Shoulder region of the rat: anatomy and fiber composition of some suprascapular nerve branches

Rat models of frozen shoulder: Classification and evaluation

Frozen shoulder (FS), also known as adhesive capsulitis, is a condition that causes contraction and stiffness of the shoulder joint capsule. The main symptoms are persistent shoulder pain and a limited range of motion in all directions. These symptoms and poor prognosis affect people's physical health and quality of life. Currently, the specific mechanisms of FS remain unclear, and there is variability in treatment methods and their efficacy. Additionally, the early symptoms of FS are difficult to distinguish from those of other shoulder diseases, complicating early diagnosis and treatment. Therefore, it is necessary to develop and utilize animal models to understand the pathogenesis of FS and to explore treatment strategies, providing insights into the prevention and treatment of human FS. This paper reviews the rat models available for FS research, including external immobilization models, surgical internal immobilization models, injection modeling models, and endocrine modeling models. It introduces the basic procedures for these models and compares and analyzes the advantages, disadvantages, and applicability of each modeling method. Finally, our paper summarizes the common methods for evaluating FS rat models.

High-intensity interval training improves fatty infiltration in the rotator cuff through the β3 adrenergic receptor in mice

Aims

Rotator cuff muscle atrophy and fatty infiltration affect the clinical outcomes of rotator cuff tear patients. However, there is no effective treatment for fatty infiltration at this time. High-intensity interval training (HIIT) helps to activate beige adipose tissue. The goal of this study was to test the role of HIIT in improving muscle quality in a rotator cuff tear model via the β3 adrenergic receptor (β3AR).

Methods

Three-month-old C57BL/6 J mice underwent a unilateral rotator cuff injury procedure. Mice were forced to run on a treadmill with the HIIT programme during the first to sixth weeks or seventh to 12th weeks after tendon tear surgery. To study the role of β3AR, SR59230A, a selective β3AR antagonist, was administered to mice ten minutes before each exercise through intraperitoneal injection. Supraspinatus muscle, interscapular brown fat, and inguinal subcutaneous white fat were harvested at the end of the 12th week after tendon tear and analyzed biomechanically, histologically, and biochemically.

Results

Histological analysis of supraspinatus muscle showed that HIIT improved muscle atrophy, fatty infiltration, and contractile force compared to the no exercise group. In the HIIT groups, supraspinatus muscle, interscapular brown fat, and inguinal subcutaneous white fat showed increased expression of tyrosine hydroxylase and uncoupling protein 1, and upregulated the β3AR thermogenesis pathway. However, the effect of HIIT was not present in mice injected with SR59230A, suggesting that HIIT affected muscles via β3AR.

Conclusion

HIIT improved supraspinatus muscle quality and function after rotator cuff tears by activating systemic sympathetic nerve fibre near adipocytes and β3AR.

Influence of Brachial Plexus Birth Injury Location on Glenohumeral Joint Morphology

PURPOSE

Patient presentation after brachial plexus birth injury (BPBI) is influenced by nerve injury location; more contracture and bone deformity occur at the shoulder in postganglionic injuries. Although bone deformity after postganglionic injury is well-characterized, the extent of glenohumeral deformity after preganglionic BPBI is unclear.

METHODS

Twenty Sprague-Dawley rat pups received preganglionic or postganglionic neurectomy on a single forelimb at postnatal days 3 to 4. Glenohumeral joints on affected and unaffected sides were analyzed using micro-computed tomography scans after death at 8 weeks after birth. Glenoid version, glenoid inclination, glenoid and humeral head radius of curvature, and humeral head thickness and width were measured bilaterally.

RESULTS

The glenoid was significantly more declined in affected compared with unaffected shoulders after postganglionic (-17.7° ± 16.9°) but not preganglionic injury. Compared with the preganglionic group, the affected shoulder in the postganglionic group exhibited significantly greater declination and increased glenoid radius of curvature. In contrast, the humeral head was only affected after preganglionic but not postganglionic injury, with a significantly smaller humeral head radius of curvature (-0.2 ± 0.2 mm), thickness (-0.2 ± 0.3 mm), and width (-0.3 ± 0.4 mm) on the affected side compared with the unaffected side; changes in these metrics were significantly associated with each other.

CONCLUSIONS

These findings suggest that glenoid deformities occur after postganglionic BPBI but not after preganglionic BPBI, whereas the humeral head is smaller after preganglionic injury, possibly suggesting an overall decreased biological growth rate in this group.

CLINICAL RELEVANCE

This study expands understanding of the altered glenoid and humeral head morphologies after preganglionic BPBI and its comparisons with morphologies after postganglionic BPBI.

Preganglionic and Postganglionic Brachial Plexus Birth Injury Effects on Shoulder Muscle Growth

PURPOSE

Brachial plexus birth injury can differ in presentation, depending on whether the nerve ruptures distal to, or avulses proximal to, the dorsal root ganglion. More substantial contracture and bone deformity at the shoulder is typical in postganglionic injuries. However, changes to the underlying muscle structure that drive these differences in presentation are unclear.

METHODS

Seventeen Sprague-Dawley rats received preganglionic or postganglionic neurectomy on a single limb on postnatal days 3 and 4. Muscles crossing the shoulder were retrieved once the rats were sacrificed at 8 weeks after birth. External rotation range of motion, muscle mass, muscle length, muscle sarcomere length, and calculated optimal muscle length were measured bilaterally.

RESULTS

Average shoulder range of motion in the postganglionic group was 61.8% and 56.2% more restricted at 4 and 8 weeks, respectively, compared with that in the preganglionic group, but affected muscles after preganglionic injury were altered more severely (compared with the unaffected limb) than after postganglionic injury. Optimal muscle length in preganglionic injury was shorter in the affected limb (compared with the unaffected limb: -18.2% ± 9.2%) and to a greater extent than in postganglionic injury (-5.1% ± 6.2%). Muscle mass in preganglionic injury was lower in the affected limb (relative to the unaffected limb: -57.2% ± 24.1%) and to a greater extent than in postganglionic injury (-28.1% ± 17.7%).

CONCLUSIONS

The findings suggest that the presence of contracture does not derive from restricted longitudinal muscle growth alone, but also depends on the extent of muscle mass loss occurring simultaneously after the injury.

CLINICAL RELEVANCE

This study expands our understanding of differences in muscle architecture and the role of muscle structure in contracture formation for preganglionic and postganglionic brachial plexus birth injury.

Integrated iterative musculoskeletal modeling predicts bone morphology following brachial plexus birth injury (BPBI)

Brachial plexus birth injury (BPBI) is the most common nerve injury among children. The glenohumeral joint of affected children can undergo severe osseous deformation and altered muscle properties, depending on location of the injury relative to the dorsal root ganglion (preganglionic or postganglionic). Preganglionic injury results in lower muscle mass and shorter optimal muscle length compared to postganglionic injury. We investigated whether these changes to muscle properties over time following BPBI provide a mechanically-driven explanation for observed differences in bone deformity between preganglionic and postganglionic BPBI. We developed a computational framework integrating musculoskeletal modeling to represent muscle changes over time and finite element modeling to simulate bone growth in response to mechanical and biological stimuli. The simulations predicted that the net glenohumeral joint loads in the postganglionic injury case were nearly 10.5% greater than in preganglionic. Predicted bone deformations were more severe in the postganglionic case, with the glenoid more declined (pre: -43.8°, post: -51.0°), flatter with higher radius of curvature (pre: 3.0 mm, post: 3.7 mm), and anteverted (pre: 2.53°, post: 4.93°) than in the preganglionic case. These simulated glenoid deformations were consistent with previous experimental studies. Thus, we concluded that the differences in muscle mass and length between the preganglionic and postganglionic injuries are critical mechanical drivers of the altered glenohumeral joint shape.

Computational analysis of glenohumeral joint growth and morphology following a brachial plexus birth injury

Children affected with brachial plexus birth injury (BPBI) undergo muscle paralysis. About 33% of affected children experience permanent osseous deformities of the glenohumeral joint. Recent evidence suggests that some cases experience restricted muscle longitudinal growth in addition to paralysis and reduced range of motion at the shoulder and elbow. It is unknown whether altered loading due to paralysis, muscle growth restriction and contracture, or static loading due to disuse is the primary driver of joint deformity after BPBI. This study uses a computational framework integrating finite element analysis and musculoskeletal modeling to examine the mechanical factors contributing to changes in bone growth and morphometry following BPBI. Simulations of 8 weeks of glenohumeral growth in a rat model of BPBI predicted that static loading of the joint is primarily responsible for joint deformation consistent with experimental measures of bone morphology, whereas dynamic loads resulted in normal bone growth. Under dynamic loading, glenoid version angle (GVA), glenoid inclination angle (GIA), and glenoid radius of curvature (GRC) (-1.3°, 38.2°, 2.5 mm respectively) were similar to the baseline values (-1.8°, -38°, 2.1 mm respectively). In the static case with unrestricted muscle growth, these measures increased in magnitude (5.2°, -48°, 3.5 mm respectively). More severe joint deformations were observed in GIA and GRC when muscle growth was restricted (GVA: 3.6°, GIA: -55°, GRC: 4.0 mm). Predicted morphology was consistent with literature reports of in vivo glenoid morphology following postganglionic BPBI. This growth model provides a framework for understanding the most influential mechanical factors driving glenohumeral deformity following BPBI.

Histological analysis and biomechanical evaluation of fatty infiltration after rotator cuff tear and suprascapular nerve injury in a rat model

BACKGROUND

Rotator cuff tears are the most common shoulder injury, and little is known about the underlying etiology of fatty infiltration after rotator cuff tear. Previous studies speculated that rotator cuff tears lead to neural injury due to tethering of the suprascapular nerve at the notch. This study aimed to evaluate fatty infiltration after suprascapular nerve injury and rotator cuff tears.

METHODS

Ninety adult male Sprague-Dawley rats were used and were divided into four groups: sham, tendon transection only, suprascapular nerve ligation, and tendon transection plus suprascapular nerve ligation. The suprascapular nerve injury models were created by tying the suprascapular nerve. At 2, 4, and 8 weeks postoperatively, histological analysis and biomechanical testing were performed to evaluate fatty infiltration and elastic change in the supraspinatus muscles.

RESULTS

The amount of fatty infiltration in the supraspinatus muscle was significantly higher in both the suprascapular nerve ligation and tendon transection plus suprascapular nerve ligation groups than in the tendon transection only group at 2, 4, and 8 weeks. The ultimate failure load and tensile strength were significantly different among the tendon transection only, suprascapular nerve ligation, and tendon transection plus suprascapular nerve ligation groups at 8 weeks postoperatively. Furthermore, the mean Young's modulus of the muscle was significantly greater in the tendon transection plus suprascapular nerve ligation group than in both the tendon transection only and suprascapular nerve ligation groups at 8 weeks postoperatively.

CONCLUSIONS

In this study, based on the results of histological and biomechanical examinations in our rat models, the etiology of fatty infiltration after massive rotator cuff tear might be different from the suprascapular nerve injury.

Tissue response after implantation of pure titanium and bioresorbable screws in scapula with postoperative irradiation: an experimental study on rats

OBJECTIVE

The study focuses on the comparison of tissue reaction to titanium and bioresorbable implants with and without postoperative irradiation on an animal model.

MATERIALS AND METHODS

Thirty-nine LEW/W rats were randomly assigned to experimental or control groups. One titanium and one bioresorbable screw (poly-L-lactide [PLLA] and L- and D-lactide poly-L/D-lactide [PDLLA]) were implanted into the left scapulas of 24 rats. Half of them received 30 Gy to the operation site and the other half received 42 Gy. In the control groups, 3 rats received 30 Gy, and 6 rats received 42 Gy to the scapula area without operation; and 6 rats had implants inserted as in the experimental group, but received no postoperative irradiation. The scapulas were removed 14 or 30 days after irradiation and a histologic analysis was performed.

RESULTS

The host tissue reaction to titanium and PLLA-PDLLA screws without postoperative irradiation was of similar intensity. In irradiated animals, the inflammatory tissue reaction was more evident around the titanium screws than around the bioresorbable screws, irrespective of the radiation dose and of the time that elapsed from the irradiation. The reaction was more evident on the 14th day than on the 30th day after the last radiation dose (70 and 86 days after surgery, respectively). The intensity of the inflammatory tissue reaction, irrespective of the implant type, was more intense in the group irradiated with 42 Gy.

CONCLUSIONS

PLLA-PDLLA implants appear to cause less tissue reaction after irradiation and could be safer reconstructive devices than titanium implants for patients undergoing surgery and adjuvant radiotherapy for cancer.

Biomechanical Basis of Shoulder Osseous Deformity and Contracture in a Rat Model of Brachial Plexus Birth Palsy

BACKGROUND

The purpose of this study was to investigate the relative contributions of two proposed mechanisms, strength imbalance and impaired longitudinal muscle growth, to osseous and postural deformity in a rat model of brachial plexus birth palsy (BPBP).

METHODS

Thirty-two Sprague-Dawley rat pups were divided into four groups on the basis of surgical interventions to induce a strength imbalance, impaired growth, both a strength imbalance and impaired growth (a combined mechanism), and a sham condition in the left forelimb. Maximum passive external shoulder rotation angle (ERmax) was measured bilaterally at four and eight weeks postoperatively. After the rats were killed at eight weeks, the glenohumeral geometry (on microcomputed tomography) and shoulder muscle architecture properties were measured bilaterally.

RESULTS

Bilateral muscle mass and optimal length differences were greatest in the impaired growth and combined mechanism groups, which also exhibited >15° lower ERmax (p < 0.05; four weeks postoperatively), 14° to 18° more glenoid declination (p < 0.10), and 0.76 to 0.94 mm more inferior humeral head translation (p < 0.10) on the affected side. Across all four groups, optimal muscle length was significantly correlated with at least one osseous deformity measure for six of fourteen muscle compartments crossing the shoulder on the affected side (p < 0.05). In the strength imbalance group, the glenoid was 5° more inclined and the humeral head was translated 7.5% more posteriorly on the affected side (p < 0.05).

CONCLUSIONS

Impaired longitudinal muscle growth and shoulder deformity were most pronounced in the impaired growth and combined mechanism groups, which underwent neurectomy. Strength imbalance was associated with osseous deformity to a lesser extent.

CLINICAL RELEVANCE

Treatments to alleviate shoulder deformity should address mechanical effects of both strength imbalance and impaired longitudinal muscle growth, with an emphasis on developing new treatments to promote growth in muscles affected by BPBP.

Age-related changes affect rat rotator cuff muscle function

BACKGROUND

The influence of age on rotator cuff function and muscle structure remains poorly understood. We hypothesize that normal aging influences rotator cuff function, muscle structure, and regulatory protein expression in an established rat model of aging.

METHODS

Seventeen rats were obtained from the National Institute on Aging. The supraspinatus muscles in 11 middle-aged (12 months old) and 6 old (28 months old) rats were studied for age-related changes in rotator cuff neuromuscular function by in vivo muscle force testing and electromyography (EMG). Changes in muscle structure and molecular changes were assessed with quantitative immunohistochemistry for myogenic determination factor 1 (MyoD) and myogenic factor 5 (Myf5) expression.

RESULTS

Old animals revealed significantly decreased peak tetanic muscle force at 0.5 N and 0.7 N preload tension (P < .05). The age of the animal accounted for 20.9% of variance and significantly influenced muscle force (P = .026). Preload tension significantly influenced muscle force production (P < .001) and accounted for 12.7% of total variance. There was regional heterogeneity in maximal compound motor action potential (CMAP) amplitude in the supraspinatus muscle; the proximal portion had a significantly higher CMAP than the middle and distal portions (P < .05). The expression of muscle regulatory factors MyoD and Myf5 was significantly decreased in old animals compared with middle-aged animals (P < .05).

CONCLUSIONS

The normal aging process in this rat model significantly influenced contractile strength of the supraspinatus muscle and led to decreased expression of muscle regulatory factors. High preload tensions led to a significant decrease in force production in both middle-aged and old animals.

Microcomputed tomography characterization of shoulder osseous deformity after brachial plexus birth palsy: a rat model study

BACKGROUND

Shoulder deformities are common secondary sequelae associated with brachial plexus birth palsy. The aim of the present study was to characterize three-dimensional glenohumeral deformity associated with brachial plexus birth palsy with use of microcomputed tomography scanning in a recently developed animal model.

METHODS

Brachial plexus birth palsy was produced by a right-sided neurotomy of the C5 and C6 nerve roots in seven five-day-old Sprague-Dawley rats. Microcomputed tomography scanning was performed when the rats were four months of age. Glenoid size, version, and inclination; humeral head size; and acromion-glenoid distance were measured. Normal shoulders of age-matched rats (n = 9) served as controls. Statistical analysis was performed with use of the unpaired two-tailed Student t test.

RESULTS

There were significant increases in glenoid retroversion (-7.6° ± 4.9° compared with 3.6° ± 2.1°; p = 0.038) and glenoid inclination (38.7° ± 7.3° compared with 11.2° ± 1.9°; p = 0.015) in the shoulders with simulated brachial plexus birth palsy in comparison with the normal, control shoulders. The glenohumeral joints were more medialized in the joints with simulated brachial plexus birth palsy as reflected by the acromion-glenoid distance measurement; however, the difference was not significant (3.20 ± 0.51 compared with 2.40 ± 0.18 mm; p = 0.12). Although the mean humeral head height and width measurements, on the average, were smaller in the brachial plexus birth palsy shoulders as compared with the normal, control shoulders, only the measurement of humeral head height was significantly different between the two groups (4.25 ± 2.02 compared with 4.97 ± 0.11 mm [p = 0.008] and 3.56 ± 0.27 compared with 4.19 ± 0.17 mm [p = 0.056], respectively).

CONCLUSIONS

In this animal model, rats with simulated brachial plexus birth palsy developed gross architectural joint distortion characterized by increased glenoid retroversion and inclination. In addition, humeral heads tended to be smaller four months after simulated brachial plexus birth palsy.

Development of a shoulder contracture model in rats

HYPOTHESIS

The capsular tissue is responsible for the pathogenesis of the shoulder contracture.

MATERIALS AND METHODS

The glenohumeral joint of Sprague-Dawley rats was immobilized using internal fixation (immobilized group). The control group underwent a sham operation (sham group). To assess the range of motion, the glenohumeral joint angle was measured repeatedly under same torque in 6 conditions: after removal from the trunk, after removal of the outer muscles other than rotator cuff after removal of the rotator cuff muscles, and after 3 types of partial capsulotomy. The abduction angle and total rotation angles were measured. The length of the synovial intima was measured with hematoxylin-eosin-stained specimens. Immunohistochemical study for type III collagen was also performed.

RESULTS

No significant differences were found in the range of motion until all the muscles were removed. The abduction angle increased significantly after serial capsulotomy in the immobilized group. Even after the capsulotomy, however, this angle remained significantly less than that in the sham group. There was a similar trend for the total rotation angle. There was morphological change in the synovium of the immobilized group; the significant decrease of synovial length and strong staining of type III collagen.

DISCUSSION

Our results show that capsule might play important role for contracture formation. Decrease of the synovial length might reflect synovial adhesion. Strong expression in Type III collagen might be related to joint stiffness.

CONCLUSION

A contracture model was successfully established. Changes in the capsule and synovium might play an important role in occurrence of contracture.

Effect of corticosteroids on the biomechanical strength of rat rotator cuff tendon

BACKGROUND

The effect of corticosteroids on tendon properties is poorly understood, and current data are contradictory and diverse. The biomechanical effect of steroids on rotator cuff tendon has not been studied, to our knowledge. The current study was undertaken to characterize the biomechanical effects of corticosteroid exposure on both uninjured and injured rat rotator cuff tendon.

METHODS

One hundred and twenty-three male Sprague-Dawley rats were randomly assigned to four groups: control (C), tendon injury (I), steroid exposure (S), and tendon injury plus steroid exposure (I+S). Unilateral tendon injuries consisting of a full-thickness defect across 50% of the total width of the infraspinatus tendon were created. Steroid treatment consisted of a single dose of methylprednisolone placed into the subacromial space. At one, three, and five weeks postoperatively, the shoulders were harvested and the infraspinatus tendon was subjected to biomechanical testing. Two specimens from each group were used for histological analysis.

RESULTS

At one week, maximum load, maximum stress, and stiffness were all significantly decreased in Group S compared with the values in Group C. Mean maximum load decreased from 37.9 N in Group C to 27.5 N in Group S (p < 0.0005). Mean maximum stress decreased from 18.1 MPa in Group C to 13.6 MPa in Group S (p < 0.0005). Mean stiffness decreased from 26.3 N/mm in Group C to 17.8 N/mm in Group S (p < 0.0005). At one week, mean maximum stress in Group I+S (17.0 MPa) was significantly decreased compared with the value in Group I (19.5 MPa) (p < 0.0005). At both the three-week and the five-week time point, there were no significant differences between Group C and Group S or between Group I and Group I+S with regard to mean maximum load, maximum stress, or stiffness. Histological analysis showed fat cells and collagen attenuation in Groups S and I+S. These changes appeared to be transient.

CONCLUSIONS

A single dose of corticosteroids significantly weakens both intact and injured rat rotator cuff tendons at one week. This effect is transient as the biomechanical properties of the steroid-exposed groups returned to control levels by three weeks.

Brachial plexus birth palsy-associated shoulder deformity: a rat model study

PURPOSE

Although recovery occurs in the majority of cases of brachial plexus birth palsy (BPBP), long-term shoulder disability is relatively common. The aim of this study was to establish an animal model to study BPBP-associated shoulder deformities.

METHODS

A right-side C5, C6 root neurotomy was performed under the surgical microscope in 5-day-old Sprague-Dawley rats (N = 9). The contralateral side served as a control. The development of shoulder deformity and range of motion loss were followed longitudinally. Animals were killed 4 months after surgery. Both shoulders were harvested, decalcified, and transected in the axial plane for glenoid version measurement and shoulder histology.

RESULTS

All animals developed shoulder internal rotation contracture within 4 weeks after the C5, C6 neurotomy. The average shoulder external rotation loss was 52 degrees +/- 7, 59 degrees +/- 10, and 82 degrees +/- 11 in comparison with the control side 1, 2, and 4 months after neurotomy, respectively. Glenoid version changed from 2 degrees +/- 2 of retroversion (left side) to 8 degrees +/- 3 of anteversion. Five shoulders were subluxated clinically with a pseudoglenoid formation observed radiographically. Histologic study demonstrated marked glenoid and humeral head deformities.

CONCLUSIONS

This neonatal rat model clearly demonstrated typical shoulder deformities similar to that resulting from Erb's palsy. This model can be useful in studying BPBP-associated shoulder deformities.

The effect of corticosteroid on collagen expression in injured rotator cuff tendon

BACKGROUND

Subacromial corticosteroid injections are commonly used in the nonoperative management of rotator cuff disease. The effects of corticosteroid injection on injured rotator cuff tendons have not been studied. Our aims were to characterize the acute response of rotator cuff tendons to injury through the analysis of the type-III to type-I collagen expression ratio, a tendon injury marker, and to examine the effects of corticosteroid on this response.

METHODS

Sixty Sprague-Dawley rats were randomly assigned to four groups: control, tendon injury, steroid treatment, and tendon injury and steroid treatment. Six rats served as sham controls. Unilateral tendon injuries were created with full-thickness defects across 50% of the total width of the infraspinatus tendon, 5 mm from its humeral insertion. Steroid treatment with a single dose of methylprednisolone (0.6 mg/kg), equivalent to that given to humans, was injected into the subacromial space under direct visualization. Steroid treatment followed the creation of an injury in the rats in the injury and steroid treatment group. At one, three, and five weeks after the injury, the total RNA isolated from tendons was quantified with real-time polymerase chain reaction with use of primers for type-I and type-III collagen and ribosomal 18s RNA.

RESULTS

The type-III to type-I collagen expression ratio remained at baseline at all time-points in the control and sham groups. At one week, the type-III to type-I collagen expression ratio increased more than fourfold above the control level in the tendon injury group (p = 0.017) and the tendon injury and steroid treatment group (p = 0.003). The ratio remained greater than twofold above the control at three weeks in both groups (p = 0.003 and p = 0.037) and returned to baseline at five weeks. Interestingly, the group that had steroid treatment only showed an increase of >4.5-fold (p = 0.001) in the type-III to type-I collagen expression ratio, without structural injury to the tendon. This ratio returned to baseline levels by three weeks.

CONCLUSIONS

A single dose of corticosteroid does not alter the acute phase response of an injured rotator cuff tendon in the rat. However, the same steroid dose in uninjured tendons initiates a short-term response equivalent to that of structural injury.

Contralateral motor rootlets and ipsilateral nerve transfers in brachial plexus reconstruction

Object. The goal of this study was to evaluate outcomes in patients with brachial plexus avulsion injuries who underwent contralateral motor rootlet and ipsilateral nerve transfers to reconstruct shoulder abduction/external rotation and elbow flexion.

Methods. Within 6 months after the injury, 24 patients with a mean age of 21 years underwent surgery in which the contralateral C-7 motor rootlet was transferred to the suprascapular nerve by using sural nerve grafts. The biceps motor branch or the musculocutaneous nerve was repaired either by an ulnar nerve fascicular transfer or by transfer of the 11th cranial nerve or the phrenic nerve. The mean recovery in abduction was 90° and 92° in external rotation. In cases of total palsy, only two patients recovered external rotation and in those cases mean external rotation was 70°. Elbow flexion was achieved in all cases. In cases of ulnar nerve transfer, the muscle scores were M5 in one patient, M4 in six patients, and M3+ in five patients. Elbow flexion repair involving the use of the 11th cranial nerve resulted in a score of M3+ in five patients and M4 in two patients. After surgery involving the phrenic nerve, two patients received a score of M3+ and two a score of M4. Results were clearly better in patients with partial lesions and in those who were shorter than 170 cm (p < 0.01). The length of the graft used in motor rootlet transfers affected only the recovery of external rotation. There was no permanent injury at the donor sites.

Conclusions. Motor rootlet transfer represents a reliable and potent neurotizer that allows the reconstruction of abduction and external rotation in partial injuries.

Effects of methylprednisolone and betamethasone injections on the rotator cuff: an experimental study in rats

Thirty-one female Sprague-Dawley rats were used to determine the effects of subacromial corticosteroid injections on the rotator cuff. The injection technique was tested in 6 animals, which were excluded from the study. The remaining 25 rats were randomly divided into three groups of 8 animals each; a single rat received no injections. Every other week for 8 weeks, one shoulder in each rat was injected with methylprednisolone, betamethasone, or saline in a dosage equivalent to that used in humans. The supraspinatus and infraspinatus tendons were removed 10 days after the last injection and evaluated. There were no pathologic changes in the tendons injected with saline. In 43% of the methylprednisolone-treated rats and 29% of the betamethasone-treated rats, the tendons were abnormally soft and light-colored. In 43% of the methylprednisolone group and 71% of the betamethasone group, fragmentation of collagen bundles and inflammatory cell infiltration were evident. Subacromial injections of methylprednisolone or betamethasone repeated frequently can cause deleterious changes in the normal structure of the rat rotator cuff. In light of these findings, therapy for subacromial impingement syndrome of the shoulder with frequent, repeated steroid injections is potentially harmful.

Carrageenan-induced subacromial bursitis caused changes in the rat's rotator cuff

This study was designed to investigate the histologic expression of the rat's supra- and infraspinatus tendons in carrageenan-induced subacromial bursitis. Thirty-two rats received subacromial injections with carrageenan (n = 28) or saline (n = 4). The tendons were analysed microscopically after staining with hematoxyline eosin, Van Giesons hematoxyline and immunofluorescent staining of fibronectin and fibrinogen. In the controls (saline x 10) and group A (carrageenan x 5) there were no changes in the tendons. In group B (carrageenan x 10) 3/8 rats showed macrophages between the collagen fibres and an increased staining of fibronectin. In group C (double dosis carrageenan) all rats had signs of fibrocartilaginous metaplasia in the supraspinatus tendon. In eight of these specimens even bony metaplasia was seen. The infraspinatus tendon showed fibrosis but no fibrocartilaginous metaplasia. The results showed that iatrogenic bursitis after carrageenan subacromial injections was associated with marked changes of the supraspinatus tendon.

Effect of steroid injections on the rotator cuff: an experimental study in rats

The aim of this study was to evaluate the effects of repeated steroid injections into the subacromial space. Thirty rats were injected either 3 or 5 times with triamcinolone in a dosage equivalent to that given to human beings or 3 or 5 times with saline into the subacromial space. One rat received no injection. The supraspinatus and infraspinatus tendons were evaluated macroscopically and microscopically. Two different staining methods were used on each sample including hematoxylin eosin and Miller's elastin/van Gieson's solution. After 5 steroid injections, we found focal inflammation, necrosis, and fragmentation of collagen bundles in the tendon in 4 of 7 rats. The tendons of the controls showed a normal structure (P < .05). There were no pathologic changes among the rats that were injected with triamcinolone 3 times. These results show that repeated subacromial injections of triamcinolone may cause damage to the rotator cuff of the rat. This finding may indicate cautious use of subacromial steroid injections in human beings.

Structural changes of the rotator cuff caused by experimental subacromial impingement in the rat

Subacromial impingement of the infraspinatus tendon was experimentally created in 28 young adult rats by thickening the undersurface of the acromion with either one or two platelike bony transplants of the ipsilateral scapular spine. Nine nonoperated and eight shoulders that had undergone a sham operation served as control groups. The rats were killed after 2 days and after 1, 2, 4, 8, 16, and 32 weeks for histologic evaluation. All rats with experimental subacromial impingement showed an infraspinatus tear on the bursal side of the tendon. An isolated tear on the articular side or within the tendon was not seen. Two plates caused larger tears than one (P = .04), and more long-standing impingement was associated with larger lesions (P = .002). Multiple chondrocytes were observed within the tendon adjacent to the bony transplants. No calcium deposits were found. In the subacromial space rapid thickening of the bursa was observed. The undersurfaces of the bony transplants showed no evidence of abrasion or remodeling caused by the tendon. The shoulders of the control groups were found intact without any alteration. Experimental subacromial impingement in the rat caused bursal side rotator cuff tears. The type of partial tears that are most frequently observed in clinical practice, that is, intratendinous and articular side tears, were not seen in this experimental model.

Ganglionic axons in motor roots and pia mater

In addition to motor axons and preganglionic axons, ventral roots contain unmyelinated or thin myelinated sensory axons and postganglionic sympathetic axons. It has been said that ventral roots channel sensory axons to the CNS. However, it now seems that these axons end blindly, shift to the pia or loop and return towards the periphery and that these units reach the CNS via dorsal roots. Sensory ventral root axons project from a variety of somatic or visceral receptors; some of them are third branches of dorsal root afferents and some seem to lack a CNS projection. Many ventral root afferents contain substance P (SP) and/or calcitonin gene-related peptide (CGRP). These fibres are not affected by neonatal capsaicin treatment and they cannot induce radicular or pial extravasation. Some thin ventral root axons are sympathetic and relate to blood vessels. Afferents containing SP and/or CGRP and sympathetic axons also occur in the spinal pia mater. The sensory axons mediate pain. They might also have vasomotor, tissue-regulatory and/or mechanoreceptive functions. The motor roots of cranial nerves IV, VI and XI contain unmyelinated axons arranged like in ventral roots outside the autonomic outflow. However, the motor root of cranial nerve V channels some unmyelinated axons into the CNS. The occurrence of thin axons in ventral roots and pia mater changes during development and ageing. After peripheral nerve injury, ipsilateral ventral roots and pia are invaded by new sensory and postganglionic sympathetic axons.

Teeth and tooth nerves

(1) Although our knowledge on teeth and tooth nerves has increased substantially during the past 25 years, several important issues remain to be fully elucidated. As a result of the work now going on at many laboratories over the world, we can expect exciting new findings and major break-throughs in these and other areas in a near future. (2) Dentin-like and enamel-like hard tissues evolved as components of the exoskeletal bony armor of early vertebrates, 500 million years ago, long before the first appearance of teeth. It is possible that teeth developed from tubercles (odontodes) in the bony armor. The presence of a canal system in the bony plates, of tubular dentin, of external pores in the enamel layer and of a link to the lateral line system promoted hypotheses that the bony plates and tooth precursors may have had a sensory function. The evolution of an efficient brain, of a head with paired sense organs and of toothed jaws concurred with a shift from a sessile filter-feeding life to active prey hunting. (3) The wide spectrum of feeding behaviors exhibited by modern vertebrates is reflected by a variety of dentition types. While the teeth are continuously renewed in toothed non-mammalian vertebrates, tooth turnover is highly restricted in mammals. As a rule, one set of primary teeth is replaced by one set of permanent teeth. Since teeth are richly innervated, the turnover necessitates a local neural plasticity. Another factor calling for a local plasticity is the relatively frequent occurrence of age-related and pathological dental changes. (4) Tooth development is initiated through interactions between the oral epithelium and underlying neural crest-derived mesenchymal cells. The interactions are mediated by cell surface molecules, extracellular matrix molecules and soluble molecules. The possibility that the initiating events might involve a neural component has been much discussed. With respect to mammals, the experimental evidence available does not support this hypothesis. In the teleost Tilapia mariae, on the other hand, tooth germ formation is interrupted, and tooth turnover ceases after local denervation. (5) Prospective dental nerves enter the jaws well before onset of tooth development. When a dental lamina has formed, a plexus of nerve branches is seen in the subepithelial mesenchyme. Shortly thereafter, specific branches to individual tooth primordia can be distinguished. In bud stage tooth germs, axon terminals surround the condensed mesenchyme and in cap stage primordia axons grow into the dental follicle.(ABSTRACT TRUNCATED AT 400 WORDS)

Sensory C-fibers in rat ventral roots are capsaicin-insensitive and they do not mediate extravasation from pial vessels

Mammalian ventral roots and pia mater contain sensory C-fibers, some of which exhibit a substance P- and/or calcitonin gene-related peptide (CGRP)-like immunoreactivity. At some locations, sensory axons containing these neuropeptides evoke peripheral plasma protein extravasation after antidromic electrical stimulation. Such axons usually disappear following treatment of neonatal rats with capsaicin. The purpose of the present study is to find out if afferent C-fibers in the rat ventral roots L4 and L5 are capsaicin-sensitive, and if antidromic stimulation of these fibers elicits extravasation in the root and/or the ventral pia mater. The results show (1) that the number of C-fibers in these ventral roots is unaffected by neonatal capsaicin treatment, as seen in the electron microscope; (2) that the occurrence and general configuration of axons with substance P- and CGRP-like immunoreactivity do not appear abnormal in neonatally capsaicin-treated rats, as revealed by fluorescence microscopy on longitudinal frozen sections; (3) that Evans blue albumin is not extravasated in the ventral root or pia mater after electrical ventral root stimulation or following systemic injection of capsaicin. We conclude, that ventral root afferents are functionally different from otherwise similar afferents at other locations.