Trevor Disease (Dysplasia Epiphysealis Hemimelica)

Dysplasia epiphysealis hemimelica (DEH), eponymously Trevor disease (or Trevor-Fairbank disease), is a rare developmental skeletal disorder defined by asymmetric osteocartilaginous overgrowth of one or more epiphyses in a growing child. The masses behave like osteochondromas but arise from the epiphysis (or an epiphyseal equivalent such as a carpal/tarsal bone) rather than the metaphysis.

The defining word is hemimelic - "half a limb". Two features follow from it:

1. The lesion affects the medial or lateral half of an epiphysis (medial side more often than lateral).
2. Involvement is almost always limited to one side of one limb, respecting the midline; the lower limb is far more often affected than the upper limb.

It was described by Mouchet and Belot in 1926 ("tarsomegalie") and characterised in the English literature by Trevor in 1950 and by Fairbank in 1956, who coined "dysplasia epiphysealis hemimelica".

According to PubMed, the imaging review by Tyler and colleagues emphasises that DEH is an asymmetric overgrowth of the cartilage of a medial or lateral epiphysis or epiphyseal equivalent, and that imaging is central to diagnosis and to distinguishing it from more sinister lesions (DOI).

Frequency and demographics:

• Very rare: estimated prevalence about 1 per 1,000,000 population
• Male predominance: roughly 3:1 male to female
• Age at presentation: childhood, most often between about 2 and 14 years; diagnosis frequently follows the appearance of the bony nidus, which can lag behind the cartilage by months to years
• No racial or strong geographic predilection has been established given the rarity

Site distribution (lower limb dominant):

• Ankle / hindfoot: the talus is the single most frequently reported site, especially in foot-and-ankle series
• Knee: the distal femur and proximal tibia epiphyses are very commonly involved
• Tarsals (navicular, cuneiforms), distal tibia, and the patella are also reported
• Upper limb and spine are rare but recognised

According to PubMed, a systematic review of foot-and-ankle DEH by Artioli and colleagues pooled 70 patients (mean age 9.6 years, predominantly male) and found the talus to be the most common location, with a mass and pain as the typical presentation (DOI).

Cause is unknown. DEH is a sporadic, non-hereditary developmental disorder of localised cartilage regulation, in which a focus of epiphyseal cartilage escapes normal growth control and forms an osteochondroma-like mass.

Key negatives that examiners test:

• Not familial - there is no Mendelian inheritance pattern and no established family clustering
• Not EXT-related - unlike solitary osteochondroma and hereditary multiple exostoses, DEH is not associated with mutations in the EXT1/EXT2 genes
• Not a true neoplasm of the metaphysis - the lesion is epiphyseal/intra-articular

According to PubMed, the contemporary imaging review by Degnan and Ho-Fung stresses that, although once conceptualised as "epiphyseal osteochondromatosis", DEH lesions differ from osteochondromas, and that the disorder can cause pain, growth disturbance and early osteoarthritis (DOI).

DEH is best understood as a disorder of localised epiphyseal cartilage proliferation. A focus of chondrocytes within the epiphysis loses normal growth restraint and proliferates, producing a cartilage-capped mass that undergoes enchondral ossification from within - exactly the mechanism of an osteochondroma, but originating in the epiphysis.

Histology: the lesion is histologically indistinguishable from an osteochondroma. There is a cartilage cap of disorganised but cytologically benign chondrocytes overlying a bony stalk/nidus, with a zone of enchondral ossification at the base. Because the histology is benign and non-specific, the diagnosis is clinical and radiological, not histological - biopsy is reserved for atypical cases.

Behaviour:

• The lesion grows with the child and tends to stop enlarging at skeletal maturity (like an osteochondroma).
• As it grows it can distort the joint surface, create a mechanical block, stretch the capsule and ligaments, and cause angular deformity or limb-length discrepancy.
• Long-standing joint incongruity predisposes to secondary osteoarthritis in adult life.

The "hemimelic" rule is an anatomical one. Imagine a line through the long axis of the limb dividing it into a medial and a lateral half: DEH affects only one of those halves, and a child rarely crosses the midline.

Why the lower limb and these sites?

• The talus, distal femur and proximal tibia carry large, actively growing epiphyses around the knee and ankle, where most reported lesions occur.
• An intra-articular, epiphyseal location means the mass projects toward the joint - hence the early presentation with a hard juxta-articular swelling, restricted movement, and joint-line catching.

Surgical anatomy points:

• At the ankle, a medial lesion lies close to the deltoid ligament, posterior tibial tendon and neurovascular bundle; a lateral lesion threatens the lateral ligament complex and the talar dome articular cartilage.
• At the knee, lesions of the femoral condyle or tibial plateau sit beneath the menisci and collateral ligaments and may abut the cruciates.
• Excision must protect the adjacent physis and articular cartilage; damage to the growth plate risks iatrogenic arrest and deformity.

The most widely cited classification is by Azouz et al (1985), which grades DEH by the extent of skeletal involvement and correlates loosely with prognosis:

• Localised form: a single epiphysis or one ossification centre is affected (for example, one tarsal bone or one femoral condyle). Best prognosis.
• Classical form: more than one epiphysis within a single lower limb is involved (for example, distal femur plus talus on the same side). This is the typical, most common pattern.
• Generalised form: the entire lower limb from the pelvis to the foot is affected, sometimes with megaepiphyses (enlargement of a whole epiphyseal centre). Worst prognosis, with the greatest deformity and functional burden.

According to PubMed, Azouz and colleagues studied 24 patients (adding 15 new cases) and subdivided DEH into localised, classical and generalised forms, also describing advanced bone age and metaphyseal/growth-plate involvement in some cases (DOI).

A more recent, prognosis-oriented scheme was proposed by Arealis et al (2014) after pooling 144 reported cases. It classifies DEH by the limb(s) and region involved:

• Type 1: single lesion in one lower limb (best prognosis; lower osteoarthritis risk even if not resected)
• Type 2: multiple lesions in the lower limb(s)
• Type 3: single lesion in one upper limb
• Type 4: multiple lesions in the upper limb(s)
• Type 5: upper and lower limb involvement
• Type 6: spinal involvement

The authors argued that type 1 lesions have the best prognosis and the lowest chance of developing osteoarthritis, and that a whole-body bone scan can identify additional clinically silent sites.

According to PubMed, Arealis et al reviewed cases from 1926 to 2013 and proposed this six-type classification that correlates with prognosis, concluding that resection (even if partial) can be a successful treatment (DOI).

The classic presentation is a young child with a painless or mildly painful hard lump near a joint of one limb, usually noticed by a parent.

Typical features in the history:

• A firm swelling around the ankle or knee, often present for months to years
• Pain in roughly half of patients, often mechanical (worse with activity)
• Limping, deformity (angular or rotational), or a leg-length difference noticed over time
• Restricted or catching joint movement, or a feeling of the joint "locking" when the mass blocks motion
• Strictly one limb - bilateral or crossing-midline involvement should make you doubt the diagnosis

According to PubMed, the foot-and-ankle systematic review found that a mass and pain were the presenting features in 54% of cases, reinforcing the picture of a juxta-articular swelling that may or may not hurt (DOI).

Inspection:

• A hard, bony, non-tender or mildly tender mass fixed to the epiphyseal region, typically medial or lateral (not circumferential)
• Angular deformity (for example, valgus or varus at the ankle/knee) and possible limb-length discrepancy
• Muscle wasting if the joint has been painful or stiff for some time

Palpation and movement:

• The mass is continuous with bone and does not move independently
• Reduced range of motion in the affected joint; a hard mechanical block or catching at the extreme of movement
• Assess joint stability - a large lesion can stretch or deform the collateral ligaments and cause instability

Always:

• Examine the whole limb and the contralateral side (to confirm the unilateral pattern and screen for additional sites)
• Document a baseline neurovascular examination, especially around the ankle where a medial mass lies near the tarsal-tunnel structures

Plain radiographs are the first-line investigation and are often diagnostic once the lesion ossifies:

• An irregular, lobulated ossified mass arising from the epiphysis on one side of the joint (medial or lateral half)
• The mass is continuous with the epiphysis and may contain multiple ossific foci that coalesce with time
• Joint surface distortion, angular deformity and sometimes an advanced bone age in the affected epiphysis
• Early in the disease the cartilaginous lesion may be radiographically occult until the ossific nidus appears, which is why a normal radiograph does not exclude DEH in a young child

MRI is the single most useful investigation and is favoured over CT in children to avoid radiation.

It is essential because it:

• Shows the cartilage cap and demonstrates that it is continuous with the epiphyseal cartilage - the diagnostic feature
• Detects the lesion before the bony nidus ossifies, when radiographs are normal
• Maps the lesion's relationship to the articular surface, physis, ligaments and neurovascular structures for surgical planning
• Helps distinguish DEH from sinister lesions and from synovial chondromatosis

According to PubMed, the imaging reviews by Tyler et al and by Degnan and Ho-Fung both highlight MRI as central to characterising the cartilage cap, defining unossified disease and planning management (DOI; DOI).

CT: useful for bony anatomy and operative planning in complex tarsal or articular lesions, and for showing the ossified nidus in three dimensions; weigh the radiation dose in children.

Whole-body bone scintigraphy / skeletal survey: helps screen for additional, clinically silent epiphyseal sites and to define the extent (and therefore the Azouz/Arealis type). Arealis et al specifically recommended a whole-body bone scan to identify multiple affected joints.

Biopsy: not routinely required. The diagnosis is clinical and radiological. Because the histology is identical to an osteochondroma (a benign cartilage cap over a bony stalk), biopsy is reserved for atypical presentations where a more aggressive lesion must be excluded.

There is no high-level evidence and no standardised protocol because the condition is so rare; management is symptom-driven and individualised.

Two broad routes:

1. Observation for small, asymptomatic lesions that are not causing deformity or mechanical block. The lesion typically stops growing at skeletal maturity. Monitor clinically and radiologically because unchecked growth makes later surgery harder.
2. Surgery (marginal excision) for lesions causing pain, deformity, mechanical block, joint incongruity, instability or limb-length problems, or where progressive growth threatens the joint.

According to PubMed, the foot-and-ankle systematic review reported that surgery was chosen in 92% of patients, of whom 95% underwent mass excision, with recurrence the most frequent complication (about 9%) - reflecting that most reported cases are symptomatic enough to operate on (DOI).

Indications: incidental or small lesions, minimal symptoms, no deformity or block, and a well-aligned, stable, congruent joint.

What it involves:

• Clinical and radiographic surveillance at intervals (for example, 6-12 monthly) until skeletal maturity
• Physiotherapy to maintain range of motion and strength; analgesia for mild mechanical pain
• Activity modification and footwear/orthotic adjustment for foot-and-ankle lesions

Key counselling point: observation is reasonable, but vigilance is essential - a lesion left to enlarge can damage the joint surface and make eventual excision and reconstruction far more difficult. According to PubMed, the systematic review cautions that unchecked mass growth complicates later surgical intervention (DOI).

Indications for surgery: significant or progressive pain, mechanical block or locking, angular deformity, joint incongruity, instability, cosmetic/functional concern, or progressive growth threatening the articular surface.

Goals:

• Marginal excision of the osteocartilaginous mass, including the cartilage cap, to relieve symptoms and reduce recurrence
• Restore joint congruity and a smooth articular surface
• Correct deformity (osteotomy) and address limb-length discrepancy where present
• Preserve the physis and articular cartilage to avoid iatrogenic arrest

Timing: excision is feasible even in young children and may be done early when a lesion is enlarging or causing deformity; the systematic review notes that excision is feasible at a young age but requires precision to avoid recurrence or secondary arthritis (DOI).

Marginal (intralesional-to-marginal) excision is the workhorse procedure.

Principles:

• Use a direct approach centred on the lesion (for example, a medial approach for a medial talar/distal tibial lesion), protecting nearby tendons, ligaments and the neurovascular bundle
• Expose the mass at its base and excise it flush with the parent epiphysis, removing the cartilage cap as completely as is safely possible - residual cap is the main source of recurrence
• Protect the articular cartilage and physis: do not violate the growth plate; preserve as much joint surface as possible
• Smooth the remaining contour to restore joint congruity; intra-articular loose fragments should be removed
• Complete excision is not always achievable when the lesion is intimately related to the joint surface or physis; the systematic review and Arealis et al both note that even partial excision can be a successful, symptom-relieving treatment (DOI)

Correcting associated deformity:

• Corrective osteotomy for established angular deformity (for example, a supramalleolar or distal femoral osteotomy) once the symptomatic mass has been addressed
• Guided growth (hemiepiphysiodesis / tension-band plating) can be used for progressive angular deformity in a child with substantial growth remaining
• Limb-length discrepancy: managed along standard lines - shoe raise for small differences, contralateral epiphysiodesis or lengthening for larger ones near maturity

Salvage / advanced disease:

• A severely incongruent, arthritic joint in older patients may need realignment osteotomy, and rarely arthrodesis for a painful, destroyed joint
• Large or complex articular/tarsal lesions benefit from CT-based planning and, where available, intra-articular techniques to preserve cartilage

If the lesion is left untreated or grows unchecked, the natural-history complications are:

• Progressive angular deformity (valgus/varus) and rotational deformity
• Joint incongruity and mechanical block, with stiffness and locking
• Limb-length discrepancy from asymmetric epiphyseal growth
• Joint instability as the mass deforms or stretches the collateral ligaments
• Secondary (early) osteoarthritis of the affected joint in adolescence or adult life - the most important long-term consequence

According to PubMed, Degnan and Ho-Fung emphasise that DEH may result in pain, growth disturbance and early development of osteoarthritis, which is why timely treatment of symptomatic lesions matters (DOI).

Recurrence is the most frequent surgical complication:

• Driven by incomplete excision of the cartilage cap, especially in the still-growing child
• The foot-and-ankle systematic review reported recurrence in about 9% of cases (DOI)

Other complications:

• Iatrogenic growth-plate injury causing arrest and progressive deformity if the physis is violated
• Articular cartilage damage and accelerated joint degeneration
• Neurovascular or tendon injury during exposure (for example, around the medial ankle)
• Residual deformity or instability if alignment and ligaments are not addressed
• General surgical risks: infection, wound problems, stiffness

According to PubMed, the paediatric series by Oberc and colleagues observed late complications in two of four operated patients (50%), underscoring that surgery in this region is technically demanding and not without morbidity ([DOI not available]; PMID 24941028).