MRI evaluation of fusion mass incorporation after anterior cervical bony fusions: preliminary findings

Can Pixel Value Ratio be Used in the Assessment of Ceramic Bone Substitute Incorporation? Observations from a Pilot Study

Background

Assessment of bone graft substitute incorporation is critical in the clinical decision making process and requires special investigations. We examined if the pixel value ratio (PVR) obtained in routine follow-up digital radiographs could be used for such assessment.

Material/Methods

Radiographic images were acquired using either computed radiography or flat panel digital radiography systems. The PVR from radiographs of thirty children with ceramic bone substitute grafting were analyzed using the software from the picture archival and communication system (PACS) workstation. Graft incorporation was also assessed using the van Hemert scale. Three independent observers (A, B, C) measured PVRs at two different time points during the first and the last follow-up visits. PVR was compared with the van Hemert scale scores and analyzed using Spearman's rank correlation.

Results

The mean intra-observer reliability was 0.8996, and inter-observer reliabilities were 0.69 (A vs. C), 0.78 (A vs. B), and 0.85 (B vs. C) for the first follow-up visit and 0.74 (A vs. C), 0.82 (A vs. B), and 0.70 (B vs. C) for the last follow-up measurements. Spearman's correlation showed a strong negative association between PVR values and van Hemert scale scores, as the healing process advanced on serial measurements at each follow-up (r=-0.94, n=60, z=-7.24, p≤0.0001). The reliability of the PVR measurements was assessed using an aluminum step wedge and ceramic graft.

Conclusions

PVR is potentially a reliable indicator of bone graft incorporation and can aid in clinical decision making provided standard radiographic techniques are used.

Radiological Determination of Postoperative Cervical Fusion: A Systematic Review

STUDY DESIGN

Systematic review.

OBJECTIVE

To determine best criteria for radiological determination of postoperative subaxial cervical fusion to be applied to current clinical practice and ongoing future research assessing fusion to standardize assessment and improve comparability.

SUMMARY OF BACKGROUND DATA

Despite availability of multiple imaging modalities and criteria, there remains no method of determining cervical fusion with absolute certainty, nor clear consensus on specific criteria to be applied.

METHODS

A systematic search in MEDLINE/Cochrane Collaboration Library (through March 2014). Included studies assessed C2 to C7 via anterior or posterior approach, at 12 weeks or more postoperative, with any graft or implant. Overall body of evidence with respect to 6 posited key questions was determined using Grading of Recommendations Assessment, Development and Evaluation and Agency for Healthcare Research and Quality precepts.

RESULTS

Of plain radiographical modalities, there is moderate evidence that the interspinous process motion method (<1 mm) is more accurate than the Cobb angle method for assessing anterior cervical fusion. Of the advanced imaging modalities, there is moderate evidence that computed tomography (CT) is more accurate and reliable than magnetic resonance imaging in assessing anterior cervical fusion. There is insufficient evidence regarding the optimal modality and criteria for assessing posterior cervical fusions and insufficient evidence to support a single time point after surgery as being optimal for determining fusion, although some evidence suggest that reliability of radiography and CT improves with increasing time postoperatively.

CONCLUSION

We recommend using less than 1-mm motion as the initial modality for determining anterior cervical arthrodesis for both clinical and research applications. If further imaging is needed because of indeterminate radiographical evaluation, we recommend CT, which has relatively high accuracy and reliability, but due to greater radiation exposure and cost, it is not routinely suggested. We recommend that plain radiographs also be the initial method of determining posterior cervical fusion but suggest a lower threshold for obtaining CT scans because dynamic radiographs may not be as useful if spinous processes have been removed by laminectomy.

LEVEL OF EVIDENCE

1.

Radiographic assessment of cervical subaxial fusion

Object

The objective of this systematic review was to use evidence-based medicine to identify the best methodology for radiographic assessment of cervical subaxial fusion.

Methods

The National Library of Medicine and Cochrane Database were queried using MeSH headings and keywords relevant to cervical fusion. Abstracts were reviewed and studies meeting inclusion criteria were selected. The guidelines group assembled an evidentiary table summarizing the quality of evidence (Classes I–III). Disagreements regarding the level of evidence were resolved through an expert consensus conference. The group formulated recommendations that contained the degree of strength based on the Scottish Intercollegiate Guidelines network. Validation was done through peer review by the Joint Guidelines Committee of the American Association of Neurological Surgeons/Congress of Neurological Surgeons.

Results

Pseudarthrosis is best assessed through the absence of motion detected between the spinous processes on dynamic radiographs (Class II). The measurement of interspinous distance on dynamic radiographs of ≥ 2 mm is a more reliable indicator for pseudarthrosis than angular motion of 2° based on Cobb angle measurements (Class II). Similarly, it is also understood that the pseudarthrosis rate will increase as the threshold for allowable motion on dynamic radiographs decreases. The combination of interspinous distance measurements and identification of bone trabeculation is unreliable when performed by the treating surgeon (Class II). Identification of bone trabeculation on static radiographs should be considered a less reliable indicator of cervical arthrodesis than dynamic films (Class III).

Conclusions

Consideration should be given to dynamic radiographs and interspinous distance when assessing for pseudarthrosis.

The use of diagnostic imaging to assess spinal arthrodesis

Despite advances in surgical techniques and internal fixation devices, pseudarthrosis remains a significant factor in the clinical failure of attempted fusions in the cervical, thoracic, and lumbar spine. This article reviews the use of diagnostic imaging in the assessment of spinal fusion, with a focus on the accuracy of different imaging modalities based on surgical exploration. A cost-effective strategy for the radiographic follow-up of patients after spinal fusion surgery also is presented.

Biocompatible osteoconductive polymer versus iliac graft. A prospective comparative study for the evaluation of fusion pattern after anterior cervical discectomy

STUDY DESIGN

One hundred fifteen patients having symptomatic cervical disc disease were recruited prospectively for this study. They were allocated randomly for either autologous iliac bone graft or biocompatible osteoconductive polymer implants. Both groups were compared clinically and radiologically.

OBJECTIVES

Complications, long-term clinical and radiologic outcome, and hospital stay were compared to determine if biocompatible osteoconductive polymer was an improvement on iliac bone graft in terms of reduced donor site pain and shortened hospital stay.

SUMMARY OF BACKGROUND DATA

Donor site morbidity is a significant problem in anterior cervical fusion. Hospital stay is another factor in the recent era of cost consciousness. Biocompatible osteoconductive polymer has been used in many centers as a biodegradable implant to circumvent these problems.

METHODS

Smith-Robinson technique was used in 74 patients, and Cloward technique was used in 41 patients. Sixty-five patients had biocompatible osteoconductive polymer implants, and 50 patients had iliac bone graft. Patients were followed-up routinely in the outpatient clinic where pain visual analogue scale and Odom's criteria were used for outcome evaluation. Plain radiography, computed tomography scan, and magnetic resonance imaging were used for radiologic evaluation.

RESULTS

The mean hospital stay was 4.8 days for those with iliac bone graft and 4.7 days for those with biocompatible osteoconductive polymer. Clinical outcome was identical in both groups. The incidence of partial graft protrusion and postoperative intersegmental kyphosis was statistically higher with iliac bone graft (P = 0.018 and P = 0.02, respectively). "Sclerosis" started to form around biocompatible osteoconductive polymer like a "halo" at 2 months. It increased with time, and sometimes was associated with new osteophyte formation; however, there was no biocompatible osteoconductive polymer incorporation or biodegradation

CONCLUSIONS

Biocompatible osteoconductive polymer acts as a good "spacer" that reduces graft collapse and intersegmental kyphosis. However, it did not show any radiologic evidence of biodegradation or incorporation during the follow-up period of 24 months.