Variation in bony landmarks and predictors of success with sacral neuromodulation

Evaluation of optical tracking and augmented reality for needle navigation in sacral nerve stimulation

BACKGROUND AND OBJECTIVE

Sacral nerve stimulation (SNS) is a minimally invasive procedure where an electrode lead is implanted through the sacral foramina to stimulate the nerve modulating colonic and urinary functions. One of the most crucial steps in SNS procedures is the placement of the tined lead close to the sacral nerve. However, needle insertion is very challenging for surgeons. Several x-ray projections are required to interpret the needle position correctly. In many cases, multiple punctures are needed, causing an increase in surgical time and patient's discomfort and pain. In this work we propose and evaluate two different navigation systems to guide electrode placement in SNS surgeries designed to reduce surgical time, minimize patient discomfort and improve surgical outcomes.

METHODS

We developed, for the first alternative, an open-source navigation software to guide electrode placement by real-time needle tracking with an optical tracking system (OTS). In the second method, we present a smartphone-based AR application that displays virtual guidance elements directly on the affected area, using a 3D printed reference marker placed on the patient. This guidance facilitates needle insertion with a predefined trajectory. Both techniques were evaluated to determine which one obtained better results than the current surgical procedure. To compare the proposals with the clinical method, we developed an x-ray software tool that calculates a digitally reconstructed radiograph, simulating the fluoroscopy acquisitions during the procedure. Twelve physicians (inexperienced and experienced users) performed needle insertions through several specific targets to evaluate the alternative SNS guidance methods on a realistic patient-based phantom.

RESULTS

With each navigation solution, we observed that users took less average time to complete each insertion (36.83 s and 44.43 s for the OTS and AR methods, respectively) and needed fewer average punctures to reach the target (1.23 and 1.96 for the OTS and AR methods respectively) than following the standard clinical method (189.28 s and 3.65 punctures).

CONCLUSIONS

To conclude, we have shown two navigation alternatives that could improve surgical outcome by significantly reducing needle insertions, surgical time and patient's pain in SNS procedures. We believe that these solutions are feasible to train surgeons and even replace current SNS clinical procedures.

Radiologically anatomic measurement analysis for the third sacral foramen and an efficient implantation protocol for sacral neuromodulation

AIMS

To define radiologically anatomic measurements for the S3 foramen and develop an efficient and straightforward implantation protocol for sacral neuromodulation (SNM) in a southern Chinese population.

METHODS

We retrospectively reviewed 793 adults without sacrococcygeal abnormalities or bony injury. We generated CT-derived three-dimensional volumetric models and collected radiologically anatomic measurements of S3 foramen. A multiple generalized linear regression model was applied to evaluate implantation protocol for SNM.

RESULTS

Height, weight, and sacral height were significantly different between enrolled patients based on sex (p < 0.001 for all), while age and sacral width were similar. The measurements L1, L2, A1, and A2 on both sides were similar, while based on sex, those of L1, A1, A2 showed significant differences [7.02 ± 0.90 (M) vs. 6.10 ± 0.99 cm (F) (p < 0.001); 83.05 ± 6.23 (M) vs. 82.08 ± 7.53° (F) (p = 0.005); and 13.31 ± 5.69 (M) vs. 11.97 ± 4.91° (F) (p < 0.001), respectively]. The multiple generalized linear regression model demonstrated that sex was a common independent factor for estimating L1, L2, A1, A2, while the consistency rate between the estimated model and actual measurements was poor. The measurements L1, L2, A1, and A2 were approximately 7.0 cm (M) versus 6.1 cm (F), 1.8 cm (M) versus 1.8 cm (F), 83° (M) versus 82° (F), and 13° (M) versus 12° (F), respectively.

CONCLUSIONS

This retrospective study indicates that the radiologically anatomic measurements for the S3 foramen have unique characteristics. Our study provides an efficient and straightforward implantation protocol for SNM, improving its use in China.