Abstract
The purpose of this study was to determine the motion pattern of the Acromio-Clavicular (AC) joint in a normal shoulder with the use of the new 4 Dimensional CT scan.
From April 2010 till January 2011 fourteen healthy volunteers (4 female, 10 male)(mean age 42±11 years) with no previous history of shoulder complaints participated in this study. The 4D CT machine scans motion, allowing a 3D reconstruction of the shoulder joint and its movements. Patients were positioned supine with their arm elevated 90° in the sagittal plane. During the 7 seconds duration of the scan they adducted their arm at that level and then elevated their arm upwards resisted by the gantry for 4 seconds, in this way simulating the clinical Bell-van Riet test for AC pathology.
In the transverse plane the mean AC joint space measured in the neutral position is 1.8±0.5 mm. While adducting the arm the AC joint narrows 0.0±0.4 mm (with a positive value being narrowing and a negative value widening). On resisted elevation the joint space is narrowed 0.2±0.6 mm. The mean antero-posterior (AP) translation in this same plane is 0.2±2.2 mm on adduction (with a positive value being posterior translation of the clavicle and a negative value anterior translation) and 0.4±2.9 mm on resisted elevation.
The new 4D CT scan demonstrates that the AC joint in a normal shoulder mainly translates in an AP direction, rather than being narrowed or widened, when the arm is adducted (with or without resisted active elevation).
