Leg Length Inequality, Scoliosis
And Low Back Pain
University Teacher in Radiology
Via Savonarola 175 - 35137 Padova - Italy
The present work aims to analyse the biomechanics of the spine and pelvis in patients with leg length inequality (LLI), using diagnostic imaging.
MATERIALS AND METHODS
Over the last 30 years we have examined more than 10,000 young and adult patients. All were submitted to a teleradiographic examination of the spine and pelvis including the femoral heads, in the standing position and in anteroposterior projection. Additionally, where clinically indicated, adult patients were submitted to in-depth examinations, often including various imaging modalities (CT, MR etc.).
During growth, LLI, even of the order of just a few mm, can cause pelvic inclination and consequently lateral deviation of the spine and head. The postural response, aimed at re-establishing equilibrium, is a compensatory counterdeviation of the spine. If the counterdeviation starts at L3 (Fig 1 A) or at a more cranial level, there will be a gradual curve, convex toward the shorter limb, termed Type A; if the counterdeviation starts at L4 (Fig 1 B1) or L5 (Fig 1 B2), there will be a brief angular lumbosacral curve, likewise convex to the shorter limb but always followed by a second curve in the opposite direction, termed Type B.
Curves that are initially of mild degree, non-structural and mobile may subsequently diminish, remain stationary or progress and become structural. The course of scoliosis is affected by the load distribution above all at the lumbosacral level. If it is asymmetric, the overload may produce: 1) wedging of the intervertebral disc L4-L5
and/or L5-S1; 2) wedging of the vertebral body L4 and/or L5; 3) torsion of the ilium with consequent asymmetric drop of the sacral base so that a line passing across the upper border of the sacrum is no longer parallel to the tangential line across the femoral heads but slopes downward the side of the greater load (Figs 2 A1, A3 and 3 B1, B2). These changes demonstrate that the load distribution at the lumbosacral level in Type A curves may be greater on the side of the shorter limb (Fig 2 A1), symmetric (Fig 2 A2), or greater on the side of the longer limb (Fig 2 A3), whereas in Type B curves it is always greater on the side of the longer limb (Fig 3 B1, B2). By modifying the orientation of the resting surface of the basal vertebrae and the sacrum, the
FIGURE 1 – Type A and Type B curves due to shorter right limb (R): A) Type A curve with counterdeviation starting at L3; B1) Type B curve with counterdeviation starting at L4; B2) Type B curve with counterdeviation starting at L5.
changes mentioned above cause spine deviation in the frontal plane on the side of the greater load. There will be either a progression or a reduction of the curve according to whether the lateral deviation due to asymmetric loading sets up an acting synergism or a compensation. Therefore, in single curve deviations we will have: either progression of the Type A curves with overload on the side of the shorter limb, since the lateral deviation due to asymmetric loading is added to the scoliotic deviation due to LLI (Fig 2 A), or reduction or disappearance of the Type A curves with overload on the side of the longer limb because of the compensation between the two deviations (Fig 2 A3). If, however, the load distribution is symmetric, in the absence of changes at the lunbosacral level, the curve will usually be stationary (Fig 2 A2). Nevertheless, it is not always possible to predict the course of scoliosis because of the shifting of the load due mostly to the appearance of further compensatory curves. In patients with LLI greater than 2 cm, there exist only Type A curves. In such cases, since at the lumbosacral level the load is usually greater on the side of the longer limb, the curve is reduced. This means that often the greater the inequality, the lesser the scoliosis and vice versa.
FIGURE 2 – Type A curves due to shorter right limb (R). The radiographic findings of the intervertebral spaces L4-L5-S1 and of the basal vertebrae and the orientation of the sacral base show that the load distribution at the lumbosacral level, in type A curves, may be: A1) greater on the side of the shorter limb (curve subject to progression); A2) symmetric (curve usually stationary and mild); or A3) greater on the side of the longer limb (curve subject to reduction or disappearance).
In the treatment of scoliosis, the compensation of LLI, using a lift under the heel of the shorter limb is always useful and effective in Type A curves with overload on the side of the shorter limb, but may be counterproductive in Type B curves or in cases of multiple curve deviations.
The fact that anomalous development of limb length occurs in more than one family member would tend to indicate genetic transmission of the condition.
The overwhelming majority of patients examined for low back pain of uncertain origin had LLI with asymmetric load distribution. Furthermore, the overload at the lumbosacral level may produce muscular stress, premature degenerative diseases of the disc-somatic and the interapophyseal joints L4-L5 and/or L5-S1, as well as dysfunction (sometimes subluxation) of the sacroiliac joint, which might give rise to low pelvic pain. The pain, with or without sciatica, if non caused by herniary pathology, almost always affects the side of the greater load.
In conclusion, our findings suggest that LLI is one of the primary cause of scoliosis, apparently idiopathic, and low back pain of mechanical origin.
FIGURE 3 – Type B curves due to shorter right limb (R) with counterdeviation starting at L4 (B1) and L5 (B2), respectively. The wedging of the intervertebral spaces L4-L5-S1, the axial asymmetry of the vertebral body L5 and the asymmetric drop of the sacral base following torsion of the left ilium show that the load distribution at the lumbosacral level, in type B curves, is exclusively greater on the side of the longer limb.
Manganiello A: Lower extremity dysmetria, scoliosis, low back pain and spondylolysis. 1. In Sevastik JA, Diab KM (Eds.): Research into Spinal Deformities 1. Amsterdam. IOS Press, 1997, pp 111-113.
Manganiello A: Lower limb length inequality and scoliosis. In Burwell RG, Dangerfield PH, Lowe TG, and Margulies JY (Eds); SPINE: State of the Art Reviews on Etiology of Idiopathic Scoliosis. Philadelphia, Hanley & Belfus, Inc, Vol. 14, No. 2, May 2000, pp. 423-429