Recent research progress from biological perspective on the mechanism of formation of osteoarthritis after anterior cruciate ligament injury

The anterior cruciate ligament(ACL)mainly plays a role in stabilizing the knee joint by limiting the forward translation of tibial force and rotational force at the tibial joint,and if this ligament is damaged,it will cause joint pain,limited mobility,knee instability,etc.According to related studies,the incidence of traumatic osteoarthritis(PTOA)after ACL injury is as high as 87%,although many studies have shown that patients with ACL injury are susceptible to PTOA,but the exact mechanism is currently unknown.This may be related to biological,structural,and mechanical factors caused by the ligament injury.Previous studies have shown that elevated inflammatory mediators in the joint cavity following ACL injury can lead to chondrocytes necrosis and degradation of the cartilage matrix.These potential biochemical mediators contribute to PTOA formation,and early intervention can reduce future episodes of PTOA.In recent years,many scholars have devoted themselves to studying the potential important factors and signaling pathways involved in the formation of osteoarthritis after ACL injury,and exploring its molecular mechanism,which has led to great progress in this field.This paper mainly studies and discusses the mechanism of osteoarthritis formation after ACL injury from the biological perspective.

The Prevalence Type of the Meniscus Tear in Patients with Anterior Cruciate Ligament (ACL) Injury, in Abu Arish General Hospital, Jazan, KSA

Background: The anterior cruciate ligament (ACL) is the main structure that prevents the forward movement of the tibia about the femur Meniscus tear which is a common finding in patients with anterior cruciate ligament (ACL) injury. Aim: To investigate the prevalence of types of meniscus tears in patients with Anterior Cruciate Ligament (ACL) Injury. Methods: A retrospective study was conducted among inpatients. Clinical evaluation included side-to-side difference in anterior tibial translation (ATT) as measured by a KT-1000 arthrometer (MEDmetric Corp) and a grade of pivot-shift test at final follow-up in all patients. Subsequent meniscal tear was defined by symptoms of joint line pain and/or locking or joint effusion requiring surgical treatment. Results: Most of patients were males (92.6%). The patients were categorized into 5 groups according to age with a mean of age 32.8 ± 10.6. The most common causes of ACL injury were falling down (43.2%), trauma (38.1%) or knee torsion (18.8%). Medial meniscal tear was found in 92 knees (55.7%), while lateral meniscal tear was found in 19 knees (10.8%) and the most common type was the longitudinal tear that was found in 31 knees (17.6%). Similarly, 66.7% of the meniscal flap tears and half of the meniscal bucket-handle tears were significantly associated with loose body (P Conclusion: The present study demonstrated that meniscus tears are more common in individuals with chronic ACL rupture. The main factors contributing to ACL injury were classified as falls, trauma, and knee torsion. Gender was identified as a critical determinant in the etiology of ACL injury. The occurrence of a ramp lesion was associated longitudinal meniscal tears, whereas chodoral injury was associated with the majority of meniscal flap tears and meniscal bucket-handle tears.

Anatomical Risk Factors for Rupture of the Anterior Cruciate Ligament:Magnetic Resonance Imaging Based Knee Joint Assessment

Anterior cruciate ligament (ACL) rupture is one of the most frequently encountered traumatic ligamentous lesions of the knee. Several intrinsic and extrinsic factors are linked to this lesion. Anatomical factors increase the anterior translation of the knee and thus promote the stretching and rupture of the anterior cruciate ligament. Objectives: To determine the anatomical risk factors favouring ACL rupture by comparing morphometric parameters of patients with knee ACL rupture to patients without ACL rupture, as well as the intercondylar notch index and the tibial slopes of the two groups and describing the ruptured ACLs and associated signs. Materials and Methods: We conducted a case-control descriptive analytical study in imaging centres of the General Henri Mondor of Aurillac Hospital Centre in France (CHM) and the Jordan Medical Centre of Yaoundé in Cameroon (CMJ). MRI exam protocols included T1 SE, T2 SE, proton density and Fat Sat sequences, with slices in all three planes. Morphometry knee variables measured in our study were: intercondylar notch index and the tibial slopes. These measurements were obtained from images stored in DICOM format and post processing software OsiriX MD®for CMJ patients and Explore®for CHM patients. Results: The study included 92 individuals, 38 in the case group and 54 in the control group. The mean age was 36.6 years for both groups;35.5 years for the cases and 37.4 years for the controls. The sex ratio was 1.87 men for 1 woman in both groups;2.16 men for 1 woman for the case group. 53% of ACL ruptures are partial, with the predominant direct sign being morphologic and signal abnormalities of the ACL. The most significant indirect sign of ACL rupture was mirror-image bone contusion that was observed in 47.3% of cases. In the case group, the mean lateral tibial slope was 4.003°, whereas it was 2.92°in the control group. The comparison of means was estimated at approximately 0.039 (p Conclusion: The increase in the lateral tibial slope was a risk factor for anterior cruciate ligament rupture in our study population. Intercondylar notch index and medial tibial slope did not show any statistical significant difference.

Five Strand Hamstring Tendon Autograft for Anterior Cruciate Ligament Reconstruction Provides No Benefit over the Gold Standard Four Strand Repair for Anterior Stability of the Knee: A Prospective Cohort Study

The Four-Strand Hamstring Tendon Autograft has been long established as the gold standard for surgical reconstruction of the Anterior Cruciate Ligament. Some studies have suggested wider grafts, such as a Five-Strand hamstring graft, may provide greater strength and a larger scaffold for incorporation of the graft into the bone tunnels, leading to greater postoperative anterior stability of the knee. 28 (n = 18 Four-Strand and n = 10 Five-Strand) patients with planned ACL reconstructive surgery by a single surgeon were recruited for this study. The KT-1000 Arthrometer (MED metric, CA, USA) was used to quantify AP translation in the subjects’ knees before (T0) and after surgery at 6 (T1) and 12 (T2) weeks. At 12 weeks there was significantly higher (p = 0.01) mean anterior laxity on Maximum Manual Test in the Five- Strand group (9.1 ± 1.7 mm) than the Four Strand Group (6.9 ± 2.3 mm). Further, there were significantly higher mean side-to-side differences (p = 0.01) on Maximum Manual Test in the Five-Strand cohort (5.1 ± 3.5 mm) compared to the Four-Strand cohort (1.9 ± 2.2 mm). A significantly larger positive mean change in anterior laxity (p = 0.02) from 6 - 12 weeks was evident in the Five-Strand group (1.4 ± 0.9) than the Four-Strand group (-0.3 ± 1.9 mm). No significant correlations were seen between graft widths and measures of anterior stability on KT-1000. This study illustrated that there was no benefit to using a Five-Strand Hamstring Tendon Autograft when compared to the gold standard Four-Strand Repair specifically with regards to anterior stability of the knee.

Lateral femoral tunnel preparation and graft fixation for anterior cruciate ligament reconstruction–A discussion

This article provides a discussion and commentary around the recent advances in arthroscopic anterior cruciate ligament reconstruction(ACLR),with a focus on the aspects of lateral femoral tunnel preparation and graft fixation techniques.The paper explores and comments on a recently published review by Dai et al,titled"Research progress on preparation of lateral femoral tunnel and graft fixation in ACLR",while providing insight into its relevance within the field of ACLR,and recommendations for future research.

Cyclops syndrome following anterior cruciate ligament reconstruction: Can relapse occur after surgery?

Symptomatic cyclops lesions are complications that can be seen at rates of up to approximately 10%after anterior cruciate ligament reconstruction.However,recurrent cyclops lesions have rarely been documented.There are case rare series in the literature regarding the treatment of recurrent cyclops lesion.Future large studies are needed to investigate factors contributing to the development of cyclops lesions and syndrome and treatment options.

Demographic characteristics of patients who underwent anterior cruciate ligament reconstruction at a tertiary care hospital in India

BACKGROUND Anterior cruciate ligament(ACL)tears are common sports-related injuries.Their incidence is not the same either for all the sports or for the same sport across various nations.This information is maintained by many sports leagues in their registries.However,very few nationwide registries exist for such injuries.This study is carried out to know the demographic characteristics of patients who underwent ACL reconstruction at our hospital in India.AIM To know the demographic characteristics of patients who underwent ACL reconstruction at a tertiary care hospital in India.METHODS All the patients who underwent ACL reconstruction from January 2020 to December 2021 were retrospectively studied.Patients with multi-ligament injuries or a history of previous knee surgery were excluded.The patients’history was obtained from the hospital records,they were interviewed telephonically,and online questionnaires were given.Their demographic data was analyzed and compared to the existing literature.RESULTS A total of 124 patients were operated on for ACL reconstruction during this period.The mean age of the patients was 27.97 years.One hundred and thirteen patients(91.1%)were male and 11(8.9%)were female.The majority of the patients(47.6%)sustained this injury by road traffic accidents(RTA)followed by sportsrelated injuries(39.5%).The commonest presenting complaint was giving way of the knee in 118 patients(95.2%).The mean duration from the injury to the first hospital visit among the patients was 290.1 d.The mean duration from the injury to surgery was 421.8 d.CONCLUSION ACL patients’demography is different in developing nations as compared to the developed world.RTA are the leading cause of ACL injuries and are followed by recreational sports as a cause.There is delayed access to healthcare leading to delayed diagnosis as well as even greater time to surgery.This,in turn,leads to poorer prognosis and longer rehabilitation.National registries for developing nations are the need of the hour due to the different demographics of ACL injuries in developing countries.

Current practice variations in the management of anterior cruciate ligament injuries in Croatia

AIM: To investigate current preferences and opinions on the diagnosis, treatment and rehabilitation of patients with anterior cruciate ligament(ACL) injury in Croatia. METHODS: The survey was conducted using a questionnaire which was sent by e-mail to all 189 members of the Croatian Orthopaedic and Traumatology Association. Only respondents who had performed at least one ACL reconstruction during 2011 were asked to fill out the questionnaire. RESULTS: Thirty nine surgeons responded to the survey. Nearly all participants(95%) used semitendinosus/gracilis tendon autograft for reconstruction and only 5% used bone-patellar tendon-bone autograft. No other graft type had been used. The accessory anteromedial portal was preferred over the transtibial approach(67% vs 33%). Suspensory fixation was the most common graft fixation method(62%) for the femoral side, followed by the cross-pin(33%) and bioabsorbable interference screw(5%). Almost all respondents(97%) used a bioabsorbable interference screw for tibial side graft fixation. CONCLUSION: The results show that ACL reconstruction surgery in Croatia is in step with the recommendations from latest world literature.

Imaging of the anterior cruciate ligament

The anterior cruciate ligament(ACL)is an important structure in maintaining the normal biomechanics of the knee and is the most commonly injured knee ligament.However,the oblique course of the ACL within the intercondylar fossa limits the visualization and assessment of the pathology of the ligament.This pictorial essay provides a comprehensive and illustrative review of the anatomy and biomechanics as well as updated information on different modalities of radiological investigation of ACL,particularly magnetic resonance imaging.

Effect of suspension training on neuromuscular function, postural control, and knee kinematics in anterior cruciate ligament reconstruction patients

BACKGROUND Suspension training(SET)is a method of neuromuscular training that enables the body to carry out active training under unstable support through a suspension therapy system.However,there have been few reports in the literature on the application of SET to anterior cruciate ligament reconstruction(ACLR)patients.It is not clear what aspects of the patient's function are improved after SET.AIM To investigate the effect of SET on the neuromuscular function,postural control,and knee kinematics of patients after ACLR surgery.METHODS Forty participants were randomized to an SET group or a control group.The SET group subjects participated in a SET protocol over 6 wk.The control group subjects participated in a traditional training protocol over 6 wk.Isokinetic muscle strength of the quadriceps and hamstrings,static and dynamic posture stability test,and relative translation of the injured knee were assessed before and after training.RESULTS The relative peak torque of the quadriceps and hamstrings in both groups increased significantly(P<0.001),and the SET group increased by a higher percentage than those in the control group(quadriceps:P=0.004;hamstrings:P=0.011).After training,both groups showed significant improvements in static and dynamic posture stability(P<0.01),and the SET group had a greater change than the control group(P<0.05).No significant improvement on the relative translation of the injured knee was observed after training in either group(P>0.05).CONCLUSION Our findings show that SET promotes great responses in quadriceps and hamstring muscle strength and balance function in ACLR patients.

The 45-Degree Arthroscope Improves Visualization of the Femoral Attachment of the Anterior Cruciate Ligament

Background: Exposure of the insertion site of the anterior cruciate ligament (ACL) is important for appropriate tunnel placement in ACL reconstruction surgery. However, observing the femoral ACL insertion site via the standard anterolateral portal is sometimes difficult. In this study, we compared views of the femoral ACL insertion site between 30-degree and the 45-degree arthroscopes. Methods: We first inserted the 30-degree and the 45-degree arthroscope into the anterolateral portal of a knee simulator in which we had drawn a lattice pattern on the lateral intercondylar notch based on the quadrant method. Next, we compared the arthroscopic views provided by the 30-degree and 45-degree arthroscopes during ACL reconstruction surgery by measuring the area of the lateral intercondylar notch visible through each of the arthroscopes. Results: In the knee simulator, the 45-degree arthroscope showed the entire area of the lateral intercondylar notch, whereas the 30-degree arthroscope had to be introduced more deeply to show the most superior and posterior quadrant, where the attachment of the anteromedial bundle of ACL is located. During the ACL reconstruction, the area of the lateral intercondylar notch in the field of view was larger through the 45-degree arthroscope than through the 30-degree arthroscope. Conclusion: The 45-degree arthroscope provides a better view of the femoral ACL insertion site via the anterolateral portal, which may be helpful during ACL reconstruction.

Osteoarthritis action alliance consensus opinion-best practice features of anterior cruciate ligament and lower limb injury prevention programs

AIM To identify best practice features of an anterior cruciate ligament(ACL) and lower limb injury prevention programs(IPPs) to reduce osteoarthritis(OA).METHODS This consensus statement started with us performing a systematic literature search for all relevant articles from 1960 through January 2017 in PubM ed, Web of Science and CINAHL. The search strategy combined the Medical Subject Heading(Me SH) and keywords for terms:(1) ACL OR "knee injury" OR "anterior cruciate ligament";(2) "prevention and control" OR "risk reduction" OR "injury prevention" OR "neuromuscular training"; and(3) meta-analysis OR "systematic review" OR "cohort study" OR randomized. We found 166 different titles. The abstracts were reviewed for pertinent papers. The papers were reviewed by at least two authors and consensus of best practice for IPP to prevent OA was obtained by conference calls and e-mail discussions. All authors participated in the discussion.RESULTS The best practice features of an IPP have the following six components:(1) lower extremity and core strengthening;(2) plyometrics;(3) continual feedback to athletes regarding proper technique;(4) sufficient dosage;(5) minimal-to-no additional equipment; and(6) balance training to help prevent injuries. Exercises focused on preventing ankle sprains, hamstring injuries and lateral trunk movements are important. Plyometric exercises should focus on correcting knee valgus movement.Exercises should focus on optimizing the hamstring to quadriceps strength ratio. In order for IPP to be successful, there should be increased education and verbal feedback along with increased athletic compliance. Additional equipment is not necessary. Balance training alone does not significantly reduce injuries, but is beneficial with other exercises. Not enough evidence to recommend stretching and agility exercises, with no ill effects identified. Therefore, we suggest making these optional features.CONCLUSION Best practice features for ACL and lower limb IPPs to help prevent OA contain six key components along with two optional.

Consensus Delphi study on guidelines for the assessment of anterior cruciate ligament injuries in children

Background:Knee examination guidelines in minors are intended to aid decisionmaking in the management of knee instability.Clinical question:A Delphi study was conducted with a formal consensus process using a validated methodology with sufficient scientific evidence.A group consensus meeting was held to develop recommendations and practical guidelines for use in the assessment of instability injuries in children.Key findings:there is a lack of evidence to analyse anterior cruciate ligament injuries in children and their subsequent surgical management if necessary.Diagnostic guidelines and clinical assessment of the patient based on a thorough examination of the knee are performed and a guide to anterior cruciate ligament exploration in children is developed.Clinical application:In the absence of a strong evidence base,these established guidelines are intended to assist in that decision-making process to help the clinician decide on the most optimal treatment with the aim of benefiting the patient as much as possible.Following this expert consensus,surgical treatment is advised when the patient has a subjective sensation of instability accompanied by a pivot shift test++,and may include an anterior drawer test+and a Lachman test+.If these conditions are not present,the conservative approach should be chosen,as the anatomical and functional development of children,together with a physiotherapy programme,may improve the evolution of the injury.

Preseason elimination impact on anterior cruciate ligament injury in the national football league

BACKGROUND Anterior cruciate ligament(ACL)injuries represent detrimental injuries in the National Football League(NFL).A significant portion of these injuries often occur in preseason exhibitions.The Coronavirus disease 2019 pandemic presented a unique disruption to preseason NFL football with the cancelation of all preseason games.AIM To compare the incidence of ACL tears through the first eight weeks of the NFL season in 2020 to the mean incidence over the previous 5 seasons(2015-2019)and determine if there was any change in incidence with the elimination of the preseason.METHODS NFL players who suffered ACL tears during the preseason and first eight weeks of the NFL season from 2015-2020 were identified.The number of ACL injuries for the 2015-2019 seasons was compared to the 2020 season for four different timeframes.For each analysis,the cumulative number of ACL injuries to that time point was used to calculate the percent difference for descriptive analysis.Additionally,the number of teams with at least one player suffering an ACL tear were identified and compared using Chi-Squared testing.Finally,a cumulative relative risk was calculated for each week played.RESULTS There were 14 ACL tears through the first four games of the 2020 season,a 118.8%(14 vs 6.4)increase in comparison to the 5-year average over the first 4 regular season weeks of 2015-2019.However,when accounting for injuries occurring during the preseason from 2015-2019,there were 18.6%(14 vs 17.2)fewer total ACL injuries through regular season week 4 with no significant difference in percentage of teams impacted when these preseason injuries were accounted for P=0.394.Results were similar(19 vs 17.2)over 8 total games played(whether regular season or preseason),and over 8 regular season games(P=0.196,P=0.600).CONCLUSION The elimination of the NFL preseason resulted in a higher rate of injuries during the first 4 games of the regular season.However,these increases are offset by the injuries typically sustained during the preseason.This suggests there may be front-loading of injuries over the course of an NFL season,such that players may be more prone to injury when the intensity of play suddenly increases,whether in the preseason or regular season.

Biomechanical Risk Assessment of Non-Contact Anterior Cruciate Ligament Injury in Taekwondo Athletes

Non-contact anterior cruciate ligament(ACL)injury can occur in many sports.It is interrelated with gender,anatomy,biomechanics,and neuromuscular control.Taekwondo athletes have a higher incidence of ACL injury than athletes from other sports.Objective:This study aimed to determine the biomechanical gender differences and mechanism of taekwondo athletes with ACL injury.Methods:A total of 28 taekwondo athletes(aged 14–19 years)were randomly selected and grouped by gender.Feet high floor,one foot high floor,and single leg squat were analyzed by a Vicon motion analysis system and Kistler 3D force platform for action.The knee joint angle and ground force were evaluated.Results:Results demonstrated biomechanical differences in knee joint between male and female athletes.Conclusion:ACL injury in taekwondo female athletes indicated the biomechanical mechanism of the knee joint,and it can be prevented by neuromuscular control training.

Recurrent cyclops lesion after primary anterior cruciate ligament reconstruction using bone tendon bone allograft:A case report

BACKGROUND Cyclops lesions are a known complication of anterior cruciate ligament(ACL)reconstruction,with symptomatic cyclops syndrome occurring in up to 11%of surgeries.Recurrent cyclops lesions have been rarely documented;this case study documents the successful treatment of a recurrent cyclops lesion.CASE SUMMARY A 28-year-old female presented following a non-contact injury to the right knee.Workup and clinical exam revealed an ACL tear,and arthroscopic reconstruction was performed.Two years later a cyclops lesion was discovered and removed via arthroscopic synovectomy.Seven months postoperatively,the patient presented with pain,stiffness,and difficulty achieving terminal extension.A smaller recurrent cyclops lesion was diagnosed,and a repeat synovectomy was performed.The patient recovered fully.CONCLUSION To the best of our knowledge,this is the first documented case of recurrent cyclops lesion after bone-patellar tendon-bone allograft ACL reconstruction presenting as cyclops syndrome.

Should antibiotics be administered before arthroscopic knee surgery? A systematic review of the literature

AIM To explore the current evidence surrounding the administration of prophylactic antibiotics for arthroscopic knee surgery. METHODS Databases were searched from inception through May of 2018 for studies examining prophylactic antibiotic use and efficacy in knee arthroscopy. Studies with patient data were further assessed for types of arthroscopic procedures performed,number of patients in the study,use of antibiotics,and outcomes with the intention of performing a pooled analysis. Data pertaining to "deep tissue infection" or "septic arthritis" were included in our analysis. Reported data on superficial infection were not included in our data analysis. For the pooled analysis,a relative risk ratio was calculated and χ~2 tests were used to assess for statistical significance between rates of infection amongst the various patient groups. Post hoc power analyses were performed to compute the statistical power obtained from our sample sizes. Number needed to treat analyses were performed for statistically significant differences by dividing 1 by the difference between the infection rates of the antibiotic and no antibiotic groups. An alpha value of 0.05 was used for our analysis. Study heterogeneity was assessed by Cochrane's Q test as well as calculation of the I^2 value.RESULTS A total of 49682 patients who underwent knee ar-throscopy for a diverse set of procedures across 19 studies met inclusion critera for pooled analysis. For those not undergoing graft procedures,there were 27 cases of post-operative septic arthritis in 34487 patients(0.08%) who received prophylactic antibiotics and 16 cases in 10911(0.15%) who received none [risk ratio(RR) = 0.53,95% confidence interval(CI): 0.29-0.99,P = 0.05]. A sub-group analysis in which bony procedures were excluded was performed which found no significant difference in infection rates between patients that received prophylactic antibiotics and patients that did not(P > 0.05). All anterior cruciate ligament reconstruction studies used prophylactic antibiotics,but two studies investigating the effect of soaking the graft in vancomycin in addition to standard intravenous(IV) prophylaxis were combined for analysis. There were 19 cases in 1095 patients(1.74%) who received IV antibioitics alone and no infections in 2034 patients who received IV antibiotics and had a vancomycin soaked graft(RR = 0.01,95%CI: 0.001-0.229,P < 0.01).CONCLUSION Prophylactic antibiotics are effective in preventing septic arthritis following simple knee arthroscopy. In procedures involving graft implantation,graft soaking reduces the rate of infection.

Applying the Socio-Ecological Model to barriers to implementation of ACL injury prevention programs: A systematic review

Background: Preventing anterior cruciate ligament(ACL) injuries is important to avoid long-term adverse health consequences. Identifying barriers to implementation of these prevention programs is crucial to reducing the incidence of these injuries. Our purpose was to identify barriers of implementation for ACL injury prevention programs and suggest mechanisms for reducing the barriers through application of a SocioEcological Model(SEM).Methods: Studies investigating ACL prevention program effectiveness were searched in Medline via PubMed and the Cochrane Library, and a subsequent review of the references of the identified articles, yielded 15 articles total. Inclusion criteria encompassed prospective controlled trials, published in English, with ACL injuries as the primary outcome. Studies were independently appraised by 2 reviewers for methodological quality using the PEDro scale. Barriers to implementation were identified when reported in at least 2 separate studies. A SEM was used to suggest ways to reduce the identified barriers.Results: Five barriers were identified: motivation, time requirements, skill requirements for program facilitators, compliance, and cost. The SEM suggested ways to minimize the barriers at all levels of the model from the individual through policy levels.Conclusion: Identification of barriers to program implementation and suggesting how to reduce them through the SEM is a critical first step toward enabling ACL prevention programs to be more effective and ultimately reducing the incidence of these injuries.

Hamstring autograft utilization in reconstructing anterior cruciate ligament:Review of harvesting techniques,graft preparation,and different fixation methods

Rupture of the anterior cruciate ligament(ACL)is a common orthopedic injury.Various graft options are available for the reconstruction of ruptured ACL.Using the hamstring muscle as an autograft was first described in 1934,and it remains a commonly harvested graft for ACL reconstruction.Hamstring autografts can be harvested using the traditional anteromedial approach or the newer posteromedial technique.An isolated semitendinosus tendon can be used or combined with the gracilis tendon.There are numerous methods for graft fixation,such as intra-tunnel or extra-tunnel fixation.This comprehensive review discusses the different hamstring muscle harvesting techniques and graft preparation options and fixation methods.It provides a comprehensive overview for choosing the optimal surgical technique when treating patients.

Estimates of voluntary activation in individuals with anterior cruciate ligament reconstruction:Effects of type of stimulator,number of stimuli,and quantification technique

Background:Accurate quantification of voluntary activation is important for understanding the extent of quadriceps dysfunction in individuals with anterior cruciate ligament reconstruction(ACLR).Voluntary activation has been quantified using both percent activation derived from the interpolated twitch technique and central activation ratio(CAR)derived from the burst superimposition technique,as well as by using different types of electrical stimulators and pulse train conditions.However,it is unclear how these parameters affect voluntary activation estimates in individuals with ACLR.This study was performed to fill this important knowledge gap in the anterior cruciate ligament literature.Methods:Quadriceps strength and voluntary activation were examined in 18 ACLR participants(12 quadriceps/patellartendon graft,6 hamstring tendon graft;time since ACLR:1.06±0.82 years,mean±SD)at 90°of knee flexion using 2 stimulators(Digitimer and Grass)and pulse train conditions(3-pulse and 10-pulse).Voluntary activation was quantified by calculating both CAR and percent activation.Results:Results indicated that voluntary activation was significantly overestimated by CAR when compared with percent activation(p<0.001).Voluntary activation estimates were not affected by pulse train conditions when using percent activation;however,3-pulse stimuli resulted in greater overestimation than 10-pulse stimuli when using CAR(p=0.003).Voluntary activation did not differ between stimulators(p>0.05);however,the Digitimer evoked greater torque at rest than the Grass(p<0.001).Conclusion:These results indicate that percent activation derived from the interpolated twitch technique provides superior estimates of voluntary activation than CAR derived from burst superimposition and is less affected by pulse train conditions or stimulators in individuals with ACLR.