Visualization of intervertebral disc degeneration in a cadaveric human lumbar spine using microcomputed tomography.

Gross features of disc degeneration (DD) that are associated with back pain include tears in the anulus fibrosus, structural changes of the endplates, and a collapse of the anulus. The aim of this study is the detailed visualization and microstructural characterization of DD using microcomputed tomography (µCT) and a dedicated image post-processing pipeline. In detail, we investigate a cadaveric spine that shows both types of DD between L1 and L2 and between L2 and L3, respectively. The lumbar spine was obtained from a male donor aged 74 years. The complete specimen was scanned using µCT with an isometric voxel size of 93 µm. Subsequently, regions of interest (ROI) were prepared featuring each complete intervertebral disc including the adjacent endplates. ROIs were then additionally scanned with a voxel size of 35 µm and by means of magnetic resonance imaging. The collapsed endplate of the superior L2 showed explicit signs of an endplate-driven degeneration, including bony endplate failures. In contrast, the intervertebral disc between L2 and L3 showed indications of an annulus-driven DD including severe disc height loss and concentric tears. Using µCT we were able to visualize and quantify bone and cartilage features in DD. We showed that in both cases a suite of structural changes accompanies cartilage degeneration, including microstructural bony adaptions to counteract changes in the biomechanical loading regimen.

CADAVERIC EVALUATION OF THE LATERAL-ANTERIOR DRAWER TEST FOR EXAMINING POSTERIOR CRUCIATE LIGAMENT INTEGRITY.

BACKGROUND: Common clinical tests often fail to identify posterior cruciate ligament (PCL) ruptures, leading to undetected tears and potential degenerative changes in the knee. The lateral-anterior drawer (LAD) test has been proposed but not yet evaluated regarding its effectiveness for diagnosing PCL-ruptures. HYPOTHESIS: The LAD will show greater tibial translation values in lateral-anterior direction in a PCL-Cut condition compared to a PCL-Intact condition, thus serving as a useful test for clinical diagnosis of PCL integrity. STUDY DESIGN: Descriptive laboratory study. METHODS: Threaded markers were inserted into the distal femur and proximal tibia in eighteen cadaveric knees. Each femur was stabilized and the tibia translated in lateral-anterior direction for the LAD test versus in a straight posterior direction for the posterior sag sign (PSS). Each test was repeated three times with the PCL both intact and then cut, in that order. During each trial, digital images were captured at start and finish positions for the evaluation of tibial marker displacement. Tibial marker translation during each trial was digitally analyzed using photography. The PSS values served as a reference standard. RESULTS: The LAD tibial translation was significantly greater (U=-3.680; p<;0.002) during the PCL-Cut (10.6±5.6mm) versus PCL-Intact (7.7±5.1mm) conditions. The PSS tibial translation was significantly greater (U=-3.724; p<0.002) during the PCL-Cut (11.0±5.3mm) versus PCL-Intact (6.4±3.5mm) conditions. There was no significant difference (t=2.029; p=0.07) in mean tibial translation in respective directions after PCL dissection during the LAD test (2.9±2.1mm) versus the PSS (4.6±2.8mm). CONCLUSION: The LAD test detected changes in cadaveric tibial translation corresponding with changes in PCL integrity to a degree at least as effective for assessing PCL integrity as the PSS. Further clinical study will be required to assess the utility of the LAD as a physical examination tool for diagnosing PCL injuries. LEVEL OF EVIDENCE: 2 (laboratory study).

Computer-assisted 3-dimensional anthropometry of the scaphoid.

Scaphoid fracture fixation using a cannulated headless compression screw and the Matti-Russe procedure for the treatment of scaphoid nonunions are performed routinely. Surgeons performing these procedures need to be familiar with the anatomy of the scaphoid. A literature review reveals relatively few articles on this subject. The goal of this anatomical study was to measure the scaphoid using current technology and to discuss the findings with respect to the current, relevant literature.Computed tomography scans of 30 wrists were performed using a 64-slice SOMATOM Sensation CT system (resolution 0.6 mm) (Siemens Medical Solutions Inc, Malvern, Pennsylvania). Three-dimensional reconstructions from the raw data were generated by MIMICS software (Materialise, Leuven, Belgium). The scaphoid had a mean length of 26.0 mm (range, 22.3-30.7 mm), and men had a significantly longer (P<.001) scaphoid than women (27.861.6 mm vs 24.561.6 mm, respectively). The width and height were measured at 3 different levels for volume calculations, resulting in a mean volume of 3389.5 mm(3). Men had a significantly larger (P<.001) scaphoid volume than women (4057.86740.7 mm(3) vs 2846.56617.5 mm(3), respectively).We found considerable variation in the length and volume of the scaphoid in our cohort. We also demonstrated a clear correlation between scaphoid size and sex. Surgeons performing operative fixation of scaphoid fractures and corticocancellous bone grafting for nonunions need to be familiar with these anatomical variations.

The functional anatomy of the cricothyroid joint.

Postoperative long-term treatment problems of male-to-female transsexuals can be caused by the underestimated mobility of the cricothyroid joint. One hundred cadaveric larynges were analysed to reveal the morphological and functional anatomy of the CTJ focusing on possible horizontal and vertical gliding movements. Furthermore, the distance of the cricothyroid space for rotational movements was measured. The articular surface of the cricothyroid joint showed three different possibilities: a well-defined facet (Type 1 61%), no definable facet (Type 2 22%) or a flat surface with or without a tiny protuberance (Type 3 17%). Side different statements and intraindividual differences between male and female specimens were included. These different types affect horizontal and vertical gliding movements, besides rotational movements. The mobility between Type 1 and the others was highly significant (P < 0.001). Regarding different motions in the cricothyroid joint, rotational movements caused significant elongation of the vocal folds, which should be taken into consideration for phonosurgical methods.

The cricothyroid joint--functional aspects with regard to different types of its structure.

The cricothyroid joint (CTJ) plays a key role in pitch adjustment of the human voice. It allows an external elongation of the vocal fold performed by the cricothyroid muscle with a consecutive stretching and increasing of tension. Phonosurgical methods such as cricothyroid approximation need sophisticated investigations on anatomical and functional principles because of the low satisfaction rates. Fifty cadaveric specimens were analyzed to reveal the morphological and functional anatomy of the CTJ focusing on possible gliding movements in a horizontal and vertical direction. The cartilaginous surfaces of the CTJ were categorized according to Maue and Dickson into three different types (type A: well-defined facet; type B: no definable facet; type C: flat cartilage surface or protuberance) and functional correlations examined. Side different statements and intraindividual differences between male and female specimens were included. Besides from rotational movements, the CTJ allowed horizontal and vertical gliding movements depending on the different types of the cartilaginous surfaces. Especially the difference concerning mobility between type A and the others was highly significant (P<0.001). Two thirds of our specimens showed a similar type in both CTJs, whereas in one third it was asymmetric. In comparison to the possible change of distances between horizontal gliding movements and rotation, rotation caused significant elongation of the vocal folds, which should be proposed in phonosurgical methods for cricothyroid approximation.

The vascular anatomy of the tensor fasciae latae perforator flap.

BACKGROUND: The purpose of this study was to differentiate between musculocutaneous and septocutaneous perforators of the tensor fasciae latae perforator flap; to evaluate their number, size, and location; and to provide landmarks to facilitate flap dissection. An additional injection study estimated the skin area of the flap. METHODS: The anatomical study was performed on 23 fixed and injected cadavers. The perforators of the tensor fasciae latae were identified and classified as septocutaneous or musculocutaneous. Diameter, location, and numbers were measured and the perforators were dissected up to their origin. The injection study was performed on 10 fresh cadavers. On one side, the ascending branch of the lateral circumflex femoral artery was injected with methylene blue; on the other side, the septocutaneous perforators were injected selectively. The size, location, and borders of the stained skin were measured. RESULTS: Forty-five thighs were included in this study. All perforators emerged from the ascending branch of the lateral circumflex artery. The average number of musculocutaneous perforators was 2.3 (range, 0 to 5), the distance from the anterior superior iliac spine was 10.9 cm (range, 4.5 to 16.1 cm), and the diameter was 0.9 mm (range, 0.2 to 2 mm). Four specimens had no musculocutaneous perforator. The average number of septocutaneous perforators was 1.8 (range, 1 to 3), the distance from the anterior superior iliac spine was 10.9 cm (range, 6.2 to 15.7 cm), and the diameter was 1.5 mm (range, 0.5 to 3 mm). Seventy-six percent of the septocutaneous perforators emerged between 8 and 12 cm from the anterior superior iliac spine. The possible pedicle length of a flap based on these vessels is 8.1 cm (range, 6.5 to 10 cm). In the injection study, the average skin area stained with methylene blue was 19.4 x 13.4 cm (range, 10 to 24 cm x 7 to 17 cm) in the ascending branch group. In the perforator group, the average skin area was 19.2 x 13.7 cm (range, 15 to 22 cm x 12 to 16 cm). CONCLUSIONS: The authors could show that the number of septocutaneous perforators for the tensor fasciae latae flap is more constant and that their diameter is greater than that of musculocutaneous perforators. The location of these perforators on a line extending from the ilium to the greater trochanter facilitates planning and dissection of a flap.

Reliability of Tuffier's line evaluated on cadaver specimens.

The aim was to evaluate the reliability of Tuffier's line usually used as sole method to identify lumbar spinous process for a correct needle placement. Fifty-eight cadaver specimens were placed in a lateral position and a flexion in the lumbar spine performed to achieve a neutralization of the lumbar lordosis. The iliac crests were palpated and the lumbar spinous process marked on the intercristal line with a pin; all specimens were dissected and the marked spinous process documented. The center of the L4 spinous process was hit in 24 male (41.38%) and 10 female (17.24%) specimens. In only two female specimens (3.45%), the upper vertebra was reached; a pin placed in L3 was not found in male cadavers. The inferior edge of the L4 spinous process was hit in male 4 times (6.90%) and in female cadavers 12 times (20.69%). In the fifth lumbar spinous process, pins were placed five times in female cadavers (8.62%) and in only one male cadaveric specimen (3.72%). In conclusion, the accuracy of the focused lumbar spinous process depends on the right bedding and the orientation of the given landmarks, so Tuffier's line stays the most important tool for anesthetists if palpation is performed very precisely.

Lipoaugmentation of the vocal folds: a survey on alternative donor sites for graft harvesting.

Lipoaugmentation is a treatment option for patients suffering from glottic insufficiency. Autologous fat is a nearly ideal material for vocal-fold augmentation from the view of biocompatibility and viscoelasticity, but there is still the problem of high graft resorption. As distribution and biological behavior of fatty tissue is very different in the human body, the aim of the study was to elucidate possible donor sites with respect to the quantity of harvested fat, the surgical accessibility to the region, the donor site morbidity and possibility of aesthetic defects and the quality of harvested tissue. Possible donor sites for harvesting were examined by magnetic resonance imaging in thirty-five patients with special emphasis to the buccal fat pad, the neck, the dorsolateral side of the proximal upper extremity, the subcutaneous layer of the abdominal wall, the superficial trochanteric region, the medial thigh, and the infrapatellar fat pad. Identified regions that failed to be chosen into consideration because of an elaborate surgical approach (superficial axillary's space, ischio-anal fossa, subcutaneous layer of buttock, popliteal fossa) were not taken into consideration. The mean volume of the buccal fat was 3.994 cm(3); the average thickness of the fat at the level of C7 was 1.721 cm, the mean value in the upper extremities was 1.913 cm laterally and 1.275 cm dorsally. The subcutaneous fat of the abdominal wall was divided into a superficial compartment (mean: 1.527 cm) and a deep one (average: 3.545 cm). In the superficial trochanteric region, the mean thickness was 2.536 cm, in the medial thigh 2.127 cm; the mean volume of the infrapatellar fat pad was 20.198 cm(3). All regions of interest showed reproducible and sufficient amounts of harvestable tissue, we found significant intersexual differences in dorsolateral side of the upper arm, subcutaneous layer of the abdominal wall and superficial trochanteric region. When harvesting subcutaneous tissue of the abdominal wall, grafts of the deep layer should be preferred, in the upper extremity the deep, muscle-neighbored parts. An alternative method is the surgically accessible fat of the neck. Solid fat pads could be harvested from the buccal region or the infrapatellar fat.

Contact areas of the tibiotalar joint.

The contact areas between the articular surfaces of the talus and tibia are essential for understanding the mobility of the ankle joint. The purpose of our study was to reveal the contact area among the superior articular surface of the trochlea tali (target surface T) and the inferior articular surface of the tibia (query surface Q) under non-weight-bearing conditions in plantar flexion and dorsiflexion. Twenty cadaveric foot specimens were dissected and scanned by a three-dimensional (3D) laser scanner to obtain data point sets. These point sets were triangulated and a registration procedure performed to avoid any intersection of the two joint surfaces. For all points of the query surface Q, the closest distance to T was measured. In 11 of the 20 ankle joints, the contact area was larger in plantar flexion, in 5 it was nearly of equal size, and in 4 the two surfaces were found in a better congruence in dorsiflexion. The two articular surfaces can be in point or line contact and cause different motions while T is gliding on Q, so the original geometry of ligaments must be carefully reconstructed after injury or during total ankle replacement.

A model for clubfoot based on micro-CT data.

The pathological anatomy of idiopathic clubfoot has been investigated for more than 180 years using anatomy, computed tomography (CT), histology and microscopy. Seven idiopathic clubfeet and two normal feet of aborted fetuses were dissected in the present study, with special emphasis on the shape of the cartilage and bones. A three-dimensional (3D) micro-CT system, which generates a series of X-ray attenuation measurements, was used to produce computed reconstructed 3D data sets of each of the separated bones. Based on the micro-CT data scans a high-definition 3D colour printing system was used to make a four times enlarged clubfoot model, precisely presenting all the bony malformations. This model reflects the complexity of the anatomy of this disease and is designed to be used in the workshops of orthopaedic surgeons and physiotherapists, for training in new surgical and manipulation techniques.

The anatomy of the proximal ulna.

The posterior border of the ulna is the most important bony landmark for all dorsal surgical approaches and the guideline for open reduction, internal fixation of displaced comminuted fractures of the proximal ulna. We examined 74 cadaveric specimens to evaluate the anatomy of the proximal ulna, especially the course of the posterior border, the point of varus angulation, the width of the shaft, and the relationship of the posterior border to the interosseous and anterior ones. In 63 specimens, the mean point of varus angulation was 85.4 mm, and the average angulation angle was 17.7 degrees. In 11 specimens, the posterior border was either radially bowed or the bow was poorly defined and not localized to a specific area along the length of the bone. In conclusion, the variations of the proximal ulna have to be considered if dorsal plates and intramedullary screws are used.

Piriformis muscle: clinical anatomy and consideration of the piriformis syndrome.

Patients with lumbosacral and buttock pain provide tacit support for recognizing the piriformis muscle as a contributing factor to the pain (piriformis syndrome). One hundred and twelve cadaveric specimens were observed to elucidate the anatomical variations of the piriformis muscle referred to the diagnostic and treatment of the piriformis syndrome. The distance between the musculotendinous junction and the insertion was measured and the piriformis categorized into three types: Type A (71, 63.39%): long upper and short lower muscle belly; Type B (40, 35.71%): short upper and long lower muscle belly; Type C (1, 0.9%): fusion of both muscle bellies at the same level. The diameter of the piriformis tendon at the level of the musculotendinous junction ranged from 3 to 9 mm (mean: 6.3 mm). The piriformis showed the following possible fusions with adjacent tendons. In type one (60, 53.57%) a rounded tendon of the piriformis reached the upper border of the greater trochanter. In type two (33, 29.46%) it first joined into the gemellus superior tendon and at last both fused with the obturator internus tendon and inserted into the medial surface of the greater trochanter. A fusion of the piriformis, obturator internus and gluteus medius tendon with the same insertion area as above was observed in type three (15, 13.39%) and finally in type four (4, 3.57%) the tendon fused with the gluteus medius to reach the upper surface of the greater trochanter. Based on this survey anatomical causes for the piriformis syndrome are rare and a more precise workup is necessary to rule out more common diagnosis.

Anatomic variations of the musculotendinous junction of the soleus muscle and its clinical implications.

The soleus muscle, like the gastrocnemius, is a powerful plantarflexor muscle in the lower limb. The soleus muscle joins the aponeurosis of the gastrocnemius muscle to form the calcaneal (Achilles) tendon. While the basic anatomy of the soleus muscle has been previously described, no study has addressed the anatomical variations of its distal attachment. We found considerable anatomic variation in the distance between this musculotendinous junction and the most proximal point of the proximal edge. This distal measuring point was defined as the most proximal point of the proximal edge of the posterior surface of the calcaneal tuberosity. Eighty human cadaver specimens were preserved according to Thiel's method; we examined one limb from each cadaver, studying 80 lower extremities in total. Following careful dissection of the lower limb, we measured the distance between the distal point of attachment of the soleus muscle fibers (the musculotendinous junction) and the designated measuring point. Our findings were divided into three groups: Group 1 (10 cases, 12.5%), where the distance between the musculotendinous junction and the designated point on the calcaneal tuberosity was between 0 and 1 inches; Group 2 (56 cases, 70%), where the distance was between 1 and 3 inches; and Group 3 (14 cases, 17.5%), where the distance was greater than 3 inches. Detailed knowledge of the anatomic variations of the soleus muscle at its insertion point onto the calcaneal tendon has clinical implications in calcaneal tendon repair following rupture and in the planning of reconstructive surgery using soleus muscle flaps.

The pyramidal lobe: clinical anatomy and its importance in thyroid surgery.

The pyramidal lobe could be a source of pitfalls in thyroidectomy, due to its frequency but unreliable preoperative diagnosis on scintigraphic images. Special attention has to be paid to the pyramidal lobe to avoid leavings of residual tissue when complete removal of the thyroid is indicated. Sixty cadaveric specimens were examined with special emphasis to the topographical anatomy and expansion of the pyramidal lobe. A pyramidal lobe was found to be present in 55% of the cadavers (32/58). It was found more frequently in men than in women. In men the median length was 14 mm and in women 29 mm. An accessory thyroid gland was present in one specimen, in four cases the isthmus was missing. The pyramidal lobe branched off more frequently from the left part of the isthmus (16) than from the right (7) or the midline (9). In two cases it originated from the left lobe. Additionally 23 scintigraphic images were analyzed to evaluate the visualization of a pyramidal lobe. Only three of them showed enlargements of the isthmus that could be taken as a pyramidal lobe. Due to its frequency the pyramidal lobe should be regarded as a normal component of the thyroid. It is not reliably diagnosed by scintigraphic imaging because scintigraphy can only give functional information but not morphological one. Therefore the anterior cervical region has to be investigated very carefully during operation in order not to leave residual thyroid tissue in total thyroidectomy.

A morphometrical study of the medullary cavity of the ulna referred to intramedullary nailing.

Intramedullary fixation is preferred for osteosynthesis in the case of long bone fractures; but the problem of the nails' adjustment to the anatomical needs remains. About 80 cadaveric ulnae were examined to elucidate the curvature of the medullary cavity, the point of varus angulation, the thickness of the radial and ulnar cortical bone and the diameter of the medullary cavity at that point. Furthermore, the point of varus angulation of the posterior border was compared to that of the medullary cavity, to evaluate if it allows any conclusion to the curvature of the medullary cavity. The point of varus angulation of the medullary cavity ranged from 45 to 110 mm (mean 71.02), its angle from 4 to 13.5 grade (mean 8.95). At this point, the thickness of the cortical bone on the radial side was between 2.5 and 7 mm (mean 4.44) and ulnar between 2 and 8 mm (mean 4.37). The diameter ranged from 4 to 10.5 mm (mean 6.96). The point of varus angulation of the posterior border was between 65 and 110 mm (mean 85.88) and differs from that of the medullary cavity observed between 45 and 110 mm (mean 71.02). The point of varus angulation of the posterior border and the medullary cavity differs from 1 to 60 mm and it is found in most cases to be more distal than the point of varus angulation of the medullary cavity so the palpable posterior border allows no reliable conclusion of the curvature of the medullary cavity.

Anatomical study for an updated comprehension of clubfoot. Part II: Ligaments, tendons and muscles.

PURPOSE: The aim of our study was to evaluate the pathological anatomy of the ligaments, tendons and muscles in clubfeet, and to show whether the dysbalance of shortened and elongated structures is an adaptive process or a primary factor inducing the misshaped bones and cartilagines. METHODS: Surgical exposure was performed on seven idiopathic clubfeet specimens, aborted between the 25th and 37th week of gestation and compared to two normal feet (27th and 36th week of gestation). RESULTS: The medial stabilisation system of the foot was found shortened, but all ligaments could be dissected. On the lateral side, the calcaneofibular ligament in particular was both 'shortened' and 'elongated', depending on the course of the fibres to the axis of motion in the subtalar and talocalcaneonavicular joint. The main difference to the normal feet was found in the thickened tendon of the tibialis posterior forming a bulbus before dividing into fascicules. CONCLUSIONS: We presume the ossification disturbance of the calcaneus to be the primary fault. This disturbance will influence the reduction of the varus position, so ligaments and tendons will be conformed to the misshaped bones.

Anatomical study for an update comprehension of clubfoot. Part I: Bones and joints.

PURPOSE: The aim of our study was to elucidate the gross anatomical changes of bones and joints in idiopathic clubfeet. METHODS: Gross dissection was carried out on seven idiopathic clubfeet of fetuses aborted between the 25th and 37th week of gestation and compared to two normal feet (27th and 36th week of gestation). Particular attention was paid to the articular surfaces, shapes and angles of all bones and their skeletal relationships. RESULTS: The talar neck-trochlea angle in clubfeet ranged from 37 degrees to 41 degrees , in normal feet from 27 degrees to 33 degrees . In clubfeet the deviation of the neck of the talus relative to the body was between 28 degrees and 43 degrees , in normal feet between 22 degrees and 24 degrees . The posterior joint surface was in an anterolateral position and even flat transversely. The head of the clubfeet tali was turned along a longitudinal axis in the opposite direction compared to the normal ones. Instead of a typically saddle-shaped posterior talar surface of the calcaneus, it was triangular and flat transversely, and a bony stability in the subtalar joint was not achieved. The angle of torsion of the calcaneus showed no significant difference between normal and clubfeet. The anterior surface was flat, medially twisted and orientated upwards. CONCLUSIONS: We presume that the calcaneus is the primary fault, which might be explained by pathologic biomechanical forces during development.

The triceps brachii muscle and its insertion on the olecranon.

BACKGROUND: The purpose of this anatomical study was to define the insertion of the tendon of the triceps brachii muscle and the course of the lateral cubital retinaculum (LCR) as an enhancement of the triceps tendon. MATERIAL/METHODS: One hundred cadaver specimens were assessed and the widths of the triceps tendon and the olecranon and the expansion of the LCR were determined. RESULTS: The width of the tendon ranged between 1.9 and 4.2 cm (mean: 2.81) and the width of the olecranon between 1.8-3.8 cm (mean: 2.5). In 65 of the 100 specimens, the width of the tendon was greater than that of the olecranon. The fibers on the medial side inserted exactly on the medial aspect of the olecranon, whereas on the lateral aspect the fibers left the olecranon to reach the posterior border of the ulna. In 28 specimens the olecranon was wider than the tendon of the triceps, and in seven extremities the tendon occupied exactly the whole area of the olecranon. The LCR measured 2.3-7.2 cm (mean: 4.04 cm). CONCLUSIONS: By preserving parts of the triceps tendon on the olecranon and preserving the lateral cubital retinaculum, the extension strength will be maximized, allowing early active elbow motion. Using the triceps brachii muscle for any approach, only the medial aspect might be used as a guideline to reach the olecranon. On the lateral side the fibers of the triceps tendon fan out as the LCR to join into the ulna and the antebrachial fascia.

Unusual vascularization and nerve supply of the fifth finger.

During a dissection course, an unusual variation in vascularization and nerve supply of the fifth finger of the right hand was found in a 73-year-old human male cadaver. The proper digital palmar artery arose from the superficial branch of the ulnar artery distel to the Guyon's canal. The proper digital palmar artery coursed first palmar to the ulnar nerve then between the abductor minimi and flexor digiti minimi muscles to reach the ulnar side of the fifth finger. Besides this, the ulnar border of the fifth finger was supplied on its palmar side by the dorsal branch of the ulnar nerve, which gave off two tiny twigs for the sensory innervation on the dorsal side of the same finger.

Unusual thyroid gland vascularization.

During a dissection course, an unusual vascularization of the thyroid gland was found in a 69-year-old human male cadaver. On the right side, two arteries from the thyrocervical trunk supplied the lower half of the right lobe of the thyroid gland: the inferior thyroid artery and an additional vessel with a main trunk, found to be split into an upper and lower branch at the level of the longus colli muscle. The upper branch supplied the inferior constrictor pharyngeal muscle and the esophagus, whereas the lower branch coursed, at first, onto the trachea and finally leaving it to anastomose with the inferior thyroid artery.