Ultrasound of the spine for dysraphism

To look for occult spinal dysraphism

Clinically features suggestive for occult spinal dysraphism:
- Sacral dimple
- Tuft of hair
- Vascular patch / haemangioma
- Overlying skin appendage / skin tags
- Other anomalies which maybe associated with tethered cord eg imperforate anus, lower limb neurology

When to do / When not to do:
- Avoid performing if patient <2/52 old (often not enough CSF). Can do if high clinical probability.
- 2/52 to 4-6/12
- Not ideal if >6/12 old as spinous processes starts to ossify, obscuring the view

Preparation:
Patient relaxed eg just finished feeding, sleeping
Position: Prone or lying on side
High resolution linear probe

What to look for / document:
Sagittal view: (through the cartilaginous spinous processes)

1. Level of conus: L2/L3 disk or above, may be lower if pre-term
- If 'low lying' in pre-term, followup scan at 40wk after corrected age.
- Low lying cord may imply cord tethering
- Count the vertebral levels (reference point):
-- from below: sacrum or 1st coccygeal segment
-- from above: last rib
- may be supplemented with lateral spine radiograph to aid in counting in difficult cases, marker can be placed at the level of conus termination

2. Morphology of conus: Normally tapers down.

3. Normal pulsating motion of the spinal cord
- Absence in tethering

4. Dependent position of spinal cord (difficult to ascertain if not enough CSF as in the case of performing in patient below 2/52 old)
- Normal: Lie on anterior 1/3 or halfway in the canal.

5. Filum terminale thickness
- Normal </=2mm

Transverse view:

6. Spinal vertebral dysraphism (posterior elements)

Developmental Dysplastic Hip

DDH:
- Acetabular dysplasia AND/OR ligamentous laxity, resulting in recurrent hip subluxation / dislocation
- Left hip affected more than Right hip

Risk factors for DDH:
1. Breech presentation
2. Female (?estrogen contributing to ligamentous laxity?)
3. Firstborn
4. Family Hx
5. Oligohydramnios , Multiple gestation - abnormal posture due to crowding in-utero

Clinical features:
1. Asymmetric thigh skin folds
2. Shortened leg
3. Decreased hip ROM when Flexed and ABducted
4. Positive Ortolani and Barlow signs

Ultrasound used to assess the hips - the cartilaginous components can be seen. ie not ossified yet

Contraindications to US Hips:
1. Generally avoid if patient <3-4/52 old, as the ligaments are normally lax. Usually done at 6/52 and after.
2. Not suitable after 6mo. Femoral head ossifies, starts around 2-3mo.
Radiographs are a better modality of choice when the bone ossifies (>12mo) - AP radiographs, not frog leg view.

Ultrasound:
Done when patient is relaxed. eg. whilst feeding
Use high-resolution linear probe.

1. Coronal view
Hip slightly flexed. (~15-20degrees)
These structures should be seen, in addition to the femoral head, greater trochanter, acetabular roof.
a. Ossified ilium is horizontally orientated
b. Triradiate cartilage
c. Labrum

Look for:
1. Morphology of the hip joint
2. Coverage of femoral head using the straight ilium line (Position)
3. Alpha angle

2. Transverse view
Hip flexed. (90 degrees)
Look for: Hip joint stability
Visualisation of the hip joint whilst performing
- Barlow maneuvre
- If dislocatin/subluxation present, perform Ortolani maneuvre

Graf system (US hip for DDH introduced by Graf - Orthopaedic Surgeon)
- To grade severity of DDH and appropriate management

Graf system		Acetabular rim	Labrum	Ossified ilium line	Alpha angle
Type I	-	Normal angular	Normal	Crosses >50% of femoral head	>60	Normal
Type IIa	Age: <3mo	Rounded	Normal	Crosses <50% of femoral head, but not displaced	50-59	Physiologic immaturity. Repeat scan in 6-8/52
Type IIb	Age: >3mo	Same finding as IIa				Refer orthopaedic
Type IIc		Same finding as IIa	Everted / horizontal position	Same finding as IIa	43-49
Type IIIa	Normal acetabular roof cartilage	Flattened	-	Displaced (<50%)	<43	Refer orthopaedic
Type IIIb	Abnormalechogenic acetabular roof cartilage	Same finding as IIIa
Type IV	-	Flattened		Complete displacement	<43	Urgent orthopaedic referral

Radiographs:
1. Asymmetric hip joints
2. Asymmetric femoral epiphysis ossification: As a complication of DDH where there is delayed ossification
3. Femoral head crossing the Perkin's line laterally
4. Acetabular angle >30degree
5. Disruption of Shenton's line

Hilgenreiner's line:
Transverse line touching the triradiate cartilage superiorly and bilaterally on AP pelvis view

Perkin's line:
Line perpendicular to Hilgenreiner's line, touching lateral margin of the ossified acetabular roof on AP pelvis view.

Acetabular angle:
Angle between Hilgenreiner's line and the acetabular roof.
Normal: <30degree

Shenton's line:
Smooth curve lining the inferior margin of the superior pubic ramus and the medial margin of the proximal femur.

Putti's triad:
1. Femoral head displace superolaterally
2. Small femoral epiphysis
3. Acetabular angle > 35degrees