Note: Take care to maintain the bone stock and to avoid additional fractures or fracture propagation and displacement.
4. Cup removal for a fracture occurred during cup insertion
Major acetabular defects and loss of the column stability are generally recognized prior to cup insertion.
If a cup is already in place, it is removed using the instruments used for its insertion.
5. Fracture assessment
The fracture patterns may be difficult to classify.
It is important to maintain and to reestablish column stability and acetabular containment of the cup.
These challenges are different from the simpler segmental defects. The use of metal augments or cortical bone grafts is no longer sufficient and the use of an antiprotrusio cage is required.
6. Cup revision and fracture fixation
Use the antiprotrusio cage in combination with nonstructural bone graft.
Choose the appropriate size that matches the dimension of the patient acetabulum. Ensure sufficient proximal and distal flanges to achieve secure fixation into the ilium and the ischium.
Bone graft insertion
The defects are often too large for the patient's own bone from the acetabular reaming or the resected femoral head to be sufficient for grafting. Allograft bone may be required.
Bone grafts should be placed into the acetabular defects prior to insertion and fixation of the pelvic reinforcement device.
Contour the cage to fit the pelvis. This will require the use of plate bending instruments.
After placement of the bone graft, insert the cage and secure it to the pelvis with multiple screws.
Safe zones for screw insertion
Avoid inserting screws into the antero-superior and antero-inferior zones when possible. However, if necessary, critical evaluation of drill and screw depth is required. Consider oscillation of drill bit to prevent neurovascular injuries.
The manufacturers would provide the appropriate sizing chart to best match each liner to cage size.
The liner is cemented into the cage.
The surgeon should determine the most optimal position of the new liner which will be cemented into the cage.
The accepted "safe zone" is:
cup inclination 40° to 55°
cup anteversion 20° to 40°
Continue with hip replacement as preoperatively planned.
7. Aftercare following revision to a protrusio cup
Routine physiotherapy protocols for elective total hip arthroplasty is followed.
Early mobilization with protective weight bearing (50%) is recommended for 10 to 12 weeks until sufficient fracture healing.
Hip dislocation precautions must be given to the patient.
Postoperative radiographs should be done at 2 to 3 weeks to determine maintenance of satisfactory cage and cup fixation stability and no fracture progression or displacement.
Follow-up radiographs should be done at 8 to 10 weeks after surgery to determine sufficient cup fixation stability and no further fracture displacement to increase the weight bearing status, and physical activities.
The follow-up radiograph should be done at 5 to 6 months after surgery to assess for healing of the defects and the fractures.
Future follow-up is similar to the routine and standard protocol for total hip arthroplasty.