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Abstract:
The Musculocutaneous nerve arises from the lateral cord of the brachial plexus, passes inferolaterally and then pierces through the coracobrachialis after supplying it, descends between the biceps and the brachialis, sending branches to both and continues as the lateral cutaneous nerveof the forearm. Variations in the origin, course, branching pattern, termination and the connections of the musculocutaneous nerve are not uncommon. These variations have clinical significance during surgical procedures, in the brachial plexus block and in diagnostic clinical neurophysiology. A detailed study was carried out on 80 upper limbs by using 40 embalmed cadavers during 4 years in anatomy department, government medical college, Surat. Dissection of the infraclavicular part of the brachial plexus was done. The variations in the origin, number and course, and their correlations to the coracobrachialis were noted.
Absence of the musculocutaneous nerve was noted in 2 upper limbs (2.5 %).The nerve was found to not pierce the coracobrachialis in (1.25%) of the limbs. In (1.25%) of the limbs, the nerve was found to rejoin the median nerve without piercing the Coracobrachialis. The observations show that the musculocutaneous nerve has significant variations and that these variations have clinical significance in post traumatic evaluations and in the exploratory innervations of the arm for peripheral nerve repair. It is important for surgeons, clinicians and anatomist to be aware of possible anatomical variations to avoid unexpected complications.
J.Orthopaedics 2012;9(3)e3
Introduction:
Variations in the formation of the brachial plexus and its terminal branches in the upper extremity are common and have been reported in the literature [1, 2]. Buch Hansen [3] reported these variations in 65.3% of the population. Variations of the musculocutaneous nerve and its branches have been previously reported [4, 5].
The musculocutaneous nerve was found to be absent, by Prasada Rao [6]. The reported variations of the musculocutaneous nerve also include the nerve not piercing the coracobrachialis [7]. The complete absence of the musculocutaneous nerve and the assumption of its innervations by the median nerve are uncommon [8]. Such variations may be present clinically or may be observed during surgery. Since there is a high incidence of variations, they are important for neurologist, orthopaedicians and traumatologists. So, a detailed study was done to observe the variations of the musculocutaneous nerve in the arm and axilla.
Material and Methods :
Eighty limbs (RT: 40; Lt: 40) from 40 embalmed cadavers were utilized during the study period of four years. The pectoral region, the axilla and the arm were dissected. The cords and the branches of the cords of the infraclavicular part of the brachial plexus were dissected. The variations of the musculocutaneous nerve were noted. The origin and course of the musculocutaneous nerve and the correlation of the musculocutaneous nerve to the coracobrachialis were noted. We were also looking for the additional fibres of biceps brachii muscle.
[Fig 1] left arm, 1.Coracobrachialis, 2.Formation of median nerve, 3.nerve to coracobrachialis, 4. Brachial artery, 5.Median nerve, 6.Branch to biceps brachii, 7. Biceps brachii, 8.Lateral cuatenous nerve of forearm .
[Fig 2] right arm 1.Lateral cord, 2.Formation of median nerve, 3. Brachial artery, 4. Coracobrachialis, 5.Musculocuatenous, 6. Median nerve, 7. Biceps brachii muscle, 8. Branches to biceps brachii, 9.lateral cuatenous nerve of forearm.
OBSERVATION
[Fig 1] left arm, 1.Coracobrachialis, 2.Formation of median nerve, 3.nerve to coracobrachialis, 4. Brachial artery, 5.Median nerve, 6.Branch to biceps brachii, 7. Biceps brachii, 8.Lateral cuatenous nerve of forearm .
[Fig 2] right arm 1.Lateral cord, 2.Formation of median nerve, 3. Brachial artery, 4. Coracobrachialis, 5.Musculocuatenous, 6. Median nerve, 7. Biceps brachii muscle, 8. Branches to biceps brachii, 9.lateral cuatenous nerve of forearm.
OBSERVATION
The musculocutaneous nerve was found to be absent in 2 limbs. In one case, the nerve was found to be absent in left upper limb.[Fig-1].The lateral root of the median nerve from the lateralcord was small and the lateral cord continued to run down for 4cm in the axilla and fused with the median nerve just before the insertion of the coracobrachialis. The nerve to the coracobrachialis was arising from the lateral aspect of the median nerve and the muscular branches to the biceps and the brachialis were arising from the median nerve. In the second case [Fig-2], the nerve was found to be small in the right sided axilla. In this case, the musculocutaneous nerve represent as a continuation of lateral cord runs 5 cm down in axilla and then merge with the median nerve.during this course it gives one branch which pierce coracobrachlis muscle. The muscular branches to the muscles of the anterior compartment of the arm arose from that median nerve.Branch from the median nerve continue as a lateral cutaneous nerve of forearm. The musculocutaneous nerve was found not pierce the coracobrachialis in 1 limb.
DISCUSSION
Renata pacholczak et al [9] observed the musculocutaneous nerve to be absent on the left side, which coincides with the findings from one case Fig-1 in the present study, where the nerve was found to be absent on the left side. The complete absence of the musculocutaneous nerve and a complete takeover of the innervations of the coracobrachialis, the biceps and the brachialis muscles by the median nerve is an unusual variation of the brachial plexus [5, 11, and 12]. Nayak [13] reported that in one limb, the musculocutaneous nerve had a low origin and that the nerve was found to not pierce the coracobrachialis, which was coincide with our second case finding in right sided upper limb Fig [2]. The musculocuatenous nerve was found to be absent completely in 3 limbs, but the nerve was found to not pierce the coracobrachialis in 3 specimens. In some cases, instead of the whole trunk of the nerve piercing the coracobrachialis, only its muscular branch or only its cuatenous branch was found to pierce the muscle.
Instead of penetrating the coracobrachialis, the nerve may pass behind it or between it and the short head of the biceps muscle. Occasionally, the nerve perforates not only the coracobrachialis, but also the brachialis or the short head of the biceps muscle [4]. These variations were observed in the present study. [fig;2.] Chitra [14] observed in 2 cases, that the musculocutaneous nerve did not pierce the coracobrachialis. Le minor [10] reported in the type V of his classification, that the musculocutaneous nerve was absent and that the fibres of the musculocutaneous nerve ran within the median nerve along its course and that in this type, the musculocutaneous nerve didnot pierce the coracobrachialis muscle. These reports coincide with those of the present study, where the musculocutaneous nerve was found to not pierce the coracobrachialis in 1 limb. The musculocutaneous nerve rejoining the median nerve after piercing the coracobrachialis is a rare variation and this is rarely reported in the literature. The musculocutaneous nerve, after piercing the coracobrachialis, rejoined the median nerve in one case which was reported by Joshi [15] and in 3.125% of the cases which were reported by Bhattarai [16].
If the musculocutaneous nerve is absent, its fibers run in the median nerve [ 6] and muscles of the anterior compartment of the arm are innervated by it [6,8].In rare cases, innervations are provided by the lateral root of the median nerve [7, 10]. These distributions of the muscular branches are different in everycase so far published in literature. In the present case [fig;3] the musculocutaneous nerve coexisted with a extra tendentious insertion of biceps brachii muscle .The embryological development of the upper limb may help in explaining this anatomical neurological variation. Mesenchyme, which comes from the dorsolateral part of the somites, migrates and forms the muscles into the limb bud. At the same time, the mesenchyme is penetrated by the ventralprimary rami of the appropriate spinal nerves, locatedopposite to the bud. Contact between nerves and muscle cells are necessary to provide mesenchymal condensation toform muscles. Nerves supplying the limbs are joined by connecting loops of nerve fibres to form plexuses.
The median nerve is formed by a combination of ventral segmentalbranches and the musculocutaneous nerve arisesfrom it. Disturbances in these processes, taking place in the 4th–7th weeks of development, lead to anatomical variationsin the innervations of muscles by appropriate nerves[6, 17].In accordance with the study of embryological development,absence of the musculocutaneous nerve is noted meaning that this nerve did not arise from the median nerve, thus its fibres run in the median nerve.. Surgeons should particularly take into consideration these possible anatomical variations when trying to explain unusual symptoms which may occur during examination of patients with median nerve injuries or thoracic outlet syndrome [18]. Absence of the musculocutaneous nerve is usually not revealed because its fibres run with the median nerve.
After injury of the median nerve (with an abnormal distribution) in the region of the armpit or shoulder, unexplainable complications are often presented. Apart from common symptoms such as the loss of pronation and reduction in flexion of the hand and wrist, paralysis of the thener muscles and loss of sensation in certain regions of the hand which are revealed when the median nerve has its normal anatomical course, clinicians may also encounter additional symptoms such as: weakness in forearm flexion and supination and hypoesthesia of the left part of the forearm . Beheiry [18] suggests a different way to prove the absence of the musculocutaneous nerve in a healthy patient such as unobtainable nerve condition test of the musculocuatenous nerve.
Conclusion
It is clear that the absence of musculocuatenous nerve is because of defect in embryological period during 4 to 7 week of intrauterine life. There is no evidence of chromosomal anomalies and notified teratogens which causing the condition. During shoulder surgery, it is important to identify or palpate the musculocuatenous nerve, as it is vulnerable to injury from retractors which are placed under the coracoid process. During the coracoids process grafting, shoulder dislocations and frequent arthroscopies may damage the muscle as well as the nerve .It is important for surgeons, clinicians and anatomists to be aware of possible anatomical variations to avoid unexpected complications. This study helps surgeons and clinicians to keep important variations of musculocuatenous nerve in mind during their treatment to the patients to avoid complications and better results.
References:
[1] Kerr AT. The brachial plexus of nerves in man, the variations in its formation and branches. AMJ Anat 1918; 23:285-395.
[2] Linel EA. The distribution of nerves in the upper limb, with reference to their variabilities and their clinical significance. Journal of Anatomy I921; 55: 79 -112(s)
[3] Buch – Hansen K. Uber Varietaten des Nervus Musculocutaneous und deren Beziehungen. Anat Anz 1955; 102:187-203.
[4] Bergman RA, Thompson SA, Afifi AK, Saadeh FA: Compendium of the human anatomic variation. Urban and Schwarzenberg, Baltimore.1988; 138-43.
[5] Williams PL, Bannister LH, Berry MM, Collins P, Dyson M, Dussek JE et al. Nervous system. In: Gray’s Anatomy. 38th edition. Churchill Livingston, Edinburgh, London I995: 1267-72.
[6] Prasada Rao PVV, Chaudhary SC. Absence of the musculocutaneous nerve: Two case reports. Clin Anat 2001; 14:31-5.
[7] Nakatani T, Mizukami S, Tanaka S: Three cases of the musculocutaneous nerve not perforating the coracobrachialis muscle. Acta Anat Nippon 1997a; 72:191-4.
[8] Ihunwo AO, Osinde SP, Mukhtar AU: Distribution of median nerve to the muscles of the anterior compartment of the arm. Cent Afr J Med 1997; 43:359-60.
[9]Renata pacholczak, Wiestawa Klimek - piotrowska, Jerzyd A Walocha, Absence of musculocutaneous nerve associated with a supernumerary head of biceps brachii: a case report. Surg radio anat DOI 10.1007/s00276-010-0771-9123ANATOMIC VARIATIONS
[10] Le Minor JM. A rare variation of the median and the musculocutaneous nerves in man. Archives Anatomy Histology Embryology 1990; 73:33-4215.
[11] McMinn RMH, editor. Last’s Anatomy: Regional and Applied. London, Churchill Livingstone, 9th edition. 1994; 78-80.
[12] Moore KL. Clinically oriented anatomy. Baltimore, Williams and Wilkins. 3rd edition. 1992; 513-16.
[13] Nayak S, Samuel VP, Somayaji N: Concurrent variations of the median nerve, the musculocutaneous nerve and the biceps brachii muscle. Neuroanatomy 2006; 5:30-2.
[14] Chitra R. Multiple bilateral neuroanatomical variations of the nerves of the arm. Neuroanatomy 2007; 6:43-5.
[15] Joshi SD, Joshi SS, Athavale SA: Hitch –hiking fibres of the lateral cord of the brachial plexus in search of their destination. J. Anat. Soc. India 2008; 57: 26-9.
[16] Bhattarai C, Poudel PP: Unusual variations in the musculocutaneous nerves. Katmandu University Medical Journal 2009; V0l. 7, No.4,
[17]Uzun A, Seelig L (2001) a variation in the formation of the median nerve: communicating branch between the musculocutaneous and median nerves in man. Folia Morphol 60:99–1018:408-10.
[18] Beheiry EE (2004) Anatomical variations of the median nerve distribution and communication in the arm. Folia Morphol 63:313–318
[19] Flatow EL, Bigliani LU, April EW: An anatomic study of the musculocutaneous nerve and its relationship with the coracoidprocess. ClinOrthop Relat Res 1989; 244:166-71.
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