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[Anatomic variations of the ilio-caval junction encountered in disk prosthesis implantation].

PURPOSE OF THE STUDY
The retroperitoneal mini-invasive anterior approach to the lumbar spine is widely used for disc excision and insertion of a prosthetic disc. A large operating window is needed. Venous wounds constitute one of the most serious complications. We analyzed the angle and position of the iliocaval on the preoperative angio-MRI in search for correlations with the intraoperative findings. Our aim was to determine whether the preoperative angio-MRI gives indications concerning the operative difficulty and the best strategy for prosthesis fitting.


MATERIAL AND METHOD
This prospective study included 35 consecutive patients who underwent surgery for implantation of a Maverick disc prosthesis. Average patient age was 46.7 years. The indication for surgery was isolated degenerative discopathy with invalidating chronic low back pain without alteration of the muscle masse or facet joints. A preoperative angio-MRI was performed with T1 spin-echo sequences for the coronal slices and T2 axial slices passing through the upper extremity of the L5-S1 disc. We searched for correlations between the MRI and operative findings. Elements studied were those used in the Capellades classification: height of the iliocaval junction (high, very high, low, very low), position of the common iliac vein (lateral, intermediate, medial), angle formed by the two common iliac veins.


RESULTS
The lateral position was the most frequent (31.5%). The average junction angle was 65 degrees). The only position where it was not possible to "pass" under the iliocaval junction was for a very low medial localization with a narrow angle (45 degrees).


DISCUSSION
Our series included a homogenous group comparable with other series in the literature. The junction angle for very low medial localizations is of considerable importance because it is impossible to fit the implant in the L5-S1 under the iliocaval junction if the angle is over 60 degrees.


CONCLUSION
The position of the iliocaval junction, and particularly its angle, are of considerable importance for insertion of an L5-S1 disc prosthesis. The preoperative angio-MRI provides information on the potential difficulty of the insertion. In addition, with this preoperative information, the patient can be warned that it may not be possible to insert the implant so that a therapeutic alternative may be proposed.