Tendon Injuries

Vijith Vijayasekaran

Extensonr tendons

Anatomy

Extensor apparatus is a likage system between the extrinsic and intrinsic systems and the interconnections compensate for certain deficits in function.

Extrinsic system

  • Muscle bellies arise in the forearm and enter the hand through six compartments formed by the extensor retinaculumwhich is a fibrous band that prevents bowstrining of the tendons
  • At the wrist the tendons are covered by a synovial sheath tha tdoes not extend in to the dorsal hand or fingers
  • All muscles inhave independent orrigon and function
  • EI and EDM usually ulnar and deep to EDC at the MCP jt
  • EDC to Little finger is absent in 50% cases. Whaen absent it is replaced by juncture tendindinum from the little finger.
  • The EDC tendons arise from a common muscle belly and thus have limited independent action.
  • The extrinsic tendons have four insertions:
  1. the MCP joint palmer plate through the sagittal band
  2. a tendinous insertion on the proximal phalanx
  3. insertion on middle phalanx
  4. insertion on the distal phalanx
  • The extrinsic tendons extensor tendons extend the MCP joints primarily and the interphalangeal joints secondarily

Intrinsic System

Composed of:

  1. 4 dorsal interossei (abductors)
  2. 3 palmer interossei (adductors)
  3. 4 lumbricals

The interossei tendons enter the hand dorsal to the intermetacarpal ligaments and lumbrical tendons pass volar to the intermetacarpal ligaments.

The tendons of the intrinsic muscles all join to form the lateral bands passing palmer to the axis of the MCP jt

The lateral bands join the extrinsic tendons proximal to the midpoint of the proximal phalanx and continue dorsal to the axis of proximal and distal interphalangeal joints.

The Intrinsic muscles flex the MCP jts and extend the IP joints

At the midportionof the proximal phalanx the central slip of the extensor mechanism trifurcates. Distal to this levelthereis an exchange from the central slipto the lateral bandsand from the lateral bands to the central slip. The central slip primarily attaches to the base of the middle phalanx but both components are capable of proximal and distal interphalangeal extension

Transverse retinacular ligaments – at the PIP jt the transverse retinacular ligaments maintain the position of the extensor mechanism and creates the limits on its dorsal palmerexcursion.

Oblique retinacular ligaments arise proximally from the middle third of the proximal phalanx and the A2 pulley and inserts into the lateral portion of the extensor tendon along the middle phalanx. When coursing palmer to the interphalangeal joint it helps stabilize the lateral bands

Its previously described function of mechanically linking simultaneous proximal and distal interphalangeal extension has been discounted.

The triangular ligaments connect the lateral bands over the dorsum of the middle phalanx, maintaining them in close proximity.

Excursion of extensor tendons over the fingers isles compared with the flexor tendons. At the pipjt excursion varies from 2 to 8 mm. This small excursion contributes to a system with a delicate balance between various components and once disturbed the deformities are progressive and restoration of balance is difficult.

Because components of linkage system may pass palmer to one joint and dorsal to next a deformity at one joint may cause reciprocal deformity at another joint

The extensor mechanism of the thumb isdifferent from that of the fingers in that each joint has an independent tendon for extension.

EPL – extends the IP joint

EPB – extends the MCP joint

ABL – extends the CMC joint

The intrinsic muscles of the thumb provide primarily rotational control but also contribute MCP flexion and IP extension.

Acute Injuries

More common than flexor tendon injuries

Excursion is less and thus preservation of length is more important

The type on of injury, deformity and surgical outcome are varied because structural and functional systems are different from tip to forearm.

Verdans Zones of injury – Four odd numbered zones overly each of the joints and four even numbered zones overly the intervening tendon segments and increasing in number from distal to proximal.

Zone I injuries (Mallet Finger)

Disruption of ext tendon over the distal interphalangeal joint produces characteristic flexion deformity jt

Maybe open or closed

More cmnly closed

Mechanism – sudden forced flexion of the DIP joint in an extended digit resulting in rupture of the ext tnedon or avulsion of the tendon with a bony fragment from its insertion.

When left untreated proximal retraction of the central slip may occur resulting in hyperext of thehPIP joint(swan – neck deformity)

Classification

Type I – closed with or without avulsion fracture.

Type II – Laceration at or proximal to the IP joint with loss of tendon continuity.

Type III; deep abrsion with loss of skin , subcutaneous cover and tensdon substance.

Type IV A - Transepiphyseal plate fractue in children

Type IV B – fracture of artic surface 20 – 50%

Type IV C -> 50% of articular surface with palmer subluxation of the distal phalanx.

Management

Splinting alone with the DIP joint in ext for 6 weeks followed by 2 weeks of night splinting. Splinting must be continuous.

In rare cases can use internal kwire cut of beneath the skin to enable pt to keep working. Keep wire in for 6 weeks and then nocte splint for 2 weeks

Open injuries may be treated with simple figure of 8 suture through the tendon or a roll type suture (dermatotenodesis) incorporating the skin and tendon In the same suture

Type IV A injuries (usually in kids is a result of transepiphy # and as ext mechanism is at to the basal epiphysis) closed reduction and splinting for 3-4 weeks

Type IV B when there is no palmar subluxation, splinting for 6 weeks with 2 weeks of night splinting

Type IVC with palmer subluxation of the distal phalanx is best managed operatively.

Zone 2 injuries (Middle Phalanx)

Usually secondary to laceration or crush injury rather than an a avulsion.

If < 50 % of tendon cut , the treatment involves routine wound care and splinting for 7 – 10 days followed by active motion.

Injuries involving > 50% should be repaired primarily and followed by 6 weeks of splinting.

Zone 3 injuries

(Boutonniere Deformity)

Caused by disruption of the central slip at the PIP jt.

Results in classic deformity with loss of extension at the PIP jt and hyperext ant the DIP jt.

Injury may be closed or open and central slip maybe avulsed with or without bony fragments.

The early injury associated with swelling , but no deformity . The Boutonnière deformity then develops gradually 10 – 14 days after initial injury.

Best assessed by splinting the finger in ext for few days and re-examining it after swelling subsides . Absent or weak ext of the PIP jt is a positive finding

Initial treatment for closed injury should be splinting the PIP jt in ext. The DIP, MCP and wrist joints are left free.

Duration: 4- 6 weeks with reapplication if deformity recurs

Surgical indication:

1)displaced avulsion fracture at the base of the middle phalanx

2)Axial and lateral instability of the PIP jt associated with loss of active and passive extension

3)failed non-operative treatment

Usual repair involves open reduction and passage of suture through the central tendon to secure it to the middle phalanx K-wire used to stabilize the PIP jt (for 10 – 14 days) followed by extension splint until signs of union

If central slip repair is not possible portion of the lateral bands can be sutured together to reconstruct the central slip. A flap maybe raised from the proximal portion of the central slip to restore active extension.

Zone 4 injuries (proximal phalanx)

Zone 4 injuries are usually partial and usually spare the lateral bands.

If no loss of extension in the IP jt repair is rarely required.

Splinting the ip joint in ext for 3-4 weeks without repair is equivalent to repair of the tendon with 5 0 nonabsorbable suture.

For complete lacerations primary repair should be performed followed by 6 weeks of splinting in ext

Zone 5 Injuries mcp joint

Mostly open and should be treated as human bite until proven otherwise.

The injury often occurs with the joint in flexion and thus the tendon injury is usually proximal to the dermal injury.

All structures should be repaired separately

The sagital bands should be repaired to prevent lateral migration of the ext dig communis tendon and the subsequent MCP ext loss.

Immobilization of the wrist in 30-45 degrees of extension and thee mcp joint in 20 – 30 degrees of flexion with the PIP joint free

Early dynamic splinting may also be used

Zone 6 Injuries (dorsal hand)

Diagnosis made by direct visualization as loss of fxn at the mcp joint may not occur ext forces may be transmitted through juncture tendinum.

Repair should be undertaken with core type sutures and splinting of the wrist and fingers for 4- 6 weeks.

If Edc tendon involved all fingers should be splinted.

If just proprius tendon the affected finger needs to be splinted with the wrist.

Early dynamic splinting may improve results

Zone 7 injuries (wrist)

Controversy exists as to whether excision of part of the retinaculum is necessary to prevent postoperative adhesions.

Important to preserve some portion of the retinaculam to prevent bowstringing

Zone 8 Injuries (dorsal forearm)

Multiple tendons may be injured in this area making it difficult to identify involved tendons. In this situation, restoration of independent wrist and thumb extensors should be given priority.

Difficulty may also be encountered with injuries at the musculotendinous junction because the fibrous septa retract into the substance of the muscle. When repairing the muscle bellies multiple figure 8 sutures are used with slowly absorbing materials. Static immobilization with wrist at 45deg ext and the MCp in 15-20 deg flex is maintained for 4-5 wks

Splinting of the elbow may also be beneficial

Flexor Tendon Injuries

Anatomy and Physiology

  • Extrinsic flexion of the fingers and the thumb is provided by the FDP, FDS, and the Fplmuscles.
  • In the distal third of the forearm the FDS tendons lie anterior to the FDP group with the middle and ring finger FDS tendons volar to those of the index finger and little finger.
  • As they exit from the carpal tunnel , the fds and fdp tendons pair off with the fds still volar.
  • At the level of the MCP jt the flexor tendons begin to course through the synovial lined fibroosseous tunnel known as the digital flexor sheath .
  • As the FDS enters the flexor sheath , it lies volar to the profundus. It flattens out and splits into two slips near the end of the A1 pulley. Theses slips diverge, pass around the profundus, and rejoin dorsal to it . This reconstitution is known as Campers chiasm. The fds the again splits into radial and ulnar slips that proceed to insert on to the middle phalanx, from the base to its mid portion
  • FDP enters the flexor sheath , the tendon initially lies dorsal and then travels through Campers chiasm to lie volar to the superficialis finally inserting into the proximal portion of the distal phalanx.
  • FDS to the little finger is the most variable with 34-42% of hands having some deficiency of the little finger FDS.
  • The tendon is absent in 23% of cases
  • Of patiens with deficient FDS 20% patients get some power transmitted from ring finger

Tendon sheath

  • Tendons in zone 3 and 5 are enveloped with paratenon - 2 layers of dense fibrous tissue separated from the tendon and each other by loose areolar tissue. This is sufficient to allow gliding in a straight line.
  • Where the tendons need to glide around a corner or a bend (zones 1, 2 & 4), a more sophisticated system is needed. This is the synovial sheath.
  • Digital flexor tendon sheath is composed of synovial and retinacular tissue components, which have separate and distinct functions.

Membranous synovial sheath

  • The membranous portion is a synovial tube that is sealed at both ends.
  • In the index, long, and ring fingers, the membranous portion of the sheath begins at the neck of the metacarpals and continues distally to end at the distal interphalangeal joint. In most instances, the small finger and thumb synovial sheaths continues proximally to end at the wrist.
  • Visceral and parietal synovial layers are identified.

Retinacular sheath

  • The retinacular (pulley) portion is a series of transverse, annular, and cruciform fibrous tissue condensations, which begin in the distal palm and end at the distal interphalangeal joint
  • Fingers have a palmar aponeurosis pulley, five annular pulleys and 3 Cruciate pulleys. The transverse carpal ligament can also be considered a pulley.
  • It is an uninterrupted synovial membrane, reinforced at the intervals by the pulley system and creates a synovial lined space. Any structure which enters the space is invested by a layer of visceral synovium.
  • The sheath has three important functions

1)Allows for smooth gliding – membranous portion

2)Retinacula reinforcing pulleys maintain the flexor tendons close to the volar surface of the phalanges preventing bowstringingthus promoting efficiency and economy in finger flexion

3)Provides an enclosed synovial fluid environment for tendon nutrition.

  • The thin part of the sheath does not load bear during flexion because the series of pulleys become approximated to form a continuous surface composed of strong fibrous bands.
  • The pulley system shortens in flexion by 38% in the fingers and 30 % in the thumb
  • Average lengths:
  • A1 – 8mm (may have indistinct border with A2)
  • A2 – 16mm
  • A3-3mm
  • A4-7mm
  • A5-4mm

Pulleys of the thumb

  • repair or reconstruction of either the A1 or oblique pulley after injury will restore normal thumb kinematics.

Biomechanics

Excursion

  • Excursion of muscle is the sum of the length the muscle can be stretched from its resting length plus the length it can contract from its resting state
  • Muscle fibers are known to shorten by approximately 40% with contraction and can be passively lengthened by approximately the same amount
  • Excursion is directly proportional to muscle fiber length
  • potential excursion is the resting fiber length of a muscle independent of connective tissue restraints, required excursion is the maximum excursion required of a muscle in situ, and available excursion is the maximum excursion of a muscle when freed from its insertion
  • mean excursion of 32 mm (range, 15–43 mm) for the flexor digitorum profundus (FDP) and of 24 mm (range, 14–37 mm) for the flexor digitorum superficialis (FDS). Wrist motion increased the excursion to 50 mm and 49 mm for the FDP and FDS, respectively
  • The active component of excursion must be understood to represent approximately ½ of total excursion.

Moment Arm

  • Moment arm is defined as the perpendicular distance between the joint axis of motion and the central longitudinal axis of the adjacent flexor tendon.
  • moment arm for metacarpophalangeal, 10 mm; proximal interphalangeal, 7.5 mm; and distal interphalangeal, 5 mm.

Radian

  • A radian (57%) is that distance on a circumference of a circle that is equal to the radius of that circle.
  • when a joint moves 57°, tendon excursion and moment arm are equal.
  • When the metacarpophalangeal joint moves through its normal range of 85°, it moves through an arc equal to 1.48 radian equivalents (85 divided by 57.29 = 1.48.)
  • moment arm of the metacarpophalangeal joint is 10 mm. Ten multiplied by 1.48 equals 14.8 mm, which is the required excursion of the flexor tendon to move the metacarpophalangeal joint through an arc of 85°
  • thus an increase in the moment arm attributable to absence or loss of integrity of a pulley can result in significant loss of function

Work of flexion

  • work of flexion that represents the resistance to gliding encountered by the tendon during flexion is a more comprehensive parameter.
  • more useful parameter to evaluate the multiple factors that are responsible for success or failure in the treatment of patients with flexor tendon injuries. This is because it measures intrinsic and extrinsic factors other than the mechanical status of the pulleys such as viscoelastic forces of the skin and subcutaneous tissues, tendon adhesions, joint stiffness, and incongruity between tendon and sheath to name a few.
  • Work of flexion increases:
  • A2 excised – 45%
  • A1 and A2 – 60%
  • A4 excised – 20%
  • A2 and A4 excised – 100%
  • A1, A2, A4 excised – 170%

Summary

  • Because excursion is not a limitless factor and is directly proportional to muscle fiber length, the effectiveness of tendon excursion is dependent on maintenance of the critical relationship between the pulleys and their respective joint axes.
  • An absent pulley results in an increased moment arm and requires increased tendon excursion to produce the same arc of motion.
  • Manske (J Orthop Res) - work of flexion(the area under the force-excursion curve, representing all the forces that resist tendon flexion) was affected to a greater degree by pulley loss than was tendon excursion, suggesting that it is a more sensitive measurement of tendon function. A2 was found to be the single most important pulley for flexor tendon function, followed by A4. However, both A2 and A4 had to be present if near-normal hand function was to be achieved; sacrificing the A1 pulley was not associated with a significant loss of flexion. The "pulley effect" of the skin and soft tissue as a supplement to the fibro-osseous pulleys in reducing tendon bow-stringing was also noted.
  • Excision of up to 25% may be acceptable either separately or in combination, without significant effects on angular rotation (Mitsionis J Hand Surg Am 1999)
  • Tendon bowstringing leads to loss of digital flexion and even a fixed flexion contracture. This fixed flexion contracture is attributable to the contractile nature of the scar tissue that builds up along the palmar aspect of the joint.
  • When bowstringing occurs, the angle of attack of the flexor tendon is increased, which causes greater forces on the pulleys and can lead to pulley elongation and additional bowstringing.
  • Effect of transverse carpal ligament section
  • 25% increase in the required excursion for the profundus and a 20% increase in excursion for the superficialis noted, but only in wrist flexion
  • May account for the weakened grip strength noted after carpal tunnel release
  • Palmar Aponeurosis
  • palmar aponeurosis pulley is formed by the transverse fibers of the palmar aponeurosis, which are anchored on each side of the synovial sheath by vertical fibers (of Legueu and Juvara) that attach to the deep transverse metacarpal ligament and thus form an archway over the flexor tendons.
  • Although the palmar aponeurosis pulley may be considered an accessory pulley, its preservation is warranted because it may provide some form of substitution if A1 or A2 pulleys are not present.
  • The palmar aponeurosis pulley is at risk during fasciectomy for Dupuytren’s disease. Transverse elements of the palmar fascia are not involved in Dupuytren’s disease and that these transverse fibers that form the roof of the palmar aponeurosis pulley may be preserved while the longitudinal and superficial diseased elements of the palmar fascia are removed.