Acceptable Leg Length Discrepancy After Hip Replacement
Overview
The two major categorizations of LLD are structural and functional. A third more minor category is environmental. In structural LLD there is an actual anatomical difference in the bones of the lower extremities where one side becomes shorter than the other. This type of LLD may be genetic, where the person is born in this way. In other cases it may be due to injury or infection through the growth phases of early childhood or adolescence. Some spinal abnormalities like scoliosis can also cause this condition. Functional LLD is where the bones are not the cause of difference but a muscle or pelvic condition has the effect of weakening the leg on one side. Conditions that can cause this are muscle inflexibility, adduction contractures and pelvic obliquity (amongst others). The third less severe category of environmental LLD is caused by discrepancies in the surface that the feet and legs are resting or walking on. Banked, uneven or curved surfaces can all cause environmental LLD. In LLD the asymmetric nature of the legs in relation to hips and back caused the centre of gravity to shift from its natural position. This then results in the body attempting to compensate by either tilting the pelvic areas towards the shorter side, increased knee flexing on the longer side, flexion of the ankle plantar and foot supination towards the shorter side.
Causes
Some children are born with absence or underdeveloped bones in the lower limbs e.g., congenital hemimelia. Others have a condition called hemihypertrophy that causes one side of the body to grow faster than the other. Sometimes, increased blood flow to one limb (as in a hemangioma or blood vessel tumor) stimulates growth to the limb. In other cases, injury or infection involving the epiphyseal plate (growth plate) of the femur or tibia inhibits or stops altogether the growth of the bone. Fractures healing in an overlapped position, even if the epiphyseal plate is not involved, can also cause limb length discrepancy. Neuromuscular problems like polio can also cause profound discrepancies, but thankfully, uncommon. Lastly, Wilms? tumor of the kidney in a child can cause hypertrophy of the lower limb on the same side. It is therefore important in a young child with hemihypertrophy to have an abdominal ultrasound exam done to rule out Wilms? tumor. It is important to distinguish true leg length discrepancy from apparent leg length discrepancy. Apparent discrepancy is due to an instability of the hip, that allows the proximal femur to migrate proximally, or due to an adduction or abduction contracture of the hip that causes pelvic obliquity, so that one hip is higher than the other. When the patient stands, it gives the impression of leg length discrepancy, when the problem is actually in the hip.
Symptoms
If your child has one leg that is longer than the other, you may notice that he or she bends one leg. Stands on the toes of the shorter leg. Limps. The shorter leg has to be pushed upward, leading to an exaggerated up and down motion during walking. Tires easily. It takes more energy to walk with a discrepancy.
Diagnosis
A systematic and well organized approach should be used in the diagnosis of LLD to ensure all relevant factors are considered and no clues are overlooked which could explain the difference. To determine the asymmetry a patient should be evaluated whilst standing and walking. During the process special care should be used to note the extent of pelvic shift from side to side and deviation along the plane of the front or leading leg as well as the traverse deviation of the back leg and abnormal curvature of the spine. Dynamic gait analysis should be conducted during waling where observation of movement on the sagittal, frontal and transverse planes should be noted. Also observe head, neck and shoulder movements for any tilting.
Non Surgical Treatment
Whether or not treatment should be pursued depends on the amount of discrepancy. In general, no treatment (other than a heel life, if desired) should be considered for discrepancies under two centimeters. If the discrepancy measures between two and five centimeters, one might consider a procedure to equalize leg length. Usually, this would involve closure of the growth plate on the long side, thereby allowing the short side to catch up; shortening the long leg; or possibly lengthening the short leg.
leg length discrepancy measurement
Surgical Treatment
Lengthening is usually done by corticotomy and gradual distraction. This technique can result in lengthenings of 25% or more, but typically lengthening of 15%, or about 6 cm, is recommended. The limits of lengthening depend on patient tolerance, bony consolidation, maintenance of range of motion, and stability of the joints above and below the lengthened limb. Numerous fixation devices are available, such as the ring fixator with fine wires, monolateral fixator with half pins, or a hybrid frame. The choice of fixation device depends on the desired goal. A monolateral device is easier to apply and better tolerated by the patient. The disadvantages of monolateral fixation devices include the limitation of the degree of angular correction that can concurrently be obtained; the cantilever effect on the pins, which may result in angular deformity, especially when lengthening the femur in large patients; and the difficulty in making adjustments without placing new pins. Monolateral fixators appear to have a similar success rate as circular fixators, especially with more modest lengthenings (20%).
The two major categorizations of LLD are structural and functional. A third more minor category is environmental. In structural LLD there is an actual anatomical difference in the bones of the lower extremities where one side becomes shorter than the other. This type of LLD may be genetic, where the person is born in this way. In other cases it may be due to injury or infection through the growth phases of early childhood or adolescence. Some spinal abnormalities like scoliosis can also cause this condition. Functional LLD is where the bones are not the cause of difference but a muscle or pelvic condition has the effect of weakening the leg on one side. Conditions that can cause this are muscle inflexibility, adduction contractures and pelvic obliquity (amongst others). The third less severe category of environmental LLD is caused by discrepancies in the surface that the feet and legs are resting or walking on. Banked, uneven or curved surfaces can all cause environmental LLD. In LLD the asymmetric nature of the legs in relation to hips and back caused the centre of gravity to shift from its natural position. This then results in the body attempting to compensate by either tilting the pelvic areas towards the shorter side, increased knee flexing on the longer side, flexion of the ankle plantar and foot supination towards the shorter side.
Causes
Some children are born with absence or underdeveloped bones in the lower limbs e.g., congenital hemimelia. Others have a condition called hemihypertrophy that causes one side of the body to grow faster than the other. Sometimes, increased blood flow to one limb (as in a hemangioma or blood vessel tumor) stimulates growth to the limb. In other cases, injury or infection involving the epiphyseal plate (growth plate) of the femur or tibia inhibits or stops altogether the growth of the bone. Fractures healing in an overlapped position, even if the epiphyseal plate is not involved, can also cause limb length discrepancy. Neuromuscular problems like polio can also cause profound discrepancies, but thankfully, uncommon. Lastly, Wilms? tumor of the kidney in a child can cause hypertrophy of the lower limb on the same side. It is therefore important in a young child with hemihypertrophy to have an abdominal ultrasound exam done to rule out Wilms? tumor. It is important to distinguish true leg length discrepancy from apparent leg length discrepancy. Apparent discrepancy is due to an instability of the hip, that allows the proximal femur to migrate proximally, or due to an adduction or abduction contracture of the hip that causes pelvic obliquity, so that one hip is higher than the other. When the patient stands, it gives the impression of leg length discrepancy, when the problem is actually in the hip.
Symptoms
If your child has one leg that is longer than the other, you may notice that he or she bends one leg. Stands on the toes of the shorter leg. Limps. The shorter leg has to be pushed upward, leading to an exaggerated up and down motion during walking. Tires easily. It takes more energy to walk with a discrepancy.
Diagnosis
A systematic and well organized approach should be used in the diagnosis of LLD to ensure all relevant factors are considered and no clues are overlooked which could explain the difference. To determine the asymmetry a patient should be evaluated whilst standing and walking. During the process special care should be used to note the extent of pelvic shift from side to side and deviation along the plane of the front or leading leg as well as the traverse deviation of the back leg and abnormal curvature of the spine. Dynamic gait analysis should be conducted during waling where observation of movement on the sagittal, frontal and transverse planes should be noted. Also observe head, neck and shoulder movements for any tilting.
Non Surgical Treatment
Whether or not treatment should be pursued depends on the amount of discrepancy. In general, no treatment (other than a heel life, if desired) should be considered for discrepancies under two centimeters. If the discrepancy measures between two and five centimeters, one might consider a procedure to equalize leg length. Usually, this would involve closure of the growth plate on the long side, thereby allowing the short side to catch up; shortening the long leg; or possibly lengthening the short leg.
leg length discrepancy measurement
Surgical Treatment
Lengthening is usually done by corticotomy and gradual distraction. This technique can result in lengthenings of 25% or more, but typically lengthening of 15%, or about 6 cm, is recommended. The limits of lengthening depend on patient tolerance, bony consolidation, maintenance of range of motion, and stability of the joints above and below the lengthened limb. Numerous fixation devices are available, such as the ring fixator with fine wires, monolateral fixator with half pins, or a hybrid frame. The choice of fixation device depends on the desired goal. A monolateral device is easier to apply and better tolerated by the patient. The disadvantages of monolateral fixation devices include the limitation of the degree of angular correction that can concurrently be obtained; the cantilever effect on the pins, which may result in angular deformity, especially when lengthening the femur in large patients; and the difficulty in making adjustments without placing new pins. Monolateral fixators appear to have a similar success rate as circular fixators, especially with more modest lengthenings (20%).
