|Year : 2021 | Volume
| Issue : 3 | Page : 164-173
The prevalence and distribution of the variants of pectoralis minor in cadaveric studies: A systematic review and meta-analysis of 32 observational studies
Adil Asghar1, Shagufta Naaz2, Sunita Naya3
1 Associate Professor, Department of Anatomy, All India Institute of Medical Sciences, Patna, Bihar, India
2 Associate Professor, Department of Anaesthesiology, All India Institute of Medical Sciences, Patna, Bihar, India
3 Assistant Professor, Department of Anatomy, All India Institute of Medical Sciences, Patna, Bihar, India
|Date of Submission||21-Oct-2020|
|Date of Decision||18-Nov-2020|
|Date of Acceptance||23-Mar-2021|
|Date of Web Publication||22-Jun-2021|
Department of Anatomy, All India Institute of Medical Sciences, Patna, Bihar
Source of Support: None, Conflict of Interest: None
Introduction: Pectoralis minor (PMi) is used as a vascularized and innervated free-muscle graft in the reconstructive surgical procedure. The present review aims to provide insights to the surgeons regarding the variants of PMi in terms of costal attachment, insertion, nerve supply and arterial supply. Methodology: Three major databases (PubMed, EMBASE, and Google Scholar) were thoroughly searched along with the full text of journals. Results: Seven studies (n = 1787) were analysed for the evaluation of costal attachment. PMi arise from 3rd to 5th rib in 33% (95% confidence interval [CI], 30–37%), but the most common variants II-5 ribs was observed in 36%, which was higher than normal. Eighteen studies (n = 2424) reported details of insertion. The variant insertion of PMi was observed in 21% (15–28; 95% CI). Seven studies reported nerve supply. Both medial pectoral nerve (MPN) and lateral pectoral nerve (LPN) innervates PMi in 93% and MPN absent in 7%. Only two studies reported arterial supply. The PMi was vascularized by single dominant artery in 77% (68–85; 95% CI) or two arteries in 19% (13–29; 95% CI) or three arteries 2% (2–8; 95% CI) or even four arteries in 1% (0–7; 95% CI). Conclusion: PMi has a constant costal attachment to the 3rd and 4th ribs. Origin of PMi from 5th rib is reported with a pooled prevalence of 73.3% and from 2nd rib is reported in 61.5%. PMi inserts to the superomedial boundary of the coracoid process in 79% only.
Keywords: Axilla, coracoid process, thoracic outlet syndrome
|How to cite this article:|
Asghar A, Naaz S, Naya S. The prevalence and distribution of the variants of pectoralis minor in cadaveric studies: A systematic review and meta-analysis of 32 observational studies. Natl J Clin Anat 2021;10:164-73
|How to cite this URL:|
Asghar A, Naaz S, Naya S. The prevalence and distribution of the variants of pectoralis minor in cadaveric studies: A systematic review and meta-analysis of 32 observational studies. Natl J Clin Anat [serial online] 2021 [cited 2021 Sep 21];10:164-73. Available from: http://www.njca.info/text.asp?2021/10/3/0/319013
| Introduction|| |
Pectoralis minor (PMi) is the pectoral muscle, which is utilized as a vascularized free-nerve muscle graft for facial reanimation and breast reconstruction. Attachment at costal cartilage makes it a perfect graft for mandibular reconstruction. The PMi has several peculiarities that make it ideal for reconstructive surgery like its dual nerve supply and blood supply. The flat and fan shape of the muscle makes the technique easy to use because it needs minimal trimming and allows a multidirectional pull without causing excess soft-tissue bulk. The orientation of muscle fibres resembles the facial muscles and subcutaneous muscles. The fleshy origin and insertion of this muscle give better motor control at the reconstruction site and better teeth exposure following mouth opening in case of a mandibular reconstruction or facial reanimation. The dual or twin innervation (medial and lateral pectoral nerves [MPN and LPN]) and vascular supply (subclavian and axillary arteries) of this muscle make it technically superior to other donor units like gracilis, latissimus dorsi, and extensor digitorum brevis. The presence of variable origin of both pectoral nerve (PN) and vessels of PMi are major difficulty and force the surgeon to explore the operative site extensively. The extensive exploration during surgery may increase operative time and postoperative complications such as hemorrhage and infection. Hence,the insight regarding origin and distribution of PN and vessels are also desirable along with the aforementioned variation based on attachments.
PMi, a muscle of scapular suspension, acts to control the position of the coracoid as trapezius acts on the scapula. This thin wedge-shaped muscular sheet lying posterior to PMi has frequent variation both in its origin and insertion (proximal and distal attachment). This muscle is very often partially or wholly absent in Poland's syndrome. Generally, PMi originates from 3rd to 5th ribs lateral to costal cartilage and the intervening fascia covering the intercostal muscles. The muscle has another attachment (insertion) at the upper surface of the coracoid process in the scapula directly or with a short thick tendon. It assists in the protraction of the scapula. The inconsistency of its attachment at the proximal and distal site is a crucial drawback as a free nerve-muscle vascularized flap. There are many variants of attachment in reported literature that make techniques of harvesting of graft difficult and sometimes lead to thoracic outlet syndrome-like symptoms (called PMi syndrome).
The current systematic review is conducted to elucidate the variants of PMi according to different attachment (origin & insertion), innervation (origin and distribution), and vascularity pattern (origin and distribution). The data from various cadaveric studies are pooled to know the distribution and array of variants based on gender and ethnicity.
| Materials and Methods|| |
The studies were observational studies which included cross-sectional and cohort studies. Both the prospective or retrospective studies were allowed. All observational studies dealing with the cadaveric examination of the pectoral region were appraised. The studies reporting the prevalence of variants of origin or insertion of PMi were selected for review. Case reports and case series without sample size or nonhuman samples were excluded from the analysis.
The following medical subheading terms were chosen as keywords for search strategy- PMi, lesser pectoralis, origin, insertion, proximal attachment, distal attachment, nerve supply, motor supply, innervation, blood supply, vascular supply, arterial supply. Boolean operators such as AND, OR, and NOT were used to form search parentheses. An exhaustive search was conducted to hunt the published manuscript in online databases such as Medline, PubMed, Embase, and Google Scholar.
These search strategies were used from January 10: 2020 to July 20: 2020. One hundred fourteen hits were collected. Each published manuscript was evaluated for the prevalence of variants of PMi. Additional searches in other databases did not include any new literature.
Data extraction and assessment of the risk of bias
The primary data were extracted from the published manuscript by two authors. The recorded contents were age, gender, number of participants, and number of events of variant PMi. The measured outcomes were analyzed after the assessment of the risk of bias (ROB) by utilizing the Anatomical Quality Assurance tool. The ROB was measured in all five domains. Each study was categorized based on the ROB: low, moderate and high. The primary outcome was events of the variant of PMi based on origin, insertion, innervation, and vascular supply in different populations. The secondary outcomes were: The estimation of costal distribution, extent, sex distribution, and laterality distribution.
The pectoral or shoulder region of one half of the body was taken as the unit of analysis. Hence, both sides of any cadaver were counted as two. The dichotomous data of events and sample size were used to compute the event rate along with the log event rate. The standard error was calculated from effect size and sample size. The confidence interval (CI) (95%) of the log event rate was figured. The 95% CIs were combined to get the final effect size with the help of Microsoft excel 2019. Both fixed and random effect models were used to analyze the data. The outcome of the random-effects model was noted due to the high heterogeneity. The level of heterogeneity was estimated as I-squared statistic (I2) and Cochrane's Q.
| Results|| |
The literature search yielded 114 articles [Figure 1]. After removing four duplicate, the rest 110 studies were surveyed based on abstract and title. The full texts of sixty-eight articles were assessed after finding them eligible on the basis of screening of abstract. Out of these, only thirty-two were eligible for systematic review and meta-analysis. There were seven studies which dealt with the origin,,,,,,, eighteen reported insertions,,,,,,,,,,,,,,,,,, seven studies reported nerve supply,,,,,,,, and two reported blood supply., The included studies with ROB (n = 32) are summarized in [Table 1]. The years of publication range from 1834 to 2019. The inter-rater agreement for risk bias was 69.2% (53–78%). No publication bias was observed, and no trimming of effect-size required for any of the outcomes of PMi.
Variants of costal attachments
A total of seven studies (n = 1787) reported variations in costal attachment.,,,,,, The results are summarized in [Table 2], [Table 3] and [Figure 2], [Figure 3]. Typical or normal origin of PMi marked as 3rd–5th ribs, which is a typical textbook presentation. The origin of PMi extends from the first to the seventh ribs. After combining the CI in the meta-analysis, the normal origin was found to be 33% (30–37; 95% CI), and similarly, the variant origin was observed in 67% (63–70; 95% CI) in 1787 pectoral specimens. Its origin is near the cartilages of the ribs and adjoining fascia investing the intercostalis muscles. The normal origin was observed in only 33% of subjects, but the most common variants 2nd–5th ribs observed as 36%, which was higher than expected [Figure 2]. 3rd and 4th ribs got 98 to 100% attachment, but the 2nd and 5th have lower frequencies of 61.5% and 73.3%, respectively [Table 2]. Several narratives in addition to the classifications of the PMi present in the text today, showing frequent muscular variations. Frequent variations at the origin are variations in the arrangement of origin, slip attachments at different ribs near costal cartilage. PMi muscle located deep to PMJ and enclosed in the clavi-pectoral fascia. Loth recommended denoting the extent of origin of PMi by Roman numeral for proximal slip and Arabic numeral for the caudal slip, for example, for denoting the attachment of the 3rd slip of PMi to the fifth rib, III-5 is used. Here in the current meta-analysis, Arabic numeral was used for both. The proximal slip of origin of PMi and the distal slip of origin from any rib was mentioned in Arabic numeral.
|Figure 3: Forest plots: showing prevalence and distribution of variants of costal attachment of pectoralis minor in cadaveric studies (n = 1787). (a) Prevalence of normal origin of pectoralis minor (3rd-5th ribs). (b) Prevalence of variants of origin, (c) Distribution of the extent of origin, (d) Distribution of pectoralis minor origin slip from each rib|
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The variants of insertion
A total of 18 studies (n = 2424) reported variations of insertion.,,,,,,,,,,,,,,,,,,, The results are summarized in [Table 3] and [Figure 4]a. The usual insertion of PMi at the base (superomedial border) of the coracoid process was 79% (95% CI, 72–85%). The variant insertion of PMi was observed in 21% (15–28; 95% CI) with moderate to high heterogeneity [Table 4]. The heterogeneity statistics (I2) was 89% due to population difference. In subgroup analysis, minimum heterogeneities were found for similar ethnic and geographical populations. Three hundred-nine anomalous insertions of PMi were described in literatures. The coracohumeral ligament (CHL) and coracoglenoid ligament (CGL) was most common variant i.e., 68% (65–71; 95% CI) [Figure 4]b. In another variant, the tendon of PMi coursed to reach rotator interval between CHL and CGL and inserted at the glenohumeral capsule in 16% (13–19; 95% CI) [Table 3]. The capsular attachment of PMi tendon might reach up to the posterior capsule after crossing the CGL beyond the insertion of teres minor and sometimes, to the anterior capsule distal to subscapularis insertion [Figure 4]. A single incidence of insertion at infraglenoid tubercle of the scapula was reported in the literature. The Rare insertions were reported at the clavicle or the origin of the Biceps and Coracobrachialis.
|Table 4: Variations in costal attachment of pectoralis minor from different studies among different populations|
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|Figure 4: Forest plots: showing the prevalence and distribution of variants of insertion of pectoralis minor in cadaveric studies (n = 2424). (a) Prevalence of variants of insertion, (b) Distribution of variants of insertion. CHL: Coraco-humeral ligament, CGL: Coraco-glenoid ligament, RI: rotator interval, GT: Greater tuberosity, CCL: Coraco-clavicular ligament, CAL: Acromio-clavicular ligament. SB: short head of biceps, CB: coracobrachialis|
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The variants of innervation
A total of seven studies reported (n = 882) the innervation of PMi and its variable origin from different part of the brachial plexus.,,,,,, PMi is supplied by both Peripheral Nervous System (PNs) (lateral and medial). The result is summarized in [Table 5] and [Figure 5]a. Lateral pectoral (LPN) and MPN were branches from corresponding cords. However, many variants were found which were either branch of formative division or corresponding cords. The LPN was traced from brachial plexus to PMi and LPN in the form of straight rootlets of divisions of upper two trunks supplied the PMi in 55% (43–66; 95% CI). The PMi was innervated by branch (LPN) of lateral cord in 23% (1–45; 95% CI) and branch along with rootlets in 12% (1–25; 95% CI) [Table 5].
|Figure 5: Forest plots: showing the distribution of innervation and vascularity of pectoralis minor. (a) Innervation (origin and distribution of LPN and MPN), LPN: Lateral pectoral nerve, MPN: Medial pectoral nerve, AD: Anterior division. (b) Vascularity (origin and distribution)|
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The MPN branched from various components of brachial plexus on examination of 882 shoulders, and sometimes it was absent in 7% (4–10; 95% CI) [Table 5] and [Figure 5]a. The innervation of PMi derived from the medial cord as MPN with the typical textbook presentation was observed in 38% (5–72; 95% CI). In 7% (4–10; 95% CI) of specimens, MPN were absent and PMi only innervated by LPN via the pectoral loop. MPN innervating PMi were traced up to its origin. The MPN was branch of medial cord in 38% (5–72; 95% CI) and the same was branch of ventral division of lower trunk in 35% (32–38; 95% CI) or lower trunk in 1.85% (7–11; 95% CI) or middle trunk in 1% (0–2, 95% CI) or rootlets of the lower and middle trunk in 0.78% (0.1–1.66; 95% CI) [Figure 5]a. Ansa pectoralis was derived from LPN, or its deep branch contributed to MPN in the innervation of PMi. Ansa pectoralis joined with MPN to innervate in 77% (60–94; 95% CI) on examination of 430 specimens. Intercosto-brachial and sometimes 3rd or 4th intercostal nerve was communicated to MPN to innervate PMi.
Variants of blood supply
The vascularity of PMi was reported in two studies having sample size (n = 180)., The PMi was vascularized by single dominant artery in 77% (68–85; 95% CI), two arteries in 19% (13–29; 95% CI), three arteries in 2% (2–8; 95% CI), and four arteries in 1% (0–7; 95% CI). The single dominant artery was a direct branch from axillary artery (AA) in 65%, thoracoacromial artery (TAA) in 29% and lateral thoracic artery (LTA) in 6% [Figure 5]b and [Figure 6]. The axillary vein (AV) drained the blood from PMi, and the number of veins varied from 1 to 3. The drainage in single AV was observed in 48% (29–68; 95% CI) or in duplicated AV 43% (23–63; 95% CI) or in AV along with lateral thoracic vein in 9% (5–23; 95% CI) [Figure 5]b and [Figure 6].
|Figure 6: Arterial supply and its distribution of pectoralis minor. AA: Axillary Artery, AV: Axillary Vein, Ta/TAA: Thoraco-acromial artery, Tl/ LTA: Lateral Thoracic Artery, Ts/STA: Superior Thoracic Artery, Pab/PAB: Abdominal Part Artery, Cb/Pc: Artery to coracobrachialis or coracoid process. AAMPN: Artery along MPN, SSA: Subscapular Artery, SCA: Circumflex scapular Artery, TDA: Thoraco-dorsal Artery|
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| Discussion|| |
The PMi has a significant attraction in reconstructive surgery especially for the treatment of facial paralysis or maxillo-facial trauma. The surgical or anatomical texts and reports, do not furnish the necessary anatomical data of PMi in the pectoral and shoulder region., Thorough knowledge of the characteristics of PMi is a necessity because of the variable spatial orientation conceived by particular muscle variants. Purposely, neither the variable assembly of PMi at costal origins nor the frequency of conjoined origin has been examined. A broad review of cadaveric data has offered the succeeding morphological narratives of this musculature.
The present review showed that 3rd and 4th ribs are almost constant origin in all specimens, which ranges from 99% to 100%. Current analysis found a presence of 5th and 2nd costal attachment in 73.3% and 61.5%, respectively. Loth showed the span of PMi origin in 200 cadavers which extended from 1st to 6th ribs. Loth stated that PMi never originated from 7th rib and 4th rib always had a slip of origin. Testut (1884) narrated an illustration in which PMi was diminished to a single slip originating from the 4th rib. Wagenseil also reported a similar origin in dissected Chinese male new-borns. In the present review, various patterns of origin are documented in [Table 1] and [Table 2]. Sieb had documented the caudal shift of origin of PMi in American–African than the American-white, which was statistically significant. The author noticed the broader PMi in American–African than in the American-white in addition to narrower at its origin in the females. The author observed a minor cranial shift of origin in the Caucasian females. Potau documented that human PMi had a similar pattern of origin like chimpanzee, baboons, but Pan had 1st to 4th costal origin. Loth gave general remarks that the various primates like the chimpanzee, orangutan or gorilla showed a more reduced costal origin of PMi than in the human. However, the monkeys had broader costal origin than humans. The caudal broadening of the costal origin extends up to the 8th rib in prosimians except in the catarrhines and anthropoids (usually extending to the 7th rib).
Usually, the PMi has insertion at the superomedial boundary of the coracoid process, spreading out from the tip till its junction of horizontal and vertical portions. Adjacent to the tip, the fibers may be fused with the fibres of coracobrachialis. The point of insertion is occasionally raised as a bony ridge. In most instances, the coracoclavicular ligament (Conoid part) partially encloses the insertion of PMi and separated by a pad of fat with bursa. Sometimes, the tendinous insertion of the superficial lamina and cranial fibres of PMi continued beyond the upper surface of the coracoid process to achieve insertion somewhere else. Still, at the same time, the deeper part of PMi has its regular insertion. Such partition of the lamina may be fairly extensive and in sporadic cases distinguishable to the origin. The whole tendon of the PMi spanned the coracoid process, but 6.7% (3–14; 95% CI) of those illustrations showed the variant attachment. Some of the tendinous or muscular slip of PMi crossed the coracoid process and located in a shallow osteofibrous canal formed by the costocoracoid ligament and the fascia wrapping the coracoacromial ligament. The tendinous or muscular insertion was tracked to its termination at the coracoacromial ligament, or the tendon gained attachment into glenohumeral capsule between the CHL and rotator cable. Most often the insertions were located in the rotator interval, and tendon fibres merged with supraspinatus tendon or lamina of the glenohumeral capsule. The fibres of the inserting tendon may join with the rotator cable, which has clinical importance. In sports persons having such anomalous insertions might lead to rotator cuff tear or tendinopathy. The next frequent insertion is the coraco-glenoid ligament in which the tendon gains attachment in the articular capsule at the supraglenoid tubercle or even at the neck of the scapula. Third, in frequency was a combination of both above mentioned, i.e., the abnormal tendon had two attachments: one into the CHL in addition to supraspinatus tendon, articular capsule, greater tubercle and another attachment at the CGL. We again did not find any significant difference in the existence of the abnormal insertion relating to laterality or gender. According to Macalister's manuscript, Gantzer was the first to record the insertion at the joint capsule of the shoulder joint after crossing the coracoacromial ligament.
The conventional anatomical text of the innervation of the PMi includes LPN and MPN which are branches of lateral and medial cords of the brachial plexus, respectively. The distributed nerve roots are C5 to T1. The PMi has been assumed to have innervation from C5 to T1 spinal segments. The LPN and MPN are predominantly motor nerves, although they have few sensory fibres. PN is a direct branch of lateral cord or derived from divisions of the upper two trunks. Subsequently, it traverses the axillary vessels anteriorly and penetrates the clavipectoral fascia. LPN has invariably straight route together with the pectoral branches of the TAA on the underneath of the PMJ muscle, running medial to the PMi before piercing the PMJ. Damage of LPN is common in mastectomy and shoulder dislocations, which leads to paralysis of muscles if denervation point is involved. LPN is the branch of the lateral cord, but it has many variations. It is formed by the union of rootlets coming from the ventral division of the upper and middle trunk. The rootlets sometimes have different names like superior or inferior PN depending upon origin from the upper two trunks of the brachial plexus. LPN carries the fibers of C5–C7 to innervate both the pectoral muscles and cutaneous distribution below the clavicle. This nerve is connected with MPN by a loop of fibres around TAA, called ansa pectoralis (pectoral loop), which is present in 77%. In another study, the pectoral loop or ansa pectoralis was present in 99% of specimens. This nerve forms loop around either TAA or LTA. David et al. examined the nerve supply to the PMi and the origin of those nerves in 29 cadavers. This recent cadaveric dissection study showed that three PN were identified as superior, middle and inferior PN. The superior PN was the twig from the upper trunk close to the origin of the suprascapular nerve. This nerve pierced the clavipectoral fascia and supplied PMJ. Similarly, the middle PN was a twig of the middle trunk, which bifurcated into superficial and deep branches. The superficial branch was distributed in PMJ but, the deep branch along with inferior PN (a twig from the lower trunk) formed a submuscular plexus within the sheath of PMi to supply the same.
MPN is the branch of the medial cord of the brachial plexus which carries C8 and T1 nerve roots and passes behind the AA beneath the PMi after origin. The origin point of LTA is utilized as a useful landmark for MPN identification during surgery. The MPN travelled as a single trunk close to the inferior margin of the PMi in 38% (29–48; 95% CI) of cases, then it broke into two branches of which one passed through the muscle, and the other branch descended laterally to it in 32% (24–42; 95% CI). It pierced the muscle as a single trunk in 22% (15–31; 95% CI) or as two or three branches in 8% (4–15; 95% CI). The entry point of MPN in the PMi located at 3rd intercostal space close to the midclavicular line, at a mean distance of 103±19 mm from the sternal border in 50 to 100%., Both exit and entry points were present on the ventral and dorsal surfaces, respectively. The entry point of nerve in PMi was located 19.1 ± 6.8 and 33.5 ± 14 mm from superior and inferior borders of this muscle, respectively. Similarly, the exit point of the nerve from PMi was situated at 23.2 ± 9 and 34.5 ± 7.3 mm from the superior and inferior borders of this muscle, respectively. The exit point of MPN from PMi was located at 82.7 ± 7 mm from the costal origin on the fourth rib. It had been observed that when the PMi had a breadth of <60 mm, the MPN pierced the PMi as a lone trunk and then exited as a single or double stem on the ventral aspect. When the PMi muscle had a breadth of more than 60 mm, the MPN divided into two or four twigs before entering the muscle bulk, and then some branches pierced the muscle bulk, and one of them came out at the inferior border of the muscle. Porzionato et al. documented a through communication between MPN and the intercostobrachial nerve via lateral cutaneous branch. Another connection had been discovered between medial cutaneous nerves of the arm or forearm and MPN., Sometimes both PN has communications with lateral or anterior cutaneous branches of the intercostal nerves. The intercostobrachial nerve had been reported sometimes to have motor fibres which distributed via both PNs., This nerve got attention from surgeons for preservation during axillary lymph node dissection. Aiyama renamed this continuation as inferior PN and found it in 5% (2–11; 95% CI) of cases which innervated the PMi. Sometimes, an additional medial pectoral branch was arising from the intercostobrachial nerve, which joined with MPN to supply both pectoral muscles (PMJ and PMi muscles). An anastomosis had also been noticed between the LPN and nerve to subclavius. Injury of the MPN is quite frequent during axillary dissection in Patey's and Madden's mastectomies. MPN is closely related to the central and anterior groups of axillary lymph nodes whereas the LPN with the apical group of axillary lymph nodes. The postoperative complication of modified radical mastectomy led to varying degrees of atrophy of the PMi. Preservation of the PMi muscle and MPN encouraged to prevent muscular atrophy and limitations of shoulder movements. Loukas et al. noticed PMJ atrophy in 6% (3–13; 95% CI) when the MPN and PMi were preserved and 54% (44–63; 95% CI) when both were injured.
The AA is divided into three parts by PMi, and its branches are classified as superficial and deep branches. Superficial arteries supplied the pectoral girdle musculature, i.e., TAA, subscapular, circumflex humeral arteries and artery accompanying the MPN (AAMPN). The short TAA trunk located just deep to the inferior border of the PMi. AAMPN travelled forward between the two roots of the LPN. While entering into the clavipectoral fascia, TAA gave off a branch which supplied medial most of PMi muscle. It entered at the level of the upper third of PMi and divided into two branches which supplied the dorsal surface of PMi. The main trunk of TAA turned across the PMi muscle and continues laterally. In 58% AAMPN separately or along with LTA supplied PMi. AAMPN divided into the lateral branch and medial at a variable distance from its origin. Both branches travelled superficial to the AV and almost parallel to LTA. The lateral branch of AAMPN ran along with the distal branch of the MPN supplied the inferior border of the PMi. The medial branch supplied the lateral parts of PMi near the coracoid process. Major arteries originated in the axillary region were more or less constant and located at four distinct places: TAA appeared under the medial margin of the PMi muscle in 55% (45–64; 95% CI) followed S-shaped course to reach the medial border of the PMi muscle. The AAMPN originated in a majority of cases 58% (48–67; 95% CI) from the 2nd part of AA, 34% (25–44; 95% CI) as an initial branch of the TAA and 8% (4–15; 95% CI) as an initial branch of the LTA, respectively. Sato examined the course of the abdominal part artery, which was a smaller branch of the 2nd part of AA supplying the inferior border of PMi in 42% (33–52; 95% CI) of cases. It ran along with inferior PN if present and also called a inferior pectoral artery. Moriya et al. noticed few direct branches of the 2nd part of AA similar to a coracoid artery or coracobrachialis arteries which were distributed to PMi near insertion [Figure 6]. STA had no contribution in vascularity of PMi in 36% (27–46; 95% CI) and if it distributed, then covered only 11% (6–19; 95% CI) surface area., TAA gave branches to PMi in 72% (62–80; 95% CI) of the cases and supplied 30% (22–40; 95% CI) of surface area of PMi. Most of the authors reported the presence of these arteries, range varying from 68.5 to 94%. Sometimes this vessel had a common origin with LTA and supplied double area of PMi, i.e., 74%. The occasional arterial supply was derived from an artery for Coracobrachialis and coracoid process, which contributed to 6.8% and 9.5% area of distributions.
The reviewed literatures did not document the height, weight and occupation of cadavers. These confounding factors are hardly going to affect the prevalence of variants. The damaged specimens or prior surgical intervention (when the person was alive) might cause errors in identification and reporting.
| Conclusion|| |
PMi has a constant costal attachment to the 3rd and 4th ribs. Origin of PMi from 5th rib is reported with a pooled prevalence of 73.3% (95% CI 69–77%) and from 2nd rib is reported in 61.5% (95% CI 56–67%). PMi inserts to the superomedial boundary of the coracoid process in 79% (95% CI 72–85%) and beyond the coracoid process 21% (95% CI 15–28%). In addition, its anomalous insertion to coraco-glenoid ligament and CHL 68% (95% CI 65-71%) and rotator interval 16% (95% CI 13–19%). Innervation of PMi with both MPN and LPN is reported in 93% (95% CI 90–96%) and only LPN in 7% (95% CI 4–10%). Thoraco-acromial artery followed by LTA is the dominant vascular supply to PMi. These significant findings will provide insight into both anatomists and surgeons.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]