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Lower Extremity and Gait

July 2012 - Donna Magid, M.D., M.Ed.

Loving the Lower Extremity... and a few friendly words about Stance and Gait

NORMAL GAIT inherently symmetric, energy-efficient and balanced; requires

  • Stability in stance (standing on leg- forces act at center of gravity)
  • Means of progression (swinging from one stance to next stance- accelerating)
  • Energy conservation

ABNORMAL GAIT therefore due to and/or produces:

  • Decreased stability
  • Change in joint forces and wear
  • Energy insufficiency (too much work)

Altered gait = leg length discrepancy, neurologic disease, injury/surgery/pain (antalgic)

In stance weight divided between 2 legs. Static stance on one leg shifts all weight to that leg. BUT Ambulation forward dynamically magnifies forces (mass x acceleration) → 3-6x body weight and at the point the magnified weight flows from the entire upper body to the tiny surface area of the superior pole femoral head can → up to 8-10x body weight (e.g. running down steps).

WEIGHT-BEARING JOINTS

  • Loading increases articular surface contact areas; load-per-area can be huge (eg 340% increase superior pole femoral head early in gait →g +800% running down stairs)
  • Cartilage resilient, accommodates (reshapes) and hydraulically cushions; both responses decrease with age. Loss of cartilage redistributes forces, changes angles of loading, accelerates degeneration.


LOWER EXTREMITY (LE)

BIRTH: very ‘bowed’ (varus); in utero molding and ‘absence’ of gravity. Age-related emodelling reflects weight-bearing, gravity, Wolff’s Law (See ‘Fractures 101”). Medial physis distal femur grows faster than lateral, also contributing to adult valgus LE.

“PHYSIOLOGIC BOWING” (GENU VARUM) NORMAL til late in 2d year; should resolve by 18-20 mo. female, 20-24 mo. male. Parents tend to self-refer 14-36 months with concerns.

>10 degrees varus 14-36 mo = ”Physiologic bowing” if can r/o possible pathologic etiology (trauma, hypophosphatemic or other rickets, septic arthritis and growth arrest, achondroplasia, infantile tibia varum/Blount disease, OI, NF,…). Should be symmetric, distributed through both femur and tibia (both bow medially), should resolve untreated

3-5 yrs: may show slight ‘overshoot’, with truly straight leg (actually =s ‘knock-knee’d”)

6-7 yrs: true adult pattern : (see Drawing)

  • MECHANICAL AXIS (A) (long image only, usually standing; from center of femoral head→ center of notch roof → center distal tibial plafond). NORMAL: 0 degrees.
  • ANATOMIC AXIS (B) (shaft-shaft at knee, standing). Normal: 6-8 degrees valgus

INFANTILE TIBIA VARA (BLOUNT DISEASE): proximal tibia grows asymmetrically bowing LE.

  • Medial proximal tibial arrest/delay → lateral proximal tibia grows, medial doesn’t, pushing lower leg into medial or varus angulation. Progressive failure and deformity medially (see diagram)
  • Etiology uncertain: early walkers, infant obesity, female, African-American

 

July 2012 - Donna Magid, M.D., M.Ed.