By Peter Tang, MD, MPH, FAOA

I think cubital tunnel syndrome is such an interesting topic because it is the second most common compressive neuropathy, but we seem to know so little about it. We don’t know what exactly causes it and we don’t know where the problem is happening. Unlike carpal tunnel syndrome, where we see significant thickening of the transverse carpal ligament during a release and it seems obvious that it is an issue of compression, I rarely find a site of compression during transpositions. Personally, I think it is an issue of tension because the nerve lies posterior to the elbow’s flexion-extension axis.

Required reading for the residents and fellows at my teaching institution is Amadio’s 1986 classic paper, “Anatomical basis for a technique of ulnar nerve transposition.” (Surgical and Radiologic Anatomy). In his paper, he describes five sites of compression that had been reported in the literature to date: Arcade of Struthers, medial intermuscular septum, medial epicondyle, cubital tunnel (the roof of the cubital tunnel, which is the fascia covering the start of the two FCU heads, has been called the Arcuate Ligament or the Ligament of Osborne; when I write about it I call it the Arcuate Ligament of Osborne to capture all the names for clarity), and the deep flexor-pronator aponeurosis. The reality is, there is just one continuous layer of fascia over the nerve from the arm to the forearm. However, it is one of my biggest pet peeves (partly because I didn’t know this myself) when trainees think that the cubital tunnel is the fascia immediately posterior to the medial epicondyle covering the retrocondylar groove. It is not. The cubital tunnel is just distal to the medial epicondyle and is illustrated nicely in Figure 2 of Amadio’s paper. All this being said, I don’t believe there are five sites of compression. Why is there is one problem site for carpal tunnel but there are five for cubital tunnel? It doesn’t make sense.

Ulnar nerve transposition surgery is one of my favorite surgeries – great anatomy, you dissect dissect around a nerve, and patients usually achieve symptom relief. However, after I had the nerve fully dissected out during a transposition, I would only find one site of the nerve that looked abnormal. I thought to myself that maybe this amount of dissection is overkill. In-situ ulnar nerve release seems very popular these days and most of the literature finds there is not one superior surgical procedure, so why not perform the least invasive option? With the exception of using endoscopic technique, if a surgeon does an in-situ release through a small incision (4-5 cm incision centered proximal/distal over the media epicondyle), then they cannot believe that there are five sites of compression in cubital tunnel syndrome because it is very difficult to release the Arcade of Struthers, which is 8 cm proximal to the medial epicondyle and the deep aponeurosis of the flexor carpi ulnaris, which is 5 cm distal to the medial epicondyle through that size incision.

When I started doing in-situ release I would look at the nerve to see if I could identify the problem area (by looking at nerve swelling and hyperemia) to prove to myself that I was doing the surgery in the correct location. In my adoption phase of this technique I would sometimes convert to a subcutaneous transposition when I could not find a problem site in the nerve that was exposed after the in-situ release. I no longer do this. Personally, I believe that the problem usually happens around the medial epicondyle/retrocondylar groove due to tension at this site. One may ask that if tension is the issue, then why does in-situ release work, because the nerve still experiences tension because it is in the same location posterior to the medial epicondyle? My thought is the in-situ release allows for some nerve subluxation anteriorly or medially out of the retrocondylar groove, which is enough to relieve the tension causing the patient’s symptoms.

One major problem with in-situ release is what to do with the nerve when it is unstable. The classic teaching if the nerve subluxes after in-situ release is to transpose. However, what if the nerve subluxes some? How much is too much? Surprisingly, there is no grading system of ulnar nerve instability after in-situ release. I developed a grading system that can at least allow us to speak uniformly about the matter. I described this classification in the December 2017 issue of Techniques in Hand & Upper Extremity along with a technique to stabilize the nerve when the nerve is unstable. This blocking flap technique consists of a rectangular flap lifted from the flexor-pronator fascia flipped posteriorly and sutured to the posterior subcutaneous tissue or triceps. The flap blocks the nerve from coming out of the retrocondylar groove as the elbow goes into flexion without compressing the nerve. The flap is just a longer version of the classic square fasciodermal sling that Eaton described for the subcutaneous transposition. (Eaton JBJS 1980)

My last deep thought (Deep Thoughts is from humorist Jack Handey whose work was on Saturday Night Live in the 90’s; there is a website, check it out, it is hilarious) about cubital tunnel syndrome relates to revision surgery. It is unclear to me why papers have popularized the notion that the procedure of choice for revision surgery is the Learmonth submuscular transposition (Learmonth, Surg Gynecol Obstet 1942). I don’t think that surgery should be done – ever. It is so invasive and destructive and there is no space for a nerve under the flexor-pronator muscles and above the elbow. I think people do it because there is no other procedure more arduous. I think if there was technique that was even more difficult where you transpose the nerve to the radial side of the elbow, this would be the new procedure du jour for failed primary cubital tunnel surgery.

Assuming the patient has the right diagnosis and there was a complete release of the nerve at the first surgery (which is usually the case), the most common cause of failure after primary release is cicatrix or scar formation. I believe successful revision surgery has less to do with where you put the nerve and more to do with preventing scar recurrence. So a scar barrier placed around the nerve such as a conduit I believe, is key. This being said, if the first surgery was an in-situ release then I would move the nerve away from the original scarred bed into a subcutaneous transposition. If the index procedures was an intramuscular or submuscular transposition, then I would put the nerve into a subcutaneous position. I believe that the subcutaneous transposition is the least invasive and least compressive of the transpositions which is why it is my preferred choice for transposition. If the first surgery was a subcutaneous transposition then I would either just do a neurolysis and then place a nerve wrap or conduit and leave it its subcutaneous position or do a permutation of Danoff’s pedicled adipose flap technique where I open a pocket like a book  in the subcutaneous layer, and place the nerve in the pocket (Danoff, J Hand Surg 2014). Again, with revision cubital tunnel surgery when cicatrix is the problem, I am always placing a conduit or wrap around the nerve to keep cicatrix away from the nerve. But the reality is, if the patient is a scar former and everywhere you dissect excessive scar will form, then the prognosis is not good.

Again just some thoughts (deep or superficial depending on your perspective). I am happy to hear your thoughts.