Ultrastructural changes in knee ligaments following immobilization

The Physiology Associated With "Bed Rest" and Inactivity and How It May Relate to the Veterinary Patient With Spinal Cord Injury and Physical Rehabilitation

In the twentieth century, bed rest was commonly prescribed by human healthcare professionals as a treatment for a variety of ailments including spinal cord injury and disease. With time, the negative impact of bed rest was recognized as a source of slow and even reduced patient healing. As treatment paradigms shifted, the utility and importance of physical rehabilitation (PR) as a critical adjunctive treatment for human patients with spinal cord injury became fully recognized. Today, standardized PR protocols exist for humans with the spinal cord disease, but the same cannot be said for our veterinary patients with spinal cord injury. The purpose of this manuscript is to discuss the effects of inactivity on the musculoskeletal system and to explore how and why PR can play a critical role in improved mobility and overall health in the veterinary patient with spinal cord injury. Research with a focus on the effects of inactivity, in the form of cage rest, for the veterinary patient with spinal cord injury is lacking.

Variations in internal structure, composition and protein distribution between intra- and extra-articular knee ligaments and tendons

Tendons and ligaments play key roles in the musculoskeletal system in both man and animals. Both tissues can undergo traumatic injury, age‐related degeneration and chronic disease, causing discomfort, pain and increased susceptibility to wider degenerative joint disease. To date, tendon and ligament ultrastructural biology is relatively under‐studied in healthy, non‐diseased tissues. This information is essential to understand the pathology of these tissues with regard to function‐related injury and to assist with the future development of tissue‐engineered tendon and ligament structures. This study investigated the morphological, compositional and extracellular matrix protein distribution differences between tendons and ligaments around the non‐diseased canine stifle joint. The morphological, structural characteristics of different regions of the periarticular tendons and ligaments (the intra‐articular anterior cruciate ligament, the extra‐articular medial collateral ligament, the positional long digital extensor tendon and energy‐storing superficial digital flexor tendons) were identified using a novel semi‐objective histological scoring analysis and by determining their biochemical composition. Protein distribution of extracellular matrix collagens, proteoglycans and elastic fibre proteins in anterior cruciate ligament and long digital extensor tendon were also determined using immunostaining techniques. The anterior cruciate ligament was found to have significant morphological differences in comparison with the other three tissues, including less compact collagen architecture, differences in cell nuclei phenotype and increased glycosaminoglycan and elastin content. Intra‐ and interobserver differences of histology scoring resulted in an average score 0.7, indicative of good agreement between observers. Statistically significant differences were also found in the extracellular matrix composition in terms of glycosaminoglycan and elastin content, being more prominent in the anterior cruciate ligament than in the other three tissues. A different distribution of several extracellular matrix proteins was also found between long digital extensor tendon and anterior cruciate ligament, with a significantly increased immunostaining of aggrecan and versican in the anterior cruciate ligament. These findings directly relate to the different functions of tendon and ligament and indicate that the intra‐articular anterior cruciate ligament is subjected to more compressive forces, reflecting an adaptive response to normal or increased loads and resulting in different extracellular matrix composition and arrangement to protect the tissue from damage.

Pathological changes of human ligament after complete mechanical unloading

OBJECTIVE

To investigate the pathologic changes with a time sequence among patients with injured ligaments after complete mechanical unloading, based on a human anterior cruciate ligament (ACL) model.

DESIGN

Pathologic examinations were done on remnants of completely ruptured ACLs at various times up to 14 wks after injury on 31 patients and on normal ACLs from five cadaver donors. Testing variables included fibroblast density, crimp amplitude, and crimp nuclear shape.

RESULTS

Sequential changes were observed: Fibroblast density significantly increased within 5-6 wks of unloading. By 7-8 wks, crimp amplitude significantly decreased, accompanied by formation of irregular fiber patterns and fragments. This was followed by crimp wavelength and nuclear shape change within 9-14 wks.

CONCLUSIONS

These pathologic findings suggest that the ACL undergoes significantly deleterious changes from 5 to 6 wks after mechanical unloading. This study may emphasize the important concept of early implementation of mechanical force in rehabilitation programs for patients with injured ligaments.

Comparison of the relative benefits of 2 versus 10 days of soft collar cervical immobilization after acute whiplash injury

OBJECTIVE

To investigate the effects of 2-day and 10-day immobilization of the cervical spine on pain, range of motion (ROM), and disability of patients with Quebec Task Force (QTF) grade II whiplash injuries.

DESIGN

Randomized controlled trial.

SETTING

University hospital emergency department.

PARTICIPANTS

Seventy patients with acute QTF grade II whiplash injuries.

INTERVENTIONS

At the intake examination within 24 hours after the whiplash trauma, the patients were randomized to 2 therapy groups (2-d or 10-d immobilization with a soft cervical collar). All patients received pain drugs (nonsteroidal anti-inflammatory drugs) and after 7 days, all patients started a standardized physiotherapy program 2 to 3 times a week.

MAIN OUTCOME MEASURES

Patients' pain and disability scores were assessed using visual analog scales and ROM was assessed using a goniometer. All parameters were measured within 24 hours after injury and after 2 and 6 months.

RESULTS

After 2 months, the different periods of immobilization (2d or 10d) were associated with comparable improvements in pain symptoms (median, 4.60 vs 4.65), ROM (median, 100.0 degrees vs 117.5 degrees ), and disability score (median, 4.90 vs 5.15). No statistically significant differences could be identified between the 2 treatment groups. After 6 months, persistent pain was reported by 4 patients in each group (12.5%).

CONCLUSIONS

In patients with QTF grade II whiplash injuries, there is no short- or long-term difference between 2-day and 10-day immobilization with a cervical collar in terms of pain, ROM, or disability.

Contribution of biomechanics, orthopaedics and rehabilitation: the past present and future

Biomechanics is a field that has a very long history. From its beginnings in ancient Chinese and Greek literature, the field of orthopaedic biomechanics has grown in the areas of biomechanics of bone, articular cartilage, soft tissues, upper extremities, spine and so on. Bioengineers in collaboration with orthopaedic surgeons have applied biomechanical principles to study clinically relevant problems, improving patient treatment and outcome. In the past 30 years, my colleagues and I have focused our research on the biomechanics of musculoskeletal soft tissues, ligaments and tendons in particular. Therefore, in this review article, the function of the knee ligaments and the associated homeostatic responses secondary to immobilisation and exercise will be described. Research on healing of the medial collateral ligament (MCL) of the knee and possible future approaches in improving the healing of the knee ligaments will be presented. Finally, improvement of the understanding of ligament reconstruction, specifically of the anterior cruciate ligament (ACL), through the use of robotics technology will be included. Throughout the manuscript, specific scientific findings that have guided or changed the clinical management of injury to these soft tissues will be emphasised.

Biomechanics of knee ligaments: injury, healing, and repair

Knee ligament injuries are common, particularly in sports and sports related activities. Rupture of these ligaments upsets the balance between knee mobility and stability, resulting in abnormal knee kinematics and damage to other tissues in and around the joint that lead to morbidity and pain. During the past three decades, significant advances have been made in characterizing the biomechanical and biochemical properties of knee ligaments as an individual component as well as their contribution to joint function. Further, significant knowledge on the healing process and replacement of ligaments after rupture have helped to evaluate the effectiveness of various treatment procedures. This review paper provides an overview of the current biological and biomechanical knowledge on normal knee ligaments, as well as ligament healing and reconstruction following injury. Further, it deals with new and exciting functional tissue engineering approaches (ex. growth factors, gene transfer and gene therapy, cell therapy, mechanical factors, and the use of scaffolding materials) aimed at improving the healing of ligaments as well as the interface between a replacement graft and bone. In addition, it explores the anatomical, biological and functional perspectives of current reconstruction procedures. Through the utilization of robotics technology and computational modeling, there is a better understanding of the kinematics of the knee and the in situ forces in knee ligaments and replacement grafts. The research summarized here is multidisciplinary and cutting edge that will ultimately help improve the treatment of ligament injuries. The material presented should serve as an inspiration to future investigators.

Biomechanical regulation of type I collagen gene expression in ACLs in organ culture

In this study, an ex vivo organ culture system that allows the application of controlled loads to the anterior cruciate ligament (ACL) was designed and used to characterize the influence of a step input in mechanical load on gene expression. A procedure for isolating bone-ACL-bone (B-ACL-B) complexes from rat knees was developed. After harvest and 24 hour culture, B-ACL-B complexes exhibited percentages of viability similar to that in intact ACLs (approximately 90%). Application of a physiologically relevant load of 5 N (superimposed on a I N tare load) resulted in changes in levels of mRNA encoding type I collagen. While levels of type I collagen mRNA significantly increased 32+/-13% (mean +/- standard errors of the mean (SEM)) over controls within the first hour of loading, levels decreased significantly to 44+/-9% of control after 2 h. Displacements induced by the 5 N load were measured by video dimensional analysis. Calculated axial strains of 0.141+/-0.034 were achieved rapidly during the first hour and remained essentially unchanged thereafter. These results demonstrate the feasibility of maintaining ligaments in organ culture and illustrate the time course expression of type I collagen following the application of a mechanical load.

Time-dependent increases in type-III collagen gene expression in medical collateral ligament fibroblasts under cyclic strains

Numerous studies have demonstrated the capacity of mechanical strains to modulate cell behavior through several different signaling pathways. Understanding the response of ligament fibroblasts to mechanically induced strains may provide useful knowledge for treating ligament injury and improving rehabilitation regimens. Biomechanical studies that quantify strains in the anterior cruciate and medial collateral ligaments have shown that these ligaments are subjected to 4-5% strains during normal activities and can be strained to 7.7% during external application of loads to the knee joint. The objective of this study was to characterize the expression of types I and III collagen in fibroblast monolayers of anterior cruciate and medial collateral ligaments subjected to equibiaxial strains on flexible growth surfaces (0.05 and 0.075 strains) by quantifying levels of mRNA encoding these two proteins. Both cyclic strain magnitudes were studied under a frequency of 1 Hz. The results indicated marked differences in responses to strain regimens not only between types I and III collagen mRNA expression within each cell type but also in patterns of expression between anterior cruciate and medial collateral ligament cells. Whereas anterior cruciate ligament fibroblasts responded to cyclic strains by expression of higher levels of type-I collagen message with almost no significant increases in type-III collagen, medial collateral ligament fibroblasts exhibited statistically significant increases in type-III collagen mRNA at all time points after initiation of strain with almost no significant increases in type-I collagen. Furthermore, differences in responses by fibroblasts from the two ligaments were detected between the two strain magnitudes. In particular, 0.075 strains induced a time-dependent increase in type-III collagen mRNA levels in medial collateral ligament fibroblasts whereas 0.05 strains did not. The strain-induced changes in gene expression of these two collagens may have implications for the healing processes in ligament tissue. The differences may explain, in part, the healing differential between the anterior cruciate and medial collateral ligaments in vivo.

The adverse effects of sectioning the posterior cruciate ligament in rabbits. Changes in the structural and morphological properties of the femur-anterior cruciate ligament-tibia complex

This study examined the changes in the structural properties of the femur-anterior cruciate ligament-tibia complex (FATC) and the histologic changes of the anterior cruciate ligament (ACL) following sectioning of the posterior cruciate ligament (PCL) of 20 rabbits. The PCL in the right knee was sectioned through an arthrotomy. The left knee underwent arthrotomy only and was used as a control. The animals were killed 3 and 6 months postoperatively. The tensile properties of the FATCs were tested, and the ACLs were histologically examined using polarized light microscopy and transmission electron microscopy. There were significant decreases in the ultimate load following sectioning of the PCL, although there were no significant changes in the stiffness. There were no significant differences in either the crimp period or the crimp amplitude of the ACL following sectioning of the PCL. There were significant increases in the number of collagen fibrils per square micrometer, and significant decreases in the collagen fibril diameter and proportion of total collagen fibril area per square micrometer following sectioning of the PCL. These findings suggest that isolated PCL injury may cause pathological changes in the ACL and its insertion sites.

Age-related changes in biomechanical properties of the Achilles tendon in rabbits

We investigated age-related changes in the mechanical properties of rabbit Achilles tendon. The animals used were immature (age 3 weeks, body mass 380 g), young adult (age 8-10 months, body mass 4.1 kg) and old (age 4-5 years, body mass 5.1 kg) rabbits. The cross-sectional area of the tendon increased with growth and the tensile strength of the young adult [67.3 (SEM 4.2) MPa] and old [66.7 (SEM 3.8) MPa] tendon was significantly higher than that of the immature tendon [23.9 (SEM 3.8) MPa]. However, there was no statistically significant difference in tensile strength between mature and old tendons. These differences may be attributable to the change in body mass. The gradient of the stress-strain curves, that is, the tangent modulus of the mature tendon [618.0 (SEM 87.0) MPa], was higher than that of the immature [281.0 (SEM 104.6) MPa] and old [530.5 (SEM 91.0) MPa] tendon, although the difference was not significant. The elongation at failure was approximately 16 percent for all age groups. These results would suggest that rabbit Achilles tendon is highly compliant during growth.

Increased expression of the beta 1, alpha 5, and alpha v integrin adhesion receptor subunits occurs coincident with remodeling of stress-deprived rabbit anterior cruciate and medial collateral ligaments

The biomechanical, biochemical, and morphological properties of the anterior cruciate and medial collateral ligaments are dramatically altered in response to deprivation of normal physical forces and joint motion. Integrin adhesion receptors are known to play important roles in the tissue remodeling that occurs in the course of normal wound repair. We propose that integrins play a similar role in the remodeling of the extracellular matrix in stress-deprived periarticular ligaments. This study tests the hypothesis that altered expression of integrins on ligament fibroblasts accompanies this remodeling. The left knees of 15 New Zealand White rabbits were surgically immobilized in acute flexion and the right knees served as controls (no operation). The anterior cruciate and medial collateral ligaments were harvested at 1, 3, 5, 9, or 12 weeks after immobilization. Sections from the ligaments were immunostained with monoclonal antibodies specific for the integrin subunits beta 1, alpha 5, alpha 6, and alpha v, as well as with a negative control antibody. Fibroblasts within both the stress-deprived anterior cruciate and medial collateral ligaments demonstrated markedly increased staining for the beta 1, alpha 5, and alpha v subunits, as compared with the controls. The increased staining was greatest at 9 weeks in the anterior cruciate ligament and at 12 weeks in the medial collateral ligament. Western blot study of ligament proteins extracted with sodium dodecyl sulfate demonstrated an increased amount of beta 1 subunit protein in both ligaments from knees that were stress deprived for 9 and 12 weeks, as compared with the control ligaments.(ABSTRACT TRUNCATED AT 250 WORDS)

Immobilization of the knee joint alters the mechanical and ultrastructural properties of the rabbit anterior cruciate ligament

The effects of immobilization of the knee joint on the mechanical and ultrastructural properties of the anterior cruciate ligament have not been well documented. Our goal was to determine these effects in a rabbit model and to assess the effect of knee flexion angle during immobilization. The knee joint was immobilized in either 170 degrees or 105 degrees of flexion, and new methodologies were utilized to determine the mechanical properties of the anterior cruciate ligament. In specimens from knees that had been immobilized, the cross-sectional area of the ligament was 74% of the control value. The stress-strain curve was altered slightly, and the strain at failure increased 32-40%. The modulus and stress at failure did not decrease significantly. There was no significant difference between the mechanical properties of the knees immobilized at 170 degrees and 105 degrees of flexion. Histological and ultrastructural evaluation demonstrated changes in the shape and intracellular make-up of the fibroblasts from the ligament after immobilization. This cellular response may account for the alterations in the mechanical properties of the anterior cruciate ligament.

Changes of cytoskeletal architecture and incorporation of 3H-proline in contracted anterior cruciate ligament

Changes of cytoskeletal architecture and incorporation of 3H-proline were investigated in contracted anterior cruciate ligaments with use of a model of contracture. In control ligaments, fibroblasts were shown by immunofluorescence microscopy to contain actin, vimentin, and myosin in their cytoplasm. Cytoskeletons were visualized by electron microscopy as a mesh network of microfilaments among cell organelles. In contracted anterior cruciate ligaments, fibroblasts were spindle-shaped and their cytoplasm could not be observed clearly in sections stained with hematoxylin and eosin. Actin staining was distributed irregularly and extensively, whereas vimentin and myosin staining was not scattered so extensively. When compared electromyographically, the actin staining appeared in cytoplasmic pseudopods of the fibroblasts. It was thought that these cytoplasmic pseudopods contained mainly actin and little or no other cytoskeletal elements such as vimentin and myosin. In autoradiographs, contracted anterior cruciate ligaments were shown, with use of 3H-proline, to experience a decrease in the number of labeled cells. On the basis of these findings of cytoskeletal rearrangement and of decreased incorporation of 3H-proline, we hypothesized that fibroblasts of the anterior cruciate ligament had the capacity to change their character during knee immobilization and to play a role in ligament contracture.

Cellular ultrastructure of the ruptured anterior cruciate ligament. A transmission electron microscopic and immunohistochemical study in 55 cases

To evaluate the cellular ultrastructure following injury, we examined the anterior cruciate ligaments in 55 patients with complete tears in different phases after the injury and compared them to a control group of 39 cadaver knees. Samples were analyzed by electron microscopy, immunofluorescence, and ultramorphometry. After an invasion of inflammatory cells into the stumps of the ruptured ligaments, a marked proliferation of fibroblasts was found at the end of Phase 1 (2-3 days after the ligament injury), that was even more pronounced at the beginning of Phase II (4-17 days). These cells were initially highly metabolically active and secreted Type III collagen precursors. In Phase III (4-45 days), fibroblast degeneration occurred with increasing frequency. Furthermore, some fibroblasts showed signs of cell death. Our findings suggest that the structural alterations of the intraligamentous fibroblasts diminish their function and, consecutively, disorganization of the developing repair tissue occurs. This mechanism might contribute to the poor healing potential of the ruptured anterior cruciate ligament.

Ligament tension affects nuclear shape in situ: an in vitro study

This study was carried out to test the hypothesis that a relationship exists between ligament tension and ligament cell geometry. Rabbit knee joints were positioned at 70 degrees of joint flexion and the medial collateral ligament (MCL) was mechanically isolated and the femur-MCL-tibia complex was stretched or compressed by displacing the crosshead of a materials testing machine: -2.0 mm (relative compression), 0.0 mm (a reproducible no-load starting point), +/-0.7 mm or + 1.4 mm (relative tension). Each MCL complex was then fixed immediately in 10% neutral buffered formalin. Contralateral knees were dissected similarly with MCLs exposed and fixed in situ at 70 degrees of flexion. Subsequent to histological processing, measurements were made of the profiles of fibrocyte nuclei (since previous work has shown that nuclear shape closely approximates fibrocyte shape) that were located in the central portion of each MCL midsubstance using a video-based computerized morphometry system. Results showed that the dimensions of nuclei in the midsubstance of experimental MCLs were significantly longer and thinner at crosshead displacements that corresponded to increased ligament tension. At +1.4 mm of displacement fibrocyte nuclei were approximately 4 microm longer and 1 microm thinner than those fixed at 0.0 mm, an observation supported by a statistically significant increase in the mean maximum-to-minimum-diameter ratio and a significant decrease in mean cell roundness. These results strongly suggest that mechanical load can directly affect ligament fibrocyte geometry in situ. If a similar phenomenon also occurs in vivo, the metabolism of ligament fibrocytes may be influenced considerably by their loading history.

[Fascicular and sub-fascicular architecture of the cruciate ligament]

The details of the collagen fascicle morphology and the vascularization of the anterior and the posterior cruciate ligament were examined by the combined use of histology, transmission- and scanning electron microscopy, morphometry and immunohistochemistry. The diameters of the collagenous fibrils in the anterior cruciate ligament ranged between 20 and 155 nm (x = 74 nm, s = 18.8 nm) and in the posterior cruciate ligament between 20 and 175 nm (x = 82 nm, s = 25.4 nm). Type III and VI collagen were found distributed throughout the matrix but concentrated in the attachment regions of the ligaments. The content of type IV collagen in the anterior cruciate ligament was low. The amount of arterioles revealed a typical pattern (anterior cruciate ligament: less than 30 years = 2.94/mm2, greater than 90 years = 2.02/mm2, proximal = 3.15/mm2, distal = 2.18/mm2; posterior cruciate ligament: less than 30 years = 4.69/mm2, greater than 90 years = 3.87/mm2, proximal = 4.08/mm2, distal = 3.98/mm2).

Ultrastructural morphometry of anterior cruciate and medial collateral ligaments: an experimental study in rabbits

This study presents morphometric analyses of collagen subfascicle area fraction and collagen fibril diameter distributions for the anterior cruciate (ACL) and medial collateral (MCL) knee ligaments from transmission electron micrographs of ligament cross sections of five mature, female New Zealand White rabbits. Statistically significant differences in subfascicular area fractions were found between the ACL and MCL (0.89 +/- 0.02, 0.97 +/- 0.01, respectively; p less than 0.001). Mean fibril diameters for the ACL and MCL were also significantly different (0.059 +/- 0.005, 0.085 +/- 0.011 microns, respectively; p less than 0.025). Fibril eccentricity (a measure of parallel alignment of collagen fibrils within the ligaments, defined as the ratio of minor to major axes of elliptical fibril outlines) was 0.89 +/- 0.03 and 0.85 +/- 0.08, respectively, for the ACL and MCL; these data were not significantly different (p greater than 0.1). The relative amount of variation in the pooled fibril diameter data due to variation between animals, ligaments, locations within ligaments, and among fibrils at individual locations are reported. The variation of fibril diameter distributions between the ACL and MCL was substantially greater than the variation between different locations within each ligament cross section as well as between different animals. The structural differences reported may help explain known differences in the biomechanical properties of the ACL and MCL.