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Postural Adjustment In Experimental Leg Length Difference Evaluated By Means Of Thermal Infrared Imaging
Limb length discrepancy (LLD) is defined as a condition in which limbs are noticeably unequal. It is a common problem frequently found in the asymptomatic population. According to Woerman and Binder-Macleod, as many as 40–70% could exhibit a physiological discrepancy between the limbs’ length. Two pathological forms of LLD have been described: anatomical, i.e. associated with a shortening of bony structures, and functional, i.e. secondary to other musculoskeletal diseases which influence the biomechanics of lower limbs. LLD can be present in both acute and chronic forms. The acute form (forced LLD) may occur in subjects with lower limb fractures or Achilles tendon ruptures. Chronic LLD may be associated with musculoskeletal disorders, such as scoliosis, pelvic and sacral misalignments, osteoarthritis, etc.
Although LLD is mostly asymptomatic, it may cause either functional or structural dysfunction. The asymmetric load of body segments secondary to LLD has a stressful mechanical effect on different muscles; in particular it may cause a tonic contraction of back and lower limb muscles, such as quadratum lumborum, latissimus dorsi and gastrocnemius. The effects of LLD on the posture have been widely studied by means of gait analysis and balance platforms, while the activity of the single muscles involved, both at rest and during active contraction, has been investigated only by means of electromyography (EMG).
Figure 1. Total body IR imaging.
It has been proved that muscular activity induces heat transfer processes among muscles and superficial tissue layers, which in turn results in cutaneous temperature variations. Since the maintaining of the orthostatic posture is obtained through the complex activity of anti-gravitational muscles, subtle cutaneous temperature variations are expected with posture change. Modern high-resolution thermal infrared (IR) imaging is able to non-invasively record and precisely quantify cutaneous temperature variations. Therefore, high-resolution IR imaging may provide a quantitative evaluation of the cutaneous thermal effects possibly associated with posture change. The aim of this study was to test the capability of IR imaging to properly describe and quantitatively measure the cutaneous temperature short-term adaptation potentially associated with posture change under ‘forced LLD’ conditions. To achieve this goal, we used an experimental model of ‘forced LLD’, obtained by placing a 20 mm foot support under the dominant foot. IR imaging on 18 male healthy volunteers was performed in three experimental conditions of standing position: (T0) neutral posture; (T1) experimental LLD; (T2) neutral posture as in T0. Should this hypothesis be verified, IR imaging may be advantageously used to obtain additional functional information to short-term posture adaptation. Temperature variations were evaluated on the cutaneous projection of postural muscles bellies. Significant and specific temperature variations among conditions were ipsilaterally observed on the tibialis anterior, gastrocnemius, quadriceps and latissimus dorsi muscles. Specific patterns characterized the cutaneous temperature as a consequence of the muscle activity associated with the posture variation. IR imaging was able to highlight specific functional activations. The method is non-invasive and it can be repeated without any discomfort for the physiopathological and clinical evaluation of LLD patients.
Figure 2. IR imaging of lower limb temperature variation for a randomly chosen subject.
In conclusion, IR imaging is a technique which may be effectively added to the existing techniques, for the assessment of LLD and postural disorders, and even for clinical purposes. In particular, it can be useful in the evaluation of patients affected by hip fractures or submitted to lower limb surgery (casts). It can also be used for the follow-up and evaluation of different treatments, such as physical therapy and arch support.
Michele Abate, Luigi Di Carlo, Sandro Di Romualdo, et al. Postural adjustment in experimental leg length difference evaluated by means of thermal infrared imaging. Physiological Measurement. 31:35-45, 2010.