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Introduction
  • Replacement of humeral head and glenoid resurfacing
    • cemented all-polyethylene glenoid resurfacing is standard of care
  • Total shoulder arthroplasty unique from THA and TKA in that
    • greater range of motion in the shoulder
    • success depends on proper functioning of the soft tissues
    • glenoid is less constrained
      • leads to greater sheer stresses and is more susceptible to mechanical loosening
  • Factors required for success of TSA
    • rotator cuff intact and functional
      • if rotator cuff is deficient and proximal migration of humerus is seen on x-rays (rotator cuff arthropathy) then glenoid resurfacing is contraindicated 
      • if there is an irreparable rotator cuff deficiency then proceed with hemiarthroplasty or a reverse ball prosthesis
      • an isolated supraspinatus tear without retraction can proceed with TSA 
        • incidence of full thickness rotator cuff tears in patients getting a TSA is 5% to 10%
        • if positive impingement signs on exam, order a pre-operative MRI
    • glenoid bone stock and version
      • if glenoid is eroded down to coracoid process then glenoid resurfacing is contraindicated
      • see Walch classification below
  • Outcomes
    • pain relief most predictive benefit (more predictable than hemiarthroplasty) 
    • reliable range of motion
    • good survival at 10 years (93%)
    • good longevity with cemented and press-fit humeral components
    • worse results for post-capsulorrhaphy arthropathy q
Classification
 
Walch Classification of Glenoid Wear
Type A well-centered 
A1 minor erosion
A2 deeper central erosion
Type B head subluxated posteriorly 
B1 posterior wear
B2 severe biconcave wear
Type C glenoid retroversion of more than 25 degrees (dysplastic in origin)

Indications
  • Indications 
    • pain (anterior to posterior), especially at night, and inability to perform activities of daily living
    • glenoid chondral wear to bone   
      • preferred over hemiarthroplasty for osteoarthritis and inflammatory arthritis
    • posterior humeral head subluxation
  • Contraindications
    • insufficient glenoid bone stock
    • rotator cuff arthropathy
    • deltoid dysfunction
    • irreparable rotator cuff (hemiarthroplasty or reverse total shoulder are preferable) q 
      • risk of loosening of the glenoid prosthesis is high ("rocking horse" phenomenon)
    • active infection
    • brachial plexus palsy
Preoperative Imaging
  • Radiographs
    • true AP
      • determine extent of arthritis and look for superior migration of humerus
    • axillary view
      • look for posterior wear of glenoid
  • CT scan
    • obtain CT scan to determine glenoid version and glenoid bone stock
  • MRI
    • evaluate rotator cuff condition
Approach
  • Deltopectoral
    • detach the subscapularis and capsule from anterior humerus
    • dislocate shoulder anteriorly
    • tight shoulders may require release of the upper half of the pectoralis tendon to increase exposure and dislocation
      • pectoralis major tendon passes on top of the biceps tendon to attach to the humerus
  • Complications
    • axillary nerve damage is the most common complication
      • axillary nerve and posterior humeral circumflex artery pass beneath the glenohumeral joint in the quadrilateral space 
Technical considerations
  • Capsule
    • anterior capsule contracture (passive ER < 40°)
      • treatment
        • anterior release and Z-lengthening
    • posterior capsule stretching
      • treatment
        • volume-reducing procedure (plication of posterior capsule)
  • Glenoid deficiency and retroversion
    • glenoid deficiency q 
      • treatment
        • build up with iliac crest autograft or part of the resected humerus 
        • do not use cement to build up the deficiency
    • retroverted glenoid  
      • treatment
        • build up posterior glenoid with allograft
        • eccentrically ream anterior glenoid
  • Glenoid component
    • convex superior to flat
    • recreate neutral version
    • peg design is biomechanically superior to keel design
    • polyethylene-backed components superior to metal-backed components
      • glenoid not large enough to accommodate both metal and PE
    • uncemented glenoid has a lower rate of loosening
    • conforming vs. nonconforming
      • both have advantages and neither is superior
      • conforming is more stable but leads to rim stress and radiolucencies
      • nonconforming leads to increased polyethylene wear
  • Humeral stem fixation
    • cemented stem or uncemented porous-coated implants 
    • position of humeral stem should be 25-45° of retroversion   
      • if position of glenoid retroversion is required, then the humeral stem should be less retroverted to avoid posterior dislocation
    • avoid valgus positioning of humeral stem
    • avoid overstuffing the humeral head
      • increases joint reaction forces and tension on the rotator cuff
      • the top of the humeral head should be 5 to 8 mm superior to the top of the greater tuberosity
    • intraoperative humerus fracture
      • greater tuberosity fracture
        • treatment
          • if minimally displaced, insert a standard humeral prosthesis with suture fixation and autogenous cancellous bone grafting of the greater tuberosity fracture
      • humeral shaft fracture
        • treatment
          • remove prosthesis and add longer stem with cement and reinforce with cerclage wiring
Rehabilitation
  • Passive or active-assisted motion only during early rehab
    • limiting factor in early postoperative rehabilitation is risk of injury to the subscapularis tendon repair q  
  • Progress to ER isometrics
  • Limit passive external rotation
    • risk of tear and pull-off of subscapularis tendon from anterior humerus
      • tear leads to anterior shoulder instability (most common form of instability after TSA)
      • treatment of subscapularis pull-off is early exploration and repair of tendon
      • test for pull-off of subscapularis
        • weak belly-press test
        • inability to put hand in back pants pockets or tuck shirt behind the back
      • avoid pushing out of chair during acute rehab
  • IR eccentric and isometric
Complications
  • Glenoid loosening
    • most common cause of TSA failure (30% of primary OA revisions)
    • risk factors
      • insufficient glenoid bone stock
      • rotator cuff deficiency
    • 2.9% reoperation rate for loosening (28% with revision)
    • radiographic lines
      • presence of radiographic lines does not correlate with symptoms
      • progression of a radiographic line does correlate with symptoms
        • progression present in 50% of patients as early as 3 to 4 years after TSA
      • radiolucency around the glenoid does not always correlate with clinical failure
        • at 3- and 7-year follow-up did not correlate with poor functional outcomes or pain
  • Humeral stem loosening
    • more common in RA and osteonecrosis
    • rule out infection
  • Subscapularis repair failure q  
  • Malposition of components
  • Improper soft tissue balancing
    • failure due to undiagnosed presence of rotator cuff tears
  • Iatrogenic rotator cuff injury
    • can occur if humeral neck osteotomy is inferior to level of rotator cuff insertion 
  • Stiffness
  • Infection
    • may have normal aspiration results
    • culture
      • arthroscopic tissue culture more sensitive (100% sensitive and specific) than fluoroscopically guided aspiration (17% sensitivity, 100% specific)
    • Propionibacterium acnes (P. acnes) 
      • most common cause of indolent infections and implant failures
        • infection rate 1-2% after primary TSA
      • characteristics
        • gram positive, facultative, aerotolerant, anaerobic rod that ferments lactose to propionic acid
        • has high bacterial burden around the shoulder 
        • forms biofilm within 18-90h (found on implant surface and on synovial tissue) >> planktonic (explains why aspiration is only 17% sensitive)
        • P. acnes PJI more common in males 
      • presentation
        • initial pain & stiffness
        • later swelling & redness
      • diagnosis
        • use anaerobic culture bottles, keep for 10-14days (mean time to detection 6 days)
        • 16s rRNA PCR
        • imaging (XR, CT, ultrasound) positive for subluxation/loosening in 24% of cases
        • if implant is removed, sonicate implant (to dislodge bacteria from surface) for sonication culture
      • treatment
        • early infection (<6 weeks) can be treated with open irrigation and debridement
        • late infection (>6 weeks) should be treated by explant and 2-stage reimplantation after IV antibiotic (penicillin G, ceftriaxone, clindamycin, vanco) x 6wk, followed by 2-6mths of PO antibiotic
  • Neurologic injury
    • axillary nerve is most commonly injured
    • musculocutaneous nerve can be injured by retractor placement under conjoint tendon
  • Periprosthetic fracture
    • acceptable fragment alignment ≤ 20° flexion/extension, ≤ 30° varus/valgus, ≤ 20° rotation malalignment
    • see table below
Wright & Cofield Classification of Periprosthetic fracture  
Type  Characteristics Treatment of Intraoperative Fracture Treatment of Postop Fracture
Type A Centered near the tip of the stem and extends proximally Span fracture with standard length prosthesis (2-3 cortical diameters) or long-stem prosthesis. Transosseous sutures for tuberosity fractures
Usually min displaced/angulated (treat nonop). If significant overlap between prox-distal fragments, treat as if stem loose and revise to long stem prosthesis.
Type B Centered at the tip of the stem and extends distally. 

Span fracture with standard length prosthesis (2-3 cortical diameters) or long-stem prosthesis. Cement in distal canal to engage prosthesis (do NOT let cement escape from fracture site). Cortical strut allograft + cerclage. 

Revise to long-stem prosthesis. Cement in distal canal to engage prosthesis 
Type C Located distal to the tip of the stem. Long-stem prosthesis, or if close to olecranon fossa, plate+screws ± cerclage wire, strut allograft ORIF (plate overlap prosthesis by 2 cortical diameters to avoid stress riser)
 

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