What is Anterior Hip Dislocation?
Hip dislocations after an injury are often seen in emergency medical situations. Because the hip is a ball and socket joint that’s strong and stable due to its bone structure and the muscles and ligaments that support it, a substantial force is usually needed to dislocate it. This powerful force often means that hip dislocations come with other serious injuries. For instance, over half of these patients also have fractures. Most hip dislocations are caused by car accidents. The most common type of hip dislocation is the posterior hip dislocation, with the anterior type only happening about 10% of the time. These injuries are serious and require immediate attention, usually a procedure in the emergency department to move the hip back into place.
The hip joint is a specialized ball-and-socket structure that is stable due to its bone and ligament structure. The part of the hip socket, the acetabulum, covers about 40% of the top part of the thigh bone during all movements, and a structure called the labrum helps to deepen the joint and provides additional stability. Moreover, the capsule around the hip joint is made up of thick fibers that prevent the hip from extending too far. The main blood supply to the top of the thigh bone comes from two arteries branching from a main artery. These branches enter the bone just below the thigh bone head, creating a rich but fragile blood supply, especially if there’s a traumatic injury. There are also nerves close to the hip joint. The sciatic nerve goes out of the pelvis and lays just behind the hip joint, and the femoral nerve sits just in front of it.
What Causes Anterior Hip Dislocation?
Anterior hip dislocations, or when the hip comes out of its socket to the front, usually happen because of a strong impact like a car crash or fall, or from a hip replacement surgery that didn’t go correctly. If there’s a trauma, the hip is usually forced into a lifted and outwardly rotated position.
There are three forms of anterior hip dislocations. The first type can occur when the hip is lifted, bent forward and rotated outward. The second and third types are due to the hip being lifted, extended backward and rotated outwards.
Research shows that hip replacement surgeries have a dislocation rate between 0.3-10% but, that risk jumps to 28% if the hip replacement needs to be fixed. Some studies suggest that anterior hip replacements have about the same risks as the posterior (or back side) methods.
As more people learn about anterior hip replacements, more of these surgeries will likely be performed. This could lead to an increase in anterior hip dislocations and complications that can arise with this method.
Risk Factors and Frequency for Anterior Hip Dislocation
Hip dislocations often happen to young adult males, commonly due to car accidents. A study found that the average age for these patients is 34.4 years old, and over 90% are male. Injured hip patients usually have related injuries, with 74.4% having fractures of the hip as the most common one. Treatment often involves closed reduction, a way to put the hip back in its place without surgery. Over 90% were treated this way and about 70% received treatment within 12 hours. One study noted that complications can increase from 22% to 52% if treatment is delayed for 12 hours or more. Dislocations of the hip that move forward, known as anterior dislocations, are rare in children.
Research by Brennan and colleagues shows that in patients who have undergone total hip arthroplasty (THA), a type of hip replacement surgery, hip dislocation happens in 3.8% of patients within ten years. Most anterior hip dislocations happen in the first month after surgery and are the most common reason for revision arthroplasty, or corrective surgery, in the first two months. Several factors can make a patient more likely to experience a dislocated hip after surgery, including:
- A history of repeat hip surgery
- Being female
- Being older, between 70 and 80 years
- Having a neuromuscular disease
- Undergoing certain lifestyle factors like alcohol consumption, drug use, and activity level
- Surgical factors like offset, abduction, anteversion, head/neck ratio
Signs and Symptoms of Anterior Hip Dislocation
People with dislocated hips often experience severe pain in the hip area. However, it’s not unusual for them to complain about pain in different places like the knee, lower back, thigh, or even lower abdomen or pelvis. Depending on the type of dislocation, the hip might be extended and externally rotated or abducted and externally rotated. It’s also important to remember that other leg injuries can change this typical pattern.
It’s important for doctors to perform a complete neurovascular examination. This means checking if there is damage to the parts of the leg that carry blood and nerves, specifically the femoral artery, vein, or nerve. While it’s challenging to completely assess the motor function of the femoral nerve due to pain and the nature of the injury, any sensory changes in the thigh and leg’s inner part should be noted as a warning sign. In addition to anterior dislocations, sciatic nerve injuries are more often associated with posterior dislocations, but should also be ruled out in any hip dislocation or fracture.
Since these dislocations usually result from significant trauma, a comprehensive evaluation for other related injuries may be needed.
Testing for Anterior Hip Dislocation
If a doctor suspects a hip dislocation, they can typically spot it in a standard x-ray of the pelvis. But to gather more information about the injury, they may also take an x-ray from the side of the affected joint. In a normal x-ray, the round tops of the thigh bones should appear the same size and have equal spacing around them. In the case of a dislocation, the x-ray will usually show one thigh bone looking larger than the other. This x-ray can also help rule out a break in the upper part of the thigh bone before any attempt is made to return the bone to its proper location.
They may also take a special type of x-ray called Judet views; these are oblique or angled views that can aid in spotting bone fragments and unseen breaks in the hip socket and upper part of the thigh bone.
Another imaging tool known as CT (computed tomography) is often suggested after the hip bone has been successfully placed back into the socket. This is done to look for hidden fractures. The CT scan can also help identify reasons why the space around the joint might look bigger even after the bone has been put back into place, such as bone fragments or tissue damage that might be hindering normal movement within the joint. In one study, CT scans found loose bodies (debris like bone or cartilage fragments) in one out of five hips that were scanned after reduction (the process of placing the bone back in the socket).
If the doctor is unable to place the hip back into the socket through external manipulation and needs to perform surgery, CT can also be useful in planning the surgical procedure. CT might reveal bone fragments or unusual tissue conditions that could explain why external attempts to reposition the bone were unsuccessful and could assist in preparing the best surgical approach.
After the initial period following the injury, an MRI (magnetic resonance imaging) might be necessary to check for soft tissue injuries or cartilage pieces that continue to cause problems. In the healing period that follows, typically four to eight weeks after the injury, an MRI can be used to spot bone death, a condition where bone tissue fails due to insufficient blood supply. In some cases, it has been suggested that an MRI is more effective than a CT scan in identifying hip injuries in children. This is because CT scans might not detect fractures in certain parts of the hip that have not yet hardened into bone.
In terms of other tests, blood tests might be necessary based on the individual patient’s condition. For example, if there’s a chance of significant blood loss due to injury to the large blood vessels in the thigh, the doctor might look at blood levels and perform tests to identify the patient’s blood type.
Treatment Options for Anterior Hip Dislocation
If a hip dislocation occurs, it’s important to quickly address the issue, ideally within six hours. However, some research suggests that there may not be significant damage even if treatment is delayed up to 72 hours. People with a dislocated hip typically experience a lot of discomfort, so they should receive pain relief medication right away. Dislocations that cannot be fixed might be due to insufficient support from the anterior or posterior wall or because tissues and structures like the labrum, ligamentum teres, capsule, iliopsoas, pulvinar, and synovium are preventing reduction.
Certain circumstances, like a non-concentric reduction (meaning there might be a lost fragment or significant soft tissue injury), associated fractures, and dislocations that can’t be corrected with closed reduction techniques, might require an open reduction. Otherwise, an urgent closed reduction should be performed in the emergency room with procedural sedation.
There are several techniques that can be used to reduce an anterior hip dislocation. These include the Allis Maneuver, Captain Morgan Technique, Reverse Bigelow Maneuver, and Stimson Maneuver. All involve different positions and movements, with the common goal of repositioning the hip joint. The techniques can range from applying constant traction to the hip joint to leveraging the hip back into place.
After the reduction, the patient’s legs should be kept slightly apart using a pillow or a device. Ice packs can help with the inflammation and analgesics can manage the pain. Patients should have a follow-up x-ray and be admitted for ongoing orthopedic care. For patients who have had a total hip arthroplasty, it’s crucial to test the stability of the hip if an anterior hip dislocation occurs. In some cases, a hip abduction brace may be recommended.
In cases necessitating surgery, there are numerous strategies available. But whichever is chosen, it’s essential to clean the joint to remove any bone or soft tissue that could prevent a proper reduction. After surgery, the hip should be held in traction for 6 to 8 weeks, until it has been definitively fixed or until the patient is pain-free.
What else can Anterior Hip Dislocation be?
When a person experiences hip pain or discomfort, the cause could be due to various health issues. These issues can include:
- Fractures in the upper part of the thigh bone (also known as femoral neck fracture)
- Misalignment of the hip joint, or hip subluxation
- A bone bruise, or bony contusion
- Injuries to the knee, spine, or pelvis on the same side of the body
- Slippage of the upper part of the thigh bone in children and teens (a condition known as slipped capital femoral epiphysis)
- Problems in the abdomen or pelvic area
These are all conditions that a doctor would consider during a check-up for hip pain.
What to expect with Anterior Hip Dislocation
Anterior hip dislocations, often accompanied by damage to the femoral head, can result in long-term problems and an increased chance of arthritis. Studies show that nearly 13.3% of patients with a complex dislocation exhibited signs of osteoarthritis. About half of all anterior dislocations come with femoral head fractures, but those without these fractures often have a good, long-term prognosis.
Osteonecrosis, or death of bone tissue, is a complication that affects 5% to 40% of all hip dislocations, depending on how quickly the joint is repositioned. If not treated within six hours, the risk increases. Up to a fifth of all traumatic hip dislocations can lead to osteonecrosis of the hip.
Patients who have had a hip dislocation are at a higher risk of developing blood clots, known as thromboembolism. This is due to lack of movement after the injury, along with damage to the blood vessels caused by stretching. The risk of venous thromboembolism after surgical hip dislocation was found to be 0.5%. It’s standard practice to take preventative measures against this in such cases. Additionally, about 2% of patients run the risk of experiencing a second dislocation, particularly those who’ve had a hip replacement.
Although it’s relatively uncommon, discomfort or nerve injury, known as neuropraxia, can occur following a hip dislocation. On average, 10% of adults and 5% of children will experience this. Thankfully, 60-70% of these patients see their symptoms ease off partially.
Recovery from Anterior Hip Dislocation
After a joint has been put back into place, patients should rest with their legs slightly apart, propped up by a pillow or a device placed between the knees. According to the provider’s judgement, a special kind of brace called an ‘abduction brace’, could also be recommended. Additionally, a knee immobilizer can provide extra support especially for hips that were dislocated backwards, but it’s not helpful for hips dislocated forward.
Following the adjustment, the patient should get x-rays and stay in the hospital to continue receiving care from orthopedic specialists.