The effects of transforaminal ligaments on the sizes of T11 to L5 human intervertebral foramina.

Objective: This study was designed to determine the effects of the presence of transforaminal ligaments (TFL) on the superior-to-inferior dimension (SI) and anterior-to-posterior dimension (AP) of the compartment containing the ventral ramus of the spinal nerve (VR) in the intervertebral foramen (IVF).

Design: Four lumbar spines, including T12 and in one case T11, were obtained from embalmed cadavers and carefully dissected to expose the contents of the IVF. All ligamentous structures in the vicinity of the IVF were preserved. The greatest SI and AP of each IVF were measured. When present, TFL help define a compartment at the exit zone of the IVF that contains the VR. The SI and AP of these compartments were also measured.

Results: Of 49 IVF examined, at least one TFL was present in 35. In the 34 IVF with horizontally oriented TFL, the mean SI of the compartments for the VR was 31.5% smaller than that of the IVF (one-way ANOVA, p < .01). No significant differences were seen between the AP of the IVF and compartments for the VR in the levels with vertically oriented TFL (n = 11).

Conclusions: TFL were found to be present in 71% of lower thoracic and lumbar IVF. If TFL were present, the SI of the compartment containing the VR in the IVF was significantly decreased (mean = 31.5%). This finding suggests that often there may be less space at the exit zone of the IVF for the ventral ramus than traditionally thought, which could contribute to the incidence of neurological symptomatology in this region, especially after trauma or degenerative changes.