The effect of injury to the posterolateral structures of the knee on force in a posterior cruciate ligament graft: a biomechanical study

To determine whether untreated grade 3 posterolateral knee injuries contribute to a significant increase in force on a posterior cruciate ligament reconstruction graft, we measured the force on the graft during joint loading of a posterior cruciate ligament-reconstructed knee with otherwise intact structures and then selectively cut the popliteofibular ligament, popliteus tendon, and the fibular collateral ligament. A posterior cruciate ligament reconstruction was performed in eight fresh-frozen cadaveric knees. One end of the graft was fixed to a tensioning jig with a load cell used to measure force in the graft as loads were applied to the knee. The force on the graft was significantly higher with the posterolateral structures cut during varus loading at 30 degrees, 60 degrees, and 90 degrees of flexion than it was in the same joint under the same loading conditions but with the posterolateral structures intact. Additionally, coupled loading of posterior drawer force and external tibial torque at 30 degrees, 60 degrees, and 90 degrees significantly increased force on the graft with the posterolateral structures cut. There was no significant increase in force on the graft under any condition with a posterior force, valgus force, or internal and external tibial torque applied alone. A significant increase in force occurs in a posterior cruciate ligament graft in knees with deficient posterolateral knee structures. We recommend that in knees with grade 3 posterolateral injuries and evidence of varus or coupled posterior-external rotation instability the posterolateral structures be repaired or reconstructed at the time of posterior cruciate ligament reconstruction to decrease the chance of later graft failure.     

Biomechanical and anatomical effects of an external rotational torque applied to the knee: a cadaveric study

BACKGROUND: External rotational torque is one of the mechanisms that may occur during a pivoting or twisting injury to the knee. HYPOTHESIS: Simulated external rotational injury by applying external rotational torque will increase knee laxity and cause soft tissue damage to the knee. STUDY DESIGN: Controlled laboratory study. METHODS: Six cadaveric knees and a custom testing system were used to produce external rotational torque of 30 degrees , 45 degrees , and 60 degrees with the knee at 30 degrees of flexion. Anterior-posterior, valgus-varus, and rotational knee laxity were quantified. After sequential rotational torque to 60 degrees , the specimens were dissected to identify injured structures. RESULTS: External rotational torque of 45 degrees and 60 degrees significantly increased knee joint laxity in all directions (P < .05). Dissection showed that all posterior cruciate ligaments were intact; all medial collateral and anterior cruciate ligaments revealed either partial or complete tears. The lateral collateral ligaments were torn in all specimens. The popliteus tendon was attenuated in 1 specimen and was completely torn in 1 specimen. The popliteofibular ligament was torn in 3 specimens. CONCLUSION: External rotational torque to 60 degrees increased knee laxity, and dissection revealed a consistent pattern of injury to the medial and lateral collateral and anterior cruciate ligaments and posterolateral corner. CLINICAL RELEVANCE: Because isolated ligament injuries are rare, recognizing these combined ligamentous injuries early is essential for repair in the acute stage.     

Injury to the anterior cruciate ligament during alpine skiing: a biomechanical analysis of tibial torque and knee flexion angle

BACKGROUND: The anterior cruciate ligament has been shown to be particularly susceptible to injury during alpine skiing. Tibial torque is an important injury mechanism, especially when applied to a fully extended or fully flexed knee. PURPOSE: We wanted to record the forces generated in the anterior cruciate ligament with application of tibial torque to cadaveric knees in different positions. STUDY DESIGN: Controlled laboratory study. METHODS: Thirty-seven fresh-frozen cadaveric knees were instrumented with a tibial load cell that measured resultant force in the anterior cruciate ligament while internal and external tibial torques were applied to the tibia at full extension, 90 degrees of flexion, full flexion, and forced hyperflexion. RESULTS: At each knee flexion position, mean force generated by 10 N.m of internal tibial torque was significantly higher than the mean generated by 10 N.m of external tibial torque. Mean forces generated by tibial torque at 90 degrees of flexion were relatively low. During flexion-extension without tibial torque applied mean forces were highest (193 N) when the knee was hyperflexed. CONCLUSIONS: Application of internal tibial torque to a fully extended or fully flexed knee represents the most dangerous loading condition for injury from twisting falls during skiing. CLINICAL RELEVANCE: Understanding of the mechanisms of falls can be used to design better equipment and to better prevent or treat injury.     

Characteristics of the isokinetic performance of patients with injured cruciate ligaments.

The torques of the quadriceps muscle in patients with cruciate ligament injuries were evaluated under isokinetic contraction. There were 30 patients with anterior cruciate ligament injuries, 19 with posterior cruciate ligament injuries, and 30 controls. The torques of concentric and eccentric contractions in anterior cruciate ligament-injured knees showed a significant difference from those in the uninjured sides at extension angles of less than 45 degrees, yet the values of the peak torques for concentric and eccentric contractions were the same as those for the uninjured sides. The torques of concentric and eccentric contractions in posterior cruciate ligament-injured knees showed a significant difference from the uninjured sides at flexion angles of more than 36 degrees. The peak torques for concentric and eccentric contraction also showed a significant difference from the uninjured sides. The concentric and eccentric peak torque angles of the injured knees were similar to those of the uninjured sides in all subjects. The ratios of eccentric to concentric peak torque of the contralateral knees in the anterior cruciate ligament-injured groups did not show a significant difference from those of the controls. The evaluation of the biomechanical change in these categories is of great advantage in determining proper methods of treatment and rehabilitation.     

Biomechanical analysis of an anatomic anterior cruciate ligament reconstruction

BACKGROUND: The focus of most anterior cruciate ligament reconstructions has been on replacing the anteromedial bundle and not the posterolateral bundle. HYPOTHESIS: Anatomic two-bundle reconstruction restores knee kinematics more closely to normal than does single-bundle reconstruction. STUDY DESIGN: Controlled laboratory study. METHODS: Ten cadaveric knees were subjected to external loading conditions: 1) a 134-N anterior tibial load and 2) a combined rotatory load of 5-N x m internal tibial torque and 10-N x m valgus torque. Resulting knee kinematics and in situ force in the anterior cruciate ligament or replacement graft were determined by using a robotic/universal force-moment sensor testing system for 1) intact, 2) anterior cruciate ligament deficient, 3) single-bundle reconstructed, and 4) anatomically reconstructed knees. RESULTS: Anterior tibial translation for the anatomic reconstruction was significantly closer to that of the intact knee than was the single-bundle reconstruction. The in situ force normalized to the intact anterior cruciate ligament for the anatomic reconstruction was 97% +/- 9%, whereas the single-bundle reconstruction was only 89% +/- 13%. With a combined rotatory load, the normalized in situ force for the single-bundle and anatomic reconstructions at 30 degrees of flexion was 66% +/- 40%and 91% +/- 35%, respectively. CONCLUSIONS: Anatomic reconstruction may produce a better biomechanical outcome, especially during rotatory loads. CLINICAL RELEVANCE: Results may lead to the use of a two-bundle technique.     

The effects of grade III posterolateral knee complex injuries on anterior cruciate ligament graft force. A biomechanical analysis.

To determine if untreated grade III injuries of the posterolateral structures contribute to increased force on an anterior cruciate ligament graft, we measured the force in the graft in cadaveric knees during joint loading after reconstruction with otherwise intact structures and in the same reconstructed knees after selected cutting of specific posterolateral knee structures. Tests were first performed on the knee with the posterolateral structures intact and then after sequential sectioning of the fibular collateral ligament, popliteofibular ligament, and popliteus tendon. The graft force was significantly higher after fibular collateral ligament transection during varus loading at both 0 degree and 30 degrees of knee flexion than it was for the same loading of the joint with intact posterolateral structures. In addition, coupled loading of varus and internal rotation moments at 0 degree and 30 degrees of flexion further increased graft force beyond that with varus force alone. The increase in graft force remained significant with additional sequential cutting of the popliteofibular ligament and popliteus tendon. We believe this study supports the clinical observation that untreated grade III posterolateral structure injuries contribute to anterior cruciate ligament graft failure by allowing higher forces to stress the graft.     

Surgical treatment of ACL/PCL/ medial-side knee injuries

The medial cruciate ligament (MCL), anterior cruciate ligament (ACL), and posterior oblique ligament (POL) frequently are injured by a combination of valgus and external rotation forces. Grade I or II MCL injuries alone or in combination with ACL or posterior cruciate ligament (PCL) injuries are treated nonoperatively, with cruciate ligament reconstruction delayed 3 to 6 weeks. Treatment of acute grade III ACL/PCL medial knee injuries remains controversial. Recommendations have included nonoperative treatment of the MCL and reconstruction of the ACL and PCL, acute reconstruction of the MCL and nonoperative treatment of the ACL, and treatment of all grade III injuries with acute repair. For chronic ACL/PCL/medial knee injuries, magnetic resonance imaging and examination under anesthesia are followed by endoscopic ACL/PCL reconstruction. Severe valgus laxity usually requires tightening of the MCL in addition to the posterior capsule, the posterior oblique area of the posteromedial capsule, and the midmedial capsular ligament. Thorough preoperative planning is essential to determine what procedures will be necessary for each patient.     

In vitro comparison of over-the-top and through-the-condyle anterior cruciate ligament reconstructions.

Knee kinematics, during standard knee examination maneuvers, were measured on 15 fresh cadaveric knees in their normal state and after isolated sectioning of the anterior cruciate ligament using a six degree of freedom electrogoniometer. Proximal iliotibial band autografts were used to perform two anterior cruciate ligament reconstructions on the cadaveric knees: an over-the-top reconstruction and a through-the-condyle procedure. Both of these reconstructions reduced the abnormal anterior translation of the anterior cruciate ligament-deficient knee seen in Lachman testing. However, neither reconstruction restored the normal anterior translation. In addition, other motions remained uncorrected: 1) the internal rotation due to internal torque at full extension; 2) coupled anterior translation during internal rotation at full extension; and 3) coupled medial translation with anterior translation in Lachman testing. There were no statistical differences noted in the joint kinematics created by either reconstruction.     

Biomechanical analysis of tibial torque and knee flexion angle: implications for understanding knee injury

Knee injuries are common in sports activities. Understanding the mechanisms of injury allows for better treatment of these injuries and for the development of effective prevention programmes. Tibial torque and knee flexion angle have been associated with several mechanisms of injury in the knee. This article focuses on the injury to the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL) and the meniscus of the knee as they relate to knee flexion angle and tibial torque. Hyperflexion and hyperextension with the application of tibial torque have both been implicated in the mechanism of ACL injury. A combination of anterior tibial force and internal tibial torque near full extension puts the ACL at high risk for injury. Hyperflexion also increases ACL force; however, in this position, internal and external tibial torque only minimally increase ACL force. Several successful prevention programmes have been based on these biomechanical factors. Injury to the PCL typically occurs in a flexed or hyperflexed knee position. The effects of application of a tibial torque, both internally and externally, remains controversial. Biomechanical studies have shown an increase in PCL force with knee flexion and the application of internal tibial torque, while others have shown that PCL-deficient knees have greater external tibial rotation. The meniscus must endure greater compressive loads at higher flexion angles of the knee and, as a result, are more prone to injury in these positions. In addition, ACL deficiency puts the meniscus at greater risk for injury. Reducing the forces on the ACL, PCL and meniscus during athletic activity through training, the use of appropriate equipment and safe surfaces will help to reduce injury to these structures.     

The 6 degrees of freedom kinematics of the knee after anterior cruciate ligament deficiency: an in vivo imaging analysis

BACKGROUND: Previous studies of knee joint function after anterior cruciate ligament deficiency have focused on measuring anterior-posterior translation and internal-external rotation. Few studies have measured the effects of anterior cruciate ligament deficiency on 6 degrees of freedom knee kinematics in vivo. OBJECTIVE: To measure the 6 degrees of freedom knee kinematics of patients with anterior cruciate ligament deficiency. STUDY DESIGN: Controlled laboratory study. METHODS: The knee joint kinematics of 8 patients with unilateral anterior cruciate ligament rupture was measured during a quasi-static lunge. Kinematics was measured from full extension to 90 degrees of flexion using imaging and 3-dimensional modeling techniques. The healthy, contralateral knee of each patient served as a control. RESULTS: Anterior cruciate ligament deficiency caused a statistically significant anterior shift (approximately 3 mm) and internal rotation of the tibia (approximately 2 degrees ) at low flexion angles. However, ligament deficiency also caused a medial translation of the tibia (approximately 1 mm) between 15 degrees and 90 degrees of flexion. CONCLUSION: The medial shift of the tibia after anterior cruciate ligament deficiency might alter contact stress distributions in the tibiofemoral cartilage near the medial tibial spine. These findings correlate with the observation that osteoarthritis in patients with anterior cruciate ligament injuries is likely to occur in this region. CLINICAL RELEVANCE: The data from this study suggest that future anterior cruciate ligament reconstruction techniques should reproduce not only anterior stability but also medial-lateral stability.     

Anatomical double-bundle anterior cruciate ligament reconstruction after valgus high tibial osteotomy: a biomechanical study

BACKGROUND: Although anatomical double-bundle anterior cruciate ligament reconstruction can successfully restore normal knee biomechanics for knees with typical varus-valgus alignment, the efficacy of the same reconstruction method for knees after a valgus high tibial osteotomy is unclear. HYPOTHESIS: Anatomical double-bundle anterior cruciate ligament reconstruction for valgus knees after a high tibial osteotomy cannot restore normal knee kinematics and can result in abnormally high in situ forces in the ligament graft. STUDY DESIGN: Controlled laboratory study. METHODS: Ten cadaveric knees were subjected to valgus high tibial osteotomy followed by an anatomical double-bundle anterior cruciate ligament reconstruction. The valgus knees were tested using a robotic/universal force-moment sensor system before and after the ligament reconstruction. The knee kinematics in response to anterior tibial load and combined rotatory loads, as well as the corresponding in situ forces of the anterior cruciate ligament bundles and grafts, were compared between the ligament-intact and ligament-reconstructed valgus knees. RESULTS: After reconstruction, the anterior tibial translation and internal tibial rotation for the valgus knee decreased approximately 2 mm and 2 degrees , respectively, at low flexion angles compared with those of the anterior cruciate ligament-intact knee (P < .05). The in situ forces in the posterolateral graft became 56% to 200% higher than those in the posterolateral bundle of the intact anterior cruciate ligament (P < .05). CONCLUSION: Performing an anatomical double-bundle anterior cruciate ligament reconstruction on knees after valgus high tibial osteotomy may overconstrain the knee and result in high forces in the posterolateral graft, which could predispose it to failure. CLINICAL RELEVANCE: Modifications of anterior cruciate ligament reconstruction procedures to reduce posterolateral graft force may be needed for valgus knees after a high tibial osteotomy.     

The biomechanical interdependence between the anterior cruciate ligament replacement graft and the medial meniscus

To establish a quantitative biomechanical relationship between the anterior cruciate ligament graft and the medial meniscus, 10 human cadaveric knees were examined using the robotic/universal force-moment sensor testing system. In response to a combined 134-N anterior and 200-N axial compressive tibial load, the resulting kinematics of the knee and the in situ forces in the anterior cruciate ligament, the anterior cruciate ligament graft, and the medial meniscus were measured. Anterior tibial translation significantly increased after anterior cruciate ligament transection, between 6.8 +/- 2.3 mm at full extension and 12.6 +/- 3.3 mm at 30 degrees of flexion. Consequently, the resultant forces on the medial meniscus, ranging from 52 +/- 30 N to 63 +/- 51 N between full extension and 90 degrees of knee flexion in the intact knee, were doubled as a result of anterior cruciate ligament deficiency. However, after anterior cruciate ligament reconstruction, anterior tibial translations were restored to the levels of the intact knee, and thus the forces on the medial meniscus were restored as well. Likewise, the in situ forces in the anterior cruciate ligament replacement graft increased between 33% and 50% after medial meniscectomy.     

Change in meniscal strain with anterior cruciate ligament injury and after reconstruction

Meniscal injury has been well documented in association with injury to the anterior cruciate ligament. The purpose of this study was to evaluate the effect of anterior cruciate ligament transection and reconstruction on meniscal strain. Four differential variable reluctance transducer strain gauges were placed in the medial and lateral menisci of nine cadaveric knees. Each specimen was mounted to a six-degree-of-freedom knee testing device. Testing was conducted with the knee fully extended and at 45 degrees and 90 degrees of flexion, both with and without applied axial load. At each angle of flexion, an anterior and posterior tibial load was applied. Next, the anterior cruciate ligament was transected and the testing sequence was repeated. Finally, the ligament was reconstructed using a central one-third patellar tendon graft and the testing sequence was repeated. The results demonstrated statistically significant increases in meniscal strain in ligament-transected knees compared with intact specimens. A reduction in meniscal strain to a level similar to that detected in the ligament-intact knees was observed after anterior cruciate ligament reconstruction. These results have important clinical implications regarding the potentially deleterious effect of the anterior cruciate ligament-deficient knee on meniscal strain and the potential benefit of anterior cruciate ligament reconstruction.     

Internal and external tibial rotation strength after anterior cruciate ligament reconstruction using ipsilateral semitendinosus and gracilis tendon autografts

The internal and external tibial rotation torques of subjects who had undergone anterior cruciate ligament reconstruction using semitendinosus and gracilis tendon grafts were measured to determine whether harvest of the tendons results in weakness of tibial internal and external rotation. Cybex NORM dynamometer examinations were performed to measure internal and external tibial torque at angular velocities of 60, 120, and 180 deg/sec in 23 subjects. The sex-specific average torque data of the reconstructed limbs were compared with those of the contralateral limbs. Relative internal and external torque scores were calculated for each subject by subtracting the peak torque of the reconstructed knee from that of the contralateral knee. These relative scores were averaged and compared with the null hypothesis that each score should be statistically similar to zero. Subjects were evaluated at an average of 51 +/- 40 months postoperatively. The mean relative internal torque scores of the reconstructed limbs showed a statistically significant decrease from those of the contralateral limbs at all angular velocities. The mean relative external torque scores of the reconstructed limbs were statistically similar to those of the contralateral limbs at all angular velocities. Subjects who had undergone ligament reconstruction using semitendinosus and gracilis tendons demonstrated internal tibial rotation weakness in their reconstructed knees compared with their contralateral knees at all angular velocities tested. These results suggest that semitendinosus and gracilis tendon harvest causes weakness of internal tibial rotation.     

Correlation between occult bone lesions and meniscoligamentous injuries in patients with traumatic knee joint disease

To identify any correlation between the distribution of occult bone lesions and meniscoligamentous injuries, magnetic resonance images of 333 patients with traumatic knee joint disease were reviewed. Bone lesions of the knee were commonly associated with medial meniscal injuries and/or anterior cruciate ligament injuries. While knees with bone lesions showed a higher incidence (P < 0.05) of anterior cruciate ligament injury than knees without bone lesions, the presence of a lateral femoral condylar lesion resulted in a significantly higher incidence of anterior cruciate ligament injuries (P < 0.01). However, no significant positive correlation was found between other occult bone lesions and meniscoligamentous injuries.     

Biomechanical evaluation of two techniques for double-bundle anterior cruciate ligament reconstruction: one tibial tunnel versus two tibial tunnels

BACKGROUND: This research was undertaken to determine whether there is a need for a second tibial tunnel in anatomic anterior cruciate ligament reconstruction. HYPOTHESIS: Anatomic two-bundle reconstruction with two tibial tunnels restores knee anterior tibial translation in response to 134 N and to 5-N.m internal tibial torque combined with 10-N.m valgus torque more closely to normal than does double-bundle reconstruction with one tibial tunnel. STUDY DESIGN: Controlled laboratory study. METHODS: Ten cadaveric knees were subjected to a 134-N anterior tibial load at 0 degrees, 30 degrees, 60 degrees, and 90 degrees and to 5-N.m internal tibial torque and 10-N.m valgus torque at 15 degrees and 30 degrees. Resulting knee kinematics and in situ force in the anterior cruciate ligament or replacement graft were determined by using a robotic/universal force-moment sensor testing system for (1) intact, (2) anterior cruciate ligament-deficient, (3) double-bundle/one tibial tunnel, and (4) double-bundle/two tibial tunnels. RESULTS: Anterior tibial translation for the reconstruction with two tibial tunnels was significantly closer to that of the intact knee than was the reconstruction with one tibial tunnel at 0 degrees and 30 degrees of flexion (0 degrees = 3.82 vs 6.0 mm, P < .05; 30 degrees = 7.99 vs 11 mm, P < .05). The in situ force normalized to the intact anterior cruciate ligament for the reconstruction with two tibial tunnels was significantly higher than the in situ force of the reconstruction with one tibial tunnel (30 degrees = 89 vs 82 N, P < .05). With a combined rotatory load, the anterior tibial translation of specimens with a tibial two-tunnel technique was significantly lower than that of specimens with one tunnel (0 degrees = 5.7 vs 8.4 mm, P < .05; 30 degrees = 7.5 vs 9.5 mm, P < .05). CONCLUSIONS: Anatomic reconstruction with two tibial tunnels may produce a better biomechanical outcome, especially close to extension. CLINICAL RELEVANCE: At the time of initial fixation, there appears to be a small biomechanical advantage to the second tibial tunnel in the setting of two-bundle anterior cruciate ligament reconstruction.     

Evaluation and treatment of chronic medial collateral ligament injuries of the knee

Injuries to the medial collateral ligament (MCL) can occur as isolated injuries or in conjunction with injuries to other structures about the knee. Most grade I and II MCL injuries without meniscal avulsion, alone or in combination with anterior or posterior cruciate ligament injuries, can be treated nonoperatively. Grade III or complete tears also can be treated nonoperatively, but only after careful exclusion of any associated injuries that may require surgical treatment. Treatment recommendations also have been based on the location of the MCL tear and the associated injuries. Surgical treatment may include reconstruction of the anterior and posterior cruciate ligaments with primary repair of the MCL. Chronic medial knee injuries often are associated with concomitant ligament injuries, which also must be treated. Treatment options include nonoperative (bracing, activity modification, and rehabilitation) and operative reconstruction.     

Anterior-posterior and rotational displacement of the tibia elicited by quadriceps contraction.

The anterior-posterior displacement and rotation of the tibia elicited by isolated loading of the quadriceps muscle was determined as a function of joint angle and muscle load using a computerized radiographic technique. Data collected from 12 fresh-frozen cadaveric knees demonstrated that quadriceps contraction can result in significant (less than 7 mm) anterior displacement of the tibia in the range of 0 degrees to 80 degrees of flexion, and a mild (less than 2 mm) posterior displacement in the range of 80 degrees to 120 degrees of flexion. Peak anterior displacement of 6.3 mm was observed at 30 degrees of flexion under a 12 kg load in the quadriceps, while a constant 1.5 mm posterior displacement was observed throughout flexion angles exceeding 80 degrees. It was further shown that the magnitude of the anterior displacement increased nonlinearly as the quadriceps force increased. Loading of the quadriceps also resulted in internal rotation of the tibia in the range of 0 degrees to 90 degrees of flexion, and in external rotation of the tibia in the range of 90 degrees to 120 degrees. Peak internal rotation of 7 degrees was observed at 15 degrees of flexion and a peak external rotation of 1 degrees was detected at 120 degrees of flexion. Larger quadriceps load resulted in larger rotation. We concluded that quadriceps contraction during knee extension has direct impact on anterior displacement and rotation of the tibia and therefore on anterior cruciate ligament stress, increasing it as the muscle's force is increased during knee extension.(ABSTRACT TRUNCATED AT 250 WORDS)     

Weight-bearing knee kinematics in subjects with two types of anterior cruciate ligament reconstructions

Weight-bearing knee kinematics in patients who received two types of anterior cruciate ligament reconstruction were studied using a fluoroscopy-based three-dimensional measurement technique. Eleven patients with more than 1-year follow-up and good or excellent results participated in this study. Six subjects received anterior cruciate ligament reconstruction using a multiply folded semitendinosus and gracilis tendon graft, and five received combined intra- and extra-articular anterior cruciate ligament reconstruction using the iliotibial tract. The step up/down activity of normal and operated knees was recorded using lateral fluoroscopy. A customized three-dimensional contour model was created from two orthogonal views of each knee and all six degrees of freedom of knee movement were determined using a model matching technique. Both the normal and the reconstructed knees exhibited posterior condylar translation and internal tibial rotation with knee flexion, consistent with previous reports of normal kinematics. There were no statistically significant differences in the axial rotations or lateral or medial condylar anterior/posterior translations between operated and normal knees or between the two groups of operated knees.     

The effects of varied joint motion and loading conditions on posterior cruciate ligament fiber length behavior

BACKGROUND: The posterior cruciate ligament has been described as being composed of 2 bands that reciprocally tighten and loosen with knee flexion, but the fiber anatomy and behavior may be more complex. HYPOTHESIS: The mechanical effects of defined loading conditions at discrete knee joint angles can vary significantly within the substance of the posterior cruciate ligament depending on the fiber region tested. STUDY DESIGN: Controlled laboratory study. METHODS: Nine intact, fresh-frozen cadaveric knees were instrumented with excursion filaments implanted within 4 fiber regions of the posterior cruciate ligament. Patterns of fiber behavior were analyzed as a function of the variable linear separation distance between tibial and femoral fiber attachment sites during joint motion under a simulated quadriceps contraction, tibial internal rotation, and tibial external rotation. Analysis of variance, the Newman-Keuls multiple comparisons procedure, and paired t tests were used to evaluate statistical significance. RESULTS: Compared with the control pattern of fiber behavior during unloaded passive knee motion from 0 degrees to 120 degrees , the quadriceps force caused loosening of most ligament fibers at knee flexion of less than 75 degrees . Tibial internal rotation significantly slackened the anterior and central fiber regions near extension and significantly tightened the central and posterior fiber regions with progressive flexion. External rotation had an effect similar to internal rotation on the anterior and central fiber regions but caused significant slackening of the posterior fiber regions from 0 degrees to 45 degrees . CONCLUSIONS: Distinct geographic regions within the posterior cruciate ligament have different functional roles depending on the joint angle and the type of load to which the knee is subjected. CLINICAL RELEVANCE: The specific graft placement parameters in a given surgical procedure relate to end-to-end length changes of the graft and may have important implications for postoperative rehabilitation and return to specific functional activities.