Leg Length Discrepancy (LLD)
- A thorough history is critical to correctly treating limb length discrepancy (LLD) and providing patients with a substantiated prognosis
- Clinical evaluation of LLD should be confirmed by radiographic assessment and include evaluation of limb length, soft tissue contractures and bony deformity.
- Clinical evaluation includes addressing the patient’s and family’s concerns, questions, and compliance issues.
- Limb length is most commonly evaluated radiographically by orthoradiography, scanogram or CT scan. Scanograms are limited in that they cannot evaluate angular deformity or foot height discrepancy, while CT scans are particularly useful for children with hip or knee flexion contractures.
- Methods for evaluating skeletal age are only moderately accurate and are not necessarily superior to chronological age in predicting future growth
Description:Limb length discrepancy (LLD) can be congenital or acquired. Some causes of congenital LLD include fibular hemimelia, tibial hemimelia, congenital femoral deficiency, hemihypertrophy or other limb hypoplasias. Acquired LLD is usually due to an insult to the growth plate by trauma, infection, radiation, or tumor. LLD can occur secondary to fracture of the long bones with malunion or nonunion. Hip dysplasia and dislocation can also cause LLD.
Patient History:A complete history of the patient is vital to understanding the nature of their LLD, possible treatment options, and eventual prognosis. Information about congenital or neuromuscular disorders, previous orthopedic surgeries, evaluation of growth charts and age of menarche all play a role in determination of a suitable treatment plan as well as identify potential complications in the perioperative period.
Limb length should be clinically evaluated then radiographically confirmed. Any discrepancies between the two, warrant further investigation. True limb length is clinically measured with a tape measure from the anterior superior iliac spine to the medial malleolus with the two limbs being placed in similar positions. This can be compared to the apparent limb length as measured from the umbilicus to the medial malleolus with the legs straight parallel to the trunk, which is therefore affected by pelvic obliquity. The most effective way to clinically estimate limb length discrepancy is by placing blocks under the shorter limb to raise the pelvis into a level position. (Morrissy, 2006)Blocks can also be placed to determine the most comfortable lifted position, which can then be measured and used to determine the necessary clinical correction, especially in a patient with complex deformities that are not singularly troubled by LLD. It may be beneficial to maintain a short limb in a patient who requires bracing due to weakness, especially one that locks the knee in extension, or one with dorsiflexion weakness in order to facilitate ground clearance during ambulation.
Soft Tissue:Soft tissue contractures around the hips, knees and ankles can also be implicated in LLD and may complicate radiographic evaluation. Hip adduction contractures produce a functionally short limb and abduction contractures produce a functionally long limb. (Lee, 1997) Hip and knee flexion contractures will cause limbs to appear shorter. Equinus contractures cause limbs to appear longer.
Joint StabilityJoint stability can lead to serious complications when lengthening treatment is pursued. Congenital femoral deficiency is commonly associated with hip and knee instability, while fibular hemimelia can have ankle instability. Knee stability in particular should be assessed prior to femoral lengthening, and the knee protected if necessary.
Bony DeformityBony angular deformity should be assessed as well as it affects both measurement of LLD and outcomes of correction eventually performed. Hip instability is a contraindication to femoral lengthening and posterolateral subluxation of the tibial plateau occurs with hypoplastic lateral femoral condyles (Cuervo, 1996), commonly found in congenitally short femurs. In the setting of an ankle or foot which cannot be salvaged, the patient may benefit more from an amputation and prosthetic device. It is also necessary to evaluate the spino-pelvic relationship as correction of LLD may lead to imbalances within the spinal column.
Social ConcernsFinally, it is important to address the concerns, compliance and emotional state of the patient and their family. The lengthening process is long and arduous, and parents do not always understand the extent of activity limitations required for proper healing. It is imperative that the compliance of the patient and family be assessed before operative intervention is offered. Lengthening is generally discouraged between ages 4 and 6 years as children within this age range may reject their parent, therapists and other caretakers during the demanding process.
Imaging Studies:The teleoradiograph is a single exposure of both limbs, from hips to ankles, projected onto one 35cm x 90cm film. It can be taken standing or supine. (Cleveland, 1988) Advantages of this method include being able to assess angular deformity and only needing one exposure. Disadvantages include handling a large, cumbersome film and partial image magnification due to parallax of the x-ray beam.
The orthoradiograph is a series of x-rays directed perpendicular to the joints whose images are then spliced together onto a single film. (Green, 1946) Magnification is therefore decreased. Patient movement between exposures may lead to inaccurate measurements. However, the orthoradiograph allows evaluation of both LLD and angular deformity on a single film. The image is best performed with blocks under the short limb to level the pelvis, which avoids inadvertent adjustments of the hip, knees or ankles by the patient. There is also the advantage that any contribution of foot deformity can be determined by comparing the levelness of the pelvis, femur and tibial lengths, and blocks used.
The scanogram is also a series of x-rays perpendicular to the joints, but can fit onto a regular-sized film because only spot images are taken, with the cassette moving underneath the patient between exposures. (Bell, 1950) This avoids magnification but is only recommended for children aged 5 and older as they are more likely to remain still during and between exposures. The main downside is the inability to concurrently evaluate angular deformities in the femur and tibia. The scanogram can also be taken in the lateral position which is useful when evaluating limb length in patients with hip or knee contractures.
Microdose CT scan may also be used to evaluate limb length digitally. Fewer slices are necessary and angular deformity is less likely to interfere with accurate measurement as sagittal slices can be obtained. (Glass, 1985) CT scans are the ideal images for patients with hip or knee contractures
Skeletal AgeEstablishing the skeletal age of patients may be of value in determining prognosis of LLD with or without treatment. The classic and commonly used Greulich and Pyle (GP) method consists of an atlas of radiographs of the left hands and wrists of boys and girls that were considered representative for their respective skeletal age groups. (Greulich, 1959) Physicians acquire a left hand and wrist radiograph then compare it to those shown in the atlas to determine the skeletal age of the patient. The main limitation is the wide confidence intervals for each radiograph. Despite this, Moseley reported accuracies generally within 1cm when using skeletal age and his straight line graph method to determine the appropriate timing for epiphysiodesis. (Moseley, 1977) The Tanner-Whitehouse (TW) method sought to improve upon the GP method by implementing modern computerized mathematical procedures to improve the accuracy of results and decrease standard error. (Tanner, 1975) It does this by assigning a numerical score for 20 different regions of interest in the left hand and wrist. Furthermore, the method also takes into account, differences in development of the long bones of the hand versus the carpal bones, which makes it more useful in the evaluation of LLD. This technique, however, is much more time consuming. It also can result in different skeletal ages for the same radiograph.
Multiple other systems and automated methods for determining bone age exist, but have not supplanted the Greulich and Pyle system in most institutions. (Gilanz, 2012; Kaplowitz, 2010; Thodberg, 2009; Mentzel 2005) The merits of using skeletal age at all have been questioned. A study of the multiplier method for growth prediction found improved accuracy of 1.1cm using chronological age, versus 1.5cm using bone age. (Aguilar, 2005) Overall, it is reasonable to use chronological age when it is within the confidence intervals of the skeletal age, but use skeletal age and multiple data points if possible when the two are disparate.
Treatment:Magnitude of discrepancy:
- 0 to 2 cm: No treatment
- 2 to 6 cm: Shoe lift, epiphysiodesis, shortening
- 5 to 20 cm: Lengthening (may or may not be combined with other procedures)
- >20 cm: Prosthetic fitting
Shoe Lift: Though believed to be less desirable than surgical correction of a LLD up to 6 cm, a shoe lift is a satisfactory answer for patients who do not desire or are not appropriate for surgery. For reasons of cosmesis, up to 2 cm of the lift can be put inside the shoe with the remainder, if necessary, on the outside. Lifts >5 cm are poorly tolerated because the muscles controlling the subtalar joint have difficulty resisting the inversion stress. If a higher lift is required, an ankle-foot orthotic extension up the posterior calf can be added for stability.
Prosthetic Fitting: Prosthetic fitting after amputation is a treatment of last resort but useful for patients with a very large discrepancy and for those with deformed and functionally useless feet (Anderson, 1984; Mallet, 1986). Discrepancies anticipated to become >15-20 cm and those involving a femoral length <50% of the contralateral femur may be treated in this way (Gillespie, 1983). This approach has the advantage of involving requiring only one definitive operation.
Children with below-knee amputations (BKA) do very well functionally. They have almost normal walking gait and can participate in recreational and sporting activities. Those with an above-knee amputation (AKA) also function well, although not as well as those with a BKA. A Van Nes rotationplasty, in which the reversed ankle functions as a knee, allows a limb that would otherwise perform as an AKA to function as a BKA and provides active control and motor power to the prosthetic knee (Setoguchi, 1994).
Children who undergo surgery and prosthetic fitting early in life show the best results. The optimal time for performing the Syme amputation is toward the end of the first year of life near walking age while the best timing for rotationplasty is at approximately 3 years of age.
Epiphysiodesis: Epiphysiodesis has a very low morbidity and complication rate and is the treatment of choice for surgical correction of LLD with discrepancy from 2 to 6 cm (Green, 1947; Menelaus, 1966; Stephens, 1978; White, 1944). For all surgical treatments of LLD, it is the discrepancy at maturity that should be corrected and not the present discrepancy in a growing child. The prediction of the effect of surgery can be made accurately within 1 cm in almost all cases (Moseley, 1977), and because there is an advantage to being tall (Gillis, 1982; Grumbach, 1988; Mayer-Bahlburg, 1985; Sandberg, 1994), it is better to err on the side of undercorrection. Slight discrepancies are well tolerated, and it is best to aim for 0.5 to 1.0 cm of undercorrection by performing the procedure slightly later than the time for perfect correction. This can also allow for additional length to accommodate a brace or stiffness in the short limb.
Percutaneous epiphysiodesis, considered by most to be the treatment of choice, is usually performed through one medial and one lateral incision with image intensifier control. Drilling the entire epiphysis through a single incision is also possible. Removal of approximately 50% of the area of the plate (leaving a strong periphery) is sufficient to ensure arrest and maintain enough bone strength to make postoperative immobilization unnecessary. Tibial epiphysiodesis should be accompanied by arrest of the proximal fibular physis if anticipated shortening is >2.5 cm (Canale, 1990). Open Phemister epiphyseodesis can also be utilized.
Shortening: Acute shortening has the same indications as epiphysiodesis but is offered to patients who are too skeletally mature for growth modulation, or who have conditions such that the extent of the discrepancy at maturity cannot be confidently predicted. Excessive shortening can risk weakness to the muscles of the well leg due to the shortened end muscle length. Although shortening of 7.5 cm has been reported without loss of function (15), it is unusual to perform shortenings of more than 5 cm in the femur and 3 cm in the tibia. There are two principal techniques:
Proximal Shortening: Performed at the level of the lesser trochanter with blade plate fixation or other internal fixation. Patients recover quadriceps strength more quickly, but this approach leaves a large scar on the lateral thigh, requires restricted weightbearing, and may require a second operation for removal of the plate.
Middiaphyseal Shortening: Performed with an intramedullary saw and intramedullary rod fixation. Major disadvantages of this technique include technical complications, risk of respiratory distress syndrome during reaming (Edwards, 1992), and significant quadriceps weakness. However, it leaves only a small scar, may allow for earlier weight bearing, and the procedure to remove the rod is of lesser magnitude than that required to remove a blade plate.
Limb Lengthening: Lengthening is a procedure of last resort and is reserved for those situations in which other methods of correction are inappropriate. A reasonable goal of lengthening for most patients is less than 8 cm for the femur and 5 cm for the tibia. Patients requiring large corrections may require simultaneous lengthening of femur and tibia, repeated staged lengthening of the same bone (Coleman, 1985), or supplementary shortening procedures on the long leg. Regardless of the technology utilized, the complication rates are high and the patient’s course can be difficult following lengthening.
A brief overview of limb lengthening is presented here and describes lengthening with an external fixation device. Please see the separate section on limb lengthening for more details.
Intensive education and observation is required for the first two weeks following the procedure. Biweekly office assessments should be made, and radiographs are taken at intervals of 2 weeks to evaluate alignment and the quality of bone in the lengthening gap (i.e., the regenerate). Maintaining motion is extremely important and should be monitored regularly. Distraction is discontinued if an unresolvable complication (usually loss of motion) supervenes. After the distraction goal has been achieved, the device is retained until radiographs show consolidation and suggest adequate strength of the regenerate bone. If the gap is slow to consolidate, the device can be shortened to provide longitudinal compression. While valid objective guidelines for what constitutes adequate consolidation for removal of the device have not been established, findings such as corticalization with three cortices visible on two radiographs and the appearance of a medullary cavity are considered signs of adequate strength. Additionally, it is possible to protect the tibia externally with a cast after device removal, allowing removal of the device from the tibia earlier than from the femur.
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