Surgical Technique Shoulder Arthroplasty System


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SURGICAL TECHNIQUE SHOULDER ARTHROPLASTY SYSTEM
COMBINING SCIENCE, SIMPLICITY AND CLINICAL SUCCESS

Table of Contents
Design Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 The Glenoid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 The New Global Advantage Humeral Body . . . . . . .2 The New Global Advantage Humeral Head . . . . . .2 The Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
Surgical Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 Patient Positioning . . . . . . . . . . . . . . . . . . . . . . . . . . .3 Surgical Incision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Incision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Pectoralis Major Tendon Release . . . . . . . . . .5 Anterior Humeral Circumflex Vessels Management . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Nerve Identification . . . . . . . . . . . . . . . . . . . . . . . .6 Musculocutaneous Nerve . . . . . . . . . . . . . . . . .6 Axillary Nerve . . . . . . . . . . . . . . . . . . . . . . . . . . .6 Subscapularis Tendon Release . . . . . . . . . . . . . .7 Capsule Release and Humeral Head Resection . . .8 Humeral Head Resection . . . . . . . . . . . . . . . . . . .8 Technique for Head Removal Using the Intramedullary Humeral Resection Guide .10 Sizing the Resected Humeral Head . . . . . . . . .12 Medullary Canal Preparation and Broaching the Humerus . . . . . . . . . . . . . . . . . .13 Medullary Canal Reaming . . . . . . . . . . . . . . . . . .13 Using the Body Sizing Osteotome . . . . . . . . . . .14 Broaching the Humerus . . . . . . . . . . . . . . . . . . . .15 Removal of Osteophytes . . . . . . . . . . . . . . . . . . .15 Glenoid Preparation . . . . . . . . . . . . . . . . . . . . . . . . .16 Pegged Glenoid Trial . . . . . . . . . . . . . . . . . . . . . .18 Keeled Glenoid Trial . . . . . . . . . . . . . . . . . . . . . .19 Humeral Head Trials . . . . . . . . . . . . . . . . . . . . . . . . .20 Use of the Eccentric Trial Heads . . . . . . . . . . . .20 Glenoid Prosthesis Insertion . . . . . . . . . . . . . . . . . .22 Pegged Glenoid Insertion . . . . . . . . . . . . . . . . . .22 Keeled Glenoid Insertion . . . . . . . . . . . . . . . . . .23 Attaching the Head to the Humeral Prosthesis . . .24 Seating the Standard Head . . . . . . . . . . . . . . . .24 Seating the Eccentric Humeral Head . . . . . . . .24 Insertion of the Humeral Head/Stem Assembly . .25 Press-Fit, Impaction Bone Grafting or Cement . . . . . . . . . . . . . . . . . . . . . . . .25 Removal of the Prosthetic Humeral Head . . . .26 Removal of the Cemented Humeral Body . . . .26 Joint Reduction and Repair of the Subscapularis Tendon . . . . . . . . . . . . . . .26 Wound Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
Postoperative Protocol . . . . . . . . . . . . . . . . . . . . . . . . . .29

GLOBAL ADVANTAGE SHOULDER ARTHROPLASTY SYSTEM
ANATOMIC SHOULDER ARTHROPLASTY
Frederick A. Matsen, III, MD
Charles A. Rockwood, Jr., MD
Design Rationale
The multiple sizes of the glenoids, humeral bodies and heads allow the Global Advantage™ Shoulder System to be used worldwide. Its design is based on the detailed investigations of the structure and mechanics of normal and prosthetic glenohumeral joints conducted at the University of Texas at San Antonio, University of Washington, University of Pennsylvania and DePuy Orthopaedics, Inc., Warsaw, Indiana. The challenges encountered by shoulder arthroplasty surgeons include surgical exposure, soft tissue balancing and component fixation. The instruments, technique and components of this arthroplasty system are designed to address these challenges.
The Glenoid
In a glenohumeral arthroplasty, the surgeon seeks to restore the glenoid articulating surface with minimal compromise of joint volume and glenoid bone stock. Overstuffing the joint (using prostheses that are bigger than the amount of bone removed) can contribute to impaired range of motion, loss of bone stock and the compromise of support afforded the component. The fit of the Global glenoid component to the bone minimizes the amount of bone cement needed. Direct support of the component by bone reinforces component stability.
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Specialized techniques and instrumentation, including retractors, straight and angled drill shafts and reamers, facilitate the exposure, orientation and preparation of the glenoid. The combination of custom spherical reaming of the bony surface and anchor peg, five-peg or keel fixation provides excellent stability for the component with minimal sacrifice of bone stock.
Laboratory research indicates that having the diametral curvature of the glenoid slightly greater than that of the humeral head offers the advantages of allowing translation and shock absorption without loading the glenoid component rim. For this reason, the surface of all Global glenoids are designed with a 6mm larger diametral curvature than the corresponding humeral head. This degree of diametral “mismatch” was selected after extensive investigation of the mechanics of the normal joint as well as the mechanical properties of prosthetic materials.
The Global Advantage Humeral Body
The Global Advantage humeral component achieves versatility through its two parts: the body and the head. Through extensive cadaveric evaluation, the body was designed to optimize the fit and fill of the proximal humerus. From this evaluation, a family of humeral body sizes has been designed to fit the wide range of humeral canals. A total of six body sizes are available with stem diameters ranging from 6 to 16mm. The humeral body is constructed of high strength titanium alloy, which affords exceptional biocompatibility.
Proper fit in the humeral canal aids in proper varusvalgus alignment. Proper fit in the metaphysis, combined with the collar, provides stability against subsidence. The four fins provide additional rotational control.
A unique system of humeral cutting and broaching instruments helps achieve optimal alignment and stability with minimal bone resection.
The Global Advantage Humeral Head
The Global Advantage shoulder offers a full range of 15 standard and 8 eccentric humeral head components that fit all body configurations. When impacted on the humeral body, the Global Advantage humeral heads fit
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over the collar. This feature optimizes the articulating surface area for a more anatomic replacement. The eccentric heads ensure complete coverage of the cut surface of the proximal humerus and maintain the head 5 to 10mm above the top of the greater tuberosity. This is an important feature since proper selection of the head diameter and neck length is critical in balancing the soft tissue. The Global Advantage humeral head is constructed of cobalt chrome alloy, which provides excellent wear characteristics.
The head is joined to the body by a reverse Morse taper lock. By having the stem of this taper lock on the humeral head, the surgeon is afforded optimal working space in the joint after the humeral body has been implanted. This feature is particularly valuable in the revision of a hemiarthroplasty to a total arthroplasty.
The Technique
Recognizing that a successful shoulder arthroplasty is critically dependent on soft tissue balancing, this document provides a detailed guide to the techniques of tendon lengthening and capsular releases, which are integral parts of this procedure. These steps cannot be effected with jigs and guides, but rather require an understanding of the principles of shoulder mechanics.
Recognizing that each shoulder arthroplasty needs to be adapted to the patient’s unique combination of soft tissue and bone anatomy, the system maximizes the surgeon’s flexibility in matching a wide variety of anatomic requirements. Because patients have high expectations of the function and durability of the arthroplasty, a premium has been placed on secure fixation, conservation of bone and optimization of mechanics. Surgical technique is a critical variable in the success of any arthroplasty; this document seeks to optimize surgical technique through detailed technique descriptions and advanced instrumentation.

Special headrest

[figure 1]

SURGICAL TECHNIQUE
Charles A. Rockwood, Jr., MD
PATIENT POSITIONING
Place the patient in a semi-Fowler position on the operating table (Fig. 1). Remove the standard headrest portion of the table and replace it with a special headrest such as the Mayfield or the McConnell (McConnell, Greenville, TX). Position the patient so that the involved shoulder extends over the top corner of the table (Figs. 1, 2 and 3). Secure the patient’s head with tape. Drape to isolate the anesthesia equipment from the sterile field.

[figure 2]

[figure 3] 3

SURGICAL INCISION: MUSCULOCUTANEOUS AND AXILLARY NERVE IDENTIFICATION AND PECTORALIS MAJOR AND SUBSCAPULARIS TENDON RELEASE
Incision
Make an incision running from the clavicle over the top of the coracoid down the anterior aspect of the arm (Figs. 4 and 5). Once the incision has been made, locate the cephalic vein on the deltoid muscle near the deltopectoral interval (Fig. 6). The cephalic vein is usually intimately associated with the deltoid because there are many feeders from the deltoid into the cephalic vein. For this reason, it is recommended that the vein be taken laterally with the deltoid muscle.
Clamp and tie feeders coming from the region of the pectoralis major muscle, allowing retraction of the deltoid with the vein laterally. Free the deep surface of the deltoid from the underlying tissues, from its origin on the clavicle down to its insertion in the humeral shaft. To obtain more exposure, it may be necessary to partially free the insertion of the deltoid from the humeral shaft, but it rarely is necessary to release the deltoid from the clavicle.
When the anterior margin of the deltoid has been completely freed from its origin to its insertion, especially along its deep surface, abduct and externally rotate the arm, which will allow the deltoid to be gently retracted laterally with two Richardson retractors. Medially retract the conjoined tendon. It is not necessary to release the conjoined tendon or to divide the coracoid process for additional exposure.
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[figure 4]
Cephalic vein
[figure 5]
Cephalic vein
[figure 6]

Richardson retractor
Anterior humeral circumflex artery & vein

Pectoralis major
tendon

Pectoralis Major Tendon Release
Release the upper 25 percent of the pectoralis major tendon from its insertion on the humerus with an electrocautery cutting blade. This will aid in the exposure of the inferior aspect of the joint (Fig. 7). If the patient has marked internal rotation contracture, release most of the pectoralis major tendon from its insertion. This tendon release should not be repaired at the completion of the operation since it will limit external rotation postoperatively.

[figure 7]

Anterior Humeral Circumflex Vessels Management
Isolate, clamp and ligate or coagulate the anterior humeral circumflex vessels lying across the anterior/inferior surface of the subscapularis tendon (Fig. 8).

[figure 8] 5

Nerve Identification
Musculocutaneous Nerve
It is important to identify the musculocutaneous and axillary nerves. Palpate the musculocutaneous nerve as it comes from the plexus into the medial and posterior aspect of the conjoined tendon (Fig. 9). Usually, the nerve penetrates the muscle approximately 11/2 to 2 in. down from the tip of the coracoid, but in some instances the nerve has a higher penetration into the conjoined muscle tendon unit. Remember the proximity of this nerve to the tendon during the retraction of the conjoined tendon.
Axillary Nerve
Locate the all-important axillary nerve by passing the volar surface of the index finger down along the anterior surface of the subscapularis muscle (Fig. 10). Rotate and hook finger anteriorly to identify the axillary nerve (Fig. 11). Occasionally, secondary to previous dislocations, scarring and adhesions, the nerve will be plastered onto the anterior surface of the subscapularis and is difficult to locate. When this occurs, pass a periosteal elevator along the anterior surface of the muscle to create an interval between the muscle and the nerve. Always identify the axillary nerve and carefully retract it out of the way, especially during the critical steps of releasing the subscapularis tendon and resecting the anterior/inferior capsule. A retractor can be used for protecting the nerve.
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Coracoid process Conjoined tendon
Musculocutaneous nerve
[figure 9]
Axillary nerve
[figure 10]
[figure 11]

Subscapularis tendon
Biceps tendon
[figure 12]
1mm nonabsorbable tape Glenohumeral joint superior view

Subscapularis Tendon Release
If when under anesthesia the shoulder has zero degrees or more of external rotation, release the subscapularis tendon from its insertion on the lesser tuberosity (Fig. 12) or divide the tendon. We believe that the ultimate repair of the tendon back to bone is stronger than a tendon to tendon repair. We prefer to free the tendon from the underlying thickened capsule and continue to free up the tendon until it is clear of any adhesions from the back of the coracoid process and from the capsule as it attaches on the anterior glenoid rim. This process requires that the subscapularis muscle tendon unit be released 360 degrees around its circumference. During this dissection, protect the axillary nerve as it crosses the inferior portion of the muscle tendon unit. It is important to have a free, dynamic and functioning subscapularis muscle tendon unit at the time of its repair.
At the time of closure, repair the tendon back to the cut surface of the neck or humerus using 1mm nonabsorbable tape. This will allow 40 degrees or more of external rotation of the arm (Fig. 13). If the shoulder has minus 20 degrees of external rotation or less, perform a coronal Z-plasty to lengthen the tendon (Figs. 14 and 15). Each centimeter of tendon lengthening will equal approximately 20 degrees of additional external rotation. When the coronal Z-plasty procedure is performed, include the thickened capsule in its repair for additional strength.

[figure 13]

[figure 14]

[figure 15] 7

CAPSULE RELEASE AND HUMERAL HEAD RESECTION
Occasionally, the capsule will be released from the neck of the humerus with the subscapularis tendon. If that occurs, dissect the anterior capsule from the posterior surface of the subscapularis to maintain a free, dynamic subscapularis tendon. Use a retractor to retract the previously identified axillary nerve anteriorly/inferiorly away from the inferior capsule. Externally rotate the arm, which will place tension on the capsule, and then release the capsule from its attachment to the humerus all the way down inferiorly to at least the six o’clock position (Fig. 16). Failure to release the capsule all the way down inferiorly will make it very difficult to bring the head up and out of the glenoid fossa. Use either a knife, electrocautery blade or scissors to release the capsule.
Once the capsule has been released, pass a small bone hook around and under the neck of the humerus (Fig. 17). Place the large plastic Darrach retractor in the joint and use it as a skid. Use the bone hook to deliver the head out of the glenoid fossa so that the arm can be extended and externally rotated off the side of the operating table (Figs. 18 and 19).
Note: Remember to release the capsule all the way down inferiorly to the six o’clock position and sometimes a bit further. Failure to complete the inferior capsular release will make delivery of the proximal humerus up and out of the wound quite difficult. The combination of lifting with the bone hook and prying with the large Darrach retractor, along with externally rotating and extending the arm off the side of the table, will produce adequate exposure.

[figure 16]
Bone hook
[figure 17]

Capsule
Retractor protecting axillary nerve
Darrach retractor Richardson retractor
Retractor

Humeral Head Resection
Preoperative evaluation of the humerus with templates helps determine the size of the prosthesis and level of head resection. The resection of the humeral head is a very critical part of the procedure. When there is no posterior glenoid erosion, remove the humeral head with the arm in 20 to 25 degrees of external rotation. Flex the elbow 90 degrees and then externally rotate the arm 20 to 25 degrees (Fig. 20).
Determine the varus-valgus angle of the head to be removed by using the humeral osteotomy template.
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[figure 18]

20-25˚

[figure 20]

[figure 19]

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Surgical Technique Shoulder Arthroplasty System