Acta chirurgiae orthopaedicae
et traumatologiae Čechoslovaca

Acta Chir Orthop Traumatol Cech. 2014; 81(6):392-398 | DOI: 10.55095/achot2014/054

Use of Artificial Bone in Lateral Interbody Fusion of the Lumbar Spine: A Prospective Radiographic StudyOriginal papers

L. Hrabálek^1,*, E. Čecháková², S. Buřval², M. Adamus³, K. Langová⁴, M. Vaverka¹

¹ Neurochirurgická klinika FN a LF UP v Olomouci

² Radiologická klinika FN a LF UP v Olomouci

³ Klinika anesteziologie a resuscitace FN a LF UP v Olomouci

⁴ Katedra biofyziky FN a LF UP v Olomouci

PURPOSE OF THE STUDY:
The aim of the study was to evaluate the extent of fusion using synthetic β-tricalcium phosphate as a bone substitute in extreme lateral interbody fusion (XLIF).

MATERIAL AND METHODS:
In this prospective study, patients undergoing XLIF with an Oracle cage filled with the artificial bone ChronOs Strip (Synthes, USA) were evaluated. The group consisted of 61 patients, 33 women and 28 men, with an average age of 50.9 years (range, 21 to 73 years). A total of 64 segments were operated on. Stand-alone interbody fusion was performed in 14 segments, lateral plate fixation in 19, transpedicular (TP) fixation before XLIF was carried out in 14 and TP fixation after XLIF in 17 segments. At one-year follow-up, dynamic X-rays to exclude instability, and CT images were obtained in order to evaluate the extent of bone fusion outside the implant (complete fusion, partial fusion, no fusion) and inside it (% of the bone fusion surface area). In addition, bone mineral density following fusion mass bone quality (expressed in Hounsfield units [HU]) was assessed inside the implant at the site of ChronOs Strip placement, using a region of interest (ROI) analysis.
For the evaluation of fusion bone quality inside the implant on CT scans with HU qualification, the authors propose the following scale:
1. No fusion (0-99 HU)
2. Uncertain fusion (100-190 HU)
3. Probable fusion (200-299 HU)
4. Reliable fusion (300 and more HU)
All results were statistically evaluated in relation to the gender, age, treated segment, surgical diagnosis, method of fixation, implant height and intervertebral space reduction at one-year follow-up.

RESULTS:
Fusion outside the implant was complete in 18 segments (28%) and partial in 27 (42%); in 19 segments (30%) it was not detected.
The bone fusion surface area inside the implant was 54.5% (0-100%) on the average. It was related to age and implant height; the surface area increased with increasing age and with increasing implant height.
Solid bone fusion inside the implant, as assessed on CT images using HU, was reliable in 36 segments (56%), probable in 11 (17%), uncertain in 10 (16%) and was not detected in seven segments (11%).
A significant relationship was found between the quality of bone fusion and the type of fixation. Of the segments treated by stand-alone XLIF, 29% showed no fusion while the segments managed by lateral plate fixation had 32% of them with probable fusion. Correlations were also found with the height of an implant (the higher the implant, the more reliable its fusion), with age (the higher age, the higher bone density) and with the spinal level (the lower level, the lower bone density).
In 45 (70%) segments, bone mineral density inside the implant was higher than the density of surrounding spongious bone. The average density inside the implant was 333.7 HU (14-1075) and that of the surrounding bone was 244.6 HU (66-500).
The intervertebral space was reduced by an average of 1.1 mm (0-6.2). All treated segments were found stable on dynamic X-rays.

DISCUSSION:
The use of a tricortical bone graft collected from the iliac crest is associated with pain at the harvest donor site in 2.8% to 39% of the cases, and this has been an impetus for many surgeons to use bone substitutes. In terms of the final outcome, i.e., solid bone fusion, the difference between the resorption rates of allogenous graft/artificial bone and ingrowth of autologous bone (from vertebral bodies) plays the most decisive role.

CONCLUSIONS:
The change of β-tricalcium phosphate to bone tissue is not always reliable and this can largely be expected when the resorption rate of ChronOs strip is low, i.e., at higher patient age and with a higher height of the implant.
The authors recommend increasing the probability of solid fusion in XLIF by using lateral plate fixation.
The method of assessing bone fusion by measuring bone density on CT scans proved to be useful because of its objectivity, and it can replace the current assessments based only on subjective judgement.

Keywords: lumbar spine, interbody fusion, arthrodesis, artificial bone

Published: December 1, 2014  Show citation