ACL deficiency affects stride-to-stride variability as measured using nonlinear methodology

Previous studies suggested that the small fluctuations present in movement patterns from one stride to the next during walking can be useful in the investigation of various pathological conditions. Previous studies using nonlinear measures have resulted in the development of the “loss of complexity hypothesis” which states that disease can affect the variability and decrease the complexity of a system, rendering it less able to adjust to the ever changing environmental demands. The nonlinear measure of the Lyapunov Exponent (LyE) has already been used for the assessment of stride-to-stride variability in the anterior cruciate ligament (ACL) deficient knee in comparison to the contralateral intact knee. However, there is biomechanical evidence that after ACL rupture, adaptations are also present in the contralateral intact knee. Thus, our goal was to investigate stride-to-stride variability in the ACL deficient knee as compared to a healthy control knee. Seven subjects with unilateral ACL deficiency and seven healthy controls walked at their self-selected speed on a treadmill, while three-dimensional knee kinematics was collected for 80 consecutive strides. A nonlinear measure, the largest LyE was calculated from the resulted knee joint flexion-extension data of both groups. Larger LyE values signify increased variability and increased sensitivity to initial conditions. Our results showed that the ACL deficient group exhibited significantly less variable walking patterns than the healthy control. These changes are not desirable because they reflect decreases in system’s complexity, which indicates narrowed functional responsiveness, according to the “loss of complexity hypothesis.” This may be related with the increased future pathology found in ACL deficient patients. The methods used in the present paper showed great promise to assess the gait handicap in knee injured patients

A Novel Approach to Measure Variability in the Anterior Cruciate Ligament Deficient Knee During Walking: The Use of the Approximate Entropy in Orthopaedics

Objective. The evaluation of variability of biological rhythmic activities through measures such as Approximate Entropy (ApEn) has provided important information regarding pathology in disciplines such as cardiology and neurology. This research lead to the “loss of complexity hypothesis” where decreased variability is associated with loss of healthy flexibility rendering the system more rigid and unable to adapt to stresses. ApEn as a measure of variability and complexity, correlates well with pathology while, in some cases, it is predictive of subsequent clinical changes. The study of human gait could benefit from the application of ApEn since it is also a rhythmical oscillation. Our aim was to assess the variability of the ACL deficient knee, since ACL rupture is a common musculoskeletal injury and is accompanied by altered gait patterns and future pathology in the joint. We hypothesized that the ACL deficient knee will exhibit more regular and less variable walking patterns than the contralateral intact knee. Methods. Ten subjects with unilateral deficiency walked on a treadmill at their self-selected speed, 20% faster, and 20% slower, while kinematics were collected (50 Hz) from 80 consecutive strides for each condition. The ApEn of the resulted knee joint flexion-extension time series was calculated. Results. Significantly smaller ApEn values were found in the ACL deficient knee when compared with the contralateral intact (F = 5.57, p = 0.022), for all speeds. ApEn values significantly increased (F = 5.79, p = 0.005) with increases in walking speed. Conclusions. The altered properties of the ACL deficient knee, which exhibits more regular and less variable patterns than the contralateral intact knee, may decrease the adaptability of the system rendering it less able to adjust to perturbations. This could explain the increased future pathology found in the deficient knee. ApEn can be an important tool in assessing pathology and therapeutic interventions in orthopaedics

Tibial Rotation in Anterior Cruciate Ligament (ACL)-Deficient and ACL-Reconstructed Knees

Excessive tibial rotation has been documented in ACL deficiency during walking. ACL reconstruction has been unable to correct this abnormality in activities that are more demanding than walking and involve both anterior and rotational loading of the knee. These findings persist regardless of graft selection for the ACL reconstruction [bone-patellar tendon-bone (BPTB) or semitendinosus-gracilis (ST/G)]. Based on this research work, we propose a theoretical perspective for the development of osteoarthritis in both the ACL deficient and the ACL reconstructed knee. We propose that excessive tibial rotation will lead to abnormal loading of the cartilage areas that are not commonly loaded in the healthy knee. Overtime this abnormal loading will lead to osteoarthritis. We hypothesize that the development of new surgical procedures and grafts, such as a more horizontally oriented femoral tunnel or a double-bundle ACL reconstruction could possibly restore tibial rotation to normal levels and prevent future knee pathology. However, in-vivo gait analysis studies are needed, that will examine the effects of these surgical procedures on tibial rotation. Prospective in-vivo and in-vitro studies are also necessary to verify or refute our theoretical proposition for the development of osteoarthritis

Anterior Cruciate Ligament Reconstruction With a Quadrupled Hamstring Autograft Does Not Restore Tibial Rotation

As a result of the morbidity associated with anterior cruciate ligament (ACL) reconstruction with a bone–patellar–tendon– bone graft, many orthopaedic surgeons prefer hamstrings as the graft for ACL reconstruction. However, this selection is not based on solid scientific evidence. In vitro research shows that this graft cannot restore control of tibial rotation. Our recent in vivo research work has also demonstrated the same result. In particular, patients undergoing ACL repair who were reconstructed with a quadrupled hamstring tendon graft showed excessive tibial rotation during a dynamic activity when compared with healthy control subjects. Although the hamstring tendon graft has a more advantageous biomechanical profile than other grafts, it seems that it could not replicate the normal ACL regarding its actual anatomy and functional rotational abilities. The improvement and development of new surgical procedures and grafts seems to be the only way to address this problem of excessive tibial rotation. We also propose that the inability of current operative techniques to restore tibial rotation to normal preinjury levels can be the cause of future pathology and osteoarthritis found in ACL-reconstructed patients in the long-term. Abnormal rotational movements could result in loading of the knee cartilage in areas that are not commonly loaded in a healthy knee. These areas resulting from insufficient cartilage thickness may not be able to withstand the newly introduced loading and, over time, knee osteoarthritis is developed

Electromechanical delay of the knee extensor muscles is not altered after harvesting the patellar tendon as a graft for ACL reconstruction: implications for sports performance

Although the scar tissue, which heals the donor site defect, has different elasticity from the neighbouring patellar tissue, it remains unclear if this scar tissue can lead to the changes of the electromechanical delay (EMD) of the knee extensor muscles. If such changes do exist, they can possibly affect both the utilization of the stored energy in the series elastic component, as well as the optimal performance of the knee joint movement. The purpose of this study was to investigate the influence of harvesting the patellar tendon during anterior cruciate ligament (ACL) reconstruction and the associated patellar tendon scar tissue development on the EMD of the rectus femoris (RF) and vastus medialis (VM) muscles. Seventeen patients who underwent an ACL reconstruction using the medial third of the patellar tendon were divided in two groups based upon their postoperative time interval. Maximal voluntary contraction from the knee extensors, surface EMG activity, and ultrasonographic measurements of the patellar tendon cross-section area were obtained from both knees. Our results revealed that no significant changes for the maximal voluntary contraction of the knee extensors and for the EMD of the RF and the VM muscles due to patellar scar tissue development after harvesting the tendon for ACL reconstruction. The EMD, as a component of the stretch reflex, is important for the utilization of the stored energy in the series elastic component and thus, optimal sports performance. However, from our results, it can be implied that the ACL reconstruction using a patellar tendon graft would not impair sports performance as far as EMD is concerned

Tibial Rotation is Not Restored after ACL Reconstruction with a Hamstring Graft

Recent research suggests ACL reconstruction does not re- store tibial rotation to normal levels during high demand activities when a bone-patellar tendon-bone graft is used. We asked if an alternative graft, the semitendinosus-gracilis (ST/G) tendon graft, could restore tibial rotation during a high demand activity. Owing to its anatomic similarity with the normal ACL we hypothesized the ST/G graft could re- store excessive tibial rotation to normal healthy levels along with a successful reinstatement of the clinical stability of the knee. We assessed tibial rotation in vivo, using gait analysis. We compared the knees of ACL reconstructed patients with an ST/G graft to their intact contralateral and healthy con- trols during a pivoting task that followed a stair descent. We also evaluated knee stability after ACL reconstruction with standard clinical tests. ACL reconstruction with the ST/G graft and with current techniques did not restore tibial ro- tation to previous physiological levels during an activity with increased rotational loading at the knee, although abnormal anteroposterior (AP) tibial translation was restored

Effectiveness of Reconstruction of the Anterior Cruciate Ligament With Quadrupled Hamstrings and Bone-Patellar Tendon-Bone Autografts: An In Vivo Study Comparing Tibial Internal-External Rotation

Background: The 2 most frequently used autografts for anterior cruciate ligament reconstruction are the bone-patellar tendon- bone and the quadrupled hamstrings tendon. Hypothesis: Hamstring tendon graft is superior to patellar tendon graft in restoring tibial rotation during highly demanding activities because of its superiority in strength and linear stiffness and because it is closer morphologically to the anatomy of the natural anterior cruciate ligament. Study Design: Case control study; Level of evidence, 3. Methods: Eleven patients with patellar tendon graft anterior cruciate ligament reconstruction, 11 patients with hamstring tendon graft anterior cruciate ligament reconstruction, and 11 controls were assessed. Kinematic data were collected (50 Hz) with a 6-camera optoelectronic system while the subjects descended stairs and, immediately after, pivoted on their landing leg. The dependent variable examined was the tibial internal-external rotation during pivoting. All patients in both groups were also assessed clinically and with the use of a KT-1000 arthrometer to evaluate anterior tibial translation. Results: The results demonstrated that reconstructions with either graft successfully restored anterior tibial translation. However, both anterior cruciate ligament reconstruction groups had significantly increased tibial rotation when compared with the controls, whereas no differences were found between the 2 reconstructed groups. Conclusion: The 2 most frequently used autografts for anterior cruciate ligament reconstruction cannot restore tibial rotation to normal levels. Clinical Relevance: New surgical techniques are needed that can better approximate the actual anatomy and function of the anterior cruciate ligament

Electromechanical Delay of the Knee Flexor Muscles Is Impaired After Harvesting Hamstring Tendons for Anterior Cruciate Ligament Reconstruction

Background Changes in electromechanical delay during muscle activation are expected when there are substantial alterations in the structural properties of the musculotendinous tissue. In anterior cruciate ligament reconstruction, specific tendons are being harvested for grafts. Thus, there is an associated scar tissue development at the tendon that may affect the corresponding electromechanical delay. Purpose This study was conducted to investigate whether harvesting of semitendinosus and gracilis tendons for anterior cruciate ligament reconstruction will affect the electromechanical delay of the knee flexors. Study Design Case-control study; Level of evidence, 3. Methods The authors evaluated 12 patients with anterior cruciate ligament reconstruction with a semitendinosus and gracilis autograft, 2 years after the reconstruction, and 12 healthy controls. Each participant performed 4 maximally explosive isometric contractions with a 1-minute break between contractions. The surface electromyographic activity of the biceps femoris and the semitendinosus was recorded from both legs during the contractions. Results The statistical comparisons revealed significant increases of the electromechanical delay of the anterior cruciate ligament–reconstructed knee for both investigated muscles. Specifically, the electromechanical delay values were increased for both the biceps femoris (P = .029) and the semitendinosus (P = .005) of the reconstructed knee when compared with the intact knee. Comparing the anterior cruciate ligament–reconstructed knee against healthy controls revealed similar significant differences for both muscles (semitendinosus, P = .011; biceps femoris, P = .024). Conclusion The results showed that harvesting the semitendinosus and gracilis tendons for anterior cruciate ligament reconstruction significantly increased the electromechanical delay of the knee flexors. Increased hamstring electromechanical delay might impair knee safety and performance by modifying the transfer time of muscle tension to the tibia and therefore affecting muscle response during sudden movements in athletic activities. However, further investigation is required to identify whether the increased electromechanical delay of the hamstrings can actually influence optimal sports performance and increase the risk for knee injury in athletes with anterior cruciate ligament reconstructions

The effect of the walking speed on the stability of the anterior cruciate ligament deficient knee

Background. The reasons behind the development of future pathology in individuals with anterior cruciate ligament deficiency are unknown. This is due to the lack of appropriate methods to assess functional dynamic knee stability. In this study, we investigated the effect of walking speed on the functional dynamic stability of the anterior cruciate ligament deficient knee. We defined functional dynamic stability as local stability or the sensitivity of the knee to small perturbations. The natural stride-to-stride variations that exist during locomotion reflect exactly the presence of these perturbations. We hypothesized that speed will affect local stability in the deficient knee, especially when compared with the contralateral intact. Methods. Ten subjects with unilateral deficiency walked on a treadmill at their self-selected speed, 20% faster, and 20% slower, while kinematic data were collected (50 Hz) for 100 consecutive footfalls for each condition. The largest Lyapunov Exponent of the resulted knee joint flexion–extension time series was calculated to quantify local stability. Findings. The deficient knee was significantly more locally unstable than the contralateral knee. Furthermore, increases in walking speed did not affect local stability for our subject population. Interpretations. The altered local stability may render the deficient knee less adaptable to the ever-changing environmental demands. This may explain the increased future pathology found in these knees. However, future efforts should attempt to evaluate this speculation using longitudinal studies. We also propose that the tools utilized in this study can be used eventually to assess functional dynamic knee stability in clinical gait analysis

High intensity running results in an impaired neuromuscular response in ACL reconstructed individuals

Anterior cruciate ligament (ACL) reconstruction reestablishes electromyographic activity during moderate activities such as walking but is unclear if this is also the case in sports activities such as high intensity running that results in accumulation of metabolic fatigue. Nine bone-patella tendon-bone ACL reconstructed athletes were evaluated 19.2 (5.7) months post-operatively using a telemetric electromyographic system. The neuromuscular response of vastus lateralis and biceps femoris muscles was tested bilaterally on separate occasions during 10 min running at moderate intensity (20% below the lactate threshold) and 10 min running at high intensity (40% above the lactate threshold). During moderate intensity running, electromyographic activity did not change for either leg. During high intensity running, electromyographic activity did not change for the vastus lateralis of the ACL reconstructed leg [267.8 (142.8)–263.8 (128.9) μV, P \u3e 0.05] while it increased significantly [294.2 (120.6)–317.1 (140.5) μV, P = 0.03] for the vastus lateralis of the intact leg. High intensity exercise that is associated with accumulation of metabolic fatigue, results in an impaired neuromuscular response for the vastus lateralis muscle of the ACL reconstructed leg