Ultrasonographic assessment of the lateral pterygoid muscle for BoNT-A injection.

The upper head of the lateral pterygoid muscle (LPM) is known to insert into the capsule of the temporomandibular joint and articular disc, and therefore its relationship with temporomandibular disorders (TMD) has been consistently suggested. The aim of the study was to determine the anatomical features of the LPM using ultrasonographic (US) imaging. Around 120 hemifaces from 60 healthy Korean volunteers were included in this study. US images were taken with the subject's mouth 2 cm open. The transducer was placed at a position where the infratemporal fossa could be observed through the mandibular notch, and its position was recorded. The locations of the coronoid process (CorP), lateral margin of the condylar process (ConP), and midpoint of CorP and ConP (MP) were measured with reference to the ala-tragus line. The thicknesses of the skin and subcutaneous tissue, the masseter muscle, the temporalis muscle, and the depth of the LPM were measured at the MP. The masseter muscle, temporalis muscle, and LPM were observed in all cases and located in order from superficial to deep. The MP was located 39.6 ± 3.3 mm anterior and 7.8 ± 1.6 mm inferior to the tragus. The thicknesses of the skin and subcutaneous tissue, the masseter muscle, the temporalis muscle, and the depth of the LPM at the MP were 9.7 ± 1.0, 10.3 ± 1.3, 10.9 ± 1.6, and 30.9 ± 1.9 mm, respectively. The information reported in this study may be useful for determining the location of the LPM and adjacent anatomical structures in TMD patients and provide accurate and safe injection guidelines.

Anatomical consideration of ultrasonography-guided intraoral injection for temporal tendinitis.

Temporal tendinitis is characterized by acute inflammation often resulting from mechanical stress, such as repetitive jaw movements associated with jaw opening and closing and teeth clenching. Treatment for temporal tendinitis typically involves the administration of local anesthetic or corticosteroid injections. However, the complex anatomical structure of the coronoid process, to which the temporalis tendon attaches, located deep within the zygomatic arch, poses challenges for accurate injections. In this study, we aimed to establish guidelines for the safe and effective treatment of temporal tendinitis by using intraoral ultrasonography (US) to identify the anatomical structures surrounding the temporalis tendon and coronoid process. US was performed using an intraoral transducer on 58 volunteers without temporomandibular joint disease. The procedure involved placing the transducer below the occlusal plane of the maxillary second molar. Measurements were taken for the horizontal distance from the anterior border of the coronoid process, observed at the midpoint (MP) of the US images, and the depth of the coronoid process and temporalis muscle from the oral mucosa. The anterior border of the coronoid process was visualized on all US images and classified into three observed patterns at the MP: type A (anterior to the MP, 56.2%), type B (at the MP, 16.1%), and type C (posterior to the MP, 27.7%). The temporalis muscle was located at a mean depth of 3.12 ± 0.68 mm from the oral mucosa. The maxillary second molar is an intraoral landmark for visualizing the anterior border of the coronoid process. The new location information obtained using intraoral US could help identify the safest and most effective injection sites for the treatment of temporal tendinitis.

A novel description of the supporting system of the orbicularis oculi muscle in the infraorbital area: Tear trough muscle fiber.

BACKGROUND: The aim of this study was to elucidate the anatomical structures of supporting system of the infraorbital area. MATERIALS AND METHODS: Forty-four hemifaces from eleven Korean and eleven Thai cadavers were used to dissect the infraorbital area. Based on the dissection and previous histologic results, they were analyzed. RESULTS: The orbicularis oculi muscle (OOc) had two portions (palpebral and orbital portion) and four subparts (pretarsal, preseptal, prezygomatic, and premaxillary part). The elliptical muscle fiber of OOc was supported by circumferential connective tissue including skin ligament, orbicularis retaining ligament, zygomatic ligament, and zygomatic cutaneous ligament. The vertical muscle fiber, the tear trough muscle fiber, and medial muscular band directly attached to the skin. CONCLUSION: Full of subcutaneous tissue in the tear trough groove, strong attachment to the bone by tear trough ligament and to the skin by tear trough muscle fiber would multiply result in the tear trough on the face.

Anatomical Considerations for the Injection of Botulinum Neurotoxin in Shoulder and Arm Contouring.

The utilization of botulinum neurotoxin in the field of body contouring is on the rise. Body contouring procedures typically focus on specific muscle groups such as the superior trapezius, deltoid, and lateral head of the triceps brachii. The authors propose identifying optimal injection sites for botulinum neurotoxin to achieve desired aesthetic contouring of the shoulders and arms. The authors conducted a modified Sihler's staining method on specimens of the superior trapezius, deltoid, and lateral head of the triceps brachii muscles, totaling 16, 14, and 16 specimens, respectively. The neural distribution exhibited the most extensive branching patterns within the horizontal section (between 1/5 and 2/5) and the vertical section (between 2/4 and 4/4) of the superior trapezius muscle. In the deltoid muscle, the areas between the anterior and posterior deltoid bellies, specifically within the range of the horizontal 1/3 to 2/3 lines, showed significant intramuscular arborization. Furthermore, the middle deltoid muscle displayed arborization patterns between 2/3 and the axillary line. Regarding the triceps brachii muscle, the lateral heads demonstrated arborization between 4/10 and 7/10. The authors recommend targeting these regions, where maximum arborization occurs, as the optimal and safest points for injecting botulinum toxin.

Does the fixture thread depth affect the accuracy of implant placement during fully guided immediate implant placement?: A human cadaver study.

BACKGROUND: The fixture thread depth reportedly influences the primary stability of dental implant, but its effect on the positional accuracy in immediate implant placement has not been reported previously. MATERIALS AND METHODS: Fifty-six single-rooted, anterior and premolar teeth were extracted from six human cadavers, followed by installing either regular-threaded implants (RT group, N = 30) or deep-threaded implants (DT group, N = 26) completely relying on the surgical guide. Optical impressions taken after osteotomy and fixture installation were superimposed with the preoperative virtual planning data to measure the vertical, angular, platform and apex deviations that occurred during osteotomy and installation. RESULTS: While the osteotomy deviations were similar between the two groups, the angular and apex deviation of the DT group (2.67 ± 2.56°; 1.04 ± 0.49 mm, respectively) were significantly larger than those of the RT group (1.61 ± 1.04°; 0.67 ± 0.41 mm, respectively) during installation (p < .05). When the installation deviations were analysed in the anterior and premolar areas separately, the angular, platform and apex deviations of the DT group (3.05 ± 3.26°; 0.75 ± 0.32 mm; 1.08 ± 0.56 mm, respectively) were significantly larger than those of the RT group (1.56 ± 0.73°, 0.59 ± 0.28 mm; 0.62 ± 0.38 mm, respectively) in the anterior site (p < .05), whereas there was no significant intergroup difference in the premolar site. CONCLUSION: In immediate-implant surgery, using an implant with a deeper thread might increase the deviations during installation, especially in the anterior area.

Changes in masticatory performance during the retention period following 4-premolar extraction and non-extraction orthodontic treatment.

OBJECTIVES: To evaluate changes in masticatory performance (MP) during the retention period after extraction and non-extraction treatment and compare it with MP in individuals with normal occlusion. MATERIALS AND METHODS: Adult patients who had completed orthodontic fixed appliance treatment comprised the extraction and non-extraction treatment groups, and those with normal occlusion comprised the control group. Their mixing ability (MA), maximum bite force (MBF), and occlusal contact area (OCA) were recorded immediately after the fixed appliance was removed and at 1 month, 6 months, and 1 year post-treatment. The MA was measured via the two-color chewing gum MA test using ViewGum software, and the MBF and OCA were measured using Dental Prescale II system. RESULTS: MA immediately after orthodontic treatment was lower than that in the normal group but showed a time-dependent gradual increase during a 1-year retention period (P < 0.01). The MA at 1 month post-treatment was not significantly different between the three groups (P > 0.05). The MA revealed a significant correlation with the MBF and OCA (P < 0.01). CONCLUSIONS: The MP immediately after orthodontic treatment was lower than that in the normal group but increased gradually, with levels comparable to those of the normal occlusion group at 1 month post-treatment. Further, extraction did not affect the recovery of the MP after orthodontic treatment. CLINICAL RELEVANCE: No other study has evaluated the changes in MP during the retention period after orthodontic treatment. The findings show that compared with MBF and OCA, the patients' MP improved faster to levels found in normal occlusion.

The Deep Temporal Arteries: Anatomical Study with Application to Augmentations Procedures of the Temple.

The aim of this study was to determine the anatomical features of the deep temporal arteries (DTAs) and thereby provide clinical information for the temple augmentation procedure. Forty-two adult hemifaces from 15 Korean and 6 Thai cadavers (12 males, 9 females; mean age at death, 79.6 years) with no history of trauma or surgical procedure on the temple area were used for anatomical study. A detailed dissection was performed to identify the locations of the anterior and posterior deep temporal arteries (ADTA and PDTA) with reference to the vertical plane passing through the zygomatic tubercle. Fifty-eight healthy Korean participants (31 males and 27 females; mean age, 24.7 years) were included in the ultrasonographic study. The distance from the bone to the DTAs was measured at the level of the zygomatic tubercle (HZt ) and the eyebrow (HEb ). The DTAs were not found within 7.2-12.6 mm posterior to the zygomatic tubercle; instead, the locations varied widely at the HEb . The distances between the bone and the ADTA were 1.7 ± 1.2 mm (mean ± SD) and 1.3 ± 0.8 mm, and those between the bone and the PDTA were 2.1 ± 1.2 mm and 2.0 ± 1.4 mm at HZt and HEb , respectively. Our findings indicate that at HZt , the area 1 cm posterior to the zygomatic tubercle may be a safe area for deep temple augmentation procedures. However, because the distribution patterns of the DTAs at HEb and depth of the DTAs are variable, additional care is required to minimize the risks of the procedure.

Face painting as an anatomical learning tool based on individual ultrasonographic examination.

Considering the shift to online education during the COVID-19 pandemic, new and easily accessible educational videos and content on clinical anatomy are necessary. This study utilized numerous references and data on the anatomy of Asian facial muscles and blood vessels to accurately depict human anatomy through face painting. It aimed to provide clinicians accurate educational video content on anatomy to help prevent possible complications during noninvasive facial and surgical procedures. A 26-year-old Korean-Chinese male volunteer was used as a face painting model. The location of the blood vessels of the face was confirmed through ultrasonography images using a real-time two-dimensional B-mode. The model's face was painted by an artist majoring in anatomy. To reveal most anatomical structures on both sides of the face, the left side showed the structures observed when the skin and superficial fat layer are removed, and the right side revealed the deeper layer structures that can be seen when some muscles are cut. Fifteen superficial and deep muscles important in esthetic procedures were meticulously painted on the face. The face painting took a total of 6 h, and the video was edited to 5 min. This study merged the advantages of 2D and 3D by painting directly on the skin surface of a living model. Thus, it can provide more dynamic surface anatomy data. These contents inform clinicians about 3D anatomic location, which can help avoid complications when performing clinical procedures on the face.

Three-dimensional topography of facial soft tissues for the safer and effective threading procedures.

INTRODUCTION: To reduce complications caused by the procedure, the target layer for thread lifting should be the superficial fat or superficial musculoaponeurotic system of the face. The aim of this study was to establish the thicknesses of the facial skin and superficial fat using a 3D scanning system to provide basic clinical data for thread lifting. MATERIAL AND METHODS: Thirty fixed Korean and Thai cadavers (male: 17, female: 13) were used. The depths of the skin and superficial fat were measured using a three dimensional (3D) structured-light scanner. Facial images of both undissected and removed skin and superficial fat were taken with the 3D scanner. The paths from the temple and the front of the tragus to the infraorbital, perioral, cheek, and mental areas were displayed on the 3D image. The thickness along the path was measured by calculating the difference between the undissected and dissected 3D images. RESULTS: The means and standard deviations of thicknesses of the skin and superficial fat were 2.1 ± 0.4 mm and 5.2 ± 1.9 mm in the 11 pathways. The facial skin became thicker going toward the lower aspect of the face from temple to infraorbtial and perioral regions. The thickness of the superficial fat around the marionette line showed the biggest change. CONCLUSIONS: The present findings indicate that a 3D scanning system can yield crucial anatomical information about the thickness of the facial skin and superficial fat for use in various minimally invasive clinical procedures including thread lifting.

Clinical anatomy considerations on the muscular and vascular components of the midface by ultrasonographic imaging.

The first signs of face aging appear in the midface, so procedures such as botulinum toxin and filler injections are performed there. However, no guidelines based on clinical anatomy describing the muscular and vascular components in vivo have been published. The aim of this research was to describe the depths of the midface muscles and the locations of vessels using ultrasonographic (US) imaging. US was applied at 12 landmarks on the midface in 88 volunteers (49 males and 39 females; 19-36 years) to detect sex differences in the depths of muscles and the locations of the vessels. The depths of the orbicularis oculi (OOc), levator labii superioris alaeque nasi (LLSAN), and zygomaticus minor (Zmi) differed significantly with sex at P7 (p = 0.001) and P8 (p = 0.017), P1 (p = 0.028), and P4 (p = 0.035), respectively. The facial artery, facial vein, angular artery, angular vein, and perforator vessels were found at P9, P2 and P10, P1, P1 and P5, and P8, P11 and P12, respectively. The findings indicate that the depths of the OOc, LLSAN, and Zmi muscles differ between the sexes and that the vessels appear at specific landmarks. This information could help in developing anatomical guidelines for several procedures.

Ultrasonography Analysis of Vessels Around the Forehead Midline.

BACKGROUND: Filler injection into the glabella is well known to be a highly dangerous procedure due to the high risk of embolism and intravascular injection. Although it is conventional practice to insert the cannula into the middle of the forehead to perform injections into the glabella or radix, vascular structures can be observed in this region during anatomic dissection procedures. OBJECTIVES: The aim of this study was to characterize the blood vessels around the forehead midline in order to provide crucial anatomic information for ensuring the safety of noninvasive procedures involving the forehead and glabella. METHODS: Ultrasonography image scanning was performed at the following 4 points on the forehead midline: trichion (P1), metopion (P2), halfway point between metopion and glabella (P3), and glabella (P4). The courses and locations of vessels were identified and classified according to their proximity to the forehead midline. RESULTS: Vessels coursing within 0.75 cm either side of the forehead midline were found in 34% to 50% of individuals. Arteries running near the forehead midline tended to be dominant on the right side of the forehead except in the P4 area. About half of the individuals had vessels in the P4 area, of which 96.7% were veins. CONCLUSIONS: The present results indicate that there are superficial vessels running close to the midline of the forehead. This anatomic information can explain the higher incidence of vascular complications during conventional aesthetic procedures. To ensure safety, the cannula entry point or needle puncture point for glabella augmentation should be reconsidered.

Three-Dimensional Evaluation of the Depressor Anguli Oris and Depressor Labii Inferioris for Botulinum Toxin Injections.

BACKGROUND: Botulinum toxin type A (BoNT-A) injection administered at an inappropriate site or depth can produce an unwanted change in facial animation because the depressor anguli oris (DAO) and depressor labii inferioris (DLI) muscles are partially overlapped. Therefore, simple BoNT-A injection guidelines, based on 3-dimensional (3D) facial anatomic references and landmarks, would be very useful. OBJECTIVES: The aim of this study was to establish novel BoNT-A injection guidelines that include the soft tissue thickness at the lower perioral region. Data were acquired with a 3D scanning system combined with dissections in order to obtain accurate injection sites and depths for the DAO and DLI. METHODS: 3D scans of the facial skin, superficial fat, and facial muscle surface were performed in 45 embalmed cadavers. The thicknesses of the skin and subcutaneous layer were calculated automatically from superimposed images at each of 5 reference points (P) in the perioral region. RESULTS: In every case (100%), P3 and P5 were located in the DLI and DAO areas, respectively (45/45). Therefore, we defined P3 as the "DLI point" and P5 as the "DAO point." The soft tissue thicknesses at the DLI and DAO points were 6.4 [1.7] mm and 6.7 [1.8] mm, respectively. CONCLUSIONS: The P3 and P5 described in this study are effective guidelines that only target the DLI and DAO. Clinicians, specifically, can easily use facial landmarks, such as the cheilion and pupil, to assign the DLI and DAO points without any measurement or palpation of the modiolus.

Effective botulinum toxin injection guide for treatment of cervical dystonia.

The aim of this study was to elucidate the distribution of the accessory nerve within the sternocleidomastoid muscle (SCM) to aid identifying the optimum sites for botulinum neurotoxin (BoNT) injections and applying chemical neurolysis. Thirty SCM specimens from 15 Korean cadavers were used in this study. Sihler's staining was applied to 10 of the SCM specimens. Transverse lines were drawn in 20 sections to divide the SCM into 10 divisions vertically, and a vertical line was drawn into the medial and lateral halves from the mastoid process to the sternoclavicular joint. The most densely innervated areas were 5/10-6/10 and 6/10-7/10 along the lateral and medial parts of the muscle, respectively. We suggest injecting BoNT in the medial region 6/10-7/10 along the SCM prior to injecting in the lateral region 5/10-6/10 along the muscle to ensure safe and effective treatment. Clin. Anat. 33:192-198, 2020. © 2019 Wiley Periodicals, Inc.

A novel anatomical consideration on the exposed segment of the facial artery.

An understanding of the location and depth of the facial artery (FA) is essential in aesthetic surgery and various cosmetic procedures. The purpose of this study was to clarify the three-dimensional (3D) topography of the exposed segment (ES) of the FA and to provide information to help minimize complications during clinical procedures. From 50 embalmed adult cadavers, the undissected and dissected hemifaces were scanned and reconstructed using the 3D scanner. Then the topographic location of the ES was identified and measured from the superimposed the 3D images. The ES was observed in 82% of the whole specimens. The exposure patterns of the ES were examined, and classified into three types: Type I, one site exposed pattern (74%); Type II, two sites exposed pattern (8%); and Type III, nonexposed pattern (18%). The extent of the ES was located at 2.2 mm above and 4.2 mm below the cheilion (Ch)-otobasion inferius line, and 20.0 to 25.2 mm from the Ch on the lateral aspect. In the frontal view, the average distance from the mid-pupillary line to the ES was 7.1 mm, and from the lateral canthal line to the ES was 6.1 mm. The ES was 7.6 mm below the skin surface. The results of this study will help to provide safe guidelines for filler injections as well as selecting the safe regions in various clinical procedures. Clin. Anat. 33:257-264, 2020. © 2019 Wiley Periodicals, Inc.

Sonographic Analysis of the Upper Labial Orbicularis Oris and Its Clinical Implications.

BACKGROUND: Purse string lips, which include the vertical wrinkles over the lips, are frequently observed in aged individuals. Botulinum toxin and fillers are routinely injected into these areas to remove the wrinkles; however, the anatomy of the orbicularis oris muscle (OOr) near the vermilion border area has not been well defined. OBJECTIVES: The aim of this study was therefore to identify any morphological differences of the upper OOr via sonographic imaging. METHODS: The upper lip muscles as observed utilizing an ultrasound device were divided into 2 muscles (pars peripheralis and pars marginalis) that were subsequently divided into a further 2 types (Type I and Type II) associated with the development of the pars marginalis. Type II was further divided into Type IIa and Type IIb depending on whether the muscle fibers were well developed and connected. RESULTS: On the midline of the lip, Type I, in which the pars marginalis was rarely observed and only appeared in traces, was observed in 20.0% of the volunteers. Type IIa, in which the pars marginalis was well-developed and appeared continuous, was observed in 42.9% of the volunteers. Type IIb, in which the pars marginalis was observed but appeared discontinuous, was observed in 37.1% of the volunteers. CONCLUSIONS: The shapes of the upper pars marginalis of the OOr varied markedly between volunteers. Type classification of the OOr based on its shape and the lip appearance serves as a reliable source of reference information to be utilized when injecting botulinum toxin into the upper lip.

Synergistic effect of hyperbaric oxygen therapy with PTH [1-34] on calvarial bone graft in irradiated rat.

OBJECTIVE: To determine the synergistic effect of parathyroid hormone (PTH) [1-34] in combination with hyperbaric oxygen (HBO) on bone graft in a rat calvarial bone defect model under impaired osteogenic conditions. MATERIALS AND METHODS: Twenty-four rats were divided into three groups. Localized radiation with a single 12 Gy dose was administered to the calvaria. Four weeks after radiation, calvarial circular defects were created in the parietal bones. All defects were filled with biphasic calcium phosphate. After the bone graft, PTH [1-34] was injected subcutaneously, and HBO was administered. At 6 weeks after the bone graft, the rats were sacrificed, and specimens were harvested. RESULTS: Histomorphometric evaluation showed that the percentage of new bone area was higher in the PTH and PTH/HBO groups than in the control group. The percent residual material area was decreased in the PTH/HBO group compared with the control group. The percentage blood vessel number was highest in the PTH group. Micro-CT evaluation showed that the new bone volume was highest in the PTH/HBO group. The residual material volume was lowest in the PTH/HBO group. CONCLUSION: Within the limitations of this study, our data indicate that PTH combined with HBO may reverse radiation-induced impairment of bone healing.

Anatomy of the Superficial Venous Structures of the Neck: A Cadaveric Study to Guide Superficial Injections.

BACKGROUND: Minimally invasive aesthetic procedures of the neck are becoming more popular. However, anatomical studies on the venous structures of the neck in relation to these procedures are lacking. OBJECTIVE: The aims of this study were to identify the locations and communication patterns of the anterior jugular vein and external jugular vein (AJV and EJV) and the communicating vein (CV) based on superficial anatomical landmarks and to determine dangerous areas for dermal filler injections into the neck. MATERIALS AND METHODS: Thirty sides of the neck from Korean adult cadavers were dissected for this study. RESULTS: Four anatomical variants were identified. In Type Ia, the CV ran along the anterior border of the sternocleidomastoid muscle (SCM) (33.4%); in Type Ib, a single vein was observed connecting the CV and the EJV at the level of laryngeal prominence (23.3%); in Type Ic, the CV proceeded separately from the medial side of the anterior border of the SCM (13.3%); and in Type II, the CV was absent while the EJV and AJV were observed (30%). CONCLUSION: Given the 4 anatomical variants identified in this study, the authors recommend exerting caution when performing dermal filler injections approximately 10, 30, and 60 mm lateral to the midsagittal line to avoid iatrogenic side effects.

Ultrasonography of the internal architecture of the superficial part of the masseter muscle in vivo.

It is unclear whether the deep inferior tendon (DIT) is equally present in vivo, and little anatomical information is available regarding the existence and morphology of the DIT in healthy young subjects. The aim of this study was to characterize the DIT of the masseter muscle in healthy young subjects using ultrasonography and to compare the morphology of this tendon with previously reported data for healthy young subjects in order to provide the most-effective injection methods for botulinum neurotoxin treatments of masseteric hypertrophy. This study investigated two fresh cadavers and 30 healthy subjects. Ultrasonography scanning in both longitudinal and transverse directions was applied to the masseter muscle. The DIT within the superficial part of the masseter was observed in both the fresh cadavers and the living subjects. The posterior region of the masseter muscle was compartmentalized (entirely covered) by the DIT in 26.7% of the specimens. The superficial part of the masseter muscle was divided by the DIT transversely and longitudinally into the superficial and deep muscle bellies in 35% and 38.3% of the specimens, respectively. The present findings suggest applying a DIT-based injection technique under guidance by ultrasonography prior to treating masseteric hypertrophy. Clin. Anat. 32:446-452, 2019. © 2019 Wiley Periodicals, Inc.

The facial artery: A Comprehensive Anatomical Review.

The facial artery is the major vessel supplying blood to the face so its location and course are very important for the safe manipulation of both surgical and non-surgical interventions. This study documents current anatomical information about the facial artery and its tributaries. The terminology of the facial artery tributaries was revisited with reference to the Terminologica Anatomica and novel nomenclature was suggested with anatomical features. The tributaries to the lower lip (inferior labial artery), labiomental region (horizontal and vertical labiomental artery), upper lip (superior labial artery), nose (inferior and lateral alar artery and nasal septal artery), angular and ocular region (angular artery and detoured branch) and the course, layers and location of the facial artery main trunk were revisited with contemporary anatomical studies. The facial artery and its tributaries have close topographical connections to the facial expression muscles, nasolabial groove, and vermilion border, and these also distinguish facial landmarks comprising the cheilion, stomion, and gonion. Interestingly, in contrast to previous descriptions, some terminal branches did not take a straight course but a detoured course. The angular artery was connected to the ophthalmic artery branches and in some cases did not originate from the facial artery. Vascular complications of the facial artery tributaries are frequently seen in the angular, dorsum of the nose, tip of the nose, and glabellar region. This detailed review focusing on facial arterial topography in the various areas of the face would help to enhance quality of treatment. Clin. Anat. 31:99-108, 2018. © 2017 Wiley Periodicals, Inc.

Classification of unusual insertion of the pectoralis minor muscle.

PURPOSE: The pectoralis minor muscle (PMi) generally originates from the third, fourth, and fifth ribs and inserts on the medial and superior margins of the anterior portion of the coracoid process. Variations in the shape and attachment point of the PMi could cause discomfort in the shoulders. The aim of this study was to observe the types of morphological insertion patterns and attachment sites of the PMi. METHODS: Seventy-four sides of fresh, embalmed Korean (42 sides; mean age 78 years) and Thai (32 sides; mean age 78 years) cadavers were dissected to analyze the morphological insertion types and attachment sites of the PMi. RESULTS: Unusual insertion patterns were evident in about 23% of the samples. When the portion of the PMi tendon ran over the coracoid process, the most common attachment site was the glenohumeral joint capsule. We also confirmed the attachment of the PMi to the clavicle. Costal attachments of the PMi that extend from the second rib to the fourth rib were observed frequently as well. CONCLUSIONS: Unusual insertion patterns of the PMi are common. Some authors consider that tendon attachment to the joint capsule can cause shoulder pain. In addition, the PMi tendon could be utilized in acromioclavicular joint reconstruction. Surgeons need to be aware of the possibility of a PMi variant being found during surgery even when this is not visible in magnetic resonance or ultrasound imaging.