ABSTRACT
OBJECTIVE: To offer anatomical supports to the approach of lateral par interarticularis for far lateral lumbar discectomy. METHODS: In 30 lumber spine specimens taken from adult cadavers the relevant osseous distances of posterolateral region of lumbar vertebrae and its changing regularity with the sequences of lumbar spine were measured: (1) width of isthmus; (2) distance from midline to lateral border of vertebral body; (3) distance from lateral margin of isthmus to lateral border of vertebral body; (4) distance from inferior border of transverse process to superior rim of superior facet; (5) distance from accessory process to superior rim of superior facet; and (6) distance from central plane of lumbar disc to superior rim of superior facet. RESULTS: From L1-L2 towards L5-S1, the operative window representing the operating area of the approach of lateral par interarticularis for far lateral lumbar discectomy became progressively smaller in its longitudinal, transverse direction and outer exit. The distance from lateral margin of isthmus to lateral border of vertebral body representing the transverse diameter of the operative window was reduced to 0.32 cm (P < 0.05). While the distance from inferior border of transverse process to superior rim of superior facet and distance from accessory process to superior rim of superior facet representing the longitudinal diameter of operative window were reduced to 0.17 cm and 0.46 cm respectively (both P < 0.05). The distance from central plane of lumbar disc to superior rim of superior facet increased gradually from -0.20 cm in L1-2 to 0.86 cm in L5-S1 (P < 0.05). The articular process extended upward and covered more lumbar disc plane. CONCLUSION: At the level L1-L2 to L4-L5, the lateral par interarticularis approach is an easy, convenient, and anatomically favorable way to reach the far lateral lumbar disc herniation, but the progressive diminution of operative window increases the bony excision in lateral par interarticularis, root of transverse process, inferior portion of pedicle and superior portion of zygapophysial joint. At the level of 15-S1, the operative window becomes very tight. The excess of bone removal and expected instability of lumbar spine make the lateral par interarticularis approach tough to be done.
