Data from: Glenohumeral joint kinematics following clavicular fracture and repairs

Background. The purpose of this biomechanical study was to determine the
effect of shortened clavicle malunion on the center of rotation of the
glenohumeral (GH) joint, and the capacity of repair to restore baseline
kinematics. Methods. Six shoulders underwent automated abduction (ABD) and
abbreviated throwing motion (ATM) using a 7-DoF automated upper extremity
testing system in combination with an infrared motion capture system to
measure the center of rotation of the GH joint. ATM was defined as pure
lateral abduction and late cocking phase to the end of acceleration.
Torsos with intact clavicle underwent testing to establish baseline
kinematics. Then, the clavicles were subjected to midshaft fracture
followed by kinematics testing. The fractured clavicles underwent repairs
first by clavicle length restoration with plate fixation, and then by
wiring of fragments with a 2-cm overlap to simulate shortened malunion.
Kinematic testing was conducted after each repair technique. Center of
rotation of the GH joint was plotted across all axes to outline 3D motion
trajectory and area under the curve. Results. Throughout ABD, malunion
resulted in increased posterior and superior translation compared to
baseline. Plate fixation restored posterior and superior translations at
lower abduction angles but resulted in excess anterior and inferior
translation at overhead angles. Throughout ATM, all conditions were
significantly anterior and superior to baseline. Translation with malunion
was situated anterior to the fractured and ORIF conditions at lower angles
of external rotation. Plate fixation did not restore baseline
anteroposterior or superoinferior translation at any angle measured.
Conclusions. This study illustrates the complex interplay of the clavicle
and the GH joint. While abnormal clavicle alignment alters shoulder
motion, restoration of clavicle length does not necessarily restore GH
kinematics to baseline. Rehabilitation of the injured shoulder must
address the osseous injury and the dynamic forces of the shoulder girdle.