Study design
This study is a randomized multicenter clinical trial examining the short-term effectiveness of a patellar brace (Patella Pro, Otto Bock, Duderstadt, Germany) in combination with exercise on short and longterm PFPS outcomes compared with exercise alone.
The study protocol was approved by the medical ethics committee of Charite University Hospital. The study protocol was registered with the
Deutsches Register Klinischer Studien (“German Clinical Trials Register”) as DRKS-ID number DRKS00003291 and published [
26]. All research was conducted in accordance with the 1964 Helsinki Declaration. The protocol of a previous study that evaluated the effects of exercise on patients with PFPS served as the model for the study design of the present study [
33].
Patients were recruited from the following study centers: (1) Klinik für Orthopädie und Unfallchirurgie, Martin Luther Krankenhaus, Berlin Grunewald, Germany, (2) Arcus Sportklinik, Pforzheim, Germany, (3) Asklepios, Harzkliniken GmbH, Fritz-König-Stift, Bad Harzburg, Germany, (4) Orthopädische Gemeinschaftspraxis, Berlin, Germany, (5) Klinik für Unfall-, Hand-, und Wiederherstellungschirurgie, Universitätsklinikum Münster, Germany, and (6) Orthopädische Klinik, Rosenheim, Germany [
26].
The recruitment period took place from April 2012 to October 2014. Adult patients aged 18–50 years with PFPS symptoms for longer than 2 months but not longer than 2 years were eligible to participate [
26].
Inclusion criteria consisted of a patient age between 18 and 50 years and the presence of three of the following symptoms lasting longer than 2 months but not longer than 2 years: anterior knee pain when running, climbing stairs, cycling, sitting with a bent knee, or performing squats [
26].
Exclusion criteria consisted of the following: Kellgren-Lawrence grade 3 to grade 4 osteoarthritis [
22], local grade 3 to grade 4 cartilage damage as noted on magnetic resonance imaging and measured using the Gluckert grading system [
20], subluxation of the patella, a history of a previous knee injury (such as to the cruciate ligaments), tendinosis of the patellar tendon, a history or active diagnosis of Osgood–Schlatter disease, osteochondritis dissecans, a varus knee with an intercondylar distance greater than 2 fingerbreadths, and a valgus knee an intermalleolar distance greater than 3 fingerbreadths [
26].
Patients who qualified as study participants on the basis of the inclusion and exclusion criteria were informed about the study design. Informed consent was obtained from all individual participants included in the study.
Our sample size calculation was based on a former intervention study by Clark et al. [
14]. In this study the difference in recovery rates between the intervention and control groups was 22 %. This difference was statistically significant (power 0.8, alpha 0.05). With a potential dropout rate of about 15 %, approximately 156 patients must be enrolled in this study to achieve a power of 0.80 and an alpha of 0.05.
After patients were recruited and informed consent was obtained, all patients were randomized into two treatment groups. In group 1 (brace group) all patients received a patellar brace (Patella Pro) (Fig.
1). With this brace, a medially directed force can be applied to the patella by a tracking system. The brace was customized for the patient by the study physician. Patients were instructed to wear the brace over a minimum period of 6 weeks for at least 6 h a day. In group 2 (non-brace group) no brace was applied and patients were instructed to not utilize a brace over the 6-week study period [
26].
In both groups, patients entered a supervised exercise and structured home exercise program (Patella Move program). Patients were instructed to perform the home exercises daily for 15 min for a period of 6 weeks. For supervised exercises, all study participants received a prescription of about 12 sessions of
Krankengymnastik am Gerät. The duration of one session is 60 min [
26]. The duration of the supervised exercise program was 6 weeks (12 units).
During the course of the study, the application of ice and topical agents, and the use of oral analgesics (e.g., non-steroidal anti-inflammatory drugs or paracetamol) was permitted and recorded.
Outcome measures
The primary outcome measures for this study were subjective assessments of recovery using a seven-point Likert scale [
33] administered at 6, 12, and 54 weeks following the start of therapy. This parameter was used for the sample size calculation. Secondary outcome measures included the modified functional Kujala score without the muscular atrophy and flexion parameters, the German version of the Knee Injury and Osteoarthritis Outcome Score (KOOS) [
23], pain at rest and with walking, stair climbing, sitting and sports activity, reported on a numerical scale (0–100) [
15], and a review of additional interventions. All these measurements were evaluated via questionnaire prior to any intervention, and 6, 12, and 54 weeks after the start of therapy.
All patients were asked after 6 weeks of therapy if they had adhered to the treatment protocol (6 h per day of the patella brace for 6 weeks, 15 min of home exercise daily, and 12 sessions of physiotherapy) [
26].