A Prospective Study of Calcium Sulfate Pellets as Bone Graft Extenders in Lumbar Posterolateral Arthrodesis

Bikash Bose, MD

Introduction:

Bone graft extenders have been used extensively in posterolateral lumbar arthrodesis (PLLA). Various forms of allograft have been used as graft extenders. However, their use has been complicated by various reports in the literature concerning antigenicity, increased pseudoarthrosis rate, availability and risks of disease transmission. Of the newest biomaterials available, Calcium Sulfate pellets have been shown to be safe for neural elements and effective in PLLA in animal models. This study was undertaken to evaluate the role of Calcium Sulfate pellets (Osteoset) in PLLA.

Method:

This was a consecutive case, prospective, non–randomized study involving 32 patients. 17 were female (53%)and 15 were male (47%). Average age was 47(+/–14, range 20–75). Average weight was 84+/–21 kgs(range 57–140). Indications for PLLA were degenerative lumbar disease, congenital spondylolisthesis, recurrent disc herniations and discogenic pain. Instrumentation was performed in all cases using either Isola system or concurrent use of BAK posterior lumbar interbody fusion. X–rays were reviewed by three blinded observers. The radiographic fusion rate was calculated for each postoperative group by averaging the results of the three observers. Each patient was graded at 3, 6, 9 and 12 months postoperatively. Each arthrodesis side (left and right)was graded as to the success of the fusion using the following four point scale: 1. Definitive evidence of contiguous bridging trabecular bone between the transverse processes, without evidence of radiolucencies. A solid fusion. 2. Thin unilateral fusion mass, but probably solid. 3. Evidence of bridging bone extending from the transverse processes but contains radiolucencies indicating a probable non–union. 4. Sparse fragments of bone between the transverse processes, without evidence of fusion. A definite non–union. In addition to the individual grades–left and right–an overall grade was assigned to the fusion site (left and right combined). This was according to the Lenke et al classification scale (Reference below).

Conclusion:

The overall scores suggested high fusion rate. For this study, grids of 2.5 in the lower were considered to unions. This study demonstrated the safety and efficacy of Calcium Sulfate pellets as bone graft extenders in PLLA.

Reference:

Lenke LG, Bridwell KH, Bullis D, Betz RR, Baldus C, Schoenecker PL. Results of In Situ Fusion for Isthmic Spondylolisthesis. J Spinal Disord, 5:433–442, 1992.