A Multi-center Clinical Study of Posterior Lumbar Interbody Fusion with the Expandable Stand-alone Cage (Tyche(R) Cage) for Degenerative Lumbar Spinal Disorders

Abstract

Objective: This multi-center clinical study was designed to determine the long-term results of patients who received a one-level posterior lumbar interbody fusion with expandable cage (Tyche(R) cage) for degenerative spinal diseases during the same period in each hospital.

Methods: Fifty-seven patients with low back pain who had a one-level posterior lumbar interbody fusion using a newly designed expandable cage were enrolled in this study at five centers from June 2003 to December 2004 and followed up for 24 months. Pain improvement was checked with a Visual Analogue Scale (VAS) and their disability was evaluated with the Oswestry Disability Index. Radiographs were obtained before and after surgery. At the final follow-up, dynamic stability, quality of bone fusion, interveretebral disc height, and lumbar lordosis were assessed. In some cases, a lumbar computed tomography scan was also obtained.

Results: The mean VAS score of back pain was improved from 6.44 points preoperatively to 0.44 at the final visit and the score of sciatica was reduced from 4.84 to 0.26. Also, the Oswestry Disability Index was improved from 32.62 points preoperatively to 18.25 at the final visit. The fusion rate was 92.5%. Intervertebral disc height, recorded as 9.94+/-2.69 mm before surgery was increased to 12.23+/-3.31 mm at postoperative 1 month and was stabilized at 11.43+/-2.23 mm on final visit. The segmental angle of lordosis was changed significantly from 3.54+/-3.70 degrees before surgery to 6.37+/-3.97 degrees by 24 months postoperative, and total lumbar lordosis was 20.37+/-11.30 degrees preoperatively and 24.71+/-11.70 degrees at 24 months postoperative.

Conclusion: There have been no special complications regarding the expandable cage during the follow-up period and the results of this study demonstrates a high fusion rate and clinical success.

Keywords: Degeneration; Expandable cage; Interbody fusion; Lumbar spine.

Fig. 1

The lateral view of the Tyche® lumbar expandable cage (Kyungwon Medical Co Ltd., Seoul, Korea before (left) and after (right) expansion. It consists of titanium and anterior part of the cage and can be expanded about 4 degrees with the cap inserted into the cage anteriorly.

Fig. 2

Lumbar spine X-ray, lateral view. The intervertebral height (A) is calculated by dividing the sum of anterior, middle, and posterior intervertebral disc heights by 3 (a+b+c/3). The angle between the superior and inferior endplates is the degree of segmental lordosis (B) at the site of surgery and total lordosis (C) is measured according to the Cobb method in which the angle appearing in each segment is based on the L1 superior endplate and the S1 superior endplate for lumbar lordosis.

Fig. 3

Lumbar spine X-ray, lateral view of pre-operative (A) and post operative (B). The inter-vertebral disc height is collapsed at pre-operative and rescued by expandable cage insertion to the level.

Fig. 4

The visual analog scale results in back pain and leg pain at post operative follow-up periods. Both the back pain and sciatica are reduced post operatively.

Fig. 5

The results of the Oswestry Disability Index score. The 'N' means the number of patients followed up. The score was decreased to the post operative six-month period, but the day after, it was increased. This may be due to the reduced number of patients being followed up.

Fig. 6

The post operative four-month follow-up computed tomography scan image of the level of cage insertion. The bony material inside the cage is seen.