Bilateral Squatting Mechanics Are Associated With Landing Mechanics in Anterior Cruciate Ligament Reconstruction Patients

Digital twin systems for musculoskeletal applications: A current concepts review

Digital twin (DT) systems, which involve creating virtual replicas of physical objects or systems, have the potential to transform healthcare by offering personalised and predictive models that grant deeper insight into a patient's condition. This review explores current concepts in DT systems for musculoskeletal (MSK) applications through an overview of the key components, technologies, clinical uses, challenges, and future directions that define this rapidly growing field. DT systems leverage computational models such as multibody dynamics and finite element analysis to simulate the mechanical behaviour of MSK structures, while integration with wearable technologies allows real-time monitoring and feedback, facilitating preventive measures, and adaptive care strategies. Early applications of DT systems to MSK include optimising the monitoring of exercise and rehabilitation, analysing joint mechanics for personalised surgical techniques, and predicting post-operative outcomes. While still under development, these advancements promise to revolutionise MSK care by improving surgical planning, reducing complications, and personalising patient rehabilitation strategies. Integrating advanced machine learning algorithms can enhance the predictive abilities of DTs and provide a better understanding of disease processes through explainable artificial intelligence (AI). Despite their potential, DT systems face significant challenges. These include integrating multi-modal data, modelling ageing and damage, efficiently using computational resources and developing clinically accurate and impactful models. Addressing these challenges will require multidisciplinary collaboration. Furthermore, guaranteeing patient privacy and protection against bias is extremely important, as is navigating regulatory requirements for clinical adoption. DT systems present a significant opportunity to improve patient care, made possible by recent technological advancements in several fields, including wearable sensors, computational modelling of biological structures, and AI. As these technologies continue to mature and their integration is streamlined, DT systems may fast-track medical innovation, ushering in a new era of rapid improvement of treatment outcomes and broadening the scope of preventive medicine. Level of Evidence: Level V.

Comparison of Limb Loading Characteristics and Subjective Functional Outcomes Between Sexes After Anterior Cruciate Ligament Reconstruction

CONTEXT

Anterior cruciate ligament reconstruction (ACLR) patients commonly adopt poor movement patterns that potentially place them at an increased risk for reinjury if untreated. Limb loading characteristics during functional tasks can highlight movement compensations.

OBJECTIVE

To examine loading symmetry during a bilateral bodyweight squatting task between sexes, compare loading metrics between limbs and sexes, and describe the relationship between loading metrics and patient-reported outcomes (PROs) after ACLR.

DESIGN

Cross-sectional study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

One hundred forty-two patients (71 male, 71 female, age = 24.4 ± 11.10 years) with a primary, unilateral, uncomplicated ACLR completed a squatting assessment and PRO measures at approximately 5.2 months post-ACLR.

MAIN OUTCOME MEASURE(S)

Normalized limb loading peak force (N/kg) and unilateral cumulative load (%) were collected bilaterally during the squatting task. Limb symmetry index (%) was calculated for normalized peak force. First, we compared limb loading symmetry (%) between sexes using an independent-samples t test. Second, we assessed differences in limb loading metrics between limbs and sexes via an analysis of covariance. Third, we used Spearman ρ correlations to determine the relationship between limb loading metrics and PROs.

RESULTS

The majority of individuals (91 of 142, 64.1%) offloaded their ACLR limb (ACLR = 6.6 ± 1.56 N/kg, contralateral = 7.3 ± 1.61 N/kg, P < .001). Females significantly offloaded their ACLR limb (ACLR = 6.3 ± 1.38 N/kg, contralateral = 7.2 ± 1.62 N/kg, P < .001) whereas males did not significantly offload their ACLR limb (ACLR = 6.98 ± 1.65 N/kg, contralateral = 7.4 ± 1.60 N/kg, P = .07). Weak relationships were observed (Ρ value range: -.23 to .19) across limb loading metrics and PROs.

CONCLUSIONS

Individuals approximately 5 months after ACLR, on average, offloaded their ACLR limb compared with the contralateral limb. Patients' tendency to offload their weight during a squat was influenced by sex. Relationships between limb loading metrics and PROs indicate patients who load their limbs disproportionately have a lower perception of their capability to complete activities of daily living and lower subjective knee function.

Analysis of Limb Loading and Lower Extremity Strength Recovery Across Time After Anterior Cruciate Ligament Reconstruction

BACKGROUND

Evidence as to how patient thigh muscle strength and limb loading (LL) during a squatting task recovers throughout rehabilitation after anterior cruciate ligament reconstruction (ACLR) is lacking.

HYPOTHESIS

Patients will improve LL and strength throughout rehabilitation. Changes in LL and strength over time will be positively correlated.

STUDY DESIGN

Prospective cohort study.

LEVEL OF EVIDENCE

Level 3.

METHODS

A total of 60 participants (28 male/32 female; age, 22.5 ± 9.35 years) participated in 2 visits post-ACLR, assessing LL and strength. Using an instrumented pressure mat, patients completed 3 sets of 3 repetitions of bodyweight squats. Peak force (N), unilateral cumulative load (%), and quadriceps and hamstring isokinetic peak torque (N·m) were calculated and recorded bilaterally. LL and peak torque were compared over time and between limbs.

RESULTS

A significant limb-by-time interaction was observed for LL peak force (N), where patients underloaded the ACLR limb at visit 1 compared with the contralateral limb (P < 0.01). Patients increased their ACLR LL across visits (P = 0.04). A limb-by-time interaction for quadriceps peak torque (N·m) was observed where the ACLR limb increased peak torque across visits (P < 0.01); however, strength deficits persisted at visit 2 (P < 0.01) when compared with the nonoperative limb. Weak correlations were observed between all change scores metrics (r, 0.20-0.25).

CONCLUSION

Patients recovering from ACLR exhibited more symmetric loading during a squatting task and improved their lower extremity strength over time. Changes in strength were not related to changes in LL during a squatting task over time.

CLINICAL RELEVANCE

Squatting tasks are safe and easily implemented throughout ACLR recovery. As changes in functional LL and strength recovery are not related, both should be considered in serial postoperative testing for more comprehensive function and strength assessments.

Whether Patients with Anterior Cruciate Ligament Reconstruction Walking at a Fast Speed Show more Kinematic Asymmetries?

OBJECTIVE

Knee kinematic asymmetries after anterior cruciate ligament reconstruction (ACLR) are correlated with poor clinical outcomes, such as the progression of knee cartilage degenerations or reinjuries. Fast walking in patients with knee conditions may exacerbate knee kinematic asymmetries, but its impact on ACLR patients is uncertain. The aim of this study is to investigate if fast walking induces more knee kinematic asymmetries in unilateral ACLR patients.

METHODS

This cross-sectional study enrolled 55 patients with unilateral ACLR from January 2020 to July 2022. There were 48 males and seven females with an average age of 30.6 ± 6.4 years. Knee kinematic data were collected at three walking speeds: self-selected, fast (150% normal), and slow (50% normal). A 3D knee kinematic analysis system measured the data, and self-reported outcomes assessed comfort levels during walking. We used SPM1D for two-way repeated ANOVA and posthoc paired t-tests to analyze kinematic differences in groups.

RESULTS

In fast walking, ACLR knees exhibited more transverse kinematic asymmetries than intact knees, including greater external rotation angle (1.8°, 38%-43%; gait cycle [GC], p < 0.05 & 1.8-2.7°, 50%-61% GC, p < 0.05) and increased proximal tibial translation (2.1-2.5 mm, 2%-6% GC, p < 0.05 & 2.5-3.2 mm, 92%-96% GC, p < 0.05). Additionally, ACLR knees showed greater posterior tibial translation than intact knees (3.6-3.7 mm, 7%-8% GC, p < 0.05) during fast walking. No posterior tibial translation asymmetries were observed in slow walking compared to normal walking levels. ACLR knees have the most comfortable feelings in slow walking speed, and the most uncomfortable feelings in fast walking speed levels (29%).

CONCLUSIONS

Fast walking induces additional external tibial rotation and proximal and posterior tibial translation asymmetries in ACLR patients. This raises concerns about long-term safety and health during fast walking. Fast walking, not self-selected speed, is beneficial for identifying postoperative gait asymmetries in ACLR patients.

Asymmetric loading strategies during squats following anterior cruciate ligament reconstruction: A longitudinal investigation with curve analyses throughout and after rehabilitation

Investigations of kinetic asymmetries during bilateral squats following anterior cruciate ligament reconstruction (ACLR) are limited to mainly cross-sectional studies and discrete value data extracted at specific knee angles. We assessed loading asymmetries during squats longitudinally throughout rehabilitation using curve analysis and compared patient-reported outcome measures (PROMs) between those with and without asymmetry. Bodyweight squats were performed by 24 individuals (13 females) post-ACLR on three occasions: (1) Early 2.9 (1.1) months; (2) Mid 8.8 (3.1) months; (3) at Return to Sport (RTS) 13.1 (3.6) months; and 29 asymptomatic controls (22 females) once. Time-normalized between-leg asymmetry curves of sagittal plane hip, knee, and ankle moments and vertical ground reaction forces were compared using functional data analysis methods. Individual asymmetrical loading for ACLR was classified when exceeding the 95% confidence interval of controls during ≥50% of the squat. At Early, ACLR had greater asymmetry than controls for knee (15%-100% eccentric phase; 0%-100% concentric) and ankle flexion moments (56%-65% concentric). At Mid, ACLR had greater asymmetry for knee (41%-72% eccentric) and ankle flexion moments (56%-69% concentric). No between-group differences were found at RTS. From Early to RTS, ACLR reduced asymmetry for hip (21%-46% eccentric), knee (27%-58% concentric), and ankle flexion moments (21%-57% eccentric). At Early, 11/24 underloaded their ACLR knee and 1 overloaded compared with controls. At RTS, 4 underloaded and 6 overloaded. No differences in PROMs were found based on loading asymmetry. Beyond the early phase of rehabilitation from ACLR, individual-level analyses are required to reveal differing loading strategies during bilateral squats.

Hip Strength Recovery After Anterior Cruciate Ligament Reconstruction

Background

Return-to-play (RTP) assessment after anterior cruciate ligament reconstruction (ACLR) rarely includes hip strength.

Hypothesis

It was hypothesized that (1) patients after ACLR will have weaker hip abduction (AB) and adduction (AD) strength compared with the contralateral limb, with larger deficits in women, (2) there will be a correlation between hip and thigh strength ratios and patient-reported outcomes (PROs), and (3) hip AB and AD strength will improve over time.

Study Design

Descriptive laboratory study.

Methods

Included were 140 patients (74 male, 66 female; mean age, 24.16 ± 10.82 years) who underwent RTP assessment at 6.1 ± 1.6 months after ACLR; 86 patients underwent a second assessment at 8.2 ± 2.2 months. Hip AB/AD and knee extension/flexion isometric strength were measured and normalized to body mass, and PRO scores were collected. Strength ratios (hip vs thigh), limb differences (injured vs uninjured), sex-based differences, and relationships between strength ratios and PROs were determined.

Results

Hip AB strength was weaker on the ACLR limb (ACLR vs contralateral: 1.85 ± 0.49 vs 1.89 ± 0.48 N·m/kg; P < .001) and hip AD torque was stronger (ACLR vs contralateral: 1.80 ± 0.51 vs 1.76 ± 0.52 N·m/kg; P = .004), with no sex-by-limb interaction found. Lower hip-to-thigh strength ratios of the ACLR limb were correlated with higher PRO scores (r = -0.17 to -0.25). Over time, hip AB strength increased in the ACLR limb more than in the contralateral limb (P = .01); however, the ACLR limb remained weaker in hip AB at visit 2 (ACLR vs contralateral: 1.88 ± 0.46 vs 1.91 ± 0.45 N·m/kg; P = .04). In both limbs, hip AD strength was greater at visit 2 than visit 1 (ACLR: 1.82 ± 0.48 vs 1.70 ± 0.48 N·m/kg; contralateral: 1.76 ± 0.47 vs 1.67 ± 0.47 N·m/kg; P < .01 for both).

Conclusion

The ACLR limb had weaker hip AB and stronger AD compared with the contralateral limb at initial assessment. Hip muscle strength recovery was not influenced by sex. Hip strength and symmetry improved over the course of rehabilitation. Although strength differences across limbs were minor, the clinical importance of these differences is still unknown.

Clinical Relevance

The evidence provided highlights the need to integrate hip strength into RTP assessments to identify hip strength deficits that may increase reinjury or lead to poor long-term outcomes.

Interlimb Asymmetry in Knee Extension Moment During Double-Leg Squatting Is Associated With Persistent Quadriceps Weakness After ACL Reconstruction

Background

Although double-leg squatting is less dynamic and places less demand on the quadriceps compared with landing tasks, the relationship between double-leg squatting biomechanics and persistent quadriceps weakness after anterior cruciate ligament reconstruction (ACLR) is unknown.

Purpose

To clarify the relationships between asymmetries in quadriceps strength and lower limb biomechanics during double-leg squatting >1 year after ACLR.

Study Design

Controlled laboratory study.

Methods

A total of 26 participants (5.5 ± 3.8 years after ACLR) were enrolled. The limb symmetry index (LSI) of isokinetic quadriceps strength was used to divide participants into the high-quadriceps (HQ) group (LSI ≥90%; n = 18) and the low-quadriceps (LQ) group (LSI <90%; n = 8). The knee, hip, and ankle extension moment (relative to body weight and support moment [sum of knee, hip, and ankle moments]) and vertical ground-reaction force during double-leg squatting were analyzed using 3-dimensional motion analysis. The association of quadriceps strength and biomechanical variables was tested using 2-way analysis of variance and univariate regression analysis.

Results

A significant group-by-limb interaction was found for the peak knee extension moment and the ratios of knee and hip extension moment to support moment (P < .001, P = .015 and P < .001, respectively). The LQ group showed a significantly smaller peak knee extension moment and knee to support moment ratio but a larger hip to support moment ratio in the involved limb than in the uninvolved limb (95% CIs: knee extension moment, -0.273 to -0.088 N·m/kg; knee to support moment ratio, -10.7% to -2.2%; hip to support moment ratio, 3.2% to 8.5%). No interlimb difference was found for the HQ group. The LSI of quadriceps strength was significantly associated with the LSI of peak knee extension moment (R² = 0.183), knee to support moment ratio (R² = 0.256), and hip to support moment ratio (R² = 0.233). The mean maximum isokinetic quadriceps strength and peak knee extension moment during squatting on the involved limb of the LQ group were 2.40 ± 0.39 and 0.90 ± 0.16 N·m/kg, respectively.

Conclusion

Asymmetrical biomechanics during double-leg squatting was associated with persistent quadriceps weakness after ACLR. The LQ group had reduced knee extensor moment on the involved side during squatting despite loading at approximately half the maximum strength.

Clinical Relevance

Quadriceps strengthening exercises, together with interventions to improve neuromuscular control, may reduce asymmetrical biomechanics during double-leg squatting.

Jump-landing kinetic asymmetries persisted despite symmetric squat kinetics in collegiate athletes following anterior cruciate ligament reconstruction

The purpose was to determine the differences/correlations in anterior cruciate ligament (ACL) loading variables and bilateral asymmetries between injured/uninjured legs and among ascending/descending phases of double-leg squats and jumping/landing phases of countermovement jumps (CMJ) in the collegiate athletes following ACL reconstruction (ACLR). Fourteen collegiate athletes performed squats and CMJ 6-14 months following ACLR. The bilateral knee/hip flexion angles, peak vertical ground reaction force (VGRF) and knee extension moments (KEM), and kinetic asymmetries were calculated. Squats showed the greatest knee/hip flexion angles, while the landing phase of CMJ showed the least (P<0.001). The uninjured leg demonstrated greater VGRF (P≤0.010) and KEM (P≤0.008) than the injured leg in CMJ. Kinetic asymmetries were less than 10% for squats but were greater for the jumping (P≤0.014, 12%-25%) and landing (P≤0.047, 16%-27%) phases of CMJ. Significant correlations were found for KEM asymmetries between phases of CMJ (P=0.050) and squats (P<0.001). Kinetic asymmetries persisted in CMJ, while kinetic symmetries were achieved in squats in collegiate athletes 6-14 months following ACLR. Therefore, the CMJ appears to be a more sensitive assessment to monitor the bilateral kinetic asymmetries compared to squats. It is suggested to assess and screen kinetic asymmetries in different phases and tasks.

Using trunk kinematics to predict kinetic asymmetries during double-leg jump-landings in collegiate athletes following anterior cruciate ligament reconstruction

BACKGROUND

Bilateral vertical ground reaction force (VGRF) and knee extension moment asymmetries are commonly observed during jumping and landing tasks following anterior cruciate ligament (ACL) reconstructions (ACLR) in collegiate athletes. Kinetic asymmetries during landings are associated with increased ACL re-injury risk. Efforts have been made to predict bilateral kinetic asymmetries using trunk kinematics during squats but not during jump-landings.

RESEARCH QUESTION

To determine the correlations between trunk kinematics (medial-lateral shoulder positions, medial-lateral hip positions, and lateral trunk bending angles) and bilateral kinetic asymmetries (VGRF and knee extension moments) during double-leg jump-landings in collegiate athletes following ACLR.

METHODS

Fifteen National Collegiate Athletic Association Division I athletes who had ACLR in the past 24 months participated. Eleven of them performed two assessments over the study period for a total of 26 assessments for data analyses. Athletes performed three double-leg countermovement jumps. Kinematics and kinetics data were collected. Medial-lateral shoulder and hip positions relative to ankle positions, lateral trunk bending angles, and kinetic asymmetries were calculated during the jumping (the lowest hip position until takeoff) and landing (the first 100 ms after initial contact) phases.

RESULTS

Medial-lateral shoulder positions correlated with VGRF (r = 0.63, p < 0.001) and knee moment asymmetries (r = 0.53, p = 0.006) in the jumping phase. Medial-lateral hip positions correlated with VGRF (r = 0.61, p < 0.001; r = 0.52, p = 0.006) and knee moment asymmetries (r = 0.55, p = 0.004; r = 0.61, p < 0.001) in both jumping and landing phases.

SIGNIFICANCE

Medial-lateral hip positions correlated with kinetic asymmetries during double-leg jump-landings in collegiate athletes following ACLR. A 2D assessment using a standard video camera might be used as a low-cost and clinically applicable tool to assess bilateral kinetic asymmetries by quantifying medial-lateral hip positions during jump-landings following ACLR.

Pelvic Rotation Is Associated With Asymmetry in the Knee Extensor Moment During Double-Leg Squatting After Anterior Cruciate Ligament Reconstruction

Asymmetry in knee extensor moment during double-leg squatting was observed after anterior cruciate ligament reconstruction, even after the completion of the rehabilitation program for return to sports. The purpose of this study was to clarify the association between asymmetry in the knee extensor moment and pelvic rotation angle during double-leg squatting after anterior cruciate ligament reconstruction. Twenty-four participants performed double-leg squatting. Kinetics and kinematics during squatting were analyzed using a 3-dimensional motion analysis system with 2 force plates. The limb symmetry index of knee extensor moment was predicted by the pelvic rotation angle (R2 = .376, P = .001). In addition, the pelvic rotation and the limb symmetry index of the vertical ground reaction force independently explained the limb symmetry index of the knee extensor moment (R2 = .635, P < .001, β of pelvic rotation = -0.489, β of vertical ground reaction force = 0.524). Pelvic rotation toward the involved limb was associated with a smaller knee extensor moment in the involved limb than in the uninvolved limb. The assessment of pelvic rotation would be useful for partially predicting asymmetry in the knee extensor moment during double-leg squatting. Minimizing pelvic rotation may improve the asymmetry in the knee extensor moment during double-leg squatting after anterior cruciate ligament reconstruction.

Reduction of risk factors for ACL Re-injuries using an innovative biofeedback approach: A phase I randomized clinical trial

OBJECTIVES

Determine the safety and initial efficacy of a novel biofeedback intervention to improve landing mechanics in patients following anterior cruciate ligament reconstruction (ACLR).

METHODS

Forty patients post-ACLR (age: 16.9 ± 2.0 years) were randomly allocated to a biofeedback intervention or an attention control group. Patients in the biofeedback group completed 12 sessions over six-weeks that included bilateral unweighted squats with visual and tactile biofeedback. Patients in the control group completed a six-week educational program. Lower extremity mechanics were collected during a bilateral stop jump at baseline, six-weeks, and 12-weeks post-intervention. Linear mixed-effects models adjusted for sex and graft type determined the main effects of and interactions between group and time.

RESULTS

No group by time interaction existed for peak knee extension moment symmetry. A group by time interaction existed for peak vertical ground reaction force symmetry (p = 0.012), where patients in the biofeedback group had greater improvements in symmetry between baseline and post-intervention that were not maintained through the retention assessments.

CONCLUSION

This novel biofeedback program did not reduce risk factors for second ACL injuries. Future work could develop and test multidisciplinary interventions for reducing second ACL injury risk factors.

CLINICALTRIALS

GOV IDENTIFIER: (NCT03273673).