BACKGROUND
The Kineflex lumbar disc is a mechanical, unconstrained, re-centering disc prosthesis developed in South Africa. The first implantation took place in October 2002. We present a single-center, prospective, longitudinal study of the first 100 patients treated with the Kineflex lumbar disc. Our objective was to evaluate the insertion technique, clinical outcomes, and patient satisfaction at 2 years postimplantation in 100 consecutive patients with 132 (68 single- and 32 2-level) Kineflex lumbar disc replacements.

METHODS
We determined the exact central placement of all disc implants in the coronal and midsagittal planes. We measured clinical outcome with the Oswestry disability index (ODI), our own questionnaire, and the time needed to return to work. All patients received radiological and clinical follow-up assessments for 2 years after the index procedure.

RESULTS
Forty-three patients were female. The mean age of the patients at operation was 44.9 years (range, 23–63 years). Postoperative hospitalization averaged 2.8 days (range, 2 to 8 days). All patients who were employed before surgery returned to work 31 ± 16.8 days after the operation. Fifty-six percent of operated disc levels had intervertebral disc heights of less than 5 mm. A 2-year clinical outcome was available

for 98 of the 100 patients (58 excellent, 30 good, 7 fair, 3 poor). The ODI score improved from 47.8 ± 16.0 preoperatively to 14.2 ± 14.0 (P < .01) at 2 years. At 2 years, 95% of disc implants were radiologically in the ideal position. The insertion technique, with a released prosthetic mechanism for final placement, allowed ideal placement in the sagittal plane in 98% of discs. The radiographic placement accuracy achieved was equal in patients with preoperative intervertebral disc height below and above 5 mm.

CONCLUSIONS
Good short-term clinical results were achieved with the Kineflex disc in a heterogeneous patient group with a high number of patients with advanced disc degeneration, severe disc space narrowing, and lumbar flat-back deformity. In this cohort, accurate implant placement could be achieved in our first 100 patients.

CLINICAL RELEVANCE
This is the first report on the Kineflex mechanical lumbar disc prosthesis.

Key Words Kineflex disc, degenerative disc disease, lumbar disc prosthesis, insertion technique, unconstrained disc prosthesis, Oswestry disability index.
SAS Journal. Winter 2007; 1; 28–35.
DOI: SASJ-2006-0005-RR

From the Department of Orthopedic Surgery, University of the Witwatersrand, Johannesburg, South Africa (Hähnle and Sweet); Linksfield Park Clinic, Johannesburg (Hähnle and Weinberg); Department of Medicine, University of the Witwatersrand (Sliwa); Department of Mechanical Engineering, University of Potchefstrom, Potchefstrom; South Africa (de Villiers); and Southern Medical, Wapadrand, South Africa (de Villiers).

Ulrich R Hähnle, Ian R Weinberg, and Malan de Villiers are codevelopers of the Kineflex disc and shareholders in SpinalMotion, Mountain View, Calif.

Address correspondence and reprint requests to Ulrich Hähnle, PO Box 52040, Saxonwold 2132, Johannesburg, South Africa (email: hahnleu@mdh-africa.org).

This submission was received January 8, 2006, and accepted for publication February 26, 2007.

We thank Stephanie Hanekom and Aldori Gehring for their enthusiastic help with patient management and follow-up.

The institutional review board of the hospital where all the cases have been performed (Linksfield Park Clinic, Nedcare, Johannesburg, South Africa) approved this study, which was conducted in accordance with the ethical standards of the Declaration of Helsinki (2000).