Protrusio acetabuli is a medialisation of the medial wall of the acetabulum. The head of the femur lies medial to the Ilio-ischial or Kohler’s line.
• It is the result of remodelling of weak, medial acetabular bone after multiple, recurring stress fractures
• Migration occurs along the resultant joint-reaction force vector
• There are a number of causes, the common ones being secondary to inflammatory cause (inflammatory destruction) or metabolic cause (qualitative deficiency in the bone).
This case of protrusion acetabuli in a 25 year young male resulted from a long standing central fracture dislocation of the acetabulum. Stiffness and short limbed gait were the presenting symptoms. Other symptoms encountered commonly are progressive pain.
Radiological findings- The medial wall of the acetabulum lies medial to the Ilio Ischial line.
Medial wall (acetabular line) and it’s relation to ilioischial line (Kohler’s line)

Protrusio acetabuli Grade III

Treatment consists of a total hip replacement. Since many cases occur in young patients, a conventional total hip replacement is not ideal since it removes more host bone. Invariably a revision hip replacement will be required in a young patient undergoing a total hip replacement. A bone sparing option like Hip resurfacing or short-stem hip replacement is preferable. Hip resurfacing is possible in mild grades where bone grafting is not required. In the more severe grades, bone grafting is mandatory. An anti protrusio cage can also be used to reconstruct a severe medial wall deficiency.
In the present case, an innovative approach was adopted for hip reconstruction. Hip resurfacing was ruled out because of the necessity for bone grafting and severity of the condition (Grade III in this case)
A bone sparing Proxima hip replacement was planned. The cup was lateralized by bone grafting.
Hard on hard bearings were chosen in view of their established favorable long term outcomes. Hard on Cross linked poly was not chosen because of the lack of long term results. A Pinnacle cup with a metal liner and a Proxima stem with a Ceramic 36 mm head were used.
Figure 2 shows the Proxima stem with a 36 mm Delta Ceramic head.

Proxima stem with Ceramic head

The Final result is shown in this x ray

Proxima hip replacement
This is probably the first case of Proxima hip replacement done for a case of Protrusio acetabuli.
This operation was performed by consultant Orthopaedic surgeon
Dr.A.K.Venkatachalam.
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