HSS Ultrasound of the Month Case #88

Clinical History A 55 year old left handed woman presents with a left index finger laceration sustained while pitting an avocado.

On exam, the patient demonstrated decreased ability to flex at the proximal interphalangeal joint.

Clinical concern was for tendon laceration.

Left index finger ultrasound evaluation was requested.

Ultrasound of the Month – Case 88

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Diagnosis Flexor digitorum superficialis tendon transection

Operative Findings & Management Complete full thickness tear of the left index FDS tendon.

Partial laceration of the FDP tendon.

Left index finger FDS laceration repair.

Left index finger partial FDP laceration repair.

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Discussion Penetrating injury to the palmar aspect of the finger most frequently results from knife wounds or broken glass.

Open lesions may lead to injury of several flexor tendons and may be associated with concomitant vascular and/or nervous injury.

Injury to the flexor digitorum superficialis (FDS) tendon is more common than injury to the flexor digitorum profundus (FDP) tendon due to the more vulnerable superficial location of the FDS. Flexor tendon injuries are categorized into five topographic zones: • Zone I: From the distal insertion of the FDP on the distal phalanx to the distal insertion of the FDS on the middle phalanx • Zone II: From the distal insertion of the FDS to the A1 pulley • Zone III: From the A1 pulley to the distal aspect of the carpal tunnel • Zone IV: Comprised of the flexor tendons within the carpal tunnel • Zone V: From the proximal aspect of the carpal tunnel to the flexor tendon musculotendinous junction

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Discussion - continued Lacerations usually affect the mid-substance of the tendon as opposed to its insertion site.

Zone II lacerations occur most frequently and are associated with a high rate of adhesions, as well as tendon entrapment or triggering.

Zone III, IV and V lacerations tend to also involve the adjacent neurovascular structures and lumbrical muscles.

Sonographic findings indicative of flexor tendon injury include focal disruption of the fibrillar tendon, unsynchronized movement of the torn proximal and distal tendon stumps with dynamic maneuvers, as well as associated tenosynovial effusion.

Dynamic ultrasound can help increase the conspicuity of a complete tendon tear, determine the size of the tendon gap and indicate the amount of tendon retraction.

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Discussion - continued Ultrasound may also be utilized to detect concomitant interdigital nerve injury, which may be evidenced by focal nerve interruption acutely or hypoechoic fusiform thickening/neuroma formation in the more subacute-chronic phase of injury.

Early diagnosis of tendon injury is crucial, as sonographic evaluation, as well as tendon repair, become more challenging following the development of adhesions and fibrosis, which may occur within one to two weeks of the injury.

Complete lacerations necessitate surgical intervention, while partial tendon tears can be treated conservatively.

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