I want to write about some small studies I have come across which describe some of the anatomical issues that seem to occur in dysplastic hips - things which us Hippies mention to each other from time to time.
This is a very simplified explaination of what goes on, and I know pretty much nothing about the Kinesiopathological Model of pain (I'd never even heard of it before I saw someone mention it on Twitter), but here goes my attempt...!
The pelvis rotates around the hip joint in the transverse, anteroposterior and vertical axes. In the transverse axis, an anterior tilt causes the ASIS (anterior-superior iliac spine) of the pelvis to move forward and inferiorly. The muscles that create this movement are the hip flexors and the back extensors. Anteriorly rotating the pelvis around the transverse axis results in hip flexion and an increased lumbar lordosis. (Posteriorly tilting the pelvis does the opposite - it causes hip extension and decreased lumbar lordosis).
As we know, hip dysplasia is where the acetabulum of the hip joint does not develop properly, either from birth or later in young adulthood. This means the hip socket is deficient, it doesn't cover the femoral head fully enough. This is usually measured by the lateral centre-edge angle, but can be deficient globally and in the anterior plane as well (Nepple et al, 2017). An anterior deficiency is shown in my expert diagram below.
So the muscles that work overtime in a dysplastic hip to make this happen can often be the hip flexors. Now comes the secret: there is a little known muscle called the Iliocapsularis muscle, it lies underneath the Iliopsoas muscle connecting the roof of the acetabulum to the superior part of the femur. I'll be honest, this is the first time I've heard of this muscle - we definitely didn't learn this one on my physio course! A study about the Iliocapsularis (Babst et al, 2011) found that in dysplastic hips, the iliocapsularis muscle was overdeveloped; it had a larger cross-sectional area than in hips with no dysplasia. It seems to make sense that dysplastic hips have overdeveloped hip flexors to pull the pelvis anteriorly and compensate for a lack of acetabulum covering the femoral head here.
There is also a study finding that glute med muscles have less cross sectional area in dysplastic hips than normal hips (Liu et al, 2012). This would seem to explain why many of us 'hippies' experience over-active hip flexors and under-active glutes. When I say 'over-active' I mean painful spasms in the hip flexors at times due to them trying to compensate for the abnormal anatomy. This neuromuscular patterning is hard to correct, even - to a certain extent - after corrective surgery, such as pelvic osteotomy or hip replacement, because this movement pattern has been developed over many years, perhaps somebody's whole life.
Now I know there is debate around whether our glutes do really 'switch off' or 'switch on' and whether we can actually palpate this activity during normal everyday movements, but... I'm not giving this explaination as a generalisation to all patients, just many with hip dysplasia who seem to report this. I understand that these studies are small and don't necessarily form a high quality evidence base in this respect, but it does seem to match up with the fact that those with hip dysplasia present with over-active hip flexors and lumbar hyperlordosis (Fukushima et al, 2018). Trying to get the hip flexors to calm down and glutes to be a bit more active is a challenge, but I have found with the right patience and targeted physio can be helpful.
This is my very basic understanding of dysplastic hip musculature although some of you reading this might have an better understanding than me. If so, I'd welcome your thoughts!
Info taken from:
Babst, D., Steppacher, S. D., Ganz, R., Siebenrock, K. A. & Tannast, M. (2011) The Iliocapsularis Muscle: an Important Stabilizer in the Dysplastic Hip. Clinical Orthopaedics & Related Research. 469. 1728-1734. Doi: 10.1007/s11999-010-1705-x
Fukushima, K., Miyagi, M., Inoue, G., Shirasawa, E., Uchiyama, K., Takahira, N. & Takaso, M. (2018) Relationship between spinal sagittal alignment and acetabular coverage: a patient-matched control study. Archives of Orthopaedic and Trauma Surgery. Doi: 10.1007/s00402-018-2992-z
Kisner, C. & Colby, L. A. (2012) Therapeutic Exercise: Foundations & Techniques (6th Ed.) Philadelphia: F.A. Davis
Liu, R. Y., Wen, X. D., Tong, Z. Q., Wang, K. Z. & Wang, C. S. (2012) Changes of gluteus medius muscle in the adult patient with unilateral developmental dysplasia of the hip. BMC Musculoskeletal Disorders. 13, 101
Nepple, J. J., Wells, J., Ross, J. R., Bedi, A., Schoenecker, P. L. & Clohisy, J. C. (2017) Three Patterns of Acetabular Deficieny Are Common in Young Adult Patients with Acetabular Dysplasia. Clinical Orthopedics & Related Research. 475. 1037-1044. Doi: 10.1007/s11999-016-5150-3
Palastanga, N. & Soames, R. (2012) Anatomy and Human Movement: Structure and Function. (6th Ed.) Edinburgh: Churchill Livingstone Elsevier
