Patellofemoral pain: More activity means more pain — and then less activity?

People with PFP are less physically active than healthy controls, with regard to both steps per day and minutes of mild, moderate, and intense activity. Increases in activity-related pain may cause patients to modify their lower extremity function during tasks associated with physical activity.

By Neal R. Glaviano, PhD, AT, ATC; Andrea Baellow, MS; and Susan Saliba, PhD, MPT, Med

It is widely accepted that engaging in regular physical activity is beneficial for promoting and maintaining overall physical health and reducing the risk of chronic disease and premature death. The American College of Sports Medicine and the Centers for Disease Control and Prevention have published guidelines on physical activity and public health that have been endorsed by the American Heart Association.^1,2 Healthcare professionals involved in testing and prescribing exercise accept these guidelines as preventive measures.

Recommendations are that healthy adults, 18 to 65 years old, engage in a minimum of 30 minutes of moderate-intensity aerobic physical activity 5 days a week or a minimum of 20 minutes of vigorous-intensity aerobic activity 3 days a week, with an overall minimum of 10,000 steps per day.¹ Recommendations also are available for increasing muscle strength and endurance to promote and maintain good health and physical independence.¹

The benefits of participating in aerobic and muscle-strengthening physical activities are vast. They include promoting and maintaining skeletal health and reducing the risk of premature chronic health conditions, including thromboembolic stroke, hypertension, type 2 diabetes mellitus, obesity, many cancers, anxiety, and depression.¹ Engaging in extra weight-bearing activities and higher-impact activities such as stair climbing or jogging can further promote and maintain skeletal health.

These recommendations become problematic, however, in populations of patients who may be refraining from or limiting physical activity because of chronic pain.

The impact of patellofemoral pain

Patellofemoral pain (PFP) is a chronic condition described as generalized anterior knee pain during a multitude of activities, typically becoming worse with prolonged activity.^3,4 Activities that induce or exacerbate pain include, but are not limited to, walking, jogging, squatting, lunging, kneeling, prolonged sitting, and walking up and down stairs.^5-8 Many of these activities are the same as those recommended by the American College of Sports Medicine as ways to promote physical health and reduce the risk of morbidity. The situation is problematic and paradoxical: People who have a chronic condition—specifically, PFP—are limited in their ability to engage in activities to benefit their overall health.

As many as 74% of adults with PFP decrease their activity level or stop activities altogether because of pain.⁹ Rathleff and colleagues¹⁰ also identified similar trends within an adolescent population: 71% of adolescents with PFP reduced or stopped sports participation and decreased their leisure time each week, compared to both healthy controls and adolescents with other types of knee pain.

These results are concerning. People with PFP have pain and symptoms for many years following their initial diagnosis,^10,11 and current conservative treatments are not always successful in producing positive long-term outcomes.¹² People with PFP who are unable to complete the recommended amount of physical activity because of pain are at serious risk of poor overall health and morbidity.

Study and findings: General discussion

We designed a study to objectively evaluate physical activity levels in people with PFP and compare those levels to physical activity levels in people without PFP. We also analyzed our findings to determine if a relationship exists between activity level and any of three subjective measures:

• worse knee pain over the past 72 hours, based on a visual analog scale (W-VAS)
• subjective function, based on the Anterior Knee Pain Scale
• fear avoidance belief, based on the Fear Avoidance Belief Questionnaire physical activity subsection.

We enrolled 40 total participants: 20 people with PFP (15 females, 5 males; median age, 22.2 [±2.6] years) and 20 healthy controls (15 females, 5 males; median age, 20.8 [±1.8] years). Participants completed the three subjective questionnaires and wore a wireless monitor over a 2-week period to collect data on daily activity level, which was assessed by both steps per day and minutes of mild, moderate, and high activity per day.

We found that people with PFP are less physically active than healthy controls. Those with PFP took 3400 fewer steps and completed almost 1 hour less of physical activity each day over the 2-week period. This hour of physical activity can be further broken down to 40 fewer minutes of mild activity, 4 fewer minutes of moderate activity, and 10 fewer minutes of high physical activity (Figure 1, page 18).

Among study participants with PFP, we also identified a positive relationship between physical activity, defined by steps per day, and the Anterior Knee Pain Scale. This finding suggests that people with better subjective function are also more active. We saw a negative relationship between steps per day and the W-VAS and Fear Avoidance Belief Questionnaire; participants with a greater level of pain were less likely to be active, and those with more fear avoidance beliefs completed fewer steps per day.

There were no relationships between the subjective scales and minutes of mild, moderate, or high activity. There were also no relationships between physical activity levels and subjective function among healthy controls.

The physical activity-pain relationship in people with PFP

The etiology of PFP is unknown, but it has long been proposed that one cause is increased stress on the patellofemoral joint. Excessive physical activity might result in repetitive stress that exceeds the joint’s ability to accommodate the load.¹³

There has been a recent increase in research evaluating physical activity in patients with PFP to gain a greater understanding of the role of activity in the pathology of PFP and its influence on the individual.^10,14,15 Briani et al reported that women with PFP who were more physically active also reported a greater level of pain (both self-reported pain for the previous month and current pain level assessed in a laboratory setting).¹⁴ An intense level of physical activity predicted almost one third of PFP cases, whereas a moderate level of physical activity predicted only 1% of cases.¹⁵

These findings are different from those of our study, which found that greater knee pain in the previous 72 hours was associated with less activity over the subsequent 2-week period. Although there are methodological differences between the studies,^14,15 it is important to consider that the directional relationship between activity and pain is unknown. It is plausible that people experiencing a greater level of pain might modify their activities to minimize subsequent pain. Within our study, we did find that elevated fear avoidance beliefs were also evident in patients who had a greater level of pain and a lower level of physical activity.

Knee pain associated with an increase in activity provides some support for the theory that repetitive loading may be a factor that contributes to the presentation of pain in these patients. We have data (in review) suggesting that less active women with PFP have altered frontal-plane kinematics during common physical activity tasks, such as running, squatting, and stair ambulation. These subjects presented with greater hip adduction and knee abduction, which has been linked to a greater level of pain and lower subjective function.^16,17 If these women participate in physical activity, therefore, altered mechanics might be responsible for increased pain. This becomes a challenging “catch-22” for PFP patients: The prospect that increased physical activity will result in knee pain is as problematic as the prospect of physical inactivity, which can lead to decreased health-related quality of life¹⁸ and increased risk of a myriad of health conditions.^19-22

Because a relationship exists between the level of physical activity and pain, it is important to evaluate the consequences of pain during functional activities. Self-reported pain has been studied during specific functional tasks in patients with PFP,^5,16,23-25 but the effect of pain on neuromuscular measures during commonly performed physical activity tasks also must be evaluated.

Bazett-Jones and co-workers²⁶ reported that increasing knee pain with repetitive single-leg squats was associated with a decrease in hip extensor strength and altered hip mechanics during running. Greuel and colleagues²⁷ also found that increased pain has an influence on running mechanics, specifically at the knee. Changes in lower-extremity function do appear to be relative to the magnitude of pain reported by patients; Ott and colleagues²⁸ found that women with PFP who reported more knee pain following aerobic exercise had a greater reduction in quadriceps activity than women who did not have pain following aerobic activity and healthy controls.

The findings of Briani et al¹⁴ also support this change in quadriceps function, as PFP patients who were more active and experiencing a greater pain level had a delay in quadriceps activation during stair ambulation. These changes in neuromuscular function have been hypothesized to be a compensatory strategy to reduce loading on the knee; however, given the chronicity of PFP, it is unknown how modifications in lower-extremity mechanics contribute to long-term joint health and the potential risk of additional pathology.

Clinical interventions

Employing interventions that decrease pain and improve individual impairments for the patient is vital.²⁹ Emerging evidence suggests that subgrouping patients with PFP may provide a more targeted intervention and improve outcomes, as opposed to treating all PFP patients the same way.³⁰ One of the challenges with PFP is the heterogeneous presentation of symptoms and pain-provoking tasks from one patient to the next. This complicates the clinician’s ability to prescribe recommendations for physical activity while minimizing pain.

To the best of our knowledge, no published studies have evaluated the effect of an intervention program specifically targeting physical activity levels for PFP patients. However, a recent treatment paradigm, RISK (Reduce overall load, Improve capacity to attenuate loads, Shift loads, Keep adapting to the runner’s goals and capacity), has been proposed for treating runners with PFP.³¹ Although this treatment approach currently focuses on runners, the concepts behind it provide strong recommendations for treating other PFP patients who have modified their activity level because of pain.

Reduction of load. Because pain contributes to altered lower-extremity mechanics, it is important to employ proper pain management early to prevent potential consequences. Reducing the load is a common treatment for patients in whom PFP has been diagnosed; a study in the United Kingdom of physiotherapists’ management strategies for PFP found that a large number recommend that their patients not participate in recreational or sporting activities if they experience any knee pain.³² This concept is also supported by Dye and co-workers,³³ who propose that tissue homeostasis of the patellofemoral joint is essential for patients with PFP. Patients must stay within their “envelop of function,” Dye advised, by minimizing activities that lead to increased pain and symptoms.³³

Strength training. It is important, after reducing load, to progress to a strength-training program to improve the capacity to attenuate the load on the knee joint. Both hip-focused and knee-focused strength-training programs have produced positive short-term outcomes with regard to both pain and subjective function.^34-37

Shifting the load during common pain-provoking tasks should be the next step. Gait retraining has produced positive improvements in running mechanics for patients with PFP, with short-term retention of beneficial improvements.³⁸ Salsich et al³⁹ also identified improvements in lower-extremity movement and control following a task-specific movement training program. This experience provides support for individualizing treatment for PFP patients, based on functional impairments that may prevent them from being physically active.

Adaptation. The final step in the RISK paradigm is to have the patient adapt to specific goals, which requires identification of the types of physical activity in which the patient aims to participate. As recommended by Barton,³¹ this step should include communication between patient and clinician, and should be adjusted as symptoms and physical activity goals change.

Conclusions

People with PFP are less physically active than healthy controls, in regard to both steps per day and minutes of mild, moderate, and intense activity. Clinicians should be aware that increases in the activity level of patients with PFP may be accompanied by worsening knee pain, which may result in modifications to lower-extremity function during tasks often associated with physical activity. Assessing activity level and pain may provide valuable information when evaluating and treating patients with PFP. Additional research in understanding activity modification within this population is warranted.

Neal R. Glaviano, PhD, AT, ATC, is Assistant Professor in the School of Exercise and Rehabilitation Sciences, University of Toledo, Ohio. Andrea Baellow, MS, is a doctoral student and Susan Saliba, PhD, MPT, MEd, is Professor, both in the Department of Kinesiology at the University of Virginia, Charlottesville.