The importance of quadriceps and hamstring muscle loading on knee kinematics and in-situ forces in the ACL

Excessive compression of the human tibio-femoral joint causes ACL rupture

The knee is one of the most frequently injured joints in the human body. A recent study suggests that axial compressive loads on the knee may play a role in injury to the anterior cruciate ligament (ACL) for the flexed knee, because of an approximate 10 degrees posterior tilt in the tibial plateau (J. Orthop. Res. 16 (1998) 122-127). The hypothesis of the current study was that excessive axial compressive loads in the human tibio-femoral (TF) joint would cause relative displacement and rotation of the tibia with respect to the femur, and result in isolated injury to the ACL when the knee is flexed to 60 degrees , 90 degrees or 120 degrees . Sixteen isolated knees from eleven fresh cadaver donors (74.3+/-10.5 yr) were exposed to repetitive TF compressive loads increasing in intensity until catastrophic injury. ACL rupture was documented in 14/16 cases. The maximum TF joint compressive force for ACL failure was 5.1+/-2.1 kN for all flexion angles combined. For the 90 degrees flexed knee, the injury occurred with a relative anterior displacement of 5.4+/-3.8mm, a lateral displacement of 4.1+/-1.4mm, and a 7.8+/-7.0 degrees internal rotation of the tibia with respect to the femur.

In vivo elongation of the anterior cruciate ligament and posterior cruciate ligament during knee flexion

BACKGROUND

Most knowledge regarding cruciate ligament function is based on in vitro experiments.

PURPOSE

To investigate the in vivo elongation of the functional bundles of the anterior cruciate ligament and posterior cruciate ligament during weightbearing flexion.

HYPOTHESIS

The biomechanical role of functional bundles of the anterior cruciate ligament and posterior cruciate ligament under in vivo loading is different from that measured in cadavers.

STUDY DESIGN

In vivo biomechanical study.

METHODS

Elongation of the anterior cruciate ligament and posterior cruciate ligament was measured during a quasi-static lunge using imaging and 3-dimensional computer-modeling techniques.

RESULTS

The anterior-medial bundle of the anterior cruciate ligament had a relatively constant length from full extension to 90 degrees of flexion. The posterior-lateral bundle of the anterior cruciate ligament decreased in length with flexion. Both bundles of the posterior cruciate ligament had increased lengths with flexion.

CONCLUSION

The data did not demonstrate the reciprocal function of the 2 bundles of the anterior cruciate ligament or the posterior cruciate ligament with flexion observed in previous studies. Instead, the data suggest that there is a reciprocal function between the anterior cruciate ligament and posterior cruciate ligament with flexion. The anterior cruciate ligament plays a more important role in low-flexion angles, whereas the posterior cruciate ligament plays a more important role in high flexion.

CLINICAL RELEVANCE

Understanding the biomechanical role of the knee ligaments in vivo is essential to reproduce the structural behavior of the ligament after injury (especially for 2-bundle reconstructions) and thus improve surgical outcomes.

Influence of a mono-centric knee brace on the tension of the collateral ligaments in knee joints after sectioning of the anterior cruciate ligament--an in vitro study

OBJECTIVE

To analyze the influence of knee bracing on the tension of the medial and lateral collateral ligaments in anterior cruciate ligament deficiency.

DESIGN

The tension of the collateral ligaments in anterior cruciate ligament deficient knees was measured with and without knee bracing using an in vitro model.

BACKGROUND

Anterior cruciate ligament deficiency increases the tension in both collateral ligaments at the knee joint. Therefore knee braces should reduce that tension increase. However, that effect has never been proven quantitatively.

METHODS

After anterior cruciate ligament-transection, the forces of the medial (anterior/posterior part) and lateral collateral ligament were measured in ten fresh human cadaver knees at 0 degrees, 20 degrees, 40 degrees, 60 degrees, 80 degrees and 100 degrees of flexion, with and without application of a mono-centric knee brace. To quantify the ligament forces, strain gauges were fixed at the bony origins of the ligaments.

RESULTS

Bracing led to a significant decrease of ligament forces (20-100 degrees: P < 0.0001) in the anterior part of the medial collateral ligament in all joint positions. In the posterior aspect, this effect was observed only at 40 degrees (P < 0.0001) and 80 degrees (P = 0.001) of flexion. In the lateral collateral ligament, bracing caused a strain reduction from 60 degrees to 100 degrees of flexion (P < 0.0001). Therefore a flexion angle dependent effect of knee bracing on the strain was seen in the posterior aspect of the medial and in the lateral collateral ligament in anterior cruciate ligament deficient knee joints.

CONCLUSIONS

Application of a mono-centric knee brace leads to a significant position dependent reduction of collateral ligament tension after anterior cruciate ligament-rupture.

The effect of tibiofemoral joint kinematics on patellofemoral contact pressures under simulated muscle loads

Altered patellofemoral joint contact pressures are thought to contribute to patellofemoral joint symptoms. However, little is known about the relationship between tibiofemoral joint kinematics and patellofemoral joint contact pressures. The objective of this paper was to investigate the effect of tibiofemoral joint kinematics on patellofemoral joint pressures using an established in vitro robotic testing experimental setup. Eight cadaveric knee specimens were tested at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion under an isolated quadriceps load of 400 N and a combined quadriceps/hamstrings load of 400 N/200 N. Tibiofemoral joint kinematics were measured by the robot and contact pressures by a TekScan pressure sensor. The isolated quadriceps loading caused anterior translation and internal rotation of the tibia up to 60 degrees of flexion and posterior translation and external rotation of the tibia beyond 60 degrees. The co-contraction of the hamstring muscles caused a posterior translation and external rotation of the tibia relative to the motion of the tibia under the quadriceps load. Correspondingly, the contact pressures were elevated significantly at all flexion angles. For example, at 60 degrees of flexion, the hamstrings co-contraction increased the posterior tibial translation by approximately 2.8 mm and external tibial rotation by approximately 3.6 degrees. The peak contact pressure increased from 1.4+/-0.8 to 1.7+/-1.0 MPa, a 15% increase. The elevated contact pressures after hamstrings co-contraction indicates an intrinsic relation between the tibiofemoral joint kinematics and the patellofemoral joint biomechanics. An increase in posterior tibial translation and external rotation is accompanied by an increase in contact pressure in the patellofemoral joint. These results imply that excessive strength conditioning with the hamstring muscles might not be beneficial to the patellofemoral joint. Knee pathology that causes an increase in tibial posterior translation and external rotation might contribute to degeneration of the patellofemoral joint. These results suggest that conservative treatment of posterior cruciate ligament injury should be reconsidered.

Effects of applied quadriceps and hamstrings muscle loads on forces in the anterior and posterior cruciate ligaments

BACKGROUND

Muscle contraction can subject healing knee ligament grafts to high loads.

PURPOSE

To directly measure the effects of quadriceps and hamstrings muscle loads on forces in the anterior cruciate ligaments and posterior cruciate ligaments.

STUDY DESIGN

Controlled laboratory study.

METHODS

Thirteen cadaveric knee specimens had load cells installed to record resultant forces in both anterior and posterior cruciate ligaments under 5 loading conditions. Cruciate force measurements were repeated with a 100-N load applied to the quadriceps tendon and again with a combined 50-N biceps load and 50-N semimembranosus-semitendinosus load.

RESULTS

Applied quadriceps loads resulted in mean changes in anterior cruciate ligament and posterior cruciate ligament forces that were less than 20 N for all loading conditions. Hamstrings load significantly increased mean posterior cruciate ligament force between 30 degrees and 105 degrees of flexion with 100 N of applied posterior tibial force.

CONCLUSIONS

At the muscle force levels used in this study, the hamstrings were more effective than the quadriceps in altering cruciate force levels, especially near 90 degrees of flexion, where they have an excellent mechanical advantage for controlling anterior-posterior tibial translation.

CLINICAL RELEVANCE

Isolated hamstrings activity generally had little or no effect on anterior cruciate ligament forces but significantly increased forces in the posterior cruciate ligament beyond approximately 30 degrees of flexion.

Effect of the posterior cruciate ligament on posterior stability of the knee in high flexion

Most biomechanical studies of the knee have focused on knee flexion angles between 0 degrees and 120 degrees. The posterior cruciate ligament (PCL) has been shown to constrain posterior laxity of the knee in this range of flexion. However, little is known about PCL function in higher flexion angles (greater than 120 degrees ). This in vitro study examined knee kinematics before and after cutting the PCL at high flexion under a posterior tibial load and various muscle loads. The results demonstrated that although the PCL plays an important role in constraining posterior tibial translation at low flexion angles, the PCL had little effect in constraining tibial translation at 150 degrees of flexion under the applied loads.

A Novel Robotic System for Joint Biomechanical Tests: Application to the Human Knee Joint

The objectives of the work reported in this article were to develop a novel 6-degree-of-freedom (DOF) robotic system for knee joint biomechanics, to complete a hybrid force-position control scheme, to evaluate the system performance, and to demonstrate a combined loading test. The manipulator of the system utilizes two mechanisms; the upper mechanism has two translational axes and three rotational axes while the lower mechanism has only a single translational axis. All axes were driven with AC servo-motors. This unique configuration results in a simple kinematic description of manipulator motion. Jacobian transformation was used to calculate both the displacement and force/moment, which allowed for a hybrid control of the displacement of, and force/moment applied to, the human knee joint. The control and data acquisition were performed on a personal computer in the C-language programming environment with a multi-tasking operating system. Preliminary tests revealed that the clamp-to-clamp compliance of the system was smaller in the vertical (Z) and longitudinal (Y) directions (0.001 mm/N) than in lateral (X) direction (0.003 mm/N). The displacement error under the application of 500 N of load was smallest in the vertical direction (0.001±0.003 mm (mean±SD), and largest in the lateral direction (0.084±0.027 mm). Using this test system, it was possible to simulate multiple loading conditions in a human knee joint in which a cyclic anterior force was applied together with a coupled, joint compressive force, while allowing natural knee motion. The developed system seems to be a useful tool for studies of knee joint biomechanics.

In situ forces of the anterior and posterior cruciate ligaments in high knee flexion: an in vitro investigation

The function of the anterior and posterior cruciate ligaments (ACL and PCL) in the first 120 degrees of flexion has been reported extensively, but little is known of their behavior at higher flexion angles. The aim of this investigation was to study the effects of muscle loads on the in situ forces in both ligaments at high knee flexion (>120 degrees). Eighteen fresh-frozen human knee specimens were tested on a robotic testing system from full extension to 150 degrees of flexion in response to quadriceps (400 N), hamstrings (200 N), and combined quadriceps and hamstrings (400 N/200 N) loads. The in situ forces in the ACL and PCL were measured using the principle of superposition. The force in the ACL peaked at 30 degrees of flexion (71.7 +/- 27.9 N in response to the quadriceps load, 52.3 +/- 24.4 N in response to the combined muscle load, 32.3 +/- 20.9 N in response to the hamstrings load). At 150 degrees, the ACL force was approximately 30 N in response to the quadriceps load and 20 N in response to the combined muscle load and isolated hamstring load. The PCL force peaked at 90 degrees (34.0 +/- 15.3 N in response to the quadriceps load, 88.6 +/- 23.7 N in response to the combined muscle load, 99.8 +/- 24.0 N in response to the hamstrings load) and decreased to around 35 N at 150 degrees in response to each of the loads. These results demonstrate that the ACL and PCL carried significantly less load at high flexion in response to the simulated muscle loads compared to the peak loads they carried in response to the same muscle loads at other flexion angles. The data could provide a reference point for the investigation of non-weight bearing flexion and extension knee exercises in high flexion. Furthermore, these data could be useful in designing total knee implants to achieve high flexion.

Effects of increasing tibial slope on the biomechanics of the knee

PURPOSE

To determine the effects of increasing anterior-posterior (A-P) tibial slope on knee kinematics and in situ forces in the cruciate ligaments.

METHODS

Ten cadaveric knees were studied using a robotic testing system using three loading conditions: (1) 200 N axial compression; (2) 134 N A-P tibial load; and (3) combined 200 N axial and 134 N A-P loads. Resulting knee kinematics were determined before and after a 5-mm anterior opening wedge osteotomy. Resulting in situ forces in each cruciate ligament were determined.

RESULTS

Tibial slope was increased from 8.8 +/- 1.8 degrees to 13.2 +/- 2.1 degrees, causing an anterior shift in the resting position of the tibia relative to the femur up to 3.6 +/- 1.4 mm. Under axial compression, the osteotomy caused a significant anterior tibial translation up to 1.9 +/- 2.5 mm (90 degrees ). Under A-P and combined loads, no differences were detected in A-P translation or in situ forces in the cruciates (intact versus osteotomy).

CONCLUSIONS

Results suggest that small increases in tibial slope do not affect A-P translations or in situ forces in the cruciate ligaments. However, increasing slope causes an anterior shift in tibial resting position that is accentuated under axial loads. This suggests that increasing tibial slope may be beneficial in reducing tibial sag in a PCL-deficient knee, whereas decreasing slope may be protective in an ACL-deficient knee.

Aggressive quadriceps loading can induce noncontact anterior cruciate ligament injury

BACKGROUND

The force responsible for noncontact anterior cruciate ligament (ACL) injuries remains controversial. The patella tendon to tibial shaft angle causes an anterior tibial shear force with quadriceps activation.

HYPOTHESIS

An aggressive quadriceps contraction can injure the ACL.

METHODS

The authors characterized noncontact ACL injury and kinematics with aggressive quadriceps loading. Thirteen fresh-frozen knees were potted in a jig held in 20 degrees of flexion while a 4500 N quadriceps contraction was simulated. Knee kinematics were recorded. A KT-1000 arthrometer and a simulated active quadriceps test assessed anterior displacement. Statistics were performed using paired t tests and 1-way analysis of variance.

RESULTS

Kinematics revealed the following mean values: anterior displacement, 19.5 mm; valgus, 2.3 degrees; and internal rotation, 5.5 degrees. Mean KT-1000 and active quadriceps test differences were 4.0 mm and 2.7 mm, respectively (statistically significant P =.002 and P =.002). Six knees showed gross ACL injury at the femoral insertion. Based on ACL injury, KT-1000 differences were statistically significant (P =.029).

CONCLUSIONS

Aggressive quadriceps loading, with the knee in slight flexion, produces significant anterior tibial translation and ACL injury. This suggests that the quadriceps is the intrinsic force in noncontact ACL injuries, producing a model for further investigation.

Femoro-tibial and menisco-tibial translation patterns in patients with unilateral anterior cruciate ligament deficiency--a potential cause of secondary meniscal tears

OBJECTIVE

To analyze menisco-tibial and femoro-tibial translation patterns in healthy and ACL-deficient knees in different knee flexion angles under muscle activity.

METHODS

The ACL-deficient and contralateral healthy knees of 10 patients were examined with an open MRI system at 30 degrees and 90 degrees of knee flexion, under isometric contraction of the extensors or flexor muscle groups. Translations between the tibia, the femoral condyles and the menisci were analyzed by three-dimensional image postprocessing.

RESULTS

Posterior translation of the femur and menisci relative to the tibia occurred during knee flexion (30-90 degrees) in all knees. In ACL-deficient knees, posterior translation of the medial femoral condyle (+1.3 +/- 3.8 mm) was significantly larger than in healthy knee (-0.9 +/- 2.9 mm; p<0.05), while the translation pattern of the menisci was similar (med. meniscus 0.6 +/- 2.3 mm vs. 0.6 +/- 2.7 mm). Under isometric contraction of the extensors (relative to the flexor muscle group), an increased posterior position of the femur and menisci was observed at 30 degrees knee flexion, but not at 90 degrees. This applied to ACL-deficient and healthy knees.

CONCLUSIONS

This study shows a significant increase of translation of the medial femoral condyle in ACL-deficient knees, whereas menisco-tibial translation remains almost unchanged. This difference in translation patterns indicates that the posterior horn of the medial meniscus might encounter shear, potentially explaining the high rate of secondary medial meniscal tears in patients with ACL-deficiency.

Kinematics of the knee at high flexion angles: an in vitro investigation

Restoration of knee function after total knee, meniscus, or cruciate ligament surgery requires an understanding of knee behavior throughout the entire range of knee motion. However, little data are available regarding knee kinematics and kinetics at flexion angles greater than 120 degrees (high flexion). In this study, 13 cadaveric human knee specimens were tested using an in vitro robotic experimental setup. Tibial anteroposterior translation and internal-external rotation were measured along the passive path and under simulated muscle loading from full extension to 150 degrees of flexion. Anterior tibial translation was observed in the unloaded passive path throughout, with a peak of 31.2+/-13.2 mm at 150 degrees. Internal tibial rotation increased with flexion to 150 degrees on the passive path to a maximum of 11.1+/-6.7 degrees. The simulated muscle loads affected tibial translation and rotation between full extension and 120 degrees of knee flexion. Interestingly, at high flexion, the application of muscle loads had little effect on tibial translation and rotation when compared to values at 120 degrees. The kinematic behavior of the knee at 150 degrees was markedly different from that measured at other flexion angles. Muscle loads appear to play a minimal role in influencing tibial translation and rotation at maximal flexion. The results imply that the knee is highly constrained at high flexion, which could be due in part to compression of the posterior soft tissues (posterior capsule, menisci, muscle, fat, and skin) between the tibia and the femur.

The effect of posterior cruciate ligament reconstruction on patellofemoral contact pressures in the knee joint under simulated muscle loads

BACKGROUND

The mechanism of cartilage degeneration in the patellofemoral joint (PFJ) and medial compartment of the knee following posterior cruciate ligament (PCL) injury remains unclear. PCL reconstruction has been recommended to restore kinematics and prevent long-term degeneration. The effect of current reconstruction techniques on PFJ contact pressures is unknown.

PURPOSE

To measure PFJ contact pressures after PCL deficiency and reconstruction.

METHOD

Eight cadaveric knees were tested with the PCL intact, deficient, and reconstructed. Contact pressures were measured at 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion under simulated muscle loads. Knee kinematics were measured by a robotic testing system, and the PFJ contact pressures were measured using a thin film transducer. A single bundle achilles tendon allograft was used in the reconstruction.

RESULTS

PCL deficiency significantly increased the peak contact pressures measured in the PFJ relative to the intact knee under both an isolated quadriceps load of 400 N and a combined quadriceps/hamstrings load of 400 N/200 N. Reconstruction did not significantly reduce the increased contact pressures observed in the PCL-deficient knee.

CONCLUSION

The elevated contact pressures observed in the PCL-deficient knee and reconstructed knee might contribute to the long-term degeneration observed in both the non-operatively treated and PCL-reconstructed knees.

Unique proximal tibial morphology in strepsirrhine primates

Although the morphology of the tibial plateau in primates has received very little attention in the literature, it does exhibit features of phylogenetic and functional interest. This paper describes the morphology of the tibial plateau (particularly the intercondylar region) in extant and fossil primates, and in three mammalian outgroups: the pen-tailed tree shrew (Ptilocercus), tree shrew (Tupaia), and flying lemur or dermopteran (Cynocephalus). Extant and fossil strepsirrhine primates exhibit an eminence with a single spine, which contrasts with the intercondylar morphology of haplorhine primates. Most extant platyrrhines, all catarrhine primates (including humans), and some fossil haplorhines possess an eminence with two spines (medial and lateral) connected by a ridge of bone that intersects the intercondylar groove. Tarsius and callitrichines possess an eminence with a reduced medial spine that superficially resembles that of strepsirrhine primates. Dermopterans also exhibit a morphology similar to that of strepsirrhines. In Scandentia, the intercondylar morphology of Tupaia is similar to that of rodents, whereas Ptilocercus resembles tarsiers and callitrichines. We hypothesize that proximal tibiae with either a single spine or reduced medial spine morphology facilitate a greater degree of knee rotation about the eminence relative to the double-spine condition, and are likely associated with more frequent adoption of vertical body positions. In contrast, a double-spine eminence limits knee rotation and is probably associated with greater use of horizontal supports. Although the polarity is complicated by the unknown phylogenetic status of likely sister taxa, it seems most probable that the single-spine morphology is a derived feature of strepsirrhines.

Risk factors associated with noncontact injury of the anterior cruciate ligament: a prospective four-year evaluation of 859 West Point cadets

BACKGROUND

The causes of noncontact anterior cruciate ligament injury remain an enigma.

PURPOSE

To prospectively evaluate risk factors for noncontact anterior cruciate ligament injuries in a large population of young athletic people.

STUDY DESIGN

Prospective cohort study.

METHODS

In 1995, 1198 new United States Military Academy cadets underwent detailed testing and many parameters were documented. During their 4-year tenure, all anterior cruciate ligament injuries that occurred were identified. Statistical analyses were used to identify the factors that may have predisposed the cadets to noncontact anterior cruciate ligament injuries.

RESULTS

Among the 895 cadets who completed the entire 4-year study, there were 24 noncontact anterior cruciate ligament tears (16 in men, 8 in women). Significant risk factors included small femoral notch width, generalized joint laxity, and, in women, higher than normal body mass index and KT-2000 arthrometer values that were 1 standard deviation or more above the mean. The presence of more than one of these risk factors greatly increased the relative risk of injury. All female cadets who had some combination of risk factors sustained noncontact anterior cruciate ligament injuries, indicating that some combinations of factors are especially perilous to the female knee.

CONCLUSION

Several risk factors may predispose young athletes to noncontact anterior cruciate ligament injury.

Synergy of medial and lateral hamstrings at three positions of tibial rotation during maximum isometric knee flexion

Rotation of the knee has been used to isolate the strength of the medial and lateral hamstrings during manual testing of the knee flexors. The purpose of this study was to determine if medial and lateral rotation of the knee during manual knee flexor strength testing increased the electromyographic activity of the respective hamstrings. Twenty-three women between 22 and 36 years old with no history of lower extremity injury or disease participated in the study. Indwelling fine wire electrodes were used to record EMG activity of the medial (semitendinosus and semimembranosus) and lateral (long and short heads of the biceps femoris) hamstring muscles during maximally resisted knee flexion with neutral, medial, and lateral rotation of the knee. Repeated measures analysis of variance with post hoc Bonferroni adjustments were used to compare EMG activity across the three tests. EMG activity increased significantly for the target hamstrings during ipsilateral rotation (P<0.05). The semitendinosus had a mean activity of 109% Max. during medial rotation as opposed to 95% Max. during lateral rotation. The semimembranosus averaged 107 and 89% Max. in medial and lateral rotation respectively. Conversely, both the long and short head of the biceps muscle showed significantly higher activity (P<0.05) during lateral compared to medial rotation (110 and 108% compared to 93 and 97%, respectively). Even though the differences are statistically significant they ranged from 2 to 13% only of maximum activity, the clinical importance of this small change in EMG activity is questionable.

The biomechanical effect of posterior cruciate ligament reconstruction on knee joint function. Kinematic response to simulated muscle loads

BACKGROUND

The effectiveness of posterior cruciate ligament reconstruction in restoring normal kinematics under physiologic loading is unknown.

HYPOTHESIS

Posterior cruciate ligament reconstruction does not restore normal knee kinematics under muscle loading.

STUDY DESIGN

In vitro biomechanical study.

METHODS

Kinematics of knees with an intact, resected, and reconstructed posterior cruciate ligament were measured by a robotic testing system under simulated muscle loads. Anteroposterior tibial translation and internal-external tibial rotation were measured at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion under posterior drawer loading, quadriceps muscle loading, and combined quadriceps and hamstring muscle loading.

RESULTS

Reconstruction reduced the additional posterior tibial translation caused by ligament deficiency at all flexion angles tested under posterior drawer loading. Ligament deficiency increased external rotation and posterior translation at angles higher than 60 degrees of flexion when simulated muscle loading was applied. Posterior cruciate ligament reconstruction reduced the posterior translation and external rotation observed in posterior cruciate ligament-deficient knees at higher flexion angles, but differences were not significant.

CONCLUSION

Under physiologic loading conditions, posterior cruciate ligament reconstruction does not restore six degree of freedom knee kinematics.

CLINICAL RELEVANCE

Abnormal knee kinematics may lead to development of long-term knee arthrosis.

Femoral rollback after cruciate-retaining and stabilizing total knee arthroplasty

Limited data comparing the kinematics of posterior cruciate ligament-retaining or substituting total knee arthroplasty with its own intact knee under identical loadings is available. In the current study, posterior femoral translation of the lateral and medial femoral condyles under unloaded conditions was examined for intact, cruciate-retaining, cruciate ligament-deficient cruciate-retaining and posterior-substituting knee arthroplasties. Cruciate-retaining and substituting total knee arthroplasties behaved similarly to the cruciate-deficient cruciate-retaining total knee arthroplasty between 0 degrees and 30 degrees flexion. Beyond 30 degrees, the posterior cruciate-retaining arthroplasty showed a significant increase in posterior translation of both femoral condyles. The posterior cruciate-substituting arthroplasty only showed a significant increase in posterior femoral translation after 90 degrees. At 120 degrees, both arthroplasties restored approximately 80% of that of the native knee. Posterior translation of the lateral femoral condyle was greater than that observed in the medial condyle for all knees, indicating the presence of internal tibial rotation during knee flexion. The data showed that the posterior cruciate ligament is an important structure in posterior cruciate-retaining total knee arthroplasty and proper balancing is imperative to the success of the implant. The cam-spine engagement is valuable in restoring posterior femoral translation in posterior cruciate-substituting total knee arthroplasty.

Lower Extremity Biomechanics Differ in Prepubescent and Postpubescent Female Athletes during Stride Jump Landings

Epidemiological evidence suggests the incidence of injury in female athletes is greater after the onset of puberty and that landing from a jump is a common mechanism of knee injury. This investigation compared lower extremity joint kinematics and joint resultant forces and moments during three types of stride jump (stride jump followed by a static landing; a ballistic vertical jump; and a ballistic lateral jump) between pre- and postpubescent recreational athletes to provide some insight into the increased incidence of injury. Sixteen recreationally active postpubescent women (ages 18–25 years) and 16 recreationally active prepubescent girls (ages 8–11 years) participated in this study. High speed 3D videography and force plate data were used to record each jumper’s performance of the stride jumps, and an inverse dynamic procedure was used to estimate lower extremity joint resultant forces and moments and power. These dependent variables were submitted to a 2 × 3 (Maturation Level × Landing Sequence) MANOVA with repeated measures on the last factor. The findings indicated that postpubescents landed with the knee more extended (4.4°) and had greater extension moments (approximately 30% greater hip and knee extension moments) and powers (40% greater knee power). Further, the post-pubescent athletes had greater knee anterior/posterior forces as well as medio-lateral resultant forces. The differences found between the two groups suggest there may be anatomical and physiological changes with puberty that lead to differences in strength or neuromuscular control which influence the dynamic restraint system in these recreational athletes. A combination of these factors likely plays a role in the increased risk of injury in postpubescent females.

Jump landing strategies in male and female college athletes and the implications of such strategies for anterior cruciate ligament injury

BACKGROUND

Female athletes are more likely than male athletes to injure the anterior cruciate ligament. Causes of this increased injury incidence in female athletes remain unclear, despite numerous investigations.

HYPOTHESIS

Female athletes will exhibit lower hamstring muscle activation and smaller knee flexion angles than male athletes during jump landings, especially when the knee muscles are fatigued.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight female and six male varsity college basketball athletes with no history of knee ligament injury performed jump landings on the dominant leg from a maximum height jump and from 25.4 cm and 50.8 cm high platforms under nonfatigued and fatigued conditions. Knee joint angle and surface electromyographic signals from the quadriceps, hamstring, and gastrocnemius muscles were recorded.

RESULTS

Women landed with greater knee flexion angles and greater knee flexion accelerations than men. Knee muscle activation patterns were generally similar in men and women.

CONCLUSION

As compared with male college basketball players, female college basketball players did not exhibit altered knee muscle coordination characteristics that would predispose them to anterior cruciate ligament injury when landing from jumps. This conclusion is made within the parameters of this study and based on the observation that hamstring muscle activation was similar for both groups. The greater knee flexion we observed in the female subjects would be expected to decrease their risk of injury.

CLINICAL RELEVANCE

Factors other than those evaluated in this study need to be considered when attempting to determine the reasons underlying the increased incidence of anterior cruciate ligament injuries consistently observed in elite female athletes.

The soleus muscle acts as an agonist for the anterior cruciate ligament. An in vitro experimental study

BACKGROUND

Although the quadriceps muscles are known antagonists for the anterior cruciate ligament and the hamstring muscles are known agonists, the influence of the calf muscles on knee stability is not well understood.

HYPOTHESIS

The soleus muscle acts as an anterior cruciate ligament agonist and the gastrocnemius muscle acts as an anterior cruciate ligament antagonist.

STUDY DESIGN

Controlled laboratory study.

METHODS

Six cadaveric knees were tested with individual and combined activation of the gastrocnemius and soleus muscles to determine the influence of simulated muscle contraction on tibiofemoral motion.

RESULTS

At all flexion angles, applying the soleus muscle force tended to translate the tibia posteriorly, whereas applying the gastrocnemius muscle force tended to translate the tibia anteriorly. Applying the soleus and gastrocnemius muscle forces together also tended to translate the tibia anteriorly. The average anterior and posterior tibial translations were greatest at 50 degrees of flexion.

CONCLUSIONS

The soleus muscle is capable of acting as an agonist for the anterior cruciate ligament and the gastrocnemius muscle can act as an antagonist.

CLINICAL RELEVANCE

A better understanding of the agonistic behavior of the soleus muscle on the anterior cruciate ligament may lead to the development of training and rehabilitation strategies that could reduce the incidence of injury and improve function in both patients with anterior cruciate ligament deficiency and patients who have undergone anterior cruciate ligament reconstruction.

A clinically applicable EMG-force model to quantify active stabilization of the knee after a lesion of the anterior cruciate ligament

OBJECTIVES

To investigate whether a simple electromyography-force (EMG-force) model can be used to measure different levels of co-contraction about the knee for healthy subjects and patients with an anterior cruciate ligament deficiency.

DESIGN

To evaluate an EMG-to-force processing model, two groups of subjects, with and without deficiency of the anterior cruciate ligament, participated in experiments in which surface EMG, kinematics and kinetics about the knee were recorded during isokinetic and functional movements.

BACKGROUND

Clinical and biomechanical evidence supports the hypothesis that higher level of co-contraction of quadriceps and hamstrings provide an active stabilization of the knee to compensate for the lost anterior cruciate ligament. To quantify the level of co-contraction, the contribution of both agonist and antagonist muscles to the net joint moment must be known.

METHODS

Surface EMG levels were calibrated to moment by means of a limited number of isokinetic contractions about the knee. With these calibration values, an estimate of the muscle moments during a vertical jump were obtained and compared with the net joint moment, calculated with inverse dynamics. Also co-contraction indices were determined.

RESULTS

The EMG-force model provided a fair estimate of the net joint moment. The co-contraction index in anterior cruciate ligament deficient subjects was significantly higher (mean 0.54 (SD, 0.04)) compared to healthy subjects (mean 0.25 (SD, 0.07)).

CONCLUSIONS

Although the EMG-to-force processing model is not perfectly accurate, it is appropriate within a clinical context.

RELEVANCE

Previous research supports the hypothesis that subjects with an anterior cruciate ligament deficiency compensate the loss of passive stability by developing higher co-activation levels of the knee muscles, i.e. active stabilization. Quantifying co-contraction may serve as a valuable parameter to evaluate clinical interventions and rehabilitation processes. The EMG-force model presented in this study appears to be a useful instrument for this purpose.

The effect of graft stiffness on knee joint biomechanics after ACL reconstruction--a 3D computational simulation

OBJECTIVE

The objective was to determine the effect of varying graft stiffness and initial graft tension on knee kinematics and graft tension after anterior cruciate ligament reconstruction.

DESIGN

A 3D computational knee model was used.

BACKGROUND

Many factors influencing the biomechanical outcome of anterior cruciate ligament reconstruction have been investigated. However, there are no reports on the effect of variations in graft stiffness on knee behavior.

METHODS

A 3D computational knee model was used to simulate anterior cruciate ligament reconstruction using three different grafts with stiffnesses similar to the anterior cruciate ligament (graft 1), a 10mm bone-patellar tendon-bone graft (graft 2), and a 14 mm bone-patellar tendon-bone graft (graft 3). The initial graft tension was set to 0 or 40 N with the knee at 30 degrees of flexion. A 134 N anterior tibial drawer load and a 400 N quadriceps load were applied to the knee, and kinematics and graft tension were calculated.

RESULTS

When fixed with no initial tension, graft 1 was found to under-constrain the knee, while graft 2 slightly over-constrained the knee, and graft 3 over-constrained the knee when compared to the intact knee. When an initial graft tension of 40 N was used, all of the reconstructed knees were more constrained than when an initial tension of 0 N was used.

CONCLUSIONS

This study suggests that graft stiffness has a direct impact on knee biomechanics after anterior cruciate ligament reconstruction. An optimal anterior cruciate ligament reconstruction can be achieved if the anterior cruciate ligament is replaced by a graft with similar structural stiffness.

RELEVANCE

This study showed that if the graft material and fixation sites are selected such that the anterior cruciate ligament structural stiffness is retained, normal knee kinematics can be restored.

Effect of hamstrings muscle action on stability of the ACL-deficient knee in isokinetic extension exercise

OBJECTIVE

To quantify the effect of hamstrings muscle action on stability of the anterior cruciate ligament deficient knee during isokinetic exercise at various speeds.

DESIGN

Mathematical modeling and forward-dynamics computer simulation were used to study the interactions between knee-extension speed, hamstrings co-contraction activity, and anterior tibial translation in the intact and anterior cruciate deficient knee.

BACKGROUND

There is much experimental evidence available to believe that hamstrings co-contraction can reduce anterior tibial translation in the anterior cruciate deficient knee. Little is known, however, about the level of hamstrings activation needed to keep anterior tibial translation within normal limits during functional activity.

METHODS

Isokinetic knee-extension was simulated with a sagittal-plane model used previously to study load sharing between the muscles, ligaments, and bones during isometric knee-extension exercise, isokinetic exercise, and squatting exercise.

CONCLUSIONS

Some amount of hamstrings activation is needed to stabilize an anterior cruciate deficient knee irrespective of how fast the knee extends. The level of hamstrings co-contraction needed to stabilize an anterior cruciate deficient knee is inversely related to extension speed. Hamstrings co-contraction is more effective in reducing anterior tibial translation than low-resistance extension exercise.

RELEVANCE

Excessive anterior tibial translation during knee-extension exercise may lead to damage of the meniscus and other passive structures inside the knee. If anterior cruciate deficient patients can be trained to co-contract their hamstrings during isokinetic knee-extension, then this exercise is appropriate for maintaining strength of the thigh muscles without compromising the anterior stability of the knee.

Biomechanics of posterior-substituting total knee arthroplasty: an in vitro study

The cam-spine system in posterior-substituting total knee arthroplasty was designed to improve posterior stability and to increase posterior femoral translation (rollback). Little is known on its effectiveness in the restoration of femoral rollback under functional loads. In the current study, the effect of cam-spine engagement on knee motion under simulated muscle loads was investigated using knees from cadavers. The translations of the lateral and medial femoral condyles of the knee before and after total knee arthroplasty were compared from 0 degrees to 120 degrees flexion. Cam-spine contact forces were measured under the same muscle loads. The posterior translations of both femoral condyles in the total knee arthroplasty were significantly lower than that of the native knee beyond full extension. Cam-spine engagement occurred between 60 degrees and 90 degrees flexion followed by an increase in posterior translation of both femoral condyles. However, the resultant femoral translation of the total knee arthroplasty was still lower than that of the native knee from 90 degrees to 120 degrees flexion. Knee motion after cam-spine engagement was independent of muscle loads, indicating the importance of the cam-spine mechanism at high flexion angles. Decreased posterior translation of both femoral condyles after total knee arthroplasty may be a limiting factor at high flexion.

Biomechanical consequences of PCL deficiency in the knee under simulated muscle loads--an in vitro experimental study

The mechanism of chronic degeneration of the knee after posterior cruciate ligament (PCL) injury is still not clearly understood. While numerous biomechanical studies have been conducted to investigate the function of the PCL with regard to antero-posterior stability of the knee, little has been reported on its effect on the rotational stability of the knee. In this study, eight cadaveric human knee specimens were tested on a robotic testing system from full extension to 120 degrees of flexion with the PCL intact and with the PCL resected. The antero-posterior tibial translation and the internal-external tibial rotation were measured when the knee was subjected to various simulated muscle loads. Under a quadriceps load (400 N) and a combined quadriceps/hamstring load (400/200 N), the tibia moved anteriorly at low flexion angles (below 60 degrees). Resection of the PCL did not significantly alter anterior tibial translation. At high flexion angles (beyond 60 degrees), the tibia moved posteriorly and rotated externally under the muscle loads. PCL deficiency significantly increased the posterior tibial translation and external tibial rotation. The results of this study indicate that PCL deficiency not only changed tibial translation, but also tibial rotation. Therefore, only evaluating the tibial translation in the anteroposterior direction may not completely describe the effect of PCL deficiency on knee joint function. Furthermore, the increased external tibial rotations were further hypothesized to cause elevated patello-femoral joint contact pressures. These data may help explain the biomechanical factors causing long-term degenerative changes of the knee after PCL injury. By fully understanding the etiology of these changes, it may be possible to develop an optimal surgical treatment for PCL injury that is aimed at minimizing the long-term arthritic changes in the knee joint.

Gait mechanics in chronic ACL deficiency and subsequent repair

OBJECTIVE

To determine how normal gait patterns may change as a result of chronic anterior cruciate ligament deficiency and subsequent reconstructive surgery.

DESIGN

Gait testing of 10 chronic anterior cruciate ligament deficient subjects prior to and 3 months following reconstructive surgery, and 10 uninjured controls.

BACKGROUND

There is controversy whether persons with chronic anterior cruciate ligament deficiency develop a "quadriceps avoidance" pattern and how anterior cruciate ligament reconstructive surgery influences gait mechanics in these same individuals.

METHODS

Gait analysis was employed to determine kinematic, kinetic, and muscle Electromyographic data.

RESULTS

Prior to surgery, no anterior cruciate ligament deficient subject exhibited a quadriceps avoidance pattern. Following surgery, the subjects exhibited a significantly greater knee extensor moment during early stance as compared to the control group. Prior to and following surgery, anterior cruciate ligament deficient subjects demonstrated a significantly greater hip extensor moment possibly to reduce anterior tibial translation. CONCLUSIONS; These data suggest that (1) development of a quadriceps avoidance pattern is less common than previously reported, (2) anterior cruciate ligament deficient subjects accommodate through alterations of hip joint mechanics, (3) surgical repair significantly alters lower extremity gait patterns, and (4) re-establishment of pre-injury gait patterns takes longer than 3 months to occur.

RELEVANCE

The results suggest that chronic anterior cruciate ligament deficient subjects do not exhibit a quadriceps avoidance gait pattern. Surgical intervention significantly alters lower extremity gait mechanics in a population that has accommodated to anterior cruciate ligament deficiency.

A dynamic model of the knee and lower limb for simulating rising movements

A two-dimensional dynamical model of the human body was developed and used to simulate muscle and knee-ligament loading during a fast rising movement. The hip, ankle, and toes were each modeled as a simple hinge joint. Relative movements of the femur, tibia, and patella in the sagittal plane were described using a more detailed representation of the knee. The geometry of the model bones was adapted from cadaver data. Eleven elastic elements described the geometric and mechanical properties of the knee ligaments and joint capsule. The patella was assumed to be massless. Smooth hypersurfaces were constructed and used to calculate the position and orientation of the patella during a forward integration of the model. Each hypersurface was formed by applying the principle of static equilibrium to approximate patellofemoral mechanics during the simulation. The model was actuated by 22 musculotendinous units, each unit represented as a three-element muscle in series with tendon. A first-order process was assumed to model muscle excitation-contraction dynamics. Dynamic optimization theory was used to calculate the pattern of muscle excitations that produces a coordinated rising movement from an initial squatting position in minimum time. The calculations support the contention that squatting is a relatively safe exercise for rehabilitation following ACL reconstruction. ACL forces remain less than 20 N for the duration of the task.

Forward-dynamics simulation of anterior cruciate ligament forces developed during isokinetic dynamometry

A mathematical (computer) model was developed and used to study the mechanics of the human knee during extension exercises employing an isokinetic dynamometer. All parts of the body were fixed to ground, except for the right shank and foot, which were free to move in the parasagittal plane. A linkage attached the dynamometer to the shank; tibiofemoral articulation consisted of single-point contact, allowing both sliding and rolling to occur. Physiologically based representations of ligaments and muscles imparted forces to the shank. A forward dynamics simulation was performed to calculate the forces developed in the knee for isokinetic speeds ranging from 0 (isometric exercise) to 300 degrees /s. Simulations were conducted for a constant-speed phase during isokinetic knee extension exercise. It was assumed for the duration of each simulated exercise that the quadriceps were fully activated and the other muscles were fully deactivated. The force in the anterior cruciate ligament was found to be governed by the force-velocity properties of the quadriceps; the model predicts that 300 deg/sec isokinetic exercise can reduce the force transmitted to the ACL by almost a factor of two compared with that present during isometric knee extension.

A minimally invasive method for the determination of force in the interosseous ligament

OBJECTIVE

The objective was to develop and utilize a minimally invasive testing system to determine the force in the interosseous ligament under axial compressive loads across the range of motion of the human forearm.

DESIGN

Eleven fresh frozen human cadaveric forearms were used (51-72 years).

BACKGROUND

Current studies investigating interosseous ligament forces altered the structure of the forearm by implanting load cells into the radius and ulna. This may affect load transfer through the forearm. Little information was available on interosseous ligament function over the entire flexion range of the elbow.

METHODS

A robotic joint testing system was used to apply a 100 N compressive load to the forearm and measure the resulting displacement. Each forearm was tested with no disruption of the bones and soft tissues of the forearm. The principle of superposition was used to calculate the forces in the interosseous ligament and was indirectly validated using fluoroscopy.

RESULTS

The force in the interosseous ligament ranged from a minimum of 8 N in neutral forearm rotation at full extension to a maximum of 43 N in supination at 30 degrees of flexion. The largest force was found in supination at all flexion angles.

CONCLUSIONS

The interosseous ligament is an important structure in the stability of the forearm. The force in the interosseous ligament depends on the elbow flexion angle and forearm rotation.

RELEVANCE

This study suggests that radial head fractures are best treated with the forearm in supination, since the interosseous ligament takes the largest load in this position. Complex injuries which have a poor prognosis, may require interosseous ligament reconstruction to improve clinical outcomes.

Cruciate-retaining and cruciate-substituting total knee arthroplasty: an in vitro comparison of the kinematics under muscle loads

The kinematics of posterior cruciate ligament (PCL)-retaining (PCR) and PCL-substituting (PS) total knee arthroplasty (TKA) were compared directly in a robotic, in vitro study, and the forces in the PCL and cam-spine mechanism were measured from 0 degrees to 120 degrees of flexion. The forces in the PCL after PCR TKA and in cam-spine contact after PS TKA increased only at a flexion of > or =90 degrees. Posterior translation of the lateral femoral condyle was significantly greater than translation of the medial femoral condyle in the intact knees, consistent with femoral rollback and internal tibial rotation. The PCR and PS TKAs partially restored these kinematics when the knee flexed >60 degrees (ie, when the forces increased in the PCL and cam-spine mechanism), whereas the PCL-deficient TKA failed to do so. The results reflect the importance of the PCL and cam-spine mechanism after PCL retention and substitution in TKA and confirm the necessity for either one, if knee kinematics are to be restored even partially.

Dynamic knee stability: current theory and implications for clinicians and scientists

We will discuss the mechanisms by which dynamic knee stability may be achieved and relate this to issues that interest clinicians and scientists concerned with dynamic knee stability. Emphasis is placed on the neurophysiologic evidence and theory related to neuromuscular control. Specific topics discussed include the ensemble firing of peripheral mechanoreceptors, the potential for muscle stiffness modulation via force and length feedback, postural control synergies, motor programs, and the neural control of gait. Factors related to answering the difficult question of whether or not knee ligament injuries can be prevented during athletic activities are discussed. Prevention programs that train athletes to perform their sport skills in a safe fashion are put forth as the most promising prospect for injury prevention. Methods of assessing neuromuscular function are reviewed critically and the need for future research in this area is emphasized. We conclude with a brief review of the literature regarding neuromuscular training programs.

The effect of weightbearing and external loading on anterior cruciate ligament strain

A force balance between the ligaments, articular contact, muscles and body weight maintains knee joint stability. Thus, it is important to study anterior cruciate ligament (ACL) biomechanics, in vivo, under weightbearing conditions. Our objective was to compare the ACL strain response under weightbearing and non-weightbearing conditions and in combination with three externally applied loadings: (1) anterior-posterior shear forces, (2) internal-external torques, and (3) varus-valgus moments. A strain transducer was implanted on the ACL of 11 subjects. All joint loadings were performed with the knee at 20 degrees of flexion. A significant increase in ACL strain was observed as the knee made the transition from non-weightbearing to weightbearing. During anterior shear loading, the strain values produced during weightbearing were greater than those of the non-weightbearing knee (shear loads <40N). At higher shear loads, the strain values became equal. During axial torsion, an internal torque of 10Nm strained the ACL when the knee was non-weightbearing while an equivalent external torque did not. Weightbearing significantly increased ACL strain values in comparison to non-weightbearing with the application of external torques and low internal torques (<3Nm). The strains became equal for higher internal torques. For V-V loading, the ACL was not strained in the non-weightbearing knee. However, weightbearing increased the ACL strain values over the range of moments tested. These data have important clinical ramifications in the development of rehabilitation protocols following ACL reconstruction since weightbearing has been previously thought to provide a protective mechanism to the healing graft.

Knee joint loading in forward versus backward pedaling: implications for rehabilitation strategies

OBJECTIVE

To use forward dynamic simulations of forward and backward pedaling in order to determine whether backward pedaling offers theoretical advantages over forward pedaling to rehabilitate common knee disorders.DESIGN. A comparison of knee joint loads was performed during forward and backward pedaling.BACKGROUND. Pedaling has been shown to be an effective rehabilitation exercise for a variety of knee disorders. Recently, backward gait has been shown to produce greater knee extensor moments and reduced patellofemoral joint loads compared to forward gait. But to date, no study has examined the efficacy of backward pedaling as a safe alternative to forward pedaling in rehabilitation programs.METHODS. A musculoskeletal model and optimization framework was used to generate simulations of forward and backward pedaling. Tibiofemoral and patellofemoral joint reaction forces were quantified.RESULTS. Lower tibiofemoral compressive loads, but higher patellofemoral compressive loads, were observed in backward pedaling. Lower protective anterior-posterior shear force was observed in backward pedaling near peak extension.CONCLUSIONS. Backward pedaling offers reduced tibiofemoral compressive loads for those patients with knee disorders such as menisci damage and osteoarthritis, but higher patellofemoral compressive loads. Therefore, backward pedaling is not recommended for patients experiencing patellofemoral pain. Further, backward pedaling should not be recommended after anterior cruciate ligament injury or reconstruction.RelevanceThe results of this study indicate that the design of rehabilitation programs including pedaling exercises should be injury specific with particular attention paid to the mechanics of the task.

Anterior cruciate ligament injuries in the female athlete. Potential risk factors

In the general population, an estimated one in 3000 individuals sustains an anterior cruciate ligament injury per year in the United States, corresponding to an overall injury rate of approximately 100,000 injuries annually. This national estimate is low for women because anterior cruciate ligament injury rates are reported to be two to eight times higher in women than in men participating in the same sports, presenting a sizable health problem. With the growing participation of women in athletics and the debilitating nature of anterior cruciate ligament injuries, a better understanding of mechanisms of injury in women sustaining anterior cruciate ligament injuries is essential. Published studies strongly support noncontact mechanisms for anterior cruciate ligament tears in women, which make these injuries even more perplexing. Speculation on the possible etiology of anterior cruciate ligament injuries in women has centered on anatomic differences, joint laxity, hormones, and training techniques. Investigators have not agreed on causal factors for this injury, but they have started to profile the type of athlete who is at risk. In the current study the most recent scientific studies of intrinsic and extrinsic risk factors thought to be contributing to the high rate of female anterior cruciate ligament injuries will be reviewed, important differences will be highlighted, and recommendations proposed to alleviate or minimize these risk factors among female athletes will be reported where appropriate.

A deficient anterior cruciate ligament does not lead to quadriceps avoidance gait

Without an intact anterior cruciate ligament (ACL) to resist anterior tibial translation, it is commonly believed that ACL-deficient patients employ alterations in walking. Although there is no consensus in the literature about the specific kinematic and kinetic adaptations in these patients with ACL tears, the gait adaptation of quadriceps avoidance is perhaps the one most popularized. The purpose of our study was to determine whether quadriceps avoidance is common in patients with ACL-deficiency. We used a video-based motion analysis system and surface electromyography (EMG) to study 18 patients with ACL-deficiency. All patients demonstrated an internal knee extension moment during early mid-stance (similar to normal subjects). Quadriceps EMG activity was noted throughout most of stance. No patients demonstrated an internal knee flexion moment, a decreased internal knee extension moment or a decreased duration of quadriceps EMG activity during stance. The findings of this study would suggest that quadriceps avoidance as a gait adaptation in ACL-deficient patients may be less common than previously reported.

In situ forces in the human posterior cruciate ligament in response to muscle loads: a cadaveric study

The objectives of this study were to determine the effects of hamstrings and quadriceps muscle loads on knee kinematics and in situ forces in the posterior cruciate ligament of the knee and to evaluate how the effects of these muscle loads change with knee flexion. Nine human cadaveric knees were studied with a robotic manipulator/universal force-moment sensor testing system. The knees were subjected to an isolated hamstrings load (40 N to both the biceps and the semimembranosus), a combined hamstrings and quadriceps load (the hamstrings load and a 200-N quadriceps load), and an isolated quadriceps load of 200 N. Each load was applied with the knee at full extension and at 30, 60, 90, and 120 degrees of flexion. Without muscle loads, in situ forces in the posterior cruciate ligament were small, ranging from 6+/-5 N at 30 degrees of flexion to 15+/-3 N at 90 degrees. Under an isolated hamstrings load, the in situ force in the posterior cruciate ligament increased significantly throughout all angles of knee flexion, from 13+/-6 N at full extension to 86+/-19 N at 90 degrees. A posterior tibial translation ranging from 1.3+/-0.6 to 2.5+/-0.5 mm was also observed from full extension to 30 degrees of flexion under the hamstrings load. With a combined hamstrings and quadriceps load, tibial translation was 2.2+/-0.7 mm posteriorly at 120 degrees of flexion ut was as high as 4.6+/-1.7 mm anteriorly at 30 degrees. The in situ force in the posterior cruciate ligament decreased significantly under this loading condition compared with under an isolated hamstrings load, ranging from 6+/-7 to 58+/-13 N from 30 to 120 degrees of flexion. With an isolated quadriceps load of 200 N, the in situ forces in the posterior cruciate ligament ranged from 4+/-3 N at 60 degrees of flexion to 34+/-12 N at 120 degrees. Our findings support the notion that, compared with an isolated hamstrings load, combined hamstrings and quadriceps loads significantly reduce the in situ force in the posterior cruciate ligament. These data are in direct contrast to those for the anterior cruciate ligament. Furthermore, we have demonstrated that the effects of muscle loads depend significantly on the angle of knee flexion.