Hip Injuries After a Car Accident
Key Takeaways
- Motor vehicle collisions are the most common cause of traumatic hip dislocations, and the dislocation often happens when the knee hits the dashboard.
- An acetabular fracture, a break in the hip socket, typically takes 9 to 12 months to completely heal, and many patients do not return to their pre-injury level of activity.
- Among patients followed for at least 10 years after a traumatic hip dislocation, 33% developed post-traumatic osteoarthritis and 17% required a total hip replacement.
Hip Joint Anatomy
The hip is a ball-and-socket joint. The ball is the femoral head at the top of the femur (thighbone), and the socket is the acetabulum, which is part of the pelvis.
Smooth articular cartilage covers both the ball and the socket so the bones glide across each other with little friction. A ring of strong fibrocartilage called the labrum circles the socket like a gasket, sealing the joint and adding stability, and strong bands of tissue called ligaments add more.
Dashboard Force in Frontal Crashes
It typically takes a major force to dislocate a hip, and motor vehicle collisions are the most common cause of traumatic hip dislocations. The dislocation often happens when the knee hits the dashboard: the blow drives the thigh backward, which pushes the ball of the femur out of the socket. Wearing a seatbelt can greatly reduce the risk of a dislocated hip in a collision.
The same path of force can break the socket instead of, or along with, dislocating it. An acetabular fracture occurs when a force drives the head of the femur against the acetabulum, and hitting the knee against the dashboard in a head-on collision is one way that force arrives.
The most commonly reported lower limb mechanisms in frontal crashes included the knee striking the dashboard, resulting in an acetabular fracture or a posterior hip dislocation. A higher probability of significant hip injury was reported in taller males and in occupants out of position during the collision, and a right femur out of position while braking would result in the knee striking the dashboard.
Early Symptoms and Leg Position
A dislocated hip is very painful, and the injured person cannot move the leg very well. The femur is pushed out backward in about 90% of hip dislocations, and this posterior dislocation leaves the knee and foot rotated in toward the middle of the body. In an anterior dislocation the hip is bent only slightly and the knee and foot rotate outward. When the dislocation is the only injury, an orthopaedic surgeon can often diagnose it just by looking at the position of the leg.
A fracture at the top of the femur is typically acutely painful, with pain usually limited to the groin and upper thigh. With most hip fractures, a person cannot stand, bear weight, or move the upper part of the leg, and the injured leg often looks shorter than the other and twisted or rotated. A small number of hip fractures, typically nondisplaced breaks of the femoral neck, may not be as painful at first, and the person may still be able to move the leg and bear weight even though it is painful.
A broken socket is almost always painful, with pain typically limited to the groin or hip and worse with movement. If a nerve was injured at the same time, the person may feel numbness, weakness, or tingling down the leg, and with a dislocation, nerve damage may leave no feeling in the foot or ankle area.
Hip Warning Signs
- Severe pain in the groin, hip, or upper thigh
- Inability to stand, bear weight, or move the upper leg
- One leg that looks shorter than the other, or twisted or rotated
- Knee and foot turned in toward the middle of the body
- Pain in the hip that gets worse with any movement
- Numbness, weakness, or tingling down the leg
- No feeling in the foot or ankle area
- Bruising on the outer hip or thigh at the point of impact
Posterior and Anterior Dislocations
A dislocation of a natural hip takes high-energy trauma such as a motor vehicle collision and is commonly seen with multiple injuries, in up to 95% of patients. Acetabular fractures occur in as many as 70% of these dislocations and femoral head fractures in 5% to 15%, and effusion, bone bruise, and meniscal tears are among the significant knee injuries seen on the same side. The page on knee injuries after a car accident covers that end of a dashboard impact.
A posterior wall acetabular fracture-dislocation is perhaps the most common fracture seen with a dislocated hip: the head of the femur strikes and breaks off the back part of the socket during the injury. Other injuries seen alongside hip dislocations include fractures of the pelvis, femur, tibia, and fibula, back and abdominal injuries, and head injuries including concussion.
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Acetabular Fractures of the Socket
Socket fractures are much less common than fractures of the upper femur or femoral head, and most are caused by a high-energy event such as a motor vehicle collision. People with these fractures often have additional injuries that require immediate treatment, including injuries to the head, chest, abdomen, or legs.
The bone can break straight across the socket or shatter into many pieces. Severity depends on the number and size of the fragments, how far each piece is out of place, damage to the cartilage of the socket and the femoral head, and damage to the surrounding muscle, tendons, nerves, and skin. Fracture patterns are described by location, such as the front or back column of the bone or the rim (wall) of the socket, and by orientation, such as a break straight across the bone.
When the socket breaks, the ball may no longer fit firmly and the cartilage of both bones may be damaged. If the joint remains irregular or unstable, ongoing cartilage damage may lead to arthritis. The page on car accident pelvic fractures covers breaks elsewhere in the pelvis.
Breaks in the Upper Femur
Most hip fractures happen in older adults with bones weakened by osteoporosis, but in a younger patient a hip fracture is typically the result of a high-energy event such as a motor vehicle or motorcycle collision.
Intertrochanteric and femoral neck fractures are the most common types. Femoral head fractures are rare, less than 1% of all hip fractures, and usually result from a high-velocity event, sometimes with a fracture of the socket as well. In small overlap crashes, intertrochanteric fractures were the most common type of hip fracture.
Blood reaches the femoral head through a structure called the posterior capsule, and this capsule is often injured with a displaced femoral neck fracture, so the fracture has less chance of healing. Even if the bone does heal, avascular necrosis may develop in the femoral head, damaging bone cells and collapsing part of the head.
Labral Tears at the Socket Rim
The labrum is the rim of cartilage that lines the hip socket and keeps the bones from grinding against each other. Car accidents, along with sports injuries and falls, are among the injuries that can cause a hip labral tear.
The most common symptoms are hip pain, especially with bending or movement, stiffness, a clicking or popping sound and feeling, and a sense of being unsteady when standing or moving. Some people with a small tear have no symptoms. In others the pain spreads into the groin, lower back, or leg, and the person may change how they walk or hold their body without noticing.
To diagnose a tear, providers may use a hip x-ray, ultrasound, MRI, or a CT scan. Labral tears cannot heal on their own, and surgery, usually a hip arthroscopy, is the only way to repair one, although some people manage their symptoms with medication and physical therapy. Recovery after a hip arthroscopy usually takes around 4 to 6 months.
MRI is the study that shows the labrum, because MRI scans provide better images of soft tissue than X-rays and help identify damage to the labrum and articular cartilage. Injecting dye into the joint during the MRI may make the damage show up more clearly.
Three Hip Injuries Compared
The table sets three common crash injuries side by side. They often overlap: a posterior dislocation can break off the back wall of the socket, and a femoral head fracture can come with a socket fracture.
| Feature | Hip Dislocation | Acetabular Fracture | Femoral Neck Fracture |
|---|---|---|---|
| What is injured | Ball of the femur forced out of the socket | The socket of the hip joint, part of the pelvis | The area of the femur just below the ball |
| Typical signs | Severe pain, leg hard to move, knee and foot turned in with a posterior dislocation | Groin or hip pain that worsens with movement | Groin and upper thigh pain, leg may look shorter and rotated |
| Imaging | X-rays and likely a CT scan | X-rays from several angles, CT commonly ordered | Most show on an x-ray, CT if x-rays do not show it |
| Common treatment | Reduction under anesthesia or sedation, surgery if fractures or instability | Plates and screws for most, hip replacement in some | Screws or a plate if aligned, often hip replacement if displaced |
| Recovery range | Sometimes 2 to 3 months, longer with fractures | Typically 9 to 12 months to completely heal | Most out of bed and in therapy the day after surgery |
X-Rays, CT, and MRI Findings
Most hip fractures can be diagnosed with an x-ray. A CT scan gives a detailed cross-sectional image and may be ordered when x-rays do not show a fracture or to plan surgery. MRI is rarely needed, but because it is very sensitive it can sometimes detect a small or incomplete fracture that cannot be seen on an x-ray.
For an acetabular fracture, x-rays are taken from a number of angles to show the pattern and how far the bones are displaced, and a CT scan is commonly ordered because of the complex anatomy of the pelvis. After a dislocated hip is put back in place, another set of x-rays, and possibly a CT scan, is taken to confirm the bones are in proper position.
Osteonecrosis can stay hidden on plain films early on. Early changes in the bone that may not show up on an x-ray can be detected with an MRI, and an MRI may also show early osteonecrosis that has not yet caused symptoms. The page on reading an MRI report explains common report terms.
Reduction, Fixation, and Joint Replacement
Putting a dislocated hip back in place is called a reduction. It uses an anesthetic or sedative followed by manipulation of the bones into position, and some reductions must be done in the operating room. Surgery is needed in rare cases when torn soft tissue or small bone fragments block the femur from returning to the socket. Surgery may also be needed when fractures come with the dislocation or the hip stays unstable after reduction.
Most acetabular fractures are treated with surgery called open reduction and internal fixation, in which the displaced fragments are repositioned and held with metal plates and screws to restore a smooth joint surface. When the socket is so damaged that repair is unlikely to succeed, the surgeon may recommend a total hip replacement.
Most fractures of the upper femur also require surgery, and surgery within 24 to 48 hours may reduce the risk of complications. A nondisplaced femoral neck fracture is most commonly treated with pins or screws, or a plate and screw device, across the break. Displaced femoral neck fractures are often treated with hip replacement, and intertrochanteric fractures are repaired with either a sliding compression hip screw and side plate or an intramedullary nail.
Recovery Ranges by Injury Type
Healing after a dislocation sometimes takes 2 to 3 months, and rehabilitation may run longer when there are additional fractures. A doctor may limit hip motion for 6 to 8 weeks to keep the hip from dislocating again, and a doctor may recommend a period of toe-touch or foot-flat walking, with no pressure on the ground on the injured side, for up to 6 to 12 weeks, depending on the severity of the injury and the treatment.
An acetabular fracture typically takes 9 to 12 months to completely heal. Most patients use crutches or a walker and are limited in putting full weight on the leg for up to 3 months, and a return to vigorous sports such as running can take 6 to 18 months. Many patients are not able to return to their pre-injury level of activity because of the complicated nature of these fractures.
After surgery for a fracture of the upper femur, most patients are able to get out of bed and start physical therapy the day after the operation, and early movement helps prevent blood clots, pneumonia, and bed sores. A patient with a hip replacement can bear full weight right away unless there are complications, while internal fixation may come with weightbearing limits.
Osteonecrosis and Sciatic Nerve Damage
As the femur is pushed out of the socket, it can tear blood vessels, and bone that loses its blood supply can die. That condition, called osteonecrosis or avascular necrosis, can ultimately lead to destruction of the hip joint, pain, and arthritis.
Hip dislocations, hip fractures, and other hip injuries can damage the blood vessels and impair circulation to the femoral head. Hip pain is typically the first symptom and may become a dull ache or throbbing pain in the groin or buttock, and the disease may take from several months to over a year to progress. Once the femoral head has collapsed, total hip replacement is the most successful treatment.
Avascular necrosis after hip dislocation occurs in approximately 2% to 10%, with rates increasing past 6 hours. A hip reduced after 12 hours carried 5.6 times greater odds of avascular necrosis than one reduced before 12 hours.
When a dislocation crushes or stretches nerves in the hip, the sciatic nerve, which runs from the lower back down the back of the leg, is the one most commonly affected. Sciatic nerve injury occurs in around 10% of hip dislocation patients, and most of them experience some nerve recovery. With an acetabular fracture, sciatic nerve injury most often causes foot drop, an inability to lift the ankle or toes from the floor when walking. Four of the 6 patients with a sciatic nerve injury after the dislocation still had sciatic nerve palsy at follow-up.
Post-Traumatic Arthritis Years Later
Even when treated successfully, an acetabular fracture can damage the smooth surface of the joint and make hip arthritis more likely during recovery or years after the injury, as the protective cartilage wears away and pain and stiffness increase. Posttraumatic arthritis is treated like other osteoarthritis, with physical therapy, walking aids, medications, and lifestyle changes, and a total hip replacement may be the best option in severe cases that limit activity.
A dislocation without a fracture carries its own risk. Posttraumatic arthritis is the most common long-term sequela of a simple dislocation of a natural hip, with an incidence of approximately 20%.
With a minimum of 10 years of follow-up, 33% of patients developed post-traumatic osteoarthritis, 11% developed avascular necrosis, and 17% required total hip arthroplasty. Patients after a traumatic hip dislocation are at high risk for these problems, especially when the dislocation comes with an acetabular or femoral head fracture.
Records That Follow the Injury
The first record of a hip injury is the emergency exam. Doctors check whether the patient can move the ankles and toes and feel the bottom of the feet, and a check of sensation, movement, and circulation in the lower leg is added for a hip fracture. Those findings sit in the chart beside the leg position on arrival and the first films.
After a dislocation, routine follow-up typically includes examinations and x-rays at 2 weeks, 6 weeks, and 3 months. Operative reports, weightbearing orders, physical therapy notes, and any later MRI fill in the months between. The page on car accident femur fractures covers breaks lower in the thighbone.
A dated note of how far a person can walk, when a limp shows up, and whether stairs or long sitting bring on pain gives each new provider something concrete to compare. Kept beside the discharge papers and therapy schedule, those notes put the day-to-day changes in one place.
Hip Pain Still Limiting Every Step?
A hip that was put back in place or rebuilt with plates in the first days can still be changing a year later, and an insurer may treat the early discharge papers as the end of the story. Sam Aguiar Injury Lawyers gathers the emergency records, the operative report, and the follow-up imaging so the full course of your hip injury is on paper. Under our Bigger Share Guarantee®, you always walk away with more than the firm after bills, liens, and case costs. Start with a free case review.