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A 16-year-old teenager presents to the office after sustaining a laceration to his left ring finger. He reports carrying a toilet when it broke in his hand. He sustained a laceration along the volar surface of the left ring finger. He can no longer bend the tip of his finger and has some numbness and tingling at the tip. On physical examination, an L-shaped laceration is observed over the volar aspect of the ring finger (Figure 1). He has very limited flexion of the proximal interphalangeal (PIP) joint and no active flexion of the distal interphalangeal (DIP) joint. Measurements show that a 2-point discrimination distal to the laceration is greater than 10 mm on the radial border and 8 mm on the ulnar border.
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Each finger has a digital nerve that runs on both the radial and ulnar borders, supplying sensation to their respective sides. Digital nerves provide discriminatory sensation that is critical for hand function and dexterity. Digital nerve injuries are often missed as clinicians may fail to perform simple tests required to make the diagnosis. Nerve injuries treated with surgical repair do better if treated early; therefore, making the correct diagnosis is critical.1,2
Two-point discrimination testing of the finger is used to determine if a digital nerve has been injured and requires repair. The American Society for Surgery of the Hand (ASSH) recommended values for 2-point discrimination (2PD) testing includes3:
- Normal: < 6 mm
- Far: 6 to 10 mm
- Poor: 11 to 15 mm
- Protective: >15 mm
Digital 2PD greater than 6 mm is highly predictive of a digital nerve injury. Microsurgical repair is performed within the first several days of injury to provide for optimal nerve regeneration.1,2 In this case, the patient has 2PD over 6 mm on both sides of his ring finger indicating a likely laceration through both digital nerves. He is unable to flex his DIP indicating a likely flexor digitorum profundus tendon laceration but can flex his PIP joint indicating an intact flexor digitorum superficialis tendon.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopedics for Physician Assistants.
References
1. Boesch CE, Medved F, Held M, Bender D, Schaller HE, Fuchsberger T. Analysis of the two-point discrimination test in daily routine practice. Eur J Plast Surg. 2017;40(4):333-336.
2. Mermans JF, Franssen BBGM, Serroyen J, Van der Hulst RR. Digital nerve injuries: a review of predictors of sensory recovery after microsurgical digital nerve repair. Hand (N Y). 2012;7(3):233-241. doi:10.1007/s11552-012-9433-1
3. American Society for Surgery of the Hand. The Hand, Examination and Diagnosis, 3rd edition. Churchill Livingstone; 1990.
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