Immediate ACL reconstruction prevents microvascular pathophysiology in the Uninjured MCL that is not fully reversed by delayed ACL reconstruction

Anterior cruciate ligament (ACL) injury induces maladaptive vascular responses that degrade medial collateral ligament (MCL) function. The purpose of this study was to determine if early or delayed ACL reconstruction can prevent or reverse the abnormal changes in vascular function that occur in the uninjured MCL after ACL injury. Twenty‐four rabbits were divided into four groups (n = 6); control, ACL‐deficient (ACL‐X), immediate ACL reconstructed (ACL‐IR) and delayed ACL reconstructed (ACL‐DR). After 8 weeks, MCLs were assessed for blood flow, responses to acetylcholine (ACh) and phenylephrine (Phe) and autoregulatory responses, using laser speckle perfusion imaging. In ACL‐X knees, blood flow in the MCL increased by 2.5‐fold compared to control. MCL hyperemia was diminished in ACL‐DR knees and was unaltered in ACL‐IR knees. MCL vasculature was unresponsive to ACh and Phe in ACL‐X. These responses were partially restored by ACL reconstruction. Autoregulatory responses were not significantly different between groups. ACL‐DR decreased hyperemia in the MCL and partially attenuated abnormal MCL vascular responses. ACL‐IR was more effective at preventing MCL hyperemia and preserving vascular responsiveness to ACh and Phe. This suggests that the vascular alterations in the uninjured rabbit MCL are largely caused by abnormal mechanical loading resulting from ACL deficiency and can be prevented through early reconstruction. Early ACL reconstruction could limit the progression of microvascular dysfunction of the MCL, and preserve physiological joint homeostasis. This might prevent joint degeneration and delay the progression of osteoarthritis. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29: 1390–1396, 2011     

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 µL (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 E₂. High‐dose histamine, and low‐dose substance P and PGE₂ 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. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:83–88, 2010     

Valgus medial collateral ligament rupture causes concomitant loading and damage of the anterior cruciate ligament

This study tested the hypothesis that application of a valgus force necessary to create a complete medial collateral ligament (MCL) injury causes damage to the anterior cruciate ligament (ACL). Twelve cadaveric knees were used to measure concomitant loading and damage to the ACL in valgus knee loading sufficient to cause a grade III MCL injury. Displacement sensors were placed on the anteromedial bundle of the ACL and posterior oblique ligament to monitor tensile strain during creation of the MCL injury. A valgus moment was applied to knees flexed at 30 degrees, displacing the joint into valgus rotation beyond MCL rupture. Following valgus loading and MCL injury, femur-ACL-tibia specimens were tested to failure to compare ACL mechanical integrity to noninjured control specimens. Average ACL strength in MCL ruptured knees (1250 +/- 90 N) was statistically lower (P < or = .05) than that for control knees (2110 +/- 50 N). Strain measurements exhibited concomitant posterior oblique ligament strain during valgus loading, whereas ACL strain increased substantially only after MCL rupture. These data indicate that the ACL can be compromised in isolated grade III MCL injuries.     

Vascular physiology and long-term healing of partial ligament tears.

Functional outcomes of anterior cruciate ligament (ACL) injury are generally poorer than those of medial collateral ligament (MCL) tears. Following ligament damage, all phases of ligament healing require an adequate blood supply. We hypothesized that the differences in healing properties of the ACL and MCL would reflect their vascular responses to joint injury. This paper examines the long-term changes in blood flow and vascular volume of rabbit knee ligaments after direct injury, and under conditions of chronic joint instability induced by section of the posterior cruciate ligament (PCL). Standardized injuries were surgically induced in adult rabbit knee ligaments: partial MCL transection, partial ACL transection, or complete PCL transection (joint instability). Sixteen weeks later the blood flow and vascular volume of the ACL and MCL were measured and compared to control and sham-operated animals. Direct ligament injury induced significant increases in standardized blood flow and vascular volume of both ACL and MCL after 16 weeks; however, the vascular volume of the ACL was not higher than the control levels in the MCL. We conclude that direct injury to both the anterior cruciate and MCLs induces long-term physiological responses. Joint laxity is a common sequel to PCL injury. Chronic joint laxity failed to induce adaptive vascular responses in the ACL, while the MCL shows significant amplification of blood supply. Although both MCL and ACL showed increased weight after PCL transection, the lack of a long-term vascular response in the ACL may be a major factor in its the diminished healing potential.     

Medial collateral ligament insertion site and contact forces in the ACL-deficient knee.

The objectives of this research were to determine the effects of anterior cruciate ligament (ACL) deficiency on medial collateral ligament (MCL) insertion site and contact forces during anterior tibial loading and valgus loading using a combined experimental-finite element (FE) approach. Our hypothesis was that ACL deficiency would increase MCL insertion site forces at the attachments to the tibia and femur and increase contact forces between the MCL and these bones. Six male knees were subjected to varus-valgus and anterior-posterior loading at flexion angles of 0 degrees and 30 degrees. Three-dimensional joint kinematics and MCL strains were recorded during kinematic testing. Following testing, the MCL of each knee was removed to establish a stress-free reference configuration. An FE model of the femur-MCL-tibia complex was constructed for each knee to simulate valgus rotation and anterior translation at 0 degrees and 30 degrees, using subject-specific bone and ligament geometry and joint kinematics. A transversely isotropic hyperelastic material model with average material coefficients taken from a previous study was used to represent the MCL. Subject-specific MCL in situ strain distributions were used in each model. Insertion site and contact forces were determined from the FE analyses. FE predictions were validated by comparing MCL fiber strains to experimental measurements. The subject-specific FE predictions of MCL fiber stretch correlated well with the experimentally measured values (R2 = 0.95). ACL deficiency caused a significant increase in MCL insertion site and contact forces in response to anterior tibial loading. In contrast, ACL deficiency did not significantly increase MCL insertion site and contact forces in response to valgus loading, demonstrating that the ACL is not a restraint to valgus rotation in knees that have an intact MCL. When evaluating valgus laxity in the ACL-deficient knee, increased valgus laxity indicates a compromised MCL.     

Simultaneous reconstruction of anterior cruciate ligament and posterior cruciate ligament by using allogeneic patellar tendon under arthroscopy

With fast development of arthroscopic surgery inChina, simple reconstruction of ACL (anteriorcrucial ligament) or PCL has been reported in number. However , the methods concerningsimultaneous reconstruction of ACL and PCL are rarelyreported. Simultaneous …     

Intrinsic healing response of the human anterior cruciate ligament: An histological study of reattached ACL remnants

A reattachment of the tibial remnant of the torn anterior cruciate ligament (ACL) to the posterior cruciate ligament is sometimes observed during surgery and apparently implies that the human ACL does have a healing response. The aim of this study was to investigate whether this reattachment tissue has similar histological characteristics of a healing response as the medial collateral ligament (MCL), which can heal spontaneously. Standard histology and immunostaining of α‐smooth muscle actin and collagen type 3 was performed. The results shows that the reattached tissue has typical characteristics of a healing response: the reattached ACL remnant could not be released by forceful traction; microscopy showed that the collagen fibers of the reattached tissue were disorganized with no preferred direction; increased neovascularization; the presence of lipid vacuoles; the mean number of cells within the biopsy tissue was 631 ± 269 cells per mm²; and 68 ± 20% was expressing α‐SMA; semi‐quantitative analysis of collagen type 3 expression showed that collagen type 3 had an high expression with an average score of 3. In conclusion, this study shows that the human proximal 1/3 ACL has an intrinsic healing response with typical histological characteristics similar to the MCL. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:296–301, 2014.     

The healing medial collateral ligament following a combined anterior cruciate and medial collateral ligament injury--a biomechanical study in a goat model.

The ideal treatment of a combined anterior cruciate ligament (ACL) and medial collateral ligament (MCL) injury to the knee is still debated. In particular, the question of whether reconstruction of the ACL can provide the knee with sufficient multidirectional stability to allow for effective MCL healing needs to be better elucidated. Therefore, the first objective of this study was to quantify the changes in the function of goat knees between time-zero and 6 weeks following a combined ACL/MCL injury treated with ACL reconstruction. Using a robotic/universal force-moment sensor testing system, the kinematics of the knee and in situ forces in the ACL/ACL graft as well as in the sham-operated and healing MCL were evaluated in response to (1) a 67 N anterior-posterior (A-P) tibial load and (2) a 5 Nm varus-valgus (V-V) moment. The second objective was to evaluate the structural properties of the healing femur-MCL-tibia complex (FMTC) and the mechanical properties of the healing MCL at 6 weeks under uniaxial tension.In response to the 67 N A-P tibial load, the A-P translations for the experimental knee increased by as much as 4.5 times from time-zero to 6 weeks (p<0.05). Correspondingly, the in situ forces in the ACL graft decreased by as much as 45% (p<0.05). There was no measurable changes of the in situ force in the healing MCL. In response to a 5 Nm V-V moment, V-V rotations were twice as much as controls, but similar for both time periods. From time-zero to 6 weeks, the in situ forces in the ACL graft dropped by over 71% (p<0.05), while the in situ force in the healing MCL was as much as 35+/-19 N.In terms of the structural properties of the healing FMTC, the stiffness and ultimate load values at 6 weeks reached 53% and 29% of sham-operated contralateral controls, respectively (p<0.05). For the mechanical properties of the healing MCL substance, the values for tangent modulus and tensile strength were only 13% and 10% of sham-operated controls, respectively (p<0.05). These results suggest that the ACL graft stabilized the knee initially, but became loose over time. As a result, the healing MCL may have been required to take on excessive loads and was unable to heal sufficiently as compared to an isolated MCL injury.     

Correlation of healing capacity with vascular response in the anterior cruciate and medial collateral ligaments of the rabbit.

In clinical terms, functional recovery after anterior cruciate ligament (ACL) injury is generally poorer than after medial collateral ligament (MCL) injury. In experimental studies of injury, the early phases of ligament healing require an augmented blood supply. We hypothesized that the differences in healing properties of the ACL and MCL would be reflected in the magnitude of their vascular responses to partial injury. This study is the first to quantify and define the time course of changes in blood flow and vascular volume following hemisection of the rabbit ACL and MCL.Adult female rabbits were assigned to control, sham operation, ACL hemisection or MCL hemisection groups. Standardized ACL or MCL injuries were surgically induced. About 2, 6 or 16 weeks later, blood flow and vascular volume of the ACL and MCL were measured.The MCL of the rabbit responded to hemisection with a large significant increase in blood flow and a substantial angiogenic response associated with inflammation and scar formation. During subsequent matrix remodelling, blood flow and vascular volume returned towards control values. In contrast, the ACL showed only a 2-fold increase in vascular volume, no increase in blood flow and atrophied after hemisection. The superior capacity of the MCL to increase its blood supply through angiogenesis and increased flow is essential for ligament healing to occur, and may be the major difference in healing potential between the ACL and MCL.     

Roles of the anterior cruciate ligament and the medial collateral ligament in preventing valgus instability

Both the medial collateral ligament (MCL) and the anterior cruciate ligament (ACL) are reported to prevent valgus instability of the knee. In this study, the anatomical mechanisms by which these ligaments prevent valgus instability were experimentally investigated. The valgus rotation angle and the magnitude of the medial joint space opening were measured in six cadaveric knees, using biplanar photography before and after the MCL and/or the ACL were severed. A significant increase in the valgus rotation angle and a large medial joint space opening were observed when the MCL was severed. An increase in the valgus rotation angle was also observed when the ACL was severed, but only a small medial joint space opening was present. The increase in the valgus rotation angle after ACL severance was nearly parallel to the increase in the internal rotation of the tibia. Thus, we concluded that both ligaments function to prevent valgus instability, but that the anatomical reasons for their function are different. The MCL prevents valgus instability by stopping an opening in the medial joint space. The ACL, on the other hand, prevents the internal rotation of the tibia. When the ACL is severed, the internal rotation increases, and causes the valgus rotation angle to also increase, despite the presence of only a small medial joint space opening. Received: May 16, 2000 / Accepted: August 3, 2000     

Healing of the medial collateral ligament following a triad injury: a biomechanical and histological study of the knee in rabbits.

The effect of a partial medial meniscectomy and anterior cruciate ligament (ACL) transection on medial collateral ligament (MCL) healing was studied in skeletally mature rabbits. Two groups of animals, group I (isolated MCL rupture) and group II (MCL rupture with ACL transection and partial medial meniscectomy), were examined. At 6 and 12 weeks postoperatively, histological examination of the healing MCL and biomechanical evaluation of the varus-valgus (V-V) knee rotation and tensile properties of the femur-MCL-tibia complex (FMTC) were performed. Group II animals experienced substantial joint degeneration by 6 weeks. Progressive osteophyte formation was observed adjacent to the MCL insertions along with proximal migration of the MCL tibial insertion between 6 and 12 weeks. Histologic examination of the healing MCL substance from both groups showed disorganized collagen, inflammation, and fibroblast proliferation that decreased over time. For group II knees, the V-V knee rotation was found to be significantly elevated (4.7 to 5.2 times the contralateral control), and did not decrease with time. In contrast, the V-V knee rotations of the group I specimens were 1.8 times greater than control immediately following injury, and approached control values by 12 weeks. Tensile testing of the FMTCs revealed that the ultimate load increased with time for both groups, but group I had significantly higher values than group II. The linear stiffness in group I was not different than that group II and did not increase with time. For the mechanical (material) properties of the healed MCL substance, the modulus of the healing tissue for group II was only 40% that of group I. The structural properties of the FMTC and the mechanical properties of the MCL substance from both groups at 6 and 12 weeks were significantly different from the contralateral controls. We further demonstrated that immediately after ACL reconstruction, the V-V rotation of group II knees could be restored to group I levels. Recent clinical studies of MCL healing following isolated complete ligament tears have suggested that nonoperative management without immobilization leads to excellent treatment outcome. However, in more severe injuries involving additional tissues, poor quality of the healed ligament tissue and articular degeneration are observed. Our results demonstrate the deleterious effects of an untreated triad injury on the healing of the MCL substance and its insertions. Examination of the MCL substance suggests that a much larger healing mass is formed following a triad injury, which partially compensates for inferior ligament mechanical properties.(ABSTRACT TRUNCATED AT 400 WORDS)     

Posttraumatic incarceration of medial collateral ligament into knee joint with anterior cruciate ligament injury

Medial collateral ligament of the knee is an important coronal stabiliser and often injured in isolation or as combination of injuries. The article reports a case of incarcerated medial collateral ligament (MCL) injury in combination with anterior cruciate ligament (ACL) injury in 20 year old male who presented to us 4 weeks after injury. Clinical examination and MRI was correlated to complete ACL tear with torn distal MCL and incarceration into the joint. Patient was taken up for ACL hamstring graft reconstruction with mini-arthrotomy and repair of the torn MCL. Patient was followed up with dedicated rehabilitation protocol with good functional results. At one year follow-up, patient exhibited full range of motion with negative Lachman, Pivot shift and valgus stress tests. This article highlights the rare pattern of MCL tear and also reviews the literature on this pattern of injury.     

Cellular senescence occurring in the rabbit medial collateral ligament during healing

Medial collateral ligament (MCL) healing proceeds in a temporally ordered fashion after injury. Despite the critical roles of fibroblasts during ligament repair, the phenotypic features of these healing fibroblasts have not been well characterized. Here, we show that healing MCL fibroblasts obtained from rabbits at 3‐week postinjury exhibited higher rates of senescent phenotypes and produced higher levels of TGF‐β1, collagens, α‐SMA, and matrix metalloproteinases (MMPs), than the corresponding fibroblasts from sham‐operated MCLs. Mechanical stretch further enhanced the cellular senescence and the expression of TGF‐β1, collagens, α‐SMA, and MMPs in both sham and healing MCL fibroblasts. In addition to MCL fibroblasts at 3‐week postinjury, the increased cellular senescence was also detected in healing MCL fibroblasts obtained at 4‐ and 6‐week postinjury. Most importantly, the association between the cellular senescence and ligament healing was confirmed in tissue sections by the senescence‐associated β‐galactosidase (SA‐β‐gal) staining. Using a recombinant TGF‐β1 and a neutralizing antibody, we found that those phenotypic changes, such as cellular senescence and the expression of collagens and MMPs, in MCL fibroblasts under mechanical loading conditions were regulated through TGF‐β1. Taken together, our results propose that cellular senescence and turnover of extracellular matrixes regulated by TGF‐β1 in MCL fibroblasts are critical for ligament healing. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:81–90, 2012     

Silk enhances the ligamentization of the polyethylene terephthalate artificial ligament in a canine anterior cruciate ligament reconstruction model

Anterior cruciate ligament (ACL) reconstruction is the leading treatment for ACL rupture. Ligament Advanced Reinforcement System (LARS), which is made of polyethylene terephthalate (PET), is the most frequently used artificial ligament for ACL reconstruction. However, PET is hydrophobic, so it is difficult to induce the ingrowth of the autologous tissue. The aim of this study is to explore the effects of silk hybrid on the ligamentization of the PET artificial ligament in a canine ACL reconstruction model. Silk/PET hybrid suspensory ligament was fabricated with silk in the weft yarn and PET in the warp yarn, while PET suspensory ligament was fabricated with PET in both the weft and warp yarns. After fabrication, the micromorphology of the ligaments was observed and mechanical testing was performed. Though the failure loads of the degummed silk/PET hybrid suspensory ligaments were significantly lower than those of the PET suspensory ligaments (P < 0.001), both of them were enough for ACL reconstructions of beagle dogs. In the animal study, 14 beagle dogs were divided into PET suspensory ligament group and silk/PET hybrid suspensory ligament group randomly, with 7 dogs in each. The dogs underwent ACL reconstructions in their right knees. At postoperative 6 months, the dogs were sacrificed, and the specimens were evaluated with gross observation, histology, immunohistochemistry, and mechanical testing. The histological and immunohistochemical results showed that the native ACL of the beagle dog held abundant fibroblasts and collagen. The PET‐regenerated ligament was loose, and there was a small amount of autologous tissue and collagen. Compared to the PET‐regenerated ligament, the silk/PET hybrid‐regenerated ligament had a compact structure, and there was more regenerated autologous tissue and collagen. In conclusion, compared to the PET ligament, the silk/PET hybrid ligament kept greater ability to induce the ingrowth of the autologous tissue, indicating that the silk hybrid had enhanced the ligamentization of the PET artificial ligament.     

In-situ force in the medial and lateral structures of intact and ACL-deficient knees

The anterior cruciate ligament (ACL) is the major contributor to limit excessive anterior tibial translation (ATT) when the knee is subjected to an anterior tibial load. However, the importance of the medial and lateral structures of the knee can also play a significant role in resisting anterior tibial loads, especially in the event of an ACL injury. Therefore, the objective of this study was to determine quantitatively the increase in the in-situ forces in the medial collateral ligament (MCL) and posterolateral structures (PLS) of the knee associated with ACL deficiency. Eight fresh-frozen cadaveric human knees were subjected to a 134-N anterior tibial load at full extension and at 15°, 30°, 60°, and 90° of knee flexion. The resulting 5 degrees of freedom kinematics were measured for the intact and the ACL-deficient knees. A robotic/universal force-moment sensor testing system was used for this purpose, as well as to determine the in-situ force in the MCL and PLS in the intact and ACL-deficient knees. For the intact knee, the in-situ forces in both the MCL and PLS were less than 20 N for all five flexion angles tested. But in the ACL-deficient knee, the in-situ forces in the MCL and PLS, respectively, were approximately two and five times as large as those in the intact knee (P < 0.05). The results of this study demonstrate that, although both the MCL and PLS play only a minor role in resisting anterior tibial loads in the intact knee, they become significant after ACL injury. Received: December 3, 1999 / Accepted: July 19, 2000     

Enhanced histologic repair in a central wound in the anterior cruciate ligament with a collagen-platelet-rich plasma scaffold.

The anterior cruciate ligament (ACL) of the knee is an intra-articular ligament that fails to heal after primary repair. The medial collateral ligament (MCL) of the knee is an extra-articular ligament that heals uneventfully in the majority of cases. Why these two ligaments have such different responses to injury remains unclear. In this article, we address two hypotheses: first, that the histologic response to injury is different in intra-articular and extra-articular ligaments, and second, that the response of the intra-articular ligaments can be altered by placing a collagen-platelet-rich plasma (collagen-PRP) hydrogel in the wound site. Wounds were created in extra-articular ligaments (MCL and/or patellar ligament) and an intra-articular ligament (ACL) in canine knees, and the histologic response to injury evaluated at 3 days (n = 3), 7 days (n = 4), 3 weeks (n = 5), and 6 weeks (n = 5). In the 3-week (n = 5) and 6-week (n = 5) animals, bilateral central wounds were made in the ACLs and the wounds in one knee of each animal treated with a collagen-PRP hydrogel while the contralateral side was untreated. Extra-articular ligament wounds had greater filling of the wound site and increased presence in the wound site of fibrinogen, fibronectin, PDGF-A, TGF-beta1, FGF-2, and von Willebrand's factor when compared to intra-articular ligament wounds. Treatment of the intra-articular wound with a collagen-PRP hydrogel resulted in increased filling of the wound site with repair tissue that had similar profiles of growth factor and protein expression to the extra-articular ligament wounds. The use of a collagen-PRP scaffold can ameliorate histologic differences noted between healing extra-articular ligamentous wounds and nonhealing intra-articular ligamentous wounds. This study supports the hypothesis that premature scaffold failure may play a key role in the normally expected failure of the ACL to heal after injury.     

膝内侧半月板“湾征”对内侧副韧带断裂的诊断意义

目的内侧副韧带损伤后,关节镜下可见内侧半月板上滑膜缘完全显示,类似海湾形状,称为"海湾全景征"(简称"湾征"),判断其作为诊断膝内侧副韧带断裂标志体征的可靠性及意义。方法 2007年3月-2011年3月,纳入59例MRI检查提示内侧副韧带断裂患者作为观察组,其中男38例,女21例;年龄16～39岁,平均23.2岁;单纯内侧副韧带断裂12例,合并外侧半月板损伤16例,前交叉韧带损伤27例,前、后交叉韧带损伤3例,髌骨脱位1例。68例MRI检查提示无内侧副韧带断裂患者作为对照组,其中男45例,女23例;年龄25～49岁,平均31.8岁;前交叉韧带损伤38例,前、后交叉韧带损伤4例,前交叉韧带合并外侧半月板损伤26例。两组治疗前后行关节镜探查比较"湾征"出现情况。结果观察组膝内侧副韧带修复重建前关节镜探查均见"湾征",明确内侧副韧带断裂;修复重建后"湾征"消失。对照组交叉韧带重建前后均未见"湾征"。结论 "湾征"可作为关节镜下膝内侧副韧带断裂的诊断指征,以及术中韧带修复重建成功与否的判断依据。     

Antiresorptive therapy conserves some periarticular bone and ligament mechanical properties after anterior cruciate ligament disruption in the rabbit knee

The purpose of this study was to assess, in an osteoarthritic (OA) model, whether bisphosphonate (BP) antiresorptive therapy altered periarticular bone and bone–ligament biomechanics and OA progression. We surgically transected the anterior cruciate ligament (ACLX) in two groups of rabbits; the first group was dosed with BP (risedronate, 0.01 mg/kg s.c. daily for 6 wk), the second group remained untreated, and a third group of normal (unoperated) control rabbits was also evaluated. We measured distal femoral bone mineral density (BMD, Dual Energy X‐ray Absorptiometry [DEXA]), medial collateral ligament (MCL) laxity, and bone mechanical function (bone cores mechanically tested in compression). These measures were related to cartilage/joint gross morphology, histology, and measures of vascular volume (gelatin–dye perfusion) for evidence of inflammatory angiogenesis and early OA. BMD by DEXA in 6 wk ACLX animals was 18% less than normal controls (p < 0.05). In contrast, BP dosing conserved periarticular BMD; risedronate‐treated rabbits had distal femoral BMD only 5% less and not significantly different than normal controls. When the same bone cores were compressed to failure, both ACLX and BP‐dosed animals were significantly weaker than normal controls (p < 0.05). However, the bone energy to failure and elastic modulus of BP‐dosed animals was conserved and not significantly different from normal controls 6 wk after ACLX. Blocking bone resorption with BP also resulted in a significantly improved bone–ligament structural complex. MCL‐complex laxity was significantly less in BP‐dosed animals (1.2 times that of normal controls) compared to untreated ACLX animals (1.7 times that of normal controls; p < 0.05). Blocking bone resorption with risedronate did not suppress osteophytosis and inflammatory angiogenesis, which were significantly increased in the periarticular bone of both untreated and BP treated ACLX animals. Thus, administering BP immediately after ACL loss conserved some periarticular bone and MCL‐complex properties in an early OA model. © 2004 Published by Elsevier Ltd. on behalf of Orthopaedic Research Society.     

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 2mM sodium nitroprusside treatment, ACL cells were more prone to apoptosis at 1mM. Based on flow cytometric analysis, DNA fragmentation at 1mM 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.     

Differences in cellular properties and responses to growth factors between human ACL and MCL cells

The anterior cruciate ligament (ACL) has poor healing responses compared with those of the medial collateral ligament (MCL). It has been implied that this is partially due to the poor reparative capacity of ACL cells for ligament injury. The present study was designed to elucidate the reparative capacities of human ACL and MCL cells by investigating their cellular properties and their responses to growth factors. Human ACL and MCL were obtained from seven fresh human cadavers. The cells were isolated from each tissue, and primary cultures were used for the examination. The growth rates of all the human ACL cells were lower than those of the human MCL cells; consistent with this, the doubling time of the ACL cells was 30 ± 7.4% longer than that of the MCL cells. The chemotactic migration of human ACL cells was 33 ± 8.1% slower and the synthesis of DNA and collagen in human ACL cells was 29 ± 6.3% and 31 ± 9.7% lower, respectively, in comparison with those of MCL cells. Cellular responses, in terms of DNA synthesis, in human ACL cells to either basic-fibroblast growth factor (1.0 and 10.0 ng/ml) or transforming growth factor-β (1.0 ng/ml) were lower than those of human MCL cells. However, no differences in the cellular responses in terms of collagen synthesis were found. Composite data show that human ACL cells have poorer cellular properties and lower responses to growth factors compared with those of human MCL cells, which suggests that the reparative capacity of human ACL cells may be poorer than that of human MCL cells. Received for publication on Sept. 2, 1998; accepted on Jan. 29, 1999