24 - Limb Length Discrepancies Flashcards
How common are limb length discrepancies?
- Very Common
- 65-75% of the population
What is a significant LLD?
o 3mm - 22mm
o There is a huge range of what people consider may be significant
A significant limb length discrepancy is dependent upon whether or not it causes symptoms or need for compensation, NOT on the numerical values
Types of LLD
- Structural LLD - Anatomical shortening
- Functional LLD - Due to biomechanics (“biomechanical”)
- Combination of structural and functional
Causes of structural LLD
o Polio
o Physeal Damage
o Congenital Dysplasia
o Post-Surgical (very important for us)
Compensation for structural LLD
o Pelvis tilts downward on short side
o Scoliosis with convex side over short limb (reducible with NWB - can become rigid)
Causes of functional LLD
- Excessive STJ pronation***
- Joint contracture
- Axial malalignment
- Induced by shoe gear
Describe excessive STJ pronation as a cause of functional LLD
Excessive STJ pronation
o Greater than 3º of eversion when compared to contralateral limb
o Note: Pronation is a CAUSE of a functional LLD – KNOW THIS
Describe axial malalignment as a cause of functional LLD
o Spinal - frontal or transverse plane deformity
o Pelvic - triplane deformity
Describe shoe gear as a cause of functional LLD
o When people run, they can have uneven shoe based on the crown of the road
o What happens is if they run with traffic and they do a loop, they will have uneven wear and tear
Symptoms associated with LLD
- Can be asymptomatic
- Pain with standing and weightbearing
- Sacroiliac joint (SI joint) pain due to pelvic tilt (pelvic tilt syndrome)
- Knee pain
- Low back pain (due to disc protrusion with scoliosis)
- Foot pathology
Describe the types of knee pain seen with LLD
o Lateral knee pain on the short limb (due to supination)
o Medial knee pain on the long limb (due to pronation)
Describe the types of foot pathology seen with LLD
o Long limb will pronate to shorten (here pronation is a COMPENSATION)
o Short limb will supinate to lengthen
NEED TO KNOW
Pronation is a compensation for structural LLD or a cause of a functional LLD
Direct clinical measurement
ASIS to medial malleolus o Inaccurate o Obese patients difficult o Joint contracture not accounted for o Torsion of bones not accounted for o Pelvic torsion not accounted for
Variations in the method for direct clinical measurement
o ASIS to lateral malleolus
o Umbilicus to medial malleolus
o Sometimes you can add in different reference points if you think you have a structural problem - Find out where exactly the excess length is (tibia, femur, etc.) - Is it one specific segment? Or is it a slight increase in length of each bone?
Indirect clinical measurement
o WB with foot in resting calcaneal stance position
o Pelvic landmarks palpated, keeping hands parallel
o ASIS and PSIS located
o Blocks of a known thickness placed under short side until landmarks are at same level
What factor is not accounted for when measuring?
- Pelvic height difference not accounted for
- Add a third reference point for accuracy
- Greater trochanter: if this measurement is equal, then the LLD occurs within the pelvis
Radiographic evaluation
- Radiographic films taken of long bones and measured for structural LLD
- We do not have the means of doing this here at DMU, but the hospitals in town have long enough x-rays in order to do this
- Take films of the entire tibia to determine where the discrepancy is located
- Use landmarks on each of the bones and compare to the opposite side to determine if it is structural or functional
Surgical correction centers
Limb deformity centers will use radiographs extensively when they surgically repair a limb
o Cut the bone, apply an external fixator
o Once a soft callus has formed, separate the bone by 1 mm per day to increase length
o Healing leads to increased length
Compensation of LLD
- Body attempts to correct LLD
- Pelvic Rotation
- Functional scoliosis – most common compensation
- We look at both the pelvis and the shoulders to see where the compensation is taking place
How is pelvic rotation a compensation for LLD?
o Posterior pelvic rotation with pronation on long limb
o Anterior pelvic rotation with supination on short limb
Scoliosis
- Must determine if scoliosis is functional and a result of a LLD or if is the primary pathology and the LLD is a compensation for the scoliosis
- Fixed scoliosis does not reduce with NWB
Treatment of LLD
- No absolute value or LLD that requires treatment
- Treatment is based on the following criteria
o Symptomatic patient
o Patient predisposed to injury
o Decreased tolerance to activity (parents will say that the child can’t keep up with other kids)
o Presence of scoliosis
o Shoulder or pelvic tilt
o Knee pain
o Altered gait
What must you address in the treatment of LLD?
Must address etiology – functional or structural
How do you treat a functional LLD?
If functional caused by increased pronation, must correct with orthosis
How do you treat a structural LLD?
If structural then a lift is used
How do you treat a combined (structural and functional) LLD?
If combined, then an orthotic with a lift
Lifts
- If discrepancy 1 cm or more, a full length lift is used to prevent equinus
- If discrepancy is less than 1 cm, a heel lift can be used
- Increase in increments of 3mm (1/8”) per week – don’t start with 1 cm
- Can get 8 mm of lift in a normal shoe
- If greater than 8 mm needed, apply 50% of lift to shoe of short side and acquire other 50% by deepening shoe on long side
EBM study
- We evaluated the gait of thirty-five neurologically normal children who had a limb-length discrepancy of the lower extremities that ranged from 0.8 to 15.8 percent of the length of the long extremity (0.6 to 11.1 centimeters).
- The twenty-two boys and thirteen girls had an average age of thirteen years (range, eight to seventeen years).
- No patient had a substantial angular or rotational deformity of the lower extremities. We found no correlation between the actual discrepancy or the per cent discrepancy and any of the dependent kinematic or kinetic variables, including pelvic obliquity.
- Discrepancies of less than 3 per cent of the length of the long extremity were not associated with compensatory strategies.
- When a discrepancy was 5.5 per cent or more, more mechanical work was performed by the long extremity and there was a greater vertical displacement of the center of body mass.
- Clinically, this degree of discrepancy was manifested by the use of toe-walking as a compensatory strategy.
- Children who had less of a discrepancy were able to use a combination of compensatory strategies to normalize the mechanical work performed by the lower extremities.
Main point of EBM study
Prospective level 3 study
o Main point – Need to determine if it is causing symptoms***
o This is an older study because not many are studying limb length deformities
