L5-S1 Anatomic Features Relevant to Minimally Invasive Decompression and Fusion: A Cadaveric and Imaging-Based Study

Area of Science:

• Spine Surgery
• Anatomy
• Radiology

Background:

• The L5-S1 spinal segment presents unique anatomical challenges for minimally invasive spine surgery (MISS).
• Variability in bony and neural structures can restrict standard surgical approaches.
• Limited studies combine cadaveric and radiologic analysis for L5-S1 MISS morphology.

Purpose of the Study:

• To characterize the anatomical and radiological features of the lumbosacral region relevant to MISS.
• To define morphometric parameters for planning and executing L5-S1 MISS procedures.

Main Methods:

• Twelve Thiel-embalmed cadavers underwent CT imaging and posterior dissection.
• Bilateral anatomical measurements and qualitative analyses of ligaments and access feasibility were performed.
• CT-based morphometrics included L5 transverse process dimensions, distances to sacral ala, extraforaminal area, and approach angles.

Main Results:

• Significant sex-based differences were found in most anatomical measurements, excluding L5 transverse process length.
• Direct intervertebral disc access was feasible in 25% of cases.
• Extraforaminal corridors were feasible in 75% of cases, with a mean approach angle of 35.2°, but frequent overlap with the ventral ramus of the fifth lumbar spinal nerve (VRL5) was noted.

Conclusions:

• Substantial interindividual morphologic variability exists at the L5-S1 segment.
• This variability compromises the feasibility of transforaminal and extraforaminal MISS approaches.
• Individualized preoperative planning, neural identification, and/or bony resection are necessary for safe L5-S1 MISS corridors.