The first time my pinky stopped working was on a bike ride down Skyline drive in California. The combination of cold rain and wind removed the heat from my ungloved hands faster than my blood could replace it. We pulled over to stop because I was having difficulty operating the brakes, which is not a good thing on a wet and rapid descent. I tried moving my hands and found that I was unable to bring my pinky in to touch my ring finger; it just stayed out there by itself, indifferent to my commands.
The inability to actively bring the pinky against the other fingers (loss of adduction) is called Wartenberg’s sign. It signifies that function of the deep branch of the ulnar nerve has been lost. This branch is the phone line to the third palmar interosseus muscle, which is the sole muscle responsible for bringing your pinky in against your other fingers. If the third palmar interosseus muscle isn’t working, the resting tension of the extensor digiti minimi pulls the pinky away from the ring finger (see the illustrations below). Once my hands warmed up, blood flow returned and my pinky worked again. Next time you think your hands are really cold, test yourself for the Wartenberg’s sign to see just how cold they really are.
Wartenberg’s sign in vivo. I am trying as hard as I can to bring my fingers together but can’t do it on the right side.
The third palmar interosseus muscle is highligted in blue. This muscle pulls the pinky in.
As a side note, I was also likely suffering from decreased function of the other small muscles of the hand supplied by the deep branch of the ulnar nerve: the 3rd and 4th lumbricals, adductor digiti minimi and flexor digiti minimi, as well as adductor pollicis (the last of which adducts the thumb, contributing to my loss of grip strength).
The extensor digiti minimi muscle is highligted in blue. Although the primary action of this muscle is to straighten the pinky, it has a slight pull outward on the pinky that manifests when the third palmar interosseus is not functining (Wartenberg’s sign). Notice that the extensr digiti minimi attaches far up on the forearm with a much more proximal nerve supply (radial nerve.)
My Hands in the Andes
At some point in our 25 day biking adventure across the Andes of Peru, my pinky stopped working. I don’t know exactly when it started, and the first few times I just chalked it up to cold weather. But then I started having difficulty with my right hand even when it wasn’t cold. I had difficulty hitting the paddle shifter on the bike, stuffing a sleeping bag in a dry bag, holding a plate, scrubbing, gripping things tightly, and writing with a pen. I realized then just how much I relied on the full function of my pinky (and ring) fingers to do many of the tasks of daily living.*
Finally I performed a little PT exam on my self to assess my hand function more specifically. Sure enough, Wartenberg’s sign was there. I was also unable to make the lumbrical position on my right hand (see picture below). The lumbrical position can only be achieved if the little muscles called the lumbricals are working properly–like the third palmar interosseus these are innervated by the deep branch of the ulnar nerve.
Notice how I am unable to straighten my pinky and ring finger in the lumbrical position in my right hand.
The verdict? The deep branch of my ulnar nerve wasn’t working. Since I had otherwise normal function of ulnar nerve innervated muscles above the wrist, I knew it was only the deep portion that was having the problem.
Here you can see the deep branch of the ulnar nerve highlighted in blue. It has a fairly roundabout pathway and passes right under the heel of the palm on which I was bearing weight while biking.
Why wasn’t the ulnar nerve working? Although my hands were often cold, the vast majority of the trip they were not cold so I ruled out temperature as the primary cause. That left me with pressure as the primary suspect and there are several pieces of incriminating evidence:
1. We were riding a bicycle anywhere from 4-10 hours a day
2. As the driver of a tandem bicycle fully loaded with gear, I could not take my hands off the handlebars so there was constant pressure on my hands. I did take my hands off once to to give my hands a break and we immediately veered across the road headed straight for a clifff. I didn’t do it again.
3. The seat was already at its lowest height and the handlebars at their highest. This arrangement was aerodynamic and shifted more weight to the front wheel and off the overburdened back wheel, but unfortunately placed a fair amount of my weight on my hands.
4. My gloves did not have padding on the palm.
5. Finally — and this is likely the reason that only my right hand suffered the damage it did — the bar tape on the right side of my handlebars ripped at the corner, directly at the place where the heel of my palm rested most of the day.
Here you can see where the thin padding ripped on the right side of my handlebars and we covered it with electric tape.
What I did about it
I tried massaging the area, as well as soaking it in tepid water then testing my function. This resulted in no improvement. The goal of these efforts was to increase blood flow to the nerve. These efforts didn’t work either because they didn’t actually increase blood flow (a tub of hot water is hard to find in the Andes) or because I had nerve damage that would take much longer to heal.
And that’s the good news, nerves do heal, but very slowly. Since I didn’t have a complete severing of my nerve I am expecting return of full function in three weeks. As long as I don’t keep damaging it.
To this end, I started wrapping my handlebars in wool socks.
Oh and I also stopped biking. We reached our fnal destination, Pisac Peru, after 893 miles and 25 days in the saddle.
If you are going to be biking for a long time, get some of those goofy biking gloves woth padding in the palm, or one of those ergonomic handlebars that is flat on top, or just take your hands off the bars from time to time. But not on curves…
It has now been over a week after I started noticing my deficits, I can make the lumbrical position better than before but still have Wartenberg’s sign. I am going to try soaking in some really hot water to see if I can jump start it.