Lines and Angles in Orthopedics

Slipped Capital Femoral Epiphysis (SCFE)

Southwick’s angle: Epiphyseal-shaft angle on lateral radiograph

• <30 degrees: mild
• 30-60 degrees: moderate
• >60 degrees: severe

Klein’s line: Line drawn along superior border of femoral neck (AP x-ray)

• In SCFE: will intersect less of the femoral head or not at all

Developmental Dysplasia of Hip (DDH)

Hilgenreiner’s line: Horizontal line through triradiate cartilage of acetabulum – femoral head ossification must be below this line

Perkin’s line: Vertical line (perpendicular to Hilgenreiner’s line) from the lateral margin of ossified acetabular roof – femoral head ossification must be medial to this line

Shenton’s line: Smooth curved line connecting medial border of femoral metaphysis with superior border of obturator foramen – arc line should be continuous

Acetabular index: Angle that acetabular line (drawn from acetabular surface) makes with Hilgenreiner’s line – should be <25 degrees in >6 months old

Center edge angle of Wiberg: Angle between vertical line from center of femoral head to and line between edge of acetabulum to center of femoral head – <20 degrees is considered abnormal (reliable only in >5 year old)

In DDH:
1. Femoral head is above Hilgenreiner’s line and lateral to Perkin’s line
2. Shenton’s line is broken
3. Acetabular index increased
4. Center edge angle of Wiberg decreased

Coxa Vara

Hilgenreiner-epiphyseal angel: Angle between Hilgenreiner’s line and a line drawn parallel to capital femoral epiphysis (Increased in Coxa Vara)

Neck-shaft angle: Normal is 127 degrees (<120 degrees is Coxa Vara)

Congenital Talipes Equinovarus (CTEV)

Kite’s angle (AP Talo-calcaneal angle): Angle between lines drawn down the axis of Talus and Calcaenus

• Normal: 20-40 degrees
• CTEV: <20 degrees

Talus-first metatarsal angle: Normal is 0-20 degrees (Negative in CTEV)

Calcaneal fracture

Bohler’s angle: Angle between line drawn from the highest point of anterior process of calcaneus to the highest point of posterior facet AND a line drawn tangentially from posterior facet highest point to tuberosity superior edge (normal is 20-40 degrees)

• Decreased in calcaneal fracture

Gissane’s angle: Angle formed by the downward and upward slopes of the calcaneal superior surface (normal is 120-145 degrees)

• Increased in calcaneal fracture

Ward’s Neutral triangle: The vast majority of calcaneus fracture lines propagate through a hypodense region of bone called Ward’s neutral triangle.

Supracondylar fracture of humerus

Bauman’s angle (Humero-capitellar angle): Angle between line parallel to longitudinal axis of humerus and line along lateral epiphysis (Normal 70-75 degrees; best to compare with contralateral side)

Anterior humeral line: Line drawn along anterior surface of humerus cortex must pass through the middle third of capitellum

Scoliosis

Cobb’s angle: A scoliosis is defined as a lateral spinal curvature with a Cobb angle of 10° or more

Other angles, lines and indices

Singh’s index: Grading of osteoporosis by quantifying trabeculae in neck of femur

Ward’s triangle: Femoral neck

Babcock’s triangle: Femoral neck

Fairbank’s triangle: Congenital coxa vara, Perthes disease, Nonunion neck of femur

Pauwel’s angle: Neck of femur fracture

Meary’s angle and calcaneal pitch: Pes planus and cavus

Distal radial indices: Radial length, volar tilt, ulnar variance

Gilula lines: Congruent arcs in normal wrist X-rays

Matta’s roof arc angle: Acetabular fractures

Alpha angle: Femoro-acetabular impingement

Metaphyseal-Diaphyseal angle of Drennan: Blount’s disease