17 Reverse Total Shoulder Arthroplasty

Matthew Baker and Uma Srikumaran

Summary

The reverse shoulder prosthesis was developed to address issues encountered while treating end stage glenohumeral arthritis in the setting of rotator cuff deficiency. Indications have since expanded to address multiple pathologies of the shoulder.

Reverse shoulder arthroplasty – cuff tear arthropathy – arthritis – biomechanics

17 Reverse Total Shoulder Arthroplasty

I. Indications ¹

Cuff tear arthropathy (Hamada classification; ▶ Fig. 17.1 ):
1. Degenerative changes associated with massive rotator cuff tears
2. Attempting anatomic replacement in the setting of massive rotator cuff tears leads to failure.
  
  Fig. 17.1 Hamada classification. Grade I, normal acromialhumeral interval (AHI); Grade II, narrowed AHI <5mm; Grade III, acetabularization of the acromion and narrowing of the AHI; Grade IVa, narrowing of AHI with glenohumeral (GH) narrowing; Grade IVb, AHI and GH narrowing with acetabularization of acromion; Grade V, flattening of the humeral head.
  
  Fig. 17.2 Rocking horse phenomenon.
Rocking horse phenomenon (▶ Fig. 17.2 ):
1. Loss of centralization of the humeral head results in eccentric wear and early failure.
Pseudoparalysis: ² , ³
1. Massive rotator cuff tear with minimal to no arthritis:
  1. Anterior superior escape
  2. There may be improvement in range of motion (ROM) but may not return to full.
2. Immunologic arthritis
3. Failed rotator cuff repair
4. Proximal humeral fractures
5. Malunions/Nonunions
6. Revision of anatomic shoulder arthroplasty/hemiarthroplasty
7. Instability or chronic dislocations
8. Tumors.
  
  In the United States and Australia more than 50% of reverse arthroplasties are done for arthritis and fracture. In the UK, the majority are done for cuff tear arthropathy including massive rotator cuff tears. ⁴

II. Contraindications ¹

Nonfunctioning deltoid
Axillary nerve injury/damage
Active infection
Neuropathic joints
Glenoid vault deficiency precluding baseplate fixation.

III. Evaluation

History:
1. Traumatic versus atraumatic
2. Degree of pain and dysfunction (perceived weakness, instability)
3. Functional demands and expectations
4. Ambulation status (use of assistive devices)
5. Metal allergies
6. Neck pain, alternative origins of pain.
Physical examination:
1. Cervical examination
2. Neurovascular examination
3. Pain localization
4. Passive, active motion
5. Strength, stability
6. Evaluate rotator cuff, scapulothoracic motion, lag signs
7. Painless weakness is likely neurologic in origin ⁵
8. Hornblower’s sign: Indicates torn teres minor and will likely need tendon transfer to regain full motion.
Imaging:
1. X-ray:
  1. Grashey and axillary at minimum (▶ Fig. 17.3 ).
2. Computed tomography (CT):
  1. Evaluate glenoid version, humeral and glenoid bone stock, alignment, and rotator cuff atrophy.
3. Magnetic resonance imaging (MRI):
  1. Evaluate glenoid version, humeral and glenoid bone stock, alignment, and rotator cuff atrophy
  2. Typically CT or MRI is used. Both modalities are usually not necessary.

IV. Approach

Deltopectoral:
1. Subscapular repair based on implant selection.
Superior:
1. Split the deltoid
  
  Fig. 17.3 Walch classification. A1, well centered with minor erosion; A2, well centered with major erosion; B1, posterior humeral head subluxation; B2, biconcave glenoid; B3, monocave glenoid preferentially worn posterior with >15 degrees glenoid retroversion or humeral head subluxation of 70%; C, dysplastic >25 degrees retroversion; D, anterior humeral head subluxation or glenoid anteversion.
2. Technical challenges:
  1. Exposure, glenosphere tilt, axillary nerve injury
  2. Can lead to improved stability as not violating the subscapularis if intact. ⁶

V. Types of implants (▶Fig. 17.4 and ▶Fig. 17.5)

Grammont:
1. Medialized center of rotation (COR) (at the glenoid–component interface)
2. Decreased shear force on the glenoid–component interface
3. Encroachment on the glenoid → scapular notching
4. Less mechanical advantage
5. Laxity of intact rotator cuff.
“Lateralized”:
1. Still medial to the anatomic COR, just less so than the Grammont style
2. More than a hemisphere
3. Address the issues associated with medialized components
4. Less scapular notching
  
  Fig. 17.4 Comparison of the center of rotation.
  
  Fig. 17.5 Effect of reverse shoulder arthroplasty and deltoid lengthening.
5. Improved soft tissue tensioning → Increased compressive forces → Decreased instability
6. More force across the glenoid–component interface.
Neck shaft angle (NSA) (▶ Fig. 17.6 ):
1. Normal: 30–55
2. RSA: 125–155
3. More horizontal NSA:
  1. Decreased scapular notching
  2. Increased contact stress → Increased wear
  3. iImproved adduction, external rotation, and extension. ⁷
    
    Fig. 17.6 (a–f) Effect of humeral stem design on humeral position and range of motion in reverse shoulder arthroplasty. ⁷
Glenosphere positioning: ⁸ – ¹⁰
1. Avoid superior tilt
2. Inferior positioning can decrease scapular notching
3. Use glenoid center line as reference
4. Use larger glenosphere for instability.