· enters flexor sheath on palmar surface of FDP
· divides into 2 halves
· slips
· flatten
· spiral around FDP
· meet on deep surface
· form chiasma (partial decussation) over PIP jt
· FDP lies on this tendinous bed
· slips insert along sides of shaft of P2
· enters flexor sheath deep to FDS
· lies superficial to chiasma of FDS
· passes distally to base of P3
· both tendons invested by common synovial sheath
· parietal and visceral layers
· each tendon receives vessels from palmar surface of phalanges
· vessels arise from digital arteries
· pass transversely to finger’s midline immediately proximal to IP jts
· pass anteriorly to tendons
· vessels invested in synovial membrane
· called vinculae
· each tendon possess long and short vincula
· short vinculum
· near attachment to sides of P2
· long vinculum
· double
· each half possesses vinculum just distal to division
· passes from P1
· short vinculum
· in angle close to insertion
· long vinculum
· from between slips of FDS
· proximal to chiasma
· fibro-osseous sheath for flexor tendon runs from MCP jt to P3
· constant thickenings in sheath act as pulleys
· two types
· ring - annular
· cross - cruciate
· MCP / P1 / PIP / P2 / DIP
· A1
· broad pulley over MCP jt
· incised for trigger finger release
· A2
· broad pulley over proximal part of proximal phalanx
· abuts A1
· must be preserved
· A3
· narrow pulley over PIP jt
· A4
· narrow pulley over middle part of middle phalanx
· A5
· narrow pulley over DIP jt
· P1 / P2 / P2
· C1
· over middle part of proximal phalanx
· between A2 and A3
· C2
· over proximal part of middle phalanx
· between A3 and A4
· C3
· over distal part of middle phalanx
· in anterior compartment of forearm
· in carpal tunnel
· in palm
· lumbrical region
· in flexor sheaths
· where both tendons run
· in flexor sheaths
· distal to insertion of FDS
· FDP tendon runs alone
· FPL enters sheath just proximal to carpal tunnel
· sheath becomes radial bursa
· FDP and FDS tendons enter common sheath just proximal to carpal tunnel
· terminates for II, III and IV just distal to carpal tunnel
· continuous with V
· sheath becomes ulnar bursa
· II, III and IV have separate sheaths
· start at neck of MC
· continues to insertion of FDP
· pulleys are thickenings in sheath
· 4 in number
· act to extend IP jts
· innervated by
· median n and ulnar n
· usually 2:2 (60%)
· may be 3:1 (20%) or 1:3 (20%)
· parallels innervation of FDP in forearm
Origin
· from tendons of FDP
· ulnarly innervated lumbricals are bicipital
· 2 heads from adjacent tendons
· medially innervated lumbricals are unicipital
· 1 head from own tendon
Path
· pass on radial side of MCP jt
· pass volar to deep transverse MC ligament
Insertion
· into radial lateral slip of extensor expansion
· abduct fingers (DAB)
· axis is 3rd MC
· 4 in number
· one in each cleft
· 2 for middle MC
· 1 for index and ring
· all interossei supplied by ulnar n
Origin
· arise from adjacent MC shafts
· 2 heads
· superficial and deep
· one from each MC
Path
· tendon passes dorsal to deep transverse MC ligament
Insertion
· superficial belly
· into lateral tubercle at base of P1
· acts as MC flexor
· deep belly
· into lateral slip of extensor expansion
· acts as IP extensor
· adduct fingers (PAD)
· axis is 3rd MC
· 3 in number
· one in each cleft except 1st cleft
· none for middle MC
· 1 for index, ring and middle
· all interossei supplied by ulnar nerve
Origin
· arise from middle finger side of own MC shaft
Path
· tendon passes dorsal to deep transverse MC ligament
Insertion
· into lateral slip of extensor expansion
· consist of
· EDC
· EIP
· EDM
· EIP and EDM lie to ulnar side of corresponding EDC tendon
· EDC to ulnar 3 fingers connected by juncturae tendinum proximal to MCP jt
· extensor tendon passes across MCP joint
· deep fibres blend with posterior MCP jt capsule
· broadens out over dorsal surface of P1
· forms extensor expansion
· divides into three slips
· central slip
· lateral slips
· central slip passes on over distal P1
· inserted into base of P2
· each lateral slip receives attachment from
· interosseous proximally
· lumbrical distally
· more proximally fibres from interossei and lumbricals contribute to extensor expansion
· fibres radiate across dorsum of proximal phalanx
· distally, fibres oblique across distal P1
· at proximal end, fibres are transverse across proximal P1
· tendons and lateral slips converge over dorsum of P2
· form terminal slip
· inserted into base of P3
· continuation of dorsal intertendinous fascia
· becomes firm at MC head
· bands envelop extensor tendons for 2 cm
· then pass volarward on either side of MCP jt
· insert into sides of volar plate
· strong narrow bands from P1 to extensor expansion
Oblique
· originate from near head of P1
· pass obliquely to lateral slips over P2
· near convergence to terminal slip
Transverse
· originate from near head of P1
· pass transversely to lateral slips over PIP jt
· fascial layer on dorsum of P2
· base is central slip attachment to P2
· sides are lateral bands
· apex is proximal edge of terminal slip