MORPHOLOGY OF PSOAS MINOR AND PSOAS ACCESSORIUS S D Joshi, S S Joshi, U K Dandekar, S R Daini Deptt. of Anatomy, Rural Medical College, P.I.M.S. Loni Distt. Ahmednagar, Maharashtra

ABSTRACT Psoas minor muscle is considered to be a vestigial muscle like palmaris longus and plantaris. It lies anterior to the . It has a small fleshy belly and a long flat tendon. This small muscle is the representative in man of a relatively large muscle which in most mammals plays an important part of flexing the lumbar part of . In some lower mammals it is larger than psoas major and acts as a flexor of ; this being utilized in running by the rabbit and the apes in brachiating. It begins to disappear in those primates which assume the erect posture. The presence of this muscle varies from person to person and on the two sides. It is present in about 40 to 60 % of the population. In the majority it is inserted on the but may also be attached to the arcuate line of and the iliac . While going through the literature we did not come across any detailed study of the muscle in the population of this region. Hence, we have conducted a detailed study of psoas minor muscle in 30 cadavers bilaterally. In the present series this muscle was absent in 70%. Average length of fleshy belly was 8.23 em and that of the tendon 15.48 em. In some cases an unusual interesting feature observed was the origin of some fibers of psoas major from the deep surface of flattened tendon of psoas minor muscle, which we have named as Psoas accessorius. Key Words-Morphology, Psoas minor, Psoas major, psoas accessorius.

INTRODUCTION blacks (Hanson P et al, 1999 "). The short fleshy belly

The Psoas Minor is also known as 'Psoas soon gives way to a long, flat tendon which may be parvous' (Bryce, 1923'; Keith, 1948l "Psoas" is a attached to the pecten pubis, iliopectineal eminence 1 7 9 12 13 4 Greekwordforthe loins -the muscle of the lower back and/ or ' ' ' ' '' · • Looking at the differences 3 regarding its presence, laterality, size and variability (Webster's comprehensive dictionary, 1986 ). This muscle although well developed and constant in most of insertion and its evolutionary significance it was lower animals, sometimes exceeding the psoas major decided to undertake a detailed study of this muscle; in size, is not constant in man' and is considered by although small and vestigial but not insignificant. many as a vestigial muscle. It begins to disappear in MATERIAL AND METHODS those primates who assume the erect posture2.This This study was carried out on 30 embalmed muscle lies anterior to psoas major (Hollinshead, 4 5 6 7 cadavers (males-24, females-6) available in this 1985 ; Moore, 1985 ; McMinn, 1990 ; Williams, 1995 ; 8 9 department, over a period of two years. Clearance of Snell, 2008 ) but Wood Jones (1953) stated that it lies institutional ethical committee was obtained before anteromedial to the psoas major except at the pelvic starting the work. These were the cadavers which brim, where its expanded tendon turns to the medial were utilized by medical students for routine side of that muscle. Kendall (1993) 10 stated that it is dissection. When all organs were removed from the relatively unimportant and is only present in about abdominal cavity then the dissection of posterior 40% of the population; while Wood Jones (1953) 9 has was undertaken.· On the anterior described it to be present, on one or both sides, in surface of Psoas major muscle, when present, Psoas about 45% of the population. In a study of racial minor muscle was cleaned right from its origin (above discrepancies, psoas minor has been reported to be the medial arcuate ligament) up to its insertion. Any absent in 50% in Orientals; 57% in whites and 67% in variations of this muscle at its attachment (both at the Correspondence Dr. S. D. Joshi origin as well as insertion) or along its whole length Pro( & Head, Dept. ofAnatomv Rural Medical College, PIMS, Loni, Dis//. Ahmednagar. Maharastra were recorded and, whenever deemed necessary, Ph . . 02422 • 272067 photographs were taken. The length and width of Email: sdjoshi _ [email protected]

J. Anat. Soc. India 59(1) 31-34 (2010) 31 Morphology of Psoas ...... SD Joshi, S S Joshi, U K Dandekar, S R Daini

fleshy belly as well as long tendon were measured continued on the superficial surface of the muscle with the help of divider, thread, scale and digital right up to its insertion. In 7 cases (43.75%) there was vernier caliper. Careful dissection of distal attachment a zone of overlapping between fleshy belly and was done to verify the insertion of tendon to the tendon (Fig.2A). neighbouring fascia and the bone.

RESULTS

In the present study psoas minor was found to be present in 9 cases (30%). It was present bilaterally in 23.3% and unilaterally only on the left side in 6.6%. In all the cases the psoas minor was present onthe anterior surface of psoas major and tended to lie medial to the psoas major towards its insertion (Fig. 1A). The origin of psoas minor was from the sides of 12'h thoracic and 1" and the intervening disc between them, except in two cases, where the origin was from a lower level i.e. from sides of 3'd and 4'hlumbar vertebrae (Fig. 3A) and disc bilaterally. In these the intervening intervertebral Fig.1A: Showing Right Psoas minor muscle -'A' lying two. cases the muscle was quite bulky. In almost all superficial to Psoas major muscle- '8'. cases the tendon, when traced inferiorly, flattened out and blended with the fascia (Fig. 18). Some aponeurotic fibres were inserted on the iliopubic eminence and the arcuate line. The average length of fleshy belly was 8.23 em (Rt-7.71cm, Lt-8.75 em) and that of the tendon was 15.52 em long (Rt-15.8 em, Lt- 15.24 em). The average maximum width of the fleshy part of muscle was 1.31 em (Rt-1.45cm, Lt-1.18 em) and that of the tendon was 0. 7cm (Rt-0.67 em, Lt-0. 73 em). In few specimens the fleshy fibres of the muscle extended further lower down on the deep surface of the tendon. In 4 cases (25 %) it was found that some fibres of psoas major were arising from the deep Fig.1B: Showing left Psoas major (B) and Psoas minor (A). surface of the flattened tendon of psoas minor ( When traced inferiorly tendon of Psoas minor merges with the dence iliopsoas fascia (indicated by black dots). Also Fig.2A,28 & Fig.3A,38) and in this position these fibres seen is the genitofemoral (black arrow).

Table 1: showing the Length and Width of Fleshy belly and the Tendon of Psoas minor muscle (In em):

FLESHY BELLY TENDON TOTAL LENGTH

Right Range Average Range Average Range Average Length 3.10.5 7.71 " 14-18.5 15.8 18-29 23.51 Width 0.8-2 1.45 0 . 5-1 0.67 Left Length 5-11 8.75 12.5-20 15.24 20-30 24 Width 0.5-2 1.18 0 .21.5 0.73

J. Anat. Soc. India 59(1) 31-34 (2010) 32 Morphology of Psoas ...... SO Joshi, S S Joshi, U K Dandekar, S R Daini

Fig.3A: Showing left Psoas major (B) and lying superficial to it is seen a well developed Psoas minor. muscle (A) vertebrae. A well defined tendon is present along the lateral Fig.2A: Showing left Psoas major (8), tendon of Psoas edge of this muscle. Also seen are the fibres of Psoas minor (A), the fleshy fibers of a muscle 'C' (Psoas accessorius (C) arising from the deep surface of Psoas accessorius) seen arising from the deep surface of Psoas minor. minor and descending superficial to Psoas major. The tendon of Psoas minor has been turned to show the origin of this muscle from the deep surface of the tendon. Edge of Psoas minor has been indicated by red arrow.

Fig.3B: Showing Left Psoas major (B), tendo~:~ of Psoas minor (A) and the sheet of Psoas accessorius (C) arising from the deep surface of Psoas minor tendon and spreading anterior to Psoas major.

The study of racial differences described by Saib ( 1934) has been referred to by Hanson P et al ( 1999) 11 Fig.28: Showing left Psoas major (B) . The tendon of Psoas wherein it was reported that the psoas minor was 'minor has been turned to expose its posterior surface absent in 50% in Orientals; 57% in whites and 67% in wherein, the fleshy fibres of Psoas minor (A) are seen to join blacks. Hanson Petal (1999) 11 studied psoas minor the tendon (red arrow). Belowthatthe origin of fleshy fibres in young blacks (21 cases) and white men (23 cases) of Psoas accessorius are seen-'C' as shown in fig.2A during routine autopsies. They observed that the psoas minor was present in 2 subjects (9%) in blacks. DISCUSSION In the whites, the psoas minor was present on both The presence of Psoas minor muscle varies sides (87%). Further, on visual inspection the psoas from person to person and on the two sides. Many minor in black subjects appeared as a slight thickening of the fascia surrounding the psoas major, workers have stated that it is present in about 60% of 5 7 12 13 15 rather than actual muscle. In contrast, in the white the population • s. ' s. ' ' • In the present study it was group the psoas minor was a well defined muscle present in 30% cases. positioned anterior to and separate from the psoas

J. Anat. Soc. India 59(1) 31-34 (2010) 33 Morphology of Psoas ...... SD Joshi, S S Joshi, U K Dandekar, S R Daini

major fascia. 3. Webster's comprehensive Dictionary, Encyclopedic edition, vol. 2, J.G.Ferguson Publishing Anatomical texts have described the origin of Company Chicago 1986, pp 1018. psoas minor from the bodies of 12"' thoracic and 1.. 5 6 7 0 6 4. Hollinshead WH; Textbook of Anatomy, 4"' Edn. lumbar vertebrae and the disc between them'· • • ·' ·'2.' Harper and Row publishers, Philadelphia, London In the present study the origin of the muscle was 1985, pp 679-681. found to be similar except in 2 cases where psoas minor was arising from sides of L3 and L4 vertebrae. 5. Moore KL; Clinically oriented anatomy, 2"d Edn. The short fleshy belly soon gives way to a long flat Williams and Wilkins, Baltimore, London 1985, pp tendon, which is attached to the pecten pubis, 275. 9 2 13 iliopectineal eminence and iliac fascia'· ·' • ·'•· The 6.McMinn RMH; Last's anatomy regional and applied, psoas minor is a weak flexor of the lumbar spine. The 8"' Edn. English Language Book Society I Churchill 5 muscle also flexes the pelvis on the trunk ·'3. As a Livingstone, Edinburg, London 1990, pp 357. flexor of the pelvis on the spine its value to the rabbit when running and to the apes while brachiating is 7.Williams PL; Gray's Anatomy, 38"' Edn. Churchill 17 Livingstone Edinburgh, London, Philadelphia 1995, quite apparent · pp870. It has also been described that the tendon of psoas minor may be mistaken for the genitofemoral 8. Snell RS; Clinical Anatomy by Regions, 8'h Edn. 17 Wolters Kluwer I Lippincott Williams and Wilkins, nerve • It is active in cats when they arch their backs •s. Baltimore, New York 2008, pp 174,175,580. It is also proposed that psoas minor could support the lumbar trunk during stance. While reviewing the 9. Wood Jones F; Buchanan's Manual of Anatomy in literature it is observed that except for the incidence The Abdomen, 8"' Edn. Bailliere, Tindall and Cox 7 and of presence or absence of the muscle no other 8 Henrietta ST, W.C. London 1953, pp 841-842. morphological features have been described and as 10. Kendall FP, McCreary EK, Provance PG; Muscles such the findings of the present work cannot be testing And function, 4"' Edn. Lippincott Williams and compared with that of any other workers. Wilkins, New York, London1993, pp 214. CONCLUSION 11. Hanson P, Magnusson SP, Sorensen H and This study has been conducted on 30 cadavers Simonsen EB; Anatomical differences in the psoas bilaterally. In the present series Psoas minor was muscles in young black and white men. J. Anat found to be present in 30% cases. The absence of the 1999,194 (2) pp 303-307. muscle described in the literature ranges from 50- 12. Romanes G.J; Cunningham's Textbook of 90%; also racial differences have been reported. Anatomy, 12"' Edn. Oxford University Press, Oxford During evolution and with the assumption of bipedal New York, Toronto 1981, pp 363. gait, the function and hence the incidence and size of 13. Woodburne RT; Essentials of Human Anatomy, 7'h psoas minor has been reduced. But, at times the Edn. Oxford University Press, New York 1983, pp 465. muscle may be large. We have found a hitherto undescribed muscle mass in the literature which 14. Palastanga N, Field D, Soames R; Anatomy and arises from deep surface of the tendon of psoas minor human movements-structure and function, 4'h Edn. and spreads out as a substantial fleshy mass on the Butterworth Heinemann, Boston, Johannesburg anterior surface of psoas major and continues in the 2002, pp469. same position till its insertion and have named it as -• 15. Hamilton WJ; Textbook of human Anatomy, 2"d Psoas Accessorius. Edn. English language book society and Macmillan press Ltd. London and Basingstoke 1978,149. REFERENCES 16. Sahana SN; Human Anatomy {Descriptive and 1. Bryce T H; Quain's elements of Anatomy, 11"' Edn. Applied}, 3rd Edn. Vol.1, Amitabha Sen for central Vo1.4, part 2, mycology, Longmans, Green and co. educational enterprises, New central book agency London 1923, pp 224. Calcutta 1977, pp 701.

2. Keith A; Human embryology and morphology, 6"' 17. Basmajian JV, Slonecker CE; Grant's method of Edn. Edward Arnold and co. London 1948, pp 629. anatomy -A clinical problem- solving approach, 11"' Edn. Williams and Wilkins, Baltimore, London 1986, pp 197.

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