Why hip position matters after a posterior approach
In a posterior-approach total hip arthroplasty (THA), the surgeon enters through the back of the hip capsule and the short external rotator muscles. Until these tissues heal, the back of the joint is weak, and certain positions can lever the femoral head out of the socket. The risky movements are hip flexion beyond 90°, adduction across the midline, and internal rotation. The abduction pillow keeps the legs apart so the operated leg cannot cross the midline, protecting the new hip from posterior dislocation.
How the abduction pillow works
The wedge-shaped pillow is placed between the legs, often secured with straps, while the client is in bed and especially during turning. It holds the operated hip in slight abduction and neutral rotation. Clients are usually turned to the unoperated side with the pillow in place so that the upper, operated leg does not drop into adduction. The pillow is part of the posterior hip precautions taught throughout the hospital stay.
| Posterior hip precaution | Reason |
|---|
| No hip flexion beyond 90° | Flexion pushes the femoral head backward |
| No crossing the legs or midline | Adduction levers the head out posteriorly |
| No turning the foot inward | Internal rotation also stresses the posterior capsule |
| Use an abduction pillow in bed | Maintains abduction during rest and turning |
Why the other options are wrong
Keeping the knee straight and extended is a goal after total knee arthroplasty, not the purpose of a hip abduction pillow. Swelling is managed with ice, elevation, and compression rather than with the pillow. The pillow sits between the legs and does not change whether the lateral incision touches the mattress.
Watch out! Do not confuse precautions for different approaches. The posterior approach restricts flexion, adduction, and internal rotation; an anterior approach mainly restricts extension and external rotation. The question tells you the approach, so use it.
Exam takeaway
Key point! After posterior-approach hip replacement, an abduction pillow prevents adduction across the midline and protects against dislocation. Combine it with no flexion beyond 90° and no internal rotation.