Pediatric orthopaedic surgeons have long debated the effects of leg length discrepancy and the magnitude of leg length discrepancy that leads to long-term problems. Back pain, lower extremity pain, and degenerative conditions have long been associated anecdotally with limb length discrepancy.1–4 Unfortunately little has been written after systematic study about the long-term effects of limb length discrepancy and the long-term consequences to patients of small limb length discrepancies.
One of the first systematic attempts to quantify the amount of discrepancy that required treatment and which patients developed symptoms associated with leg length discrepancy was carried out by Richard Gross in 1978. He performed a survey of physicians in the pediatric orthopaedic study group asking the amount of discrepancy that they would consider treating. In addition, he surveyed 74 of his adult patients with a leg length discrepancy >1.5 cm. In the survey, he asked if the leg length discrepancy was a problem, if the patient felt unbalanced, if the patient wore a lift, and if the patient had back pain. He concluded that leg length discrepancies <2 cm were unlikely to be a problem.
The purpose of this review is to address what we have learned since the publication of this paper and to assess the quality of the data.
A search of the English-speaking medical literature was carried out for papers dealing with the effects and treatment of mild to moderate leg length discrepancies. An internet based search utilizing PubMed was carried out using multiple terms describing limb length discrepancy. The bibliography of papers identified were also examined to aid in identifying additional studies. These studies were then reviewed to allow expansion of the internet search. Case reports and level V evidence consisting purely of expert opinion without objective data were excluded from the literature search. Further, papers concerned primarily with the risk of various procedures producing a limb length discrepancy were excluded.
Examination of the identified papers revealed 2 basic types of studies. First, natural history studies in which the patients with existing leg length discrepancy were examined looking for problems associated with lower limb length discrepancy and the frequency of pathology in these patients. Secondly, papers reporting the results of gait analyses of patients with lower limb length discrepancies.
One of the first questions that the literature addresses is how common mild leg length discrepancies are. Knutson5 in 2005 published a meta-analysis in the chiropractic literature reporting the results of a the magnitude of leg length discrepancies in the general population. He included a total of 573 patients in the meta-analysis. He concluded that 90% of patients had at least a 1 mm leg length discrepancy and only 10% of the general population had exactly equal leg lengths. Approximately 50% of the population has a 4 mm discrepancy or less and ~90% of the population has a 10 mm discrepancy or less (Fig. 1). In 1983 Gross6 surveyed 35 adult marathon runners who had completed at least 1 marathon between 1978 and 1981 and assessed their leg length discrepancy by scanogram. He subdivided the amount of leg length discrepancy into 0 to 4 mm, 5 to 9 mm, and >10 mm. None of these patients felt that leg length discrepancy was an impediment to running. Four of the 18 runners were noted to have a leg length discrepancy >5 mm and used a lift. One runner with <5 mm leg length discrepancy also used a lift.
In 2005, Tallroth et al7 reported the results of 81 patients with a mean leg length discrepancy of 7.5 mm who were undergoing total hip arthroplasty. He noted that 84% or 68 of the total hip arthroplasties were on the longer leg. Murray et al8 in 2017 reported in the Journal of Manipulative and Physiologic Therapeutics the radiographs of 575 patients. He defined leg length discrepancy as >5 mm and noted a significantly increased risk of signs of degenerative joint disease in patients with a leg length discrepancy of >5 mm. He noted that these signs were more often on the long side but this was not quantified.
Harvey et al9 in 2010 in the Annals of Internal Medicine reported a longitudinal study of 2964 patients with full length radiographs who were followed for 30 months. Radiographs were examined looking for an increase in osteoarthritis grade. When examining patients who had a leg length discrepancy of over 1 cm, 53% of the knees on the short leg showed an increased osteoarthritis grade, whereas knees on the long leg showed an increased osteoarthritis grade in 36%. In patients with a leg length discrepancy >2 cm, the likelihood of an increase in osteoarthritis grade in the short leg was 68% and in the long leg, 37%. His data suggested that there was an increased risk of knee osteoarthritis in patients with a leg length discrepancy as little as 0.5 cm. Tallroth et al10 in 2017 reported the results of 194 patients with a standing long leg radiograph obtained between age 34 and 54 years. These patients were followed longitudinally for 29 years, so he then assessed these radiographs examining the amount of leg length discrepancy present and compared that with the number which required knee arthroplasty. He found that 70% of the patients who required total knee arthroplasty had a leg length discrepancy >5 mm. He found that 3 of 62 patients or 5% of the patients with no leg length discrepancy had a total knee arthroplasty. He further noted that 10 of 107 patients with a leg length discrepancy of 9% had total knee arthroplasty. Of these 10 patients who had total knee arthroplasty and who had a leg length discrepancy, 7 of the 10 were on the long leg.
Murray and Azari11 in 2015 reported in the Journal of the Canadian Chiropractic Association, the results of an examination of 575 patients with radiographs of the lumbar spine. He defined a leg length discrepancy as >5 mm. He noted a correlation of leg length discrepancy with degenerative joint disease at L5-S1 in both sexes. He further noted a correlation of leg length discrepancy with degenerative joint disease at L4-L5 in men but not women. ten Brinke et al1 reported in 1999 the results of 132 consecutive patients admitted for treatment of a herniated disc with a leg length discrepancy of >1 mm. He noted a prevalence of herniated nucleus pulposus on the short side in men and a statistically significant association of herniated nucleus pulposus on the short side in women. Defrin et al12 in 2005 in the Archives of Physical Medicine and Rehabilitation identified 33 patients with low back pain with a leg length discrepancy of ≤10 mm or less. Twenty-two of these patients were randomly selected in a nonblinded manner and treated with a shoe lift for 12 weeks. He noted that there was a significant difference in the amount of reported reduced pain and disability associated with the back pain and concluded that patients with low back pain and a mild leg length discrepancy might benefit from a shoe lift in the short term.
Campbell et al13 in 2018 in the Archives of Physical Medicine and Rehabilitation reported a meta-analysis of papers reporting shoe lifts for a leg length discrepancy. On the whole, he noted poor quality of the papers he reviewed and ultimately included 349 patients who were reported in nonrandomized trials with musculoskeletal complaints. 88% of these patients reported either partial or complete pain relief with the use of the lift.
Khamis and Carmeli in 201714 reported a gait and posture lab study involving 7 healthy volunteers. These volunteers were studied while wearing sandals that produced leg length discrepancies of 5, 10, 15, 20, 30, and 40 mm. Compensatory strategies appeared as early as a 5 mm lift and showed increasing long knee flexion and increased hip abduction and external rotation to accommodate the discrepancy. With discrepancies of 10 mm and up, increasing strategies that dynamically increased the short limb length were utilized by the volunteers.
Song et al15 in 1997 reported gait lab analysis of 35 patients with a range of limb length discrepancies from 0.6 to 11.1 cm. Patients with small discrepancies with a mean of 1.6 cm revealed no compensatory strategies. Among the patients who utilized toe walking as a compensatory strategy, the mean limb length discrepancy was 6.5 cm. There were 8 patients who used persistent pelvic obliquity to compensate for their leg length discrepancy with a leg length discrepancy between 2 and 15.8 cm. Nine patients had an increased range of pelvic obliquity throughout the gait cycle to compensate for their leg length discrepancy.
Aiona et al16 examined 43 patients with a range of leg length discrepancies >2 cm with both acquired and congenital leg length discrepancies. Gait analyses were performed on these children. Strategies identified to compensate for the leg length discrepancy included pelvic obliquity, long knee flexion, short limb ankle equinus, and early plantar flexion crossover on the short side. Interestingly, femoral discrepancies utilized more distal strategies in order to compensate for the limb length discrepancy.
Studies attempting to determine the natural history of lower limb length discrepancies provide insight, but have a number of significant weaknesses that are inherent to the type of study carried out. Studies of the natural history of limb length discrepancy provide some of the best information regarding the long-term effects of limb length discrepancies. In particular, Tallroth and colleagues7,10 have shown that limb length discrepancy can be associated with hip pathology, especially on the long side. This would seem to suggest that the long side may be uncovered by small discrepancies leading to an exacerbation or the production of hip dysplasia. Short side arthropathy may represent an exaggeration of the effects of hip impingement.
These natural history studies are difficult to perform and require following or identifying minimally symptomatic or asymptomatic patients over a long period of time. Because of the long period of time, this type of study suffers from difficulties controlling the patients identified and the pathology involved. There is little control over the amount of leg length discrepancy in the patients studied; while a large random group with an even distribution of limb length discrepancies would be ideal, this sort of patient collection is rarely identified. There is little differentiation between acquired and congenital limb length discrepancies in these studies. The source of the leg length discrepancy varies in the patients who are identified. There is little differentiation in studies between functional and true limb length discrepancies and whether the leg length discrepancy originates in the femur, the tibia, the foot or some combination of these locations. This is particularly true in patients with congenital limb length discrepancies. This can also be true in patients who have a leg length discrepancy secondary to an injury in which either overt or subclinical injuries to joints can occur. Compensatory strategies utilized by each patient differ, although the pathology a patient develops may very well be determined by the compensatory strategy utilized by the individual. There is no data on the type of compensatory strategy utilized by various patients, and there is no data on the past history of lift use or the origin of the limb length discrepancy.
Gait analysis of individuals with limb length discrepancies show a variety of different compensatory mechanisms that may shed light on the development of long-term pathology.17 Because these compensatory mechanisms place stress on different areas of the lower extremities or spine, or alternatively require exaggerated motion in these areas, it may be that understanding the compensatory mechanisms is the key to understanding and treating the pathology.
Gait studies likewise have significant limitations. Like natural history studies that examine patients with existing leg length discrepancies, authors have little control over the amount of leg length discrepancy in the patient population. These patients have often adapted to a leg length discrepancy over a large amount of time and have often developed differing compensation strategies. It is important to remember that patients frequently have progressively increasing limb length discrepancies and during growth may exhibit differing compensation strategies at differing ages. Associated pathology also differs among the patients and the studies rarely control for congenital or acquired etiologies.
Gait studies that utilize normal volunteers with a created leg length discrepancy benefit from excellent control over the amount of leg length discrepancy, but there is little evidence that would suggest that the adaptive changes are the same as patients with a preexisting leg length discrepancy and the studies are carried out in an artificial environment with level ground with few of the changes seen in real life.
Isolated cases of individuals with limb length discrepancies performing well in athletic pursuits are certainly present. Usain Bolt is reported18 to have a 1.3 cm leg length discrepancy, and video analysis of his gait during races reveals his right leg striking the ground with 13% more force and his left leg spending 14% more time on the ground. Clearly, at least in some situations, small leg length discrepancies are consistent with extraordinary athletic performance.
In conclusion, the evidence for the effect of leg length discrepancy and the amount of leg length discrepancy that we should be treating is quite poor and probably has advanced little since Gross’s initial survey of pediatric orthopaedic surgeons. There seems to be a consensus that a leg length discrepancy >2 cm can be a problem. There is some evidence that leg length discrepancy >5 mm can lead to hip, knee, or low back problems. There may also be some poor evidence that suggest that patients who do have symptoms of low back pain associated with a leg length discrepancy as little as 5 mm may benefit from a lift or some sort of equalization in the short term.
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. July 20, 2017.