Migration and healing of ligament cells under inflammatory conditions

Healing of acute anterior cruciate ligament rupture on MRI and outcomes following non-surgical management with the Cross Bracing Protocol

OBJECTIVE

Investigate MRI evidence of anterior cruciate ligament (ACL) healing, patient-reported outcomes and knee laxity in patients with acute ACL rupture managed non-surgically with the Cross Bracing Protocol (CBP).

METHODS

Eighty consecutive patients within 4 weeks of ACL rupture were managed with CBP (knee immobilisation at 90° flexion in brace for 4 weeks, followed by progressive increases in range-of-motion until brace removal at 12 weeks, and physiotherapist-supervised goal-oriented rehabilitation). MRIs (3 months and 6 months) were graded using the ACL OsteoArthritis Score (ACLOAS) by three radiologists. Mann-Whitney U tests compared Lysholm Scale and ACL quality of life (ACLQOL) scores evaluated at median (IQR) of 12 months (7-16 months) post-injury, and χ2 tests compared knee laxity (3-month Lachman's test and 6-month Pivot-shift test), and return-to-sport at 12 months between groups (ACLOAS grades 0-1 (continuous±thickened ligament and/or high intraligamentous signal) versus ACLOAS grades 2-3 (continuous but thinned/elongated or complete discontinuity)).

RESULTS

Participants were aged 26±10 years at injury, 39% were female, 49% had concomitant meniscal injury. At 3 months, 90% (n=72) had evidence of ACL healing (ACLOAS grade 1: 50%; grade 2: 40%; grade 3: 10%). Participants with ACLOAS grade 1 reported better Lysholm Scale (median (IQR): 98 (94-100) vs 94 (85-100)) and ACLQOL (89 (76-96) vs 70 (64-82)) scores, compared with ACLOAS grades 2-3. More participants with ACLOAS grade 1 had normal 3-month knee laxity (100% vs 40%) and returned to pre-injury sport (92% vs 64%), compared with participants with an ACLOAS grades 2-3. Eleven patients (14%) re-injured their ACL.

CONCLUSION

After management of acute ACL rupture with the CBP, 90% of patients had evidence of healing on 3-month MRI (continuity of the ACL). More ACL healing on 3-month MRI was associated with better outcomes. Longer-term follow-up and clinical trials are needed to inform clinical practice.

Combined effects of tumor necrosis factor-α and interleukin-1β on lysyl oxidase and matrix metalloproteinase expression in human knee synovial fibroblasts in vitro

Previous studies have demonstrated that inflammatory cytokines are associated with matrix metalloproteinases (MMPs) and/or lysyl oxidases (LOXs) produced by anterior cruciate ligament (ACL) fibroblasts, which may contribute to the poor healing ability of the ACL. To evaluate whether the synovium also participates in ACL healing, the inflammatory microenvironment of the knee joint cavity was mimicked following ACL injury, and the combined effects of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) on the expression of MMPs and LOXs in synovial fibroblasts were studied. Cell viability was evaluated using trypan blue staining in the presence of TNF-α and IL-1β, and the expression of LOXs and MMPs was measured by reverse transcription-quantitative polymerase chain reaction. MMP-2 activity was also measured by zymography. The results indicated that the combined effects of TNF-α and IL-1β inhibited LOX expression, while promoting MMP-1, −2 and −3 expression and MMP-2 activity in synovial fibroblasts. These changes may impede healing by altering the balance between the degradative and biosynthetic arms of the ligament tissue remodeling process. Collectively, the present results suggest that the poor healing ability of cruciate ligaments may be due to the sensitivity of the synovium to inflammatory factors. Therefore, the synovium potentially serves a key regulatory role in the joint cavity microenvironment and in the healing process of the ACL, and thus should be considered as a therapeutic target to aid in the treatment of patients with ACL trauma.

Influence of TNF-α and biomechanical stress on matrix metalloproteinases and lysyl oxidases expressions in human knee synovial fibroblasts

PURPOSE

It was reported that not only ACL but also the synovium may be the major regulator of matrix metalloproteinases (MMPs) in synovial fluids after ACL injury. In order to further confirm whether synovium is capable of regulating the microenvironment in the process of ACL injury, the complicated microenvironment of joint cavity after ACL injury was mimicked and the combined effects of mechanical injury and inflammatory factor [tumour necrosis factor-α (TNF-α)] on expressions of lysyl oxidases (LOXs) and MMPs in synovial fibroblasts derived from normal human synovium were studied.

METHODS

Human normal knee joint synovial fibroblasts were stimulated for 1-6 h with mechanical stretch and inflammatory factor (TNF-α). Total RNA was harvested, reverse transcribed and assessed by real-time polymerase chain reaction for the expression of LOXs and MMP-1, 2, 3 messenger RNAs. MMP-2 activity was assayed from the collected culture media samples using zymography.

RESULTS

Compared to control group, our results showed that 6% physiological stretch increased MMP-2 and LOXs (except LOXL-3), decreased MMP-1 and MMP-3; injurious stretch (12%) decreased LOXs (except LOXL-2)and increased MMP-1, 2 and 3; the combination of injurious stretch and TNF-α decreased LOXs and increased MMP-1, 2 and 3 in synovial fibroblasts in a synergistical manner.

CONCLUSION

This study demonstrated that combination of mechanical injury and inflammatory factors up-regulated the expressions of MMPs and down-regulated the expressions of LOXs in synovial fibroblasts, eventually alter the balance of tissue healing. Thus, synovium may be involved in regulating the microenvironment of joint cavity. Based on the mechanism, early interventions to inhibit the production of MMPs or promote the production of LOXs in the synovial fibroblasts should be performed to facilitate the healing of tissue.

The reharvested patellar tendon has the potential for ligamentization when used for anterior cruciate ligament revision surgery

PURPOSE

The aim of the present study was to make an in-depth clinical, radiographical, and histological evaluation of patients who underwent anterior cruciate ligament (ACL) revision surgery with reharvested central third patellar tendon autograft.

METHODS

Four patients (two women and two men) underwent ACL revision surgery with reharvested patellar tendon autograft 71 (66-120) months after the primary reconstruction. The patients were followed prospectively and underwent a clinical examination and magnetic resonance imaging (MRI) at two and 10 years. Furthermore, they underwent a second-look arthroscopy involving a biopsy procedure from the reconstructed ACL 3 years after revision surgery.

RESULTS

The clinical results were poor both at two and 10 years, but the knees were stable and had a firm endpoint in all four patients in the Lachman test. At the second-look arthroscopy, the graft appeared macroscopically normal in all four patients. Histologically two patients had a normal or close to normal appearance of the reconstructed ACL with no or slight increase in cellularity and vascularity. Two patients had a marked increase in cellularity and vascularity, and the findings revealed that ligamentization was present in all four patients.

CONCLUSIONS

The clinical outcome 10 years after ACL revision surgery was poor in these four patients. In contrast, the reharvested patellar tendon appeared close to normal on MRI, and the second-look arthroscopy with the concomitant histological findings revealed that the grafts were viable 3 years after revision. Therefore, the reharvested patellar tendon seems to have the potential for ligamentization when used for ACL revision surgery.

LEVEL OF EVIDENCE

Case series, Level IV.

Differential response to CoCl2-stimulated hypoxia on HIF-1α, VEGF, and MMP-2 expression in ligament cells

The adult human anterior cruciate ligament (ACL) has a poor functional healing response, whereas the medial collateral ligament (MCL) does not. The difference in intrinsic properties of these ligament cells can be due to their different response to their located microenvironment. Hypoxia is a key environmental regulator after ligament injury. In this study, we investigated the differential response of ACL and MCL fibroblasts to hypoxia on hypoxia-inducible factor-1α, vascular endothelial growth factor, and matrix metalloproteinase-2 (MMP-2) expression. Our results show that ACL cells responded to hypoxia by up-regulating the HIF-1α expression significantly as compared to MCL cells. We also observed that in MCL fibroblasts response to hypoxia resulted in increase in expression of VEGF as compared to ACL fibroblasts. After hypoxia treatment, mRNA and protein levels of MMP-2 increased in both ACL and MCL. Furthermore we found in ACL pro-MMP-2 was converted more into active form. However, hypoxia decreased the percentage of wound closure for both ligament cells and had a greater effect on ACL fibroblasts. These results demonstrate that ACL and MCL fibroblasts respond differently under the hypoxic conditions suggesting that these differences in intrinsic properties may contribute to their different healing responses and abilities.

Combined effects of TNF-α, IL-1β, and HIF-1α on MMP-2 production in ACL fibroblasts under mechanical stretch: an in vitro study

The dynamics between inflammatory factors, mechanical stress, and healing factors, in an intra-articular joint, are very complex after injury. Injury to intra-articular tissue [anterior cruciate ligament (ACL), synovium] results in hypoxia, accumulation of various pro-inflammatory factors, cytokines, and metalloproteases. Although the presence of increased amounts of matrix-metalloproteinases (MMP) in the joint fluid after knee injury is considered the key factor for ACL poor healing ability; however, the exact role of collective participants of the joint fluid on MMP-2 activity and production has not been fully studied yet. To investigate the combined effects of mechanical injury, inflammation and hypoxia induced factor-1α (HIF-1α) on induction of MMP-2; we mimicked the microenvironment of joint cavity after ACL injury. The results show that TNF-α and IL-1β elevate the activity of MMP-2 in a dose- and time-dependent manner. In addition, mechanical stretch further enhances the MMP-2 protein levels with TNF-α, IL-1β, and their mixture. CoCl(2) -induced HIF-1α (100 and 500 µM) also increases the levels and activity of MMP-2. Mechanical stretch has a strong additional effect on MMP-2 production with HIF-1α. Our results conclude that mechanical injury, HIF-1α and inflammatory factors collectively induce increased MMP-2 production in ACL fibroblasts, which was inhibited by NF-κB pathway inhibitor (Bay-11-7082).

TGF-β1 promoted MMP-2 mediated wound healing of anterior cruciate ligament fibroblasts through NF-κB

The adult human anterior cruciate ligament (ACL) has poor functional healing response. Transforming growth factor (TGF)-β1 enhances the wound repair by stimulating matrix proteins deposition as well as the proliferation and migration of cells. However, the function of the TGF-β1-induced matrix metalloproteinases' (MMPs) activities in the wound healing process is poorly understood. In this study, exogenous MMP-2 is added to mimic the TGF-β1-induced MMP-2 expression. Role of NF-κB pathway is further examined. Our results show that TGF-β1 induces dramatic elevation of MMP-2 activities and the MMP-2/tissue inhibitors of metalloproteinases ratio. Furthermore, the exogenous MMP-2 significantly promoted in vitro wound healing abilities of ACL fibroblasts that are significantly blocked with the addition of its inhibitors. TGF-β1 also increases the proliferation of ACL fibroblasts whereas MMP-2 alone does not, indicating that MMP-2 activities are not involved in the proliferation. TGF-β1-induced MMP-2 activity is inhibited by Bay11-7082 and Bay11-7085 (NF-κB inhibitors). Our results demonstrate that increased TGF-β1 facilitates the ACL healing process by promoting the fibroblasts migration and proliferation. The migration process is mediated by MMP-2 and NF-κB pathway is involved in TGF-β1-mediated MMP-2 release.

Injury-induced changes in mRNA levels differ widely between anterior cruciate ligament and medial collateral ligament

BACKGROUND

The drastic difference in healing capacity between the anterior cruciate ligament and the medial collateral ligament is still largely unexplained. Few studies have compared the profiles of messenger ribonucleic acid expression for healing-associated molecules in ligaments during the course of healing.

HYPOTHESIS

Injury responses of the injured anterior cruciate ligament and medial collateral ligament are characterized by very different profiles of angiogenesis-promoting and repair-associated gene expression during the healing process.

STUDY DESIGN

Controlled laboratory study.

METHODS

Reverse-transcriptase polymerase chain reaction was used to assay expression of messenger ribonucleic acid for 11 healing- and angiogenesis-associated molecules at 3 days and 2, 6, and 16 weeks after anterior cruciate ligament or medial collateral ligament injury in adult female New Zealand White rabbits.

RESULTS

Marked differences were found in the postinjury changes in messenger ribonucleic acid levels in the anterior cruciate ligament compared to the medial collateral ligament. Notably, messenger ribonucleic acid levels for the important repair-associated growth factor transforming growth factor-beta1 did not increase in injured anterior cruciate ligament at any time point. Similarly, unlike the injured medial collateral ligament, no statistically significant increases in messenger ribonucleic acid levels for the important scar matrix protein collagen III were detected in injured anterior cruciate ligament. In contrast, matrix metalloproteinase messenger ribonucleic acid levels were markedly elevated in injured anterior cruciate ligament but only modestly increased in medial collateral ligament.

CONCLUSION

The results suggest that injury leads to an antifibrotic, catabolic response in the rabbit anterior cruciate ligament, possibly to prevent fibrosis and diminish the risk for loss of joint motion.

CLINICAL RELEVANCE

The development of effective biologically based treatments for anterior cruciate ligament injuries will need to incorporate strategies to deal with the significant differences in the molecular responses to injury of these tissues.

Preliminary effects of hyaluronic acid on early rehabilitation of patients with isolated anterior cruciate ligament reconstruction

OBJECTIVE

To investigate the effects of Hyaluronic acid (HA) on early rehabilitation of patients with isolated anterior cruciate ligament (ACL) reconstruction.

DESIGN

Randomized, controlled clinical trial.

SETTING

A total 120 patients with isolated ACL injury who had received patellar tendon autograft reconstruction were randomly assigned to four groups (groups I-IV), with 30 subjects in each group.

INTERVENTIONS

All patients received 16 weeks of a regular rehabilitation program and an intra-articular injection of HA or saline weekly for 3 weeks. Additionally, patients in group I received the HA commencing at 4 weeks after surgery, patients in group II at 8 weeks, and patients in group III at 12 weeks. Patients in group IV did not receive HA but did receive the same volume of normal saline as control subjects at 4 weeks after surgery. The rehabilitation program started at the same time after surgery for all groups.

MAIN OUTCOME MEASUREMENTS

Outcomes were measured at 4, 8, 12, and 16 weeks after reconstruction, and at follow-up 1 year later. These included the changes in Lysholm knee scoring scale, knee range of motion, ambulation speed (AS), and muscle peak torque (MPT) of knee flexion and extension.

RESULTS

There were improvements in groups I-III shortly after receiving the HA, but not in the saline group (group IV). Patients in groups II and III showed more improvement in AS and MPT after rehabilitation program and at follow-up. Besides, the best results 1 year later occurred in the group receiving HA at 8 weeks after surgery (group II).

CONCLUSION

HA therapy results in more functional and MPT improvement in ACL rehabilitation, and the intervention at 8 weeks after surgery results in the best outcome.

Endothelial dysfunction and decreased vascular responsiveness in the anterior cruciate ligament-deficient model of osteoarthritis

Chronic inflammation associated with osteoarthritis (OA) may alter normal vascular responses and contribute to joint degradation. Vascular responses to vasoactive mediators were evaluated in the medial collateral ligament (MCL) of the anterior cruciate ligament (ACL)-deficient knee. Chronic joint instability and progressive OA were induced in rabbit knees by surgical transection of the ACL. Under halothane anesthesia, laser speckle perfusion imaging (LSPI) was used to measure MCL blood flow in unoperated control (n = 12) and 6-wk ACL-transected knees (n = 12). ACh, bradykinin, histamine, substance P (SP), and prostaglandin E(2) (PGE(2)) were applied to the MCL vasculature in topical boluses of 100 microl (dose range 10(-14) to 10(-8) mol). In normal joints, ACh, bradykinin, histamine, and PGE(2) evoked a dilatory response. Substance P caused a biphasic response that was dilatory from 10(-14) to 10(-11) mol and constricting at higher doses. In ACL-deficient knees, ACh, bradykinin, histamine, and SP decreased perfusion, whereas PGE(2) had a biphasic response that decreased perfusion at 10(-14) to 10(-11) mol and was dilatory at higher concentrations. Sodium nitroprusside increased perfusion in resting and phenylephrine-precontracted vessels with no significant differences between ACL-transected and control knees. Femoral artery occlusion and release increased perfusion by 74.3 +/- 11.1% in control knees but only by 25.8 +/- 4.4% in ACL-deficient knees. The altered responsiveness of the MCL vasculature to these inflammatory mediators may indicate endothelial dysfunction in the MCL, which may contribute to the progression and severity of OA and to the adaptation of the joint in an altered mechanical environment.

Differential sensitivity to NO-induced apoptosis between anterior cruciate and medial collateral ligament cells

It is well known that the anterior cruciate ligament (ACL) of the knee joint has poorer healing responses than the medial collateral ligament (MCL). Nitric oxide (NO) induces free radicals and plays a key role in the induction of apoptosis in various wound-healing models. We hypothesized that the poor healing response of the ACL may be ascribed to high susceptibility to apoptosis, and we investigated the difference in susceptibility to apoptosis between ACL and MCL cells after treatment with sodium nitroprusside, a NO donor. Apoptosis was evaluated by phase contrast microscopy, electron microscopy, DNA gel electrophoresis, and flow cytometric analysis. Although morphological changes and DNA ladders were observed in both ACL and MCL cells after 2 mM sodium nitroprusside treatment, ACL cells were more prone to apoptosis at 1 mM. Based on flow cytometric analysis, DNA fragmentation at 1 mM sodium nitroprusside was significantly greater in ACL cells than in MCL cells (58.6% +/- 1.6% vs. 11.9% +/- 2.2%). Caspase-3 inhibitor (Ac-Asp-Glu-Val-Asp-CHO) and caspase-9 inhibitor (Ac-Leu-Glu-His-Asp-CHO) completely inhibited this DNA fragmentation. In conclusion, the ACL and MCL cells exhibit essential differences, and the differential sensitivity to NO-induced apoptosis between the ACL and MCL cells may be a reflection of these differences.

Enhanced repair of the anterior cruciate ligament by in situ gene transfer: evaluation in an in vitro model

The inability of the ruptured anterior cruciate ligament (ACL) of the knee joint to heal spontaneously presents numerous clinical problems. Here we describe a novel, gene-based approach to augment ACL healing. It is based upon the migration of cells from the ruptured ends of the ligament into a collagen hydrogel laden with recombinant adenovirus. Cells entering the gel become transduced by the vector, which provides a basis for the local synthesis of gene products that aid repair. Monolayers of bovine ACL cells were readily transduced by first-generation, recombinant adenovirus, and transgene expression remained high after the cells were incorporated into collagen hydrogels. Using an in vitro model of ligament repair, cells migrated from the cut ends of the ACL into the hydrogel and were readily transduced by recombinant adenovirus contained within it. The results of experiments in which GFP was used as the transgene suggest highly efficient transduction of ACL cells in this manner. Moreover, during a 21-day period GFP+ cells were observed more than 6 mm from the severed ligament. This distance is ample for the projected clinical application of this technology. In response to TGF-beta1 as the transgene, greater numbers of ACL cells accumulated in the hydrogels, where they deposited larger amounts of type III collagen. These data confirm that it is possible to transduce ACL cells efficiently in situ as they migrate from the ruptured ACL, that transduction does not interfere with the cells' ability to migrate distances necessary for successful repair, and that ACL cells will respond in a suitable manner to the products of the transgenes they express. This permits optimism over a possible clinical use for this technology.

Distribution of substance-P nerve fibers in intact and ruptured human anterior cruciate ligament: a semi-quantitative immunohistochemical assessment

Numerous studies have reported qualitative and quantitative analysis of nerve supply in the anterior cruciate ligament; however, as yet relatively little is known about the distribution of substance-P nerve endings in the human anterior cruciate ligament. The objective of this work was to evaluate the distribution of substance-P nerve fibers in intact human anterior cruciate ligament, and determine if rupture of the ligament has any influence on occurrence of these receptors. The intact anterior cruciate ligament group (group 1) of osteoarthritis knee, undergoing total knee arthroplasty, consisted of nine patients (eight females) with a mean age of 65.3 years at surgery. The anterior cruciate ligament rupture group (group 2) consisted of 20 patients (18 males and 2 females) with a mean age of 27.8 years at reconstruction. Healing time of the torn ligament in vivo, determined by the time period between the rupture and reconstruction, lasted from 1 to 40 months and the patients were divided into 3 groups (I, II and III) embracing diverse time periods. All harvested anterior cruciate ligaments were sectioned in thirds so that there was a proximal, middle and distal third for each ligament. The distribution of nociceptive receptors was studied by immunohistochemistry with monoclonal antibody to substance-P, including the semi-quantitative assessment. No significant difference was found between the number of substance-P nerve fibers in the proximal, middle and distal third of the intact anterior cruciate ligament (p>0.05). During the first 4 months after injury (group I) the mean number of neuropeptide-containing fibers was greater in the proximal than in the distal third (p=0.048996). The number of SP-positive nerve fibers in the proximal third decreased between 5 and 12 months after rupture, in a statistically significant manner (p=0.045864). This study showed that distribution of the nociceptive nerve supply, positively stained for substance-P, is equal among the intact anterior cruciate ligament. The substance-P nerve ending density was significantly affected by the injury as well as by the time since rupture. The results of this study provide immunohistochemical evidence suggesting that between 1 to 4 months after rupture the site of the injury undergoes neurogenic inflammation, which could have an influence on the healing course of the torn ligament.

Periosteal augmentation of a tendon graft improves tendon healing in the bone tunnel

Secure fixation of tendon or ligament to bone has been a challenging problem. The periosteum is an osteogenic organ that regulates bone growth and remodeling at the outer surface of cortical bone and also is known to play an important role in forming a tendon insertion site to bone. Therefore, we hypothesized that a freshly harvested periosteum can be used as a stimulative scaffold to biologically reinforce the attachment of tendon graft to bone. Using a rabbit hallucis longus tendon and calcaneus process model, we found that a periosteal augmentation of a tendon graft could enhance the structural integrity of the tendon-bone interface, when the periosteum is placed between the tendon and bone interface with the cambium layer facing toward the bone. Clinically, the use of an autogenous periosteum patch would be an optimal choice for biologic augmentation of the tendon graft in the bone tunnel, because the tissue is readily available for harvest from the patient's body.

Localization of cytokines in tendinocytes of the superficial digital flexor tendon in the horse

Although inflammatory activation of cytokines have been analyzed in various tissues, there have only been a few and as-yet-inconclusive studies on cytokines in equine tendons. In this study, the localizations of 4 cytokines (IL-1alpha, IL-1beta, TNFalpha and IFNgamma) in tendinocytes of the equine superficial digital flexor tendon (SDFT) were analyzed by the use of an immunohistochemical method. In inflamed tendons positive staining for all 4 cytokines antibodies were detected in endotedinieum cells and vascular epithelial cells. In contrast, negative or trace immunoreactions were obtained in many tendinocytes in the normal tendon. The variation in cellular immune responses depending on the kind of cytokine may reflect the physiological/pathological condition of the SDFT.

Interarticular bone tunnel healing

PURPOSE

To evaluate the healing behavior of an interarticular bone tunnel exposed continuously to a synovial environment.

TYPE OF STUDY

Experimental in vivo animal model.

METHODS

Twenty-six adult rabbits had 3.2-mm diameter tunnels drilled in the femur and tibia of both hind-limb stifle joints parallel to but without violation of the native anterior cruciate ligament (ACL). The animals were euthanized at 1, 2, 4, and 12 weeks postoperatively. Decalcified sections were made of the bone tunnels and new bone formation was computer quantified using histomorphometric methods at each time interval.

RESULTS

In this model, bone tunnel healing velocity was most rapid between 1 and 2 weeks after surgery. Both femoral and tibial interosseous tunnels showed substantial bone ingrowth (71% of bone tunnel volume) by 2 weeks postoperatively. The peripheral tunnel segment, that third of the tunnel furthest from the joint surface, healed rapidly and was 99% occluded with bone (99% confidence interval, 93.7% to 100%) at 2 weeks. Tunnel ingrowth was delayed and incomplete in the articular third of the tunnel, especially the femoral side. At 12 weeks, by volume, only 69.1% (99% confidence interval, 52.3% to 85.7%) of the interarticular third of the femoral tunnel was ingrown with new bone. Peripheral third bone tunnel healing was significantly greater than articular third tunnel healing at all time intervals; P <. 005 for the femoral and P <. 05 for the tibial tunnel.

CONCLUSIONS

Interarticular bone tunnels heal from the outside in. At 12 weeks, bone healing was slower and incomplete in the articular segment of the tunnel, closest to the joint surface. The same biologic factors that impede intersubstance ACL healing may interfere with bone tunnel healing and be another cause of bone tunnel enlargement after ACL reconstruction.

Does nitric oxide help explain the differential healing capacity of the anterior cruciate, posterior cruciate, and medial collateral ligaments?

This study compared the ability of rabbit medial collateral ligament, posterior cruciate ligament, and anterior cruciate ligament tissue to synthesize nitric oxide, and determined its effects on matrix synthesis, an important component of ligament repair. It is not known whether ligament cells can produce nitric oxide and, if so, whether it influences healing of ligament injuries. The anterior cruciate and posterior cruciate ligament tissue produced large amounts of nitric oxide in response to the inflammatory cytokine interleukin-1. Medial collateral ligament, in contrast, produced only modest amounts of nitric oxide. Furthermore, anterior cruciate ligament and, to some degree, posterior cruciate ligament synthesized nitric oxide spontaneously in culture, whereas medial collateral ligament never did so. When nitric oxide was supplied to these tissues, it strongly inhibited collagen synthesis by the two cruciate ligaments, but had little effect on collagen synthesis by the medial collateral ligament. Endogenously synthesized nitric oxide was also able to inhibit collagen synthesis as well as proteoglycan synthesis by the two cruciate ligaments, but had little effect on matrix synthesis by the medial collateral ligament. We propose a novel hypothesis, based on nitric oxide production and matrix synthesis, that may help explain why the two cruciate ligaments have such limited healing capacity compared with the medial collateral ligament.

Novel method for the quantitative assessment of cell migration: a study on the motility of rabbit anterior cruciate (ACL) and medial collateral ligament (MCL) cells

A novel method of quantitating cell migration has been proposed for the potential utilization of tissue engineered scaffolds. Applying Alt's conservation law to describe the motion of first passage ACL and MCL cells, we have developed a quantitative method to assess innate differences in the motility of cells from these two ligamentous tissues. In this study, first passage ACL and MCL cells were cultured from four mature New Zealand white rabbits. One side of the cell monolayer was scraped completely away to create a wound model. The cell moved into the cell-free area, and cell density profiles were analyzed at 6 h and 12 h. Values of the random motility coefficient (mu) were then estimated by curve fitting the 6 h and 12 h data to a mathematical model, derived from the conservation law of cell flux. During 6 h of incubation in medium supplemented with 1% FBS, MCL cells (mu(MCL) = 4.63 +/- 0.65 X 10(-6) mm(2)/sec) were significantly (p < 0.05) more mobile than ACL cells (mu(ACL) = 2.51 +/- 0.31 X 10(-6) mm(2)/sec). At 12 h, the MCL cells also appeared to move faster (mu(ACL) = 4.39 +/- 0.63 X 10(-6) mm(2)/sec, mu(MCL) = 6.59 +/- 1.47 X 10(-6) mm(2)/sec), but the difference was not statistically significant (p = 0.18). Exposure of the cells to growth factors PDGF-BB or bFGF for 6 h had no significant effect on the migration of the ACL and MCL cells. However, exposure of the ACL cells (p < 0.05) and the MCL cells (p = 0.19) to 1 ng/mL of PDGFBB for 12 h enhanced their migration. Incubation with a high concentration (100 ng/mL) of PDGF-BB or bFGF at concentrations tested (1 or 100 ng/mL) for 12 h, produced little or no migratory stimulation on these ligament cells. Our findings support the previous qualitative observations made by numerous investigators. The novel methodology developed in this study may provide a basis for tissue engineering, and the results may be applied to tissue reconstruction techniques of the knee ligaments.

Omega-3 fatty acids enhance ligament fibroblast collagen formation in association with changes in interleukin-6 production

Altering dietary ratios of n-3 and n-6 polyunsaturated fatty acids (PUFA) represents an effective nonpharmaceutical means to improve systemic inflammatory conditions. An effect of PUFA on cartilage and bone formation has been demonstrated, and the purpose of this study was to determine the potential of PUFA modulation to improve ligament healing. The effects of n-3 and n-6 PUFA on the in vitro healing response of medial collateral ligament (MCL) fibroblasts were investigated by studying the cellular coverage of an in vitro wound and the production of collagen, PGE2, IL-1, IL-6, and TNF. Cells were exposed to a bovine serum albumin (BSA) control or either eicosapentaenoic acid (EPA, 20:5n-3) or arachidonic acid (AA, 20:4n-6) in the form of soaps loaded onto BSA for 4 days and wounded on Day 5. AA and EPA improved the healing of an in vitro wound over 72 hr. EPA increased collagen synthesis and the overall percentage of collagen produced, but AA reduced collagen production and total protein. PGE2 production was increased in the AA-treated group and decreased in the EPA-treated group, but was not affected by wounding. IL-1 was not produced at the time point evaluated, but TNF and IL-6 were both produced, and their levels varied relative to the PUFA or wounding treatment. There was a significant linear correlation (r2 = 0.57, P = 0.0045) between IL-6 level and collagen production. These results demonstrate that n-3 PUFA (represented by EPA in this study) positively affect the healing characteristics of MCL cells and therefore may represent a possible noninvasive treatment to improve ligament healing. Additionally, these results show that MCL fibroblasts produce PGE2, IL-6, and TNF and that IL-6 production is related to MCL collagen synthesis.

Current trends in anterior cruciate ligament reconstruction. Part 1: Biology and biomechanics of reconstruction

With today's increasing emphasis on sporting activities, the incidence of anterior cruciate ligament injuries has also increased. Epidemiologic studies estimate that the prevalence of anterior cruciate ligament injuries is about 1 per 3000 Americans. Management of these injuries has evolved from nonoperative treatment to extracapsular augmentation and primary ligament repair to anterior cruciate ligament reconstruction. Treatment of these injuries has significantly improved over the last few decades with the application of knowledge gained from both basic science and clinical research. This article is composed of two parts. The first part reviews the biology and biomechanics of the injured anterior cruciate ligament and the basic science of reconstruction. In the second part, to be published later, current operative concepts of reconstruction, as well as clinical correlations, are reviewed. Summarizing the latest information on basic scientific as well as clinical studies regarding the anterior cruciate ligament, this article intends to demonstrate the correlation between the application of basic science knowledge and improvement of clinical outcomes.

Ligament tissue engineering using synthetic biodegradable fiber scaffolds

Tissue engineering offers the possibility of replacing damaged human ligaments with engineered ligament tissues. Hence, we attempted to culture in vitro ligament tissues by seeding human anterior cruciate ligament (ACL) and medial collateral ligament (MCL) cells onto synthetic biodegradable polymer fiber scaffolds. The ACL and MCL cells readily attached to the scaffold fibers. These cells and their secreted matrix soon surrounded the scaffold fibers and bridged the gaps in between. Beginning at 2 weeks, portions of the scaffolds were completely filled with tissue matrix. By 5 weeks, the scaffolds became single bundles of tissue. Thus the cell/fiber system appears to be a viable system for culturing ligament tissues. Additionally, cell proliferation under mechanical and biochemical stimuli was studied for up to 4 days. Whereas mechanical stimulus and transforming growth factor enhanced proliferation, inflammatory agents (lipopolysaccharide and complement C5a) had a negative effect. This work can thus contribute to a sound strategy for culturing replacement ligament tissues in vitro.

PT-12, a putative ras-activated proliferation-dependent gene, is expressed in patellar tendon and not in anterior cruciate ligament

We describe a gene (PT-12) that is expressed in the patellar tendon and not in the anterior cruciate ligament. We used a recently developed polymerase chain reaction-based subtractive cDNA analysis to discover genes that are overexpressed in the patellar tendon but not expressed in the anterior cruciate ligament; the long-term objective was to find genes that are central to the self-repair of the patellar tendon, in contrast with the inability of the anterior cruciate ligament to launch a repair response following injury. PT-12 is a homologue of human S2 or mouse LLRep3 ribosomal genes, which are known to be overexpressed in highly proliferating cells. This study opens a new vista to the development of techniques and reagents to study the differences between two periarticular tissues (i.e., the patellar tendon and anterior cruciate ligament) that differ primarily in their ability to self-repair.

Adhesion strength differential of human ligament fibroblasts to collagen types I and III

Fibroblasts embedded in the amorphous healing tissue matrix of ligaments migrate into damaged sites during the inflammatory process that precedes the formation of new connective tissue after ligament injury. Cell motility involved in this migration is strongly influenced by cellular adhesion to proteins of the extracellular matrix. The adhesion mechanism of interest in this study is the attachment of fibroblasts from the anterior cruciate and medial collateral ligaments to types I and III collagen, two fibrillar collagens secreted by fibroblasts during tissue repair. Types I and III collagen constitute a major portion of these ligaments and are assembled by fibroblasts into long cable-like fibrils in the extracellular space. In this study, a micropipette aspiration technique was used to measure the force required to separate fibroblasts of the anterior cruciate and medial collateral ligaments from substrates composed of type I or III collagen, each at a concentration of 2 or 5 microg/ml. Approximately 1,200 fibroblasts from the anterior cruciate ligament and 1,600 from the medial collateral ligament were used, and the adhesion force and area of these cells were determined. Fibroblasts from the anterior cruciate ligament exhibited greater adhesion force than did those from the medial collateral ligament for all concentrations of types I and III collagen. In addition, the adhesiveness of fibroblasts from both ligaments was dependent on seeding time for all experimental conditions. To determine the adhesiveness per unit area, defined here as the adhesion strength, the adhesion force was normalized by the adhesion area. At early seeding times (15-45 minutes), fibroblasts from the anterior cruciate ligament exhibited greater adhesion strength on surfaces coated with type-I collagen than did those from the medial collateral ligament. However, for both collagen substrates, adhesion strength for fibroblasts from the anterior cruciate ligament decreased with seeding time whereas that for fibroblasts from the medial collateral ligament remained relatively constant for all seeding periods (15-75 minutes).

Cytokines and the role they play in the healing of ligaments and tendons

Cytokines are small proteins with the properties of locally acting hormones. They are essential for the healing of connective tissues following injury. Various cytokines are expressed endogenously during the healing responses of those ligaments and tendons which possess them, and there is evidence that the exogenous application of certain cytokines promotes healing. Because healing is a multistep process, several different cytokines may need to be applied at different times to achieve a satisfactory response. Sustained, localised delivery of the appropriate cytokines presents a technical challenge to their clinical use in the repair of ligaments and tendons. Slow release devices and gene transfer are being evaluated as strategies for obviating this limitation.