Acetabular Bone Loss: Paprosky Classification and Reconstruction

Paprosky described the system in 1994 from a consecutive revision series. Unlike the AAOS (D'Antonio) classification, which describes defect morphology (segmental versus cavitary) without directing treatment, Paprosky's system is built around a single operative question: can the remaining rim and columns support a hemispherical cementless cup with supplemental screws?

• It is applied to a standardised AP pelvis radiograph, is validated against intraoperative findings, and each grade maps to a reconstruction strategy.
• The grade predicts remaining host-bone contact, which drives biological fixation: cementless ingrowth surfaces generally require on the order of 50 percent or more viable host contact and a stable rim.
• It also stratifies the risk of pelvic discontinuity — essentially confined to IIIB and severe IIIA defects.

The radiographic grade is a hypothesis to be confirmed at surgery — plain films underestimate osteolysis, and the final decision is made after component extraction and debridement.

• Sequence: remove the failed component with curved gouges or an explant-type system to minimise iatrogenic bone loss; excise the interface membrane completely; send tissue for culture and histology in every revision; curette lytic cavities to bleeding host bone.
• Rim test: seat a trial hemispherical shell. A trial that is inherently stable against the rim with an interference fit at two thirds or more of the circumference supports hemispherical reconstruction. A trial that 'wobbles' superiorly indicates a IIB or IIIA pattern; one that falls medially indicates a IIC or IIIB pattern.
• Estimate host contact: visually map viable, bleeding host bone against the trial; aim for greater than about 50 percent contact for ingrowth fixation, ideally with contact spanning the anterosuperior and posteroinferior 'support points'.
• Discontinuity stress test: grasp the ischium (or place a Cobb inferiorly) and stress it against the ilium while observing the acetabular fracture line for motion — independent movement of the inferior hemipelvis confirms discontinuity and changes the entire construct.
• Column palpation: finger along the posterior column into the sciatic notch and along the anterior column; defects not visible radiographically are frequently found here.

• Identify the implants in situ from previous operation notes: cup manufacturer and size (dictates liner options and extraction tools), screw number and position, cemented versus cementless.
• Restore the hip centre: template the new cup at the anatomical centre (level of the teardrop) rather than accepting a high hip centre; every centimetre of proximal placement compromises abductor mechanics and increases joint reactive force. A deliberate high hip centre is a fallback, not a plan, and demands a longer femoral neck or lateralised liner to preserve offset.
• Template the defect: on the AP pelvis, superimpose a hemispherical template at the anatomical centre — the uncovered superolateral zone predicts augment size and position; CT-based three-dimensional planning is standard for IIIB and custom implants.
• Plan fixation trajectories: posterosuperior dome screws into the sciatic buttress (longest, safest corridor), posteroinferior screws into the ischium; avoid the anterosuperior quadrant.
• Exclude infection before any revision: inflammatory markers, aspiration with synovial fluid cell count and culture — bone loss reconstruction in an infected bed fails.
• Prepare a bailout ladder: hemispherical cup, jumbo cup, augments, cup-cage components and allograft should all be available even for an anticipated Type II — intraoperative upgrading of the defect is common.

• Porous tantalum has porosity around 75 to 80 percent, a modulus of elasticity between cancellous and cortical bone, and a high coefficient of friction against bone — giving superior initial scratch fit and rapid, extensive bone ingrowth compared with older sintered-bead or fibre-metal surfaces.
• These properties allow reliable osseointegration at lower host contact than traditional cementless cups, which is precisely why the reconstruction ladder shifted: defects that once needed structural graft or cages are now managed with tantalum shells and modular augments.
• Augments are effectively 'metallic structural allograft' — immediate mechanical support without resorption, at the cost of not restoring bone stock.
• Highly porous titanium three-dimensional-printed equivalents now offer comparable porosity and are the basis of most custom triflanges.
• Principle for the construct: every interface must be either ingrowing (implant on bleeding host bone) or rigidly unitised (cement between cup and augment or cup and cage); a mobile interface is a failed interface.

• Aseptic loosening and construct failure: commonest cause of re-revision in Type III reconstruction. Prevent with maximal host contact, multiple screws, unitised interfaces, protected weight bearing (typically toe-touch or partial for 6 to 12 weeks in major constructs). Manage failure by re-grading the (now worse) defect and climbing the ladder — often to cup-cage or triflange.
• Missed or iatrogenic pelvic discontinuity: prevent by CT in Type III, gentle reaming, and the intraoperative stress test; manage established discontinuity with cup-cage, distraction, or triflange, with posterior column plating reserved for acute healable patterns.
• Dislocation: the leading early complication of complex acetabular revision (abductor deficiency, large exposures, altered centre). Rates after major revision are commonly reported around 5 to 10 percent and higher after triflange. Mitigate with careful restoration of centre and offset, dual mobility bearings, and constrained liners only into rigidly fixed shells.
• Vascular injury: external iliac and obturator vessels during medial dissection and anterosuperior screws. Prevention: CT angiography for intrapelvic components, quadrant system for screws, vascular surgery on standby and a retroperitoneal approach when the component is intrapelvic.
• Sciatic nerve injury: during posterior column work, ischial flange placement and distraction; identify, protect, avoid prolonged retraction, slot ischial flanges.
• Infection: revision arthroplasty carries a substantially higher periprosthetic infection rate than primary surgery; exclude infection preoperatively, take multiple deep samples, and follow a two-stage pathway if infection is confirmed.
• Graft resorption and collapse: the defining failure of structural allograft — anticipate in any hip reconstructed with bulk graft and follow radiographically.

• Global burden: aseptic loosening and osteolysis remain leading causes of acetabular revision worldwide; as primary hip arthroplasty volumes rise across Asia, Latin America and Africa, complex acetabular revision is an expanding global need.
• Registry evidence: national registries (NJR of England and Wales, AOANJRR, AJRR, Swedish and Norwegian arthroplasty registers, NZJR) consistently show that revision arthroplasty has substantially lower implant survivorship and higher re-revision, dislocation and infection rates than primary surgery, and that cementless hemispherical fixation dominates acetabular revision practice in registry populations. Registries do not currently stratify by Paprosky grade, which limits comparative-effectiveness conclusions for augments versus cages versus triflanges — the evidence for major constructs remains observational case series.
• Society guidance: no society issues a defect-specific guideline, but relevant frameworks include EFORT and AAOS consensus material on periprosthetic joint infection exclusion before revision, the International Consensus Meeting (Philadelphia) infection criteria, and national getting-it-right programmes advocating network-level centralisation of complex (Type III and discontinuity) revisions to high-volume units with multidisciplinary support — a model adopted in several European systems.
• Practice variation by resource setting: custom triflanges and porous tantalum systems are expensive and not universally available; in resource-limited settings, structural and impaction allografting with cemented cups, reinforcement rings (Burch-Schneider, Müller) and jumbo cups remain mainstream and produce acceptable results when principles of host contact and rim support are respected. Bone banking availability similarly shapes the ladder.
• Antibiotic and thromboprophylaxis practice follows local national guidance; the universal constants are preoperative infection exclusion and multiple intraoperative deep cultures.

• Jumbo cup versus augment in IIB and lesser IIIA: enthusiasts of jumbo cups cite simplicity and excellent survivorship; critics cite hip-centre elevation, anterior column loss and psoas irritation. No randomised comparison exists.
• Cup-cage versus distraction versus triflange for chronic discontinuity: all are supported only by case series from originating centres; selection is driven by defect geometry, bone quality, surgeon experience and cost rather than comparative evidence.
• High hip centre: deliberately accepting a centre up to about 2 cm proximal with a smaller cup on better bone remains defended by some units, though most modern teaching favours anatomical restoration with augments.
• Structural allograft in the young patient: despite mid-term resorption, its unique capacity to restore bone stock keeps it alive as an option for patients facing multiple future revisions.
• Custom triflange timing: whether to go custom first in massive IIIB or reserve it for failed off-the-shelf reconstruction is unresolved; lead time, cost and inflexibility weigh against routine first-line use.
• Inter-observer reliability: studies show only moderate agreement in assigning Paprosky grades from radiographs, particularly between IIIA and IIIB — one argument for routine CT and for treating the classification as a planning framework, not a verdict.