This is Barry Bellosis, one of the musculoskeletal radiology fellows at Stanford University. 17 year old male with left dorsolateral wrist pain after a collision injury and fall on an outstretched hand. Concerned for perilunate dislocation. The patient in this case presented with this wrist radiograph. In here, we can see that there is molar dislocation of the lunate with loss of alignment to the radius and also the capitate. Here in our frontal view, we can see that we lost the second arc which we will talk about and also a suspicious fracture at the waist of the scaphoid right here. The normal arcs that we talked about in the wrists are the gluteal tricarpal arcs. So the first arc outlines the proximal convexities of the scaphoid from here all the way to the lunate and then to the tricretrium. The second arc outlines the distal concave surfaces of the same bone. So from here and all the way to the tricretrium. The third arc on the other hand outlines the main proximal curvatures of the capitate which is here and also the hamate which is right here. We use this arc to evaluate for any incongruency that could suggest dislocation. One thing that we talked about is the perilunate versus the lunate dislocation. Both are in the same spectrum of ligamentous injury. Here on our perilunate dislocation, we can see we lost the arc and also have like this piece of pi sign. Additionally on our lateral radiograph, we can see that the lunate is in alignment with the radius. However, the distal carpal row such as our capitate is dorsally dislocated. This is consistent with perilunate dislocation. On the other hand here on the different patient, we can see again, we lost the normal proximal carpal arc right here, and then we have the piece of pi sign again. However, we see that the lunate lost its alignment with the radius whereas the capitate remains in alignment. So this is a lunate dislocation where the lunate volarly subluxed because of a ligamentous injury. Additionally, we can see this fracture is associated with this dislocation involving the radius and the tracheotrum. CT without contrast can be used to evaluate for cold fractures associated with this dislocation. For example in this patient, we do see the fracture here in the tracheotrum and the distal rages which we can also see here on CT. However, in some cases fractures may be a cold and rager graph and if there is concern then CT without contrast should be pursued.

2nd Edition, CASE 17

2nd Edition

Hand and Wrist

perilunate dislocation

wrist injury

lunate dislocation

radiograph

CT scan