Welcome to Leg Day #2 of the SplintER Series. Following up with the Leg Day #1’s primer on tibial plateau fractures, another key orthopedic injury of the leg is hip dislocation. A hip dislocation occurs when there is separation of the head of the femur from the acetabulum of the pelvis in either an anterior or posterior direction.1
What structures are at risk?
Hip dislocations are true orthopedic emergencies and should be reduced expediently. Disruption of the femoral neurovascular bundle and blood supply to the femoral head places patients with hip dislocation at risk for femoral head avascular necrosis (AVN).1,2 This principle underlies the required urgency of reduction. Patients with a delay in hip reduction of >6 hours have a much higher relative risk of AVN (4.8% vs 52.9%).2
The sciatic nerve may also be injured during posterior dislocations in 8-20% of cases.3 Delayed reduction is associated with an increased relative risk of sciatic injury.4 The sciatic nerve originates from L4-S3 and can be tested by assessing foot sensation as well as motor function with ankle plantar and dorsiflexion.
The joint surfaces are also commonly affected in hip dislocations. Post-traumatic arthritis is a phenomenon that occurs in up to 20% of patients following a single traumatic dislocation and can be a source of chronic pain.3,4
How are hip dislocations classified?
Hip dislocations can be classified in 2 principal ways. Firstly and most intuitively, anatomical classification divides hip dislocations into anterior and posterior.
- Posterior dislocations are by far the most common and account for 90% of cases.1 These typically occur with the hip in flexion and adduction, such as secondary to a dashboard injury during a high energy motor vehicle collision (MVC) or after fall from a significant height.
- Anterior dislocations are rare, accounting for only 10% of all hip dislocations.1,3 These result from forced abduction with external rotation of the thigh and often related to a motor vehicle accident or fall. They can also be caused by significant posterior trauma to the hip joint.1
Hip dislocations can also be classified according to their complexity and associated injuries. Given the high-energy mechanism commonly required to dislocate the hip, these injuries have a high rate of concomitant lesions including femoral neck and acetabular fractures. This is reflected in Stewart and Milford’s classification system (Table 1).5,6 Of note, patients with an artificial hip or hip arthroplasty often dislocate from benign mechanisms such as deep sitting with the hips flexed above 90° – such as getting up from a low toilet.
|Table 1. Stewart and Milford’s classification system for hip dislocation|
|I||No acetabular fracture or only a minor chip|
|II||Posterior rim fracture that is stable after reduction|
|III||Posterior rim fracture with instability after reduction|
|IV||Dislocation accompanied by fracture of femoral head or neck|
How should I evaluate a suspected hip dislocation?
An anterior dislocation most often presents with a flexed, abducted, and externally rotated. In contrast, a posterior dislocation most often results in the extremity positioned a flexed, adducted, and internally rotated fashion.
Pulses and peripheral perfusion should be assessed. From a neurological perspective, focus on sciatic nerve function. This can be done by assessing dorsiflexion of foot or great toe (deep peroneal nerve). Femoral nerve injury infrequently occurs with anterior dislocation. Motor function of the femoral nerve is difficult to assess given the patients typical pain level and mal-positioning of the hip; however, a sensory deficit over the anteromedial thigh should raise suspicion.5
The entire leg
Be sure to pay particular attention to ipsilateral joints and bones since a large force is transmitted through the lower extremity to cause the dislocation. Knee and patellar fractures are common concomitant injuries.7 Also remember that ligamentous injuries, classically the posterior cruciate ligament (PCL), is commonly associated with dashboard injuries.
What imaging should I order?
Plain film radiography
Most hip dislocations will be evident on a standard AP film of the pelvis.1,3 Loss of articulation of the femoral head with the acetabulum and disruption of Shenton’s line [Radiopaedia.org] are usually seen. Confirmation of anatomical direction of displacement of femoral head (anterior vs posterior) can be established with a cross table lateral view of the hip.3
Normally, both femoral heads should routinely appear the same size. In an anterior dislocation, the dislocated femoral head may appear larger than the contralateral side. The opposite is true in posterior dislocation. The joint space should be examined for bony fragments, widening, or evidence of an effusion.
Remember to obtain at least an AP film of the pelvis post-reduction to confirm successful relocation of the hip joint.
CT scans of the abdomen and pelvis are routinely obtained on major trauma patients. If a CT abdomen/pelvis scan is being performed, the hip should be examined for pathology. However, it is paramount that a dedicated CT scan of the hip does not delay the reduction.
CT scan imaging is generally recommended after all successful, closed hip reductions to evaluate for femoral head fractures, acetabular fractures, and loose bodies. CT is also recommended when closed reduction fails in the ED, because it may identify bone fragments or soft tissue abnormalities that both explain the inability to perform a closed reduction and assist in operative planning.3
MRI is not routinely recommended.
How should I manage it?
The key is to perform an emergent closed reduction as soon as possible to minimize risks of such complications as AVN of the femoral head. Procedural sedation with adequate analgesia, muscle relaxation, and sedation is of paramount importance to success. Various closed reduction techniques are available, including the Captain Morgan technique, the Allis maneuver, and the Bigelow maneuver.1
Captain Morgan technique
First described in Annals of Emergency Medicine in 2011 based on the character on a spirit bottle, this technique has the patient lie supine with an assistant stabilizing the pelvis on the bed. If you do not have an assistant, you can strap the pelvis to the backboard for stabilization.
Place your foot on the patient’s bed with your knee flexed and positioned behind the patient’s knee. Place your hand/forearm under the patient’s distal thigh with your other hand over the patient’s ankle. Upward force to the hip is generated by the your knee while your hand on the ankle maintains a gentle, consistent downward force. Keep in mind that the majority of force should be created with your calf rising upwards and not with the downward force of your hand. This leverages the hip back into place.8
Allis and Bigelow maneuvers
These apply similar mechanical principles and forces, namely manual in-line traction with evolving hip extension and a degree of external rotation. For both, the patient lies supine on the bed with the provider standing alongside him/her with an assistant stabilizing the pelvis.
In the Allis maneuver, the provider holds the affected leg just below the knee which should be flexed to 90 degrees. Traction is applied in line with the femur. As the hip begins to reduce, gradually extend and externally rotate the hip to facilitate reduction.
For the Bigelow maneuver, the provider’s forearm is placed behind the knee and second hand on the patient’s ankle. In-line traction is applied with the hip flexed to 90 degrees. Gradually abduct, externally rotate, and extend the hip until it is reduced.1,3,5,7
When should I consult orthopedic surgery?
At most institutions, orthopedic surgery is consulted if:1,5,7
- The ED team is unable to reduce the hip joint
- The patient presents in delayed fashion (>6 hours)
- There are associated fractures, incarcerated fragments, or persistent neurovascular deficit after your reduction
Expert Commentary: Dr. Kori Hudson
Hip dislocations can pose a challenge to the emergency physician in clinical practice, especially those in smaller departments and those who practice in single coverage. As noted above, prompt recognition and reduction are paramount. Adequate relaxation and procedural sedation are often required. And, as with all procedures, appropriate preparation, having all required equipment, personnel, and a plan in place for a primary reduction technique and a back-up plan should be prepared before starting the procedure.
Once the joint has been reduced, radiographs should be obtained to confirm reduction, and a knee immobilizer can be used to help reduce the likelihood of repeat dislocation. The knee immobilizer may seem counter-intuitive, and evidence for their use is somewhat limited. The thought is that the immobilizer helps not only limit flexion of the knee, but also limits flexion of the hip. Abduction pillows or so-called wedge pillows may also be used at night to limit adduction and internal rotation of the hip. The patient can be discharged with the knee immobilizer +/- abduction pillow, and assuming no other fractures or associated injuries, the patient may go home with crutches or a walker for toe-touch weight bearing until they follow up with an orthopedist.
Thumbnail image credit:
- Hip dislocation xray: Posterior hip dislocation by James Heilman, MD – Own work, CC BY-SA 3.0.