Leg Length Discrepancy
Defined
as difference in rate of growth between two limbs:
-
usually
due to abnormal physeal growth
-
fracture
malunions
-
bone
loss from osteomyelitis or tumor resections
Evaluation
includes determination of whether shortening is true or apparent.
Apparent
limb length discrepancy (LLD) may be due to:
-
suprapelvic
obliquity
o scoliosis
-
intrapelvic
obliquity
o pelvic fracture
-
infrapelvic
obliquity
o hip contracture
o knee contracture
o ankle contracture
 |
True Shortening Apparent Shortening
Assessment
of true shortening involves measuring the absolute length of the limbs
involving one of a number of methods:
-
tape
measure
-
leveling the pelvis with blocks
 |
|
-
scanogram
- CT scans
-
Long
leg standing films
Why
does leg length inequality matter?
-
back
pain
-
scoliosis
-
hip
and/or knee osteoarthritis
A
study by Gross (1978) showed & recommended:
-
less
than 2.0 cm showed no difficulties
-
more
than 3.5 cm, 80% had complaints
-
LLD
of 3 cm was compatible with high level sports
-
Observation
for less than 2 cm at maturity, especially if the patient has weakness or
spasticity on the short side
Many
options exist for limb lengthening, although are somewhat controversial:
-
skeletally
immature
o stapling
o epiphysiodesis
-
skeletally
mature for discrepancy greater than 3 cm
o lengthening using frame or
IMN
o acute shortening, can fairly
easily accommodate 8 cm in femur or 3 cm in tibia
-
suggested
approaches, given a normal height range are as follows:
o 0 – 2 cm: no treatment
o 2 – 6 cm: chow lift,
epiphysiodesis, shortening
o 4 – 15 cm: lengthening
procedure
o > 15 cm: prosthetic
fitting
Epiphysiodesis
-
first
described by Phemiser in 1933
-
performed
by excising a square of bone from the medial and/or lateral margin of the
growth plate and rotating it 90°
-
permanent,
difficult to undo physeal bar created if not satisfied with result
-
complications include
miscalculation of timing and technical errors
Epiphyseal Stapling
-
described
by Blount in 1949
-
potentially
the same problems as the epiphysiodesis
-
staples
may be removed and physis will usually resume growth
The
goal is equal limb length at maturity, unfortunately it is often difficult to
predict future growth in a child.
Stapling may permit less precise estimations whereas epiphysiodesis is
unforgiving. Growth rates have been
extensively studied and growth tables exist to help predict the growth
remaining in a given limb at a given age. Growth is fairly constant from
chronologic ages 6 to 9 with the femur growing roughly 2.0 cm (SD 0.27 cm) and
the tibia 1.6 cm (SD 0.23 cm). During
the adolescent growth spurt, yearly increments are extremely variable. Using bone age, rather than chronological
age is a more useful and reliable gauge in predicting growth. This can be performed using standardized
books containing figures of radiographs of the hand and wrist and comparing
them to the patient. (Greulich)
Acute Shortening Procedures
- generally considered for patients with same amounts of LLD as those for epiphysiodesis but who are too old for correction with physeal closure
- femoral shortening usually preferred to tibial shortening
- up to 5 cm usually well tolerated in femur (3 cm in tibia), greater resulting in ineffective recovery of muscle-tendon units
- involves open shortening with plate fixation, proximal shortening with blade plate or newer closed femoral shortening using intramedullary nail
Growth Stimulation
- multiple techniques for stimulation of the short extremity have been tried with irreproducible and clinically insignificant results
o electrical stimulation
o sympathectomy
o surgical creation of AV fistulae
o placement of foreign bodies next to the physes
o packing bone beneath periosteum near physes
Limb Lengthening
- lengthening is generally reserved for patients with the most severe deformities
o multiple potential complications
§ pin tract infections
§ joint contractures
§ joint subluxation or dislocation
§ nonunion/malunion
o prolonged treatment times
- usually 4 to 20 cm
- relatively stable joints above and below are a prerequisite
- rotational or angular malalignment usually decreases total length attainable
- patient should be emotionally mature (usually older than 8 or 9 years)
- ring fixators have focused interest on the biology of lengthening
o rate of lengthening is critical
o osteogenesis begins in IM canal as multipotential cells diffentiate into osteoblasts
o bone formation resembles intramembranous growth (vs endochondral) as no cartilage matrix is laid down
o cells appear to lay down in longitudinal direction of retreating bone end
o patients allowed to fully weight bear and to do regular exercise to prevent joint contractures
- many modifications on the original theme (Ilizarov)
o uniplanar frame lengthening
over an IM rod is becoming popular
-
difficult
decision concerning timing of removal of frame
Prosthetic Fitting
- generally least desirable form of treatment, but may be best choice with large discrepancy or severe deformity
- considered when predicted discrepancy at maturity exceeds 15 to 20 cm
- single operation vs multiple procedures and complications
- Syme amputation follows by prosthetic fitting results in a functional BKA that results in near-normal gait and activity level
o best performed when child is younger than 1 year
- for patient with severe proximal focal femoral deficiency, Syme with or without a knee fusion may be the best option
o Van Nes rotationplasty, which reverses the ankle joint to power a modified below-knee prosthesis is also an option (best if completed before 3 to 4 years)
Fortunately, growth disturbances are often
not purely random and unpredictable.
They are usually a progressive inequality due to growth in one extremity
being inhibited. Studies have shown
that 95% of patients with LLD have constant inhibition that is predictable over
time. Polio is one example where the
growth is usually not predictable.
Three
common methods of predicting the future difference in LLD have been described:
-
White
and Menelaus (arithmetic method)
o Distal femur grows 0.9 cm/yr
o Proximal tibia grows 0.6
cm/yr
o Inaccurate in young children
o Uses chronological age, not
skeletal
o Until maturity (15 ¼ for a
girl and 17 ¼ for a male)
o Simplistic, but a good guide
for timing of epiphysiodesis
-
Green
and Anderson (growth-remaining method)
o 100 kids from Boston (50%
with polio) had their normal leg evaluated
o correlated growth to
skeletal maturity with Greulich and Pyle bone age atlas
o accuracy improved by
plotting over 3-4 yrs to assess growth inhibition
-
Moseley
(straight-line graph method)
o Derived from Green and
Anderson data/tables
o Use more complicated straight
line tables
In
evaluating the various techniques used to assess limb-length discrepancy,
studies vary with respect to interpretation of success. General success has been reported with both
of these methods, although a recent review has reported rather disappointing
results with all three commonly used methods, suggesting further refinement is
needed.
|
Determining Leg Length Discrepancy: The Arithmetic Method |
|
|
Leg Length Data (same data for all three
samples) Sex: Female Age (yr) Skeletal
age (yr) Right leg
length (cm) Left leg
length (cm) 7 + 10 8 + 10 66.0 58.2 8 + 4
9 + 4 64.4 61.9 9 + 3 10 + 3 70.0 66.2 |
|
|
Prerequisite growth information Distal femoral plate grows
10 mm/yr.
Girls stop growing at 14 years of age. Proximal tibial plate
grows 6 mm/yr.
Boys stop growing at 16 years of age. |
|
|
Assessment of past growth 1.
Longest time interval for data = age at last visit – age at first 2.
Years of growth remaining = 14 (16 for boys) – age at last visit 3.
Past growth of legs = present length – first measured length 4.
Growth rate of long leg
5.
Growth inhibition |
1.
Longest time interval for data = 9 yr 3 mo – 7 yr 10 mo = 1 yr 5 mo = 1.42
yr 2.
Years of growth remaining = 14 yr – 9 yr 3 mo = 4 yr 9 mo = 4.75 yr 3.
Past growth of: Long leg = 70 – 60 = 10.0 cm Short leg = 66.2 – 58.2 = 8.0 cm 4.
Growth rate of long leg 5.
Inhibition |
|
Prediction of future growth 1.
Future growth of long leg = years remaining X growth rate 2.
Future increase in discrepancy = future growth of long leg X inhibition 3.
Discrepancy at maturity = present discrepancy + future increase |
1.
Future growth of long leg = 4.75 X 7.04 = 33.4 cm 2.
Future increase in discrepancy = 33.4 X 0.2 = 6.7 cm 3.
Discrepancy at maturity = (70.0 – 66.2) + 6.7 = 10.5 cm |
|
Prediction of effect of surgery Effect of epiphysiodesis = growth rate X years remaining |
Effect of epiphysiodesis Femoral = 0.9 X 4.75 = 4.28 cm Tibial = 0.6 X 4.75 = 2.85 cm Both = 1.6 X 4.75 = 7.13 cm |
Taken from Chapman’s Volume
4, p. 4347.
|
Determining Leg Length Discrepancy: The Growth Remaining Method |
|
|
Prerequisite growth information Distal femoral plate grows
10 mm/yr. Girls stop growing at 14 years of age. Proximal tibial plate
grows 6 mm/yr.
Boys stop growing at 16 years of age. |
|
|
Assessment of past growth 1.
Growth of both legs = present length – first length 2.
Present discrepancy = length of long leg – length of short leg 3.
Growth inhibition
|
1.
Growth of long leg = 70.0 – 60.0 = 10.0 cm 1.
Growth of short leg = 66.2 –
58.2 = 8.0 cm 2.
Present discrepancy = 70.0 – 66.2 = 3.8 cm 3.
Growth inhibition |
|
Prediction of future growth 1.
Plot present length of long leg on Green-Anderson leg length graph
for appropriate sex 2.
Project to right parallel to standard deviation lines until maturity
to determine mature length of long leg 3.
Future growth of long leg = mature length – present length 4.
Future increase in discrepancy = future growth long X inhibition 5.
Predicted discrepancy at maturity = present discrepancy + future increase |
1. 2.
Length of long leg at maturity = 81.1 3.
Future growth of long leg = 81.1 – 70.0 = 11.1 cm 4.
Discrepancy at maturity = 3.8 + 2.2 = 6.0 cm |
|
Prediction of effect of surgery 1.
The effect of epiphysiodesis of the distal femoral and proximal
tibial plates for a given sex and skeletal age can be determined by the
Green-Anderson growth = remaining graph. 2.
The effect of lengthening is not affected by growth. |
1.
Correction from proximal tibial arrest = 2.7 cm Correction from distal femoral arrest = 4.1 cm Correction from combined arrest = 2.7 + 4.1 = 6.8 cm |
Taken from Chapman’s Volume
4, p. 4348.
Moseley
Straight-line Graph Method
Generously
donated by James Roach, M.D.
Most images and much of the
general information from this section were “borrowed” from a powerpoint presentation
by James Roach, M.D. Much was also
“borrowed” from Chapman’s, Volume 4, Chapter 170 ‘Limb-Length Discrepancy
in Children’.
