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, whether the patient has a native hip versus a prosthetic hip joint is the first question any examiner should answer 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. Non-native 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).
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 be 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 dislocation to occur. Important risk factors that mechanically predispose individuals with prosthetic hip implants to dislocate include:
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.
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.
After a thorough history and physical, imaging of the affected joint is necessary. Radiographs can typically see posterior dislocation with an anterior-posterior pelvis view. Specifically, one should compare the femoral head size, violation of Shenton's line, the presence of a lesser trochanter shadow which reveals an internally rotated femur, and the presence/absence of a femoral neck fracture. If an acetabular fracture is suspected, additional Judet views may be utilized. A CT scan may be of significant utility depending on the mechanism and patient presentation. A CT scan should be considered mandatory for traumatic hip dislocations. CT will give the definitive direction of dislocation, illuminate if loose bodies are present, and is more sensitive for associated fractures. MRI evaluation is controversial and should not be routinely employed.
The management of posterior hip dislocations can be divided into operative and non-operative techniques. Both types of management are aimed at a reduction as soon as possible. Numerous studies have cited that time to reduction is crucial because the longer the hip is dislocated, the higher the risk of complications, specifically avascular necrosis in the native hip. Most authors recommend a reduction time of fewer than 6 hours, while there is some evidence that fewer than 12 hours may be a critical time; regardless, the rate of secondary complications increases dramatically with increased time-to-reduction.
Non-Operative Management/Closed Reduction
Closed reduction is achieved with a physical technique/maneuver. Several techniques can be utilized to reduce hip dislocations; one example is listed below. A notable complication of closed reduction and one that every operator must be cautious to avoid is ipsilateral femoral neck fractures. If the reduction appears to be beyond the skill range of the operator, consider consulting an orthopedic surgeon for expert reduction or advice.
Technique for closed reduction:
This should be performed urgently and is indicated in the following situations: dislocations not amendable to closed reduction, the presence of incarcerated bony fragments, delayed presentation, non-concentric reduction, and/or presence of associated fractures of the femoral neck, femoral head, or acetabulum. Types of operative management include open reduction with the removal of incarcerated fragments, open reduction with internal fixation, or rarely through arthroscopy. There are operative techniques that may be utilized to facilitate reduction such as the Kocher-Langenbeck (posterior) approach or Smith-Peterson (anterior) approach. Further description of these techniques is beyond the scope of this article.