ACDF is used to treat a variety of cervical pathologies (degenerative disease, myelopathy, etc.) Post-operative pseudarthrosis, nonunion, is defined as a failure of fusion between cervical levels. Pseudarthrosis is a leading cause of pain postoperatively resulting in 45%-56% of revision surgeries. The “gold standard” graft for ACDFs is an autograft from the patients iliac crest. Autografts lead to a higher level of fusion rates, however, can cause a number of donor site morbidities. To reduce these morbidities, allografts are frequently used as an alternative. • Allografts usually are freeze-dried or fresh-frozen. Freeze-dried allografts have gone through more processing which leads to a more sterile option, but can lead to a weaker bone graft. Fresh-frozen allografts go through less processing, leading to preserved structural integrity but increased chances on immune response.

Objective

The objective of this retrospective study is to compare the fusion rates in anterior cervical discectomy and fusion surgery using freeze-dried versus fresh-frozen allografts.

Methods

The study comprised 79 patients. Fifty-one patients received freeze-dried allograft (106 total spinal levels) and 28 patients received fresh-frozen allograft (50 total spinal levels). Fusion was assessed through trabecular bridging on follow-up anterior-posterior/lateral radiographs. Trabecular bridging was assessed on the superior and inferior borders of each spinal level and given a fusion grade. Complete fusion is defined as >50% bridging between superior and inferior borders of the bone graft; union is complete fusion in <26 weeks; delayed union is complete fusion after 26 weeks; and fibrous union is <50% bridging at ≥1 borders over 52 weeks.

Results

All spinal levels reached complete fusion for both graft types. Of the freeze-dried treated cervical spinal levels, 77.35% (82/106) reached union (adequate trabecular bridging within 6 months) without delay compared with 80% (35/50) for the fresh-frozen bone graft group (P = 0.85). There was no significant difference in time-to-fusion analysis and no significant association between delayed union and any patient factors. In assessing Neck Disability Index (NDI), freeze-dried allografts did show a significantly greater decrease in NDI scores at 6 months (P = 0.03). At the 1 year follow-up, improvements in NDI were consistent in both allografts (P = 0.9647).

Conclusions

From this study, freeze-dried and fresh-frozen allografts showed comparable rates of union, and both allografts can be used interchangeably for anterior cervical discectomy and fusion.