Background: Forearm fractures are common
injuries in both adults and children. Despite efforts to obtain
anatomical alignment, axial rotational malunions occur, resulting
in a decreased range of motion and a poor appearance. The objective
of this study was to quantify loss of forearm rotation after simulation
of ulnar malunions in supination and pronation.
Methods: Six fresh-frozen cadaveric upper extremities (mean
age at the time of death, 79.4 ± 2.8 years)
were used to quantify loss of forearm rotation after simulation
of axial rotational malunions of the ulna. First, maximum forearm
rotation in supination and pronation was measured at torques of
6.8, 13.6, and 20.4 kilograms-centimeter applied with use of a custom
jig. Following a midshaft ulnar osteotomy, a custom adjustable internal
fixation plate was used to simulate axial rotational malunions of
the ulna of 0, 15, 30, and 45 degrees in both directions. Measurements
in supination and pronation were then repeated at the prespecified
torques. Analysis of variance, with a p value of 0.05, was used
for statistical analysis.
Results: In all instances, a decrease in forearm
rotation after simulation of the ulnar rotational malunion was accompanied
by an increase in rotation in the opposite direction. Supination
and pronation were significantly influenced, whereas the total arc
of rotation was not affected by ulnar rotational malunion. At a
torque of 20.4 kilograms-centimeter, pronation malunions of 15,
30, and 45 degrees resulted in a mean loss of supination (and standard error
of the mean) of 5 ± 1, 11 ± 1,
and 20 ± 1 degrees, respectively, and supination
malunions of 15, 30, and 45 degrees resulted in a mean loss of pronation
of 4 ± 1, 10 ± 2,
and 18 ± 4 degrees, respectively. The ratio
of the simulated rotational malunion to the loss of motion was larger
Conclusions: Ulnar rotational malunions do not
lead to a significant change in the total arc of forearm rotation.
Instead, loss of motion in one direction is accompanied by increased
motion in the opposite direction. Even with a 45-degree ulnar rotational malunion,
forearm rotation decreases no more than 20 degrees.
Clinical Relevance: Ulnar rotational malunions
have less effect on forearm rotation than that reported after radial malunions.
This may be a consideration when treating forearm fractures or correcting
rotational malunion of the forearm.