Folding your thumb

[Function]

Hi everyone

 

Try folding your thumb completely into your handpalm.

At the same time, try to keep your other fingers stretched.

 

You're not able to, aye?

 

The opposite, you can do: you can fold your other fingers in, keeping your thumb stretched.

Folding your index finger in (completely!), it is impossible to keep your middle and ring finger stretched. You can stretch your little finger almost completely.

Folding your middle finger in (completely!), it is impossible to keep any other fingers stretched, except for your thumb.

Folding your ring finger delivers you the same result, with even a more remarkable influence on the little finger.

Folding your little finger makes it unable for you to stretch your middle and ring finger. You can stretch your index finger.

 

I'm looking for a reasonable explanation for this, and I hoped someone here might help me.

I'm having my anatomy atlas in front of me, but haven't had any anatomy class so far, except for osteology. I'm having anatomy next term (which actually begins 9 February).

 

I'm seeing that:

• M. flexor pollicis longus affects thumb movement. It is not connected to anything else influencing other finger movements.
• M. flexor digitorum profundus is connected to all fingers but your thumb, as well is the m. flexor digitorum superficialis.
• M. palmaris longus has a direct connection to the index, middle and ring finger. This might be a reason for the inability to keep one of those 3 folded, while the others are being kept stretched.
• Tendo musculi extensor pollicis longus is connected to the thumb and is lying under the tendines musculi extensor digitorum
• Connexus intertendinei connects the tendons of all fingers but the thumb.
• M. adductor pollicis connects some other muscles and tendons.

There are lots of other muscles, of course, to see, but I thought these might be the most important ones.

 

Can someone explain this to me?

 

Thanks.

 

F.

[Greg H.]

Actually, I can fold my middle finger in completely and still stretch my index finger and my littlest finger straight on both hands.

Edited January 27, 2015 by Greg H.

[zapatos]

I can fold my thumb into my palm without moving the other fingers.

[Function]

Actually, I can fold my middle finger in completely and still stretch my index finger and my littlest finger straight on both hands.

 

Using solely your middle finger?

And this stretching, is it with ease or do you really have to do effort?

I can fold my thumb into my palm without moving the other fingers.

 

Everyone I've asked to was unable to. Please do mind that your thumb may not be supported to that if muscle contraction were to disappear, yoru htumb is no longer folded.

Sorry if this might sound offensive, but I don't believe in some rare East-Flemish joint/muscle/tendon abnormality.

Edited January 27, 2015 by Function

[Greg H.]

 

Using solely your middle finger?

And this stretching, is it with ease or do you really have to do effort?

 

Here's a list:

Thumb - cannot fold into the palm of my hand completely on either hand.

Index finger: when folded completely, only the thumb and pinky remain straight.

Middle finger as above

Ring finger: Only index and thumb remain straight

Pinky:Unable to fold completely without also folding in the ring finger - other fingers remain straight.

 

It's more or less the same on both hands - my right hand isn't what I would call a good baseline, however, due to some knuckle and nerve damage when I was young.

[Strange]

I can fold my thumb into my palm without moving the other fingers.

 

Me too.

[zapatos]

Everyone I've asked to was unable to. Please do mind that your thumb may not be supported to that if muscle contraction were to disappear, yoru htumb is no longer folded.

Sorry if this might sound offensive, but I don't believe in some rare East-Flemish joint/muscle/tendon abnormality.

But you belive your sample size accurately represents the entire population?

[Function]

But you belive your sample size accurately represents the entire population?

 

Of course it doesn't.

It just seems hardly possible to me that everyone I know has the same anatomical abnormality causing this inability.

[Greg H.]

 

Of course it doesn't.

It just seems hardly possible to me that everyone I know has the same anatomical abnormality causing this inability.

I doubt it's an abnormality of any kind. It may be a genetic thing for the local population, or it have something to do with hand size, or even a ratio of hand to finger size.

 

But making blanket statements like your OP without using a statistically significant sample size is just inviting other people to trivially prove you wrong.

[zapatos]

I can also bend eight fingers at the first knuckle at a sharp angle to its furthest extension, while keeping the rest of the finger rigidly straight. And I can bend those eight fingers backwards at the middle joint only. I used to toss a ball with my kids where I would always catch the ball as it fell onto the back of my hands, like it was falling into a shallow cup.

Lots of people are double jointed. Take a look at joint hypermobility.

http://en.wikipedia.org/wiki/Hypermobility_(joints)

[Function]

Hi everyone

 

Before the following long, anatomical part: both the number of people being restricted by this phenomenon and the people not being restricted, are increasing.

 

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Now the anatomical part - an expansion of the problem

 

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made a small expansion of the phenomenon (btw let's call it "the phenomenon = TP" from now on, as this will make stuff easier.

 

• Flexion in metacarpophalangeal joint I + extension interphalangeal joint I [math]\Rightarrow[/math] full extension (carpometacarpal, metacarpophalangeal and all interphalangeal joints) possible in II-V
• Extension in metacarpophalangeal joint I + flexion in interphalangeal joint I [math]\Rightarrow[/math] full extension possible in II-V, with exception of a very light (almost unnoticeable), automatically induced flexion in the distal and proximal interphalangeal joints II and even a smaller flexion in the distal interphalangeal joint III
• Full flexion metacarpophalangeal joint I + full flexion interphalangeal joint I [math]\Rightarrow[/math]
  • Full flexion in distal interphalangeal joint II
  • At forced extension of the index:
    • Maximal angle of the proximal interphalangeal joint II of approximately 90°
  • Flexion of the distal interphalangeal joint III with a maximal forced angle of approx. 135° and
  • Flexion of the proximal interphalangeal joint III with a maximal forced angle of approx. 150°
  • Forces extension of the proximal interphalangeal joint IV is possible after making a weird forced "click" in this joint, as a consequence of which the joint will form a dorsal concave angle of approx. 150°; note that the distal interphalangeal joint IV will still be in flexion when this "click" occured, with thhis joint in rest, but with a forced maximal angle of 180° (full extension) possible
  • Extension of the proximal interphalangeal joint V is possible
  • Very light flexion of the distal interphalangeal joint V with a forced maximal angle (so when the proximal IPh-joint is also forced in full extension) of about 170°; forcing this will cause a slight pain, distal from the hypothenar
  • The "click" mentioned before can also be induced in phalanx III with the same characteristics
    
  • Interestingly enough and I found this really bizarre and perhaps an explanation could be found, this being given: if the click mentioned before is being induced (forced) in a finger, forcing its proximal interphalangeal joint in (hyperextension), all fingers lying medial (ulnary) of this finger will no longer be affected by the thumb flexion and will thus no longer be limited in extension!
  • The "click" is not possible in phalanx II.
• Passive flexion of the metacarpal I, distal phalanx I and proximal phalanx I will not induce the forced flexion in other fingers. The cause of the phenomenon might thus be tendinous.
• A sole passive flexion of the proximal phalanx I, but an active flexion of the distal phalanx I will induce the phenomenon. The cause might thus be correlated to the M. flexor pollicis longus.

Other muscles of interest:

• M. flexor digitorum superficialis
  • Origin: epicondylus medialis humeri + proc. coronoideus + caput radii (anterior part)
  • Insertion: basis phalangi medii II-V
  • Innervation: N. medianus
• M. flexor digitorum profundus
  • Origin: facies anterior ulnae + membrana interossea
  • Insertion: basis phalangi distalis II-V
  • Innervation: N. ulnaris + N. interosseus antebrachii from N. medianus
• M. flexor pollicis longus
  • Origin: facies anterior radii
  • Insertion: basis phalanx distalis I
  • Innervation: N. interosseus antebrachii anterior from N. medianus

Although flexor pollicis longus and flexor digitorum profundus are being innervated by the same nerve, this hardly seems a 'nervous' affaire to me: if this would be the case, imo, flexion of the fingers should, vice versa and in the same way, force flexion in the thumb and also in all other fingers, which is not the case.

 

I will present this question soon to my professor of anatomy, unless someone can give me a great answer here, or give me suggestions I can suggest, asking them to be confirmed by her.

 

If some things in this expansion are not clear, please tell me so and I will try to explain it a bit better.

Edited April 1, 2015 by Function

[Function]

IMPORTANT UPDATE

 

Found what might be the cause of these symptoms.

 

I found the Linburg-Comstock syndrome very well describing above descriptions:

 

"The Linburg-Comstock (LC) syndrome is distinguished by the inability to actively flex the interphalangeal (IP) joint of the thumb without simultaneously flexing the distal IP joint of the index finger. Any resistance to this 'parasitic' reaction causes pain on the palmar side of the wrist or in the distal part of the forearm; this is due to an anomalous tendinous connection between the flexor pollicus longus (FPL) and the flexor digitorum profundus (FDP)."

 

http://www.ncbi.nlm.nih.gov/pubmed/10904829

 

The condition is solved surgically by cutting these tendinous connections.

It is thus, as was - comprehensibly - denied before, an anomaly.

 

Sigh... Apparently the thing I found is interestingly enough to give a name... Sadly enough, 36 years too late

Edited April 6, 2015 by Function