Axillary arch muscle and pectoralis quartus: an unusual combination of two variant supernumerary muscles in the axillary region - a case report.

Variant anatomy in the axillary region is of great clinical significance. It is one of the most frequently accessed regions for radical dissection surgery. During routine dissection of embalmed cadavers, we found a rare case of two accessory muscular slips emerging from the lateral border of latissimus dorsi (LD) and the inferolateral border of pectoralis major (PM), crossing the neurovascular structures in the axilla and merging distally together to the brachial fascia at the upper end of humerus below the bicipital groove. The accessory slip from LD is commonly referred to as the "axillary arch" in literature. We identified the accessory slip from the PM crossing over the axilla as pectoralis quartus. These aberrant slips can cause neurovascular compression in the axilla and can have clinical implications. Prior knowledge of the variant anatomy is the key to successful surgery in the axilla, thereby avoiding inadvertent injuries and post-operative complications.

Anatomy of the axillary arch: from its incidence in human to an embryologic and a phylogenetic explanation of its origins.

INTRODUCTION: Typically, the axillary arch is defined as a fleshy slip running from latissimus dorsi to the anterior aspect of the humerus. Phylogeny seems to give the most relevant and plausible explanation of this anatomical variant as a remnant of the panniculus carnosus. However, authors are not unanimous about its origin. We report herein the incidence of axillary arch in a series of 40 human female dissections and present an embryologic and a comparative study in three domestic mammals. MATERIALS AND METHODS: Forty formalin-preserved Caucasian human female cadavers, one rat (Rattus norvegicus), one rabbit (Oryctolagus cuniculus) and one pig (Sus scrofa domesticus) cadavers were dissected bilaterally. A comparative, analytical and a descriptive studies of serial human embryological sections were carried out. RESULTS: We found an incidence of axillary arch of 2.5% (n = 1 subject of 40) in Humans. We found a panniculus carnosus inserted on the anterior aspect of the humerus only in the rat and the rabbit but not in the pig. The development of the latissimus dorsi takes place between Carnegie stage 16-23, but the embryological study failed to explain the genesis of the axillary arch variation. However, comparative anatomy argues in favour of a panniculus carnosus origin of the axillary arch. CONCLUSIONS: With an incidence of 2.5% of cases, the axillary arch is a relatively frequent variant that should be known by clinician and especially surgeons. Moreover, while embryology seems to fail to explain the genesis of this variation, comparative study gives additional arguments which suggest a possible origin from the panniculus carnosus.

Effects of cognitive loading and force on upper trapezius fatigue.

Background: Musculoskeletal disorders (MSDs) are particularly common in the shoulder/neck region for some tasks that involve low force exertions, for example computer work. It has been demonstrated that muscle activity may be stimulated by cognitively demanding tasks. There is a lack of studies on the relationship between qualitative levels of cognitive loading, level of muscle activity, and muscle fatigue. Aims: To investigate the effects of quantitative levels of cognitive loading on conduction velocity changes and isometric endurance times for the upper trapezius. Methods: Participants performed a combination of three levels of a cognitively demanding computer task (0, 1.59 and 3 Bits) while simultaneously performing either of two isometric endurance tests (20 and 40% MVC) for the upper trapezius. Results: Information load had a significant effect (P < 0.05) on normalized conduction velocity slopes for the 40% but not for the 20% maximum voluntary contraction conditions. Information load had a highly significant effect on endurance times for both exertion levels (P < 0.01). Conclusions: This study found that performing a high-difficulty cognitive task while simultaneously performing increasingly higher levels of static isometric shoulder abduction exertions, fatigued the trapezius muscle quicker than performing an equivalent exertion with low cognitive load. This is particularly relevant to workplaces with increasing levels of automation that require high levels of decision making and computer use.

Unusual origin of the levator scapulae muscle from mastoid process.

Anatomic variations of the neck musculature are uncommon and incidentally found during cadaveric dissection. The levator scapulae muscle is found in the floor of the posterior cervical triangle. It connects the axial skeleton with the superior appendicular skeleton and acts as a scapular elevator. Normally, it originates from the transverse processes of first four cervical vertebrae and inserts into the superomedial border of the scapula. During a routine cadaveric dissection, we encountered an additional slip of the left levator scapulae originating from the left mastoid process. This muscle is frequently implicated in the etiopathology of neck and shoulder pain. Knowledge of this variation is not only interesting to anatomists, but also to surgeons operating on the posterior neck and physicians managing patients with cervical or shoulder pain.

Congenital Partial Absence of Trapezius with Variant Pattern of Rectus Sheath.

Musculocutaneous pedicled/free flaps are an essential prerequisite for reconstructive surgery. Amongst the trunk muscles commonly harvested for flaps, the trapezius and rectus abdominis provide satisfactory coverage for cranial and trunk defects. unilateral/bilateral or partial congenital absence of trapezius muscle is well documented and may result in muscular imbalances compromising posture and limb movements. During routine cadaveric dissection, we encountered a case of bilateral partial absence of occipital part of the trapezius muscle. Concurrently, the ventral abdominal musculature displayed the aponeurosis of transversus abdominis muscle solely forming the posterior wall of the rectus sheath. These conjointly occurring anomalies advocate a compensatory strengthening of the anterior wall of rectus sheath in response to the congenital absence of occipital part of the trapezius, probably to counteract the postural instability. The present study focuses on recognition of compensatory mechanisms resulting from congenital variations as identification of such processes may prevent chronic debilitating conditions.

The abnormalities of trapezius muscle might be a component of Poland's syndrome.

Poland's syndrome is a rare unilateral congenital anomaly characterized by the absence of the pectoral muscle and hand anomalies. By the time, new components including the absence or hypoplasia of many muscles have been identified, however, the anomalies of trapezius muscle have not been reported in patients with Poland's syndrome. The accepted etiological theory is the temporary interruption of blood supply of the subclavian artery and its branches in the early gestational period. The artery of the trapezius muscle is also one of the branches of subclavian artery. Just because of that, it is likely to trapezius muscle be affected in patients with Poland's syndrome. We are presenting a case of Poland's syndrome associated with unilateral partial absence of trapezius muscle to support this hypothesis.

A biceps muscle Latissimus dorsi in a dog / Una segunda cabeza del músculo Latissimus dorsi en un perro

This article reports the finding of a twin unreported muscle begin. In one dog, both, left and right muscle latissimus dorsi were biceps. The thin second head of m. latissimus dorsi that we founded, could be an intermediate step of comparative anatomy changes from reptilian to mammal. Man breast surgery and cardiomyoplasty, use dog latissimus dorsi as experimental, to know this information can be useful to these situations.

Este artículo describe el hallazgo del origen de un músculo gemelo no reportado. En un perro, los dos músculos latissimus dorsi, izquierdo y derecho, eran biceps. La segunda cabeza delgada del M. latissimus dorsi observada, podría ser un paso intermedio de los cambios de la anatomía comparada de reptil a mamífero. Conocer esta información puede ser útil para la cirugía de tórax y cardiomioplastía en el humano, donde el músculo latissimus dorsi del perro, es utilizado en forma experimental.