Wrist biomechanics

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Wrist biomechanics

  1. 1. MUN Wrist Biomechanics and Carpal Instability
  2. 2. MUN Wrist Biomechanics • Anatomy • Kinematics • Force transmission
  3. 3. MUN Anatomy • 8 bones • Complex interlocking shapes • Intrinsic and extrinsic ligaments
  4. 4. MUN
  5. 5. MUN Wrist ligaments
  6. 6. MUN 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
  7. 7. MUN Kinematics • Three axes of motion – FEM 90 – 70 degrees – Flex/ext split between radiocarpal & midcarpal – RUD 20 – 50 degrees – PSM 90 – 90 degrees
  8. 8. MUN Axes of Motion
  9. 9. MUN Kinematics • Rows • Columns (Navarro) • Oval ring • Longitudinal columns (Weber) • “Link Joint”
  10. 10. MUN Link Joint
  11. 11. MUN 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
  12. 12. MUN
  13. 13. MUN Kinematics • Center of rotation : head of capitate
  14. 14. MUN 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
  15. 15. MUN 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
  16. 16. MUN Force Transmission • Principal force transmission is through capitate lunate and proximal pole of scaphoid • 75% radius 25% ulna
  17. 17. MUN Classification of Carpal Instability • CID (dissociative) – DISI – VISI • CIND (non-dissociative) – Radiocarpal,Midcarpal,Ulnar transloc’n • CIC (complex) – Perilunate Dislocation
  18. 18. MUN Progressive periLunate Instability • Stage I – scapholunate instability • Stage II – capitate dislocation • Stage III – triquetral dislocation • Stage IV – lunate dislocation • Spectrum of injury
  19. 19. MUN PLI
  20. 20. MUN Mechanism of injury • Impact on thenar side of wrist causes hyperextension , ulnar deviation and intercarpal supination • Progressive damage around lunate • Bony or ligamentous
  21. 21. MUN Normal wrist
  22. 22. MUN Volar Intercalated Segment Instability
  23. 23. MUN Dorsal Intercalated Segment Instability
  24. 24. MUN Gilula lines
  25. 25. MUN Carpal Angles
  26. 26. MUN Carpal Height • L2/L1 = 0.54 • New ratio L2/capitate = 1.57
  27. 27. MUN Scapholunate Instability • Most common form • Rarely diagnosed acutely • Local tenderness • Scaphoid shift(Watson) • Associated with other injuries eg distal radius
  28. 28. MUN 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
  29. 29. MUN Scapholunate Instability: Radiographs • Scapholunate gap >2mm • Foreshortened scaphoid • Cortical ring sign • Taliesnik,s “V” sign • Lack of parallelism?
  30. 30. MUN Scapholunate Instability
  31. 31. MUN DISI
  32. 32. MUN Scapholunate Instability
  33. 33. MUN
  34. 34. MUN
  35. 35. MUN Scapholunate Instability: Treatment • Acute (0-3 wks) : open repair vs arthroscopically-assisted PCP x 8wks • Chronic (>4 wks) : repair + reconstruction – STT – Blatt – SLC
  36. 36. MUN Scapholunate instability
  37. 37. MUN Acute repair SLIL
  38. 38. MUN Blatt Capsulodesis
  39. 39. MUN STT Fusion
  40. 40. MUN STT Arthrodesis
  41. 41. MUN Scapholunate Instability: Arthrosis • SLAC • PRC • Arthrodesis • RSL
  42. 42. MUN 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
  43. 43. MUN VISI
  44. 44. MUN 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
  45. 45. MUN Lesser and Greater arcs
  46. 46. MUN Perilunate Dislocation
  47. 47. MUN Perilunate repair
  48. 48. MUN Ulnar Translocation • Rare • Difficult to treat • Non-traumatic causes : RA,Madelung’s
  49. 49. MUN Ulnar Translocation
  50. 50. MUN
  51. 51. MUN Carpal Instability: Unresolved Issues • Role of arthroscopy • Method of reconstruction SLIL eg bone- tendon-bone • Ulnar side pathomechanics • Role of MRI
  52. 52. MUN Grade III
  53. 53. MUN Grade IV

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