August 2010

Patellofemoral taping: Pain relief mechanisms

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A recent study from the National Institutes of Health sheds new light on the underlying mechanisms of patellar taping in PFPS, helps explain some previous contradictory findings, and provides strong evidence for patient specific treatments.

By Frances T. Sheehan, PhD

Patellofemoral pain syndrome (PFPS) arising from idiopathic anterior knee pain (AKP), is one of the most common problems of the knee, constituting 14-17% of all injuries presenting to a sports injury clinic1,2 with an incidence rate 13.5% among cadets at the U.S. Naval Academy.3 It is characterized by insidious AKP that is aggravated by deep knee flexion, prolonged sitting, and repetitive flexion/extension.4 The cause of PFPS is thought to be multifactorial. One potential pathway involves weakness, incorrect timing, and/or inadequate force production of the vasti medialis oblique (VMO), resulting in pathological patellofemoral kinematics, which in turn cause increased stress on the patellofemoral cartilage.5,6 Currently it is not possible to measure in vivo patellofemoral cartilage stress, so studies have focused on quantifying the relationship between patellofemoral kinematics and patellofemoral contact area,7 given that a decrease in contact area would result in an increase in contact stress if the force of contact remained the same.

Conservative treatment (patellar taping, patellar bracing, selective strengthening of the vastus medialis, iliotibial band stretching, ankle-foot orthotics, or a combination of any of the above8-13) is typically the first approach to treating PFPS, but if this fails, surgical options are often pursued. In a systematic review Bizzini and colleagues14 summarized that all the above listed conservative techniques reduce pain, but the majority of the studies reviewed did not meet a sufficient level of quality to reach a definitive conclusion. More importantly, the actual mechanism for the pain relief for most conservative treatments remains in question.15,16

Taping mechanisms

Figure 1: Applying the McConnell medial glide tape. A: Taping begins with an assessment of the patellafemoral joint’s lateral hypermobility. B,C: Hypafix is applied to the skin covering the knee. D,E: Next, a medial glide of the patella is obtained by manually pushing the patella medially to its end range of motion. Rigid strapping tape is then used to maintain the medial glide of the patella by pulling the skin and patella medially.

One conservative treatment that is widely used by clinicians for patients with PFPS is McConnell taping.17 This involves pushing the patella medially, then securing it in this position with tape on the skin (Figure 1). Originally, the McConnell taping technique was developed to correct excessive patellofemoral lateralization and permit participation in normal daily activity. It is typically used in conjunction with a physical therapy regimen11,17,18 and is believed to reduce pain through two mechanisms.

In the short term, the force of the tape medializes the patella within the femoral groove,17,19 temporarily unloading the inflamed peripatellar tissues,20 which leads to a reduction in pain. This short-term pain reduction enables the patient to more actively participate in rehabilitation and promotes earlier activation of the VMO,21,22 increased VMO activity with decreased VL activity,23 and increased quadriceps torque.24 This in turn increases patellofemoral dynamic stability, helping the patient maintain correct patellofemoral kinematics. Thus, when taping is used in concert with rehabilitation, pain ultimately is reduced or eliminated through lasting changes in muscle control, which in turn improves the knee’s dynamic stability to a point where taping is no longer needed. In a study examining the effects of bracing, which is hypothesized to relieve pain in a manner similar to taping, Powers and colleagues25 demonstrated that bracing the knee in pain free controls resulted in a medialization of the patella and an increase in joint contact area. If the force on the cartilage remained unchanged, this increase in contact area would have resulted in a decrease in contact stress.

Conflicting evidence

Figure 2: The exact directions associated with the three movement directions (medial, superior and anterior) are based on establishing a three-dimensional coordinate system, but can be approximated using two-dimensional approximations based on the anatomical landmarks from which the coordinate system is established.37 Similarly, the rotations are based on an xyz-body fixed Cardan rotation sequence,42 but can be approximated using anatomical lines (as shown above).

Taping has clearly been demonstrated to reduce pain in patients with PFPS.16,21-24,26-29 A meta-analysis27 involving six studies (288 participants) demonstrated that medially directed taping decreased reported pain by 14.7 points on a 100-point visual analog scale in comparison to no tape. One confounding variable in determining the effectiveness of taping in the reduction of pain is the fact that studies with negative findings are often not published.18,30 In an attempt to elucidate the underlying mechanisms of pain relief with taping, studies have examined the timing/activity changes in the VMO and alterations to the patellar position after taping. Some studies have demonstrated a change in VMO timing/activity relative to the vasti lateralis,19,21,22 but other studies have shown no changes in these muscles with taping.6,31 In the evaluation of patellofemoral static posture pre- and post-taping,19,28,32-36 only four studies have found significant changes in patellar medial position or congruence angle after taping.33-36Unfortunately, these changes were negated by a short bout of exercise post-taping. These studies were limited by the fact that kinematic changes were evaluated statically and only in the axial plane (in terms of patellar shift and tilt, Figure 2).

A study by Wilson and colleagues16 raised further concerns about the potential link between patellofemoral pain reduction and medial realignment of the patella with taping. Across three treatment centers, a total of 71 patients were tested. Subjects reported their pain level on an 11-point scale (0-10) after four single-step downs from an 8-inch platform. The first condition was untaped; for the next three, the knee was taped in a medial, lateral, or neutral direction, with the three tape conditions tested in random order. The lateral taping was applied in a similar manner to the medial taping, but the patella was pulled laterally with the tape supporting this lateral glide. For the neutral case the same taping materials were applied to the anterior aspect of the knee, but no medial or lateral glide was produced. All three taping conditions provided significant decreases in reported pain, yet the neutral and lateral taping conditions produced more pain relief than the medial taping condition; the average pain score for the untaped, medially taped, laterally taped and neutral taped conditions was 5.2±2.7, 4.4±3.0, 3.5±2.4, and 3.4±2.4, respectively. The authors concluded that their results reinforced the concept that taping does not achieve its effect by medializing the patella.

Figure 3: Change in patellar kinematics with taping (y-axis) versus the value at baseline (un-taped condition, x-axis). Cine-PC MRI provides kinematics throughout a range of volitional motion (typically 40° to full extension). For simplicity, all correlations were calculated for the kinematics at 10° of knee extension, as this was a knee angle that all subjects reached and was within terminal extension (where the patella is most free from the sulcus groove). All plots have a dotted line, representing the average value of the kinematics in an asymptomatic population at 10° of knee extension (medial displacement = -0.11 mm, medial tilt = 14.7 and varus rotation = 0.52º). 37 The blue squares represent knees that were lateral or valgus relative to the control population average in the untaped condition, whereas the red circles represent knees that were medial or in varus rotation relative to the control population. Figure 3A plots the change in medial translation with taping versus the value of medial translation at baseline (without taping). Figures 3B and 3C demonstrate the change in medial tilt and varus rotation, respectively, with taping versus the value of medial translation at baseline (without taping). Modified from Figure 2 in Derasari et al.32

Cine kinematics

A recent study within our lab32 shed new light on the underlying mechanisms of patellar taping in PFPS, helps explain some of the previous contradictory findings, and provides strong evidence for patient specific treatments. Our study used a new dynamic MR imaging technique (cine-PC MRI) to track pre- and post-taping patellofemoral kinematics during volitional activity in 19 knees diagnosed with idiopathic anterior knee pain. Each knee underwent MRI under two testing conditions (un-taped and taped), which were randomly ordered. The post-taping kinematics were evaluated after a short bout of exercise. For each condition, subjects were placed supine in a 1.5-Tesla MR scanner.37 Subjects were instructed to generate knee extension without hip movement at 35 cycles per minute to the beat of an auditory metronome. During this movement a full cine-PC MRI image set (x,y,z velocity and anatomic images over 24 time frames) was acquired. Using integration, the three translations and three rotations of the patella relative to the femur (Figure 2) throughout the subject’s range of motion (typically from 40° of knee flexion to full extension) were calculated with an accuracy of 0.5 mm.38 All comparisons and correlations were completed for the kinematics at 10° knee extension, as this was a knee angle closest to full extension that all subjects reached. In the final analysis, this study demonstrated that the taping did alter patellofemoral kinematics, but not in the manner expected.

The only significant change in kinematics with taping was an inferior shift in the position of the patella (1.6mm, p =0.04). From a mechanics standpoint, this result is logical in that taping not only creates a medial force, but it also places a strut across the knee, limiting patellar superior displacement. This inferior shift likely explains some of the pain relief taping affords patients. A more inferiorly placed patella has been shown to increase patellofemoral cartilage contact,7 which would decrease overall contact stress. This concept that taping reduces pain by creating a strut across the knee, pushing the patella inferiorly, explains why there is pain relief with neutral and lateral taping.16 In these other taping conditions, the medialization force is no longer present, but the strut across the knee remains.

Patient-specific findings

Another key result was that the change in patellofemoral kinematics with taping was correlated to the baseline values (un-taped condition) of these kinematics (Figure 3). In knees that began with a lateral shift (relative to an asymptomatic control population) in the un-taped condition (baseline), taping resulted in a medial shift. Conversely, for those patients that had a medial shift at baseline, taping resulted in a lateral shift. This same pattern was observed for medial/lateral tilt and varus/valgus rotation as well. Taping fostered a change towards medial tilt and varus rotation, only if the subject began with lateral tilt and valgus rotation, respectively, in the un-taped condition.

In short, taping helped to normalize the patellar position within the sulcus groove. This explains the volume of literature reporting no change in the PF static posture with taping. Our32 study did not find significant changes in the axial plane PF kinematics (patellar tilt and shift) with taping across the patient population, because this group presented with a mix of baseline values. Thus, on average, there was no change in axial plane kinematics, but taping normalized the PF kinematics within the sulcus groove in individual patients, likely affording even further pain reduction. This highlights the concept that the patella has six degrees of freedom; alterations in any of its three directions or three rotations can be considered maltracking, which may result in pain39 and may eventually lead to a break down in the cartilage.40

The correlation between the change with taping and the baseline values (for patellofemoral lateral shift, lateral tilt and varus rotation) supports the notion that treatment must be tailored to specific subgroups of patients. Findings from previous studies also support this concept. For example, one study demonstrated that patellar taping had no effect on joint proprioception in a population of 32 patients with PFPS, yet when the population was divided into two groups, taping did improve proprioception for those patients with poor proprioception at baseline, but not for those who came into the study with good proprioception.6 Similarly, Cowan21 demonstrated that taping altered the temporal characteristics of VMO and VL activation in patients with PFPS, but not in controls. Lastly, using a Star Excursion Balance test, Aminaka and Gribble29demonstrated that patients with PFPS increased their leg reach distance with taping, while asymptomatic controls decreased their leg reach distance with taping. Thus, since the etiology of patellofemoral pain is clearly multifactorial, treatment of PFPS must also be multifactorial, and an understanding of the likely mechanisms behind the pain is key to effective utilization of available treatment options.

This ability to measure complete three degree of freedom patellofemoral kinematics during a volitional task was a clear advancement over past studies evaluating the effects of taping on static patellofemoral posture. This advancement demonstrated that taping produced a consistent inferior shift in patellar kinematics, which could provide pain relief through increased cartilage contact areas.7 In addition, it demonstrated that taping normalized the position of the patella within the groove, likely affording further pain relief.

Patellofemoral pain syndrome remains one of the most common problems of the knee with an incidence rate four times higher than the rate of all anterior cruciate ligament injuries in similar populations.3,41 As with ACL injury, PFPS has been demonstrated to be more prevalent in female subjects than in male subjects (2.3 and 3 times as likely in female vs male subjects for PFPS3 and ACL injury,41 respectively). Yet, PFPS historically has garnered far less research interest than ACL injury. Thus, it is critical that a concerted effort is put forth to better understand the mechanisms of PFPS so that effective prevention and rehabilitation strategies can be designed, as is being done for the ACL injury.

Frances T. Sheehan, PhD, is a staff scientist in the Functional and Applied Biomechanics Section, Rehabilitation Medicine Department, at the Clinical Center of  the National Institutes of Health in Bethesda, MD.

ACKNOWLEDGMENT

This research was supported by the Intramural Research Program of the NIH, and the Clinical Center at the NIH.  Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Institutes of Health or the U.S. Public Health Service.

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One Response to Patellofemoral taping: Pain relief mechanisms

  1. Peter Fabian says:

    Appreciate the opportunity to read about your study. I enjoyed the various factors of the patellar mechanics that were included. Would you consider mentioning in the introduction other factors in your multifactorial survey of biomechanical effects on the pf mechanics? I’m thinking here of a valgus moment at the knee possibly related to hip abduction weakness. How would this malalignment contribute to abnormal forces and pf pain. Is it worth mentioning, at least in regards to future studies?

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