Major bone loss involving the acetabulum can be seen during revision THA due to component loosening, migration or osteolysis and can also occur as a sequela of infected THA. Uncemented highly porous ingrowth acetabular components can be used for the reconstruction of the vast majority of revision cases, especially where small to mid-sized segmental or cavitary defects are present which do not compromise stable mechanical support by the host bone for the cup after bone preparation is complete. A mechanically stable and near motionless interface between the host bone and the implant is required over the initial weeks post-surgery for bone ingrowth to occur, regardless of the type of porous surface employed. As bone deficiency increases, the challenge of achieving rigid cup fixation also increases, especially if the quality of the remaining host bone is compromised. A stepwise approach to enhanced fixation of the highly porous revision acetabular component is possible as follows:. Maximise Screw Fixation. Use of a limited number of screws in the dome only (as routinely occurs with a cluster hole design) is inadequate, except for primary arthroplasty cases or very routine revision cases with little or no bone loss and good bone quality. Otherwise an array of screws across the acetabular dome and continuing around the posterior column to base of the ischium is strongly recommended. This can help prevent early rocking of the cup into a more vertical position due to pivoting on dome screws used alone, via cup separation inferiorly in zone 3. A minimum of 3 or 4 screws in a wide array are suggested and use of 6 or more screws is not uncommon if bone quality is poor or defects are large. Cement the Acetabular Liner into the Shell. This creates a locking screw effect, which fixes the screw heads in position and prevents any screws from pivoting or backing out. Acetabular Augments (vs Structural Allograft). When critical segmental defects are present which by their location or size preclude stable support of the cup used alone, either a structural allograft or highly porous metal augment can provide critical focal support and enhance fixation. Highly porous metal augments were initially developed as a prosthetic allograft substitute in order to avoid the occasional graft resorption and loss of fixation sometimes seen with acetabular allograft use. Cup-Cage Construct. If one or more of the above strategies are used and fixation is deemed inadequate, it is possible to add a ½ or full acetabular cage “over the top” of the acetabular component before cementing a polyethylene liner in place. The full cup cage construct can be used for maximal fixation in cases of pelvic dissociation, alone or in combination with the distraction method as described by Paprosky. Use of a ½ cage is technically simpler and requires less exposure than a full cage, but still greatly enhances rigidity of fixation when transverse screws into the ilium are combined with standard screws in the cup including vertically into the dome. These techniques used in combination with highly porous tantalum implants have allowed durable fixation for the full range of reconstructive challenges and bone defects encountered. Newer 3-D printed titanium highly porous materials have recently been introduced by multiple manufacturers as a potential alternative that may be more cost effective, but these implants and materials will require clinical validation over the years ahead

The cemented acetabular component has been essentially abandoned, due to the reliable and durable fixation provided by bone ingrowth into cementless acetabular components of many different designs. A variety of porous surfaces including sintered beads, titanium fibermetal, plasma sprayed titanium, and ultraporous tantalum have been shown to result in significant osteointegration, and provide long term fixation of cementless acetabular components. New ultraporous metals will also likely prove to perform similarly, however, their advantages in the primary THA are unclear. Most currently available cementless acetabular components rely on obtaining initial “interference” or “frictional” fit provided by relative underreaming. Many designs incorporate additional features such as screws, pegs, and fins to limit implant micromotion and augment initial fixation until early tissue ingrowth occurs. “Underreaming” by more than 1 mm has been associated with incomplete component seating and increased incidence of acetabular fracture. Knowledge of the geometry of the component by the surgeon is recommended, since some designs are elliptical and have a built-in degree of interference fit. Screws used to augment acetabular fixation in the primary THA can typically be restricted to the area of the acetabular dome (cluster configuration) and cups with multiple holes are usually unnecessary and may be undesirable as they allow access of wear debris to the acetabular implant-bone interface. In order to minimize backside wear and dissociation of the acetabular liner, modular components need to have a well-designed locking mechanism. Retrieval studies have shown that the peripheral rim of the acetabular liner is most susceptible to oxidative degradation and the integrity of the locking mechanism in this area can be compromised with time. Non-modular, “one piece” components eliminate these concerns, but most of these designs rely on initial frictional fit alone for stability. In the event that the position of a nonmodular component needs to be changed intra-operatively, the quality of frictional fit after repositioning can be diminished and may not be sufficient for implant stability. Modular components that incorporate screws, allow for acetabular component repositioning and adjunctive fixation with screws. Many newer acetabular component designs can accommodate a modular liner for either a metal on polyethylene, ceramic on ceramic or metal on metal bearing