PERTHES DISEASE
Also known as Legg-Calvé-Perthes Disease,
this is an idiopathic avascular necrosis of the proximal femoral epiphysis.
It has a peak presentation at 5-8 years and is seen more commonly in boys (4:1) and Caucasians.
It is bilateral in 10-20% of cases.
Owing to the remodeling potential of the immature skeleton,
prognosis is worse in those that present older with less ability to correct any deformities that have occurred.
It is considered a diagnosis of exclusion with other causes of avascular necrosis to be ruled out prior to diagnosis.
Imaging findings:
While radiographs remain first line in imaging,
MRI is being used with increasing frequency,
especially in establishing early diagnosis and for assessment of cartilage in management planning.
Plain radiograph:
Dependent on the stage of disease - although changes are often seen in the early stage,
radiographs may be normal
Early changes
- Asymmetric small epiphysis
- Widening of joint space due to effusion
- Increased density of epiphysis
Late changes
- Subchondral lucency (Crescent sign) Fig. 5
- Flattening and fragmentation of epiphysis Fig. 6 Fig. 7
- Coxa magna deformity at femoral neck Fig. 7
Reconstitution/Healed
- Re-ossification
- Normalisation of femoral head and bone density Fig. 8
- There may be a persistent abnormal head dependent on severity
MRI:
- High T2 marrow oedema
- Loss of fatty marrow signal on T1 images
- Reduced enhancement post contrast
Treatment is dependent on the age of presentation and severity of disease.
In early cases,
symptom control may be all that is needed and particularly in younger patients,
re-ossification following spontaneous revascularization may well produce a adequate femoral head with satisfactory joint coverage.
Various surgical techniques are available for later/severe disease.
Total hip replacement may be needed for those that develop severe secondary arthritis.
SLIPPED UPPER FEMORAL EPIPHYSIS (SUFE)
Slipped upper femoral epiphysis (SUFE) is the most common hip disorder in adolescents and essentially represents a Salter Harris type I injury.
Although considered idiopathic in some regards,
there are a combination of mechanical,
physiological and hormonal factors which play a role.
During the adolescent growth spurt,
there is widening of the physis with the orientation of the growth plate changing from horizontal to oblique.
Subsequently there is an increase in vertically orientated shear forces resulting in slippage.
20% are bilateral with approximately half of these cases picked up on initial presentation.
It is seen most commonly in boys,
particularly Afro-Caribbeans,
with an increasing prevalence associated with obesity.
Peak age is considered between 10-17 years in boys and 8-15 years in girl.
There is relation with several endocrine disorders such as hypothyroidism,
hypopituitarism and hypogonadism.
Imaging findings:
Plain radiograph:
AP and frog-leg lateral views can be performed,
although frog-leg views are considered more sensitive
- Widening of physis with demineralisation of metaphysis in early stages
- Posteromedial slip in acute phase with an apparently small epiphysis Fig. 9
- Trethowan Sign – a line drawn along the lateral femoral neck (line of Klein) fails to intersect the epiphysis Fig. 10
- Loss of Capener sign – Failure of the proximal metaphysis to overlap the posterior acetabulum Fig. 11
- Metaphyseal blanch sign – increased density of proximal metaphysis
Plain radiographs are generally sufficient with CT/MRI rarely used.
MRI may be of benefit in assessing the contralateral hip although findings are non-specific,
demonstrating marrow oedema.
Treatment is now generally favoured to be surgical,
with pinning of not only the affected side but also often prophylactically on the contralateral side.
Complications of the condition include avascular necrosis,
osteoarthritis,
chondrolysis and deformity.
AVULSION INJURIES
Avulsion injuries of the pelvis are relatively common entities seen predominantly following athletic activity.
Adolescents are particularly prone to such injuries,
resulting from a combination of their immature skeleton as well being able to produce excessive tensile forces for sustained periods.
In the growing skeleton,
the unfused apophysis represents the physiological weak point,
particularly following eccentric muscular contraction,
whereas in adults,
injuries generally instead occur at the myotendinous junction.
Peak incidence is in those aged 14-25,
with soccer,
gymnastics and tennis the most commonly implicated sports.
In the pelvis,
there are seven recognized sites of injury Fig. 12,
which are seen in varying prevalence.
The ischial tuberosity is the most commonly involved location,
representing the insertion of the hamstrings and adductor magnus Fig. 13 .
Other common sites are the anterior superior iliac spine (ASIS) where the attachments for sartorius and the tensor muscle of the fascia lata are seen Fig. 14 ,
and the anterior inferior iliac spine (AIIS),
which forms the attachment for the straight head of the rectus femoris muscle Fig. 15 .
Plain radiography is usually sufficient in diagnosis,
demonstrating a displaced fragment at the site of muscle insertion.
Further imaging,
particularly MRI,
is generally reserved where the apophysis is unossified or where soft tissue evaluation is required for management planning.
Treatment is dependent on the site of involvement however is typically conservative,
with early bed-rest,
analgesia and restricted activity.
Surgical management is considered in those where there is significant fracture displacement.
In contrast with avulsion fractures,
which results in acute injury following strong muscular contraction,
traction apophysitis represents chronic inflammation of the apophysis following repetitive microtrauma.
Diagnosis can often be made on clinical examination however imaging can have a role in assessment in atypical presentation or where symptoms are not improving
Imaging findings:
Plain radiograph:
- Typically normal
- Apophyseal irregularity and fragmentation Fig. 17
MRI:
- Widening/enlargement of the apophysis
- T2 hyperintense oedema within the apophysis,
adjacent bone/muscle,
tendon and soft tissue
- Post contrast enhancement of apophysis and adjacent involved structures
CHONDROBLASTOMA
This is a rare benign bone tumour (1-2% of all primary bone tumours),
which arises at the cartilaginous growth plate.
It is also known as a Codman tumour.
Although rare,
it is the most common epiphyseal benign bone tumour in skeletally immature patients.
The proximal femur is the third most affected commonly site,
with the most common being the proximal humerus and proximal tibia.
In the proximal femur,
the greater trochanter or capital epiphysis may be affected.
They occur in the second decade of life,
with a median age at presentation of 15 years and a male to female ratio of 2:1.
14% are associated with a secondary aneurysmal bone cyst.
Imaging findings:
Plain radiograph:
- Well defined lytic lesion with smooth or lobulated margins and a sclerotic rim Fig. 18
- Located eccentrically in the epiphysis or apophysis.
- Mineralisation is present in 40-60%
- Range from 1-10cm in size
- There may be an associated joint effusion.
MRI:
- Typical signal characteristic of cartilage or chondral lesions,
with hypointense T1-weighted signal and hyperintense T2-weighted/STIR signal Fig. 19
- If an aneurysmal bone cyst is present,
fluid-fluid levels may be seen.
Treatment is with curettage and packing.
ISCHIOPUBIC SYNCHONDROSIS ASYMMETRY
The ischiopubic synchondrosis is a temporary joint between the superomedial pubic ossification centre and the inferolateral ischial ossification centre.
This synchondrosis ossifies in childhood,
before puberty.
Enlargement of the ischiopubic synchondrosis is a normal phenomenon of growth and development. It is frequently observed bilaterally in younger children,
however in older children it can be unilateral and asymmetric.
This asymmetry is more common on the side of the non-dominant foot.
It can cause confusion and may be misinterpreted as being post-traumatic or as a tumour or focus of infection.
Although this is considered a normal variant and an incidental finding on imaging,
asymmetric enlargement can be syndromic in symptomatic patients with groin pain.
It is then known as van Neck-Odelberg disease or ischiopubic synchondrosis syndrome.
Imaging findings:
- Plain radiograph: lucent swelling of the ischiopubic synchondrosis Fig. 20
- MRI: can rule out other pathological causes e.g.
chondral tumours,
and confirm the presence of a synchondrosis.
There may be evidence of mechanical stress with bone marrow oedema on either side of the synchondrosis Fig. 21