Stabiliser or primary mover?

Many want to either class a muscle as a ‘stabiliser’ or a ‘primary mover’ – the rotator cuff being one example.

So how do we decide? Referring to the featured image, one could argue that the rotator cuff is NEITHER, as it is a blend of many fibres.

So… can we determine a muscles classification based on its tissue types?

Stability in the body is the ability to control osseous and articular movement statically, or through a desired range. 

Maintenance of stability may require fast and strong contractions, as well as slow and prolonged. These are simple demands from ADLs, and this is why there are many T2 fibres in the cuff muscles.

So how can we classify muscles as either stabilisers or primary movers?
My answer is, we cannot.

1. Joint position in a task decides which muscles are most advantaged.
Which ever muscle is most advantaged will likely achieve higher EMG readings, and earlier onset of contraction.

2. Direction of pull in relation to articular surfaces
Using the cuff muscles as an example, they provide greater approximation VS shearing forces throughout GH ROMs compared to other acting muscles.

3. Moment arm / proximity of pull to joint axis
This determines mechanical advantage, which can assist point 2. It also controls rate of angular movement for each (decreased) unit of muscle length.

Using the definition of stability, we can realise that fibre type is not a reliable way to classify a muscles function. Every muscle traversing a joint has the ability to affect its static and dynamic stability.
Joint position will determine which muscles are best angled to provide movement, also which have a direction of pull which is advantageous to approximation and congruence. Ultimately, it is the co-ordination of co-contration which maintains joint centration.

Joints of Luschka

Heard of the Joints of Luschka?

Also called uncovertebral joints, these are pseudojoints that have a synovial membrane with synovial fluid but no joint capsule. They exist between cervical vertebrae C3 – C7 and develop with age (6-18). The joint is comprised of a uncinate processes above, and the uncus below.

How are they made?
As the intervertebral discs degenerate, these projections approximate with the body of the next vertebra forming the uncovertbral joints.

What is their function?
1. Allow for flexion and extension and limit lateral flexion in the cervical spine.
2. Reinforce the intervertebral discs posterolaterally and therefore reduce the risk of disc herniation.
3. Prevent posterior translation movements of the vertebral bodies.
4. Provide stability and guide the motion of coupled rotation and lateral flexion.

Pelvic Alignment, Movement and Spinal ‘Subluxation’

I read an enjoyable and thought provoking blog by Dave Leyland on the topic of Pelvic Alignment. The ever elusive human body fuels many opinions making this a good topic for discussion and thoughts.

With that said, here are mine.

‘Alignment’ first reared its head in my early student days when reading some chiropractic content online. In addition, ‘subluxations’ in the spine were also mentioned and I thought this pushed quite a mechanical and fragile view of the body. After some investigation I found out the ‘spinal subluxation’ reference is not quite what it sounds, chiros are mostly relating to a movement restriction… so if a spinal segment is unable to extend upon its adjacent vertebrae, you would say it is flexed. If it was unable to rotate left you would say it is right rotated (even if its position is neutral, it is always in relation to the movement restriction), and this is said to be possible for any vertebral movement variation.

With regards to the pelvis, I would say there also can exist some movement restrictions/preferences which could explain small asymmetries in alignment, I would agree with Dave and put this down to the usage of muscles attaching to the pelvis (which could be an important finding).


However, we know symmetry is a rarity in function (eg right side dominance), so why are we/patients so keen to gain it in structure? The question I would like to push forward is, in palpatory assessment – are we really feeling pelvic bone movement/position?

Lets take these 2 examples:

Pubic tubercle level – hypertonia in the rectus abdominis on one side can raise tissues in this area assymetrically… is one bony tubercle either side of the symphysis really higher? Or are we feeling soft tissue tension?

The SIJ – this has been found to move a few degrees on average (depending on what article you read), but in say the stork test, we need to ask are we really feeling the PSIS and sacral bone move, or are our hands moving with the superficial tissues? … more importantly, is this tissue movement clinically relevant?

My opinion is yes, and here is why.

The relevance of a hypertonic ipsilateral rec. abdominis depends on the skill set of the practitioner interpreting the collective assessment. But if we are ‘treating what we find’, I think it can and should be treated, especially if that patient is complaining of pubic symphyseal pain (screening of adductors also needed).

More interesting is the stork test result, as we all know, the SIJ has no monoarticular muscles, but does have fascia and other connective tissue traversing it. The importance and understanding of fascia dynamics is growing in the industry, and in this example of a clinical test, I think the movement felt is soft tissue/fascia more than the joint.

Why is this important? Well these tissues are going to move according to underlying osseous structures, also according to muscular involvement – controlling the global connective issue drag. Is it the contralateral lumbar mulifidus and musculature which help pull and stabilise in this test? Is it a lack of their involvement which leads to a positive finding? I am yet to read an explanation/ theory other than SIJ movement. I will say however that if SIJ movement is the sole explanation – the tissue movement in most cases would indicate more than a few degrees! Which is why I believe otherwise.

So there is a piece of my mind on the topic, I am keen to hear others thoughts and opinions on this.

NOTE: If you are keen to read more on the pelvis, I recommend literature by physiotherapist Diane Lee who specialises in this area, and incidentally regards the stork test as clinically relevant for SIJ involvement (link).

Sub occipital facts

Did You Know:

The Rectus Capitis Posterior Minor not only attaches to the occiput, but also to the DURA MATER (latin for ‘tough mother’). This is the connective tissue sheath which surrounds the spinal chord and brain.

Tension in this muscle could cause headaches by disrupting the normal cerebrospinal fluid fluctuations… and hence the functioning of the vertebral artery and sub occipital nerve.


Massage of the suboccipitals and cervical traction can be great for headache relief. This can help detontize the muscles and so reduce compression on occipital nerves and arteries.

Occipital neuralgia (aka C2 neuralgia,) is a medical condition characterized by chronic pain in the upper neck, back of the head and behind the eyes… these areas are largely governed by the lesser and greater occipital nerves!

–> A common site of entrapment for the Greater Occipital Nerve is at the Oblique Capitis Inferior muscle.

The Odd Facet

Heard of the Odd Facet?

These images show how the patella articulates with the underlying trochlear groove and femoral condyles from knee extension to flexion.

From full extension to 90 degrees flexion, the femur articulates with the medial and lateral facets of the patella. (In this range the patella also holds the quadriceps tendon away from the femur.)

Beyond 90 degrees of flexion, the patella slips off the trochlear groove of the femur and the lateral and medial facets of the patellar make contact on the femoral condyles.

Then at 135 degrees the lateral femoral condyle protrudes anteriorly to such a point that a rotation of the patellar occurs. This rotation allows the Odd Facet to articulate on the medial condyle.

Screen Shot 2015-03-20 at 17.07.22

NB: Pressures change through out loaded flexion. In the squat for example, the compressional forces experienced during this excursion increase and the superior patellar articulations experience the greatest forces.

1. This facet is suspected to be responsible for causing osteochondritis dissecans.
Why? The area of patellar contact (on the lateral margin of the medial condyle) matches the site where the lesion is commonly found.
How? Damage most likely occurs during the transition from the medial facets to the odd facet. Between these facets is a ‘peak’ or ‘crest’… this causes pressure to intensify.

2. It is also suggested that this anatomical feature may account for cartilage lesions typically found in patellofemoral syndrome.

Article: http://www.bjj.boneandjoint.org.uk/content/58-B/3/287.long