Shoulder Arthroplasty Implants: An Analysis of Types, Indications, and Selection Factors

Shoulder arthroplasty, commonly known as shoulder replacement, is a surgical procedure that involves replacing the damaged parts of the shoulder joint with artificial components called implants. This procedure aims to alleviate pain, restore mobility, and improve the overall quality of life for individuals with severe shoulder conditions.

Historically, shoulder arthroplasty has undergone various stages of development, starting with Dr. Jules Emile Péan’s ivory total shoulder in 1893¹. Since then, significant advancements in materials, designs, and geometries have led to the modern implants used today. This article provides a comprehensive analysis of the different types of shoulder arthroplasty implants available, including anatomical, reverse, and partial replacements. It discusses the indications for each type and explores the factors that influence implant selection, such as patient age, activity level, and glenoid bone quality.

Types of Shoulder Arthroplasty Implants

Shoulder implants are available in a few different shapes and a range of sizes. Replacement options include partial and total using either anatomic or reverse implants². Conditions that can damage the shoulder joint include:

1. Osteoarthritis
2. Rotator cuff injuries
3. Fractures
4. Rheumatoid arthritis and other inflammatory disorders
5. Osteonecrosis ²

Depending on the type of joint damage, the following shoulder replacement options may be recommended:

Anatomic Total Shoulder Arthroplasty

Anatomic total shoulder arthroplasty (aTSA) involves replacing both the ball (humeral head) and the socket (glenoid) of the shoulder joint with implants that closely resemble the natural anatomy of the joint². The aTSA implant typically consists of a metal ball that is attached to the upper arm bone (humerus) and a plastic socket that is fitted into the shoulder blade (scapula). The head of the implant is made of an alloy of cobalt chrome and smaller amounts of other metals or titanium, and the socket is made of high molecular weight polyethylene, which is a type of plastic³.

Currently, surgeons utilize stemless humeral implants if at all possible because they minimize the trauma to the humerus by not entering the humeral canal³. If the quality of the proximal humeral bone is insufficient to allow a stemless implant, then a traditional stemmed humeral component will be utilized³.

Surgeons from the Hospital for Special Surgery designed a special implant called the Comprehensive Primary Shoulder System, with a cobalt-chrome or titanium ball and a titanium stem. The system’s specialized ball component creates a new humeral head that conforms to the patient’s exact anatomy⁴.

Reverse Total Shoulder Arthroplasty

Reverse total shoulder arthroplasty (rTSA) is an alternative to aTSA that involves “reversing” the ball-and-socket configuration of the shoulder joint. In rTSA, the artificial ball is attached to the shoulder blade, and the artificial socket is attached to the upper arm bone². This design allows the deltoid muscle to take over the function of the rotator cuff. The Reverse Shoulder Prosthesis (RSP) was the first reverse shoulder design to successfully incorporate a center of rotation (COR) lateral to the glenoid⁵. The design of the RSP baseplate provides 2000N of compression between the prosthesis-bone interface, providing stable initial fixation as well as ideal conditions for bony ingrowth for long-term fixation⁵.

Partial Shoulder Arthroplasty

Partial shoulder arthroplasty, also known as hemiarthroplasty, involves replacing only the ball of the shoulder joint while leaving the socket intact². This procedure is typically recommended for patients with a severe fracture or arthritic conditions of the shoulder in which only the humeral head or ball of the joint is damaged and the glenoid socket is normal or intact⁶. This surgery is often chosen in cases of avascular necrosis, a problem of bone death and cartilage collapse seen mainly on the ball side, often in younger patients with healthy glenoid cartilage⁷.

Indications and Contraindications for Each Type of Implant

The choice of shoulder arthroplasty implant depends on several factors, including the underlying shoulder condition, the extent of joint damage, the patient’s age and activity level, and the quality of the glenoid bone. The most common indications for shoulder arthroplasty are osteoarthritis, inflammatory arthritis, proximal humerus fractures, irreparable rotator cuff tears, rotator cuff arthropathy, and avascular necrosis of the humeral head⁸.

Anatomic Total Shoulder Arthroplasty

aTSA is indicated for patients with end-stage glenohumeral arthritis who have an intact and functional rotator cuff³. This type of implant is designed to restore the normal biomechanics of the shoulder joint and provide pain relief, improved range of motion, and increased strength³.

Contraindications:

1. Insufficient glenoid bone stock
2. Rotator cuff arthropathy
3. Deltoid dysfunction
4. Active infection
5. Brachial plexus palsy ¹⁰

Reverse Total Shoulder Arthroplasty

rTSA is indicated for patients with rotator cuff tear arthropathy, irreparable rotator cuff tears, or failed previous shoulder replacements with rotator cuff deficiency¹¹. This type of implant is designed to provide pain relief and improve shoulder function in patients with compromised rotator cuff muscles¹¹.

Contraindications:

1. Good rotator cuff function
2. Active infection
3. Severe osteoporosis
4. Poor general health
5. Unrealistic expectations ¹²

Partial Shoulder Arthroplasty

Partial shoulder arthroplasty is indicated for patients with isolated damage to the humeral head, such as a severe fracture or arthritis, when the glenoid socket is still in good condition⁶. This procedure is less invasive than total shoulder arthroplasty and may be suitable for younger patients or those with lower functional demands⁶.

Contraindications:

1. Coracoacromial ligament deficiency ¹⁴
2. Infection
3. Neuropathic joint
4. Unmotivated patient ¹⁴

Factors Influencing Implant Selection

Patient Age

Patient age is an important factor to consider when selecting a shoulder arthroplasty implant. Younger patients tend to be more active and have higher functional demands, which may influence the choice of implant and the surgical approach¹⁵. Older patients may have decreased bone density and muscle strength, which may affect the stability and longevity of the implant¹⁷. Patient age and baseline platelet count are also considerable influences¹⁸.

Activity Level

The patient’s activity level is another crucial factor in implant selection. Patients who engage in high-impact activities or have physically demanding jobs may require a more durable implant that can withstand greater stress and wear¹⁹. Conversely, patients with lower activity levels may be suitable candidates for less invasive procedures or implants that preserve more bone stock¹⁹. The member’s deltoid must be intact, and the member must have at least 90 degrees of passive shoulder range of motion (elevation/flexion)²¹.

Glenoid Bone Quality

The quality of the glenoid bone is essential for the success of shoulder arthroplasty. Adequate bone stock is necessary to ensure secure fixation of the glenoid component²². Patients with significant glenoid bone loss may require specialized implants, such as augmented glenoid components or bone grafting, to achieve stability and prevent implant loosening²⁴. Glenoid deformity has an important effect on outcomes and complication rates after shoulder arthroplasty for primary glenohumeral arthritis. The B2/B3 glenoid has particularly been associated with a poorer outcome with shoulder arthroplasty compared with other glenoid types²⁵. One of the primary challenges is striking a balance between deformity correction and joint line preservation²⁵.

Different types of glenoid components are available, including keeled, pegged, and metal-backed components²⁶. The choice of glenoid component depends on factors such as the amount of bone loss, the desired level of stability, and the surgeon’s preference.

Clinical Trials and Studies

Several clinical trials and studies have compared the outcomes of different types of shoulder arthroplasty implants. These studies have provided valuable insights into the effectiveness, longevity, and complications associated with each type of implant.

| Study |

Works cited

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