DSM: A lute player friend of mine has been having progressively more difficulty with his left hand. Focal Dystonia, probably. Nothing so bad as Leon Fleisher’s difficulties years ago or anything like that. But still a major impediment to his performance practice and concertizing.
CMT: There’s still the problem of diagnostic accuracy for Focal Dystonia—and the imprecision of knowing how a loss of “representational specificity” or other changes in the brain can come about through over-use of the hand; the uncertainty of explaining why Botox injected peripherally actually brings about an improvement in this condition if the cause is ‘central’, in the brain. Is your friend sure that it’s Focal Dystonia and not Carpal Tunnel Syndrome or something else?
DSM: Well, no. The neurologists he’s seen have been inconclusive. One hand surgeon wanted to persuade him to be operated for Carpal Tunnel, but my friend regards that as a last resort. And the neurologists’ EMG and imaging and other studies have not been terribly helpful in ruling anything in or out yet. His main complaint has to do with a loss of strength in the lumbrical muscles in his hand, especially the ones involved in moving the middle finger and the ring finger. So it’s not a textbook picture of Focal Dystonia. I suspect he’ll have to go to one of the Performing Arts Medicine clinics that have neurologists experienced in this, as opposed to the well-meaning neurologists and electromyographers he’s seen so far, who have no particular expertise in the problems of musicians.
CMT: There are probably some string players with variant anatomy who just happen to have asymmetrically strong mechanical connections between the ring and middle extrinsic flexor muscles.
Supposedly the phenomenon of middle-ring ‘enslaving’ or ‘subordination’ has a big neural component. If it’s ‘central’ or ‘neural’ then in principle it should be susceptible to retraining through exercises. The connections between adjacent digits involving tendons and muscle fiber groupings of the deep flexor (flexor digitorum profundus) play a big part, though. The ‘peripheral’ biomechanical component shouldn’t be underestimated—it definitely contributes to some of the ‘enslaving’ or ‘subordination’ of one finger to the other. But recent work is showing that enslaving effects among different hand muscles involve both central neural interaction among the structures controlling flexor muscles and lumbricals in the hand as well as peripheral mechanical interactions.
It’s possible that your friend is someone who just happens to have anatomy with substantial tendon sharing. In medical school, I dissected a hand with two lumbrical muscles at each place where you’d ordinarily find only one, and the muscles inserted to adjacent digits. This anatomical variation is not at all uncommon. And if you’re born with this anatomical variation and choose to play lute, then the motions involved in virtuosic lute playing may place particularly great stresses on your aberrant anatomy, in ways that might not affect persons with conventional anatomy quite so severely.
DSM: So what’s going on when we retrain or ‘retune’ the biomechanics with Constraint-Induced Therapy or other physical therapy techniques?
CMT: Well, we learn independent ring and middle finger motion by altering how we activate the controlling networks in the brain, in the primary motor cortex. Neurons in motor cortex aren’t like house-wiring: they don’t make simple direct connections to individual muscles. Instead, our evolution as mammals has set us up to flex and extend our fingers together and to grasp things. Independent digit movements outside of the index finger and thumb require complex inter-neuron coordination to get the desired balance in muscle force at each joint.
Completely independent digit motion is the result of a complex pattern of activation that isolates a movement by preventing other movements mechanically and perhaps by inhibiting some muscles as well. This is why it takes lots of repetitions to learn such skills. Learning new motor skills changes the way muscles and movements are represented topographically among the cells of the motor cortex, and also the way sensory information is represented in the sensory cortex.
Here’s some anatomy, just to give you an idea of where things are, and why the geometry and biomechanics of the hand are so vulnerable as they are.
Upper Left | Lower Left | Lower Right | Upper Right |
1. Distal palmar fat pad | 7. Tendon extensor digitorum communis | 14. Tendons and mm. dorsal | 20. Proximal phalanx, fifth digit |
The photomacrograph of a transverse whole-section of the hand passes through the four fingers. The slice is taken of a cadaver hand, a frozen section, distal to the thumb—right at the end of the hand, before the fingers start. You can see that the little finger is separated from the others, which makes sense if you look at your own hand. The gap between the little finger and the ring finger comes proximally further into the hand, compared to the gaps between the other fingers. The articulation (22) between the proximal (20) and middle (23) phalanges is seen in the cross-sectional slice in the picture above. This is a pretty bulky hand. Probably not the hand of a musician. But the image helps to give you and idea of the anatomical relationships just the same.
Notice how the extensor tendon to the ring (fourth) finger is very closely applied to its dorsal surface. Not much clearance there! The tendons and distal ends of both interosseous and lumbrical muscles (8, 11, 14, 15, 18) are identified in the picture in relation to the middle digit proximal phalanx (12). The first (2) and second (6) lumbricals are seen close to, and on the radial side of, their tendons of origin. The two lateral (first and second) lumbricals arise from the radial side of the palmer aspect of the first and second tendons of flexor digitorum profundus. The two medial (third and fourth) arise from adjacent sides of the second and third, and the third and fourth tendons of flexor digitorum profundus. The muscles insert into the radial border of the tendon of extensor digitorum on the back of the proximal phalanx. The compactness of this anatomy reveals why the mechanical leverage and pulley-and-lever structures are so exquisitely sensitive. The fulcrums for the action of the lumbricals on the phalanges operate at a relatively high mechanical advantage (force ratio), and therefore small disturbances in the muscles themselves or in the tendon bundle and the tendons’ insertion points can give rise to surprisingly large disturbances in the motion—velocity of attack and release, power, etc.—at the phalanx.
Principles of Neuroplasticity—Strategies for Rehabilitation for Focal Dystonia through Forced Use:
- Based on the assumption that patients will more readily use the extremity that is normal (unaffected) unless you restrict it.
- Forcing the use of the affected extremity will modify muscle structure and increase function.
- Effective for pianists but not for guitarists or lutenists.
Constraint-Induced Therapy (Sensory Motor Retuning):
- Elbert, Sterr, and colleagues studied 7 musicians with Focal Dystonia.
- Forced use on the instrument with a splint that restricted the movement of each finger; 10 days, 7 hrs each day.
- Six of 7 improved; less improvement for guitarists or lutenists than for pianists.
In the absence of a definitive diagnosis, the Physical Therapist or Rehabilitation Medicine practitioner may treat on an empirical basis:
- Treat the initial injury as part of [an empirically conjectured—] inflammatory, healing process.
- Decrease stress and stop negative abnormal patterns of movement.
At least in me, there are strong linkages between the middle and ring fingers when I attempt to flex the middle finger at the distal (end) joints. This probably involves mechanical linkages between the profundus muscles for those two fingers—linkages at the level of both proximal tendon and muscle. Nobody knows whether those linkages can evolve over time under conditions of high repetition stress or over-use.
DSM: Obviously, if inflammation is present, you’d expect that some fibrosis and linkage would occur as part of the healing and response to the inflammation.
CMT: But if no overt tendonitis or other inflammatory process is going on, it’s not clear whether a fibrotic proliferative reaction would occur, to give rise to the kind of symptoms your friend is experiencing. Assuming it’s not Focal Dystonia, the Constraint-Induced Therapy of “retuning” exercises can help to compensate for any abnormal anatomical linkages that might be in his hand. Best of luck to your lutenist friend!
- David Leisner, Manhattan School of Music, Guitar Dept Co-Chair. Rehab re: Focal Dystonia and over-use injury.
- Brin M, Comella C, Jankovic J. Dystonia: Etiology, Clinical Features, and Treatment. Lippincott, 2004.
- Byl N. Aberrant Learning Associated with Upper Extremity Overuse. UCSF Physical Therapy Dept, 2004. [1MB pdf]
- Chalfoun J, Younes R, Ben-Ouezdo F. Physiological Muscle Forces, Activation and Displacement. Working Paper, CNRS, 2004. [1MB pdf]
- Chamber Music Today, Black-Key Biomechanics, 30-OCT-2006. Performing Arts Medicine Clinics.
- Elbert T, et al. Alteration of digital representations in somatosensory cortex in focal hand dystonia. Neuroreport. 1998; 9:3571-5.
- Lee E, Joumaa V, Herzog W. New insights into the passive force enhancement in skeletal muscles. J Biomech. 2007;40:719-27.
- Leijnse J.Why the Lumbrical muscle should not be bigger--a force model of the lumbrical in the unloaded human finger. J Biomechanics 1997; 30: 1107-14. [1MB pdf]
- Munsat T, Jankovic J, eds. Dystonia. Demos, 2005.
- Rassier D, Herzog W. Force enhancement and relaxation rates after stretch of activated muscle fibres. Proc Biol Sci. 2005;272(1562):475-80.
- Stacy M, ed. Handbook of Dystonia. Informa, 2006.
- Warner T, Bressman S, eds. Clinical Diagnosis and Management of Dystonia. Informa, 2007.
No comments:
Post a Comment