The patient is placed in the upright beach-chair position with the head
firmly secured and the arm draped free. The involved arm is positioned
sufficiently off the side of the table to allow for unobstructed movement in
adduction and hyperextension of the shoulder. The patient is managed with the
administration of a general anesthetic in addition to a scalene block. An
extended deltopectoral approach is employed and as much as two-thirds of the
pectoralis major tendon is released. The subdeltoid, subacromial, and
subcoracoid spaces are released. If the subscapularis tendon is intact, it is
released off of the lesser tuberosity, just medial to the long head of the
biceps, in order to allow atraumatic dislocation of the humeral head with
gentle external rotation and extension of the arm. The capsule is then
released completely around the humeral neck. Aggressive resection of any
osteophytes is then performed. A neck cut is made in 30° of retroversion,
and the canal is reamed. This cut is made at a slightly higher level than for
a traditional arthroplasty (Figs.
1-A,
1-B, and 1-C). Sequential
broaches are used to prepare the canal. The proximal part of the humerus is
then reamed with use of the first (smallest) metaphyseal reamer
(Fig. 2-A). Any remaining
osteophytes and a portion of the calcar are then resected back to a recessed
position (Fig. 2-B). The
humeral broach is left in place until implantation of the glenoid component is
completed. At that point, final preparation of the proximal part of the
humerus is performed with use of the next two metaphyseal reamers. This
sequence allows for sufficient resection of the proximal part of the humerus
to aid in glenoid exposure. The delay in the use of the last two humeral
reamers until the glenoid preparation is complete maintains adequate humeral
bone stock to support retraction during glenoid preparation.
Glenoid exposure is accomplished by retracting the proximal part of the
humerus posteriorly with use of a posterior glenoid retractor and performing
an aggressive 360° subperiosteal periglenoid capsular release. A Hohmann
retractor is then placed anteriorly on the glenoid neck, and a second Hohmann
retractor is placed at the superior aspect of the glenoid
(Fig. 3). With protection of
the axillary nerve, the inferior capsule is then resected. Once satisfactory
visualization of the glenoid is achieved, a centering hole is drilled with use
of a 2.0-mm drill with a slight inferior tilt, followed by the 6.5-mm tap
(Figs. 4-A and 4-B). The tap is
left in the glenoid to serve as a guide for the placement of the cannulated
glenoid reamers. Sequential cannulated convex reamers are then used to prepare
the glenoid for the baseplate insertion
(Fig. 5).
CRITICAL CONCEPTSINDICATIONS:Irreparable rotator cuff tear associated with glenohumeral arthritisIrreparable rotator cuff tear associated with glenohumeral instabilityFailed hemiarthroplasty or total shoulder replacement associated with
rotator cuff deficiencyCONTRAINDICATIONS:Nonfunctional deltoid muscleActive infectionExcessive glenoid bone lossSevere neurologic deficiencies (Parkinson disease, Charcot joints,
syringomyelia)Refusal to modify postoperative physical activitiesMetal allergyPITFALLS:The pitfalls of the procedure are mechanical failure of the device,
recurrent instability, and glenosphere/humeral socket dissociation. These
problems can be addressed by considering the size of the gleonosphere and its
relation to the center of rotation, stability, and range of motion as
described below.AUTHOR UPDATE:Since the inception of our study, there have been several changes to both
the surgical technique and the device itself. These modifications were made to
reduce the chance of early mechanical failure, recurrent instability, and
dissociation of the components and to provide the surgeon with more component
size options to target specific abnormalities and patient sizes.Three modifications have been made to reduce the likelihood of mechanical
failure. First, we now use 5.0-mm locking cortical screws instead of 3.5-mm
nonlocking screws to secure the glenoid baseplate
(Fig. 10). The locking design
prevents toggling at the bone-baseplate interface, and the larger-diameter
shank provides an increased force to failure. These biomechanical advantages
were confirmed in an in vitro analysis by Harman et
al.5. Second, we now
recommend that the baseplate be inserted at a slight (10° to 15°)
inferior tilt with respect to the glenoid in order to minimize shear forces
across the bone-baseplate interface and to make the compressive forces more
uniform across this
interface6. Finally,
for patients with suboptimal glenoid bone quality in whom fixation of the
baseplate may be in question, we now recommend medialization of the center of
rotation. A more medial center of rotation close to the glenoid surface
minimizes stress at the bone-prosthesis junction. Variably sized glenospheres,
with more medial centers of rotation, are now available. For patients with
optimal bone quality, however, a glenosphere with a more lateralized center of
rotation can be selected to maximize function. This is achieved by having a
center of rotation that is more anatomic in order to improve the tension in
any remaining subscapularis or infraspinatus muscle (Figs.
11-A and
11-B) as well as potentially
to provide more glenohumeral motion. The glenospheres that have a more lateral
center of rotation to the glenoid will have an increased range of motion
because the humerus is further away from the scapula, which decreases the
chance of impingement of the humerus on the acromion or the inferior portion
of the scapula.Two modifications have been used to improve the stability of the
glenohumeral articulation. First, larger glenospheres (36 mm [neutral offset],
36 mm [—4-mm offset], 40 mm [neutral offset], and 40 mm [—4-mm
offset]) are now available. These larger heads allow for greater coverage than
the smaller-diameter original 32-mm head does. Second, deeper
(semiconstrained) sockets have been added to provide greater conformity at the
articulation. However, the surgeon must be aware that the theoretical range of
motion will be reduced in association with the use of the more constrained
combination (Figs. 12-A and
12-B).Finally, to reduce the chance of component dissociation, two modifications
have been made. To reduce the risk of dissociation of the glenosphere from the
baseplate, a 3.5-mm retaining screw is now used to lock the glenosphere to the
baseplate. This augments the Morse taper between the glenosphere and the
baseplate. Additionally, a metal shell has been added to the polyethylene
liner on the humeral socket. This decreases the likelihood of dissociation of
the polyethylene socket from the humeral stem.The algorithm for glenosphere selection is shown in
Figure 13. The distance of the
center of rotation from the glenoid for each different glenosphere is shown in
Table I.
CRITICAL CONCEPTS
INDICATIONS:
Irreparable rotator cuff tear associated with glenohumeral arthritisIrreparable rotator cuff tear associated with glenohumeral instabilityFailed hemiarthroplasty or total shoulder replacement associated with
rotator cuff deficiency
Irreparable rotator cuff tear associated with glenohumeral arthritis
Irreparable rotator cuff tear associated with glenohumeral instability
Failed hemiarthroplasty or total shoulder replacement associated with
rotator cuff deficiency
CONTRAINDICATIONS:
Nonfunctional deltoid muscleActive infectionExcessive glenoid bone lossSevere neurologic deficiencies (Parkinson disease, Charcot joints,
syringomyelia)Refusal to modify postoperative physical activitiesMetal allergy
Nonfunctional deltoid muscle
Active infection
Excessive glenoid bone loss
Severe neurologic deficiencies (Parkinson disease, Charcot joints,
syringomyelia)
Refusal to modify postoperative physical activities
Metal allergy
PITFALLS:
The pitfalls of the procedure are mechanical failure of the device,
recurrent instability, and glenosphere/humeral socket dissociation. These
problems can be addressed by considering the size of the gleonosphere and its
relation to the center of rotation, stability, and range of motion as
described below.
AUTHOR UPDATE:
Since the inception of our study, there have been several changes to both
the surgical technique and the device itself. These modifications were made to
reduce the chance of early mechanical failure, recurrent instability, and
dissociation of the components and to provide the surgeon with more component
size options to target specific abnormalities and patient sizes.
Three modifications have been made to reduce the likelihood of mechanical
failure. First, we now use 5.0-mm locking cortical screws instead of 3.5-mm
nonlocking screws to secure the glenoid baseplate
(Fig. 10). The locking design
prevents toggling at the bone-baseplate interface, and the larger-diameter
shank provides an increased force to failure. These biomechanical advantages
were confirmed in an in vitro analysis by Harman et
al.5. Second, we now
recommend that the baseplate be inserted at a slight (10° to 15°)
inferior tilt with respect to the glenoid in order to minimize shear forces
across the bone-baseplate interface and to make the compressive forces more
uniform across this
interface6. Finally,
for patients with suboptimal glenoid bone quality in whom fixation of the
baseplate may be in question, we now recommend medialization of the center of
rotation. A more medial center of rotation close to the glenoid surface
minimizes stress at the bone-prosthesis junction. Variably sized glenospheres,
with more medial centers of rotation, are now available. For patients with
optimal bone quality, however, a glenosphere with a more lateralized center of
rotation can be selected to maximize function. This is achieved by having a
center of rotation that is more anatomic in order to improve the tension in
any remaining subscapularis or infraspinatus muscle (Figs.
11-A and
11-B) as well as potentially
to provide more glenohumeral motion. The glenospheres that have a more lateral
center of rotation to the glenoid will have an increased range of motion
because the humerus is further away from the scapula, which decreases the
chance of impingement of the humerus on the acromion or the inferior portion
of the scapula.
Two modifications have been used to improve the stability of the
glenohumeral articulation. First, larger glenospheres (36 mm [neutral offset],
36 mm [—4-mm offset], 40 mm [neutral offset], and 40 mm [—4-mm
offset]) are now available. These larger heads allow for greater coverage than
the smaller-diameter original 32-mm head does. Second, deeper
(semiconstrained) sockets have been added to provide greater conformity at the
articulation. However, the surgeon must be aware that the theoretical range of
motion will be reduced in association with the use of the more constrained
combination (Figs. 12-A and
12-B).
Finally, to reduce the chance of component dissociation, two modifications
have been made. To reduce the risk of dissociation of the glenosphere from the
baseplate, a 3.5-mm retaining screw is now used to lock the glenosphere to the
baseplate. This augments the Morse taper between the glenosphere and the
baseplate. Additionally, a metal shell has been added to the polyethylene
liner on the humeral socket. This decreases the likelihood of dissociation of
the polyethylene socket from the humeral stem.
The algorithm for glenosphere selection is shown in
Figure 13. The distance of the
center of rotation from the glenoid for each different glenosphere is shown in
Table I.
Next, a fixed-angle hydroxyapatite-coated glenoid baseplate is screwed into
place with secure purchase (Figs. 6-A and
6-B). Four 5.0-mm locking peripheral fixation screws are inserted
into the glenoid baseplate. In cases in which the locking screw pathway does
not have sufficient bone, 3.5-mm nonlocking cortical screws are used and are
angled to achieve secure fixation in bone. An appropriately sized glenosphere
(32 mm [neutral offset], 32 mm [—4-mm offset], 36 mm [neutral offset],
36 mm [—4-mm offset], 40 mm [neutral offset], or 40 mm [—4-mm
offset]) (Fig. 7) is then
selected, depending on the degree of soft-tissue contracture, the size of the
patient, the quality of glenoid bone, and the expected degree of instability.
The glenosphere is placed onto the baseplate by means of a Morse taper. A
retaining screw is then placed into the central hole on the glenosphere to
augment the Morse taper attachment to the baseplate
(Fig. 8). A trial humeral
socket is chosen from a selection of sizes (neutral, neutral-semiconstrained,
+4 mm, +4 mm-semiconstrained, +8 mm, or +8 mm-semiconstrained), depending on
the desired soft-tissue tension, glenohumeral range of motion, and
glenohumeral joint stability. After the placement of trial components,
soft-tissue tension, range of motion, and stability are assessed by evaluating
the difficulty of reduction, the arc of motion, and the difficulty of
dislocation. After reduction with the humeral broach and a trial humeral
socket (Fig. 9), transosseous
sutures are placed into the lesser tuberosity for future subscapularis repair.
Next, the appropriate size of humeral implant that will allow a 2-mm
circumferential cement interface around the component is selected and is
cemented in place with use of antibiotic-laden cement. Our standard practice
has been to use antibiotic-laden cement for all arthroplasties with cement as
it has been found to reduce the risk of deep wound
infection4. The
joint is then reduced and is checked for stability, especially in abduction,
extension, and internal rotation (the position of greatest instability), and
the achievement of full passive elevation is confirmed. Finally, the
subscapularis is repaired through drill-holes, followed by routine closure
with use of number-2 braided polyester sutures.
Postoperative Rehabilitation
A shoulder immobilizer is worn for six weeks while pendulum-type exercises
are performed. After the first six weeks, a sling is used and supine
active-assisted range-of-motion exercises are initiated. Active-assisted
elevation can begin at six weeks, but resistive exercises are delayed until
twelve weeks. The patient is encouraged to begin active forward flexion
beginning at six weeks as comfort allows. Strengthening and stretching
exercises should continue, with maximal functional improvement occurring at
about one year postoperatively.