الفهرس 
Anatomy of the Acetabulum andOnly 14 pages are availabe for public view
 |  | from | 254 |  |  |
| | | from | 254 | | |
Abstract
Dislocation of a total hip arthroplasty (THA) is a traumatic event
for both the patient and the surgeon. In primary hip arthroplasty, its
incidence has been reported to be between 0.6% and 9.9%. With
revision surgery, it can be as high as 20%.
Many factors are associated with dislocation classified as patient
factors such as: age, gender, original pathology or neuromuscular
dysfunction, and surgical factors such as: the surgical approach,
implant positioning, implant choice and soft tissue repair.
Management of instability includes a thorough history taking,
clinical examination and radiographic evaluation.
There are many lines of treatment of hip instability according to
the cause; treatment of infection, revision of the malpositioned
component or increasing the soft tissue tension. Other trends include
large head diameter, bipolar arthroplasty and the use of the constrained
acetabular liner.
Constrained acetabular liners also have been shown to be an
effective treatment modality for patients with recurrent instability of the hip. It is used in cases of marked abductor muscle deficiency,
multiple failed revisions for instability and intraoperative
multidirectional instability.
Various designs of the constrained acetabular component are
available, they all have in common that they work by capturing the
femoral head within the acetabular component by means of a locking
mechanism.
However, the use of the constrained component increases the
possibility for developing much higher stresses at the shell-bone or
liner-shell interface, also it decreased range of motion before
impingement compared to the non-constrained component with
possible adverse effects on polyethylene wear and osteolysis.
Various modes of failure were reported; Type I: in the shell-bone
interface, Type II: in the shell-liner interface, Type III: the locking
mechanism, Type IV: bipolar-femoral head interface.
A constrained acetabular component is a reasonable and reliable
method for restoring stability in patients with complex recurrent
instability and can dependably prevent dislocation in those who are at
high risk because of absent or deficient soft tissues about the hip.
However, because of the early appearance of radiolucent lines around
some components and concerns about long-term fixation, the use of
these devices should be reserved for situations in which other methodsare inadequate or have already failed and when a correctable cause of
instability cannot be identified.