So, the ulnar nerve at Guillon's Canal is a distinct anatomic space. We all know about the basic anatomy. It's slightly ulnar to the carpal tunnel. It was originally described by Guillon in 1861. It subsequently has been known as the Luge de Guillon. But it wasn't until 1965 that compression was first described by DuPont. The anatomy around the Guillon's Canal was further characterized in the 1970s. It was in 1976 that MacFarlane characterized what was called the pisohymae tunnel as a compressive area. And it's really a fibrous arch of the hypothenar muscles by the pisohymae ligament. It's interesting, if you look at the literature and the pictures, this is a picture from Green's textbook. It implies that the ligament is volar to the nerve. But if you really look back at the original description, the pisohymae limit, as MacFarlane described, is really going to be dorsal to the nerve. In 1978, Denman characterized what he termed the pisoretinacular space. It's actually the space for the deep branch of the motor nerve as it courses in the hand around the hook of the handmaid. The tunnel is classically 45 millimeters in length. Different authors, depending on how they measure it, have described it differently. The proximal and volar extent or border of Guillon's Canal is the volocarpal ligament. Distally, it ends at the fibrous arch of the hypothenar muscles. The floor is your transverse carpal ligament. Radial border is the hook of the handmaid. That's around which the deep branch of the ulnar nerve lies. The ulnar border is the piso-tricuitral ligament to the hypothenar muscles. Guillon's Canal has classically been divided into three zones. Zone 1, 2, and 3. Zone 1 is defined as the area where both the sensory and motor branches exist. Zone 2 is where the deep motor branch. And zone 3 is the pure sensory branch. Different authors have postulated that you can actually identify where the compression is based on the patient's symptoms. Theoretically, if it's both motor and sensory findings, it's zone 1. If it's just motor, it's zone 2, and similarly sensory. Classically, an ulnar artery aneurysm is going to be in zone 3. The best picture I could find is going back to 1985 from Richard Gelberman. This is from his core article. You can see, in one, the ulnar nerve proper. Number two is the sensory branch of the ulnar nerve. Three is your deep motor branch. Four, when we're going to talk about surgery and when you're going to think about decompressing them, there's a small branch that comes off the deep motor. That's the motor branch to the hypothenar muscles. That's important to identify. Number five here in his article describes that fibrous arch at the beginning of the hypothenar muscles. That's the source of compression. I think we all know the distribution of the ulnar nerve sensory to the small finger and the ulnar half of the ring classically. But as Dr. Boyer already talked about, some people have a Richard Canoe-type anastomosis. It may not be classic. The motor innervation is your hypothenar muscles, your ulnar tube lumbricals, intraocular abductor, and half of the flexor pollicis brevis. When you get into the tunnel, the artery itself is more superficial and radial to the nerve, so that's going to be your source of identification when you're in the tunnel. Classically, six millimeters distal to the pisiform is where you'll see the division. Classically, your definition from zone one to zone two. And then your deep branch in zone two is going to course around the hook of the hamate, which is why hamate hook injuries are known to cause ulnar neuropathy, especially to the motor branch. And the branch of the hypothenar muscles, as I showed in Gelberman's picture, dives deep to that arch directly after the takeoff. Carpal tunnel is much more common than Guillain's Canal. You can't get an overuse phenomenon. There's been a lot of reports recently with the popularity of cycling. A lot of cyclists have been diagnosed as having ulnar nerve compression of the wrist. Postulates include whether it's a dorsiflex posture of the wrist as the cyclist is riding for a certain period of time or maybe compression from the handlebars across Guillain's Canal. Unlike carpal tunnel, that's usually more of intravenous neuropathy. In ulnar neuropathy and Guillain's Canal, you'll often find a specific site of compression. And the best article still goes back to Richard Gelberman in 1985, looking at the most likely space-occupying lesions. In his article, 46 or almost a third of the cases were from ganglion. They noted anomalous muscles in about a sixth of cases and fractures in 19 of the 135. But I actually wonder when one looks back at this article whether there's some bias in there because this is a compilation of literature reports of causes of ulnar neuropathy of the wrist. And one has to wonder whether people more present more their anomalies more than the more classic findings. So I wonder whether there is some skewing towards anomalous muscles, which in my experience I've only seen once. Other causes of ulnar neuropathy of the wrist are an aneurysm of the ulnar artery and a handmade hook injury. Classic MRI showing a ganglion within Guillain's Canal. There's a large lipoma emanating from the luge de Guillain, ulnar artery aneurysm, and a handmade hook fracture. Symptoms I think we all know, numbness in the ring of small fingers. Patients will have a loss of dexterity and have intrinsic weakness because the intrinsic muscles innervated by the deep branch of the ulnar nerve are important for dexterity. If someone has a hypothenar hammer or ulnar artery aneurysm, you'll see cobesity, vascular insufficiency, or a mass. When a patient comes to your office with ulnar nerve symptoms, think about the more common things. You need to start in your neck, you start at the cubital tunnel. Cervical spine problems are going to be number one as far as causing numbness or symptoms in the ulnar nerve distribution. And cubital tunnel, as Dr. Lee just talked about, is going to be number two. But when you get down to the hand, look for point tenderness. Someone that fell has a handmade hook injury. You need to do a vascular examination, do an Allen's test compared to the other side, and look for vascular or capillary refill, and palpate for any masses or any swelling that you see. Remember, the sensory branch of your ulnar nerve comes up about eight centimeters proximal to the wrist. So someone who has a more proximal source of ulnar nerve compression at the elbow or in the neck is going to have numbness along the dorsal aspect of the hand, whereas ulnar nerve entrapment at the wrist is going to spare the dorsal sensory branch of the ulnar nerve, so it's just going to be a loss of volar sensation. Your motor examination, looking for atrophy. Again, if you think about the takeoff of the ulnar nerve at the elbow, ulnar nerve at the elbow is going to give motor innervation to your profundus of the ring and small fingers. So patients with a more proximal source of ulnar nerve compression, specifically cubital tunnel, might have weakness of the profundus, which you won't see in ulnar nerve entrapment at the wrist. And I do agree with Dr. Boyer's Sims-Weinstein testing. I do in my office. I think it does help. I will x-ray these patients. X-rays are helpful. It's very, very rare, unless you have the best x-ray tech in the world, to get a great carpal tunnel view that's going to show a handmade hook fracture. Some of them, I'm suspicious about. I think the best cost-effective test is to get the CT. Axial slices will show you whether you have your handmade hook injury. I do believe in MR in someone who has a palpable mass. If you feel swelling along the ulnar aspects of the wrist within Guillain's Canal, I will go do the MR. Not as much for your diagnosis. I think that MR technology will help give you an idea of what the mass may be. But more importantly, I think it helps give me a surgical guide for the extent of the lesion, so I know where I'm going to explore, and in someone that you're worried about an ulnar artery aneurysm, angiography. And that's going to be talked about, ulnar artery aneurysms, in a talk this afternoon. The literature is unclear about the value of electrodiagnostic testing. In someone that I am considering for surgical decompression, I will get it. I think it's helpful to differentiate for a more possible lesion, but it's oftentimes not diagnostic, but it can help in your diagnosis, but it really is a clinical diagnosis. Treat the underlying condition. If someone has a handmade hook fracture, they're not going to get better from conservative treatment. I'm an advocate of just removing the handmade hook. I'm not an advocate of trying to repair one. But in someone such as a cyclist, try splint activity modification to protect their wrist. If someone's a cyclist, put them in a neutral position, ask them to protect their wrist as they're cycling, and then surgery for cases that don't respond. If you're going to operate on someone with ulnar nerve entrapment of the wrist, release the whole tunnel. Don't just go for a part of it. I think you need to come proximal to distal. In someone that doesn't have a mass, I'll do it under a MAC-type anesthetic, a local anesthetic with a little bit of sedation. I think it works perfectly fine, or a regional anesthetic. But on the other hand, always use a tourniquet. Your branches from your ulnar artery are there. You want good, good visualization of the branch of the nerve, especially to be able to visualize where it's going around the hook of the handmade into your hypothenar muscles. Fifteen percent of the time, a communicating branch has been demonstrated the distal aspect of the incision. Look for that and make sure you don't cut that in your exposure, otherwise the patient is going to have possible neuroma or dysesthesia at the distal aspect of the incision. The handmade hook is going to give you a good guide for where to make your incision. It's helpful to go proximal to distal. I think the anatomy is much more predictable at the proximal aspect of the wrist Find your ulnar artery, find your ulnar nerve, and then dissect distally. That's going to allow you to find the superficial branch of the nerve and subsequently the motor branches. Look for the leading edge of the hypothenars and identify the nerve as entering underneath that arch, that arcade at the origin of the hypothenar muscles. As Gilbert described, as that arrow points to, make sure you look for the branch of the hypothenar muscles. You do not want to denervate your hypothenar muscles. The most important thing is to look for masses. You're going to know that before you come in, but even after your exploration, Gilbert demonstrated in his article that you'll oftentimes find ganglions emanating from the piso-metacarpal or the piso-tricuitral ligamentous area, so always palpate for masses, even if you didn't suspect one on your preoperative evaluation. When you have a mass, decompression is generally successful. However, because of the rarity of this diagnosis, there's really absolutely no Level 1 studies looking at the results of release of the ulnar nerve at Guillain's Canal, but you do have good results with appropriate surgical indications. So a trapment of the wrist is a rare cause of ulnar neuropathy. Someone presenting to your office, think about the elbow or the neck. Mass compression can be more likely than you'll see in carpal tunnel compression, and image these patients because I think it will help give you a good guide to your surgical plan. Look at your handmaid, look at your ulnar artery, make sure that the vascular examination is normal, and there's very predictable branching of the nerve within the canal. If you know your anatomy, you should be able to decompress them successfully. Thank you very much. Thank you.

ulnar nerve

Guillon's Canal

compression

diagnosis

surgical decompression