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FLEXOR TENDON

Anatomy and Physiology

  • Comprise of collagen fibrils (85% type 1 collagen) arranged in parallel fibres

  • Organised into fascicles surrounded by endotenon, which permits gliding between fibrils

  • The epitenon covers the outer surface and allows gliding within the sheath

  • Blood supply:

    • Vessels entering through musculotendinous junction, the bone insertion​s of the tendon and at certain points through the mesotendon via vinculae

    • Diffusion through synovial fluid

  • Flexor tendon zones:​

    • Zone 1 - Distal to FDS insertion​

    • Zone 2 - Between FDS insertion and proximal edge of A1 pulley

    • Zone 3 - Between proximal edge of A1 pulley to distal edge of transverse carpal ligament

    • Zone 4- Deep to transverse carpal ligament

    • Zone 5 - Proximal to transverse carpal ligament

Anatomy and Physiology
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Tendon healing

  • Three phases of tendon healing

    • Inflammation​ (first week) - cell proliferation and clean up

    • Proliferation (week 2-4) - fibroblasts and capillary buds migrate in and produce random collagen

    • Remodelling (months 2-6) - longitudinal organisation of collagen fibres in line with stress

  • Tendons with paratenon​

    • Fibroblasts and capillary buds migrate into the injured area​

  • Tendons with synovial sheath (controversial)

    • Extrinsic - fibroblasts migrate from the sheath into the injured site (also form adhesions)​

    • Intrinsic - tenocytes migrate across closely approximated ends and heal with nutrients from synovial fluid

Clinical findings

  • Test individual tendon function

  • Each FDS and FDP must be assessed while blocking movement of adjacent digits​

  • The FDP is examined by blocking PIP flexion in each digit (each FDP tendon has an independent muscle belly)

  • The FDS is examined by preventing flexion of the other digits (all FDS tendons share a common muscle belly)

  • Normal variants​

  • FDS tendon for little finger is absent in 15% of population​

  • Linburg's syndrome: Adhesions between FPL tendon and index finger FDP tendon within carpal tunnel cause the index finger to flex with flexion of the thumb IPJ (in 30% of the population)

Tendon healing
Clinical findings
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General considerations

  • Loupe magnification

  • Theatre environment

  • Incisions to maintain viability of skin flaps, permit wide exposure, prohibit formation of scar contractures - mid-lateral, Bruner or combination

  • Ideal characteristics of flexor tendon repair

    • ​Easy suture placement

    • Secure knots

    • Smooth opposition of tendon ends with no bulge

    • Minimal gapping potential

    • Minimal compromise of tendon vascularity

    • Strong enough to tolerate early active movement postoperative therapy regimens

  • Preserve pulleys​ to prevent bowstringing

    • Thumb ​- oblique pulley

    • Digits - A2 and A4 pulleys

    • Pulley repair controversial

  • Core sutures​

    • Strength of repair is proportional to number of strands crossing the repair​

    • Small grasping  sutures avoid pullout

    • Knots buried in repair site assist in  smooth gliding

  • Tensile strength-time relationship​

    • Weakest 7-10 days after repair - re-rupture most common 10 days after repair​

    • Most strength returned at 4-6 weeks after repair

    • Maximal strength at 6 months after repair

General considerations
Primary repair

Primary repair

  • If condition of soft tissue allows, perform primary repair within several days

    • Increased adhesions after 1 week​

    • Muscle contraction interferes with primary repair after 3 weeks

  • Core sutures (3-0 or 4-0 Prolene or Ethilon):

    • 2-core Modified Kessler​

    • 4-core Adelaide repair

  • Epitendinous sutures to reduce gapping between tendons and increase tendon strength by approximately 40% (5-0 or 6-0 Prolene or Ethilon):

    • Continuous running epitendinous​

    • Silfverskiold cross stitch

    • Horizontal mattress

  • Anchor suture/ button technique for zone 1 FDP injuries with insu​fficient tendon distally for repair

  • Splinting in POP or thermoplastic splint

    • All fingers even if single digit injury, except thumb which can be splinted ​alone

    • Dorsal extension blocking splint from proximal forearm to fingertips

      • Wrist - neutral to slight extension​

      • MCPJ - 70-90* flexion

      • IPJs - position at rest

Postoperative therapy
Complications
Delayed reconstruction

Postoperative therapy

  • Early controlled motion prevents adhesions and improves healing and stranght of tendon repairs

  • Requires cooperative patient and close interaction with surgeon and hand therapist

  • Small children or non-compliant patients may require elbow splint to prevent splint removal

Complications

  • Infection

  • Rupture of repair

  • Contracture

  • Pathological scarring

  • Damage to digital nerves or arteries

  • Complex regional pain syndrome

Delayed reconstruction

  • 1-stage reconstruction with tendon graft

    • Only if flexor sheath is intact and full passive motion is present​

  • 2-stage reconstruction​

    • After soft tissues are quiet​

    • 1st stage - temporary silicone implant (Hunter rod) to create a tunnel for the graft

    • 2nd stage (wait at least 2-3 months) - exchange rod for tendon graft (from palmaris longus, extensor digitorum longus, plantaris)

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