A patient presents with a laceration to the flexor side of her left forefinger. The student tells you function was normal.

“How did you determine that?” you ask.

“Range of motion.”

You ask the patient to repeat the range of motion test, but this time you apply active resistance and simultaneously check the opposite side for comparison. There is significant weakness on the left compared to the right. You just discovered a partial tendon laceration and prevented an easy misdiagnosis.

Range of motion is not sufficient to rule out a partial tendon laceration. Strength testing picks up partial lacerations because some of the muscle fibers were connected to the part of the tendon that was lacerated. You can’t always visualize the laceration so this strength testing a useful part of the examination.

There are some interesting articles about this that indicate range of motion can not even be used to rule out a complete tendon laceration. A patient had complete transection of the FDS and FDP yet intact range of motion via the vincula (connections between tendons). Resisted range of motion made the diagnosis (Sasaki J Hand Surg Br 1987)

Take Home Points:

-For suspected tendon laceration, don’t just test range of motion, test resisted range of motion