Dissectional Orientation: Morphological Variations of Teres Minor Muscle and its Nerve Supply

SUMMARY: The teres minor is one of the rotator cuff muscles that comprise the superior margin of the quadrangular space. Quadrangular space syndrome (QSS) refers to the entrapment or compression of the axillary nerve and the posterior humeral circumflex artery in the quadrangular space, often caused by injuries, dislocation of the shoulder joint, etc. Patients who fail the primary conservative treatments and have persistent symptoms and no pain relief for at least six months would be considered for surgical interventions for QSS. This cadaveric study of 17 cadavers (males: 9 and females: 8) was conducted in the Gross Anatomy Laboratory at the Department of Anatomy, Faculty of Medicine Siriraj Hospital, Mahidol University. The cadavers were preserved in a 10 % formaldehyde solution and obtained ethical approval by the ethical commission of the Siriraj Institutional Review Board. The morphology of the teres minor muscle-tendon junction, the bifurcation type of the axillary nerve, and the length and number of the terminal branches of the nerve to the teres minor were documented. Specimens with quadrangular space contents and surrounding muscles that had been destroyed were excluded from the study. The results showed that 47.06 % of the specimens had type A bifurcation, 47.06 % had type B bifurcation, and the remaining 5.88 % had type C bifurcation. It was observed that 58.82 % had nonclassic muscle-tendon morphology, while 41.18 % were classic. The average length of the terminal branches of the nerve to the teres minor in males was 1.13 cm, with the majority having two branches. For females, many showed one terminal branch with an average length of 0.97 cm. Understanding the differences in anatomical variations can allow for a personalized treatment plan prior to quadrangular space syndrome surgical procedures and improve the recovery of postsurgical interventions for patients.

El músculo redondo menor es uno de los músculos del manguito rotador que comprende el margen superior del espacio cuadrangular. El síndrome del espacio cuadrangular (QSS) se refiere al atrapamiento o compresión del nervio axilar y la arteria circunfleja humeral posterior en el espacio cuadrangular, a menudo causado por lesiones, dislocación de la articulación humeral, entre otros. En los pacientes en los que fracasan los tratamientos conservadores primarios y presentan síntomas persistentes y ningún alivio del dolor durante al menos seis meses se considerarían para intervenciones quirúrgicas para QSS. Este estudio cadavérico de 17 cadáveres (hombres: 9 y mujeres: 8) se llevó a cabo en el Laboratorio de Anatomía Macroscópica del Departamento de Anatomía de la Facultad de Medicina del Hospital Siriraj de la Universidad Mahidol. Los cadáveres se conservaron en una solución de formaldehído al 10 % y obtuvieron la aprobación ética de la comisión ética de la Junta de Revisión Institucional de Siriraj. Se documentó la morfología de la unión músculo-tendón del músculo redondo menor, el tipo de bifurcación del nervio axilar y la longitud y el número de las ramas terminales del nervio para el músculo redondo menor. Se excluyeron del estudio los especímenes con contenido de espacios cuadrangulares y músculos circundantes que habían sido destruidos. Los resultados mostraron que el 47,06 % de los especímenes presentó bifurcación tipo A, el 47,06 % una bifurcación tipo B y el 5,88 % restante una bifurcación tipo C. Se observó que el 58,82 % presentaba una morfología músculo-tendinosa no clásica, mientras que el 41,18 % era clásica. La longitud pmedia de los ramos terminales del nervio hasta el músculo redondo menor en los hombres era de 1,13 cm, y la mayoría tenía dos ramos. En el caso de las mujeres, mostraron un ramo terminal con una longitud promedio de 0,97 cm. Comprender las diferencias en las variaciones anatómicas puede permitir un plan de tratamiento personalizado antes de los procedimientos quirúrgicos del síndrome del espacio cuadrangular y mejorar la recupe- ración de las intervenciones posquirúrgicas de los pacientes.

Anatomical Variations Of The Axillary Nerve: A Cadaveric Study

Background: Axillary nerve is one of the most common nerves which is prone to iatrogenic injuries (6% of all thebrachial plexus injuries). Knowledge of the anatomical variations of the axillary nerve in respect to its originfrom the posterior cord of brachial plexus, its site of division into anterior and posterior branch and its mode ofsupply to the deltoid muscle is highly important for anatomists, orthopedic surgeons, radiologists and anesthetistsfor proper exploration of the axillary region.Material and Methods: The study was carried out in the Department of Anatomy, Institute of PostgraduateMedical Education and Research, Kolkata, West Bengal. The sample size was 50 upper limbs of 25 formalinhardened human cadavers of both sexes.Results: Out of 50 samples, in 16% cases the Axillary nerve took origin as a common trunk. Regarding the site ofdivision of the axillary nerve into anterior and posterior branches it was found to be above the quadrangularspace in 12% cases and within the quadrangular space in 88% cases. . Regarding the mode of supply of thedeltoid muscle it was seen that the anterior part of the deltoid was supplied by the anterior division of theaxillary nerve in 100% cases; middle part of the deltoid solely by anterior division of the axillary nerve in 60%cases and in remaining 40% cases both from anterior and posterior branch i.e. dual supply (fig-3); the posteriorpart of the deltoid was seen to be supplied by the posterior branch in 100% cases.Conclusion: The knowledge of variations of axillary nerve is very important for anatomists, aneasthesists,orthopaedic surgeons and general physicians during surgical interventions of the axilla and intra-muscularinjections to the deltoid muscle.

Variation in Branching Pattern of Axillary Nerve.

In our present case the axillary nerve on both sideswas arising from posterior cord. About 2.5cm fromits origin at the lateral border of subscapularis, it gave 2 branches i.e anterior and posterior branch. The axillary nerve branched before entering the quadrangular space. Knowledge of the precise relationship of the branches of the axillary nerve, its relationship to the shoulder capsule and its common variations within deltoid muscle is necessary for performing surgical procedures over shoulder and reduce the incidence of iatrogenic nerve damage.