Femur-anterior Cruciate Ligament-tibia Complex Research Articles

Effect of Early and Delayed Mechanical Loading on Tendon-to-Bone Healing After Anterior Cruciate Ligament Reconstruction

Modulation of the mechanical environment may profoundly affect the healing tendon graft-bone interface. The purpose of this study was to determine how controlled axial loading after anterior cruciate ligament reconstruction affects tendon-to-bone healing. Our hypothesis was that controlled cyclic axial loading after a period of immobilization would improve tendon-to-bone healing compared with that associated with immediate axial loading or prolonged immobilization. One hundred and fifty-six male Sprague-Dawley rats underwent anterior cruciate ligament reconstruction with use of a flexor digitorum longus autograft. A custom-designed fixture was used to apply an external fixator across the knee parallel to the anterior cruciate ligament graft. Animals were randomly assigned to be treated with immobilization (n = 36) or controlled knee distraction along the long axis of the graft to achieve approximately 2% axial strain beginning (1) immediately postoperatively (n = 36), (2) on postoperative day 4 ("early delayed loading," n = 42), or (3) on postoperative day 10 ("late delayed loading," n = 42). The animals were killed at fourteen or twenty-eight days postoperatively for biomechanical testing, micro-computed tomography, and histomorphometric analysis of the bone-tendon-bone complex. Data were analyzed with use of a two-way analysis of variance followed by a post hoc Tukey test with p < 0.05 defined as significant. Delayed initiation of cyclic axial loading on postoperative day 10 resulted in a load to failure of the femur-anterior cruciate ligament-tibia complex at two weeks that was significantly greater than that resulting from immediate loading or prolonged immobilization of the knee (mean and standard deviation, 9.6 ± 3.3 N versus 4.4 ± 2.3 N and 4.4 ± 1.5 N, respectively; p < 0.01). The new-bone formation observed in the tibial tunnels of the delayed-loading groups was significantly increased compared with that in the immediate-loading and immobilization groups at both two and four weeks postoperatively (1.47 ± 0.11 mm(3) [postoperative-day-10 group] versus 0.89 ± 0.30 mm(3) and 0.85 ± 0.19 mm(3), respectively, at two weeks; p < 0.003). There were significantly fewer ED1+ inflammatory macrophages and significantly more ED2+ resident macrophages at the healing tendon-bone interface in both delayed-loading groups compared with the counts in the immediate-loading and immobilization groups at two and four weeks (2.97 ± 0.7 [postoperative day 10] versus 1.14 ± 0.47 and 1.71 ± 1.5 ED2+ cells, respectively, per high-power field at two weeks; p < 0.02). The numbers of osteoclasts in the delayed-loading groups were significantly lower than those in the immediate-loading and immobilization groups at two and four weeks postoperatively (0.35 ± 0.15 [postoperative-day-10 group] versus 1.02 ± 0.08 and 1.44 ± 0.2 cells, respectively, per high-power field at two weeks; p < 0.01), and the delayed-loading groups also had significantly reduced interface tissue vascularity compared with the other groups (p < 0.003). Delayed application of cyclic axial load after anterior cruciate ligament reconstruction resulted in improved mechanical and biological parameters of tendon-to-bone healing compared with those associated with immediate loading or prolonged postoperative immobilization of the knee.

The Effect of Osteoclastic Activity on Tendon-to-Bone Healing

Healing of a tendon graft in a bone tunnel depends on bone ingrowth into the interface between tendon and bone. Excessive osteoclastic activity may contribute to bone resorption, tunnel widening, and impaired healing. We hypothesized that inhibition of osteoclastic activity by osteoprotegerin (OPG) would increase bone formation around a tendon graft in anterior cruciate ligament reconstruction in a rabbit model, while increased osteoclastic activity due to the application of receptor activator of nuclear factor-kappa B ligand (RANKL) would impair bone ingrowth. Sixty skeletally mature, male New Zealand White rabbits underwent bilateral anterior cruciate ligament reconstruction. OPG (100 microg per tunnel) or RANKL (10 microg per tunnel) was delivered to the tendon-bone interface with use of a synthetic calcium phosphate carrier vehicle. Twenty animals were killed at two, four, and eight weeks after surgery. Two rabbits from each group were prepared for histological evaluation, and the other rabbits were used for biomechanical testing. A significantly greater amount of bone surrounded the tendon at the healing tendon-bone interface in the OPG-treated limbs compared with the controls and the RANKL-treated limbs at all time-points (p < 0.05). There were significantly fewer osteoclasts in the OPG-treated limbs compared with the controls and the RANKL-treated limbs (p < 0.05). The average tunnel area in the OPG group was significantly smaller than that in the RANKL group (p = 0.003 at two weeks and p = 0.004 at four weeks). The femur-anterior cruciate ligament-tibia complex of the OPG-treated limbs had significantly increased stiffness compared with RANKL-treated limbs at eight weeks (p = 0.04). Osteoprotegerin significantly improves bone formation around the grafted tendon and improves the stiffness at the healing tendon-bone junction in a rabbit model.

The Effect of Osteoclastic Activity on Tendon-to-Bone Healing

Background: Healing of a tendon graft in a bone tunnel depends on bone ingrowth into the interface between tendon and bone. Excessive osteoclastic activity may contribute to bone resorption, tunnel widening, and impaired healing. We hypothesized that inhibition of osteoclastic activity by osteoprotegerin (OPG) would increase bone formation around a tendon graft in anterior cruciate ligament reconstruction in a rabbit model, while increased osteoclastic activity due to the aplication of receptor activator of nuclear factor-kappa B ligand (RANKL) would impair bone ingrowth. Methods: Sixty skeletally mature, male New Zealand White rabbits underwent bilateral anterior cruciate ligament reconstruction. OPG (100 μg per tunnel) or RANKL (10 μg per tunnel) was delivered to the tendon-bone interface with use of a synthetic calcium phosphate carrier vehicle. Twenty animals were killed at two, four, and eight weeks after surgery. Two rabbits from each group were prepared for histological evaluation, and the other rabbits were used for biomechanical testing. Results: A significantly greater amount of bone surrounded the tendon at the healing tendon-bone interface in the OPG-treated limbs compared with the controls and the RANKL-treated limbs at all time-points (p < 0.05). There were significantly fewer osteoclasts in the OPG-treated limbs compared with the controls and the RANKL-treated limbs (p < 0.05). The average tunnel area in the OPG group was significantly smaller than that in the RANKL group (p = 0.003 at two weeks and p = 0.004 at four weeks). The femur-anterior cruciate ligament-tibia complex of the OPG-treated limbs had significantly increased stiffness compared with RANKL-treated limbs at eight weeks (p = 0.04). Conclusions: Osteoprotegerin significantly improves bone formation around the grafted tendon and improves the stiffness at the healing tendon-bone junction in a rabbit model. Clinical Relevance: Inhibition of excessive osteoclastic activity may improve tendon-to-bone healing.

Effects of Administration of Exogenous Growth Factors on Biomechanical Properties of the Elongation-type Anterior Cruciate Ligament Injury with Partial Laceration

Background No studies have been conducted to clarify the in vivo effect of growth factor application on healing in the injured anterior cruciate ligament. Hypothesis Administration of exogenous growth factors significantly increases the structural properties of the injured anterior cruciate ligament. Study Design Controlled laboratory study. Methods Thirty-six rabbits were randomly divided into 4 groups of 9 animals each after an overstretched injury was made in the right anterior cruciate ligament. In group 1, no treatment was applied around the injured anterior cruciate ligament. In group 2, 0.2 mL fibrin sealant was applied around it. In group 3, 4 ng transforming growth factor–β1 mixed with 0.2 mL fibrin sealant was applied. In group 4, 20 μg platelet-derived growth factor–BB mixed with 0.2 mL fibrin sealant was applied. Each rabbit was sacrificed at 12 weeks after the surgery. In addition, 9 knees randomly harvested from all the left knees were used to obtain normal control data. The femur–anterior cruciate ligament–tibia complex specimens were biomechanically and histologically evaluated. Results Concerning the maximum load and the stiffness, group 3 was significantly greater than groups 1 and 2, whereas there were no significant differences among groups 1, 2, and 4. Groups 1, 2, 3, and 4 were significantly lower than the control group. Conclusions The application of 4 ng transforming growth factor–β1 significantly enhances healing in the injured anterior cruciate ligament. Clinical Relevance Administration of certain growth factors is of value to be studied as one of the future therapeutic options for the overstretched anterior cruciate ligament injury.

Biomechanical evaluation of a newly devised model for the elongation-type anterior cruciate ligament injury with partial laceration and permanent elongation

Objective. To biomechanically evaluate a newly devised model for the elongation-type anterior cruciate ligament injury with partial laceration and permanent elongation. Design. Thirty-six rabbits were randomly divided into 4 groups of 9 animals each, after a quantitative injury was given to the right anterior cruciate ligament. The 4 groups were sacrificed at 0, 6, 12, and 24 weeks after surgery, respectively. Biomechanical and histological evaluations were performed at each period. Background. No adequate animal models have been established for the elongation-type anterior cruciate ligament injury in which the mid-substance is permanently elongated with partial laceration. Methods. The anteromedial and posterolateral half of the anterior cruciate ligament was transected at the proximal and distal one-third levels, respectively. Then, the anterior cruciate ligament was stretched by applying an anterior drawer force to the tibia at 90 degrees of knee flexion. Results. The treatment significantly increased the anterior translation of the knee into approximately 150–250% at each period after surgery. The maximum load and the stiffness of the femur–anterior cruciate ligament–tibia complex significantly decreased to 30% or less immediately after surgery, and then gradually increased to 50% at 12 weeks. Conclusions. In this model, this quantitative treatment created serious injuries with partial laceration and permanent elongation in the anterior cruciate ligament to similar degrees. Also, incomplete tissue healing occurred in the anterior cruciate ligament to similar degrees after the treatment. Relevance This model will be useful to study new therapeutic methods for the elongation-type anterior cruciate ligament injury.

The Characterization of Mechanical Properties of a Rabbit Femur-Anterior Cruciate Ligament-Tibia Complex During Cyclic Loading

The purpose of this study was to investigate the effect of cyclic loading, which produced the condition of ACLs during sports activities, on tensile properties of femur-ACL-tibia complexes (FATCs). Paired FATCs of 40 New Zealand white rabbits were tested on a materials testing machine. One specimen of each pair was designated as a control and loaded until failure. The contralateral specimen was loaded cyclically (1.4 Hz, 1 hr.) with 20%, 30%, 40%, or 50% of ultimate tensile strength (UTS) of the control and then loaded until failure. The UTS and mode of failure were recorded after each test. Five specimens ruptured during cyclic loading in the 50% group. In the 40% group, the mean value of UTS of cycled specimens was significantly lower than that of controls. There was no statistically significant difference in UTS values between control and cycled specimens in the 20% and 30% groups. Cycled specimens had a significantly higher incidence of substance failure than controls. Our results demonstrated that FATCs have the strength to withstand cyclic loading within normal sports activity levels. However, FACTs can be damaged by cyclic loading under strenuous sports activity levels. We speculate that cyclic loading makes the ACL substance weaker than the insertion site.

The effects of cyclic loading on tensile properties of a rabbit femur–anterior cruciate ligament–tibia complex (FATC)

The purpose of this study was to investigate the effect of cyclic loading on tensile properties of femur–ACL–tibia complexes (FATCs). Paired FATCs of New Zealand white rabbits were tested. One specimen of each pair was designated as a control and loaded until failure. The contralateral specimen was cyclically loaded and then loaded until failure. In specimens cyclically loaded with 40% of control ultimate tensile strength (UTS), UTS decreased significantly compared to controls. Half the specimens of the 50% group were ruptured during cyclic loading. Load-to-failure of FATCs can be decreased by cyclic loading in the range of 40∼50% of their UTS. Cycled specimens had a significantly higher incidence of intrasubstance failure pattern as compared to controls. This result correlates well with clinical experience.

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

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

Quadriceps tendon and patellar ligament: cryosectional anatomy and structural properties in young adults.

Structural tensile properties analyses of 10-mm-wide central sections of quadriceps tendon-bone (QT-B) and bone-patellar ligament (B-PL) complexes from young male donors (mean age 24.9 years, range 19-32 years) were complemented by a cryosectional analysis: each QT-B complex was composed of the segment of the quadriceps tendon with the proximal half of the patella attached, each B-PL complex was composed of the distal half of the patella with the patellar ligament attached. A servohydraulic materials testing machine was used to assess ultimate failure load of 16 unconditioned and 16 preconditioned QT-B and B-PL complexes at an extension rate of 1 mm/s. Ligaments/tendons were preconditioned during 200 cycles from 50 to 800 N at 0.5 Hz. On cryosections the quadriceps tendons were significantly longer and thicker and exhibited a significantly larger bony attachment area than the patellar ligaments. Cross-sectional areas of 10-mm-wide, full-thickness, central parts of unconditioned quadriceps tendons were significantly greater and measured 64.6 +/- 8.4 mm2 with respect to the cross-sectional area of patellar ligaments, measuring 36.8 +/- 5.7 mm2 (P < 0.0025). Ultimate failure loads for unconditioned complexes resulted at 2173 +/- 618 N for QT-B complexes and at 1953 +/- 325 N for B-PL complexes (P = 0.43). Ultimate failure load values measured 2353 +/- 495 N for preconditioned QT-B complexes and 2376 +/- 152 N for preconditioned B-PL complexes, respectively (P = 0.77). Despite the fact that initial testing length, thickness, cross-sectional shape and area of unconditioned QT-B and B-PL complexes were significantly different, displacement at ultimate load, energy to failure and total energy were not. In terms of ultimate tensile strength, the 10-mm-wide central part of the QT-B complex compared favourably to the tensile properties of the human femur-anterior cruciate ligament-tibia complex from a comparable young age group. The evidence from anatomic, cryosectional and structural properties analyses suggests that the QT-B complex may be a valuable and versatile adjunct to the surgeon's armamentarium in reconstructive cruciate ligament surgery.

Mechanical properties of the anterior cruciate ligament chronically relaxed by elevation of the tibial insertion

The effects of stress deprivation on the mechanical properties of the anterior cruciate ligament were studied in a canine model. Fifty-eight mature mongrel dogs were divided into two groups. In the relaxed group (n = 30), the tibial insertion of the anterior cruciate ligament in each right knee was surgically elevated proximally 3 mm from the tibia; the elevation was anatomically reduced in the sham group (n = 28). In order to obtain control data, the left knee in each dog was left untreated. A femur-anterior cruciate ligament-tibia complex was excised from each knee for biomechanical tests at 6 or 12 weeks after surgery. To simplify data analysis, the treat/nontreat ratio (the ratio of the data obtained from the treated knee to that from the nontreated knee) was used. The cross-sectional area of the ligament increased significantly in both groups; the area in the relaxed group (average treat/nontreat ratio = 1.37) was significantly larger than that in the sham group (1.16) at 6 weeks but not at 12 weeks. The treat/nontreat ratio of tensile strength in the relaxed group significantly decreased to 0.67 and 0.58 at 6 and 12 weeks, respectively; in the sham group, it significantly decreased to 0.79 at 6 weeks but subsequently increased to 0.87 at 12 weeks. Only at 12 weeks was a significant difference observed between the two groups. This study demonstrated that, in the anterior cruciate ligament, stress deprivation results in a rapid increase in the cross-sectional area, although this effect disappears by 12 weeks, and in a decrease in mechanical strength, although a relatively long period of more than 6 weeks is required for the deterioration.

Mechanical properties of the human anterior cruciate ligament

The aim was to measure the stiffness and strength of the femur-anterior cruciate ligament-tibia complex tested in a physiological manner with a force exerted anteriorly on the tibia, at knee joint flexion angles of 0 °, 10 ° and 30 ° and at speeds of 50 and 500 mm/min. Ligaments were preconditioned by cycling five times, with data from the fifth cycle used to determine the stiffness of the ligament in a low-load range. The ligaments were then tested to failure with the knee at 30 ° flexion. The specimens were divided into two groups, middle-aged (40–60) and old (>60). For each group no statistical difference was observed between stiffness of the ligament at different joint flexion angles or speeds. Seven of the 21 specimens in the older age group failed by avulsion at the bone-ligament interface. All the other specimens failed by tears in the substance of the ligament. Ultimate failure load was found to have a significant correlation with bodyweight. It was 1.6 and 1.3 times bodyweight for the middle-aged and older age groups respectively. This study has highlighted the importance of identifying different modes of failure, of making corrections for bodyweight and testing in a physiological manner. The results allow a better understanding of the mechanical behaviour of the anterior cruciate ligament and provide design data for anterior cruciate ligament grafts and prostheses.

Hamstrings and gastrocnemius co-contraction protects the anterior cruciate ligament against failure: an in vivo study in the rat.

An anesthetized rat model was used to study the effects of muscle contraction on the ultimate tensile load and the energy absorption at failure of the anterior cruciate ligament. In both knees, the joint capsule and ligaments, except for the anterior cruciate ligament, were divided, and the menisci were removed with the aid of a stereomicroscope. The cruciate ligament of the right knee was tested in tension until failure by femorotibial distraction during contraction of the hamstrings and calf muscles induced by electrical stimulation of the ischiatic nerve. The cruciate ligament of the left knee, which was loaded to failure with nonstimulated (relaxed) muscles, served as the control. The mean ultimate tensile load during muscle contraction was 86 N compared with 53 N when tested with relaxed muscles (p < 0.001). The energy absorption at failure was 0.41 and 0.19 J during contraction and relaxation, respectively (p < 0.05). This study suggests that previous investigations evaluating the force and energy necessary to rupture the anterior cruciate ligament (with use of a femur-anterior cruciate ligament-tibia complex stripped of all soft tissues and without gastrocnemius-hamstring muscle contractions) are incomplete and probably not representative of the in vivo situation.

A new device to measure the structural properties of the femur-anterior cruciate ligament-tibia complex.

Previous studies of biomechanical properties of femur-anterior cruciate ligament-tibia complex (FATC) utilized a wide variety of testing methodologies, particularly with respect to ligament orientation relative to loading direction. A new device was designed and built to test the anterior-posterior displacement of the intact porcine knee at 30 and 90 deg of flexion, as well as the tensile properties of the FATC at any loading direction and flexion angle. Tensile tests were performed with the knees at 30 and 90 deg of flexion with the loading direction along either the axis of the tibia (tibial axis) or the axis of the anterior cruciate ligament (ligament axis). The results showed that the stiffness, ultimate load and energy absorbed were all significantly increased when the FATC was tested along the ligament axis. This study demonstrates the importance of alignment in the evaluation of the biomechanical characteristics of the femur-ACL-tibia complex.

Prevention of ligament and meniscus atrophy by active joint motion in a non-weight-bearing model.

This study describes the effect of active joint motion on the maintenance of ligament and meniscus mass in a non-weight-bearing model of disuse. Denervation and fixation models of immobilization have shown that resorption of isotope and atrophy of mass occurred for hard tissue (bone) and soft tissues (ligament, tendon, or meniscus). A unilateral ankle disarticulation model of disuse that maintains active knee motion without weight bearing was studied for 8 weeks in dogs that were chronically prelabeled with three different isotopes. The effects of non-weight-bearing without denervation or fixation were analyzed for the resorption of isotopes, and net atrophy of bone mass (femur or tibia) and soft-tissue mass (collateral or cruciate ligaments, menisci). A large and similar loss of all three isotopes, as well as collagen and calcium mass occurred for whole femur and tibia; this indicated that mass loss was equivalent to bone resorption and suggests little replacement with new bone. No loss of isotope or mass per whole tissue occurred for the collateral and cruciate ligaments or menisci. The strength of the femur-anterior cruciate ligament-tibia complex was analyzed by a tensile failure test when a fast rate of deformation was applied; the results did not differ qualitatively or quantitatively between control and experimental limbs. The absence of weight bearing for 8 weeks resulted in marked bone atrophy without resorption or atrophy of soft tissues, or decrease of the mechanical strength for the femur-ligament-tibia complex.

The influence of an experimental immune synovitis on the failure mode and strength of the rabbit anterior cruciate ligament.

The strength and failure mode of a fresh femur-anterior cruciate ligament-tibia complex was studied in normal rabbits and after the induction of an experimental immune synovitis. Five modes of failure were observed: (1) through the anterior cruciate ligament alone; (2) through a small piece of bone with the anterior cruciate ligament attached; (3) through a condyle; (4) through the metaphysis; and (5) through the diaphysis. In the normal complex, failure always occurred through the anterior cruciate ligament. In the controls, the average ratio of failure-load to body weight was seventy-four newtons per kilogram. After induction of an immune synovitis this ratio was significantly reduced, to twenty-two newtons per kilogram. Synovial cathepsin-D enzyme activity in these knees was 5.27 micromoles per hour per milligram of protein, which was significantly elevated when compared with the control level of 0.26. Histological examination of the anterior cruciate ligament after induction of the immune synovitis but before strength-testing demonstrated loss of the normal undulating fiber orientation, disorganization of the normal cellular pattern, and a decrease in the staining of the interstitial matrix with Mallory trichrome. There was a moderate infiltration of mononuclear and polymorphonuclear inflammatory cells in the body of the ligament. Histological studies of the ligament after strength-testing showed that the failure resulted in a mop-like appearance and morphological characteristics similar to those observed before testing.