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Micro-invasive ultrasound-guided carpal tunnel release provides excellent outcomes
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Carpal tunnel syndrome is the most common compression neuropathy and it affects nearly 12 million Americans and up to 7% of manual labor workers. More than 500,000 carpal tunnel releases are performed annually in the United States to treat patients with severe or refractory symptoms. The primary goal of carpal tunnel release is to transect the transverse carpal ligament to reduce median nerve compression and thereby relieve pain, numbness and tingling, and improve function.
Traditional open carpal tunnel release (CTR) is safe and effective, but can be associated with relatively large and sometimes painful scars, pillar pain and a lengthy recovery course. Compared to open CTR, endoscopic CTR results in improved early postoperative outcomes, but it is a more expensive procedure and carries a greater risk of transient postoperative nerve symptoms.
Due to continued advancements in ultrasound technology, clinicians are increasingly integrating ultrasound into their practices. Currently available ultrasound machines can image structures smaller than 1-mm in size in real-time, thus providing new opportunities for image-guided procedures. We have successfully implemented CTR using ultrasound guidance with excellent patient outcomes. Ultrasound-guided CTR can be performed through a minimally invasive incision and has been demonstrated to facilitate patient recovery. Herein, we present our technique for ultrasound-guided CTR using the SX-One MicroKnife (Sonex Health).
Pre-procedure mapping
Once carpal tunnel syndrome is confirmed in a patient via electrodiagnostic testing, surgical candidates are scanned in clinic to ensure adequate visualization of major anatomic structures including the following: Median nerve; palmar cutaneous branch; thenar motor branch (Figure 1); 3rd common palmar digital nerve; osseous boundaries of the carpal tunnel (scaphoid, pisiform, trapezium, hook of hamate*); ulnar vessels within Guyon’s canal; transverse safe zone (TSZ) between the ulnar aspect of the median nerve and the radial aspect of the ulnar vessels or hook of the hamate (HH), whichever lies more radial*; distal transverse carpal ligament (TCL; Figure 2)*; and superficial palmar arterial arch (including Doppler)*.
Source: Ryan T. Hubbard, MD, and Brett J. Kindle, MD
Surgical technique
The wrist and forearm are prepared using sterile technique. The patient is positioned supine or side-lying with the arm abducted on an arm board or similar surface. The wrist is minimally extended with a sterile towel or bolster; hyperextension is unnecessary.
A sterile ultrasound probe cover is placed on the transducer and ultrasound and a sterile marker are used to identify and mark key anatomic landmarks, which are designated with an asterisk (*) in the pre-procedure mapping section above. Additionally, the incision site between the median nerve and ulnar artery is marked at the level of the proximal wrist crease. The skin marks may be used as reference points during the procedure.
A final ultrasound scan of the TSZ is performed to confirm there is acceptable visualization and the anatomy is normal along the anticipated line of the TCL transection.
The procedure can be performed using a variety of anesthesia techniques, including wide-awake local anesthesia no tourniquet. Regardless of the anesthesia, we use ultrasound guidance to inject local anesthetic into the carpal tunnel within the TSZ—between the median nerve and ulnar vessels/hamate—to provide anesthesia and hydrodissect the tendons and synovial tissue from the TCL (Figures 3 and 4). Hydrodissection improves visualization and creates working space for the device. Direct ultrasound visualization ensures accuracy and safety.
The SX-One MicroKnife (Figure 5) is a commercially available device with integrated usability and safety features that facilitate single-handed operation, allowing the user to hold the ultrasound probe in the other hand. The device has a centrally located, retractable, retrograde cutting blade that is bordered by two inflatable balloons which create working space between the carpal tunnel contents and blade. Following device preparation, ultrasound guidance and a #15 blade is used to make a small incision at the level of the proximal wrist crease, penetrating the antebrachial fascia. The blunt-tipped device is gently advanced into the carpal tunnel using ultrasound guidance so that it passes between the hamate and median nerve within the TSZ, similar to that done with endoscopic CTR (Figure 6). The tip is advanced such that the blade, when activated, will engage the distal TCL (Figure 7). The position of the device relative to the TSZ and surrounding neurovascular structures is confirmed with ultrasound. The balloons are inflated to increase the area of the TSZ (Figure 8). Then, the position of the device relative to the regional anatomy is reconfirmed and the retrograde cutting knife is deployed (Figure 9). The TCL is cut distal to proximal using continuous ultrasound visualization (Figure 10). The blade can be tracked with cross-section and longitudinal views.
Following TCL transection, the blade is retracted, the balloons are deflated, and the TCL is probed using ultrasound visualization to ensure complete release (lift-up test; Figures 11 and 12). Sonographically, the device tip will easily pass superficial to the hamate, often with a “palpable snap” as the tip moves through the TCL transection site. Following confirmation of TCL transection, the device is removed using direct ultrasound guidance. Some hand surgeons prefer to probe with a blunt elevator or probe, and/or “palpate” the transection through the palm. If incomplete transection is suspected, the device can be repositioned using ultrasound guidance and the procedure can be repeated.
Post-procedure protocols vary. Our incisions are < 5-mm long and sutures are not required (Figure 13). We typically dress the wound with Steri-Strips (3M) overlaid with Tegaderm (3M) followed by a folded 4x4 gauze and Coban Self-Adherent Wrap (3M).
Patient outcomes
Patients may begin immediate wrist and hand motion and resume normal activities as tolerated. No splinting or opioids are prescribed. Occupation therapy is offered per patient preference. Most patients take only a few acetaminophen tablets and/or NSAIDs within the first 12 to 24 hours for soreness. The majority of patients return to normal activities within 24 to 48 hours with all patients returning to preprocedural activities by 7 days postoperatively. Many of our patients have reported relief of pain and numbness as early as the night of the procedure. One patient claimed this procedure was significantly better than his or her previous experience with mini-open CTR on the contralateral wrist. Our procedures are currently performed in a hospital outpatient procedure room, but this technique is being performed in surgery centers, ORs and clinic office spaces because only local anesthesia is needed.
Ultrasound CTR has an established track record of safety and efficacy in the peer-reviewed literature, including a level-1 study by Rojo-Manaute and colleagues that documents superior earlier outcomes compared to mini-open CTR. Our clinical experience with ultrasound CTR has been excellent. Most notably, our patients report rapid improvement of symptoms, high postoperative satisfaction and return to normal activity that was significantly faster than what is expected with mini-open CTR. The micro-knife makes it easy to learn the technique and become efficient at performing ultrasound CTR. The expandable balloons are particularly helpful in that they increase the working space and enhance surgeon confidence during the procedure. Our operating times typically range from 5 to 10 minutes. Multiple other physicians who perform ultrasound CTR with this technique report similar experiences.
- References:
- Nakamichi K, et al. J Hand Surg. 2010;doi:10.1016/j.jhsa.2009.12.016.
- Rojo-Manaute JM, et al. J Ultrasound Med. 2016;doi:10.7863/ultra.15.07001.
- For more information:
- Ryan T. Hubbard, MD, and Brett J. Kindle, MD, can be reached at Andrews Institute for Orthopaedics and Sports Medicine, 1040 Gulf Breeze Pkwy., Suite 208, Gulf Breeze, FL 32561; Hubbard’s email: rth25gtown@gmail.com. Kindle’s email: brett.kindle@bhcpns.org.
Disclosures: Hubbard and Kindle report no relevant financial disclosures.