Rotator Cuff Tear

Etiology:

1. Attritional change ← repetitive microtrauma = overuse of shoulder from professional / athletic activities
2. Subacromial impingement between humeral head + coracoacromial arch
3. Tendon degeneration ← hypovascularity ← aging
4. Acute trauma (rare)

Prevalence in asymptomatic patients:

in 40% of patients >50 years (full-thickness tear); in >60% of patients >60 years (partial & full thickness)

Age: most commonly >50 years; young athletic patient may have “rim-rent” tear (= avulsion of attachment at greater tuberosity

Location:

Supraspinatus tendon tear:

• “critical zone” of anterior supraspinatus tendon 1 cm medial to attachment (= area of relative hypovascularity)

Infraspinatus tendon tear (30–40%):

• precludes arthroscopic repair
• worst postoperative prognosis
• isolated tear more common in throwing sports

Teres minor tendon tear (rare):

• also affected by posterior instability

Subscapularis tendon tear:

• more common in superior articular surface
• associated with supraspinatus tendon tear + rotator interval lesion + biceps tendon pathology
• cysts of lesser tuberosity + edema (common)

• clinical assessment (during US):
  • test of supraspinatus m.
    1. supraspinatus weakness
       • straight hanging and 20° abducted arm pushed against applied force = assessment of strength
    2. impingement: 97% sensitive + 67% PPV
       • “arc of pain”: 98% sensitive + 67% PPV
    3. weakness of abduction: 64% sensitive + 78% PPV
       • drop-arm test = active abduction of arm to 90° then slowly lowering arm: if arm drops abruptly test is positive (98% specific, 10% sensitive)
       • combination of (a) + (b) + (c) = 98% chance of rotator cuff tear
  • test of infraspinatus m. + teres minor m.
    • weakness of external rotation: 76% sensitive + 79% PPV
      • resist inward force with elbow flexed 90° + shoulder internally rotated
  • test of subscapularis m.
    • passive positioning of arm behind back with palm facing outward: failure to hold forearm + hand off the back = positive test
  • patient age
  • night pain: 88% sensitive + 70% PPV

Assessment:

1. Depth of tear
   1. incomplete rupture = partial-thickness tear involves either bursal or synovial surface or remains intratendinous
      • Articular-surface partial-thickness tear >>bursal-surface partial thickness tear
      • PASTA = partial thickness articular supraspinatus tendon avulsion (at attachment of tendon to greater tuberosity = footprint)
      • PAINT = partial articular tear with intratendinous extension
      • fluid-filled defect not extending across the entire tendon width
      • disruption of superior / inferior tendon fibers only
   2. complete rupture = full-thickness tear from subacromial bursal surface to articular surface of glenohumeral joint
      • pure transverse tear
      • pure vertical / longitudinal tear
      • tear with retraction of tendon edges
      • global tear = massive tear / avulsion of cuff involving more than one of the tendons
2. Size of tear
   Depth of partial tear (normal thickness = 12 mm):
   1. small = grade 1 (<25%) = <3 mm
   2. medium = grade 2 (25–50%) = 3–6 mm
   3. large = grade 3 (>50%) = >6 mm
   
   Greatest dimension of full-thickness tear:
   1. small = <1 cm
   2. medium = 1–3 cm
   3. large = 3–5 cm
   4. massive = >5 cm
3. Geometry of tear (as viewed from tendon surface)
   1. crescentic = minimal retraction of tendon
   2. U-shaped = massive tear that may extend to level of glenoid fossa
   3. L-shaped = massive tear with longitudinal component
4. Injury extension (to adjacent structures)
   1. in anterior direction: supraspinatus tendon → medial aspect of coracohumeral ligament (rotator interval) → superior subscapularis tendon fibers
   2. in posterior direction: supraspinatus tendon → infraspinatus tendon → teres minor tendon
   3. involvement of long head of biceps brachii tendon
      • Injury / disruption of LHBB tendon in up to 77%
      • Subluxation / dislocation in up to 44%
5. Muscle atrophy (decreased bulk, fatty infiltration) as strongest prognosticator of surgical outcome
   • Muscle cross-sectional area measurement correlates with muscle strength!
   • on SAG OBL plane at level of medial coracoid process:
     • “tangent” sign = supraspinatus muscle does not cross a line drawn through superior border of scapular spine + superior margin of coracoid process
     • scapular ratio of <50% = occupation ratio of cross-sectional area of supraspinatus m. to area of supraspinatus fossa
6. Impingement anatomy

X-ray (AP view):

• usually normal in acute rotator cuff tear
• acromiohumeral distance ≤2 mm (with active abduction to 90°) ← absence / retraction of supraspinatus tendon
• flattened / ill-defined superior soft-tissue contour with heterogeneous decreased density → fatty replacement (on supraspinatus outlet [modified Y] view)

X-ray (late findings):

• superior migration of humeral head = acromiohumeral distance <7 mm
• cuff arthropathy = sclerosis, subchondral cysts, osteolysis, notching / pitting of greater tuberosity ← repetitive contact between humeral head + acromion
• remodeling of acromial undersurface with matching sclerosis, faceting, concavity of inferolateral aspect of acromion

US (scans in hyperextended position, 75–100% sensitive, 43–97% specific, 65–95% NPV, 55–75% PPV):

Sequence of examination:

biceps, subscapularis, supraspinatus, infraspinatus, teres minor, posterior glenohumeral joint

• direct primary signs of tendon tear
  • focal absence of rotator cuff= partial thickness:
    • well-defined hypo- / anechoic defect in tendon replaced by fluid → with extension either to bursal /or articular surface
    • abrupt + sharply demarcated focal thinning
    • small comma-shaped area of hyperechogenicity (= small tear filled with granulation tissue / hypertrophied synovium)
  • nonvisualization of retracted tendon in massive supraspinatus tear (most reliable sign):
    • discontinuity of rotator cuff filled with joint fluid
    • defect filled with hypoechoic thickened bursa + peribursal fat
    • “naked tuberosity” sign = retracted tendon leaves a bare area of bone
    • deltoid muscle directly on top of humeral head
    • hypervascularity of defect on color Doppler
• indirect primary signs of tendon tear
  • “double cortex” / “cartilage interface” sign = 2 hyperechoic lines representing cartilage + cortex ← fluid-enhanced increase in through-transmission
  • compressibility = loss of normal convex contour of peribursal fat ← displacement of fluid with compression by transducer over hypoechoic defect
  • “sagging peribursal fat” sign = depression of hyperechoic peribursal fat into area of torn tendon
  • increased echogenicity + decreased bulk of muscle = muscle atrophy (in 77% of rotator cuff tears)
• secondary signs of tendon tear:
  • cortical irregularity of greater tuberosity
  • shoulder joint effusion = anechoic fluid in axillary pouch, posterior recess, biceps tendon sheath

False negative: longitudinal tear, partial tear

False positive: intraarticular biceps tendon, soft-tissue calcification, small scar / fibrous tissue

Arthrography (71–100% sensitive, 71–100% specific for combined full + partial thickness tears):

• opacification of subacromial-subdeltoid bursa
• contrast enters substance of rotator cuff tendons

MR (41–100% sensitive and 79–100% specific for combined full + partial thickness tears):

• discontinuity of cuff with retraction of musculotendinous junction
• focal / generalized intense / markedly increased SI on T2WI (= fluid within cuff defect) in <50%
• fluid within subacromial-subdeltoid bursa (most sensitive)
• low / moderate SI on T2WI (= severely degenerated tendon, intact bursal / synovial surface, granulation / scar tissue filling the region of torn tendinous fibers)
• cuff defect with contour irregularity
• abrupt change in signal character at boundary of lesion
• supraspinatus muscle atrophy (MOST SPECIFIC)

Pitfalls:

• hyperintense focus in distal supraspinatus tendon
• gray signal isointense to muscle on all pulse sequences:
  1. partial volume averaging with superior + lateral infraspinatus tendon
  2. vascular “watershed” area
  3. magic angle effect = orientation of collagen fibers at 55° relative to main magnetic field
• hyperintense focus within rotator cuff on T2WI:
  1. partial volume averaging with fluid in biceps tendon sheath / subscapularis bursa
  2. partial volume averaging with fat of peribursal fat
  3. motion artifacts: respiration, vascular pulsation, patient movement
• fatty atrophy of muscle
  1. impingement of axillary / suprascapular nn. = quadrilateral space syndrome

DDx:

1. Partial-thickness tear with diffuse less-than-fluid intensity on T2WI
2. Tendon degeneration (tendinopathy)
3. Tendinitis
4. Full-thickness tear containing granulation tissue