Spontaneous regeneration after resection of various lengths of hypoglossal nerve in rats.

OBJECTIVES: The objective of this study was to investigate spontaneous neural regeneration and functional recovery after resection of various lengths of the hypoglossal (XII) nerve in adult rats. METHODS: Twelve weeks after XII nerve resection at lengths ranging from 0.0-15.8 mm, the tongue deviation angle of rats was measured to evaluate the severity of paralysis; thereafter, the XII neurons in the XII nucleus were labeled with Fluoro-Gold (FG), which was injected into the tongue to visualize regenerated XII neurons re-innervating the tongue muscles. RESULTS: In the XII nerve-resected rats, the regenerative rates, that is, the percentage of the total number of FG-positive neurons on the injured side relative to that on the uninjured side, were divided into two groups; the regenerative rates were more than 77% and less than 6%, respectively. Upon comparing the two groups, the boundary resection length was approximately 10.0 mm. Moreover, the former and latter groups demonstrated tongue deviation angles less than or greater than 15°, respectively. CONCLUSIONS: The critical nerve gap length for spontaneous neural regeneration was approximately 10.0 mm in XII nerve-resected adult rats, and nerve regeneration occurred in both morphological and functional aspects after resection at less than the critical length.

The calcaneofibular ligament groove at the inferior fibula, an ultrasonographic anatomical landmark.

PURPOSE: Calcaneofibular ligament (CFL) injuries are harder to diagnose than anterior talofibular ligament (ATFL) ones. This study aimed to clarify the fibular attachment of the CFL and verify the bony landmark for evaluating the CFL on ultrasonography. METHODS: Fifty-nine ankles were used in this anatomical study. To confirm the control function of the CFL, we performed passive movement manually using cadaveric ankles and observed the ankle positions where the CFLs were tense. Histological observation of CFL attachment of the fibula was performed using Masson's trichrome stain. The ATFL and CFL were removed, and the bone morphology of the CFL attachment and inferior fibular end was imaged using a stereomicroscope and a 3D scanner. Using ultrasonography, we evaluated the bone morphology of the fibular attachment of the CFL in short-axis images of 27 healthy adult ankles. RESULTS: The CFL was tensed according to ankle motions: supination, maximum dorsi flexion, maximum plantar flexion, and mild plantar flexion-external rotation. Below the CFL attachment of the fibula was a slight groove between the inferior tip and the obscure tubercle of the fibula. This groove was observed in 81.5% of cases using short-axis ultrasonography. CONCLUSION: The CFL was tensed in various ankle positions to control the movements of the talocrural and subtalar joints. There was a slight groove at the inferior end of the fibula where the CFL coursed downward. We called it the CFL groove and proposed that it could serve as a landmark for the short-axis image of ultrasonography.

Difference in the fibular attachment structure between the superior and inferior fascicles of the anterior talofibular ligament using ultrasonography and histological examinations.

PURPOSE: The anterior talofibular ligament (ATFL) is divided into superior (SB) and inferior bands (IB). Although the differences in length and width are known, the structure of the fibular attachment had not been elucidated. The present study aimed to clarify the differences in the fibular attachment structure between ATFL's SB and IB using cross-sectional images along the ligament. METHODS: An anatomical study using 15 formalin-fixed ankles was performed. The lateral ankle ligament complex was collected after a longitudinal image of SB/IB was visualized by ultrasonography. The specimens were decalcified and sectioned longitudinally at the center of SB/IB using a microtome. Histological evaluation of the enthesis structure at the fibular attachment of SB/IB was performed using hematoxylin-eosin and Masson's trichrome stains. RESULTS: A fibrillar pattern could not be observed in the longitudinal image at the IB level by ultrasonography. The lengths of ATFL's SB and IB were 20.6 ± 1.6 and 15.3 ± 1.3 mm, respectively, with thicknesses of 1.8 ± 0.4 and 1.0 ± 0.4 mm, respectively. The ATFL's IB was significantly shorter and thinner than the ATFL's SB. The fibular attachment of ATFL's SB had distinct enthesis structure, whereas in the attachment structure of the ATFL's IB, there were several variations including a type with a narrower enthesis structure than the ATFL's SB and a type that merged with or wrapped around the calcaneofibular ligament. CONCLUSION: The fibular attachment structure between ATFL's SB and IB differs. Our results could be useful information when performing ultrasonography and MRI diagnosis.

Relationship between inferior fascicle of anterior talofibular ligament and articular capsule in lateral ankle ligament complex.

PURPOSE: The lateral ankle ligament complex (LALC) is composed of anterior talofibular (ATFL), calcaneofibular (CFL), and posterior talofibular (PTFL) ligaments, all of which have a connection/continuous fiber. However, the structural link between the LALC and the articular capsule remains unknown. The goal of our study was to determine the connection between ATFL's inferior fascicle and the articular capsule. METHODS: In this study, we utilized 84 formalin-fixed ankles to elucidate the structure of LALC. Between ATFL and CFL, the bundle number of ATFL and arciform fiber was investigated. The specimens were decalcified and sectioned coronally using a freezing microtome, in the case of double bundles of ATFL, to study the connection between the inferior fascicle of ATFL and the articular capsule. RESULTS: ATFL had a single (25%), double (74%), and triple (1%) bundle number, respectively. The arciform fiber connecting the ATFL and the CFL was found in the superficial layer of all ankles (100%). There were two types of relationships between the inferior fascicle of ATFL and the articular capsule: 36 ankles (58%) were extracapsular, and 26 of 62 ankles (42%) were integrated with the inferior-lateral articular capsule. There are two kinds of relationships between the inferior fascicle of the ATFL and the articular capsule: extracapsular and integrated-capsular. CONCLUSIONS: The inferior fascicle of ATFL has a variant and integrated-capsular type is reinforced inferior-lateral articular capsule and enters the joint to form continuous fibers with PTFL, making LALC. These anatomical findings are helpful in ultrasonography diagnosis and arthroscopic ankle surgery.

Continuous and Connective Fibers of the Lateral Ankle Ligament Complex.

The lateral ankle ligament complex (LALC) is an intricate structure; therefore precise anatomic knowledge is required by the surgeon. However, the structural relationship of the LALC remains unclear. Here, the features of the posterior talofibular ligament (PTFL) and the relationship to the LALC at the distal fibula were clarified in a cadaver study. The lengths of most of the anterior and posterior parts, and the widths of the anterior-posterior and superior-inferior parts, were measured with a digital caliper. In addition, the relationship between the anterior talofibular ligament (ATFL) and PTFL inside of the capsule is described. The small fiber bundles of the PTFL were manually divided, and the footprint of each bundle at the fibula and talus was clarified. The relationship between the ATFL and CFL, outside of the capsule, was examined on axial slices at the inferior fibula. The lengths of the most anterior and most posterior parts of the PTFL were 9.8 ± 1.7 and 29.4 ± 1.9 mm, respectively. The widths of the anterior-posterior and superior-inferior parts were 10.0 ± 0.9 and 5.8 ± 1.1 mm, respectively. Approximately 83% of the fibers between the ATFL and PTFL were continuous. The anterior-inferior fibers of the PTFL were continuous with the inferior fibers of the ATFL inside of the capsule. The ATFL and CFL converged with connective tissue from outside of the capsule at the distal fibula. The results of this study should prove useful to further clarify the relationships of the LALC both inside and outside of the capsule at the distal fibula.

Hypoglossal nerve injury with long nerve resection leading to slow motoneuron death.

Crush injury to peripheral nerves in adult animals is considered not to trigger retrograde neuronal cell death; however, several studies reported neuronal cell death following severe injuries including nerve transection, resection, or avulsion. However, the rate of neuronal cell death varied among studies. In this study, we evaluated the outcomes of very severe nerve injury by long nerve resection in adult rats. Right hypoglossal (XII) nerve was exposed, and a 9-mm section was resected. At 4, 8, and 12 weeks after the resection, the number of XII neurons were counted in from the rostral to caudal sections. The number of XII neurons in the injured right side was reduced after the XII nerve resection compared with the uninjured left side. The mean rates of surviving neurons at 4, 8, and 12 weeks after the nerve resection were 83.5 %, 73.9 %, and 61.1 %, respectively, which were significantly lower than those of the control. The number of XII neurons after extensive XII nerve resection declined gradually over a relatively long time period, revealing that extensive nerve resection led to slow cell death of the injured neurons.