BACKGROUND
Degenerative spondylolisthesis is associated with a significant segmental kyphosis at the level of the listhesis. We treated 7 disc spaces with Grade 2 listhesis and/or kyphosis of the slipped disc level with Kineflex disc replacement.

METHODS
Out of a single-center prospective registry, involving 310 lumbar disc replacement patients, 7 patients underwent a single-level Kineflex disc replacement at the level of a degenerative spondylolisthesis with either segmental kyphosis or a Grade 2 slip.

Preoperative and follow-up radiological parameters studied were: pelvic incidence, pelvic tilt, sacral slope, lumbar lordosis L1-S1, degree of segmental listhesis, segmental lordosis, and range of motion (ROM). Clinical outcome measures were Visual Analog Scale pain score (VAS), Oswestry Disability Index (ODI), and patient satisfaction.

RESULTS
Five replacements were performed at the L4-L5 level, and 2 were performed at a L3-4 level, above a pre-existing L4-S1 posterolateral fusion. Mean age was 50 (32–62) years. Average follow-up was 23.8 ± 13.1 months. Six of 7 patients considered their outcome as good or excellent. The mean VAS score decreased from 8.4 ± 1.9 to 2.7 ± 2.2 (P < .01). The ODI decreased from 45.2 ± 9.9 preoperatively to 19.7 ± 12.8 (P < .01).

There were increases in lumbar lordosis (from 47.4o ± 10.6 to 61.3o ± 8.0 (P < .03)), in segmental lordosis (from 0.17° ± 7.0° to 16.4° ± 2.0° (P < .03)), and in sacral slope (from 34.5° ± 4.8° to 40.7° ± 4.5° (P < .03)). There were decreases in pelvic tilt (from 22.6° ± 6.3° to 15.5° ± 5.9° (P < .05)), and degree of segmental listhesis (from 24.4% ± 7.7 to 3.7% ± 3.4 (P < .03)). Pelvic incidence and ROM did not change.

CONCLUSIONS
Disc replacement resulted in significant improvement in clinical outcome and excellent sagittal balance and slip correction. However, the influence of improved sagittal spinal alignment on clinical outcomes needs to be investigated in larger studies including a control group.

CLINICAL RELEVANCE
This study is the first focused on disc replacement in degenerative spondylolisthesis.

Key Words Spondylolisthesis, total disc replacement, radiological outcome, clinical outcome. SAS Journal. Spring 2008. 2:92–101. DOI: SASJ-2007-0125-NT

From the University of the Witwatersrand, Johannesburg, South Africa (Hahnle, Sliwa, Sweet, Candy); Linkfield Park Clinic, Johannesburg, South Africa (Hahnle, Weinberg); University of Potchefstroom, South Africa (de Villiers)

Ulrich R. Hähnle, Ian R. Weinberg, and Malan de Villiers are co-developers of the Kineflex Disc Prosthesis and shareholders in Spinal Motion (Mountainview, California).

Address correspondence to Ulrich R. Hähnle, University of the Witwatersrand, PO-Box 52040, Saxonwold 2132, Johannesburg, South Africa (e-mail: hahnleu@mdh-africa.org)

This manuscript was submitted December 16, 2007, and accepted for publication April 21, 2008.

Institutional Review Board approval was obtained from the University of the Witwatersrand Ethics Committee.