Biomechanics and Performance of Single-Leg Vertical and Horizontal Hop in Adolescents Post-Anterior Cruciate Ligament Reconstruction

Chen P., Wang L., Dong S., Ding Y., Zuo H., Jia S., Wang G., Chen C., Zheng C.

Background: A limb symmetry index (LSI) of >90% for single-leg horizontal hop distance is recommended as a cutoff point for safe return to sports after anterior cruciate ligament reconstruction (ACLR). Despite achieving this threshold, abnormal lower limb biomechanics continue to persist in athletes after ACLR. Symmetry in single-leg vertical hop height appears to be more difficult to achieve and can be a better representation of knee function than single-leg horizontal hop distance. Purpose: To explore whether an LSI of >90% for single-leg vertical hop height can represent normal lower limb biomechanics in athletes during a bilateral vertical jump after ACLR. Study Design: Controlled laboratory study. Methods: According to the LSI for single-leg vertical hop height, 46 athletes who had undergone ACLR with an autologous ipsilateral bone–patellar tendon–bone or hamstring tendon graft were divided into a low symmetry group (LSI <90%; n = 23) and a high symmetry group (LSI >90%; n = 23), and 24 noninjured athletes were selected as the control group. The kinematic and kinetic characteristics during a bilateral vertical jump were compared between the low symmetry, high symmetry, and control groups. Results: During the propulsion phase of the bilateral vertical jump, the operated side in the high symmetry group showed a lower knee extension moment than the nonoperated side ( P = .001). At peak vertical ground-reaction force, the operated side in the high symmetry group showed a lower knee internal rotation moment compared with the control group ( P = .016). Compared with the nonoperated side, the operated side in the high symmetry group showed a higher hip extension moment ( P = .002), lower knee extension moment ( P < .001), lower ankle plantarflexion moment ( P < .001), and lower vertical ground-reaction force ( P = .023). Conclusion: Despite achieving an LSI of >90% for single-leg vertical hop height, athletes after ACLR showed abnormal lower limb biomechanical characteristics during the bilateral vertical jump. Clinical Relevance: Symmetrical single-leg vertical hop height may not signify ideal biomechanical or return-to-sports readiness in this population.

Romanchuk N.J., Livock H., Lukas K.J., Del Bel M.J., Benoit D.L., Carsen S.

Background: The rates of anterior cruciate ligament (ACL) graft failure or contralateral ACL rupture range from 17% to 30% in pediatric patients after ACL reconstruction (ACLR). A contributing factor to the high reinjury rate in this population may be the limited evidence regarding appropriate criteria for allowing unrestricted return to activity (RTA) postoperatively. Purpose: To review the literature and identify the most commonly used criteria when determining unrestricted RTA after ACLR in pediatric patients. Study Design: Systematic review; Level of evidence, 4. Methods: A search was performed of the Medline/PubMed, Cochrane Central Register of Controlled Trials, Embase, CINAHL, and SPORTDiscus databases using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. The authors identified studies that included pediatric patients (<19 years of age) and specified the criteria used to determine RTA after ACLR. Results: A total of 27 articles met all criteria for review, of which 13 studies only used 1 criterion when determining RTA. Objective criteria were the most common type of criteria for RTA (17 studies). Strength tests (15 studies) and hop tests (10 studies) were the most commonly used tasks when deriving RTA criteria. Only 2 studies used validated questionnaires to assess the patient’s physiological readiness for RTA, and only 2 studies used an objective assessment of movement quality before RTA. Conclusion: Only 14 of the 27 reviewed studies reported using >1 criterion when determining RTA. Furthermore, few studies used patient-reported outcome measures or lower limb kinematics as RTA criteria, indicating that more research is needed to validate these metrics in the pediatric population.

Matsuzaki Y., Chipman D.E., Hidalgo Perea S., Green D.W.

Anterior cruciate ligament (ACL) injuries and surgical intervention in the pediatric population have increased in the recent years. Although surgical techniques have advanced, evidence-based rehabilitation guidelines that consider all aspects of the youth athlete are currently lacking. The purpose of this commentary is to review the current evidence on unique considerations for the pediatric and adolescent population during rehabilitation and return to sport after ACL reconstruction (ACLR), with a focus on children under 18 years of age. This review revealed that returning a youth athlete to sport after ACLR requires knowledge and appreciation of various aspects of the growing athlete different from adults. In addition to postoperative precautions that contribute to a slow rehabilitation process, young athletes need additional time for strength gains. Address risk of reinjury and for contralateral injury by using neuromuscular training and rigorous return-to-sport training programs. Consider return to sport after 9 months because the reinjury rate is high in this population. A combination of time and objective measures, both quantitative and qualitative criteria, and psychological readiness should be used to assess readiness to return to sport and decrease risk of future injury. Healthcare providers should be aware of the psychosocial impact of injury on the youth athletes and refer to sport psychology when necessary.Level V.

Kotsifaki A., Van Rossom S., Whiteley R., Korakakis V., Bahr R., Sideris V., Smith P.G., Jonkers I.

Background: After anterior cruciate ligament reconstruction (ACLR), a battery of strength and hop tests is frequently used to determine the readiness of an athlete to successfully return to sports. However, the anterior cruciate ligament reinjury rate remains alarmingly high. Purpose: To evaluate the lower limb function of athletes after ACLR at the time when they had been cleared to return to sports (RTS). We aimed to evaluate if passing discharge criteria ensures restoration of normal lower limb biomechanics in terms of kinematics, kinetics, work, and percentage work contribution during a triple hop for distance. Study Design: Controlled laboratory study. Methods: Integrated 3-dimensional motion analysis was performed in 24 male athletes after ACLR when cleared to RTS and 23 healthy male controls during the triple-hop test. The criteria for RTS were (1) clearance by the surgeon and the physical therapist, (2) completion of a sports-specific on-field rehabilitation program, and (3) limb symmetry index >90% after quadriceps strength and hop battery tests. Lower limb and trunk kinematics, as well as knee joint moments and work, were calculated. Between-limb differences (within athletes after ACLR) and between-group differences (between ACLR and control groups) were evaluated using mixed linear models. Results: Although achieving 97% limb symmetry in distance hopped and displaying almost 80% symmetry for knee work absorption in the second rebound and third landing, the ACLR cohorts demonstrated only 51% and 66% limb symmetry for knee work generation in the first and second rebound phases, respectively. During both work generation phases of the triple hop, the relative contribution of the involved knee was significantly smaller, with a prominent compensation from the hip joint ( P < .001, for all phases) as compared with the uninvolved limb and the controls. In addition, patients deployed a whole body compensatory strategy to account for the between-limb differences in knee function, mainly at the hip, pelvis, and trunk. Conclusion: Symmetry in the triple hop for distance masked important deficits in the knee joint work. These differences were more prominent during work generation (concentric-propulsive) than work absorption (eccentric-landing). Clinical Relevance: Symmetry in hop distance during the triple hop test masked significant asymmetries in knee function after ACLR and might not be the appropriate outcome to use as a discharge criterion. Differences between limbs in athletes after ACLR were more prominent during the power generation than the absorption phase.

Korakakis V., Kotsifaki A., Korakaki A., Karanasios S., Whiteley R.

To evaluate the perspectives and clinical practice of physiotherapists regarding rehabilitation after anterior cruciate ligament reconstruction (ACLR).Online survey.Survey platform.Greek physiotherapists.The survey consisted of 7 sections: participant demographics, importance of ACLR rehabilitation, clinical measurements, practice, criteria to progress rehabilitation, return to running and return to sport.Significant variability in measures and criteria used for clinical decision-making were found including: limb symmetry in strength and function, knee range of motion and effusion, progression, and return to sport criteria. The majority of the practitioners (28.3%) extrapolate knee strength from hop capacity. Return to running ranged from 3 to 5 months post-operatively reflecting that this was tied to physical capacities, not time from surgery. 70.0% of the Greek physiotherapists would allow return to sport ≤9 months after ACLR. Agreement was found in using: physical measures, function, and dynamic stability in ACLR rehabilitation, but the mode and interpretation varied substantially. Less than 29.0% of the physiotherapists reported using patient-reported outcome measures in their decision-making.Current ACLR rehabilitation practices in Greece are largely not aligned with the contemporary scientific evidence and guidelines.

Roe C., Jacobs C., Hoch J., Johnson D.L., Noehren B.

Context: There is a lack of consensus regarding test batteries for return to sport (RTS) after anterior cruciate ligament reconstruction (ACLR). Objective: To report the RTS test batteries for individuals after ACLR and to examine alignment with the American Academy of Orthopaedic Surgeons (AAOS) Appropriate Use Criteria (AUC). Finally, to examine how published RTS batteries prior to the AAOS AUC (2010-2015) compared with those after publication of the AUC (2016-2020). Data Source: A systematic search of PubMed (2010-2020). Study Selection: Studies were included if they were published from 2010 to 2020, patients underwent primary ACLR and were tested between 6 months and 2 years postoperatively and included a minimum of 2 assessments. Studies were excluded if patients were tested outside the designated time; had undergone a revision, contralateral, or multiligament injury; included healthy participants; were level 5 evidence or the study was a systematic review. A total of 1012 articles were reviewed and 63 met the criteria. Study Design: Systematic review. Level of Evidence: Level 4. Data Extraction: Information regarding the RTS batteries and patient demographics were extracted from the included articles. Results: A total of 63 studies met the inclusion and exclusion criteria (22 from 2010-2015 and 41 from 2016-2020). The most common RTS batteries included the hop test, quadriceps strength test, and patient-reported outcome measures. No study met all 7 AUC; the most common criteria met were functional skills (98.4%), followed by confidence (22.2%), then range of motion and knee stability (20.6%). Conclusion: The test batteries in the current literature show high variability and a lack of essential components necessary for RTS. No study met the AUC guidelines, suggesting a disconnect between recommended guidelines and clinical practice. Test battery research has expanded over the past decade; however, standardized, clinically applicable batteries that encompass all criteria are needed.

Larwa J., Stoy C., Chafetz R.S., Boniello M., Franklin C.

Anterior cruciate ligament (ACL) injuries are the most common ligament injury of the knee, accounting for between 100,000 and 200,000 injuries among athletes per year. ACL injuries occur via contact and non-contact mechanisms, with the former being more common in males and the later being more common in females. These injuries typically require surgical repair and have relatively high re-rupture rates, resulting in a significant psychological burden for these individuals and long rehabilitation times. Numerous studies have attempted to determine risk factors for ACL rupture, including hormonal, biomechanical, and sport- and gender-specific factors. However, the incidence of ACL injuries continues to rise. Therefore, we performed a systematic review analyzing both ACL injury video analysis studies and studies on athletes who were pre-screened with eventual ACL injury. We investigated biomechanical mechanisms contributing to ACL injury and considered male and female differences. Factors such as hip angle and strength, knee movement, trunk stability, and ankle motion were considered to give a comprehensive, joint by joint analysis of injury risk and possible roles of prevention. Our review demonstrated that poor core stability, landing with heel strike, weak hip abduction strength, and increased knee valgus may contribute to increased ACL injury risk in young athletes.

Kotsifaki A., Korakakis V., Graham-Smith P., Sideris V., Whiteley R.

Background: Single-leg vertical and horizontal hop tests are commonly used to assess performance of healthy athletes and as a measure of progress during rehabilitation from knee injury. It is unclear if they measure similar aspects of leg function, as the relative joint contributions of the hip, knee, and ankle joints during propulsion and landing are unknown. Hypothesis: The proportion of work done by the hip, knee, and ankle will not be the same for these 2 jump types and will vary for propulsive and landing phases. Study Design: Cross-sectional cohort study. Level of Evidence: Level 3. Methods: Twenty physically active participants completed instrumented single-leg hop analysis in both vertical and horizontal directions. Joint peak power, work generated or absorbed, and percentage contribution of each joint during propulsive and landing phases were compared between tasks using paired t tests. Results: Vertical hop was performed with roughly similar contributions of the hip, knee, and ankle for both propulsion (31%, 34%, 35%, respectively) and landing (29%, 34%, 37%, respectively). Horizontal hop distance was mostly (87%) determined by the hip and ankle (44% and 43%), but landing was mostly (65%) performed by the knee with lesser contribution from the hip and ankle (24% and 11%). Propulsive phase showed a proximal-to-distal temporal sequence for both hop types, but landing was more complex. Conclusion: Performance during vertical and horizontal hops (jump height and jump distance, respectively) measures different aspects of hip, knee, and ankle function during the propulsive and landing phases. Clinical Relevance: Assessment of knee joint function during rehabilitation should not be done using a horizontal hop. The knee contributes about a third to vertical hop height, but only about an eighth to horizontal hop distance. Practitioners carrying out performance testing using either vertical or horizontal hops should be mindful of the relative contributions for meaningful training inferences to be derived.

Taylor J.B., Westbrook A.E., Head P.L., Glover K.M., Paquette M.R., Ford K.R.

AbstractBackground Traditional testing to identify asymmetries after anterior cruciate ligament reconstruction include four similar horizontal hopping tests. The purpose of this study was to determine whether a single-leg vertical hopping test can identify performance and biomechanical asymmetries, and whether performance asymmetries provide unique information compared to traditional tests. Methods Twelve women with history of anterior cruciate ligament reconstruction [age: 21.1 years (SD 3.2), height: 165.8 cm (SD 6.0), mass: 68.3 kg (SD 8.8)] completed traditional horizontal hop testing. Participants also performed a single-leg vertical hop for maximal height while instrumented for three-dimensional motion analysis. Paired t-tests were performed to identify side-to-side differences in performance variables and Spearman's rank correlations were performed of limb symmetry indices to identify whether the single-leg vertical hop test provides unique information. Repeated measures MANOVAs were performed to identify single-leg vertical hop biomechanical asymmetries. Findings Participants exhibited significant side-to-side performance differences during the single-leg vertical hop [mean difference = 0.02 m (SD 0.03), P = .04]. Only weak to moderate relationships were identified between limb symmetry indices of the single-leg vertical hop and other horizontal hopping tests. The vertical hop elicited significant asymmetries of joint kinematics (P = .04) and angular impulse (P = .04). Specifically, the involved limb showed lower peak ankle dorsiflexion (P = .004) and knee abduction (P = .02) angles, lower sagittal plane impulse at the knee (P = .02) and greater sagittal plane impulse at the hip (P = .03). Interpretation The single-leg vertical hop can identify performance and biomechanical asymmetries in individuals after anterior cruciate ligament reconstruction, potentially providing complementary information to standard horizontal hopping tests.

Wren T.A., O’Callahan B., Katzel M.J., Zaslow T.L., Edison B.R., VandenBerg C.D., Conrad-Forrest A., Mueske N.M.

Background Understanding movement variability is important to guide biomechanical assessment. Variability may change with age, and more repetitions of a movement need to be assessed when variability is high. Research question This study quantified the trial-to-trial (within subject) variability of three tasks commonly assessed during sports biomechanical testing: vertical drop jump, heel touch (single leg squat from step), and single leg hop. We hypothesized that pre-teen athletes would exhibit greater variability than more mature teenage athletes when performing all of these movements. Methods Fifty-five uninjured pediatric athletes ages 7–15 years performed 3 repetitions of vertical drop jump, heel touch, and single leg hop for distance tasks during 3D motion analysis testing. Trial-to-trial variability was assessed using the standard deviation (SD) and range (maximum–minimum) of clinically relevant kinematic and kinetic metrics among the multiple repetitions of each task performed by each participant. Variability was compared between age groups using 2-sided t-tests. Standard error of measurement (SEM) and minimum detectable difference (MDD) were also calculated for each variable of interest. Results For drop jump and heel touch, kinetic variability was similar between groups, but the younger group had greater kinematic variability. However, the older group was much more variable than the younger group during single leg hop landing, particularly in terms of kinetics and sagittal plane kinematics. Overall, kinematic variability had a median within-subject SD of 1−9°, median range of 2–17°, and 95th percentile for range of >15−20° for many of the variables examined. MDD was >10° for many kinematic variables, >0.2 Nm/kg for all frontal plane moments, >0.4 Nm/kg for most sagittal plane moments, and >0.5 W/kg for most energy absorption variables. Significance The high within-subject trial-to-trial variability in performing sports tasks suggests that multiple trials should be analyzed for a more complete and representative evaluation.

Hughes G., Musco P., Caine S., Howe L.

Objectives To identify reported (1) common biomechanical asymmetries in the literature after anterior cruciate ligament (ACL) reconstruction in adolescents during landing and (2) timescales for asymmetry to persist postsurgery. Data Sources We identified sources by searching the CINAHL, PubMed, Scopus, and SPORTDiscus electronic databases using the following search terms: asymmetry OR symmetry AND landing AND biomechanics OR kinematics OR kinetics. Study Selection We screened the titles and abstracts of 85 articles using our inclusion criteria. A total of 13 articles were selected for further analysis. Data Extraction Three reviewers independently assessed the methodologic quality of each study. We extracted the effect sizes directly from studies or calculated them for biomechanical variables assessing asymmetry between limbs of participants with ACL reconstruction. We conducted meta-analyses on variables that were assessed in multiple studies for both double- and single-limb landings. Data Synthesis Asymmetry was more commonly identified in kinetic than kinematic variables. Anterior cruciate ligament reconstruction appeared to have a large effect on asymmetry between limbs for peak vertical ground reaction force, peak knee-extension moment, and loading rate during double-limb landings, as well as mean knee-extension moment and knee energy absorption during both double- and single-limb landings. Conclusions Our findings suggested that return-to-sport criteria after ACL reconstruction should incorporate analysis of the asymmetry in loading experienced by each limb rather than movement patterns alone.

Barber-Westin S., Noyes F.R.

Context: Anterior cruciate ligament (ACL) reconstruction (ACLR) is frequently performed in patients younger than 20 years whose goal is to return to sport (RTS). Varying reinjury rates have been reported, and the factors responsible are unclear. Studies differ with regard to age, graft type, surgical techniques, postoperative rehabilitation, RTS guidelines, and methods used to determine ACL failures. Objective: To determine RTS rates; the effect of participation in high-risk sports, sex, and graft type on ACL reinjury rates; and whether objective test criteria before RTS correlate with lower reinjury rates. Data Sources: A systematic review of the literature from inception to May 31, 2019, was conducted using the PubMed and Cochrane databases. Study Selection: Studies on transphyseal ACLR in athletes <20 years old with a minimum mean follow-up of 2 years that reported reinjury rates, the number that RTS, and detailed the type of sport were included. Study Design: Systematic review. Level of Evidence: Level 4. Results: A total of 1239 patients in 8 studies were included; 87% returned to sport and 80% resumed high-risk activities. Of the patients, 18% reinjured the ACL graft and/or the contralateral ACL. Nine percent of patellar tendon autografts and 15% of hamstring autografts failed (odds ratio [OR], 0.52; P = 0.002). Of reinjuries, 90% occurred during high-risk sports. Male patients had a significantly higher rate of ACL graft failure than female patients (OR, 1.64; P = 0.01). There was no sex-based effect on contralateral ACL injuries. Only 1 study cited objective criteria for RTS. Conclusion: A high percentage of athletes returned to sport, but 1 in 5 suffered reinjuries to either knee. Male patients were more likely to reinjure the ACL graft. Objective criteria for RTS were rarely mentioned or not detailed. The need for testing of knee stability, strength, neuromuscular control, agility, and psychological measures before RTS remains paramount in young athletes.

Beischer S., Gustavsson L., Senorski E.H., Karlsson J., Thomeé C., Samuelsson K., Thomeé R.

Capin J.J., Snyder-Mackler L., Risberg M.A., Grindem H.

Clinicians rely on rigorous systematic reviews to guide practice. We therefore suspect many clinicians will note the results of the 2019 systematic review and meta-analysis by Webster and Hewett, ‘What is the Evidence for and Validity of Return-to-Sport Testing after Anterior Cruciate Ligament Reconstruction Surgery? A Systematic Review and Meta-Analysis’.1 We agree that it is important to evaluate the association between return-to-sport (RTS) test batteries and outcomes after ACL reconstruction. The third review question in Webster and Hewett (2019) is particularly pertinent: ‘Is passing RTS test batteries associated with reduced rates of subsequent knee injury (all knee injuries and ACL injury)?’1 We are authors of several of the original data papers cited in the systematic review, and we are concerned about the study methodology and its conclusions. We highlight major problems with including two studies and present revised analyses that demonstrate the impact these studies had on the conclusions. First, we question the validity of pooling studies with substantial clinical and methodological diversity.2 The meta-analysis combined studies where only some athletes returned to sport3 4 and studies where all, or mostly all, returned to sport;5–7 studies with skeletally immature patients7 and studies with elite athletes;6 and studies where substantially different RTS test batteries were used. Our second concern is that Webster and Hewett1 did not assess risk of bias, a fundamental precept of systematic review methodology clearly stated in the PRISMA reporting guideline.8–10 Assessment of study quality (as performed by Webster and Hewett1) does not quantify risk of bias.11 A risk of bias assessment identifies factors within studies that can skew results, and these factors must be considered carefully in the decision to pool data and in the conclusion. Important bias domains for review questions 2 and 3 include …

Nagai T., Schilaty N.D., Laskowski E.R., Hewett T.E.

Quadriceps weakness is a common clinical sign following anterior cruciate ligament injury and reconstruction surgery (ACLR). The aim of this study was to compare strength deficits and the limb symmetry index (LSI) from three different types of functional tests: isokinetic dynamometry, hop test, and leg press. A total of 26 subjects with ACLR (average 8.3 months post-operation) participated in the study. The peak knee extension torque was tested with isokinetic dynamometry at 60/180/300 °/s (ISO60/180/300). Hop distance was tested during single hop (SH) and triple hop (TH). Unilateral peak leg power (POWER) was tested during a bilateral leg press test. LSI was calculated as the ratio of the involved limb over the uninvolved limb values. Pearson correlation coefficients and paired t-tests were used to establish relationships among ISO60/180/300, SH/TH, and POWER values and compare these values between the limbs, respectively. Within-subject one-way analysis of variance (ANOVA) with post hoc analyses was used to compare LSI values among different tests. ISO60/180/300 values were significantly positively correlated with SH/TH and POWER (P < 0.05), while SH/TH and POWER values were not significantly correlated. Significant limb differences were found in all tests (P = 0.001–0.008). ANOVA revealed significant LSI differences among different tests. Specifically, post hoc analyses revealed that LSI during SH was significantly higher than LSI during ISO60. Similarly, LSI during TH was significantly higher than LSIs from ISO60, ISO180, and POWER tests. Peak knee extension torque values were positively associated with hop distance and leg power during the leg press test. However, LSI values should be interpreted with caution as hop tests provided significantly higher LSI values than isokinetic testing. Both isokinetic dynamometry and unilateral leg press machine could be used to isolate and strengthen the quadriceps in the involved limb. The current “gold standard” isokinetic testing at slow speed (ISO60) provided the lowest LSI value among all functional tests; therefore, the current study supported a continued use of isokinetic testing when examining individual’s readiness and return-to-sport. III.