Study design, ethics, and informed consent
This is a longitudinal observational diagnosis study. All methods were performed in accordance with the relevant guideline. Data were retrospectively extracted from a data registry. The registry is the nationwide database from an enterprise (OPED GmbH, Valley, Germany). The register was initiated in January 2018, data until October 2020 were included in this analyses. As all data was retrieved completely anonymized from a registry, ethical approval is not relevant for this type of analysis.
Informed consent was obtained from all participants and (below 16 years of age) from their legal guardian. All data were assessed as a part of the functional assessment during the rehabilitation after ACL-reconstruction, no measurement or measures for study purposes were additionally undertaken.
Inclusion and exclusion criteria
The data from all database patients (children, adolescent, adult males, females, and diverse) with an acute unilateral ACL rupture with or without concomitant ipsilateral knee injuries (meniscal tear, lateral ligament involvement, unhappy triad) and having passed an arthroscopically applied, anatomical reconstruction was included.
Independent outcome variables
The following potential outcome modifiers were extracted: age range (0–15, 16-20, 21-25, 26–30, 31–40, 41-50, and above 50 years)), gender/sex (male, female, divers/unknown), time since reconstruction [days], time between injury and reconstruction [days], concomitant intra-articular injuries (isolated ACL tear, meniscal tear, lateral ligament, unhappy triad), graft type (hamstrings, patellar, or quadriceps tendon autograft), and pain intensity during the measurement (visual analogue scale 0-10 cm).
Functional tests
All functional tests were performed from experienced personnel. A standard operating procedure and test manual is used to perform the standardized test battery. Details on the outcomes, the underlying function, the tool used, the conduction, and the testing criteria are displayed in table 1.
Table 1: Overview of the functional outcomes. Each functional ability is described by the corresponding outcome and tool used to assess the ability, its test quality criteria, conduction and the (positive) decision criteria.
Function
|
Outcome
|
Tool
|
Test quality criteria
|
Conduction
|
Range of motion
|
Flexion [degrees]
|
intertial sensor
|
high concurrent validity correlations [19]
|
Active knee flexion RoM in upright standing and holding a table
|
"Extension" [degrees]
|
intertial sensor
|
Unknown, the method is somewhat different from traditional RoM assessments, further indicated by the ""
|
Active knee extension, starting point is sitting on the floor on a 10 cm height box, with a 15 cm–diameter roll under the knee. The roll is removed and the knee is stretched
|
Joint Position Sense
|
Absolute angle reproduction error [degrees]
|
intertial sensor
|
Unknown,
ICC = 0.31 - 0.82 (sitting) and 0.17 - 0.75 (prone) [20]
|
Start point see Flexion. A target angle in flexion RoM must be reached and reproduced after a 3 second break
|
Dynamic Balance
|
Composite score
|
Y-Balance test (imprinted on a carpet or affixed on the floor)
|
Good interrater test-retest reliability, acceptable level of measurement error [21]
|
Single-(test)leg standing, other leg must be moved anterior, posterior later and posterior medial as fast as possible without losing postural control. Composite score is calculated by adding all three single values divided by three times the limb length, this all multiplied by one hundred.
|
Vertical jumps and hops measurement
|
Knee displacement [cm]
|
Drop Jump,
Intertial sensor
|
ICC = 0.93 [22]
|
Bipedal hip-width stance on a box with a 32 cm target-height. A bipedal drop jump follows: frontal step – drop – reactive jump with the shortest possible ground contact time
|
Hopping height [mm]
|
Vertical hop,
intertial sensor
|
ICC= 0.89 -0.97 [23],
Average error with intertial sensors: -0.4 to 2.2 cm [24], ICC = .98
|
Unipedal stance on the ground, one-legged counter movement jumps
|
horizontal jumps and hops
|
Time to completion [seconds]
|
Speedy jump,
intertial sensor
|
ICC = 0.792 - 0.825 [25]
|
A small trail must be passed as fast as possible in one-legged hops
|
Number of hops in 30 seconds [n]
|
Side hops
intertial sensor
|
Unknown
|
Participants have to hop the participants hop over laterally (to the foot’s respective side) over a square on the floor with 30 x 30 cm edge length with hands on their hips as fast as possible [26]
|
Hopping distance [cm]
|
Single leg hop for distance
|
The measurement properties for the SLHD are excellent, reliability is ICC = 0.97 (CI 0.9-0.99) and the standard error of measurement is 3.5 % [27]
|
The participants stand on one leg with the toes behind the rear line of the square. He/she then hops as far as possible and has to land in a controlled manner. The whole hop must be performed one-legged.
|
RoM = range of motion, ICC = intraclass correlation coefficient, ACL = anterior cruciate ligament, RTS = return to sports.
Outcome assessments
All range of motion, joint position sense, vertical jumps and hops measurement, side hops, and the speedy jump outcomes were assessed using a single inertial sensor (Orthelligent Pro, OPED GmbH, Valley, Germany). The non-invasive external three-dimensional wireless sensor was positioned at the highest circumference of the lower leg using an elastic band, the sensor itself was placed on the tibia.
The sensor consists of a 9-axis MEMS MotionTracking device (TDK InvenSense, Chūō, Tokio, Japan), with 3 accelerometers (measurement range ±2 g to ±16 g), a 3-axis gyroscope (±250 to ±2000 degrees per second), and a 3-axis magnetometer. The device was zeroed prior to each measurement.
Sample rate was (accelerometer) 4.5 kHz to (Gyroscope) 9.0 kHz. The data was down-sampled (4:1) and filtered for the further analysis. A low pass and Kalman filter was applied.
Statistical Analysis
The statistical analyses were performed blinded to the data retrieval from the database.
Range data plausibility check was undertaken for all independent and dependent outcomes, the data were cleared accordingly.
Repeated measures mixed models (multilevel analysis) investigated the impact and interaction of the individual (random effects) predictors (level 2), and of time (level 1) on the functional outcomes’ values. Following the checking for potential violations of the underlying assumptions (heteroscedasticity, non-linearity, normal distribution of the residuals), 2-LL estimates were adopted to build the models. Due to the considerable amount of missing information on the graft type, these analyses were, partially, contributed separately. In detail, the analyses which were once modelled including and once without the graft type are highlighted with an empty row (in the tables) between the graft type and the other contributors. The size of the estimates highlight the size of the effect of the independent on the dependent variable (always in the units used), the direction is indicated by the leading sign (minus indicates a negative association).
All analyses were performed in SPSS version 25 (IBM Corporation, New York, NY, USA), an alpha-error of 5 % was considered as a relevant cut-off significance value, all p-values below are interpreted as statistically significant.