Shoulder:Glenohumeral Arthritis/Anatomic Shoulder Arthroplasty

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Anatomy is key to successfully reproduce patient’s physiologic joint kinematics. By virtue of its mobility, the glenohumeral joint is predisposed to instability. One factor affecting stability is the radius of curvature mismatch between the humeral head and glenoid. Further, only 20 to 30% of the humeral head is in contact with the glenoid.[1] The rotator cuff acts as an essential dynamic stabilizing force centering the humeral in the mid-portion of range of motion and is crucial for anatomic total shoulder arthroplasty to be effective.[2] The supraspinatus helps to center the humeral head against the force of the deltoid in lower degrees of abduction, while the infraspinatus and teres minor help to clear the greater tuberosity under the coraco-acromial arch when the arm is moved in abduction and external rotation.[2][3] Lastly, even though the shoulder is not a weight-bearing joint, joint reaction forces as high as 2,4 times body weight have been reported during shoulder rehabilitation.[4]

Humeral head

Proximal humerus anatomy is subject to great variability, which is further significantly modified by arthritic changes.[5][6] As anatomic total shoulder arthroplasty can restore physiologic shoulder kinetics, a thorough knowledge of normal anatomy appears mandatory as one cannot simply rely on perioperative measures (Figure).[7] The non-arthritic humeral head has a mean three-dimensional measured diameter of 46.2 + 5.4 mm (range, 37.1 to 56.9 mm) and a humeral height of approximately 19 mm (Figure).[8][9][10][11][12]

Illustration of a right non-arthritic humeral head. The humeral head diameter, the center of rotation (COR), the intramedullary canal axis and the medial offset (distance between the intramedullary canal axis and the COR) are represented.

The osteoarthritic head is flattened and widened with a mean diameter of 59 ± 9 mm.[5] The humeral head has the particularity to be elliptic in the periphery and become spherical in its central part, meaning that the cut surface will be about 2 mm larger from medial to lateral than from anterior to posterior.[12] While spherical humeral head implants are mainly used in shoulder arthroplasty, elliptic implants have been proposed to reproduce anatomy and theoretically improve the rotational range of motion. The ratio between humeral head size and height is relatively constant.[13] The highest point of the humeral head lies 8 + 3.2 mm above the greater tuberosity (Figure).[12]

Lastly, relative to the humeral canal, the head has a posterior and medial offset of 0.35 to 2.6 mm and 5.6 to 9.7 mm, respectively (Figures).[14][15]

Illustration of a right non-arthritic humeral head. The humeral head-greater tuberosity distance, the neck-shaft angle (NSA), the best fit center and the total lateralization are represented. The total lateralization reflects the glenohumeral offset, taking into account potential glenoid bone loss.
Illustration of a right non-arthritic humeral head. The humeral head-greater tuberosity distance, the neck-shaft angle (NSA), the best fit center and the total lateralization are represented. The total lateralization reflects the glenohumeral offset, taking into account potential glenoid bone loss.
Superior view of a right shoulder. Representation of the medial, posterior and global (GO) offsets.
Superior view of a right shoulder. Representation of the medial, posterior and global (GO) offsets.

These parameters are helpful to select the appropriate humeral head implant, as this crucial step will ultimately determine the joint center of rotation. However, current biomechanical data does not support significant superiority of the elliptic design over the spherical one regarding the range of motion in internal and external rotation.[16] Terrier et al. illustrated in a numerical shoulder model that a 5 mm malposition of the humeral head implant resulted in impingement or subluxation for an inferior or superior shift, respectively. Both resulted in increased stress on the cement mantle.[17] While joint center of rotation can be determined three-dimensionally by a best-fit sphere using preserved non-articular landmarks, this technique has been translated to a two-dimensional process to allow intraoperative as well as postoperative radiographic evaluation (Figures).[6][18]

However, there is no consensus on cut-off values for joint center of rotation modification, as values as low as 2.5 mm can have been reported to impact impingement free range of motion.[19] Further, if the humeral head is implanted 5 mm too high in regard to the tuberosity, shoulder function will not solely be impaired by a 4 mm decrease in infraspinatus and subscapularis lever arms but also by the tight inferior capsule.[20] Cadaveric studies revealed that an increased humeral component sizing (commonly called “overstuffing”) would modify the center of rotation and add stress to the rotator cuff (Figure). Overstuffing not only decreases shoulder range of motion but also changes rotator cuff lever arm exposing patients to the potential risk of secondary cuff failure.[21][22] Restoring physiologic soft-tissue tension will provide stability and prevent complications such as aseptic loosening and osteolysis induced by stress shielding.[23] Lastly, controversy exists regarding the superiority of resurfacing humeral head over stemmed implants to reproduce physiological shoulder biomechanics.[6][24]

Neck shaft angle

The mean neck-shaft angle or inclination of the proximal humerus is approximately 135 degrees but varies between 115 and 148 degrees (Figure). A study of 2058 humeri by Jeong et al. note that 22% are either < 130 degrees or > 140 degrees.[25] Thus, fixed neck shaft angle humeral stems rely on surgeons to adapt their surgical techniques to accommodate patient anatomy. Modern modular systems provide centered and eccentric humeral heads as well as multiple neck-shaft angle options.

Humeral torsion

Humeral head torsion is important in anatomic total shoulder arthroplasty as it directly affects joint center of rotation and thereby influences mobility in external rotation and shoulder stability.[26][27][28] A cadaveric study by Pearl and Volk reported a mean humeral retrotorsion of 29.8 degrees with a 95% confidence interval of 7 to 52 degrees (Figure).[29] While they used the trochlear axis as a reference, other reported values were based on the transepicondylar axis (which differs from 3 to 8 degrees). Furthermore, current systems use a jig aligned on the forearm as a reference, in this case, a 10 to 15 degrees (carrying angle) must be added to the reported values (Figure). When using a stem with lateral fins, another reliable landmark is to place it 12 + 4 mm behind the bicipital groove.[30] It should, however, be emphasized that the groove rotates about 16 + 7 degrees and appears therefore as an unsuitable landmark in fracture or posttraumatic cases.[31] Lastly, Raniga et al. reported that in Walch B type glenoids, humeral retrotorsion is significantly lower compared to none-arthritic shoulders (14 + 9 degrees vs. 36 ± 12 degrees, p<0.001), suggesting a potential correlation between humeral retrotorsion and glenoid retroversion.[32]

Illustration of right humerus and proximal radius and cubitus. The axes used to characterize the humeral retrotorsion and the carrying angle are the humeral neck, the diaphyseal, the trans-epicondylar, and the forearm axis. The humeral retrotorsion is defined by the angle between the humeral neck axis and the trans-epicondylar axis. The carrying angle is determined by the angle between the diaphyseal axis and the forearm axis. A humeral osteotomy guide relative to the forearm has to take into account the carrying angle.
Illustration of right humerus and proximal radius and cubitus. The axes used to characterize the humeral retrotorsion and the carrying angle are the humeral neck, the diaphyseal, the trans-epicondylar, and the forearm axis. The humeral retrotorsion is defined by the angle between the humeral neck axis and the trans-epicondylar axis. The carrying angle is determined by the angle between the diaphyseal axis and the forearm axis. A humeral osteotomy guide relative to the forearm has to take into account the carrying angle.

Glenohumeral offset

Osteoarthritis results in loss of glenohumeral offset secondary to humeral and glenoid bone wear. While glenohumeral offset is subject to inter-person-variability, a diminished glenohumeral offset implies altered deltoid and rotator cuff moment arms, as well as modified capsular tension (Figure 2).[8][12] This is thought to influence the postoperative range of motion by limiting active abduction as well as creating a tendency to inferiorly sublux the humeral head.[27][33] Conversely, thick glenoid components create overstuffing (Figure). Bodrogi et al. recently described a reliable CT-based method to assess changes between pre and post-arthroplasty glenohumeral offset measures.[34] In the absence of humeral head sphericity (particularly in the setting of osteoarthritis), their method relied on the center of the humeral shaft (rather than the center of the humeral head) as described by Jacobsen and Friedman’s line to be independent of retroversion on the glenoid side.[35]

Medullary canal

Finally, the intramedullary canal not only becomes tighter but also increasingly retroverted from proximal to distal.[11] Fixation of the humeral component is widely varied. Diaphyseal press-fit stems induce proximal stress shielding. Cementation is reliable at time zero but difficult in revision. The goals of reduced stress shielding, easier stem revision, and preservation of vascularity have led to a progressive shift towards short metaphyseal stem or stemless fixation.[23] While a comparative cadaveric study revealed decreased micromotion and enhanced rotational stability in cemented stems,[36] optimal stem fixation, length, and filling ratio to avoid stress shielding,[37] subsidence,[38] and misalignment remains controversial.[39]

Glenoid anatomy

Glenoid loosening remains the primary cause of anatomic total shoulder arthroplasty failure.[40] Similar to the humeral side, osteoarthritis appears to modify normal glenoid anatomy significantly. The glenoid seems relatively small and shallow compared to the humerus, with only 9 cm2 of articular surface.[41] The glenoid is pear-shaped with a superior to an inferior dimension of 39 mm an inferior glenoid width averaging 29 mm.[12] There is a radii mismatch between the glenoid and humeral head, while the radius of curvature is greater in the anteroposterior than the superoinferior direction (41 vs. 32 mm).[1] Biomechanically, perfect conformity leads to a more stable joint but increased stress on the glenoid. On the other hand, an increased mismatch in radii will lead to increased translation of the humerus onto the glenoid with rim loading of the glenoid component causing a “rocking horse” effect.[42][43] Based on current techniques, the best compromise appears to be a mismatch ranging between 4 and 8 mm.[44] However, it should be noted that these findings are based on a spherical humeral head. It has been proposed that conformed designs are better suited for elliptical heads.[45]

Glenoid version and inclination

Reported three-dimensional CT-derived measures report mean normal glenoid retroversion of 6 ± 4 degrees and inclination of 7 ± 5 degrees. Retroversion has been correlated (r = 0.7, P < 0.001) to posterior humeral head subluxation (59% ± 7%).[46] The contralateral shoulder may be a reliable model, like side to side differences are limited to 5 degrees in 95% of the cases.[47] It is also important to assess the version in three dimensions, as in cases with >10 degrees version, it is not solely direct posteriorly but also in superior, inferior, and anterior directions.[48] A further important hint when performing anatomic total shoulder arthroplasty is that the version of the inferior part of the glenoid shows substantial less variability compared to the upper part and should therefore be used as the preferred intra-operative landmark in order to achieve adequate implant positioning.[49]

Concerning inclination, Moor et al. proposed the critical shoulder angle as a measure of scapular morphology with the benefit of combining measurements of glenoid inclination and lateral acromion coverage.[50] They identified an angle inferior to 30 degrees as being associated with primary shoulder osteoarthritis. This finding is supported by subsequent biomechanical studies reporting increased joint reaction forces in case of a lower critical shoulder angle.[51][52] Critical shoulder angle >35 degrees is, on the other hand, related to an increased incidence of rotator cuff tears secondary to increased supraspinatus loading to compensate for increased joint instability as a consequence of increased glenohumeral joint shear forces.[50][53][54] In the setting of anatomic total shoulder arthroplasty, an increased critical shoulder angle has been related to an increased incidence of glenoid radiolucencies.[54]

Humeral head subluxation

The Walch classification, with subsequent modifications, is the most common means of assessing glenoid changes secondary to primary osteoarthritis.[55][56] Walch classified glenoid deformity based on posterior glenoid retroversion and humeral head subluxation. In opposition to type A glenoids (symmetrical bone loss), type B glenoids (asymmetrical bone loss) have been associated with progressive posterior glenoid bone loss over time.[57] This factor is important when evaluating posterior humeral head subluxation; in type B3 glenoids, the head might be centered in regard to the glenoid but be posteriorly translated in relation to the scapula. Iannoti et al., by using three-dimensional standardized measures, reported a continuum of measures among the different type B and C glenoids rather than defined categories (B1, B2, B3, and C) in regard to glenoid retroversion and humeral head subluxation.[58] Currently, it is still debated if posterior humeral subluxation is the cause or consequence of increased retroversion.[59] Static posterior humeral head subluxation and posterior glenoid wear have both been associated with premature osteoarthritis in young men and related to higher complication rates after anatomic total shoulder arthroplasty.[60][61][62][63] Recently, Beeler et al. identified a flat acromion roof as a potential risk factor for posterior humeral head subluxation and posterior glenoid wear.[64] This hypothesis was confirmed by a subsequent study by Meyer et al., reporting a median of 4 degrees more glenoid retroversion and a 5 degrees less steep acromion in type B2 and C compared to type A and B1 glenoids (P ≤ 0.022).[65]


The rotator cuff and the horizontal force couple are critical to glenohumeral stability.[66] By respecting cuff insertion and restoring bony anatomy, force couples should be adequately restored. Soft tissue balancing, by the combination of the anterior subscapularis tendon and capsule release sometimes associated with a capsulorraphy of the redundant posterior capsule, is indicated to reach Matsen’s criteria (40 degrees of external rotation, 60 degrees of internal rotation and a 50% posterior shift of the humeral head over the glenoid).[67] If bony correction is necessary, one should carefully reevaluate adequate humeral implant size as center of rotation likely changed secondary to the additional bone removal. When facing a retroverted glenoid, posterior instability can be compensated for by anteriorly offsetting the humeral head component, leading to a significant anterior humeral displacement on muscle activation as well as an anterior shift of the center of pressure (p<0.05).[68][69] A major downside of this technique, however, is increased tension on the subscapularis with potentially higher rates of subscapularis failures. Chronic irreparable subscapularis deficiency is a contraindication to anatomic total shoulder arthroplasty as it tends to destabilize the joint secondary to an upward migration of the humeral head and eccentric contact pressure onto the glenoid.[70] While subscapularis preserving approaches have been described, most surgeons access the glenohumeral joint by subscapularis detachment with either a tenotomy, peel, or lesser tuberosity osteotomy. Effective subscapularis repair[71] during surgery is therefore mandatory; a review of biomechanical cadaveric studies suggests superior load to failure for the osteotomy at time zero but no difference at cyclic loading[72][73] While de Wilde suggested that a C-block lesser tuberosity osteotomy might prevent postoperative subscapularis fatty infiltration, a recent systematic review reported no statistical difference in clinical and radiological outcomes between tenotomy, peel and osteotomy.[74][75][76] In case of postoperative rupture, a prompt secondary repair can be considered to prevent instability but has been associated with variable results.[77][78] The addition of anterior latissimus dorsi transfer seems biomechanical superior to the pectoralis major transfer in anatomic total shoulder arthroplasty due to an improved internal rotation moment arm and more similar line of pull relative to the subscapularis.[79]

Glenoid bone loss

Correcting glenohumeral bone loss is an important step when implanting the glenoid component. Implanting the component in excessive retroversion will result in posterior translation of the humeral head and subsequent rim-loading known to cause early component loosening.[80][81] According to a finite element model by Farron et al., 10 degrees of retroversion should be considered as the cut-off value.[82] In their analysis, an implant with 20 degrees of retroversion resulted in a 326% increased stress within the cement mantel and a 706% increase of micromotion at the bone-cement interface. Recent work using statistical shape modeling allowed a computer reconstruction of the premorbid glenoid with a precision of about 1 mm and 2 degrees for version and inclination.[83][84] Several techniques to correct retroversion were developed. If version is corrected alone by means of anterior glenoid reaming, it will lead to significant joint line medialization and central cortex perforation when correction exceeds 15 degrees.[85] Consequently, posterior augmented glenoid implants were developed to avoid the medialization of the joint line, with encouraging early results.[86] However, severe deformity has been associated with loosening of such components.[87]

Proper implantation technique avoiding superior inclination or retroversion is thought to be crucial to avoid edge-loading causing micromotion and subsequent breakdown at the bone-implant interface, ultimately leading to aseptic loosening.[82][88] For the same reason, an intact cuff is also mandatory to conserve physiologic joint kinematics and therefore limit polyethylene wear.[89] While most current anatomic total shoulder arthroplasty heads are metallic, experimental studies suggest that a change towards ceramic heads could reduce polyethylene wear rate by up to 26.7%.[90] A wide range of onlay all-polyethylene glenoid shapes (pear-shaped versus elliptic) and sizes are currently available on the market, with no current consensus on optimal designs regarding back-surface (flat versus curved), anchorage (keel versus peg) or level of conformity.[91] Further, a recent cadaveric study comparing inlay (implanted into the bone socket and therefore allowing for circumferential bone support) with onlay components revealed superior outcome regarding joint reaction forces and fatigue failure in favor of the inlay design.[92] There is also renewed interest towards metal-back glenoids in response to the reported encouraging survival rates of modern designs.[93] While the theoretical benefit of more stable fixation and easy conversion to reverse shoulder arthroplasty seems appealing, long-term outcomes are awaited based on the long list of retrieved pre-existing metal-back designs.[94]


Clinical Practice Guideline

The goal of this section is to provide clinicians with recommendations based on the best available evidence; to inform clinicians of when there is no evidence; and finally, to help clinicians deliver the best health care possible.

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Conservative (Nonoperative) Treatment

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Surgical (Operative) Treatment



The deltopectoral approach consisted of a 10 to 15 cm skin incision being made from the coracoid process toward the deltoid insertion. The infraclavicular fossa (Mohrenheim fossa) is found, the cephalic vein identified and the consistent medial branches, which give the appearance of the Mercedes Benz symbol, are ligated. A self-retaining retractor is used to maintain exposure between the deltoid and pectoralis major. The subacromial bursa was resected to allow the placement of a Hohmann retractor under the deltoid over the top of the coracoid process. The arm was abducted and internally rotated. The subacromial bursa is resected to allow the placement of a Brown-Deltoid retractor.

Subscapularis Tenotomy

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Osteotomy of the Lesser Tuberosity

The osteotomy is initiated at the bicipital groove with a 2-mm saw blade and then completed with a curved osteotome. An approximately 2.5 cm2 in the coronal plane and 5 mm thick fleck of lesser tuberosity is taken such that the osteotomy entered the joint medially without violating the humeral head.[95][96]

A complete release of the subscapularis tendon is then performed and the tendon is pushed in the subscapularis fossa. A glenoid retractor is placed anteriorly. The humeral head is resected with a guide or a free-handed anatomic cut respecting native humeral head version and inclination.

Subscapularis Repair

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Lesser Osteotomy Repair

Before placement of the humeral stem, two holes are created with a 2-mm drill bit in the bicipital groove at the superior and inferior aspects of the lesser tuberosity osteotomy. One hole was created in the metaphysis just medial to the lesser tuberosity osteotomy. The sutures are then passed from lateral to medial by entering the bicipital groove, passing around the humeral stem, and exiting medially (Figure 16). A racking hitch is positioned to rest in the bicipital groove. The two sutures are passed through the subscapularis just medial to the lesser tuberosity osteotomy. The needle is removed from each construct to leave two superior and two inferior limbs (Figure 17). Then, one of the superior limbs and one of the inferior limbs were shuttled through the superior racking hitch knot (Figure 18). The suture limbs are passed through a tensioner to remove slack and to tension the repair (Figure 19).

Figure 16. Passage of the sutures. A suture with a half racking suture on the end is passed from lateral to medial through the inferior two holes, and (B) a separate suture is passed through the superior hole.
File:Sensitive-content.pngal. The stem is placed so that the sutures pass around the prosthesis. (A) The sutures are passed through the subscapularis tendon, and (B) the wedged ends are cut to provide access to four free limbs.
Figure 18. Passage of the sutures through the knots. (A) One suture limb from each pair is selected and (B) passed through the half racking suture.
Figure 19. Tensioning of the sutures. The suture limbs passed through the half-racking suture are tensioned. Tensioning is done under visual inspection.

Postoperative Rehabilitation

A sling was worn for 4 weeks following surgery. During the first 4 weeks, these patients only performed active hand, wrist, and elbow exercises, as well as active scapular retraction exercises. At 4 weeks postoperatively, the sling is discontinued and passive forward elevation with a rope and pulley and passive external rotation with a stick were initiated as tolerated. At 8 weeks postoperatively, active assisted progression to active ROM is allowed as tolerated. Strengthening is also routinely started at 8 weeks postoperatively. Activities are allowed as tolerated at 16 weeks postoperatively with a lifetime recommendation for no repetitive lifting over 25 lb (11.3 kg).


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