Comparison of Clinical and Biomechanical Outcomes between Partial Fibulectomy and Drug Conservative Treatment for Medial Knee Osteoarthritis.

BACKGROUND: Upper partial fibulectomy has been preliminarily proved to have the efficacy for pain alleviation and improvement of function in patients with mild to moderate medial compartment knee osteoarthritis (KOA). However, the previous studies lack the control group with other treatments. The aim of this prospective, randomized controlled study is to compare the clinical and biomechanical effects between upper partial fibulectomy and drug conservative treatment on improvement of clinical pain, function, and gait for patients with mild to moderate medial knee osteoarthritis (KOA) and further discuss its biomechanical mechanism. METHODS: From August 2016 to February 2017, 49 and 48 patients with mild to moderate medial KOA were allocated to fibulectomy and drug groups. We assessed the patients' visual analog scale (VAS) pain score, Hospital for Special Surgery (HSS) knee score, limb alignment, passive flexion/extension range of motion (ROM) of the knee, and 3D gait kinematics and kinetics parameters before and after intervention. Repeated-measures ANOVA with Dunnett's post hoc assessment and multivariate analysis of variance were applied for intragroup and intergroup comparisons, respectively. RESULTS: The improvement in the fibulectomy group on the VAS pain score, HSS knee score, walking speed, and walking knee range of motion (ROM) was statistically better than that in the drug group. The decreased overall peak knee adduction moment (KAM) (decreased by 16.1%) and hip-knee-ankle (HKA) angle (decreased by 0.99° from a more varus alignment to a more neutral alignment) of the affected and operated side 1 year after surgery were observed in the fibulectomy group. CONCLUSION: This research demonstrated that as a biomechanical intervention, upper partial fibulectomy can be a better choice in pain relief and function and gait improvement than drug conservative treatment for patients with early-stage knee OA. The long-term clinical outcomes, indication, and rationale for the improvement in clinical symptoms should be investigated further.

Microparticles Locally Deliver Active Interleukin-1 Receptor Antagonist In Vivo.

Despite significant research in therapeutic protein delivery, localized and sustained delivery of active therapeutic proteins remains a challenge. Delivery is a particular challenge for therapeutic proteins with a short half-life. Herein, localized delivery of interleukin-1 receptor antagonist (IL-1Ra) by mineral coated microparticles (MPs) is assessed in a healing rat medial collateral ligament (MCL). The local tissue concentration and systemic serum concentration of IL-1Ra, the anti-inflammatory activity of IL-1Ra delivered with MPs, and whether IL-1Ra loaded MPs (IL-1Ra MPs) are immunogenic in a healing ligament are also examined. IL-1Ra MPs significantly increase the local concentration of IL-1Ra compared to soluble IL-1Ra at 7 and 14 days after treatment but do not elevate the systemic concentration of IL-1Ra at these time points, indicating localized delivery of IL-1Ra. IL-1Ra MPs significantly reduce inflammation caused by the MPs themselves, indicating the IL-1Ra is active. Finally, IL-1Ra MPs do not induce a foreign body response and decrease the immunogenicity of human IL-1Ra in a healing rat MCL. Overall, mineral coated microparticles have the ability to locally deliver active therapeutic proteins for an extended period of time.

Skeletal ligament healing using the recombinant human amelogenin protein.

Injuries to ligaments are common, painful and debilitating, causing joint instability and impaired protective proprioception sensation around the joint. Healing of torn ligaments usually fails to take place, and surgical replacement or reconstruction is required. Previously, we showed that in vivo application of the recombinant human amelogenin protein (rHAM(+)) resulted in enhanced healing of the tooth-supporting tissues. The aim of this study was to evaluate whether amelogenin might also enhance repair of skeletal ligaments. The rat knee medial collateral ligament (MCL) was chosen to prove the concept. Full thickness tear was created and various concentrations of rHAM(+), dissolved in propylene glycol alginate (PGA) carrier, were applied to the transected MCL. 12 weeks after transection, the mechanical properties, structure and composition of transected ligaments treated with 0.5 µg/µl rHAM(+) were similar to the normal un-transected ligaments, and were much stronger, stiffer and organized than control ligaments, treated with PGA only. Furthermore, the proprioceptive free nerve endings, in the 0.5 µg/µl rHAM(+) treated group, were parallel to the collagen fibres similar to their arrangement in normal ligament, while in the control ligaments the free nerve endings were entrapped in the scar tissue at different directions, not parallel to the axis of the force. Four days after transection, treatment with 0.5 µg/µl rHAM(+) increased the amount of cells expressing mesenchymal stem cell markers at the injured site. In conclusion application of rHAM(+) dose dependently induced mechanical, structural and sensory healing of torn skeletal ligament. Initially the process involved recruitment and proliferation of cells expressing mesenchymal stem cell markers.

Elastin governs the mechanical response of medial collateral ligament under shear and transverse tensile loading.

Elastin is a highly extensible structural protein network that provides near-elastic resistance to deformation in biological tissues. In ligament, elastin is localized between and along the collagen fibers and fascicles. When ligament is stretched along the primary collagen axis, elastin supports a relatively high percentage of load. We hypothesized that elastin may also provide significant load support under elongation transverse to the primary collagen axis and shear along the collagen axis. Quasi-static transverse tensile and shear material tests were performed to quantify the mechanical contributions of elastin during deformation of porcine medial collateral ligament. Dose response studies were conducted to determine the level of elastase enzymatic degradation required to produce a maximal change in the mechanical response. Maximal changes in peak stress occurred after 3h of treatment with 2U/ml porcine pancreatic elastase. Elastin degradation resulted in a 60-70% reduction in peak stress and a 2-3× reduction in modulus for both test protocols. These results demonstrate that elastin provides significant resistance to elongation transverse to the collagen axis and shear along the collagen axis while only constituting 4% of the tissue dry weight. The magnitudes of the elastin contribution to peak transverse and shear stress were approximately 0.03 MPa, as compared to 2 MPa for axial tensile tests, suggesting that elastin provides a highly anisotropic contribution to the mechanical response of ligament and is the dominant structural protein resisting transverse and shear deformation of the tissue.

Effect of elastin digestion on the quasi-static tensile response of medial collateral ligament.

Elastin is a structural protein that provides resilience to biological tissues. We examined the contributions of elastin to the quasi-static tensile response of porcine medial collateral ligament through targeted disruption of the elastin network with pancreatic elastase. Elastase concentration and treatment time were varied to determine a dose response. Whereas elastin content decreased with increasing elastase concentration and treatment time, the change in peak stress after cyclic loading reached a plateau above 1 U/ml elastase and 6 h treatment. For specimens treated with 2 U/ml elastase for 6 h, elastin content decreased approximately 35%. Mean peak tissue strain after cyclic loading (4.8%, p ≥ 0.300), modulus (275 MPa, p ≥ 0.114) and hysteresis (20%, p ≥ 0.553) were unaffected by elastase digestion, but stress decreased significantly after treatment (up to 2 MPa, p ≤ 0.049). Elastin degradation had no effect on failure properties, but tissue lengthened under the same pre-stress. Stiffness in the linear region was unaffected by elastase digestion, suggesting that enzyme treatment did not disrupt collagen. These results demonstrate that elastin primarily functions in the toe region of the stress-strain curve, yet contributes load support in the linear region. The increase in length after elastase digestion suggests that elastin may pre-stress and stabilize collagen crimp in ligaments.

The effect of platelet-rich plasma on normal soft tissues in the rabbit.

BACKGROUND: Platelet-rich plasma is reported to contain multiple growth factors, and has been utilized in orthopaedic surgery to aid healing in multiple tissues. To date, the use of autologous platelet-rich plasma has not been studied for its effects on normal soft tissue. METHODS: Eighteen adult New Zealand White rabbits were injected with 0.5 mL of autologous platelet-rich plasma in the right or left quadriceps muscle, Achilles tendon, medial collateral ligament, subcutaneous tissue, tibial periosteum, and ankle joint. Saline solution was injected on the contralateral side as a control. The soft tissues were examined histologically at two weeks (six rabbits) and six weeks (six rabbits), and soft tissues from six rabbits that had been reinjected at six weeks were examined at twelve weeks. RESULTS: Inflammatory skin lesions were visible at forty-eight hours at superficial platelet-rich plasma sites. All lesions resolved by six days. Compared with findings in control specimens, histological analysis of platelet-rich plasma injection sites at two weeks showed a marked inflammatory infiltrate with lymphocytic and monocytic predominance. Intra-articular injection showed villous synovial hyperplasia and chronic synovitis. Tendon and ligament sites showed new collagen deposition. Intramuscular injection sites showed thrombosis, necrosis, and calcium deposition. Subcutaneous sites also showed calcium deposition without necrosis as well as collagen nodules representing early scar tissue. Histological examination of platelet-rich plasma injection sites at six and twelve weeks demonstrated a persistent but diminished inflammatory infiltrate. Focal areas of scar tissue were seen with fibroblasts, collagen formation, and neovascularity. All saline solution sites at all times were nonreactive. CONCLUSIONS: Platelet-rich plasma can initiate an inflammatory response in the absence of an inciting injury in normal soft tissue in rabbits.

The influence of interleukin-4 on ligament healing.

Despite a complex cascade of cellular events to reconstruct the damaged extracellular matrix, ligament healing results in a mechanically inferior scarred ligament. During normal healing, granulation tissue expands into any residual normal ligamentous tissue (creeping substitution), resulting in a larger region of healing, greater mechanical compromise and an inefficient repair process. To control creeping substitution and possibly enhance the repair process, the antiinflammatory cytokine, interleukin-4 (IL-4), was administered to rats before and after rupture of their medial collateral ligaments. In vitro experiments showed a time-dependent effect on fibroblast proliferation after IL-4 treatment. In vivo treatments with IL-4 (100 ng/mL IV) for 5 days resulted in decreased wound size and type III collagen and increased type I procollagen, indicating a more regenerative early healing in response to the IL-4 treatment. However, continued treatment of IL-4 to day 11 antagonized this early benefit and slowed healing. Together, these results suggest that IL-4 not only influences the macrophages and T lymphocytes but also stimulates fibroblasts associated with the proliferative phase of healing in a dose-, cell-, and time-dependent manner. Although treatment significantly influenced healing in the first week after injury, IL-4 alone was unable to maintain this early regenerative response.

Combined use of bFGF and GDF-5 enhances the healing of medial collateral ligament injury.

Basic fibroblast growth factor (bFGF) and growth and differentiation factor (GDF)-5 stimulate the healing of medial collateral ligament (MCL) injury. However, the effect of isolated and combined use of bFGF/GDF-5 remains still unclear. We investigated cellular proliferation and migration responding to bFGF/GDF-5 using rabbit MCL fibroblasts. Rabbit MCL injury was treated by bFGF and/or GDF-5 with peptide hydrogels. Gene expression and deposition of collagens in healing tissues were evaluated. bFGF/GDF-5 treatment additively enhanced cell proliferation and migration. bFGF/GDF-5 hydrogels stimulated Col1a1 expression without increasing Col3a1 expression. Combined use of bFGF/GDF-5 stimulated type I collagen deposition and the reorganization of fiber alignment, and induced better morphology of fibroblasts in healing MCLs. Our study indicates that combined use of bFGF/GDF-5 might enhance MCL healing by increasing proliferation and migration of MCL fibroblasts, and by regulating collagen synthesis and connective fiber alignment.

Pentadecapeptide BPC 157 (PL 14736) improves ligament healing in the rat.

We improved medial collateral ligament (MCL) healing throughout 90 days after surgical transection. We introduced intraperitoneal, per-oral (in drinking water) and topical (thin cream layer) peptide therapy always given alone, without a carrier. Previously, as an effective peptide therapy, stable gastric pentadecapeptide BPC 157 (GEPPPGKPADDAGLV, an anti-ulcer peptide effective in inflammatory bowel disease therapy (PL 14736)) particularly improved healing of transected tendon and muscle and wound healing effect including the expression of the early growth response 1 (egr-1) gene. After MCL transection BPC 157 was effective in rats when given once daily intraperitoneally (10 microg or 10 ng/kg) or locally as a thin layer (1.0 microg dissolved in distilled water/g commercial neutral cream) at the site of injury, first application 30 min after surgery and the final application 24 h before sacrifice. Likewise, BPC 157 was effective given per-orally (0.16 microg/ml in the drinking water (12 ml/day/rat)) until sacrifice. Commonly, BPC 157 microg-ng-rats exhibited consistent functional, biomechanical, macroscopic and histological healing improvements. Thus, we suggest BPC 157 improved healing of acute ligament injuries in further ligament therapy.

Neural stimulation does not mediate attenuated vascular response in ACL-deficient knees: potential role of local inflammatory mediators.

Chronic inflammation associated with osteoarthritis (OA) alters normal responses and modifies the functionality of the articular vasculature. Altered responsiveness of the vasculature may be due to excessive neural activity associated with chronic pain and inflammation, or from the production of inflammatory mediators which induce vasodilation. Using laser speckle perfusion imaging (LSPI), blood flow to the medial collateral ligament (MCL) of adult rabbits was measured in denervated ACL transected knees (n = 6) and compared to unoperated control (n = 6) and 6-week anterial cruciate ligament (ACL)-transected knees (n = 6). Phenylephrine and neuropeptide Y were applied to the MCL vasculature in topical boluses of 100 microL (dose range 10(-14) to 10(-8) mol and 10(-14) to 10(-9) mol, respectively). Denervation diminished vasoconstrictive responsiveness to phenylephrine compared to both control and ACL-transected knees. Denervation minimally enhanced vascular responses to neuropeptide Y (NPY) compared to ACL deficiency alone, which nevertheless remained significantly diminished from control responses. To evaluate the potential role of inflammatory dilators in the diminished contractile responses, phenylephrine was coadministered with histamine, substance P, and prostaglandin E(2). High-dose histamine, and low-dose substance P and PGE(2) were able to inhibit contractile responses in the MCL of control knees. Excessive neural input does not mediate diminished vasoconstrictive responses in the ACL transected knee; inflammatory mediators may play a role in the deficient vascular responsiveness of the ACL transected knee.

Systemic vanadate ingestion improves early medial collateral ligament repair.

The medial collateral ligament (MCL) of the knee is frequently injured in sport. Repair is slow and often complicated by scar formation which may result in impairment of function. Vanadate is a promising efficacious treatment for tissue injuries and this study aimed to examine its effect in rats on the histological and biomechanical features of MCL healing. Rats received either 0.025 g/kg per day vanadate or equivalent amounts of drinking water (control) by intragastric gavage for 1 week before and 2 weeks after wounding. Repaired sites were dissected out for histological and biomechanical tests 28 days after wounding. Fibre bundles in the vanadate-treated group were uniform and evenly spaced. Furthermore, vanadate significantly increased the diameter of collagen fibrils in the healing tissue. Stiffness and ultimate force of the femur-medial collateral ligament-tibia complex for the vanadate-treated group were significantly higher than for the controls. The results suggest that vanadate significantly improves the histological and biomechanical properties of healing MCL.

Effect of dermatan sulfate glycosaminoglycans on the quasi-static material properties of the human medial collateral ligament.

The glycosaminoglycan of decorin, dermatan sulfate (DS), has been suggested to contribute to the mechanical properties of soft connective tissues such as ligaments and tendons. This study investigated the mechanical function of DS in human medial collateral ligaments (MCL) using nondestructive shear and tensile material tests performed before and after targeted removal of DS with chondroitinase B (ChB). The quasi-static elastic material properties of human MCL were unchanged after DS removal. At peak deformation, tensile and shear stresses in ChB treated tissue were within 0.5% (p>0.70) and 2.0% (p>0.30) of pre-treatment values, respectively. From pre- to post-ChB treatment under tensile loading, the tensile tangent modulus went from 242+/-64 to 233+/-57 MPa (p=0.44), and tissue strain at peak deformation went from 4.3+/-0.3% to 4.4+/-0.3% (p=0.54). Tissue hysteresis was unaffected by DS removal for both tensile and shear loading. Biochemical analysis confirmed that 90% of DS was removed by ChB treatment when compared to control samples, and transmission electron microscopy (TEM) imaging further verified the degradation of DS by showing an 88% reduction (p<.001) of sulfated glycosaminoglycans in ChB treated tissue. These results demonstrate that DS in mature knee MCL tissue does not resist tensile or shear deformation under quasi-static loading conditions, challenging the theory that decorin proteoglycans contribute to the elastic material behavior of ligament.

[Effect of platelet derived growth factor BB on healing of medial collateral ligament in rats].

OBJECTIVE: To examine an effect of the locally-used platelet derived growth factor-BB (PDGF-BB) on the healing of the medial collateral ligament (MCL) in the knee joints of rats. METHODS: Forty-eight rats were equally randomly divided into 2 groups: the experimental group (group A) and the control group (group B). MCL of all the rats were ruptured to establish the wound models. In group A, 5 microg of PDGF-BB was locally injected in the wound of each rat and then the wound was sutured; but in group B, the wound was only sutured. After 2 weeks, histological evaluations were performed to determine whether PDGF-BB could promote the healing of MCL. RESULTS: There were significantly more fibroblasts formed during the ligament healing process in group A than in group B (213.44 +/- 15.32 vs. 180.42 +/- 12.78, P < 0.01). The fibroblasts were more mature and more regularly-arranged in group A than in group B. The type, content, and crosslink of the collagen were improved to a greater extent in group A than in group B (P < 0.01). CONCLUSION: PDGF can promote the healing of the injured ligament.

Effect of cyclic strain and plating matrix on cell proliferation and integrin expression by ligament fibroblasts.

The role of cell surface integrins in cell migration, proliferation, and attachment to matrix molecules is well known. Integrin-matrix interactions have been implicated in mechanotransduction and load transmission from the outside to the inside of the cell. In this study, the effect of cyclic strain on the cell proliferation, attachment, and expression of integrin subunits beta1, beta3, and alpha5 was determined in anterior cruciate ligament (ACL) and medial collateral ligament (MCL) fibroblasts grown on polystyrene, Type I collagen, laminin, elastin, and fibronectin. ACL fibroblast proliferation was not affected by growth substrate whereas MCL cells reached confluence more rapidly on fibronectin compared with collagen or polystyrene. Exposure to 5% cyclic strain resulted in a significant decrease in ACL and MCL fibroblast proliferation on fibronectin and Type I collagen. MCL cells showed a greater strain-dependent inhibition of cells grown on a fibronectin substrate than those grown on collagen. This matrix-dependent effect of strain on cell proliferation was not seen with ACL cells. Attachment of ACL and MCL fibroblasts was stronger to fibronectin compared with Type I collagen, laminin, and polystyrene. In the absence of applied load, the expression of beta1, beta3, and alpha5 subunits was not substrate dependent and the expression of beta1 and alpha5 integrin subunits was higher in MCL cells than ACL cells on all substrates. In contrast, the expression of beta3 integrin subunit was higher in ACL cells than MCL cells. In response to 5% strain, beta1, and alpha5 expression increased in all fibroblasts with MCL cells having a higher magnitude of expression. beta3 expression showed a 90% increase in response to load when grown on laminin for both MCL and ACL fibroblasts and demonstrated no change in expression on Type I collagen or fibronectin. The duration of applied strain from 2 versus 22 h had no effect on cell proliferation or integrin expression.

The healing rabbit medial collateral ligament of the knee responds to systemically administered glucocorticoids differently than the uninjured tissues of the same joint or the uninjured MCL: a paradoxical shift in impact on specific mRNA levels and MMP-13 protein expression in injured tissues.

The impact and molecular mechanism of action of glucocorticoids in connective tissues is largely unclear, even though widely used, and whether factors such as injury and inflammation modulate this response has not been elucidated. This study describes the role of glucocorticoids in the regulation of mRNA levels for collagens I and III, MMP-13, biglycan, decorin, COX-2 and the glucocorticoid receptor in connective tissues of normal and injured joints in an established rabbit in vivo MCL scar model, and examines the potential mechanism(s) involved. In vitro promoter studies were performed using an MMP-13 promoter-luciferase expression construct in transient transfection assays with a rabbit synovial cell line (HIG-82) to identify sites of glucocorticoid-mediated transcriptional regulation and the promoter elements involved. The in vivo results indicate that scar tissue from different phases of healing (early inflammatory, granulation tissue and neovascular, and later remodelling phases, respectively) displays a different pattern of responsiveness to glucocorticoid treatment than uninjured tissue and that this responsiveness is gene dependent. The most significant impact was seen for genes such as collagen I, collagen III and MMP-13, all of which are involved in connective tissue structure and remodelling. The in vitro studies confirmed the apparent in vivo glucocorticoid-mediated response of MMP-13 mRNA and implicated the AP-1 site of the MMP-13 promoter in this regulation. Immunohistochemistry studies showed increased MMP-13 protein expression, consistent with the mRNA findings, following glucocorticoid treatment in injured tissue but not normal tissues. In conclusion, connective tissue responsiveness to glucocorticoid treatment varies depending on injury and the stage of healing of the tissue, and consequently, glucocorticoid-responsiveness may be modulated differently in states of injury and inflammation.

Herbal remedies improve the strength of repairing ligament in a rat model.

Herbal remedies have been reported to be effective in controlling inflammation for acute soft tissue injuries. There exist, however, no reports of their effects on collagen production and remodeling; thus mechanical strength studies of the tissues have not been reported. This study tested the effects of a herbal remedy on the strength of healing medial collateral ligaments (MCL) in rats. Sixteen rats receiving surgical transection to their right MCLs and eight receiving sham operation were tested. Eight of the MCL-injured animals were treated with an adhesive herbal plaster application to their right knees, while the other eight in the MCL injured group and the sham group were treated with plain adhesive plaster to their right knees. The MCLs were harvested and tested at either 3 or 6 weeks post-operation. The ultimate tensile strength (UTS) and stiffness normalized to the uninjured side of each animal of the herb and sham groups were significantly larger than those of the control at both 3 and 6 weeks (p = 0.001). No significant difference was found in stiffness between the herb and sham groups (p > 0.05). We concluded that the herbal remedy improves the UTS and stiffness of repairing MCLs at 3 and 6 weeks after injury.

Effects of herbal application on the ultrastructural morphology of repairing medial collateral ligament in a rat model.

The present study investigated the effects of an external herbal application on the ultrastructural morphology of repairing medial collateral ligament (MCL) in a rat model. Eight MCL-transected/herb-treated rats (group 1) were compared with 8 MCL-transected/placebo-treated controls (group 2) and 8 MCL-intact/placebo-treated rats (group 3). At 3 and 6 weeks posttransection, MCL specimens were examined under electron microscope. With analysis of 370,709 collagen fibrils, all herb-treated animals had significantly larger fibrils than the controls (p < .001) at 6 weeks postinjury. The mean diameter of those peripheral collagen fibrils of group 1 was larger than the sham group (p < .001). The mass-averaged diameters of group 1 (50.49 to 143.07 nm) and group 3 (59.69 to 188.88 nm) were larger than group 2 (50.59 to 121.94 nm). The area coverage by collagen fibrils ranged from 46.86 to 94.97% for group 1 and 43.70 to 68.08%f or group 3 as compared with 40.01 to 50.77% for group 2. Mode obliquity was 0.56 to 0.84 among groups. We concluded that herbal remedy increases collagen fibril size of healing rat MCLs homogeneously at 6 weeks posttransection.

The influence of a cyclooxygenase-1 inhibitor on injured and uninjured ligaments in the rat.

BACKGROUND: Results of previous studies have shown that piroxicam, a cyclooxygenase-1-2 inhibitor, improves the strength of healing ligaments, whereas celecoxib, a cyclooxygenase-2 inhibitor, impairs ligament healing. HYPOTHESIS: The selective cyclooxygenase-1 inhibitor, SC-560, will improve the strength of ligament healing in an in vivo rat model. STUDY DESIGN: Controlled laboratory study. METHODS: Eighty male Sprague-Dawley rats underwent surgical transection of their medial collateral ligament. Postoperatively, 20 rats were given SC-560 at a low dose and 20 at a high dose for the first 6 days of recovery; the other 40 received a normal diet. The animals were sacrificed 14 days later, and both the injured and uninjured ligaments were mechanically tested to failure in tension. RESULTS: No significant differences in the strength of injured ligaments were found between drug and placebo treatment. However, the contralateral uninjured ligaments in the SC-560-treated groups failed at 27% higher energy and 22% higher load. CONCLUSIONS: This cyclooxygenase-1 inhibitor did not improve the strength of ligament healing but did significantly improve the strength of the contralateral uninjured ligament. CLINICAL RELEVANCE: A pure cyclooxygenase-1 inhibitor is probably not indicated as a positive influence on ligament healing but might provide benefits in ligament injury prevention.

Lack of hormonal influences on mechanical properties of sheep knee ligaments.

BACKGROUND: The number of anterior cruciate ligament injuries in female athletes exceeds that in male athletes at similar competitive levels. This difference has been attributed by some authors to hormone-mediated alteration in knee laxity in women. HYPOTHESIS: Sheep anterior cruciate and medial collateral ligament strength and stiffness are not altered by administration for 6 months of estrogen or a selective estrogen receptor agonist (raloxifene). STUDY DESIGN: Controlled laboratory study. METHODS: Thirty-eight mature ewes were divided into five groups: sham operation (N = 6), ovariectomy (N = 9), ovariectomy and estradiol implant (N = 7), low-dose raloxifene (N = 9), and high-dose raloxifene (N = 7). After 6 months, the animals were sacrificed and ligaments were tested along with those from five rams' knees. RESULTS: No differences were found between treatment groups for maximum force, stiffness, energy to failure, or failure site. The ultimate stress of the rams' anterior cruciate ligaments was significantly higher than that of the ewes. CONCLUSIONS: Estrogen and estrogen receptor agonists at physiologic levels do not lead to decreased knee ligament strength. CLINICAL RELEVANCE: The female hormonal milieu may not be responsible for the increased incidence of anterior cruciate ligament injury in female athletes compared with their male counterparts.

The biomechanical response to doses of TGF-beta 2 in the healing rabbit medial collateral ligament.

Ligament injuries result in significant disability in over 100,000 patients each year. Despite current methods of treatment, 13% of patients with medial collateral ligament (MCL) injury develop early signs of arthritis, suggesting an incomplete return of knee stability. The principal hypothesis of this work was that the addition of TGF-beta 2 to the healing MCL would accelerate the development of scar strength and stiffness. Forty-four rabbits were divided evenly into four groups, with each group receiving either 0.1, 1 or 5 microg of TGF-beta 2 and the fourth group receiving 1 microg TGF-beta 2 and 1 microg of PDGF. Each rabbit underwent bilateral transection of the MCL, with one side having treatment with one of four doses of growth factor and the other side left untreated. All animals were sacrificed at 6 weeks and the structural properties of maximum load at failure, stiffness, and energy absorbed at failure measured. All treatment groups demonstrated an increase in scar mass, but no group had a significant increase in scar load at failure at 6 weeks. The addition of 0.1 microg TGF-beta 2 led to a significant increase in scar stiffness. The addition of PDGF had no significant effect on any of the parameters studied. This study suggests the mechanical stiffness, but not the load at failure, of ligament scar can be significantly altered by the administration of TGF-beta 2.