Flexor Tendon Injuries - Hand (2023)

• rare

  • occurs in 4.83 per 100,000

• mechanism of injury

  • commonly results from volar lacerations and may have concomitant neurovascular injury

• pathophysiology

  • tendon healing

    • occurs via 2 pathways

      • intrinsic

        • produced by tenocytes within the tendon

      • extrinsic

        • stimulated by surrounding synovial fluid and inflammatory cells

        • implicated in the formation of scarring and adhesions

    • occurs in 3 phases

  • Phases of Tendon Healing
    Phase	Days	Histology	Strength
    Inflammatory	0-5	Cellular proliferation	None
    Fibroblastic	5-28	Fibroblastic proliferation with disorganized collagen	Increasing
    Remodeling	>28 days	Linear collagen organization	Will tolerate active range of motion

• flexor digitorum profundus (FDP)

  • functions as a flexor of the DIP joint

  • assists with PIP and MCP flexion

  • shares a common muscle belly in the forearm

  • has dual innervation

    • index and long fingers are innervated by the AIN of the median nerve

    • ring and small fingers are innervated by the ulnar nerve

• flexor digitorum superficialis (FDS)

  • functions as a flexor of the PIP joint

  • assists with MCP flexion

  • individual muscle bellies exist in the forearm

    • FDS to the small finger is absent in 25% of people

  • innervated by the median nerve

• flexor pollicis longus (FPL)

  • located within the carpal tunnel as the most radial structure

  • innervated by the AIN of the median nerve

• flexor carpi radialis (FCR)

  • primary wrist flexor

  • inserts on the base of the second metacarpal

  • closest flexor tendon to the median nerve

  • innervated by the median nerve

• flexor carpi ulnaris (FCU)

  • primary wrist flexor

  • inserts on the pisiform, hook of hamate, and the base of the 5th metacarpal

  • innervated by the ulnar nerve

• located at the level of the proximal phalanx where FDP splits FDS

Pulley system

• digits 2-5 contain

  • 5 annular pulleys (A1 to A5)

    • thicker and stiffer than cruciate pulleys

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    • A2 and A4 arise from the periosteum

      • most important pulleys to prevent flexor tendon bowstringing

    • A1, A3, and A5 arise from the volar plate

  • 3 cruciate pulleys (C1 to C3)

    • collapsible and flexible

      • allows the annular pulleys to approximate each other during digital flexion

• thumb contains

  • 3 annular pulleys (A1, Av, A2)

    • A2 contributes least to arc of motion of thumb

  • 1 interposed oblique pulley

    • most important pulley to prevent flexor tendon bowstringing (along with A1 pulley)

• 2 sources exist

  • diffusion through synovial sheaths

    • occurs when flexor tendons are located within a sheath

    • it is the more important source distal to the MCP joint

  • direct vascular perfusion

    • nourishes flexor tendons located outside of synovial sheaths

    • supplied by

      • vincular systemosseous bony insertions, reflected vessels from the tendon sheath, and longitudinal vessels from the palm

      • osseous bony insertionsreflected vessels from the tendon sheath, and longitudinal vessels from the palm

      • reflected vessels from the tendon sheath

      • longitudinal vessels from the palm

• loss of active flexion strength or motion of the involved digit(s)

• inspection

  • observe resting posture of the hand and assess the digital cascade

    • evidence of malalignment or malrotation may indicate an underlying fracture

  • assess skin integrity to help localize potential sites of tendon injury

  • look for evidence of traumatic arthrotomy

• motion

  • passive wrist flexion and extension allows for assessment of the tenodesis effect

    • normally wrist extension causes passive flexion of the digits at the MCP, PIP, and DIP joints

    • maintenance of extension at the PIP or DIP joints with wrist extension indicates flexor tendon discontinuity

  • active PIP and DIP flexion is tested in isolation for each digit

• neurovascular

  • important given the close proximity of flexor tendons to the digital neurovascular bundles

• may have associated fracture

• used to assess suspected lacerations

• wound care and early range of motion

  • indications

    • partial lacerations < 60% of tendon width

  • outcomes

    • may be associated with gap formation or triggering

• flexor tendon repair and controlled mobilization

  • indications

    • lacerations > 60% of tendon width

• flexor tendon reconstruction and intensive postoperative rehabilitation

  • indications

    • failed primary repair

    • chronic untreated injuries

• FDS4 transfer to thumb

  • single stage procedure

  • indications

    • chronic FPL rupture

• indications

  • > 75% laceration

  • ≥ 50-60% laceration with triggering

    • epitendinous suture at the laceration site is sufficient

    • no benefit of adding core suture

• fundamentals of repair

  • easy placement of sutures in the tendon

  • secure suture knots

  • smooth juncture of the tendon ends

  • minimal gapping at the repair site

  • minimal interference with tendon vascularity

  • sufficient strength throughout healing to permit application of early motion stress to the tendon

• timing of repair

  • perform repair within three weeks of injury (2 weeks is ideal)

    • delayed treatment leads to difficulty due to tendon retraction

• approach

  • incisions should always cross flexion creases transversely or obliquely to avoid contractures (never longitudinal)

  • meticulous atraumatic tendon handling minimizes adhesions

• technique

  • core sutures

    • # of suture strands that cross the repair site is more important than the number of grasping loops

      • linear relationship between strength of repair and # of sutures crossing repair

      • 4-6 strands provide adequate strength for early active motion

    • high-caliber suture material increases strength and stiffness and decreases gap formation

    • locking-loops decrease gap formation

    • ideal suture purchase is 10mm from cut edge

    • core sutures placed dorsally are stronger

  • circumferential epitendinous suture

    • improves tendon gliding by reducing the cross-sectional area

    • improves strength of repair (adds 20% to tensile strength)

    • allows for less gap formation (first step in repair failure)

    • simple running suture is recommended

      • produces less gliding resistance than other techniques

  • sheath repair

    • theoretically improves tendon nutrition through synovial pathway

    • controversial

      • clinical studies show no difference with or without sheath repair

      • most surgeons will repair if it is easy to do

  • pulley management

    • historically believed to be critical to preserve

      • A2pulleys in digits

      • A4 pulleys in digits

      • oblique pulley in thumb

    • however recent biomechanical studies have shown

      • 25% of A2can be incised with little resulting functional deficit

      • 100% of A4 can be incised with little resulting functional deficit

  • FDS repair

    • in zone 2 injuries, repair of one slip alone improves gliding

    • compared to repair of both slips

• outcomes

  • repair failure

    • tendon repairs are weakest between postoperative day 6 and 12

    • repair usually fails at suture knots

    • repair site gaps > 3mm are associated with an increased risk of repair failure

  • adhesion formation

    • increased risk with zone 2 injuries

Wide-awake flexor tendon repair

• anesthesia

  • performed under tumescent local anesthesia using lidocaine with epinephrine

    • dosing

      • usually epinephrine 1:100,000 and 7mg/kg lidocaine

      • from 1:400,000 to 1:1000 is safe

      • if < 50cc is needed

        • 1% lidocaine with 1:100,000 epi for a 70kg person

      • if 50-100cc is needed

        • dilute with saline (50:50) to get 0.5% lidocaine, 1:200,000 epi

      • if 100-200cc is needed for large fields (tendon transfer, spaghetti wrist)

        • dilute with 150cc saline to get 0.25% lidocaine and 1:400,000 epi

      • for longer surgery > 2 hours

        • add 10cc of 0.5% bupivacaine with 1:200,000 epi

    • location

      • proximal and middle phalanges, use 2ml

      • distal phalanx, use 1ml

      • palm, use 10-15ml

  • no tourniquet, no sedation

• 4 advantages

  • allows intraoperative assessment for repair gaps by getting awake patient to actively flex digit

  • reduces need for postop tenolysis by allowing intraoperative assessment of whether repair will fit through pulleys

    • allows on-the-spot debulking of bunched repairs

    • allows division of A4 pulley and venting (partial division) of A2 pulleys

  • allows repair of tendons inside tendon sheaths as patients can demonstrate that the inside of the sheath has not been inadvertently caught

  • facilitates postop early active motion

    • immobilize for 3 days

    • begin active midrange motion after day 3 (form a partial fist with 45 degree flexion at MP, PIP and DIP joints, or "half a fist 45/45/45 regime")

Flexor tendon reconstruction

• requirements

  • supple skin

  • sensate digit

  • adequate vascularity

  • full passive range of motion of adjacent joints

• techniques

  • single-stage procedures

    • only perform if the flexor sheath is pristine and the digit has full ROM

  • two-stage procedures

    • Hunter-Salisbury

      • Stage I - SR is placed to create a favorable tendon bed

      • Stage II (3-4 months) - SR is retrieved and a tendon graft is placed through the mesothelium-lined pseudosheath

        • pulvertaft weave proximally and end-to-end tenorrhaphy distally

    • Paneva-Holevich

      • Stage I

        • SR is placed in the flexor sheath, pulleys are reconstructed (as needed), and a loop between the proximal stumps of FDS and FDP is created in the palm

      • Stage II

        • SR is retrieved, FDS is cut proximally and reflected distally through the pseudosheath and either attached directly to FDP stump or secured with a button

      • advantages

        • graft (FDS) size is known at the time of silicone rod selection

          • less graft diameter-rod diameter mismatch

        • FDS graft is intrasynovial

          • fewer adhesions than extrasynovial grafts

        • relies on only 1 tenorrhaphy site (distal or proximal) to heal at any one time (vs. Hunter technique where 2 tennoprhaphy sites are healing simultaneously)

      • disadvantages

        • graft tensioning is at the distal end during stage II

          • the proximal end has already healed after stage I

  • graft selection

    • palmaris longus (absent in 15% of population)

      • most common

    • plantaris (absent in 19%)

      • indicated if longer graft is needed

    • extensor digitorum longus to 2nd-4th toes

    • extensor indicis proprius

    • flexor digitorum longus to 2nd toe

    • FDS

  • pulley reconstruction

    • one pulley should be reconstructed proximal and distal to each joint

    • pulley reconstruction should occur first if a tendon graft is being used

    • methods

      • belt loop method

      • FDS tail method

• outcomes

  • subsequent tenolysis is required more than 50% of the time

• indications

  • localized tendon adhesions with minimal to no joint contracture and full passive digital motion

  • may be required if a discrepancy between active and passive motion exists after therapy

• timing of procedure

  • wait for soft tissue stabilization (> 3 months) and full passive motion of all joints

• technique

  • careful technique to preserve A2 and A4 pulleys

• postoperative care

  • follow with extensive therapy

• especially in zone II

• leads to improved tendon healing biology

• limits restrictive adhesions and leads to increased tendon excursion

• Immobilization

  • indicated for children and non-compliant patients

  • casts/splints are applied with the wrist and MCP joints positioned in flexion and the IP joints in extension

• Early passive motion

  • Duran protocol

    • low force and low excursion

    • active finger extension with patient-assisted passive finger flexion and static splint

  • Kleinert protocol

    • low force and low excursion

    • active finger extension with dynamic splint-assisted passive finger flexion

  • Mayo synergistic splint

    • low force and high tendon excursion

    • adds active wrist motion which increases flexor tendon excursion the most

• Early active motion

  • moderate force and potentially high excursion

  • dorsal blocking splint limiting wrist extension

  • perform “place and hold” exercises with digits

• most common complication following flexor tendon repair

• higher risk with zone 2 injuries

• treatment

  • physical therapy

  • tenolysis

    • perform if 4-6 months after tendon repair and significant loss of excursion

Rerupture

• 15-25% rerupture rate

• treatment

  • if < 1cm of scar is present, resect the scar and perform primary repair

  • if > 1cm of scar is present, perform tendon graft

    • if the sheath is intact and allows passage of a pediatric urethral catheter or vascular dilator, perform primary tendon grafting

    • if the sheath is collapsed, place Hunter rod and perform staged grafting

• rates as high as 17%

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