Ulnar neuropathy
If you do not have carpal tunnel syndrome, the next commonest cause of tingling fingers is a problem with the other main nerve to the hand – the ‘ulnar’ nerve. This nerve passes from the shoulder, down the inside of the upper arm, round the back of the elbow (the ‘funny bone’ is where the nerve passes round the elbow) and down the medial side (that is the little finger side) of the forearm to eventually send branches to the little finger, the adjacent side of the ring finger, part of the back of the hand, and many of the small muscles within the hand.
This nerve can be trapped or subject to chronic minor injury at several sites along this path with the commonest ones being around the elbow. Like carpal tunnel syndrome, ulnar nerve problems can wake the sufferer at night, be aggravated by activities, result in weakness of the hand muscles and produce loss of sensation in severe cases. There are however important differences in the clinical presentation of problems with the different nerves:
Most significantly, which fingers are worst affected by tingling is the best clue as to which nerve to suspect – the thumb side of the hand suggests carpal tunnel syndrome whereas the little finger side suggests problems with the ulnar nerve.
Ulnar nerve problems are commoner in the non-dominant arm while CTS is commoner in the dominant hand, and the commonest ulnar nerve problems are aggravated by bending the elbow because that stretches the nerve. Weakness and wasting of the small muscles of the hand, best seen on the back of the hand as ‘guttering’ between the bones, is a late sign of trouble with the ulnar nerve. Oddly, pain around the elbow itself is not a marked feature.
TERMINOLOGY
Because there are several distinct anatomical sites at which the ulnar nerve can be compromised there is more variety in terminology than for carpal tunnel syndrome which is, by definition, a problem at a particular site.
Ulnar neuropathy – this is a generic term covering any problem with the ulnar nerve
Ulnar neuropathy at the elbow (UNE) – this is a useful term lumping together all of the different problems which occur in the region of the elbow, from proximal to distal (ie armpit to hand direction) these are:
Ligament of Struthers – about 1% of the population have a fibrous band which is attached to a bony spur of the humerus (the main bone of the upper arm), usually found about 5 cm above the elbow and extends down to the medial epicondyle – the bony prominence on the inside of the elbow. This structure can cause compression of the median nerve, brachial artery or ulnar nerve.
Medial epicondyle – at the elbow the humerus swells to produce two bony prominences (the epicondyles) which can be felt on the inside and outside of the elbow. With the palm held facing upwards the medial epicondyle is the one facing the body and the lateral epicondyle is the one facing away from the body. The point of the elbow is actually the end of one of the forearm bones and is called the olecranon. Between the olecranon and the medial epicondyle in a normal elbow is a groove through which passes the ulnar nerve where it can sometimes be felt as a cord like structure. In some individuals, when the elbow is bent, the nerve will pop out of this groove and flick over the medial epicondyle to lie in front of it (ie on the palm side) rather than behind it – a movement referred to as subluxation. It is not known for certain whether a nerve which subluxes is more likely to develop problems. If the groove between the medial epicondyle and olecranon is shallow then the nerve is exposed to being leaned on and compressed against the bone when we lean on the elbow and even with a normal ulnar groove the nerve is stretched around the elbow whenever the elbow is flexed. Most people are familiar with ‘hitting the funny bone’ – what you are actually doing is hitting the nerve!
Cubital tunnel – sometimes confusingly referred to as CTS and thus confused with carpal tunnel syndrome – just below the elbow the ulnar nerve passes between the two heads of flexor carpi ulnaris muscle. This anatomical terminology requires a bit of explanation. The simplest form of muscle is a single long structure which is attached to one point on a bone at each end. However some muscles have a more complicated structure and the muscle may divide at one end to form attachments to several different bones – think of the muscle as having several ‘anchor points’. In muscles like this the parts going to the different anchor points are referred to as ‘heads’. The flexor carpi ulnaris muscle bends the wrist joint and it has two anchors at the elbow, one attachment to the humerus (in fact to the medial epicondyle) and one to the ulna – one of the bones of the forearm – at the olecranon process. The two heads of the muscle are normally connected by a thin fibrous layer, directly under which lies the ulnar nerve. Close to the attachments to the medial epicondyle and olecranon this fibrous layer sometimes has an ‘edge’ which can be thickened, known as Osborne’s ligament, which can alternatively be thought of as a band connecting the medial epicondyle to the olecranon. In a few patients there is an additional muscle at this site called the anconeus epitrochlearis which can be seen on ultrasound imaging and which may be implicated in compression of the ulnar nerve. The exact boundaries of the cubital tunnel are slightly open to debate but most authorities consider that the tunnel starts at the level of the medial epicondyle and olecranon and extends more or less to the point at which the two heads of the flexor carpi ulnaris muscle join.
Some authors believe that it is important to identify exactly where the precise site of pathology is along this 5 cm or so of nerve around the elbow but the evidence that variations in treatment approach based on such precise anatomical diagnosis make any difference to outcomes is inconclusive.
It is also possible to have compromise of the ulnar nerve in a site at the wrist known as the canal of Guyon. Like the carpal tunnel this space is bounded by bones and a ligament but the ligament forming the roof of the canal of Guyon is a much weaker and less substantial structure than the transverse carpal ligament forming the roof of the carpal tunnel. Another interesting difference is that there is a large artery passing through the canal of Guyon whereas there is usually no major artery in the carpal tunnel. Problems with the ulnar nerve at this site often seem to be a result of structural anomalies such a ganglion cysts in the canal.
Finally, the terminal branch of the ulnar nerve in the palm which provides motor nerve fibres controlling the small hand muscles, is sometimes injured – this is sometimes seen for example in woodworkers who use the heel of the hand and palm to drive a chisel.
DIFFERENCES IN AETIOLOGY
There is considerably more variation in the anatomy of the elbow in the region of the ulnar nerve than there is in the carpal tunnel and the mechanisms by which the nerve can be compromised are probably more varied, and quite often mixed. Whereas in carpal tunnel syndrome the predominant mechanism seems likely to be an increase in pressure in the tunnel, for the ulnar nerve at the elbow some patients may have a well defined anatomical tunnel in which the pressure may be raised but in others the nerve will be subject to prolonged/regular stretching or to direct pressure injury from outside when the elbow is leaned on. It may also be irritated frictionally by moving over the medial epicondyle with movement. In many cases several of these mechanisms are probably acting at once.
DIAGNOSIS
As with carpal tunnel syndrome the diagnosis that there is a problem with the ulnar nerve is generally an easy one to make and it is usually possible to make a good estimate of whether the problem is in the region of the wrist, elbow, or shoulder by looking at the pattern of weak muscles and the extent of sensory disturbance. However localizing the problem exactly around the elbow, if one believes that it matters, generally requires nerve conduction studies and imaging with MRI or ultrasound. The bony spur that indicates the presence of a ligament of Struthers can also be seen on plain x-rays. As with carpal tunnel syndrome the ability of nerve conduction studies to reliably identify the presence of ulnar nerve problems at the elbow is not very well quantified. There are clearly significant numbers of false negative tests but the precise percentage is unknown as there is no wholly reliable way of making the diagnosis which can be used for comparison.
TREATMENT
Treatment of ulnar neuropathy at the elbow is less satisfactory than treatment of carpal tunnel syndrome. Some patients are able to control the symptoms by avoiding flexion of the elbow and not leaning on it. If such conservative measures fail then surgeons have tried many different operations ranging from equivalents of carpal tunnel decompression in which attempts are made to remove or alter structures which may be compressing the nerve through to transposition procedures in which the nerve is moved to a different site – around to the front of the elbow. Much of the surgical literature is devoted to arguing the relative merits of one operation or another but there is very little comparing surgical with non-surgical treatment. One Dutch paper (Beekman 2004) followed up 46 affected arms which were treated conservatively and 28 which were treated surgically for 14 months. Only 5 (11%) of the conservatively treated arms and 7 (25%) of the surgically treated ones were completely cured at 14 months. Patients who showed the phenomenon of ‘conduction block’ or slowing of conduction in the elbow segment on their nerve conduction studies had better results while patients with greater nerve swelling on ultrasound imaging had worse outcomes – all patients with an ulnar nerve diameter of >3.5mm remained symptomatic at follow-up regardless of treatment.
Steroids – curiously there have been few attempts to treat ulnar nerve problems at the elbow with steroid injection. However a paper has just appeared reporting a trial of steroid injection and in contrast to the obvious effectiveness of this mode of treatment in CTS it seems to have been of no benefit in ulnar neuropathy at the elbow (Veen 2015). This would seem to lend support to the idea that the two conditions are not just similar ‘tunnel syndromes’ differing only in anatomical site and nerve affected
Revision date - 6th July 2015
