Hip Dislocation FAQ’s
What are the surgery-related factors that can lead to a hip dislocation?
If the implant is not positioned correctly, which means the inclination of the cup is not correct or the angle at which the stem is inserted into the thigh bone is not correct, the hip can dislocate. Another reason could be an incomplete soft tissue repair on the posterior (back) aspect. In the posterior approach to the hip, the posterior soft tissue structures are taken down and those need to be repaired adequately so that the capsule of the hip is closed properly and that helps in preventing artificial hip dislocation.
What are the patient-related factors that can lead to a hip dislocation?
Patient-related factors are factors in which the patient does not cooperate with recommended precautions that must be followed for about six weeks after the surgery. It is important that the patient should not be moving the hip in a certain position. Especially the leg should not turn in. You should be keeping your knee separated if you have had a hip replacement for about four to six weeks after the surgery. What I tell my patients is you should be looking at the inside if your knee, not on the outside of your knee after the surgery.
What are the implant-related factors that can lead to a hip dislocation ?
The implant-related factors are factors related directly to the design of the implant. As an example, if we use larger heads for replacing the joint, the jump distance is more and therefore the possibility of the hip dislocating is less. Also, there are certain implants which have a better range of motion, and because the range of motion allowed by the design of the prosthesis is more, the possibility of hip dislocating is more.
What does cup abduction and anteversion mean?
Cup abduction is the angle at which the cup is inclines “away” from the body. The place is the horizontal plane- the plane that goes from one hip to another and includes the entire spine.
Cup anteversion is the angle at which the cup is inclined in “front” of the body. This is in the plane perpendicular to the horizontal plane which excludes the spine.
What can the surgeon do during the operation to prevent the implant from dislocating?
Dislocation is an early postoperative complication after total hip replacement, and one of the ways to decrease that is by doing the surgery more accurately and placing the implants very accurately. It involves preoperative planning, it involves preoperative radiographic templating, and robotic assistance and computer-navigated assistance has recently been of significant help in planning the hip replacement surgery and also recently knee replacement surgery.
In addition, there are also rigorous intraoperative tests for hip stability. A good repair of the soft tissues during closure also helps decrease the risk of hip dislocation. The hip joint is made of a cup and stem and there is a ball in between the cup and the stem. The cup has to be accurately positioned inside the pelvis and it has to be in the correct abduction and anteversion.
Correct abduction means that the cup inclination should be at around 40 degrees in the horizontal plane and anteversion means that in the vertical plane the cup needs to be placed at about 20 degrees. Intraoperatively we look at the preoperative template, look at the coverage of the cup, and that helps in deciding the abduction.
We also see the height of the cup intraoperatively based on how much higher it is located with reference to the teardrop in the pelvis. The anteversion in addition can be determined by accurately positioning the cup over the inferior acetabular ligament, which is the ligament inside the cup overlying its lower end. Also, I use a cup-angled guide which I place over the cup and that has two parts over it and it helps me decide how much horizontal the cup is in and how much incline the cup is.
On the stem side, I decide the anteversion of the stem, which means the inclination of the stem with reference to shaft of the lower leg when I place it inside, because the knees bend in 90 degrees of flexion during the placement of the stem at the time it is broached. Also, before making the neck resection we look at something called as the resection length of the neck, which means the length at which the neck is resected.
We also look at something called the center distance, which means we measure the distance between two points in the bone inside the hip and postoperatively we make sure that that length is in accordance with the preoperative template. If the height offset and the anteversion of the stem is restored, the possibility of a surgical hip dislocation is lower than when done with good soft tissue closure.
What is effective treatment for recurrent hip dislocation?
Artificial hip dislocation means that the ball pops out of the joint and if this happens more than three times it needs surgery. Hip dislocation is an early postoperative complication. If it happens the first time it involves something called a hip reduction, which means that the patient is anesthetized and the head is placed back into the socket without surgery.
After reduction, an x-ray is obtained to ensure that the reduction of the hip is accurate and the hip dislocation has been resolved. If the hip dislocates more than three times, typically it needs a revision surgery to prevent it from happening again.
What sort of surgery is performed for recurrent hip dislocation?
The most important thing that I do is see what is causing the hip dislocation. There are surgeon factors, patient factors, and implant factors. If there are surgeon factors, as an example if the cup is placed incorrectly or the stem is placed incorrectly, a CT scan is performed which shows very accurately where the implant has been placed and usually reposition of these implants can fix the issue of recurrent hip dislocation.
If the length of the hip is smaller compared to the preoperative length, the hip is also unstable and the solution to that is increasing the length of the stem. If the femoral anteversion, which means the placement of the implant to the thigh bone, if it is rotated abnormally that rotation has to be corrected to fix the issue of recurrent hip dislocation.
If there are patient-related factors they need to be resolved. It means the patient has to follow hip dislocation precautions postoperatively.
Implant-related factors can be resolved using newer implants where the geometry of the implant allows a better range of motion and decreases the risk of dislocation. Using the larger head decreases the possibility of hip dislocation because the jump distance is increased.
One of the devices that can be used in prevention of hip dislocation, especially when a cause is not very clear, is called a constrained liner. The head is locked into the cup and the possibility of a hip dislocation is dramatically decreased. The patient does not have to follow hip dislocation precautions after this type of surgery and the problem is usually resolved for life.
What are the symptoms of a hip dislocation?
After artificial hip replacement, dislocation may happen within the first few weeks of surgery and usually it happens with the hip is rotated in a certain way that it shouldn’t be rotated, implying that the hip dislocation precautions that the patient should be following have not been followed. There is sudden pain.
There is shortening of the extremity. The extremity is rotated inwards and the patient is unable to walk. The patient has to be immediately taken to the hospital where the patient is sedated and the hip is reduced, which means that the head is popped back into the socket.
How common is dislocation after a hip replacement?
Dislocation is a fairly rare complication of a hip replacement. If the hip is approached through the posterior approach, the hip commonly dislocates backwards. Hip dislocation is certainly possible but less common even after anterior hip replacement in which the head pops in front of the hip joint.
How soon does hip dislocation have to be treated?
The hip dislocation is treated emergently. There have been times that the hip has dislocated but it took time for the patient to get to the hospital or anesthetic could not be administered to the patient because of medical reasons. It is okay to keep the hip dislocated for a few days so long as there is no imminent neurovascular deficit, which means that there is no deterioration in neurological function or blood supply.
Once the hip is relocated, the outcomes are not going to be significantly different than a hip that is reduced immediately after dislocating and the outcomes will depend on the cause of the hip dislocation.
Is there a hip prosthesis that cannot dislocate?
There is no hip prosthesis that cannot dislocate. Even a constrained prosthesis which is used to treat recurrent dislocation does dislocate if not placed properly or if not taken care of properly.
Can a partial hip replacement dislocate?
It is certainly possible for a partial hip replacement to dislocate if the hip dislocation precautions are not followed. Most partial hip replacements are done using a posterior approach and posterior hip dislocation precautions do need to be followed after partial hip replacement, also known as hemiarthroplasty.
Can a native hip be dislocated?
Yes, a native hip also can be dislocated, although it is extremely hard to dislocate a native hip joint, which means a joint that has not been replaced. It is caused most commonly by motor vehicle accidents.
What are the things that a patient should and should not be doing after a hip replacement surgery to avoid the hip getting dislocated?
Most surgeons and physical therapists follow something called the 90-degrees rule, which means that the hip should not be bent beyond 90 degrees. You shouldn’t be squatting after hip replacement surgery. Remember that the hip dislocation precautions are not something which have to be observed for life, but only for four to six weeks after the surgery.
I feel it is more important to keep the knees separated after hip replacement surgery to decrease the hip getting dislocated. It is okay to cross your ankles, but the knees should be separated after the surgery for a few weeks while the soft tissues heal. Physical therapists after hip replacement surgery will reinforce this, although the surgeon also will talk to the patient before and after the surgery and reinforce these precautions. Sleeping with a pillow in between the legs ensures that the knees are separated.
The hip can be accidentally bent when picking up things, so patients are given a grasper and told to wear socks after the surgery. The patients are advised not to turn their legs inwards. They are told not to cross their legs. They are told not to turn their body with their legs fixed. However, these are difficult to follow. One thing I tell patients is keep the knees separated and don’t bend beyond 90 degrees. I keep it easy and simple and if the patients remember only this they will be following proper hip dislocation precautions.
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