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Abstract

Background:

Knee stability can be conferred passively by ligaments and menisci and actively by the neuromuscular system. We sought to determine the relationship between passive tibiofemoral alignment and dynamic constraint in patients undergoing anterior cruciate ligament (ACL) reconstruction (ACLR) and matched control participants who have been followed for more than a decade.

Purpose/Hypothesis:

It was hypothesized that (1) anterior tibial position would be greater in the surgical knee compared to the contralateral knee and when compared to knees of control participants, and (2) the surgical limb differences would be greater in the dynamic state during a 1-leg hop-for-distance landing task.

Study Design:

Controlled laboratory study.

Methods:

A total of 21 participants were recruited from a recently completed longitudinal clinical trial (NCT00434837): 10 patients who had undergone ACLR 10 to 15 years earlier and 11 matched control participants without knee injury. The 3-dimensional (3D) tibiofemoral position was extracted from each participant's computed tomography images as a measure of passive alignment. Dynamic 3D knee kinematics were recorded using biplane videoradiography during the landing of a 1-leg hop-for-distance activity. Side-to-side differences in knee kinematics between limbs were used as a measure of dynamic constraint. Peak anterior tibial position was the primary outcome measure, and peak anterior tibial position as a function of flexion angle was the secondary outcome measure.

Results:

The passive tibial position of patients with ACLR was 7.5 ± 2.3 mm more anterior compared to that of uninjured participants and 3.1 ± 1.1 mm more anterior than their contralateral limb (P < .05). The mean peak dynamic anterior position was not different between surgical and contralateral limbs in ACLR patients (P = .83). When anterior position was explored as a function of flexion angle, peak anterior tibial position was up to 10.3 mm greater in the ACLR surgical limbs (P = .01) and 7.5 mm in the contralateral limbs (P = .001) compared to the limbs of control participants.

Conclusion:

Passive alignment is abnormal long after ACLR, whereas side-to-side dynamic constraint is largely restored, but with a persistent bias toward greater anterior tibial position that is present bilaterally.

Clinical Relevance:

Compared with similar studies at earlier postoperative time points, the results at long-term follow-up suggest that ACL graft function deteriorates with time, which can be compensated for to some degree by the neuromuscular system.

Keywords

anterior cruciate ligament (ACL)anterior cruciate ligament reconstruction (ACLR)kinematics biplane videoradiography 1-leg hop

A major goal of anterior cruciate ligament (ACL) reconstruction (ACLR) is to restore knee stability. Doing so allows the injured athlete to resume preinjury activities while simultaneously reducing the risk of secondary damage to menisci. While many patients return to some level of recreational sport, evidence has shown that few patients who have undergone ACLR achieve their preinjury level of competition,^32,48 and many go on to develop posttraumatic osteoarthritis (PTOA) despite surgical and rehabilitative interventions.^28,41 The reasons why ACLR fails in these regards remains unknown. Further to this point, comprehensive measures of knee laxity, patient characteristics, societal factors, surgical treatment, and the need for subsequent revision surgery explained only 10% to 20% of the variation in patient-reported outcomes in a multivariable regression analysis of nearly 1600 patients with ACLR followed prospectively for 10 years (NCT00478894).³³ Thus, factors not yet fully captured by these clinical trials may be important determinants of long-term joint health.

Data from large animal models have provided evidence that correlations exist between abnormal joint contact mechanics and the severity of cartilage damage.^3,8,9 Thus, incomplete restoration of kinematic function² is likely a contributing factor in the shortcomings of ACLR. To this end, human studies have demonstrated that residual kinematic abnormalities in anterior tibial position and external rotation are present during dynamic movements up to 2 years after ACLR⁴³; however, the 1° to 2° or millimeter differences compared to contralateral limb kinematics are relatively small. At the same time, evidence from patients with ACLR osteoarthritis suggests that the contralateral limb kinematics may also change over time,^19,22 which could obscure the magnitude of abnormality when the contralateral limb is used as an internal control. The temporal changes of these kinematic observations are unknown, yet their relevance to contralateral injury risk and interpretation of kinematic abnormality has important implications.

The relationship between passive ACL graft laxity and dynamic knee function has also been a long-standing topic of interest, particularly to identify the extent that a deficit in passive constraint can be compensated dynamically by the neuromuscular system.^5,25 It is also unclear how this relationship may evolve over time^10,45 in a way that protects the graft and the long-term health of the articular cartilage or, conversely, promotes graft microdamage and abnormal kinematics.

The objective of the present work was to quantify bilateral passive and dynamic tibiofemoral positions in patients with ACLR and matched healthy control participants at 10 to 15 years of follow-up when degenerative changes are expected to emerge.²⁸ We hypothesized that (1) the anterior tibial position would be greater in the surgical knee compared to the contralateral knee and between the knees of control participants and (2) that the surgical limb differences in anterior tibial position would be greater in the dynamic state compared to the passive state during a 1-leg hop-for-distance landing that challenges the ACL graft.

Methods

Participants and Inclusion Criteria

A total of 21 participants were recruited from a recently completed prospective randomized controlled trial (RCT) (NCT00434837).^1,13,20 Ten patients had undergone ACLR using either a bone–patellar tendon–bone or 4-stranded hamstring autograft 10 to 15 years earlier to their participation in this ancillary study. Eleven control participants were matched demographically to the patients with ACLR at the time of their parent RCT enrollment. The index leg for the control participants was randomly assigned at the time of enrollment. Inclusion criteria for both groups required histories free of severe meniscal or ligamental injuries and no signs of degenerative joint changes, and females could not be pregnant.²⁰ Individuals were not eligible to participate in the present ancillary study if they had sustained additional ACL or graft injuries to either knee, required further knee surgery, or were pregnant. All participants provided written informed consent in accordance with the institutional review board–approved ancillary study protocol.

Clinical Outcomes

As part of the parent RCT, all participants underwent a clinical knee examination by a physical therapist who specialized in sports. Knee status was graded according to the 2000 International Knee Documentation Committee (IKDC)²⁴ criteria, by which knees were rated as “normal” (grade A), “nearly normal” (grade B), “abnormal” (grade C), or “severely abnormal” (grade D).

Dynamic Tibiofemoral Kinematics

Dynamic knee function was measured during the landing portion of a 1-leg hop-for-distance activity. This activity was chosen because of its widespread use in gauging return-to-sport readiness.^4,39,40,42 Biplane videoradiography (BVR) (W.M. Keck Foundation XROMM Facility, Brown University, Providence, Rhode Island) was used to record tibiofemoral kinematics due to its subdegree (<1°) and millimeter (<0.4 mm) accuracy.^23,34 Two specialized radiographic sources and 2 analog image intensifiers coupled to high-speed digital cameras, which were shuttered at 250 frames per second, were used to record tibiofemoral motion as the participant's knee passed through the field of view during the landing. The BVR system geometry was set and calibrated such that the relative positions of the 2 cameras were known and the 3-dimensional (3D) motion could be digitally reconstructed using model-based tracking.^23,34 All participant-specific bone models required for model-based tracking were derived from computed tomography (CT) scans obtained in each knee (GE Lightspeed 16; GE USA) while the participant lay supine on the imaging table with their knees relaxed in extension and their ankles taped together to eliminate potential motion artifact. The bone models were additionally used to derive bone-based anatomic coordinate systems for tibiofemoral kinematic calculations.³¹ The anatomic coordinate systems were automatically defined based on bony geometry and aligned such that flexion-extension and medial-lateral translation occurred about the X axis, abduction-adduction and anterior-posterior translation occurred about the Y axis, and internal-external rotation and inferior-superior translation occurred about the Z axis. The origins of the femoral and tibial coordinate systems were located at the midpoint of the inertial axes used to define the femoral and tibial medial-lateral axes (see left panel in Figure 1 for examples of anatomic coordinate system alignment). The knee alignment during the CT image acquisition served as the position to evaluate passive tibiofemoral alignment. Details of the biplane system geometry, image capture parameters, and CT scan parameters are available in the online supplement.

Figure 1.

Peak anterior tibial position and corresponding flexion angles in passive (left panel, A and B) and dynamic states (right panel, C and D). The group means ± 1 SD are denoted by the horizontal bars. *P < .05. Data from 1 representative control and 1 patient with anterior cruciate ligament reconstruction (ACLR) are represented by diamond and square shapes, respectively. Tibiofemoral alignment in the computed tomography scanner is shown for these 2 participants on the far left, with the anatomic coordinate system X-Y-Z axes shown in red, green, and blue, respectively. The more anterior position of the tibial coordinate system origin of the patient with ACLR relative to the femoral origin (black circles) is illustrated by the gold arrow and outlines oriented in the anterior direction.

Lastly, a force platform (Kistler model 9260AA; Kistler USA) was used to synchronously record the vertical ground reaction force during the 1-leg hop-for-distance landing. The 1-leg hop distance was reduced to 65% of their maximum distance to ensure participants could land repeatably within the BVR system field of view. Up to 5 hop trials were recorded for each leg, while 1 hop trial was selected for final analysis based on the quality of the BVR capture. Criteria for this decision required both the femur and tibia to be visible within the BVR field of view at ground contact with minimal occlusion from the contralateral leg for at least 0.2 seconds after ground contact. This time frame was of interest because it spans the time from ground contact to peak ground reaction force during landing—a time when the knee is near extension and the ACL undergoes greater loading.⁴⁹ It is also a time frame when the ACL is at, or near, peak strain in healthy persons.^18,44 Contact was defined as the BVR frame when the vertical ground reaction force exceeded 50 N.^30,51

Kinematic Analysis

The orientation of the tibial anatomic coordinate system relative to the femoral anatomic coordinate system was resolved for each dynamic frame of data recorded. The 3D motion was expressed in 6 degrees of freedom as described above. The passive positions of the femoral and tibial CT models were extracted from the orientations of the bones in the participants’ CT images and expressed as the orientation of the tibia relative to the femur in the same manner as the dynamic kinematic calculations.

Passive Outcome Measures

The bilateral passive anterior tibial positions and the corresponding flexion angles were calculated for each participant. This passive position was defined by the orientations of the tibial and femoral anatomic coordinate systems in each participant's CT scan (Figure 1, left panel).

Dynamic Outcome Measures

Peak anterior tibial position within the first 0.2 seconds of ground contact was the primary outcome measure. Because anterior tibial position depends on knee flexion angle,^16,38,47 both mean knee flexion angle at the time of ground contact and peak anterior tibial position as a function of flexion angle were evaluated. The latter was evaluated by regressing peak anterior position (dependent variable) by flexion angle (independent variable). Knee ranges of motion in flexion, axial tibial rotation, and anterior tibial translation were extracted as exploratory outcome measures. Ranges of motion in these degrees of freedom were defined as the range (maximum-minimum) of the tibiofemoral alignment between ground contact and 0.2 seconds after contact. All measures were calculated bilaterally.

Statistical Analysis

After testing for equal variance, 2-sided unpaired t tests were used to test for differences in participant characteristics. Because of the small sample size, the distribution of IKDC scores was evaluated descriptively. Generalized estimating equations were used to test for differences in the primary and secondary kinematic outcome measures between limbs within the ACLR and control groups and between the ACLR and control groups. Classical sandwich estimation was used to protect against possible model misspecification. Pairwise comparisons between groups were tested within the models via orthogonal contrasts. The Holm test was used to adjust for multiple comparisons while maintaining a 2-tailed alpha of .05. An adjusted P value <.05 was used to determine statistical significance. All analyses were conducted in commercial software (SAS Version 9.4; SAS Institute).

Results

There was no difference in mean participant age (P = .28), BMI (P = .14), or length of follow-up since parent trial enrollment (P = .73) between experimental groups shown in the first 3 rows of Table 1. More than 90% of patients with ACLR had normal or nearly normal knees, and 91% of control participants had normal knees (Table 1).

Table 1

Participant Characteristics and Clinical Outcomes ^a

	ACLR Group (n = 10)	Control Group (n = 11)
Age, y	33.8 [10.0]	38.1 [7.5]
BMI	26.9 [4.2]	24.3 [3.2]
Length of follow-up	12.1 [1.2]	11.9 [1.4]
Patient sex
Female	5 (50.0)	5 (45.5)
Male	5 (50.0)	6 (54.5)
Graft type
BPTB	7 (70.0)	NA
HS	3 (30.0)	NA
IKDC score
Normal	3 (30.0)	10 (90.9)
Nearly normal	6 (60.0)	1 (9.1)
Abnormal	0 (0.0)	0
Severely abnormal	1 (10.0)	0

Data are presented as n (%) or mean [SD]. BMI, body mass index; BPTB, bone–patellar tendon–bone graft; HS, 4-strand hamstring graft; International Knee Documentation Committee; NA, not applicable.

Whereas passive state flexion angles were consistent bilaterally in patients with ACLR (P = .82) and between patients with ACLR and control participants (P = .20) (Figure 2B), the passive ACLR tibial position was 7.5 ± 2.3 mm more anterior compared to that of uninjured control participants (95% CI, 2.6-12.4 mm; P = .02) and 3.1 ± 1.1 mm more anterior than the contralateral limb (95% CI, 0.77-5.4 mm; P = .04) (Figure 2A).

Figure 2.

Regression models of the peak anterior tibial position at the corresponding flexion angle at which it occurred during the hop landing. Shaded bands show the 95% confidence interval about the regression. *P < .05 in the y-intercept of the anterior tibial position as a function of flexion angle. **P < .05 between the slopes of the linear regressions. ACLR, reconstructed limb of patients with ACLR; ACLR Contralateral, contralateral limb of patients with ACLR; Control Contralateral, contralateral limb of control participants; Control Index, index limb of control participants.

Knee flexion angle at peak anterior tibial position during the 1-leg hop-for-distance landing was also consistent bilaterally in patients with ACLR (P = .38) and between ACLR surgical knees and control knees (P = .90) (Figure 2D). Contrary to the passive alignment, peak dynamic anterior tibial position during the 1-leg hop-for-distance landing was not significantly different between surgical and contralateral limbs in patients with ACLR (0.44 ± 2.1 mm; 95% CI, –4.0 to 4.9 mm; P = .83) or compared to control participants (5.0 ± 3.1 mm; 95% CI, –1.44 to 11.5 mm) (P = .12) (Figure 1C).

Dynamic anterior tibial position as a function of flexion angle (ie, regression model slope) was bilaterally symmetric for both patients with ACLR and control participants (P = .24 for both comparisons) (Figure 2, B and D). Compared to control participants, only the ACLR contralateral limb regression model slope reached significance with approximately 1 mm–greater peak anterior tibial translation for every degree decrease in knee flexion (P = .02; 95% CI, 0.2-2.1) (Figure 2C). The most striking finding was the difference in regression model intercepts, which were 10.3 mm greater in the ACLR surgical limbs (95% CI, 1.7-19.0 mm; P = .01) (Figure 2A) and 7.5 mm in the contralateral limbs (95% CI, 1.8-13.2 mm; P = .001) (Figure 2C) compared to control limbs.

In the analyses of secondary outcomes (Figure 3), ACLR surgical limbs were constrained in greater external rotation by –2.9° (95% CI, –0.1° to –5.8°) compared to the contralateral limbs of control participants (P = .042). When compared to the contralateral limb, this constraint in greater external tibial rotation was not statistically significant (P = .06; 95% CI, 0.3° to –6.3°). No other significant differences in range of motion were found between limbs or groups.

Figure 3.

Range of motion for flexion, internal rotation, and anterior translation. Error bars represent ± 1 SD. *P < .05. ACLR, anterior cruciate ligament reconstruction.

Discussion

The results of this study supported the hypotheses that (1) anterior tibial position would be greater in the surgical knees compared to the contralateral knees of patients with ACLR and compared to control participant knees and (2) that surgical limb differences in anterior tibial position would be greater in the dynamic state compared to the passive state during a 1-leg hop-for-distance landing.

The finding that the tibiae of patients undergoing ACLR were positioned approximately 3 mm more anterior compared to their contralateral limb in a passive state suggests a deficit in ACL graft function. The magnitude of side-to-side difference we noted was similar to arthrometer measures of laxity in the ACLR population,^1,12,13 and consistent with a similar observation reported by Markes et al²⁹ in magnetic resonance images of ACLR knees within the first 3 years of surgery. Moreover, the magnitude of graft dysfunction in the passive state appears to be even greater when compared to age-matched control participants. Here, tibiae of the reconstructed knees were translated a mean of 7.5 mm more anteriorly as compared to either limb of control participants, as shown in Figure 1A. The trend that the ACLR contralateral limb also showed a greater anterior position than both limbs of the control participants (P = .06-.10) may suggest that the increased position reflects a naturally occurring risk factor, such as increased tibial slope.¹¹ For example, Giffin et al²¹ found that an increased tibial slope of approximately 4.4° caused an increase in anterior translation of the tibia relative to the femur at rest in full extension by about 3.6 mm. Coupled with a more compliant ACL graft, increased posterior tibial slope could help explain the dramatic differences in anterior tibial position we observed and is an ongoing area of investigation.

Peak anterior tibial position at the time of the 1-leg hop-for-distance landing was similarly abnormal: for the same flexion angle, the tibia of patients with ACLR was translated anteriorly by approximately 4 mm over their contralateral limb, and up to 10 mm compared to that of the control participants. We chose to examine peak anterior translation as a function of knee flexion given the known coupled motion between the degrees of freedom.^16,38,47 Although flexion angle at the time of peak anterior tibial translation was not significantly different between patients undergoing ACLR and control participants (Figure 1D), it was highly variable with an SD of ±12.0°. Examining coupled motion between anterior tibial position and knee flexion angle was a way to control for this variability. We also chose to evaluate absolute tibiofemoral position rather than a change from a standardized neutral position; doing so circumvented the need to manipulate participants’ natural standing posture to avoid occlusion from the contralateral limb in the BVR field of view while simultaneously revealing important differences in passive tibiofemoral alignment in the unloaded CT position.

Contrary to existing work that has examined side-to-side differences in peak anterior tibial position during a forward 1-leg hop landing,^17,22 the magnitude of the dynamic anterior tibial position abnormality relative to that of uninjured control participants observed here represents a 5- to 7-fold difference and is a major departure from what was previously known about kinematic abnormalities after ACLR. Given the significant difference in passive anterior tibial position, it is possible that anterior tibial translation increases with time since surgery as graft function deteriorates. Although the magnitude of change was small, Tashman et al⁴³ similarly noted an increase in mean anterior tibial translation of 0.85 mm within the first year after ACLR. It seems plausible that this 0.9 mm/year drift toward greater anterior tibial position compounded over a 10- to 15-year follow-up period could amount to the 10-mm magnitude difference relative to that of the uninjured participants we observed here.

Another possible explanation for the large difference in ACLR limb kinematics is the choice of dynamic activity. We chose the 1-leg hop-for-distance because of its use in rehabilitation programs and inclusion as a return-to-sport criterion.^4,39,40,42 Whether the large kinematic differences we noted are related to the time since surgery or to the dynamic nature of the 1-leg hop cannot be discerned without further study. To this point, Nishida et al³⁶ reported task dependency in estimated ACL elongation in healthy athletes, with ACL elongation being greatest during the landing of a challenging vertical, 1-leg, 180° turn hop compared to either running at different speeds or landing a vertical drop jump. Thus, choosing a challenging neuromuscular activity may be essential for discerning biomechanical changes after ACLR.

An unexpected finding was that the dynamic peak tibial position of the contralateral limb of patients with ACLR was also significantly more anterior by approximately 7.5 mm during the 1-leg hop-for-distance landing compared to that of control participants. In other words, the peak anterior tibial position of the contralateral limb of patients with ACLR was closer to that of their reconstructed limb than to that of control limbs. It is possible that the more anterior tibial position was a factor that led to injury in the first place and could be related to nonmodifiable anatomic features such as posterior tibial slope, as discussed earlier. Further to this point, posterior tibial slope has been shown to be an independent risk factor for ACL injury⁶ and to relate to graft laxity, radiographic joint changes, and inferior Knee injury and Osteoarthritis Outcome Scores.²⁶ Meanwhile, recent reviews have summarized the growing evidence that ACL injury triggers central nervous system adaptations that manifest as altered sensorimotor cortical activation, diminished proprioception, and peripheral motor impairments.^14,35 Given the systemic nature of these adaptations, it could be expected that sensorimotor changes would not be isolated to ipsilateral function, but rather span bilaterally as the postural locomotor network strives to regain symmetry.²⁷ It is worth noting that previous studies in this ACLR cohort^7,50 have described bilateral differences in neuromuscular activation patterns that mirror the kinematic abnormalities described here. Hofbauer et al²² similarly described bilateral kinematic changes between 5 and 12 months post-ACLR during a forward 1-leg hop landing, with the difference between limbs becoming smaller, with flexion angle and external rotation moving toward greater symmetry. However, few studies have investigated longitudinal kinematic changes alongside a reference healthy cohort. Erhart-Hledik et al¹⁹ described bilateral changes in gait kinetics from 3 to 8 years post-ACLR with the contralateral limb dovetailing the surgical limb biomechanics. Taken together, we speculate that the dynamic constraint conferred by the neuromuscular system likely played a role in the degree of symmetry between ACL-reconstructed and contralateral limbs, which did not completely compensate for what we believe to be diminished ACL graft function at long-term follow-up.

Exploratory analyses of secondary kinematic variables revealed that ACLR limb internal-external tibial rotation range of motion was constrained toward greater external rotation by 2.9° compared to both the contralateral limb and control limbs, which aligns with previous BVR measures at 12 months post-ACLR describing a 1.9° offset during the loading response phase of downhill running.⁴³ Our results suggest that this offset does not improve with time and could be a contributing factor to the development of PTOA after ACLR alongside the more dramatic offset in anterior tibial position.⁴⁶ While our focus on anterior tibial position revealed the likely presence of ACL graft laxity, the range of motion results do not suggest the presence of general joint laxity in the degrees of freedom we evaluated and, in fact, suggest overconstraint in internal-external tibial rotation (eg, Figure 3). Evaluating varus-valgus and inferior-superior degrees of freedom in future work could reveal additional insight into meniscal and cartilage function in these patients. Similarly, evaluating biomechanical strategies that span the lower limb kinetic chain could provide insight into how adjacent joint biomechanics may modulate knee kinematics,³⁷ but these measures were not pursued here due to the limited field of view associated with BVR imaging.

A few limitations are worth noting. The sample size was limited by the number of patients remaining in the parent study who met the inclusion criteria for this analysis, in turn restricting our ability to explore the potential effects of sex¹³ and introducing the possibility of a selection bias in our participant recruitment. Conversely, recruiting from this curated population served to limit participant heterogeneity and enhance the detectible effect size. Post hoc power analyses revealed that we could detect a between-group difference in magnitude of 2 SD units with 80% power while accommodating the Bonferroni-adjusted comparisons and a 2-tailed alpha of .05. The significant differences between ACLR in passive anterior tibial position shown in Figure 1A approached this threshold with effect sizes ranging from 0.80 to 1.46 SD units. The significantly constrained tibial range of motion in Figure 3 reached an effect size of –1.17 SD units. Whereas we found significant differences in these tests, limited power in other kinematic comparisons (0.03-0.84 SD units) diminished our ability to detect true differences, which was likely true of dynamic peak anterior position (Figure 1C). Here, effect sizes ranged from 0.05 to 0.83 SD units. Conversely, the variation in participant kinematics enhanced our analyses of peak anterior tibial position as a function of flexion angle. In the analyses shown in Figure 2, we had 80% power to detect differences in regression model slopes and intercepts of 0.2 mm/deg and 2 mm, respectively; the smallest differences in model slopes and intercepts were 0.2 mm/deg and –1.9 mm, respectively, in control participants, where we expected the outcomes to be symmetric.

To the best of our knowledge, this work is one of the first reports of kinematics obtained up to 15 years post-ACLR surgery using highly accurate BVR. Conversely, we do not have sufficient power to explore possible effects that autograft type may have had on our outcome measures; however, clinical, functional, and patient-reported outcomes of the parent study suggest that graft type is likely a negligible confounding factor at this follow-up time.^12,13 It is also possible that the 5-year range within the follow-up period could have contributed to the variation in kinematic outcomes, although a longitudinal study design would be needed to rigorously explore this line of questioning. The large difference between tibiofemoral kinematics reported at the 2-year follow-up⁴³ versus ≥10 years provides strong motivation for future studies that determine the relationship between early passive and dynamic kinematic outcomes and long-term joint function in patients with ACLR and matched control participants. Lastly, we focused only on the 1-leg hop-for-distance activity as opposed to walking, the most common form of physical activity in the United States.¹⁵ Because of its frequency, walking is likely to be highly relevant to mechanical mechanisms that may promote PTOA. Conversely, the 1-leg hop-for-distance was chosen because of its challenging nature, its widespread use as a return-to-sport test,^4,39,40,42 and its potential to reveal underlying kinematic abnormalities that may be more difficult to detect during a less challenging task.³⁶

Conclusion

This study demonstrated that passive alignment is abnormal long after ACLR, whereas dynamic constraint in the context of bilateral symmetry is largely restored, but with a persistent bias toward greater peak anterior tibial position. Compared to similar studies at earlier postoperative time points, the results at long-term follow-up suggest that ACL graft function deteriorates with time, which can be compensated for to some degree by the neuromuscular system, but not completely.

Supplemental Material

sj-pdf-1-ojs-10.1177_23259671251414857 – Supplemental material for Passive Laxity With Functional Stability Reveals Potential Bilateral Dynamic Compensatory Mechanisms in Patients Undergoing ACL Reconstruction at Long-term Follow-up

Supplemental material, sj-pdf-1-ojs-10.1177_23259671251414857 for Passive Laxity With Functional Stability Reveals Potential Bilateral Dynamic Compensatory Mechanisms in Patients Undergoing ACL Reconstruction at Long-term Follow-up by Jillian E. Beveridge, Madalyn Hague, Meggin Q. Costa, Lauren R. Parola, Janine Molino and Braden C. Fleming in Orthopaedic Journal of Sports Medicine

Footnotes

Acknowledgements

The authors thank Ms. Erika Travares and Analicia Behnke for their technical assistance collecting BVR data.

Final revision submitted December 12, 2025; accepted December 18, 2025.

One or more of the authors has declared the following potential conflict of interest or source of funding: This research was supported by the National Institutes of Health (NIH) National Institute of Arthritis and Musculoskeletal and Skin Diseases (K99AR069004, R01AR047910, R01AR074973, and R01AR078924), NIH National Institute of General Medical Sciences (P30-GM122732 [Bioengineering Core of the COBRE Centre for Skeletal Health and Repair] and P30-GM139664 [RIH Injury Control COBRE]), and Lucy Lippitt Endowment. B.C.F. is a co-founder of Miach Orthopaedics and receives royalties. His spouse also has an equity interest in the company. B.C.F. maintains a conflict of interest management plan that is managed by Rhode Island Hospital. The current study does not involve Miach Orthopaedics or their products. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

Ethical approval for this study was obtained from the Institutional Review Board of Brown University Health (Protocol No. 201305).

ORCID iDs

Jillian E. Beveridge

Lauren R. Parola

Janine Molino

Braden C. Fleming

Supplemental Material

Supplemental Material for this article is available at .

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