Posterior dislocation

Posterior dislocations is when the femoral head lies posteriorly after dislocation.^[5] It is the most common pattern of dislocation accounting for 90% of hip dislocations,^[5] and those with an associated fracture are categorized by the Thompson and Epstein classification system, the Stewart and Milford classification system, and the Pipkin system (when associated with femoral head fractures).^[7][8]

Anterior dislocation

Anterior dislocations is when the femoral head lies anteriorly after dislocation. Anterior dislocations are subdivided into two types being inferior (obturator) dislocation and superior (iliac or pubic) dislocation.^[4][5] There is also a Thompson and Epstein classification system for anterior hip dislocations.^[8]

To note, Central dislocation is an outdated term for displacement of the femoral head towards the body's center into a fractured acetabulum and is no longer used.^[7] Moreover, the term "congenital" dislocation is no longer recommended, except for very rare conditions, in which there is a "teratologic" fixed dislocation location present at birth.^[16]

Posterior dislocation

For posterior dislocation, the affected limb will be in a position of flexion, adduction, and internal rotation.^[4][5][16] This is to say, the affected leg will be bent upwards at the hip, while being shifted and pointed towards the middle of the body.^[11][17] Sciatic nerve injury is also present in 8%-20% of cases, conferring numbness and weakness to aspects of the lower leg.^[4][5]

Anterior dislocation

For anterior dislocation, the affected limb will be in a position of abduction and external rotation.^[4][5][16] The degree of flexion depends on whether it is a superior or inferior dislocation, with the former resulting in hip extension and the latter, hip flexion.^[4][5][13] This is to say that with superior and inferior anterior dislocations, the affected leg will be bent at the hip backwards and upwards respectively, while being shifted and pointed away from the body. Femoral nerve palsies can also be present, conferring leg numbness and weakness, however are uncommon.^[16]

Functional anatomy

The hip joint includes the articulation of the spherical femoral head (of femur) and the concave acetabulum (of pelvis). It forms a ball-and-socket joint that is encased by an articular capsule, reinforced and stabilized by muscle, tendon, and ligaments.^[18] Even so, the joint is quite flexible in movement, allowing three degrees of freedom.^[19]

Major ligaments conferring stability to the hip joint include the iliofemoral ligament, the ischiofemoral ligament, the pubofemoral ligament, and the ligament of the head of the femur.^[20] The former three ligaments form the zona orbicularis or annular ligament which encases the femoral neck, stabilizing the joint capsule.^[20] The strength of a healthy hip, reinforced and stabilized by the aforementioned structures can withstand over 1000 lbs. of force.^[20]

Cause

With this, to dislocate a healthy hip requires a great deal of force.^[5] About 65% of cases are related to motor vehicle collisions, with falls from elevation and sports injuries causing the majority of the rest.^[5] Moreover, wear and tear of the body with aging increases the older population's susceptibility to hip dislocation.^[21]

Posterior dislocations happen with direct trauma to a bent (flexed) knee as is the case with a dashboard injury in a motor vehicle accident.^[4][5] The positioning of the hip at the time of impact determines associated injuries, with abduction of the hip making a complex hip dislocation more likely, while adduction and flexion of the hip favors a simple hip dislocation.^{[citation needed]}

Anterior dislocations happen with trauma forcing external rotation and abduction of the hip.^[4][5] In the setting of forced external rotation and abduction of the hip, the hip flexed and extended leads to the inferior and superior sub-types of anterior hip dislocation, respectively.^[4][5] Hip dysplasia also makes one more susceptible to hip dislocation.^[22] Hip dysplasia is a congenital condition in which the hip is deformed in a way that decreases the congruency between the head of the femur and the acetabulum of the pelvis.^[22] Bony congruence is a stabilizing factor to the hip joint, so the decrease in this conferred by hip dysplasia makes one more susceptible to dislocation.^[22]

Nonoperative

The hip should be reduced as quickly as possible to reduce the risk of osteonecrosis of the femoral head.^[4] This is done through manual traction of the thigh inline with the dislocation under general anesthesia and muscle relaxation, or conscious sedation.^[4][7] Fractures of the femoral head and other loose bodies should be determined prior to reduction. Of note, femoral neck fractures, femoral head fractures, and incarcerated fracture fragments preventing joint reduction are contraindications.^[25][5][26] Common closed reduction methods include the Allis method, Stimson Gravity Technique, and the Bigelow maneuvers.^[4][27] Once reduction is completed, management becomes less urgent and appropriate workup including CT scanning can be completed.^[7]

Operative

Open (surgical) reduction indications include an irreducible dislocation, fracture with fragments preventing congruent reduction, fracture requiring an ORIF, delayed presentation, and non-concentric reduction.^[4][5] Approaches to surgical reductions include the posterior approach for posterior dislocations (Kocher-Langenbeck), and the anterior (Smith-Petersen) approach for anterior dislocations.^[4][5][28] A CT scan or Judet views should be obtained prior to transfer to the surgical suite.^[7]

Rehabilitation

Individuals with hip dislocation should participate in physical therapy and receive professional prescriptive exercises based on their individual abilities, progress, and overall range of motion. The following are some typical recommended exercises used as rehabilitation for hip dislocation. It is important to understand that each individual has different capabilities that can best be assessed by a physical therapist or medical professional, and that these are simply recommendations.^[29]