Orthopedics

GOTHENBURG, Sweden — Japanese researchers found that bilateral pedicle screw fixation lead to greater reductions in back pain, lower extremity pain and numbness in patients with degenerative spondylolisthesis than treatment with unilateral screws.

Yasuchika Aoki, MD, and colleagues concluded from their prospective, randomized controlled study that unilateral pedicle screw fixation procedures were to bilateral pedicle screw fixation for degenerative spondylolisthesis treated via transforaminal lumbar interbody fusion (TLIF).

“TLIF with unilateral pedicle screws is less invasive and cost effective to perform, Aoki of Toho University Sakura Medical Center in Sakura, Japan, and Chiba Rosai Hospital in Chiba, Japan, said during his presentation at the International Society for the Study of the Lumbar Spine Annual Meeting 2011. “However, it resulted in less improvement of patient symptoms.”

He told Orthopedics Today, “The unilateral fixation shows a lower fusion rate (87.5%) than the bilateral fixation (95.7%), with no significant difference.”

Level 1 study

Aoki and his colleagues sought to determine whether unilateral fixation was as effective as bilateral fixation for the treatment of adult degenerative spondylolisthesis. They randomized 50 patients to undergo one-level TLIF using either unilateral or bilateral pedicle screw fixation and followed them for 2 years. Surgeons placed a single unilateral screw in the unilateral cases. In the bilateral cases, Aoki said, surgeons used pedicle screws on the bilateral side and implanted two interbody fusion cages.

He and his team obtained more than 2-years follow-up for 94% of the cohort — 47 patients — with evaluation parameters consisting of the 10-point visual analog scale (VAS) for back and lower extremity pain, and lower extremity numbness and improvement in back disability based on the lumbar Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ) results.

Patient demographics were similar at the outset of the study.

Surgical time, clinical outcomes

Discussing the findings, Aoki said, “Our results showed that mean surgical time was significantly shorter and blood loss was significantly lower in the unilateral group, suggesting that unilateral pedicle screw fixation is less invasive. Overall, subjective surgical outcomes showed no significant differences between the two groups.”

During the discussion period, Aoki noted some bilateral cases in the series took as much as 60 minutes longer to complete than the unilateral cases, but eventually the difference in surgical time between the two types of procedures was reduced to 30 minutes or 40 minutes.

Patients in both groups attained the same level of walking ability postoperatively based on the JOABPEQ results, he said.

“At the final follow-up, VAS scores were significantly lower for the bilateral group” than the unilateral group, Aoki said.

Aoki noted one limitation of the study is the number of interbody fusion cages used, which may have influenced the clinical outcomes and could have affected postoperative spinal stability.

“TLIF is generally recommended, but we just have to pay attention. We may choose to unilaterally fuse patients, but we would like to recommend [avoiding] using single pedicle screws and to be aware of the limitations of unilateral pedicle screw fixation,” he said. – by Susan M. Rapp

Reference:

• Aoki Y, Yamagata M, Ikeda Y, et al. A prospective randomized controlled study comparing unilateral and bilateral pedicle screw fixation in transforaminal lumbar interbody fusions for degenerative spondylolisthesis. Paper #P58. Presented at the International Society for the Study of the Lumbar Spine Annual Meeting 2011. June 14-18. Gothenburg, Sweden.

• Yasuchika Aoki, MD, can be reached in the Department of Orthopaedic Surgery, Toho University, Sakura Medical Center, 564-1 Shimoshizu, Sakura-city, Chiba, 285-8741, Japan; email: yasuaoki35@fc4.so-net.ne.jp.
• Disclosure: Aoki has no relevant financial disclosures.

The strength of this study is that it was a prospective randomized control trial. There was no information on the average age in the two groups, no male to female ratio, and the degree of slip. Presumably these were similar in the two groups. The data showed bilateral pedicle screw fixation resulted in more improvement of back pain, lower extremity pain and lower extremity numbness. However, there was no mention of the bony union rate in the two groups. Presence or absence of union may be a cause for the difference in back pain relief, and possibly relief of lower extremity symptoms. Results of a longer follow-up period would be very useful.

— John C.Y. Leong, FRCS, MCAS
Honorary Professor, Department of Orthopaedics & Traumatology, The University of Hong Kong
President, The Open University of Hong Kong
Orthopaedics Today Europe Editorial Board
Disclosure: Leong has no relevant financial disclosures.