The management of injuries to the medial side of the knee

Injuries to the medial side of the knee are the most common knee ligament injuries. The majority of injuries occur in young athletes during sporting events, with the usual mechanism involving a valgus contact, tibial external rotation, or a combined valgus and external rotation force delivered to the knee. Although most complete grade III medial knee injuries heal, some do not, which can lead to continued instability. For these patients, a thorough understanding of the presenting history and a physical examination are important because these injuries can often be confused with posterolateral corner injuries. The main anatomic structures of the medial side of the knee are the superficial medial collateral ligament, deep medial collateral ligament, and posterior oblique ligament. In addition, accurately locating 3 bony prominences over the medial aspect of the knee-the adductor tubercle, gastrocnemius tubercle, and medial epicondyle-is important to conduct a proper physical examination and for surgical repairs and reconstructions. Clinical diagnosis of medial knee injuries is primarily performed via the application of a valgus stress in full extension and at 30° of knee flexion. In addition, an examination of the amount of anteromedial tibial rotation is performed at 90° of flexion, while the dial test, performed at 30° and 90° of flexion, is important because it evaluates for rotational abnormalities. Valgus stress radiographs are useful to objectively determine the amount of medial compartment gapping and to discern whether there is medial or lateral compartment gapping when a medial or posterolateral corner knee injury cannot be differentiated, especially with a chronic injury. The majority of acute grade III medial knee injuries will heal after a nonoperative rehabilitation program. In most instances when there is a knee dislocation or multiligament injury, a primary repair with sutures may be indicated. In severe midsubstance injuries or chronic medial knee injuries, an anatomic medial knee reconstruction with grafts may be indicated. Rehabilitation principles for acute medial knee injuries involve controlling edema, regaining range of motion, and avoiding any significant stress on the healing ligaments. A well-guided rehabilitation program can result in excellent functional outcomes in the majority of patients.     

The Influence of Tibial Positioning on the Diagnostic Accuracy of Combined Posterior Cruciate Ligament and Posterolateral Rotatory Instability of the Knee

Background

To determine if tibial positioning affects the external rotation of the tibia in a dial test for posterolateral rotatory instability combined with posterior cruciate ligament (PCL) injuries.

Methods

Between April 2007 and October 2007, 16 patients with a PCL tear and posterolateral rotatory instability were diagnosed using a dial test. The thigh-foot angle was measured at both 30° and 90° of knee flexion with an external rotation stress applied to the tibia in 2 different positions (reduction and posterior subluxation). The measurements were performed twice by 2 orthopedic surgeons.

Results

In posterior subluxation, the mean side-to-side difference in the thigh-foot angle was 11.56 ± 3.01° at 30° of knee flexion and 11.88 ± 4.03° at 90° of knee flexion. In the sequential dial test performed with the tibia reduced, the mean side-to-side difference was 15.94 ± 4.17° (p < 0.05) at 30° of knee flexion and 16.88 ± 4.42° (p = 0.001) at 90° of knee flexion. The mean tibial external rotation was 5.31 ± 2.86° and 6.87 ± 3.59° higher in the reduced position than in the posterior subluxation at both 30° and 90° of knee flexion.

Conclusions

In the dial test, reducing the tibia with an anterior force increases the ability of an examiner to detect posterolateral rotary instability of the knee combined with PCL injuries.     

Tests for posterolateral instability of the knee in normal subjects. Results of examination under anesthesia

An apparently normal knee was examined in each of 100 subjects while they were under general or epidural anesthesia for an unrelated operation. The Lachman, anterior drawer, posterior drawer, and pivot-shift tests were negative in all knees. All knees were stable to varus and valgus stress at both 0 and 30 degrees of flexion. The external-rotation recurvatum test also was negative in all knees. A positive reversed pivot-shift sign was present in 35 per cent of the knees, suggesting that it may not signify abnormality, at least not without a negative test on the contralateral knee. The results of the posterolateral drawer test were variable, difficult to quantify, and did not always have a firm end-point. The amount of maximum external rotation of the tibia, measured from the reference line of the medial border of the foot, was extremely variable at both 30 and 90 degrees of flexion of the knee. External rotation, as determined by this reference, was slightly greater (averaging 9 degrees) at 90 than at 30 degrees of flexion. The normal range of maximum external rotation of the foot was 10 to 45 degrees at 30 degrees of flexion of the knee and 15 to 70 degrees at 90 degrees of flexion. The presence of a large angle of external rotation and a positive reversed pivot-shift sign correlated strongly with increased ligamentous laxity and mild varus alignment of the knee.     

全关节镜下膝关节后外复合体重建

目的 介绍全关节镜下腘肌腱重建、腘肌腱联合腘腓韧带重建或膝关节后外复合体(posterolateral corner,PLC)解剖重建的手术技术,探讨全关节镜下PLC重建治疗膝关节后外不稳定的效果.方法 2008年8月至2010年4月,共完成全关节镜下后十字韧带(posterior cruciate ligament,PCL)+PLC重建手术34例.患者在接受手术时平均年龄34.1岁(15～52岁);男32例,女2例;从受伤到手术平均10.7个月.所有病例均为陈旧性损伤,且均为复合韧带损伤.所有PCL损伤的病例都存在PLC损伤.合并前十字韧带损伤6例(17.6%),合并前十字韧带、内侧副韧带损伤2例(5.9%),合并内侧副韧带损伤5例(14.7%).对膝关节PLC损伤进行分型,采用不同的重建技术进行治疗.对于A型旋转不稳定,采用全关节镜下腘肌腱重建、腘肌腱联合腘腓韧带重建;对于C型后外不稳定,采用全关节镜下PLC解剖重建.结果 14例患者获得随访并进行二次关节镜检查,平均随访18.5个月(13～25个月).终末随访包括:膝关节查体、KT-1000测量、膝关节应力像和胫骨外旋稳定性.使用膝关节应力像测量胫骨后移程度,胫骨后移由术前平均15.56mm减少为术后5.16mm,手术前后差异有统计学意义.使用屈膝30°位胫骨外旋试验评估膝关节后外旋转不稳定.对比患侧与健侧胫骨外旋的差值,由术前平均14.92°减小为术后-0.22°,手术前后差异有统计学意义.术后患者平均屈曲受限4.23°,无伸膝受限.结论 对于膝关节PLC损伤导致的不稳定,采用全关节镜下PLC重建的手术技术,能够有效恢复膝关节后外旋转不稳定.这种手术技术能够与PCL重建联合应用.

Abstract：

Objectiye To introduce the surgical technique of arthroscopy assisted anatomical posterolateral corner (PLC) reconstruction,including popliteal ligament,popliteofibular ligament and lateral collateral ligament,and evaluate the results of this technique.Methods From August 2008 to April 2010,34arthroscopic posterior cruciate ligament (PCL) and PLC reconstruction surgeries were performed.The average age of the patients was 34.1 (15-52) years.There were 32 males and 2 females.The average time period from injury to surgery was 10.7 months.All patients were chronic injuries and combined ligament injuries,including PCL and PLC injuries.Some cases had other ligament injury,including 6 patients of anterior cruciate ligament (ACL) injury (17.6%),2 of ACL combined medial cruciate ligament (MCL) injuries (5.9%),and 5 of MCL injuries (14.7%).According to Fanellis classification,for type A posterolateral rotation instability,we performed arthroscopic popliteal ligament reconstruction or popliteal ligament combined popliteofibular ligament reconstruction.For type C posterolateral instability,we performed arthroscopic PLC anatomical reconstruction.Results During the follow-up period,14 patients had undergone a second look arthroscopic examination and removal of hardware.The average follow-up time was 18.5 months (13-25 months).At the final follow-up,physical examination,stability evaluation with KT-1000 and Telos stress view,and dial test were performed.The posterior displacement of the knee had decreased from 15.56 mm preoperatively to 5.16mm postoperatively.The external rotation instability had decreased from 14.92° preoperatively to -0.22°postoperatively.The average limitation of knee flexion was 4.23° and no knee extension was limited.Conclusion With the surgical technique of arthroscopy assisted anatomical PLC reconstruction,we can restore the external rotation stability of knee.This technique can be performed combine with PCL reconstruction.     

Biomechanical studies of the ligaments of the knee joint (anterior cruciate ligament and medial collateral ligament) using amputated limbs

In order to study the biomechanical behavior of the ligaments around the knee joint (anterior cruciate ligament-ACL and medial collateral ligament-MCL), experiments were carried out using ten human amputated specimens. Specially designed small omega-shaped transducers were attached on the selected surface of the ligaments, and elongation of the ligaments were measured under valgus or anterior drawer stress in various flexion or rotation of the joint which was made by specific jig sets. The results showed that the load-elongation response varied depending on the sites of the ligaments and that the anterior instability caused by transection of the ACL gave definite effect on the strain behavior of the MCL and, vice versa, the medial instability caused by transection of the MCL gave considerable effect on that of the ACL. This experiment demonstrated a quantitative relationship between these ligaments which suggests the clinical importance of these ligaments for the knee joint stability.     

Instability of knees with ligament lesions. Cadaver studies of the anterior cruciate ligament

We studied the importance of the two parts of the anterior cruciate ligament (ACL), the medial collateral ligament (MCL), and the posterior medial capsule (PMC) to translatory and spontaneous axial rotatory instability in 15 osteoligamentous knee preparations. Instability was recorded continuously from zero to 90 degrees of flexion with application of a constant force to the tibia. Isolated cutting of the ACL caused a moderate anterior translatory movement, which increased if the MCL was also cut. Transection also of the PMC resulted in an even larger range of anterior translatory movement. Combined lesions to the MCL and the PMC and the posterolateral part of the ACL did not cause such instability provided the anteromedial part of the ACL was intact. Application of a valgus moment to specimens with injured ACL and medial structures induced a spontaneous anteromedial subluxation of the tibia in a semiflexed position. When flexion was increased to 70-80 degrees, a sudden reduction was observed.     

Instability of knees with ligament lesions: Cadaver studies of the anterior cruciate ligament

We studied the importance of the two parts of the anterior cruciate ligament (ACL), the medial collateral ligament (MCL), and the posterior medial capsule (PMC) to translatory and spontaneous axial rotatory instability in 15 osteoligamentous knee preparations. Instability was recorded continuously from zero to 90 degrees of flexion with application of a constant force to the tibia. Isolated cutting of the ACL caused a moderate anterior translatory movement, which increased if the MCL was also cut. Transection also of the PMC resulted in an even larger range of anterior translatory movement. Combined lesions to the MCL and the PMC and the posterolateral part of the ACL did not cause such instability provided the anteromedial part of the ACL was intact.

Application of a valgus moment to specimens with injured ACL and medial structures induced a spontaneous anteromedial subluxation of the tibia in a semiflexed position. When flexion was increased to 70–80 degrees, a sudden reduction was observed     

Instability of knees with ligament lesions: Cadaver studies of the anterior cruciate ligament

We studied the importance of the two parts of the anterior cruciate ligament (ACL), the medial collateral ligament (MCL), and the posterior medial capsule (PMC) to translatory and spontaneous axial rotatory instability in 15 osteoligamentous knee preparations. Instability was recorded continuously from zero to 90 degrees of flexion with application of a constant force to the tibia. Isolated cutting of the ACL caused a moderate anterior translatory movement, which increased if the MCL was also cut. Transection also of the PMC resulted in an even larger range of anterior translatory movement. Combined lesions to the MCL and the PMC and the posterolateral part of the ACL did not cause such instability provided the anteromedial part of the ACL was intact.

Application of a valgus moment to specimens with injured ACL and medial structures induced a spontaneous anteromedial subluxation of the tibia in a semiflexed position. When flexion was increased to 70-80 degrees, a sudden reduction was observed     

Acute posterolateral rotatory instability of the knee

We reviewed the clinical records and operative notes of seventeen consecutive patients who were treated by surgical repair for acute posterolateral rotatory instability in order to determine the diagnostic features of the instability and the effectiveness of our surgical repair in thirteen patients who returned for objective and subjective evaluation after a mean follow-up of 53.3 months. Sixteen of the seventeen knees had a positive external-rotation recurvatum test; fifteen, a positive adduction-stress test at 30 degrees of knee flexion; and twelve, a positive posterolateral-drawer test. Associated rotatory instabilities were found in ten of the seventeen knees, with anterolateral rotatory instability being the most frequent. Two patients had associated peroneal-nerve palsy. One or more components of the arcuate ligament complex were injured in all seventeen knees. None of the thirteen patients who were followed required subsequent reconstruction for any chronic instability. Of these thirteen, the results in 85 per cent were rated good subjectively and in 77 per cent, good objectively. Eighty-five per cent of these patients had returned to athletic activity at their preinjury level; the remaining 15 per cent did not participate in sports activities. A positive posterolateral-drawer test or external rotation recurvatum test, or both, was diagnostic of posterolateral rotatory instability. The adduction stress test at 30 degrees of knee flexion was usually positive, but was not diagnostic. Accurate diagnosis and treatment of posterolateral rotatory instability in the acute stage can result in subjectively and objectively acceptable knee function.     

The posterior cruciate ligament and rotatory knee instability. An experimental study

The importance of the posterior cruciate ligament in relation to valgus-varus and axial rotatory stability in the knee joint was investigated. Mobility patterns were drawn from 20 osteoligamentous preparations after successive transection of the posterior cruciate ligament (PCL), the medial and lateral collateral ligaments, and the posterior joint capsule. The knee joint remained grossly stable after isolated transection of the PCL, and further cutting of either one of the collateral ligaments or of the posterior capsule yielded no greater instability than one should expect from isolated cutting of each of these structures. The posterior cruciate ligament was the stabilizing factor in flexion and external rotation after injury to the lateral collateral ligament and the posterolateral capsule, and it restricted internal rotation after cutting of the medial cruciate ligament and the posteromedial capsule. Valgus instability was markedly increased during the whole range of movement when PCL was included in injury to the medial compartment ligaments, and when included in a lateral compartment injury a further varus instability was found, though only in the flexed or semiflexed knee. No hyperextension could be demonstrated after these injuries.     

Rehabilitation of the medial collateral ligament-deficient elbow: an in vitro biomechanical study

The purpose of this study was to determine the relative contribution of muscle activity and the effect of forearm position on the stability of the medial collateral ligament (MCL)-deficient elbow. Simulated active and passive elbow flexion with the forearm in both supination and pronation was performed using a custom elbow testing apparatus. Testing was first performed on intact specimens, then on MCL-deficient specimens. Elbow instability was quantified using an electromagnetic tracking device by measuring internal-external rotation and varus-valgus laxity of the ulna relative to the humerus. Compared with the intact elbow, transection of the MCL, with the arm in a vertical orientation, caused a significant increase in internal-external rotation during passive elbow flexion with the forearm in pronation, but forearm supination reduced this instability. Overall, following MCL transection the elbow was more stable with the forearm in supination than pronation during passive flexion. In the pronated forearm position simulated active flexion also reduced the instability detected during passive flexion, with the arm in a varus and valgus gravity-loaded orientation. The maximum varus-valgus laxity was significantly increased with MCL transection regardless of forearm position during passive flexion. We concluded that active mobilization of the elbow with the arm in vertical orientation during rehabilitation is safe in the setting of an MCL-deficient elbow with the forearm in a fully supinated and pronated position. Splinting and passive mobilization of the MCL-deficient elbow with the forearm in supination should minimize instability and valgus elbow stresses should be avoided throughout the rehabilitation period.     

Instability of cadaver knees after transection of capsule and ligaments

The importance of the medial collateral ligament and the anterior cruciate ligament of the knee in relation to valgus and varus instability was investigated. Mobility patterns were drawn from ten osteoligamentous knee preparations after successive transections of the structures. Cutting the entire collateral medial ligament caused only slight valgus instability, even when the knee was flexed. Further transection of the anterior cruciate ligament increased the instability considerably, but the knee remained stable in extension. The valgus instability after the transections was maximal at about 60 degrees of flexion.     

Diagnosis and treatment of posterolateral knee injuries

Posterolateral knee injuries can be very debilitating. It is important to understand the complex anatomy and pertinent diagnostic tests to properly treat posterolateral knee injuries. The fibular collateral ligament, popliteus tendon, and the popliteofibular ligament are the main static stabilizers against abnormal varus and posterolateral translational moments. Important radiographic imaging studies for the posterolateral knee include full length anteroposterior radiographs, taken with the patient standing, to assess for varus alignment in patients with chronic injuries and high field (1.5 tesla or higher) magnetic resonance imaging with specific posterolateral knee sectioning. A physical examination that includes the external rotation recurvation test, varus stress test at 30 degrees, dial test at 30 degrees and 90 degrees, posterolateral drawer test, reverse pivot shift, and an assessment for a varus thrust gait are essential to properly diagnose a posterolateral knee injury. Patients with acute (< 3 weeks) anatomic repairs of Grade III posterolateral knee injuries have the best functional outcome. Although various surgical reconstruction techniques have been developed to treat chronic or irreparable acute posterolateral knee injuries, these techniques have not achieved outcomes comparable with the treatment of other ligament injuries of the knee. Techniques for anatomic reconstructions of these structures are just being developed. Improved education of clinicians as to the proper diagnosis of posterolateral knee injuries is necessary because a large number of these injuries still are missed on initial examinations. In addition, additional research into the most optimal posterolateral knee reconstruction techniques and outcome studies are needed to improve the treatment of this debilitating knee injury.     

The effect of medial release on flexion and extension gaps in cadaveric knees: implications for soft-tissue balancing in total knee arthroplasty

This cadaver study examined the effects of medial structure release for varus deformity correction during total knee arthroplasty. Twelve specimens were used to investigate the amount of varus correction achieved with sequential release of medial structures. Varus-valgus and internal-external rotation angles were measured using the Isotrack II motion tracking system. Each release sequence was tested at full extension and 45 degrees and 90 degrees of flexion to compare any differences obtained in the joint gaps. After release of the posteromedial capsule oblique ligament complex, superficial medial collateral ligament (MCL), pes anserinus, and semimembranosus tendons, valgus rotation increased to 6.9 degrees in full extension and 13.4 degrees in 90 degrees of flexion. The largest increase (3.2 degrees) in valgus rotation occurred after the superficial MCL was released. Initial release of the superficial MCL led to a more gradual correction with release of subsequent structures. Changes seen in 90 degrees flexion were significantly greater than those in full extension. While the cadaveric model is limited by the lack of deformity in the specimens, the data provide several clinically relevant conclusions. In many cases requiring major medial release for severe varus deformity, potential flexion-extension differences in the resulting tibiofemoral gaps may require new consideration. These data may help explain the heightened interest in and variety of approaches for addressing femoral component rotation and issues of flexion stability since a significantly larger correction is obtained in flexion. Minimal changes in internal-external rotation of the tibia occurred until both the pes anserinus and semimembranosus tendons were released (4 degrees of external rotation).     

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     

Elbow subluxation and dislocation. A spectrum of instability.

After sequential releases of the ligaments and capsules of 13 fresh autopsy specimen elbows, external rotation and valgus moments with axial forces resulted in posterior dislocations in 12 of the 13 with the anterior medical collateral ligament (AMCL) intact. Kinematic displacements measured with a three-dimensional electromagnetic tracking device showed that dislocation involved posterolateral rotation of 34 degrees-50 degrees and 5 degrees-23 degrees valgus at about 80 degrees flexion. Dislocation is the final of three sequential stages of elbow instability resulting from posterolateral rotation, with soft-tissue disruption progressing from lateral to medial. In each stage, the pathoanatomy correlated with the pattern and degree of instability. Testing for valgus stability of the elbow during simulated active flexion revealed no significant increase (-0.3 degrees-2.4 degrees) in valgus laxity after reduction compared with the intact specimens (p greater than 0.05, beta = 0.1, delta = 2.5 degrees). In no case did the digitized AMCL origin-to-insertion distance increase beyond normal during the dislocation (p less than 0.01). The mechanism of dislocation during a fall on the outstretched hand would involve the body "rotating internally" on the elbow, which experiences an external rotation/valgus moment as it flexes. Posterior dislocations should therefore be reduced in supination. If valgus stability in pronation is demonstrated, the AMCL can be assumed to be intact, and rehabilitation in a hinged cast-brace with the elbow in full pronation can be commenced immediately.     

Subject-specific finite element analysis of the human medial collateral ligament during valgus knee loading.

The objectives of this study were (1) to develop subject-specific experimental and finite element (FE) techniques to study the three-dimensional stress-strain behavior of ligaments, with application to the human medial collateral ligament (MCL), and (2) to determine the importance of subject-specific material properties and initial (in situ) strain distribution for prediction of the strain distribution in the MCL under valgus loading. Eight male knees were subjected to varus-valgus loading at flexion angles of 0 degrees, 30 degrees, and 60 degrees. Three-dimensional joint kinematics and MCL strains were recorded during kinematic testing. Following testing, the MCL of each knee was removed to allow measurement of the in situ strain distribution and to perform material testing. A FE model of the femur-MCL-tibia complex was constructed for each knee to simulate valgus loading at each flexion angle, using subject-specific bone and ligament geometry, material properties, and joint kinematics. A transversely isotropic hyperelastic material model was used to represent the MCL. The MCL in situ strain distribution at full extension was used to apply in situ strain to each MCL FE model. FE predicted MCL strains during valgus loading were compared to experimental measurements using regression analysis. The subject-specific FE predictions of strain correlated reasonably well with experimentally measured MCL strains (R(2)=0.83, 0.72, and 0.66 at 0 degrees, 30 degrees, and 60 degrees, respectively). Despite large inter-subject variation in MCL material properties, MCL strain distributions predicted by individual FE models that used average MCL material properties were strongly correlated with subject-specific FE strain predictions (R(2)=0.99 at all flexion angles). However, predictions by FE models that used average in situ strain distributions yielded relatively poor correlations with subject-specific FE predictions (R(2)=0.44, 0.35, and 0.33 at flexion angles of 0 degrees, 30 degrees, and 60 degrees, respectively). The strain distribution within the MCL was nonuniform and changed with flexion angle. The highest MCL strains occurred at full extension in the posterior region of the MCL proximal to the joint line during valgus loading, suggesting this region may be most vulnerable to injury under these loading conditions. This work demonstrates that subject-specific FE models can predict the complex, nonuniform strain fields that occur in ligaments due to external loading of the joint.     

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

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

Stability after medial collateral ligament release in total knee arthroplasty.

Six knees from cadavers were tested for change in stability after release of the medial collateral ligament with posterior cruciate-retaining and substituting total knee replacements. Load deformation curves of the joint were recorded in full extension and 30 degrees, 60 degrees, and 90 degrees flexion under a 10 N-m varus and valgus torque, 1.5 N-m internal and external rotational torque, and a 35 N anterior and posterior force to test stability in each knee. The intact specimen and posterior cruciate ligament-retaining total joint replacement were tested for baseline comparisons. The superficial medial collateral ligament was released, followed by release of the posterior cruciate ligament. The knee then was converted to a posterior-stabilized implant. After medial collateral ligament release, valgus laxity was statistically significantly greater at 30 degrees, 60 degrees, and 90 degrees flexion after posterior cruciate ligament sacrifice than it was when the posterior cruciate ligament was retained. The posterior-stabilizing post added little to varus and valgus stability. Small, but significant, differences were seen in internal and external rotation before and after posterior cruciate ligament sacrifice. The posterior-stabilized total knee arthroplasty was even more rotationally constrained in full extension than the knee with intact medial collateral ligament and posterior cruciate ligament.     

The static stabilizing function of the popliteal tendon in the knee. An experimental study

We investigated the importance of the anterior cruciate ligament (ACL), its two components (the AMP and PLP), and the lateral compartment ligaments with special attention to the popliteal tendon (PT) in relation to valgus-varus, axial rotation, and anterior-posterior instability. Mobility patterns were drawn from 15 osteoligamentous knee preparations after successive transection of the structures. Even when combined lesion involved the lateral collateral ligament (LCL), the PT, and the posterolateral capsule (PLC), anterior tibial displacement was not effected until the ACL was cut. The lateral structures acted as secondary restraints to anterior displacement, and prevented simultaneous anterolateral rotation during application of the anterior force. LCL and PLC transection affected varus stability in full extension, and instability improved on additional section of the PT, even if the ACL remained intact. Maximum instability after combined lateral lesion occurred at 40 degrees of flexion, whether the ACL was transected or not. Further flexion caused a rapid decrease of instability. The PT was shown to effectively restrain varus instability from 0 to 90 degrees of flexion. It was experimentally established with regard to axial rotation that marked posterolateral instability was impossible with an intact PT. Maximum instability was recorded at 30 degrees of flexion after combined lesion to the lateral structures. Even in the extension, considerable posterolateral instability was observed. The restraining effect of the PLC was prominent in extension.