An in vitro study of the Müller anterolateral femorotibial ligament tenodesis in the anterior cruciate ligament deficient knee

The biomechanical effectiveness of the Müller anterolateral femorotibial ligament (ALFTL) iliotibial band tenodesis on anterior stability and internal rotational stability of the ACL deficient knee was investigated in six cadaver knees. Anterior drawer and internal rotation of the tibia were measured at 15 degrees increments from 0 degrees to 90 degrees in response to 50 N of anteriorly applied tibial force and 3 Nm of internally applied internal torque, respectively, in the intact knee, the ACL excised knee, and following the ALFTL reconstruction. A strain gage was used to measure the resting graft tension and to measure strain in the graft during the load-displacement tests. The Müller ALFTL tenodesis failed to return normal anterior stability to the ACL deficient knee (P less than 0.05). The tenodesis did, however, reduce the anterior laxity of the ACL deficient knee from 30 degrees to 90 degrees of knee flexion (P less than 0.05). The tenodesis overconstrained internal tibial rotation of the ACL excised knee from 30 degrees to 90 degrees (P less than 0.05). Measurements of strain in the tenodesis supported the load-displacement findings that the tenodesis was most effective in constraining anterior drawer and internal tibial rotation from 30 degrees to 90 degrees of knee flexion.     

Implications of muscular defense in testing for the anterior drawer sign in the knee. A stress radiographic investigation

This study was performed with the aim of shedding some light on the effect of muscular guarding during clinical testing of the knee for anteroposterior laxity. Twenty physicians were tested on a knee phantom, for force used during testing for the anterior drawer sign. The force used averaged 109 N (range, 70 to 180 N). Fifteen patients were examined by stress radiography. Radiographs were taken with the knee flexed to 90 degrees (the drawer test position) and with the knee flexed to 15 degrees (the Lachman position). A comparison was made between the laxity measured on forward traction in the relaxed knee, and during traction while the patient was instructed to counteract the forward displacement of the tibia by tensing the hamstrings, thus simulating muscular defense. The test procedure was executed first with 80 N and then with 160 N applied. The opposing effect of tensing the hamstrings on the anterior shift of the tibia was significantly less at 15 degrees of knee flexion (with 80 N, P less than 0.02; with 160 N, P less than 0.05) than at 90 degrees. With the hamstrings tensed and the knee flexed to 90 degrees, no statistically significant gain in drawer sign was achieved by increasing the force from 80 to 160 N. With the knee in the Lachman position, increasing the force produced a significantly greater anterior drawer sign (P less than 0.01).     

The biomechanics of anterior cruciate ligament rehabilitation and reconstruction

The rehabilitation of knee injuries involving the anterior cruciate ligament (ACL) is controversial. This paper describes strain in the normal and reconstructed ACL during a series of passive and active tests of knee flexion with and without varus, valgus, and axial rotation torques on the tibia. Strain in the human knee ACL was significantly different depending on whether the knee flexion angle was changed passively or via simulated quadriceps contraction. The knee joint capsule was found to be important for strain protection of the ACL. Quadriceps activity did not strain the normal or reconstructed ACL when the knee was flexed beyond 60 degrees, but significantly strained the tissue from 0 to 45 degrees of knee flexion. Immobilization may not protect the ACL if isometric quadriceps contractions are allowed to occur. Properly placed reconstructions exhibited strain behavior which closely followed the anteromedial band of the ACL.     

An in vivo strain gage study of elongation of the anterior cruciate ligament

The purpose of this paper is to study the load-elongation characteristics of a Grade II sprain of the anterior cruciate ligament (ACL) at the time of local anesthesia arthroscopy. The data may be used to increase diagnostic and prognostic accuracy when evaluating Grade II ACL sprains and to structure properly a rehabilitation program following ACL injury. This report is based on the data from two in vivo strain gage studies of Grade II ACL sprains. Following instrumentation of the ligament, several events common to physical examination and rehabilitation programs were tested. The Lachman test produced greater elongation of the anteromedial fibers than did the anterior drawer or pivot shift test. A fairly high force of 80 pounds may be required by the examiner's hands to test satisfactorily the anteromedial fibers in the acutely injured large athlete. The proper order for a rehabilitation program should be crutch walking, cycling, walking, slow running, and faster running. Patients should be cautioned to run on a perfectly level surface. Cycling produced 7% as much elongation as an 80 pound Lachman test, and the one leg half squat 21% as much. Quadriceps rehabilitation can be done more safely using these exercises. Quadriceps exercises by knee extension against a 20 pound weight boot in the range of full extension to 22 degrees flexion created peak elongation of the anteromedial fibers ranging from 87 to 121% of that produced by an 80 pound Lachman test. We recommend that quadriceps exercises and testing by knee extension through a full range of motion not be done during the first year following ACL injury or reconstruction.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of anterior cruciate ligament reconstruction on knee joint kinematics under simulated muscle loads

BACKGROUND: Numerous studies have investigated anterior stability of the knee during the anterior drawer test after anterior cruciate ligament reconstruction. Few studies have evaluated anterior cruciate ligament reconstruction under physiological loads. PURPOSE: To determine whether anterior cruciate ligament reconstruction reproduced knee motion under simulated muscle loads. STUDY DESIGN: Controlled laboratory study. METHODS: Eight human cadaveric knees were tested with the anterior cruciate ligament intact, transected, and reconstructed (using a bone-patellar tendon-bone graft) on a robotic testing system. Tibial translation and rotation were measured at 0 degrees, 15 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion under anterior drawer loading (130 N), quadriceps muscle loading (400 N), and combined quadriceps and hamstring muscle loading (400 N and 200 N, respectively). Repeated-measures analysis of variance and the Student-Newman-Keuls test were used to detect statistically significant differences between knee states. RESULTS: Anterior cruciate ligament reconstruction resulted in a clinically satisfactory anterior tibial translation. The anterior tibial translation of the reconstructed knee was 1.93 mm larger than the intact knee at 30 degrees of flexion under anterior load. Anterior cruciate ligament reconstruction overconstrained tibial rotation, causing significantly less internal tibial rotation in the reconstructed knee at low flexion angles (0 degrees-30 degrees) under muscle loads (P < .05). At 30 degrees of flexion, under muscle loads, the tibia of the reconstructed knee was 1.9 degrees externally rotated compared to the intact knee. CONCLUSIONS: Anterior cruciate ligament reconstruction may not restore the rotational kinematics of the intact knee under muscle loads, even though anterior tibial translation was restored to a clinically satisfactory level under anterior drawer loads. These data suggest that reproducing anterior stability under anterior tibial loads may not ensure that knee joint kinematics is restored under physiological loading conditions. CLINICAL RELEVANCE: Decreased internal rotation of the knee after anterior cruciate ligament reconstruction may lead to increased patellofemoral joint contact pressures. Future anterior cruciate ligament reconstruction techniques should aim at restoring 3-dimensional knee kinematics under physiological loads.     

Ultrasound evaluation of gravity induced anterior drawer following anterior cruciate ligament lesion

Ultrasound is not so far a standard procedure to visualize the anterior drawer following anterior cruciate ligament (ACL) lesions. This is because the described techniques are either technically difficult or depend on the experience of the performer and are not standardized. The purpose of this prospective analysis on ACL intact, ACL deficient and ACL reconstructed knees was to compare the diagnostic accuracy of prone ultrasonographic Lachman testing with KT-1000 measurements in the same study population. Our technique is based on a prone position of the patient. The thigh lies on the table surface such that the patella has no contact. The lower leg is placed on a roll in the ankle area and flexed to 30 degrees . The transducer (5 MHz) is positioned over the medial aspect of the popliteal fossa to visualize the femoral condyle as well as the tibial head. Under ultrasound control the lower leg is manually lifted as far the thigh stays in contact with the surface defining the start position. The lower leg is then released and drawn by gravity into the anterior drawer position, the final position. The distance between the posterior tangent from the medial femoral condyle to the medial tibial plateau was registered by three independent ultrasound measurements of the injured knee. The uninvolved opposite knee served as an internal control. The same procedure was done using a KT-1000 device (89 and 133 Newton and manual maximum force). The patients were split into two groups: acute injury (A), and (B) 6 months following ACL repair with a patellar tendon graft. All patients then underwent arthroscopy. In group A with acute ACL lesions the anterior drawer resulted in 14.1 mm (+/- 3.5) and was significantly (P < 0.001) different from the contralateral knee (7.7 mm +/- 2.9). The KT 1000 showed a comparable difference with 14.4 mm (+/- 3.9) for the injured knee and 8.3 mm (+/- 3.4) for the uninjured (P < 0.001). Sonometrically, group B patients showed no clear difference between the repaired (9.9 mm +/- 2.7) knee and its control (8.1 mm +/- 2.5). This was found for the KT-1000 results as well. The results derived from the ultrasound evaluation of the anterior drawer correlated well with those from the KT-1000 (r = 0.46). Based on a minimum intra-individual difference of 5 mm in the ultrasound measured anterior drawer, the sensitivity of the test in group A resulted in 0.96, and the specificity in 0.98. The described technique is reproducible, painless and easy to perform in order to evaluate acute ACL tears using any commercially available ultrasound device. The reproducibility is similar to the KT-1000 device. We recommend this technique for use in cases of acute ACL tears as well as in the follow-up of ACL repair.     

Impingement pressure and tension forces of the anterior cruciate ligament

This study examined the impingement behavior of the uninjured ACL and the impingement pressure and tension forces of the ACL to draw conclusions for ACL reconstructions. A miniature pressure sensor was inserted between the ACL and the intercondylar roof of 15 knees of human cadavers before and after a 3-mm notch roof resection (thickness of the sensor); tension of the ACL was measured after attaching the tibial insertion to a load cell. A long-arm goniometer was used to determine corresponding extension angles. The beginning of contact of the ACL with the notch roof was between -1 and -2 degrees of knee extension. Pressure for full passive extension was 855.6+/-279.1 and 346.4+/-287.7 kPa, and ACL tension averaged 101.9+/-38.4 N. Tension forces in passive hyperextension were higher than those detected when a 200-N Lachman test was performed (83.5+/-25.1 N). There was a significant correlation between extension capability and impingement pressure. Impingement of the ACL was detected in all knees. Full passive extension exerts biomechanical pressure and tension on the ACL. Tension forces of the ACL are higher in passive hyperextension than during a Lachman test with 200 N. The impingement behavior found for the uninjured ACL is simulated in an ACL reconstruction when the center tibial tunnel position is used.     

MRI of normal anterior cruciate ligament (ACL) and reconstructed ACL: comparison of when the knee is extended with when the knee is flexed

The purpose of this study was to evaluate, using MRI, the morphology of normal anterior cruciate ligament (ACL) and ACL grafts when the knee was extended compared with when the knee was flexed. Eighteen normal controls and 22 ACL graft patients were studied. Spin-echo (SE) T1-weighted images (TR 330 ms/TE 15 ms, NEX 1) were obtained with a slice thickness of 3 mm. Oblique sagittal images parallel to the ACL were obtained at various flexed angles of the knee joint. In 12 of the 18 normal controls the ACL appeared convex toward the posterior side when the knee was extended and gradually became straight when the knee was flexed. In 15 of the 22 ACL graft patients the grafts appeared straight when the knee was extended and became convex toward the anterior side when the knee was flexed. It is concluded that the morphological changes seen on MR images of ACL grafts from when the knee is extended to when the knee is flexed are different from those in the normal ACL. Received: 11 January 1996; Accepted: 27 December 1996     

The role of the anteromedial and posterolateral bundles of the anterior cruciate ligament in anterior tibial translation and internal rotation

BACKGROUND: A rupture of the entire fibers of the anterior cruciate ligament leads to knee instability due to increased anterior tibial translation and increased internal tibial rotation. The influence of isolated deficiency of the anteromedial or posterolateral bundle of the anterior cruciate ligament on the resulting knee kinematics have not yet been reported. HYPOTHESIS: Transection of the anteromedial bundle will lead to increased anterior tibial translation at 90 degrees. Transection of the posterolateral bundle will show an increased anterior tibial translation as well as a combined rotatory instability at 30 degrees. STUDY DESIGN: Controlled laboratory study. METHODS: Kinematics of the intact knee were determined in response to a 134-N anterior tibial load and a combined rotatory load of 10 N.m valgus and 4 N.m internal tibial rotation using a robotic/universal force moment sensor testing system. Subsequently, the fibers of the anteromedial and posterolateral bundle were resected in an alternating order and the new translation in response to the same external loading conditions measured. Statistical analysis was performed using a 2-way ANOVA test. RESULTS: Transection of the anteromedial bundle increased anterior tibial translation at 60 degrees and 90 degrees of knee flexion significantly. Isolated transsection of the posterolateral bundle increased anterior tibial translation in response to 134-N anterior load at 30 degrees of knee flexion significantly and resulted in a significant increase in combined rotation at 0 degrees and 30 degrees in response to a combined rotatory load compared with the intact knee and isolated resection of the anteromedial bundle. CONCLUSION: The anteromedial and posterolateral bundles stabilize the knee joint in response to anterior tibial loads and combined rotatory loads in a synergistic way. CLINICAL RELEVANCE: The results of the current study suggest that, from a biomechanical point of view, it may be beneficial to reconstruct both bundles of the anterior cruciate ligament to better restore normal anterior tibial translation and combined rotation.     

The role of the medial collateral ligament and posteromedial capsule in controlling knee laxity

BACKGROUND: The medial aspect of the knee has a complex capsular structure; the biomechanical roles of specific structures are not well understood. HYPOTHESIS: The 3 strong stabilizing structures, the superficial and deep medial collateral ligaments and the posteromedial capsule, make distinct contributions to controlling tibiofemoral laxity. STUDY DESIGN: Controlled laboratory study. METHODS: Changes in knee laxity under anterior-posterior drawer, valgus, and internal-external rotation loads were found by sequential cutting in 18 cadaveric knees. Three cutting sequences allowed the roles of the 3 structures to be seen in isolation and in combination. Some force contributions were also calculated. RESULTS: The posteromedial capsule controlled valgus, internal rotation, and posterior drawer in extension, resisting 42% of a 150-N drawer force when the tibia was in internal rotation. The superficial collateral ligament controlled valgus at all angles and was dominant from 30 degrees to 90 degrees of flexion, plus internal rotation in flexion. The deep collateral ligament controlled tibial anterior drawer of the flexed and externally rotated knee and was a secondary restraint to valgus. CONCLUSION: Distinct roles in controlling tibiofemoral laxity have been found for these structures that vary according to knee flexion and tibial rotation. CLINICAL RELEVANCE: The restraining functions demonstrated provide new information about knee stabilization, which may allow better evaluation of structural damage at the medial aspect of the knee.     

Force sharing between two grafts in the anatomical two-bundle anterior cruciate ligament reconstruction

The normal anterior cruciate ligament (ACL) can be generally divided into two main bundles, anteromedial bundle (AMB) and posterolateral bundle (PLB), and each bundle shared its function in response to external loads including anterior tibial drawer force. While we developed the anatomically oriented ACL reconstruction technique via two femoral tunnels and two parallel tibial tunnels (the “anatomical” two-bundle ACL reconstruction), there were few biomechanical studies about this technique. The purpose of this study was to investigate the force sharing between two separate grafts (anteromedial graft, AMG; posterolateral graft, PLG) in this anatomical two-bundle technique by measuring the force of each bundle in response to anterior tibial load. The anatomical two-bundle technique was performed on 11 patients via two tunnels at the supero-posterior portion of the AMB footprint and the supero-posterior portion of the PLB footprint on the posterior margin of the lateral femoral condyle and two tunnels created in the center of the AMB and the PLB tibial footprints. After two doubled semitendinosus grafts were fixed with two EndoButton-CL^®s on the femur, they were temporarily fixed to the tension-adjustable force gauge on the tibial cortex. After each bundle of the graft was settled at the tension of 25 N at 20°, the force exerted on the two bundles was measured with the force gauge during applied anterior tibial force of 134 N at 0°, 30°, 60° and 90° of flexion. While the AMG carried 42.3±5.7% of and the PLG shared 57.7±5.7% of the total force at 0°, the former took 64.1±11.1% and the latter was assigned 33.9±11.1% at 90°. This study has demonstrated that the force distribution between the two grafts in the anatomical two-bundle technique was similar to that between the two bundles in the normal ACL.     

Injuries to the posterior cruciate ligament of the knee

The posterior cruciate ligament (PCL) is the strongest ligament about the knee and is approximately twice as strong as the anterior cruciate ligament. Its main function is to prevent the posterior dislocation of the tibia in relation to the femur, providing 95% of the strength to resist the tibial posterior displacement. Along with the anterior cruciate ligament (ACL) the PCL controls the passive 'screw home' mechanism of the knee in terminal knee extension. It also provides mechanical support for the collateral ligaments during valgus or varus stress of the knee. PCL ruptures are uncommon apparently due to its strong fibre structure. The most frequent injury mechanism in isolated PCL tears is a direct blow on the anterior tibia with the knee flexed thus driving the tibia posteriorly. Automobile accidents (in which the knee hits the dashboard) and soccer injuries (in which an athlete receives a blow to the anterior surface of the tibia during knee flexion) characteristically produce this type of injury. In other PCL injury mechanisms (hyperextension, hyperflexion or rotational injuries with associated valgum/varum stress), other knee structures are also often damaged. The most characteristic diagnostic finding in a knee with a PCL rupture is the 'posterior sag sign' meaning the apparent disappearance of the tibial tubercle in lateral inspection when the knee is flexed 90 degrees. This is due to gravity-assisted posterior displacement of the tibia in relation to the femur. A positive posterior drawer test performed at 90 degrees of flexion and a knee hyperextension sign are sensitive but nonspecific tests. False negative findings are frequent, especially in acute cases. If necessary, the clinical diagnosis of the PCL tear can be verified by magnetic resonance imaging, examination under anaesthesia, arthroscopy, or a combination of these modalities. If a PCL avulsion fragment has been dislocated, surgical treatment is recommended. In isolated, complete midsubstance tears of the PCL the majority of the recent studies recommend conservative treatment, since abnormal residual posterior laxity1 in most of these knees is consistent with functional stability and minimal symptoms. This has been the case even in athletes. In isolated PCL tears, the outcome seems to depend more on the muscular (quadriceps) status of the knee than on the amount of residual posterior laxity. Therefore, the conservative treatment protocol emphasises intensive quadriceps exercises, and only a short (under 2 weeks) immobilisation period followed by early controlled activities and early weightbearing.(ABSTRACT TRUNCATED AT 400 WORDS)     

Anterior tibial translation during eccentric, isokinetic quadriceps work in healthy subjects

The effect of increasing isokinetic, eccentric quadriceps torques on sagittal translation of the tibia was examined in six healthy volunteers and compared to the translation at 20 degrees of knee flexion during a drawer test with 90 N force. The tibial translation increased in a linear fashion with a mean of 0.5 mm per 20% torque increase. In 20 degrees of knee flexion, 10% of eccentric quadriceps peak torque consumed 80% of the anterior tibial translation induced by the 90 N Lachman test while eccentric quadriceps peak torque utilized 100% of the translation at the same test. The in vivo relation between muscle force and tibial translation is of importance in the treatment of patients with injury to the cruciate ligaments. The results indicate that an already low eccentric quadriceps torque causes a tibial translation that reaches the limit of the passive knee joint displacement where strain is assumed to develop in the anterior cruciate ligament. Already low eccentric quadriceps torque levels may therefore be harmful during rehabilitation after anterior cruciate ligament surgery.     

Comparison of estimated anterior cruciate ligament tension during a typical and flexed knee and hip drop landing using sagittal plane knee modeling

Noncontact mechanisms, such as landing from a jump, account for over 70% of all anterior cruciate ligament injuries. Increased knee and hip flexion during landing has been suggested to decrease anterior cruciate ligament tension; however, current literature utilizing knee modeling approaches has not investigated this. Our purpose was to compare estimated anterior cruciate ligament tension in females between a typical and flexed knee and hip drop landing performance. A sagittal plane knee model based on kinematic, kinetic, electromyography, and cadaveric data was used to estimate forces on the anterior cruciate ligament during a typical and flexed drop landing for 23 females. Model estimated peak anterior cruciate ligament tension decreased by 10% during the flexed landing performance (p=0.008). This was accounted for by an increase in hamstring shear force by 6% of body weight and a reduction in patellar tendon shear force and femur-tibia shear force by 3% of body weight each. Results suggest that simple verbal cues for increased knee and hip flexion during landing may be effective in reducing anterior cruciate ligament tension and potential risk of injury during landing.     

前交叉韧带部分断裂的诊治

目的 :探讨前交叉韧带 (anteriorcruciateligament,ACL)部分断裂的诊断方法和治疗方式。方法 :2 0 0 0年 3月～ 2 0 0 2年 6月收治ACL部分断裂患者 2 4例 ,其中 7例以前内束断裂为主 ,17例以后外束断裂为主。所有病例均经关节镜检查确诊 ,其中行关节镜下ACL重建者 16例。结合症状、体征和MRI进行诊断 ,并比较前内束断裂和后外束断裂临床表现的差异。术后随访 9～ 13个月 ,平均 11个月。对手术前后膝关节Lysholm评分结果进行统计分析。结果 :本组病例出现关节不稳的 ,ACL前内束断裂者占 2 8 6 % ,后外束断裂者占 98 2 % ;体检前抽屉试验 (ADT)、Lachman试验和轴移试验 (PST)阳性率 ,前内束断裂者分别为 71 4 %、14 3%和 0 ;后外束断裂者分别为 17 6 %、98 2 %和 76 5 %。ACL重建术后Lysholm评分平均为 93 4 7± 2 6 2 ,较术前 (6 3 5 3± 8 11)明显提高(P <0 0 1)。结论 :ACL部分断裂根据损伤部位的不同临床表现也存在差异。后外束断裂者出现关节不稳较前内束常见 ,前内束断裂主要表现为前抽屉试验阳性 ,而后外束断裂常表现为Lachman试验和轴移试验阳性。对于伴有关节不稳的 ,手术重建ACL效果良好。     

膝关节韧带联合损伤的关节镜治疗后康复护理效果分析

目的探讨关节镜下膝关节前交叉韧带、后交叉韧带、内侧副韧带、外侧副韧带、后外侧结构联合损伤的康复护理效果。方法2003年10月—2005年11月,采用关节镜下重建交叉韧带,修复或重建侧副韧带和后外侧结构治疗急性膝联合韧带损伤12例。术后早期等长肌力练习、早期完全负重、早期本体感觉练习、早期被动练习。出院后随诊并功能评分。结果12例均获得随访,随访时间6~24个月,平均14个月。Lysholm评分:优2例,良8例,可2例。关节稳定性良好,有2例腘绳肌腱重建者抽屉试验Ⅰ度阳性。膝关节屈曲超过120°者9例,90~120°者3例。结论膝关节联合韧带损伤关节镜手术治疗配合正确的康复护理可取得良好效果。     

An in vitro study of an intraarticular and extraarticular reconstruction in the anterior cruciate ligament deficient knee

The biomechanical effectiveness of an extraarticular ACL reconstruction, an intraarticular ACL reconstruction, and the combination of these on both anterior stability and internal rotational stability of the ACL deficient knee was investigated in six cadaver knees. The extraarticular reconstruction consisted of the Müller anterolateral femorotibial ligament iliotibial band tenodesis, and the intraarticular reconstruction used the middle third of the patellar tendon in the manner of Clancy. The extraarticular reconstruction was found to overconstrain internal tibial rotation of the ACL excised knee between 30 degrees and 90 degrees (P less than 0.05). While the isolated extraarticular reconstruction did not return normal anterior stability to the ACL deficient knee (P less than 0.05), it did significantly reduce the anterior laxity of the ACL deficient knee between 30 degrees and 90 degrees of knee flexion (P less than 0.05). For the combined reconstruction, the intraarticular procedure was performed and then only enough tension was applied to the extraarticular reconstruction to take up slack in the tenodesis without shifting the rotatory position of the tibia from that produced by the intraarticular procedure alone. Neither the intraarticular reconstruction nor the combined procedure resulted in any significant shifts from normal (P less than 0.05) in the rotatory position of the unloaded tibia; during loading neither resulted in rotational displacements significantly different from normal; and both of these procedures reduced the increased anterior laxity of the ACL deficient knee to a level not statistically different from normal. Because the extraarticular reconstruction shared the load when performed with the intraarticular reconstruction as part of a combined procedure, we concluded that it would be useful as an adjunctive procedure in appropriate clinical situations.     

The functions of the fibre bundles of the anterior cruciate ligament in anterior drawer,rotational laxity and the pivot shift

This paper reviews the functional anatomy of the anterior cruciate ligament (ACL), which has a parallel array of collagen fascicles that have usually been divided into two ‘fibre bundles’: anteromedial (AM) and posterolateral (PL), according to their tibial attachment sites. The PL bundle has shorter fibres, and so it is subjected to greater tensile strains than the AM bundle when the whole ACL is stretched; its oblique orientation in the coronal plane imbues it with greater ability to resist tibial rotation than the more vertical AM fibre bundle. Most studies have found that the AM bundle is close to isometric when the knee flexes, while the PL bundle slackens approximately 6 mm. There is little evidence of significant fibre bundle elongation in response to tibial rotation. Selective bundle cutting studies have been performed, allowing both the bundle tensions and their contributions to resisting tibial anterior translation and tibial rotation to be calculated. These show that the function of the PL bundle was dominant near knee extension in some studies, particularly when resisting anterior drawer and that its contribution reduced rapidly with knee flexion through 30 degrees. There has been little study of the contributions of the fibre bundles in control of tibial internal–external rotation or the pivot shift: one study found that the AM bundle had larger tensions than the PL bundle during a simulated pivot shift, but another study found that cutting the PL bundle allowed a larger increase in coupled tibial anterior translation than cutting the AM bundle. It was concluded that the AM bundle is most important for resisting tibial anterior drawer—the primary function of the ACL—while the PL bundle is tight near knee extension, when it has a role in control of tibial rotational laxity. There is a clear need for further study of dynamic knee instability, to gain better understanding of how best to reconstruct the ACL and associated tissues.     

Relative contribution of the ACL, MCL, and bony contact to the anterior stability of the knee

Ligaments and other soft tissues, as well as bony contact, all contribute to anterior stability of the knee joint. This study was designed to measure the in situ force in the medial collateral ligament (MCL), anterior cruciate ligament (ACL), posterolateral structures (PLS), and posterior cruciate ligament (PCL) in response to 110 N anterior tibial loading. The changes in knee kinematics associated with ACL deficiency and combined MCL+ACL deficiency were also evaluated. Utilizing a robotic/universal force-moment sensor system, ten human cadaveric knee joints were tested between 0° and 90° of knee flexion. This unique testing system is designed to determine the in situ forces in structures of interest without making mechanical contact with the tissue. More importantly, data for individual structures can be obtained from the same knee specimen since the robotic manipulator can reproduce the motion of the intact knee. The in situ forces in the ACL under anterior tibial loading to 110 N were highest at 15° flexion, 103 ± 14 N (mean ± SD), decreasing to 59.2 ± 30 N at 90° flexion. For the MCL, these forces were 8.0 ± 3.5 N and 38.1 ± 25 N, respectively. Forces due to bony contact were as high as 34.1 ± 23 N at 30° flexion, while those in the PLS were relatively small at all flexion angles. Combined MCL+ACL deficiency was found to significantly increase anterior tibial translation relative to the ACL-deficient knee only above 60° of knee flexion. These findings confirm the hypothesis that there is significant load sharing between various ligaments and bony contact during anterior tibial loading of the knee. For this reason, the MCL and osteochondral surfaces may also be at significant risk during ACL injury. Received: 29 December 1997 Accepted: 16 July 1998