Sagittal balance parameters influence indications for lumbar disc arthroplasty or ALIF

Abstract

Chronic lower back pain is a potentially incapacitating condition associated with disc degeneration. Although therapy is primarily pharmaceutical, surgery comprising arthrodesis constitutes an alternative. Anterior intersomatic lumbar arthrodesis (ALIF, anterior interbody lumbar fusion) is the reference approach, although total disc arthroplasty may also be undertaken. Analysis of pelvic and spinal parameters provides the best indication of sagittal balance.

Materials and methods: This was a prospective study in a continuous series of 99 patients presenting chronic lower back pain due to disc disease. Pelvic incidence, sacral slope, pelvic tilt, spino-sacral angle (SSA) and the four back types in the Roussouly classification were studied in radiographs of the whole spine under load using an EOS imaging system.

Results: The pre-operative SSA value for the study population was 126.09° ± 8.45° and the mean spine tilt angle was 90° compared with 95° in healthy subjects. Following surgery, the SSA was considerably increased in the discal arthroplasty, resulting in a significantly more balanced spinal position. In the group of patients undergoing arthrodesis using the ALIF technique, no such significant improvement was found despite the use of a lordosis cage. We showed that in cases of low pelvic incidence, it was necessary to maintain a Roussouly type 1 or 2 back without increasing lordosis. The results demonstrated the value of L4-L5 disc prostheses in these subjects. L5-S1 arthrodesis seemed a more suitable approach for treating patients with elevated sacral slope (back type 3 or 4). This new type of analysis of sagittal parameters should be performed prior to all surgical procedures involving lumbar prostheses.

Figures

Fig. 1

Digitalized image of the analysis of a case analyzed with Optispine® software (SMAIO. Lyon, France), with the different curvatures of the spine shape based on Berthonnaud parameters

Fig. 2

Spino-sacral angle: angle between a line delimited by the central point of C7 vertebral body, and central point of S1 sacral plateau and a second line, which is the sacral slope line

Fig. 3

Sagittal view of a TYPE 4 spine according to Roussouly classification preoperatively (a) and postoperatively (b) after an ALIF procédure at L4/L5 level

Fig. 4

Type 3 spine according to Roussouly’s classification, a preoperatively there is lost of lumbar lordosis, and b postoperatively after total disc arthroplasty at level L4/L5 there is an increase of the segmental lordosis without modification of the global lumbar lordosis. Preop SS is 46.7° and postoperatively due to the restoration of L4/L5 disc height the spine recovered its original shape corresponding to a type 3. SSA preop: 124°, SSA postop: 134°