4b. Identification of Elbow Joint Center

Locate the elbow joint axis of rotation for the rigid hinges with a pair of pointed outside calipers. The elbow joint center of rotation has been located when the calipers do not wobble mediolaterally. ^[1]

Process to Identify Elbow Joint Center

1. Initially place masking tape over the elbow joint locations. Ask the patient to flex and extend their elbow between 30-90` while holding the socket on the limb. Mark your hypothesized location for the joint center.
   • The elbow joint centers may or may not fall over the epicondyles. If the point moves in an arc as shown by (A), then the point must be moved posteriorly on the socket toward the true center of rotation. If the point moves in an arc, (B), then the point must be moved distally. If the point moves in the arc, (C) then the point must be moved anteriorly and proximally.

2.	Place the outside calipers on the center points so they are nearly parallel to the humerus. Hold the socket on the limb to avoid movement of the socket on the residual limb. Begin with the elbow flexed to 90` and the calipers nearly parallel to the humerus. Observe the movement of the calipers while the individual slowly extends his/her arm to approximately 30` and returns it to 90`. If the calipers move medially or laterally, the joint centers are too anterior or posterior
3	Observe the movement of the calipers while the individual slowly flexes his elbow to approximately 130`. Maintain the test socket on the limb with the opposite hand.
4	Change the direction of the calipers until they are perpendicular to the humerus. Ask the patient to again flex their arm between 30-90`. Observe the movement of the calipers. If the calipers move medially or laterally, the joint centers are too distal or proximal.