Medial collateral ligament healing one year after a concurrent medial collateral ligament and anterior cruciate ligament injury: An interdisciplinary study in rabbits

The optimal treatment for concurrent injuries to the medial collateral and anterior cruciate ligaments has not been determined, despite numerous clinical and laboratory studies. The objective of this study was to examine the effect of surgical repair of the medial collateral ligament on its biomechanical and biochemical properties 52 weeks after such injuries. In the left knee of 12 skeletally mature New Zealand White rabbits, the medial collateral ligament was torn and the anterior cruciate ligament was transected and then reconstructed. This is an experimental model previously developed in our laboratory. In six rabbits, the torn ends of the medial collateral ligament were repaired, and in the remaining six rabbits, the ligament was not repaired. Fifty-two weeks after injury, we examined varus-valgus and anterior-posterior knee stability; structural properties of the femur-medial collateral ligament-tibia complex; and mechanical properties, collagen content, and mature collagen crosslinking of the medial collateral ligament. We could not detect significant differences between repair and nonrepair groups for any biomechanical or biochemical property. Our data support clinical findings that when the medial collateral and anterior cruciate ligaments are injured concurrently and the anterior cruciate ligament is reconstructed, conservative treatment of the ruptured medial collateral ligament can result in successful healing.     

Healing of the medial collateral ligament after a combined medial collateral and anterior cruciate ligament injury and reconstruction of the anterior cruciate ligament: Comparison of repair and nonrepair of medial collateral ligament tears in rabbits

The optimal treatment for a combined injury of the medial collateral and anterior cruciate ligaments is controversial, and the question remains as to whether repair of the medial collateral ligament and reconstruction of the anterior cruciate ligament improves healing of the medial collateral ligament. We compared reconstruction of the anterior cruciate ligament with and without repair of the medial collateral ligament in a rabbit model of a combined injury of these two ligaments. The anterior-posterior translation and varus-valgus rotation of the knee, the structural properties of the femur-medial collateral ligament-tibia complex, and the mechanical properties of the midsubstance of the medial collateral ligament were evaluated immediately after surgery and at 6 and 12 weeks postoperatively. Repair of the medial collateral ligament led to significantly less varus-valgus rotation of the knee than did no repair, but the anterior-posterior translation of the knees in the repair and nonrepair groups were not significantly different at any study time. At 12 weeks, the cross-sectional area and ultimate load in the repair group were 60 and 53% greater, respectively, than in the nonrepair group. Among 12 specimens that were repaired (six specimens at 6 weeks and six specimens at 12 weeks), failure occurred within the midsubstance in four (two at each time period); in all of the specimens that were not repaired, failure occurred at the tibial insertion site. There was no significant difference between the modulus of the midsubstance in the repaired and the nonrepaired medial collateral ligaments. Thus, the improved structural properties of the femur-medial collateral ligament-tibia complexes that were repaired resulted from an increase in cross-sectional area of the repaired medial collateral ligament and healing of the tibial insertion site. Postoperative healing time had little effect on the tensile properties. In this rabbit model, repair of the medial collateral ligament with reconstruction of the anterior cruciate ligament may lead to better healing of the medial collateral ligament in the early phase than does reconstruction of the anterior cruciate ligament alone.     

The effects of transection of the anterior cruciate ligament on healing of the medial collateral ligament. A biomechanical study of the knee in dogs

The effect of concurrent injury to the anterior cruciate ligament on the healing of injuries of the medial collateral ligament was studied in dogs. In Group I, isolated transection of the medial collateral ligament was performed; in Group II, transection of the medial collateral ligament with partial transection of the anterior cruciate ligament; and in Group III, complete transection of both the medial collateral ligament and the anterior cruciate ligament. The three groups of animals were examined six and twelve weeks postoperatively with respect to varus-valgus rotation of the knee and tensile properties of the femur-medial collateral ligament-tibia complex. The varus-valgus rotation of the knee was found to be the largest in Group-III specimens at all time-periods and was 3.5 times greater than the control values at twelve weeks. Group-I and Group-II specimens also showed large varus-valgus rotations at time zero, but the rotations returned to the control values by twelve weeks. For the structural properties of the femur-medial collateral ligament-tibia complex, the values for ultimate load for Groups I and II reached the control values by twelve weeks, while that for Group III remained at only 80 per cent of the control value. Both energy absorbed at failure and linear stiffness for all three groups were less than those for the controls at six weeks, and only linear stiffness returned to the control values by twelve weeks. For the mechanical (material) properties of the healed ligament substance, the values for modulus and tensile strength were markedly lower than the control values for all groups at six weeks. By twelve weeks, the tensile strength of Group-I specimens had increased to 52 per cent of the control value, while those of Groups II and III were only 45 and 14 per cent, respectively. Our results demonstrate that healing of the transected medial collateral ligament is adversely affected by concomitant transection of the anterior cruciate ligament. Both varus-valgus rotation and mechanical properties of the healed ligament failed to recover in knees that had combined transection of the anterior cruciate and medial collateral ligaments. The structural properties of the femur-medial collateral ligament-tibia complex in tension recovered more rapidly as a consequence of the large mass of reparative tissue that formed in the medial collateral ligament of the anterior cruciate-deficient knees.     

Die Wertigkeit der sonographischen Diagnostik des verletzten Kniegelenkes in der unfallchirurgischen Praxis

In a period of two years (January 1990 to December 1991) 136 kneejoints were examined by ultrasound and arthroscopy, 40 out of 42 arthroscopically proven lesions of the anterior cruciate ligament were detected by ultrasound. The sensitivity therefore was 95.24%. We found three cases of ruptures of the posterior cruciate ligament, wich were not detected clinically. 16 cases of ruptured medial collateral ligaments and 27 cases of elongations of the same ligament were diagnosed. Ultrasound examination of the knee and especially of the cruciate ligaments showed to be an accurate tool in order to obtain additional information on an injured knee even if clinical examination is difficult or impossible. Sonography is able to exclude lesions of the cruciate ligaments precisely. Therefore it helps to restrict the necessity of acute or early arthroscopy of knee joints.     

Adaptation of post-traumatic angiogenesis in the rabbit knee by apposition of torn ligament ends.

Apposition of torn ligament ends has been shown to have a beneficial effect on healing of the medial collateral ligament; however, the mechanism underlying this improved recovery is unclear. Excessive post-traumatic angiogenesis, an inherent component of soft-tissue regeneration, may be functionally detrimental in relatively hypovascular tissues such as ligaments. The present study therefore examined the relationship between contact of transected ligament ends and vascular remodeling. Female New Zealand White rabbits were subjected to a gap injury, Z-plasty apposition, or sham operation to the midsubstance of the medial collateral ligament. Six weeks after treatment, the volume of vessels supplying the healing zone of the medial collateral ligament, as well as the ipsilateral lateral collateral ligament, posterior cruciate ligament. menisci, and medial capsule, was quantified by carmine red vascular casting. The volume of vessels supplying the neoligamentous scar formed by gap injury to the medial collateral ligament was found to be twice that of ligaments that had undergone the sham operation, and lateral collateral ligament and meniscal vascularity was also augmented in the injured joint. The medial collateral ligaments that underwent Z-plasty apposition exhibited a level of vascularity comparable with that of the control ligaments that had undergone the sham procedure, whereas meniscal and lateral collateral ligament vascularities remained elevated in this group. Capsular and posterior cruciate ligament vascularities were unaffected by gap injury or Z-plasty to the ipsilateral medial collateral ligament. These findings indicate that injury to the medial collateral ligament not only stimulates angiogenesis in the healing ligament, but other ipsilateral soft tissues also undergo vascular remodeling. Furthermore, apposition of an injured medial collateral ligament modifies these pro-angiogenic events, and this may partly explain why contact of torn ligament ends is beneficial for post-traumatic recovery of an injured joint.     

A biomechanical evaluation of the Lenox Hill knee brace

This study was conducted to determine the effectiveness of the Lenox Hill knee brace in limiting anterior translation and external rotation of the tibia in reference to the femur in normal and ligament-deficient knees. Four fresh cadaver knees were fitted with Lenox Hill knee braces according to the manufacturer's guidelines. A computer-assisted testing apparatus was constructed that allowed each knee to be tested as a function of knee flexion angle, joint load, and soft tissue integrity. Each knee served as its own control. While 45 kg of anterior force was applied to the tibia of the anterior cruciate ligament deficient knees, the Lenox Hill knee brace was able to decrease anterior translation from an average of 10 mm, to 5.7 mm, at 30 degrees of flexion when no vertical load was present. This limiting effect was lost when the medial collateral ligament was sectioned in addition to the anterior cruciate ligament or when both the medial and the lateral collateral ligaments were sectioned along with the anterior cruciate ligament. When 20 Newton-meters (Nm) of torque was applied to the femurs at 30 degrees of flexion without vertical load, the Lenox Hill knee brace limited external rotation of the tibia in all tested categories. For intact knees at 30 degrees of flexion and no vertical load, the Lenox Hill knee brace decreased external rotation from 18 degrees to 10 degrees. In the anterior cruciate ligament-sectioned knees, external rotation was decreased from an average of 20.2 degrees to 16.1 degrees. In the knees with sectioned anterior cruciate and medial collateral ligaments, the average reduction was from 21.2 degrees to 15.4 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased expression of the β1, α5 and αv integrin adhesion receptor subunits occurs coincident with remodeling of stress-deprived rabbit anterior cruciate and medial collateral ligaments

The biomechanical, biochemical, and morphological properties of the anterior cruciate and medial collateral ligaments are dramatically altered in response to deprivation of normal physical forces and joint motion. Integrin adhesion receptors are known to play important roles in the tissue remodeling that occurs in the course of normal wound repair. We propose that integrins play a similar role in the remodeling of the extracellular matrix in stress-deprived periarticular ligaments. This study tests the hypothesis that altered expression of integrins on ligament fibroblasts accompanies this remodeling. The left knees of 15 New Zealand White rabbits were surgically immobilized in acute flexion and the right knees served as controls (no operation). The anterior cruciate and medial collateral ligaments were harvested at 1, 3, 5, 9, or 12 weeks after immobilization. Sections from the ligaments were immunostained with monoclonal antibodies specific for the integrin subunits β₁, α₅, α₆, and α_v, as well as with a negative control antibody. Fibroblasts within both the stress-deprived anterior cruciate and medial collateral ligaments demonstrated markedly increased staining for the β₁, α₅, and α_v subunits, as compared with the controls. The increased staining was greatest at 9 weeks in the anterior cruciate ligament and at 12 weeks in the medial collateral ligament. Western blot study of ligament proteins extracted with sodium dodecyl sulfate demonstrated an increased amount of β₁ subunit protein in both ligaments from knees that were stress deprived for 9 and 12 weeks, as compared with the control ligaments. These studies establish that stress deprivation in this animal model is accompanied by increased expression of integrin cell-surface receptors containing the β₁, α₅, and α_v subunits on anterior cruciate and medial collateral ligament fibroblasts, with a time course similar to that previously reported for indices of extracellular matrix remodeling induced by stress deprivation. This outcome suggests an important role for these integrins in the remodeling of stress-deprived ligaments.     

Isolierte und kombinierte Kniebandverletzungen

Complex knee ligament injuries are characterized by simultaneous rupture of the anterior cruciate ligament (ACL) and/or the posterior cruciate ligament (PCL) and at least one collateral ligament. Isolated injury to the medial collateral ligament (MCL) and PCL have a high healing capacity and can be treated conservatively in many cases. Ruptures of the MCL can also be treated conservatively in complex injuries if the cruciate ligaments are reconstructed. Ruptures of the lateral structures usually need surgical reconstruction. Indications for acute surgical repair include meniscus dislocation, entrapment of collateral ligament portions in the joint, knee dislocation with severe knee instability, and displaced bony avulsions. The anatomy of the knee ligaments must be carefully respected in surgical reconstruction. Acute repair of collateral ligament injuries is possible only in the first 2 weeks after trauma. Acute arthroscopy is indicated only in combination with reconstructive surgery.     

Complex instability of the anterior knee

Complex knee instability involves the anterior cruciate ligament (ACL) and one or more major stabilizers of the knee [medial collateral ligament (MCL), lateral collateral ligament (LCL), posterior cruciate ligament (PCL)]. The medial side has a high healing potential and does not need operative treatment in most cases if ACL reconstruction is performed. Reconstruction of the medial ligament complex is indicated in gross instability of the medial meniscus fixation, dislocation of the MCL into the joint, and large dislocated bony avulsions. Injuries on the lateral side do not heal spontaneously and require acute operative treatment (first 2 weeks). Frank knee dislocations and gross multiligament injuries should be reduced acutely, and the integrity of the vascular structures must be examined closely. In a European multicenter study, operative treatment with reconstruction of both cruciate ligaments and functional rehabilitation gave better results than conservative treatment with immobilization of the joint.     

Periarticular ligament changes following ACL/MCL transection in an ovine stifle joint model of osteoarthritis.

Anterior cruciate ligament (ACL) injuries often lead to significant functional impairment, and are associated with increased risk for induction of degenerative joint disease. However, few studies have described the effect of ligament transection on the remaining intact knee ligaments. This study sought to determine specifically what impact combined ACL/medial collateral ligament (MCL) transection had on the remaining intact knee ligaments, particularly from the histological, biochemical, and molecular perspectives. Twenty weeks post-ACL/MCL transection, the cut ends of sheep MCLs were bridged by scar, while the posterior cruciate ligaments (PCLs) and lateral collateral ligaments (LCLs) seemed gross morphologically normal. Water content and cell density increased significantly in the MCL scars and the intact PCLs but were unchanged in the LCLs. Collagen fibril diameter distribution was significantly altered in both MCL scar tissue and uninjured PCLs from transected joints. MMP-13 mRNA levels in MCL scars and PCLs from ligament transected joints were increased, while TIMP-1 mRNA levels were significantly decreased in the PCLs only. This study has shown that some intact ligaments in injured joints are impacted by the injury. The joint appears to behave like an integrated organ system, with injury to one component affecting the other components as the "organ" attempts to adapt to the loss of integrity.     

Ligament injuries associated with tibial plateau fractures

Thirty-nine patients with tibial plateau fractures and concomitant ligament injury were evaluated at least one year after injury. Ligamentous injury was determined by stress roentgenograms, plain roentgenograms, operative findings, and Pelle-grini-Stieda's ossification. There were 22 isolated medial collateral, eight lateral collateral, one isolated anterior cruciate, and eight combined ligament injuries. All types of tibial plateau fractures were associated with ligamentous injury, although split compression and local compression were most common. Twenty patients (Group 1) did not have operative repair of the injured ligaments, and 19 patients (Group 2) had primary repair of the injured ligaments. Open reduction and internal fixation of the plateau fracture(s) were performed in 13 patients in Group 1 and 19 patients in Group 2. Follow-up evaluation (100-point scale), including subjective, functional, and anatomic factors, revealed 12 excellent and good, four fair, and three poor results in the 19 patients with ligamentous repair. There were ten excellent and good, two fair, and eight poor results in those without ligament repair. Ten of the 12 patients with 10 degrees or more of instability had poor results. These poor results included five unrepaired medial collateral ligaments, two unrepaired lateral collateral ligaments, and three patients with cruciate ligament injury. This study confirms the view that instability is a major cause of unacceptable results in tibial plateau fractures. Operative repair of medial and lateral collateral ligaments, with appropriate treatment of the bony plateau fracture, may reduce late instability and may improve overall morbidity in these concomitant injuries. Cruciate ligament injury associated with a tibial plateau fracture carries a poor prognosis.     

Time-dependent increases in type-III collagen gene expression in medical collateral ligament fibroblasts under cyclic strains.

Numerous studies have demonstrated the capacity of mechanical strains to modulate cell behavior through several different signaling pathways. Understanding the response of ligament fibroblasts to mechanically induced strains may provide useful knowledge for treating ligament injury and improving rehabilitation regimens. Biomechanical studies that quantify strains in the anterior cruciate and medial collateral ligaments have shown that these ligaments are subjected to 4-5% strains during normal activities and can be strained to 7.7% during external application of loads to the knee joint. The objective of this study was to characterize the expression of types I and III collagen in fibroblast monolayers of anterior cruciate and medial collateral ligaments subjected to equibiaxial strains on flexible growth surfaces (0.05 and 0.075 strains) by quantifying levels of mRNA encoding these two proteins. Both cyclic strain magnitudes were studied under a frequency of 1 Hz. The results indicated marked differences in responses to strain regimens not only between types I and III collagen mRNA expression within each cell type but also in patterns of expression between anterior cruciate and medial collateral ligament cells. Whereas anterior cruciate ligament fibroblasts responded to cyclic strains by expression of higher levels of type-I collagen message with almost no significant increases in type-III collagen, medial collateral ligament fibroblasts exhibited statistically significant increases in type-III collagen mRNA at all time points after initiation of strain with almost no significant increases in type-I collagen. Furthermore, differences in responses by fibroblasts from the two ligaments were detected between the two strain magnitudes. In particular, 0.075 strains induced a time-dependent increase in type-III collagen mRNA levels in medial collateral ligament fibroblasts whereas 0.05 strains did not. The strain-induced changes in gene expression of these two collagens may have implications for the healing processes in ligament tissue. The differences may explain, in part, the healing differential between the anterior cruciate and medial collateral ligaments in vivo.     

Effects of joint load on the stiffness and laxity of ligament-deficient knees. An in vitro study of the anterior cruciate and medial collateral ligaments

We measured the effects of serial section of the medial collateral ligament and anterior cruciate ligament and of the anterior cruciate ligament and medial collateral ligament on anterior-posterior force-versus-displacement and tibial torque-versus-rotation response curves for seven fresh frozen cadaver knees at zero and 20 degrees of flexion before and after application of as much as 925 newtons of compressive load on the tibiofemoral joint. Section of the anterior cruciate ligament always increased anterior laxity in an unloaded specimen; joint load reduced this increase by a greater amount at zero degrees than at 20 degrees of flexion. Joint load was more effective in limiting anterior laxity in anterior cruciate-deficient specimens at low levels of applied anterior force; at higher levels of applied force, the effects of joint congruency were overcome and ligament restraints came into play. Section of the medial collateral ligament increased anterior laxity in an unloaded knee only for specimens in which the anterior cruciate ligament had been previously sectioned; joint load eliminated this increase at full extension but did not do so at 20 degrees of flexion. The medial collateral ligament was the more important of the two ligaments in controlling torsional laxity. Secondary section of either ligament (the other ligament having been sectioned first) produced a greater increase in laxity than did primary section of that ligament in an intact knee. Increases in torsional laxity due to primary section of either ligament were unaffected by the application of joint load. Joint load reduced increases in laxity that were due to secondary section of the medial collateral ligament.     

Knee dislocations: where are the lesions? A prospective evaluation of surgical findings in 63 cases

OBJECTIVE: To evaluate soft-tissue injury patterns in a large series of patients with knee dislocations to identify frequency and associations that may aid in surgical planning. DESIGN: Prospective clinical study. SETTING: Two institutions, both level I trauma centers. PATIENTS: Sixty patients with 63 dislocatable knees. RESULTS: Cause of injury was motor vehicle injury in 34 patients, sports in 23 patients, and falls in 3 patients; 71% of knees studied had bicruciate injuries. Eight knees had associated major intraarticular fractures. Vascular disruption occurred in 14% of knees. Peroneal nerve palsies occurred in 14% of knees. All injured knees with complete peroneal nerve palsies had anterior cruciate ligament, posterior cruciate ligament, and lateral collateral ligament disruptions. The incidence of vascular injury was the same for patients injured in sports as for those injured in road trauma. Reattachable ligamentous avulsions occurred in 19% for anterior cruciate ligament, 51% for posterior cruciate ligament, 64% for medial collateral ligament, and 84% for lateral collateral ligament injuries. Certain injury patterns also had a high association of tendon and capsule avulsions. Proximal lateral collateral ligament injuries were commonly associated with popliteus tendon avulsions and seldom with distal biceps avulsions. Distal lateral collateral ligament injuries were commonly associated with distal biceps avulsions and seldom with popliteus tendon avulsions. Reattachable meniscal capsular avulsions off the tibia occurred predominantly when the collateral ligament injury was a distal avulsion. CONCLUSIONS: This study showed a wide variety of injury patterns. Knees had to have at least two ligaments injured to be dislocatable but not necessarily both cruciate ligaments. Sports injuries have the same pattern of injury as motor vehicle accidents, suggesting similar forces of injury. The study demonstrates a high incidence of reattachable avulsion injuries to ligaments and soft tissues in dislocatable knees. These may not be as easily dealt with if surgery is delayed beyond 3-4 weeks.     

Integrin display increases in the wounded rabbit medial collateral ligament but not the wounded anterior cruciate ligament

The differential capacities of the anterior cruciate and medial collateral ligaments to heal may be related to differences in cellular function. This study tested the hypothesis that differential expression of integrins occurs in these ligaments after injury. The integrins are a family of cell surface receptors that mediate adhesion, migration, and other cellular functions critical to the healing of a wound. A similar complement and amount of the β₁ subfamily of integrins are known to be present on the unperturbed anterior cruciate and medial collateral ligaments in humans and rabbits. A partial laceration was surgically created in these two ligaments in 12 anesthetized New Zealand White rabbits. Immunohistochemistry was performed on sections from the ligaments at 1, 3, 7, and 10 days after injury, using monoclonal antibodies directed against the integrin subunits β₁, α₅, α₆, and α_v. Between 3 and 7 days, the wounded medial collateral ligament demonstrated a striking increase in staining for the β₁, α₅, and α_v subunits on the fibroblasts, within the repair site, and on capillary endothelium. Increased staining was most marked for the β₁ subunit and less marked for the α₅ and α_v subunits. The α₆ subunit stained exclusively vascular structures within the healing medial collateral ligament. In marked contrast, the anterior cruciate ligament, which does not mount an effective repair response, demonstrated no comparable alteration of integrin expression from baseline levels. This study demonstrates that increased expression of integrins occurs coincident with wound healing in the medial collateral ligament, whereas this expression remains at baseline levels in the nonhealing wounded anterior cruciate ligament. This observation suggests that a failure to alter expression of integrins subsequent to injury may play a role in the defective healing of the anterior cruciate ligament.     

Synergistic effect of growth factors on cell outgrowth from explants of rabbit anterior cruciate and medial collateral ligaments

Cellular migration and proliferation are integral aspects of wound healing. An in vitro assay for cellular migration and proliferation using explants of rabbit anterior cruciate and medial collateral ligaments was developed previously. This study presents the effects of serum-free culture medium supplemented with basic fibroblast growth factor, bovine insulin, transforming growth factor-β1, and platelet-derived growth factor-B, added either individually or in combination, on cell outgrowth in explants of rabbit anterior cruciate and medial collateral ligaments. Outgrowth was assessed at 3 and 6 days by counting the number of cells surrounding the tissue explants. For explants of both ligaments, cell outgrowth was dependent on the presence of 10% fetal bovine serum or the combination of growth factors. Little outgrowth occurred in explants of either ligament in the presence of basic fibroblast growth factor, transforming growth factor-β1, or bovine insulin. Platelet-derived growth factor-B at concentrations of 20 and 100 ng/ml seemed to increase cell outgrowth from medial collateral ligament explants at 6 days. The outgrowth from the explants of both ligaments was much greater in the presence of all four growth factors than the sum of the outgrowth with the individual factors. This synergistic effect was as much as 10-fold and 20-fold for the anterior cruciate ligament explants at days 3 and 6, respectively, but no more than 3-fold for the medial collateral ligament explants at these times. Medial collateral ligament explants exhibited greater cell outgrowth than anterior cruciate ligament explants in 10% serum and in the presence of the four growth factors.     

An irreducible knee dislocation: a case report

An 8-year-old man presented after sustaining an injury during a fall. A closed reduction attempt failed, and after several tests, an open reduction was performed. With posterolateral dislocation of the knee, there can be anterior cruciate ligament, posterior cruciate ligament, and medial collateral ligament disruption. At the 6-month (final) follow-up, the patient had no subjective pain or instability. With this type of injury, the approach can be conservative monitoring or repair of all of the ligaments. Because of the age and activity level of our patient, we opted for repair of the medial collateral ligament initially with the possibility of late anterior cruciate ligament and/or posterior cruciate ligament reconstruction.     

In vivo and in vitro investigation of the long-term behavior and fatigue strength of carbon fiber ligament replacement

The long-term behavior of carbon fiber ligament replacements was evaluated in sheep. In vitro assessments of both isolated carbon fiber prostheses and resected animal ligaments were performed. The right knee in 45 sheep was reconstructed. In 30 animals, only the medical collateral ligaments were replaced, but with different systems of anchorage to bone. In 15 animals, a combined replacement of medial collateral ligament and anterior cruciate ligament was performed. In the first group the animals were sacrificed three months postoperation, while in the latter group evaluation was performed one year after surgery. After one year the strength of the medial collateral ligament complex was higher than that of the normal sheep ligaments. The elasticity and extensibility were similar to those of the normal ligaments. No case of partial rupture or rupture of the medial collateral ligament replacements was seen, but four of 12 anterior cruciate replacements showed signs of partial rupture. In vitro testing showed that rupture is more likely to occur where movement occurs around a small radius of bending, and this may be a factor in these cases where the anterior cruciate ligament enters a bony tunnel at an acute angle. Histologic assessment showed good biocompatibility, similar to that reported by other authors. With an operative technique designed to increase the radius of bending where the carbon fiber enters bone, these ligament replacements have a fatigue strength and elasticity adequate for long-term survival.