The Patella Pro study — effect of a knee brace on patellofemoral pain syndrome: design of a randomized clinical trial (DRKS-ID:DRKS00003291)

The incidence of anterior knee pain is high. Callaghan and Selfe conducted a literature search of English-language publications dated from January 2000 to December 2005 that showed the incidence of patellofemoral pain syndrome (PFPS) to be between 3% and 40%[1]. The authors found that evidence for the incidence of PFPS was taken almost entirely from source data in sports medicine or military settings[1]. Women are affected more than twice as often as men[2‐4].

Patellofemoral pain syndrome (PFPS) is a common cause of anterior knee pain and mainly affects young women who do not have significant pathological changes in articular cartilage[3‐9]. Therefore, PFPS is mainly a diagnosis of exclusion and, as such, demands careful clinical examination[5], which can detect such characteristics of PFPS as patellar maltracking[10].

A classic PFPS symptom is anterior knee pain that is provoked by prolonged sitting with bent knees, stair climbing, and sports activities[5‐8]. Other associated manifestations include crepitus and functional deficit[5‐8]. PFPS symptoms cause many athletes to limit their sports activities[2], and some authors have stated that PFPS can contribute to long-term patellofemoral osteoarthritis[11, 12].

The role of patellar maltracking in the emergence of PFPS has long been a controversial issue. Recent studies, however, show that maltracking of the patella probably plays a key role[13‐15]. There is evidence in the literature that the cause of patellar maltracking and subsequent imbalance of the vastus medialis and lateralis in some patients with PFPS may not be structural in nature; rather, dynamic or functional malalignment may underlie PFPS in these patients[6, 7]. Functional or dynamic valgus may influence patellar tracking and lead to lateralization of the patella[14]. Recent research has shown that functional malalignment does not originate in the knee joint but results from internal rotation of the femur due to weakness of hip external rotators and abductors (gluteus medius and minimus)[16‐19]. Further muscular imbalances involving the quadriceps and hamstrings can be found in these patients[20‐22].

Muscular dysfunction probably plays a key role in the pathogenesis of PFPS; therefore, physiotherapy is the most frequently studied form of treatment[23, 24], and there is strong evidence for the role of exercise in the treatment of PFPS in the literature. In a recent meta-analysis of 10 prospective randomized studies[23], each showed a positive effect of exercise on pain reduction. Positive results have been attributed to active stretching exercises, squats, cycle ergometry, isometric quadriceps exercises, active leg raises, leg press, and ascending and descending climbing exercises. Four of the exercise programs also included exercises to strengthen the hip abductors. In one study, exercises to stabilize the trunk, including the rectus abdominis, were analyzed. The most frequent duration of the exercise programs was 6 weeks, and exercises were performed two to four times daily.

Patellar braces are non-adhesive devices that, like taping, apply an external, medially directed force that may counteract lateral patellar maltracking. Draper et al.[13] have demonstrated by real-time MRI that a knee brace that applies a medially directed force on the patella can reduce patellar lateralization and tilt in women with PFPS significantly better than a bandage. Powers et al.[25] analyzed an orthosis that applied a medially directed force on the patella in PFPS patients and reported decreased pain and increased activation of the quadriceps. Selfe et al.[26, 27] investigated the effect of patellar bracing and taping on the three-dimensional mechanics of the knee during a controlled step-down task in healthy and PFPS patients. These studies showed that bracing and taping offered coronal-plane and torsional control of the patella during eccentric contraction of the quadriceps in both PFPS patients and healthy subjects[26‐29]. In addition to these biomechanical effects, Thijs et al.[30] showed that there was a significantly higher level of neuromotor and proprioceptive function with the application of the brace and sleeve, respectively, than without a brace or sleeve. Callaghan et al.[31] have shown that patellar taping modulates brain activity in several areas of the brain during a proprioceptive knee movement task. According to the meta-analysis published by D'hondt et al.[32], the use of a patellar brace has positive effects on pain, function (Kjuala score), and patellofemoral congruence angle compared with an untreated control group. However, because of the low quality of the studies, the authors concluded that this evidence should be regarded as limited. Warden et al.[33] also found disputable evidence for the use of orthoses in PFPS patients. In this meta-analysis, only one of three studies reported a significant effect with a medially directed patella brace, whereas in the other two studies the effect was not significant. In these studies no difference was found between medially directed bracing and sham bracing.

Therefore, we conclude that there is a need for further well-designed studies to evaluate the effect of patellar bracing on pain in PFPS. The Patella Pro (Otto Bock, Duderstadt, Germany) is a new knee brace designed to apply a medially directed force on the patella to counteract lateral maltracking. The main characteristic of this patella brace is the dynamic tracking system. The risk of improper tracking of the patella is particularly high for flexion angles between 0 and 30 degrees, when the patella is not guided by the patellofemoral groove. The tracking system of the Patella Pro was designed with a sleeve that can apply a dynamic medially directed force on the patella and track the patella within this range of motion. The pressure from the tracking system decreases with increasing flexion angle[34], thus protecting the patella from pressure where it is not needed. The ability of this brace to counteract lateral patellar maltracking, thus improving biomechanical function, was demonstrated in a biomechanical cadaver study at the German Sports University in Cologne[28], which showed that the Patella Pro has the potential to medialize the patella during the entire range of motion.

The Patella Pro clinical trial will target patients 18–50 years of age presenting with symptoms of PFPS. The details of the study protocol are presented here. Our hypothesis is that there is a synergistic effect between the Patella Pro brace and exercise.

Patients who qualify as study participants on the basis of inclusion and exclusion criteria are informed about the study. This information includes written general information on patellofemoral pain syndrome and a written description of the present study. These instructions include information about the purpose of the study and potential risks. All participants must sign an informed-consent form.

The Patella Pro study was designed after reviewing the literature on therapy for patients with PFPS[9, 29]. The PEX study protocol published by Van Linschoten et al.[9] served as the model for this trial because it is a high-quality protocol for a trial examining an intervention for patients with a PFPS.

Treatment options for PFPS patients are patellar taping and bracing[7]. The exact mechanism of action of both modalities is unknown. Some authors have been able to demonstrate biomechanical effects of taping and brace application; others have demonstrated improved proprioception and effects on brain activity[30, 31]. A meta-analysis of studies limited in number and quality has shown that brace therapy may have a positive effect on PFPS[33]. Conflicting results of studies of the effects of patellar bracing[33] could also be the result of the brace design. The present study will contribute to the elucidation of this research question. We expect an answer about the clinical effect of the Patellar pro brace for the treatment of PFPS. Unfortunately we cannot answer if the effect is due to the medially directed force or a proprioceptive effect.

Based on the available literature regarding tape application in PFPS patients[33, 42, 43], our research group expects to discover benefits of brace treatment, including perceived recovery and improvements in pain severity and functional disability, in the Patella Pro study.

A limitation of the present study design is that only patients with an existing MRI and x-ray are included. This could be a selection bias, as only those patients with greater attention to their pathological condition are selected. Another limitation could be the age band going up to 50 as this group may have other symptoms. However, the exclusion criteria will mediate against some of these.

IR: Ingo Rembitzki, physiotherapist, employee of Otto Bock, Duderstadt. SS: PD Dr. Sven Scheffler, orthopedic surgeon in a private practice in Berlin. MH: Dr. Mirco Herbort, orthopedic surgeon at the department of trauma-, hand-, and reconstructive surgery at the Westfalian Wilhelms University in Münster. FS: Frederike Sprenker, study nurse at the orthopedic and trauma department of the Martin Luther Hospital, Berlin and medical student at the Freie Universität Berlin. AA: Dr. Andrea Achtnich, resident at the orthopedic and trauma department of the Martin Luther Hospital, Berlin. PB: Prof. Gerd Peter Brüggemann, director of the biomechanical institute, Deutsche Sport Hochschule, Köln. RB: Dr. Raymond Best, orthopedic surgeon at the Sportklinik Stuttgard, team physician of the first league soccer team VFB Stuttgard. FH: Dr. Frank Hoffmann, chief physician at the department of orthopedic surgery, Klinikum, Rosenheim. AG: Dr. Andreas Gösele Koppenburg, orthopedic surgeon at the cross clinic Basel, team physician, Leopard/Trek cycling team. CL: Dr. Christian Liebau, chief physician at the department of orthopedic surgery, Askleps Klinik, Bad Harzburg.