January 2016

Conference coverage: 4th PFP research retreat

1PFP-iStock4924309Studies presented at the Patellofemoral Pain Research Retreat in Manchester, UK, illustrate the progress researchers are making toward the ultimate goal of being able to tailor exercise protocols and other interventions to best address the needs of specific patient subgroups.

By Jordana Bieze Foster

In the lower extremity research community, patellofemoral pain (PFP) experts have long been trailblazers when it comes to identifying subgroups of patients who experience pain or respond to interventions in unique ways. The fourth PFP Research Retreat, held in September in Manchester, UK, expanded on that theme and broadened it, increasingly looking at subgroups defined by nonmechanical variables, in addition to those defined by biomechanics.

Abstracts for the studies presented at the retreat, as well as a thoroughly revised consensus statement, will be published later this year in the British Journal of Sports Medicine (BJSM).

Tailored interventions

Of course, the ultimate goal of identifying subgroups of patients with PFP is being able to tailor interventions to best address the needs of each subgroup. This is easier said than done, but a number of studies presented at the research retreat did take steps toward achieving that goal by focusing on previously identified subgroups characterized by age, gender, and distal factors.

It’s been well established that women are far more likely than men to experience PFP,1 and more recent findings suggest that men and women have different risk factors.2 But a study presented in Manchester also indicates that men and women with PFP may respond differently to strengthening interventions.

The presentations and discussions at the most recent PFP research retreat explored the influence of nonmechanical variables on pain to a greater extent than ever before.

The authors of a North American multicenter study3 comparing knee and hip exercise programs in patients with PFP revisited the data for 60 men and 125 women to look for gender-specific responses. They found that male and female patients experience similar increases in hip abduction and knee extension strength, but that men had greater gains in hip external rotation strength than women (10.5% vs 5.8%) and women had greater gains in hip extension strength (11.3% vs 7.4%).4

Although the gender differences were not statistically significant—a common problem when trying to tease subgroup data out of a study powered for analysis of a larger population—they do suggest gender-specific interventions for PFP may be worth clinical consideration and further study, said Lori Bolgla, PT, PhD, ATC, an associate professor in the Department of Physical Therapy at Augusta University in Augusta, GA, who presented the findings.

The teen years

1PFP-iStock_78186173Age continues to be a subgroup of interest in the PFP community, thanks in large part to the prolific Michael S. Rathleff, PT, PhD, a senior researcher at the Research Unit for General Practice in Aalborg, Denmark, who was one of several keynote speakers in Manchester.

Expanding on a theme from the 2013 PFP Research Retreat (see “Conference Coverage: 3rd PFP Research Retreat,” November 2013, page 19), Rathleff reiterated that, in a study of 121 adolescents with PFP randomized to receive patient education or patient education plus exercise therapy, those in the exercise group were more likely to have recovered at one year than those in the education-only group—but even in the exercise group, only 38% had actually recovered by that time. This figure is much lower than what has been reported for adult populations.5,6

The published version of the adolescent study, which appeared in the March 2015 issue of BJSM,7 also noted the patients in the exercise group who rarely complied were no more likely than those in the education group to have recovered at one year.

“I think this makes sense,” Rathleff said. “The exercises only work if you do them. It’s an easy visualization of the importance of adherence.”

And, as it turns out, even when adolescents do their exercises, they still may not be getting the full benefit. In a study in press with the Journal of Strength and Conditioning Research, Rathleff and colleagues had adolescents with PFP perform hip and knee exercises using an elastic band with an embedded sensor8 that recorded time under tension as an indication that the band was in use.

After six weeks, only 5% of all sets performed met the prescribed duration of time under tension, and half of all sets included fewer repetitions than prescribed, Rathleff said. The total exercise dose received averaged just 17% of what was prescribed, while the exercise dose that was self-reported by the participants was three times the actual dose, he said.

This disturbing finding suggests that, for clinicians who treat adolescents with PFP, developing effective exercise protocols may be even more difficult than previously thought. It also calls into question the previously mentioned finding that adherence leads to positive outcomes.

“Do patients who are adherent really do better if the self-reported exercise dose is vastly exaggerated? The self-reported data in this population is questionable at best,” Rathleff said.

It’s possible, Rathleff said, that exercise is less effective in adolescents than adults because teens tend to have a longer duration of pain; in a pair of 2013 studies, the self-reported average duration was 38 months for boys and 36 months for girls in adolescents aged 15 to 19 years9 and 28 months in those aged 12 to 16 years.10

Another possibility is that hip and knee weakness—established targets for intervention in adults with PFP—may not be risk factors in adolescents. The 2013 study on younger adolescents found no evidence of weaker hip or knee strength in the patients with PFP than in healthy controls,10 and a recent study from Cincinnati Children’s Hospital found that young female athletes who went on to develop PFP actually had greater hip abduction strength than those who didn’t.11

“It could be that the lower strength we see in older adolescents is not a risk factor but is purely a consequence of diminished activity due to pain,” Rathleff said.

Foot focus

Patients with PFP who respond positively to the use of foot orthoses account for one of the first biomechanics-based subgroups to be identified by researchers. Although several studies have proposed different variables that are likely to predict such a positive response, few have actually tested the effectiveness of tailoring interventions based on clinical prediction criteria. But researchers from the University of Queensland in Brisbane, Australia, used just such an approach in a case study presented in Manchester.11

Assessing a 23-year-old woman who had had bilateral PFP for 10 years, the researchers determined the difference in midfoot width between weightbearing and nonweightbearing positions was greater than 11 mm in both limbs; two previous studies12,13 have reported that midfoot width changes of that magnitude or greater are associated with a positive response to orthotic intervention.

The case study, however, went beyond treatment with foot orthoses alone. The patient performed foot-focused exercises—calf stretching, arch forming exercises, and foot posture retraining—for 16 weeks, using foot orthoses for just the first three weeks. Following the intervention, her midfoot width difference had decreased to about 8 mm in both limbs, and the researchers were also surprised to find her hip strength had increased as well.

“Using foot orthoses in the short term provided pain control that led to more effective exercise,” said Mark Matthews, a doctoral student at the university who presented the findings. “The exercise intervention was focused on the foot, but we seemed to see changes throughout the whole limb.”

Particulars of PFOA

Patients with patellofemoral osteoarthritis (PFOA) represent one of the most intriguing PFP subgroups, as they are also a subgroup of the knee OA patient population. Neither PFP researchers nor knee OA researchers, however, have made much progress in developing interventions for patients with PFOA. A study from the University of Melbourne in Australia did report that patellar taping was associated with reduced malalignment and knee pain in that subgroup,14 and one from the University of Bristol in the UK found that a combination of taping and quadriceps strengthening was associated with benefits at 10 weeks, but not at one year.15

One challenge in studying interventions for patients with PFOA is that knee OA often is not limited to a single compartment, and diagnostic tests are not useful for differentiating between PFOA and tibiofemoral OA, noted keynote speaker David Felson, MD, MPH, a professor of medicine and epidemiology at the Boston University School of Medicine in Massachusetts and a professor of medicine and public health at the University of Manchester.

“Does it matter if we can diagnose patellofemoral osteoarthritis? Not for medical treatment, but for surgical treatment it does matter. For rehabilitation it may matter, and that’s where our challenge is,” Felson said. “The proof of treatment effectiveness lies in whether the targeted therapy is effective for patellofemoral osteoarthritis and not tibiofemoral osteoarthritis.”

Another challenge in developing potential exercise interventions for patients with PFOA is that, while some researchers have reported kinematic differences between patients with PFOA and controls, others have not.16-18 Hypothesizing that this inconsistency may be related to the different tasks studied, investigators from Philadelphia analyzed the biomechanics of two relatively challenging tasks—sit to stand (STS) and step down—in nine women with PFOA and nine healthy controls. They found that peak torque for knee extension and hip extension, abduction, and external rotation was lower in the PFOA patients than the controls, and that the patients demonstrated greater hip internal rotation than controls during the STS task.19

“The sit-to-stand task seemed to be the one that brought out the association between angles and torques at the hip,” said Lisa Hoglund, PT, PhD, an associate professor of physical therapy at the University of the Sciences in Philadelphia, PA, who presented the results in Manchester.

The potential importance of hip external rotation strength in patients with PFOA was also underscored at the research retreat by a University of Queensland study in which more than one third of 80 patients with PFP also had early radiographic PFOA and one-quarter had more severe PFOA.20 The study found that low hip external rotation isometric torque was associated with greater PFOA severity, along with older age and higher body mass index.

The findings of Hoglund and colleagues led them to then assess whether a 10-session intervention to improve hip and trunk strength in the same study population would lead to better performance on functional tasks, including the Timed Up and Go (TUG) test in addition to STS and step-down tests.21 Along with improved pain and self-reported function in the PFOA group, the researchers found an association between improved hip extension strength and reduced TUG time and an association between improved hip abduction and external rotation peak torque and less internal rotation during STS and step down.

“As the patients became stronger, some of the angles became smaller,” Hoglund said.

More than mechanics

Although biomechanics remains a comfort zone for many PFP researchers, the presentations and discussions at the most recent research retreat explored nonmechanical influences to a greater extent than ever before. Evidence continues to suggest that sensory information processing, kinesiophobia, and other psychosocial factors may help define PFP subgroups and offer a basis for alternative or adjunctive approaches to treatment.

A 2013 study by Rathleff and colleagues found that adolescent girls with PFP exhibit significantly lower pressure–pain threshold levels than controls, not only at the knee but also at the tibialis anterior—suggesting that a central mechanism may be underlying the pain experienced by that particular subgroup.22 At the research retreat, Rathleff presented new findings suggesting differences between young women with PFP (participants from the adolescent study three years later) and controls with respect to conditioned pain modulation response. Specifically, cuff-induced pain at the arm reduced the perception of similar painful stimulation at the knee in the controls but not in the patients with PFP.23 The new study also found significant between-group differences for the pressure–pain threshold at the patella, tibialis anterior, and lateral epicondyle.

Australian researchers, however, have not found significant differences in pressure–pain threshold values between patients with PFP and controls at either the patella or the tibialis anterior, according to unpublished research summarized in a Manchester presentation by Bill Vicenzino, BPhty, GradDipSportsPhty, MSc, PhD, a professor in the School of Health and Rehabilitation Sciences at the University of Queensland.24 This suggests pressure–pain threshold may be yet another factor that could be used to define PFP subgroups.

The same presentation included findings from surveys conducted by Danish and Australian researchers related to cold sensations; previous research suggests that patients with PFP are less likely to respond to physical therapy if they report that their legs feel cold even in warm surroundings.25 A small percentage of patients with PFP reported cold knees even in warm surroundings in the Danish (six of 28) and Australian (three of 20) surveys, Vicenzino said. However, half of the Danish respondents and 40% of the Australian respondents said their knee pain is worse when the environment is cold.

“Maybe there are some easy ways we can tap into some of these subgroups,” Vicenzino said. “We may not need to do fancy laboratory tests. We may be able to do it with simple questions.”

Like their colleagues in the anterior cruciate ligament injury field (see “Conference coverage: 7th ACL research retreat,” May 2015, page 31), PFP researchers are starting to explore whether behavioral variables can help with the subgrouping process. In Manchester, researchers from the University of Melbourne reported that knee confidence and fear of movement influence PFP severity in patients with PFOA following anterior cruciate reconstruction,26 and a team from the University of Queensland reported that kinesiophobia is a predictor of poor single-leg standing balance in patients with PFP.27

“Interventions to address kinesiophobia may enhance exercise interventions in certain patients,” said Natalie Collins, PT, PhD, a postdoctoral research fellow at the University of Queensland, who presented her group’s findings at the research retreat.

REFERENCES
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  3. Ferber R, Bolgla L, Earl-Boehm JE, et al. Strengthening of the hip and core versus knee muscles for the treatment of patellofemoral pain: a multicenter randomized controlled trial. J Athl Train 2015;50(4):366-377.
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  16. Fok LA, Schache AG, Crossley KM, et al. Patellofemoral joint loading during stair ambulation in people with patellofemoral osteoarthritis. Arthritis Rheum 2013;65(8):2059-2069.
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  24. Vicenzino B, Rathleff C, Matthews M, et al. Characterizing mechanical and thermal pain sensitivity in patellofemoral pain to gain an insight into its heterogeneity: a preliminary exploration. Presented at the fourth International Patellofemoral Pain Research Retreat, Manchester, UK, September 2015.
  25. Selfe J, Harper L, Pedersen I, et al. Cold legs: a potential indicator of negative outcome in the rehabilitation of patients with patellofemoral pain syndrome. Knee 2003;10(2):139-143.
  26. Hart HF, Collins NJ, Ackland DC, et al. Is patellofemoral pain related to knee confidence, stability and fear of movement in people with patellofemoral joint osteoarthritis after anterior cruciate ligament reconstruction? Presented at the fourth International Patellofemoral Pain Research Retreat, Manchester, UK, September 2015.
  27. Hatton AL, Stableford K, Hug F, et al. Static single-leg standing balance deficits and associated factors in adults with patellofemoral pain. Presented at the fourth International Patellofemoral Pain Research Retreat, Manchester, UK, September 2015.
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