Date post: | 22-May-2015 |
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Health & Medicine |
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MUN ORTHOPEDICS
Wrist Biomechanicsand Carpal Instability
MUN ORTHOPEDICS
Wrist Biomechanics
• Anatomy
• Kinematics
• Force transmission
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Anatomy
• 8 bones
• Complex interlocking shapes
• Intrinsic and extrinsic ligaments
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Wrist ligaments
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Wrist ligaments
• Volar stronger than dorsal
• Double V shape with weak area ; space of Poirier
• Important interosseous ligaments are SLIL and LTIL
• Dorsal ligaments tend to converge on triquetrum
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Kinematics
• Three axes of motion– FEM 90 – 70 degrees– Flex/ext split between radiocarpal & midcarpal– RUD 20 – 50 degrees– PSM 90 – 90 degrees
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Axes of Motion
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Kinematics
• Rows
• Columns (Navarro)
• Oval ring
• Longitudinal columns (Weber)
• “Link Joint”
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Link Joint
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Kinematics
• Rows– Proximal and Distal with scaphoid as a bridge– Motion within and between rows
• Columns– Central(flex/ext) lunate,capitate,hamate– Lateral (mobile) scaphoid,trapezoid,trapezium– Medial (rotation) triquetrum
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Kinematics
• Center of rotation : head of capitate
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Kinematics
• Radial deviation : scaphoid flexes proximal pole goes dorsal “pulling” lunate into palmar flexion
• Ulnar deviation : scaphoid extends proximal pole goes volar pulling lunate into dorsiflexion
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Kinematics
• Triquetrohamate helicoid joint
• Ulnar deviation : “low” position distal and dorsiflexed pulling lunate into dorsiflexion
• Radial deviation : “high”position proximal and palmar flexed pulling lunate into palmar flexion
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Force Transmission
• Principal force transmission is through capitate lunate and proximal pole of scaphoid
• 75% radius 25% ulna
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Classification of Carpal Instability
• CID (dissociative)– DISI– VISI
• CIND (non-dissociative)– Radiocarpal,Midcarpal,Ulnar transloc’n
• CIC (complex)– Perilunate Dislocation
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Progressive periLunate Instability
• Stage I – scapholunate instability
• Stage II – capitate dislocation
• Stage III – triquetral dislocation
• Stage IV – lunate dislocation
• Spectrum of injury
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PLI
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Mechanism of injury
• Impact on thenar side of wrist causes hyperextension , ulnar deviation and intercarpal supination
• Progressive damage around lunate
• Bony or ligamentous
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Normal wrist
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Volar Intercalated SegmentInstability
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Dorsal Intercalated SegmentInstability
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Gilula lines
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Carpal Angles
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Carpal Height
• L2/L1 = 0.54• New ratio L2/capitate
= 1.57
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Scapholunate Instability
• Most common form
• Rarely diagnosed acutely
• Local tenderness
• Scaphoid shift(Watson)
• Associated with other injuries eg distal radius
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Scapholunate Instability:Classification
• Type 1 – dynamic– Neg Xray;+ve Watson:+ve cine
• Type 2 – static– +ve plain films
• Type 3 – degenerative
• Type 4 – secondary– Kienbock’s ; SNAC
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Scapholunate Instability:Radiographs
• Scapholunate gap >2mm
• Foreshortened scaphoid
• Cortical ring sign
• Taliesnik,s “V” sign
• Lack of parallelism?
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Scapholunate Instability
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DISI
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Scapholunate Instability
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Scapholunate Instability:Treatment
• Acute (0-3 wks) : open repair vs arthroscopically-assisted PCP x 8wks
• Chronic (>4 wks) : repair + reconstruction– STT– Blatt– SLC
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Scapholunate instability
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Acute repair SLIL
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Blatt Capsulodesis
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STT Fusion
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STT Arthrodesis
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Scapholunate Instability:Arthrosis
• SLAC
• PRC
• Arthrodesis
• RSL
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Triquetrolunate instabliity
• Limited understanding of ulnar side
• TL or TH ??
• Ulnar pain post injury
• Click
• +ve ballottement test
• Beware ulnar impaction syndrome
• Conservative Rx; rarely need limited fusion
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VISI
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Perilunate Dislocation
• Perilunate & Lunate are same basic injury
• Still missed in ER
• Rx of choice : open reduction & repair of ligaments/bones
• Dorsal and volar approach
• Late: fusion or PRC
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Lesser and Greater arcs
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Perilunate Dislocation
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Perilunate repair
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Ulnar Translocation
• Rare
• Difficult to treat
• Non-traumatic causes : RA,Madelung’s
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Ulnar Translocation
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Carpal Instability:Unresolved Issues
• Role of arthroscopy
• Method of reconstruction SLIL eg bone-tendon-bone
• Ulnar side pathomechanics
• Role of MRI
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Grade III
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Grade IV