An important outcome from diagnostic imaging is that we can accurately determine the LSTV classification. The modern classification of LSTV anatomy was first introduced by Antonio Castellvi to characterize the different types of transitional anatomy observed in patients (Castellvi et al., 1984). However, this classification has several limitations. First, the classification was developed to identify lumbosacral disc herniations in patients. Second, it fails to consider contact of the enlarged transverse process to the iliac crest. These limitations were addressed by Dr. Arthur Jenkins and his team in their revised LSTV classification dubbed Jenkins classification (Jenkins, O’Donnell, et al., 2023).
Type 1
Type 1A - Enlarged transverse process on the last lumbar segment with less than 10mm gap, but over 2mm gap, between the transverse process and sacral ala on one side only. The other side has “normal” distance over 10mm.
Type 1B - Both transverse processes of the last lumbar segment have less than 10mm gap, but over 2mm gap, between the transverse process and sacral ala.
Type 2
Type 2A - Incomplete lumbarization/sacralization with enlarged transverse process that creates a pseudo-articulation with itself and the sacrum (less than 2mm distance) on one side only. The other side has “normal” distance of above 10mm.
Type 2B - Symmetrical anatomy where both transverse processes have a pseudo-articulation on both sides with the sacrum with less than 2mm distance.
Type 2C - Hybrid anatomy where one transverse process has Type II anatomy (i.e., forms pseudo-articulation with the sacrum) and the other transverse process has Type IA anatomy (i.e., has between 2mm to 10mm distance between itself and the sacrum).
Type 3
Bilateral lumbarization/sacralization with complete osseous (bone) fusion of the transverse processes to the sacrum.
Type 4
Type 4A - Lumbarization/sacralization with complete osseous fusion of transverse process to the sacrum on one side only. The other side has Type I anatomy with transverse process at distance of less than 10mm from sacrum.
Type 4B - Lumbarization/sacralization with complete osseous fusion (i.e., Type 3 like anatomy) on one side and an incomplete lumbarization/sacralization of the transverse process on other side (i.e., type 2 like anatomy).
Type 4C - Lumbarization/sacralization with complete osseous fusion of transverse process to the sacrum on one side only. The other side has “normal” anatomy with transverse process at distance of more than 10mm from sacrum.
