Plain x-ray
· usually first recognised when there is structural failure and collapse of joint surface
· has been recognised as early as 6 months
· in most patients does not appear for more than 1 year
· may be delayed up to 2.5 years
· if patient immobilised, may see relative increase in density of dead bone
· less common with internal fixation and early mobilisation
Bone scan
· earliest indication given by bone scan
· ‘cold’ femoral head
· prognostic value limited
· if fracture displaced, inevitable that superior retinacular vessels damaged
· potential for recovery depends on
· inferior retinacular vessels
· artery from ligamentum teres
· if fracture displaced, ischaemia can still occur
· from traumatic haemarthrosis
· causes raised intra-articular pressure and venous obstruction
Necrosis
· 1/3 of heads completely viable
· 1/3 of heads have some viable bone
· almost always as wedge based on fovea
· may be only a few mm in depth
· may be all of head inferior to upper fovea
· necrosis most common in anterosuperolateral subchondral region
· 1/3 of heads have little or no viable bone
Revascularisation
· rapid if large viable wedge in fovea
· slow if completely necrotic
· relies on growth of vessels across fracture
· growth across fracture may be impeded by
· movement at fracture
· continuing impaction of head
· organisation and fibrosis of soft tisse and clot across fracture
· last area to regain supply is superolateral subchondral region
· 75% of fractures unite
· union dependent on
· mechanical factors (stability)
· vascular factors (viability)
· union more likely with viable or at least partly viable head
· occurs in 20% of fractures
· more common
· in displaced fractures
· in fractures in extreme valgus
· where all or most of femoral head necrotic
· unclear whether influenced by
· type of fixation device
· delay to reduction
· once collapse occurs
· osteophytes develop at living margin of femoral head
· joint space diminishes when articular sequestrum disintegrates
· disability varies
· 20% symptom-free
· 50% mild-moderate disability
· 30% severe disability
· incidence of femoral head necrosis is 15%
· increased incidence with
· associated acetabular lip fracture
· following open reduction
· when reduction delayed > 24 hrs
· ischaemia from damage to retinacular vessels
· rupture of capsule at base of neck
· constriction of capsule if femoral head buttonholes through it
· incidence of necrosis increases with displacement
· Hawkins 1 - rare
· Hawkins 3 - 35%
· union usually occurs
· subtalar arthritis common
· occurs in 10-15% of fractures
· more common with
· displaced fractures
· fractures with carpal dislocations
· usually affects proximal pole
· if revascularisation incomplete
· proximal pole collapses
· degenerative arthritis occurs
Conditions
· compressed air used in construction of tunnels under rivers or harbours to preven water seeping through ground
· pressures required usually 4 atm
· workmen compressed and decompressed in manlocks
· time for decompression depends on working pressure and time
Incidence
· incidence is 20%
· 50% have more than one lesion
· 2/3 are clinically silent shaft marrow infarcts
· 1/3 are juxta-articular lesions
· 1/3 of these produce symptoms from structural failure and collapse
· most common sites are
· distal femoral shaft (40%)
· proximal tibial shaft (20%)
· humeral head (25%)
· femoral head (10%)
Conditions
· professional divers at greater risk
· work from dive bell or connected to surface by lines
· exposed to prolonged high pressures
· recreational divers
· have limited exposure time because of SCUBA gear
· are exposed to limited depths
Incidence
· varies according to stringency of decompression
· 50% in Japanese shellfish divers
· 5% in British Navy
· 80% are marrow infarcts
· 20% are juxta-articular
· only 15% progress to structural failure
· most common sites are
· distal femoral shaft (60%)
· proximal tibial shaft (20%)
· humeral head (20%)
· femoral head (1%)
· unlikely to occur
· compressed air pressure < 1.2 atm
· diving depth < 30 m
· incidence higher in those who have suffered decompression sickness
· increasing numbers of exposures increase the risk
· during compression, increased pressure causes nitrogen to become dissolved in tissues
· during decompression, dissolved nitrogen cleared by circulation
· removed in expired air by pressure gradient in alveoli
· showers of nitrogen bubbles can occur in circulation and tissues
· may be silent wrt. decompression sickness but may lead to bone necrosis
· bone more prone to necrosis
· fatty marrow remains supersaturated following decompression
· intravascular and extravascular gas bubbles can occur
· have intravascular occlusive effect and extravascular compressive effect
· tissue disruption may cause fat emboli
· result is ischaemia
· most common in distal femur
Clinical
· asymptomatic
Radiological
· small dense areas with irregular outlines in medulla
· may progress to linear streaks
· most common in humeral head
Clinical
· usually sudden onset of shoulder pain
· ROM usually not severely limited
Radiological
· small dense areas with irregular outlines adjacent to joint
· may coalesce to give snow-cap appearance
· dense linear opacity may traverse bone
· dysbaric form characterised by
· multiple small lesions due to small vessel occlusion
· dense appearance due to calcification
· collapse not inevitable, even with large necrotic areas
· if occurs, changes then as in general form
· osteophyte formation
· degenerative osteoarthritis
· allowed to continue
· no evidence that have increased risk of juxta-articular lesions
· advised to stop work
arthroplasty usually not indicated because patients are young manual workers
· develops in children and adolescents
· most common in Ashkenazi (European) Jews
· autosomal recessive
· due to deficiency of lysosomal enzyme glucocerebroside hydrolase
· results in accumulation of insoluble glucosylceramide in cells of monocyte-macrophage system
· type 1 (90%) associated with orthopaedic problems
· most likely due to packing of marrow spaces with bloated macrophages
· leads to
· compression of intraosseous sinusoids
· scarring and further ischaemia
· results from accumulation of large macrophages rich in glucosylceramide in
· liver
· spleen
· bone marrow
· produces (with increasing severity)
· focal radiolucent areas in long bones
· cortical thinning and flask-shaped metaphyses (Erlenmeyer flask)
· pathological fracture
· most medullary infarcts are asymptomatic
· may develop acute ‘bone crisis’
· like sickle cell disease
· difficult to differentiate from osteomyelitis
· pain settles after few days
· then develop large medullary infarction on x-ray
· most commonly involves femoral heads
· in children, similar to Perthes’ disease
· in adults, similar to idiopathic necrosis
· new development is enzyme replacement
· seen in Africans incl. Negroes
· Hb is tetramer
· two pairs of polypeptide chains (alpha, beta, gamma or delta)
· adult Hb is
· 97% HbA (alpha2, beta2)
· 3% HbA2 (alpha2, delta2) (increased in thalassaemia)
· foetal Hb is HbF (alpha2, gamma2)
· abnormality is peptide substitution in beta chain
· abnormal haemoglobin designated HbS cf. HbA
Sickle cell disease
· two abnormal genes related to haemoglobin formation
· homozygous sickle cell disease (Hb SS)
· combination of HbS with another haemoglobinopathy (Hb SC)
· combination of HbS with thalassaemia (Hb SThal)
· sickling occurs in sickle cell disease with relative hypoxia
Sickle cell trait
· sickle cell gene with normal adult haemoglobin gene
· heteroxygous Hb SA
· sickling only occurs in sickle cell trait with extreme hypoxia
· under anaesthesia, in extreme cold, at high altitudes
· patients have slight protection against falciparum malaria
· HbS changes shape when deoxygenated
· red cell assumes sickle shape
· may become trapped in capillaries
· leads to vascular occlusion, infarction and thrombosis
· two main problems
1. vaso-occlusion
· suffer recurrent crises of abdominal and bone pain
2. anaemia
· sickled cells have shorter lifespan
· due to bone infarcts
· acute episodes of pain and tenderness
· may be fever and leukocytosis
· may affect several bones
· if end of long bone affected, develop joint pain and effusion
· usually involves shaft near metaphysis of
· femur
· tibia
· humerus
· endosteal vessels occluded
· periosteal vessels remain viable
Young children
· usually associated with bone crisis
· x-ray changes usually resolve
Older children and adults
· often clinically silent
· x-ray changes do not resolve
· may be sclerotic areas from
· calcification
· new bone formation
· extensive subperiosteal reaction may give appearance of bone in bone
· most common site is osteonecrosis of femoral head
Children
· occurs in 10% (50% asymptomatic)
· similar picture to Perthes’ disease
· may involve part or all of epiphysis
Adults
· occurs in 40%
· similar pattern to idiopathic necrosis
· seen in children age 6-24 mths
· appears as HbF disappears and HbS appears
· dorsum of hands and feet become swollen and painful
· symptoms subside after 1-2 wks
· x-ray changes at 2 wks
· reflect absence of endosteal blood supply and presence of periosteal blood supply
· subperiosteal new bone formation
· patchy erosion of cortex by periosteal granulation tissue
· bone may remodel and return to normal
· growth may cease temporarily
· bone crises diffficult to distinguish from osteomyelitis
· bone marrow infarct may become secondarily infected
· increased risk of infection because of impairment of splenic function
· Salmonella often involved from ischaemic bowel
· seen with high-dose therapy
· due to
· direct cellular damage
· vascular narrowing
· most common in women
· pelvis and upper femur for gynaecological tumour
· shoulder for breast cancer
· bone formation rather than resorption inhibited
· small cortical defects filled with fibrous tissue
· due to failure of filling in of resorption areas
· marrow spaces filled with fibrous tissue
· often patchy calcification
· typical osteonecrosis may occur
· pathological fracture may occur
· ‘stress fracture’ with slow slip into varus
· due to osteoporosis rather than osteonecrosis
· result is irregular patches of increased and decreased radiodensity
· should not be assumed to be metastases from original cancer
· usually healthy woman age 60+ yrs
· sudden onset of severe knee pain
· almost always medial femoral condyle
· exquisite local tenderness
· may be effusion
· other side rarely involved
· initially localised depression of condylar surface
· then articular sequestrum becomes partially separated as hinged flap
· may separate completely
· result is crater with base of fibrocartilage
X-ray
· initially normal
· later develop
· subchondral lucent line (crescent sign)
· flattening of condyle
· patchy sclerosis
· may be rapid collapse with varus deformity
Bone scan
· focal increase in uptake
MRI
· discrete well-defined low-signal areas in subchondral region
· secondary to
· steroid therapy
· SLE
· sickle cell disease
· much less common
· gradual onset of pain
· lateral condyle in 60%
· bilateral in 50%
·