Introduction:
Bone loss at the acetabulum results in the loss of structural integrity and impairment of mechanical support for an implanted prosthetic socket.

The treatment goals for bone loss are:

• Correction of hip mechanics by positioning the cup in the anatomic location.
• The repair of defects by closing any segmental defects to achieve containment.
• The replacement of bone loss by filling the cavity defects with allograft bone chips.
• Achieving mechanical stability of the implant by impacting the chips and the use of bone cement. These goals can be achieved by using the acetabular X-change® Revision Instruments System. They help provide a stable acetabular reconstruction by packing the contained acetabulum with allograft bone chips at the correct anatomical location.

Surgical exposure:
Identification of the major landmarks and of the sciatic nerve is carried out.

A wide exposure of the entire socket is essential. After removing the old components and any cement, the fibrous interface is thoroughly freed from the irregular acetabular wall using sharp spoons and curettes.

Special care is given to locate the transverse ligament at the inferior aspect of the acetabulum. This is the best landmark for positioning the inferior edge of the socket. Beginning at this position the reconstruction can be built up in order to restore acetabular form.

Preparation of the acetabulum:
After removal of the soft tissue, multiple small but superficial drill holes to enhance surface contact and to initiate vascular invasion into the graft. The acetabulum is then lavaged.

Where there are peripheral segmental defects flexible stainless steel meshes can be trimmed and adapted to the defects around a trial socket held in the anatomical position against the transverse ligament

At the periphery these are fixed with small bicortical screws at a minimum of three points, normally more, to secure rigidity. Medial segmental defects may also be covered with the metal mesh or, in the case of a very small defect, with a structural cortico cancellous bone graft. The acetabulum is thus reformed leaving only cavity defects to be filled.
In cases of massive bone stock loss including loss of anterior and/or posterior columns and in cases of pelvic discontinuity, it may be advisable to use rings or cages in combination with impacted morsellised allograft.
Where a cage is not adequately supported by host bone, a block allograph may be shaped to support the cage.

medial defect

peripheral segmental defect

defects closed with metal wire meshes

Preparation of the graft:
Allografts from fresh frozen femoral heads are recommended. Autogenous cancellous chips may be mixed with the allograft if the surgeon so wishes.

Allograft chips are prepared using rongeurs or by passing the femoral heads through a bone mill which produces chips of substantial size.

At least 2 femoral heads should be available

Acetabular Reconstruction:
After rinsing, the acetabulum is packed tightly with chips first in the small cavities, then subsequently layer by layer in the entire socket.

The impactors are used vigorously to hammer the chips in situ. Care is taken to reconstruct the anatomy of the hip by packing in as much chip graft material as is necessary. Care is taken to reconstruct the anatomy of the hip by packing in as much chip graft material as is necessary until the socket is built up to the height of the transverse ligament (restoration of acetabular form). The impacted graft layer must be at least 5mm thick. For impaction near the rim the small impactors are used in combination with the large impactor.

In this way the entire acetabular hemisphere is finally covered with a layer of impacted allograft chips

Reverse reaming does not constitute ‘impaction’ grafting and is not a satisfactory technique

Cement Pressurisation:
A clean, dry bed for the bone cement is established. Bone cement is introduced into the acetabular cavity in a relatively viscous state.

Typically, using Simplex Cement and with a theatre temperature of 21°C, the cement should be mixed for at least one minute, left to stand for at least one minute and inserted into the cavity at approximately 3-4 minutes.

Pressure is applied to the cement using considerable pressure to force it into the bone graft.

The appropriate size polyethylene cup is implanted, using the introducer guide rods to ensure correct anatomical alignment. The appropriate size cup is 2-4mm in diameter smaller than the diameter of the last used impactor, creating space for the cement layer.

The appropriate size of Polyethylene cup is implanted, using the introducer guide rods to ensure correct anatomical alignment.

The cup is held in position carefully until the cement polymerises.