Assessment of Landing Stability in Patients After Anterior Cruciate Ligament Injury and Reconstruction: A Systematic Review and Meta-analysis

Abstract

Context:

Dynamic postural control deficits are prevalent in people with anterior cruciate ligament injury (ACLI) or reconstruction (ACLR). Time to stabilization (TTS) and the dynamic postural stability index (DPSI) are used to assess dynamic postural stability during a jump-landing task. However, results vary on whether landing stability can adequately demonstrate dynamic postural deficits in patients with ACLI and ACLR.

Objective:

To (1) describe common methods and parameters for determining TTS and DPSI, and (2) identify the differences in TTS and DPSI across different jump-landing tasks and directions between the ACLI or ACLR and control groups.

Data Sources:

PubMed, Embase, Web of Science, Cochrane Library, Scopus, CINAHL, and SPORTDiscus were searched for articles from conception until March 2024.

Study Selection:

Clinical studies assessing dynamic postural stability between patients with ACLI and ACLR and controls were included. Eleven articles were included in the analysis.

Study Design:

Systematic review and meta-analysis.

Level of Evidence:

Level 4.

Data Extraction:

The following information was extracted from included articles: demographic data, sample size, methodology, landing stability test outcomes, and calculation methods of outcomes. Different jump tasks were explored, and meta-analyses were conducted on the landing stability test outcomes.

Results:

In forward jump-landing tasks, knees affected by ACLI or ACLR needed more time than controls to achieve stabilization, showing a moderate effect in the anteroposterior direction (based on 2 studies, 47 affected knees versus 44 healthy knees; standardized mean difference [SMD] = 0.438), and a large effect in the vertical direction (based on 3 studies, 77 affected knees versus 74 healthy knees; SMD = 0.656).

Conclusion:

These findings demonstrate impaired dynamic stability in ACLI/ACLR patients, highlighting the importance of TTS as an effective measure for assessing landing stability.

Inadequate postural stability is considered a potential risk factor for initial and recurrent anterior cruciate ligament injuries (ACLIs) after anterior cruciate ligament reconstruction (ACLR).^8,28 Recurrent ACLIs often exhibit a noncontact injury pattern similar to the initial injury, indicating unresolved neuromuscular deficits during typical dynamic movements involved in sports activities.^27,28 Persistent neuromuscular deficits after ACLI may reflect neuroadaptations that developed subsequent to the initial injury, belying a merely straightforward musculoskeletal injury. ²¹ Previous studies have found sustained somatosensory functional impairments in the injured limb, which may persist for several years after intervention and rehabilitation. ³⁴ Therefore, the assessment of postural control deficits in patients with ACLI or ACLR holds significant clinical relevance and research value. However, despite numerous methods for measuring postural control, ¹⁰ no standardized measurements have been established for postural control deficits after ACLIs.

Previous studies have often used static postural stability tasks to assess lower-limb postural stability and neuromuscular function in patients with ACLI or ACLR.^2,7,20 However, static measures may not adequately reflect postural stability during dynamic sporting activities or provide sufficient challenge for physically active people.^6,14 Therefore, evaluating postural stability through dynamic activities that closely simulate athletic movements may offer greater insight and clinical relevance. Webster and Gribble ³⁹ found that the dynamic postural stability of healthy knees was significantly better than that of knees with ACLR. However, Head et al ¹⁵ found no significant differences between injured and healthy limbs in ACLR. The differences in the results of existing studies may be attributed to variations in the jump-landing tasks implemented and parameters measured. Therefore, the existing research needs to be compiled and summarized, the testing methods of dynamic postural stability in patients with ACLI and ACLR clarified, and a meta-analysis of the results performed.

This systematic review and meta-analysis aimed to (1) describe common methods and parameters for dynamic postural stability assessment, and (2) identify the differences in dynamic postural stability between the ACLI or ACLR group and a control group.

Methods

Study Design

The systematic review and meta-analysis was designed and conducted in accordance with the reporting guidelines of Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA). ²⁶ The PRISMA checklist is presented in Online Supplementary Material 1. We conducted a comprehensive literature review across 7 databases to identify studies evaluating dynamic postural stability in patients with ACLI or ACLR. Selected studies were screened systematically, and relevant variables—such as demographic information, testing protocols, and outcome measures—were coded using a standardized data extraction form. Finally, we performed statistical analyses, employing a random-effects model to synthesize the extracted data and calculate pooled effect sizes. The study protocol has been registered with the International Prospective Register of Systematic Reviews.

Search Strategy

A systematic literature search was conducted independently by 2 of the authors on 7 electronic databases: PubMed, Embase, Web of Science, Cochrane Library, Scopus, CINAHL, and SPORTDiscus, from inception until March 1, 2024. Four main groups of search terms were defined: (1) ACL-related terms, (2) injury/reconstruction-related terms, (3) methods-related terms, and (4) outcome-related terms. In each group, relevant keywords were combined with “OR,” and then the 4 groups were combined with “AND.” Details of the full search strategy are shown in Table 1. The reference lists of the included articles were checked manually.

Table 1.

Details of electronic database search strategies of the systematic review

(1) ACL-related terms	(ACL OR “Anterior Cruciate Ligament” OR “Cruciate Ligament, Anterior” OR “Anterior Cruciate Ligaments” OR “Cruciate Ligaments, Anterior”) [Title/Abstract]
(2) ACLI/ACLR-related terms	(injur* OR tear* OR rupture* OR instabil* OR unstable OR repair* OR reconstruct* OR surg* OR impair* OR ACLR) [Title/Abstract]
(3) Methods-related terms	(land* OR jump* OR “step down” OR hop OR leap* OR drop* OR “time to stabilization" OR "time-to-stabilization” OR TTS OR DPSI OR “dynamic postural stability index”) [Title/Abstract]
(4) Outcome-related terms	(stabil* OR dynam* OR balance OR postur* OR “time to stabilization” OR “time-to-stabilization” OR TTS OR DPSI OR “dynamic postural stability index”) [Title/Abstract]
Search strategies	(1) AND (2) AND (3) AND (4)

Inclusion Criteria

Given the controversy surrounding the protocols and outcomes of dynamic postural stability testing, 3 authors with experience in kinesiology, orthopaedics, and physical therapy reached a consensus on 2 indicators that are often used in measuring dynamic lower-limb postural controls: time to stabilization (TTS),^{3,4,6,13,17,22,23,29,30,39} and dynamic postural stability index (DPSI).^15,16,32,36 The TTS assessment evaluates the time required to reduce the resultant ground reaction force (GRF) after completing a jump-landing task, with a longer duration indicating decreased dynamic stability. ⁶ Similarly, the DPSI reflects a person’s ability to disperse GRFs after completing a jump-landing task. The total DPSI is obtained by determining a combined modified root mean square by calculating all 3 GRF components (mediolateral [ML], anteroposterior [AP], and vertical), with higher scores indicating decreased dynamic stability. ⁴² The formula for obtaining the DPSI is provided in Online Supplementary Material 2.

The inclusion criteria were the following: (1) investigations of dynamic postural stability using measurements of aforementioned outcome after performing a specific motor task and landing onto a stable force plate with a single limb; (2) comparisons between knees of patients with ACLI or ACLR and healthy knees of participants without a history of ankle injury, or comparisons between injured and healthy contralateral knees in patients with ACLI or ACLR; (3) peer-reviewed, full-text, English-language articles; and (4) case-control, cross-sectional, cohort, and randomized controlled trials. The exclusion criteria were the following: (1) patients with other lower limb injuries, such as ankle and hip joint injuries; (2) no comparison between the affected knees of ACLI or ACLR patients and the healthy knees of healthy controls; and (3) case reports, case series, and other study designs.

Article Selection and Data Extraction

Two authors independently reviewed the articles and extracted data. Unresolved disputes were discussed with the senior author until a consensus was reached. Titles, abstracts, and full texts of articles were screened step by step, and duplicates were removed. The following information was extracted: evidence level, demographic characteristics (age, sex), time from injury or surgery (months), graft type of reconstruction, sample size, details of test methodology including jump task, sampling frequency (Hz), and duration of trials (seconds), signal processing methods (input signal and signal smoothing type), and numerical data (means and standard deviations). In the event that numerical data were confusing or not fully reported, the corresponding authors of the articles were contacted by email to obtain clarification. All extracted variables are summarized in Online Supplementary Material 3.

Quality and Risk of Bias Assessment

All the authors discussed the standards for each item before formally rating them, after which 2 authors rated the included studies independently. Discrepancies in the scores were discussed between the 2 reviewers until a consensus was reached. In cases where consensus could not be reached, a third reviewer was consulted to resolve the disagreement.

The Newcastle-Ottawa Scale (NOS) was used to assess the methodological quality and risk of bias in the included observational studies. ⁴⁰ The NOS is a validated assessment tool that provides specialized versions for case-control, cohort, and cross-sectional studies, focusing on 3 main domains: selection, comparability, and exposure/outcome. ⁴⁰ Case-control studies are scored for quality on the NOS as follows: 0 to 3 points, poor; 4 to 6 points, fair; and 7 to 9 points, good. Cross-sectional studies are scored for quality as follows: 0 to 4 points, unsatisfactory; 5 to 6 points, satisfactory; and 7 to 8 points, good. ⁴⁰

Statistical Analysis

A meta-analysis of studies with similar measurement units, comparison types (e.g., between groups), and movement directions (e.g., eversion) was performed using Stata Version 14 (Stata Corp LP). Subgroup analyses were performed for studies with the same jump tasks. All extracted and pooled data were presented as standardized mean differences (SMD) using Cohen’s d between controls and the injured ankle with 95% CIs. Higher SMDs indicated larger postural stability deficits, with 0.2-0.5, 0.5 to 0.8, and >0.8 indicating a small, moderate, and large effect size, respectively. A random-effects model was employed to account for the variability in participant characteristics, inclusion criteria, and test methodologies across the included studies, thereby yielding more conservative and generalizable pooled estimates. Heterogeneity was assessed using the Q and I² statistics, with P < 0.05 and I² values ≥75% indicating statistical significance and high heterogeneity, respectively.

Results

Study Selection and Characteristics

In total, 6412 eligible unique studies were retrieved by electronic and manual searches, of which 11 met the inclusion criteria (Figure 1). Of the 11 studies included in this review, most were categorized as Level 3 to Level 4 evidence. Specifically, 1 study (9.1%) was classified as Level 1, ³² 7 studies (63.6%) were Level 3,^{5,13,15,16,29,30,39} and 3 studies (27.3%) were Level 4.^3,4,23 These studies included a total of 192 affected knees (ACLI/ACLR) and 186 healthy knees, and all patients were allowed to return to sports. The reported number of male patients who underwent ACLI or ACLR was 79, compared with 113 female patients. The range of mean age of patients was 18.1 to 35.6 years. Of the 104 patients that reported the type of graft used for the reconstruction, 61 (58.7%) patients used hamstring tendon, 37 (35.5%) patients used bone-patellar-tendon-bone graft, and 6 (5.8%) patients used quadricep tendon graft. Nine studies stated that their patients had no combined injuries or pain affecting lower limb balance,^{3-5,13,15,16,23,29,32} while 2 studies did not report the presence of combined injuries in their patient populations.^29,39 Of the 11 studies, 2 assessed the DPSI,^15,16 8 assessed the TTS,^{3-5,13,23,29,30,39} and 1 evaluated both DPSI and TTS. ³² Further details, including evidence level, demographic characteristics (age, sex), time from injury or surgery, graft type of reconstruction, sample size, details of test methodology (jump task and sampling frequency), and signal processing methods (input signal and signal smoothing type) are presented in Online Supplementary Material 3.

Figure 1.

Flow chart of the systematic review selection process.

Quality and Risk of Bias Assessment

Semiquantitative assessment of the 11 studies was performed using the NOS scale, and the scores ranged from 4 to 7. Two studies were rated good quality, 8 were satisfactory quality, and 1 was rated unsatisfactory quality. Almost all studies showed convincing comparability, validated assessment of the outcomes, and appropriate statistical testing. Four studies exhibited justified and satisfactory calculation of sample size. However, all the studies lacked sample representativeness. The results of the quality and risk of bias assessments and NOS scale scores are shown in Online Supplementary Material 4.

Jump Tasks Performed

Although the participants in each included study performed landing actions, the execution of the jump tasks was not entirely consistent. Five jump tasks were performed for TTS assessment, whereas 4 jump tasks were performed for DPSI assessment, all of which can be summarized into 6 types: forward jump, lateral jump, diagonal jump, step down, height-reached jump, and run-and-stop. A detailed description of the jump tasks is shown in Table 2.

Table 2.

Detailed description of searched jump tasks

First authors (year)	Jump task	Device	Start posture	Jump distance	Jump/descend height	Progress angle, deg a	Land posture	Duration of each trial, seconds	Number of tests	Measured outcomes
Calisti 3 (2023)	Forward jump	AMTI	Stand on both legs	40% of body height	Jump over a 30-cm hurdle	0	Land on the test leg, place hands on hips	8	5	TTS
Colby 5 (1999)	forward jump	Bertec force plate (Bertec Corp)	Stand on the test leg, place hands on hips	Leg length	Jump over a 7.5-cm barrier	0	Land on the test leg, place hands on hips	30	10	TTS
Phillips 30 (2008)	Forward jump	Kistler force plates (Kistler Instrument Co)	Stand on the test leg	Maximum hop distance	NR	0	Land on the test leg	5	5	TTS
Head 15 (2019)	Forward jump	AMTI	Stand on both legs	40% of body height	Jump over a 12 inch hurdle	0	Land on the test leg, place hands on hips	10	3	DPSI
Heinert 16 (2018)	Forward jump	Bertec force plate (Bertec Corp)	Stand on both legs	40% of body height	Jump over a 12 inch hurdle	0	Land on the test leg, place hands on hips	10	5	DPSI
Heinert 16 (2018)	Lateral jump	Bertec force plate (Bertec Corp)	Stand on both legs	33% of body height	Jump over a 6-inch hurdle	0	Land on the test leg, place hands on hips	10	5	DPSI
Heinert 16 (2018)	Diagonal jump	Bertec force plate (Bertec Corp)	Stand on the nontest leg	110 cm	NR	55	Land on the test leg, place hands on hips	10	5	DPSI
Patterson 29 (2013)	Diagonal jump	AMTI	Stand on the nontest leg	110 cm	NR	55	Land on the test leg, place hands on hips	15	3	TTS
Patterson 29 (2013)	Step down	AMTI	Stand on both legs, place hands on hips	NR	Drop from a 35-cm box	0	Land on the test leg, place hands on hips	15	3	TTS
Gholipour Aghdam 13 (2024)	Step down	AMTI	Stand on both legs	NR	Drop from a 30-cm box	0	Land on the test leg	15	6	TTS
Colby 5 (1999)	Step down	Bertec force plate (Bertec Corp)	Stand on both legs, place hands on hips	NR	Drop from a 19cm box	0	Land on the test leg, place hands on hips	30	10	TTS
Niemeyer 23 (2019)	Step down	Capacitive force measurement platform (Zebris FDM, Zebris Medical GmbH)	Stand on both legs	NR	Drop from a 32-cm box	0	Land on the test leg	15	3	TTS
Robey 32 (2009)	Height-reached jump	AMTI	Stand on both legs	40% of body height	50% of the maximum jump height	0	Land on the test leg, place hands on hips	30	3	TTS, DPSI
Webster 39 (2010)	Height-reached jump	Bertec force plate (Bertec Corp)	Stand on both legs	70 cm	50% of the maximum jump height	0	Land on the test leg, place hands on hips	10	10	TTS
Chaput 4 (2022)	Height-reached jump	Bertec force plate (Bertec Corp)	Stand on both legs	70 cm	50% of the maximum jump height	0	Land on the test leg, place hands on hips	10	3	TTS
Phillips 30 (2008)	Run-and-stop	Kistler force plates (Kistler Instrument Co)	Run at 2 to 3 m/s	NR	NR	0	Land on the test leg	5	5	TTS

AMTI, Advanced Mechanical Technologies Inc; NR, not reported.

^aJump forward with an angle of progression in an anterior-medial direction.

TTS Assessment

Nine studies reported dynamic postural stability index data and were included in the meta-analysis. Subgroups were grouped according to direction of TTS.

Forward Jump

Three studies selected forward jump task to investigate TTS between affected knees and healthy knees. The subgroup analyses for the AP and ML directions included 47 affected knees and 44 healthy knees. For the AP direction, the pooled results revealed a moderate effect for longer TTS in affected knees (SMD = 0.438; 95% CI, 0.021 to 0.855; I² = 0%), whereas for the ML direction, the pooled results revealed no significant difference (SMD = 0.393; 95% CI, –0.186 to 0.972; I² = 45.6%). The subgroup analyses for the vertical directions included 77 affected knees and 74 healthy knees, and the pooled results revealed a large effect for longer TTS in affected knees affected knees (SMD = 0.656; 95% CI, 0.258 to 1.055; I² = 27.8%) (Figure 2a).

Figure 2.

Results of TTS for the (a) forward jump, (b) step down, (c) height-reached jump, and (d) diagonal jump and run-and-stop tasks. Results of the DPSI for the (e) forward, lateral, and diagonal jump tasks, and 3 directions postural stability index for the (F) forward jump task only. ACLD, anterior cruciate ligament deficient; ACLI, anterior cruciate ligament injury; ACLR, anterior cruciate ligament reconstruction; DPSI, dynamic postural stability index; RVTTS, resultant vector TTS; SE, sequential averaging; SMD, standardized mean difference; TTS, time to stabilization; UTOP, unbounded third-order polynomial.

Step Down

Four studies selected a step down task to investigate TTS between affected knees and healthy knees. The subgroup analyses for the AP and ML directions included 41 affected knees and 41 healthy knees. For the AP direction, the pooled results revealed no significant difference (SMD = 0; 95% CI, –0.435 to 0.434; I² = 0%), and for the ML direction, the pooled results also revealed no significant difference (SMD = –0.096; 95% CI, –0.532 to 0.339; I² = 0%). The subgroup analyses for the vertical directions included 49 affected knees and 50 healthy knees, and the pooled results revealed a large effect for longer TTS in affected knees affected knees (SMD = 0.375; 95% CI, –0.338 to 1.087; I² = 66.6%) (Figure 2b).

Height-Reached Jump

Robey et al ³² found no significant differences in the TTS in AP, ML, or vertical direction between affected knees and healthy control knees. Two studies combined APTTS and MLTTS into RVTTS and also revealed no significant difference (SMD = 0.439; 95% CI, –0.48 to 1.358; I² = 64.2%) (Figure 2c).

Diagonal Jump

One study involving 17 patients and 17 healthy controls implemented the diagonal jump to assess dynamic postural stability and reported significant differences between groups in APTTS, MLTTS, and RVTTS. Large effect sizes were observed in MLTTS (SMD = 0.815; 95% CI, 0.114 to 1.516) and RVTTS (SMD = 0.806; 95% CI, 0.105 to 1.507), whereas a moderate effect size was observed in APTTS (SMD = 0.712; 95% CI (0.018 to 1.407) (Figure 2d).

Run-and-Stop

One study involving 30 patients and 30 healthy controls implemented jogging to assess dynamic postural stability and reported significant differences between groups in vertical TTS with a large effect size (SMD = 0.824; 95% CI, 0.296 to 1.352) (Figure 2d).

Dynamic Postural Stability Index

Three studies selected forward jump task to investigate total DPSI between affected knees and healthy knees, including 41 affected knees and 41 healthy knees. The pooled results of total DPSI for the forward jump task revealed no significant difference (SMD = 0.442; 95% CI, –0.444 to 1.328; I² = 74.1%) (Figure 2e). Two studies selected forward jump task to investigate stability index (SI) in AP, ML, and vertical directions (APSI, MLSI, and VPSI) between affected knees and healthy knees, including 26 affected knees and 26 healthy knees. The pooled results of APSI, MLSI, and VPSI for the forward jump task revealed no significant difference (I² = 92.7%, 75.0%, and 77.9%, respectively) (Figure 2f).

Discussion

The current study compiled existing evidence on the evaluation of dynamic postural stability in patients with ACLI and ACLR using single-limb landing stability after performing a specific motor task. The most important finding of this review was that patients with ACLI or ACLR demonstrated longer AP and vertical TTS in the forward jump task than controls. For the AP direction, the pooled analysis (based on 47 affected knees versus 44 healthy knees) revealed a moderate effect size (SMD = 0.438; 95% CI, 0.021 to 0.855), derived from 3 independent SMDs. For the vertical direction, derived from 77 affected knees and 74 healthy knees, the pooled analysis size revealed a large effect size (SMD = 0.656; 95% CI, 0.258 to 1.055), based on 4 SMDs.

Mechanism of Dynamic Posture Control Deficits

Dynamic postural stability deficits of the lower limbs of patients with ACLI and ACLR may be attributed to deficits in muscle strength and altered knee proprioception. Postoperative quadriceps and hamstring muscle atrophy in patients undergoing ACLR may induce reduced muscle strength, and existing research has demonstrated that patients who underwent ACLR demonstrated lower knee joint moments in executing jump-landing tasks.^6,27 This decrease in muscle strength and joint moment impairs the ability to effectively absorb landing forces and stabilize the knee, thereby contributing to the decrease of landing stability. In addition, knee proprioception changes after ACLI and subsequent ACLR have been reported extensively.^19,20 Altered proprioceptive feedback can delay neuromuscular activation and compromise the coordination needed to correct joint position during landing, ultimately leading to an increased TTS.

Furthermore, altered neuromuscular function and kinetics were observed in patients with ACLR. Despite undergoing ligament reconstruction, the complete restoration of sensory function may not occur. ⁴³ Neuromuscular function and kinetic differences between jumping and landing have been confirmed in injured knees, including higher GRFs^19,27; greater flexion angles of the hip, knee, and ankle ³⁸ ; increased valgus knee moments ³¹ ; increased AP shear forces affecting the tibia ²⁵ ; increased tibial rotation ³¹ ; and changes in muscle activation patterns.^19,25 These factors all contribute to asymmetry between healthy and injured knees and decreased landing stability of the injured knees.

Different Testing Methods

Jump Tasks in Assessment

This systematic review summarized 6 types of jump tasks implemented in dynamic postural stability testing and conducted subgroup analyses. Of these, the forward jump and step down tasks are the most commonly implemented. Meta-analysis showed that the TTS after a forward jump is more sensitive in detecting dynamic postural stability deficits in the ACLI or ACLR population than the TTS after a step down task. One possible reason is that, in the included cases, a long time had elapsed since the surgery or injury, and almost all patients had returned to sport. Because step down is a common daily activity, patients have likely adapted to their deficits in landing stability. In contrast, the forward jump followed by single-leg landing is a task that occurs less frequently in daily activities, thereby exposing more reliably landing stability deficits.

Directions of Outcomes

This systematic review detailed the 4 directions of outcomes, and subgroup analyses were performed for each direction. In the forward jump group, patients with ACLI or ACLR required more time to stabilize in the AP and vertical directions. The compromised ability of the injured ACL to restrict the anterior translation of the tibial plateau could be a contributing factor to the decreased AP in patients after forward jump landing. ⁹ Furthermore, McNair and Marshall ¹⁸ found that the magnitude of the vertical GRF upon landing from a jump is correlated with anterior tibial translation. Therefore, patients may alter their landing biomechanical movements to reduce the vertical GRF, ultimately resulting in prolonged landing stability time.

Calculation Methods

The TTS values varied considerably across the calculation methods, and Fransz et al ¹¹ identified 18 calculation methods through a systematic search of the relevant literature. Of these methods, the smoothing type of signal process is an important component in calculating the TTS and is divided mainly into the sequential averaging (SE) method and the unbounded third-order polynomial (UTOP) method. Wikstrom et al ⁴¹ found that the UTOP method demonstrated a greater ability to distinguish the differences between healthy subjects and subjects with functional ankle instrument than the SE method. Furthermore, differences in trial duration significantly affected the TTS, with longer trial durations inducing higher TTS values (up to 285%). ¹¹ Therefore, we recommend that, in employing TTS for dynamic postural stability assessment, a calculation paradigm should be established based on the current best evidence.

Research Implications

Our findings indicate that, among the various jump tasks, TTS after a forward jump in the AP and vertical directions emerges as the most sensitive measure for detecting dynamic postural deficits in people with ACLI or ACLR. In contrast, TTS in the ML direction or after other jump tasks did not distinguish consistently between injured and uninjured groups.

Even the subtle differences in intergroup TTS should not be overlooked as numerous studies that conducted video analysis of ACLI mechanisms reported that ACLIs occur within the first 100 ms after initial ground contact during landing and cutting tasks. ¹ A longer stabilization time implies a greater likelihood of patients sustaining another injury after landing. This indicates that the TTS could predict the risk of reinjury in patients with ACLR. For example, 1 prospective cohort study involving 278 healthy athletes found that athletes who experienced noncontact ACL ruptures took longer to stabilize after backward jump landing compared with uninjured athletes (1.58 ± 0.39 and 1.09 ± 0.52 seconds, respectively; P = 0.005), ⁸ indicating that TTS can be used to identify healthy people at potential risk for ACL rupture.

Clinical Implications

In a clinical setting, postural stability is often determined statically, but static assessments cannot precisely evaluate the stability of patients with lower-limb injuries.^33,35 In contrast, dynamic jump-landing tasks can reveal dynamic posture deficits in patients with ACLR and ACLI, thereby emerging as an important indicator for assessing dynamic postural stability in ACLI and ACLR. The dynamic postural instability exhibited by patients with ACLI and ACLR indicates underlying neuromuscular capacity deficits. Therefore, the clinical treatment goal is not only to reconstruct natural biomechanics but also to restore neuromuscular function, along with effective rehabilitation motor learning, to potentially regain physiological ACL functionality for neuromuscular control and dynamic knee joint stability. ²⁴ A systematic review found that younger age, greater neuromuscular dosage, more exercise variations in neuromuscular training, and verbal feedback can reduce the risk of ACL injury by 17.2% to 17.7%. ³⁷ Since ACLIs occur mostly during dynamic activities and may happen in multiple planes, the clinical diagnosis, treatment, and postoperative rehabilitation must focus not only on static stability but also on dynamic postural stability in different directions during dynamic tasks.

Limitations

This study has significant limitations that should be acknowledged. First, despite the extensive literature search across 7 databases, the articles analyzed and the participant cohorts included remained very limited, exposing the paucity of literature on some subgroups for subgroup analysis. Second, a key limitation of this meta-analysis is the very small number of effect sizes available, which does undermine the robustness and generalizability of the results. Third, the cross-sectional design made it impossible to distinguish between dynamic postural stability deficits present before the initial injury and those that developed during ACLI progression. Longitudinal evaluations from the preinjury state to ACLI or ACLR are needed to clarify this point. Notably, among the studies included in this meta-analysis, 3 focused on female participants, whereas 5 specifically targeted athletes. Given that studies have reported gender differences in jump-landing strategies, ¹² and athletes’ knees may adapt to high-load activities, this likely introduced selection bias in the current study. Fourth, significant heterogeneity was found across the studies in the testing methods and calculation methods used to obtain the TTS. As mentioned earlier, landing strategies vary with the types of jumping tasks, and variations in calculation methods do result in considerable variability in the TTS. Although we performed subgroup analysis to enhance the reliability of the pooled results, a comprehensive and standardized experimental paradigm is needed to ensure the comparability of subsequent research endeavors. Fifth, the effects of graft types were not assessed in this meta-analysis. This is a major deficit since graft harvest no doubt effects muscle performance. Sixth, we did not control for injury severity or identify the dominant leg, which differs among the ACL subgroups. ³ Although 1 of the included studies did assess the dominant leg, none evaluated the severity of the injured knees, which prevented us from further refining the grouping.

Conclusion

Dynamic postural stability in patients with ACLI and ACLR can be assessed by stabilization time after jump-landing tasks, with the TTS in the AP and vertical directions after a forward jump-landing task being the most effective indicators. However, further validation of the prognostic value of the DPSI is needed. Furthermore, methodological exploration is required to improve sensitivity and reliability in evaluating dynamic postural deficits in these patients using jump-landing tasks, including refining testing parameters and data analysis.