Lumbricals, Some Getting Stronger, Others Discouragingly Staying the Same

G   reat strength is necessary in the fingers, yes, but it comes with playing, if one plays rightly—that is, musically. From the moment one senses that the finger must ‘sing’, it becomes stronger. That is quite a different matter from playing exercises or etudes merely for the sake of strengthening, and saying ‘I must exercise my fingers and make them strong.’ Such playing as this latter sort does not help at all.”
  —  Vladimir Horowitz.

M y guitarist-pianist friend and colleague at work comes and visits with me this week, says that for more than a month he’s been doing exercises to strengthen the lumbrical muscles in his hands. The left hand has been responding, but the right hand—especially the ring finger and pinky—has been staying the same or, paradoxically, might even be getting weaker.

H e worries about focal dystonia. (Jason Solomon of Georgia Guitar Quartet has an excellent article about that here.) He worries about carpal tunnel syndrome (CTS). I am not a neurologist, but I know enough to know when to go and hire one. I ask my friend about whether he has any numbness or difference in sensation among the fingers on the right hand, or between the right and left...

T he fact that my friend is a professional software developer/engineer who spends 70+ hours at a laptop keyboard each week is something the neurologist will need to know, as part of the evaluation—in addition to the heavy hours on guitar and piano. In other words, if what my friend is experiencing is some type of repetitive stress injury (RSI), then characterizing the various types and intensities of repetitive motions will be clinically important.

T he state-of-the-art of hand biomechanics and hand problems of musicians have been a recurring interest for me for some years, so, in response my friend’s immediate situation, I go online and scan the current medical journal literature, to see what, if anything, is new in the last year or two. For his benefit and maybe for your own, I gather some relevant things together in the list of links below.

W here exactly is the ‘carpal tunnel’? The carpal tunnel is the narrow space anatomically between the small carpal bones of the wrist and the ligament called the flexor retinaculum. Here’s how you can find it: Put your left index finger in the center of your right palm, then move the finger about two inches down your palm toward your arm, stopping when your finger approaches the edge of the fleshy part of your hand. Your finger now lies directly over the carpal tunnel. The carpal tunnel is the U-shaped depression with carpal bones below and on either side. The flexor retinaculum ligament stretches over the top of the ‘U’ to make a tunnel-like space. The cross-section of the tunnel is only a centimeter or so, and nine flexor tendons (two to each finger and one to the thumb) have to pass through that little tunnel. The space is so narrow that some of the tendons are bundled on top of each other instead of going side-by-side the way they do outside the tunnel.

B esides tendons, the median nerve also goes through the carpal tunnel. By contrast, the ulnar nerve does not run in the carpal tunnel. The median nerve supplies most of the palm, the thumb, the index finger, the middle finger, and part of the ring finger. The first and second lumbricals (i.e. the two that are most ‘lateral’ on the radial side; index and middle fingers) are innervated by the median nerve. The third and fourth lumbricals (i.e. the most medial two; middle, ring, and little fingers) are innervated by the deep branch of the ulnar nerve. So if what’s going on is actually CTS, then you might expect weakness predominantly in lumbricals and/or interosseous muscles serving the thumb or index finger or middle finger or maybe the middle fingerward side of the ring finger. And you might think ‘ulnar neuropathy’ if the ring finger and/or pinky are predominantly affected.

B ut, gee, knowledge of the neuroanatomy of peripheral nerves in your arm and wrist and hand only gets you part of the way toward figuring out what is going on. In part, this is because of the interconnections elsewhere, including the motor cortex in your brain. Besides clinical evaluation, electrodiagnostic (EDX) tests are usually needed to confirm the diagnosis.

T he lumbrical and interosseous muscles are important in several motions—including flexing and plucking, increasing and diminishing the ‘spread’ of the fingers, and extending/raising the fingers. The lumbricals are used during an ‘upstroke’ when you are writing with a pen or pencil. These are the muscles that make the fingers separate and spread out or, alternately, converge and come together. The lumbrical muscles, with the help of the interosseous muscles, simultaneously flex the metacarpophalangeal (MCP) joints while extending both interphalangeal (IP) joints. In bats and other animals, these muscles are the ones that enable them to spread the wings and grab the air at one instant and flex and draw them in a few tens of milliseconds later and let the air go. If a bat acquired a repetitive stress injury of its lumbricals, on both sides or one side different from the other, it wouldn’t have long to live. Same thing for a seal: you can’t swim and catch fish if your lumbricals are faltering. Serious musicians—people whose livelihood or soul depends on playing—worry about this, as intently as a seal or bat.

T he EDX testing for these conditions is steadily getting more sensitive and more precise. For example, Sheehan and coworkers (link below) studied people referred with suspected carpal tunnel syndrome (CTS) by measuring the ‘second lumbrical-interosseous distal motor latency difference’ (2LI-DML) as well as by other, more standard tests like ‘median-ulnar palmar velocity difference’. The referred cases included 74% who turned out to be CTS. Sheehan suggests that 2LI-DML, which is a more sensitive test than other nerve conduction velocity tests for detecting mild abnormalities, is useful as a screening test for latent CTS on the asymptomatic side.

M otor distal latency (MDL) differences between the median-thenar and ulnar-hypothenar (M-U) muscles and between the median-second lumbrical and ulnar-interossei muscles (2L-INT) have also recently been used to diagnose early or ‘mixed’ cases. After all, there is no law of Nature that says a person can’t have CTS and UNE or CTS and focal dystonia at the same time. In people in whom the conventional nerve conduction tests are so far ‘normal’ despite the symptoms they are having, the neurologist can measure both motor and sensory W-P conduction and in a large percentage of cases this can establish a diagnosis.

U lnar neuropathy at the elbow (UNE) is the second most common compressive neuropathy of the upper limb. Compared to ‘ulnar neuropathy at the elbow’ (UNE), ulnar neuropathy at the wrist (UNW) is rarer and more difficult to localize with routine electrodiagnostic (EDX) tests. In terms of expectation-setting, it is reasonable to anticipate that it may take some time (and multiple visits) to establish an accurate diagnosis and decide on the right treatment plan. In general, these are not things that can be sorted out in a single, quick office visit.

T he important thing—if you are having symptoms like the ones my guitarist friend is having—is to get yourself examined by a neurologist who is experienced in problems of performing artists and who has the equipment and training to perform the newer EDX tests that are available. You can search for practitioners who are diplomates of the American Board of Electrodiagnostic Medicine here. I regret that I don’t know what comparable search resources there may be for consultants having EDX professional certifications in other countries.

• DSM. Strengthening lumbrical muscles. CMT blog, 09-FEB-2008.
  
• American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM)
  
• David Leisner, Manhattan School of Music (guitarist and expert on focal dystonia and other hand problems in musicians)
  
• Performing Arts Medicine Association (PAMA)
  
• Deutsche Gesellschaft für Musikphysiologie und Musikermedizin (DGMM)
  
• Performing Arts Clinic, Brigham & Women's Hospital (Harvard)
  
• Arts Medicine Europe
  
• Chang M, et al. Comparison of motor conduction techniques in the diagnosis of carpal tunnel syndrome. Neurology. 2002;58:1603-7.
  
• Chiodo A, Chadd E. Ulnar neuropathy at or distal to the wrist: Traumatic vs. cumulative stress cases. Arch Phys Med Rehab 2007;88:504-12. [1MB pdf]
  
• Cowdery S, et al. Electrodiagnosis of ulnar neuropathy at the wrist: conduction block versus traditional tests. Neurology. 2002;59:420-7.
  
• Dimachkie M, Verma A. Ulnar neuropathy at the elbow. Neurol Medlink 2009;1-9.
  
• Gohl A, et al. Median and ulnar neuropathies in university pianists. Med Prob Perf Artist 2006;21:17-24.
  
• Gordon T, et al. The resilience of the size principle in the organization of motor unit properties in normal and reinnervated adult skeletal muscles. Can J Physiol Pharmacol. 2004;82:645-61.
  
• Jones S, Hernandez C. Investigation of the prevalence of upper-limb neuropathies in different types of college musicians by use of Neurometrix device. Intl J Biol 2010;2:132-42.
  
• Lederman R. Focal peripheral neuropathies in instrumental musicians. Phys Med Rehab Clin N Am 2006;17:761-79.
  
• Lederman R. Neuromuscular problems in musicians. Neurologist 2002;8:163-74.
  
• Nunes-Marques D, et al. Flamenco guitar as a risk factor for overuse syndrome. Med Prob Perf Artist 2003;18:11-7.
  
• Sakai N. Interosseous muscle pain in the pianist's hand. Med Prob Perf Artist 2007;22:24-9.
  
• Sheehan G, et al. Lumbrical-interosseous latency comparison in the diagnosis of carpal tunnel syndrome. Electroencephalogr Clin Neurophysiol. 1995;97:285-9.
  
• Todnem K, et al. The impact of extended electrodiagnostic studies in ulnar neuropathy at the elbow. BMC Neurol. 2009;9:52-9. [1MB pdf]
  
• Toledo S, et al. Sports and performing arts medicine. 5. issues relating to musicians. Arch Phys Med Rehab 2004;85:72-4.