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Updated: Sep 18 2024

Reverse Shoulder Arthroplasty

Images
https://upload.orthobullets.com/topic/3076/images/scapno.jpg
https://upload.orthobullets.com/topic/3076/images/reverse ball.jpg
https://upload.orthobullets.com/topic/3076/images/scapularnotching.jpg
https://upload.orthobullets.com/topic/3076/images/cuff_tear_arthropathy..jpg
  • Summary
    • Reverse Shoulder Arthroplasty is a type of shoulder arthroplasty that uses a convex glenoid hemispheric ball and a concave humerus articulating cup to reconstruct the glenohumeral joint.
    • The center of rotation is moved inferiorly and medialized which allows the deltoid muscle to act on a longer fulcrum and have more mechanical advantage.
    • Reverse Shoulder Arthroplasty is indicated for conditions such as rotator cuff tear arthropathy, comminuted 4-part proximal humerus fractures and prior failed shoulder arthroplasty.
  • Epidemiology
    • Epidemiology
      • popularized in Europe and now increasingly used in North America since 1990
  • Biomechanics
    • The advantage of a reverse shoulder arthroplasty is that the center of rotation (COR) is moved inferiorly and medialized 
      • allows the deltoid muscle to act on a longer fulcrum and have more mechanical advantage to substitute for the deficient rotator cuff muscles to provide shoulder abduction
        • allows increased (but not normal) shoulder abduction
      • does not significantly help shoulder internal or external rotation
    • Reverse shoulder arthroplasty can be combined with latissimus dorsi transfer to assist with external rotation
  • Indications
    • Clinical conditions
      • cuff-tear arthropathy
        • severe glenohumeral joint arthritis with superior escape in the setting of a massive rotator cuff tear
      • pseudoparalysis
        • an inability to actively elevate the arm in the presence of free passive ROM and in the absence of a neurologic lesion
        • occurs secondary to irreparable rotator cuff tear in setting of glenohumeral arthritis
      • antero-superior escape
        • incompetent coracoacromial arch
        • humeral "escape" in subcutaneous tissue with hemiarthroplasty
      • proximal humerus fractures in the elderly
        • 3 or 4-part fractures in patients age > 70
        • head-splitting fractures
        • significant osteopenia or poor bone quality
          • where GT has poor potential for healing
      • rotator cuff insufficiency 'equivalent'
        • non-union or mal-union of the tuberosity following trauma or prior arthroplasty
      • failed arthroplasty
        • in setting of prior HA or aTSA with cuff insufficiency 
        • when all other options have been exhausted
      • rheumatoid arthritis
        • only if glenoid bone stock is sufficient
    • Patient characteristics (in clinical conditions above)
      • low functional demand patients
      • physiological age >70
      • sufficient glenoid bone stock
      • working deltoid muscle
        • intact axillary nerve
  • Contraindications
    • Axillary nerve dysfunction
      • important to separate permanent from temporary
    • Deltoid deficiency
      • global deficiency is a contraindication
      • partial deltoid deficiency is a relative contraindication but RSA may give reasonable results
    • Acromion deficiency
    • Glenoid osteoporosis
    • Active infection
  • Operative Planning
    • Radiographs
      • recommended views
        • true AP (Grashey)
          • determine extent of arthritis and look for superior migration of humerus
        • axillary lateral
          • look for posterior glenoid wear
        • scapular-Y
    • CT scan
      • indications
        • If unable to obtain an adequate axillary lateral, CT can be useful to determine glenoid version and glenoid bone stock
        • estimate degree of osteopenia
    • MRI
      • indications
        • evaluate rotator cuff integrity and fatty infiltration
  • Approach
    • Deltopectoral
      • advantages:
        • preserves deltoid muscle
        • exposure of the lower pole of the glenoid to facilitate glenoid implant positioning
        • can extend inferiorly for increase exposure to proximal humerus if needed
        • can perform a simutlatenous latissimus dorsi transfer if needed
        • decreased risk of axillary nerve palsy
      • disadvantages
        • need to take-down subscapularis for adequate exposure
        • need for extensive capsular release which may lead to instability
        • lack of exposure to posterior glenoid
        • potential for stiffness given immobilization required for subscapularis healing
    • Anterosuperior
      • method
        • the anterior deltoid is divided from the anterior edge of the acromioclavicular arch, allowing increased glenoid exposure.
      • advantages
        • increased glenoid exposure
        • able to preserve subscapularis
        • decreased post-operative instability due to preservation of anterior stabilizers
        • ease of axial preparation of the humerus
        • easier fixation of greater tuberosity for fractures
      • disadvantages
        • increased risk of injury to distal branches of axillary nerve
        • violates anterior deltoid muscle
        • risk of excess height or superior tilt of glenoid
  • Techniques
    • Humeral preparation
      • humeral head typically osteotomized anywhere between 0 and 30 degrees of retroversion (typically 20)
        • more retroversion is gaining popularity as it may improve post-op external rotation
        • humeral head can be saved for autograft if needed
        • osteotomy generally not needed in setting of fracture
      • long head of biceps is tenotomized or tenodesed
      • ream and broach humerus similar to conventional TSA
      • the humeral height and version typically judged by humeral calcar or tuberosity fragment
        • if calcar missing in the setting of fracture, height can be judged by pectoralis insertion which resides 5.6 cm from top of fractured humeral head
    • Glenoid preparation
      • labrum is excised and capsule is released circumferentially
        • important to expose inferior glenoid by subperiosteally elevating tissue to ensure proper baseplate positioning
      • accurate central guidewire placement is dictated by availability of the best bone stock for baseplate screw fixation
      • place baseplate as inferiorly as possible with an inferior tilt
        • shown to decrease implant loosening and scapular notching
        • navigation systems increasingly used for accurate baseplate placement
      • superior screw is generally aimed toward coracoid base and inferior screw aimed towards scapular body
      • mount glenosphere onto baseplate
        • size chosen based on patient size, motion and preservation of stability
        • females/smaller pateints typically recieve a 36 mm and large men recieve a 40 mm.
    • Tuberosity repair
      • anatomic repair of the greater tuberosity is associated with improved shoulder external rotation, function and patient satisfaction compared to tuberosity resection or malunion
  • Rehabilitiation
    • Immediate
      • patient placed in sling post-op
    • Early rehab
      • passive or active-assisted motion only during early rehab
    • Sling discontinued at 3 weeks if subscapularis is NOT repaired, and 6 weeks if subscapularis is repaired
      • limit passive ER or active IR during this time
      • avoid pushing out of chair during acute rehab
      • subscapularis re-tear would lead to anterior shoulder instability
        • treatment
          • early exploration and repair
  • Complications
    • Scapular notching
      • incidence
        • occurs in 44%-96% of grammont style prosthesis
          • due to 155º humeral component neck-shaft angle that effectively medializes humeral component
        • decreased incidence with lateralization of baseplate
        • related to impingement by the medial rim of the humeral cup during adduction
      • risk factors
        • superior tilt of glenoid component
        • medialization of center of rotation
        • high BMI
    • Dislocation
      • incidence
        • reported rate between 2% - 3.4%
        • position of dislocation most commonly extension, internal rotation, and adduction 
        • most common cause of early failure
      • risk factors
        • irreparable subscapularis (strongest risk)
        • proximal humeral bone loss
        • failed prior arthroplasty
        • proximal humeral nonunion
        • fixed pre-operative glenohumeral dislocation
    • Glenoid Loosening
      • incidence
        • glenoid prosthetic loosening is most common mechanism of failure
          • incidence significantly increases (~25% at 5-year followup) after revision RSA
      • treatment
        • treat using staged procedure to fill glenoid cavity with autogenous bone and await incorporation with a hemiarthroplasty prior to reimplantation of a new glenosphere
    • Deep Infection
      • incidence
        • 1-2% risk of deep surgical cite infection following shoulder arthroplasty
        • susceptible to infection due to large subacromial dead space created by reverse prosthesis
        • most common organisms include c.acnes and staphylococci
      • Risk Factors
        • Younger age (less than 65) and male are the greatest risk factors
        • Arthroplasty for traumatic reasons
        • History of failed arthroplasty
      • treatment
        • 2-stage revision is considered gold standard
        • most common antibiotic treatment of choice for c.acnes is vancomycin and clindamycin
    • Acromial or scapular spine fractures
      • incidence
        • 4% after RSA
      • risk factors
        • female sex
        • osteoporosis
        • medialized preoperative center of rotation
      • treatment
        • conservative management leads to 40-50% union rate
          • operative management with ORIF or tension band wiring of acroimal fractures has increased union rates
      • Levy Classification for Post-operative Acromial fractures after Reverse Shoulder Arthroplasty
      • Type 1
      • Acromion anterior to posterolateral acromial corner
      • Type 2
      • Mid acromion between base and posterolateral corner
      • Type 3
      • Acromial base
    • Neurapraxia of axillary nerve
      • incidence
        • 0.5-1% rate after RSA
      • risk factors
        • anterosuperior approach
        • humerus lengthening
      • treatment
        • usually transient
      • Sirveaux Classification of Scapular Notching
      • Grade 1
      • Limited to scapular pillar
      • Grade 2
      • In contact with inferior screw of baseplate
      • Grade 3
      • Beyond the inferior screw
      • Grade 4
      • Extends under baseplate approaching central peg
  • Outcomes
    • Overview
      • results are dependent on indication, with cuff tear arthropathy (CTA) having the best results
    • Radiographic
      • radiographic results deteriorate after 6 years and clinical results after 8 years
    • Survivability
      • some cases series' have noted 10 year survivability is approximately 90% for implant retention
    • Complications
      • various studies have shown that complication rate amongst surgeons decrease after a surgeon has performed at least 18-45 cases
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