Keys To Recognizing And Treating Limb Length Discrepancy
Limb length discrepancy is reportedly the third most common cause for running injuries, most often occurring below the hip and appearing first on the longer side.28,29 Researchers have implicated asymmetrical pronation producing a functional limb length discrepancy as a causative factor in sciatica.30 As I previously noted, the longer limb is subject to osteoarthritis of the hip and increased risk of stress fractures while the shorter limb has a higher incidence of knee pain and degenerative joint disease.
Essential Insights On Symptomatology
The most common symptoms associated with limb length discrepancy are low back pain, which usually appears on the longer side first.31-33 Other complications include sacroiliac malalignment, functional scoliosis, sciatica, disc herniation, posterior vertebral facet impingement, hip and knee pain as well as degenerative joint disease, especially on the longer side. Additional findings include: piriformis and iliotibial band syndromes; greater trochanteric bursitis; plantar fasciitis; posterior tibial stress syndrome; patellofemoral pain syndrome; hallux valgus; altered gait patterns; pelvic obliquity toward the shorter limb; contracture of the Achilles tendon on the short limb; and short limb metatarsalgia.1,17,21,34-38
In the sports participant, chronic unilateral overuse injuries that persist despite appropriate care sometimes diffuse and clinicians sometimes may falsely attribute them to LLD. Even “minor” discrepancies in runners may produce symptomatology due to the “rule of three” theory, which states that running forces average three times body weight — three times that required for normal walking — for which the body will compensate at the weakest link in the musculoskeletal chain.21
Who To Treat
The orthopedic literature is confusing regarding the amount of discrepancy adults can tolerate without treatment. Treatment often depends on whether symptoms are present and the degree of musculoskeletal malalignment present. However, an incidental finding of an LLD in an athlete might well be worth equalizing in order to improve symmetry, efficiency and performance as well as to prevent injury. Subotnick states that one should treat discrepancies of as little as 6 mm in an athlete.25
Other authors feel that the commonly occurring 1 to 1.5 cm discrepancies do not lead to symptoms and may not need treatment.5 However, discrepancies as small as 1 cm have been associated with back pain and plantar fasciitis.32,39 Harvey and associates, in a study of 3,026 subjects with radiographically confirmed LLD, determined that those with 1 cm discrepancies were more likely to develop knee pain and osteoarthritis on the shorter limb.40 In those with 2 cm or greater discrepancies, pain and osteoarthritis were present bilaterally. Additionally, this study points out that LLDs as small as 5 mm may be associated with increased odds of prevalent symptomatic knee osteoarthritis. It is because of this and the documented prevalence of osteoarthritis in the hip on the longer limb that some authors contend that any LLD should receive treatment.40,41
As I mentioned earlier, even minor discrepancies may result in major problems when the musculoskeletal system is placed in stress situations. A basic tenet in a biomechanics-based medical practice is that excessive loads, whether they are brief, high impact, loading or cumulative stresses, have the potential to cause structural damage to all facets of the musculoskeletal system. In any case, the ideal situation for all individuals is for both limbs to be of equal length and function symmetrically. Specifically, there should be normal application of pressure for the normal duration of time applied equally through each limb at each phase of the walking or running cycles.