Wrist biomechanics
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The document discusses wrist biomechanics and carpal instability. It describes the anatomy of the wrist including its 8 bones and complex ligaments. It discusses the kinematics of wrist motion along three axes and the rows and column structure. Common types of carpal instability are described such as DISI, VISI, and perilunate dislocations. Scapholunate instability is discussed in depth, including classification, diagnosis, and treatment options like repair and reconstruction procedures. Other topics covered include triquetrolunate instability, VISI, perilunate dislocations, and unresolved issues in the field.
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Wrist biomechanics
- 1. MUN Wrist Biomechanics and Carpal Instability
- 2. MUN Wrist Biomechanics • Anatomy • Kinematics • Force transmission
- 3. MUN Anatomy • 8 bones • Complex interlocking shapes • Intrinsic and extrinsic ligaments
- 4. MUN
- 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. MUN Kinematics • Three axes of motion – FEM 90 – 70 degrees – Flex/ext split between radiocarpal & midcarpal – RUD 20 – 50 degrees – PSM 90 – 90 degrees
- 9. MUN Kinematics • Rows • Columns (Navarro) • Oval ring • Longitudinal columns (Weber) • “Link Joint”
- 10. MUN Link Joint
- 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. MUN
- 13. MUN Kinematics • Center of rotation : head of capitate
- 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. 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. MUN Force Transmission • Principal force transmission is through capitate lunate and proximal pole of scaphoid • 75% radius 25% ulna
- 17. MUN Classification of Carpal Instability • CID (dissociative) – DISI – VISI • CIND (non-dissociative) – Radiocarpal,Midcarpal,Ulnar transloc’n • CIC (complex) – Perilunate Dislocation
- 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. MUN PLI
- 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. MUN Normal wrist
- 24. MUN Gilula lines
- 26. MUN Carpal Height • L2/L1 = 0.54 • New ratio L2/capitate = 1.57
- 27. MUN Scapholunate Instability • Most common form • Rarely diagnosed acutely • Local tenderness • Scaphoid shift(Watson) • Associated with other injuries eg distal radius
- 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. MUN Scapholunate Instability: Radiographs • Scapholunate gap >2mm • Foreshortened scaphoid • Cortical ring sign • Taliesnik,s “V” sign • Lack of parallelism?
- 31. MUN DISI
- 33. MUN
- 34. MUN
- 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
- 39. MUN STT Fusion
- 41. MUN Scapholunate Instability: Arthrosis • SLAC • PRC • Arthrodesis • RSL
- 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. MUN VISI
- 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. MUN Lesser and Greater arcs
- 48. MUN Ulnar Translocation • Rare • Difficult to treat • Non-traumatic causes : RA,Madelung’s
- 50. MUN
- 51. MUN Carpal Instability: Unresolved Issues • Role of arthroscopy • Method of reconstruction SLIL eg bone- tendon-bone • Ulnar side pathomechanics • Role of MRI
- 52. MUN Grade III
- 53. MUN Grade IV