Keys To Recognizing And Treating Limb Length Discrepancy
Given the common presentation of limb length discrepancy, this author reviews the historical methods for diagnosis as well as an objective method for dynamic assessment. He also addresses the clinical significance of limb asymmetry and how computer-assisted gait analysis plays a key role in assessing treatment.
Human gait requires the controlled loss and regaining of the center of gravity as it shifts from one base of support to another. For efficient locomotion, a symmetrical, well-aligned musculoskeletal system is necessary. With symmetrical function and good alignment, there is decreased energy expenditure and increased muscular efficiency, resulting in decreased stress and fatigue.
Unfortunately, most of us are not structurally or functionally symmetrical. A diversity of symptoms may occur as a result of limb length discrepancies, many of which proper treatment can alleviate.
Limb length discrepancy (LLD) is a very common occurrence in the pediatric and adult population. In fact, the majority of individuals have some degree of limb inequality either in structure or function. The average discrepancy is less than 1.1 cm and usually patients easily compensate for this.1 In effect, these individuals lengthen or shorten their lower extremities to minimize their asymmetry.
However, even seemingly insignificant discrepancies may become symptomatic in stress situations such as running. Larger discrepancies pose more of a problem and require more complex solutions. In any event, the underlying question is whether the LLD and its attendant compensatory pathomechanics are creating progressive pathologic alterations in structure and function.
A survey of 376 patients conducted at the Growth Study Center of Children’s Hospital in Boston found that 95.5 percent of those tested have significant limb length discrepancies.2 Pearson’s classic 1951 study of 830 schoolchildren found that 93 percent had some lateral hip asymmetry.3 In the Children’s Hospital study as well as Klein and Buckley’s earlier study, discrepancies increased with age until full maturity.2,4 In the adult population, LLD is reportedly as high as 90 percent.5,6 Due to the widespread occurrence of LLD, physicians often consider this a “normal” finding although one should never confuse commonality with normalcy. “Normal” implies ideal and limb asymmetry, no matter how commonly it occurs, is never the ideal alignment for optimum musculoskeletal system function.7
A Review Of LLD Types And Etiology
There are three types of LLD: structural, functional and environmental.
The structural or anatomic type is due to a difference in the actual length of the tibia or femur. This may be of congenital, post-trauma or post-surgery etiology as LLD commonly occurs following hip or knee replacement.
The functional type is due to asymmetrical foot or limb function, which may have occurred from a variety of asymmetrical musculoskeletal findings. These include hip flexion or adduction contractures, flexion or hyperextension deformities of the knee or ankle, pelvic obliquity, genu varum, genu valgum, musculoskeletal injuries, asymmetrical pronation or supination, etc. Differentiation of these two types is not always straightforward since it is not unusual to have both occur together.
The third type of LLD is referred to as environmental and is caused by the unevenness created by walking or running on crowned road surfaces, banked running tracks or along the beach. Excessive asymmetrical shoe wear may also create an environmental LLD. This third type may exist independently or be an additional pathologic influence into an existing functional and/or structural LLD.