Lower Extremity (LE) and Gait; Reporting LE

LOWER EXTREMITY (LE) AND GAIT; REPORTING LE

2024- Donna Magid, M.D., M.Ed, FAUR

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

LOWER EXTREMITY (LE)

MECHANICAL AXIS (A)

from center of femoral head→ center of notch roof → center distal tibial plafond).

NORMAL: 0 degrees.

ANATOMIC AXIS (B)

Normal: 6-8 degrees valgus

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)

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

Medial proximal tibial arrest/delay →’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

REPORTING LOWER EXTREMITY RADIOGRAPHS

Lower extremity radiographs provide either a stitched or Eos-type low-dose image of the bilateral lower extremities, inferior pelvis through the ankles. While the req will usually state “leg length” or “LLD” (leg length discrepancy), there are two sets of measurements to be made: MECHANICAL AXIS and LENGTH.

Start report with age and gender, if skeletally immature (these cases should have gone to Peds); normal infants <2 are bowed (varus mechanical axis); 2-3 yr olds in transition; and older children and adults should approximate a mechanical axis of zero. Right and left axes should also be symmetric. Comment if PELVIC OBLIQUITY (one side of pelvis cephalo-caudally angled relative to contralateral— “tilt” used to refer to only angulation/rotation in AP plane, ie thrusts). If there are obvious findings—plate and screw epiphysiodeses, osteochondromata, healing/healed fractures, rickets, etc—comment briefly.

MECHANICAL AXIS: open the ANGLE measurement tool; angles require 2 lines determined by 3 landmark points. First landmark drops in the estimated center of the (ossified) femoral head if it were a complete sphere. Second landmark goes in the mid-point of the distal femoral physis (child) or at estimated roof of notch (adult), Third landmark goes to mid plafond distal tibia. Subtract given angle from 180 for axis. If not zero, determine if axis is VALGUS (tibia long axis angles laterally relative to femur’s) or VARUS (tibial axis angles medially relative to femur).

LENGTH: Drag the angle measurements laterally, just off legs, to clear the playing field. Open the LENGTH tool.

FEMUR Landmarks are the most proximal ossified femoral head superior pole and the most distal intercondylar point mid distal articular femur. Round up anything greater or equal to .x5 to next tenth; report only one digit to right of decimal point.

TIBIA landmarks (you may have to move femur lines off femurs to clear field) are the most proximal ossified point between the tibial spines, and the most distal mid articular plafond.

Caveat: get in the habit of consistency; ie drop the little box landmark that determines the measurement line in the same way each time—try to bisect the box by centering it over chosen bony landmark. Actually takes some practice.

REPORT TEMPLATE:

EXAM: add “…one view” to the auto-populated “Lower Extremity”

INDICATION: ‘Gait abnormality’, or ‘leg length discrepancy’, if clinician did not provide .

If there are 2 Exams (eg LLD and Bilat Knees) one needs TWO indications.

FINDINGS: Mechanical axes- 2 degrees valgus right, zero degrees valgus left.

right femur measures approximately 20,4 cm, the left 20.9 cm.

Right tibia measures 15.8 cm, the right 16.0 cm,

IMPRESSION: Lower extremity mechanical axes and bone lengths as measured,

Report the facts; one need not do the math (total lengths) nor further opine on ‘normal/abnormal’.

If second number to right of decimal 5 or greater, round up 1^st number to right of decimal. (18.54 =s “18.5 cm”, 18.56 =s ’18.6 cm”)

If total knee or hip arthroplasty, “Arthroplasty modifies measurement landmarks”

Occasionally I add an opinion for children in that tricky 2-3 yr period where bowing resolves (“Likely within limits for a girl 21 months old” but don’t if unsure of your judgment/experience (again, Peds should get the under-16 yrs).. Remember (read the Lower Extremity hand out!) girls lose physiologic bowing slightly earlier, 20-24 months, boys 24-28 months.

2024 - Donna Magid, M.D., M.Ed. FAUR