Possible implications of an accessory abductor digiti minimi muscle: a case report
© Ballesteros and Ramirez. 2007
Received: 24 July 2007
Accepted: 03 December 2007
Published: 03 December 2007
Accessory ADM was first reported in 1868 although muscular, vascular and nervous variations of the hypothenar eminence are rare, contrary to anomalous muscles in the wrist which are relatively common.
This case report presents a bilateral variation of an accessory abductor digiti minimi muscle in a male specimen. Ulnar artery and ulnar nerves were taken into account regarding their position and trajectory related to this variation.
Muscle size may be an important factor in considering whether a variation is able to produce neurovascular compression and clinical implications.
This case report presents an abductor digiti minimi (ADM) muscle's bilateral accessory head, involving ulnar artery (UA) and ulnar nerve (UN) trajectories' sensorial and motor components. Although muscular, vascular and nervous variations of the hypothenar eminence are rare (differing from anomalous muscles in the wrist), they have been reported [1–10]. According to Sheppard, three cases of accessory ADM were first reported by Wood in 1868. Most authors call such additional ADM head an "accessory" component which can be unilaterally or bilaterally presented, producing compression in Guyon's canal. Harvie et al., found an accessory ADM in 41% of 116 volunteers' asymptomatic ultrasound examinations, greater prevalence being found in male samples and bilateral presentation in 50% of cases for both genders.
The flexor digiti minimi brevis muscle can also be present in this area; Madhavi et al., have stated that it relates to the common phylogeny of these muscles from the same muscle mass . Soldado-Carrera et al., found this variation to be associated with decreased flexor digitorum superficialis muscle fourth tendon caliper and median nerve split. Murata  found an accessory ADM in 35 hands, having one (17%), two (80%) and three fascicles (3%). Furthermore, Wulle  presented eleven cases of accessory ADM, but having "longus" presentation.
This class of muscular variation entrapping neuro-vascular bundles may have sensorial and/or muscular implications in a range of compression neuropathies [5, 6]. Entrapment neuropathies can produce heterotopic projected pain, symptomatic consequences arising from mechanical nerve injury passing through a narrow anatomical space or under a muscular structure which may potentially compress the neuro-vascular package [13–15]. We think that muscle size, tightness and course may be important factors in considering whether such variations are able to produce compression.
This scenario can cause nerve oedema and ischemia by muscle structure friction over the peryneuro which can cause neuritis and raise endoneural pressure. Involvement of vegetative contributions must be taken into account when assessing the effects of such sensorial injuries, due to their ability to produce complex pain syndromes [16, 17]. In addition to traumatic neuropathic pain, symptoms in distal nerve distribution (dysesthesia, paresthesia and anaesthesia), paresis, hyporeflex, hypotonicity and atrophy, such as inferior motor neuron lesion, may be equally feasible [18, 19]. The deep UN motor branch may be compressed by this ADM accessory head and compromise palmar and dorsal interosseous muscles, hypothenar eminence muscles, lumbricals III and IV and hallux adductor, thereby producing a clinical "claw hand" appearance or resembling Guyon's canal syndrome.
Having dealt with this variation's possible sensorial and motor effects, vascular effects must also be considered. UA compression (left hand) may produce peripheral vascular disease from two possible events depending on the type of compression (i.e. constant or intermittent muscular compression). Muscular hyperfunction can reduce these arterial branches' distal irrigation, causing hypoesthesia or hyperesthesia in the hand. Likewise, muscular spasm can produce anaerobic metabolism and consequent nerve irritation by anoxic acidified setting with neurogenic inflammation and peripheral hyperalgesia [20, 21]. Permanent loss of vascular supply during muscular spasm can lead to vascular claudication and pain [22, 23].
We believe (from a functional perspective) that precipitating factors (gender, occupation, side dominance, traumatic history, anatomical characteristics) may develop neurovascular compression and symptoms in an anomalous muscle; we thus present this anatomical case. The morphological characteristics led to all the above explained symptomatic possibilities; however, lacking clinical judgment, further statements lose their functional value and become merely speculative.
Muscular variations compromising neurovascular bundles may produce clinical symptoms such as dysaesthesic pain, sensory loss, wakefulness and paresis, highlighting these anatomical discrepancies' importance when they are presented. However, the existence of an accessory ADM is usually asymptomatic and only rarely results in nerve compression. It does appear that muscle size, tightness and course may be an important factor in considering whether such variation is able to produce UN compression at Guyon's canal or UA compression resulting in a poor relationship between blood-flow and artery diameter. A larger sample of cadaver specimens is needed. Also, further clinical studies are required to confirm the existence of these variations' clinical effects.
List of abbreviations
Abductor digiti minimi muscle
We thank Javier Ariza Alvares (MD) for his contribution in acquiring data.
- Curry B, Kuz J: A new variation of abductor digiti minimi accessorius. J Hand Surg 2000, 25:585–7.View ArticleGoogle Scholar
- Soldado-Carrera F, Vilar-Coromina N, Rodriguez-Baeza A: An accessory belly of the abductor digiti minimi muscle: a case report and embryologic aspects. Surg Radiol Anat 2000, 22:51–4.View ArticlePubMedGoogle Scholar
- Kanaya K, Wada T, Isogai S, Murakami G, Ishii S: Variation in insertion of the abductor digiti minimi: an anatomic study. J Hand Surg 2002,27(2):325–8.View ArticleGoogle Scholar
- Bozkurt MC, Tagil SM, Ersoy M, Tekdemir I: Muscle variations and abnormal branching and course of the ulnar nerve in the forearm and hand. Clin Anat 2004, 17:64–6.View ArticlePubMedGoogle Scholar
- Sheppard JE, Prebble TB, Rahn K: Ulnar neuropathy caused by an accessory abductor digiti minimi muscle. Wis Med J 1991, 90:628–31.PubMedGoogle Scholar
- Netscher D, Cohen V: Ulnar nerve compression at the wrist secondary to anomalous muscles: a patient with a variant of abductor digiti minimi. Ann Plast Surg 1997, 39:647–51.View ArticlePubMedGoogle Scholar
- Murata K, Tamai M, Gupta A: Anatomic study of variations of hypothenar muscles and arborization patterns of the ulnar nerve in the hand. J Hand Surg 2004, 29:500–9.View ArticleGoogle Scholar
- Wulle CM: abductor digiti minimi longus: anatomical rarity? Handchir Mikrochir Plast Chir 1987, 19:43–5.PubMedGoogle Scholar
- Harvie P, Patel N, Ostlere SJ: Ulnar nerve compression at Guyon's canal by an anomalous abductor digiti minimi muscle: the role of ultrasound in clinical diagnosis. Hand Surg 2003, 8:271–5.View ArticlePubMedGoogle Scholar
- Harvie P, Patel N, Ostlere SJ: Prevalence and epidemiological variation of anomalous muscles at Guyon's canal. J Hand Surg 2004, 29:26–9.Google Scholar
- Madhavi C, Holla SJ: Anomalous flexor digiti minimi brevis in Guyon's canal. Clin Anat 2003, 16:340–3.View ArticlePubMedGoogle Scholar
- Hankins CL, Flemming S: A variant of Kaplan's accessory branch of the dorsal cutaneous branch of the ulnar nerve: a case report and review of the literature. J Hand Surg 2005, 30:1231–5.View ArticleGoogle Scholar
- Dworkin RH, Backonja M, Rowbotham MC, Allen RR, Argoff CR, Bennett GJ, Bushnell MC, Farrar JT, Galer BS, Haythornthwaite JA, Hewitt DJ, Loeser JD, Max MB, Saltarelli M, Schmader KE, Stein C, Thompson D, Turk DC, Wallace MS, Watkins LR, Weinstein SM: Advances in neuropathic pain: diagnosis, mechanisms, and treatment recommendations. Arch Neurol 2003, 60:1524–34.View ArticlePubMedGoogle Scholar
- Castaldo JE, Ochoa JL: Mechanical injury of peripheral nerves: fine structure and dysfunction. Clin Plast Surg 1984, 11:9–16.PubMedGoogle Scholar
- Ginanneschi F, Dominici F, Milani P, Biasella A, Rossi A: Evidence of altered motor axon properties of the ulnar nerve in carpal tunnel syndrome. Clin Neurophysiol 2007, 118:1569–76.View ArticlePubMedGoogle Scholar
- Hoffman KD, Matthews MA: Comparison of sympathetic neurons in orofacial and upper-extremity nerves: implications for causalgia. J Oral Maxillof Surg 1990, 48:720–6.View ArticleGoogle Scholar
- Tracey DJ, Cunningham JE, Romm MA: Peripheral hyperalgesia in experimental neuropathy : mediation by a2-adrenoreceptors on post-ganglionic sympathetic terminals. Pain 1995, 60:317–27.View ArticlePubMedGoogle Scholar
- Gordon L, Ritland GD: Nerve entrapment syndromes. Conn Med 1974, 38:97–102.PubMedGoogle Scholar
- Sarno JB: Suprascapular nerve entrapment. Surg Neurol 1983, 20:493–97.View ArticlePubMedGoogle Scholar
- Basbaum AI: Distinct neurochemical features of acute and persistent pain. Proc Natl Acad Sci 1999, 96:7739–43.View ArticlePubMedGoogle Scholar
- Simone DA, Ochoa J: Early and late effects of prolonged topical capsaicin on cutaneous sensibility and neurogenic vasodilatation in humans. Pain 1991, 47:285–94.View ArticlePubMedGoogle Scholar
- Nawaz S, Walker RD, Wilkinson CH, Saxton JM, Pockley AG, Wood RF: The inflammatory response to upper and lower limb exercise and the effects of exercise training in patients with claudication. J Vasc Surg 2001, 33:392–9.View ArticlePubMedGoogle Scholar
- Pritchard MH, Pugh N, Wright I, Brownlee M: A vascular basis for repetitive strain injury. Rheumatology (Oxford) 1999, 38:636–9.View ArticleGoogle Scholar
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