Abnormality of the contralateral ligament after injuries of the medial collateral ligament. An experimental study in rabbits

Joint instability leads to long-term alterations to knee synovium and osteoarthritis in a rabbit model

OBJECTIVES

Joint instability is believed to promote early osteoarthritic changes in the knee. Inflammatory reactions are associated with cartilage degradation in osteoarthritis (OA) but their possible synergistic or additive effects remain largely unexplored. The goal of the present study was to investigate the in vivo effects of Botulinum Toxin A (BTX-A) induced joint instability on intraarticular alterations in an otherwise intact rabbit knee joint model.

METHODS

Ten 1-year-old female New Zealand White rabbits (average 5.7 kg, range 4.8-6.6 kg) were randomly assigned to receive three monthly unilateral intramuscular injections of BTX-A (experimental group), or no treatment (control group). After 90 days, all knees were analyzed for specific mRNA levels using RT-qPCR. The synovium and cartilage tissue was assessed for histological alterations using the OARSI scoring system.

RESULTS

Cartilage and synovial histology showed significant higher OARSI scores in the BTX-A group animals compared to the untreated controls and contralateral limbs. There were no differences between the untreated control and the contralateral experimental limbs. Gene expression showed significant elevations for collagen I, collagen III, nitric oxide, TGF-β, IL-1 and IL-6 compared to the healthy controls.

CONCLUSION

BTX-A induced joint instability in a muscle weakness model uniquely leads to alterations in gene expression and histological changes in the synovial membranes and cartilage in otherwise intact knee joints. These results lead to the conclusion that joint instability may promote an inflammatory intraarticular milieu, thereby contributing to the development of OA.

Comparative analysis of inter- and intraligamentous distribution of sensory nerve endings in ankle ligaments: a cadaver study

BACKGROUND

The aim of this study was to analyze the inter-, intraligamentous, and side-related patterns of sensory nerve endings in ankle ligaments.

METHODS

A total of 140 ligaments from 10 cadaver feet were harvested. Lateral: calcaneofibular, anterior-, posterior talofibular; sinus tarsi: lateral- (IERL), intermediate-, medial-roots inferior extensor retinaculum, talocalcaneal oblique and canalis tarsi (CTL); medial: tibionavicular (TNL), tibiocalcaneal (TCL), superficial tibiotalar, anterior/posterior tibiotalar portions; syndesmosis: anterior tibiofibular. Following immunohistochemical staining, the innervation and vascularity was analyzed between ligaments of each anatomical complex, left/right feet, and within the 5 levels of each ligament.

RESULTS

Significantly more free nerve endings were seen in all ligaments as compared to Ruffini, Pacini, Golgi-like, and unclassifiable corpuscles (P ≤ .005). The IERL had significantly more free nerve endings and blood vessels than the CTL (P ≤ .001). No significant differences were seen in the side-related distribution, except for Ruffini endings in right TCL (P = .016) and unclassifiable corpuscles in left TNL (P = .008). The intraligamentous analysis in general revealed no significant differences in mechanoreceptor distribution.

CONCLUSIONS

The IERL at the entrance of the sinus tarsi contained more free nerve endings and blood vessels, as compared to the deeper situated CTL. Despite different biomechanical functions in the medial and lateral ligaments, the interligamentous distribution of sensory nerve endings was equal.

CLINICAL RELEVANCE

The intrinsic innervation patterns of the ankle ligaments provides an understanding of their innate healing capacities following injury as well as the proprioception properties in postoperative rehabilitation.

Effects of joint contracture on the contralateral unoperated limb in a rabbit knee contracture model: a biomechanical and genetic study

In most animal models, unoperated contralateral limbs are used as controls. However, in some experimental circumstances, the contralateral limb may represent a skewed control. The main purpose of this study was to determine if the unoperated contralateral limb could be used as a control, or if a different unoperated animal's limb should be used instead. Seventeen rabbits were divided into two groups. Group 1 rabbits (n = 12) underwent surgery on their right limbs to induce a contracture. Group 2 rabbits (n = 5) underwent no surgery. The left non-operated limbs of rabbits in group 1 were biomechanically and genetically compared to the limbs of unoperated rabbits in group 2 with the use of a validated joint measuring device and custom microarray, respectively. After 8 weeks of immobilization, there was a statistically greater flexion contracture in the unoperated contralateral limbs compared to the limbs of animals that received no surgery(8.4 ± 8.9° vs. 0 ± 0°; p-value = 0.03). When animals were remobilized for an additional 16 weeks, the significance between groups was lost (11.9 ± 21.4° vs. 8.9 ± 9.5°; p = 0.38). Similarly, there was a statistically significant increase in nine genes at 8 weeks (p < 0.001). However, at 24 weeks, only the PMCA 1 gene was statically increased (p < 0.001). In our rabbit model, the non-operated limb develops a small flexion contracture at 8 weeks. After 16 weeks of remobilization, there is no biomechanical or genetic difference between contralateral non-operated limbs and limbs of animals not undergoing any surgical intervention. Given the biomechanical and genetic findings, the contralateral non-operated limb can be used as a valid control.

Wound healing differences between Yorkshire and red Duroc porcine medial collateral ligaments identified by biomechanical assessment of scars

BACKGROUND

Currently, there are no large animal models to assess potential genetic contributions to ligament biomechanics during an injury repair response. Yorkshire and red Duroc pigs display phenotypically and genetically different skin wound healing responses; red Duroc skin scars were hyper-contracted and hyper-pigmented, whereas Yorkshire skin scars were not. Such findings raise the question whether connective tissues of synovial joints display a similar differential healing response in these pig breeds. This study assessed medial collateral ligament healing in Yorkshire and red Duroc pigs at the functional (biomechanical) level.

METHODS

Surgical injury was created in the right hind limb medial collateral ligament of Yorkshire and red Duroc pigs. After 10 weeks of healing, low-load (laxity and creep) and high-load (failure) mechanical properties were measured.

FINDINGS

Large, complete ligament scars formed by 10 weeks post-injury. A differential healing response was observed between the breeds, where red Duroc ligament scars had larger cross-sectional areas, exhibited greater static and total creep responses, failed at greater deformations and strains (P ≤ 0.05), and failed with strong trends for higher loads and lower moduli (P=0.06) than Yorkshire ligament scars.

INTERPRETATION

The ligament healing response of red Duroc pigs differs from Yorkshire pigs. Previously observed breed differences in dorsal skin wound healing are not restricted to skin. Such findings support a genetic basis for breed differences in response to connective tissue injury. Since this animal model is physiologically comparable to humans, these findings could provide further insight into identification of specific genetic contributions to ligament repair in human populations.

Tibial interference screw fixation in anterior cruciate ligament reconstruction with and without autograft bone augmentation

PURPOSE

Because tibial fixation of soft-tissue grafts in anterior cruciate ligament (ACL) reconstruction is problematic, this study aimed to develop a means of delivering bone graft evenly around tendon autograft and define any mechanical, radiologic, or histologic benefit using an ovine model.

METHODS

A device to deliver bone graft evenly throughout the tibial tunnel was developed. Forty mature sheep underwent simulated quadruple hamstring tendon-ACL reconstruction by use of a bioresorbable interference screw, either with or without bone graft augmentation of the tibial tunnel. Endpoint data were derived at time 0 and after 6 weeks in vivo. Radiostereometric analysis provided quantitation of the translational characteristics; computed tomography evaluated tunnel volume, and measures of yield strength and stiffness were obtained. Sequential fluorochrome administration assessed bone formation, and light microscopy surveyed the biological response.

RESULTS

Radiostereometric analysis highlighted differences in the translational characteristics of ACL-deficient knees when compared with intact knees. Reconstructed knees (with or without autograft) showed significantly greater translation when compared with unoperated knees at 6 weeks; autograft bone augmentation provided no benefit. Neither tunnel volume nor yield strength nor stiffness was improved with the addition of autograft bone. No untoward histologic responses were observed. Bone apposition rates were similar between treatment groups. An even distribution of bone graft throughout the tunnels was observed.

CONCLUSIONS

This model has confirmed the ability of the bone graft-delivery system to evenly distribute bone graft throughout the tunnels. However, the study has failed to show improvement in stability or fixation strength after augmentation with autograft bone.

CLINICAL RELEVANCE

The autograft bone-delivery system may provide a means of establishing an osteoconductive/inductive environment. At this early juncture (6 weeks), no benefit could be defined. Its use in combination with bone morphogenetic proteins or stem cells may provide more rapid fixation, rehabilitation, and reconstitution of bone volume within the tunnel.

Risk factors for a contralateral anterior cruciate ligament injury

Contralateral anterior cruciate ligament (ACL) injuries are together with the risk of developing osteoarthritis of the knee and the risk of re-rupture/graft failure important aspects to consider after an ACL injury. The aim of this review was to perform a critical analysis of the literature on the risk factors associated with a contralateral ACL injury. A better understanding of these risk factors will help in the treatment of patients with unilateral ACL injuries and in the development of interventions designed to prevent contralateral ACL injuries. A Medline search was conducted to find studies investigating risk factors for a contralateral ACL injury, as well as studies where a contralateral ACL injury was the outcome of the study. Twenty studies describing the risk of a contralateral ACL rupture, or specific risk factors for a contralateral ACL injury, were found and systematically reviewed. In 13 of these studies, patients were followed prospectively after a unilateral ACL injury. The evidence presented in the literature shows that the risk of sustaining a contralateral ACL injury is greater than the risk of sustaining a first time ACL injury. Return to a high activity level after a unilateral ACL injury was the most important risk factor of sustaining a contralateral ACL injury. There was inconclusive evidence of the relevance of factors such as female gender, family history of ACL injuries, and a narrow intercondylar notch, as risk factors for a contralateral ACL injury. Risk factors acquired secondary to the ACL injury, such as altered biomechanics and altered neuromuscular function, affecting both the injured and the contralateral leg, most likely, further increase the risk of a contralateral ACL injury. This literature review indicates that the increased risk of sustaining a contralateral ACL injury should be contemplated, when considering the return to a high level of activity after an ACL injury.

Myofibroblast upregulators are elevated in joint capsules in posttraumatic contractures

We hypothesized specific growth factors are increased in the elbow capsules of patients with post traumatic elbow contractures. A model of surgically induced joint contracture in rabbit knees was developed to study the growth factor expression in joint contractures. This study demonstrates this model mimics the human condition and analyzes how the growth factor levels decrease with time in rabbit knees with contractures. Reverse transcription polymerase chain reaction was used to measure mRNA levels of transforming growth factor-beta1, connective tissue growth factor, ED-A of fibronectin, and alpha-smooth muscle actin normalized to a housekeeping gene, glyceraldehyde-3-phosphate dehydrogenase. In the joint capsules of patients with elbow contractures, mRNA levels were increased for transforming growth factor- beta1, connective tissue growth factor, and alpha-smooth muscle actin. In the joint capsules of rabbit knees with contractures, mRNA levels were increased for transforming growth factor- beta1, connective tissue growth factor, ED-A of fibronectin, and alpha-smooth muscle actin. The mRNA levels for transforming growth factor-beta1, connective tissue growth factor, and alpha-smooth muscle actin decreased with time in rabbit knees. The elevated levels of these myofibroblast up-regulators and fibrogenic growth factors could explain the previously reported increase in myofibroblasts and collagen mRNA levels. The rabbit knee model correlated well with the human post traumatic elbow contractures.

Denervation alters mRNA levels of repair-associated genes in a rabbit medial collateral ligament injury model

Previous experiments revealed that denervation impairs healing of the MCL. This suggested the hypothesis that denervation would decrease repair-associated mRNA levels in the injured MCL when compared with normally innervated injured MCL. Adult, skeletally mature female rabbits were assigned to one of four groups: unoperated control, femoral nerve transection alone (denervated controls), MCL partial tear or denervated MCL partial tear. At three days, two weeks, six weeks or sixteen weeks post-surgery, cohorts of 6 rabbits from each experimental group were killed. Ligaments were harvested, RNA extracted and RT-PCR was performed using rabbitspecific primers. In the denervated injury group, mRNA levels for the angiogenesis-associated gene MMP-13, matrix components Collagen I and III, growth factor TGF-beta and angiogenesis inhibitors TIMP-3, and TSP-1 had all increased by two-weeks post-injury, in comparison to the non-denervated injury group (p < or = 0.01). An increased level of TSP-1 mRNA was also detected in the denervated injured group at sixteen weeks post injury (p < or = 0.01). Contrary to the initial hypothesis, denervation led to increased mRNA levels for many relevant molecules during the early stages of MCL healing. Thus, inappropriate timing of over-expression of some molecules may potentially contribute to the decreased quality of the scar tissue, particularly molecules such as TSP-1. Neuronal derived factors strongly influence the in vivo metabolic activity of ligament and scar fibroblasts in the initial phases of healing.

Joint capsule matrix turnover in a rabbit model of chronic joint contractures: Correlation with human contractures

To evaluate changes in matrix molecules of the joint capsule, the right knees of 24 skeletally mature female NZW rabbits were immobilized while the contralateral limb served as an unoperated control. The immobilization was discontinued at 8 weeks and the rabbits were divided among four groups (n = 6) based on the number of weeks the right knees were remobilized: 0, 8, 16, or 32. Three rabbits (six knees) that did not have operations provided normal control joint capsules. The mRNA levels for collagen types I, II, and III, and MMP-1 and -13 were significantly increased in the joint capsules of the contracture knees in all groups when compared to normal and contralateral limb joint capsules. In contrast, the mRNA levels for TIMP-1, -2, and -3 were decreased in the joint capsules of the contracture knees in all groups when compared to normal and contralateral limb joint capsules. The mRNA levels for lumican and decorin were increased in the joint capsules of the contracture knees in all groups when compared to normal capsules. Many of the changes observed in this animal model are similar to those observed in human joint capsules from posttraumatic elbow contractures, supporting the value of this rabbit model.

Homotypic variation of canine flexor tendons: implications for the design of experimental studies in animal models

Water, collagen and glycosamimoglycan contents, cross-sectional area, stiffness and elastic modulus were carefully quantitated in flexor digitorum superficialis tendons from mature canines. From these data the within- and between-animal variability was estimated and used to demonstrate sample size calculations for both two-group and paired (within-animal) study designs. The estimated between-dog variance was typically 50% or less of the total variance for the parameters investigated. In other words, the correlation among the tendons within an animal for most measures was not strong. Therefore, for some variables (e.g., elastic modulus) in this animal and tendon model, there is no appreciable gain in statistical power by using a paired study design. A two-group design could be used, but any within-animal correlation must be accounted for in the analysis. For other variables such as collagen content, a paired design would gain substantial power.

Animal models of tendon and ligament injuries for tissue engineering applications

Animal modeling continues to be an important component to the critical evaluation of new techniques to treat tendon and ligament injuries. Appropriate choice and analysis of these models is essential. Factors that should be considered in assessing a potential model include the tissue type (ligament versus tendon and intrasynovial versus extrasynovial), the type of injury to be modeled, the techniques of measuring the response to treatment, the ease of comparison to previously published models and finally, the ease of translation to human trials and eventually to clinical usage.

Medial collateral ligament and partial anterior cruciate ligament transection: mRNA changes in uninjured ligaments of the sheep knee

Following knee ligament injury, clinical and experimental investigations usually focus on the injured ligament, and uninjured ligaments of the same joint are largely ignored and presumed to remain unchanged. The purpose of this study was to characterize changes in mRNA levels for a relevant subset of molecules in the uninjured knee ligaments following combined unilateral medial collateral ligament (MCL) and partial anterior cruciate ligament (ACL) transection in sheep. Semiquantitative reverse transcription-polymerase chain reaction was performed for collagen types I, III, and V; matrix metalloproteinase-13 (MMP-13); and tissue inhibitor of metalloproteinase-1 for both injured and uninjured knee ligaments at 6 and 12 weeks after injury. Collagen type I, III, and V mRNA levels were significantly increased in MCL scars at 6 weeks as well as in the uninjured lateral collateral ligament and the anteromedial band of the ACL (AM-ACL). MMP-13 mRNA levels were also elevated in the MCL at 6 and 12 weeks and in the AM-ACL 6 weeks after injury. In contrast, significant changes in the posterior cruciate ligament were not detected at either time point, indicating specificity in the transient alterations. These results suggest that following injury, responses occur in uninjured ligaments that are specific although transient in nature. These responses may be an adaptive attempt to preserve function until the scar tissue can stabilize the mechanical environment following injury.

Carpal bone postures and motions are abnormal in both wrists of patients with unilateral scapholunate interosseous ligament tears

PURPOSE

The recent ability to measure 3-dimensional in vivo carpal kinematics has facilitated the noninvasive study of complex carpal bone motion.

METHODS

In this study we examined the flexion/extension carpal kinematics of both wrists in 8 patients with unilateral scapholunate interosseous ligament (SLIL) tears by using computed tomographic (CT) imaging and a markerless bone registration technique. Carpal bone neutral posture and flexion/extension motion of both wrists of the injured patients were compared with the same parameters in wrists of 10 uninjured male and female volunteers (normals).

RESULTS

The neutral posture of the injured scaphoid and lunate were significantly more extended than those of normals. In these patients, however, the postures of the scaphoid and lunate in the contralateral uninjured wrists also were abnormal and were similar to those of the injured wrist. In addition, extension of the lunate and flexion of the scaphoid in both the injured and uninjured wrist were significantly different from normal but not different from each other.

CONCLUSIONS

This study was unable to attribute altered carpal posture and motion to SLIL tears because abnormalities were found in both wrists of patients with unilateral injury. The etiology of abnormal wrist kinematics in the asymptomatic wrist of patients with unilateral tears of the scapholunate ligament is not known.

Ultimate tensile strength of a Leeds-Keio/autograft ACL reconstruction utilizing PLLA tibial staple fixation

An ovine model of anterior cruciate ligament reconstruction was utilized to evaluate the biomechanical and histological response of a polylactic acid tibial fixation staple (Gunze Ltd., Japan/Zimmer, Japan). This was performed in a comparison with metallic staples, currently utilized for this procedure. The prosthesis consisted of autograft combined with a Leeds-Keio (L-K) ligament. Early post-operative mobilization was followed by retrieval of specimens at 6, 12 and 24 weeks post-reconstruction. Evaluation of the mechanical characteristics of the graft reconstructions (tensile strength) showed no significant differences (P>0.05) between the staple types for each time period. The histological response to the polylactic acid staple was minimal over the time period studied, with no adverse tissue reactions observed. The mode of reconstruction failure was observed to change with time (P<0.05) presumably as the graft characteristics alter. Overall the absorbable staples performed at a comparable level with the metallic staples within the scope of the study.

The effect of cranial cruciate ligament insufficiency on caudal cruciate ligament morphology: An experimental study in dogs

OBJECTIVES

To investigate the effect of cranial cruciate ligament (CrCL) insufficiency on morphology of the canine caudal cruciate ligament (CdCL).

STUDY DESIGN

In vivo experimental study.

ANIMALS

Five adult foxhounds.

METHODS

Two years after CrCL transection, the histologic appearance of CdCLs from CrCL-deficient and unoperated contralateral control (CrCL-intact) stifle joints were evaluated using light and transmission electron microscopy.

RESULTS

CdCLs from CrCL-deficient joints had extracellular matrix changes, characterized by chondroid metaplasia and disruption of cell architecture. Percent of small-diameter fibrils in CdCLs from CrCL-deficient joints was significantly greater (P <.05) than that in CdCLs from CrCL-intact joints. Collagen fibril density in CdCLs from CrCL-deficient joints (41.09 +/- 5.39%) tended to be less than that in CdCLs from CrCL-intact joints (52.96 +/- 6.92%); however, this difference was not significant (P =.056). Mean eccentricity (ratio of minor to major diameters) of collagen fibrils was significantly (P <.0001) lower for CdCLs from CrCL-deficient joints (0.85 +/- 0.016) when compared with that for CdCLs from CrCL-intact joints (0.87 +/- 0.015).

CONCLUSIONS

Significant alterations were found in the morphology of CdCLs from CrCL-deficient joints. These changes may be associated with repetitive microtrauma to the CdCL secondary to instability or enzymatic degradation in the hostile synovial environment of an unstable joint.

CLINICAL RELEVANCE

Regardless of the cause, the switch to a predominantly small-diameter collagen fibril profile may reflect compromised material properties of the CdCL. This should be taken into account when considering surgical techniques that rely on the CdCL to stabilize CrCL-deficient stifles.

Denervation impairs healing of the rabbit medial collateral ligament

Little is known about the contribution of innervation to ligament healing after traumatic disruption, although there is good evidence of an important role for the peripheral nervous system in the healing of fractures and skin injuries. Tissues such as ligament, with a low resting blood supply, are dependent on substantial increases in blood flow and vascular volume during the initial stages of repair. We hypothesized that this initial healing response would be strongly promoted by neurogenic inflammation. Since the saphenous nerve (a major sensory branch of the femoral nerve) supplies the medial half of the knee joint, we elected to use femoral nerve transection as a model to determine the role of sensory and autonomic innervation in the initial outcome of repair of the injured medial collateral ligament. Twelve adult, female NZW rabbits underwent right medial collateral ligament transection. Of these, six rabbits underwent right femoral nerve transection to disrupt the somatic sensory and autonomic nerve supply to the knee joint and six were kept neurologically intact (controls). At six weeks post-injury, the animals were assessed by laser Doppler perfusion imaging (LDI) to determine the local blood flow, at both the injury site and at the uninjured contralateral ligament. The animals were then killed, the knee joints were removed and the biomechanical characteristics of the healing bone-median collateral ligament (MCL)-bone complexes assessed. In a separate cohort of 16 rabbits, vascular volumes of the injured ligaments were measured by infusion of a carmine red/gelatin solution. At six weeks post-injury, in vivo measurement of perfusion with LDI revealed that normally innervated ligaments had an almost three-fold higher average blood flow. Carmine red/gelatin infusion revealed a 50% higher density of blood vessels as compared to denervated ligaments. The force required for ultimate failure was found to be 50% higher in normally innnervated MCL's as compared to denervated MCL's: 153.14 +/- 20.71 N versus 101.29 +/- 17.88 N (p < 0.05). Static creep was increased by 66% in denervated MCL's: 2.83 +/- 0.45% versus 1.70 +/- 0.12% (p < 0.05). Total creep was increased by 45% in denervated MCL's: 5.29 +/- 0.62% compared to 3.64 +/- 0.31% in innervated MCL's (p < 0.05). We conclude that intact innervation makes a critical contribution to the early healing responses of the MCL of adult rabbits.

Pregnancy affects cellular activity, but not tissue mechanical properties, in the healing rabbit medial collateral ligament

Recently, evidence has been accumulating that ligament and joint laxity is altered in women and rabbits during pregnancy. Furthermore, many female adolescents injure ligaments through participation in athletics and other activities. Therefore, to determine whether pregnancy has different effects on the injured and uninjured medial collateral ligament of the rabbit knee, we investigated cellular changes (mRNA levels) and alterations in tissue properties (biomechanics) accompanying pregnancy in animals with the medial collateral ligament injured during adolescence and bred for their primigravid pregnancy as young adults. Assessment of mRNA levels for matrix molecules, matrix metalloproteinases and tissue inhibitor of metalloproteinase-1, growth factors and sex hormone receptors, inflammatory cytokines, inducible nitric oxide synthase, and cyclooxygenase-2 by semiquantitative reverse transcription-polymerase chain reaction revealed that pregnancy had different impacts on scar and uninjured tissue for six of 15 genes assessed. A pregnancy-associated increase in laxity of the medial collateral ligament was observed for rabbits in the uninjured primigravida group; however, no increase was observed for injured rabbits during pregnancy. The injured ligament was already significantly more lax than the normal counterpart, and pregnancy did not lead to additional laxity or prevent the normal decline in laxity as the scar matured in nonpregnant animals. These results indicate that the impact of pregnancy on laxity and cell activity of the medial collateral ligament is dependent on whether the ligament is uninjured or injured. Pregnancy had no significant effect on structural (stiffness and failure load), material (stress at failure and Young's modulus), or viscoelastic (cyclic and static relaxation) properties of tissue from uninjured or injured medial collateral ligament. Therefore, the properties of the healing ligament were not adversely affected during pregnancy in this experimental model. However, it remains to be determined if these results with an injured medial collateral ligament can be extrapolated to the injured anterior cruciate ligament.

The early effect of ibuprofen on the mechanical properties of healing medial collateral ligament

We tested the hypothesis that injured ligaments in rabbits treated with ibuprofen would have decreased values of mechanical properties compared with the values of those treated with a placebo. In 24 New Zealand White rabbits, the medial collateral ligament of one hindlimb was ruptured; the contralateral ligament served as an internal control. The rabbits were treated orally, twice daily, with a 14-day course of either 35 mg of ibuprofen per kilogram of body weight or a placebo. The rabbits were sacrificed at 14 or 28 days, and the ligaments were tested in tension to failure at 0.15 mm/sec. There was no statistically significant difference in the values of mechanical properties of ligaments from rabbits treated with ibuprofen versus those treated with placebo at either 14 or 28 days after injury. Our findings suggest that there is no early deleterious effect of a short course of ibuprofen on the mechanical behavior of medial collateral ligaments.

Animal models of tendon and ligament injuries for tissue engineering applications

Improved methods are needed for prevention and treatment of injuries to the musculoskeletal soft tissues. Tissue engineering techniques have led to more effective clinical protocols for treating these injuries. Improvement of tissue healing through the addition of biologic factors, and the development of biologically active tissue engineered replacements, are two promising areas of research. An essential component of progress in this field is the use of animal models of tendon and ligament injuries, which allows for rigorous testing of hypotheses related to disease pathogenesis and treatment. Because these animal models must be appropriate for the condition being studied, no single model exists that is appropriate for all investigations. It generally is necessary to differentiate between tendon and ligament tissues. Furthermore, ligaments should be divided into intraarticular and extraarticular models, whereas tendons should be divided into intrasynovial and extrasynovial models. Other important factors in the appropriate use of an animal model include size of the animal, anatomic features, and techniques available for tissue analysis. The tissues used should be large enough to allow for accurate and reproducible manipulations (injury creation, repair, reconstruction). In addition, it is preferable to use tissues that are amenable to quantitative analysis.

Cytokine-induced tendinitis: a preliminary study in rabbits

This study was designed to determine the effects of a single injection of a species-specific preparation of cytokines into rabbit patellar tendons and to compare the results with a known model of tendinitis, the collagenase-injection model. New Zealand White rabbits were divided into two groups and two time periods (4 and 16 weeks) and injected in the midsubstance of the right patellar tendon with either cytokines or collagenase under ultrasound guidance to confirm intratendinous needle placement. The left patellar tendon was injected with 0.025 ml of saline solution and served as a control. The rabbits were returned to cage activity after injection. At death, two rabbits in each group underwent histological analysis; the remaining eight animals in each time frame were evaluated biomechanically and then biochemically with use of the patella/whole patellar tendon/tibia complex. Histologic results at 4 weeks in the tendons injected with cytokines demonstrated increased cellularity, which was resolving by 16 weeks. The matrix appeared unchanged. The tendons injected with collagenase demonstrated increased angiogenesis of the matrix, hypercellularity, and fibrosis around the tendon at 4 weeks. At 16 weeks, myxoid changes, focal fibrosis, and collagen-bundle disarray with persistent increase in cellularity were noted. Biomechanically, a significant decrease in ultimate load at 16 weeks was seen in the tendons injected with cytokines but no change was seen in cross-sectional area. The tendons injected with collagenase demonstrated a significant increase in cross-sectional area at 4 and 16 weeks compared with those injected with cytokines. Biochemically, there was no significant difference in collagen content between the two groups at 4 or 16 weeks but the tendons injected with collagenase demonstrated a significant increase in crosslinking at 16 weeks. Our conclusion is that the tendons injected with the cytokine preparation represent a model of mild, seemingly reversible tendon injury. The cytokine preparation produces no matrix damage or evidence of collagen degradation and is species specific.

Patellar tendon augmentation after removal of its central third limits joints tissue changes

The central third of the patellar tendon is commonly used to reconstruct the injured anterior cruciate ligament. Some studies have noted changes in joint tissues following this procedure. It has been postulated that these changes may be associated with increased stress on the remaining tendon following harvest of the graft. In our study, the central third of the patellar tendon was excised in three groups of rabbits. The central tendon defects in two of the three groups were fitted with different augmentation devices to augment the host tendon during the healing process. All rabbits followed a daily treadmill exercise regimen for 12 weeks following the operation. Biomechanical testing of the tendon revealed that in nonaugmented tendons the cross-sectional area and the length of the patellar tendon significantly increased 112 and 16%, respectively. There was histological evidence of host-tendon remodeling throughout the cross section and extensive fibrosis in the infrapatellar fat pad. Augmentation of the tendon significantly reduced these changes, with the least change noted in the group with the greatest augmentation. The rabbits with augmentation devices retained tendon dimensions similar to those of the contralateral intact tendon, and tendon remodeling occurred only in the defect area. The rabbits with augmentation devices exhibited little to no fibrosis of the fat pad. Structural properties of augmented and nonaugmented tendons were similar despite the size differences, indicating higher tissue quality in the augmented tendons. This study suggested that complications of the knee joint (i.e., tendon proliferation and fat pad fibrosis) noted after anterior cruciate-ligament reconstruction with the autogenous patellar tendon may be limited by the implantation of an augmentation device.

Inhibition of the Quadriceps Muscles in Patients with Anterior Knee Pain

The present study was aimed at determining muscle inhibition (MI) and knee extensor moments in 42 subjects with unilateral anterior knee pain syndrome. The results were compared to a normal, healthy population with no history of knee injury. Also, the effects of 1 week of a nonsteroidal anti-inflammatory drug (NSAID) on MI and knee extensor moments were tested in a randomized controlled trial. At baseline, the involved leg showed significantly higher MI than the noninvolved leg. In both legs, MI was significantly higher and knee extensor moments lower than the corresponding values of the nonimpaired subjects. There was a direct relationship between knee pain during testing and the extent of MI. Higher MI, in turn, was associated with lower knee extensor moments. The study demonstrated significant MI in the quadriceps muscles of the involved and noninvolved legs of subjects with unilateral anterior knee pain syndrome. The results indicate that the noninvolved leg cannot be considered a normal control for a contralateral injury. NSAIDs did not affect MI or knee extensor moments, despite significantly reducing pain. This finding suggests that factors other than pain are responsible for the MI observed in this specific subject population, or that after removal of pain, more time is required to fully restore muscle function.

Method to assess in vivo knee stability longitudinally in an animal model of ligament injury

The purpose of this study was to develop a method to prospectively quantify passive knee stability in an animal model of joint injury over time. Knee stability is defined here as the amount of translation or rotation of the tibia relative to the femur for a given application of force or moment, respectively. Five animals that had undergone transection of the anterior cruciate ligament and three control animals that had undergone a sham operation were anaesthetized and positioned in a stereotaxic frame. Motion of the tibia relative to the femur was quantified with use of reflective markers secured to modified bone pins and a three-dimensional motion analysis system. External forces and moments in the transverse plane of the tibia were measured with use of force transducers based on a strain-gauge design. Longitudinal measurements of knee stability were made before either sham surgery (control animals) or transection of the ligament (experimental animals), immediately after surgery, and at 2 and 4 months after transection. The results showed that the animals tolerated the procedures well and that systematic measurements could be obtained. The method described here has the practical advantage over cross-sectional experimental designs in that the number of subjects can be decreased while maintaining statistical power and has the further conceptual advantage that individual changes can be accounted for over time.

Quadriceps inhibition following arthroscopy in patients with anterior knee pain

OBJECTIVES: This study was aimed at investigating muscle strength and quadriceps inhibition in patients with unilateral anterior knee pain syndrome. DESIGN: Functional assessments were made before an arthroscopic knee surgery and 6 weeks and 6 months following the surgical intervention. BACKGROUND: Traumatic knee injuries have been associated with severe muscle inhibition of the knee extensor muscles. Muscle inhibition is a serious hindrance in the rehabilitation process and prevents full functional recovery of the affected joint. METHODS: 30 patients participated in the study. Isometric quadriceps strength was measured using a KinCom dynamometer. Muscle inhibition was assessed using the interpolated twitch technique which requires applying a single electrical twitch to the femoral nerve during a maximal isometric knee extensor contraction. Pain was assessed with a 100 mm visual analogue pain scale. RESULTS: Pre-surgery, substantial muscle inhibition and pain was observed in the affected leg compared with the contralateral leg. Over the 6 month period there was a decrease in pain and muscle inhibition, although the decrease in muscle inhibition failed to reach statistical significance. Muscle strength showed a decrease 6 weeks post-surgery followed by an increase 6 months following surgery compared with pre-surgical values. CONCLUSIONS: The arthroscopic intervention was successful in reducing pain in patients with unilateral anterior knee pain syndrome. However, muscle inhibition was still substantial 6 months following surgery and was significantly higher in the affected and contralateral limb than in normal subjects.

Rabbit medial collateral ligament scar weakness is associated with decreased collagen pyridinoline crosslink density

This study was carried out to quantify the potential associations between material strength and both collagen concentration and pyridinoline collagen crosslink density in the healing medial collateral ligament of the rabbit and to compare these parameters with those of normal ligaments. The right hindlimbs of 24 skeletally mature (12-month-old) New Zealand White rabbits were subjected to a standardized 4 mm midsubstance "gap" injury to the medial collateral ligament. The animals were killed in groups of six at postoperative intervals of 3, 6, 14, or 40 weeks, and the femur-medial collateral ligament-tibia complexes were mechanically tested in tension to failure. Subsequent to mechanical testing, the failure sites of the ligaments were assessed for concentrations of hydroxyproline and hydroxylysyl pyridinoline. Nine additional rabbits served as age-matched normal controls. In healing ligaments, normal collagen concentrations were reached in less than 14 weeks, but the hydroxylysyl pyridinoline crosslink densities remained low and were only 45% of the control values after 40 weeks of healing. Similarly, mechanical values remained much less than the controls. Linear regression analysis of data on scar tissue alone showed a moderately strong positive correlation between hydroxyproline concentration and material strength (r2 = 0.51, p = 0.0001) but no correlation between crosslink density and strength of scar tissue. A similar pattern of correlation was obtained between the elastic modulus of the scar tissue and the biochemical variables, but the r2 values were lower.(ABSTRACT TRUNCATED AT 250 WORDS)