Apparent and True Shortening of the Limb in Orthopedic Examination

Definitions

True Shortening

• Fractures with overlap or comminution (e.g., fracture neck of femur)
• Dislocation of the hip
• Bone destruction (tuberculosis, Perthes' disease, septic arthritis)
• Congenital dislocation of the hip (CDH)
• Slipped capital femoral epiphysis (SCFE)
• Congenital coxa vara
• Acetabular dysplasia

Apparent (Functional) Shortening

• Adduction contracture of the hip (most common cause - the adducted limb appears shorter)
• Pelvic tilt secondary to scoliosis
• Fixed flexion deformity of the hip
• Abduction contracture (produces apparent lengthening instead)

Key rule: An adduction deformity causes apparent shortening; an abduction deformity causes apparent lengthening.

Method of Examination

Step 1 - Preliminary Positioning

"If there is adduction deformity of the affected limb, the normal limb must also be adducted to the similar extent before the measurements." - S Das, A Manual on Clinical Surgery

Step 2 - Measuring True Length (True Shortening)

• Whole limb: Measure from the ASIS to the tip of the medial malleolus
• Thigh only: Measure from the ASIS to the joint line of the knee (the joint line, not the adductor tubercle or upper border of patella, as both of those are either moveable or hard to find in obese patients)

Step 3 - Measuring Apparent Length (Apparent Shortening)

• Measure from a fixed midline point on the body, usually the umbilicus, to the medial malleolus (or between the medial and lateral malleoli)

From Rheumatology (Elsevier, 2022): "Measurements from the umbilicus will show an apparent shortening of the leg on the side with the higher pelvis. However, when measured from the anterior superior iliac spine, the legs will have the same length."

Step 4 - Shortening Above the Greater Trochanter

1. Bryant's Triangle

• Patient lies in the dorsal (supine) position
• Three lines are drawn:
  1. A vertical line drawn downward from the ASIS onto the bed surface
  2. A line from the tip of the ASIS to the tip of the greater trochanter (the hypotenuse)
  3. A horizontal line from the tip of the greater trochanter to meet the first vertical line
• The horizontal line is compared with the same line on the normal side
• Diminution in the horizontal line = upward elevation of the greater trochanter (seen in transcervical/subcapital fracture of neck of femur, separation of upper femoral epiphysis)
• Diminution or increase in the hypotenuse line = anterior or posterior displacement of the trochanter (e.g., posterior dislocation of hip)

2. Nelaton's Line (Roser-Nelaton Line)

• Patient lies on the sound (normal) side
• A line (or measuring tape) is placed from the most prominent part of the ischial tuberosity to the tip of the ASIS
• Normally, with the hip in moderate flexion (~45°), this line touches the tip of the greater trochanter
• If the greater trochanter is elevated above this line, it indicates upward displacement (fracture or dislocation)
• The advantage of Nelaton's line: it does not require comparison with the other side, as upward displacement is self-evident

3. Schoemaker's Line

• Draw (or project) a line from the tip of the greater trochanter through the ASIS and extend it anteriorly
• Normally this line meets or crosses the midline at or above the umbilicus
• If the greater trochanter is elevated, the line crosses the midline below the umbilicus

4. Morris' Bitrochanteric Test

• The distance from the outer border of the greater trochanter to the symphysis pubis is measured on both sides using calipers
• Reveals medial displacement (posterior/central dislocation) or lateral displacement (anterior dislocation) of the trochanter

5. Chiene's Test

• Normally, a tape joining the tips of the greater trochanters is parallel to another tape joining the two ASIS
• When a trochanter is raised, these two lines converge towards the affected side

Standing Block Test (for functional/apparent LLD)

• If the pelvis can be leveled this way = true leg length discrepancy
• If the pelvis cannot be leveled = functional/apparent discrepancy (due to hip contracture or scoliosis that prevents correction)

Summary Table

Clinically important: A limb with adduction contracture (as in tuberculous hip arthritis) will show apparent shortening with a normal ASIS-to-malleolus length - only the umbilicus-based measurement will be asymmetric.