wrist biomechanics

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  • 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 5. MUN Wrist ligaments 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 8. MUN Axes of Motion 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 : highposition 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 translocn 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 22. MUN Volar Intercalated Segment Instability 23. MUN Dorsal Intercalated Segment Instability 24. MUN Gilula lines 25. MUN Carpal Angles 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 Kienbocks ; SNAC 29. MUN Scapholunate Instability: Radiographs Scapholunate gap >2mm Foreshortened scaphoid Cortical ring sign Taliesnik,s V sign Lack of parallelism? 30. MUN Scapholunate Instability 31. MUN DISI 32. MUN Scapholunate Instability 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 36. MUN Scapholunate instability 37. MUN Acute repair SLIL 38. MUN Blatt Capsulodesis 39. MUN STT Fusion 40. MUN STT Arthrodesis 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 46. MUN Perilunate Dislocation 47. MUN Perilunate repair 48. MUN Ulnar Translocation Rare Difficult to treat Non-traumatic causes : RA,Madelungs 49. MUN Ulnar Translocation 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