Functional Evaluation of the Operated Lumbar Spine with Axial Loaded Computed Tomography (AL-CT)

This study evaluated Axial Loaded-CT (AL-CT) of an operated spine (with and without instrumentation) to assess the limits and possibilities of this diagnostic imaging procedure.

We considered 100 patients divided into two groups: Group 1: 89 patients, evaluated only post-operatively; Group 2: 15 patients who underwent AL-CT before and after lumbar spine instrumentation with different devices, for the purpose of correcting spinal instability. Some patients came at first observation after previous conventional surgery and were enrolled in both groups.

A satisfactory evaluation of the spine was attained in all the patients, even in the presence of beam-hardening artifacts associated with stainless steel posterior fixation.

The evaluation of the conventionally operated spine disclosed the residual stability of the studied segments and allowed a comparison of any abnormal intersegmental movement. The comparison between pre- and post-surgical scans in the instrumented spines enabled the evaluation of: the stability of the surgically stabilized segment; the “internal” stability of the implant; the relative stability of the adjacent spinal levels; the degree of correction of the presurgical instability/deformity.

AL-CT seems to be able to image the operated spine clearly, even when instrumented, showing even minimal residual abnormal movements at and adjacent to the operated level(s). The functional aspects of the examination (axial loading) allowed a good evaluation of the post-surgical load transmission patterns even in the presence of large stainless steel implants.

Biomechanics of the Spine

Biomechanics of the spine is a vast area of research that has generated numerous studiesin recent years on the part of doctors (mainly orthopaedic surgeons), bioengineers and physicists. This paper is a short introduction to some of the topics of major interest in spine biomechanics.

The first topic is the development of the spine with a “mechanical” explanation of the physiological curvatures. As the spine is a multiarticular complex structure, understanding the mechanism responsible for its dynamics requires in-depth knowledge of the spine's basic components: the vertebrae and their architecture, the intervertebral joints, the ligaments and muscles. A short morphofunctional description of each of these anatomical parts is given mentioning their biomechanical features.

Of particular interest, in relation to spinal trauma, is the architecture of the cancellous bone of the vertebrae responsible for most resistance to compressive weight loads. This specific characteristic is gradually lost over the years either due to disease or to a progressive resorption of the horizontal lamellae and thinning of the vertical columns typical of osteoporosis.

Numerous studies have been conducted in vivo and in vitro to shed light on the mechanisms leading to particular traumatic lesions or degenerative arthrosis. These have given rise to various theories formulated to account for the distribution of loads and strength in the elements making up the functional spinal unit. These theories include the old “two vertical columns” theory, subsequently replaced by the “three columns theory”, and the latest “four columns” model which divides the spine longitudinally depending on carrying strength. The latest theory was formulated in the wake of in vivo CT studies using an axial loading device which allows axial loads to be applied even though patients are in a supine position.

A short mention is made of the possible biomechanical applications of neuroradiological techniques, namely cine-MR scans, which allow detailed study of the ligaments, muscles and disc, especially the cervical spine under dynamic conditions.

Lastly, the controversial concept of spinal stability and instability is discussed. Further studies are necessary to establish appropriate criteria for treatment of traumatic or degenerative lesions since an impairment to spine statics can result in permanent neurological damage.

Utilizzo dell'Axial Loader nello studio della colonna lobosacrale

Lo scopo dello studio è di valutare le modificazioni indotte dall'applicazione di carico assiale durante I'esame RM della colonna lombosacrale. Sono stati sottoposti all'indagine 75 pazienti consecutivi con varie patologie degenerative del rachide lombosacrale, anche già trattati chirurgicamente. I risultati hanno dimostrato varie modificazioni dopo applicazione del carico, in particolare la osservazione più frequente è stata l'aumento della stenosi. In un caso l'esame ottenuto dopo applicazione di carico ha modificato radicalmente il trattamento ponendo indicazione all'intervento chirurgico. Dalle osservazioni preliminari riteniamo che le modificazioni indotte dal carico assiale siano interessanti da valutare con RM; sarà comunque indispensabile uno studio su una popolazione omogenea per diagnosi clinica per verificarne la effettiva utilità.

Spinal pain

The spinal pain, and expecially the low back pain (LBP), represents the second cause for a medical consultation in primary care setting and a leading cause of disability worldwide [1]. LBP is more often idiopathic. It has as most frequent cause the internal disc disruption (IDD) and is referred to as discogenic pain. IDD refers to annular fissures, disc collapse and mechanical failure, with no significant modification of external disc shape, with or without endplates changes. IDD is described as a separate clinical entity in respect to disc herniation, segmental instability and degenerative disc desease (DDD). The radicular pain has as most frequent causes a disc herniation and a canal stenosis. Both discogenic and radicular pain also have either a mechanical and an inflammatory genesis. For to be richly innervated, facet joints can be a direct source of pain, while for their degenerative changes cause compression of nerve roots in lateral recesses and in the neural foramina. Degenerative instability is a common and often misdiagnosed cause of axial and radicular pain, being also a frequent indication for surgery. Acute pain tends to extinguish along with its cause, but the setting of complex processes of peripheral and central sensitization may influence its evolution in chronic pain, much more difficult to treat. The clinical assessment of pain source can be a challenge because of the complex anatomy and function of the spine; the advanced imaging methods are often not sufficient for a definitive diagnosis because similar findings could be present in either asymptomatic and symptomatic subjects: a clinical correlation is always mandatory and the therapy cannot rely uniquely upon any imaging abnormalities. Purpose of this review is to address the current concepts on the pathophysiology of discogenic, radicular, facet and dysfunctional pain, focusing on the role of the imaging in the diagnostic setting, to potentially address a correct approach also to minimally invasive interventional techniques. Special attention will be done to the discogenic pain, actually considered as the most frequent cause of chronic low back pain.

Axial loaded imaging of the lumbar spine 18 years later. Is it still a valuable examination?

This paper reviews experience with 12100 Axial Loader (AL) studies of the lumbar spine both in CT and in MRI 18 years after the development of axial loaded CT and MRI. The Axial Loader device is described together with the CT and MR acquisitions. Disc, intersomatic and articular facet changes are described with a breakdown of the classification of abnormalities as elementary or complex dynamic modifications.

Neuroradiology of spine degenerative diseases

Degenerative disease of the spine is one of the most common clinical entities and affects the intervertebral discs, including opposing vertebral endplates, the intervertebral posterior joints and the ligaments. The most severe primary spinal degenerative changes are found in the lower cervical and lumbar spine regions. The spine contains three different types of joints, each of which presents its own pattern of degenerative disease: (i) cartilaginous joints, represented by the intervertebral disc or, more specifically, the functional unit defined as the 'vertebro-disc connection'; (ii) synovial joints, represented by the posterior intervertebral joints, sacro-iliac and costovertebral joints; (iii) fibrous joints, mainly found in the principal ligaments such as the posterior longitudinal ligament and the yellow ligaments. With regard to radicular pain, root compression alone does not fully account for root pain following disc-root conflict, but it is, nevertheless, considered to be the main cause of pain. We will try to explain that the origin of pain is multi-factorial and that inflammation probably predominates over merely mechanical mechanisms. To conclude, we will consider whether vertebral arthrosis can be construed as the body's decision to favour the spine's static function over its dynamic role when joint 'hypermobility' linked to chronic load in old age could cause severe structural damage to the bony vertebral structures. This hypothesis should also embrace a further concept: ageing of the spine is not merelychronological. Themostaccurate interpretation tha tcan account for similar degenerative phenomena encountered in the young is that of abnormal static and dynamic loading stress.