head, it may be necessary to release a little more pectoralis tendon to sufficiently mobilize the proximal humerus. Next, identify and cauterize the anterior humeral circumflex artery and its vena commitante (three sisters), which lie on the inferior margin of the subscapularis and serve as the dividing point between the upper two-third (tendinous portion) and the lower one-third (direct muscular insertion). The subscapularis may be chronically torn, but in many cases, the vessels and its inferior muscular portion remain intact.

The subscapularis, if present, may be released in three ways. A direct peel of the tendon allows for lengthening of the tendon if it is contracted and later repair is desired. Drill holes will need to be placed in the humerus prior
to stem placement if this is the desired technique. An osteotomy provides the theoretical advantage of bone to bone healing. If the osteotomy is too large, it may compromise metaphyseal stem fixation and stability. If it is too small, then it is similar to the peel technique. This technique also requires drill holes be placed prior to stem placement. Finally, tenotomy offers a reproducible technique with the ease of tendon to tendon repair. Outcomes of all three techniques are not significantly different in the literature15; therefore, the surgeon should use the same technique they utilize in anatomic total shoulder arthroplasty (ATSA). The author’s preferred technique is a tenotomy performed approximately 1 to 1.5 cm medial to the lateral margin of the lesser tuberosity, leaving a robust cuff of tissue laterally for the repair while avoiding the musculotendinous junction medially. Tagging sutures are placed through the subscapularis tendon to control mobilization and later release of the anterior capsule. At least one suture is placed at the superior margin of the tendon to guide repair and restoration of anatomy. The rotator interval is then released in a lateral to medial direction to the anterosuperior glenoid and base of the coracoid process.






After release of the subscapularis tendon, the inferior capsule is released directly off the humerus. It is helpful to place a blunt retractor into the axillary recess to place the capsule under tension. Electrocautery is utilized to release the capsule directly off the inferior humeral neck while carefully externally rotating the arm to gain progressive posterior access (FIGURE 23.11). The release is carried inferiorly to the superior edge of the latissimus tendon. The release is carried in a superior to inferior direction while an assistant progressively externally rotates the arm allowing the release to be carried from anterior/lateral to posterior/medial until at least 90° of external rotation is achieved. This is essential to allow posterior subluxation of the humerus for glenoid exposure, to remove osteophytes, and to restore/improve postoperative range of motion. The axillary nerve is protected by use of the blunt retractor, use of electrocautery on coagulation setting, and keeping the electrocautery device directly on the humerus. Osteophytes should be removed from the anterior and inferior humerus to clearly identify the anatomic neck. Inferior and posterior osteophytes may also be removed after the humeral head osteotomy if they do not come off with the resected head.

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Jun 23, 2022 | Posted by in ORTHOPEDIC | Comments Off on Operative Technique Using an Onlay Humeral Component
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