Femoral Bone Loss in Revision Hip Arthroplasty: Paprosky Classification and Stem Selection

Revision femoral surgery is a problem of achieving durable fixation in compromised bone. Every decision follows from a single question: what bone remains that can support an implant?

• Metaphysis intact (Type I) — primary-type fixation still possible.
• Metaphysis gone, diaphysis intact (Type II, IIIA) — move fixation distally into the diaphysis.
• Diaphysis compromised (IIIB) — fixation must be achieved in a short, often capacious segment: only a tapered fluted design can do this reliably.
• No isthmus (Type IV) — the femur cannot grip an uncemented stem. Options: rebuild the tube (impaction grafting), cement into what remains (elderly), replace the proximal femur with allograft plus stem (APC), or replace it with metal (proximal femoral replacement).

Two further principles:

1. Bypass defects by at least two cortical diameters of intact bone (relevant for cortical perforations, stress risers, and old screw holes) to reduce periprosthetic fracture risk.
2. Restore the abductor mechanism — a perfectly fixed stem with a detached trochanter is a failed hip. Trochanteric fixation and soft-tissue strategy is part of the plan, not an afterthought.

Key discriminators to state in the exam:

• I versus II: is the metaphyseal cancellous bone supportive?
• II versus III: does the bone loss extend into the metadiaphysis?
• IIIA versus IIIB: greater or less than 4 cm of diaphyseal scratch-fit.
• III versus IV: is there any isthmus capable of gripping a stem at all?

• Position: lateral decubitus on a radiolucent table, well-padded supports, whole limb draped free including knee.
• Imaging and equipment: full-length calibrated femur films; image intensifier available; company-specific extraction kit, high-speed burr, flexible osteotomes, trephines, cement removal instruments (or ultrasonic), cerclage cables, revision stem system with trials, allograft available, dual mobility or constrained options on the shelf.
• Preparation: exclude infection preoperatively (inflammatory markers, aspiration for culture and synovial white cell count); send at least 5 intraoperative tissue samples with separate instruments; tranexamic acid, cross-match, cell salvage.
• Approach: posterior approach with extended proximal and distal exposure; identify and protect the sciatic nerve.
• Dissection / removal: dislocate, remove head; attempt stem extraction in situ; if fixed stem or long cement column, perform an extended trochanteric osteotomy — length templated to reach the stem tip or cement plug while preserving 4 to 5 cm of distal diaphysis; osteotomise one third of the canal circumference laterally, hinge on vastus lateralis and anterior soft tissues; prophylactic cerclage cable distal to the osteotomy before reaming.
• Reconstruction: sequential conical reaming by hand down the true canal axis to firm endosteal cortical engagement over 2 to 3 cm minimum; insert the fluted taper to templated depth with reproducible advancement per blow ceasing to advance; test axial (impactor load) and rotational stability; trial proximal bodies for length, offset, version; trial reduction with stability testing through full arc; commit proximal body, engage taper cleanly and dry.
• At-risk structures: sciatic nerve (posterior retraction, lengthening greater than about 4 cm), femoral cortex (perforation with straight reamers in a varus femur — this is the ETO indication), lateral cortex at ETO hinge, medial femoral circumflex remnants.
• Fixation of osteotomy / closure: reduce the ETO fragment around the proximal body; two or three cerclage cables; consider trochanteric claw-cable device if the fragment is fractured or the abductors avulsed; repair posterior capsule and short external rotators; layered closure over a drain if preferred.
• Aftercare: check radiograph as the subsidence baseline; toe-touch to partial weight bearing 6 weeks (protects ETO and permits taper settling), then progressive loading; posterior precautions; radiographs at 6 weeks, 3 months, 1 year measuring subsidence against the baseline.
• Pitfalls and salvage: subsidence greater than 10 mm with instability — re-revise with a larger taper or longer stem; ETO nonunion (uncommon with cables, most unite) — revision fixation with grafting; intraoperative fracture — cables plus longer bypass; irreducible instability — dual mobility or constrained liner.

The calcar:

• Modern revision philosophy bypasses the calcar rather than reconstructing it — no modern revision stem depends on calcar support. Calcar-replacing proximal bodies restore soft-tissue tension and version, not load transfer.
• Residual proximal shell bone should be preserved and closed around the stem — even non-structural proximal bone contributes to soft-tissue attachment, vascularity and future revisions, and Wagner-type remodelling can partially restore it.
• Strut allograft with cables can reinforce a severely thinned medial or lateral cortex or an ETO in poor bone.

The trochanter and abductors:

• ETO fragment: cerclage cables (usually two or three); avoid overtightening on a thin fragment.
• Trochanteric escape or fracture: claw-plate or grip-cable device; accept fibrous union with reasonable function in the low-demand patient — repeated fixation attempts in avascular bone often fail.
• Absent abductors (multiply revised, PFR): highest dislocation risk of any hip scenario — use dual mobility or constrained liners, consider abductor reconstruction to the implant or trochanteric slide, and counsel the patient about limp and lifelong precautions.

• Types I-II: excellent — survivorship of diaphyseal-fixing stems above 95 percent at 10 years in classic series.
• IIIA: extensively coated cylindrical stems 96 to 97 percent survivorship in Paprosky's own series; fluted tapered stems comparable at mid-term.
• IIIB: cylindrical stems historically failed in roughly one in five or worse; fluted tapered stems restored survivorship to around 90 to 95 percent at mid-term — this outcome differential is the single most examinable fact in the topic.
• IV: all options carry higher complication rates. Impaction grafting gives durable results in experienced centres with the polished taper technique but with meaningful fracture and subsidence rates; PFR survivorship is limited more by instability and infection than fixation.

Complications across revision femoral surgery:

• Dislocation — the commonest complication of revision hip arthroplasty overall; mitigate with restored offset and version (modularity), soft-tissue repair, and liberal use of dual mobility in abductor-deficient hips.
• Periprosthetic fracture — intraoperative (impaction, reaming, extraction) and late tip fractures; prophylactic cerclage and two-cortical-diameter bypass are the preventive levers.
• Subsidence — tapered stems; usually early and self-limiting below 5 mm.
• Infection — always exclude before aseptic revision; multiple samples intraoperatively.
• Stress shielding — stiff large-diameter cobalt-chrome stems; favour titanium tapers in capacious canals.
• Modular junction failure — fracture and fretting; support the junction, size appropriately.

• Registry evidence: the NJR (England and Wales), AOANJRR (Australia), SHAR (Sweden) and AJRR (United States) consistently report aseptic loosening, infection, dislocation and periprosthetic fracture as the leading reasons for femoral re-revision; registry data show the international migration from cylindrical cobalt-chrome to fluted tapered titanium stems for major bone loss over the last two decades, and steadily rising use of dual mobility in revision.
• AAOS and NICE address hip arthroplasty broadly; neither prescribes a stem for a given Paprosky class — implant choice remains a principles-based surgical decision, which is exactly how examiners frame it.
• BOA/BHS revision network guidance (United Kingdom) supports concentrating complex (Type IIIB and IV) revisions in higher-volume revision units with allograft access and multidisciplinary infection services — a model echoed in several European systems.
• Resource-limited settings: modular revision systems, bone banks and megaprostheses may be unavailable. Pragmatic alternatives include long cemented stems, monoblock Wagner-type tapers (cheaper, no junction), and cement-in-cement techniques; the classification and its fixation logic remain universally applicable even where the implant menu is narrow.
• Fresh-frozen allograft availability (impaction grafting, APC) varies enormously worldwide with regulatory and tissue-banking infrastructure — this drives genuine regional variation in Type IV management, with PFR used earlier where allograft is unavailable.

• Modular versus monoblock tapered stems: modularity aids intraoperative flexibility but introduces junction fracture and corrosion risk; comparative series show similar survivorship, and several units have returned to monoblock tapers for straightforward IIIA/IIIB femurs, reserving modularity for complex version or length problems.
• How short can the fixation segment be? The 2 to 3 cm figure for tapered stems is empirical; distal fixation into a short supracondylar segment blurs into "total femoral" territory and the failure threshold is not precisely defined.
• Impaction grafting versus tapered stems in Type IV: bone-stock restoration versus reproducibility; impaction grafting results are strongly centre-dependent, and many surgeons now attempt a tapered stem with cables even in near-Type IV femurs.
• PFR versus APC in the younger Type IV patient: APC restores bone but risks nonunion and resorption; PFR is reliable early but mortgages the future. No randomised data exist and practice follows unit expertise.
• Routine dual mobility in revision: increasingly adopted given dislocation dominance in registries, but with unresolved questions about intraprosthetic dislocation and long-term wear in younger patients.