The results suggest that the use of a bullet-shaped cage, higher PDH, the presence of scoliotic curvature, and undersized fusion cages are possible risk factors for cage migration. One patient with postoperative cage migration following bilateral screw fixation underwent revision surgery, and the pedicle screw fixation was found to be disrupted. Other than in this patient, cage migration occurred only in those treated by unilateral fixation. The potential for postoperative cage migration and limitations of unilateral fixation should be considered by spine surgeons.

Object Many surgeons currently prefer to use transforaminal lumbar interbody fusion (TLIF), placing 1 unilateral pedicle screw (PS) and 1 cage. However, no study has examined whether unilateral fixation improves surgical outcome. The authors conducted a prospective randomized controlled trial with a minimum 2-year follow-up to analyze TLIF outcomes for 2 techniques: placement of a unilateral PS and a cage compared with placement of bilateral PSs and 2 cages. Methods Fifty patients with degenerative spondylolisthesis undergoing single-level TLIF were randomly assigned to receive either unilateral or bilateral fixation. Parameters compared between the groups were surgical invasiveness, severity of intermittent claudication, pre- and postoperative visual analog scale (VAS) scores (from 0 to 10 for back pain, lower-extremity pain, and lower-extremity numbness), postoperative disability scores for lumbar spinal disorders (Japanese Orthopaedic Association Back Pain Evaluation Questionnaire [JOABPEQ]), and fusion rates. Results The mean operative time for TLIF was significantly (p = 0.05) shorter and mean estimated blood loss was significantly lower in the unilateral than in the bilateral group. Intermittent claudication improved in response to each technique, but there was no significant intergroup difference. The unilateral group had a nonsignificant tendency toward less improvement in VAS score for back pain (1.5 vs 3.7 for the bilateral group) and exhibited significantly less improvement in VAS score for lower-extremity pain (2.1 vs 5.1, respectively) and numbness (1.7 vs 4.4). There were no significant differences between the groups in postsurgical scores for all 5 items of the JOABPEQ. The fusion rates were 87.5% (21 of 24 patients) in the unilateral group and 95.7% (22 of 23) in the bilateral group. Conclusions Transforaminal lumbar interbody fusion involving unilateral PS fixation and a single-cage technique is less invasive than a 2-cage technique and bilateral fixation, and it improved patients' symptoms. However, it resulted in less improvement in back pain, lower-extremity pain, and lower-extremity numbness. When considering unilateral PS fixation and a single cage, the surgeon should be aware of the potential limitations of this technique. Clinical trial registration no.: UMIN000007833 (UMIN).

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Chondrogenesis is an essential component of endochondral fracture healing, though the molecular and cellular events by which it is regulated have not been fully elucidated. In this study, we used a rat model of closed fracture healing to determine the spatial and temporal expression of genes for cartilage-specific collagens. Furthermore, to determine the effects of basic fibroblast growth factor (bFGF) on chondrogenesis in fracture healing, we injected 100 microg recombinant human bFGF into the fracture site immediately after fracture. In normal calluses, pro-alpha1(II) collagen mRNA (COL2A1) was detected in proliferative chondrocytes beginning on day 4 after the fracture, and pro-alpha1(X) collagen mRNA (COL10A1) in hypertrophic chondrocytes beginning on day 7. In FGF-injected calluses, the cartilage enlarged in size significantly. On day 14, both COL2A1- and COL10A1-expressing cells were more widely distributed, and the amounts of COL2A1 and COL10A1 mRNAs were both approximately 2-fold increased when compared with uninjected fractures. Temporal patterns of expression for these genes were, however, identical to those found in normal calluses. The number of proliferating cell nuclear antigen-positive cells was increased in the non-cartilaginous area in the bFGF-injected calluses by day 4. The present molecular analyses demonstrate that a single injection of bFGF enhances the proliferation of chondroprogenitor cells in fracture callus, and thus contributes to the formation of a larger cartilage. However, maturation of chondrocytes and replacement of the cartilage by osseous tissue are not enhanced by exogenous bFGF, and this results in the prolonged cartilaginous callus phase. We conclude that, in the healing of closed fractures of long bones, exogenous bFGF has a capacity to enlarge the cartilaginous calluses, but not to induce more rapid healing.

Revision surgery after TLIF appears relatively safe because the migrated cage tends to locate more laterally than in patients with cage migration after posterior lumbar interbody fusion. Cage migration subsequent to TLIF may not cause compression of neural tissues, so conservative treatment may suffice for these patients. Unilateral pedicle screw fixation may not provide sufficient stability to prevent cage migration in patients with degenerative scoliosis. Further study is needed to clarify surgical indications for unilateral pedicle screw fixation in TLIF.