Leg-Length Discrepancy

Question 1

What are three general causes of leg length discrepancy?

Answer 1

1) Congenital disorders
   hemihypertrophy
   PFFD
   DDH
   dysplasias
2) Paralytic disorders
   cerebral palsy
   polio
3) Physis disruption
   tumor
   infection
   trauma

Question 2

Leg length discrepancy is a/w osteoarthritis of which side?

Answer 2

The long leg side; d/t decreased femoral head coverage, leads to OA in 84% of cases

Question 3

What physical exam testing is done for leg length discrepancy?

Answer 3

1) block testing is excellent screening
2) tape measurement from ASIS to medial mal
3) check for ankle/knee/hip contractures

Question 4

What is the most accurate diagnostic test with contractures of the hip, knee, or ankle?

Answer 4

CT scanography

Question 5

What age does growth arrest?

Answer 5

Boys 16yo

Girls 14yo

Question 6

How much growth occurs in the leg each year?

Answer 6

23mm/yr; 15mm comes from the knee

Question 7

How much growth occurs at the proximal and distal ends of the femur and tibia?

Answer 7

proximal femur - 3 mm / yr (1/8 in)
distal femur - 9 mm / yr (3/8 in)
proximal tibia - 6 mm / yr (1/4 in)
distal tibia - 5 mm / yr (3/16 in)

Question 8

What are the treatments for various projected leg length discrepancies?

Answer 8

1) 5cm; limb lengthening of short side

2) Physeal bar resection if 2yrs worth of growth remaining

Question 9

How does lengthening or shortening along the anatomical axis of the femur affect the mechanical axis?

Answer 9

Lengthing- causes lateral mechanical axis deviation

Shortening- causes medial mechanical axis deviation

Question 10

A 14-year-old boy sustains a significant distal femoral physeal fracture. Assuming that he has a complete growth arrest, what is the predicted leg length discrepency?

Answer 10

~2cm
The distal femoral physis grows at 0.9mm/yr
Proximal tibia 0.6mm/yr