Pelvic Discontinuity

Pelvic discontinuity is a complete separation of the superior hemipelvis (ilium and acetabular dome) from the inferior hemipelvis (ischium and pubis) through the acetabulum, involving both the anterior and posterior columns. It may be an acute fracture, an established non-union, or the gradual dissolution of the columns by osteolysis.

Acute intraoperative discontinuity. Created during component removal or cup impaction, usually in reasonable-quality bone. It behaves like an acute transverse-pattern acetabular fracture and has high healing potential if compressed and stabilised.

Chronic discontinuity. Already established at presentation, usually with severe associated bone loss, classically Paprosky IIIB and occasionally IIIA. The fracture surfaces are sclerotic, atrophic or osteolytic, and union potential is low, particularly in irradiated bone.

Why it behaves badly. The two hemipelves move independently under load, the inferior segment typically flexing and internally rotating relative to the ilium. Any implant fixed to only one segment, or spanning the gap without rigid fixation to both, suffers cyclical micromotion at its interface, which prevents ingrowth and causes early loosening or implant fracture.

Who gets it. The large majority of reported cases are women. The risk factors:

• Female sex (thinner columns, osteoporosis)
• Rheumatoid and other inflammatory arthropathies
• Prior pelvic irradiation, which leaves an osteonecrotic, avascular bed with essentially zero healing potential
• Massive particle-induced osteolysis
• Prior acetabular fracture, multiple prior revisions, and developmental dysplasia with deficient columns

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Paprosky frames the bone loss. Discontinuity is recorded as a modifier, most commonly attached to type IIIB: superior migration greater than 3 cm, a broken Kohler line, severe ischial lysis and an unsupportive rim. Berry and colleagues (Mayo) additionally stratified discontinuity by associated bone loss and prior irradiation, the two variables that still drive treatment.

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Biology, not defect size, decides the construct. Three questions set the strategy:

1. Is it acute or chronic? Acute means fracture surgery: compress and heal.
2. Can it heal? Healing potential depends on bone quality, vascularity (irradiation), inflammatory disease and defect size.
3. Can host bone support a porous implant? If contact with viable ilium and ischium is achievable, a cup-cage or distraction works; if the landmarks are destroyed, a custom triflange.

Compress or bridge. An acute fracture in healthy bone is compressed and allowed to heal. In a chronic discontinuity with dead, irradiated or rheumatoid bone union will not occur, so it is bridged with a cup-cage or custom triflange; applying a compression-only strategy to non-healing bone is a classic failure pathway.

The reconstruction ladder. The options form a ladder climbed on biology: posterior column plate plus porous cup, then acetabular distraction, then the cup-cage, then the custom triflange. Structural allograft with a conventional cage, in which the allograft fills the defect and the cage bridges and protects it during incorporation, sits off the ladder, mentioned only to dismiss it. Plate the acute, distract or cup-cage the chronic, triflange the catastrophic; cage and allograft belong to history.

Results by construct. Each construct has its own track record:

• Acute discontinuity treated with plate plus cup is the best-prognosis group; most heal when compressed in healthy bone.
• For chronic discontinuity treated with a cup-cage, modern series report survivorship for aseptic failure commonly in the 80 to 90 percent range at 5 to 10 years, the benchmark against which alternatives are judged.
• Distraction has encouraging mid-term results from the originating centres, with radiographic stability in the large majority; longer-term multicentre data are still accruing.
• The custom triflange has good mid-term fixation survivorship in most series but a high overall complication rate. Dislocation is the leading complication (deficient abductors, large exposure), followed by infection and nerve injury, and dual-mobility or constrained liners are commonly used.
• Structural allograft plus cage had high mid-term mechanical failure and loosening rates and is now rarely used as definitive treatment for discontinuity.

Two independent series, two different constructs, the same observation — and it changes what you do at the six-week film.

• Cup-cage (Abolghasemian, 26 discontinuities): three hips showed early radiographic migration of the components, then stabilised and finished with a successful outcome.
• Distraction with porous tantalum (Sporer, 20 analysed): four patients migrated early, then remained clinically asymptomatic and radiographically stable.

Why it happens. Both constructs are designed to settle. A cup-cage relies on biological ingrowth into a shell that the cage protects while union occurs; a distraction construct relies on the elastic recoil of the columns gripping an oversized cup. In each case a small early positional change can represent the construct seating rather than failing.

The condition attached to it. Abolghasemian's authors are specific: early migration does not necessarily mean failure provided the continuity of the bone graft at the discontinuity site is not disrupted. That is the discriminator — graft intact and the patient comfortable means serial radiographs; graft disrupted, progressive migration or pain means re-revision.

What to do. Do not re-revise on a single early film. Repeat the radiograph at a defined interval, compare the same landmarks, and treat progression rather than position as the failure signal. Equally, do not use this as reassurance for a construct that is migrating and symptomatic.

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• Global epidemiology: published series put discontinuity at roughly 1 to 5 percent of acetabular revisions, but quote the anchor rather than the range where you can: Berry's Mayo series found it in 31 of 3505 acetabular revisions — 0.9 percent — which sits below the commonly repeated range and is the largest denominator any of these figures rests on. The spread across series reflects how hard the diagnosis is to make rather than genuine geographic variation, since a discontinuity missed preoperatively and not stress-tested at operation is simply recorded as a type IIIB defect. As revision burden rises worldwide with ageing arthroplasty cohorts, absolute case numbers are increasing in every registry region.
• Registry perspective: national registries (NJR, AJRR, AOANJRR, SHAR, Norwegian, NZJR) capture revision for acetabular loosening and bone loss but do not code discontinuity as a discrete entity, so evidence rests on institutional series and multicentre cohorts rather than registry survivorship curves — an important limitation to state in an examination answer.
• Society guidance: AAOS and NICE address hip revision pathways (infection exclusion, centralisation of complex revision) rather than discontinuity-specific technique; the AO principles of column fixation underpin the plate-plus-cup strategy for acute discontinuity. In several health systems (for example UK revision networks and similar European models), complex acetabular revision including discontinuity is increasingly regionalised to high-volume revision centres.
• Resource-setting variation: custom triflanges and porous tantalum systems are costly and require CT-to-implant infrastructure; in resource-limited settings, plate-plus-cup, ring/cage constructs with impaction or structural graft, and staged strategies remain in use, accepting higher mechanical failure risk. Distraction with a standard jumbo porous cup is comparatively resource-efficient where porous shells are available.

Algorithm

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• Cup-cage versus distraction versus custom triflange for chronic discontinuity: no comparative trials exist; selection is driven by bone stock, surgeon experience and implant availability. Distraction advocates cite single-component simplicity; triflange advocates cite fixation into all three residual bones.
• Should the discontinuity be made to heal at all? Bridging constructs succeed without union; whether adding compression plating or grafting to a cup-cage improves durability is unproven.
• Bearing choice: dual-mobility versus constrained liners cemented into cages — constrained liners reduce dislocation but transmit torque to a fragile fixation interface; many revision surgeons now favour dual-mobility.
• 3D-printed custom implants: expanding indications and enthusiastic early series, but cost-effectiveness and long-term survivorship compared with off-the-shelf cup-cage remain undefined.
• Weight-bearing protocols: protected weight bearing for 8 to 12 weeks is conventional but evidence-light; earlier loading may be tolerated by well-fixed distraction or triflange constructs.

Related pages. Companion page on the same condition: Pelvic Discontinuity in Revision Hip Arthroplasty covers the same entity from the revision-arthroplasty side; the two overlap substantially and should be read together rather than in place of one another. The defect it sits inside: Acetabular Bone Loss and the Paprosky Classification — discontinuity is the modifier most often attached to type IIIB. The constructs: Custom Triflange Acetabular Components for when the landmarks are gone, and Revision Total Hip Arthroplasty for the wider operation. The femoral side of the same revision: Cement-in-Cement Revision. What it must be separated from: Acetabular Fractures — an acute periprosthetic transverse pattern behaves like fracture surgery and is compressed, not bridged — and Periprosthetic Fracture of the Hip.