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Some interesting information about the female pelvis.

Please note that every body’s architecture is unique, so your personal mileage may vary.

Most people have an understanding that the female pelvis changes during puberty and make the assumption that an adult female’s pelvis remains the same post puberty (maybe with some changes during pregnancy), however this is not the case. If you picture a skeleton you are probably picturing a male pelvis. For whatever reason, that’s the norm when you get a skeleton (maybe it’s because I can order a decent quality male skeleton for about $200, but for a skeleton with a female pelvis I’m going to have to pay over $1700). So when we tend to visualize the bones of a person, we are probably visualizing male.

The picture above shows the changes between the pelvis of a fifteen year old female (light pink) and the pelvis of a 25 year old female.  Up until the point of puberty, a female and male pelvis are very similar to each other. In puberty, the female pelvis will widen across the crests of the hip and flare open to create more of a shelf designed to help create space and support the changes of pregnancy, the pelvic outlet will become wider and rounder and the pubic angle is more “u” shaped than “v” shaped. From puberty to 40’s is when a female pelvis tends to be at it’s widest usually when estrogen levels are at their highest. Post menopause, the female pelvis appears to narrow (possibly up to 8%) and the change in shape, narrowing at the openings again and across the width. (1) The male pelvis will narrow with age as well, but it doesn’t to change shape and the narrowing tends to be about 1/2 the rate of the female pelvis. (2) Female pelvis also come in several shapes - gynecoid (more circular - about 60% of females have this pelvis shape), platypelloid (more oval side to side - about 3% of females have this shape), android (more heart shaped about 12 % of caucasian and 8% of non caucasian women have this) and anthropoid (more oval front to back - about 30% of caucasian and 50% of non caucasian females have this shape). (3)  The picture below shows the changes of the female pelvis from the age of 40 to 80 (light pink).

It’s important to remember that whenever a bony structure of the body, like the pelvis, changes, everything that is attached to that bony structure moves with it. In the pelvis this means that a good number of muscles and ligaments will shift, as will the nerve pathways. While both genders will have the same bones, similar soft tissue and nerves as each other, the change in the bony structure of the pelvis means the location / alignment of these structures might be slightly different just based on gender and where a woman is in her hormonal cycles. (Some research is looking into if there are actually smaller shifts in the pelvis based on where someone is in the menstrual cycle).

Females are twice as likely as males to have an anteverted hip alignment. This means that the head of the femur (thigh bone) is more likely to be located forward in the hip socket, which means more of the ball of the joint is located outside of the socket. This is not the bony prominence you feel on the front of the hip, but is a bit more to the side of the front. If this positional deviations is severe enough that the person walks with a toed in alignment, it can overload the structures on the front of the hip. (4)

When ideally aligned, the female pelvis (after puberty) will have a slight tip forward, this will move the ASIS (the boney prominence you feel on the front of the hip) to be slightly in front of of the pubic bone, this alignment may cause any pressure across the ASIS to be felt more strongly. If the body alignment is prone (face down), gravity will increase this tilt even more unless the person is actively engaging the lower glutes and their hamstrings to try to counter it.

Bone density and bone weight are other considerations. In comparison to a male of the same size, the bones in a female’s pelvis will be lighter in weight and thinner. A woman will typically lose up to 25% of her bone mass in the first decade after menopause, but even at her peak of bone mass, she would have lighter bones and less density than men her age.

The female coccyx is more moveable (compared to the males’. Females are 5 times more likely than males to develop coccydynia (tailbone pain) because of the wider pelvic structure, more weight on the coccyx when seated, and if a woman has given birth vaginally this will increase further. (5)

Another part of the change of the pelvis has to do with the pelvic floor muscles. Women are more susceptible to problems in the pelvic floor musculature because of the structure of their pelvic floors (men tend to have shorter thicker muscle here, women’s tend to be larger and thinner) and the fact that their reproductive organs are internal and create pressure on the pelvic floor.  Many females are told to grip their pelvic floor muscles as part of "core conditioning".  This way of training has negative implications.  Just like any other muscle, the pelvic floor muscles need to be able to engage at the needed level and to release as well.  Constant gripping or even consciously holding them in a lower level contraction all of the time can cause the the muscles remain in a shortened state and become too tight. While this can cause incontinence (yes it’s a bit ironic), it will also start to disrupt the position of the coccyx, can affect the position of the pelvis, create too much inter abdominal pressure (which can affect proper  movement of the diaphragm during breathing) and create SI (sacro illiac) joint issues (the pelvic floor muscles stabilize this joint from the inside). The pelvic floor muscles also need to change whenever the pelvis shifts, when it is too tight, shifting becomes problematic. Pelvic floor muscles that are too tight can also make vaginal penetration range from painful to excruciating.  Pelvic floor muscles are partially innervated by estrogen receptors which means that as the levels of estrogen in the body fluctuate - whether during menstrual cycle, peri-menopause, menopause or due to medications that change estrogen levels (like inhibitors given for cancer and other medical conditions), the ability of these muscles to fire and work efficiently will also be affected.(6)

(1) - Comparative ontogeny of the hominid pelvis and implication for the evolution of birth. authors - Zollikofer, Ponce de Leon, Sanchez-Villagra, van Schaik, pub 2016 - http://www.zora.uzh.ch/id/eprint/132307/1/diss_v1.p…

(2) - Adult pelvic shape change is an evolutionary side effect. authors - Mitteroecker and Fischer https://www.ncbi.nlm.nih.gov/pmc/articles/PMC493298…

(3) - Anatomy of the bony pelvis: a study in android structure. author Lateefa Al Dakhyel - https://www.slideshare.net/haranobalok37/anatomy-of…

(4) - Differences in lower extremity anatomical and postural characteristics in males and females between maturation groups. authors - Shultz, Nguyen, Schmitz - JOSPT - March 20018 https://www.jospt.org/doi/pdf/10.2519/jospt.2008.26…

(5) - Coccydynia: an overview of the anatomy, etiology, and treatment of coccyx pain. authors - Lirette, Chaiban, Tolba, and Eissa - The Ochsner Journal, 2014 14(1)ce

(6) - Hormonal Influences on the Pelvic Floor.  author - G Willy Davila - Pelvic Floor Dysfunction - A Multidisciplinary Approach - Springer, 2009

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