Trident Multi-tined Cannula for Cervical MBRFA Compared to the Conventional Cannula

According to the National Center for Health Statistics, neck pain is the third most commonly reported musculoskeletal complaint in the United States. Cervical zygapophysial or "facet" joint pain is responsible for at least 25% of patients with chronic neck pain and is higher in patients with neck pain after a whiplash injury. Individuals with verified facetogenic pain or cervicogenic headaches can be treated with cervical medial branch radiofrequency ablation (CMBRFA). CMBRFA is a minimally invasive percutaneous procedure that utilizes thermal energy to coagulate nerves from the facet joints, and thereby interrupt the nociceptive pain signals. The targeted nociceptive nerves are the medial branches of the cervical dorsal rami and the third occipital nerve.

The gold standard method of facet pain diagnosis is anesthetizing the medial branches that innervate the involved facet joint and subsequently evaluating the significance of symptom improvement; this process is known as a medial branch block (MBB). There is significant practice variability in what is considered a "positive" MBB. A single cervical MBB with 100% symptom improvement has a false positive rate of 27-60%. The false positive rate decreases with stricter selection criteria. The efficacy of CMBRFA was established in the late 1990's and early 2000's when using a strict selection criteria; 100% symptom improvement with concordant dual medial branch block ± placebo-control block.

In 1996, Lord et al. published in New England Journal of Medicine research showing that when the rigorous diagnostic criteria were adhered to, 63% (CI 95%: 57-69%) and 38% (CI 95%:32-44%) of patients were pain free at 6 and 12 months following CMFRFA. Though comparative dual MBB ± placebo with 100% symptom improvement reduces false positive rates, it is time consuming and expensive, exposes patients to extra radiation and procedural risk, is not required by insurance, and is not the Spine Interventional Society (SIS) recommended gold standard for patient selection for facetogenic pain in the lumbar spine. Currently insurance requires ≥80% symptom improvement with dual facet block. These insurance requirements are consistent with the research supported SIS guidelines for the diagnosis of lumbar facetogenic pain and such practical patient selection criteria are commonly utilized in clinical practice. A recent cross-sectional study reported that when CMBRFA is performed on patients selected by >80% symptom improvement after dual medial branch block, outcomes are similar to patients selected with a stricter selection protocol similar to the original CMBRFA studies however, this needs to be validated in prospective studies.

In early explanatory studies, providers used a conventional monopolar cannulae to ablate targeted medial branch nerves. C-CMBRFA cannula produce the largest lesions along the shaft of the cannula with minimal extension distal to the tip. To increase the likelihood of medial branch ablation the conventional cannula is placed parallel to the targeted medial branch in a posterior to anterior approach with sagittal and oblique passes, and 2-3 lesions per medial branch. Disadvantages to the conventional technique is the procedural time needed for multiple passes and burns and the risk of ventral advancement of the cannula towards vital neurovascular structures. Since the original explanatory C-CMBRFA studies, there have been technologic advances in RFA cannulae in an effort to improve safety and efficiency of CMBRFA.

The Trident multitined cannula was designed to allow a perpendicular/lateral approach to the medial branch nerves. Such approach results in point contact against bone, prevents unintended advancement towards neurovascular structures, and as a result adds to the safety of the procedure. There is also reported efficiency during Trident RFA since only 1 pass and a single lesion at each medial branch is required. A single burn cycle at each site is a possibility because of the unique lesion shape and size. The Trident cannula most commonly used for CMBRFA is 18-gauge and has a 5 mm exposed tip. Once the cannula tip is placed at the target location, 3 tines are deployed anterior and laterally from the cannula tip in an equilateral triangle configuration. Computer simulation calculations predict that a two-minute lesion at 75°C would result in thermal coagulation in an area measuring 7.6 mm wide by 7.6 mm length in the axial plane (at the periosteal surface) and 9.1 mm in height in the sagittal plane (soft tissue lesion) [data provided by Diros Technology Inc.]. These values are comparable to the findings of Finlayson et al who compared thermal lesions morphology of 2 multitined cannulae and a conventional monopolar cannula in an ex vivo model. In the axial plane, with the Trident cannula perpendicular to the periosteum, the mean lesion width and length were 7.3 x 8.8 mm respectively. In the sagittal plane, the mean lesion height was 7.3 mm. Considering that the mean distance between the medial branch nerve at the waist of the articular pillar, and the tip of the superior facet has been documented to be between 7.1-7.4 mm for C3 through C6 and 5.5 mm for C7, a single Trident lesion placed at the waist of the lateral mass should cover approximately one half of the periosteal surface. This should be adequate to accommodate medial branch nerve anatomical variation. Ultimately, the Trident cannula results in an approach that may be technically easier, quicker, safer, more comfortable and as effective as the traditional parallel/posterior approach however, there are no studies comparing Trident to conventional cannula during CMBRFA.