Children's Orthopaedics
12-year old Harry was a heart-sink patient whose longstanding low back pain had stubbornly resisted any organic explanation. His mother looked at me with a triumphant gleam in her eyes. “We know what’s causing it” she told me, “The physiotherapist says that Harry’s left leg is 3mm shorter than the right.”
With an inward sigh, I launched into my standard pitch on limb length discrepancy (LLD) and its implications, but afterwards stopped to think about what I had said. Much of it was received wisdom for which I had little if any evidence.
In fact, there is a surprising amount of consensus in the literature regarding two key aspects of lower LLD; firstly, its ubiquitous nature and secondly, the threshold at which any intervention should be considered. It is also reassuring to know that this evidence derives from a wide variety of sources.
Simple population studies show that up to a quarter of the population have a LLD of at least 1cm.1 Perhaps unsurprisingly, the chiropractic literature includes claims of LLD in 90% of the population; however, Knutson showed that these were not necessarily trivial differences as the mean difference in his series was over 5mm.2 ...
Unexpected support regarding intervention thresholds comes from the same chiropractic paper, which suggests that, for most people, anatomical leg-length inequality does not appear to be clinically significant until the magnitude reaches approximately 2cm.2
Gait studies consistently show that a discrepancy less than 2cm does not cause gait asymmetry,3 nor are the kinematics or kinetics of gait altered significantly.4 The relationship between LLD and low back pain is less clear although the weight of opinion is again in favour of the proposition that LLD of less than 2cm is not associated with any increase in the incidence of low back pain.5 Development of a scoliosis would not be unexpected, but it is difficult to explain why as many as one-third of reported curves are convex on the longer side.6 There is no evidence for increased incidence of hip or knee arthrosis for LLDs of 2cm or less.7 In the words of Gross,1 “It is concluded that there seems little indication for equalisation of discrepancies less than 2 cm. For larger amounts of discrepancy, "clinical judgment" still must be weighed on an individual basis, as individual variation among patients with leg length discrepancy confounds any precise classification of functional disability.”
And what of young Harry? Naturally his back pain resolved immediately when his therapist provided him with a 3mm shoe raise. Physiotherapists 1, Orthopaedic Surgeons 0.
Mr Mark Paterson, Consultant Orthopaedic Surgeon, The Royal London Hospital, UK
May 2013
References
1. Gross RH. Leg length discrepancy: how much is too much? Orthopedics 1978;1:307-10.
2. Knutson GA. Anatomic and functional leg-length inequality: a review and recommendation for clinical decision-making. Part I, anatomic leg-length inequality: prevalence, magnitude, effects and clinical significance. Chiropr Osteopat 2005;13:11.
3. Kaufman KR, Miller LS, Sutherland DH. Gait asymmetry in patients with limb-length inequality. J Pediatr Orthop 1996;16:144-50.
4. Goel A, Loudon J, Nazare A, et al. Joint moments in minor limb length discrepancy: a pilot study. Am J Orthop 1997;26:852-56.
5. Soukka A, Alaranta H, Tallroth K, et al. Leg-length inequality in people of working age. The association between mild inequality and low-back pain is questionable. Spine 1991;16:429-31.
6. Moseley CF. Leg length discrepancy. Pediatric Orthopaedics. Lovell WW, Winter RB (eds). Philadelphia, Lippincott Williams & Wilkins, Fifth Edn, 2001:1107-08.
7. Stanitski DF. Limb length inequality: assessment and treatment options. J Am Acad Orthop Surg 1997;7:143-53.
