Instrument Tracking Reduces Radiation Exposure and Increases Efficiency in Prone Lateral Lumbar Interbody Fusion: A Retrospective Cohort Study

Context and Persistent Challenges of the PL-LIF

PL-LIF aims to improve traditional lateral interbody fusion by pairing transpsoas access with the biomechanical and logistical advantages of prone positioning.4 Unlike lateral decubitus LLIF, which typically requires subsequent patient repositioning or table rotation to accomplish posterior fixation, PL-LIF undertakes the transpsoas exposure with the patient already prone, thereby permitting single-position posterior instrumentation and gravity-facilitated lordotic correction.9 Despite these potential improvements, adoption of PL-LIF remains tempered by 2 enduring intraoperative concerns: the need for prolonged psoas retraction and the subsequent risk for lumbar plexus injury and elevated radiation exposure to patients and operating room personnel.2,6 To reduce neural injury rates, earlier lateral surgical practices emphasized limiting cumulative psoas retraction time to less than 20 minutes.2

Interestingly, a new emerging study suggests that retractor duration may reflect anatomic difficulty and surgeon efficiency rather than an independent causal driver of plexus injury. In this retrospective cohort study of 658 patients, the authors evaluated the applicability of the “20-minute rule” during LLIF and found no significant difference in retractor time between patients with postoperative nerve injury (19.6 ± 11.2 minutes) and those without (17.5 ± 8.0 minutes). They found that the 20-minute threshold demonstrated poor predictive value (sensitivity 50%, specificity 73.8%, and positive predictive value 3.4%). The authors concluded that strict adherence to the 20-minute rule does not prevent nerve injury and recommend prioritizing safe, deliberate techniques over speed. However, despite the study’s retrospective nature and limited data collection, the trend toward longer retractor times in patients with nerve injury (bordering the 20-minute threshold) raises concern for time-dependent neural risk, particularly given the study’s low event rate and limited power to detect small but clinically meaningful differences. The truth is likely multifactorial. Retractor time may contribute to injury risk, but so may other variables such as anatomy, retractor placement, and neuromonitoring response. Regardless of root cause, this study clearly shows a greater than 4-fold increase as retractor time increases, with no clear increase until after the 20-minute mark is exceeded. Given this biological plausibility and the historical use of the 20-minute cutoff as a safety guideline, we elected to retain it as a practical benchmark for evaluating surgical efficiency and minimizing traction-related complications.

Concurrently, minimally invasive approaches often incur higher cumulative fluoroscopic exposure than compared with open techniques due to the need for intraoperative localization, anatomical visualization, and instrument navigation with associated long-term risk for radiation-related complications.6,16,17 In operative workflows, an effective adjunct should streamline the surgical approach while maintaining—and ideally enhancing—safety. Our aim was strictly exploratory: to examine whether instrument tracking using TrackX is associated with operative efficiency (decreased psoas retractor time) and improved radiation stewardship (x-ray image count and radiation exposure) in PL-LIF.

Instrument Tracking, Efficiency, and Radiation

Fluoroscopy-based instrument tracking provides continuous spatial context and rapid anatomical remapping after soft tissue shift.18 In this series, the use of instrument-tracking software during prone lateral interbody fusion was associated with a median radiation exposure of 8.43 mGy (IQR 6.04) and a median of 14 fluoroscopic images (IQR 8) across 39 patients. Additionally, psoas retractor time decreased across the operative timeline, while x-ray image count and per-level radiation dose remained low. These values are markedly lower than those reported in prior series without such software, including Striano et al19 (108.6 ± 16.9 mGy for single-level LLIF/extreme lateral interbody fusion [XLIF]) and Godzik et al20 (171 ± 60th mGy in a prone lateral cadaveric model). Similarly, Lamartina and Berjano’s Pro-XLIF study7 reported mean fluoroscopic use of 151.4 ± 99.8 shots (adjusted mean 108 shots) compared with 108.3 ± 56.7 shots (adjusted mean 91) for standard XLIF. Compared with previously published series, our cohort showed low radiation exposure and fluoroscopic image counts. These findings compare favorably with the existing literature, but because the comparison is historical and indirect, they should not be interpreted as establishing a definitive reduction caused by instrument tracking.

In addition, procedure speed improved with operative experience without an associated increase in total x-ray image number per case, in contrast with the usual pattern, where adopting a new technology may manifest as higher radiation exposure before decreasing and leveling off.21 Findings parallel prior minimally invasive transforaminal lumbar interbody fusion reports demonstrating reduced operative time and radiation with tracking technologies3,22,23 while extending generalizability to PL-LIF, a procedure with distinct corridor geometry and ergonomic constraints. We also observed improvement in patient-reported outcomes through 12 months, supporting maintained clinical efficacy with the addition of instrument tracking. Mean improvements exceeded MCIDs for all measures, which supports that patients experienced pragmatic improvements in daily function, not only statistical shifts. The pattern is consistent with early recovery by 6 months and continued, with smaller gains by 12 months, which matches typical trajectories for lumbar surgery. VR-12 PCS captured global physical health improvement, while ODI and ZCQ domains reflected condition-specific relief and better function, providing convergent validity across measures.

Taken together, these comparisons suggest that software-assisted instrument tracking was associated with low radiation dose and reduced fluoroscopy demand in prone lateral approaches relative to previously described techniques. In addition to lowering exposure, instrument tracking could help standardize workflow and decrease reliance on continuous fluoroscopy, with potential implications for procedural safety, although these benefits warrant confirmation in larger prospective studies.

Mechanisms and Alternative Explanations

Operative efficiency likely reflects convergent mechanisms: uninterrupted visualization reduces microdelays in reconstructing 3-dimensional orientation24; reduced task switching lowers cognitive load25; rapid remapping diminishes navigation downtime18; accumulating trust in positional fidelity lessens reliance on confirmatory fluoroscopy12; and ergonomic conservation through fewer axial and cervical rotations sustains fine motor precision later in the case. Furthermore, integrating neuromonitoring in both lateral and prone-lateral approaches is essential, providing real-time physiological feedback that markedly reduces unnecessary fluoroscopy and greatly enhances confidence in maintaining a safe surgical corridor.2,26 Alternative explanations include chronological learning, Hawthorne effect, and complexity drift. However, the absence of early elevated imaging argues against a purely chronological effect, and a Hawthorne effect would likely attenuate rather than stabilize. While the drift toward simpler cases could reduce retraction time, stable radiation uses, and imaging counts suggest minimal selection bias. Residual confounding remains possible and warrants controlled validation.

Clinical, Safety, and Implementation Implications

Shorter retraction intervals may reduce lumbar plexus irritation risk,6,26 while sustained low radiation exposure mitigates cumulative occupational and patient risk.16,17 When layered upon established minimally invasive benefits of lower blood loss, reduced tissue disruption, shorter hospitalization, and lower opioid requirements,27 instrument tracking functions as a force multiplier. Continuous localization may directly support high-quality neuromonitoring by correlating instrument trajectory with evolving signals and enabling earlier recognition of subtle corridor shifts.2,26,28 Time-stamped positional data and synchronized neuromonitoring streams could seed predictive analytics for adaptive retraction intervals and surgical tray optimization. Implementation considerations include potential offsets of capital cost through shorter operative duration, fewer radiation-associated confirmation shots, and reduced shielding wear. Ergonomic benefits (reduced head turns and fewer search actions) may decrease fatigue and musculoskeletal strain, factors relevant to surgeon longevity yet underreported. Selective deployment may yield the greatest marginal benefit in patients with high iliac crest, variant psoas morphology, obesity, prior retroperitoneal surgery, or multilevel constructs, while straightforward single-level cases may see narrower incremental gain.

Limitations and Future Directions

Limitations include modest sample size (39 patients, 52 levels), retrospective data collection, and a single-surgeon, single-center design. The primary shortcoming is the absence of a contemporaneous nontracking control group, which precludes direct comparison of operative timing, clinical outcomes, and radiation exposure and limits causal attribution of observed findings to instrument tracking. The cohort was predominantly white and non-Hispanic, which may further limit generalizability to more diverse populations and practice settings. Potential confounders (body mass index, psoas morphology, deformity parameters, and prior surgery) were not stratified. Anatomic complexity factors, including iliac crest height, psoas size and morphology, and deformity severity, were not stratified. Although only one patient was excluded due to the need for angled instrumentation, and all remaining cases were included in chronological order during the study period without additional exclusions, the results may nevertheless be biased toward less complex anatomy and may underestimate psoas retraction time and radiation utilization, limiting generalizability to higher-complexity cases. Radiation metrics were derived from system-reported output rather than patient organ-specific dosimetry. Future work should employ multicenter prospective or randomized study designs with appropriate comparators, incorporate anatomic and patient-reported outcomes, perform time-driven activity-based cost analysis, include ergonomic and fatigue assessments, and utilize high-resolution positional plus neuromonitoring logs for predictive modeling of escalation or impending threshold breaches in retraction duration. Simulation or structured proctorship studies may determine whether formalized training with instrument tracking technology further compresses early efficiency curves. Integration with adaptive dose modulation and machine learning-driven alerting warrants exploration.