Dr. Vishal Sarwahi (standing) presented findings from Paper 703 during the AAOS 2018 Annual Meeting in New Orleans.

AAOS Now

Published 5/1/2018
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Peter Pollack

Prone Radiographs May Save Fusion Levels for AIS Patients

Standing spines often impacted by gravity
Saving levels is one of the biggest concerns when performing spinal fusion to correct adult idiopathic scoliosis (AIS), according to Vishal Sarwahi, MD. “Fusion corrects the spine and prevents progression, but also reduces flexibility. Our goal is to fuse no more levels than necessary to correct the scoliosis and leave the patient balanced,” he added.

Dr. Sarwahi presented findings from Paper 703, “Touched Vertebra (TV) on Standing X-ray is a Good Predictor for Lowest Instrumented Vertebra; TV on Prone X-ray is Better,” during the AAOS 2018 Annual Meeting.

Curves change
“About seven or eight years ago or so, I began to note the effect of gravity on scoliotic curvature,” he said. “When the patient is standing, the curve often looks worse, and when the patient is prone, the curve and the Cobb angle generally become smaller.”

According to Dr. Sarwahi, previous studies have demonstrated good results utilizing touched vertebra as the lowest instrumented vertebra (LIV).

“In our experience, we find that TV moves proximally on supine or prone radiographs,” he explained. “We anticipated that using TV on prone radiographs may allow even shorter fusion when determining the LIV.”

Dr. Sarwahi and his colleagues prospectively collected data on 210 patients from the following three cohorts:

  • Group 1: prone radiographs used to determine LIV (n = 83)
  • Group II: standing anteroposterior radiographs used to determine LIV (n = 27)
  • Group III: nonsurgical scoliosis controls (Risser 4/5, Cobb < 30°) to determine “acceptable” end vertebra tilt and disk wedging (n = 100)

Patients were excluded if they required only thoracic fusion.

Fewer levels needed
In Group I (prone), the median preoperative Cobb angle was 53.75°, kyphosis was 32.2°, and coronal balance was 1.6 cm. The postoperative median Cobb angle was 12.9°, kyphosis was 37°, and coronal balance was 1.4 cm. Compared to patients in the control group, Group I patients had similar coronal balance, but significantly lower disk wedging and LIV tilt. Compared to patients in Group II (standing), those in Group I saved an average 1.05 (range: 0 to 3) levels.

In Group II (standing), the median preoperative Cobb angle was 54.4°, kyphosis was 26.8°, and coronal balance was 2.3 cm. The postoperative median Cobb angle was 19.2°, kyphosis was 24.6°, and coronal balance was 1.8 cm. The researchers estimate that Group II patients could have saved an average 2.24 (range: 1 to 4) levels, if prone radiographs had been used to determine LIV.

At two-year follow-up, Dr. Sarwahi and his colleagues found that patients in Group I maintained coronal balance and correction, despite shorter fusion levels, and LIV tilt and disk wedging were within acceptable levels, based on control participants.

“We were able to verify that prone radiographs may reduce fusion levels and produce acceptable outcomes for the patient,” said Dr. Sarwahi. “We found that the method is applicable to all types of idiopathic scoliosis, regardless of curve type and size, or whether the patient has single or multiple curves. There are times when the TV does not change from standing to prone. In that case, we still suggest fusing the TV rather than attempting to reduce levels.

“This is a minimum two-year follow-up we have presented,” he continued. “We keep collecting our data, and we hope to present a larger study in the future, with more patients, longer follow-up, and more surgeons.”

Dr. Sarwahi’s coauthors are Stephen Wendolowski, BS; Jesse M. Galina, BS; Beverly Thornhill, MD; and Terry D. Amaral, MD.

Peter Pollack is the senior staff writer for AAOS Now. He can be reached at ppollack@aaos.org.