Laboratory Studies
Laboratory studies are not typically necessary for the patient with an isolated interphalangeal joint dislocation. However, if management of the dislocation requires open reduction, general anesthesia, or anesthetic limb block, then preoperative laboratory studies may facilitate patient care. On occasion, therapeutic drug levels, cardiac studies, coagulation studies, or preoperative microbial studies may be required if the dislocation involves an open joint or concurrent soft tissue contamination.
Radiography
Edema, tenderness, or deformity at a joint or along the digit should prompt radiographic evaluation. Findings can be subtle; pain out of proportion to radiographic findings should heighten the physician’s suspicion for significant injury.
If radiographs are obtained and no identifiable fracture is visible, yet the patient remains in a significant amount of discomfort, an occult fracture may be present. Proper splinting and urgent referral may be indicated.
A child or adolescent with open growth plates who remains in pain even though radiographs reveal no fracture may have a growth plate injury. Proper splinting and urgent referral may be indicated.
The following views should be taken:
- Anteroposterior
- Lateral (to check the lateral radiograph for joint congruency or rotation)
- Oblique
- Stress views can be examined if ligamentous laxity is documented or suspected. (see image below)
- Postreduction images must follow even the most apparently routine reductions
Radiograph displaying a stress test of a torn ulnar collateral ligament.
In rare circumstances, computed tomography (CT) or magnetic resonance imaging (MRI) may be necessary to make a definitive diagnosis.[15]
Radiographs of the affected finger help further define the anatomy of the dislocation, rule out associated fractures, and assess the adequacy of reduction. For dorsal dislocations at the proximal interphalangeal (PIP) joint (see the images below), the initial radiographs are often obtained after reduction because the athlete, trainer, or coach commonly reduces the dislocation at the scene. If the finger is still dislocated when the radiographs are obtained, the middle phalanx may be hyperextended and often deviated to the ulnar side.
Acute dorsal proximal interphalangeal joint fracture-dislocation. 
Acute dorsal proximal interphalangeal fracture-dislocation. A concentric reduction could not be maintained in a splint. 
Dorsal thumb interphalangeal dislocation. 
Dorsal thumb interphalangeal dislocation. In a volar dislocation (see the image below), rotation may be noticeable on the lateral view. The head of the proximal phalanx lies in a different plane from that occupied by the base of the middle phalanx.
Volar proximal interphalangeal (PIP) joint dislocation. Common fractures to look for include avulsions and impacted fractures. Avulsions at the volar base of the middle phalanx (or the distal phalanx, in the case of distal interphalangeal [DIP] joint injury) from the volar plate may not affect the treatment plan if they are small. Larger fractures at this location make the injury a fracture-dislocation, which may be unstable in extension (see the image below).
Complex unstable fracture of the proximal phalanx. Avulsions at the dorsal base of the middle phalanx (or the distal phalanx, in the case of DIP joint injury) from the extensor tendon should prompt careful testing of extensor function and probably require splinting in extension; splinting in hyperextension should be avoided. Most central slip injuries, however, involve only soft tissue.
Impacted fractures of the joint surface are often best visualized on a true lateral view, allowing direct comparison of the radial and ulnar articular surfaces.
Key considerations in the radiographic assessment of reduction include the following:
- Congruence of the articular surfaces
- Absence of rotational deformity
- Fractures around the metacarpophalangeal (MCP) and carpometacarpal (CMC) joints
With respect to articular congruence, the head of the more proximal phalanx should form a U shape that fits symmetrically within the U shape of the base of the more distal phalanx. If the joint space is not equal throughout on both views, the examiner should be highly suspicious for persistent subluxation secondary to entrapment of soft-tissue structures within the joint.
A volar PIP dislocation in which the head of the proximal phalanx buttonholes between the central slip and the lateral band has a rotational component. This can be observed on the lateral view, where the radial and ulnar aspects of each joint surface would be superimposed.
To rule out fractures around the MCP and CMC joints, anteroposterior, lateral, and oblique views of the entire hand are indicated (see the images below). In the dorsal dislocation patterns, the oblique or lateral view reveals the dorsal prominence of the affected joint. Common fractures to look for include avulsion-type fractures of the metacarpal bases, associated with the CMC dislocation.
Displaced fourth and fifth metacarpal fractures, anteroposterior view. 
Displaced fourth and fifth metacarpal fractures, lateral view. 
Fourth and fifth metacarpal fractures, oblique view. 
Fourth and fifth metacarpal fractures after intramedullary pinning, anteroposterior view. 
Fourth and fifth metacarpals after intramedullary pinning, lateral view. The Breuerton view of the MCP joints may be useful. This view is taken with the fingers flat on the plate, the metacarpals at 65° of inclination to the fingers, and the tube at 15° from the ulnar side of the hand. The Breuerton view demonstrates the MCP bony surface.
Modified lateral views of the metacarpals are sometimes necessary because little of the shaft or head can be observed on a true lateral radiograph of the hand. To study the index and middle finger, the hand should be pronated 30° from the lateral. To study the ring and small fingers, the hand should be supinated 30° from the lateral.
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