A.- TYPES OF SHOULDER REPLACEMENT PROSTHESIS

1.- Hemiarthroplasty

• Replacement Hemiarthroplasty: Replaces the humeral head with a stemmed prosthesis, used after proximal humerus fractures or when bone loss/osteoporosis prevents resurfacing implant fixation.
• Resurfacing Hemiarthroplasty: Suitable for moderate humeral head deformity with a preserved glenoid, in cases like osteoarthritis or avascular necrosis.

2.- Total Arthroplasty

• Total Shoulder Arthroplasty (TSA): Resurfaces/replaces the humeral head and glenoid, indicated for joint cartilage loss with an intact, functional rotator cuff.
• Reverse Shoulder Replacement: Reverses joint components, creating a constrained implant with a medialized rotation center, ideal for severe rotator cuff damage.

Fig 1: Types of Shoulder replacement prosthesis

Fig 2: Main implant categories

B.- INDICATIONS

The main goal of total shoulder  arthroplasty is to decrease pain and restore an acceptable range of motion to the shoulder joint.

The following figure shows the indications for each type of prosthesis.

Fig 3: Indications

Fig 4: Resurfacing hemiarthroplasty

Fig 5: Total Anatomic shoulder arthroplasty

Fig 6: Replacement hemiarthroplasty

Fig 7: Conversion of hemiarthroplasty to reverse prosthesis

Fig 8: Total Anatomic shoulder arthroplasty

Fig 9: Reverse shoulder replacement

Fig 10: Reverse shoulder replacement

C.- CONTRAINDICATIONS

There are several general contraindications where this surgery may not be advisable. These include:

Active or Recent Infections

Severe Muscle or Tendon Damage.

Inadequate bone stock to support the implant.

Severe Paralysis or Neuromuscular Disorders: Conditions that affect the ability to control the shoulder joint can reduce the success of the procedure.

Fig 11: Contraindications

D.-IMAGING

Multiple imaging techniques are used in the pre-surgical study and in the post-surgical follow-up of shoulder prostheses.

Fig 12: Imaging

The main objective of preoperative imaging tests is to assess the integrity of the rotator cuff and bone stock.

1.-Plain Radiograph

1.1.- Preoperative assessment

• Standard X-rays are often the initial imaging studies used to evaluate the shoulder joint.
• X-rays help assess: The extent of joint damage,Joint alignment, Bone quality, and Any deformities or fractures.

Fig 13: Plain Radiograph: Preoperative assessment

1.2.- Postoperative assessment

• Radiographs are taken immediately after the surgery and at follow-up visits to assess the position and alignment of the implant components, as well as the presence of any complications such as fractures, dislocations, or loosening of the components.

Fig 14: Plain Radiograph: Postoperative assessment

2.- Computed Tomography

2.1.- Preoperative assessment

2.2.1.- Glenoid Morphology Alterations

A planning CT with 2D and 3D images study is commonly performed to assess glenoid version, morphology, and available bone stock for placing a prosthesis.

Fig 15: Glenoid Morphology Alterations

Fig 16: Planning CT

2.2.2.- Glenoid version

Normal glenoid version is 0° ± 4 (mean ±standard deviation), between 4° anteversion and 4° retroversion

Fig 17: Glenoid version

2.2.3.- Glenoid bone stock

Glenoid bone loss is a critical factor in shoulder arthroplasty planning. It influences decisions on the extent of augmentation or reaming needed.

The goal is to achieve a neutral version of the shoulder implant for optimal results.

• Paleoglenoid Method.
• Pico Method

Fig 18: Glenoid bone stock

2.2.- Postoperative assessment

In certain cases a computed tomography (CT) may be necessary to assess the bone stock, loosening of components, osteolysis.

Fig 19: CT: Postoperative assessment

3.- Nuclear Medicine

Nuclear medicine techniques are useful in finding the cause of pain, mainly septic loosening and aseptic and periprosthetic fractures not detected with other radiological techniques.

4.- Magnetic resonance

Preoperative soft-tissue assessment of shoulder musculature is most often performed with ultrasound or MRI

5.- Ultrasound

Ultrasounds are used in Soft Tissue Evaluation, Identification of Fluid Collections and Guided Interventions.

Fig 20: NM, MRI and US

E.- SURGERY

The main aim after  shoulder replacement is to achieve good functional outcomes with improved survival of the prosthesis.

Fig 21: Surgery

F.- COMPLICATIONS

The complication rate for shoulder arthroplasties ranges from 20% to 33%.

Radiologists must understand prosthesis types and associated complications for effective management. General complications include infection, periprosthetic fractures, loosening, heterotopic ossification, implant failure, and nerve injury, with specific issues varying by prosthesis type.

Fig 22: Different complications of shoulder arthroplasties

1.- All types of shoulder prosthesis

1.1.- Infections

• Rare but serious complication, occurring in 0.98% of the cases.
• Most Common After Reverse Shoulder Arthroplasty due to Hematoma formation, Lack of rotator cuff and Advanced age
• Risk Factors:
• Endogenous: Diabetes, Obesity, Immunosuppression, Oncological diseases, Rheumatoid arthritis, Chronic infections
• Exogenous: Prolonged surgery duration, Blood
• transfusion, Hypothermia
• Radiographic signs: Progressive irregular lucency, often delayed in appearance. Cross-sectional Imaging (CT/MRI): Limited due to artifacts
• Nuclear Medicine: Bone scintigraphy, gallium citrate scintigraphy, and 111In WBC imaging: Sensitive but lack specificity (e.g., bone remodeling for up to a year)

1.2.- Heterotopic ossification

Heterotopic ossification is a common complication following shoulder arthroplasty, occurring in approximately 45% of cases within the first year after surgery.

It typically develops early and can be easily detected through standard radiography. More precise details can be obtained through CT

Low-grade heterotopic ossification usually does not impact functional outcomes, while high-grade heterotopic ossification may cause limited active shoulder elevation.

Patients with cuff tear arthropathy are at a higher risk of developing more significant heterotopic ossification.

1.3.- Nerve injury

Nerve damage primarily affects the axillary nerve, with the brachial plexus being less commonly involved. This often occurs due to nerve stretching during luxation-reduction maneuvers in surgery.

However, deltoid muscle dysfunction can result from axillary nerve damage or deltoid detachment, leading to reduced abduction and inferior shoulder instability.

Fig 23: Infection, Heterotopic ossification and Nerve injury

1.4.- Periprosthetic Fracture

• Periprosthetic humerus fractures are of particular importance, as they frequently lead to the need for revision surgery.
• These fractures can take place intraoperatively or postoperatively, occurring 0.9–3.5% and 1.0–3.0% of the time, respectively.

Fig 24: Periprosthetic Fracture

1.5.- Prosthetic loosening/ Periprosthetic radiolucency

Fig 25: Periprosthetic radiolucency

1.6.- Rotator cuff insufficiency and Nonunions

• Early diagnosis of rotator cuff failure after shoulder arthroplasty allows for acute cuff repair instead of revising to a reverse geometry implant.
• Cuff failure is indicated by superior migration of the humeral head by 5 mm, measured from the center of the humeral head to the glenoid on an anteroposterior radiograph.
• Oversized humeral heads increase the risk of cuff failure.
• Revision surgery for soft-tissue failure has poorer outcomes than for bone or prosthesis issues.

Fig 27: Rotator cuff insufficiency and non unions

2.- Specific complications of Reverse shoulder arthroplasty

2.1.- Scapular notching

Scapular notching is a common radiographic finding occurring after reverse total shoulder arthroplasty, and it refers to an erosive lesion of the inferior scapular neck because of the impingement of the humeral implant during adduction.

The clinical importance of notching is unclear, and the optimal treatment of severe notching is unknown

Scapular notching after reverse total shoulder arthroplasty is a common finding, occurring in 70% of cases

Fig 28: Scapular notching

2.2.- Luxation /Instability

• Anterosuperior dislocation or instability is a unique but common complication of reverse shoulder arthroplasty, occurring in up to 20–31% of patients, often with no identifiable trauma.
• Instability occurs in the anterior-superior direction, which is the opposite of anterior-inferior glenohumeral dislocation in the native shoulder, after a combination of adduction, extension, and internal rotation of the arm.
• Diagnosis is usually possible with standard radiographs. The humeral component dislocates anteriorly on scapular Y and axillary radiographs, and superiorly on anteroposterior radiographs, along the direction of the deltoid muscle.

Fig 29: Luxation /Instability

2.3.- Scapular spine and acromion fractures

• Prevalence: Occur in 1% of reverse total shoulder arthroplasties Increased risk of prosthetic revision

Radiological Classification:

Type I: Involves part of the anterior and middle deltoid origin

Type II: Involves the entire middle deltoid origin and part of the posterior deltoid origin

Type III: Involves the entire middle and posterior deltoid origin

Diagnostic Challenges:

Diagnosis can be difficult with standard radiographs

CT Scans: Often used for detection

Clues: Decreasing acromion-to-tuberosity distance and increasing acromial tilt in consecutive radiographs may aid in detection

Fig 30: Scapular spine and acromion fractures