High Tone in the Distal
Transverse Arch?
Hi
Carrie,
I've been reading your posts on OT Exchange and explored your website.
You are a great resource for me, a relatively new school-based OT.
I learned something about the palmar arch, and know that I need to be
looking at it during evaluations. I know that no arch indicates low
tone and will require hand exercises to increase tone and subsequent
strength. And, when a high arch occurs, I suppose the opposite is true
and that higher tone exists and this is where it gets fuzzy for me. Do
I need to inhibit the tone? And to what end? What's the implications of
a high arch?
Carrie's
answer:
O.K.
to make sure we are
on the same page, I am assuming when you refer to the palmar arch, you
mean the distal transverse (metacarpal) arch. You really got me
thinking with your e-mail, I've been pondering the last day and dug out
some of my fine motor resources to read.
According to James Strickland, MD
(hand surgeon) in Hand Function in the Child (ed.Henderson & Pehoski) the intrinsics are
"responsible for the changes in the configuration of the osseous [bony]
arches..." p. 18 So yes, a high arch would be be due to higher tone in
the intrinsics. I would go according to functional need. If the hand has high tone, is
there cramping of the muscles especially with writing? Then use weight
bearing on the hands to inhibit some of the tone.
One of the primary purposes of the distal transverse arch is to provide
a base of stability for movements the ulnar fingers. I read the
following on the web:
DISTAL TRANSVERSE ARCH
"Hertling and Kessler (p. 257) call this the
metacarpal arch, because it is formed by the metacarpal heads;
metacarpals 2 and 3 are stable while 4 and 5 are relatively mobile. You
can observe the arch's combination of "radial" stability and "ulnar"
mobility by loosely closing your fist, then squeezing more tightly,
when you will observe movement in the more mobile fourth and fifth
metacarpals."
Another experiment that you can do with your hand, is to pull on a
rope. You'll feel that the real power is generated on the radial side.
The muscles in the hypothenar eminence [and the radial fingers]
are innervated by slow firing nerves and the ulnar fingers are
innervated by quicker firing nerves for speed and dexterity. It's part
of the reason, a pencil should never be held opposed to the ring
finger. This is from Mary Benbow's work.
A child needs to hold the ring/little fingers still and tucked into the
hand, to form a still foundation for the transverse arch. The arch
provides the index/middle fingers a stable base for their movements
while writing. A child has to learn to keep the ulnar side of the hand
still (it is more mobile according to the above source). So watch for
that separation of the two sides of the hand. Also, is the child
achieving adequate opposition of the thumb to each of the fingers?
I'm having a hard time envisioning difficulties with having too high of
a distal transverse arch...I haven't seen this. I'd watch for the more
common fine motor difficulties, to see if they are having an impact the
child's functionality. Here's what I watch for: separation of the two
sides of the hand, radial stability with free movement of the ulnar
(dexterity) fingers and thumb, good wrist extension to support the
finger movements (try picking up a manipulative with your wrist fully
flexed), and good flexion of the thumb interphalangeal joint with an open web space.
Thanks for writing, It's always fun to receive a thought provoking
e-mail.
Carrie