Periprosthetic Fractures after TKA — Classification & Management

Periprosthetic fractures around a total knee arthroplasty (TKA) are a serious complication with an incidence of approximately 0.3–2.5% for distal femur fractures and 0.5–1.7% for proximal tibia fractures. The incidence is increasing as the population of patients with TKA grows and ages. Periprosthetic fractures are associated with significant morbidity, mortality (up to 30% at 1 year in elderly patients), and the need for complex reconstructive surgery. Management requires a systematic approach considering fracture pattern, implant stability, bone stock, and patient factors.

• Risk factors: osteoporosis (the most important — the majority occur in elderly women); anterior femoral notching (cutting into the anterior femoral cortex during femoral preparation creates a stress riser — significantly increases the risk of periprosthetic supracondylar femur fracture); rheumatoid arthritis (bone fragility + steroid use); flexion contracture (altered biomechanics); neurological disease (altered gait and fall risk); revision TKA (greater bone deficiency); corticosteroid use; stress shielding around the implant
• Anterior femoral notching: when the anterior femoral box cut during femoral preparation inadvertently cuts into the anterior femoral cortex, a cortical stress riser is created; experimental studies (Lesh et al.) have shown that notching >3 mm reduces the fracture load of the distal femur by approximately 18–30%; the risk of periprosthetic supracondylar fracture is estimated to be 2–3× higher with anterior femoral notching; prevention — careful sizing and positioning of the femoral component to avoid over-resecting the anterior cortex; intraoperative fluoroscopy helps confirm the anterior cut level
• Mechanism of injury: low-energy falls in elderly osteoporotic patients account for the majority; high-energy trauma in younger patients; stress fractures (tibial plateau periprosthetic fractures can present insidiously without a specific trauma)

• Retrograde intramedullary nail (RIMN): inserted through the intercondylar notch of the TKA femoral component (requires an `open box` femoral component design — the intercondylar box must be open to allow nail passage); provides axial and rotational stability; excellent for displaced supracondylar fractures (Lewis-Rorabeck Type II) with a stable well-fixed implant; cannot be used with a `closed box` (posterior-stabilised TKA with a fully enclosed intercondylar housing) — confirm implant design pre-operatively from the implant record; the nail is inserted in a minimally invasive technique; interlocking screws provide rotational control
• Distal femoral locking plate (DFLP): the alternative when RIMN is not possible (closed box PS TKA) or when fracture extends too distally for nail interlocking screws; a lateral locking plate with multiple locking screws in the distal femoral condyles; the distal locking screws must be carefully placed to avoid penetrating the posterior condylar box of the femoral component (check with fluoroscopy); minimally invasive plate osteosynthesis (MIPO) technique reduces soft tissue stripping and preserves fracture haematoma; the locking plate is superior to a conventional plate in osteoporotic bone (locking screws do not rely on friction — they lock to the plate, maintaining angular stability)
• Revision TKA with stemmed component (Type III / loose implant): when the TKA component is loose (Lewis-Rorabeck Type III or Felix Type B), revision surgery is required; a long-stemmed revision femoral or tibial component bridges the fracture zone — the stem extends past the most distal fracture line by at least two cortical diameters; this provides stability to both the revision arthroplasty and the fracture; press-fit or cemented stems may be used; modular revision TKA systems allow tailored stem length and offset
• Distal femoral replacement (DFR) mega-prosthesis: for severely comminuted periprosthetic supracondylar fractures with poor bone stock where ORIF is not feasible and stemmed revision is insufficient; the distal femur is replaced with a modular endoprosthesis; provides immediate stability and allows early mobilisation; the medial gastrocnemius flap may be needed for soft tissue coverage if extensive bone resection is required; this is associated with high complication rates but may be the only option for salvage

• Classification (Ortiguera-Berry): Type I — stable implant, intact extensor mechanism; Type II — stable implant, disrupted extensor mechanism; Type III — loose patellar component (A: good bone stock, B: poor bone stock); management — Type I: conservative (immobilisation); Type II: ORIF + extensor mechanism repair or reconstruction; Type IIIA: revision patellar resurfacing; Type IIIB: patellectomy or trabecular metal patellar augment; patellar fractures after TKA have very poor outcomes due to compromised bone blood supply (from prior resurfacing surgery) and the biomechanical demands of the extensor mechanism

• Confirming implant design before fixation: the single most important pre-operative step is to identify the TKA implant make, model, and design — specifically whether the femoral component has an open or closed intercondylar box; an open-box cruciate-retaining (CR) TKA allows retrograde nail passage; a closed-box posterior-stabilised (PS) TKA does not; if the implant record is unavailable, a lateral X-ray with fluoroscopy and reference to published implant databases can identify the component design; proceeding with RIMN insertion in a closed-box PS TKA will jam the nail against the intercondylar housing and may damage the implant
• The role of conservative management in the elderly: Type I (undisplaced, stable implant) periprosthetic fractures can theoretically be managed conservatively in a brace or cast; however, prolonged immobilisation in elderly osteoporotic patients carries significant risks — deep vein thrombosis, pulmonary embolism, pressure sores, deconditioning, and pneumonia; most orthopaedic surgeons prefer surgical fixation even for undisplaced fractures in elderly patients to allow early mobilisation; the decision must be individualised based on patient fitness for anaesthesia and surgery
• The `two-cortical-diameter rule` for stem length in revision: when a stemmed revision component is used to manage a Type III periprosthetic fracture (loose implant), the stem tip should extend beyond the most distal fracture line by at least two femoral or tibial cortical diameters; this ensures that the fracture is bridged by a sufficient length of well-fixed stem to provide mechanical stability; shorter stems that do not bridge the fracture will fail by cantilever bending at the fracture site

• Lewis-Rorabeck for distal femur: Type I (undisplaced, stable implant) — conservative or ORIF; Type II (displaced, stable implant) — ORIF (RIMN or DFLP); Type III (any displacement, LOOSE implant) — revision TKA with stemmed component or DFR mega-prosthesis
• Anterior femoral notching: stress riser; 2–3× increased periprosthetic fracture risk; notching >3 mm reduces fracture load by ~18–30%; prevent with careful sizing and fluoroscopic confirmation of anterior cut
• RIMN: through intercondylar notch; REQUIRES open-box (CR) femoral component; CANNOT be used with closed-box PS TKA; confirm implant design from records before proceeding
• DFLP: locking plate for osteoporotic bone (angular stability — locking screws lock to plate); used when RIMN not possible (closed box PS); MIPO technique; avoid posterior condylar box penetration
• Felix tibial classification: I = plateau (at component); II = at stem tip; III = diaphyseal; IV = tibial tubercle avulsion; A = stable implant → ORIF; B = loose implant → revision with longer stem
• Tibial tubercle avulsion (Felix IV): threat to extensor mechanism; ORIF with tension band wire; protect extension; loss of active extension is devastating
• DFR mega-prosthesis: severely comminuted + poor bone stock + ORIF not feasible; immediate stability; allows early mobilisation; high complication rate; salvage procedure
• Patellar fracture (Ortiguera-Berry): Type I (stable implant + intact extensor) — conservative; Type II (extensor disrupted) — ORIF + repair; Type IIIA (loose, good bone) — revision; Type IIIB (loose, poor bone) — patellectomy
• Two-cortical-diameter rule: stem tip must extend beyond distal fracture line by ≥2 cortical diameters; shorter bridging = cantilever failure
• Risk factors: osteoporosis; anterior notching; RA; flexion contracture; neurological disease; revision TKA; steroid use