Periprosthetic Distal Femur Fracture

Periprosthetic distal femur fractures (PDFFs) are fractures occurring around or immediately proximal to a total knee arthroplasty (TKA) femoral component. They represent one of the most challenging complications in arthroplasty surgery, combining the difficulties of complex fracture fixation with the constraints imposed by existing implants.

• Incidence: 0.3–2.5% after primary TKA; up to 5.6% after revision TKA
• Rising incidence due to ageing population and increasing arthroplasty numbers
• Predominantly affects elderly osteoporotic women (>70 years)
• Most occur within 5 years of arthroplasty, often after low-energy falls
• High morbidity and mortality — 1-year mortality reported up to 15–30% in elderly cohorts
• Risk factors: osteoporosis, rheumatoid arthritis, anterior femoral notching, corticosteroid use, revision implants, stemmed femoral components, stress risers at implant tip
• Anterior femoral notching during TKA reduces cortical bone stock — biomechanically significant stress riser, though clinical impact is debated

Multiple classification systems exist. The Su classification and the Lewis & Rorabeck classification are most commonly used clinically and in examinations.

Lewis & Rorabeck Classification (1997)

Su Classification (2004) — based on fracture relationship to femoral component

The Unified Classification System (UCS) by Duncan & Haddad (2014) is also increasingly used — it classifies all periprosthetic fractures by bone, implant stability, and bone stock, guiding whether fixation or revision is more appropriate.

Systematic preoperative evaluation is essential to determine fracture pattern, implant stability, and patient fitness for surgery.

• Clinical assessment: mechanism of injury, prior knee function, pain, pre-injury mobility, comorbidities, anticoagulation status
• Neurovascular exam: popliteal vessels and peroneal nerve at risk in displaced fractures
• Implant review: obtain original operative notes and implant stickers — identify make, model, stem length, constraint level
• Plain radiographs: full-length femur AP/lateral + knee AP/lateral; assess fracture pattern, implant positioning, signs of loosening (radiolucent lines, cement mantle disruption, osteolysis)
• CT scan: recommended for comminuted or complex fractures; helps plan fixation strategy and assess distal bone stock
• Implant loosening signs: periosteal reaction, subsidence, change in component position on serial films, cement-bone interface lucency >2 mm
• Infection screen: CRP, ESR, WBC — infection changes management entirely; aspiration if clinical suspicion
• Bone density assessment: DEXA if not recently performed — informs implant choice and postoperative rehabilitation

Treatment decision depends on four key factors: fracture displacement, implant stability, distal bone stock, and patient physiology.

• Non-operative management is rarely successful in displaced fractures — high rates of malunion, nonunion, and functional decline
• Operative intervention preferred in most displaced fractures in medically fit patients
• Multidisciplinary approach mandatory — orthogeriatrics, anaesthetics, physiotherapy, OT

Open reduction and internal fixation (ORIF) is the treatment of choice when the implant is stable and adequate distal bone stock exists.

Retrograde Intramedullary Nail (RGN)

• Requires an open-box femoral component with intercondylar notch access — not possible with closed-box designs
• Advantages: load-sharing device; relative stability; minimally invasive; early mobilisation
• Disadvantages: limited distal fixation in very short distal segments; cannot be used with stemmed or constrained implants occupying the femoral canal
• Entry point: intercondylar notch, just anterior to PCL attachment — accurate entry prevents iatrogenic posterior cortex perforation
• Nail tip should bypass proximal stress riser by at least 2–3 cortical diameters

Locking Plate (Distal Femoral Locking Plate — DFLP)

• Workhorse for most PDFFs — applicable regardless of component box design
• Fixed-angle locking screws bypass cement mantle and engage distal condylar bone
• Minimally invasive plate osteosynthesis (MIPO) technique preserves biology and periosteal blood supply
• Screw trajectories must be planned to avoid component flanges, cement, and locking pegs
• Dual plating (medial + lateral) may be required for comminuted osteoporotic fractures — improves construct stiffness
• Cable cerclage can supplement fixation around implant stems
• Non-union rate with locking plate: approximately 5–10% in published series

Combined Nail + Plate

• Emerging technique for highly comminuted or osteoporotic cases
• Provides superior biomechanical construct — reduces implant failure and nonunion rates
• Technically demanding — requires careful planning to avoid screw-nail conflict

When the TKA component is loose, or when distal bone stock is insufficient for fixation, arthroplasty-based solutions are preferred.

• Revision TKA with stemmed components: bypasses the fracture zone; achieves fixation in metaphyseal/diaphyseal bone above the fracture; requires adequate proximal bone stock
• Distal Femoral Replacement (DFR): megaprosthesis replacing the distal femur — indicated when distal bone stock is insufficient (<4 cm) or fracture is highly comminuted
• DFR provides immediate stability, allows early weight bearing, avoids nonunion risk
• DFR disadvantages: significant soft tissue dissection, risk of infection, aseptic loosening, extensor mechanism disruption, and poorer functional outcomes in some series
• DFR increasingly used in elderly low-demand patients — provides predictable early recovery
• Modular rotating hinge DFR allows reconstruction even with significant ligamentous insufficiency
• Recent comparative studies (Streubel et al., Fakler et al.) suggest DFR may be preferable to complex ORIF in fractures with very limited distal bone stock

• Weight bearing status determined by fracture pattern, fixation quality, and bone quality
• ORIF with stable fixation: toe-touch weight bearing progressing to full weight bearing by 6–12 weeks
• DFR: immediate full weight bearing in most cases — major advantage in elderly patients
• DVT prophylaxis mandatory — LMWH or DOAC as per institutional protocol
• Early physiotherapy: quadriceps activation, range of motion exercises commenced within first week
• Orthogeriatric co-management reduces medical complications and length of stay
• Bone protection therapy (bisphosphonates, calcium, vitamin D) should be initiated or optimised perioperatively
• Serial radiographs at 6 weeks, 3 months, 6 months — assess callus formation and implant stability

For the experienced arthroplasty or trauma surgeon, several nuanced decision points arise in the management of PDFFs:

• Implant identification is paramount: contact manufacturer if stickers unavailable — wrong nail entry into a closed-box component causes catastrophic damage
• Component alignment must be restored: malalignment of the femoral component after fracture healing results in edge loading, polyethylene wear, and premature failure — coronal and sagittal alignment must be verified intraoperatively with fluoroscopy
• Cement mantle disruption: a previously well-fixed cemented component can become acutely loose during fracture displacement — always reassess intraoperatively
• Biological augmentation: consider bone graft or bone graft substitute at fracture site in comminuted osteoporotic cases, particularly with locking plate fixation
• Screw trajectory planning: use component-specific templates or intraoperative fluoroscopy to avoid screw-component conflict — screws abutting or penetrating the component cause noise, pain, and accelerated polyethylene wear
• Dual plating: for comminuted fractures with <4 cm distal segment, a medial buttress plate or cable plate supplementing the lateral locking plate significantly improves construct rigidity and reduces nonunion
• DFR vs complex ORIF: in patients >75 years with Su type III or severely comminuted fractures, DFR increasingly favoured — faster rehabilitation, avoids nonunion, and comparable or superior functional outcomes in low-demand patients
• Infection exclusion: never perform definitive fixation without ruling out occult PJI — intraoperative frozen sections and tissue cultures should be sent if any suspicion
• The role of anabolic agents: teriparatide has been reported to enhance periprosthetic fracture healing — consider in select cases with osteoporosis and high nonunion risk

• Lewis & Rorabeck Type III = loose implant — fixation alone will fail; revision or DFR required
• Su Type III = fracture within femoral box — no distal fixation possible with plate or nail; consider DFR
• Retrograde nail requires open-box component — always check operative notes before planning
• Anterior femoral notching is a debated but recognised risk factor — reduces cortical strength at the notch level
• Mortality at 1 year approaches that of hip fracture — early surgery, orthogeriatric co-management, and early mobilisation are essential
• UCS (Duncan & Haddad) classifies all periprosthetic fractures uniformly — useful for revision planning
• Screw-component conflict causes pain, noise, and accelerated polyethylene wear — plan trajectories carefully
• DFR allows immediate weight bearing — preferred in elderly low-demand patients with poor distal bone stock
• Always exclude infection before definitive fixation — intraoperative cultures mandatory if suspicion exists