In the United States, hip dislocations are responsible for significant morbidity and potentially mortality with deleterious consequences to the surrounding anatomy, neighboring joints, and an individual's functional ability.
In the evaluation of posterior hip (femur) dislocation, the first question an examiner should answer is whether the patient has a native hip or a prosthetic hip joint, as the clinical approach varies significantly. Additionally, it is paramount to evaluate for associated injuries such as fractures, as this will also drastically alter management.
The native hip joint is inherently stable and requires a significant amount of force to cause dislocation; as such, hip dislocation in native joints are often secondary to traumatic events such as motor vehicle accidents. Due to the traumatic nature and force required to dislocate a native hip joint, it is not surprising that 95% of patients who present with a hip dislocation after a motor vehicle collision had an associated injury requiring inpatient management. Thus, with native hip dislocation, a detailed neurologic and musculoskeletal examination with additional x-ray or CT scans for assessment is mandatory. Conversely, prosthetic or non-native hip dislocations are a relatively common occurrence to emergency departments nationwide as the inherent stability of the joint is less than that of a native joint. Prosthetic joint dislocations are most often associated with minor mechanisms and require a more reserved approach.
Hip dislocations may occur in either an anterior or posterior fashion that is dependent upon the inciting mechanism. In posterior dislocations, the femoral head is displaced posteriorly in relation to the acetabulum. Hip flexion, adduction, and internal rotation will produce posterior dislocations, whereas hyper-abduction with the extension will produce an anterior dislocation, with the large majority of atypical and axial-loading injury patterns producing posterior dislocation. 
Age, race, and gender are important risk factors for these types of injuries with the incidence being two times greater in women than in men. Posterior hip dislocations (90%) are much more common than anterior hip dislocations; additionally, there is significant morbidity and mortality associated with posterior hip dislocations if there are any associated fractures. In addition to severe pain, other associated injuries include acetabular fracture, hip/femur fracture, osteonecrosis, sciatic nerve damage, recurrent dislocations, bone bruise (33%), ipsilateral knee meniscal tears (30%), knee effusion (37%) and labral tear (30% rate) . In addition, thoracic aortic injury has been reported to be associated with posterior hip dislocation in 8% of cases due to abrupt deceleration injuries .
Following dislocation, physicians will typically attempt to reduce the dislocation with sedation via a closed procedure/technique. Emergent closed reductions are warranted, especially in the setting of native hip joints to ameliorate the risk of osteonecrosis. If all attempts at a closed reduction fail, an orthopedic surgeon will perform the reduction with an open, surgical procedure. After the reduction, whether it is open or closed, there are strict precautions patients must follow to prevent re-dislocation and further injury. If a patient suffers recurrent dislocations, bracing or even further corrective surgery is often indicated. 
A hip dislocation occurs when the internal forces of the hip (labrum, capsule, ligamentum teres, muscles, bones, and mechanical anatomy) are overpowered by the transmission of a large amount of energy through the joint.
In the setting of a hip prosthesis, the normal hip anatomy and support structures may be violated or replaced (external rotators, joint capsule, acetabular surface and femoral head) during surgery. This violation can result in a decrease in the amount of inherent/anatomic force that helps maintain the femoral head within the acetabulum, therefore reducing the amount of energy necessary for a dislocation to occur. Important risk factors that mechanically predispose individuals with prosthetic hip implants to dislocate include:
Surgical approach utilized (for example, anterior versus posterior)
Type of prosthesis (hemi versus total arthroplasty)
Prior hip surgery
Malposition of the prosthesis during surgery
Drug/alcohol abuse, and
Neuromuscular disease such as Parkinson.
Typical mechanisms of dislocation for the non-native hip include falls, bending down to tie one's shoes, sitting on a low/short chair then attempting to stand, or crossing one's legs when sitting, standing, or lying down.
As previously mentioned, native hip dislocations are secondary to traumatic events; a common mechanism occurs during motor vehicle collisions when a person's flexed knee strikes the dashboard of the car, creating an axial load transferring a large amount of force through the hip joint.
History and Physical
Posterior hip dislocation is rarely, if ever, an occult injury due to the amount of pain elicited as well as an inability to ambulate or bear weight on the affected extremity afterward. The patient's history will usually involve a description/experience in which there was a significant "clunk" or "popping" followed immediately by pain. A physical deformity with ipsilateral shortening/hip flexion, adduction, and internal rotation will be visible. It is also important to examine the pelvis and ipsilateral knee. If necessary, especially in the setting of native hip dislocation, ATLS principles of practice should be applied. A thorough neurovascular examination should be performed and documented at presentation, before and after reduction and serial examination thereafter.
The following can be suggestive signs of vascular or sciatic nerve injury:
Painful buttock, posterior thigh, and leg.
Altered sensation in posterior leg and foot.
Weakness or total loss of dorsiflexion (peroneal branch) or plantar flexion (tibial branch).
Diminished or absent deep tendon reflexes at the ankle.
After a thorough history and physical examination, imaging of the affected joint is necessary.
Standard anteroposterior pelvic radiographs: Several contour lines that should be continuous and smooth helps systematic interpretation. Iliopectineal and ilioischial lines represent anterior and posterior columns of the acetabulum respectively. Careful assessment of the posterior wall of the acetabulum as posterior wall fracture is the most commonly encountered acetabular fracture pattern in hip dislocation. Shenton's line irregularity occurs in hip dislocation or in the neck of femur fractures without dislocation. Assess if the femoral head fracture is present whether it is above or below fovea capitis. The femoral head appears smaller than the contralateral side.
Crosstable lateral view: Identify the direction of dislocation.
Additional Judet views (45 degree internal and external oblique views), inlet and outlet views: This can be helpful in identifying acetabular fractures.
Computed tomography CT: Post reduction CT is mandatory for all traumatic hip dislocation. It identifies any associated femoral head or acetabular fracture and delineates its extent. Also, it is helpful in finding out any incarcerated bony fragments or loose bodies.
Magnetic Resonance Imaging MRI: It is controversial and should not be routinely employed . However, It can be helpful in assessing soft tissue injuries e.g labrum, cartilage. Also, MRI is superior to CT in the pediatric population with an immature skeleton.
Femoral head avascular necrosis
Femoral neck fracture
Femur injuries and fractures
Slipped capital femoral epiphysis
Snapping hip syndrome
Traumatic hip subluxation
The Thompson and Epstein is a classfication system for posterior dislocation of the hip .
I With or without a minor fracture.
II With a large single fracture of the posterior acetabular rim.
III With comminution of the acetabular ring.
IV With a fracture of the acetabular floor.
V With a fracture of the femoral head.
Type V dislocations were sub-classified according to Pipkin .
I Fracture below the fovea; not involving weight-bearing surface of the head.
II Fracture above the fovea; involving weight-bearing surface of the head.
III Type I or II fracture with associated femoral neck fracture.
IV Type I or II fracture with associated acetabulum fracture.
Simple dislocations have better outcome and quicker functional recovery, whilst the more complex the dislocation the higher the incidence of complications. There are several prognostic factors. The most important one is the time lapse between the injury and reduction. Better results were achieved with early reduction . Other prognostic factors include fracture-dislocation type, congruency and stability of of the hip joint post reduction and severity of trauma .
The following is a list of complications that can develop after posterior hip dislocation:
Avascular necrosis of the femoral head.
Post-traumatic arthritis with increased incidence of post complex dislocations.
Sciatic nerve injury.
It was noted that the incidence of complications was higher in Thompson-Epstein type IV . Therefore counseling such patients regarding the prognosis and possible complications might increase patient's satisfaction. There is an increased incidence of avascular necrosis and post-traumatic arthritis with increased severity of trauma. Incidence was higher in hips reduced after 12 hours in comparison with hips reduced before 12 hours . In the literature, the reported incidence of sciatic nerve injury is approximately 10% in adults and 5% in children. Usually, the peroneal branch is injured and partial recovery occurs in at least 60% to 70% of patients. There is no association between the type of injury or treatment and subsequent recovery .
Postoperative and Rehabilitation Care
A successfully reduced hip requires rest, ice, anti-inflammatory, and narcotic medications during the post-reduction acute phase. Weight-bearing is advised based on the type of dislocation. In type I posterior dislocations, patients are allowed to weight bear as early as pain allows. In type II to V dislocations, protected weight-bearing for 4 - 6 weeks is recommended. Complex dislocations with associated fractures and/or instability may require an abduction brace postoperatively. Abduction brace keeps the hip in abduction and slight external rotation, whilst allowing controlled flexion and extension. One week after reduction, patient can start pendulum exercises and passive range of motion exercises. This should be followed by more advanced exercises e.g. upright knee raise and resistive hip abduction. More detailed instructions should be provided by the physiotherapist.
Enhancing Healthcare Team Outcomes
Most posterior hip dislocations occur from traumatic events. Often an attempt will be made to reduce the hip in the emergency department. It is important for the pharmacist to provide and assist with adequate pain relief while the orthopedic nurse and clinicians collaborate to reduce the dislocation. an interprofessional team approach will result in the best care of the patient.
(Click Image to Enlarge)
Left Hip Joint, Femur, Ischium, Pubis, Ilium, Fovea Capitis, Iliofemoral ligament
Contributed by Gray's Anatomy Plates
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