Paget’s disease of bone

1. High-Yield Summary

Paget’s disease of bone (osteitis deformans) is a chronic, focal skeletal remodeling disorder characterized by hyperactive, disorganized osteoclastic bone resorption coupled with accelerated, chaotic osteoblastic bone deposition. The resulting osseous architecture is expanded, structurally disorganized, hypervascular, and mechanically brittle, exhibiting a pathognomonic mosaic histological pattern with prominent irregular cement lines.

• Epidemiology and Anatomic Distribution: Affects predominantly older adults over 55 years of age with a slight male predilection (1.4:1 to 1.8:1) and marked geographical clustering in the United Kingdom, Western Europe, North America, and Australasia. Disease is monostotic in 15% to 35% and polyostotic in 65% to 85% of cases, with predilection for the pelvis (70%), lumbar and thoracic spine (53%), femur (55%), skull (42%), and tibia (32%).
• Hallmark Diagnostic Triad: Manifests with deep, boring nocturnal bone pain present at rest, markedly elevated total serum alkaline phosphatase (SAP) with normal serum calcium and phosphate in ambulatory patients, and pathognomonic radiographic features including cortical thickening, trabecular coarsening, skeletal expansion, and advancing osteolytic resorption wedges (“blade of grass” or “candle flame” sign).
• Definitive Medical Management: First-line pharmacotherapy is a single intravenous infusion of zoledronic acid (5 mg IV over 15 to 30 minutes), which achieves biochemical remission (normalization of SAP) in over 90% to 95% of patients with durable remission lasting 2 to 5 years or longer. Oral risedronate (30 mg daily for 2 months) serves as an effective secondary oral option. Baseline 25-hydroxyvitamin D and calcium repletion is mandatory prior to infusion to prevent acute hypocalcemia.
• Surgical Imperatives & Hypervascularity Control: Elective orthopaedic procedures (total joint arthroplasty, deformity osteotomies) require preoperative bisphosphonate therapy administered 2 to 3 months prior to surgery to quiet active hypervascularity and prevent massive intraoperative hemorrhage. Tranexamic acid and cell saver blood salvage are standard adjuncts.
• Arthroplasty & Fracture Principles: Secondary osteoarthritis with protrusio acetabuli, coxa vara, and femoral anterolateral bowing demands modern uncemented porous-coated components, flexible canal reamers, and mandatory heterotopic ossification prophylaxis (indomethacin or radiation). Pathologic transverse “chalk-stick” fractures carry high nonunion rates (up to 20% to 40%) and require full-length reamed intramedullary nail stabilization. Malignant transformation to pagetic osteosarcoma occurs in less than 1% of patients and carries a lethal prognosis.

2. Anatomy

Paget’s disease of bone exhibits a predilection for specific axial and appendicular skeletal sites. The structural alterations, altered vascularity, and distorted bony landmarks create complex challenges for diagnostic assessment and surgical intervention.

Anatomic Predilection Sites

• Pelvis (70%): The most common site of skeletal involvement. Primarily affects the ilium, ischium, and acetabular periacetabular columns. Sclerotic thickening of the iliopectineal and ilioischial lines produces the classical “pelvic brim sign.” Remodeling and softening of the acetabular floor under hip joint reaction forces leads to progressive protrusio acetabuli, with medial displacement of the femoral head beyond Kohler’s ilioischial line.
• Spine (53%): Lumbar and thoracic vertebral bodies and posterior arches are predominantly affected. Expansion of the vertebral body and facet complexes causes concentric spinal canal stenosis and neural foraminal narrowing. Manifests radiographically as the “picture frame” vertebra (peripheral cortical thickening surrounding an osteopenic central sponge) or the “ivory vertebra” (dense uniform sclerosis).
• Femur (55%): Involves the proximal femur, subtrochanteric diaphysis, and femoral shaft. Chronic remodeling under body weight vectors causes progressive coxa vara (neck-shaft angle < 120°) and severe anterolateral femoral bowing. The tensile convex lateral cortex develops horizontal micro-fissure pseudofractures (Looser zones) prone to catastrophic transverse fracture propagation.
• Cranium / Skull (42%): Involves the calvarium and skull base. Marked diploic expansion widens the skull vault, producing progressive enlargement of the head and frontal bossing. Softening of the skull base under the weight of the brain causes platybasia (flattening of the sphenoid angle) and basilar invagination, with upward migration of the odontoid process into the foramen magnum. Petrous temporal bone expansion leads to cochlear capsule distortion and narrowing of the internal acoustic meatus.
• Tibia (32%): Produces marked anterior diaphyseal bowing (“sabre shin” deformity) with profound cortical thickening along the anterior convex tension cortex.

Vascular Architecture and Hemodynamic Alterations

Active pagetic bone undergoes extensive neoangiogenesis and vascular remodeling. The physiologic microcirculation is replaced by a hypercellular, thin-walled sinusoidal network accompanied by microscopic direct arteriovenous (A-V) shunts within the marrow stroma. Intraosseous and periosteal blood flow can increase up to 20-fold above normal physiological baseline. In subcutaneous locations (such as the anterior tibia and calvarium), this intense hyperemia causes palpable cutaneous warmth. In patients with extensive polyostotic involvement exceeding 15% to 20% of the skeleton, the cumulative drop in systemic peripheral vascular resistance produces a compensatory elevation in stroke volume and heart rate, predisposing elderly individuals to high-output congestive heart failure.

Microstructural and Sclerotic Alterations

Normal lamellar cortical bone organized into Haversian systems is dismantled and replaced by coarse, disorganized woven bone. The pathognomonic histological hallmark is the “mosaic” or “jigsaw-puzzle” pattern of bone matrix, defined by thick, scalloped, irregular basophilic cement lines (reversal lines) that demarcate random units of lamellar and woven bone. Although pagetic bone appears hyperdense and hypertrophied on radiographs, its disordered collagen orientation, irregular mineralization, and excessive cement lines render it biomechanically stiff, inelastic, and fragile under tensile and torsional loads.

Surgical Internervous Planes and Danger Corridors

• Direct Anterior (Hueter) Approach to the Hip: Internervous plane between the femoral nerve (sartorius and rectus femoris) and superior gluteal nerve (tensor fasciae latae). Sparing of the abductor mechanism is advantageous, but exposure can be constrained in patients with severe coxa vara or severe pelvic deformity. The lateral femoral cutaneous nerve must be carefully mobilized.
• Anterolateral (Watson-Jones) Approach: Utilizes the interval between the superior gluteal nerve (tensor fasciae latae) and femoral nerve (rectus femoris). Provides direct access to the anterior acetabulum and femoral neck, helpful for addressing anterior femoral bowing.
• Lateral Transgluteal (Hardinge) Approach: Develops an interval splitting the vastus lateralis (femoral nerve) and anterior fibers of the gluteus medius/minimus (superior gluteal nerve). Provides direct, unencumbered exposure of the proximal femur in coxa vara, but carries risk of postoperative abductor lurch if the superior gluteal nerve branch to the tensor fasciae latae (coursing 3 to 5 cm proximal to the greater trochanter) is stretched.
• Posterolateral (Moore / Southern) Approach: Gluteus maximus muscle-splitting interval (inferior gluteal nerve). Provides wide, expansile visualization of the acetabulum and proximal femur for complex protrusio reconstruction and femoral osteotomy. The sciatic nerve is at heightened risk of traction or thermal injury and must be visualized and protected, particularly when the posterior acetabular wall and ischium are expanded.
• Anterior Midline Approach to the Knee: Medial parapatellar arthrotomy utilizing the interval between the rectus femoris and vastus medialis. Meticulous subperiosteal peeling of contracted medial tissues is required; thermal necrosis of dense pagetic tibial bone must be prevented by copious saline irrigation during resection.

3. Pathogenesis

The primary cytopathological lesion of Paget’s disease resides in the osteoclast lineage. The normal tightly coupled cycle of bone remodeling is disrupted, initiated by aggressive, uncontrolled osteoclastic hyper-resorption, followed by rapid, disordered, compensatory osteoblast bone deposition.

Cellular Pathology & Giant Osteoclasts

Pagetic osteoclasts are morphological giants: they measure up to several times the diameter of normal osteoclasts and contain up to 50 to 100 nuclei per cell, compared to the normal physiological complement of 3 to 5 nuclei. These cells display increased resistance to apoptosis, heightened hypersensitivity to bone resorptive stimuli, and an expanded resorptive surface area. Electron microscopy frequently demonstrates paracrystalline, microfilamentous intranuclear inclusion bodies within pagetic osteoclasts that morphologically resemble paramyxovirus nucleocapsids (measles virus, canine distemper virus, or respiratory syncytial virus). This finding suggests a model wherein slow viral infection acts as an environmental trigger in a genetically predisposed host, although persistent viral RNA isolation remains variable.

Genetic Susceptibility and Molecular Signaling

The genetic basis of Paget’s disease is strongly linked to mutations in the SQSTM1 gene, located on chromosome 5q35. SQSTM1 encodes the scaffold protein sequestosome-1 (p62), an essential regulator of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway downstream of receptor activator of nuclear factor-κB (RANK). Mutations clustering in the ubiquitin-associated (UBA) domain of p62 disrupt its ability to bind polyubiquitinated proteins for autophagic and proteasomal degradation. This leads to constitutive, ligand-independent activation of NF-κB, driving excessive osteoclast differentiation, fusion, and survival.

SQSTM1 mutations account for 40% to 50% of familial cases with autosomal dominant inheritance and 5% to 10% of sporadic presentations. Additional susceptibility loci include TNFRSF11A (encoding RANK), ZNF687, CSF1 (macrophage colony-stimulating factor), and OPTN (optineurin). Furthermore, local bone marrow stromal cells in pagetic lesions overproduce interleukin-6 (IL-6), macrophage colony-stimulating factor (M-CSF), and receptor activator of NF-κB ligand (RANKL). Interleukin-6 acts as a potent autocrine and paracrine stimulator that amplifies osteoclast recruitment and cross-talks with osteoblasts to perpetuate disordered matrix formation.

Three Histological and Radiographic Phases

• Phase 1: Osteolytic (Incipient / Destructive) Phase: Characterized by intense, localized osteoclastic resorption. Normal lamellar bone is rapidly resorbed, creating sharp demarcation zones. In long bones, this phase appears as an advancing osteolytic cutting cone (“blade of grass” or “candle flame” sign) moving along the diaphysis. In the skull, it produces large geographic radiolucent areas termed osteoporosis circumscripta.
• Phase 2: Mixed (Osteolytic-Osteoblastic / Active) Phase: Characterized by simultaneous, high-turnover bone resorption and haphazard osteoblastic bone deposition. Osteoblasts deposit large quantities of unmineralized osteoid without organized lamellar orientation. Normal fatty bone marrow is replaced by hypercellular, highly vascular fibrous connective tissue filled with dilated sinusoids. Radiographs demonstrate trabecular coarsening, cortical thickening, and the classical calvarial “cotton wool” sign.
• Phase 3: Sclerotic (Osteosclerotic / Burned-Out / Quiescent) Phase: Osteoclastic resorption subsides while disorganized bone formation plateaus. The vascular fibrous marrow undergoes gradual involution and fatty replacement. The newly formed woven bone mineralizes into a dense, expanded, disorganized mass. Histologically, irregular basophilic cement lines crisscross the bone in a chaotic mosaic pattern. The bone is hyperostotic and sclerotic on radiographs (“ivory vertebra”), yet biomechanically brittle and prone to fatigue micro-fractures.

4. Natural History

Paget’s disease is an insidious, progressive condition that typically emerges in the sixth decade of life. It does not spread from one bone to another; all skeletal lesions are established at the inception of disease and progress along the length of the involved osseous segments over decades.

Epidemiological Profile

The prevalence of Paget’s disease rises markedly with advancing age, being rarely encountered prior to age 40 and reaching 2% to 4% in individuals over age 55, with estimates exceeding 5% in octogenarians in high-prevalence regions. A slight male predilection exists, with reported male-to-female ratios ranging from 1.4:1 to 1.8:1. Geographically, the condition demonstrates high clustering in the United Kingdom (particularly northwest England, where historical prevalence reached 6% to 8%), followed by France, Spain, Italy, Australia, New Zealand, and North America. Conversely, the condition is rare in Scandinavia, sub-Saharan Africa, and East Asia. Over the past four decades, global epidemiological data indicate a secular decline in both disease incidence and clinical severity in high-prevalence nations, likely reflecting changes in environmental triggers, dietary habits, and declining paramyxoviral exposure.

Progression and Functional Impact if Untreated

Untreated Paget’s disease leads to progressive structural and mechanical failure:

• Progressive Skeletal Deformity: Uncoupled remodeling causes soft, woven bone to deform under physiological weight-bearing forces. Femoral anterolateral bowing and tibial anterior bowing create significant leg length discrepancies and abnormal joint reaction force vectors.
• Secondary Joint Incongruity and Coxarthrosis: Alteration in subchondral bone elasticity combined with acetabular protrusio and coxa vara accelerates the destruction of adjacent articular cartilage, predisposing to rapid-onset, painful secondary osteoarthritis of the hip and knee.
• Transverse Chalk-Stick Fractures: Chronic cyclic tensile stress along the convex surface of bowed long bones generates horizontal cortical fissure micro-fractures (Looser zones). Left unaddressed, these stress micro-fractures propagate instantaneously across the brittle cross-section, causing complete, non-comminuted transverse “chalk-stick” fractures from minimal low-energy trauma.
• Neurologic and Cranial Compromise: Skull expansion and skull base softening produce basilar invagination, foramen magnum stenosis, and conductive or sensorineural hearing loss. Vertebral expansion causes progressive central spinal stenosis, neural foraminal stenosis, radiculopathy, and compressive myelopathy.

5. Clinical Presentation

The clinical spectrum of Paget’s disease ranges from completely asymptomatic discovery on screening blood tests or radiographs to disabling pain, profound skeletal deformity, and neurological deficits.

History

• Asymptomatic Detection: Approximately 60% to 70% of individuals are asymptomatic at initial diagnosis. The disorder is frequently discovered incidentally during routine biochemical screening revealing an isolated elevation in total serum alkaline phosphatase (SAP), or on plain radiographs obtained for unrelated complaints.
• Pagetic Bone Pain: The most frequent presenting symptom in active disease. Patients describe a deep, dull, boring, or aching pain localized directly within the involved osseous segment. A key clinical hallmark is that pagetic bone pain is constant, present at rest, and characteristically worsens at night, driven by elevated intraosseous pressure, microfractures, and high-flow vascular congestion.
• Mechanical Joint Pain: Patients frequently present with joint pain in the hip or knee that must be carefully distinguished from pagetic bone ache. Mechanical joint pain is provoked by weight-bearing, ambulation, and stair climbing, and relieved by rest, signifying secondary degenerative osteoarthritis secondary to altered joint alignment, coxa vara, or protrusio acetabuli.
• Cranial and Otologic Symptoms: Patients with skull involvement report an insidious increase in hat size, ill-fitting eyeglasses or dental prostheses, and chronic dull calvarial headaches. Hearing loss occurs in up to 30% to 50% of patients with cranial involvement, manifesting as conductive hearing loss (ossicular chain fixation or otosclerosis of the cochlear capsule) or sensorineural hearing loss (neural compression within the internal acoustic meatus, loss of cochlear hair cells, or vascular steal). Tinnitus and vertigo frequently coexist.
• Spine and Neurologic Symptoms: Vertebral enlargement and posterior element expansion present with neurogenic claudication (leg paresthesias, pain, and heaviness triggered by walking and relieved by spinal flexion), motor weakness, radiculopathy, and spastic paraparesis from compressive myelopathy. Symptoms may be compounded by a “vascular steal” phenomenon, in which hypervascular pagetic vertebrae divert blood from the spinal cord anterior spinal artery supply.
• Cardiovascular Symptoms: Exertional dyspnea, fatigue, and peripheral edema in extensive polyostotic disease (> 15% to 20% skeletal involvement) secondary to high-output cardiac failure.

Physical Examination

• Visual Inspection and Palpation: Asymmetric skull vault enlargement, frontal bossing (“leontiasis ossea” in advanced facial involvement), engorgement of superficial scalp veins, exaggerated thoracic kyphosis, anterolateral femoral bowing, anterior tibial bowing (“sabre shin”), and leg-length discrepancy. Palpation over superficial involved bones (anterior tibia, calvarium, clavicle) reveals localized cutaneous hyperthermia (warmth) and occasional audible bruits reflecting high-flow arteriovenous shunts.
• Hip Joint Provocation (FABER / Patrick’s & Log-Roll Test): Technique: With the patient supine, the examiner flexes, abducts, and externally rotates the hip (FABER), followed by passive internal/external rotation of the extended limb (Log-Roll) -> Positive Finding: Groin or anterior hip pain confirms secondary pagetic coxarthrosis, distinguishing joint degeneration from deep pagetic bone pain [Sensitivity 82-88%, Specificity 75-80%].
• Spinal Canal & Claudication Provocation (Bicycle Test of van Gelderen): Technique: The patient pedals a stationary bicycle upright with lumbar spine extended, followed by pedaling while leaning forward in lumbar flexion -> Positive Finding: Rapid reproduction of buttock/leg cramping and paresthesias during lumbar extension with prompt relief during lumbar flexion confirms pagetic spinal canal stenosis and neurogenic claudication over peripheral vascular disease [Sensitivity 85-90%, Specificity 88-92%].
• Otologic Tuning Fork Evaluation (Weber and Rinné Tests): Technique: 512-Hz tuning fork applied to the cranial vertex (Weber) and alternating between the mastoid process and external auditory meatus (Rinné) -> Positive Finding: Lateralization to the unaffected ear confirms sensorineural hearing loss; bone conduction exceeding air conduction indicates conductive ossicular fixation [Sensitivity 78-84%, Specificity 85-90%].
• Myelopathic Neurological Screen: Evaluation of deep tendon reflexes (hyperreflexia in thoracic spinal compression vs hyporeflexia in lumbar radiculopathy), sustained ankle clonus (> 3 beats), Hoffman sign, and positive extensor plantar response (Babinski sign) to identify upper motor neuron compression.

6. Imaging and Diagnostic Studies

Diagnosis and structural staging rely on plain radiography, whole-body radionuclide scintigraphy, selective cross-sectional imaging, and biochemical profiling.

Plain Radiography

Plain radiography is the gold standard for structural diagnosis and anatomical staging. Orthogonal views of the affected bone display characteristic findings depending on the underlying phase of disease:

• Skull: Osteoporosis circumscripta cranii appears as a well-demarcated, geographic radiolucency primarily involving the frontal and occipital bones during the early lytic phase. In mixed and sclerotic phases, the “cotton wool” sign develops, characterized by fluffy, nodular areas of sclerotic bone deposition superimposed on a widened, radiolucent diploic space. Calvarial thickening obscures the distinction between the inner and outer cortical tables. Platybasia and basilar invagination manifest as cephalad migration of the odontoid peg more than 5 mm above McGregor’s or Chamberlain’s line.
• Long Bones (Femur, Tibia, Humerus): An advancing osteolytic wedge (“blade of grass” or “candle flame” sign) initiates in subchondral bone of the epiphysis/metaphysis and progresses along the diaphysis. Trabeculae coarsen along altered stress lines, with cortical thickening, overall osseous expansion, and loss of normal corticomedullary differentiation. Anterolateral femoral bowing and anterior tibial bowing develop under physiological loading. Transverse tensile micro-fractures (Looser zones / “banana fractures”) appear as short horizontal radiolucencies perpendicular to the cortex along the convex tension surface (lateral femoral cortex, anterior tibial cortex).
• Spine: The “picture frame” (windowpane) vertebra shows prominent cortical thickening along the superior, inferior, anterior, and posterior borders of the vertebral body surrounding an osteopenic central sponge. The “ivory vertebra” shows uniform, dense, homogeneous sclerosis of an expanded vertebral body without endplate collapse. Hypertrophy of the pedicles, lamina, and facets causes concentric central canal and neural foraminal narrowing.
• Pelvis: Sclerosis and cortical thickening of the iliopectineal and ilioischial lines create the classic “pelvic brim sign.” Acetabular remodeling causes medial wall thinning and progressive protrusio acetabuli (medial migration of the femoral head beyond Kohler’s ilioischial line), accompanied by joint space narrowing and secondary superomedial coxarthrosis.

Radionuclide Bone Scintigraphy

Technetium-99m methylene diphosphonate (99mTc-MDP) whole-body bone scintigraphy is the most sensitive diagnostic imaging modality for mapping total skeletal disease distribution and active metabolic burden. Active pagetic lesions demonstrate intense, avid, uniform radiotracer uptake throughout the entire affected bone (“pagetic superscan” appearance in affected regions), reflecting marked osteoblastic bone turnover and hyperemia. A baseline whole-body bone scan is essential to identify asymptomatic or radiographically occult lesions. Any hot focus on bone scintigraphy must be corroborated with targeted plain radiographs to assess structural integrity and exclude osteoblastic metastases. Completely sclerotic, burned-out, or quiescent lesions may demonstrate normal or decreased radiotracer uptake (“cold” pagetic lesions).

Advanced Cross-Sectional Imaging (CT and MRI)

• Computed Tomography (CT): Optimal modality for evaluating complex osseous architecture, cortical bone integrity, and articular congruency. Indicated in pagetic spinal stenosis to define central, lateral recess, and neural foraminal osseous encroachment. High-resolution temporal bone CT delineates petrous bone remodeling, ossicular chain fixation, and cochlear capsule otosclerosis in progressive hearing loss. CT is invaluable for preoperative 3D planning of complex total joint arthroplasty, precisely measuring acetabular bone stock in protrusio and multiplanar bowing in long bones. CT clearly distinguishes non-displaced tensile fissure fractures from true malignant cortical destruction.
• Magnetic Resonance Imaging (MRI): Indicated for evaluating neurologic compromise (spinal cord compression, radiculopathy, cauda equina syndrome, basilar invagination) and suspected malignant transformation. In uncomplicated Paget’s disease, T1-weighted images show preservation of normal, high-signal marrow fat within the expanded medullary cavity interspersed with coarse low-signal trabeculae. Preservation of marrow fat is an essential negative predictive sign that excludes secondary sarcoma or osteomyelitis.
• MRI in Suspected Sarcomatous Degeneration: Malignant transformation into pagetic osteosarcoma is characterized by complete loss of normal marrow fat, aggressive cortical bone destruction, and the emergence of an invasive extraosseous soft-tissue mass showing low T1 signal, heterogeneous high T2/STIR signal, and intense gadolinium enhancement.

Laboratory Evaluation

• Total Serum Alkaline Phosphatase (SAP): The primary biochemical biomarker of overall disease activity and bone remodeling rate. Reflects osteoblast activity coupled to osteoclast resorption and correlates directly with the extent of active skeletal involvement. In active polyostotic disease, SAP typically rises 3- to 20-fold above the upper limit of normal (ULN), often exceeding 500 to 2000 IU/L (reference range 30 to 120 IU/L). Serial SAP measurements are the primary tool for assessing treatment efficacy and monitoring for disease recurrence.
• Bone-Specific Alkaline Phosphatase (BSAP): Highly sensitive marker of osteoblast activity, indicated when total SAP is only mildly elevated (such as monostotic disease) or when concurrent liver cirrhosis, hepatitis, or biliary tract disease confounds total SAP interpretation. Serum gamma-glutamyl transferase (GGT) or 5′-nucleotidase should be measured simultaneously to exclude hepatic sources of alkaline phosphatase elevation.
• Bone Resorption Biomarkers: Serum C-telopeptide of type I collagen (CTX) and urine/serum N-telopeptide (NTX) reflect osteoclast bone resorption. These markers decline precipitously within 24 to 72 hours of bisphosphonate administration, providing early confirmation of therapeutic response prior to changes in SAP. Serum procollagen type I N-terminal propeptide (P1NP) provides a rapid measure of bone formation suppression.
• Serum Calcium and Phosphate Homeostasis: Serum calcium and inorganic phosphate concentrations are characteristically normal in ambulatory patients with Paget’s disease due to tightly coupled remodeling.
• Critical Risk of Acute Immobilization Hypercalcemia: When patients with active polyostotic Paget’s disease undergo sudden, prolonged immobilization (following a chalk-stick fracture, cast immobilization, spinal cord injury, or prolonged bed rest after major surgery), mechanical skeletal loading ceases. Osteoblastic bone formation abruptly halts, while autonomous, high-turnover osteoclastic bone resorption continues unchecked. This unleashes massive skeletal calcium release into the circulation, precipitating severe, life-threatening acute immobilization hypercalcemia, hypercalciuria, acute nephrocalcinosis, acute kidney injury, and cardiac arrhythmias.
• Baseline 25-Hydroxyvitamin D Repletion: Serum 25(OH)D and serum calcium must be evaluated and corrected prior to initiating potent nitrogen-containing bisphosphonates. Administering potent antiresorptives in the presence of unrecognized vitamin D deficiency or borderline hypocalcemia can trigger acute, symptomatic hypocalcemia, secondary hyperparathyroidism, and tetany.

7. Classification

The progression of Paget’s disease of bone is staged according to its biological, histopathologic, and radiographic evolution, which directly dictates clinical management and surgical timing:

8. Treatment

Management of Paget’s disease integrates potent antiresorptive pharmacotherapy to normalize bone turnover with precision orthopaedic surgical techniques designed to manage structural deformities, secondary joint destruction, and brittle bone fractures.

Medical Therapy / Pharmacotherapy

• First-Line Therapy: Intravenous Zoledronic Acid (Zoledronate): The gold standard antiresorptive regimen is a single intravenous infusion of zoledronic acid (5 mg administered in 100 mL solution over at least 15 to 30 minutes). Large randomized controlled trials demonstrate that zoledronic acid achieves biochemical remission (normalization of total SAP) in 88% to 96% of patients at 6 months, superior to oral bisphosphonates. The median time to therapeutic response is approximately 6 weeks, with durable biochemical and clinical remission lasting 2 to 5 years or longer following a single dose.
• Pre-Infusion Repletion Protocol: Prior to infusion, serum 25-hydroxyvitamin D must be confirmed > 50 nmol/L (> 20 ng/mL) and serum calcium must be within normal limits. Oral calcium (500 to 1000 mg daily) and vitamin D (800 to 2000 IU daily) must be administered for at least 10 to 14 days following the infusion to prevent acute post-infusion hypocalcemia resulting from rapid remineralization of the pagetic skeleton (“hungry bone” physiology).
• Adverse Effects & Renal Thresholds: An acute-phase response (transient low-grade fever, flu-like symptoms, myalgias, and arthralgias) occurs in 15% to 25% of patients within 24 to 72 hours, effectively controlled with prophylactic oral acetaminophen or ibuprofen. Zoledronic acid is contraindicated in patients with severe renal impairment (estimated glomerular filtration rate [eGFR] < 35 mL/min/1.73 m²). Adequate hydration must be verified prior to infusion.
• Alternative Oral Bisphosphonate Regimens: Oral risedronate (30 mg orally once daily for 2 months) is the preferred oral alternative, achieving biochemical remission in 70% to 75% of patients. Oral alendronate (40 mg orally once daily for 6 months) achieves remission in 60% to 70% but carries a higher burden of gastrointestinal intolerance and esophageal ulceration. Oral bisphosphonates must be taken upon waking with a full glass of water, remaining upright and fasting for at least 30 minutes. Intravenous pamidronate (60 to 90 mg IV infused over 2 to 4 hours, repeated to a cumulative dose of 180 to 360 mg) is an alternative when zoledronate is unavailable.
• Second-Line & Fallback Options (Calcitonin & Denosumab): Subcutaneous salmon calcitonin (50 to 100 IU administered daily or three times weekly) is strictly indicated in patients with severe renal failure (eGFR < 30 mL/min) where bisphosphonates are contraindicated, or for rapid temporary analgesia during severe acute bone pain. Calcitonin provides central endorphin-mediated pain relief within days, but biochemical suppression is modest (SAP reduction 30% to 50%), and long-term use is limited by antibody-mediated tachyphylaxis. Denosumab (60 mg subcutaneously every 6 months) is an emerging off-label alternative that potently inhibits RANKL, useful in refractory disease or severe renal impairment, though close monitoring for rebound bone turnover and hypocalcemia is mandatory.

Operative Indications & Surgical Management

Surgical intervention is indicated for:

• End-stage secondary osteoarthritis of the hip or knee refractory to medical and conservative therapy.
• Complete transverse “chalk-stick” fractures of long bones.
• Symptomatic, non-healing tensile micro-fractures (fissure fractures / Looser zones) with impending completion.
• Severe skeletal angular deformities (coxa vara, anterolateral femoral bowing > 15° to 20°, tibial bowing) causing joint degeneration or functional gait failure.
• Spinal stenosis with progressive compressive myelopathy, radiculopathy, or cauda equina syndrome.
• Basilar invagination causing brainstem or upper cervical cord compression.
• Suspected malignant transformation (pagetic osteosarcoma) requiring oncologic biopsy and resection.

Preoperative Medical Suppression & Hemorrhage Mitigation

Active pagetic bone possesses an extensive network of hypervascular, high-flow arteriovenous sinusoids within its marrow stroma. Unprepared elective surgery on active pagetic bone is associated with profuse, life-threatening intraoperative hemorrhage (blood loss frequently exceeding 1500 to 3000 mL). Elective orthopaedic procedures (total joint arthroplasty, deformity osteotomy, spinal decompression) must be preceded by full therapeutic bisphosphonate suppression (preferably intravenous zoledronic acid 5 mg or a completed course of oral risedronate) administered 2 to 3 months prior to the index operation. This interval allows osteoclasts to become quiescent, promotes involution of the hypervascular fibrovascular stroma, normalizes intraosseous blood flow, and reduces intraoperative blood loss by up to 50% to 70%. Standard intraoperative blood conservation protocols must include intravenous tranexamic acid (TXA, 1 to 2 g IV at induction), cell saver autologous blood salvage, controlled hypotensive anesthesia, and availability of cross-matched blood products.

Total Hip and Knee Arthroplasty

• Total Hip Arthroplasty (THA): The surgical management of pagetic coxarthrosis is complicated by coxa vara, anterolateral femoral bowing, medullary canal stenosis or sclerosis, and protrusio acetabuli with medial wall deficiency. Acetabular preparation requires careful peripheral rim reaming to establish stable cortical fit while strictly avoiding deep medial reaming that can breach the paper-thin medial wall. The medial acetabular defect is densely packed with morselized autologous femoral head bone graft to reconstruct the anatomical hip center. Modern uncemented hemispherical porous-coated titanium cups supplemented with multiple dome screws provide reliable biological osseointegration and durable long-term stability.
• Femoral Component Selection and Technique: Sclerotic bone and anterolateral femoral bowing create an acute risk of eccentric anterior or lateral cortical blowout during broaching. Flexible canal reamers under intraoperative fluoroscopic guidance should be used to define the intramedullary axis. Modern uncemented, tapered or modular fluted titanium stems provide superior long-term survivorship (> 95% at 10 years). Historically, early-generation cemented femoral components experienced high rates of aseptic loosening (15% to 25% at 10 years) due to ongoing disorganized remodeling of the pagetic bone-cement interface. If severe femoral bowing exceeds 15° to 20° preventing coaxial stem seating, a concurrent subtrochanteric transverse or closing-wedge osteotomy is performed, stabilized with a modular diaphyseal-engaging fluted stem.
• Heterotopic Ossification (HO) Prophylaxis: Exposure and reaming of pagetic bone releases potent osteoinductive cytokines, resulting in an exceptionally high incidence of Brooker grade III and IV heterotopic ossification (up to 30% to 50% without prophylaxis). Routine prophylaxis is mandatory: oral indomethacin (75 mg sustained release once daily for 3 to 6 weeks postoperatively, with gastroprotective proton pump inhibitors) or single-fraction external beam radiation therapy (700 to 800 cGy administered within 24 to 48 hours postoperatively).
• Total Knee Arthroplasty (TKA): Severe anterior tibial bowing or distal femoral bowing distorts normal anatomical and mechanical axes. Conventional straight intramedullary alignment rods cannot pass down bowed canals and risk cortical perforation and severe component malalignment. Extramedullary alignment cutting guides or computer-assisted navigation systems are mandatory. Sclerotic pagetic bone generates high frictional resistance; surgeons must utilize sharp, heavy-duty saw blades, frequent blade changes, and continuous iced saline irrigation to prevent bone thermal necrosis, which predisposes to delayed osseointegration or early loosening. Modular stem extensions are frequently necessary to bypass metaphyseal deformities and transmit loads to the diaphysis.

Fracture Management & Deformity Correction

• Pathomechanics of “Chalk-Stick” Fractures: Pagetic fractures occur perpendicular to the long axis of the bone under low-energy bending or torsional loads, snapping cleanly across brittle, sclerotic cortex like a piece of chalk. Most frequently located in the subtrochanteric femur, femoral diaphysis, or proximal tibia, these fractures carry an exceptionally high risk of delayed union, nonunion (up to 20% to 40%), and early hardware failure due to poor intrinsic vascularity and stress concentration at the rigid bone-implant interface.
• Management of Tensile Stress Micro-Fractures: Incomplete horizontal fissure lines (Looser zones) on the tensile convex cortex of bowed long bones that remain symptomatic despite 3 months of bisphosphonate therapy represent impending complete chalk-stick fractures. Prophylactic surgical stabilization with a load-sharing intramedullary nail is strongly recommended to prevent catastrophic displaced fracture.
• Intramedullary (IM) Nailing: Reamed intramedullary nailing is the gold standard for long bone pagetic fractures. A load-sharing intramedullary nail protects the entire deformed bone and permits early weight-bearing mobilization. Dense, sclerotic, obliterated medullary canals require sequential reaming starting with small-diameter flexible reamers under continuous fluoroscopic control. Over-reaming the canal by 1.5 to 2.0 mm beyond the chosen nail diameter is essential to prevent nail jamming or cortical splitting in bowed shafts.
• Plate Osteosynthesis: Open reduction and internal fixation with long locking compression plates (LCP) is reserved for periarticular fractures where IM nails cannot achieve adequate distal/proximal purchase, or where extreme multiplanar bowing prohibits nail passage. Plating constructs must span the entire length of the bone to prevent stress concentrations at plate ends, which otherwise trigger periprosthetic fractures through brittle pagetic bone.
• Deformity Correction Osteotomies: Severe angular deformities (femoral anterolateral bowing > 20°, severe tibial sabre shin) that generate debilitating gait abnormalities, patellofemoral maltracking, or rapid adjacent joint osteoarthritis are managed with planned single-stage or staged corrective osteotomies (closing wedge or chevron osteotomies) stabilized with rigid intramedullary nails or long locking plates. Preoperative medical suppression and full-length standing mechanical alignment radiographs are mandatory.

9. Outcome

Modern multimodal management of Paget’s disease, combining nitrogen-containing bisphosphonates with modern joint arthroplasty and load-sharing fracture fixation, achieves predictable pain relief, durable functional restoration, and high implant survivorship.

Patient-Reported Outcome Measures (PROMs)

• Hip Arthroplasty Functional Gains: In patients undergoing total hip arthroplasty for secondary pagetic coxarthrosis, validated PROMs demonstrate dramatic improvements. Mean Harris Hip Scores (HHS) improve from severe impairment preoperatively (averaging 38 to 45 points) to good or excellent postoperatively (averaging 84 to 92 points) at 5 to 10 years of follow-up. Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain and physical function subscores show statistically and clinically significant gains. Visual Analog Scale (VAS) pain scores decrease from a mean of 7.8/10 preoperatively to 1.4/10 at final follow-up.
• Knee Arthroplasty Outcomes: Total knee arthroplasty in pagetic gonarthrosis yields marked gains in Knee Society Scores (KSS clinical and functional), improving from preoperative scores < 50 points to postoperative scores exceeding 85 points. Oxford Knee Scores (OKS) and EuroQol-5D (EQ-5D) health-related quality of life metrics improve to levels comparable to non-pagetic primary TKA cohorts.

Biochemical Remission Rates and Durability

Intravenous zoledronic acid (5 mg) induces complete biochemical remission (normalization of total SAP) in 88% to 96% of treated patients by 6 months post-infusion, with median time to response of 64 days. Long-term prospective extension studies demonstrate that over 85% of patients maintain normal SAP levels at 2 to 3 years without retreatment, and approximately 70% remain in complete biochemical remission at 5 years. By comparison, oral risedronate achieves biochemical remission in 74% of patients at 6 months, with median remission duration of approximately 1.5 to 2 years before biochemical relapse occurs.

Long-Term Implant Survivorship

• Uncemented Total Hip Arthroplasty: Modern uncemented porous-coated femoral stems and hemispherical porous titanium acetabular cups demonstrate 10- to 15-year implant survivorship rates of 93% to 96% for aseptic loosening. This contrasts with early cemented cohorts, where 10-year aseptic cup loosening rates reached 15% to 25% due to ongoing remodeling at the bone-cement interface.
• Total Knee Arthroplasty Survivorship: Modern TKA utilizing extramedullary alignment guides, copiously irrigated bone resections, and modular stem extensions achieves 10-year implant survivorship exceeding 90% to 94% for aseptic loosening, provided coronal mechanical alignment is restored within 3° of neutral and disease activity is chemically suppressed.

Fracture Union Rates

Reamed intramedullary nailing of pagetic femoral and tibial fractures achieves bony union in 85% to 92% of cases. However, time to solid radiographic union is substantially prolonged, averaging 18 to 26 weeks (compared to 10 to 14 weeks in non-pagetic long bone fractures). Postoperative bisphosphonate therapy suppresses excessive remodeling at the fracture site once soft callus has formed, without impairing secondary endochondral ossification.

10. Complications

Complications associated with Paget’s disease range from mechanical failures and neurological entrapments to life-threatening metabolic crises and malignant degeneration:

Malignant Transformation: Pagetic Osteosarcoma

Malignant sarcomatous degeneration represents the most catastrophic complication of Paget’s disease of bone. It occurs in less than 0.5% to 1% of all patients with Paget’s disease, but accounts for up to 20% to 30% of all osteosarcomas diagnosed in adults older than 60 years of age. Transformation arises from chronic, rapid polyclonal cell turnover, repeated replicative stress, and genetic instability in pagetic osteogenic and stromal cells. Histologically, high-grade osteosarcoma accounts for approximately 70% of cases, followed by undifferentiated pleomorphic sarcoma (UPS / malignant fibrous histiocytoma, 20%), fibrosarcoma, and chondrosarcoma.

The clinical hallmark of malignant transformation is a sudden, rapid exacerbation of deep, relentless bone pain in a previously stable or quiescent pagetic bone, characteristically unresponsive to bisphosphonate therapy. Patients typically present with a rapidly expanding, tender soft-tissue mass, localized swelling, or an acute pathologic fracture through a destructive lytic lesion. Plain radiographs reveal focal, aggressive permeative osteolysis, cortical bone destruction, loss of pagetic trabecular coarsening, and soft-tissue extension. Contrast-enhanced MRI demonstrates complete replacement of the normal fatty marrow signal by a low T1 / heterogeneous high T2 enhancing tumor extending through breached cortex into adjacent soft-tissue compartments.

The prognosis for pagetic osteosarcoma is dismal, with historical 5-year overall survival rates of less than 5% to 10%. Elderly patients tolerate aggressive multi-agent chemotherapy poorly. Surgical management requires wide radical oncologic resection or amputation when anatomically feasible, alongside palliative radiotherapy and multimodal analgesic support.

11. Pearls and Pitfalls

Clinical & Diagnostic Pearls

• The Baseline Whole-Body Mapping Rule: Always obtain a baseline 99mTc-MDP whole-body bone scintigram in any patient newly diagnosed with Paget’s disease. Serum alkaline phosphatase reflects whole-body skeletal metabolic activity and cannot distinguish whether high turnover is occurring in a safe site (such as the iliac crest) versus a dangerous site (such as the skull base or cervical/thoracic spine).
• The Preservation of Fat Signal Rule: On MRI of uncomplicated pagetic bone, normal high T1-weighted bone marrow fat signal is consistently preserved between thickened trabeculae. Complete loss of marrow fat signal replaced by confluent low T1 / high T2 soft-tissue tumor is a critical red flag for malignant transformation to pagetic osteosarcoma.
• Vitamin D Repletion Before Antiresorptives: Never administer intravenous zoledronic acid without first verifying normal serum calcium and 25-hydroxyvitamin D (> 50 nmol/L). In patients with subclinical vitamin D deficiency, potent bisphosphonate-induced suppression of bone resorption halts skeletal calcium efflux while the bone continues to take up calcium, precipitating severe symptomatic hypocalcemia and tetany.
• Differentiating Bone Pain from Joint Pain: Deep, dull bone pain present at rest and worsening at night reflects active pagetic metabolic turnover and responds promptly to bisphosphonates. Mechanical groin pain provoked by weight-bearing and relieved by rest indicates secondary degenerative coxarthrosis and requires joint arthroplasty rather than repeated bisphosphonate cycles.

Intraoperative & Surgical Pearls

• Preoperative Quenching of Hypervascularity: Elective joint arthroplasty or osteotomy should never be performed in active, untreated Paget’s disease. Administer IV zoledronic acid 5 mg at least 8 to 12 weeks prior to elective surgery to suppress active osteoclastic turnover and close the hypervascular sinusoidal network, reducing intraoperative blood loss by up to 50% to 70%.
• Prophylactic Nailing of Tensile Fissures: Symptomatic horizontal cortical micro-fractures (Looser zones) along the convex tension cortex of the femur or tibia that fail to resolve after 3 months of medical therapy must be prophylactically stabilized with a full-length reamed intramedullary nail before they propagate into catastrophic displaced chalk-stick fractures.
• Avoiding Extramedullary Cortical Blowout: Never force a straight rigid femoral broach into a bowed pagetic femur. Execute a slightly more distal and lateral femoral neck cut to optimize straight-line access to the medullary canal, and utilize flexible reamers under continuous fluoroscopic guidance. If bowing exceeds 15° to 20°, perform a planned corrective subtrochanteric osteotomy.
• Prevention of Bone Thermal Necrosis: Dense, sclerotic pagetic bone generates extreme friction during cutting and reaming. Always use brand-new, sharp, heavy-duty saw blades, frequent blade changes, and continuous iced saline irrigation during total knee resections to avoid osseous thermal necrosis and delayed implant integration.
• Mandatory Heterotopic Ossification Prophylaxis: Hip arthroplasty in pagetic bone carries an exceptionally high risk of Brooker grade III-IV heterotopic ossification (up to 30% to 50%). Routine prophylaxis with oral indomethacin (75 mg SR daily for 3 to 6 weeks) or single-fraction radiation therapy (700-800 cGy within 24 to 48 hours) is mandatory.

Pitfalls to Avoid

• Operating During Active Hypervascularity: Operating on active Paget’s disease without prior medical suppression leads to profuse, uncontrolled bone hemorrhage, hemodynamic instability, and high transfusion requirements.
• Misinterpreting Isolated SAP Elevation: Attributing elevated serum alkaline phosphatase exclusively to liver pathology without checking GGT, 5′-nucleotidase, or bone-specific ALP delays diagnosis of active skeletal Paget’s disease.
• Over-Reaming the Protrusio Acetabulum: Aggressive medial acetabular reaming in protrusio acetabuli penetrates the paper-thin medial wall, causing intrapelvic cup displacement. Ream the peripheral rim only and reconstruct the medial floor with impacted morselized autograft.
• Using Short Rigid Plates for Fractures: Using short bridge plates to fix transverse pagetic fractures creates high stress concentrations at the plate ends, leading to catastrophic periprosthetic refracture or screw pullout in brittle sclerotic bone. Always prefer full-length load-sharing intramedullary nails or span the entire bone.
• Prolonged Immobilization Without Calcium Monitoring: Placing a patient with polyostotic Paget’s disease on prolonged bed rest or in a cast without monitoring serum calcium can precipitate life-threatening acute immobilization hypercalcemia and cardiac arrest.
• Dismissing Rapid Focal Pain Acceleration: Overlooking sudden, severe, focal pain acceleration in a previously stable pagetic bone can lead to a missed diagnosis of malignant transformation to pagetic osteosarcoma.

12. Controversy

Intensive SAP Normalization vs. Symptom-Driven Medical Therapy

A major clinical controversy centers on whether asymptomatic patients with elevated serum alkaline phosphatase should receive aggressive antiresorptive therapy aimed at biochemical normalization, or whether therapy should be reserved strictly for symptomatic patients. The PRISM (Paget’s Disease: Randomized Trial of Intensive versus Symptomatic Management) multicenter trial randomized 1,324 patients with Paget’s disease to either intensive therapy (aimed at normalizing SAP using bisphosphonates) or symptomatic therapy (bisphosphonates administered only for bone pain). At a median follow-up of 3 years, and extended to 5 years in the PRISM-EZ study, the intensive treatment arm achieved significantly greater reductions in SAP, but showed no statistically significant reduction in fracture incidence, orthopaedic surgical interventions, hearing loss progression, or quality of life improvements compared to symptom-driven management.

Conversely, clinical guidelines from the Endocrine Society and international consensus panels (Ralston et al. 2019) advocate a targeted strategy: treating asymptomatic patients if active pagetic lesions involve high-risk anatomical sites (such as the skull base, spine, weight-bearing long bones near articular surfaces, or acetabulum) to prevent progressive skeletal bowing, protrusio acetabuli, spinal cord compression, and basilar invagination. Proponents argue that the PRISM cohort consisted primarily of older patients with long-standing, burned-out skeletal deformities where structural damage was already established, and that early antiresorptive intervention in younger patients with incipient lytic lesions prevents irreversible structural deterioration.

Cemented vs. Uncemented Total Hip Arthroplasty Fixation

The optimal mode of component fixation in total hip arthroplasty for pagetic coxarthrosis remains debated. Historically, cemented fixation was standard. However, long-term retrospective registry and single-institution studies revealed high rates of aseptic loosening (15% to 25% at 10 years), particularly on the acetabular side. The continuous, disordered remodeling of pagetic subchondral bone at the bone-cement interface degrades the micromechanical cement interlock, leading to progressive radiolucent lines and cup loosening.

Modern uncemented porous-coated femoral stems and highly porous hemispherical titanium cups demonstrate reliable biological osseointegration and durable long-term implant survivorship (> 95% at 10 years). Some reconstructive surgeons continue to advocate cemented femoral stems in elderly osteoporotic patients with wide, cylindrical medullary canals, provided that modern third-generation cementing techniques (pulsatile canal lavage, distal cement restrictor, vacuum mixing, retrograde pressurization) are rigorously applied and the disease is biologically quiescent. Modern consensus strongly favors uncemented porous acetabular components with screw augmentation, combined with uncemented tapered or modular fluted femoral stems.

Prophylactic Stabilization Thresholds for Tensile Fissure Fractures

The clinical management of incomplete horizontal cortical fissure fractures (Looser zones) along the tensile cortex of bowed long bones remains nuanced. While all surgeons agree that complete chalk-stick fractures require surgical fixation, opinions diverge on the timing of prophylactic surgical stabilization for incomplete tensile lesions. Conservative proponents argue that initiating high-potency intravenous bisphosphonate therapy (zoledronic acid) combined with protected weight-bearing and crutches can achieve radiographic cortical healing without surgical intervention in up to 40% to 50% of cases. Conversely, orthopaedic trauma surgeons advocate aggressive early prophylactic intramedullary nailing for any tensile fissure fracture associated with persistent localized pain or extending across more than 30% of the cortical diameter. Prophylactic nailing eliminates the risk of sudden catastrophic displacement, permits immediate unrestricted weight-bearing, and avoids the substantial morbidity and nonunion risk of emergency fracture fixation in brittle pagetic bone.

13. Evidence-Based Synthesis

Modern clinical decision-making is grounded in high-quality randomized controlled trials and prospective registry analyses, corroborated by seminal biomechanical and anatomical descriptions.

14. References

• Corral-Gudino L, Tan AJ, Del Pino-Montes J et al. Bisphosphonates for Paget’s disease of bone in adults. Cochrane Database Syst Rev. 2017. doi:10.1002/14651858.CD004956.pub3 [Level I: Systematic Review / Meta-Analysis]
• Reid IR, Miller P, Lyles K et al. Comparison of a single infusion of zoledronic acid with risedronate for Paget’s disease. N Engl J Med. 2005. doi:10.1056/NEJMoa044241 [Level I: Randomized Controlled Trial]
• Ralston SH, Corral-Gudino L, Cooper C et al. Diagnosis and Management of Paget’s Disease of Bone in Adults: A Clinical Guideline. J Bone Miner Res. 2019. doi:10.1002/jbmr.3657 [Level V (Expert Consensus / Guideline): Clinical Practice Guideline]
• Parvizi J, Klein GR, Sim FH. Surgical management of Paget’s disease of bone. J Bone Miner Res. 2006. doi:10.1359/jbmr.06s214 [Level IV: Clinical Review & Surgical Cohort]
• Parvizi J, Schall DM, Lewallen DG et al. Outcome of uncemented hip arthroplasty components in patients with Paget’s disease. Clin Orthop Relat Res. 2002. doi:10.1097/00003086-200210000-00020 [Level IV: Retrospective Cohort Study]

15. Master Class Pro-Tip

When undertaking total hip arthroplasty in a patient with severe pagetic coxa vara and anterolateral femoral bowing, never attempt to force a straight rigid femoral broach down the diaphyseal axis from a conventional trochanteric fossa starting point. The pagetic endosteal sclerosis and anterior cortical bow create an immediate hazard of eccentric anterior or lateral cortical blowout. Preoperatively administer intravenous zoledronic acid at least 8 to 12 weeks prior to the index procedure to suppress the intense periosteal and marrow hypervascularity. Intraoperatively, execute a slightly more distal and lateral femoral neck osteotomy to optimize straight-line access to the medullary canal, and systematically prepare the canal using flexible reamers under continuous fluoroscopic monitoring. If femoral bowing exceeds 15 to 20 degrees or severe canal deformity precludes concentric implant seating, do not hesitate to perform a planned concurrent subtrochanteric transverse or closing-wedge osteotomy stabilized with a modular diaphyseal-engaging fluted titanium stem. Finally, always institute mandatory heterotopic ossification prophylaxis with indomethacin or single-fraction radiation therapy, as the surgical exposure of pagetic bone unleashes an exceptionally potent osteoinductive cascade.

Master Class Surgical Pearl: Complex Arthroplasty in Pagetic Skeletal Deformity