Neurovascular injury is a potential complication of fractures
of the forearm or elbow in both adults and children1-5. The prevalence
of nerve injury after supracondylar humeral fractures is reported
to range from 6 to 16 percent1,2,5.
Evaluation of nerve injuries in a number of series will probably
show that the anterior interosseous nerve is the most frequently
injured2. The standard test of
anterior interosseous nerve function is to ask the patient to put
the thumb and index finger together to form a circle. If the anterior
interosseous nerve is damaged, the flexor pollicis longus and flexor
digitorum profundus cannot flex the interphalangeal joint of the thumb
and the distal interphalangeal joint of the index finger4. However, this sign is not so straightforward
in a young child, who might not flex the joint because of pain,
apprehension, or inability to understand the instructions.
Over a nine-month period, six children between the ages of five
years and ten months and eight years (average age, six years and
eight months) had neurological motor loss after a type-III supracondylar
fracture of the humerus. During examination, the senior author (S.
T. C.) asked the children to flex the distal interphalangeal joint
of the index finger of the involved extremity and noted that five
of the six children used the contralateral hand to passively flex
the finger (Fig. 1).
Four continued to do so during follow-up examinations. The neurological
deficit slowly resolved in four of the five children who had exhibited
the passive flexion sign; after return of nerve function, they no
longer used the contralateral hand to flex the digit. The fifth
child, who had persistent nerve palsy, continued to do so.
To determine if this passive flexion sign might be present in
children without a neurological deficit because of cast wear or
other factors, 100 children between the ages of one and fourteen years
(average age, seven years) who had a forearm or elbow fracture without
neurological injury were asked to flex the index finger of the involved
extremity. None used the contralateral hand for passive flexion.
We believe that this simple test is diagnostically useful because
it demonstrates that (1) the child understands the instructions;
(2) movement of the digit is not painful, making a compartment syndrome
unlikely; and (3) the child cannot actively flex the digit, indicating
that the anterior interosseous nerve probably is injured. A similar test
of extrinsic thumb flexor function would probably be as reliable,
but we have used index finger flexion because it seems easier to
explain to young patients.
Although our patient sample was small, and this sign was not
exhibited by every child with a neurological deficit, it appears
to be a simple screening tool for neurological injury. We found no
false-positive signs in the 100 children without a neurological
deficit.
Careful observation of a patient is the most important diagnostic
tool at a physician's disposal. This is especially true for children
because it often is difficult to determine whether their failure to
respond to instructions is due to an inability to understand or
to a physical inability to respond. The simple passive flexion sign
seems to be fairly sensitive (only one false-negative result in
our six patients) and very specific (no false-positive results in
100 patients) for anterior interosseous nerve injury in children.
However, other median nerve injury patterns might produce the passive flexion
sign, and false-positive signs of anterior interosseous nerve injury
might be found in a larger group of patients.
We believe that the passive flexion sign is a simple, fast,
and useful screening test for anterior interosseous nerve injury.
A positive finding should indicate the need for a more thorough neurovascular
examination of children with an elbow or forearm fracture.
S. Terry Canale, M.D.
James H. Beaty, M.D.
William C. Warner, Jr., M.D.
R. Scott Sharp, M.D.
Campbell Foundation
910 Madison Avenue, Suite 500
Memphis, Tennessee 38103