Last week my EPL tendon went snafu. For no reason, my left thumb just stopped doing what it always has. It didn't hurt, but it didn't work. It was rather disconcerting. I wondered if it was the first sign of some hideous degenerative nerve condition that would put me in a wheelchair. But after searching with the dreaded Dr Google, I figured out I'd just torn the EPL tendon. Who knew tendons can wear away painlessly and break? Who knew we can diagnose these things without an xray, just with an eyeball? So, I had surgery in hospital yesterday to fix it.

I looked at anatomy drawings and it dawned on me, we can see all the tendons on the back of our hands if we flex them the right way in the right light. And by golly, my right thumb had two tendons, but my left only had one. It was so obvious. Have a look at your own hand. We have two long tendons running down the back of every digit (though these look like one single tendon on our fingers, the two are obvious on our thumbs). Essentially, one tendon pulls on the top knuckle, and one pulls on the one below. These cords run down our hands through tunnels that keep them neat — like rolling over pulleys. They run right over our wrists and connect to muscles attached to the long bones of our forearm. Every time you wiggle your fingers, muscles are tugging from somewhere deep in your forearm, a long way from your hand.

Somehow as babies we all learn which muscle moves each knuckle to get full finger control. No wonder it takes months to learn fine motor skills…