Cite This Article

Coss, J. Denq, W. Tomesch, A. Cutting Edge Blade Encounters: A Review on Hand Anatomy. Ortho Pearls. August 21, 2024; Available: https://www.orthoempearls.com/articles/cutting-edge-blade-encounters-a-review-on-hand-anatomy

What is the diagnosis?

Complex Hand Injury: 

-Lacerations to the flexor digitorum superficialis (FDS), flexor pollicis longus (FPL) and the flexor carpi radialis (FCR)

-Median nerve laceration

-Fractures to the scaphoid tubercle and trapezium

• Pearl:  Approximately 20% of all visits to the hospital emergency room involve injuries to the hand. 1 The dominant hand is affected more often than the non-dominant hand and is usually injured when using a sharp object or catching a falling object. 2

What is the mechanism of injury?

In this case the injury was obvious with the history of the hand sustaining trauma from a saw during a woodworking related injury. Flexor tendon injuries can occur secondary to a sharp object (i.e., glass or knife) or result from blunt trauma in strength-based sports (i.e., football, basketball, wrestling), these typically occur at tendinous attachments to the bone.  In developed and industrialized countries, flexor tendon injuries may occur more commonly following workplace accidents. In contrast, regions of lower socioeconomic levels see flexor tendon injuries resulting from knife or glass incisions secondary to quarrels. 1

What physical exam findings are expected?

In this case in particular a thorough evaluation of the integumentary, musculoskeletal, vascular and neurological systems is paramount as damage to each is expected.

In regard to vascular supply: decreased capillary refill would be expected if significant vascular injury was sustained.

In regard to musculoskeletal and neurologic: decreased ability in range of motion/motor ability secondary to either musculoskeletal trauma versus neurological injury of the median nerve would be suspected.

• Flexor Digitorum Superficialis (FDS) → Flexor of proximal interphalangeal joint (PIP) joint, assists with the metacarpophalangeal (MCP) flexion. Innervated by median nerve and the individual muscle belly exists in the forearm. 

• Flexor Pollicis Longus (FPL) → Located within the carpal tunnel as the most radial structure. Innervated by the anterior interosseous nerve (AIN) of the median nerve 

• Flexor Carpi Radialis (FCR) → Primary wrist flexor and is the closest flexor tendon to the median nerve, inserts on the base of the second metacarpal. Innervated by the median nerve. 

In regard to integumentary: evaluation of the skin and wound for foreign bodies or other abnormalities is needed.

• Pearl:The median nerve can be evaluated by testing palmar abduction of the thumb (recurrent motor branch), and testing strength of the “OK” sign (anterior interosseous branch). 

Which imaging modalities can be used?

In the ED multiple imaging studies can be utilized. Obtaining anterior-posterior/lateral/oblique radiographs to rule out fractures or retained foreign bodies is a useful adjunct to primary history and physical examination. When the continuity of a flexor tendon is in question or to assess a suspected partial laceration, an ultrasound can be considered, as expertise allows [3]. When concern for significant neurovascular trauma to a limb cross sectional CT imaging with or without contrast can be utilized, in this case the patient fortunately had no clinical signs of significant vascular injury thus CT was not obtained. 

Image 2. Plain radiographs of the left hand. Author’s own images. Arrows indicate a small associated fracture.

What is the management in the ED?

In the ED the appropriate management includes full evaluation of the wound as above including a detailed physical exam. Pain control with IV medications, local anesthetic and dedicated nerve blocks assist in evaluation, washout and repair. Tetanus should be updated if the patient is due. For open fractures IV antibiotics and a course of oral antibiotics are given. After laceration repair, a splint can be placed – consider thumb spica.

• Pearl: Evaluation should be completed prior to administration of local anesthesia or sedation to accurately detect any potential neurological or vascular injury.

When do you consult Orthopedics?

Orthopedics/Hand Surgery should be consulted in the ED if available, or urgent outpatient follow-up should be coordinated. Primary repair should occur within 12 hours, and secondary repair of flexor tendon injuries can occur up to 4 weeks after injury.