Jana Holder

Introduction & Purpose ACL injury rehabilitation progressions typically advance from controlled bilateral to high‑velocity, unilateral, multiplanar tasks, yet load prescription remains predominantly qualitative. Currently, ACL loading is primarily assessed via surrogate measures (e.g., knee joint moments). These approximations can miss ligament-level mechanics. Given that ACL loading is mediated by ligament strain, model-based ACL strain estimates provide a more mechanistic basis for progression (Bates et al., 2020). However, direct comparisons of ACL strain across commonly used single‑leg assessment tasks are lacking. We therefore quantified ACL strain during the single‑leg squat (SLS), single‑leg counter-movement jump (SLCMJ), and single‑leg forward jump (SLJF), and tested the hypothesis that SLJF elicits the highest peak strain, followed by SLCMJ and SLS. Methods Eleven active participants (5 male, 6 female participants, 1.73 ± 0.08 m, 71.4 ± 9.9 kg, 28 ± 3 years old) performed SLS, SLCMJ, and SLJF with a marker-based 3D motion capture system. Marker coordinates and ground reaction forces were processed in OpenSim. ACL strains were estimated using musculoskeletal simulations incorporating a multi-body knee model with 14 ligament bundles (including ACL) combined with the COMAK framework (Smith et al., 2016). Peak ACL strain (%) for the complete squatting movement and for landing phase (ground contact) till deepest center of mass position were extracted. Differences across exercises were tested with a repeated-measures ANOVA (α = 0.05) with adjusted post hoc pairwise comparisons. Ethical approval and informed consent were obtained. Results Tasks had a significant, large effect on ACL strain. Post hoc comparisons revealed significant differences (p < 0.017) for SLCMJ > SLS (p = 0.003) and SLJF > SLS (p < 0.001), but not for SLJF > SLCMJ (p = 0.035) (Figure 1). Discussion SLJF, especially horizontal landings, produces the highest ACL strain, followed by vertical SLCMJ and SLS. Our rank ordering aligns with studies that contrasted vertical and horizontal single leg jumps using joint work, which show higher demands on the knee joint in horizontal versus vertical jumps (Kotsifaki et al., 2021). Some limitations should be acknowledged. The musculoskeletal model and COMAK framework were not yet validated for sport specific dynamic movements, only for gait simulations. However, our simulation results are within the same range as in-vivo and cadaver studies (Bates et al., 2020). Conclusion Strain-based exercise classification enables more precise dosing of ACL-relevant mechanical load than purely kinematic or uniplanar moment metrics, informing progression and return-to-sport decisions. This study can be taken as start point to establish evidence-based rehabilitation programs based on ACL loading rather than surrogate measures or expert opinions. References Bates, et al. (2020). Timing of Strain Response of the ACL and MCL Relative to Impulse Delivery During Simulated Landings Leading up to ACL Failure. J Appl Biomech, 36(3), 148–155. https://doi.org/10.1123/jab.2019-0308 Kotsifaki, et al. (2021). Vertical and Horizontal Hop Performance: Contributions of the Hip, Knee, and Ankle. Sports Health, 13(2), 128–135. https://doi.org/10.1177/1941738120976363 Smith, et al. (2016). The Influence of Component Alignment and Ligament Properties on Tibiofemoral Contact Forces in Total Knee Replacement. J Biomech Eng, 138(2), 021017. https://doi.org/10.1115/1.4032464

This study aimed to identify subpopulations of patients with hip osteoarthritis who exhibit distinct adaptations in gait biomechanics, and to evaluate subpopulation-specific effects of total hip replacement on gait biomechanics. Three datasets were analyzed: (1) a cohort of 109 unilateral hip osteoarthritis patients before total hip replacement, (2) a subset of the first dataset of 63 patients re-evaluated after total hip replacement and (3) a control group of 56 healthy individuals. For all participants, three-dimensional joint angle and moment waveforms of the pelvis, ipsilateral hip and knee, as well as sagittal-plane ankle motion and the foot progression angle, were obtained. The analytical framework integrated k-means clustering, support vector machine classifiers, Shapley Additive exPlanations, and statistical waveform analyses. Clustering of the pre-operative dataset revealed three distinct subpopulations characterized by unique patterns in gait kinematics and joint moments. These subpopulations also differed in age, Kellgren-Lawrence score, and walking speed. Prior to total hip replacement, between 51.4% and 85.2% of hip osteoarthritis patients were classified as pathologic; following surgery, this proportion decreased to 27.8% − 51.8%. Hip flexion and rotation angles and moments were identified as the most important features for patient classification. The magnitude of gait improvement after total hip replacement varied across subpopulations, indicating subpopulation-specific responses to surgical intervention. In conclusion, patients with hip osteoarthritis demonstrate distinct subpopulation-specific gait adaptations, both before and after total hip replacement. Preoperative classification of patients into the identified subpopulations using machine learning approaches may facilitate the prediction of postoperative gait recovery and support the development of personalized treatment and rehabilitation strategies.

Background: The accurate estimation of residual growth is crucial for the appropriate timing of growth-guiding surgery in patients with axial leg deviations. Skeletal age methods such as the Modified and the Abbreviated Modified Fels Knee System were developed on historical patient cohorts and the applicability to the modern pediatric population with axial leg deviation has not yet been evaluated. Questions/purposes: Are both final adult height prediction methods (the Modified Fels Knee System (FKS) and the Abbreviated Modified Fels Knee System (aFKS)) accurate to determine SA and the final adult height on long leg radiographs in patients with axial leg deviations? Which multiplier table shows highest association between predicted and true final adult body height? Do FKS- and aFKS- skeletal age determination methods improve final adult body height prediction accuracy compared to the simple use of chronological age? Methods: A single center, retrospective study of 31 patients who underwent temporary hemiepiphysiodesis due to axial leg deviations in the frontal plane between 2018 and 2020 was conducted. Skeletal age at the time of surgery was determined on an anterior-posterior long leg X-ray using FKS and aFKS. Adult height predictions were calculated using three different multiplier tables (Paley et al., Sanders-Greulich and Pyle (SGP), Sanders-Peak Height Velocity (PHV)). The accuracy of adult height prediction was determined by comparing the mean differences and mean absolute differences between predicted and true adult height. Results: All adult height predictions overestimated the true adult height. The final height prediction using aFKS and the SGP multiplier showed the lowest overestimation (mean 3.2 cm, SD 5.5 cm). The PHV multiplier table showed the highest correlation between predicted and true adult height (FH_{PRE_FKS_PHV}: r = 0.913, p < 0.001 and FH_{PRE_aFKS_PHV}: r = 0.862, p < 0.001). The simple use of chronological age at the time of surgical intervention (CA_SI) with the Paley multiplier table showed the highest median delta absolute values and lowest correlations with true adult height (median 7.4 cm, 25%-75% percentile: 3.5–10.0 cm, r = 0.838, p < 0.001). Nevertheless, no significant differences in delta absolute values between various adult height predictions methods could be shown. Conclusions: Overall, the results of the present retrospective cohort study show that there was no significant improvement in final height prediction accuracy when using the FKS or the aFKS method compared to the simple use of chronological age. One reason could be that patients with varus/valgus malalignment have specific growth characteristics that are not accounted for in multiplier tables or the FKS and aFKS method. Since there is no significant difference in prediction accuracy between the methods, the choice of method may depend on other factors, such as clinical preference or availability of resources. However, due to the small sample size, the study cannot definitively rule out potential differences between the prediction methods, and larger studies are required to validate these findings.

Validation of central peak height method for final adult height predictions on long leg radiographs

The correction of valgus leg malalignment in children using implant-mediated growth guidance is widely used and effective. Despite the minimal invasive character of the procedure, a relevant number of patients sustain prolonged pain and limited mobility after temporary hemiepiphysiodesis. Our aim was to investigate implant-associated risk factors (such as implant position and screw angulation), surgical- or anesthesia-related risk factors (such as type of anesthesia, use, and duration), and pressure of tourniquet or duration of surgery for these complications. Thirty-four skeletally immature patients with idiopathic valgus deformities undergoing hemiepiphysiodesis plating from October 2018–July 2022 were enrolled in this retrospective study. Participants were divided into groups with and without prolonged complications (persistent pain, limited mobility of the operated knee between five weeks and six months) after surgery. Twenty-two patients (65%) had no notable complications, while twelve patients (35%) had prolonged complications. Both groups differed significantly in plate position relative to physis (p = 0.049). In addition, both groups showed significant differences in the distribution of implant location (p = 0.016). Group 1 had a shorter duration of surgery than group 2 (32 min vs. 38 min, p = 0.032) and a lower tourniquet pressure (250 mmHg vs. 270 mmHg, p = 0.019). In conclusion, simultaneous plate implantation at the femur and tibia and metaphyseal plate positioning resulted in prolonged pain and a delay of function. In addition, the amplitude of tourniquet pressure or duration of surgery could play a factor.

Compressive knee joint contact force during walking is thought to be related to initiation and progression of knee osteoarthritis. However, joint loading is often evaluated with surrogate measures, like the external knee adduction moment, due to the complexity of computing joint contact forces. Statistical models have shown promising correlations between medial knee joint contact forces and knee adduction moments in particularly in individuals with knee osteoarthritis or after total knee replacements (R² = 0.44–0.60). The purpose of this study was to evaluate how accurately model-based predictions of peak medial and lateral knee joint contact forces during walking could be estimated by linear mixed-effects models including joint moments for children and adolescents with and without valgus malalignment. Peak knee joint moments were strongly correlated (R² > 0.85, p < 0.001) with both peak medial and lateral knee joint contact forces. The knee flexion and adduction moments were significant covariates in the models, strengthening the understanding of the statistical relationship between both moments and medial and lateral knee joint contact forces. In the future, these models could be used to evaluate peak knee joint contact forces from musculoskeletal simulations using peak joint moments from motion capture software, obviating the need for time-consuming musculoskeletal simulations.

Background: Malalignments of the lower extremity are common reasons for orthopedic consultation because it may lead to osteoarthritis in adulthood. An accurate and reliable radiological assessment of lower limb alignment in children and adolescents is essential for clinical decision-making on treatment of limb deformities and for regular control after a surgical intervention. Objective: First, does the analysis of full-length standing anteroposterior radiographs show a good intra- and interobserver reliability? Second, which parameter is most susceptible to observer-dependent errors? Third, what is the Standard Error of Measurement (SEM_95%) of the absolute femoral and tibial length? Methods: Two observers evaluated digital radiographs of 144 legs from 36 children and adolescents with pathological valgus alignment before a temporary hemiepiphysiodesis and before implant removal. Parameters included Mechanical Femorotibial Angle (MFA), Mechanical Axis Deviation (MAD), mechanical Lateral Distal Femoral Angle (mLDFA), mechanical Medial Proximal Tibial Angle (mMPTA), mechanical Lateral Proximal Femoral Angle (mLPFA), mechanical Lateral Distal Tibial Angle (mLDTA), Joint Line Convergence Angle (JLCA), femur length, tibial length. Intra- and interobserver reliability (ICC_2,1), SEM_95% and proportional errors were calculated. Results: The intra- and interobserver reliability for almost all measurements was found to be good to excellent (Intra-ICC_2,1: 0.849–0.999; Inter-ICC_2,1: 0.864–0.996). The SEM_95% of both observers was found to be ± 1.39° (MFA), ± 3.31 mm (MAD), ± 1.06° (mLDFA) and ± 1.29° (mMPTA). The proportional error of MAD and MFA is comparable (47.29% vs. 46.33%). The relevant knee joint surface angles show a lower proportional error for mLDFA (42.40%) than for mMPTA (51.60%). JLCA has a proportional error of 138%. Furthermore, the SEM_95% for the absolute values of the femoral and tibial length was 4.53 mm for the femur and 3.12 mm for the tibia. Conclusions: In conclusion, a precise malalignment measurement and the knowledge about SEM_95% of the respective parameters are crucial for correct surgical or nonsurgical treatment. The susceptibility to error must be considered when interpreting malalignment analysis and must be considered when planning a surgical intervention. The results of the present study elucidate that MAD and MFA are equally susceptible to observer-dependent errors. This study shows good to excellent intra- and interobserver ICCs for all leg alignment parameters and joint surface angles, except for JLCA. Trial registration: This study was registered with DRKS (German Clinical Trials Register) under the number DRKS00015053. Level of evidence: I, Diagnostic Study.

Gait analysis as a clinical examination method has been increasingly used in recent years. In particular, the external knee adduction moment was often used as a surrogate measure for internal medial knee joint loading, e.g., in elderly individuals with medial knee osteoarthritis. Therefore, the knee adduction moment is also associated with the progression of knee osteoarthritis. Children and adolescents with valgus malalignment have been found to experience a reduced external knee adduction moment, but internal knee joint contact forces, particularly in the lateral compartment, were not previously studied. First, medial and lateral knee joint contact forces were studied using muskulosceletal modeling in young individuals with and without valgus malalignment treated by guided growth. In addition, a systematic literature review was conducted to explore the relationship between external joint moments and internal joint contact forces. Finally, this relationship was investigated in children and adolescents with and without valgus malalignment. Furthermore, we examined whether statistical models could be determined to accurately predict internal knee joint contact forces by commonly used parameters from three-dimensional gait analysis, such as external knee joint moments. It was found that guided growth normalized knee joint contact forces after treatment. In addition, the static radiographic mechanical axis angle correlated better after the treatment when the patients showed a typical limb alignment compared to the correlation before guided growth with the valgus malalignment due to compensating strategies during gait. Furthermore, the systematic review showed that the peak medial knee joint contact force was best predicted by the knee adduction moment and even better together with the knee flexion moment in the first half of stance. However, for the second half of stance of the medial knee joint contact force and the entire stance of the lateral knee joint contact force, only low correlations with knee adduction and/or flexion moment were found. Finally, statistical models could be determined with high accuracy for both medial and lateral knee joint contact force, for both peaks in the first and second half of stance, and for both study groups of children and adolescents with and without valgus malalignment by including knee adduction and flexion moment as predictors. These results demonstrate the importance of examining not only the external knee adduction moment but also the knee flexion moment and, even better, the medial and lateral knee joint contact forces when evaluating knee joint loading. With these statistical models, clinicians can predict the medial and lateral knee joint contact forces without the need to perform musculoskeletal simulations and can therefore use standard three-dimensional gait analysis parameters such as knee adduction and flexion moment. This can improve guided growth treatment in children and adolescents with valgus malalignment with regard to implantation or explantation of the growth restricting plates or to rebound. Instrumented gait analysis could be particularly helpful in borderline cases, as kinematic compensation mechanisms during gait may play a role and the static radiograph alone does not provide information about dynamic joint loads. Die Ganganalyse als klinische Untersuchungsmethode hat in den letzten Jahren zunehmend an Bedeutung gewonnen. Insbesondere das externe Knieadduktionsmoment wird häufig als Maß für die interne mediale Kniegelenkbelastung verwendet, z.B. bei älteren Personen mit medialer Gonarthrose. Daher wird das Knieadduktionsmoment auch mit dem Fortschreiten der Gonarthrose in Verbindung gebracht. Bei Kindern und Jugendlichen mit Valgusfehlstellung wurde ein geringeres externes Knieadduktionsmoment festgestellt, aber die internen Kniekontaktkräfte, insbesondere im lateralen Kompartiment, wurden bisher nicht untersucht. In dieser Arbeit wurden zunächst die medialen und lateralen Kniegelenkkontaktkräfte mittels muskuloskelettaler Modellierung bei jungen Kindern und Jugendlichen mit und ohne Valgusfehlstellung untersucht, die durch eine Wachstumslenkung behandelt wurden. Außerdem korrelierte die röntgenologische mechanische Beinachse nach der Behandlung mit korrigierter Beinachse besser, als vor der Wachstumslenkung mit einer Valgusfehlstellung, da hier Kompensationsstrategien beim Gehen eine größere Rolle spielen. Schließlich wurde dieser Zusammenhang bei Kindern und Jugendlichen mit und ohne Valgusfehlstellung untersucht. Darüber hinaus wurde untersuchten, ob statistische Modelle erstellt werden können, um die internen Kniegelenkkontaktkräfte anhand von häufig verwendeten Parametern aus der dreidimensionalen Ganganalyse, wie z.B. den externen Kniegelenkmomenten, genau vorherzusagen. Es zeigte sich, dass durch die Wachstumslenkung die Kniegelenkkontaktkräfte normalisiert wurden. Darüber hinaus verbesserte sich das Verhältnis zwischen dynamisch gemessenen Kniegelenkkontaktkräfte und statisch gemessener mechanischer Beinachse. Des Weiteren zeigte die systematische Literaturrecherche, dass die maximale mediale Kniegelenkkontaktkraft in der ersten Hälfte der Standphase am besten durch das Knieadduktionsmoment und noch besser zusammen mit dem Knieflexionsmoment vorhergesagt wurde. Für die zweite Hälfte der Standphase der medialen Kniegelenkkontaktkraft und die gesamte Standphase der lateralen Kniegelenkkontaktkraft wurden jedoch nur geringe Korrelationen mit dem Knieadduktionsmoment und/oder dem Knieflexionsmoment gefunden. Schließlich konnten statistische Modelle mit hoher Genauigkeit sowohl für die mediale als auch für die laterale Kniegelenkkontaktkraft, für beide Maxima in der ersten und zweiten Hälfte der Standphase und für beide Studiengruppen von Kindern und Jugendlichen mit und...