Periprosthetic Hip Fracture

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Periprosthetic hip fractures around total hip arthroplasty are classified using the Vancouver system based on fracture location, stem stability, and bone stock. The key clinical question is whether the stem is stable or loose - this determines treatment. Type B1 (stable stem, good bone) is treated with ORIF using cable plates. Type B2 (loose stem, good bone) requires revision to a longer stem. Type B3 (loose stem, poor bone) needs revision with bone augmentation (impaction grafting, megaprosthesis). Type A fractures (around trochanters) are usually treated conservatively, while Type C (below stem) is treated as a standard femoral shaft fracture.

Periprosthetic hip fractures are fractures around a total hip arthroplasty. They are increasingly common as more THRs are performed and the population ages.

Risk Factors

Patient: Osteoporosis, female, advanced age, rheumatoid arthritis.

Implant: Revision surgery, cementless stems (higher risk than cemented), osteolysis.

Technical: Cortical perforation, stress risers.

Periprosthetic fractures result from the complex interaction between bone quality, implant characteristics, and mechanical forces.

Mechanisms of Fracture

Intraoperative fractures:

• Occur during primary or revision arthroplasty
• Femoral preparation: Broaching, reaming, or rasping can split cortex
• Implant insertion: Press-fit stems generate hoop stresses that can crack cortex
• Uncemented stems: Higher intraoperative fracture risk (1-3%) vs cemented (0.1-1%)
• Risk factors: Osteoporotic bone, tight canal, oversized components, varus positioning

Postoperative fractures (more common):

• Early (less than 5 years post-THR): Usually trauma-related, often at stress risers
• Late (greater than 5 years post-THR): Combination of bone loss and trauma
• Spontaneous: Severe osteoporosis or osteolysis may result in atraumatic fracture

Bone Changes Around Implants

Stress shielding:

• Stiff femoral stem carries load, bypassing proximal femur
• Reduced mechanical stimulus leads to bone resorption (Wolff's law)
• Proximal bone density decreases up to 30% in first 2 years
• More pronounced with:
  • Fully porous-coated stems (stiffer)
  • Larger diameter stems
  • Younger, more active patients
• Clinical significance: Weakened bone at risk of fracture with minimal trauma

Osteolysis:

• Wear particles (polyethylene, metal, ceramic) trigger inflammatory response
• Macrophages release cytokines (TNF-α, IL-1, IL-6) activating osteoclasts
• Progressive bone resorption creates cavitary and cortical defects
• Gruen zones 1 and 7 (proximal medial and lateral) most commonly affected
• Compromises both fracture risk and fixation options

Cortical remodeling:

• Adaptive remodeling around stem alters bone architecture
• Proximal: Cortical thinning from stress shielding
• Distal (stem tip): Cortical thickening from stress concentration
• Hypertrophy: Calcar remodeling, endosteal scalloping
• Net effect: Altered bone quality makes fracture more likely

Biomechanical Factors

Stress concentration at stem tip:

• Stem tip acts as fulcrum during loading
• Bending moment greatest 2-3 cortical diameters below stem tip
• Type C fractures commonly occur at this location
• Longer, stiffer stems increase stress concentration

Torsional stress:

• Hip rotation generates torsional forces on femoral shaft
• Cemented stems: Cement-bone interface can fail in torsion
• Uncemented stems: Bone-implant interface may fail if not well-fixed
• Spiral fractures result from excessive torsion

Cyclic loading:

• Repeated loading cycles cause fatigue micro-damage
• Normally repaired by bone remodeling
• If damage accumulates faster than repair: stress fracture
• May present as impending fracture with progressive pain

Understanding the anatomy of the proximal femur and hip arthroplasty is essential for classifying and managing periprosthetic fractures.

Proximal Femoral Anatomy

Bone anatomy:

• Greater trochanter: Insertion of hip abductors (gluteus medius, gluteus minimus). Fractures here (Type AG) affect abduction strength.
• Lesser trochanter: Insertion of iliopsoas. Avulsion (Type AL) may indicate underlying osteolysis and stem loosening.
• Femoral shaft: Cortical bone tube surrounding the stem. Bone quality critical for fixation.
• Calcar: Medial cortex at femoral neck base, often resected or resorbed around stems.

Vascular supply:

• Femoral head blood supply disrupted by arthroplasty (not relevant to fracture healing)
• Femoral shaft: Nutrient artery plus periosteal blood supply
• Fracture healing relies on periosteal and endosteal blood supply
• Extensive soft tissue stripping during ORIF may compromise healing

Hip Arthroplasty Components

Femoral stem types:

• Cemented: Cement mantle transmits forces to bone. Fracture through cement or at cement-bone interface. Generally more stable initially.
• Uncemented: Press-fit, relies on bone ingrowth. May have extensive porous coating (fully coated) or proximal coating (proximally coated). Stress shielding can weaken proximal bone over time.

Stem geometry:

• Straight stems: Easier to bypass with long revision stems
• Curved/anatomic stems: May limit revision options
• Modular stems: Allow length adjustment but have junction points that may fail

Biomechanical Considerations

Forces on proximal femur:

• Hip joint reaction force: 3-5x body weight during walking
• Abductor muscle force: Stabilizes pelvis in single-leg stance
• Torsional forces: Rotational stress on femoral shaft
• Bending moments: Anterior bow of femur creates bending stress

Effect of stem on bone stress:

• Stress shielding: Stiff stem bypasses proximal bone, reducing load. Leads to bone resorption (Wolff's law). Common in fully coated stems.
• Stress concentration: Stem tip acts as stress riser. Type C fractures often occur 2-3 cortical diameters below stem tip.
• Cortical windows: Surgical defects (e.g., cerclage wire holes, screw holes from prior surgery) create weak points.

Fracture stability determinants:

• Stem fixation: Loose stem cannot support ORIF. Must revise if loose.
• Bone stock: Poor bone (osteoporosis, osteolysis, radiation) reduces healing potential and screw purchase.
• Fracture pattern: Transverse fractures more stable than comminuted or spiral patterns.

Thorough clinical assessment guides diagnosis, classification, and treatment planning.

History

Mechanism of injury:

• Low-energy trauma: Fall from standing height most common. Indicates pathological fracture through weakened bone.
• High-energy trauma: Rare but possible (MVA). May have associated injuries.
• Spontaneous: Severe osteoporosis or osteolysis may cause atraumatic fracture.

Pain characteristics:

• Acute onset: Suggests acute fracture
• Chronic/progressive pain: May indicate impending fracture or loosening
• Pain location: Groin (hip), thigh (shaft), knee (referred from hip)

Functional history:

• Pre-injury mobility: Walking aids, distance, independence
• Time since THR: Recent vs remote (affects loosening likelihood)
• Previous revisions: Higher risk of bone loss and complications
• Reason for THR: Osteoarthritis, fracture, inflammatory arthritis (affects bone quality)

Medical history:

• Osteoporosis: Fragility fractures, DEXA scan results, current treatment
• Medications: Bisphosphonates, steroids, anticoagulation
• Comorbidities: Cardiac, respiratory, renal disease (affects surgical risk)
• Smoking, alcohol: Impair bone healing

Physical Examination

Inspection:

• Deformity: Shortening, rotation (usually external rotation if displaced)
• Swelling: Thigh swelling common, ecchymosis may appear after several days
• Surgical scars: Previous hip incisions (lateral, posterior, anterolateral)
• Leg length: Measure from umbilicus to medial malleolus (compare to contralateral)

Palpation:

• Tenderness: Localized to fracture site (trochanteric, shaft, distal thigh)
• Crepitus: May be palpable with gentle manipulation
• Soft tissue: Check for tense compartments (rare but possible)

Range of motion:

• Hip ROM: Painful and limited. Do not force motion if fracture suspected.
• Knee ROM: Check to rule out ipsilateral knee injury

Neurovascular examination (CRITICAL):

• Femoral artery: Palpate femoral, popliteal, dorsalis pedis, posterior tibial pulses
• Femoral nerve: Test quadriceps strength (knee extension), sensation over anterior thigh
• Sciatic nerve: Test ankle dorsiflexion (deep peroneal), plantarflexion (tibial), sensation
• Document carefully: Baseline neurovascular status essential for medicolegal reasons

Systems Assessment

Medical optimization:

• Cardiorespiratory fitness: Exercise tolerance, functional capacity
• Anemia: Common in elderly, may need pre-op transfusion
• Anticoagulation: Warfarin, DOACs - plan reversal for surgery
• Nutrition: Albumin, protein-calorie malnutrition impairs healing

Frailty assessment:

• Cognitive function: Delirium risk, ability to comply with weight-bearing restrictions
• Social support: Home situation, carers, discharge planning needs
• Goals of care: Some patients may decline surgery if severe comorbidities

Systematic imaging and laboratory investigations establish diagnosis, guide classification, and inform treatment planning.

Plain Radiography

Essential views:

• AP pelvis: Assesses both hips, allows comparison to contralateral side. Shows acetabular component, pelvic discontinuity if present.
• AP hip: Centered on affected hip, better visualization of stem and proximal femur.
• Lateral hip: Cross-table or frog lateral. Shows anterior/posterior displacement, stem position in sagittal plane.
• Full-length femur: AP and lateral of entire femur from hip to knee. Essential to see entire prosthesis and exclude distal fracture.

Radiographic assessment (Vancouver classification):

1. Fracture location:

• Type A: Fracture line involves trochanters (AG = greater, AL = lesser). Stem tip uninvolved.
• Type B: Fracture around or at level of stem. Most common and challenging.
• Type C: Fracture well below stem tip. Prosthesis not directly involved.

2. Stem stability (CRITICAL for B1 vs B2 distinction):

Signs of loose stem:

• Subsidence: Stem has migrated distally compared to immediate post-op X-rays. Measure distance from lesser trochanter to stem shoulder.
• Lucent lines: Radiolucent line around stem greater than 2mm, especially if progressive or circumferential.
• Cement mantle fracture: Broken cement indicates stem loosening (cemented stems).
• Varus/valgus tilt: Stem alignment changed from original position.
• Pedestal formation: Bone formation at stem tip blocking further subsidence (indicates prior loosening).

Signs of stable stem:

• No subsidence: Stem position unchanged from post-operative X-rays.
• Bone ingrowth: Spot welds, cortical hypertrophy, trabecular remodeling (uncemented stems).
• Intact cement mantle: No fracture lines in cement (cemented stems).
• No lucent lines: Or only thin, non-progressive radiolucent lines less than 1mm.

3. Bone stock:

• Good bone: Adequate cortical thickness, normal bone density, minimal osteolysis.
• Poor bone: Severe osteoporosis, extensive osteolysis (especially Gruen zones 1, 7, 8), cortical thinning, cavitary defects.

Advanced Imaging

CT scan:

• Indications: Complex fracture patterns, assess bone stock, surgical planning for revision, evaluate cement mantle.
• Advantages: Better visualization of fracture displacement, bone defects, osteolysis. 3D reconstructions helpful for complex cases.
• Limitations: Metal artifact from prosthesis. Metal artifact reduction software (MARS) improves image quality.

MRI:

• Rarely indicated for acute fractures (metal artifact prohibitive)
• Possible uses: Assess soft tissues (muscle tears), occult fractures, infection (if suspected)

Bone scintigraphy/SPECT-CT:

• Not routine for acute fractures
• Possible use: Differentiate fracture from loosening in chronic pain, assess for infection

Laboratory Investigations

Routine blood tests:

• FBC: Hemoglobin (anemia common, may need transfusion), WCC (infection screen)
• U&E: Renal function (important for surgical planning, contrast if CT needed)
• Coagulation: INR if on warfarin, assess bleeding risk
• Bone profile: Calcium, phosphate, ALP (osteoporosis/metabolic bone disease screen)
• CRP/ESR: Elevated in fracture, but very high levels raise infection concern

Infection screen (if any suspicion of prosthetic joint infection):

• CRP and ESR: Elevated in infection but also in fracture
• Aspiration: If infection suspected, aspirate hip under image guidance for cell count, culture, alpha-defensin
• Synovial fluid analysis: WCC greater than 3000 cells/μL or PMN greater than 80% suggests infection

Bone health assessment:

• Vitamin D: Deficiency common in elderly, correct before surgery
• PTH: If hypercalcemia or renal dysfunction
• DEXA scan: May be arranged electively post-operatively to guide osteoporosis treatment

Type A (Trochanters)

AG: Greater trochanter fracture. AL: Lesser trochanter fracture.

Usually conservative treatment unless significant displacement affecting abductor function (AG) or suggests stem loosening (AL avulsion from osteolysis).

Type B (Around Stem)

B1: Fracture around stem, stem STABLE, adequate bone stock.

• ORIF with cable plate (cerclage cables + plate).

B2: Fracture around stem, stem LOOSE, adequate bone stock.

• Revision to longer stem +/- ORIF.

B3: Fracture around stem, stem LOOSE, poor bone stock.

• Revision with augmentation (impaction grafting, allograft struts, tumor prosthesis if severe).

Type C (Below Stem)

Fracture distal to stem (not involving prosthesis directly).

Treat as standard femoral shaft fracture: Plate (with cables proximally if needed) or IM nail (if space allows above fracture for nail entry).

Periprosthetic hip fractures and their treatment carry significant complication risks, both from the fracture itself and the surgical management required.

Medical Complications

Thromboembolic events: DVT/PE risk 2-5% despite prophylaxis. Elderly patients with prolonged immobility at highest risk. Mechanical and pharmacological prophylaxis essential.

Cardiopulmonary complications: MI, pneumonia, respiratory failure more common in elderly patients undergoing revision surgery. Medical optimization and early mobilization critical.

Mortality: 30-day mortality 2-5%, one-year mortality 10-20%. Higher in elderly, comorbid patients. Comparable to native hip fractures. Early surgery and medical optimization improve outcomes.

Successful outcomes require structured postoperative care addressing both the fracture and the underlying prosthesis.

Discharge Planning

Equipment needs: Elevated toilet seat, shower chair, reaching aids, walking frame or crutches.

Home modifications: Remove trip hazards, install grab rails, ensure bedroom/bathroom on same level if possible.

Support services: Consider home care package, meals on wheels, community physiotherapy. Involve occupational therapy.

Patient education: Hip precautions (avoid low chairs, crossing legs), weight-bearing restrictions, signs of complications, when to seek help.

Australian Epidemiology and Practice

Periprosthetic Hip Fractures in Australia:

• AOANJRR data shows increasing incidence of periprosthetic fractures as primary THA population ages
• Approximately 1-2% cumulative revision rate for periprosthetic fracture at 15 years post primary THA
• Cementless stems have higher intraoperative fracture risk; cemented stems have higher postoperative risk

RACS Orthopaedic Training Relevance:

• Vancouver classification is essential FRACS knowledge for Part II examination
• Understanding B1 vs B2 differentiation and treatment algorithm frequently examined in vivas
• Intraoperative assessment of stem stability is critical decision point

AOANJRR Registry Data:

• Registry tracks periprosthetic fracture as a specific revision indication
• Long cementless stems used for revision have documented outcomes
• Proximal femoral replacement increasingly used for B3 fractures with severe bone loss

PBS Considerations:

• Osteoporosis treatment including bisphosphonates and denosumab PBS-subsidised for fracture prevention
• Vitamin D supplementation widely recommended for osteoporosis management
• Falls prevention programs available through Medicare-funded chronic disease management

eTG Recommendations:

• Perioperative antibiotic prophylaxis per eTG (cefazolin first-line)
• VTE prophylaxis mandatory following periprosthetic fracture surgery
• Antibiotic guidelines for management of infected revision cases

Australian Practice Patterns:

• Major arthroplasty centres have established periprosthetic fracture pathways
• Cable plate systems (Dall-Miles, Ogden) and locking plate systems widely available
• Megaprosthesis and proximal femoral replacement available at tertiary centres for salvage