Primary benign bone lesions

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Begin with age, skeletal maturity, lesion discovery and symptom attribution. Ask whether pain is focal, load-related, nocturnal or preceded imaging; whether a lump grows; and whether fracture, fever, weight loss or cancer history exists. Record previous films, family exostoses, limb deformity and endocrine signs. Many enchondromas and non-ossifying fibromas are bystanders, so a common source such as osteoarthritis should still be sought. Conversely, unexplained progressive pain must not be dismissed because a report says likely benign.

Inspect for mass, skin change, venous prominence, limb alignment, muscle wasting and joint restriction. Palpate size, warmth, fixation and tenderness without repeatedly stressing weakened bone. Examine the joint above and below and record distal nerve and vascular findings, particularly with an osteochondroma near a neurovascular bundle. If fracture is possible, splint first. Avoid needle aspiration or steroid injection until a tumour-aware plan determines what structure is being entered.

Read the radiograph systematically. Identify bone and longitudinal segment, epiphyseal, metaphyseal or diaphyseal position, medullary versus surface origin, lytic or sclerotic character, transition zone, periosteal response, matrix, cortical expansion or breach and soft-tissue mineralisation. A non-ossifying fibroma is eccentric and cortically based in a child; enchondroma is central with chondroid calcification; osteochondroma shows medullary continuity with the parent bone; simple cyst is central and metaphyseal.

Cross-sectional imaging answers defined questions. MRI covers the entire lesion and surrounding compartment before biopsy, demonstrating oedema, marrow and soft-tissue extent, cartilage-cap thickness and neurovascular proximity. CT clarifies cortical integrity, subtle mineralisation and spinal or pelvic geometry. Ultrasound can assess a superficial cartilage cap or vascular complication in expert hands. Do not mistake intense scintigraphic uptake for malignancy: benign fracture, fibrous dysplasia and active cyst can also be avid.

Classify behaviour before naming histology. A lesion confidently benign and asymptomatic may need no intervention or interval radiographs according to type, age and fracture risk. Indeterminate lesions need specialist radiology review and often MRI. Aggressive or discordant lesions enter the regional bone-sarcoma service. This referral occurs before biopsy because poor tract placement can contaminate an uninvolved compartment, force wider resection or compromise limb salvage.

Mechanical assessment runs in parallel. Functional pain, progressive cortical thinning, lesion size and site determine fracture risk more than the word benign. Protect a proximal femoral, peritrochanteric or other weight-bearing lesion when failure would be catastrophic. A pathological fracture through a potentially primary tumour is immobilised and discussed before internal fixation. When benign diagnosis is secure, options include observation, percutaneous injection for selected cysts, curettage with graft or cement, prophylactic fixation or en-bloc excision.

Treatment is lesion-specific. An asymptomatic solitary osteochondroma usually remains untouched; excise when it causes pain from mechanical irritation, neurovascular compromise, deformity or suspicious adult change. Enchondroma in a long bone can be observed when classic and painless; curettage follows attributable pain, fracture or diagnostic concern. Aneurysmal bone cyst and giant-cell tumour need specialist curettage or resection strategies because local recurrence is relevant. Denosumab for giant-cell tumour is specialist oncology treatment and can alter operative planes.

Follow-up must state what change should trigger return. Compare size, cortex, matrix and symptoms using the same projection where possible. After curettage or fixation, track graft incorporation, recurrence and hardware, progressing load only when structural recovery permits. Children need growth and deformity surveillance. New pain or growth after maturity, cartilage-cap enlargement, cortical breakthrough or a soft-tissue mass demands re-staging rather than routine continuation of a benign surveillance schedule.

Key points

Most benign bone lesions are incidental, but no lesion is safely labelled from name recognition alone: integrate age, exact skeletal site, margin, matrix, cortex and symptoms.
First-line imaging is a high-quality radiograph in two planes including the full lesion; prior films are invaluable for growth and stability.
A narrow geographic margin, intact cortex and uninterrupted solid periosteal response favour slow behaviour, whereas a permeative margin, cortical escape and mass are aggressive.
MRI is the reference local-staging test for marrow extent, cartilage cap, neurovascular relation and soft-tissue component when biology or treatment requires clarification.
CT best defines cortex and mineralised matrix, while bone scan or PET answers selected multiplicity or activity questions but cannot establish benign histology.
Never biopsy, curette or internally fix a suspected primary bone tumour outside the specialist pathway; the incision and tract must be removable with definitive surgery.
Protect weight bearing when a lesion causes functional pain, occupies substantial cortex or has fractured, and obtain tumour-aware orthopaedic advice before definitive fixation.
Observe classic asymptomatic low-risk lesions with an explicit imaging plan; operate for fracture risk, pain attributable to the lesion, deformity, compression or uncertain/aggressive biology.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Developmental growth disturbance

Osteochondroma arises from displaced growth-plate cartilage and may be solitary or part of hereditary multiple exostoses with EXT-pathway variants.

Benign cartilage neoplasia

Enchondroma is an intramedullary hyaline-cartilage tumour, often incidental in small bones or long-bone metaphyses and usually biologically quiet.

Fibro-osseous replacement

Fibrous dysplasia reflects mosaic GNAS activation, replacing normal bone with immature woven bone and fibrous tissue in one or several sites.

Cystic and aggressive processes

Unicameral cysts form near active physes, aneurysmal bone cysts expand with blood-filled spaces, and epiphyseal giant-cell tumour can destroy cortex and recur despite benign histology.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Slow geographic growth
Indolent lesions allow host bone to wall them off with a narrow transition and sclerotic margin, reflecting time for organised remodelling.
2
Matrix-specific mineralisation
Cartilage produces rings and arcs, osteoid becomes cloudlike dense matrix and fibrous tissue creates ground-glass appearance, narrowing the diagnostic family.
3
Cortical stress reduction
Medullary expansion, endosteal scalloping or cystic replacement reduces the load-bearing cross-section and can cause fracture despite benign biology.
4
Local compression
An exostosis or expanding lesion can irritate tendon, deform a joint, compress nerve or vessel and create symptoms without malignant transformation.
5
Secondary transformation risk
Selected lesions and syndromes carry a small but meaningful malignant risk, signalled by adult growth, changing pain, aggressive anatomy or increasing cartilage cap.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Geographic benign margin

A sharp transition with a sclerotic rim indicates slow expansion that has allowed adjacent bone to organise a response.

Chondroid rings and arcs

Lobulated medullary lucency containing ring-and-arc calcification supports a cartilage lesion but does not alone determine grade.

Medullary continuity

Cortex and marrow flowing continuously into an exostosis is the defining anatomical feature of osteochondroma.

Ground-glass matrix

Homogeneous hazy mineralisation with expansion and rind-like cortex suggests fibrous dysplasia in the appropriate age and site.

Impending mechanical failure

Functional pain, marked cortical loss and a high-load location indicate fracture risk even when the lesion is biologically benign.

Aggressive discordance

Rapid symptom change, wide transition, interrupted periosteum or soft-tissue extension overrides a reassuring provisional lesion name.

Red flags requiring action

Night or rest pain that is progressive and not explained by a fracture is incompatible with casual discharge of an incidental benign label.
A wide or ill-defined transition zone, cortical breakthrough, aggressive periosteal reaction or soft-tissue mass requires specialist sarcoma review.
A pathological fracture through an uncharacterised lesion needs splintage and tumour-centre discussion before definitive fixation contaminates tissue planes.
Increasing size after skeletal maturity, new pain or a thick cartilage cap over an osteochondroma raises concern for secondary chondrosarcoma.
Multiple enchondromas, osteochondromas or cystic lesions require syndrome, deformity and malignant-risk assessment rather than isolated lesion treatment.
Spinal lesion with weakness, sensory change, gait dysfunction or bladder or bowel disturbance requires emergency MRI and spinal surgical input.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line orthogonal plain radiographsFirst stepFirst line
Why
Characterise location, margin, matrix, cortex, periosteal response and fracture and compare with prior imaging.
Interpretation and limitations
A complete two-plane study often identifies a classic low-risk lesion; aggressive or indeterminate morphology requires specialist escalation.
02
MRI of the whole lesion and compartment
Why
Define marrow and soft-tissue extent, cartilage cap, fracture, neurovascular relation and viable biopsy targets.
Interpretation and limitations
This is the reference local-staging study before biopsy; perform it before contaminating oedema and haemorrhage from intervention.
03
CT for cortex and matrix
Why
Resolve subtle mineralisation, cortical breach, surface anatomy and complex pelvic or spinal geometry.
Interpretation and limitations
CT complements rather than replaces MRI when a soft-tissue component or intramedullary extent is important.
04
Selected laboratory screen
Why
Investigate infection, metabolic disease, myeloma or metastatic cancer when age, symptoms or multiplicity makes them plausible.
Interpretation and limitations
Normal bloods do not prove a lesion benign; choose FBC, CRP, calcium, ALP, renal profile and protein studies from the differential.
05
Specialist-planned image-guided core biopsy
Why
Obtain tissue when imaging cannot securely classify biology and histology will change treatment.
Interpretation and limitations
Biopsy is the diagnostic reference only when imaging, pathology and surgical teams agree a tract that can be excised at definitive surgery.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Primary bone sarcoma

Aggressive margins, destructive growth, mass and unexplained progressive pain require tumour-pathway staging even when the lesion resembles a benign entity superficially.

Skeletal metastasis or myeloma

Older age, multiplicity, axial distribution, cancer history, anaemia or hypercalcaemia redirects assessment toward systemic malignant disease.

Brodie abscess

Subacute osteomyelitis can form a geographic lucency with surrounding sclerosis; fever may be absent, so inflammatory and infection context matters.

Normal anatomical variant

Bone island, fibrous cortical defect, pseudocyst and traction-related irregularity can mimic tumour but follow characteristic location and benign morphology.

Stress or healing fracture

Callus, cortical lucency and marrow reaction can look aggressive; mechanism, serial change and a visible fracture line support trauma-related remodelling.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01IncidentalClassify before reassuringFirst stepA bone lesion appears unexpectedly on imaging obtained for another reason.

1Review high-quality radiographs, patient age, precise location, margin, matrix and all prior images.
2Ask directly about focal pain, growth, fracture, constitutional symptoms and relevant cancer or family history.
3Discharge only a confidently characteristic no-risk variant; otherwise define interval imaging or specialist review explicitly.
4EscalationEscalate any aggressive or clinically discordant feature to the bone-tumour service before local intervention.

02Mechanical riskPrevent pathological fractureFunctional pain, cortical compromise or a high-load site makes structural failure plausible.

1Restrict weight bearing and provide appropriate immobilisation or aids while completing imaging.
2Image the entire lesion in two planes and add CT for cortex or MRI for occult fracture and extent.
3Discuss the case with tumour-aware orthopaedics before curettage, injection or fixation.
4When benign diagnosis is secure, combine lesion treatment and prophylactic stabilisation according to site and residual cortex.

03Aggressive lesionPreserve the oncological fieldPain, growth, cortical escape, aggressive margin or mass prevents confident benign classification.

1Do not biopsy, aspirate, inject or internally fix the lesion in a non-specialist pathway.
2Obtain complete local radiographs and follow regional instructions for MRI before referral or immediately at the centre.
3Send images and clinical details urgently to the designated bone-sarcoma multidisciplinary service.
4DefinitiveAllow that service to stage the patient, select the biopsy target and place a tract removable with definitive resection.

04Confirmed benignMatch treatment to consequenceSpecialist review establishes a benign lesion and its symptoms or fracture risk are understood.

1Observe an asymptomatic stable low-risk lesion with a lesion-specific surveillance plan.
2Use curettage, graft, cement, injection or excision only where pain, fracture, deformity, compression or biology justifies morbidity.
3Add fixation when the remaining bone cannot safely carry rehabilitation load.
4Monitor recurrence, healing, growth and neurovascular function and re-stage any unexpected change.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Provides analgesia without altering biopsy histology while mechanical protection and definitive imaging are arranged.

Paracetamol while lesion assessment proceeds

Use 500 to 1,000 mg orally when required, separated by four hours or more and capped at 4 g in 24 hours, with a lower daily maximum for low body weight or liver risk.

Check combination preparations and hepatic or alcohol history; pain relief does not make a weakened cortex safe to load.

Can control unresectable or highly morbid giant-cell tumour and may form part of a planned neoadjuvant strategy.

Denosumab for selected giant-cell tumour

Specialist centres may use 120 mg subcutaneously on days 1, 8 and 15 of the first month and then every four weeks, with calcium and vitamin-D support according to the product licence.

This is not routine treatment for an undiagnosed lesion; monitor hypocalcaemia and dental risk, consider pregnancy prevention and recognise that prolonged use changes bone and operative assessment.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Pathological fracture

Cystic or expansile replacement weakens cortex and can fail through ordinary activity, sometimes being the first presentation in a child or young adult.

Deformity and growth disturbance

Physeal proximity, repeated fracture or multiple exostoses can cause limb-length difference, angular deformity and altered joint mechanics.

Neurovascular compression

Surface lesions near the fibular neck, pelvis or shoulder can compress nerves or vessels and may form pseudoaneurysm or thrombosis.

Local recurrence

Incomplete curettage of aneurysmal bone cyst or giant-cell tumour can permit regrowth, requiring planned surveillance and sometimes repeat reconstruction.

Malignant transformation

Rare change in osteochondroma, enchondromatosis or fibrous dysplasia is suggested by adult growth, escalating pain and aggressive cortical or soft-tissue features.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Record lesion-specific pain, palpable size, joint motion, distal nerve and vascular findings and loading ability at baseline.
Compare radiographs using the same anatomical coverage for growth, cortical change, matrix evolution and new fracture.
During protected loading, reassess pain and function promptly; sudden deterioration can signal completion of a pathological fracture.
After curettage or excision, monitor wound, recurrence, graft or cement interface, fixation and return of mechanical strength.
In a growing child, follow limb length, alignment and physeal effects rather than lesion dimensions alone.
Restart the sarcoma diagnostic pathway for new adult growth, rest pain, cortical breakthrough or a mass regardless of previous benign histology.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Behaviour precedes the name

A precise description of margin, matrix and cortex is safer than forcing an indeterminate lesion into a familiar benign label.

Benign can still fracture

Histology predicts metastatic behaviour, not whether enough load-bearing cortex remains for unrestricted walking.

MRI comes before biopsy

Intervention creates haemorrhage and oedema that obscure true extent and can contaminate tissue outside the future resection.

The tract becomes tumour field

A correctly planned biopsy route is removed en bloc; a misplaced route can increase the definitive operation substantially.

Pain may be incidental

A classic enchondroma beside an arthritic joint should not undergo curettage unless clinical and imaging correlation attributes symptoms.

Adult growth changes risk

An osteochondroma should stop enlarging after maturity, so renewed expansion requires cartilage-cap and sarcoma assessment.

11Common pitfallsFrequent interpretation and management errors.

01
Calling a lesion benign from a single feature without integrating age, site, matrix, margins and symptoms.
02
Biopsying, injecting or curetting an aggressive lesion before regional tumour-centre discussion.
03
Internally fixing a pathological fracture through an uncharacterised primary lesion and contaminating the whole compartment.
04
Allowing full weight bearing because the likely histology is benign despite major cortical compromise.
05
Operating on an incidental enchondroma when another joint or tendon disorder explains the patient's pain.
06
Continuing routine surveillance despite new pain, adult growth or cortical breakthrough.