Knee strength symmetry at 4 months is associated with criteria and rates of return to sport after anterior cruciate ligament reconstruction

Outcomes After Anterior Cruciate Ligament Reconstruction With Quadriceps Tendon in Adolescent Athletes at Mean Follow-up of 4 Years

Background

Despite increasing use of quadriceps tendon (QT) autograft in anterior cruciate ligament (ACL) reconstruction (ACLR), limited data exist regarding its outcomes in high-risk adolescent athletes.

Purpose

To (1) report the outcomes after QT ACLR in adolescent athletes and (2) identify patient-related and surgery-related factors that may influence failure rates after QT ACLR.

Study Design

Case series; Level of evidence, 4.

Methods

All patients aged 14 to 17 years who underwent primary anatomic, transphyseal, single-bundle QT ACLR between 2010 and 2021 with a minimum 2-year follow-up were included for analysis. Demographic and surgical data as well as preoperative International Knee Documentation Committee (IKDC) and Marx activity scores were collected retrospectively. All patients were also contacted to assess postoperative patient-reported outcomes (PROs), including IKDC and Marx activity scores, and return-to-sports (RTS) data. Outcomes of interest included rates of revision ACLR and ipsilateral complications, contralateral ACL tears, difference in pre- and postoperative PROs, and rates of RTS. Patient and surgical characteristics were compared between groups who required revision ACLR versus those who did not.

Results

A total of 162 patients met inclusion criteria, of which 89 adolescent athletes (mean age 16.2 ± 1.1 years, 64% female) were included for analysis at mean follow-up of 4.0 years. Postoperative IKDC scores were significantly higher than preoperative scores (88.5 vs 37.5; P < .001), whereas Marx activity scores decreased postoperatively (14.3 vs 12.2; P = .011). Successful RTS occurred in 80% of patients at a mean time of 9.7 ± 6.9 months, and 85% of these patients returned to the same or higher level of sports. The most common reasons for failure to RTS included lack of time (n = 7, 70%) and fearing reinjury in the operative knee (n = 5, 50%). The overall revision ACLR rate was 10% (n = 9), and contralateral ACL tears occurred in 14% (n = 12) of patients. The overall ipsilateral knee reoperation rate was 22.5% (n = 20). No statistically significant differences in patient or surgical characteristics were observed between patients who underwent revision ACLR and those who did not.

Conclusion

At a minimum 2-year follow-up after QT ACLR, adolescent athletes experienced significantly improved postoperative IKDC scores, high rates of RTS, and low rates of graft failure, despite a relatively high ipsilateral reoperation rate. Surgeons may utilize this information when identifying the optimal graft choice for adolescent athletes who have sustained an ACL injury and wish to return to high level of sporting activities.

Knee Extensor Torque Steadiness and Quadriceps Activation Variability in Collegiate Athletes 4, 6, and 12 Months After ACL Reconstruction

Background

Quadriceps performance after anterior cruciate ligament reconstruction (ACLR) is typically characterized by peak force/torque, but the ability to generate consistent knee extensor torque may be clinically meaningful.

Purpose/Hypothesis

The purpose of this study was to evaluate knee extensor torque steadiness and quadriceps activation variability in collegiate athletes 4 to 12 months after ACLR. It was hypothesized that between-limb asymmetries in torque steadiness and activation variability would be observed and that steadiness would be associated with activation variability and peak knee extensor torque symmetry.

Study Design

Case-control study; Level of evidence, 3.

Methods

A total of 30 National Collegiate Athletic Association Division I athletes completed maximal voluntary isometric contractions 4, 6, and 12 months after ACLR. Torque and surface electromyography of the superficial quadriceps were recorded. Torque steadiness was calculated as the mean difference between initial and low-pass filtered torque signals and was expressed as a percentage of peak torque. Quadriceps activation variability was calculated similarly and was expressed as a percentage of peak electromyography. Linear mixed models were used to assess change in torque steadiness and activation variability over time. Associations between torque steadiness of the operated limb, activation variability, and quadriceps strength symmetry were evaluated using the Spearman correlation coefficient.

Results

Limb-by-time interactions were detected for torque steadiness and activation variability (P < .001), with reductions (improvements) in limb steadiness and activation variability observed with increasing time since surgery. Between-limb differences in torque steadiness and activation variability were observed at 4 and 6 months postoperatively (P < .05). Significant associations between operated limb torque steadiness and quadriceps activation variability were observed at 4 months (P < .001) and 6 months (P < .01). Torque steadiness of the operated limb was associated with peak knee extensor torque symmetry at 4 months (r S = -0.49; P < .01) and 6 months (r S = -0.49; P < .01).

Conclusion

In collegiate athletes, impaired knee extensor torque steadiness of the operated limb and associated abnormal quadriceps activation patterns were observed 4 to 12 months after ACLR, and the consistency of knee extensor torque production was associated with greater quadriceps strength asymmetries, particularly 4 to 6 months after surgery. Operated limb torque steadiness and activation variability improved from 4 to 12 months after ACLR. Clinical assessment of knee extensor torque steadiness after ACLR may improve prognosis and specificity of rehabilitation efforts.

Changes in passive hamstring stiffness after primary anterior cruciate ligament reconstruction: A prospective study with comparison of healthy controls

BACKGROUND

The mechanical properties of knee flexors muscles contribute to reducing anterior cruciate ligament loading. This case-control study evaluated the passive knee flexors stiffness after primary anterior cruciate ligament reconstruction with comparison of healthy controls.

METHODS

After anterior cruciate ligament reconstruction, 88 participants (24.5 [8.6] years, 56,8% males) had two isokinetic tests at 4 and 8 postoperative months with measurement of the passive resistive torque of knee flexors and extensors/flexors strength. In the control group, 44 participants (24.5 [4.3] years, 56,8% males) had one visit with the same procedures. Passive knee flexors stiffness was calculated as the slope of the passive torque-angle curve on the last 10° of knee extension (Nm/°). We investigated the impact of timing and type of surgery (autograft and combined meniscus repair) and persistent knee extension deficits on knee flexors stiffness.

FINDINGS

At 4 and 8 postoperative months, passive knee flexors stiffness was lower on the operated limb than on the non-operated limb (P < 0.001) but both limbs had significant lower values than controls (P < 0.001). Stiffness was positively correlated with knee flexors strength (P < 0.010), and knee flexors stiffness at 4 months was lower in individuals who underwent surgery <6 months from injury (P = 0.040). Knee extension deficit or the type of surgery did not have a significant influence on knee flexors stiffness.

INTERPRETATION

Similarly to neuromuscular factors that are traditionally altered after anterior cruciate ligament reconstruction, evaluating passive knee flexors stiffness changes over time could provide supplementary insights into postoperative muscle recovery.

Changes in the Force-Velocity Relationship of Knee Muscles After Anterior Cruciate Ligament Reconstruction Using the Isokinetic 2-Point Model

PURPOSE

After anterior cruciate ligament reconstruction (ACL-R), knee muscle strength symmetry is used as part of the return-to-sport criteria. However, little is known about the changes in the force-velocity (F-V) relationship, which could affect athletic performance. This study investigated the F-V relationship of knee muscles at 4 and 8 months after ACL-R, using the 2-point method tested by isokinetic dynamometry.

METHODS

A total of 103 physically trained individuals (24.6 [9.3] y, 59.2% male) who underwent primary ACL-R were included. Demographic information and surgery characteristics were collected at 6 weeks postoperatively. Isokinetic knee flexors' and extensors' peak torques were measured at 60° and 240° per second in the concentric mode at 4 and 8 months postoperative. Peak torques and angular velocities were converted to force and linear velocity for calculating maximum isometric force (F0) and the slope of the regression line (F-V slope).

RESULTS

At 4 and 8 months postoperative, F0 was significantly lower and F-V slope was significantly less steep (less negative) on the operated leg compared with the nonoperated leg for knee extensors (P < .001) and flexors (P < .001-.002). The limb symmetry index calculated using F0 was lower than the limb symmetry indexes assessed at 60° and 240° per second, especially for knee flexors (P < .001). The use of patellar tendon grafts was associated with lower F0 and a less steep F-V slope compared with hamstring tendon grafts (P < .010).

CONCLUSION

The isokinetic 2-point model assessing the F-V relationship provides additional and relevant insight for evaluating knee muscle strength after ACL-R.

Effects of a 20-Week High-Intensity Strength Training Program on Muscle Strength Gain and Cardiac Adaptation in Untrained Men: Preliminary Results of a Prospective Longitudinal Study

BACKGROUND

As strength sports gain popularity, there is a growing need to explore the impact of sustained strength training on cardiac biventricular structure and function, an area that has received less attention compared to the well-established physiological cardiac adaptation to endurance training.

OBJECTIVE

This study aims to implement a 20-week high-intensity strength training program to enhance maximal muscle strength and evaluate its impact on cardiac biventricular adaptation in healthy, untrained men.

METHODS

A total of 27 healthy and untrained young men (mean age 22.8, SD 3.2 years) participated in a strength training program designed to increase muscle strength. The training program involved concentric, eccentric, and isometric exercise phases, conducted over a consecutive 20-week time frame with a frequency of 3 weekly training sessions. Participants were evaluated before and after 12 and 20 weeks of training through body composition analysis (bioelectrical impedance), a 12-lead resting electrocardiogram, 3D transthoracic echocardiography, cardiopulmonary exercise testing, and muscle isokinetic dynamometry. The progression of strength training loads was guided by 1-repetition maximum (RM) testing during the training program.

RESULTS

Of the initial cohort, 22 participants completed the study protocol. No injuries were reported. The BMI (mean 69.8, SD 10.8 kg/m² vs mean 72, SD 11 kg/m²; P=.72) and the fat mass (mean 15.3%, SD 7.5% vs mean 16.5%, SD 7%; P=.87) remained unchanged after training. The strength training program led to significant gains in 1-RM exercise testing as early as 4 weeks into training for leg extension (mean 69.6, SD 17.7 kg vs mean 96.5, SD 31 kg; P<.001), leg curl (mean 43.2, SD 9.7 kg vs mean 52.8, SD 13.4 kg; P<.001), inclined press (mean 174.1, SD 41.1 kg vs mean 229.2, SD 50.4 kg; P<.001), butterfly (mean 26.3, SD 6.2 kg vs mean 32.5, SD 6.6 kg; P<.001), and curl biceps on desk (mean 22.9, SD 5.2 kg vs mean 29.6, SD 5.2 kg; P<.001). After 20 weeks, the 1-RM leg curl, bench press, pullover, butterfly, leg extension, curl biceps on desk, and inclined press showed significant mean percentage gains of +40%, +41.1%, +50.3%, +63.5%, +80.1%, +105%, and +106%, respectively (P<.001). Additionally, the isokinetic evaluation confirmed increases in maximal strength for the biceps (+9.2 Nm), triceps (+11.6 Nm), quadriceps (+46.8 Nm), and hamstrings (+25.3 Nm). In this paper, only the training and muscular aspects are presented; the cardiac analysis will be addressed separately.

CONCLUSIONS

This study demonstrated that a short-term high-intensity strength training program was successful in achieving significant gains in muscle strength among previously untrained young men. We intend to use this protocol to gain a better understanding of the impact of high-intensity strength training on cardiac physiological remodeling, thereby providing new insights into the cardiac global response in strength athletes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04187170; https://clinicaltrials.gov/study/NCT04187170.