J Korean Soc Spine Surg.  2001 Sep;8(3):235-241. 10.4184/jkss.2001.8.3.235.

Evaluation of Posterolateral Fusion Mass at Lumbosacral Junction Using Standard AP and Ferguson Radiographs

• Lee HM
• Park MS
• Lee SH
• Kim KH
• Jahng JS
• Moon SH

• KMID: 2209740
• DOI: http://doi.org/10.4184/jkss.2001.8.3.235

Abstract

PURPOSE: To evaluate the reliance of standard AP radiograph and Ferguson radiograph in assessment of instrumented lumbosacral fusion mass with interobserver and intraobserver reproducibilities.
MATERIALS AND METHODS
Postoperative standard AP radiograph and Ferguson radiograph were used to evaluate the fusion mass at the lumbosacral region of 44 consecutive patients who underwent posterolateral L4-S1 or L5-S1 instrumented fusion with pedicle screws & autogenous iliac bone graft. Ferguson radiograph was performed with the x-ray beam oriented toward the cranial portion at 40degree relative to the x-ray table. All observations were performed independently by three observers, blinded to the history, diagnosis, and patient identity. The fusion mass was graded as solid, pseudarthrosis or questionable. A second review was repeated at 2 weeks after index review. Interobserver and intraobserver reproducibilities were analyzed with Fleiss'method.
RESULTS
Ferguson radiographs were more reliable than standard AP radiographs in detecting the fusion mass. Kappa values with the interobserver reproducibility were higher in Ferguson radiographs than in the standard AP radiographs. Kappa values with the intraobserver reproducibility of all three observers were higher in Ferguson radiographs than in the standard AP radiographs. The questionable fusion masses in the standard AP radiographs were revealed solid or pseudarthrosis in Ferguson radiographs in 67%.
CONCLUSIONS
Ferguson radiograph is a more reliable method than standard AP radiograph in evaluating instrumented posterolateral fusion mass in lumbosacral region.

Keyword

Lumbosacral region; Posterolateral fusion; Radiologic evaluation; Ferguson radiograph

MeSH Terms

Diagnosis
Humans
Lumbosacral Region
Pseudarthrosis
Transplants

Figure

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  Fig. 1. A 40-year-old woman with spinal stenosis from L4 to S1 not responding to conservative treatment underwent decompression and bilateral instrumented posterolateral fusion from L4 to sacrum 12 months ago. This anteroposterior view(A) illustrates bilateral pseudarthrosis recorded by all observers. Ferguson view(B) illustrates bilateral posterolateral fusion mass recorded by all observers.

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  Fig. 2-A. The cortical bones of the transverse processes and sacral ala can be misdiagnosed as the cracks(pseudarthroses)(white arrows). The heads of pedicle screws tend to obscure the fusion mass between the L5 transverse processes and sacral ala. Fig. 2-B. The use of the Ferguson view eliminates the superimposition of the L5 transverse process on the posterior part of the superior ala of the sacrum, widens the L5-S1 intertransverse space, and enhances direct visualization. The heads of pedicle screws are located at the transverse processes and thus the fusion mass between the L5 transverse processes and sacral ala are well visualized.

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