Abstract
Introduction The main objective of this study is to describe the morphology and the mechanism of organization of the lumbar lordosis regarding the both position and shape of the pelvis. According to the orientation of the sacral plate, a classification of the lumbar lordosis is proposed. A symptomatic cohort of patient suffering of low back pain is analysed according to this new classification.
Methods 160 asymptomatic, young adult volunteers and 51 symptomatic low back patients were x-rayed in a standardized standing position. Analysis of the spine and pelvis was performed with the SagittalSpine® software. The pelvic parameters were: pelvic incidence, sacral slope, pelvic tilt. Thoracic kyphosis and lumbar lordosis were divided by the inflexion point. The lumbar lordosis was bounded by the sacral plate and the inflexion point. At the apex, the lumbar curve was divided in two tangent arcs of circle, quantified by an angle and a number of vertebrae. The upper one was geometrically equal to the sacral slope. Regarding the vertical line, a lordosis tilt angle was designed between the inflexion point and the anterior limit of the sacral end. The second group was operated with a disc prosthesis at the degenerated level.
Results The value of the lumbar lordosis was very variable. The best correlation was between lumbar lordosis and sacral slope, then between sacral slope and pelvic incidence in both groups. The upper arc of a circle remained constant, when the lower one changed with the sacral slope. There were good correlations of the sacral slope with the position of the apex, and with the lordosis tilt angle. When restoring the disc height at level L4L5 or L5S1 by a prosthesis insertion the local balance is modified but the global balance is unchanged. The prosthesis insertion at level L5S1 modifies significantly the balance at L4L5 which seems to be the most important level to restore a good lumbar lordosis.
Discussion Regarding the sacral slope, the lumbar lordosis can be classified in four types. When the sacral slope is low, the lumbar lordosis can be short and curved with a low apex and a backward tilt (type 1), either both long and flat with a higher position of apex (type 2). When the sacral slope increases, lumbar lordosis increases in angle and number of vertebrae with an upper apex, and it tilts progressively forward (type 3and 4). Depending of the both shape and position of the pelvis, the morphology of the lumbar lordosis could be the main mechanical cause of lumbar degenerative diseases. Total disc arthroplasty at one level L4L5 or L5S1 can significantly restore a good balance in the lumbar without modification on the global balance of the spine. When two levels are involved in the DDD process, the fusion at L5S1 and a prosthesis at L4L5 do not modify the global balance and the clinical results are similar to one level disc arthroplasty. This has to be underlined because all studies with two levels arthroplasties showed worst clinical outcomes than one level.
The abstracts were prepared by Assoc Prof Bruce McPhee. Correspondence should be addressed to him at the Division of Orthopaedics, The University of Queensland, Clinical Sciences Building, Royal Brisbane Hospital, Herston, Brisbane, 4029, Australia.
