There are two types of hip joint
dislocations: posterior and anterior. The position of the leg is important in
determining the type of hip dislocation. When the hip is dislocated, the leg is
usually shortened and it assumes a different position than the normal leg (the
other leg). If the dislocation is posterior, the leg will be in adduction and
internal rotation. If the dislocation is anterior, the leg will be in abduction
and external rotation. Notice that the affected extremity is shortened and
externally rotated. Leg shortening can also be seen in hip fractures and the
leg will be shortened and externally rotated.
Dislocation of the hip following
total hip surgery may require revision surgery, but it is rare. The majority of
hip dislocations after total hip dislocations are posterior, and they are
usually treated without surgery. Most occur within the first month of THA; 1-4%
in primary, 16% in revision. There is more incidence of dislocation in revision
hip replacement.
Causes & Risk Factors:
- Posterior Approach (try to repair the capsule adequately)
- Malposition of the component
- Ideally, the normal cup component will be in 20° of anteversion and 40° of abduction
- When the hip dislocates posterior, always check for retroversion of the cup.
- Prior hip fracture surgery, especially in the elderly
- Weakness of the abductor muscle—must achieve soft tissue tension and function
- Alcohol abuse
- Improper neck length—looseness of the hip
The patient should be careful to
avoid all activities that cause dislocation after total hip surgery. The
patient should use a pillow between the legs while sleeping on their back and
they should be careful to not cross their legs in their sleep. Patients cannot
sleep on their sides as well. The patient should not bend the body at the waist
farther than 90°. When sitting, the patient must avoid chairs that make it
difficult to stand up, and sit at more than a 90° angle. The patient must not
sit with their legs crossed in the chair. The patient must be made aware that
if the leg is changed from its usual position, or becomes shortened, then the
hip is probably dislocated and their doctor should be consulted.
X-rays of the dislocated total hip
should include AP and lateral views. Look for eccentric wear and look for the
position of the prosthesis. CT scans may be needed before or after reduction of
the dislocation to check the version of the components. Treatment is variable
and depends on the situation. The treatment should be tailored for each case.
The majority of these cases with early dislocations can be treated successfully
with closed reduction and immobilization.
The treatment should start with
closed reduction of the total hip and immobilization. Hip stability is checked after
reduction of the dislocation. Immobilization can be done by a brace or a hip
spica. Trochanteric osteotomy and advancement of the trochanter and tensioning
the abductor muscle. Screws or wires can be used. The prosthesis must be in
good alignment for this procedure to work. Constrained acetabular components
are used when the abductor muscle is deficient and the component position is
good. Revision total hip is done in recurrent dislocation with malposition of
the component or polyethylene wear.
