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Chapter Summary
• Context: Prone Transpsoas (PTP) lumbar interbody fusion represents a transformative evolution of the lateral retroperitoneal approach, shifting patient positioning from traditional lateral decubitus directly into the prone position. While classic Lateral Lumbar Interbody Fusion (LLIF) established the benefits of wide interbody cage placement and indirect decompression, performing the procedure in the prone position leverages gravity to allow abdominal contents and the retroperitoneal corridor to drop anteriorly away from the spine. Furthermore, prone positioning naturally increases lordosis through hip extension, aligns the spine in the familiar dorsal orientation for the surgeon, and enables immediate, seamless posterior instrumentation (decompression, percutaneous or open screw placement, and osteotomies) without changing patient position. However, working through the psoas in the prone position demands adapted retroperitoneal access, dynamic neurophysiological monitoring of the lumbar plexus, and specialized retractor systems.
• Chapter Objective: Present the rationale, anatomical dynamics, surgical steps, and clinical outcomes of Prone Transpsoas (PTP) lumbar interbody fusion. The reader will master the step-by-step technique of prone lateral access, understand gravity-induced retroperitoneal displacement, utilize neuromonitoring to safeguard the lumbar plexus, and integrate anterior interbody reconstruction with posterior prone instrumentation.
• The prone paradigm and anatomical advantagesIn traditional lateral decubitus, the psoas muscle and retroperitoneal contents can drape over the spine. In prone position with extended hips, the psoas muscle is stretched and moves posteriorly, the femoral nerve tension is relaxed, and the peritoneal visceral sac falls anteriorly under gravity (Figure 70.1). This widens the safe retroperitoneal corridor and naturally accentuates lumbar lordosis.
• Indications and pre-operative evaluationPTP is indicated for degenerative disc disease, grade I-II spondylolisthesis, degenerative scoliosis, adjacent segment disease, and revision fusion from L1 to L5. Preoperative axial MRI and CT in supine and prone position map the retroperitoneal corridor, psoas morphology, and lumbar plexus location, as well as the height of the iliac crest at L4-L5.
• Surgical setup and positioningThe patient is positioned prone on a specialized radiolucent frame with hip extension to optimize lordosis and relieve plexus tension. True biplanar fluoroscopy or 3D navigation is established. The lateral retroperitoneal incision is marked along the mid-coronal disc line.
• PTP access and interbody reconstructionRetroperitoneal dissection is performed with continuous triggered EMG monitoring. Once the psoas fascia is reached, blunt muscle splitting in the anterior-to-middle third of the disc space is performed under neuromonitoring. A specialized prone retractor is anchored. Thorough discectomy, contralateral release, and endplate preparation precede insertion of a wide, hyperlordotic lateral cage across the apophyseal ring.
• Single-position posterior completion and outcomesBecause the patient is already prone, posterior fixation (percutaneous or open pedicle screws, facet fusion, direct decompression, or osteotomies) begins immediately without re-draping or repositioning. Published clinical series confirm excellent fusion rates, significant lordosis gains, low plexus neuropraxia rates, and high OR workflow efficiency.
• Clinical Application: In clinical practice, PTP is particularly valuable when significant lordosis restoration and posterior column reconstruction are required concurrently with anterior column support. Placing the patient prone with extended hips immediately increases segmental lordosis across target levels. The surgeon palpates the retroperitoneal space bluntly, feeling the anterior border of the psoas muscle. Continuous EMG monitoring guides safe dilator passage anterior to the femoral nerve. Once the wide lordotic cage is deployed, the surgeon transitions instantly to posterior pedicle screw placement and compression in the standard prone position. This seamless integration makes PTP an ideal technique for multi-level degenerative reconstruction and adult deformity correction.
