Glenohumeral arthritis is a common condition in the aging population, and it can have profound effects on patients’ quality of life. Total shoulder arthroplasty (TSA), hemiarthroplasty, and reverse total shoulder arthroplasty (RTSA) have all been well-described in the context of shoulder osteoarthritis, and the number of these procedures has been steadily rising over the past decade. This can be attributed to an increasingly elderly population, improved surgical implant technology, and increased surgeon familiarity with the procedure resulting in overall excellent outcomes (>90%) [1, 2]. For example, between 2000 and 2008, the annual number of shoulder arthroplasties increased 2.5-fold, with an 11% rise in the elderly population (over the age of 65), and an increase in the number of implant manufacturers to eight [3]. The primary goals of shoulder arthroplasty are to provide pain relief, stability, and restore motion [4]. These may be achieved through a thorough understanding of the indications for surgery, indications for each prosthetic type, and proper technique. The purpose of this article is focus on the technical aspects of primary anatomic TSA, and aim to provide a framework to follow to achieve a successful surgical result.

Unconstrained TSA is indicated in the treatment of degenerative or inflammatory conditions affecting the shoulder joint, including primary osteoarthritis (OA), avascular necrosis (AVN), rheumatoid arthritis (RA), and post-traumatic arthritis (PTA) when the rotator cuff is intact [5]. Glenoid component loosening is the most common complication following TSA, and is often due to technical errors leading to component malposition, which increases stress forces across the glenoid component [2, 6-8]. A careful pre-operative evaluation is necessary in all cases, including standard radiographs, including true AP in neutral, internal, and external rotation, and axillary views of the shoulder. The true AP views are useful to assess bone quality, presence and location of osteophytes, humeral canal diameter for templating, as well as neck/shaft angle, and humeral head diameter [6, 9]. The axillary view is used to recognize posterior glenoid wear and retroversion, although it may overestimate these in most cases [10]. Two- or three-dimensional CT scan may be used to better characterize glenoid version by using Friedman’s line, drawn from the medial tip of the scapula body to the midpoint of the glenoid fossa (Fig. 1) [11, 12]. A line perpendicular to this drawn from the anterior edge of the glenoid fossa defines neutral version; if the posterior edge of the glenoid fossa lies medial to this line, it is retroverted. Rouleau et al. [11] more recently described the paleoglenoid (line along the high, anterior glenoid), intermediate glenoid (connecting the anterior and posterior glenoid edge), and neoglenoid (along the worn, posterior glenoid) reference lines, and found that the intermediate glenoid line is more reliable at predicting version in type B2 glenoids, discussed below (Fig. 2). Other techniques, such as the scapula body line described elsewhere, have also been used to predict glenoid version [12]. MRI may be indicated when a rotator cuff tear is suspected, as well as in patients with rheumatoid arthritis of the shoulder, who are known to have a high incidence of atraumatic cuff tears [12, 13].

Fig. (1). Graphic depicting the Friedman (red), scapula body (yellow) and intermediate (blue) line methods of determining scapular version. (Adapted from Rouleau DM, Kidder JF, Pons-Villanueva J, Dynamidis S, Defranco M, Walch G: Glenoid version: How to measure it? Validity of different methods in two-dimensional computed tomography scans. J Shoulder Elbow Surg 2010;19 [8]:1230-1237.).

Fig. (2). Image depicting a type B2 glenoid (A) With three reference lines described by Walch: (B) The paleoglenoid, which represents the native glenoid version, (C) Intermediate glenoid, and (D) The neoglenoid, representing the new version of the glenoid. (Adapted from Rouleau DM, Kidder JF, Pons-Villanueva J, Dynamidis S, Defranco M, Walch G: Glenoid version: How to measure it? Validity of different methods in two-dimensional computed tomography scans. J Shoulder Elbow Surg 2010;19 [8]:1230-1237.).

Humeral head subluxation (HHS) is another factor that should be recognized preoperatively, as higher degrees of preoperative subluxation correlate to elevated rates of failure [14, 15]. Subluxation may recur postoperatively and can contribute to early glenoid component loosening [16, 17]. The Papilion and Shall method is the most accepted measure of HHS, and it involves comparing the center of the humeral head with the midpoint of a line connecting the anterior and posterior edges of the glenoid to determine if the head is subluxated anteriorly or posteriorly [18]. This technique was described using fluoroscopy, and was later adapted by Walch et al. [19] to account for glenoid types with significant posterior wear. They determined a more accurate measure of HHS on two-dimensional (2D) CT scan by referencing the humeral head diameter to Friedman’s line. In this method, the axial cut demonstrating the widest anterior-to-posterior humeral head diameter is selected, and the percentage of humeral head posterior to Friedman’s line is measured. Posterior HHS greater than 55% is defined as subluxated. Furthermore, it has been suggested that HHS is multi- rather than unidirectional. Given than 2D CT only allows for assessment of subluxation in one plane, three-dimensional (3D) CT may in fact be more accurate at detecting out-of-plane HHS [20, 21].

When preparing to resect the humeral head, adequate exposure is paramount, which may be achieved with the placement of a large Darrach retractor in the glenohumeral joint and blunt Hohmanns in the subacromial space and inferior neck [9]. This should be followed by removal of osteophytes to better expose the plane of the articular surface. This in turn determines the proper version and angle of the humeral osteotomy. Variable-angle systems, in which a freehand cut is made through the plane of the articular margin, are especially reliant on native neck anatomy exposure. If normal anatomical landmarks are absent, fixed-angle systems may be used which employ a cutting guide (intra- or extra-medullary) to determine the osteotomy site [49]. The osteotomy site can later be revised if needed following canal preparation, and the trial component itself may be used as a cutting guide. The version of the osteotomy is also determined by the plane of the articular margin, which ranges from 0° to 55° of retroversion [50]. However, determining the appropriate amount of retroversion intraoperatively can be very challenging when the anatomy is unreliable. Pre-operative templating with appropriate advanced imaging is highly recommended to avoid errors.

Restoring the anatomic humeral head size is important, as it has been shown that even small changes in head size can negatively affect shoulder biomechanics. For example, Harryman et al. [51] demonstrated that increasing the humeral head thickness by 5 mm resulted in a 20° to 30° loss in range of motion. Decreasing the head size can also negatively impact outcome by reducing the surface arc for motion between the head and the glenoid, resulting in point loading on the glenoid, and early greater tuberosity (GT) impingement. Furthermore, anatomic positioning of the head is also critical; superior placement increases supraspinatus tension, inferior placement results in early GT impingement, anterior placement causes increased subscapularis tension, and early posterior impingement, while posterior placement causes increased tension on the rotator cuff, and early anterior impingement [49].

Proper glenoid preparation may be the most critical step in total shoulder arthroplasty since most causes of failure are attributable to glenoid-sided wear and loosening. Careful pre-operative planning is required in order to better understand the bony anatomy and adjust the surgical plan accordingly. The goals of glenoid preparation are to correct any abnormalities in version, while leaving behind enough bone to support the implant. The glenoid wear pattern classification by Walch et al. [52] is the most widely used method of assessing the glenoid, and it provides crucial information that will guide the surgeon intraoperatively. In type A1, the humeral head is centered, and there is some glenoid erosion medially, while in type A2, the erosion is major. In type B1, the humeral head is subluxated posteriorly, but there is no erosion, while the type B2 glenoid (biconcave) demonstrates posterior erosion, as well as posterior subluxation. In type C, the glenoid is severely retroverted (>25°), but not necessarily worn posteriorly [53].

Types B2 and C glenoids are the most challenging to treat, and require a different approach than the usual concentric reaming method of glenoid preparation. The goal is to restore neutral glenoid version [54], as failure to do so increases the shear loads across the humerus and can lead to early implant loosening, and failure [55, 56]. However, when faced with severe posterior-sided wear or a dysplastic glenoid, overcorrection may have a negative effect. This can occur with compromise of the available bone stock for glenoid implant placement and decreasing the soft-tissue tensioning on the implant leading to instability [53]. In such cases, restoring the glenoid to within 10° of the patient’s native anatomy may be a better option, although accurately predicting this position is a challenge in its own right, even with advanced imaging [57].

There are three main options to choose from when faced with a type B2 or C glenoid: asymmetric reaming, posterior bone grafting, and posteriorly-augmented implants. In the case of posterior erosion less than 1 cm and retroversion less than 15°, the anterior glenoid can be reamed eccentrically to off-set this deformity. Corrections greater than 15° should be avoided since they may violate the glenoid vault, resulting in implant penetration upon insertion [58-60]. When the deficiency exceeds 1 cm, and the glenoid is retroverted more than 25°, bone grafting with internal fixation should be used, although this technique has had mixed results [53, 61-63]. Neer et al. [61] described excision of the worn area of the glenoid down to bleeding bone and insertion of a pre-contoured corticocancellous humeral head autograft to fill the defect. The graft is then secured by means of cortical screws, inserted either anteriorly or posteriorly, or by wedging the graft into the glenoid medial to the defect like a keystone, and securing it with non-absorbable sutures (Fig. 3). A sequential approach involves preparing the high side first, followed by placement of column holes, provisional fixation of the humeral head graft on the low side with K-wires or 2.5 mm drill bits, and ending with 3.5 mm cortical screw insertion, which are countersunk so as to not interfere with the implant [63]. Between 15° and 25° of retroversion, implants with posterior augments may result in better clinical outcomes and fewer complications when compared to bone graft although there remains little evidence to support this recommendation [64]. However, despite these technical advances, the rates of glenoid component loosening, residual posterior humeral component subluxation, and shoulder instability remain high for the type B2, and C glenoid treated with TSA [6, 65].

Fig. (3). Illustration depicting steps in glenoid bone grafting. (A) Glenoid with significant posterior erosion. (B) Preparation of the anterior glenoid. (C) Bone graft placement in deficient area, temporarily held in place with drills. (D) Replacement of the drills with 3.5 mm cortical screws. (Adapted from Steinmann SP, Cofield RH. Bone grafting for glenoid deficiency in total shoulder replacement. Journal of shoulder and elbow surgery / American Shoulder and Elbow Surgeons [et al] 2000;9:361-7.).

More recently, Mizuno et al. [66] described the use of semiconstrained RTSA in patients over the age of 70 with type B2 glenoid deformities that were not amenable to correction with conventional asymmetric reaming of the high side of the glenoid. Conceptually, they felt that the screw fixation of the glenoid baseplate in might provide better stability in comparison to the cemented polyethylene glenoid component of the TSA. Their study reviewed twenty-seven patients with primary glenohumeral OA who underwent RTSA for a biconcave glenoid deformity, ten of whom required adjunctive bone grafting due to severe posterior wear, and all of whom had intact rotator cuffs. The mean pre-operative retroversion was 32°, and mean subluxation of the humeral head relative to the axis of the scapula was 87%. The surgical technique consisted of asymmetric reaming of the glenoid to achieve <10° of retroversion, and 10° of inferior tilt, followed by fixation of the glenoid baseplate with either four or five screws, depending on the amount of available bone stock. If the retroversion could not be corrected to <10°, or if >20% of the baseplate was unsupported after reaming, autogenous humeral head or iliac crest bone graft was used. The results were promising, with significant postoperative improvements in mean Constant scores, and shoulder range of motion, and a 93% overall patient satisfaction rate at a mean final follow-up of fifty-four months. The RTSA also prevented the recurrence of posterior humeral component subluxation in all cases. While more high quality studies are required to aid in establishing specific guidelines for the use of RTSA in patients with primary glenohumeral OA with severely deficient glenoids, it appears to be a promising option.

Shoulder arthroplasty can be a life-altering procedure for patients suffering from arthritis of the shoulder, and success rates are very high with few complications. In order to achieve successful results and maximize implant longevity, careful preoperative planning is paramount, and should be individualized to each patient’s clinical and radiographic presentation. Advanced imaging is essential, especially when faced with a deformed glenoid. Glenoid preparation may be complex in the case of significant retroversion and posterior erosion. Eccentrically reaming the high side of the glenoid is usually safe in the case of mild posterior erosion and retroversion, but overcorrection places the residual bone stock at risk of failure. When the deformity is severe, the available options include bone graft augments, or implant augments, although clinical results are mixed. A promising novel approach that may improve clinical outcomes involves using RTSA to treat severe glenoid deformities, although the surgical indications for the use of this technique require further study.