An in vitro study of anterior cruciate ligament strain induced by quadriceps and hamstrings forces

Strain in the anteromedial fibers of the anterior cruciate ligament [ACL(am)] was studied in six cadaver knees. ACL(am) strain was measured in five knees during the application of isometric quadriceps forces alone and simultaneously applied isometric quadriceps and hamstrings forces at 10 degrees increments from 0 degrees to 90 degrees of knee flexion. ACL(am) strain during muscle loading was measured with respect to the ACL(am) strain measured with the knee in its resting position (neutral or near neutral position). A sixth knee was used to investigate the reproducibility of the resting position and quadriceps-induced ACL(am) strains. The strains induced in the ACL(am) by the quadriceps were significantly greater than 0 at knee flexion angles from 0 to 40 degrees and not significantly different from 0 for 50 to 90 degrees. The ACL(am) strains induced by simultaneously applied hamstrings and quadriceps forces were not significantly different from 0 at any of the knee flexion angles tested. Simultaneously applied hamstrings and quadriceps forces significantly reduced ACL(am) strain at 10, 20, and 90 degrees of knee flexion compared to the ACL(am) strain induced by quadriceps forces alone. The hamstrings are potentially capable of both significantly reducing and negating quadriceps-induced ACL(am) strain at 10 and 20 degrees of knee flexion.     

The anterior cruciate ligament enigma. Injury mechanisms and prevention

The reasons for the higher frequency of anterior cruciate ligament injuries in women are largely conjecture. These injuries may result from direct contact or, more frequently, from no direct contact to the knee during activities that most athletes consider routine to their sport. This implies that there are intrinsic factors that lead to anterior cruciate ligament rupture. For the anterior cruciate ligament to tear, there must be excess anterior tibial translation or rotation of the femur on the tibia. In the former case, the tibia can move anteriorly during quadriceps activation that is not counterbalanced by hamstring activation. Patients describe their injury as occurring when landing, stopping, or when planting to change directions. The knee typically was near full extension. Mechanically, the angle of the patellar tendon and tibial shaft increases as the knee approaches full extension. This gives a mechanical advantage to the quadriceps. During cutting maneuvers, athletes tend to cut with a knee near extension (0 degree-20 degrees) when the quadriceps are active and the hamstrings are neither very active nor at a knee flexion angle that offers much of a mechanical advantage. In performing cutting and landing maneuvers, women tend to perform the activities more erect; that is, with their knee and hips closer to extension. One possible factor to help reduce the frequency of anterior cruciate ligament injuries in women may be in proper instruction for performing cutting and landing maneuvers which will lower their center of gravity thereby denying the quadriceps the opportunity to shift the tibia anteriorly.     

Gender differences in surface rolling and gliding kinematics of the knee

The purpose of the current study was to determine whether knee surface rolling and gliding kinematics differed between genders during open and closed kinetic chain movement conditions. Eleven unimpaired adults (six men and five women) participated in this study. Sagittal plane path of instant center of rotation measurements were obtained with videographic motion analysis and applied to a mathematical knee model from which joint surface rolling and gliding kinematics were obtained. In addition, normalized electromyographic data were collected from subjects' quadriceps and hamstring muscles. During closed kinetic chain knee extension, as the knee approached terminal extension, female participants showed significantly greater relative joint surface gliding than male participants. Female participants also extended the knee in the closed kinetic chain with less relative hamstring activity than males. The relationship between joint surface gliding and relative hamstring activity in females during closed kinetic chain knee extension may explain, in part, the greater incidence of noncontact anterior cruciate ligament injury that occurs in females.     

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.     

Coactivation of the hamstrings and quadriceps during extension of the knee

The electromyographic activities of six muscles of the thigh were recorded, using bipolar surface electrodes, during active extension of the knee by six healthy men. The signal amplitudes were normalized to those recorded during isometric maximum voluntary contractions. Extension of the knee from 90 to 0 degrees (full extension) was performed at the rate of 10 degrees per second with the leg unimpeded and with weights of 1.8, 3.6, 5.4, or 7.2 kilograms attached to the ankle. The hamstrings were found to coactivate with the quadriceps during the terminal phase of extension. Coactivation of all three hamstrings was found to occur at joint angles of as much as 9 degrees, with the maximum at full extension of the knee and the strength of the signals ranging to as much as 20 per cent. The signals of all of the flexors and extensors increased with increasing loads on the ankle and, with the exception of the rectus femoris at 9 degrees of flexion, they also increased as the knee extended. The results of this study support the hypothesis that the hamstrings function synergistically with the anterior cruciate ligament to prevent the anterior tibial displacement that is produced by active contraction of the quadriceps in the terminal degrees of extension of the knee. This information is important for the physical conditioning of healthy individuals in preparation for athletic endeavors. Furthermore, if coactivation of the hamstrings with the quadriceps is mediated by sensors other than, or in addition to, those of the anterior cruciate ligament, then strengthening of the hamstrings appears to be an important adjunct to rehabilitation programs after repair or reconstruction of that ligament.     

Muscle exercise after anterior cruciate ligament reconstruction of the knee--Part II: The development of the exercise method by simultaneous isometric contraction of the quadriceps and the hamstrings, and its biomechanics

An attempt was made to investigate the stress of the ACL in the simultaneous isometric contraction (IMC) of the quadriceps and the hamstrings by means of analysis of two-dimensional models, and to estimate electromyographically the forces of those muscles in that contraction. The anterior drawer force (ADF) in the simultaneous IMC decreased as the flexion angle of the knee increased. The average value of the angles, where the ADF became zero, was 7.4 degrees. The integrated EMGs of the quadriceps and the hamstrings in the simultaneous maximum IMC were equal to 30-60% of those in separate maximum IMC. Clinical relevance: In the early stage of the rehabilitation after the ACL reconstruction, the simultaneous IMC of the quadriceps and the hamstrings is useful as one of the muscle exercise method, because that can be performed at the knee position near the full extension and can generate sufficient muscle force for exercise.     

Muscle exercise after the anterior cruciate ligament reconstruction of the knee--Part I: The force given to the anterior cruciate ligament by separate isometric contraction of the quadriceps or the hamstrings

An attempt was made to investigate the force of the anterior cruciate ligament (ACL) in separate isometric contraction (IMC) of the quadriceps and the hamstrings by means of the analysis of two-dimensional models. In IMC of the quadriceps, the average value of the anterior drawer force (ADF) was equal to 14% of the quadriceps tension at the knee flexion of 5 degrees. The ADF decreased as the flexion angle increased. The average value of the angles, where the ADF became zero, was 45.3 degrees, and the standard deviation was 12.5 degrees. In IMC of the hamstrings, the posterior drawer force was given at the every flexion angle. Clinical relevance: In the early stage of the rehabilitation after the ACL reconstruction, the quadriceps exercise by IMC should be performed at the knee flexion of more than 70 degrees (average + 1.96 X S.D.). The hamstrings exercise by IMC can be carried out regardless of flexion angle.     

The gastrocnemius muscle is an antagonist of the anterior cruciate ligament.

Since the proximal tendon of the gastrocnemius muscle wraps around the posterior aspect of the tibia, its contraction could potentially strain the anterior cruciate ligament (ACL) by pushing the tibia anteriorly. However, the relationship between contraction of the gastrocnemius muscle and ACL strain has not been studied in vivo. The objectives of this study were to evaluate the ACL strain response due to isolated contractions of the gastrocnemius muscle and to determine how these strains are affected by cocontraction with the hamstrings and quadriceps muscles. Six subjects with normal ACLs participated in the study; they underwent spinal anesthesia to ensure that their leg musculature was relaxed. Transcutaneous electrical muscle stimulation (TEMS) was used to induce contractions of the gastrocnemius, quadriceps and hamstrings muscles while the strains in the anteromedial bundle of the ACL were measured using a differential variable reluctance transducer. The ACL strain values produced by contraction of the gastrocnemius muscle were dependent on the magnitude of the ankle torque and knee flexion angle. Strains of 2.8% and 3.5% were produced at 5 degrees and 15 degrees of knee flexion, respectively. The ACL was not strained at 30 degrees and 45 degrees. Changes in ankle angle did not significantly affect these strain values. Co-contraction of the gastrocnemius and quadriceps muscles produced ACL strain values that were greater than those produced by isolated activation of either muscle group when the knee was at 15 degrees and 30 degrees. Co-contraction of the gastrocnemius and hamstrings muscles produced strains that were higher than those produced by the isolated contraction of the hamstrings muscles. At 15 degrees and 30 degrees of knee flexion. the co-contraction strain values were less than those produced by stimulation of the gastrocnemius muscle alone. This study verified that the gastrocnemius muscle is an antagonist of the ACL. Since the gastrocnemius is a flexor of the knee, this finding may have important clinical ramifications in ACL rehabilitation since flexor torques are generally thought to be protective of a healing ACL graft.     

Muscle exercise after anterior cruciate ligament reconstruction. Biomechanics of the simultaneous isometric contraction method of the quadriceps and the hamstrings

Biomechanical analysis of two-dimensional models composed from roentgenographic pictures and electromyographic analysis on simultaneous isometric contraction exercises of the quadriceps and hamstrings were conducted in 20 healthy adult males. During simultaneous isometric contraction at 5 degrees knee flexion, an anterior drawer force equivalent to 15% of the tension of the quadriceps was exerted to the tibia, and decreased with increased angle of flexion. The mean angle at which this force became zero was 7.4 degrees, with a standard deviation of 5.0 degrees. When the angle increased further, a posterior drawer force to the tibia occurred and gradually increased. Each tension of the quadriceps or hamstrings during maximum simultaneous isometric contraction of the quadriceps and hamstrings was estimated as 30%-60% of that during separate isometric contractions of each muscle. In the early stage of the rehabilitation after the anterior cruciate ligament reconstruction, the simultaneous isometric contraction of the quadriceps and the hamstrings is useful as one of the muscle exercise methods because it can be performed safely with the knee position near the full extension and can generate sufficient muscle force to be an effective exercise.     

Mechanisms of anterior cruciate ligament injury

This study examined the mechanisms of anterior cruciate ligament (ACL) injury. In the first part of the study, using a comprehensive, standardized questionnaire, 89 athletes (100 knees) were interviewed about the events surrounding their ACL injury. A noncontact mechanism was reported in 71 (72%) knees and a contact injury in 28 (28%) knees; one patient was unsure if there was any contact. Most of the injuries were sustained at footstrike with the knee close to full extension. Noncontact mechanisms were classified as sudden deceleration prior to a change of direction or landing motion, while contact injuries occurred as a result of valgus collapse of the knee. Hamstring flexibility parameters revealed a statistically higher level of laxity in the injured athletes compared with a matched group of 28 controls. In the second part of the study, videotapes of 27 separate ACL disruptions were reviewed and confirmed that most noncontact injuries occur with the knee close to extension during a sharp deceleration or landing maneuver. Because the knee is in a position to allow the extensor mechanism to strain the ACL and maximum, eccentric muscle force conditions usually apply, the quadriceps may play an important role in ACL disruption. Passive protection of the ACL by the hamstring muscles may be reduced in patients with above-average flexibility.     

Quadriceps and hamstrings peak torque ratio changes in persons with chronic anterior cruciate ligament deficiency

STUDY DESIGN: Cross-sectional analytical study in which subjects served as their own controls. OBJECTIVE: To assess the concentric and eccentric peak torque in the hamstrings and quadriceps muscles, hamstrings/quadriceps amplitude ratios, and lean thigh volume differences in the involved and uninvolved limb of subjects with anterior cruciate ligament (ACL) deficiency. BACKGOUND: Although the hamstrings/quadriceps ratios for concentric and eccentric activity have been studied, the more functional eccentric hamstings/concentric quadriceps ratio has not been previously described in chronic ACL deficient individuals. METHODS AND MEASURES: Eighteen subjects (36 +/- 11 years; 12 men, 6 women) with unilateral chronic ACL deficiency were recruited. Changes in activities of daily living, lean thigh volume (LTV) and isokinetic peak torque and total work capacity of both the quadriceps and hamstring muscles were investigated. The uninvolved limb served as control. RESULTS: Eccentric quadriceps peak torque in the ACL deficient limb was reduced by 38% compared with the 16% reduction of concentric quadriceps peak torque. Eccentric hamstrings peak torque was reduced by 15% compared with an 8% reduction in concentric hamstrings peak torque. LTV in the ACL deficient limb was 11% smaller than the uninvolved limb (3,541 +/- 899 vs 3,161 +/- 742 cc, uninvolved versus ACL deficient limb). The relation between LTV and eccentric peak torque was stronger in the uninvolved (r = 0.82) compared with the ACL deficient limb (r = 0.66). The eccentric hamstrings/quadriceps ratio was significantly higher in the ACL deficient (0.80 +/- 0.26) compared with the uninvolved limb (0.55 +/- 0.13). However, the eccentric hamstrings/concentric quadriceps ratio was similar between ACL deficient (0.75 +/- 0.17) and uninvolved (0.77 +/- 0.20) limbs, while the concentric hamstrings/eccentric quadriceps ratio was significantly higher in the ACL deficient (0.79 +/- 0.26) compared with the uninvolved (0.50 +/- 0.14) limb. CONCLUSIONS: Quadriceps and hamstrings peak torque values were significantly decreased in ACL deficient compared with the uninvolved limb. Eccentric muscle activity was affected to a greater degree than concentric muscle activity in the quadriceps muscle after ACL injury. The eccentric hamstrings/concentric quadriceps ratios were similar in ACL deficient and normal limbs, indicating that muscular co-ordination strategies may have been altered to maintain normal limb activity despite the strength losses particularly evident in quadriceps muscle function.     

Anterior tibial translation during different isokinetic quadriceps torque in anterior cruciate ligament deficient and nonimpaired individuals

STUDY DESIGN: Factorial quasi-experimental design. OBJECTIVES: To quantify the effect of different levels of isokinetic concentric and eccentric knee extensor torques on the anterior tibial translation in subjects with anterior cruciate ligament (ACL) deficiency. Electromyogram (EMG) activity of 4 leg muscles was recorded in order to detect any co-activation of extensors and flexors. BACKGROUND: The rehabilitation after an ACL injury is of importance for the functional outcome of the patient. In order to construct a rehabilitation program after that injury, it is important to understand the in vivo relationships between muscle force and tibial translation. METHODS AND MEASURES: Twelve patients with unilateral ACL injury and 11 uninjured volunteers performed 36 repetitions of a quadriceps contraction at different isokinetic concentric and eccentric torque levels, on a KinCom machine (60 degrees x s(-1)), with simultaneous recordings of tibial translation (CA-4000) and EMG activity from quadriceps and hamstrings muscles. Tibial translations and EMG levels were normalized to the maximum of each subject. RESULTS: The individual anterior tibial translation increased with increased quadriceps torque in a similar manner in both quadriceps contraction modes in all legs tested. During concentric mode, translation was similar in all groups, but during eccentric mode, the mean translation was 38% larger in the ACL injured knees. No quadriceps-hamstrings co-activation occurred in any test or group. CONCLUSIONS: An ACL deficient knee can limit the translation within a normal space during concentric muscle activity but not during eccentric activity. That limitation depends on other mechanisms than hamstrings co-activation.     

Factors explaining chronic knee extensor strength deficits after ACL reconstruction

Persistent quadriceps muscle weakness is common after anterior cruciate ligament (ACL) reconstruction. The mechanisms underlying these chronic strength deficits are not clear. This study examined quadriceps strength in people 2–15 years post‐ACL reconstruction and tested the hypothesis that chronic quadriceps weakness is related to levels of voluntary quadriceps muscle activation, antagonistic hamstrings moment, and peripheral changes in muscle. Knee extensor strength and activation were evaluated in 15 ACL reconstructed and 15 matched uninjured control subjects using an interpolated triplet technique. Electrically evoked contractile properties were used to evaluate peripheral adaptations in the quadriceps muscle. Antagonistic hamstrings moments were predicted using a practical mathematical model. Knee extensor strength and evoked torque at rest were significantly lower in the reconstructed legs (p < 0.05). Voluntary activation and antagonistic hamstrings activity were similar across legs and between groups (p > 0.05). Regression analyses indicated that side‐to‐side differences in evoked torque at rest explained 71% of the knee extensor strength differences by side (p < 0.001). Voluntary activation and antagonistic hamstrings moment did not contribute significantly (p > 0.05). Chronic quadriceps weakness in this sample was primarily related to peripheral changes in the quadriceps muscle, not to levels of voluntary activation or antagonistic hamstrings activity. © 2011 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:633–640, 2011     

Hamstrings cocontraction reduces internal rotation, anterior translation, and anterior cruciate ligament load in weight-bearing flexion.

Strengthening of the hamstrings is often recommended following injury and reconstruction of the anterior cruciate ligament. It has been suggested that hamstrings activity stabilizes the knee and reduces anterior cruciate ligament load during weight-bearing flexion; however, the effects of hamstrings cocontraction on the kinematics and mechanics of the normal knee have not been assessed at physiological load levels. The aim of this study was to determine whether the addition of hamstrings force affects knee rotations, translations, and joint and quadriceps force during flexion with loads at physiological levels applied to the muscles and joints. Eight cadaveric knee specimens were tested with a servohydraulic mechanism capable of applying controlled dynamic loads to simulate quadriceps and hamstrings muscle forces throughout a physiological range of motion. A constant vertical load of physiologic magnitude was applied to the hip, and quadriceps force was varied to maintain equilibrium throughout flexion. Two conditions were tested: no hamstrings force and a constant hamstrings force equivalent to the vertical load. Hamstrings force significantly reduced internal rotation (p<0.0001) and anterior translation (p<0.0001), increased quadriceps force (p<0.0001) and normal resultant force on the tibia (p<0.0001), and reversed the direction of the shear force on the tibia (p<0.0001). These results suggest that hamstrings strengthening following anterior cruciate ligament injury may benefit anterior cruciate ligament-deficient and reconstructed knees by reducing the load in the ligament; however, they also imply that this comes at the expense of efficiency and higher patellofemoral and joint forces.     

Variations in medial‐lateral hamstring force and force ratio influence tibiofemoral kinematics

A change in hamstring strength and activation is typically seen after injuries or invasive surgeries such as anterior cruciate reconstruction or total knee replacement. While many studies have investigated the influence of isometric increases in hamstring load on knee joint kinematics, few have quantified the change in kinematics due to a variation in medial to lateral hamstring force ratio. This study examined the changes in knee joint kinematics on eight cadaveric knees during an open‐chain deep knee bend for six different loading configurations: five loaded hamstring configurations that varied the ratio of a total load of 175 N between the semimembranosus and biceps femoris and one with no loads on the hamstring. The anterior–posterior translation of the medial and lateral femoral condyles’ lowest points along proximal‐distal axis of the tibia, the axial rotation of the tibia, and the quadriceps load were measured at each flexion angle. Unloading the hamstring shifted the medial and lateral lowest points posteriorly and increased tibial internal rotation. The influence of unloading hamstrings on quadriceps load was small in early flexion and increased with knee flexion. The loading configuration with the highest lateral hamstrings force resulted in the most posterior translation of the medial lowest point, most anterior translation of the lateral lowest point, and the highest tibial external rotation of the five loading configurations. As the medial hamstring force ratio increased, the medial lowest point shifted anteriorly, the lateral lowest point shifted posteriorly, and the tibia rotated more internally. The results of this study, demonstrate that variation in medial‐lateral hamstrings force and force ratio influence tibiofemoral transverse kinematics and quadriceps loads required to extend the knee. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1707–1715, 2016.     

The influence of gender-specific loading patterns of the stop-jump task on anterior cruciate ligament strain

BACKGROUND: Studies have shown that women are at higher risk of sustaining noncontact anterior cruciate ligament (ACL) injuries in specific sports. Recent gait studies of athletic tasks have documented that gender differences in knee movement, muscle activation, and external loading patterns exist. The objective of this study was to determine in a knee cadaver model if application of female-specific loading and movement patterns characterised in vivo for a stop-jump task cause higher ACL strains than male patterns. METHODS: Gender-specific loading patterns of the landing phase of the vertical stop-jump task were applied to seven cadaver knees using published kinetic/kinematic results for recreational athletes. Loads applied consecutively included: tibial compression, quadriceps, hamstrings, external posterior tibial shear, and tibial torque. Knee flexion was fixed based on the kinematic data. Strain of the ACL was monitored by means of a differential variable reluctance transducer installed on the anterior-medial bundle of the ACL. FINDINGS: The ACL strain was significantly increased (P<0.05) for the female loading pattern relative to the male loading pattern after the posterior tibial shear force was applied, and showed a similar trend (P=0.1) to be increased after the final tibial torque was applied. INTERPRETATION: This study suggests that female motor control strategies used during the stop-jump task may place higher strains on the ACL than male strategies, thus putting females at greater risk of ACL injury. We believe these results suggest the potential effectiveness of using training programs to modify motor control strategies and thus modify the risk of injury.     

Analysis of the shear force exerted on the tibia during standing on bilateral legs with knee flexion

Biomechanical analysis of the two-dimensional models composed of roentgenographic pictures and electromyographic analysis about the shear force (Fs) exerted on tibia during standing on bilateral legs was conducted in 21 young adult males. The simultaneous contraction of the quadriceps and hamstrings was observed in all electromyograms (EMGs). Amplitude observed on EMGs of the hamstrings increased as the trunk flexion angle increased. The calculated average values of Fs were negative at every knee flexion angle; Negative value means posteriorly directed force. As the trunk flexion angle increased, posterior drawer force increased at knee flexion angles of 30 degrees and 60 degrees. The simultaneous contraction of the quadriceps and the hamstrings was considered to represent the main factor that influenced these results. The standing on bilateral legs with knee and trunk flexion was considered to be applicable in the early stages after anterior cruciate ligament reconstruction.     

Knee biomechanics after UKA and its relation to the ACL--a robotic investigation.

Unicompartmental knee arthroplasty (UKA) has regained popularity in recent years. However, limited data exist on how UKA affects knee biomechanics. The role of the anterior cruciate ligament (ACL) after fixed bearing UKA remains controversial. In this study, a robotic testing system was used to apply a quadriceps/hamstrings load to cadaveric knee specimens in the intact state, after medial UKA, and after transection of the ACL in UKA. The load was applied to the knee from full extension to 120 degrees of flexion in 30 degrees increments. UKA generally did not affect anterior-posterior (AP) femoral position, but did cause external tibial rotation and variations in varus-valgus rotation compared to the intact knee. ACL transection after UKA shifted the femur posteriorly compared to the intact and UKA knees and increased internal tibial rotation compared to the UKA knee at low flexion. The AP motion of the articular contact position in the implant was increased after ACL transection. These data might help explain the mechanism of tibial component loosening and provide insight into further investigations of polyethylene wear in UKA. Based on the kinematic data, the ACL should be functional to provide patients the greatest opportunity for long-term success after medial UKA.     

Arthroscopic anterior cruciate ligament reconstruction with quadriceps tendon-patellar bone autograft

BACKGROUND: Surgical reconstruction of the anterior cruciate ligament (ACL) is indicated in the ACL-deficient knee with symptomatic instability and multiple ligaments injuries. Bone patellar tendon-bone and the hamstring tendon generally have been used. In the present study, we describe an alternative graft, the quadriceps tendon-patellar bone autograft, by using arthroscopic ACL reconstruction. METHODS: From March of 1996 through March of 1997, a quadriceps tendon-patellar bone autograft was used in 12 patients with ACL injuries. RESULTS: After 15 to 24 months of follow-up, the clinical outcome for those patients with this graft have been encouraging. Ten patients could return to the same or a higher level of preinjury sports activity. According to the International Knee Documentation Committee rating system, 10 of the 12 patients had normal or nearly normal ratings. Recovery of quadriceps muscle strength to 80% of the normal knee was achieved in 11 patients in 1 year. CONCLUSION: The advantages of the quadriceps tendon graft include the following: the graft is larger and stronger than the patellar tendon; morbidity of harvest technique and donor site is less than that of patellar tendon graft; there is little quadriceps inhibition after quadriceps harvest; there is quicker return to sports activities with aggressive rehabilitation. A quadriceps tendon-patellar autograft is a reasonable alternative to ACL reconstruction in patients who are not suitable for either a bone-patellar tendon-bone autograft or a hamstring tendon autograft.     

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.