Megaprosthesis for Non-Oncologic Salvage (PFR and DFR)

A megaprosthesis (endoprosthetic or segmental replacement) substitutes a metallic segment for a portion of the femur plus the adjacent joint. Originally developed for limb salvage in bone tumours, it is increasingly used in non-oncologic salvage where the remaining bone cannot support conventional revision fixation.

• Proximal femoral replacement (PFR): replaces the proximal femur including the calcar and trochanters; articulates with the acetabulum via bipolar, dual mobility, constrained or conventional bearings.
• Distal femoral replacement (DFR): replaces the distal femur including both condyles; articulates via a rotating-hinge knee because the collaterals are resected with the bone.
• Total femoral replacement (TFR): the final salvage when proximal and distal segments are both unreconstructable — combines both, at further functional cost.

The philosophical shift: the surgeon abandons biological reconstruction (union, ingrowth into host bone at the metaphysis) in exchange for immediate mechanical stability and weightbearing. This trade favours the elderly, frail, low-demand patient for whom prolonged restricted weightbearing carries mortality risk comparable to hip fracture.

This is the classic modern viva. Neither option is universally correct; the decision is threshold-based.

Synthesis for the exam: DFR offers immediate full weightbearing and eliminates nonunion, at the cost of arthroplasty-magnitude complications. ORIF preserves bone and biology but exposes the frail patient to nonunion (reported in roughly 10 to 20 percent of osteoporotic distal femoral fractures) and the physiological cost of restricted mobility. Randomised evidence remains limited; current best practice individualises by bone stock, articular status, implant fixation and frailty, ideally within an ortho-geriatric pathway.

• Infection workup in every case: CRP/ESR, joint aspiration for cell count, differential and culture; consider alpha-defensin; multiple intraoperative tissue samples with antibiotics held until sampled (unless septic).
• Imaging: full-length femur radiographs both limbs for length templating; judet/oblique views of acetabulum for PFR (assess socket); CT for bone stock mapping, component fixation, and rotation reference; templating of resection level against modular implant segment lengths.
• Implant logistics: modular megaprosthesis system with a full range of segment lengths, stem diameters (cemented and cementless), dual mobility and constrained acetabular options for PFR, rotating-hinge components and tibial revision options for DFR. Have a total femur bail-out available for extensive cases.
• Team: anaesthetic optimisation, cell salvage/blood availability, plastic surgery on standby if soft tissue is marginal, ortho-geriatric co-management.

Why PFR over alternatives: immediate stability and weightbearing without reliance on bone healing; alternatives (APC, modular tapered stem plus strut) require intact distal fixation zones and biological incorporation.

• Position: supine, tourniquet if limb length allows (often not used with long incisions), radiolucent table, sandbag for 90-degree flexion.
• Imaging/equipment: rotating-hinge DFR system with modular segments; revision tibial components (stems, cones) available; fluoroscopy for stem work.
• Approach: anterior midline incision using the previous TKA scar; medial parapatellar arthrotomy. In stiff knees use quadriceps snip in preference to forced eversion; protect the patellar tendon insertion continuously — a smooth pin in the tubercle is a legitimate guard.
• Resection: excise the fracture/nonunion zone or failed component with dead bone back to bleeding, structurally sound diaphysis; mark femoral rotation (linea aspera posterior; whiteside/epicondylar references are gone). Measure the resection and rebuild length to match the contralateral templated femur — over-lengthening tightens the extensor and risks stiffness and wound problems; shortening causes extensor lag and instability in mid-flexion is absorbed by the hinge.
• Rotation: set femoral component rotation off the linea aspera (perpendicular reference) and tibial component off the medial third of the tubercle; combined rotational error causes patellar maltracking and abnormal hinge loading.
• Articulation — why rotating hinge: the collateral ligaments are resected with the condyles; a fixed hinge concentrates torque at the stem–bone interface and fails by loosening; the rotating hinge allows axial rotation, dissipating torque, and is the standard of care.
• At-risk structures: popliteal vessels posteriorly during distal resection (flex the knee, protect with a retractor on bone), common peroneal nerve with correction of long-standing valgus, patellar tendon insertion.
• Fixation: cemented stems in the elderly osteoporotic femur and tibia; cementless ingrowth femoral stems where bone quality allows; hybrid constructs common.
• Extensor mechanism: repair arthrotomy meticulously; if the tubercle was osteotomised, fix with wires/screws; manage patella per revision TKA principles (retain well-fixed button; resurface or leave per stock).
• Aftercare: immediate full weightbearing; early range of motion (extension splint only if extensor repair is tenuous); DVT prophylaxis; staged physiotherapy targeting independent transfers then community ambulation with an aid.
• Pitfalls: patellar tendon avulsion (catastrophic — prevent, do not treat), malrotation, over-lengthening, retained infected/dead bone at the resection margin.

Stress shielding is intrinsic to large-diameter stiff stems: proximal (PFR) or distal (DFR) cortical resorption adjacent to the body of the implant. Mitigation: line-to-line cementing, hydroxyapatite collars encouraging extracortical bone bridging at the shoulder, and compliant pre-stress fixation designs.

Complications, not implant survival, define this field. Failure is usefully classified using the Henderson classification of endoprosthetic failure: type 1 soft-tissue failure (instability, extensor failure), type 2 aseptic loosening, type 3 structural failure (implant/periprosthetic fracture), type 4 infection, type 5 tumour progression (not applicable in non-oncologic use).

• Realistic goal: household to limited community ambulation with a walking aid; most PFR patients have a persistent abductor lurch/Trendelenburg gait.
• DFR patients typically achieve 90 to 110 degrees of flexion; a small extensor lag is common.
• The overriding early benefit is immediate weightbearing and preserved independence — in the frail elderly this is a survival intervention, analogous to hip fracture arthroplasty.
• Counsel explicitly on lifelong reoperation risk, infection risk of 10 to 20 percent, and dislocation precautions after PFR.

• Silver-coated megaprostheses: elemental or galvanic silver surfaces release ions with broad antibacterial activity; comparative series (largely from European tumour and revision centres) report reduced infection rates and higher DAIR success versus uncoated implants, without significant systemic argyria at implant doses. Evidence is observational; use is concentrated in high-infection-risk reimplantation.
• Antibiotic-loaded cement remains the workhorse local delivery method in cemented salvage constructs.
• Iodine coatings and other antimicrobial surfaces are emerging with promising early series but limited comparative data.

• Global epidemiology: non-oncologic megaprosthesis use is rising worldwide, driven by the growing revision burden, periprosthetic fractures in ageing populations, and the recognised mortality cost of immobility in the frail elderly. In many series, non-oncologic indications now match or exceed tumour indications for PFR.
• Society guidance: no society issues a dedicated megaprosthesis guideline, but relevant frameworks apply — BOA/BGS BOAST-style fragility fracture standards (early surgery, immediate unrestricted weightbearing, ortho-geriatric co-management) underpin the DFR-in-fracture rationale; AO principles frame the fixation-versus-replacement decision; ICM (International Consensus Meeting) on musculoskeletal infection recommendations govern staged reimplantation and antimicrobial strategies; NICE and EFORT guidance on hip fracture and arthroplasty infection are applied by analogy.
• Registry evidence: national arthroplasty registries (NJR, AOANJRR, AJRR, SHAR, Norwegian, NZJR) capture hinged and segmental constructs incompletely and mostly within revision cohorts; they consistently show that revision-of-revision and hinge constructs carry the highest re-revision rates, dominated by infection and instability. Dedicated endoprosthesis registries and multicentre collaboratives (largely European) supply the best comparative data, including for silver coatings.
• Resource-setting variation: modular megaprosthesis systems are expensive and logistics-heavy. In lower-resource settings, alternatives — prolonged traction, resection arthroplasty, long cemented stems with cerclage, or amputation — remain in use; cost-effectiveness analyses in high-income systems increasingly favour DFR over failed fixation pathways in the very frail because reoperation and prolonged dependency dominate cost.

• DFR versus ORIF for elderly distal femoral fracture: genuine equipoise for fractures with fixable distal bone; randomised trials are ongoing and current practice varies widely between units and countries.
• Age threshold: how young is too young for a non-oncologic megaprosthesis? Most agree biological reconstruction should be exhausted first in patients with long life expectancy, but the boundary is undefined.
• Bipolar versus dual mobility versus constrained articulation for PFR: all reduce dislocation versus conventional heads; comparative data are observational and confounded by abductor status.
• Cemented versus cementless and compliant fixation: long-term stress shielding versus interface durability remains unresolved in salvage bone.
• Silver and antimicrobial coatings: promising observational data, no randomised evidence, and cost limits universal adoption.
• Total femoral replacement versus amputation in catastrophic failure of the frail host: decision-making is individualised with scant comparative outcome data.