Anterior Cruciate Ligament Strength Research Articles

The Effect of Oral Contraceptive Hormones on Anterior Cruciate Ligament Strength

Females are up to eight times more likely to injure their anterior cruciate ligaments (ACLs) than males. While anatomical and biomechanical factors likely contribute to this disparity, hormonal differences have also been found to predispose women to ACL injury. The ACL’s strength is affected by various female hormones such as relaxing and estrogen. Oral contraceptives (OCs) can directly alter these hormone levels, however no study to date has done a comprehensive comparison of differing contraceptive regimens on ACL strength. Untreated rats were compared to rats treated with one of the five following clinically-used OCs: Norethindrone only, Norethindrone plus Ethinyl Estradiol, Etynodiol Diacetate plus Ethinyl Estradiol, Norgestimate plus Ethinyl Estradiol, and Drospirenone plus Ethinyl Estradiol. Doses were scaled from human doses to account for differences in bioavailability and body weight, and OCs were administered daily via oral gavage for four rat estrous cycles (20 days). 42 rats were then sacrificed (6 rats/group), and ACL specimens underwent biomechanical testing and were preloaded to 1N and then preconditioned for 10 cycles at a rate of 0.25mm/s. Strength (MPa) and stiffness (N/mm) were assessed. ACL strength (MPa) was calculated by normalizing maximum load before failure (N) by ACL cross sectional area (mm2). ACL specimens were also isolated for quantitative real-time polymerase chain reaction analysis to assess collagen and matrix metalloproteinase (MMP) expression. Readings from the left and right ACLs for each rat were averaged. Data was then analyzed with One-Way ANOVA and post hoc Bonferroni and Holm multiple comparison statistical calculations. The average strength of ACLs from rats treated with Norethindrone only (42.1 ± 1.4 MPa), Drospirenone plus Ethinyl Estradiol (41.5 ± 1.9 MPa), Etynodiol Diacetate plus Ethinyl Estradiol (41.0 ± 3.3 MPa), and Norethindrone plus Ethinyl Estradiol (38.7 ± 3.0 MPa) was significantly increased when compared to untreated rats (29.1 ± 4.9 MPa) (p = 0.001, p = 0.004, p = 0.004 and p = 0.037 respectively). There was no significant difference with Norgestimate plus Ethinyl Estradiol (34.9 ± 1.4 MPa) OCs. ACL strength directly correlated with each formulation’s ratio of progestin to estrogen potency. The order from strongest to weakest ACLs as well as highest to lowest progesterone to estrogen ratios was Norethindrone only, Drospirenone plus Ethinyl Estradiol, Etynodiol Diacetate plus Ethinyl Estradiol, Norethindrone plus Ethinyl Estradiol, and then Norgestimate plus Ethinyl Estradiol. The higher ratio formulation (Drospirenone plus Ethinyl Estradiol) also increased the expression of type I collagen by 8.1 ± 2.7-fold (p = 0.02) and decreased MMP1 by 0.06 ± 0.04-fold (p = 0.04) when compared to untreated rats. The low progestin-to-estrogen (Norgestimate plus Ethinyl Estradiol) ratio formulation only increased type I collagen expression 4.7 ± 0.6-fold (p = 0.26) and decreased MMP1 expression only 0.38 ± 0.13-fold (p = 0.25). Oral contraceptives act to influence ACL strength differently depending on their formulation, likely by increasing type I collagen and decreasing MMP1 expression. Norethindrone only, Drospirenone plus Ethinyl Estradiol, Etynodiol Diacetate plus Ethinyl Estradiol, and Norethindrone plus Ethinyl Estradiol formulations increased ACL strength when compared to Norgestimate plus Ethinyl Estradiol and untreated rat ACLs. Formulations with no estrogen, like Norethindrone only, or formulations with a higher progestin to estrogen ratio, such as Drospirenone plus Ethinyl Estradiol or Etynodiol Diacetate plus Ethinyl Estradiol, may be more protective for the ACL than formulations with low progestin to estrogen ratios, such as Norgestimate plus Ethinyl Estradiol.

The Effect of Oral Contraceptive Hormones on Anterior Cruciate Ligament Strength

Background: Women are 2 to 9 times more likely to experience an anterior cruciate ligament (ACL) injury than men. Various hormones including relaxin, progesterone, and estrogen influence ACL strength. Oral contraceptives (OCs) alter these hormone levels; however, studies have yet to comprehensively compare different OCs’ effects on the ACL. Hypothesis: OCs with increased progestin-to-estrogen ratios will (1) increase ACL collagen expression, (2) decrease ACL matrix metalloproteinase expression, and (3) increase ACL strength. Study Design: Controlled laboratory study. Methods: Untreated female rats were compared with rats treated with 1 of 5 clinically used OCs: norethindrone (NE) only, NE plus ethinylestradiol (EE), etynodiol diacetate (ED) plus EE, norgestimate (NG) plus EE, and drospirenone (DS) plus EE. Doses were scaled from human doses to account for differences in bioavailability and body weight, and OCs were administered daily via oral gavage for 4 rat estrous cycles (20 days). A total of 36 rats were then sacrificed (6 rats/group). ACLs underwent biomechanical testing to assess ACL strength, stiffness, and maximum load before failure. ACL specimens were also isolated for quantitative real-time polymerase chain reaction analysis to assess collagen, matrix metalloproteinase, and relaxin receptor–1 expression. Results: While the primary structural property of interest (ACL maximum load before failure) was not significantly improved by OC treatment, the main material property of interest (ACL strength) in rats treated with NE only, DS + EE, ED + EE, and NE + EE was significantly increased compared with untreated controls (P = .001, P = .004, P = .004, and P = .04, respectively). The order from strongest to weakest ACLs, which was also the same order as the highest to lowest progestin-to-estrogen ratios, was groups treated with NE only, DS + EE, ED + EE, NE + EE, and lastly NG + EE. Higher ratio formulations also increased the expression of type I collagen (P = .02) and decreased the expression of matrix metalloproteinase–1 (P = .04). Conclusion: OC formulations with higher progestin-to-estrogen ratios may be more protective for the ACL than formulations with lower ratios. Clinical Relevance: OC formulations with high progestin-to-estrogen ratios may benefit female athletes by reducing their ACL injury risk by decreasing the effects of relaxin on the ACL.

The Influence of Oral Contraceptive Hormones on Anterior Cruciate Ligament Strength [7H

INTRODUCTION: Females are up to eight times more likely to injure anterior cruciate ligaments (ACLs) than males, and hormonal differences predispose women to ACL injury. Various hormones—including relaxin and estrogen—impact ACL strength. Oral contraceptives (OCs) alter these hormone levels; however, studies have not yet compared different OCs’ influences on ACL strength. METHODS: Untreated and pregnant rats were compared to rats treated with Norethindrone only, Etynodiol Diacetate-plus-Ethinyl Estradiol, or Norgestimate-plus-Ethinyl Estradiol. OC doses adjusted for bioavailabilty and body weight were administered daily via oral gavage for four estrous cycles (20 days). Thirty-two rats were sacrificed; specimens were assessed for maximum load before failure and ultimate stress. Data were analyzed with One-Way ANOVA and post-hoc Bonferroni-Holm calculations. RESULTS: Ultimate stress of ACLs from Norethindrone (43.46 ± 3.47 MPa) and Etynodiol Diacetate-plus-Ethinyl Estradiol-treated rats (43.62 ± 9.70 MPa) was significantly increased when compared to untreated rats (28.20 ± 7.28 MPa) (P = .0203 and P = .0298 respectively). Maximum ACL load before failure from Norethindrone-treated rats (39.14 ± 2.75 N) was increased compared to untreated rats (33.10 ± 3.70 N) (P = .0414) and Norgestimate-plus-Ethinyl Estradiol-treated rats (31.27 ± 3.43 N) (P = .0406). Pregnant rats weren’t significantly different from other rats. CONCLUSION: OCs influence ACL strength differently depending on formulation. Norethindrone and Etynodiol Diacetate-plus-Ethinyl Estradiol increase ACL strength compared to Norgestimate-plus-Ethinyl Estradiol, pregnant, and untreated conditions. Formulations lacking estrogen or with high progestin:estrogen ratios, like Etynodiol Diacetate-plus-Ethinyl Estradiol, may better protect the ACL than formulations with smaller ratios, like Norgestimate-plus-Ethinyl Estradiol.

Testosterone may increase rat anterior cruciate ligament strength

BackgroundWomen are more likely than men to injure the anterior cruciate ligament (ACL). Human and animal trials have linked circulating estradiol to injury rate and ligament strength. Fewer studies have examined the role of testosterone. The purpose of this study was to determine if male rats with normal testosterone levels would have stronger ACLs than castrated rats. MethodsEight castrated (group C) and eight normal (group N) 12-week-old, male Sprague–Dawley rats were used for the study. Mean testosterone levels were 0.14ng/mL (95% CI: 0.10 to 0.17) in group C and 3.54ng/mL (95% CI: 1.32 to 5.76) in group N. After euthanasia, ACL cross-sectional area was calculated, and a servohydraulic material testing unit was used to measure ligament properties. ResultsSpecimens from both groups had similar cross-sectional area, but N specimens showed greater mean load-to-failure (34.5N [95% CI: 31.6 to 37.4] vs 29.2N [95% CI: 27.9 to 30.6]) and ultimate stress (38.7MPa [95% CI: 34.1 to 43.3] vs 31.8MPa [95% CI: 29.8 to 33.8]). Mean energy was 27.7mJ (95% CI: 23.1 to 32.2) in the N group and 23.4mJ (95% CI: 18.2 to 28.6) in the C group. ConclusionsRats with normal circulating testosterone had higher ACL load-to-failure and ultimate stress, indicating that testosterone may influence ACL strength and the injury rate of the ligament.

The Influence of Castration on Collagen Expression and Anterior Cruciate Ligament Strength in Rats

Sex specific responses to specific steroid sex hormones have been suggested as a potential cause for the disparate anterior cruciate ligament (ACL) injury rate between male and females athletes. Type-I (T1C) and type-3 collagen (T3C) are crucial structural components that define the ligament's ability to withstand tensile loads. Transcription of mRNA is an important mediator of downstream collagen synthesis and remodeling. Sex differences in collagen mRNA expression and ACL strength have been reported but the specific impact of testosterone on collagen mRNA expression and ACL strength is not clear. PURPOSE: To examine the influence of castration on T1C and T3C mRNA expression and mass normalized peak failure load in the ACLs of skeletally mature male rats METHODS: Seventeen 12 week old male Sprague-Dawley rats were separated into castrated (C) (389.1 + 25.9g) or non-castrated control (CNTL) groups (417.7 + 35.4g). After 16 days rats were euthanized and real time polymerase chain reaction was used to determine T1C and T3C mRNA expression and to calculate the T1C:T3C ratio in tissue from the right ACL. The left ACL was isolated and attached to a hydraulic materials testing device in order to measure ACL load to failure normalized for animal weight. Non-parametric Wilcoxon rank sum tests were used to compare the means of mRNA expression and failure load between the C and CNTL groups. RESULTS: Castrated rats had lower expression of T3C mRNA (p=0.001), a higher T1C:T3C ratio (p=0.015) and higher load to failure (p=0.021) than CNTL rats. The C rats also had a higher expression of T1C mRNA that approached significance (p=0.066). CONCLUSIONS: Castrated male rats had significantly higher T3C mRNA expression, the ratio of T1C:T3C collagen mRNA expression and downstream ACL load to failure in male Sprague-Dawley rats. Supported by the National Institute of Child Health and Human Development Grant 5 K12 HD-043489, National Institute of Arthritis and Musculoskeletal and Skin Diseases Grant 1R03AR54573-1A1

Sex, Collagen Expression, and Anterior Cruciate Ligament Strength in Rats

Sex-specific responses to steroid sex hormones have been suggested as a potential cause for the disparate anterior cruciate ligament (ACL) injury rates between male and female athletes. Type 1 collagen (T1C) and type 3 collagen (T3C) are crucial structural components that define the ligament's ability to withstand tensile loads. Messenger RNA (mRNA) is an important mediator of downstream collagen synthesis and remodeling, but the sex-specific mechanisms of collagen mRNA expression and ACL strength are unknown. To examine the influence of sex on T1C and T3C mRNA expression and mass-normalized stiffness and peak failure load in the ACLs of skeletally mature rats. Observational study. Basic sciences and biomechanical testing laboratories. Nineteen 12-week-old male (n = 9) and female (n = 10) Sprague Dawley rats. We used real-time polymerase chain reaction to determine T1C and T3C mRNA expression and a hydraulic materials testing device to measure ACL stiffness and failure load. Nonparametric Wilcoxon rank sum tests were used to compare the groups. Female rats had lower amounts of T3C mRNA expression and higher normalized ACL tangent stiffness and failure load than male rats. These findings suggest that sex-specific differences in T1C and T3C mRNA expression may play an important role in the downstream mechanical properties of the ACL.

Novel matrix based anterior cruciate ligament (ACL) regeneration

Among the five ligaments in the knee the anterior cruciate ligament (ACL) is among the most important for stability and also the most commonly injured. Due to a lack of vascularization, the ACL has poor healing potential, therefore moderate to severe damage warrants medical intervention. Ligaments are complex, highly organized tissues; they are longitudinally arranged with a great deal of order that begins at the molecular level and carries through to the tissue level. The components of the ligament and their location and orientation heavily influence the tissue's mechanical behavior. ACL replacements have faced a variety of limitations that prevented their extensive use, including implant fatigue or fraying of the device. In the face of these problems, investigators have begun to examine a variety of matrix based techniques to create options for ACL repair, replacement, and regeneration. This article will discuss ACL structure and mechanics, past replacement options and their limitations, and recent tissue engineered options for ACL repair. These techniques employ a wide variety of designs, materials, and methods to heal damaged ACL tissue or regenerate lost tissue in order to regain full ACL strength and mechanics.

Anterior cruciate ligament strength. Can it be estimated by non-destructive testing?

For structural and material bone strength, non-destructive tests exist, while no such tests have been developed for ligaments. In the present study we compared the geometry and bone mineral content (BMC) of the rat tibia with the tensile strength of the anterior cruciate ligament (ACL). A significant correlation was found between the mediolateral diameter of the tibial condyle and ACL load to failure (r=0.83). Calculating the area of the condyle as an ellipse increased this correlation to r=0.93. No significant correlation was found to BMC. If this correlation is also found in humans, the mediolateral tibial head diameter may be used to estimate the strength of the ACL non-destructively.

Graft selection, placement, fixation, and tensioning for anterior cruciate ligament reconstruction

The ideal graft for replacement of the anterior cruciate ligament (ACL) is one that retains at least an equivalent level of normal ACL strength, allows for secure fixation, enables unrestricted rehabilitation, and has no graft harvest morbidity. The choices for ACL grafts are both biologic and synthetic. Among the biologic choices are autografts and allografts. One must decide on the type of biologic tissue, whether patellar tendon, hamstring tendon, iliotibial band, or Achilles tendon. In addition to selecting a graft, the ACL substitute must be correctly placed with secure fixation and under appropriate tension. Correct placement of a graft requires an accurate understanding of the normal anatomic attachment sites of the ACL, both on the tibia and the femur. Ideal fixation will allow secure initial fixation and sufficient stability until the native bone and/or tissue heals. This fixation must also be strong enough to allow the recommended postoperative rehabilitation. The tension of the graft must be sufficient to achieve stability but not so excessive that it captures the joint. ACL reconstruction depends on the surgeon understanding these options and possessing the necessary skills to perform the procedure. The goals of the surgery—restoring normal knee stability and allowing expedient recovery—depend on the surgeon knowing the ACL graft choices, the proper placement within the joint, the ideal fixation, and the proper tension.

Allograft anterior cruciate ligament reconstruction in a sheep model. The effect of synthetic augmentation.

The purpose of this study was to assess the effect of synthetic augmentation of a bone-patellar tendon-bone allograft on the basis of biomechanical, morphologic, and histologic evaluation. The anterior cruciate ligament was reconstructed in the left knee of 66 adult sheep. Half the knees received bone-patellar tendon-bone grafts alone, while the other half were augmented. All of the knees, including the contralateral controls, had gross and histologic examination, hydroxyproline assay for collagen content, and biomechanical testing in groups at 0, 4, 16, and 52 weeks postoperatively. Biomechanical testing included anteroposterior translation, ultimate tensile strength, energy to failure, stiffness, and mode of failure. Eight fresh bone-patellar tendon-bone allografts were compared to eight cryopreserved bone-patellar tendon-bone allografts for baseline data on the effects of the cryopreservation. Cryopreservation did not have any effect on graft characteristics. Gross and histologic examination did not reveal any significant difference between the augmented and nonaugmented groups at any of the time periods. In addition, hydroxyproline content of the allograft was not altered by augmentation throughout the study period. Biomechanical laboratory evaluation demonstrated the augmented group had significantly reduced anteroposterior translation (P less than 0.05) at 52 weeks compared to the nonaugmented group. The ultimate tensile strength was significantly higher (P less than 0.05) in the augmented group at 4 weeks, but at 52 weeks both groups had attained only 50% of the normal anterior cruciate ligament strength. Stiffness and energy to failure were similar in both groups at all time periods. From the results of this study, synthetic augmentation appears to improve initial strength and prevent late allograft laxity while allowing normal remodeling processes to occur in the bone-patellar tendon-bone allograft anterior cruciate ligament reconstruction.