Scoliosis and Long-Leg Alignment Films

Scoliosis films and long leg alignment films are standing full length radiographs used to measure deformity of the spine and the lower limbs.

Scoliosis imaging is a standing posteroanterior (PA) full spine view. It includes the cervicothoracic junction, the whole thoracolumbar spine, the pelvis and the iliac crests (to assess skeletal maturity by the Risser sign). A standing lateral view of the whole spine shows the sagittal profile.

The Cobb angle is the measure of curvature. Lines are drawn along the upper endplate of the upper end vertebra and the lower endplate of the lower end vertebra of the curve, and the angle between perpendiculars to these lines is recorded. Scoliosis is defined as a lateral curvature of 10 degrees or more with vertebral rotation.

Low dose digital slot scanning systems give a whole body image in a single pass at a dose of about 0.1 to 0.2 mSv for a pair of views, a fraction of conventional films (0.2 to 0.5 mSv), and allow three dimensional modelling.

Idiopathic scoliosis (80% of cases) is commonest in adolescent girls, affecting 2 to 3% of adolescents at 10 degrees or more. The female to male ratio rises from 1 to 1 at small curves to about 8 to 1 for curves over 30 degrees.

Other causes are congenital (vertebral anomalies, with associated renal and cardiac defects), neuromuscular (cerebral palsy, muscular dystrophy, spinal muscular atrophy), syndromic (neurofibromatosis, Marfan syndrome, Ehlers-Danlos syndrome), and secondary to tumour, infection or leg length discrepancy.

Risk of progression depends on skeletal immaturity, curve size and location, and sex. Curves over 25 to 30 degrees in a growing child are treated by bracing. Curves over 40 to 50 degrees are treated by surgery because of the risk of progression in adulthood and, for curves over 70 to 80 degrees, cardiopulmonary compromise.

Long leg films are standing weight bearing anteroposterior views of both legs from the hips to the ankles on one exposure (or a stitched image), with the patellae facing forward and a calibration marker. They are used to measure leg length discrepancy and angular deformity. They also plan corrective osteotomy, epiphysiodesis and lengthening, and knee replacement.

Indications. Suspected scoliosis (shoulder or waist asymmetry, rib hump on forward bending) to confirm and measure the curve. Monitoring of known scoliosis (usually every 4 to 12 months during growth). Pre-operative and post-operative assessment of spinal fusion. Kyphosis and sagittal balance assessment. Leg length discrepancy.

Genu varum, genu valgum, Blount disease, rickets, skeletal dysplasia. Pre-operative planning for osteotomy and knee arthroplasty. Post-traumatic malalignment. Not for routine screening of asymptomatic children, because of radiation, unless a screening programme has defined thresholds.

Contraindications and precautions. Pregnancy: avoid unless essential. In children and adolescents, use a PA projection, low dose digital or slot scan techniques, and breast and thyroid shielding where it does not obscure the spine. Limit repeat imaging by clinical need. Remove clothing with metal, and position the patient with arms forward and relaxed.

Preparation and technique. Stand with feet together and weight evenly shared (a block under the short leg may be used for pelvic levelling, and the use of a block is recorded). For sagittal films, the fists rest on the clavicles. Both legs and knees should be fully extended, with the patellae pointing forward, for long leg views. Include a calibration ball or ruler for measurement.

Normal appearances. In the coronal plane, the spine is straight with a lateral deviation under 10 degrees; shoulders, ribs and pelvis are level.

In the sagittal plane, the thoracic kyphosis is 20 to 45 degrees (T5 to T12) and the lumbar lordosis 40 to 60 degrees (L1 to S1). The C7 plumb line falls close to the posterior superior corner of S1 (sagittal vertical axis within 4 cm). Risser stage 0 (no ossification of the iliac apophysis) to 5 (fusion) shows maturity, with growth slowing at Risser 3 to 4.

Legs: the mechanical axis (a line from the centre of the femoral head to the centre of the ankle) passes through the centre of the knee (within 8 mm medially or laterally). The hip-knee-ankle angle is 180 degrees (plus or minus 3), the lateral distal femoral angle is 87 to 90 degrees, the medial proximal tibial angle is 85 to 90 degrees, and the joint line convergence angle is under 2 degrees.

Leg lengths are within 1 cm of each other in most people.

Interpretation.

• Scoliosis: report the Cobb angle for each curve (main thoracic, thoracolumbar, lumbar), the apex, the direction (convexity to the right or left), the end vertebrae, rotation, vertebral anomalies (hemivertebra, block vertebra, bars), the Risser stage, and coronal and sagittal balance.
• Curves of 10 to 25 degrees are observed, 25 to 40 degrees in a growing child are braced, and over 40 to 50 degrees are considered for fusion.
• Progression is defined as an increase of 5 degrees or more on serial films, taking into account measurement variation of 3 to 5 degrees between observers and with positioning.
• Features suggesting a secondary cause that need MRI of the whole spine: a left thoracic curve, a rapid progression, early onset under 10 years, pain (especially at night), abnormal neurology, abnormal abdominal reflexes, foot deformity (pes cavus), a short curve with marked rotation, or congenital anomalies.
• Causes found are syrinx, Chiari malformation, tethered cord, tumour (osteoid osteoma with a painful concave side curve) and diastematomyelia.
• Sagittal profile: thoracic hyperkyphosis (over 45 degrees: Scheuermann disease, postural, osteoporotic), hypokyphosis (idiopathic scoliosis tends to flatten the thoracic spine), and abnormal lumbar lordosis.
• Leg length discrepancy: measured from the top of the femoral head to the plafond of the tibia on each side. Under 2 cm is usually compensated by a shoe raise. A discrepancy of 2 to 5 cm may be treated by epiphysiodesis of the longer limb; over 5 cm needs lengthening. Growth remaining is estimated from skeletal age and charts.
• Angular deformity: varus (mechanical axis falling medial to the knee centre, with a medial mechanical axis deviation), or valgus (axis falling lateral). The level of deformity is assigned to the femur or tibia by the lateral distal femoral angle and medial proximal tibial angle.
• Physiological bowing resolves by age 2 to 3 years. Persistent or progressive varus suggests Blount disease, rickets (metaphyseal changes on films), skeletal dysplasia or trauma.
• Pre-operative planning: osteotomy correction is based on the measured angles, and templating for knee arthroplasty uses the hip-knee-ankle angle.

Critical values and findings needing immediate action.

• Scoliosis with neurological signs, pain, or atypical features: urgent MRI of the whole spine and neurosurgical or orthopaedic spine referral.
• Rapidly progressive curve (over 5 degrees in 4 to 6 months) or curve over 40 to 50 degrees in a growing child: urgent spinal surgical assessment.
• Large curve (over 70 degrees) with respiratory symptoms: respiratory function assessment and surgical review.
• Infantile scoliosis (under 3 years): MRI, because of the high rate of intraspinal anomalies.
• Congenital scoliosis: renal ultrasound and echocardiography for associated anomalies.
• Tibia vara or genu valgum with rickets features: biochemistry and vitamin D treatment.
• Pathological deformity with suspected tumour or infection: further imaging and referral.

Limitations and artefacts.

• Cobb angle measurement varies by 3 to 5 degrees (more with different end vertebrae or inconsistent positioning). The same method, vertebral levels and posture are therefore used each time, and a change under 5 degrees is not progression.
• Positioning matters: leaning, rotation, flexed knees and a pelvic tilt from leg length discrepancy change the curve. A block or measured raise is used and recorded for levelling.
• Standing films show the curve under gravity, while bending or supine films show flexibility, which is relevant for surgical planning.
• Risser staging is crude. Skeletal maturity is better estimated by hand and wrist bone age or the triradiate cartilage closure and menarche status.
• Radiation dose accumulates with repeated films during growth. Slot scan technology, PA projection and shielding reduce breast dose. Serial imaging should be limited to the intervals that management needs.
• Long leg films with a flexed knee, rotated limb, or perspective error give false angles, and magnification must be corrected by a marker.
• Foreshortened films stitched from separate exposures can misalign.
• Lateral films are limited by overlapping shoulders in the upper thoracic spine.
• Surface measurements (scoliometer, rib hump) are used for screening only, and clinical examination (forward bend test) leads to referral for imaging.

Special groups.

• Adolescents: peak progression during the growth spurt, before menarche in girls; most mild curves do not progress.
• Infants and young children: infantile scoliosis (often resolving) needs MRI; juvenile scoliosis (3 to 10 years) has a high rate of progression and neural axis anomalies.
• Neuromuscular scoliosis: early onset, long C-shaped curves with pelvic obliquity, with progression continuing after skeletal maturity; imaging sitting or supine in non-ambulant patients.
• Adults: degenerative (de novo) scoliosis, with sagittal imbalance, spinal stenosis and back pain; films are used for fusion planning.
• Pregnancy: avoid; use ultrasound or MRI for non-radiation assessments.
• Regions: late presentation with severe curves is common in resource limited settings, and spinal tuberculosis causes angular kyphosis.
• Screening programmes in schools are used in some areas. Rickets and Blount disease cause leg deformity in children.

Follow up tests. MRI of the whole spine for atypical features, supine or bending films for curve flexibility, hand and wrist bone age, renal ultrasound and echocardiography for congenital curves, pulmonary function tests for large curves, vitamin D, calcium, phosphate and alkaline phosphatase for rickets,

genetic testing for syndromic causes (neurofibromatosis, Marfan), scanogram or CT for leg length when films are inadequate, and orthopaedic spine review.