Posterior lumbar interbody fusion (PLIF) is an effective surgical method for the treatment of degenerative lumbar disc herniation[5]. In 1991, Hambly et al.[15] took the lead in using unilateral pedicle screw combined with autogenous bone graft fusion to treat patients with lumbar degeneration, and the final follow-up of the patients with bone graft fusion rate was 85%. A number of subsequent studies have shown that unilateral pedicle screw fixation is weaker than bilateral fixation, but it can effectively reduce the stress shielding of fusion segments and create more favorable conditions for fusion. and it also has obvious advantages in operation time, blood loss, hospitalization cost, etc.[16]
The effective fusion of spinal intervertebral bone graft in PLIF operation is an important index to evaluate the long-term effect. some studies suggest that successful intervertebral bone graft fusion will bring better functional results and better overall satisfaction to patients[17, 18]. Christensen et al.[8, 18] believe that once unstable segmental fusion is successful, the symptoms of low back pain can be significantly alleviated. In spinal fusion surgery, a suitable graft material is often needed to induce the formation of new bone at the operative site[19]. With the development of medical biomaterials technology, interbody fusion cage has been widely used in clinic, and the purpose of cage is to provide a sufficient fusion environment for bone graft, so as to accelerate postoperative rehabilitation and fusion[20]. Cage can be easily sterilized and stored, which greatly reduces the risk of diseases transmitted by allogeneic bone transplantation. In the case of vertebral body collapse caused by intervertebral disc degeneration, interbody fusion with cage can effectively share the load of the anterior column of the vertebral body and restore the height of the intervertebral space[21]. Although numerous analyses have confirmed that the use of cage has achieved good clinical results, cage still has many inherent shortcomings. Such as the insertion of fusion cage to reduce the available contact area of bone fusion, increase the probability of infection, increase the cost of hospitalization and so on. Closkey[22] suggest that in order to achieve good bone graft fusion effect, more than 30% of the endplate surface area should be in direct contact with the local bone, and the use of cage often reduces the bone contact area in the fusion area. Studies have also shown that cage is a foreign body that may increase the risk of infection or immune problems in patients[23]. Lazennec[24] has reported the risks of cage subsidence and corrosion in long-term animal model studies. In addition, cage is still an obstacle to use in developing countries such as China because of its high cost. However, the traditional intervertebral bone graft materials are often taken from the patient's autogenous ilium. although this method has the advantages of low surgical cost and increased bone contact area, some studies have pointed out that this method is often accompanied by a serious incidence of donor sites. Up to 6%ཞ39% of patients have persistent pain associated with the donor site of the transplanted bone[7]. Simmons[11] suggested that the laminae and spinous processes removed during the operation be given to a qualified technician who cuts them into corticocancellous pieces measuring 2–4 mm, ensuring that each chip has a cancellous side. These chips are implanted into the intervertebral disc space. Recent studies have also shown that local bone fragments obtained by laminectomy are used as bone grafts for PLIF, resulting in the same fusion rate as autogenous iliac bone[6, 12]. However, some people do not agree with this view. Abdul[21] found that the increase of intervertebral disc height and VAS score in the intervertebral fusion cage group was significantly better than that in the local bone graft group in the treatment of lumbar degenerative spondylolisthesis(Ⅰ°/Ⅱ°) with PLIF operation.
Though the similar clinical results were obtained from both of the groups for single level PLIF in the present study, we still believe that local bone grafts without cages have more advantages than those with cages. The main reasons are as the following: The non-use of cage can significantly reduce the cost of surgery for patients, which is particularly important for many developing countries. Although cage has good biocompatibility, it is still a foreign matter and has potential risks.
In conclusion, local bone graft has the same advantages as bone graft fusion cage in unilateral PLIF. Comparing with local bone graft using a single cage, we believe that the purely local bone graft is a more ideal way in unilateral PLIF.