Morphometric analysis of the disc working zone for endoscopic lumbar discectomy

Objective To analyze the disc working zone of intervertebral foramens (ⅣF) for percutaneous posterolateral approach to the lumbar disc with dissection and measurement of adult cadaveric spine speciments.Methods Twenty-five lumbar IVFs of cadaveric spines (age:45-65 years; body height:150-176 cm) were studied.The heights of the intervertebral space at the most posterior margin (h) and the angles between the nerve root and the plane of the disc (β) at the sagittal plane and the distance from the nerve root to posterolateral margin of disc(d) were measured.The distances from nerve root to the lateral edge of articular process at the plane of the inferior endplate of the upper vertebra (a1) and the plane of the superior endplate of the vertebra below (a2) were measured.We also measured the distance between the nerve root and the dura at two planes of the vertebra endplate (b1,b2) after removing the lamina and articular processes.Results The disc in the ⅣF is contained in the shaped zone at the sagittal plane or the coronal plane.The parameters of two trapezoids are displayed:h is (7.0±1.1) mm; β is 77.6°±8.4°; d is (3.4±2.3)mm; a1 is (9.4±2.2) mm; a2 is (10.8±4.6) mm; b1 is (9.9±2.7) mm; and b2 is (17.7±2.1) mm.All values increase as the level goes down except the value of β,which decreases.Conclusion The disc working zone of ⅣF is a complicated three-dimensional structure changed from the Kambin's triangle,which could be simulated by construction of two trapezoid on sagittal and coronal planes.The anatomic study of the structure is able to help the clinical transforaminal managements of the lumbar disc.For example,the dimension of working cannula could be figured out by the height of the intervertebral space.The angle of the needle inserted is affected by the distance from nerve root to the disc in this structure. Key words: Lumbar vertebrae;  Intervertebral disk;  Autopsy