Reduction of Posterior Hip Dislocation

Hip dislocations, regardless of their etiology, are orthopedic emergencies that require immediate diagnosis, evaluation, and treatment.[1, 2] The adult hip joint is remarkably stable. It is reinforced with thick capsular and labral structures. The presence of a dislocation injury indicates a large force from a traumatic mechanism (a traction force ≥90 lb [~40 kg]) or the existence of underlying pathology leading to inherent instability of the joint. Posterior dislocations make up 80-95% of traumatic hip dislocations.

In the presence of a large force injury, Advanced Trauma Life Support (ATLS) measures may have to be initiated in the initial assessment of the patient. Pediatric hip dislocations may occur with smaller amounts of force[3] and have been documented after gymnastic maneuvers and falls from standing. Elderly patients or those with Ehlers-Danlos syndrome or Down syndrome are also more likely to dislocate a hip with smaller amounts of traumatic force.

Posterior traumatic hip dislocations occur when the force acts with adduction, internal rotation, and some degree of flexion of the hip. The incidence of this injury has increased as a consequence of high-velocity motor vehicle use.[2] Injuries in which the front-seat passengers are involved in a head-on collision that drives the dashboard into their lower extremities (ie, dashboard injuries) have become a notorious cause of posterior traumatic hip displacement. This mechanism of injury is associated with an incidence of simultaneous severe knee injury in 26% of patients, including patellar fractures in 4% of patients.

The increasing popularity of extreme sports has also led to an increase in hip dislocations. One study showed that snowboarders are more likely than skiers to experience hip dislocations.[4] The difficulty in detecting a knee injury in a patient who has a dislocated hip underscores the need for the clinician to maintain a high index of suspicion for multiple lower-extremity injuries (eg, acetabular and femoral head, neck, or shaft fractures) as well as occult visceral damage. A review by Onche et al highlighted the high rate of other extremity injuries associated with hip dislocations.[5]

Posterior hip dislocations are also seen after total hip arthroplasty. Relatively minor forces, such as flexing the hip to pick an item up from the floor, can result in postoperative hip dislocation. Several studies[6, 7]  have indicated that slight alterations in surgical technique (eg, slightly larger femoral head and slightly less acetabular component anteversion) may decrease postoperative dislocation rates.

Multiple studies have demonstrated that the ultimate morbidity increases as the time interval from injury to reduction increases.[8, 9] Complications such as osteonecrosis of the femoral head, arthritic degeneration of the hip joint, and long-term neurologic sequelae become more likely as reduction is delayed. Whereas the goal is to perform an adequate reduction as quickly as possible, careful prereduction evaluation must be performed to properly diagnose the injury. If adequate closed reduction cannot be attained or if a nerve palsy becomes apparent after closed reduction is achieved, emergency operative reduction is required.

Closed reduction is indicated in the following scenarios:

• Emergency closed reduction for traumatic hip dislocation - Closed reduction is indicated for a dislocation with or without neurologic deficit when no associated fracture is present, as well as for a dislocation with an associated fracture if neurologic deficits are not present
• Closed reduction attempt before open surgical reduction for traumatic hip dislocation - Open surgical reduction is usually required for a hip dislocation with an associated fracture and neurologic deficits (the displaced fracture fragment is most likely compressing the nerve); if emergency open reduction is not possible, an attempt to decompress the nerve with closed reduction is indicated and should be performed

Closed reduction is contraindicated in the following scenarios:

• Open traumatic hip dislocation (suggestive of extremely large forces) - Such injuries are associated with high infection rates and up to 50% mortality from the injury; patients with such injuries are generally brought directly to the operating room for treatment with surgical irrigation, debridement, and open reduction; if operative management is delayed, closed reduction may be attempted, with follow-up operative management as soon as possible
• Multiple failed closed reduction attempts - If the hip cannot be relocated after two or three reduction attempts, emergency operative exploration is indicated; further closed reduction attempts should not be initiated at this point

Anatomy

The hip joint (see the image below) is a ball-and-socket synovial joint: the ball is the femoral head, and the socket is the acetabulum. The hip joint is the articulation of the pelvis with the femur, which connects the axial skeleton with the lower extremity. The adult os coxae, or hip bone, is formed by the fusion of the ilium, the ischium, and the pubis, which occurs by the end of the teenage years. The two hip bones form the bony pelvis, along with the sacrum and the coccyx, and are united anteriorly by the pubic symphysis. For more information about the relevant anatomy, see Hip Joint Anatomy.

Hip joints, anterior view.

History and physical examination

Obtain and document a thorough preprocedural history that includes the following:

• History of prior injuries and surgical procedures
• Mechanism of trauma
• Amount of time elapsed since the traumatic event
• Description of the presenting symptoms
• Any subjective loss of strength or sensation
• Patient’s age in reference to skeletal maturity

Perform and document a thorough physical examination, with special attention paid to the following:

• Ecchymoses
• Swelling
• Pallor
• Abrasions and lacerations
• Paresthesia
• Weakness
• Notable deformities of the hip
• Presence and character of femoral, popliteal, and pedal pulses

The exact position in which the hip and distal leg are held should be noted, and a comparison examination of the contralateral hip should be done (bilateral hip dislocations[10, 11] are a rare but well-described occurrence). Emphasis should be placed on assessing the neurovascular status of the distal limb, particularly in assessing the sciatic distribution.

Typically, the patient with a posterior traumatic hip dislocation presents with a notably shortened lower limb held in a position of hip flexion, adduction, and internal rotation.[8] The femoral head may sometimes be palpable at the ipsilateral buttock. Whereas this presentation is reliable in patients with simple hip dislocations, the presence of fractures in the ipsilateral femur or pelvis may dramatically alter the patient's presenting position. A high incidence of undetected hip dislocations in patients with ipsilateral fractures, as well as the marked increase in long-term morbidity when initial reduction is delayed, illustrates the need to be able to recognize atypical presentations of this injury.

Assess the patient for additional injuries, particularly life-threatening injuries that may have resulted from the same high-force trauma that caused the hip dislocation. Follow Advanced Trauma Life Support (ATLS) protocols when these are deemed appropriate. Continue management of the hip dislocation as soon as proper evaluation and resuscitation of the patient have insured hemodynamic stability.

Diagnostic imaging

Obtain diagnostic imaging of the patient's bilateral hips and pelvis, choosing the modality that can be performed and evaluated in the shortest duration of time and make the diagnosis. Choices include the following:

• A single anteroposterior (AP) pelvis view that shows both hips
• An AP pelvis and a lateral or oblique Judet view
• A computed tomography (CT) scan of the hip that includes the area from the iliac crest to the symphysis pubis

Plain film radiographs are usually the diagnostic modality of choice because they can be performed and evaluated in a very short amount of time. Because of the observance of ATLS protocols, an AP view of the pelvis, including adequate views of the bilateral hips, is commonly the only film acquired before the diagnosis is confirmed; if the patient is unstable in this setting, it may be the only option.

An additional lateral or oblique Judet view of the pelvis may yield more information about the presence and direction of the dislocation than a single AP pelvis view would. However, additional radiographs may be difficult to obtain secondary to the patient's pain, and the acquisition of the additional views should not delay patient care (eg, by interfering with acute resuscitation).

Posterior hip dislocations can be visualized well on an AP film[8]  by the presence of the femoral head outside and just superior to the acetabulum. They are commonly associated with ipsilateral acetabular fractrues (81% of posterior hip dislocations in adults have posterior acetabular fractures) or femoral fractures.

CT of the hip can also be performed to diagnose and describe the anatomy of the dislocation and identify small fracture fragments. Although this diagnostic modality provides excellent visualization of the injury, it should be done only if it can be both performed and evaluated in an extremely timely manner; the reduction attempt must not be delayed.

Equipment that may be used for reducting a posterior hip dislocation includes the following:

• Oxygen supply
• Bag-valve mask
• Oxygen saturation monitor
• Wall suction, suction tubing, and Yankauer suction catheter
• Intravenous catheter (≥20 gauge)
• Medications as needed for procedural sedation
• Normal saline (0.9% NaCl) flushes

Anesthesia

Procedural sedation is usually indicated. A dedicated clinician should be responsible only for the procedural sedation. For more information, see Procedural Sedation.

General anesthesia in the operating room is an alternative.

Positioning

Various techniques have been proposed to accomplish closed reduction of posterior hip dislocations, including maneuvers performed with the patient in supine or prone positions and maneuvers performed by one or several practitioners.[12]

The Bigelow maneuver is a well-established reduction method that may be performed with minimal assistance with the patient in the supine position. The patient is placed supine on a stretcher that is elevated to the height of the waist of the practitioner performing the reduction. The injured hip is initially held in a position of adduction and internal rotation, with one practitioner applying longitudinal distraction and an assistant applying pressure on the patient's anterior superior iliac spines so as to stabilize the patient's pelvis. (See the image below.)

The initial position for closed reduction of a posteriorly dislocated hip.

Long-term orthopedic follow-up should be arranged in conjunction with the orthopedic specialist, who will continue to treat this patient. Many patients require inpatient management for this or other injuries. If outpatient management is deemed appropriate, the patient should have a follow-up appointment within a few days of the injury.

Outpatient instructions should include the following:

• The patient should not bear weight on the injured hip for several weeks or until the first follow-up appointment
• The hip should be splinted and maintained in a safe position that does not allow for any tension on the healing capsular structures
• The patient should return for emergency care immediately if he or she experiences an increase in pain, an onset of groin pain, or any numbness or weakness in the ipsilateral leg
• The patient should follow instructions for pain medicine, as deemed appropriate; narcotics, nonsteroidal anti-inflammatory drugs (NSAIDs), or both are usually warranted

Obtain informed consent. Prepare for and perform procedural sedation. (See Periprocedural Care.)

Have an assistant stabilize the pelvis by grasping the bilateral anterior superior iliac spines and applying gentle posterior force. Apply longitudinal distraction of the injury by grasping the patient’s distal femur, bringing the femoral head from behind the acetabular rim. The leg should be held in a position of relative adduction and internal rotation. Several moments of persistent traction may be needed to relax the large musculature of the hip; this joint laxity helps to facilitate the subsequent maneuvers.

Once the leg has been brought out to length, bring the hip to 90° of flexion while allowing the ipsilateral knee to flex passively. Gently abduct, externally rotate, and extend the hip while distracting the femoral head anteriorly. Large amounts of rotational force should be avoided because they have been associated with iatrogenic femoral neck fractures. When the femoral head returns to the acetabulum, an audible or palpable "clunk" can be appreciated.

While the procedural sedation is still in effect, gently take the reduced hip through a full passive range of motion (ROM), being mindful of any additional fractures or injuries the patient may have sustained. The stable reduced hip should remain in anatomic position through these maneuvers. Repeat hip dislocation during this passive ROM exercise is diagnostic of clinical joint instability. Longitudinal skeletal traction is required to stabilize such an injury. Place the affected extremity in a pillow brace to ensure stability during transport.

Once reduction has been achieved, repeat radiography is required to ensure concentric anatomic placement of the femoral head. Whereas plain film radiography is usually enough to adequately visualize the reduction, computed tomography (CT) is superior in that it may also show small intra-articular fragments and marginal impaction, as well as residual subluxation of as little as 2 mm within the joint.[8]

A study by Mayer et al suggested that magnetic resonance imaging (MRI) is worth considering after closed reduction of posterior hip dislocations in children and adolescents, on the grounds that it permits evaluation of intra-articular pathology without radiation exposure.[13]  A study by Thanacharoenpanich et al found that postreduction MRI was superior to CT for assessing structural pathologies in children and adolescents who had sustained posterior hip dislocation.[14]

Osteonecrosis

Osteonecrosis of the femoral head may be caused by traumatic hip dislocation, occurring secondary to acute interruption of the femoral head's vascular supply from the ligamentum teres and retinaculum. Its incidence is 6-27% in timely reductions and as high as 48% in delayed reductions. It occurs more often in traumatic hip dislocations that include posterior dislocation rather than anterior dislocation, associated femoral head fracture, or associated acetabular fracture. Avascular necrosis (AVN) of the femoral head has been reported as late as 8 years after the initial injury.[15, 16]

The substantial incidence of osteonecrosis is the reason why traumatic hip dislocations represent a temporal emergency, and reductions performed at longer time intervals from the moment of the injury have been shown by repeated studies to be associated with higher incidences of osteonecrosis.

Although it is widely held that hip reduction should be performed within 6 hours of the injury[17, 3] to reverse the potential impingement of the femoral and posteromedial circumflex vessels, several studies have demonstrated excellent outcomes with reductions performed at even shorter intervals. These results suggest that decreasing the time to reduction as much as possible is advisable for achieving the best probability of either decreasing the severity of osteonecrosis or avoiding it entirely.

Patients who present after successful reduction with groin pain (particularly groin pain that radiates to the ipsilateral thigh) are likely describing the pain of osteonecrosis of the femoral head. Hip radiographs are indicated. Radiographic signs of osteonecrosis within the femoral head are used to stratify patients into a classification system that has prognostic value and aids in future therapeutic decision-making for the treatment of osteonecrosis.

The staging system for osteonecrosis is as follows[18] :

• Stage 1 – Normal appearance of the femoral head; patient is symptomatic - A technetium-99 bone scan may be used to confirm the diagnosis
• Stage 2 – Femoral cysts, sclerotic changes, or both
• Stage 3 – Crescent sign of subchondral collapse of the femoral head
• Stage 4 – Joint space narrowing with acetabular cysts, osteophytes, and cartilage damage

The size of the osteonecrotic portion of the femoral head and the stage of progression at the time of treatment initiation determine whether or not the ultimate outcome will be the loss of structural integrity and severe osteoarthritic degeneration of the hip.

Neurologic injury

Neurologic injury is one of the most common complications of hip dislocations, even when successful closed reduction is accomplished.[19]

The sciatic nerve can be lacerated, stretched, compressed, or encased in heterotopic ossification.[19] Neurologic symptoms may become apparent after a patient initially presents with a normal neurologic examination. The symptoms may begin after proper closed reduction has been achieved, and the reduction technique itself may cause notable traction forces to be applied to the sciatic nerve, which may result in further injury.

If sciatic dysfunction is apparent, prevention of equinus deformity must be addressed by ensuring adequate ankle dorsiflexion.[19] The application of ankle dorsiflexion splints is needed if the patient is unable to actively dorsiflex the ipsilateral ankle.

A sciatic stretch test may be used to predict whether future symptoms of damage to the sciatic nerve may occur. This is performed after a successful reduction in patients with no symptoms of neurologic dysfunction. The test is performed as follows:

• Place the patient supine on a stretcher
• Have the patient actively flex the relocated hip to a comfortable 90° of flexion
• Passively extend the knee on the same side as the hip relocation with gentle force; do not attempt to extend the knee past the patient's comfortable range limit
• If the passive knee extension produces pain in the sciatic distribution of the same leg, damage to the sciatic nerve may have occurred; symptoms of this injury are more likely to reveal themselves in the future, and the patient should be informed of this likelihood and counseled that paresthesia or neurapraxia may occur in the coming weeks or months

If neurologic symptoms persist from the time of the injury despite adequate reduction, surgical nerve exploration may be performed several weeks after the injury. Emergency nerve exploration is usually not indicated if successful concentric closed reduction can be achieved and maintained in a simple traumatic dislocation.

However, if no neurologic deficit is apparent at the time of the injury, and such symptoms do appear several days to weeks later, they may be signs of nerve dysfunction attributable to heterotopic ossification or scar-tissue formation and may indicate the need for surgical neurolysis as soon as possible. The patient without initial neurologic deficits should, therefore, be made aware of this possibility and be instructed to seek treatment immediately if such symptoms occur.

Loose foreign bodies

Loose foreign bodies may result from hip dislocations; this may result in residual pain and possible loss of motion. Hip arthroscopy may be required in cases of persistent pain.[20, 21, 22]

Osteoarthrosis

Postdislocation osteoarthrosis is a complication among adults with traumatic hip dislocations. This complication occurs in as many as 24% of adults with traumatic hip dislocations without fractures and in 88% of those with hip dislocations that occurred with concomitant hip or acetabular fracture, particularly in those with acetabular fragments with more than 3 mm of displacement. Although degenerative changes among children have been demonstrated, osteoarthritis after traumatic hip dislocation in the pediatric population has not been described.

Irreducibility

Interposition of the muscle or labrum renders as many as 4% of adult simple posterior traumatic dislocations irreducible. Hip dislocations associated with any type of fracture may have a larger subset of irreducible injuries as a consequence of interposition of osseous fragments and connective-tissue components. These patients should be brought to the operating room as soon as possible for open reduction; repeated (ie, two or three) attempts at closed reduction should not be performed, because studies have associated repeated attempts with poor long-term results.

If adequate closed reduction cannot be accomplished, the dislocated hip should be held in a position of relative extension with the ipsilateral knee in flexion until open reduction is initiated. This is the position that puts the least amount of strain on the sciatic nerve.