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

Biomechanics laboratory-based prediction algorithm to identify female athletes with high knee loads that increase risk of ACL injury

OBJECTIVE

Knee abduction moment (KAM) during landing predicts non-contact anterior cruciate ligament (ACL) injury risk with high sensitivity and specificity in female athletes. The purpose of this study was to employ sensitive laboratory (lab-based) tools to determine predictive mechanisms that underlie increased KAM during landing.

METHODS

Female basketball and soccer players (N=744) from a single county public school district were recruited to participate in testing of anthropometrics, maturation, laxity/flexibility, strength and landing biomechanics. Linear regression was used to model KAM, and logistic regression was used to examine high (>25.25 Nm of KAM) versus low KAM as surrogate for ACL injury risk.

RESULTS

The most parsimonious model included independent predictors (β±1 SE) (1) peak knee abduction angle (1.78±0.05; p<0.001), (2) peak knee extensor moment (0.17±0.01; p<0.001), (3) knee flexion range of motion (0.15±0.03; p<0.01), (4) body mass index (BMI) Z-score (-1.67±0.36; p<0.001) and (5) tibia length (-0.50±0.14; p<0.001) and accounted for 78% of the variance in KAM during landing. The logistic regression model that employed these same variables predicted high KAM status with 85% sensitivity and 93% specificity and a C-statistic of 0.96.

CONCLUSIONS

Increased knee abduction angle, quadriceps recruitment, tibia length and BMI with decreased knee flexion account for 80% of the measured variance in KAM during a drop vertical jump.

CLINICAL RELEVANCE

Females who demonstrate increased KAM are more responsive and more likely to benefit from neuromuscular training. These findings should significantly enhance the identification of those at increased risk and facilitate neuromuscular training targeted to this important risk factor (high KAM) for ACL injury.

Influences of hamstring stiffness and strength on anterior knee joint stability

BACKGROUND

Excessive anterior tibial translation is a prospective risk factor for anterior cruciate ligament injury, thus factors which limit this motion may reduce injury risk. Stiffness quantifies a muscle's resistance to lengthening, and stiffer hamstrings may resist changes in length induced by anterior tibial translation more effectively.

METHODS

Anterior tibial translation, hamstring strength, and hamstring stiffness were assessed in 30 physically active volunteers. Simple correlations were used to evaluate relationships between stiffness, strength, and anterior tibial translation. Anterior tibial translation data were arranged into high and low groups based on the median value, and hamstring strength and stiffness were compared between these groups via t-tests.

FINDINGS

Anterior tibial translation was correlated with hamstring stiffness (r=-0.538; P=0.002), but not with hamstring strength (r=-0.088; P=0.644). Hamstring stiffness and strength were not correlated (r=0.054; P=0.778). Hamstring stiffness was greater in the low anterior tibial translation group (t(28)=2.186; P<0.037; ES=0.36), but hamstring strength did not differ between these groups (t(28)=1.057; P<0.300; ES=0.17).

INTERPRETATION

Greater hamstring stiffness, but not strength, results in a more stable knee joint evidenced by less anterior tibial translation. These findings suggest that the hamstrings' ability to resist lengthening rather than their overall force production capacity may be an important contributor to anterior cruciate ligament injury risk. As muscle stiffness can be modified acutely and chronically, enhancing hamstring stiffness may be an important addition to anterior cruciate ligament injury prevention programs.

Effect of ACL transection on internal tibial rotation in an in vitro simulated pivot landing

BACKGROUND

The amount of resistance provided by the ACL (anterior cruciate ligament) to axial tibial rotation remains controversial. The goal of this study was to test the primary hypotheses that ACL transection would not significantly affect tibial rotation under the large impulsive loads associated with a simulated pivot landing but would increase anterior tibial translation.

METHODS

Twelve cadaveric knees (mean age of donors [and standard deviation] at the time of death, 65.0 ± 10.5 years) were mounted in a custom testing apparatus to simulate a single-leg pivot landing. A compound impulsive load was applied to the distal part of the tibia with compression (∼800 N), flexion moment (∼40 N-m), and axial tibial torque (∼17 N-m) in the presence of five trans-knee muscle forces. A differential variable reluctance transducer mounted on the anteromedial aspect of the ACL measured relative strain. With the knee initially in 15° of flexion, and after five combined compression and flexion moment (baseline) loading trials, six trials were conducted with the addition of either internal or external tibial torque (internal or external loading), and then six baseline trials were performed. The ACL was then sectioned, six baseline trials were repeated, and then six trials of either the internal or the external loading condition, whichever had initially resulted in the larger relative ACL strain, were carried out. Tibiofemoral kinematics were measured optoelectronically. The results were analyzed with a nonparametric Wilcoxon signed-rank test.

RESULTS

Following ACL transection, the increase in the normalized internal tibial rotation was significant but small (0.7°/N-m ± 0.3°/N-m to 0.8°/N-m ± 0.3°/N-m, p = 0.012), while anterior tibial translation increased significantly (3.8 ± 2.9 to 7.0 ± 2.9 mm, p = 0.017).

CONCLUSIONS

ACL transection leads to a small increase in internal tibial rotation, equivalent to a 13% decrease in the dynamic rotational resistance, under the large forces associated with a simulated pivot landing, but it leads to a significant increase in anterior tibial translation.

Measurement of in vivo anterior cruciate ligament strain during dynamic jump landing

Despite recent attention in the literature, anterior cruciate ligament (ACL) injury mechanisms are controversial and incidence rates remain high. One explanation is limited data on in vivo ACL strain during high-risk, dynamic movements. The objective of this study was to quantify ACL strain during jump landing. Marker-based motion analysis techniques were integrated with fluoroscopic and magnetic resonance (MR) imaging techniques to measure dynamic ACL strain non-invasively. First, eight subjects' knees were imaged using MR. From these images, the cortical bone and ACL attachment sites of the tibia and femur were outlined to create 3D models. Subjects underwent motion analysis while jump landing using reflective markers placed directly on the skin around the knee. Next, biplanar fluoroscopic images were taken with the markers in place so that the relative positions of each marker to the underlying bone could be quantified. Numerical optimization allowed jumping kinematics to be superimposed on the knee model, thus reproducing the dynamic in vivo joint motion. ACL length, knee flexion, and ground reaction force were measured. During jump landing, average ACL strain peaked 55±14 ms (mean and 95% confidence interval) prior to ground impact, when knee flexion angles were lowest. The peak ACL strain, measured relative to its length during MR imaging, was 12±7%. The observed trends were consistent with previously described neuromuscular patterns. Unrestricted by field of view or low sampling rate, this novel approach provides a means to measure kinematic patterns that elevate ACL strains and that provide new insights into ACL injury mechanisms.

Knee joint laxity and its cyclic variation influence tibiofemoral motion during weight acceptance

PURPOSE

to better understand how sex differences in anterior knee laxity (AKL) affect knee joint biomechanics, we examined the consequence of greater absolute baseline (males and females) and cyclic increases in AKL during the menstrual cycle (females) on anterior tibial translation (ATT) as the knee transitioned from non-weight-bearing to weight-bearing conditions, while also controlling for genu recurvatum (GR).

METHODS

males and females (71 females and 48 males, aged 18-30 yr) were measured for AKL and GR and underwent measurement of ATT. Women were tested on the days of their cycle when AKL was at its minimum (T1) and maximum (T2); males were matched in time to a female with similar AKL. Linear regressions examined relationships between absolute baseline (AKLT1, GRT1) and cyclic changes (Δ = T2 - T1; AKLΔ, GRΔ) (females only) in knee laxity with ATT as measured at T1 and T2 and Δ (T2 - T1) (females only).

RESULTS

AKL and GR increased in females, but not in males, from T1 to T2. Greater AKLT1 and GRT1 predicted greater ATTT1 and ATTT2 in males (R = 21.0, P < 0.007). The combination of greater AKLT1, AKLΔ, and less GRΔ predicted greater ATTT1 and ATTT2 in females (R = 12.5-13.1, P < 0.05), with AKLΔ being a stronger predictor (coefficient, P value) of ATTT2 (0.864, P = 0.027) compared with ATTT1 (0.333, P = 0.370). AKLΔ was the sole predictor of ATTΔ (R = 0.104 and 0.740, P = 0.042).

CONCLUSIONS

greater absolute baseline and cyclic increases in AKL were consistently associated with greater ATT produced by transition of the knee from non-weight-bearing to weight-bearing. Because the anterior cruciate ligament is the primary restraint to ATT, these findings provide insight into the possible mechanisms by which greater AKL may be associated with at-risk knee biomechanics during the weight acceptance phase of dynamic tasks.

Three-dimensional motion analysis validation of a clinic-based nomogram designed to identify high ACL injury risk in female athletes

AIMS

Prospective measures of high knee abduction moment (KAM) during landing identify female athletes at increased risk for anterior cruciate ligament (ACL) injury. Laboratory-driven measurements predict high KAM with 90% accuracy. This study aimed to validate the clinic-based variables against 3-dimensional motion analysis measurements.

METHODS

Twenty female basketball, soccer, and volleyball players (age, 15.9 ± 1.3 years; height, 163.6 ± 9.9 cm; body mass, 57.0 ± 12.1 kg) were tested using 3-dimensional motion analysis and clinic-based techniques simultaneously. Multiple logistic regression models have been developed to predict high KAM (a surrogate for ACL injury risk) using both measurement techniques. Clinic-based measurements were validated against 3-dimensional motion analysis measures, which were recorded simultaneously, using within- and between-method reliability as well as sensitivity and specificity comparisons.

RESULTS

The within-variable analysis showed excellent inter-rater reliability for all variables using both 3-dimensional motion analysis and clinic-based methods, with intraclass correlation coefficients (ICCs) that ranged from moderate to high (0.60-0.97). In addition, moderate-to-high agreement was observed between 3-dimensional motion analysis and clinic-based measures, with ICCs ranging from 0.66 to 0.99. Bland-Altman plots confirmed that each variable provided no systematic shift between 3-dimensional motion analysis and clinic-based methods, and there was no association between difference and average. A developed regression equation also supported model validity with > 75% prediction accuracy of high KAM using both the 3-dimensional motion analysis and clinic-based techniques.

CONCLUSION

The current validation provides the critical next step to merge the gap between laboratory identification of injury risk factors and clinical practice. Implementation of the developed prediction tool to identify female athletes with high KAM may facilitate the entry of female athletes with high ACL injury risk into appropriate injury-prevention programs.

Differences in time-frequency representation of lower limbs myoelectric activity during single and double leg landing in male athletes

This study compared the instantaneous median frequency (IMF) obtained by means of a Choi-Williams transform of an electromyogram of the lower-limb muscles during single-leg (SL) and double-leg (DL) landings performed by fifteen male athletes. The IMF values of the rectus femoris (RF), biceps femoris (BF) and hip adductors (HA) were compared between two landing tasks, within each landing, and before and after ground contact (GC). The IMF values of the RF did not change between landings in contrast to those of the BF, which presented from 20- to 40-ms higher SL values before GC and from 40 to 60 ms after GC. HA presented higher SL values during the 40-60 ms range before GC. Within each landing, the RF IMF decreased from 40 ms to 60 ms after GC in the SL. Similar results were found for the HA IMF, which decreased from 40ms to 80 ms after GC. The BF IMF showed no significant change. These results suggest muscle recruitment related to anterior cruciate ligament protection since the IMF values of the RF decreased in the SL, whereas the BF IMF increased. Results for the HA showed the importance of hip muscles in stabilizing the core region, allowing the activation of distal muscles with greater safety.

A 'plane' explanation of anterior cruciate ligament injury mechanisms: a systematic review

Although intrinsic and extrinsic risk factors for anterior cruciate ligament (ACL) injury have been explored extensively, the factors surrounding the inciting event and the biomechanical mechanisms underlying ACL injury remain elusive. This systematic review summarizes all the relevant data and clarifies the strengths and weaknesses of the literature regarding ACL injury mechanisms. The hypothesis is that most ACL injuries do not occur via solely sagittal, frontal or transverse plane mechanisms. Electronic database literature searches of PubMed MEDLINE (1966-2008), CINAHL (1982-2008) and SportDiscus (1985-2008) were used for the systematic review to identify any studies in the literature that examined ACL injury mechanisms. Methodological approaches that describe and evaluate ACL injury mechanisms included athlete interviews, arthroscopic studies, clinical imaging and physical exam tests, video analysis, cadaveric studies, laboratory tests (motion analysis, electromyography) and mathematical modelling studies. One hundred and ninety-eight studies associated with ACL injury mechanisms were identified and provided evidence regarding plane of injury, with evidence supporting sagittal, frontal and/or transverse plane mechanisms of injury. Collectively, the studies indicate that it is highly probable that ACL injuries are more likely to occur during multi-planar rather than single-planar mechanisms of injury.

The effects of opposition and gender on knee kinematics and ground reaction force during landing from volleyball block jumps

The aim of this study was to examine the effect of opposition and gender on knee kinematics and ground reaction force during landing from a volleyball block jump. Six female and six male university volleyball players performed two landing tasks: (a) an unopposed and (b) an opposed volleyball block jump and landing. A 12-camera motion analysis system (120 Hz) was used to record knee kinematics, and a force platform (600 Hz) was used to record ground reaction force during landing. The results showed a significant effect for level of opposition in peak normalized ground reaction force (p = .04), knee flexion at ground contact (p = .003), maximum knee flexion (p = .001), and knee flexion range of motion (p = .003). There was a significant effect for gender in maximum knee flexion (p = .01), knee flexion range of motion (p = .001), maximum knee valgus angle (p = .001), and knee valgus range of motion (p = .001). The changes in landing biomechanics as a result of opposition suggest future research on landing mechanics should examine opposed exercises, because opposition may significantly alter neuromuscular responses.

Training affects knee kinematics and kinetics in cutting maneuvers in sport

PURPOSE

The current study examined how different training affects the kinematics and applied moments at the knee during sporting maneuvers and the potential to reduce loading of the anterior cruciate ligament (ACL). The training programs were 1) machine weights, 2) free weights, 3) balance training, and 4) machine weights + balance training.

METHODS

Fifty healthy male subjects were allocated either to a control group or to one of four 12-wk training programs. Subjects were tested before and after training, performing running and cutting maneuvers from which knee angle and applied knee moments were assessed. Data analyzed were peak applied flexion/extension, varus/valgus, and internal/external rotation moments, as well as knee flexion angles during specific phases of stance during the maneuvers.

RESULTS

The balance training group decreased their peak valgus and peak internal rotation moments during weight acceptance in all maneuvers. This group also lowered their flexion moments during the sidestep to 60 degrees . Free weights training induced increases in the internal rotation moment and decreases in knee flexion angle in the peak push-off phase of stance. Machine weights training elicited increases in the flexion moment and reduced peak valgus moments in weight acceptance. Machine weights + balance training resulted in no changes to the variables assessed.

CONCLUSIONS

Balance training produced reductions in peak valgus and internal rotation moments, which could lower ACL injury risk during sporting maneuvers. Strength training tended to increase the applied knee loading known to place strain on the ACL, with the free weights group also decreasing the amount of knee flexion. It is recommended that balance training be implemented because it may reduce the risk of ACL injury.

Identification of spinal tissues loaded by manual therapy: a robot-based serial dissection technique applied in porcine motion segments

STUDY DESIGN

Serial dissection of porcine motion segments during robotic control of vertebral kinematics.

OBJECTIVE

To identify which spinal tissues are loaded in response to manual therapy (manipulation and mobilization) and to what magnitude.

SUMMARY OF BACKGROUND DATA

Various theoretical constructs attempt to explain how manual therapies load specific spinal tissues. By using a parallel robot to control vertebral kinematics during serial dissection, it is possible to quantify the loads experienced by discrete spinal tissues undergoing common therapeutic procedures such as manual therapy.

METHODS

In 9 porcine cadavers, manual therapy was provided to L3 and the kinematic response of L3-L4 recorded. The exact kinematic trajectory experienced by L3-L4 in response to manual therapy was then replayed to the isolated segment by a parallel robot equipped with a 6-axis load cell. Discrete spinal tissues were then removed and the kinematic pathway replayed. The change in forces and moments following tissue removal were considered to be those applied to that specific tissue by manual therapy.

RESULTS

In this study, both manual therapies affected spinal tissues. The intervertebral disc experienced the greatest forces and moments arising from both manipulation and mobilization.

CONCLUSION

This study is the first to identify which tissues are loaded in response to manual therapy. The observation that manual therapy loads some tissues to a much greater magnitude than others offers a possible explanation for its modest treatment effect; only conditions involving these tissues may be influenced by manual therapy. Future studies are planned to determine if manual therapy can be altered to target (or avoid) specific spinal tissues.

Barriers to predicting the mechanisms and risk factors of non-contact anterior cruciate ligament injury

High incidences of non-contact anterior cruciate ligament (ACL) injury, frequent requirements for ACL reconstruction, and limited understanding of ACL mechanics have engendered considerable interest in quantifying the ACL loading mechanisms. Although some progress has been made to better understand non-contact ACL injuries, information on how and why non-contact ACL injuries occur is still largely unavailable. In other words, research is yet to yield consensus on injury mechanisms and risk factors. Biomechanics, video analysis, and related study approaches have elucidated to some extent how ACL injuries occur. However, these approaches are limited because they provide estimates, rather than precise measurements of knee - and more specifically ACL - kinematics at the time of injury. These study approaches are also limited in their inability to simultaneously capture many of the contributing factors to injury.This paper aims at elucidating and summarizing the key challenges that confound our understanding in predicting the mechanisms and subsequently identifying risk factors of non-contact ACL injury. This work also appraise the methodological rigor of existing study approaches, review testing protocols employed in published studies, as well as presents a possible coupled approach to better understand injury mechanisms and risk factors of non-contact ACL injury. Three comprehensive electronic databases and hand search of journal papers, covering numerous full text published English articles were utilized to find studies on the association between ACL and injury mechanisms, ACL and risk factors, as well as, ACL and investigative approaches. This review unveils that new research modalities and/or coupled research methods are required to better understand how and why the ACL gets injured. Only by achieving a better understanding of ACL loading mechanisms and the associated contributing factors, one will be able to develop robust prevention strategies and exercise regimens to mitigate non-contact ACL injuries.

Rotational laxity greater in patients with contralateral anterior cruciate ligament injury than healthy volunteers

Rotational stability of the knee has been traditionally difficult to quantify, limiting the ability of the orthopedic community to determine the potential role of rotational laxity in the etiology of anterior cruciate ligament (ACL) injuries. The purposes of this multicenter cohort study were to evaluate the reliability of a robotic axial rotation measurement system, determine whether the uninjured knees of patients that had previous contralateral ACL reconstruction demonstrated different rotational biomechanical characteristics than a group of healthy volunteers, and determine whether knee rotational biomechanical characteristics differ between male and female non-injured limbs in groups of both healthy volunteers and patients with a previous contralateral ACL injury. Fourteen healthy volunteers and 79 patients with previous unilateral ACL injury participated in this study. Patients were tested using a computerized tibial axial rotation system. Only the normal (non-operated) knee data were used for analysis. In order to assess the reliability of the robotic measurement system, 10 healthy volunteers were tested daily over four consecutive days by four different examiners. Rotational laxity and compliance measures demonstrated excellent reliability (ICC = 0.97). Patients with a contralateral ACL injury demonstrated significantly increased tibial internal rotation (20.6° vs. 11.4°, P < 0.001) and reduced external rotation (16.7° vs. 26.6°, P < 0.001) compared to healthy volunteers. Females demonstrated significantly increased internal and external rotation, as well as significantly increased rotational compliance compared with males (P < 0.05). Computer-assisted measurement techniques may offer clinicians an accurate, reliable, non-invasive method to select the most appropriate preventative or surgical interventions for patients with increased knee rotational laxity.

Tibial translation and muscle activation during rehabilitation exercises 5 weeks after anterior cruciate ligament reconstruction

The aim of this study was to compare different rehabilitation exercises with respect to dynamic anterior tibial translation and muscle activation 5 weeks after an anterior cruciate ligament (ACL) reconstruction. Another aim was to compare the ACL-reconstructed knee with the ACL-injured and the uninjured knees for differences in anterior tibial translation and muscle activation during the exercises. Sagittal tibial translation and muscle activation were measured during the Lachman test (static translation) and during seven rehabilitation exercises (dynamic translation) in 19 patients. Results obtained 5 weeks after ACL reconstruction were compared with those obtained before the ACL reconstruction (ACL-deficient and uninjured knee). After ACL reconstruction the seated knee extension produced more anterior tibial translation than the straight leg raise and standing on one leg. The ACL reconstruction reduced the static and the dynamic tibial translation and the tibial translations measured in ACL-reconstructed knees were similar to those measured in uninjured knees. After ACL reconstruction, the patients used a joint stiffening strategy that used more hamstring activation and reduced the dynamic tibial translation. Although all exercises tested are suitable for rehabilitation after ACL reconstruction, to protect the graft from excessive strain, the straight leg raise and squat on one leg are preferable for quadriceps training in the early phase of rehabilitation.

Kinematics of the anterior cruciate ligament during gait

BACKGROUND

The function of the anteromedial (AM) and posterolateral (PL) bundles of the anterior cruciate ligament (ACL) during gait has not been reported.

HYPOTHESIS

The AM and PL bundles have distinct functional behavior during the stance phase of treadmill gait.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Three-dimensional models of the knee were created by magnetic resonance images from 8 healthy subjects. The contour of the 2 bundle attachments were constructed on each model. Each bundle was represented by a straight line connecting its tibial and femoral attachment centroids. Next, the knee kinematics during the stance phase of gait was determined with a dual fluoroscopic imaging system. The relative elongation, sagittal plane elevation, coronal plane elevation, and transverse plane deviation of the 2 bundles were measured directly from heel strike to toe-off.

RESULTS

At heel strike, the AM and PL bundles had first peak elongation of 9% +/- 7% and 9% +/- 13%, respectively. At 50% progress of the stance phase, both bundles were maximally elongated, 12% +/- 7% for the AM bundle and 13% +/- 15% for the PL bundle. No significant difference was found for each bundle between 40% and 60% of the stance phase (P > .05). With increasing knee flexion, the sagittal plane and coronal plane elevations of the 2 bundles decreased, whereas the deviation angles increased.

CONCLUSION

Both bundles are anisometric and function in a similar manner during the stance phase of gait. They were maximally elongated throughout the midstance where they were stretched maximally to resist anterior tibial translation.

CLINICAL RELEVANCE

This information can be useful for further improving anatomical ACL reconstructions to better reproduce the 2 bundle functions. It may also be useful for designing postoperative rehabilitation regimens to prevent overstretch of the grafts.

Comparison of single- and double-bundle anterior cruciate ligament reconstructions in restoration of knee kinematics and anterior cruciate ligament forces

BACKGROUND

Anterior cruciate ligament (ACL) deficiency alters 6 degrees of freedom knee kinematics, yet only anterior translation and internal rotation have been the primary measures in previous studies.

PURPOSE

To compare the 6 degrees of freedom knee kinematics and the graft forces after single- and double-bundle ACL reconstructions under various external loading conditions.

STUDY DESIGN

Controlled laboratory study.

METHODS

Ten human cadaveric knees were tested with a robotic testing system under 4 conditions: intact, ACL deficient, single-bundle reconstructed with a quadrupled hamstring tendon graft, and double-bundle reconstructed with 2 looped hamstring tendon grafts. Knee kinematics and forces of the ACL or ACL graft in each knee were measured under 3 loading conditions: an anterior tibial load of 134 N, a simulated quadriceps muscle load of 400 N, and combined tibial torques (10 N.m valgus and 5 N.m internal tibial torques) at 0 degrees , 15 degrees , 30 degrees , 60 degrees , and 90 degrees of knee flexion.

RESULTS

The double-bundle reconstruction restored the anterior and medial laxities closer to the intact knee than the single-bundle reconstruction. However, the internal rotation of the tibia under the simulated quadriceps muscle load was significantly decreased when compared with the intact knee after both reconstructions, more so after double-bundle reconstruction (P < .05). The entire graft force of the double-bundle reconstruction was more similar to that of the intact ACL than that of the single-bundle reconstruction. However, the posterolateral bundle graft in the double-bundle reconstructed knee was overloaded as compared with the intact posterolateral bundle.

CONCLUSION

The double-bundle reconstruction can better restore the normal anterior-posterior and medial-lateral laxities than the single-bundle reconstruction can, but an overloading of the posterolateral bundle graft can occur in a double-bundle reconstructed knee.

CLINICAL RELEVANCE

Both single-bundle and double-bundle techniques cannot restore the rotational laxities and the ACL force distributions of the intact knee.

Anterior Cruciate Ligament Injury: Compensation during Gait using Hamstring Muscle Activity

Previous research has shown that an increase in hamstring activation may compensate for anterior tibial transalation (ATT) in patients with anterior cruciate ligament deficient knee (ACLd); however, the effects of this compensation still remain unclear. The goals of this study were to quantify the activation of the hamstring muscles needed to compensate the ATT in ACLd knee during the complete gait cycle and to evaluate the effect of this compensation on quadriceps activation and joint contact forces. A two dimensional model of the knee was used, which included the tibiofemoral and patellofemoral joints, knee ligaments, the medial capsule and two muscles units. Simulations were conducted to determine the ATT in healthy and ACLd knee and the hamstring activation needed to correct the abnormal ATT to normal levels (100% compensation) and to 50% compensation. Then, the quadriceps activation and the joint contact forces were calculated. Results showed that 100% compensation would require hamstring and quadriceps activations larger than their maximum isometric force, and would generate an increment in the peak contact force at the tibiofemoral (115%) and patellofemoral (48%) joint with respect to the healthy knee. On the other hand, 50% compensation would require less force generated by the muscles (less than 0.85 of maximum isometric force) and smaller contact forces (peak tibiofemoral contact force increased 23% and peak patellofemoral contact force decreased 7.5% with respect to the healthy knee). Total compensation of ATT by means of increased hamstring activity is possible; however, partial compensation represents a less deleterious strategy.

Increasing pre-activation of the quadriceps muscle protects the anterior cruciate ligament during the landing phase of a jump: an in vitro simulation

We hypothesize that application of an unopposed quadriceps force coupled with an impulsive ground reaction force may induce anterior cruciate ligament (ACL) injury. This situation is similar to landing from a jump if only the quadriceps muscle is active; an unlikely but presumably dangerous circumstance. The purpose of this study was to test our hypothesis using in vitro simulation of jump landing. A jump-landing simulator was utilized. Nine cadaveric knees were tested at an initial flexion angle of 20 degrees . Each ACL was instrumented with a differential variable reluctance transducer (DVRT). Quadriceps pre-activation forces (QPFs) ranging from 25N to 700N were applied to each knee, followed by an impulsive ground reaction force produced by a carriage-mounted drop weight (7kg) that impulsively drove the ankle upward. ACL strain was monitored before landing due to application of QPF (pre-activation strain) and at landing due to application of the ground reaction force (landing strain). No ACLs were injured. Pre-activation strains exhibited a positive correlation with QPF (r=0.674, p<0.001) while landing strains showed a negative correlation (r=-0.235, p=0.032). Total ACL strain (pre-activation+landing strain) showed no correlation with QPF (r=0.023, p=0.428). Our findings indicate that elevated QPF increases pre-activation strain but reduces the landing strain and is therefore protective post-landing. Overall, there is a complete lack of correlation between "total" ACL strain and QPF suggesting that the total strain in the ACL is independent of the QPF under the simulated conditions.

The influence of muscle load on tibiofemoral knee kinematics

A comparative kinematics study was conducted on six cadaver limbs, comparing tibiofemoral kinematics in five conditions: unloaded, under a constant 130 N ankle load with a variable quadriceps load, with and without a simultaneous constant 50 N medial and lateral hamstrings load. Kinematics were described as translation of the projected centers of the medial (MFT) and lateral femoral condyles (LFT) in the horizontal plane of the tibia, and tibial axial rotation (TR) as a function of flexion angle. In passive conditions, the tibia rotated internally with increasing flexion to an average of -16 degrees (range: -12/-20 degrees , SD = 3.0 degrees ). Between 0 and 40 degrees flexion, the medial condyle translated forwards 4 mm (range: 0.8/5.5 mm, SD = 2.5 mm), followed by a gradual posterior translation, totaling -9 mm (range: -5.8/-18.5 mm, SD = 4.9 mm) between 40-140 degrees flexion. The lateral femoral condyle translated posteriorly with increasing flexion completing -25 mm (range: -22.6 to -28.2 mm, SD = 2.5 mm). Dynamic, loaded measurements simulating a deep knee bend were carried out in a knee rig. Under a fixed ankle load of 130 N and variable quadriceps loading, tibial rotation was inverted, mean TR = 4.7 degrees (range: -3.3 degrees /11.8 degrees SD = 5.4 degrees ), MFT = -0.5 mm (range: = -4.3/2.4 mm, SD = 2.4 mm), LFT = 3.3 mm (range: = -3.6/10.6 mm, SD = 5.1 mm). Compared to the passive condition, all these excursions were significantly different (p < or = 0.015). Adding medial and lateral hamstrings force of 50 N each reduced TR, MFT, and LFT significantly compared to the passive condition. In general, loading the knee with hamstrings and quadriceps reduces rotation and translation compared to the passive condition. Lateral hamstring action is more influential on knee kinematics than medial hamstrings action.

The relationships among sagittal-plane lower extremity moments: implications for landing strategy in anterior cruciate ligament injury prevention

CONTEXT

Excessive quadriceps contraction with insufficient hamstrings muscle cocontraction has been shown to be a possible contributing factor for noncontact anterior cruciate ligament (ACL) injuries. Assessing the relationships among lower extremity internal moments may provide some insight into avoiding muscle contraction patterns that increase ACL injury risk.

OBJECTIVE

To examine the relationships of knee-extensor moment with ankle plantar-flexor and hip-extensor moments and to examine the relationship between knee moment and center of pressure as a measure of neuromuscular response to center-of-mass position.

DESIGN

Cross-sectional study.

SETTING

Applied Neuromechanics Research Laboratory.

PATIENTS OR OTHER PARTICIPANTS

Eighteen healthy, recreationally active women (age = 22.3 +/- 2.8 years, height = 162.5 +/- 8.1 cm, mass = 57.8 +/- 9.3 kg).

INTERVENTION(S)

Participants performed a single-leg landing from a 45-cm box onto a force plate. Kinetic and kinematic data were collected.

MAIN OUTCOME MEASURE(S)

Pearson product moment correlation coefficients were calculated among the net peak knee-extensor moment (KEMpk), sagittal-plane ankle (AM) and hip (HM) net internal moments, and anterior-posterior center of pressure relative to foot center of mass at KEMpk (COP).

RESULTS

Lower KEMpk related to both greater AM (r = -0.942, P < .001) and HM (r = -0.657, P = .003). We also found that more anterior displacement of COP was related to greater AM (r = -0.750, P < .001) and lower KEMpk (r = 0.618, P = .006).

CONCLUSIONS

Our results suggest that participants who lean the whole body forward during landing may produce more plantar-flexor moment and less knee-extensor moment, possibly increasing hip-extensor moment and decreasing knee-extensor moment production. These results suggest that leaning forward may be a technique to decrease quadriceps contraction demand while increasing hamstrings cocontraction demand during a single-leg landing.

Early versus late start of isokinetic hamstring-strengthening exercise after anterior cruciate ligament reconstruction with patellar tendon graft

BACKGROUND

Hamstring strengthening after anterior cruciate ligament reconstruction is a vital component of the rehabilitation program.

PURPOSE

The objective of this trial was to investigate the effects of hamstring isokinetic training used in the early phase of the rehabilitation program on the stability, strength, symptoms, and functional outcomes of patients throughout 12 months after anterior cruciate ligament surgery.

STUDY DESIGN

Randomized controlled clinical trial; Level of evidence, 2.

METHODS

Forty-eight men underwent anterior cruciate ligament reconstruction with an ipsilateral bone-patellar tendon-bone autograft. The patients were randomly assigned to perform daily isokinetic hamstring exercises at postoperative 3 weeks (group I) or to perform daily isokinetic hamstring exercises at postoperative 9 weeks (group II). The patients were evaluated monthly for the first 4 months and at the 12th month for postoperative hamstring and quadriceps strength, as well as for knee function via the Cincinnati Knee Rating Scale and International Knee Documentation Committee form.

RESULTS

Hamstring isometric strength at 30 degrees of knee flexion (at the first and second months) and concentric isokinetic strength (at 2, 3, 4, and 12 months) at the angular velocity of 60 deg/s were significantly (P <.05-.01) greater in group I compared with group II. Average scores of the Cincinnati Knee Rating Scale for symptoms were significantly (P <.05-.001) higher in group I compared with group II at all evaluation periods. Walking and stair-climbing scores at 1, 2, 3, and 4 months and squatting score at all evaluation periods were also better (P <.05-.01) in group I compared with group II. In addition, group I exhibited better (P <.01-.001) Lachman test results compared with group II for all postoperative evaluation periods. The International Knee Documentation Committee final rating scores were significantly (P <.01) greater at 2, 3, and 4 months in group I compared with group II.

CONCLUSION

The results of this study suggest that hamstring as well as quadriceps strength can be increased via early hamstring strengthening after anterior cruciate ligament reconstruction with no negative impact on knee function.

Changes in ACL length at different knee flexion angles: an in vivo biomechanical study

Recently, there has been a tremendous impetus on anatomical reconstruction of the anterior cruciate ligament (ACL), and the double-bundle reconstruction concept has been advocated by many authors. It is, therefore, important to understand how the lengths of the two bundles of the ACL vary during different knee flexion angles as this could influence the angle of graft fixation during surgery. The aim of this study is to determine the change in length of the ACL bundles during different knee flexion angles. Ten subjects with normal knees were evaluated. A high-resolution computer tomography scan was performed, and 3D knee images were obtained. These images were then imported to customized software, and digital length measurement of four virtual bundles (anatomical single bundle, AM, PL and over the top) was evaluated from fixed points on the femur and tibia. Length-versus-flexion curves were drawn, and statistical analysis was performed to evaluate changes in length for each bundle at varying angles of knee flexion (0 degrees, 45 degrees, 90 degrees and 135 degrees). All virtual bundles achieved greatest lengths at full extension. There was a significant difference between the posterolateral bundle length when compared to the other bundles at full extension. There were no significant differences between the lengths of the anteromedial and the over the top single bundles at all angles of knee flexion. Three-dimensional computer tomography can be used to assess the length changes of the virtual anterior cruciate ligament bundles, thereby allowing a better understanding of bundle function in clinical situations.

In situ forces in the anteromedial and posterolateral bundles of the anterior cruciate ligament under simulated functional loading conditions

BACKGROUND

The in situ forces of the anteromedial (AM) and posterolateral bundles (PL) of the anterior cruciate ligament (ACL) under simulated functional loads such as simulated muscle loads have not been reported. These data are instrumental for improvement of the anatomical double-bundle ACL reconstruction.

HYPOTHESIS

The load-sharing patterns of the 2 bundles are complementary under simulated muscle loads.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Eight cadaveric knees in this study were sequentially studied using a robotic testing system. Each knee was tested under 3 external loading conditions including (1) a 134-N anterior tibial load; (2) combined rotational loads of 10 N x m of valgus and 5 N x m internal tibial torques; and (3) a 400-N quadriceps muscle load with the knee at 0 degrees , 15 degrees , 30 degrees , 60 degrees , and 90 degrees of flexion. The in situ forces of the 2 bundles of ACL were determined using the principle of superposition.

RESULTS

Under the anterior tibial load, the PL bundle carried peak loads at full extension and concurrently had significantly lower force than the AM bundle throughout the range of flexion (P <.05). Under the combined rotational loads, the PL bundle contributed to carrying the load between 0 degrees and 30 degrees , although less than the AM bundle. Under simulated muscle loads, both bundles carried loads between 0 degrees and 30 degrees . There was no significant difference between the 2 bundle forces at all flexion angles (P > .05).

CONCLUSION

Under externally applied loads, in general, the AM bundle carried a greater portion of the load at all flexion angles, whereas the PL bundle only shared the load at low flexion angles. The bundles functioned in a complementary rather than a reciprocal manner to each other.

CLINICAL RELEVANCE

The data appear to support the concept that both bundles function in a complementary manner. Thus, how to re-create the 2 bundle functions in an ACL reconstruction should be further investigated.

Kinematic and kinetic features of normal level walking in patellofemoral pain syndrome: more than a sagittal plane alteration

Patients with patellofemoral pain syndrome (PFPS) often report discomfort and pain during walking. To date, most of the studies conducted to determine gait alterations in PFPS patients have focused on sagittal plane alterations. Physiological and biomechanical factors, however, suggest that frontal and transverse plane alterations may be involved in PFPS. We therefore decided to conduct a kinematic and kinetic evaluation on all three planes in 9 PFPS subjects and 9 healthy sex- and age-matched controls. General gait characteristics were similar in patients and controls, with the exception of swing velocity, which was lower in PFPS patients. Patients also displayed an increased knee abductor and external rotator moments in loading response, and reduced knee extensor moment both in loading response and in terminal stance. We speculate that these findings may be linked both to a pain-avoiding gait pattern and to alterations in the timing of activation of different components of the quadriceps muscle, which is typical of PFPS. The relevance for clinicians is this gait pattern may represent a biomechanical risk factor for future knee osteoarthritis. We therefore recommend that treatments aimed at PFPS should also attempt to restore a correct walking pattern.

Effect of axial load on anterior tibial translation when transitioning from non-weight bearing to weight bearing

BACKGROUND

While the application of compressive joint loads and thigh muscle activity are associated with anterior tibial translation in vitro, less is known during early load acceptance in vivo. We investigated the effects of increasing axial loads on anterior tibial translation and thigh muscle activity in healthy knees during transition from non-weight bearing to early weight bearing.

METHODS

Participants (11 males, 11 females) underwent 20%, 40%, and 60% body weight acceptance trials at 20 degrees knee flexion while electromagnetic sensors measured anterior tibial translation (mm), and surface electromyography recorded quadriceps and hamstring muscle onset times (ms) and amplitudes (% maximal voluntary isometric contraction). Repeated measures ANOVA compared values across loads. Pearson correlations examined relationships between anterior tibial translation and muscle onset times and amplitudes within each load.

FINDINGS

As load increased, anterior tibial translation (Mean (standard deviation)) (20%=4.7 (1.7) mm<40%=7.1 (1.9) mm<60%=8.8 (2.1) mm), and quadriceps (20%=23.6 (14.9)% maximal voluntary isometric contraction <40%=32.7 (11.8)% maximal voluntary isometric contraction <60%=41.1 (13.5)% maximal voluntary isometric contraction) and hamstring (20%=15.5 (15.7)% maximal voluntary isometric contraction <40%=23.0 (16.4)% maximal voluntary isometric contraction <60%=27.6 (19.1)% maximal voluntary isometric contraction) activation increased, while quadriceps (20%=96.7 (28.4) ms>60% 80.2 (21.8) ms) and hamstring (20%=141.5 (65.0) ms and 40%=126.3 (68.8)>60% 107.6 (28.4) ms) onset times decreased (P0.05). There were no relationships between anterior tibial translation and muscle activation amplitudes (R=0.033-0.294) or onset times (R=-0.031-0.374) (P>0.09).

INTERPRETATION

Greater axial loads near full knee extension during early weight acceptance result in greater anterior tibial translation, regardless of faster and stronger activation amplitudes. These findings support injury prevention programs aimed to reduce impact forces as they may in turn reduce anterior tibial translation and corresponding ligamentous strain during dynamic activity.

Graft orientation influences the knee flexion moment during walking in patients with anterior cruciate ligament reconstruction

BACKGROUND

Anterior cruciate ligament graft orientation has been proposed as a potential mechanism for failure of single-bundle anterior cruciate ligament reconstruction and has been considered important in the restoration of normal ambulatory knee mechanics.

PURPOSE

To evaluate the possibility that patients adapt their mechanics of walking to the orientation of the anterior cruciate ligament graft. This was determined by testing the hypothesis that peak external knee flexion moment (net quadriceps moment) during walking in patients with anterior cruciate ligament reconstruction is correlated with coronal and sagittal anterior cruciate ligament graft orientations.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Gait analysis was performed to assess dynamic knee function during walking in 17 subjects with unilateral anterior cruciate ligament reconstructions. Magnetic resonance imaging was used to measure coronal and sagittal anterior cruciate ligament graft orientations.

RESULTS

A negative correlation was observed between peak external knee flexion moment during walking and coronal angle of the anterior cruciate ligament graft (1.0 m/s walking speed, r = -0.87, P < .001; 1.3 m/s, r = -0.66, P = .004; 1.6 m/s, r = -0.24, P > .05); no correlation was found with the sagittal graft angle (1.0 m/s walking speed, r = 0.21, P > .05; 1.3 m/s, r = 0.20, P > .05; 1.6 m/s, r = 0.13, P > .05).

CONCLUSION

The negative correlation between peak external knee flexion moment during walking and the coronal angle of the anterior cruciate ligament graft indicates that as the anterior cruciate ligament graft is placed in a more vertical coronal orientation, patients reduce their net quadriceps usage during walking.

CLINICAL RELEVANCE

This finding supports the hypothesis that graft placement plays a critical role in the restoration of normal ambulatory mechanics after anterior cruciate ligament reconstruction and thus could provide a partial explanation for the increased incidence of premature osteoarthritis at long-term follow-up in patients with anterior cruciate ligament reconstruction.

How isometric are the medial patellofemoral, superficial medial collateral, and lateral collateral ligaments of the knee?

BACKGROUND

Ligament isometry is a cornerstone in the description of normal knee function and thorough knowledge is mandatory for successful repair of torn ligaments.

PURPOSE

This study was undertaken to validate a novel experimental model for the study of ligament strains and to determine the length changes in the superficial medial collateral, lateral collateral, and medial patellofemoral ligaments.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Passive motions and loaded squats of 12 cadaveric specimens were performed while controlling ankle load and optically tracking the motion of the bones. Preexperiment and postexperiment computed axial tomography scans allow the transformation of rigid body motion to relative motion of relevant anatomic landmarks on the femur, tibia, and patella.

RESULTS

The superficial medial collateral ligament is a near-isometric ligament with a strain of less than 2%. The ligament is a little more slack in midflexion (30 degrees to 50 degrees ) and in deep flexion, but length changes are not significant (P > .05). The lateral collateral ligament behaves near isometric (<2% strain) from 0 degrees to 70 degrees of knee flexion. Cartilage compression in a loaded environment relieves tension from the collateral ligaments (P < .05). The medial patellofemoral ligament is nonisometric. The cranial part of the medial patellofemoral ligament is most taut at full extension, while the caudal part is most taut at 30 degrees of knee flexion.

CONCLUSION

Ligament insertion sites on the femur, patella, and fibula can be derived from computed axial tomography scans. The described model allows the study of dynamic ligament behavior. The superficial medial collateral ligament is a near-isometric ligament with no significant length changes. The medial patellofemoral ligament behaves differently in its cranial and caudal parts.

CLINICAL RELEVANCE

In knees with chronic medial collateral ligament insufficiency, isometric repair of the superficial medial collateral ligament can be attempted. A medial patellofemoral ligament reconstruction with a double fixation on the medial patellar border is supported. The cranial bundle should be tightened at full extension and the caudal bundle at 30 degrees of knee flexion.

Lower limb muscle activity and kinematics of an unanticipated cutting manoeuvre: a gender comparison

This investigation compared the amplitude and the timing of the muscle activity of the lower limb, as well as the three-dimensional kinematics of the hip, knee and ankle joints, of male and female elite soccer players performing an unanticipated cutting manoeuvre. These data were recorded for 15 female and 15 male participants for five successful cutting manoeuvres. For this manoeuvre to be performed in an unanticipated manner, the participants were instructed to execute one of three tasks, which were signalled to them with a target board composed of three different coloured lights. Female participants performed the cutting manoeuvre with greater lateral gastrocnemius activity in comparison with the male participants. It was also observed that they contracted their vastus lateralis to a greater extent than their vastus medialis, whereas the men adopted the opposite strategy. These neuromuscular control strategies adopted by the female athletes may elucidate the reasons for which women struck the ground with a more abducted knee during the cutting task. Given that this knee position places greater strain on the anterior cruciate ligament, a restoration of the medial/lateral activation balance of the lower limb muscles may reduce one's risk of injury.

Sagittal-plane trunk position, landing forces, and quadriceps electromyographic activity

CONTEXT

Researchers have suggested that large landing forces, excessive quadriceps activity, and an erect posture during landing are risk factors for anterior cruciate ligament (ACL) injury. The influence of knee kinematics on these risk factors has been investigated extensively, but trunk positioning has received little attention.

OBJECTIVE

To determine the effect of trunk flexion on landing forces and quadriceps activation during landing.

DESIGN

Two (sex) x 2 (task) repeated-measures design.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Forty healthy, physically active volunteers (20 men, 20 women).

INTERVENTION(S)

Participants performed 2 drop-landing tasks. The first task represented the natural, or preferred, landing strategy. The second task was identical to the first except that participants flexed the trunk during landing.

MAIN OUTCOME MEASURE(S)

We measured peak vertical and posterior ground reaction forces and mean quadriceps electromyographic amplitude during the loading phase of landing (ie, the interval from initial ground contact to peak knee flexion).

RESULTS

Trunk flexion decreased the vertical ground reaction force (P < .001) and quadriceps electromyographic amplitude (P < .001). The effect of trunk flexion did not differ across sex for landing forces or quadriceps electromyographic activity.

CONCLUSIONS

We found that trunk flexion during landing reduced landing forces and quadriceps activity, thus potentially reducing the force imparted to the ACL. Research has indicated that trunk flexion during landing also increases knee and hip flexion, resulting in a less erect landing posture. In combination, these findings support emphasis on trunk flexion during landing as part of ACL injury-prevention programs.

Prevention of non-contact anterior cruciate ligament injuries in soccer players. Part 1: Mechanisms of injury and underlying risk factors

Soccer is the most commonly played sport in the world, with an estimated 265 million active soccer players by 2006. Inherent to this sport is the higher risk of injury to the anterior cruciate ligament (ACL) relative to other sports. ACL injury causes the most time lost from competition in soccer which has influenced a strong research focus to determine the risk factors for injury. This research emphasis has afforded a rapid influx of literature defining potential modifiable and non-modifiable risk factors that increase the risk of injury. The purpose of the current review is to sequence the most recent literature that reports potential mechanisms and risk factors for non-contact ACL injury in soccer players. Most ACL tears in soccer players are non-contact in nature. Common playing situations precluding a non-contact ACL injury include: change of direction or cutting maneuvers combined with deceleration, landing from a jump in or near full extension, and pivoting with knee near full extension and a planted foot. The most common non-contact ACL injury mechanism include a deceleration task with high knee internal extension torque (with or without perturbation) combined with dynamic valgus rotation with the body weight shifted over the injured leg and the plantar surface of the foot fixed flat on the playing surface. Potential extrinsic non-contact ACL injury risk factors include: dry weather and surface, and artificial surface instead of natural grass. Commonly purported intrinsic risk factors include: generalized and specific knee joint laxity, small and narrow intercondylar notch width (ratio of notch width to the diameter and cross sectional area of the ACL), pre-ovulatory phase of menstrual cycle in females not using oral contraceptives, decreased relative (to quadriceps) hamstring strength and recruitment, muscular fatigue by altering neuromuscular control, decreased "core" strength and proprioception, low trunk, hip, and knee flexion angles, and high dorsiflexion of the ankle when performing sport tasks, lateral trunk displacement and hip adduction combined with increased knee abduction moments (dynamic knee valgus), and increased hip internal rotation and tibial external rotation with or without foot pronation. The identified mechanisms and risk factors for non-contact ACL injuries have been mainly studied in female soccer players; thus, further research in male players is warranted. Non-contact ACL injuries in soccer players likely has a multi-factorial etiology. The identification of those athletes at increased risk may be a salient first step before designing and implementing specific pre-season and in-season training programs aimed to modify the identified risk factors and to decrease ACL injury rates. Current evidence indicates that this crucial step to prevent ACL injury is the only option to effectively prevent the sequelae of osteoarthritis associated with this traumatic injury.

In vivo anterior cruciate ligament elongation in response to axial tibial loads

BACKGROUND

The knowledge of in vivo anterior cruciate ligament (ACL) deformation is fundamental for understanding ACL injury mechanisms and for improving surgical reconstruction of the injured ACL. This study investigated the relative elongation of the ACL when the knee is subject to no load (<10 N) and then to full body weight (axial tibial load) at various flexion angles using a combined dual fluoroscopic and magnetic resonance imaging (MRI) technique.

METHODS

Nine healthy subjects were scanned with MRI and imaged when one knee was subject to no load and then to full body weight using a dual fluoroscopic system (0 degrees-45 degrees flexion angles). The ACL was analyzed using three models: a single central bundle; an anteromedial and posterolateral (double functional) bundle; and multiple (eight) surface fiber bundles.

RESULTS

The anteromedial bundle had a peak relative elongation of 4.4% +/- 3.4% at 30 degrees and that of the posterolateral bundle was 5.9% +/- 3.4% at 15 degrees. The ACL surface fiber bundles at the posterior portion of the ACL were shorter in length than those at the anterior portion. However, the peak relative elongation of one posterolateral fiber bundle reached more than 13% whereas one anteromedial fiber bundle reached a peak relative elongation of only about 3% at 30 degrees of flexion by increasing the axial tibial load from no load to full body weight.

CONCLUSIONS

The data quantitatively demonstrated that under external loading the ACL experiences nonhomogeneous elongation, with the posterior fiber bundles stretching more than the anterior fiber bundles.

Biomechanical comparison of single-tunnel-double-bundle and single-bundle anterior cruciate ligament reconstructions

BACKGROUND

Anatomic double-bundle reconstruction has been thought to better simulate the anterior cruciate ligament anatomy. It is, however, a technically challenging procedure, associated with longer operation time and higher cost.

HYPOTHESIS

Double-bundle anterior cruciate ligament reconstruction using a single femoral and tibial tunnel can closely reproduce intact knee kinematics.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight fresh-frozen human cadaveric knee specimens were tested using a robotic testing system to investigate the kinematic response of the knee joint under an anterior tibial load (130 N), simulated quadriceps load (400 N), and combined torques (5 N.m valgus and 5 N.m internal tibial torques) at 0 degrees, 15 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion. Each knee was tested sequentially under 4 conditions: (1) anterior cruciate ligament intact, (2) anterior cruciate ligament deficient, (3) single-bundle anterior cruciate ligament reconstruction using quadrupled hamstring tendon, and (4) single-tunnel-double-bundle anterior cruciate ligament reconstruction using the same tunnels and quadrupled hamstring tendon graft as in the single-bundle anterior cruciate ligament reconstruction.

RESULTS

Single-tunnel-double-bundle anterior cruciate ligament reconstruction more closely restored the intact knee kinematics than single-bundle anterior cruciate ligament reconstruction at low flexion angles (< or =30 degrees ) under the anterior tibial load and simulated muscle load (P < .05). However, single-tunnel-double-bundle anterior cruciate ligament reconstruction overconstrained the knee joint at high flexion angles (> or =60 degrees ) under the anterior tibial load and at 0 degrees and 30 degrees of flexion under combined torques.

CONCLUSION

This double-bundle anterior cruciate ligament reconstruction using a single tunnel can better restore anterior tibial translations to the intact level compared with single-bundle anterior cruciate ligament reconstruction at low flexion angles, but it overconstrained the knee joint at high flexion angles.

CLINICAL RELEVANCE

This technique could be an alternative for both single-bundle and double-tunnel-double-bundle anterior cruciate ligament reconstructions to reproduce intact knee kinematics and native anterior cruciate ligament anatomy.

Inhibition of anterior tibial translation or axial tibial rotation prevents anterior cruciate ligament failure during impact compression

BACKGROUND

Anterior cruciate ligament injury is prevalent in activities involving large and rapid landing impact loads.

HYPOTHESIS

Inhibition of anterior tibial translation/axial tibial rotation forestalls the ligament from failing at the range of peak compressive load that can induce ligament failure when both factors are unrestrained.

STUDY DESIGN

Controlled laboratory study.

METHODS

Sixteen porcine knee specimens were mounted onto a material testing system at 70 degrees of flexion and were divided into 4 test groups: impact compression without restraint (IC), anterior tibial translation restraint (ICA), axial tibial rotation restraint (ICR), and combination of both restraints (ICC). Compression was successively repeated with increasing actuator displacement until ligament failure or visible bone fracture was observed. During compression, rotational and translational joint data were obtained using a motion capture system.

RESULTS

The IC group underwent ligament failure via femoral avulsion; the peak compressive force during failure ranged from 1.4 to 4.0 kN. The ICA, ICR, and ICC test groups developed visible bone fracture with the ligament intact; the peak compressive force during fracture ranged from 2.2 to 6.9 kN. Posterior femoral displacement and axial tibial rotation for the ICA and ICR groups, respectively, were significantly lower relative to the IC group (P < .05). Both factors were substantially reduced in the ICC group, but peak compressive force was higher compared with the IC group (P < .05).

CONCLUSION

Substantial inhibition of these factors in an impact setup, which can induce ligament failure with the factors unrestrained, was able to prevent failure.

CLINICAL RELEVANCE

Adequate inhibition of anterior tibial translation and axial tibial rotation by knee bracing during injurious impact is necessary for effective ligament protection.

Thigh strength and activation as predictors of knee biomechanics during a drop jump task

PURPOSE

To examine whether normalized quadriceps and hamstring strength would predict quadriceps and hamstring muscle activation amplitudes and whether these neuromuscular factors would predict knee kinematics and kinetics during a drop jump task.

METHODS

Thirty-nine females and 39 males were measured for isometric quadriceps and hamstring strength and were instrumented to obtain surface electromyography, kinematic, and kinetic measures during the initial landing of a drop jump. Multiple linear regressions first examined the relationship between thigh strength and activation then examined whether these neuromuscular variables were predictive of hip and knee flexion excursions, knee extensor moments (KEM), and anterior knee shear forces during the deceleration phase of the drop jump.

RESULTS

Females versus males produced lower normalized thigh strength and demonstrated greater quadriceps and hamstring activation amplitudes during the drop jump. Lower thigh muscle strength was a weak (males) to moderate (females) predictor of greater quadriceps activation amplitudes. However, thigh strength and activation were poor predictors of hip and knee joint excursions and KEM. Regardless of sex and thigh strength, anterior shear forces were greater in individuals who demonstrated less hip flexion and greater knee flexion excursions and greater peak quadriceps activation and internal KEM during the landing.

CONCLUSIONS

Although thigh muscle strength explained some of the variance in quadriceps and hamstring activation levels as measured with surface electromyography, we failed to support the hypothesis that these neuromuscular factors are strong predictors of sagittal plane hip and knee flexion excursions or KEM. Although greater quadriceps activation amplitude was a significant predictor of greater anterior tibial shear forces, its contribution was relatively small compared with kinematic and kinetic variables.

Recovery in functional non-copers following anterior cruciate ligament rupture as detected by gait kinematics

OBJECTIVES

To evaluate if gait compensation strategies for selected kinematic variables can be identified in anterior cruciate ligament (ACL) deficient non-copers using two-dimensional (2D) clinical gait analysis.

DESIGN

Prospective observational design, repeated measures.

SETTING

University hospital, out-patients department.

PATIENTS

Sixty-three patients that attended the acute knee screening service were diagnosed with an acute ACL rupture and consented to participate. A sub-set of 15 copers/adapters and 13 non-copers were eligible for final analysis because they were contactable for sub-classification and had gait analysis at 1 and 4 months post-injury.

MAIN OUTCOME MEASURES

2D video gait analysis for sagittal plane hip, knee and ankle kinematics and time-distance variables.

RESULTS

At 4 months post-injury non-copers demonstrated significantly less recovery of knee angle (F((1,1))=5.79, p<0.024), hip displacement angle (F((1,1))=4.89, p<0.036), step length (F((1,1)) =6.80, p=0.015), cadence (F((1,1))=5.85, p=0.023) and velocity (F((1,1))=10.89, p=0.003), compared to copers/adapters. Also non-copers demonstrated altered correlations between gait parameters.

CONCLUSION

At 4 months post-injury non-copers had an inferior gait performance compared to copers/adapters for kinematics and time-distance variables. 2D clinical kinematic gait analysis, particularly of the hip and knee can inform early rehabilitation techniques and monitor recovery.

The effect of anterior cruciate ligament reconstruction on kinematics of the knee with combined anterior cruciate ligament injury and subtotal medial meniscectomy: an in vitro robotic investigation

PURPOSE

The aims of this study were to determine: (1) the kinematic effect of subtotal medial meniscectomy on the anterior cruciate ligament (ACL)-deficient knee and (2) the effect of ACL reconstruction on kinematics of the knee with combined ACL deficiency and subtotal medial meniscectomy under anterior tibial and simulated quadriceps loads.

METHODS

Eight human cadaveric knees were sequentially tested using a robotic testing system under 4 conditions: intact, ACL deficiency, ACL deficiency with subtotal medial meniscectomy, and single-bundle ACL reconstruction using a bone-patellar tendon-bone graft. Knee kinematics were measured at 0 degrees, 15 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion under an anterior tibial load of 130 N and a quadriceps muscle load of 400 N.

RESULTS

Subtotal medial meniscectomy in the ACL-deficient knee significantly increased anterior and lateral tibial translations under the anterior tibial and quadriceps loads (P < .05). These kinematic changes were larger at high flexion (>or=60 degrees) than at low flexion angles. ACL reconstruction in knees with ACL deficiency and subtotal medial meniscectomy significantly reduced the increased anterior tibial translation, but could not restore anterior translation to the intact level with differences ranging from 2.6 mm at 0 degrees to 5.5 mm at 30 degrees of flexion. ACL reconstruction did not significantly affect the medial-lateral translation and internal-external tibial rotation in the presence of subtotal meniscectomy.

CONCLUSIONS

Subtotal medial meniscectomy in knees with ACL deficiency altered knee kinematics, especially at high flexion angles. ACL reconstruction significantly reduced the increased tibial translation in knees with combined ACL deficiency and subtotal medial meniscectomy, but could not restore the knee kinematics to the intact knee level.

CLINICAL RELEVANCE

This study suggests that meniscus is an important secondary stabilizer against anterior and lateral tibial translations and should be preserved in the setting of ACL reconstruction for restoration of optimal knee kinematics and function.

Evaluation of kinematics of anterior cruciate ligament-deficient knees with use of advanced imaging techniques, three-dimensional modeling techniques, and robotics

Measuring knee biomechanics in six degrees of freedom with acceptable accuracy has been proven to be technically challenging. At our bioengineering laboratory, we have employed both an in vitro robotic testing system and an in vivo combined dual fluoroscopic and magnetic resonance imaging technique to analyze the impact of anterior cruciate ligament rupture on the knee joint. When measuring the tibiofemoral kinematics of nine cadavers with the robotic testing system, we found that anterior cruciate ligament deficiency not only altered anterior translation and axial rotation of the tibia, but it also increased the medial translation of the tibia as well. The in vivo dual fluoroscopic imaging analysis of tibiofemoral kinematics in ten anterior cruciate ligament-deficient patients revealed analogous findings: an increased medial translation of the tibia of approximately 1 mm between 15 degrees and 90 degrees of flexion was found in anterior cruciate ligament-deficient knees, in addition to an increased anterior translation (approximately 3 mm) and internal rotation (approximately 2 degrees) of the tibia at low flexion angles. In a subsequent study of tibiofemoral cartilage contact, we found that the cartilage contact points shifted posteriorly--as was expected on the basis of the increased anterior tibial translation--as well as laterally on the surface of the tibial plateau. The data demonstrate how rupture of the anterior cruciate ligament initiates a cascade of events that eventually results in abnormal tibiofemoral cartilage contact in both the anteroposterior and mediolateral directions. If the restoration of normal knee homeostasis is the ultimate goal of ligament reconstruction, the normal function of the anterior cruciate ligament should be restored as closely as possible in all degrees of freedom.

Sex comparison of hamstring structural and material properties

BACKGROUND

Musculotendinous stiffness provides an estimate of resistance to joint perturbation, thus contributing to joint stability. Females demonstrate lesser hamstring stiffness than males, potentially contributing to the sex discrepancy in anterior cruciate ligament injury risk. However, it is unclear if the sex difference in hamstring stiffness is due to differences in muscle size or to inherent/material properties of the musculotendinous unit. It was hypothesized that hamstring stiffness, stress, strain, and elastic modulus would be greater in males than in females, and that hamstring stiffness would be positively correlated with muscle size.

METHODS

Stiffness was assessed in 20 males and 20 females from the damping effect imposed by the hamstrings on oscillatory knee flexion/extension following joint perturbation. Hamstring length and change in length were estimated via motion capture, and hamstring cross-sectional area was estimated using ultrasound imaging. These characteristics were used to calculate hamstring material properties (i.e., stress, strain, and elastic modulus).

FINDINGS

Stiffness was significantly greater in males than in females (P<0.001). However, stress, strain, and elastic modulus did not differ across sex (P>0.05). Stiffness was significantly correlated with cross-sectional area (r=0.395, P=0.039) and the linear combination of cross-sectional area and resting length (R(2)=0.156, P=0.043).

INTERPRETATION

Male's hamstrings possess a greater capacity for resisting changes in length imposed via joint perturbation from a structural perspective, but this property is similar across sex from a material perspective. Females demonstrate lesser hamstring stiffness compared to males in response to standardized loading conditions, indicating a compromised ability to resist changes in length associated with joint perturbation, and potentially contributing to the higher female ACL injury risk. However, the difference in hamstring stiffness is attributable in large part to differences in muscle size.

Comprehensive warm-up programme to prevent injuries in young female footballers: cluster randomised controlled trial

OBJECTIVE

To examine the effect of a comprehensive warm-up programme designed to reduce the risk of injuries in female youth football.

DESIGN

Cluster randomised controlled trial with clubs as the unit of randomisation.

SETTING

125 football clubs from the south, east, and middle of Norway (65 clusters in the intervention group; 60 in the control group) followed for one league season (eight months).

PARTICIPANTS

1892 female players aged 13-17 (1055 players in the intervention group; 837 players in the control group).

INTERVENTION

A comprehensive warm-up programme to improve strength, awareness, and neuromuscular control during static and dynamic movements.

MAIN OUTCOME MEASURE

Injuries to the lower extremity (foot, ankle, lower leg, knee, thigh, groin, and hip).

RESULTS

During one season, 264 players had relevant injuries: 121 players in the intervention group and 143 in the control group (rate ratio 0.71, 95% confidence interval 0.49 to 1.03). In the intervention group there was a significantly lower risk of injuries overall (0.68, 0.48 to 0.98), overuse injuries (0.47, 0.26 to 0.85), and severe injuries (0.55, 0.36 to 0.83).

CONCLUSION

Though the primary outcome of reduction in lower extremity injury did not reach significance, the risk of severe injuries, overuse injuries, and injuries overall was reduced. This indicates that a structured warm-up programme can prevent injuries in young female football players.

TRIAL REGISTRATION

ISRCTN10306290.

Mechanisms of noncontact anterior cruciate ligament injury

OBJECTIVE

To examine and summarize previous retrospective and observational studies assessing noncontact anterior cruciate ligament (ACL) injury mechanisms and to examine such reported ACL injury mechanisms based on ACL loading patterns due to knee loadings reported in in vivo, in vitro, and computer simulation studies.

DATA SOURCES

We searched MEDLINE from 1950 through 2007 using the key words anterior cruciate ligament + injury + mechanisms; anterior cruciate ligament + injury + mechanisms + retrospective; and anterior cruciate ligament + injury + mechanisms + video analysis.

STUDY SELECTION

We selected retrospective studies and observational studies that specifically examined the noncontact ACL injury mechanisms (n = 7) and assessed ACL loading patterns in vivo, in vitro, and using computer simulations (n = 33).

DATA EXTRACTION

The motion patterns reported as noncontact ACL injury mechanisms in retrospective and observational studies were assessed and critically compared with ACL loading patterns measured during applied external or internal (or both) forces or moments to the knee.

DATA SYNTHESIS

Noncontact ACL injuries are likely to happen during deceleration and acceleration motions with excessive quadriceps contraction and reduced hamstrings co-contraction at or near full knee extension. Higher ACL loading during the application of a quadriceps force when combined with a knee internal rotation moment compared with an external rotation moment was noted. The ACL loading was also higher when a valgus load was combined with internal rotation as compared with external rotation. However, because the combination of knee valgus and external rotation motions may lead to ACL impingement, these combined motions cannot be excluded from the noncontact ACL injury mechanisms. Further, excessive valgus knee loads applied during weight-bearing, decelerating activities also increased ACL loading.

CONCLUSIONS

The findings from this review lend support to ACL injury prevention programs designed to prevent unopposed excessive quadriceps force and frontal-plane or transverse-plane (or both) moments to the knee and to encourage increased knee flexion angle during sudden deceleration and acceleration tasks.

The relationship between anterior tibial shear force during a jump landing task and quadriceps and hamstring strength

BACKGROUND

Eccentric quadriceps contraction during landing and the resulting anterior tibial shear force are anterior cruciate ligament injury risk factors, while hamstring contraction limits anterior cruciate ligament loading. Anterior tibial shear force is derived from quadriceps and hamstring co-contraction, and a greater quadriceps/hamstring strength ratio has been associated with heightened lower extremity injury risk. The purpose of this investigation was to evaluate relationships between anterior tibial shear force during landing and quadriceps and hamstring strength.

METHODS

Anterior tibial shear force was calculated during a jump landing task in 26 healthy females. Isokinetic eccentric quadriceps strength and concentric hamstrings strength were assessed at 60 degrees /s, 180 degrees /s, and 300 degrees /s. Correlational analyses were conducted to evaluate relationships between lower extremity strength and anterior tibial shear force.

FINDINGS

Quadriceps (r=0.126 to 0.302, P>0.05) and hamstrings strength (r=-0.019 to 0.058, P>0.05) and the quadriceps/hamstring ratio (r=0.036 to 0.127, P>0.05) were not significant predictors of anterior tibial shear force.

INTERPRETATION

Quadriceps and hamstring strength are not indicative of sagittal-plane knee loading during landing. Contractile force resulting from maximal strength testing may not represent that produced during landing, as it is unlikely that landing requires maximal effort. Additionally, peak anterior tibial shear force, quadriceps torque, and hamstrings torque are generated at different points in the knee flexion/extension range of motion. Therefore, peak anterior tibial shear force is a function of the available strength at a given point in the range of motion rather than of peak strength. These findings illustrate the limitations of peak strength values in predicting dynamic loading during landing.