Total shoulder arthroplasty

A standard total shoulder arthroplasty, also known as anatomic total shoulder arthroplasty or total shoulder replacement, aims to replace both the glenoid and humeral head to replicate the normal anatomic alignment of the glenohumeral joint and is the commonest form of shoulder replacement surgery.

Indications

• osteoarthritis: primary or secondary

• inflammatory arthropathy, e.g. rheumatoid arthritis.

• failed partial joint replacement (e.g. shoulder resurfacing arthroplasty, hemiarthroplasty)

• advanced osteonecrosis with secondary osteoarthritis ^1-3

Preoperative imaging assessment

The placing of a total shoulder arthroplasty into the approximate anatomic position is dependent on the rotator cuff muscles and the state of the in situ bony structures. Thus, a successful outcome relies upon intact rotator cuff muscles and adequate glenoid bone stock to ensure joint functionality and durability postoperatively.

Insufficiency of these structures predisposes the patient to possible hardware malpositioning, failure and prosthetic fractures. If there is preoperative concern for the integrity of any of these structures, it is wise to perform a full preoperative imaging assessment.

Components

• glenoid component

  • can be metal- or polyethylene-backed

  • PE is radiolucent but it has a radiopaque marker to allow postprocedure identification on imaging

• humeral component: metal backed with a ball at the end to act as the humeral head

• both glenoid and humeral components may be either cemented or cementless

Radiographic features

Plain radiograph

The postoperative assessment is usually done using AP, Grashey, axillary and Y projections:

• humeral head component must be centered within the glenoid cavity

• humeral shaft component must be centered in the proximal humeral shaft

• a uniform periprosthetic lucency <2 mm is acceptable

  • periprosthetic lucency is very common (up to 96%) in cemented PE pegged glenoid components ⁴

If there is concern for rotator cuff abnormality, MRI is recommended as subscapularis muscle insufficiency is the most common rotator cuff complication postoperatively. 

Complications

Complications tend to affect the glenoid more than the humeral component ¹:

• glenoid component failure, e.g. surface erosion, fracture/delamination, component seating, loosening ⁵ ("rocking-horse phenomenon" ^6,7)

• loosening >2 mm is a common hardware complication

  • irregular progressive lucency indicates hardware failure as well

  • loosening may be complicated by dislocation and/or fracture

• periprosthetic fracture especially with a history of inflammatory arthropathy

• infection is a rare postoperative complication.

• intraoperative injury to adjacent structures e.g. brachial plexuses, axillary artery, rotator cuff muscles

• subscapularis muscle insufficiency resulting in instability ^1,3

• overstuffing (shoulder arthroplasty)

Practical points

On the immediate postoperative radiographs, periprosthetic radiolucency is commonly noted, which might be related to poor cement penetration into the bone, nevertheless, the persistence of this finding on follow-up images is indicative of total shoulder arthroplasty loosening ¹.

See also

• reverse total shoulder arthroplasty