No matter your choice of expletive – from the old “Dangnabbit!!” to the more modern “F**k!”, it’s definitely NOT funny to hit your “funny bone”.
What actually IS your funny bone?
While your Humerus (the bone in your upper arm) might like to claim centre stage at the local Stand-up Comedy show…
…the real culprit is actually a nerve – specifically the ulnar nerve!
At the elbow, the ulnar nerve resides between 2 boney “knobs” on your elbow: the olecranon process (on the backside) and the medial epicondyle (on the inner side of your elbow).
Unfortunately for the ulnar nerve, it is especially vulnerable to getting hit and creating those incredibly uncomfortable pain/tingly sensations for 3 reasons.
1st – Typically nerves lie relatively deep to the skin and are covered by layers of muscle and fat. Unfortunately for this winding nerve, at the elbow, it’s literally stuck between a rock (ie. the bone) and a hard place (ie. whatever table you “decide” to hit your elbow with…).
2nd – All nerves are wrapped in some amount of cushioning connective tissue, with usually approx. 50% of the nerve’s diameter consisting of this protective sheath (1). Unfortunately for the ulnar nerve at the elbow, only approximately 21% of its diameter is covered by this protective sheath, which means even LESS protection than other nerves (1). As most of us have experienced, such as when we sit on our foot, there’s only so much compression a nerve can tolerate before it starts “talking back” to us (eg our foot goes tingly and painful).
3rd – Because the ulnar nerve wraps around the backside of the elbow, it essentially has to take “the long way” around when the elbow is in flexion (or in the bent position, such as when bringing your phone to your ear), thereby increasing tension on the nerve. More tension leads to more compression around the nerve, which reduces the nerve’s blood flow and therefore reduces its oxygen & nutrients that the nerve needs to survive. This in turn, increases the nerve sensitivity and “irritability”. In end range flexion, the ulnar nerve has been shown to stretch out almost 5mm and narrow in size by up to 50% (1)!
But not to fear as nerves are relatively resilient structures! Normally this tension is okay, as nerves can handle 6-8% stretch (only slowing blood flow) for up to approx. 1 hour and up to 15% stretch (stopping blood flow) for a few seconds to a minute (1). In addition to this intrinsic feature, either end of the ulnar nerve (up by the shoulder or down into the hand) can also glide towards the elbow, helping to reduce the overall tension in the nerve. However, if there is an adhesion anywhere else along the nerve, this nerve “gliding” is restricted and can contribute to additional tension in the nerve, further reducing blood flow and increasing the nerves sensitivity!
In summary, the ulnar nerve is extremely vulnerable to both compressive forces as well as tension forces at the elbow. Fortunately, most “funny bone” symptoms are short-lived, lasting only seconds to a few minutes. So, the next time you accidentally hit your funny bone, give your nerve some slack and try straightening your elbow to help reduce the strain on this particular nerve!
However, if you are having any of the following symptoms that last more than a few minutes...
pain (sharp, ache-y) into your inner elbow and/or forearm
“weird” nerve-y symptoms such as burning, buzzing, tingling, numbness into the pinky side of your hand and the little and ring fingers
weakness with your grip and/or pinch strength
loss of dexterity/feeling clumsy in your affected hand
symptom progression: initially symptoms are intermittent at first, but become more frequent, and eventually constant over time
symptoms are generally worst at night
(2)
… it’s possible that your ulnar nerve may be getting injured and it’s important to seek physiotherapy care to prevent permanent nerve damage. The sooner you seek care, the better your prognosis! Once symptoms last longer than 1 year and progress to the point of muscle loss or atrophy in the hand, full recovery is less likely to occur (2).
While the ulnar nerve is most frequently compressed at the elbow (due to the reasons listed above), it’s possible that it may be getting compressed anywhere else along its pathway (from the shoulder to the wrist) (3). Find out where by getting yourself checked out by any of us here at InReach Physiotherapy!
By: Susan Herdman, Registered Physiotherapist
Book a telephysio / online physio / virtual physio / video physiotherapy appointment with a registered physiotherapist in British Columbia. InReach Online Physio services communities in northern and rural BC, such as Masset, Queen Charlotte, Fraser Lake, Fort Nelson, Fort St James, Dease Lake, Fort St John, Dawson Creek, the Gulf Islands, and more!
REFERENCES:
Butler, D.S. The Sensitive Nervous System. Noigroup Publications, Adelaide, Australia, 2000.
Rekant MS, Wilson MS, & Nelson C (2021). Chapter 54: Surgery Management of Compression Neuropathies of the Elbow in Skirven, Osterman, Fedorczyk, Amadio, Feldscher, & Shin’s Rehabilitation of the Hand and Upper Extremity (7th Edition, pp. 745-759). Philadelphia, PA: Elsevier.
Adelsberger L & Bickhart NE (2016). Chapter 7: Ulnar Nerve Compression in Saunders, Astifidis, Burke, Higgins, & McClinton’s Hand and Upper Extremity Rehabilitation: A Practical Guide (4thEdition, pp. 69-74). St. Louis, Missouri: Elsevier.