Athletes exposed to rapid maneuvers need a high level of dynamic knee stability and robustness, while also controlling whole body movement, to decrease the risk of non‐contact knee injury. The effects of high‐level athletic training on such measures of movement control have not, however, been thoroughly evaluated. This study investigated whether elite athletes (who regularly perform knee‐specific neuromuscular training) show greater dynamic knee robustness and/or different movement strategies than non‐athletic controls, in relation to overall knee function. Thirty‐nine women (19 athletes, 20 controls) performed standardized rebound side hops (SRSH) while a motion capture system synchronized with two force plates registered three‐dimensional trunk, hip, and knee joint angles and moments. Dynamic knee robustness was evaluated using finite helical axis (FHA) inclination angles extracted from knee rotation intervals of 10°, analyzed with independent t tests. Angle and moment curves were analyzed with inferential methods for functional data. Athletes had superior knee function (less laxity, greater hop performances, and strength) but presented similar FHA inclination angles to controls. Movement strategies during the landing phase differed; athletes presented larger (a) hip flexion angles (during 9%‐29% of the phase), (b) hip adduction moments (59%‐99%), (c) hip internal rotation moments (83%‐89%), and (d) knee flexion moments (79%‐93%). Thus, elite athletes may have a greater ability than non‐athletes to keep the knee robust while performing SRSH more efficiently through increased engagement of the hip. However, dynamic knee robustness associated with lower FHA inclination angles still show room for improvement, thus possibly decreasing knee injury risk.

Despite a vast literature on one-leg hops and cutting maneuvers assessing knee control pre/post-injury of the anterior cruciate ligament (ACL), comprehensive and reliable tests performed under unpredictable conditions are lacking. This study aimed to: (1) assess the feasibility of an innovative, knee-challenging, one-leg double-hop test consisting of a forward hop followed by a diagonal hop (45°) performed medially (UMDH) or laterally (ULDH) in an unanticipated manner; and (2) determine within- and between-session reliability for 3-dimensional hip and knee kinematics and kinetics of these tests. Twenty-two healthy women (22.3 ± 3.3 years) performed three successful UMDH and ULDH, twice 1–4 weeks apart. Hop success rate was 69–84%. Peak hip and knee angles demonstrated moderate to excellent within-session reliability (intraclass correlation coefficient [ICC] 95% confidence interval [CI]: 0.67–0.99, standard error of measurement [SEM] ≤  3°) and poor to excellent between-session reliability (ICC CI: 0.22–0.94, SEM ≤ 3°) for UMDH and ULDH. The smallest real difference (SRD) was low (≤ 5°) for nearly all peak angles. Peak hip and knee moments demonstrated poor to excellent reliability (ICC CI: 0–0.97) and, in general, moments were more reliable within-session (SEM ≤ 0.14 N.m/kg.m, both directions) than between-session (SRD ≤ 0.43 N.m/kg.m). Our novel test was feasible and, in most but not all cases, provided reliable angle estimates (within-session > between-session, both directions) albeit less reliable moments (within-session > between-session, both directions). The relatively large hip and knee movements in the frontal and transverse planes during the unanticipated hops suggest substantial challenge of dynamic knee control. Thus, the test seems appropriate for evaluating knee function during ACL injury rehabilitation.

Background: Rupture of the anterior cruciate ligament (ACL) is common and mainly occurs in non-contact situations in sports, often due to momentarily poor movement control. Assessment of movement quality during sport-like tasks iscrucial to understand how to decrease the high risk of reinjury for ACL-injured persons, but also how to prevent primary injury. This thesis addresses movement quality after ACL injury and includes development and evaluation of a novel standardized rebound side hop test (SRSH) for reliability and agreement of landing mechanics, and compares these outcomes between asymptomatic persons with different athletic levels, and between different hop tests.

Methods: This thesis involves five papers based on two separate data collections performed in a motion analysis laboratory. Paper I is a long-term follow up of ACL-injured persons treated with or without ACL reconstruction (ACLR) compared to asymptomatic persons (total N = 99, age 35-63), while papers II-V included ACLR persons, and asymptomatic elite athletes and non-athletes (total N = 79, age 17-34). A motion capture system synchronized with force plates and surface electromyography (EMG) registered trunk, hip and knee angles and moments and knee muscle activity during the hop for distance, vertical hop, and SRSH. Novel measures of dynamic knee robustness were also evaluated using finite helical axis inclination angles extracted from knee rotation intervals of 10˚.

Results: On average 23 years after injury, ACL injured persons performed the vertical hop with diverse angles compared to controls and their non-injured leg.The younger groups of ACLR persons and controls generally displayed excellent reliability and agreement for SRSH landing mechanics. These outcomes differed between the groups, and between legs for ACLR persons, despite similar dynamic knee robustness and acceptable knee function outcomes. Curve analyses further displayed differences between athletes and non-athletes, mainly with greater hip moments for athletes, although with similar values for dynamic knee robustness. Finally, greater knee angles and moments considered strenuous for the ACL were evident during the first rebound landing in SRSH compared to the other landings.

Conclusions: Persons who have suffered an ACL injury, regardless of whether treated with ACLR or not, appear to use task-coping strategies in preparation for and during landings to decrease knee joint loading, probably to preserve dynamic knee robustness. More attention should be given to the trunk and hip in clinics when evaluating movement quality after ACL injury to reduce the risk of future injuries due to movement compensation. High-level athletic training may also improve the ability to maintain dynamic knee robustness whilst performing a sport-like side-to-side task more efficiently through increased engagement of the hip. Finally, side hop landings should be assessed when evaluating and correcting for erroneous landing mechanics to improve knee landing control.

Bakgrund: Främre korsbandsskada (ACL-skada) är en vanlig idrottsskada som huvudsakligen uppstår i situationer utan kontakt med annan spelare till följd aven tillfälligt dålig rörelsekontroll. Utvärdering av rörelsekvalitet under idrottsliknande tester behövs för att bättre förstå hur risken för ACL-skador och återskador kan minskas. Denna avhandling är inriktad på rörelsekvalitet efter ACL-skada och behandlar utveckling samt utvärdering av ett nytt standardiserat sidohopp (SRSH). Tillförlitlighet och överensstämmelse av ledvinklar och moment utvärderas och jämförs mellan personer med och utan ACL-skada, mellan personer med olika atletbakgrund, samt mellan olika hopptester.

Metoder: Denna avhandling omfattar fem studier, vilka är baserade på två separata datasamlingar utförda i ett rörelsesanalyslaboratorium. Studie I är en långtidsuppföljning av personer med ACL-skada behandlade både med och utan ACL-rekonstruktion, vilka jämförs med knäfriska kontroller (totala N = 99, 35-63 år). Studie II-V inkluderade personer med ACL-rekonstruktion, knäfriska kontroller och elitatleter (totala N = 79, 17-34 år). Ett rörelseanalyssystem synkroniserat med kraftplattor och ytelektromyografi registrerade bål, höft och knävinklar och moment, samt lårmuskelaktivitet under enbenshopp (på längden, på höjden, samt SRSH). Även nya utfallsmått som utvärderar knäets robusthet under rörelse analyserades med helixvinklar från intervaller av knärörelse på 10˚.

Resultat: I genomsnitt 23 år efter ACL-skada utförde båda grupperna ett enbenshopp på höjden med olika ledvinklar, både jämfört med kontroller samt deras oskadade ben. De yngre ACL-skadade personerna och kontrollerna visade generellt utmärkt tillförlitlighet och överensstämmelse av ledvinklar och moment under SRSH. Dessa utfallsmått skiljde sig mellan grupperna och mellan benen för ACL-skadade personer, trots att lika resultat av knäets robusthet samt acceptabla knäfunktionsresultat visades. Kurvanalyser visade även på skillnader mellan atleter och icke-atleter, främst med större höftmoment för atleter, trots lika resultat av knäets robusthet. Den första landningen i SRSH visade större knävinklar och moment som anses belasta ACL jämfört med övriga landningar.

Slutsatser: Personer med ACL-skada, oavsett om de behandlats med ACLrekonstruktion eller ej, verkar tillämpa rörelsestrategier för att hantera landningar från enbenshopp genom att minska belastningen på knäleden, troligen för att bevara knäets robusthet. I klinik bör ett större fokus läggas på bål och höftrörelser vid utvärdering av rörelsekvaliteten efter ACL-skada. Detta för att minska risken för framtida skador på grund av rörelsekompensation. Vidare förbättrar idrottsträning på hög nivå troligen förmågan att upprätthålla knäets robusthet samtidigt som utförandet av sidohoppstester blir effektivare genom ett ökat engagemang av höften. Slutligen bör sidhoppslandningar användas vid utvärdering och korrigering av landningsmekanik för en förbättrad knäkontroll.

The purpose of this paper is to provide an overview of available methods for reliability investigations when the outcome of interest is a curve. Curve data, or functional data, is commonly collected in biomechanical research in order to better understand different aspects of human movement. Using recent statistical developments, curve data can be analysed in its most detailed form, as functions. However, an overview of appropriate statistical methods for assessing reliability of curve data is lacking. A review of contemporary literature of reliability measures for curve data within the fields of biomechanics and statistics identified the following methods: coefficient of multiple correlation, functional limits of agreement, measures of distance and similarity, and integrated pointwise indices (an extension of univariate reliability measures to curve data, inclusive of Pearson correlation, intraclass correlation, and standard error of measurement). These methods are briefly presented, implemented (R-code available as supplementary material) and evaluated on simulated data to highlight advantages and disadvantages of the methods. Among the identified methods, the integrated intraclass correlation and standard error of measurement are recommended. These methods are straightforward to implement, enable results over the domain, and consider variation between individuals, which the other methods partly neglect.

We propose a novel one-leg standardised rebound side-hop test (SRSH) specifically designed for detailed analysis of landing mechanics. Anterior cruciate ligament reconstructed persons (ACLR, n = 30) and healthy-knee controls (CTRL, n = 30) were tested for within-session and test-retest (CTRL only, n = 25) reliability and agreement. Trunk, hip and knee angles and moments in sagittal, frontal, and transversal planes during landing, including time to stabilisation (TTS), were evaluated using intra-class correlations (ICCs), average within-person standard deviations (S_W) and minimal differences. Excellent within-session reliability were found for angles in both groups (most ICCs > 0.90, S_W ≤ 5°), and excellent to good for moments (most ICCs > 0.80, S_W ≤ 0.34 Nm/kg). Only knee internal rotation moment showed poor reliability (ICC < 0.4). Test-retest results were excellent to fair for all angles and moments (ICCs 0.47–0.91, S_W < 5° and ≤ 0.25 Nm/kg), except for peak trunk lateral bending angle and knee internal rotation moment. TTS showed excellent to fair within-session reliability but poor test-retest results. These results, with a few exceptions, suggest promising potential of evaluating landing mechanics during the SRSH for ACLR and CTRL, and emphasise the importance of joint-specific movement control variables in standardised tasks.

PURPOSE: Little is known regarding movement strategies in the long term following injury of the anterior cruciate ligament (ACL), and even less about comparisons of reconstructed and deficient knees in relation to healthy controls. The present purpose was to compare trunk, hip, and knee kinematics during a one-leg vertical hop (VH) ~20 years post-ACL injury between persons treated with surgery and physiotherapy (ACLR), solely physiotherapy (ACLPT), and controls (CTRL). Between-leg kinematic differences within groups were also investigated.

METHODS: Sixty-six persons who suffered unilateral ACL injury on average 23 ± 2 years ago (32 ACLR, 34 ACLPT) and 33 controls performed the VH. Peak trunk, hip, and knee angles during Take-off and Landing phases recorded with a 3D motion capture system were analysed with multivariate statistics.

RESULTS: Significant group effects during both Take-off and Landing were found, with ACLPT differing from CTRL in Take-off with a combination of less knee flexion and knee internal rotation, and from both ACLR and CTRL in Landing with less hip and knee flexion, knee internal rotation, and greater hip adduction. ACLR also presented different kinematics to ACLPT and CTRL in Take-off with a combination of greater trunk flexion, hip flexion, hip internal rotation, and less knee abduction, and in Landing with greater trunk flexion and hip internal rotation. Further, different kinematics and hop height were found between legs within groups in both Take-off and Landing for both ACL groups, but not for CTRL.

CONCLUSION: Different kinematics for the injured leg for both ACL groups compared to CTRL and between treatment groups, as well as between legs within treatment groups, indicate long-term consequences of injury. Compensatory mechanisms for knee protection seem to prevail over time irrespective of initial treatment, possibly increasing the risk of re-injury and triggering the development of osteoarthritis. Detailed investigation of movement strategies during the VH provides important information and a more comprehensive evaluation of knee function than merely hop height. More attention should also be given to the trunk and hip in clinics when evaluating movement strategies after ACL injury.

LEVEL OF EVIDENCE: Prospective cohort study, Level II.