A client of mine had pain and dysfunction in one of her hand intrinsics—the first palmar interosseous (Image 10B)—which was functionally impairing her life. In my 40 years of practice, she is the only client for whom detailed knowledge of this muscle mattered, but for her, it was 100 percent of the cause of her problem, and I am so grateful I was sufficiently conversant with this muscle to help her.
“Keri” was a yoga instructor who, one day without any specific precipitating event, started to experience pain in the palm of her right hand. Over a few days, the pain increased to the point that she could not place any weight-bearing pressure through her hand. As a result, she couldn’t perform many yoga asanas (downward dog, for example), and therefore, was unable to teach many of her classes. Given that Keri had rent, car, electric, and food bills to pay, this condition was clearly impacting her life.
She first went to a massage therapist who palpated her shoulders (cervicothoracic region), and finding myofascial trigger points, informed Keri that the trigger points were referring pain into her hand, so they were the source of her problem. Keri went to the massage therapist for a few massages. Her shoulders felt better, but her hand pain did not improve.
Keri then went to a chiropractic physician who palpated the motion of her cervical spinal joints. Finding joint dysfunction hypomobilities, the chiropractor told Keri that pinched nerves in her neck were causing the pain in her hand. She had a few treatments with the chiropractor who adjusted her neck each session. Her neck felt better, but her hand pain remained unchanged.
Keri then went to an orthopedic surgeon who specialized in the wrist and hand. He took an X-ray and diagnosed her as having excessive space in the saddle joint of her thumb. He told her that this caused hypermobility of her thumb, which was causing the pain in her hand. He recommended she have an operation to tighten the ligaments of the joint. Keri did not proceed with this.
At this point in time, Keri happened to be at an anatomy of yoga workshop in New York City. When she described her problem to the instructor, he told her that the person who had written the text (me) they were using in the class was nearby in Connecticut.
Keri made an appointment right away. She presented to me with pain in her palm that was located between her second and third metacarpals, closer in against the second metacarpal. Given that three professionals had all missed the source of her problem, and the gravity of the situation for her, I felt it important to perform an extremely thorough history and physical exam. I spent two hours checking everything, from the possibility of cervical disc conditions and joint dysfunction in her neck to thoracic outlet syndromes, pronator teres syndrome, carpal tunnel syndrome, and all upper-extremity musculature in the back, neck, shoulders, arm, and forearm that might be causing myofascial trigger point referral pain into her hand. Every orthopedic and palpation examination procedure came out negative.
I then turned my attention to her hand, where she was experiencing the actual pain. I palpated each and every intrinsic muscle of the hand. And at the location where she felt the pain, I found her first palmar interosseous to be tight. The palpation protocol was done by having her squeeze a pen or highlighter between her index and middle fingers, thereby engaging index finger adduction musculature, namely the first palmar interosseous muscle (Image 1).1 Engagement of the first palmar interosseous could clearly be felt, and upon digital pressure into this muscle, the characteristic pain that Keri had been experiencing was reproduced.
It was as simple as that. A tight palmar interosseous muscle was the source of her pain. Armed with a specific target for treatment, I employed heat, massage, and stretching to the first palmar interosseous, which, after only a few sessions, was successful in removing all the pain and dysfunction.
What lessons can be learned from this case study? While I don’t excuse the chiropractic and orthopedic physicians for having misdiagnosed Keri and recommending care that was not needed for her condition, I can understand it. There is an old saying: If all you have is a hammer, everything looks like a nail. Surgeons generally like to operate; and chiropractors generally like to adjust joints. But I find it extremely disconcerting that the massage therapist, who should be a myofascial expert, missed something so simple. The client reported pain in a specific spot in her palm, and the therapist never even ventured there. Might this be because the massage therapist was not comfortable with her knowledge of the intrinsic musculature of the hand so she avoided focusing her attention on the palm?
Either way, I believe this case study illustrates the importance of learning all the muscles in the body, including those small hand intrinsics that perhaps we have avoided learning. Who knows, it might make all the difference in the future for a client who presents with pain in their hand or perhaps in some other somewhat obscure muscle of the body.
The Basics of the Intrinsics
In most massage therapy school curricula, there isn't enough time in the muscle anatomy and physiology classes to learn all the muscles of the body. Usually, the muscles that are skipped are the smaller muscles, including the intrinsic muscles of the hand.
Intrinsic hand muscles are those that are wholly located within the hand. In other words, their proximal attachments (origins), bellies, and their distal attachments (insertions) are all located within the hand. These muscles can be contrasted with the hand’s extrinsic muscles that have their proximal attachments in the arm or forearm, their bellies in the forearm, and then travel distally with their tendons crossing the wrist to attach into the hand. These extrinsic muscles include the muscles of the wrist flexor and extensor groups, the long finger flexors and extensors, and the long muscles of the thumb (Table 1, Images 2 and 3).
Most massage therapists have learned and are fairly comfortable with the hand’s extrinsic muscles. However, in my experience teaching continuing education workshops across the US and internationally, most therapists, whether they are newly out of school or have been practicing for years, are not conversant with the intrinsic muscles of the hand.2
This is unfortunate, because although these muscles might not exhibit pain and dysfunction as often as some of the more well-known muscles of the upper extremity (e.g., rotator cuff, deltoid), there are times when clients present with issues with these hand intrinsics. And given that massage therapy is one of the few professions that focuses on soft tissues, it would be hoped that a massage therapist could help these clients.
So, how difficult is it to truly learn the intrinsic muscles of the hand? Surprisingly, it’s quite easy, especially if we approach learning these muscles in five simple steps. If you have always wanted to learn the intrinsic muscles of the hand but have never felt it was the right time or have never quite found the right approach, consider this your invitation. Here are the five steps we will take:
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Overview of the intrinsic groups
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Compare the muscles of the thenar and hypothenar groups
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Identify muscles of the central compartment group
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Learn the actions of the intrinsic muscles
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Learn the attachments of the intrinsic muscles
1. Overview of the Intrinsic Groups
There are essentially three groups of intrinsic muscles in the hand: thenar eminence group, hypothenar eminence group, and central compartment group. The muscles of the thenar eminence are muscles of the thumb (pollicis) and form the eminence of tissue on the radial/thumb side of the palm. The muscles of the hypothenar eminence are muscles of the little finger (digiti minimi) and form the eminence of tissue on the ulnar/little-finger side of the palm. The muscles of the central compartment are between the thenar and hypothenar groups—in other words, located centrally, as the name implies (Image 4).
2. Comparing Muscles of the Thenar and Hypothenar Groups
There are three muscles in the thenar group, all of which have pollicis (Latin for “thumb”) in their name (Image 5).
Similarly, there are three muscles in the hypothenar group, all of which have digiti minimi (Latin for “little finger”) in their name (Image 6). Further, these three muscles in each group are named abductor, flexor, and opponens.
For the thenar eminence thumb group, the muscles are the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. Note that the word brevis is included in the abductor and flexor muscles to distinguish them from the same-named extrinsic longus thumb muscles from the forearm; there is no longus opponens, so brevis is not necessary for its name.
For the hypothenar eminence, little-finger group, the muscles are the abductor digiti minimi manus, flexor digiti minimi manus, and opponens digiti minimi. Here, note that the word manus is included to distinguish them from the same-named muscles for the little toe of the foot (digiti minimi pedis muscles). It is a central tenant of anatomy nomenclature that words are added into the name of a muscle only when needed to distinguish that muscle from another similar muscle of the body. In our case here, brevis versus longus, manus versus pedis. So, we have abductor, flexor, and opponens pollicis muscles; and abductor, flexor, and opponens digiti minimi muscles respectively in the thenar and hypothenar groups.
3. Muscles of the Central Compartment Group
The central compartment group has one pollicis muscle and three individual muscle groups. The pollicis muscle is the adductor pollicis (yes, of the thumb, but its belly is in the central compartment, hence its inclusion in the central compartment group). The three individual muscle groups comprise the four lumbrical manus muscles (manus to differentiate them from the lumbrical pedis muscles of the foot), the three palmar interossei, and the four dorsal interossei manus (Image 7).
Note: There is one odd-duck intrinsic hand muscle I have left out of this big-picture approach—the palmaris brevis (Image 8). The palmaris brevis overlies the hypothenar eminence musculature but is often not included in the hypothenar group because it is not a muscle of the little finger (and including it in the hypothenar group would ruin the beautiful symmetry of the thenar/hypothenar comparison).
4. The Actions of the Intrinsics
Generally, for any muscle that we learn, we need to learn its name, its attachments, and its actions (and perhaps nerve innervation; see “Nerve Innervations of the Intrinsics”). Learning the actions of the intrinsics is actually quite easy because most of their names tell us their actions (or at least the major action).
In the thenar group, the abductor pollicis brevis abducts the thumb, the flexor pollicis brevis flexes the thumb, and the opponens pollicis opposes the thumb. Similarly, in the hypothenar group, the abductor digiti minimi manus abducts the little finger, the flexor digiti minimi manus flexes the little finger, and the opponens digiti minimi opposes the little finger. How wonderful!
The actions of the central compartment are not quite as self-evident. The adductor pollicis certainly adducts the thumb, but the others have actions that are not stated in their names. However, there are a few principles here that can help. The lumbricals flex fingers 2–5 (index to little fingers) at the metacarpophalangeal joints but extend those fingers at the interphalangeal joints. One can think of the letter L having the same 90-degree hinged angle that the lumbricals create at the metacarpophalangeal joints of the fingers with these actions (Image 9).
For the interossei, the dorsal interossei manus all abduct the fingers to which they attach, and the palmar interossei all adduct the fingers to which they attach (Images 10A and 10B). (Think DAB PAD: Dorsals ABduct; Palmars ADduct.) Knowing the specific fingers to which they attach can be figured out (see “Interossei”). And the palmaris brevis, attaching into the palmar fascia, tenses the palmar fascia as its function; this can help to increase our grip strength.
5. The Attachments of the Intrinsics
Most often, when learning a muscle, we first learn its attachments, because knowing the attachments allows us to figure out its action(s). After all, a muscle is just a pulling machine, so knowing its attachments gives us its line of pull, hence its actions. But with the hand intrinsics, because of the organization into thenar and hypothenar groups, and because the names so often indicate the actions, we began with the actions and have left the attachments until now.
Stepping back from the big picture, we have already stated there is an abductor, flexor, and opponens in both the thenar and hypothenar groups. But of further help is the fact that these three muscles in each group are arranged, from superficial to deep, in alphabetical order: from Abductor to Flexor to Opponens (Images 5 and 6).
Now, looking at the actual attachments, the principal proximal attachments of the thenar and hypothenar muscles are onto carpal bones. The thenar group muscles attach onto the tubercles of the scaphoid and trapezium; the hypothenar group muscles attach onto the pisiform and hook of the hamate. The distal attachments of the thenar muscles are onto the thumb; and the distal attachments of the hypothenar muscles are onto the little finger. This could be examined in greater detail (e.g., additional fascial attachments proximally, and metacarpal vs. phalangeal attachments distally), but this is a good landing place as our primer for these muscles.
In the central compartment, the adductor pollicis and the palmar and dorsal interossei all attach proximally onto metacarpals and distally onto the phalanges of their respective fingers (see Image 6, Image 9, and “Interossei”). This leaves the lumbricals, which attach proximally into the flexor digitorum profundus tendons and distally into the extensor digitorum muscle tendons (see Image 6); and the palmaris brevis, which, as stated, attaches into the palmar fascia (see Image 7).
Great Knowledge to Have
In conclusion, I believe I have laid out a simple five-step approach that allows us to understand and have a certain mastery of the intrinsic musculature of the hand. If you already had some familiarity with the intrinsic musculature, hopefully this has helped to organize them into a clear context. If this is your first exposure to the hand intrinsics, then perhaps you might want to read through this another time or two until it all makes intuitive sense.
How important is this knowledge? That depends on the clients who come into your practice. The case study that began this article is a perfect example. Perhaps we will not need to know the specific knowledge of the hand intrinsics for most of our clients, but for some clients that present to us, this knowledge could prove
to be invaluable.
Notes
1. Because this procedure also requires middle-finger radial abduction, the second dorsal interosseous manus muscle also engages. But this was not of concern because the dorsal interosseous musculature is on the dorsal side of the hand, so it would not cause confusion with palpation into the palm.
2. This same discussion could be had regarding the intrinsic muscles of the foot in the lower extremity.
A Deeper Dive—Nerve Innervations of the Intrinsics
Learning the innervation of the hand intrinsics is extremely easy. We begin with the big picture, then look at the couple of exceptions to this organization.
The Overall
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The thenar group is innervated by the median nerve.
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The hypothenar and central compartment groups are innervated by the ulnar nerve.
The Exceptions
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The ulnar nerve contributes to the innervation of the flexor pollicis brevis and opponens pollicis.
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Lumbricals manus No. 1 and No. 2 are innervated by the median nerve (not the ulnar nerve).
A Deeper Dive—Interossei
Learning which fingers the palmar and dorsal interossei attach into does not have to be memorized; it can be reasoned out. Keeping in mind that the dorsals abduct and the palmars adduct, the specific fingers can be ascertained.
The three palmar interossei attach into fingers 2, 4, and 5 (index, ring, and little), because the thumb (finger 1) always gets its own muscles; and the middle finger, finger 3, cannot adduct, it only abducts (radial and ulnar abduction), so there is no palmar interosseous into it. This leaves fingers 2, 4, and 5 each needing a palmar interosseous to adduct it.
The four dorsal interossei attach into fingers 2, 3, and 4 (index, middle, and ring). Why? Because the thumb always gets its own muscles; and the little finger has its own abductor in the hypothenar group (abductor digiti minimi manus), which leaves fingers 2, 3, and 4. And because the middle finger (finger 3) can abduct in two directions (ulnar and radial) there are two dorsal interossei onto that finger, totaling four dorsal interossei.
Of course, all this is predicated on understanding the kinesiology of frontal-plane abduction and adduction of the fingers, the essence of which is that abduction and adduction of fingers 2–5 is relative to an axis—an imaginary line that goes through the center of the middle finger—when the middle finger is in anatomic position.
So dorsal interossei attach onto their respective fingers on the sides of the proximal phalanges that are away from the reference line; and palmar interossei attach onto the sides of the proximal phalanges that are oriented toward the reference line.
