Heterotopic ossification
Heterotopic ossification (HO) is formation of mature bone in periarticular soft tissues after surgery or trauma.
Risk increases with factors such as:
- previous HO
- ankylosing spondylitis
- hypertrophic osteoarthritis
- major local tissue trauma
- some neurological injuries
Classification
Brooker classification grades radiographic HO around the hip from small islands to apparent ankylosis.
Prevention
For high-risk patients, prophylaxis may include:
- NSAID therapy when safe
- single-fraction radiotherapy in selected very high-risk situations
Local protocols guide timing and patient selection.
Treatment
Excise only when HO is mature and causes substantial pain or functional restriction. Plan recurrence prophylaxis when indicated.
HO is mature lamellar bone forming within soft tissues after surgery, trauma or neurological injury.
Risk factors include:
- previous HO
- hypertrophic OA
- ankylosing spondylitis
- male sex in some series
- extensive tissue trauma
- neurological injury
Cemented stem failure patterns
Radiographs should be assessed systematically rather than simply labelled “loose”.
Look for:
- progressive radiolucent lines
- cement mantle fracture
- stem subsidence
- varus migration
- calcar changes
- osteolysis
- stem fracture
Gruen zones provide a standard map for describing femoral interface abnormalities.
A fractured stem often reflects loss of proximal support with persistent distal fixation, creating a cantilever fatigue situation.
Principle
Implant failure is usually a mechanical story visible over serial radiographs. Compare films over time and identify the fixation point, migration pattern and bone response.
Clinical significance
Radiographic HO can be asymptomatic. Symptoms become relevant when there is:
- pain
- restricted movement
- functional limitation
- impingement
Brooker grading describes radiographic severity around the hip, but management is based on symptoms and function rather than grade alone.
Prevention
In selected high-risk patients:
- NSAID prophylaxis
- single-fraction radiotherapy
may reduce risk. Choice depends on contraindications, local protocols and overall patient factors.
Excision
Surgical excision is reserved for significant symptomatic mature HO. Planning includes:
- CT where anatomy is complex
- neurovascular relationships
- recurrence prophylaxis
- expected motion gain
Femoral stem failure
A stem should be evaluated by serial radiographs for:
- subsidence
- varus migration
- radiolucent lines
- osteolysis
- cement fracture
- pedestal formation
- cortical hypertrophy
- stem fracture
Gruen zones
Gruen zones standardise description of femoral interface changes. Their value is consistency over serial films rather than attaching a diagnosis to one isolated line.
Cemented stem failure
Failure can involve:
- cement-bone interface
- stem-cement interface
- cement mantle fracture
- migration
Interpretation depends on stem design philosophy.
Uncemented stem failure
Assess:
- subsidence
- lack of osseointegration
- progressive radiolucency
- migration
- proximal stress shielding
- distal fixation patterns
Stem fracture
Fatigue fracture suggests persistent cyclic loading, often because support has been lost proximally while another region remains fixed.
FRCS synthesis
For any suspected stem failure, tell the mechanical story from serial films: where is it fixed, where is it moving, what has migrated and where has bone been lost?