May 2011

Effects of knee bracing on patellofemoral pain

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Research suggests that different bracing designs may have different mechanisms of action for relief of patellofemoral pain syndrome, which is consistent with the heterogeneous nature of the condition and underscores the need to understand each design’s function prior to treatment.

By Song Joo Lee, MS, Yupeng Ren, MS, Nicole A. Wilson, PhD, Sang Hoon Kang, PhD, and Li-Qun Zhang, PhD

Runner’s knee or anterior knee pain are interchangeable terminology for patellofemoral pain syndrome (PFPS). PFPS is defined as pain originating from the patellofemoral joint and associated structures excluding other intra-articular and peripatellar pathology.1,2 PFPS is the most common diagnosis among runners and in sports medicine centers. PFPS accounts for 16% to 25% of all injuries in runners and 11% of musculoskeletal complaints seen in the office.3-5

The current literature suggests that the main contributors to PFPS are overuse, articular cartilage damage from trauma, and abnormal patellar tracking.1,6 PFPS is progressively developed via the alteration of patellar alignment or patellar tracking, increased patellofemoral joint forces, or some combination.1,7-11 Patellar tracking is dependent on the bony architecture of the knee and the magnitudes and directions of forces from the soft tissue structures surrounding the patellofemoral joint, including the quadriceps muscles and the patellar and quadriceps tendons (Figure 1).12,13 Furthermore, muscle imbalances at the hip, including weakness of the gluteus medius and gluteus maximus, can also affect patellar tracking.14,15 Abnormal patellar tracking, particularly lateral tracking, can increase patellofemoral contact pressure and subsequently trigger pain by activating nociceptive fibers in the subchondral bone located underneath the patellofemoral articular surface.8,16-19 Other abnormal factors related to patellofemoral contact pressure, such as contact area, location of pressure, and joint stress, may also contribute to the development of PFPS.16-19

Figure 1. Schematic of the patellofemoral joint (anterior view)

People with PFPS describe pain behind, underneath, or around the patella. Common symptoms include stiffness, pain, or both on prolonged sitting with the knees flexed, and pain with activities that load the patellofemoral joint, such as climbing or descending stairs, squatting, or running.1 Individuals with PFPS can feel the pain through daily repeatable weight-bearing activities. Stair climbing and squatting can potentially generate forces on the patella from three to nine times body weight.1,20 Symptomatic patellofemoral joints likely have a reduced capacity to tolerate loading,16 and  this can limit activity. PFPS patients are also predisposed to further development of arthritis and permanent disability.8,21,22 Therefore, effective treatment for PFPS is essential.

Various treatment methods may be beneficial for patients with PFPS, such as resting to reduce the loading on the patellofemoral joint and surrounding soft tissues, physical therapy to correct muscle imbalances that affect patellar tracking, non-steroidal anti-inflammatory drugs (NSAIDs), bracing, patellar taping, and foot orthoses.1 Among the aforementioned methods, bracing and patellar taping to realign and stabilize the patella are often considered the first-line conservative treatments to reduce pain among patients with PFPS.8,19,23-32

Potential mechanisms

Although some studies have shown no effect of bracing on patellar alignment,33 other studies found patellofemoral bracing to be associated with decreases in lateral patellar translation with bracing under static conditions,32,34 decreases in both lateral tilt and translation of the patella during dynamic loading,35 and subjective improvements in knee stability and pain.23,27 Moreover, current literature proposes additional mechanisms by which patellofemoral braces may reduce symptoms. Such potential mechanisms include dissipation of lateral patellar forces, increase in patellofemoral contact area, decrease in patellofemoral contact pressure, unloading of the knee extensor mechanism, increase in temperature, neurosensory feedback, circulation, and psychological effects such as improved confidence.6,18,19,32,36

Studies of patellar alignment,25,26,32,33 patellofemoral joint contact area,32,36 peak pressure,36 peak pressure location,36 and center of pressure36 have reported conflicting results, depending on the tasks and the type of braces studied, that make it difficult to pinpoint the exact mechanism by which bracing relieves symptoms of patellofemoral pain. Muhle and colleagues33 reported that in patients with patellar subluxation or dislocation, wearing a knitted knee support with a silicone insert surrounding the patella did not significantly affect patellar tilt angle, bisect offset, or lateral patellar displacement during knee extension, as evaluated using kinematic magnetic resonance imaging. On the other hand, Shellock and colleagues25,26 found improved patellar alignment associated with wearing a patella stabilizing brace (a neoprene cuff with U-shaped buttress and two neoprene straps)25 in patients with lateral patellar subluxation and a patellofemoral knee brace (a neoprene knee cuff, neoprene strap, circular adhesive patch over the patella, and a VMO [vastus medialis oblique] activator component) in patients with patellofemoral joint symptoms.26 Furthermore, in Shellock and colleagues’ studies,25,26 patients who corrected or improved patellar subluxation25 or displacement 26 also reduced knee pain25,26

The effect of patellofemoral bracing on knee pain in PFPS patients was also investigated by Powers et al.24 In particular, they assessed the influence of patellofemoral bracing (using the same device as Muhle and colleagues) on pain, knee extensor torque, and gait function in 16 female PFPS patients. Only increased knee flexion angle was found in braced trials and no statistically significant differences in torque production, pain levels, and stride characteristics were found between braced and unbraced trials. Although Powers et al found that half of all subjects (eight of 16) experienced decreased knee pain with bracing, they hypothesized that the lack of statistically significant difference between braced and unbraced trials in torque production, pain levels, and stride characteristics might be due to no change in patellar tracking associated with wearing the brace. Previous studies33,37 also did not report altered patellar tracking associated with wearing the same brace. Yet Powers’ earlier study32 indicated that small changes in patellar displacement from bracing could induce large increases in total patellofemoral joint contact area, which could lead to reduced knee pain. The effects on patellofemoral joint contact area were seen with two different brace designs: the bracing system with VMO activator component used by Shellock and colleagues in their 2000 study, and an elastic sleeve with rigid medial and lateral bars and a cantilever system that applies a medial force on the patella with knee extension.

The collected findings suggest that bracing may employ different strategies to reduce patellofemoral pain symptoms besides correction of patellar tracking. Thus, it is clinically important to understand the effect of different types of braces on the reduction of patellofemoral pain during functional tasks since various types of patellofemoral bracing products exist and each employs a different strategy to relieve patellofemoral pain symptoms during functional tasks.32,36

Dynamic mechanics

One study compared the effect of different types of braces on dynamic patellofemoral contact mechanics. Wilson et al36 investigated the effects of four different types of neoprene braces on patellofemoral contact pressure in nine fresh-frozen cadaver lower limbs. The detailed parameters associated with this study were contact area, peak pressure, peak pressure location, and center of pressure during dynamic simulated knee flexion/extension under five conditions (Figure 2): no brace, a knee sleeve shaped as a sleeve with no hole over the patella, a patellar stabilization sleeve with a J-shaped buttress pad and medial external stabilization strap, a patellar stabilization sleeve with a C-shaped buttress pad and a lateral to medial external stabilization strap, and a wrap-style patellar stabilization brace consisting of a bifurcated strap with a C-shaped buttress pad positioned lateral to the patella.36 All braces were made by the same manufacturer. Once each cadaver knee was secured, the knee was preconditioned and knee flexion angles during simulated walking were applied to the knee. In the meantime, forces and moments exerted on the tibia during flexion and extension were measured, along with contact area and pressure in the patellofemoral joint. Moreover, each knee was also tested at static knee flexion angles of 0°, 30°, 60°, 90° and 120° for each aforementioned bracing condition to compare with previously published results that only considered static conditions.36

The results of the study revealed that all four bracing conditions increased patellofemoral contact area compared to the unbraced condition during simulated dynamic knee flexion.36 However, testing at static knee flexion angles did not show any significant differences in contact area, peak pressure, or center of pressure between the unbraced condition and any of the braced conditions.36 Overall, only the wrap-style patellar stabilization brace decreased peak pressure in the patellofemoral joint.36 In other words, while the compression applied by sleeve-type braces increased contact area, the compression also increased contact force; thus, overall patellofemoral contact pressure did not change. Such effects may result from the sleeve design of the brace that allows generalized compression on the quadriceps tendon complex. On the other hand, the wrap-style patellar stabilization brace allowed knee pressure to decrease in magnitude and created a proximal shift in the location of the peak patellofemoral pressure.36 Therefore, during knee flexion, the wrap brace shifted the location of the highest pressures to a region of the patella with increased articular cartilage thickness. Previous literature suggests that a 10% reduction in cartilage thickness leads to a 10% increase in peak hydrostatic pressure.17,36 Clinically, small changes in the location of the areas of the highest pressure could likely lead to a decrease in PFP symptoms.36 Furthermore, such results suggest that wrap-style braces may be effective for treatment of disorders associated with degenerative cartilage changes.36

Overall, the literature suggests that bracing can decrease PFPS symptoms via different mechanisms, which may also relate to each other: correcting patellofemoral maltracking and shifting the location of the highest pressures to a different region of the patella or decreasing the pressure on the patella. Therefore, understanding the underlying biomechanics of the patellofemoral joint during dynamic conditions is important when choosing and designing a knee brace for patients with PFPS.

Looking ahead

This leads to the next set of questions for future studies to address:

  • What are detailed differences in patellar kinematics between healthy and PFPS individuals during functional activities under full weight-bearing conditions?
  • How can these differences help in choosing or designing a brace to decrease PFPS symptoms?
  • What is the meaning of patellofemoral maltracking during functional tasks?

Three-dimensional patellar kinematics during functional activities can be assessed using a sophisticated six degree of freedom goniometer. According to a study by Lin et al,13 as knee flexion angles increase during squatting, the patella shows gradual medial spin in healthy subjects and continuous lateral spin in subjects with patellofemoral pain. Furthermore, subjects with patellofemoral pain shifted the patella more laterally during deep squatting than the healthy individuals.13 Such results imply that the patella is not adequately stabilized during active knee flexion/extension in patients with PFPS.13 Contemporary literature suggests that weakness of the VMO muscle may cause the patella to shift and rotate laterally during knee flexion.21,38-40 Even though the VMO is one of the important contributors to patellofemoral maltracking, ultimately such maltracking is due to an imbalance in the relative contributions of gluteus maximus and gluteus medius activities, the bony architecture of the knee, and the magnitudes and directions of forces from the soft tissue structures surrounding the patellofemoral joint (including the quadriceps muscles and the patellar and quadriceps tendons), as mentioned previously.14,15,41 All of these factors have implications for the future of patellofemoral bracing.

In addition to the biomechanical mechanisms for reducing symptoms of PFPS with bracing, neuromuscular mechanisms to reduce pain with bracing have also been proposed. In Muhle and colleagues’ study, although the authors did not find a statistically significant effect of bracing on patellar displacement, patients reported subjective pain relief and comfort with the patellar realignment brace.33 They proposed that such reduced symptoms may not necessarily come from patellar kinematics but possibly from altered feedback mechanisms related to the neurophysiologic imbalance between quadriceps muscles while wearing a brace. Previous studies have also reported neurophysiological imbalances, particularly imbalanced activation of timing between the VMO and vastus lateralis (VL) muscles in PFPS patients.42,43 Imbalanced timing, such as a 5-ms delay in VMO activation, can lead to increases in lateral patellofemoral joint loading.44 As in Muhle’s interpretation, bracing may be able to alter feedback mechanisms in the quadriceps muscles. This theory would seem to be supported by a recent functional MRI study, which reported that wearing a knee brace or sleeve could alter brain activation during knee movement by providing different intensities of peripheral inputs to the skin.45

Bracing can be an effective conservative treatment for decreasing the symptoms of PFPS.  Currently, there is no optimal type of bracing for all patients with PFPS since multi-dimensional mechanisms including psychological, biomechanical, and neuromuscular aspects have been proposed to reduce the symptoms of PFPS with different types of bracing. Prior to choosing a brace for individuals with PFPS, it is essential for practitioners to understand previous injury, pain history and physical activities for each patient in order to create an individualized bracing treatment.

Song Joo Lee, MS, is a PhD candidate in the department of biomedical engineering at Northwestern University and a research assistant at the Rehabilitation Institute of Chicago (RIC). Yupeng Ren, MS, is a research associate at RIC. Nicole A. Wilson, PhD, is a medical student at Rush Medical College. Sang Hoon Kang, PhD, is a research associate at RIC and a postdoctoral fellow in the department of physical medicine & rehabilitation at Northwestern University. Li-Qun Zhang, PhD is a senior research scientist and director of the biodynamics and muscle fibers lab at RIC, and Raisbeck Professor of Orthopaedic Surgery and associate professor of physical medicine & rehabilitation and biomedical engineering at Northwestern University.

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