Knee pain and TrPs

Inspired by Sánchez Romero et al 2020,[1] and Ma et al 2020.[2]

Photo by Alora Griffiths on Unsplash – modified by MC in Adobe Spark Post.

MTrP – myofascial trigger point

TrP – myofascial trigger point (most of us do not bother with the M, but it is implicit)

OA – osteoarthritis

PFPS – patellofemoral pain syndrome

VMO – vastus medialis oblique

VL – vastus lateralis

key to acronyms

I came across these papers in August, and I have been waiting for the opportunity to mention them on the blog.

They represent two of the most common causes of knee pain, and both papers focus on TrPs. The first paper examines the prevalence of TrPs in painful knee OA. It is a secondary analysis of a cross-sectional study published in 2019 of 114 patients with OA recruited from older adult care centres in Madrid.[3]

The authors are a group that are keen on studying TrPs, so they examined a number of muscles in the lower limb for active and latent TrPs, as well as measuring a number of pain and functional outcomes related to knee OA.

  • tensor fasciae latae
  • hip adductors
  • hamstrings
  • quadriceps
  • gastrocnemius
  • popliteus

In the cross-sectional study the group found a number of differences in clinical outcomes based on sex and age distribution, as might be expected, but they found no relationship between the number and presence of TrPs and the sex or age distribution.

The secondary analysis attempted to look a bit closer and try to correlate the prevalence of TrPs in different muscle groups with pain and disability outcomes in knee OA. They found that the prevalence of TrPs varied from 11 to 50% in the muscles examined (see list above), and there were no impressive correlations between the prevalence of TrPs in individual muscles and the pain or disability outcomes.

TrPs in the hamstrings correlated negatively with pain

The prevalence of TrPs in the hamstrings (both latent and active) correlated negatively with pain, and that correlation was poor. There were no correlations between TrPs in any of the other muscles and pain. The number of latent TrPs in tensor fascia latae correlated positively with two functional outcomes, but this correlation was also poor (ie r<0.3).

This data does fit my world view, and therefore I can be accused of confirmation bias in highlighting these papers that do not seem to show much of a relationship between myofascial pain and osteoarthritis. But there is just a slight suggestion of some link, and that will keep the advocates grasping at subtleties no doubt. To be fair, of course, everything is linked in the complex organism that is a human, and our statistical methods rarely, if ever, allow us to see the subtleties.

Now on to another common category of knee pain – patellofemoral pain syndrome. When I was starting out with an interest in sports medicine some 35 years ago, the most common term used for this condition was chondromalacia patellae – a term derived from the fibrillar appearance of the cartilage on the underside of the patella at arthroscopy. It took a long time for this term to be dropped despite the fact that it was never correlated with symptoms in the first place. We still do not know much about the condition or its pathophysiology, but a lot of attention has been given to patella tracking in the groove of the femur and the power and direction of pull of the various components of quadriceps femoris – ‘the quads’. There has been a lot of attention paid to the Q angle (effectively the angle between the long axes of the femur and tibia, but there are different ways of measuring it) and the VMO – the most oblique fibres of vastus medialis ie those that have the greatest potential to keep the patella in its groove on the femur when the bulk of the quads are trying to pull it off to the lateral side.

a position of importance way beyond the evidence base

Well, so far, there is no conclusive data linking Q angles to PFPS, but we continue to focus on the power of the VMO. Indeed, the importance of building up the VMO is so well accepted within the physical therapy world that few question it or realise that it has no real basis beyond any other form of exercise. The whole story reminds me of the rather similar status of ‘core stability’, which also holds a position of importance way beyond the evidence base.

Ma and colleagues from Shanghai, recruited 50 patients with PFPS and randomised them to TrP needling in the 3 most accessible muscles of the quads or sham TrP needling. I was intrigued to see that the sham technique was the same as one I had discussed with Thomas Lundeberg some 20 years ago. They basically cut the point off the end of the needle, smoothed it down and just pretended to move it in and out with the same action as applied when needling a TrP (Hong style – see previous blog).

The treatment was applied once a week for 6 weeks, and outcomes were VAS pain, a functional outcome and surface EMG amplitude of VMO/VL during maximal isokinetic contraction. The EMG assessment was performed at baseline and 6 weeks, but the other outcomes were also performed at 3 weeks and 3 months.

There were significant improvements in pain in both groups during the treatment phase, but the real TrP needling group was better than sham at all time points, and continued to improve, whereas the sham group deteriorated after the end of the treatment phase. The functional outcome was also better in the TrP needling group, and the VMO/VL amplitude increased significantly at 6 weeks in this group but not in the sham group.

Has anyone noticed anything funny yet?

No?

This was a trial of TrP needling rather than acupuncture based in China! I think it is the first I have seen.

Reference list

1         Sánchez Romero EA, Fernández Carnero J, Villafañe JH, et al. Prevalence of Myofascial Trigger Points in Patients with Mild to Moderate Painful Knee Osteoarthritis: A Secondary Analysis. J Clin Med 2020;9:2561. doi:10.3390/jcm9082561

2         Ma Y-T, Li L-H, Han Q, et al. Effects of Trigger Point Dry Needling on Neuromuscular Performance and Pain of Individuals Affected by Patellofemoral Pain: A Randomized Controlled Trial. J Pain Res 2020;13:1677–86. doi:10.2147/JPR.S240376

3         Sánchez-Romero EA, Pecos-Martín D, Calvo-Lobo C, et al. Clinical features and myofascial pain syndrome in older adults with knee osteoarthritis by sex and age distribution: A cross-sectional study. Knee 2019;26:165–73. doi:10.1016/j.knee.2018.09.011


Declaration of interests MC