|Year : 2018 | Volume
| Issue : 2 | Page : 116-118
Bilateral absence of third and fourth lumbricals: A case report with clinico-evolutionary insight
NA Priyadharshini1, V Dinesh Kumar2, R Rajprasath1
1 Department of Anatomy, Pondicherry Institute of Medical Sciences, Puducherry, India
2 Department of Anatomy, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India
|Date of Submission||16-May-2018|
|Date of Acceptance||21-Jul-2018|
|Date of Web Publication||13-Dec-2018|
N A Priyadharshini
Department of Anatomy, Pondicherry Institute of Medical Sciences, Puducherry
Source of Support: None, Conflict of Interest: None
Lumbricals are wormlike, intrinsic muscle of the hand. During routine dissection of a male cadaver of age approximately ranging between 50 and 55 years, the absence of third and fourth lumbricals on both the palm was observed. First and second lumbricals showed no anatomical variation. Other muscles of hypothenar eminence supplied by deep branch of ulnar nerve which also supplies the third and fourth lumbricals were normal. Lumbricals are principle extensors of interphalangeal joint, and its role in flexion of metacarpophalangeal joint is meager. Variability in the presence of medial two lumbricals has evolutionary correlation and also shows its minimal role in the extension of interphalangeal joint of its respective digits. Henceforth, knowledge of absence of lumbricals is crucial for surgeons while planning for hand surgery.
Keywords: Flexor digitorum profundus, hand surgery, lumbricals, variations
|How to cite this article:|
Priyadharshini N A, Kumar V D, Rajprasath R. Bilateral absence of third and fourth lumbricals: A case report with clinico-evolutionary insight. J Curr Res Sci Med 2018;4:116-8
|How to cite this URL:|
Priyadharshini N A, Kumar V D, Rajprasath R. Bilateral absence of third and fourth lumbricals: A case report with clinico-evolutionary insight. J Curr Res Sci Med [serial online] 2018 [cited 2020 May 25];4:116-8. Available from: http://www.jcrsmed.org/text.asp?2018/4/2/116/247486
| Introduction|| |
The lumbricals of the hand are named after the Latin word “Lumbricus” meaning of earthworm, beacuse of their appearance. These muscles are unique, as their origins and insertions are on tendons without bony attachments. Disproportionate to their size and shape, they are important for humans in performing precision pinch. They connect two extrinsic antagonistic muscles, extending between flexor digitorum profundus (FDP) and extensor hood at the level of the metacarpophalangeal (MCP) joint. The first and second lumbricals are innervated by the median nerve which also supplies the thenar muscles of the hand. This feature along with the arrangement of lumbricals in the radial side of flexor tendons helps in achieving effective coordination during three-digit precision pinch movements. Third and fourth lumbricals, being innervated by the ulnar nerve, are bipennate in nature. Zone 3 transmetacarpal amputations have poorer outcomes if lumbricals are damaged or their blood supply is disrupted. This might be due to the imbalance of the viscoelastic forces about the extensor mechanism, causing intrinsic contracture. Hereby, we document a case of bilateral absence of third and fourth lumbricals with relevant clinical and the phylogenetic significance.
| Case Report|| |
During routine dissection classes for the 1st-year medical students, in a male cadaver of age approximately 50–55 years, bilateral absence of third and fourth lumbrical was noticed [Figure 1] and [Figure 2]. There was no remnant of fibers of the muscle to substantiate for mechanical injury or surgical removal of the muscle. No variations were observed in the course of deep branch of ulnar nerve which usually supplies the third and fourth lumbricals. Muscles of hypothenar eminence supplied by deep branch of ulnar nerve were normal. Normally, lumbricals take origin from FDP tendon in the palm. First and second lumbricals, which are unipennate, originate from the FDP tendon and inserted into distal twig of dorsal digital expansion, innervated by median nerve were observed. The feature was similar on both the hands. No other neurovascular variation was seen.
|Figure 1: Dissection of left palm with dotted arrows showing first and second lumbricals and thick arrows pointing absence of third and fourth lumbricals; FDP: Flexor digitorum profundus tendon|
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|Figure 2: Dissection of right palm showing first and second lumbricals in dotted arrows and thick arrows pointing absence of third and fourth lumbricals; FDP: Flexor digitorum profundus tendon|
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| Discussion|| |
Lumbricals are quite unique as they serve as a mechanical link for the articular system of the digits that produces dynamic-controlled extension of the interphalangeal joints. Lumbrical is certainly not a strong muscle as it has smallest physiological cross-sectional area. The long fiber length (40–48 mm) of the lumbricals is responsible for the large excursions possible by them. Even though the direct contribution of the lumbricals for the MCP joint flexion is debatable, its indirect contribution to interphalangeal joint extension is substantial. They also play a vital role in conveying the proprioceptive feedback regarding the interphalangeal joints by acting as “tensiometers” between flexors and extensors. This can be explained from the evolutionary perspective, whereby the increase in number of muscle spindles and decrease in the size of muscle has been observed from nonprimates to humans, to aid in performing repetitive alternating movements. The contribution of lumbricals in precise pinch movements and functional grasp could possibly explain variation in the morphology and nerve supply between the lateral two and medial two muscles. On contraction, the first two lumbricals, which are mostly unipennate, bring the digits toward the radial side of the hand, helping to achieve the precise pinch movements. These two along with the thenar muscles are supplied by median nerve in common. In contrast, the third and fourth lumbricals are mostly bipennate and are supplied by the ulnar nerve in common with the hypothenar and interossei muscles. The main function of these is to assist the much stronger synergistic interosseous muscles in extending the interphalangeal joints.
In the present case, we had a rare anomaly of bilateral absence of third and fourth lumbricals. Variant morphology of lumbricals is mostly reported in terms of its supernumerary bellies, variation in attachments, or its nature (unipennate/bipennate). Third lumbrical has been labeled as the “most variable” one, owing to the fact that misplaced/split insertions are common in it along with additional origins in few cases. Koizumi et al. stated that fourth lumbrical was the most frequently absent among the lumbricals. In one cadaver, unilateral absence of second, third, and fourth lumbricals have been documented. Of 30 cadavers examined in a study, third lumbrical was found to be absent in one case (3.3%). Another study reported absent fourth lumbrical in four out of 68 hands.
Lumbricals contain entirely type II myosin heavy chain and minimal type I myosin. The aging-associated loss in the fiber number that is observed in larger skeletal muscles was not present in the lumbrical muscles, owing to the greater number of motor neurons. It can be inferred that the absence of lumbricals witnessed in the present case is not due to denervation injuries or occupational-associated atrophy. As the lumbrical passes volar to the interpalmar plate ligament and the interosseous muscle passes dorsal to it, absence of the lumbricals might limit the proximal movement of the related joints and cause intermetacarpal pain while making a fist. We did not have any clinical history to corroborate the above-said findings. From biomechanical perspective, the absence of two lumbricals, which is mostly congenital, would have resulted in minor changes in range of motion of the involved joints. It can be presumed that interosseous muscle could have compensated the role of lumbrical in extension of interphalangeal joints. The congenital etiology for the absence of lumbricals and the relation between loss of the intrinsic muscle strength owing to the absence of lumbricals and activities of daily life still need further study. Nevertheless, the knowledge regarding these variations might be helpful during radiological interpretations and hand surgeries such as muscle-release procedures.
| Conclusion|| |
We conclude that the knowledge regarding the bilateral absence of third and fourth lumbricals, which is quite uncommon, is very important for the clinicians and surgeons while designing hand surgeries. It would be interesting to elucidate the cause behind and quantify how much it can affect the mobility of the phalanges connected with specific activities.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]