Changes in knee biomechanics after a hip-abductor strengthening protocol for runners with patellofemoral pain syndrome.
Ferber R, Kendall KD, Farr L. J Athl Train. 2011 Mar-Apr;46(2):142-9.
Over the years we have gained a better appreciation for the influence of the hip on knee injuries and symptoms. While observing patients with anterior knee pain or other knee injuries you may have noticed that during squats (or similar movements) their hip adducts causing dynamic knee valgus (probably related to weak hip abductors). While some research has supported these findings there is a need for more research assessing all of these variables together and evaluating how they change in response to interventions. The purpose of this study was to explore the relationship between hip abductor strength and frontal plane knee movement by evaluating a 3-week hip abduction strengthening protocol among runners with PFPS (15 active runners; they also assessed pain). The authors also included 10 control runners who did not have PFPS (they did not do the strength training). Among the biomechanical variables assessed was stride-to-stride knee-joint variability; which is based on the concept that our movements vary even when we plan to perform a similar motion over and over (think about walking; each step is slightly different than the others). Previous research indicated that reduced variability is associated with running-related injuries (including PFPS) and that there is an optimal amount of variability needed to allow our gait to respond to unexpected changes. In this study, biomechanics was assessed during treadmill running before and after the 3-week strengthening program. Hip abduction strength was assessed isometrically. The daily strengthening program included two exercises performed bilaterally (standing hip abduction with elastic resistance, standing hip extension with elastic resistance). At baseline, hip abduction strength was ~29% lower among runners with PFPS than control runners (pain-free). Runners with PFPS had lower stride-to-stride knee-joint variability than controls. After the 3-week daily strengthening program, hip abduction strength increased ~33% as did the stride-to-stride knee-joint variability; which made their strength and variability similar to the control group. The runners with PFPS also had less knee pain (~43% less) after the strengthening program.
This study is a nice validation of biomechanical and neuromuscular alterations many of us have seen and attempted to address in the clinical setting. The three-week strengthening program increased strength, decreased pain, and improved stride-to-stride knee-joint variability. The study did not see any differences in peak dynamic knee valgus (which is related to the hip adduction) between runners with and without PFPS. It would be interesting to see this study replicated with other functional tasks or as a randomized controlled trial with a larger sample size. Regardless, this seems to be nice evidence supporting the inclusion of hip abduction strengthening in our rehabilitation programs when we have a patient with anterior knee pain and hip abduction weakness. A part of me also wonders how the addition of hip external rotation strengthening, neuromuscular training (teaching an individual proper squatting mechanics), and balance training to their program would help. Do they add additional benefits or is a simple two exercise program sufficient for these patients? Have you started to include hip strengthening to your rehabilitation plans for patients with anterior knee pain?
Written by: Jeffrey B. Driban
Reviewed by: Stephen Thomas
Another good topic and interesting from the standpoint that they only utilized two exercises and had increased strength over a 3 week period.
I include hip ABD strengthening with most (if not all) my patients with anterior knee pain.
If the patient has dynamic knee valgus I implement Glut max also to get some Ext/ER.
Usually starting with table exercises (theraband/cuff weights) than progressing to CKC ex with ABD emphasis (using bands).
JOSPT November 2003 did a study with such a topic. They emphasize Glut med/max strengthening and emphasized maintaining a stable pelvis. I follow their exercise progression initially.
JOSPT Oct 2010 looked at Sedentary Females with and without PF pain. Found ABD's weaker when compared to their uninjured side. The reasearch def seems to support it.
I agree with you that neuromuscular training and balance ex would be key.
I liked this article/review bc it shows we can probably have patients/athletes focus on a few exercises at home and gain the benefit of increased strength.
Again, nice topic.
Thanks Tom for the recommended articles. The thing I keep thinking about is that just using two exercises were so effective in this study. You can't ask for an easier home exercise program to give a patient (or exercises to tell them to start on their own) and then that would give us more time in the clinic to address neuromuscular and balance training (if our exam indicates the need). I think this is definitely the way to go with a motivated population like runners and other athletes.
The question in my mind is that we need to find a test to differentiate true hip abduction weakness vs. inhibition. To solve this I evaluate lower extremity movement dysfunction during the classic step-down test (observing for femoral internal rotation and adduction pattern) and the side-lying hip abduction isometric strength test. Most of my athlete's exhibit a movement dysfunctional pattern but often not isometric weakness. Thereby I make them do slow hip abduction mini-band exercises until fatigue. This often solves the dysfunctional step-down test in one session as also the inhibited isometric strength test. I often question why those of us that work with athletes that have no real strength-loss problems resolve to physical therapist population rehabilitation protocols and prescribe exercises such as "clam-shells". Athletic trainers do not typically work with populations that show true muscle weakness. Is there any tests available (besides EMG) that can differentiate muscle inhibition and below optimal isometric strength tests)?
Thanks for the comment. You bring up a few valid points. I also have used a step-down or step-up test to observe lower extremity biomechanics. I sometimes notice that this test shows greater irregularities when the participant is fatigued. While isometric testing is a common procedure in all of the rehab fields I often caution individuals from relying solely on those tests because they don't replicate the strength requirements of physical activity or activities of daily living. With that said I would suggest that dysfunctional movement patterns may have two causes: 1) neuromuscular control and 2) muscle weakness (whether strength or endurance related). Based on my experience, I agree that when neuromuscular control is the primary cause then neuromuscular training or isolation exercises seem to have a clinical benefit before strength gains are really noticeable (coincidentally I see this most commonly with scapular movement exercises). I am not aware of research really addressing these quick-onset changes (typically within a session or two). Some of our patients though do have true muscle weakness when evaluated in the context of their activities (for example, explosive activities like jumping or endurance-based activities like running). Unfortunately, I am not aware of any validated tests to identify these deficits but I suspect many of us use tests like the step-down test to look for dysfunctional movement patterns. A handheld dynamomemter, which is very expensive for a clinical setting, would provide a more precise measure of isometric strength but the strength/endurance requirements of an individual are unique to each patient and their activities. A person twice as strong as another could still have problems if their muscles are not capable of meeting the patient's functional demands.
The exercises performed in this study may have had neuroumusclar control benefits by making the patient focus on performing controlled movements (but we can't tell for sure). I think this study probably benefited from both some neuromuscular control adaptations and positive strength/endurance gains that addressed the functional weakness or endurance deficit of the patients with PFPS. As I stated in my previous comment I think this study highlights that these are two easy exercises a patient could do on their own; thus providing us more time to address issues of neuromuscular control or to do activity-specific training. It would be interesting to see the two exercise program (from this study) compared to doing the two exercises plus closed-chain activities and/or neuromuscular control training. It's possible that the additional exercises are beneficial (which I suspect) but it is also possible that the two exercises are sufficient and the additional exercises are only adding minor benefits (a plateau effect in the returns from our rehab programs). Eventually, we may see research exploring this question.
If anyone else has comments on how to clinically detect functional weaknesses in the lower extremity post a comment. Thanks!
Hi all. This blog is great!!! I was really learning a ton until I read Guido's response.
"Thereby I make them do slow hip abduction mini-band exercises until fatigue. This often solves the dysfunctional step-down test in one session as also the inhibited isometric strength test."
— How does fatiguing a muscle solve a compensitory dysfunction or result in strengthening of a thereafter strength test???
"Athletic trainers do not typically work with populations that show true muscle weakness."
— ahhhh….yeah you do….. You just can't measure it with your hands. That's why you need a dynamometer to assess higher levels of strength.
Other than these comments, the ones by Jeff and Tom seem right on target. Kudos!!!