Physiological and mechanical adaptations of rabbit medial collateral ligament after anterior cruciate ligament transection

Progressive physiological and mechanical changes in the medial collateral ligament of the adult rabbit were investigated for as long as 48 weeks after disruption of the anterior cruciate ligament. Eighty-one New Zealand White rabbits were separated into experimental, sham-operated control, and normal control groups. The experimental group underwent unilateral transection of the right anterior cruciate ligament, sham-operated animals served as controls for comparison, and normal animals were evaluated as age-matched, undisturbed (no surgery) controls. Blood flow to the medial collateral ligament (as a physiological measure) and mechanical function (structural and material properties) were assessed at 6, 14, and 48 weeks. The results indicated that loss of the anterior cruciate ligament leads to early mechanical deterioration of the medial collateral ligament with a corresponding loss of physiological homeostasis. Six to 14 weeks after the transection, values for cross-sectional area of the medial collateral ligaments rapidly increased to 1.5 times control values. The ligament became twice as large as the control ligament by 48 weeks. Concomitantly, medial collateral ligament stress at failure of the medial collateral ligament complex decreased rapidly 6-14 weeks after the transection and eventually fell to one-half that of controls by 48 weeks. In terms of low-load behaviour, laxity and load relaxation were significantly greater than that of controls 6 weeks after transection and were further increased by 14 weeks. By 48 weeks, laxity values had recovered somewhat and load-relaxation measures had recovered to near control values. At both 6 and 14 weeks, a statistically significant elevation in blood flow was demonstrated compared with controls. By 48 weeks, however, blood flow was no different from that of the sham-operated control. Thus, early after transection of the anterior cruciate ligament, both low-load and high-load mechanical properties of the medial collateral ligament deteriorated and the rate of blood flow was temporarily elevated. By 48 weeks, blood flow declined to near control values, with a corresponding recovery in viscoelastic behaviour. These findings suggest that, after transection of the anterior cruciate ligament, viscoelastic behaviour of the medial collateral ligament may be related to changes in blood flow and that restoration of normal flow patterns and vascular responses may be linked to tne recovery of some low-load mechanical properties in the anterior cruciate ligament-deficient medial collateral ligament.     

Vascular structure and function in the medial collateral ligament of anterior cruciate ligament transected rabbit knees

To determine if decreased vascular responsiveness in the medial collateral ligament (MCL) of anterior cruciate ligament transected (ACL‐t) rabbit knees is due to pericyte deficiency associated with angiogenesis. Vascular responses to potassium chloride (KCl), phenylephrine, acetylcholine, and sodium nitroprusside (SNP) were evaluated in ACL‐t rabbit knees (n = 6) and control knees (n = 5) using laser speckle perfusion imaging. Ligament degeneration was determined by ultrasound imaging. Vascular and pericyte volume were measured using quantitative immunohistochemical volumetric analysis using CD31 and α‐smooth muscle actin antibodies with co‐localization analysis. Perfusion was increased in the ACL‐t rabbits 2.5‐fold. Responsiveness to phenylephrine, SNP, and acetylcholine was significantly decreased in the ACL knee while no change in KCl responses was seen. MCL ultrasound imaging revealed decreased collagen organization, increased ligament thickness, and increased water content in the ACL‐t MCL. Vascular Volume was increased fourfold in ACL deficient knees, while pericyte volume to endothelial volume was not changed. No difference in CD31 and α‐SMA co‐localization was found. Blood vessels in the MCL of ACL‐t knees do not lack smooth muscle. The MCL vasculature can undergo constrictive response to KCl, but have impaired receptor mediated responses and impaired nitric oxide signaling. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:1104–1110, 2014.     

Combined anterior cruciate ligament and medial collateral ligament injuries in adolescents

Although literature supports bracing of most medial collateral ligament (MCL) injuries followed by arthroscopic repair of anterior cruciate ligament (ACL) tears in adults with combined ACL-MCL injuries, little is published regarding the treatment of these injuries in the pediatric population. The purpose of this study was to present our outcomes after treatment of combined ACL-MCL injuries in a series of adolescents. All 180 patients who underwent ACL reconstruction at our children's hospital from January 1997 to January 2003 were reviewed to identify those patients with concomitant grade II or III MCL injuries. Clinical data were obtained from chart review. All patients were treated with a hinged brace for their MCL injury followed by delayed arthroscopic reconstruction of their ACL using a transphyseal technique with Achilles tendon soft tissue allograft. Patients were contacted by phone to complete Lysholm knee questionnaires and assess return to athletic competition. Data were compared with a control cohort of patients who underwent isolated ACL reconstruction using the same technique. Twelve (6.7%) of 180 patients had combined ACL-MCL injuries. There were 6 boys and 6 girls; the mean age was 15.6 years (range, 14-17 years). Follow-up averaged 5.3 years (range, 2.6-8.2 years), and no patients were lost to follow-up. At last examination, all patients had a stable knee on both Lachman and valgus stress tests; the mean Lysholm knee score was 96 (range, 94-100). All patients were able to return to their preinjury level of athletics. One patient required manipulation for arthrofibrosis. When compared with the control group of 19 isolated ACL reconstructions, there was no significant difference with regards to Lysholm scores or return to athletics.Bracing of grade 2 or 3 MCL injuries followed by ACL reconstruction was an effective means of treating combined ACL-MCL injuries in this small series of adolescent patients.     

Combined injuries of the medial collateral ligament and the anterior cruciate ligament

Aim of this retrospective study is to evaluate the effect of acute and late anterior cruciate ligament (ACL) reconstruction in patients with a combined injury of the ACL and the medial collateral ligament (MCL). All MCL injuries were treated non-operatively. In 27 patients (group I) we performed early ACL reconstruction (within the first 3 weeks after injury). The postoperative rehabilitation protocol included brace treatment for all patients over a period of 6 weeks. In 37 patients we performed late ACL reconstruction (after a minimum of 10 weeks). In this group initial non-operative MCL treatment (6 weeks brace treatment) was followed by a period of accelerated rehabilitation. Patients with late ACL reconstruction had a lower rate of loss of motion after finishing the postoperative rehabilitation programme and a lower rate of re-arthroscopies for a loss of extension (group I: 4 patients, group II: 1 patient). The difference in the mean quadriceps muscle strength (group I: 83.3%, group II: 86.3%) was not statistically significant. After a mean interval of 22 months, we saw no difference in the frequency of anterior or medial instabilities or in the loss of motion. The Lysholm score was significantly better in the group with late ACL reconstruction (group I: 85.3, group II: 89.9). The position on the Tegner activity scale decreased in both groups, to 5.5 in group I (preoperatively: 6.0) and to 5.6 in group II (preoperatively: 5.9). With regard to the lower rate of motion complications in the early postoperative period, the lower rate of re-arthroscopies, and the significantly better results in the Lysholm score, we prefer late ACL reconstruction in the treatment of combined injuries of the ACL and the MCL.     

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 effect of medial collateral ligament insufficiency on the reconstructed anterior cruciate ligament: A study in the rabbit

The treatment for severe combined anterior cruciate ligament (ACL) and medial collateral ligament (MCL) ruptures is disputed. Using a rabbit model, we examined the effect of insufficiency of medial structures on the reconstructed ACL in combined ACL and MCL injury. 40 rabbits were divided into 2 groups. In both groups, ACL was subjected to in situ freezethaw treatment. In group F, only freeze-thaw treatment of ACL was given. In group FM, partial resection of MCL was also done. We killed 5 rabbits on each of 4 occasions: immediately after the operation (time 0), at 6, 12 and 24 weeks postoperatively. At each time, we measured valgus instability and mechanical properties of the ACL. Valgus instability in group FM persisted from time 0 to 24 weeks, and was significantly greater than that in group F. The tensile strength and tangent modulus of the ACL in group FM were lower than those in group F. We found that continuous valgus instability reduces the mechanical properties of the in situ frozen ACL.     

The effect of medial collateral ligament insufficiency on the reconstructed anterior cruciate ligament: a study in the rabbit

The treatment for severe combined anterior cruciate ligament (ACL) and medial collateral ligament (MCL) ruptures is disputed. Using a rabbit model, we examined the effect of insufficiency of medial structures on the reconstructed ACL in combined ACL and MCL injury. 40 rabbits were divided into 2 groups. In both groups, ACL was subjected to in situ freeze-thaw treatment. In group F, only freeze-thaw treatment of ACL was given. In group FM, partial resection of MCL was also done. We killed 5 rabbits on each of 4 occasions: immediately after the operation (time 0), at 6, 12 and 24 weeks postoperatively. At each time, we measured valgus instability and mechanical properties of the ACL. Valgus instability in group FM persisted from time 0 to 24 weeks, and was significantly greater than that in group F. The tensile strength and tangent modulus of the ACL in group FM were lower than those in group F. We found that continuous valgus instability reduces the mechanical properties of the in situ frozen ACL.     

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 rabbit medial collateral ligament following an o'donoghue triad injury: Effects of anterior cruciate ligament reconstruction

The effects of healing time and anterior cruciate ligament reconstruction on healing of the medial collateral ligament and stability of the knee joint were evaluated in a rabbit model of an O'Donoghue triad injury (rupture of the medial collateral ligament with removal of the anterior cruciate ligament and part of the medial meniscus). At time 0 and at 6 and 12 weeks postoperatively, 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 substance of the medial collateral ligament were evaluated. Although anterior-posterior translation increased significantly with time, we could not demonstrate a significant temporal effect on varus-valgus rotation. The ultimate load, elongation at failure, and energy absorbed to failure improved with time. In addition, with time, failure of the complex occurred more often in the ligament substance than at the osseous insertion. Because healing time did not affect the cross-sectional area or modulus of the medial collateral ligament, the improved structural properties of the complex resulted not from improvements in the mechanical properties of the tissue but rather from healing of the tibial insertion site. By 12 weeks, the reconstructed knees had only minor signs of osteoarthrosis on the tibiofemoral surfaces; this is in contrast to the findings in anterior cruciate ligament-deficient knees in our earlier study. Initially, reconstruction also improved stability of the knee. Additionally, at 12 weeks, the stiffness of the complexes from the reconstructed group was 1.3 times that of the anterior cruciate ligament-deficient group (p < 0.05), and the ultimate load had increased by a factor of 1.6 (p < 0.05). Our findings demonstrate that reconstruction of the anterior cruciate ligament in the rabbit helps to stabilize the joint, improves healing of the medial collateral ligament, and may decrease the incidence of early-onset osteoarthrosis after an O'Donoghue triad injury.     

内侧副韧带合并前交叉韧带损伤的临床治疗策略

膝关节内侧副韧带Hughston Ⅲ级损伤常合并有前交叉韧带损伤,韧带重建术是目前该类损伤主要的治疗方式。其中,前交叉韧带重建术已经从传统的等长重建发展到解剖重建,使膝关节术后的前后稳定性和患者的运动水平得到了更满意的临床效果;目前内侧副韧带的重建方式较多,但是大多不能很好的恢复膝关节的旋转稳定性,内侧副韧带三角矢量重建在恢复膝关节外翻稳定性的同时,能够有效的恢复旋转稳定性。对于合并有内侧副韧带和前交叉韧带的损伤,二者造成旋转稳定性的叠加损失,内侧副韧带三角矢量重建发挥的作用就显得更加重要。作者提出了一种治疗内侧副韧带和前交叉韧带合并损伤的临床治疗策略,旨在更好地指导、应用于临床。     

Medial collateral knee ligament healing: Combined medial collateral and anterior cruciate ligament injuries studied in rabbits

We examined the histological appearance and biochemical properties of the healing medial collateral ligament (MCL) of a rabbit knee after combined MCL and anterior cruciate ligament (ACL) injury treated with ACL reconstruction and with or without MCL repair. By so doing, we hoped to understand better our previous biomechanical observations (Ohno et al. 1995) and possibly learn where to focus future investigation into improving the quality of the healing MCL.

Ligaments were examined at 6 and 12 weeks of healing. We found healing of all ligaments with hypercellularity and fibroblast elongation along the axis of loading, as expected. Unexpected, however, was the finding of multiple osteophytes in both the repaired and nonrepaired specimens at the medial borders of the joint and at the MCL insertions. These were felt to affect possibly the biomechanics of the MCL by causing stress risers at the point where they undermine the ligament. Biochemically, we demonstrated a correlation between collagen content and hydroxypyridinium crosslinks and modulus of elasticity. While this implies that the modulus is dependent on collagen content and hydroxypyridinium crosslink density, modulus is also probably dependent on other factors such as collagen organization, type and internal structure. Overall, the detailed characterization and correlation between the histological, biochemical, and biomechanical properties of the healing MCL in the severe knee injury model provide insight into the functional behavior of the healing MCL.     

膝前、后交叉韧带与内侧副韧带损伤的一期修复重建

目的探讨膝关节镜下重建前、后交叉韧带联合有限切开修复内侧副韧带恢复膝关节稳定和功能的疗效。方法 2003年4月-2010年10月,收治14例(14膝)前、后交叉韧带伴内侧副韧带损伤患者。男10例,女4例;年龄21～71岁,平均41岁。致伤原因:交通事故伤11例,高处坠落伤3例。患者受伤至入院时间为1～4 d,平均2 d。Lysholm评分为(17.00±8.29)分,国际膝关节文献委员会(IKDC)评分为(20.93±8.28)分。伴膝关节脱位9例,半月板损伤5例。关节镜下采用同种异体肌腱(2例)或自体腘绳肌腱(12例)重建前、后交叉韧带,有限切开修复内侧副韧带。结果术后切口均Ⅰ期愈合;3例出现下肢麻木,自行缓解。患者均获随访,随访时间为12～18个月,平均14个月。患者膝关节均于3个月内达屈曲120°,伸直0°。术后1年膝关节IKDC评分为(89.93±6.26)分,Lysholm评分为(88.93±4.82)分,与术前比较差异有统计学意义(P<0.01)。结论对于膝关节韧带多发伤,关节镜配合有限切开修复重建韧带,避免了开放关节腔,同时由于创伤小,术后关节粘连轻,关节功能恢复快。     

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.     

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.     

Natural history of anterior cruciate and medial collateral ligament healing--literature review]

The review discusses natural history of ligament healing of the knee. Medial collateral ligament heals by progressing through a series of inflammatory, proliferative and remodeling phases. Anterior cruciate ligament, after rupture, appears to retract initially, with no evidence of bridging scar formation. Why anterior cruciate ligament does not heal after rupture still remains unclear.     

An anterior cruciate ligament and medial collateral ligament tear in a skeletally immature patient: a new technique to augment primary repair of the medial collateral ligament and an allograft reconstruction of the anterior cruciate ligament

The goal of this case report is to fill a dual purpose. We describe a case involving a tear of the anterior cruciate ligament (ACL) and medial collateral ligament (MCL) in a skeletally immature athlete. At the same time, we describe a new technique with which we repaired the ACL with an allograft posterior tibialis tendon through intra-articular tunnels. A trial of conservative therapy for the MCL was performed. During surgery, its instability was assessed. No improvement was seen in stability, so a primary repair of the MCL was performed and augmented with an autograft gracilis tendon. The patient did well postoperatively, subsequently achieving equal stability and range of motion when compared with the opposite limb. He was back to competitive sports at 6 months.     

Immobilization increases the vulnerability of rabbit medial collateral ligament autografts to creep

Rehabilitation after soft-tissue autograft reconstructions is controversial because there is indirect evidence that some grafts fail by creeping over time. The vulnerability of soft-tissue grafts to creep over healing time and the effects of the load environment during healing on this vulnerability have never been studied specifically. We hypothesized that immobilization would decrease the magnitude of the vulnerability of ligament grafts to creep. Thirty-nine skeletally mature New Zealand White rabbits underwent a standardized medial collateral ligament autograft procedure to the right hindlimb, and 19 of the rabbits also had the limb rigidly pinned into flexion. Subgroups were killed at 3 or 8 weeks, and all isolated tibia/medial collateral ligament/femur complexes were tested for creep at 4.1 MPa under a standardized protocol. Eight normal medial collateral ligament controls were tested similarly. Results showed that all grafts were quantitatively more susceptible to cyclic and static creep than were normal medial collateral ligament controls (p < 0.05). By 3 weeks of healing, immobilization significantly increased the magnitude of the vulnerability of the grafts to cyclic, static, and total creep (all: p < 0.05). Furthermore, the grafts had more unrecovered creep strain than did the controls following a 20-minute recovery period. Contrary to our hypothesis, immobilization resulted in increased vulnerability of these ligament autografts to creep even with this relatively nonprovocative test of short duration and low stress. We postulate that following immobilization, this increase in the magnitude of susceptibility of the grafts to creep will result in functionally significant elongation of the graft if it is exposed to higher loads and over longer periods of time in vivo.     

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.     

The effect of section of the medial collateral ligament on force generated in the anterior cruciate ligament

Ten fresh-frozen knees from cadavera were instrumented with a specially designed transducer that measures the force that the anterior cruciate ligament exerts on its tibial attachment. Specimens were subjected to tibial torque, anterior tibial force, and varus-valgus bending moment at selected angles of flexion of the knee ranging from 0 to 45 degrees. Section of the medial collateral ligament did not change the force generated in the anterior cruciate ligament by applied varus moment. When valgus moment was applied to the knee, force increased dramatically after section of the medial collateral ligament; the increases were greatest at 45 degrees of flexion. Section of the medial collateral ligament had variable effects on the force generated in the anterior cruciate ligament during internal rotation but dramatically increased that generated during external rotation; these increases were greatest at 45 degrees. Section of the medial collateral ligament increased mean total torsional laxity by 13 degrees (at 0 degrees of flexion) to 20 degrees (at 45 degrees of flexion). Application of an anteriorly directed force to the tibia of an intact knee increased the force generated in the anterior cruciate ligament; this increase was maximum near the mid-part of the range of tibial rotation and minimum with external rotation of the tibia. Section of the medial collateral ligament did not change the force generated in the anterior cruciate ligament by straight anterior tibial pull near the mid-part of the range of tibial rotation.(ABSTRACT TRUNCATED AT 250 WORDS)