Getting to the Bottom: The Ischial Tuberosity
This bony protrusion bears the weight of the trunk when we sit and is the attachment site for hamstring muscles.
The posterior aspect of the body, along with its muscles, tendons, bones and attachments, is easy to overlook because it’s out of sight and, therefore, often out of mind. Until, that is, pain occurs. The ischial tuberosity—also known as the “sit bones” or even “sitz bones” (from the German word sitzen) (Garikiparithi 2017)—has many different connections, although it is mainly associated with the hamstring muscles (Drake et al. 2010).
It lies posterior-inferior to the acetabulum and is divided into upper and lower areas. The upper area orients vertically and is divided into two parts. The medial area serves as the combined origin of the semitendinosus muscle and the long head of the biceps femoris. The lateral part is where the semimembranosus muscle attaches (Drake et al. 2010). The lower, horizontal area is divided medially and laterally by a bony ridge. Part of the adductor magnus muscle attaches here. The interior-facing medial area is covered by a bursa and connective tissue (Drake et al. 2010).
Here are some additional facts about the ischial tuberosity:
- The gluteus maximus wraps over the top of the ischial tuberosity to attach from the iliotibial band to the sacrum (Keil 2017).
- The blood supply to the ischium itself comes mainly from the obturator artery and the internal pudendal artery. According to OrthopaedicsOne (2008), “There are numerous nutrient foramina along the ischial tuberosity where these vessels enter the bone with the soft tissue attachments.”
- People who spend too much time sitting on hard surfaces may develop Weaver’s bottom, a form of bursitis (also known as ischial bursitis) (MedicineNet.com 2016).
- It’s rare to experience an isolated fracture of the ischium; however, avulsion fractures may occur with acute hamstring injuries (OrthopaedicsOne 2008).