|Year : 2013 | Volume
| Issue : 4 | Page : 174-177
Additional heads of dorsal interosseous muscle in Caucasian cadavers and their clinical significance
Vaishaly Kishore Bharambe, Sapna Prashant Shevde, Vatsalaswamy Puranam, Nilesh Subhash Kanaskar
Department of Anatomy, Padmashree Dr. D Y Patil Medical College, Hospital and Research Centre, Dr. D Y Patil Vidyapeeth, Pimpri, Pune, Maharashtra, India
|Date of Web Publication||21-Jan-2014|
Vaishaly Kishore Bharambe
D-9 State Bank Nagar, Panchvati, Pashan Road, Pune - 411 008, Maharashtra
Dorsal interossei are group of four intrinsic muscles of the hand that are of immense importance in its day-to-day functions. The finding of any variation related to these muscles is of significance from point of view of hand surgeons. In the present article, we report additional heads of dorsal interosseous muscle (DIM) in four upper limbs of a male cadavers. The muscles took origin from the dorsal surface of the adjacent metacarpal bones as well as from the distal row of carpal bones, had a belly separate from the two pennae of the DIM, distally joining the tendon of corresponding DIM. We discuss the anatomical details and clinical implications of this variation.
Keywords: Additional head, dorsal interossei, muscle architecture
|How to cite this article:|
Bharambe VK, Shevde SP, Puranam V, Kanaskar NS. Additional heads of dorsal interosseous muscle in Caucasian cadavers and their clinical significance. Sahel Med J 2013;16:174-7
|How to cite this URL:|
Bharambe VK, Shevde SP, Puranam V, Kanaskar NS. Additional heads of dorsal interosseous muscle in Caucasian cadavers and their clinical significance. Sahel Med J [serial online] 2013 [cited 2019 Oct 15];16:174-7. Available from: http://www.smjonline.org/text.asp?2013/16/4/174/125580
| Introduction|| |
The interossei along with other muscles of the human hand constitute a complex apparatus that acts to move and stabilize the fingers during grasping and manipulation.
The human hand has four dorsal interosseous muscles (DIMs). These are generally bipennate muscles, each arising from adjacent sides of two metacarpal bones. The two heads join to form a thin tendon and insert on the bases of the proximal phalanges and dorsal digital expansions such that the first and second DIMs are inserted on the radial aspect of the index and middle finger, while the third and fourth DIMs get inserted on the ulnar aspect of middle and ring finger respectively.  Thus, the first and fourth DIMs are responsible for the abduction of the index and ring finger away from the central axis passing through the middle finger and the second and the third DIMs are responsible for movement of the middle finger away from its own axis on the radial or ulnar side.
There have been very few reports of variations of these muscles such as completely divided first DIM and a supernumerary DIM. ,
We report four cases in which the DIM had an extra head. Such extra heads are rare and can affect the normal biomechanical behavior of hand and their existence should be taken into consideration while studying the architectural design of muscles to understand their functional capacities. ,
| Case Report|| |
During routine dissection of 25 cadavers preserved in 10% formalin by medical students, four upper limbs (ULs) were found showing additional heads to DIMs. All the variant muscles were found in adult male cadavers.
UL1 and UL2 belonged to the same cadaver, UL1 being the left sided and UL2 being the right sided. Each showed presence of an additional head to the second DIM, taking origin from the radial side of dorsal aspect of third metacarpal and from the dorsal surface of capitate bone, passing distally posterior to the second DIM, joining its slender tendon to insert into the radial aspect of proximal phalanx of the middle finger partly joining with the dorsal digital expansion [Figure 1]. UL3 was right sided and also showed the presence of an additional head to second DIM [Figure 2].
|Figure 1: Dorsal view of left hand showing dorsal surface of third metacarpal (a), additional head of second dorsal interosseous muscle (DIM) (b) joining the second DIM (d). The common tendon of insertion of second DIM (c) is seen attaching to the radial aspect of proximal phalanx of index finger|
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|Figure 2: Dorsal view of right hand showing tendons of extensor digitorum communis to index finger (a) and extensor indicis proprius (b), tendons of extensor digitorum communis to middle, ring and little finger (c) and additional head of second dorsal interosseous muscle (d) lying deep to these tendons|
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The UL4 was left sided and showed the presence of three additional heads of DIM in relation to second, third and fourth DIMs respectively. The additional head to the second DIM had attachments very similar to those described above. The additional head of third DIM was proximally attached to the trapezoid and capitate bones and to radial side of dorsal aspect of fourth metacarpal, its fibers joining distally into the ulnar penna of the third DIM. The additional head of fourth DIM was proximally attached to ulnar side of the dorsal aspect of fourth metacarpal and also to the dorsal aspect of hamate, distally joining the tendon of fourth DIM to get attached to the ulnar aspect of proximal phalanx of the ring finger [Figure 3].
|Figure 3: Dorsal view of left hand showing tendon of extensor digiti minimi (a), additional heads of fourth dorsal interosseous muscle (DIM) (b), second DIM (c) and third DIM (d), tendons of extensor carpi radialis longus (e) and extensor pollicis longus (f)|
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Thus out of the 25 cadavers dissected, three cadavers showed the presence of additional heads to the DIMs, giving an incidence of 12%. Although one cadaver showed bilateral existence of the variation, the other two cadavers showed the variation unilaterally with One cadaver showed bilateral existence of the variation, while the other two showed the variation unilaterally. Considering each DIM individually, incidence of additional head to second DIM was observed to be 12%, while the incidence of additional head to third and fourth DIM was observed to be 4%.
The nerve supply to all the additional heads was found to be the deep branch of ulnar nerve. The DIMs lying deep to those described above were dissected and no variation was observed in their attachments. The corresponding opposite side ULs in case of UL3 and UL4, showed no variations.
Summary of above findings are given in [Table 1]. With A summary of the findings are given in [Table 1]
| Discussion|| |
The human hand consists of many muscles capable of carrying out movements of very complex nature. The DIMs are abductors of second, third and fourth digits, these movements being essential for smooth functioning of the hand.
There have been reports of variations in anatomy of DIM since the 18 th century.  Bergman et al. observed that interossei are occasionally doubled in one or more spaces or may even be absent and that the second DIM may have three heads.  All four limbs in the present report showed the presence of additional head to the second DIM [Figure 1], [Figure 2], [Figure 3]. A muscle belly taking origin from the hamate and joining the second DIM in its insertion has also been described by Bergman et al.  in UL4 in the present report, a similar DIM taking origin from hamate was observed. However, it joined the tendon of insertion of fourth DIM and through it got attached to ulnar aspect of proximal phalanx of the ring finger [Figure 3].
Natsis et al. reported finding of one supernumerary fourth DIM, lying superficial to the fourth DIM muscle of the right hand.  This muscle was proximally attached to the dorsal surface of fourth metacarpal and distally to head of fifth metacarpal. A similar muscle was observed in the present report in UL4, the difference in the two muscles being that the muscle described in the present report was distally attached through the tendon of fourth DIM to the ulnar aspect of proximal phalanx of the ring finger and thus would contribute to the abduction action of the fourth DIM while the muscle described by Natsis is likely to act as an adductor of the 5 th digit.
Eladoumikdachi in a study carried out by dissecting 14 cadaver hands, has described interossei having three different muscle heads, each with a different distal destination. 
Although the present finding of additional heads to second, third and fourth DIM in the same hand (UL4) is a rare variation with incidence of 4%, a higher incidence of 12% was observed of additional head to second DIM only. The present report gives details of dimensions of every extra head of DIM found, however no comparable data is available.
Skeletal muscle function is related quantitatively to its architecture.  The DIMs, having short fibers, function better for force generation. All interosseous muscles (IMs) together, are estimated to contribute to 40-90% of grip strength of hand.  Additional heads to IMs would naturally add to this grip strength.
Randall has found the presence of musculus accesorius interosseous in gibbons.  Thus, the additional head to the DIMs could be a fallback to the structure of the primate ancestors.
Additional heads of DIMs are mostly asymptomatic. However, they do have some clinical implications. Each dorsal interosseous occupies its own separate anatomical compartment.  Chopra described a case of exercise induced chronic compartment syndrome of the 1 st DIM compartment.  Compartment syndrome is caused by an elevation of interstitial pressure in a closed fascial compartment. An additional head to DIM can be presumed to cause increased intracompartmental pressure locally and thus result in chronic compartment syndrome.
Magnetic resonance imaging (MRI) has been used to diagnose anatomical variations of hand muscles.  Andreisek stresses on the value of MRI to assess skeletal muscles and their abnormalities. In a study carried out on 19 patients with suspected abnormality of intrinsic hand muscles, MRI was used to evaluate IMs and detect the cause of pathology successfully. 
The DIM has been used as a musculocutaneous flap to cover small defects of the hand, its preferential use being explained by easy access to it from the dorsum of the hand.  Following MRI evaluation, if the existence of an additional head to DIM be known, it could be used similarly.
Finally, the authors would like to state that, unusual variations in anatomy are interesting, though if they are asymptomatic, often it is difficult to judge their clinical relevance. However, considering the number of cases observed during routine dissection, authors wished to document the existence of these additional heads to DIMs.
| Acknowledgment|| |
The authors would like to thank Bhavya Gupta for her help in the photography.
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[Figure 1], [Figure 2], [Figure 3]