A randomized-controlled study design was applied
Patients who underwent arthroscopic partial meniscectomy (APM) as part of the clinical routine at our medical university hospital were considered for inclusion. In the case of degenerative meniscus lesions surgical indication was made conservatively (no success with conservative therapy, giving way, blocked knee joint).
Exclusion criteria were: (1) scheduled combined or staged surgical procedures (e.g. osteotomy or ligament reconstruction, (2) scheduled bicompartmental meniscectomy, (3) full-thickness chondral lesions as determined with preoperative MRI (4) rheumatoid arthritis or (5) osteoarthritis (Kellgren–Lawrence Grade other than 0 or 1). The concept of unloading a recently partly resected medial meniscus was regarded as appropriate only for the case of a neutral or slightly varus leg axis. The concept of unloading a recently partly resected lateral meniscus was regarded as appropriate only for the case of a neutral or slightly valgus leg axis. Therefore, the patient’s mechanical tibiofemoral angle (mTFA) was taken from a weight-bearing whole leg radiograph during bipedal stance at the time of enrollment. The mTFA was measured as suggested by previous researchers [
11,
15,
35]. The center of the femoral head was connected to the center of the distal femur to define the mechanical axis of the femur. The mechanical axis of the tibia was defined as a line from the center of the proximal tibia to the center of the ankle joint. The angle between the mechanical axis of the femur and the mechanical axis of the tibia was taken as mTFA [
11]. The angle was determined to one decimal place. The applied method was reported as being accurate and reliable in previous research [
35]. A knee with a mTFA from 2.9° varus to 2.9° valgus was defined as neutrally aligned. Knees with a varus or valgus mTFA in excess thereof were defined as varus and valgus knees, respectively. Then the additional exclusion criteria (6) scheduled medial APM in a valgus knee and (7) scheduled lateral APM in a varus knee were applied.
APM was conducted as part of the clinical routine, either as day surgery or as part of a short hospital stay. Tourniquets were used depending on the surgeon’s preference. Great attention was paid to maintaining a stable peripheral rim during APM. In none of the procedures was the rim fully interrupted/resected. Complete interruption of the peripheral rim is considered to be complete meniscus loss from a functional standpoint. All procedures were conducted by experienced orthopaedic consultants or under their direct supervision. At the time of APM additional exclusion criteria were applied: (1) unanticipated full-thickness chondral lesions, (2) unanticipated need for additional procedures (e.g. chondral procedures), (3) APM performed in both compartments and (4) intraoperative change to other meniscus procedures (e.g. total meniscectomy, meniscus repair). Physical exercise started from the day of surgery. Neither active nor passive range of motion was restricted. Weight-bearing was restricted to 50 percent bodyweight for ten days. All patients were prescribed a series of physical therapy on an outpatient basis (8–10 sessions of 40 min each).
The intervention under investigation was the postoperative treatment after APM. Patients were randomized to either the brace group, the insole group or the control group. In the brace group, patients used an unloading knee brace “OA Nano” (DJO UK Ltd., Guildford, Surrey, UK). The brace applied a valgus force in patients who had undergone medial APM and a varus force in patients who had undergone lateral APM. The above-mentioned brace is designed for light to moderate knee OA and provides unloading with a lightweight magnesium frame. This was done to unload the joint compartment in which the meniscus had just been partly resected. The knee brace was worn by the patients for a minimum of 5 h a day over a period of 12 weeks as protocolled in an individual diary. In the insole group, patients received a custom-made wedge insole of 5 millimeters. To achieve postoperative compartment unloading patients who had undergone medial APM received a lateral wedge insole. Patients who had undergone lateral partial meniscectomy received a medial wedge insole. Again, insoles were worn for a minimum of 5 h a day over a period of 12 weeks. To facilitate patients’ adherence to the treatment protocol they were given insoles for both outdoor and indoor shoes. Patients in the control group did not receive any specific additional compartment-unloading therapy.
Based on previous recommendations [
41] the clinical outcome was assessed with patient-reported outcome measures (PROMs) in a threefold manner: (a) knee-specific outcome, (b) physical activity and (c) general health. For the knee-specific outcome the International Knee Documentation Committee Subjective Knee Evaluation Form (IKDC Score) was applied [
13]. Validity, reliability and responsiveness were demonstrated for many knee disorders as well as meniscal pathologies [
12,
14]. The 18 items are summed up for the raw score, which is then transferred to a 0–100 scale (0: worst, 100: best). The Knee Injury and Osteoarthritis Outcome Score (KOOS) [
29] was used as a second knee-specific outcome instrument. The KOOS consists of the five subscales pain (9 items), symptoms (7 items), activities of daily living (17 items), sport and recreation function (5 items), and knee-related quality of life (4 items). Each scale is summed up and transferred to a 0–100 scale (0: worst, 100: best). Also the KOOS was proven to be an appropriate instrument for determining the outcome of meniscal surgery [
28,
30]. Physical activity was assessed with the MARX score, which determined activity in terms of running, cutting, decelerating and pivoting [
22]. In each category points were given depending on frequency (0–4 points), which gave a total scale of 0–16 (0: worst, 16: best). General health was determined with the Short-form 12 (SF-12) that provides results in the form of a physical score and a mental score [
40]. All above-mentioned outcome parameters were collected preoperatively, and postoperatively at 6 weeks, 3 months, 6 months and 12 months.
The Ethics Committee of the Medical University of Innsbruck approved the study protocol (No. AN-2014-0004 333/4.6). The study was registered at clinicaltrial.gov (Identifier: NCT02190188).
Statistical analysis
Sample characteristics are given as means and standard deviations as well as absolute and relative frequencies. Analysis of the impact of the intervention was performed with the help of linear mixed models. The models included the outcome parameter (IKDC, KOOS, MARX, SF-12) as dependent variable, time point and study group as fixed effects, the two-way interaction of group and time, and a diagonal covariance structure. Separate models were run for the various outcome parameters. In such a model the impact of the intervention is reflected by the group-by-time interaction term. P values below 0.05 were considered to be statistically significant. All statistical analyses were performed with SPSS 21.0 (IBM, Chicago, IL, USA).
The power analysis for the study was done for the main hypotheses and considered the two-way interaction of group-by-time (three groups, five time points) in a repeated measure analysis of variance that is a group difference in parameter change over time. In such an analysis, a difference in change over time with an effect size of
f = 0.14 can be detected with power = 0.80 (
α = 0.05, correlation among repeated measures is 0.70 and non-sphericity correction is 1.0) if the sample size is
N = 16 per group (
N = 48 in total). To account for an attrition rate of 30% we aimed to include
N = 63 at baseline. Power analysis was done with the software G*Power 3.1.9.2 [
8].