Hip Dislocation

United States statistics

Up to 70% of all hip dislocations are due to motor vehicle accidents.

Hip dislocations in younger individuals are relatively rare, with only 5% of cases occurring in patients younger than 14 years. Most injuries are in boys and are related to low-energy sports injuries or falls. ^[10]

Very little documentation concerning the occurrence of hip dislocations during sporting events exists. American football and rugby are the sports in which hip dislocations have been most widely reported. ^[6] An estimated 3% of all football injuries involve hip fracture or dislocation. Rugby, followed by alpine skiing and snowboarding, is the sport with the second highest number of hip dislocations. ^[6]

One study found rates of hip dislocation with or without fracture of the hip joint significantly higher in snowboarders than skiers over a 10-year period (5 times higher in snowboarders than in skiers), ^[7] and one case each of hip dislocation has been documented in the literature in competitive gymnastics and professional basketball. ^{[1, 5]} Case reports also exist of hip dislocations and fractures in racecar drivers and equestrians. ^[12]

A study by Moran et al found that male athletes sustained more sports-related hip dislocations than female athletes, with the greatest number of hip dislocations occurring in adolescents aged 15 to 19 years. The researchers also reported that more hip dislocations were sustained during contact sports (91.2%) than noncontact sports (8.8%). The sports with the highest rates of hip dislocation were football (55.6%), snowboarding (9.5%), skiing (8.8%), and basketball (7.1%). Nearly 83% of football-related hip dislocations resulted from being tackled by or colliding with another player. ^[13]

The hip joint is based on the articulation of the femoral head and the acetabulum of the pelvis, and it is a synovial ball-and-socket type joint. The femur is held in the acetabulum by 5 separate ligaments as follows:

• The iliofemoral ligament attaches to the anterior inferior iliac spine of the pelvis and the intertrochanteric line of the femur.

• The pubofemoral ligament originates at the superior ramus of the pubis, also attaching to the intertrochanteric line of the femur.

• The ischiofemoral ligament connects the ischium to the greater trochanter of the femur.

• The transverse acetabular ligament consists of the labrum covering the acetabular notch.

• The femoral head ligament joins the femoral head with the transverse ligament and acetabular notch.

The relative strength of these ligaments joined together, along with the angulation of the proximal femur in relation to the acetabulum, make dislocation of the hip joint difficult. The large sciatic nerve lies just inferoposterior to the hip joint, whereas the femoral nerve lies just anterior to the hip. The proximal shaft of the femur and the femoral neck has a plentiful blood supply from the medial circumflex femoral artery and its branches. The femoral head, on the other hand, has an extremely tenuous blood supply from a small branch of the obturator artery that passes with the femoral ligament.

Two general categories of hip dislocations exist, anterior and posterior. Posterior dislocations compose 70-80% of all hip dislocations and 90% of all sports-related hip dislocations. Alpine skiing is an exception, with one study showing higher rates of anterior dislocations in skiers. ^[7] In order to cause a posterior dislocation, a large force is required to strike the flexed knee with the hip flexed, adducted, and internally rotated. This injury occurs more commonly during contact and collision sports (eg, American football, rugby) when a running player is tackled from behind and falls onto a flexed knee and hip. As the opposing player falls onto the tackled player's back, his added weight drives the torso and pelvis toward the ground, and the femoral head is thus driven out the socket posteriorly.

Anterior dislocations occur when an athlete's hip is flexed, with the leg abducted and externally rotated. The thigh and leg act as a lever, with the fulcrum being the posterior edge of acetabular socket, popping the femoral head out of the socket anteriorly. These injuries are more common in sports (eg, basketball, gymnastics) in which players are running at high speeds, jumping, and landing awkwardly on the inner or medial aspect of the knee. This force drives the femoral head out of the acetabulum anteriorly, tearing ligaments, and often fracturing the femoral head and/or acetabulum. The increased rates of dislocation in alpine skiing are likely due to the large rotational forces, abduction, and external rotation applied to the hip by the ski equipment during a fall.

Related Medscape Reference topics

Acetabulum Fractures

Femoral Neck Fracture

Fracture, Hip

High-speed, high-impact sports are the most common setting for hip dislocations.

Unsafe and poorly maintained playing surfaces may add to the risk of participating in high-impact sports. For instance, wet surfaces provide an environment where athletes are more prone to lose control of their bodies while running and jumping. However, no evidence exists to link these factors with an increased incidence of hip dislocations. One case report describes a basketball player who slipped on a wet court and dislocated his hip. ^[5]

Although warming up before an activity and stretching on a regular basis may help prevent some sporting injuries, no evidence suggests that this decreases the risk of hip dislocation.

No correlation exists between athletic experience and hip dislocations.

The amount of energy to the hip and the associated trauma during the initial injury are the most important factors related to prognosis. Fortunately, sports-related hip dislocations are usually caused by less energy than is generated during motor vehicle accidents. The prognosis is best when the hip is reduced as soon as possible, preferably less than 12 hours post injury. The prognosis is also dependent upon the amount of related fractures or damage associated with the joint. The less associated damage to the surrounding structures there is, the better the prognosis for full recovery.

Complications

A number of acute and chronic complications of hip dislocations exist, not all of which can be avoided with proper medical care and strict follow-up by the injured athlete. Acutely, avoiding the sequelae of sciatic nerve damage and the existence of bony fragments and soft tissues in the joint space is important. A thorough physical examination and review of the radiographic findings are required to avoid the consequences of these conditions.

Chronic complications (eg, avascular necrosis, osteoarthritis) may not be avoided with good follow-up care. Radiographs should be obtained at the previously described intervals, and an MRI should be performed within 6 weeks post injury to evaluate for avascular necrosis (see Maintenance Phase, Other Treatment). Unfortunately, even with compliant patients, early diagnosis, early and appropriate treatment, and good follow-up, some patients develop chondrolysis, avascular necrosis, and early degenerative joint disease (DJD).

Although no studies on the prevention of hip dislocation exist, athletes who participate in high-performance activities need to understand the importance of performing proper warm-up techniques before competition and maintaining good overall flexibility and strength. These attributes are especially important during athletic events (eg, American football, rugby, alpine skiing) when high speeds can generate relatively large forces, which can cause serious injuries to competing athletes.