Ligaments at the posterior superior iliac spine

Question

In Causes of Back Dimples, it was determined that these 'Dimples of Venus' are created by

a short ligament stretching between the posterior superior iliac spine and the skin. They are thought to be genetic. (@Johnny)

The linked article in the answer to my original question says nothing more other than the fact that dimples of venus are normal dimples (not medically significant).

DrLumbago.com states:

The sacroiliac joints move together as a single unit. From the back it is common to see a pair of dimples on the buttock near the base of the spine. These are sometimes called the “dimples of Venus” and they are a landmark for the top portion of the sacroiliac joints.

Posterior superior iliac spine (PSIS) marked in red

^{Image made by DBCLS (Polygondata is from BodyParts3D) CC BY-SA 2.1 jp, via Wikimedia Commons}

Ligaments of the PSIS

Cooperstein & Hickey (2016) has an image of ligaments connected to the PSIS, but unless I am mistaken, the image doesn't seem to have the ligament(s) involved with the dimples of venus.

It seems from the description in Kumar, et al. (2014) that the "dimples of venus ligament(s)" are connected to the skin, and seeing that ligaments are fibrous connective tissues that normally connect bones to other bones, I am intrigued to know more. What is the name of these "dimple of venus ligaments" and what is their purpose?

References

Cooperstein, R., & Hickey, M. (2016). The reliability of palpating the posterior superior iliac spine: a systematic review. The Journal of the Canadian Chiropractic Association, 60(1), 36.
PMCID: PMC4807681

Kumar, A., Kanojia, R. K., & Saili, A. (2014). Skin dimples. International journal of dermatology, 53(7), 789-797. DOI: 10.1111/ijd.12376

Answer 1

It seems from the description in Kumar, et al. (2014) that the "dimples of venus ligament(s)" are connected to the skin, and seeing that ligaments are fibrous connective tissues that normally connect bones to other bones, I am intrigued to know more. What is the name of these "dimple of venus ligaments" and what is their purpose?

First, re: what a ligament is, you're correct in your understanding that ligaments generally bind bones to bones (vs. tendons), but the term is used more broadly as connective tissue that binds things together, holds them in place, is a remnant of a fetal structure, or a mesenteric fold. Your wikipedia link acknowledges this. Some examples are:

• Round ligament of the liver: a remnant of fetal structure

• Broad ligament of the uterus: a mesenteric fold

• Median arcuate ligament: this one actually binds two muscles together
• Sternopericardial ligament: binds the pericardium to the sternum

The unnamed short ligaments Kumar describes (and wikipedia, quora, and stack exchange have repeated), are probably unnamed because they are difficult to isolate and study, and they are not clinically relevant. They may even be theoretical. There are no studies on them indexed in medline, and they aren't discussed in any anatomy text I've read. Dimples are generally thought to be caused by fibrous connections between the skin and muscle, bone, or other deep tissue. If you ever cut into the back of a cadaver or surgical patient, you'll see that there are a great number of unnamed fibrous connections to the skin. It's not unreasonable for Kumar to invoke them as the cause for these dimples.