An MRI Study Of Psoas Major And Abdominal Large Vessels With Respect To The X/DLIF Approach

ObjectiveThis study was aimed to determine the distribution of psoas major and abdominal large vessels at L1/2～L4/5 lumbar intervertebral spaces and combined with the distribution of nerve at L1/2～L4/5 lumbar intervertebral spaces reported by Moro and Benglis in order to select an appropriate X/DLIF approach to avoid nerve and large vessels injury. BackgroundExtreme lumbar interbody fusion (XLIF) or direct lateral interbody fusion (DLIF) is a new minimally invasive anterior lumbar interbody fusion (ALIF) technique. Caused less tissue trauma and good fusion effect ,it has been used to treat various lumbar diseases. However, it involves risks to injure the lumbar nerve plexus and abdominal large vessels when it gains access to the lumbar spine via lateral approach that passes through the retroperitoneal fat and psoas major muscle. it is critical to accurately choose the point at which to pass through the psoas major. This precision is necessary to reach the lumbar intervertebral space to accomplish the operation and avoid the large vessel and nerve injury. If the puncture site is too anterior, it is easy to injure the large vessels. However, if the puncture site is too posterior, it is easy to injure the lumbar nerve roots that have descended inside the psoas major. In addition, the thickness of the psoas major at the location of the puncture site also affects the operation's safety. If the psoas major is very thick, the peritoneum is easily dissected, the retroperitoneal space is larger, the operation is safer and the risk of peritoneal injury and abdominal viscera injury is reduced. The converse is true as well. However, the distribution of abdominal large vessels and the psoas major of each lumbar intervertebral space is inconsistent; a relevant anatomical study of their distribution has not yet been reported.MethodsAn MRI scanning machine (MAGNETOM AVANTO A Tim system, SIEMENS) was used to transversely tomoscan intervertebral spaces L1/2,L2/3,L3/4 and L4/5 in 48 patients(24 males and 24 females, average age 54.2 years ), to obtain T1-and T2-weighted imagines of the L1/2-L4/5 intervetebral spaces. According to Moro's method, lumbar intervertebral spaces were divided into six zones from the anterior to the posterior, i.e., the area between the anterior and posterior edges of the vertebral body were divided in zones A, I, II, III and IV. The area anterior to the anterior edge of the vertebral body was defined as zone A, and the area posterior to the posterior edge of the vertebral body was defined as zone P. The thickness of psoas major was measured and the distribution of abdominal large vessels was analyzed at each zone of each lumbar intervertebral space via images analysis software (Synogo fastview) on the MRI machine.To determine which zone at the L1/2-L4/5 intervetebral spaces does not injure vena cava and abdominal aorta when perform X/DLIF. combined with the distribution of nerve at L1/2～L4/5 lumbar intervertebral spaces reported by Moro and Benglis in order to select an appropriate X/DLIF approach to avoid nerve and large vessels injury.The difference in thickness of psoas major was compared under age, gender and lumbar spaces factors via SPSS PC version 10.0, respectively. P<0.05 was considered statistically significant.Results1. Distribution of vena cava at each zone of the L1/2-L4/5 intervetebral spacesAt the intervertebral spaces L1/2, vena cava was located to the right of zone A (70.8﹪) and at the juncture of the right of zone A and the right of zoneⅠ(29.2﹪). At the intervertebral spaces L2/3,vena cava also was located to the right of zone A (43.8﹪) and at the juncture of the right of zone A and the right of zoneⅠ(56.2﹪). At the intervertebral spaces L3/4, vena cava was located to the right of zone A (29.2﹪) and at the juncture of the right of zone A and the right of zoneⅠ(64.6﹪), and the right of zoneⅠ(6.2%). At the intervertebral spaces L4/5, vena cava was located to the right of zone A (18.8﹪) and at the juncture of the right of zone A and the right of zoneⅠ(52.0﹪), and the right of zoneⅠ(29.2﹪). Vena cava migrate from the right of zone A to the right of zoneⅠat L1/2-L4/5.2. Distribution of abdominal large vessels at each zone of the L1/2-L4/5 intervetebral spacesThe abdominal aortas at intervertebral spaces L1/2, L2/3 and L3/4 were located mostly to the left of zone A (95.8﹪, 85.4﹪, 79.1﹪, respectively); at the L4/5 intervertebral space, about 62.6﹪of the abdominal aortas divided in two branches: these branches were located at zone A. More specifically, 48.0﹪of the abdominal aortas divided in two branches at this location and these branches were located to both the left and right of zone A. The other 14.6﹪divided in two branches but these branches adhered tightly just together in the anterior surface of the vertebral body.3. Thickness and distribution of psoas major at each zone of the L1/2-L4/5 intervetebral spacesTwo-Factor Variance Analysis of Repetitive Measurements on SPSS10.0 (at the significance levelα=0.05 and in two-tailed test) was used to analyze the thickness of the psoas major at each zone of the L1/2～L4/5 intervertebral spaces for 48 patients, and the results showed no statistical significance for the age factor, but showed statistical significance for the gender factor. The psoas major was tenuous and near the dorsa at the intervertebral spaces L1/2 and L2/3, large and near the ventral aspect at the intervertebral spaces L3/4 and L4/5. For 24 male patients, the thickness of the left and right psoas major at each intervertebral zone of L1/2～L4/5 intervertebral spaces demonstrated a variation of increase first and then decrease from zone A to zone P. The peak of L1/2～L3/4 was located at zone IV and the peak of L4/5 was located at zone II. For 24 female patients, the thickness of left psoas major at each intervertebral zone for L1/2～L4/5 lumbar intervertebral spaces also demonstrated first increase and then decrease from zone A to zone P. The peak of L1/2～L3/4 was located at zone IV and the peak of L4/5 was located at zone III. The thickness of right psoas major at each intervertebral zone of L1/2～L2/3 lumbar intervertebral spaces demonstrated variation with the gradual increase from zone A to zone P, the peak located at zone P, while the thickness of the right psoas major at L3/4～L4/5 lumbar intervertebral spaces demonstrated a variation of increase first and then decrease from zone A to zone P, with the peak of L3/4 located at zone IV and the peak of L4/5 at zoneⅢ.Conclusions1. The right-side X/DLIF approach does not injure the vena cava at zone II~ P of intervertebral spaces L1/2, L2/3, L3/4 and L4/5. Combined with the distribution of the nerve roots that Benglis and Moro reported on, the safe zone of right-side X/DLIF approaches was located at zone II~IV of L1/2, at zone II~III of L2/3, at zone II of L3/4 and L4/5.2. For male right-side X/DLIF approaches to L1/2 ~ L3/4 intervertebral spaces, the needle should be inserted to separate the psoas major at the anterior surface of the peak of the psoas major. For male right-side X/DLIF approaches of the L4/5 intervertebral space we should insert the needle to separate the psoas major at the peak of the psoas major. For all female right-side X/DLIF approaches, it is advisable to insert the needle to separate the psoas major at the anterior surface of the peak of the psoas major. The needle insertion point at L1/2 and L2/3 intervertebral spaces has to have a little bit removed from the peak.3. The left-side X/DLIF approaches at zone II~ P of L1/2 ~ L3/4 intervertebral spaces and at the ?~P zone of L4/5 intervertebral space does not injure the aorta. Combined with the distribution of the nerve roots that Benglis and Moro reported on, the safe zones of left-side X/DLIF approaches are at zone II~IV of L1/2, at zone II and zone III of L2/3, at zone II of L3/4, and at zone I and zone II of L4/5.4. For male left-side X/DLIF approaches of L1/2 ~ L3/4 intervertebral spaces, should involve insertion of the needle to separate the psoas major via the anterior surface of the peak of the psoas major. For male left-side X/DLIF approaches of L4/5 intervertebral space, has to involve the insertion of a needle to separate the psoas major via the peak or slight to the anterior surface of the psoas major. For female X/DLIF approaches we should insert all needles to separate the psoas major via the anterior surface of the peak of the psoas major.