A study published in Spine examines the radiographic and clinical evaluation of patients undergoing extreme lateral interbody fusion to examine the impact cage size and instrument type has on outcomes one year after surgery.
The researchers examined clinical and radiographic data for 140 consecutive patients who had surgery at 223 levels. The average follow-up was 15.5 months. The researchers found:
1. After one year, the patients reported these improvements:
• Disability improved by 44 percent
• Low back pain improved by 49 percent
• Leg pain improved by 48 percent
• Quality of life improved by 50 percent
2. The foraminal height improved from 15.7 mm to 21.2 mm after one year. The patients also reported the disc height going from 4.6 mm to 9.4 mm on average; discal lordosis improving from 4.0 to 8.1; and segmental lordosis improving from 10.7 to 13.7.
3. In 20 percent of the cases, the cage settled 1 mm or more immediately postoperatively. After one year, 62 percent of the cages settled 1 mm or more.
4. The cage settled more than 4 mm in 5 percent of the cages immediately after surgery. After one year, the cage settled more than 4mm in 24 percent of the cases.
5. There was an association between pedicle screw fixation and a higher rate of cage settling 1 mm or more when compared with lateral plating. However, the settling magnitude at the anterior inferior endplate was higher for lateral plating. For lateral plating it was 4.9 mm, compared to 3.5 mm.
6. The cage factors associated with the cage settling more than 4 mm after one year were:
• Taller cage height
• Narrower cage width
• Shorter cage length
7. In cases where immediate postoperative cage settling didn't occur, the risk of settling more than 4 mm one year after surgery was 6.8 times higher with narrow cages.
The researchers concluded, "Risk of cage settling after extreme lateral interbody fusion may be reduced with the use of wider cages to engage more central endplate bone, longer cages to span the ring apophysis and osteophytes, and avoid overdistraction of the intervertebral disc space with shorter cages."