Key Points

This observational study tested a 6-week exercise programme based on a recent consensus statement on 27 individuals with patellofemoral pain.
Significant improvements were seen in knee function, kinesiophobia and muscle inhibition.
No significant improvements were seen in quadriceps strength, running gait biomechanics or numerical pain rating scale (although pain scores were very low at baseline).

BACKGROUND & OBJECTIVE

Patellofemoral pain (PFP) is one of the most common causes of anterior knee pain seen in the clinic. In 2015, a group of experts on PFP met for the International Patellofemoral Pain Research Retreat. They produced a consensus statement on the management of PFP that included guidance on exercise therapy, taping, orthoses and combined interventions (1).

This study aimed to investigate a multi-modal rehab programme based on these guidelines. The authors hypothesized that a 6-week exercise programme would improve pain, function, kinesiophobia and running biomechanics, as well as quadriceps strength and inhibition.

Patellofemoral pain is one of the most common causes of anterior knee pain seen in the clinic.

Improvement in symptoms may not require significant increases in strength and may be explained by other changes such as graded return to function, reduced kinesiophobia, or decreased muscle inhibition.

METHODS

This study had an observational design. 27 participants with PFP were recruited that fulfilled the inclusion criteria. Multiple outcome measures were taken at baseline and after the 6-week exercise intervention. These included:

Numerical pain rating scale (NPRS)
Knee Injury and Osteoarthritis Outcome Score (KOOS) and the Kujala Anterior Knee Pain Scale to assess function
Tampa Scale for Kinesiophobia
3D kinematic and kinetic data from running on a 15m runway
Quadriceps strength on isokinetic dynamometer
Arthrogenic Muscle Inhibition (AMI) of the quadriceps

Four main exercises (with progressions/regressions) were recommended with 3 sets of 10 to 25 reps – squats, bridges, side band walks, and open kinetic chain quads exercise (plus stretches for the calf and hamstrings). See the video for demonstration of these exercises.

PFP EXERCISE INTERVENTION

Participants were encouraged to self-progress the exercises based on symptoms, and the programme was designed to take around 30 minutes to complete. Exercises were completed daily for the 6-week intervention period.

RESULTS

Knee function, kinesiophobia and quadriceps muscle inhibition improved significantly after the 6-week programme.
Although numerical pain rating didn’t improve significantly, all patients were pain-free at the 6-week stage.
Improvements in the KOOS exceeded the clinical meaningful difference, but changes in the Kujala scale and Tampa Scale for Kinesiophobia did not.
Participants achieved high KOOS scores, suggesting that there were no limitations in sport or activities of daily living following the rehab programme, although some symptoms still remained.
There were no significant improvements in quadriceps strength or running biomechanics.

LIMITATIONS

A third of the study participants dropped out, meaning only 16 of the 27 completed the study. As a result, it was underpowered to assess many of the outcome measures.
No long-term results were recorded beyond the 6-week stage and there was no control group to compare to.
Baseline numerical pain scores were very low on average (just 0.9), which likely explains why improvements in this were not statistically significant despite subjects being pain-free.
The exercise programme was progressive but didn’t appear optimized to improve strength. Typically, loading at 8-12 repetition maximum or heavier is recommended to increase strength (2), not 10-25 reps as used in this study.

CLINICAL IMPLICATIONS

Despite the limitations mentioned above, when viewed in the context of other research there are some conclusions we can take away from this study:

Rehab exercises (such as strength training) don’t appear to significantly change running gait kinematics such as hip adduction or knee flexion angle. Specific cues that are used during running are required to do this, such as an increase in step rate using a metronome.
Quadriceps muscle inhibition may be a feature of PFP and can improve following an exercise programme.
A small selection of 3 to 4 exercises designed to strengthen the quadriceps and glutes may be effective in improving pain and function in PFP.
Improvement in symptoms may not require significant increases in strength and may be explained by other changes such as graded return to function, reduced kinesiophobia, or decreased muscle inhibition.
Stronger individuals may require heavier loading to produce sufficient overload to increase strength.

Studies like this highlight the importance of reading beyond the abstract! The statement ‘Pain did not improve significantly’ could easily be misinterpreted to suggest the exercise intervention wasn’t effective. If you only read the abstract, you wouldn’t know that pain was less than 1 out of 10 to start with!

Of note, the study participants were told that the exercises performed must be pain-free. This might have created an extra barrier to progression. A less cautious approach that allowed mild pain (providing it settled quickly) and encouraged higher levels of loading may have been more effective, especially in gaining strength.

A final but important thought on this study is: why did a third of people drop out? Was the exercise programme too time consuming? 30 minutes per day is a fairly significant time commitment. Was it challenging enough? Perhaps people didn’t feel it was of benefit if there was minimal exertion involved. These are important considerations as no exercise programme is effective if the patient doesn’t do it!

+STUDY REFERENCE

Greaves H, Comfort P, Liu A, Lee Herrington, Richard Jones (2021) How effective is an evidence-based exercise intervention in individuals with patellofemoral pain? Phys Ther Sport, 13, 51, 92-101.

SUPPORTING REFERENCE

Crossley KM, van Middelkoop M, Callaghan MJ, Collins NJ, Rathleff MS, Barton CJ. 2016 Patellofemoral pain consensus statement from the 4th International Patellofemoral Pain Research Retreat, Manchester. Part 2: recommended physical interventions (exercise, taping, bracing, foot orthoses and combined interventions). Br J Sports Med. 2016 Jul;50(14):844-52. doi: 10.1136/ bjsports-2016-096268. Epub 2016 May 31. PMID: 27247098; PMCID: PMC4975825.
American College of Sports Medicine. American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Med Sci Sports Exerc. 2009 Mar;41(3):687-708. doi: 10.1249/MSS.0b013e3181915670. PMID: 19204579.