Correlation between anatomical variations and morphofunctional alterations of the upper extremity. An anatomical review
Authors: Valenzuela Juan Jose , Orellana Mathias Ignacio , Gold Marjorie Hanna , Santana Edmundo Andres , Molina Francisco Javier , De la Paz García Guernica 
Published: April 2020

IntroductionThe upper extremity is one of the most complex and functional body segments of the human body formed by a wide variety of structures, whether musculoskeletal, nervous system and integumentary system, which together allow great functionality in many daily life activities. In case any type of alteration of these structures will affect the function of the structure or extremity segment and can also be associated with pathologies of neighboring regions such as the cervical and thoracic region. Due to their considerable number of structures, the anatomical variations of the structural components of the upper extremity are common to occur, being the most common the variations of muscular and vascular components behaving as predisposing factors or risk factor for some type of pathology musculoskeletal or vascular. The objective of this study was to review the literature of the neuromusculoskeletal anatomical variations described in the upper extremity and its possible clinical correlation with some pathology or syndrome in the upper extremity.MethodsA systematic search in the literature was carried out in different databases in order to respond to the relationship between anatomical variations of neuromusculoskeletal structures with pathologies presented in the upper extremity, using the search strategy proposed by the Prism statement for reviews.ResultsThe analysis of the full text studies after having applied the exclusion criteria showed that the anatomical variations present in the upper extremity, in one third of the studies correlated some anatomical variant with alterations of nerve entrapment such as carpal tunnel syndrome, Guyon canal syndrome among others, being frequent that said compressions would be attributed to some type of accessory muscle or variation in its insertion site, which demonstrates the importance of knowing the normal anatomy to be able to investigate these structures and their possible variations avoiding a non‐specific differential diagnosis or not associated with the underlying pathology which could only improve the clinical symptomatology but not the underlying cause. On the other hand, other anatomical variations with specific pathologies of the structure are described and finally there are anatomical variations that do not present any type of clinical condition in people who present it.ConclusionsThis review of the literature does not address a single type of anatomical variation but gives guidelines to take into account that different structures of the upper extremity with some type of anatomical variation that may be a predisposing factor to some type of pathology of the upper limb, and also gives rise to new studies that show the importance of taking into account the anatomical structure for making different clinical decisions.Search Flowchart of the reviewFigure 1
Nerve entrapment and its correlations with the anatomic variations of the upper extremity

Nerve

Anatomic Variation

Clinical presentation

Author

Median Nerve

Insertions of the Gantzer muscle in the flexor digitorum superficialis and the braquialis fascia.

Carpal tunnel syndrome.

Zdilla MJ. et al, 2019

Anomalous Innervation of the Median Nerve in the Arm in the Absence of the Musculocutaneous Nerve.

Flexor paralysis of the arm or sensory loss in the lateral forearm.

Raza K. et al, 2017

Origin of the anterior interosseous nerve in the space between the arc of the flexor digitorum superficialis and the teres pronator and proximal to this point.

Nerve entrapment syndromes of the anterior interosseous nerve.

Riveros A. et al, 2018

Gantzer muscle.

Median or anterior interosseous nerve entrapment.

Martinoli C. et al, 2010

Accessory brachialis muscle.

Median nerve entrapment

Sookur PA. et al, 2008

Palmaris Profundus muscle.

Neuropathy of the median nerve

Pirola E. et al, 2009

A biventered first lumbrical extending into the carpal tunnel combined with bilateral fifth superficial flexor digitorum tendon regression.

Carpal tunnel syndrome

Silawal S. et al, 2018

Pronator teres distal insertions.

Median nerve entrapment

Olewnik L. et al, 2017

Radial Nerve

Accessory head of the extensor carpi radialis longus muscle merging with extensor carpi radialis brevis muscle.

Radial syndrome and epicondylalgia.

Yang K. et al, 2018

Aberrant course of superficial radial nerve in the forearm that perforates the Brachioradialis tendon to become subcutaneous.

Waterberg syndrome.

Kumar P. et al, 2017

Muscular elevator of the latissimus dorsi tendon.

Radial Nerve entrapment

Moore CW. et al, 2018

Musculocutaneous Nerve

4 headed biceps brachii

Musculocutaneous nerve entrapment

Moore CW. et al, 2018

Ulnar Nerve

Epitrochlear anconeus.

Ulnar nerve entrapment.

Bladt L. et al, 2009

Accessory Abductor Digiti Minimi.

Compressive neuropathy of the ulnar nerve.

Harvie P. et al, 2004

Epitrochlear anconeus.

Ulnar nerve entrapment.

Erdem Bagatur A. et al, 2015

Accessory extensor digitorum brevis.

Guyon tunnel syndrome

Moore CW. et al, 2018

Accessory abductor minimi digiti manus muscle.

Guyon tunnel syndrome

Ahmadreza A. et al, 2015

Accessory belly of the flexor digiti minimi.

Ulnar nerve entrapment

Ardouin L. et al, 2015

Axillary Nerve

Muscular elevator of the latissimus dorsi tendon

Axillary nerve entrapment

Moore CW. et al, 2018