Wrist Biomechanics and Carpal Instability MUN ORTHOPEDICS

Wrist Biomechanics Anatomy Kinematics Force transmission MUN ORTHOPEDICS

Anatomy 8 bones Complex interlocking shapes Intrinsic and extrinsic ligaments MUN ORTHOPEDICS

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Wrist ligaments MUN ORTHOPEDICS

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 MUN ORTHOPEDICS

Kinematics Three axes of motion FEM 90 – 70 degrees Flex/ext split between radiocarpal & midcarpal RUD 20 – 50 degrees PSM 90 – 90 degrees MUN ORTHOPEDICS

Axes of Motion MUN ORTHOPEDICS

Kinematics Rows Columns (Navarro) Oval ring Longitudinal columns (Weber) “Link Joint” MUN ORTHOPEDICS

Link Joint MUN ORTHOPEDICS

Kinematics Rows Columns 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 MUN ORTHOPEDICS

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Kinematics Center of rotation : head of capitate MUN ORTHOPEDICS

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 MUN ORTHOPEDICS

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 MUN ORTHOPEDICS

Force Transmission Principal force transmission is through capitate lunate and proximal pole of scaphoid 75% radius 25% ulna MUN ORTHOPEDICS

Classification of Carpal Instability CID (dissociative) DISI VISI CIND (non-dissociative) Radiocarpal,Midcarpal,Ulnar transloc’n CIC (complex) Perilunate Dislocation MUN ORTHOPEDICS

Progressive periLunate Instability Stage I – scapholunate instability Stage II – capitate dislocation Stage III – triquetral dislocation Stage IV – lunate dislocation Spectrum of injury MUN ORTHOPEDICS

PLI MUN ORTHOPEDICS

Mechanism of injury Impact on thenar side of wrist causes hyperextension , ulnar deviation and intercarpal supination Progressive damage around lunate Bony or ligamentous MUN ORTHOPEDICS

Normal wrist MUN ORTHOPEDICS

Volar Intercalated Segment Instability MUN ORTHOPEDICS

Dorsal Intercalated Segment Instability MUN ORTHOPEDICS

Gilula lines MUN ORTHOPEDICS

Carpal Angles MUN ORTHOPEDICS

Carpal Height L2/L1 = 0.54 New ratio L2/capitate = 1.57 MUN ORTHOPEDICS

Scapholunate Instability Most common form Rarely diagnosed acutely Local tenderness Scaphoid shift(Watson) Associated with other injuries eg distal radius MUN ORTHOPEDICS

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 MUN ORTHOPEDICS

Scapholunate Instability: Radiographs Scapholunate gap >2mm Foreshortened scaphoid Cortical ring sign Taliesnik,s “V” sign Lack of parallelism? MUN ORTHOPEDICS

Scapholunate Instability MUN ORTHOPEDICS

DISI MUN ORTHOPEDICS

Scapholunate Instability MUN ORTHOPEDICS

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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 MUN ORTHOPEDICS

Scapholunate instability MUN ORTHOPEDICS

Acute repair SLIL MUN ORTHOPEDICS

Blatt Capsulodesis MUN ORTHOPEDICS

STT Fusion MUN ORTHOPEDICS

STT Arthrodesis MUN ORTHOPEDICS

Scapholunate Instability: Arthrosis SLAC PRC Arthrodesis RSL MUN ORTHOPEDICS

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 MUN ORTHOPEDICS

VISI MUN ORTHOPEDICS

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 MUN ORTHOPEDICS

Lesser and Greater arcs MUN ORTHOPEDICS

Perilunate Dislocation MUN ORTHOPEDICS

Perilunate repair MUN ORTHOPEDICS

Ulnar Translocation Rare Difficult to treat Non-traumatic causes : RA,Madelung’s MUN ORTHOPEDICS

Ulnar Translocation MUN ORTHOPEDICS

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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 MUN ORTHOPEDICS

Grade III MUN ORTHOPEDICS

Grade IV MUN ORTHOPEDICS