Pelvis

Function

Four bones locked together

Four bones make up the pelvis: a hip bone on each side, plus the sacrum and the coccyx (tailbone)¹. The sacrum forms from five vertebrae (bones of the spine) that fuse together, a process that does not start until after age 20¹.

Each adult hip bone starts as three bones: the ilium, the ischium (the lower rear part) and the pubis¹. These fuse together in the late teenage years¹. On the outer side of the hip bone, the three meet to form the acetabulum (hip socket), the deep cup of the hip joint¹.

The ilium (the wide upper part of the hip bone) is the largest part¹. It is firmly joined to the sacrum at the sacroiliac joint, which barely moves¹. At the front, the pubis (the bone at the lower front of the pelvis) of each side meets its partner at the pubic symphysis¹. Each hip bone is where one leg attaches, and each is firmly joined to the sacrum at the base of the spine¹.

How it carries the body’s weight

The pelvis’s main job is to carry the upper body’s weight¹:

• It holds up that weight during sitting¹.
• It passes that weight on to the legs during standing¹.

It also gives muscles of the trunk and legs a place to attach, and it shields the organs inside the pelvis¹.

The body’s centre of gravity sits in the region of the pelvis¹. The shoulder girdle (the shoulder blades and collarbones) moves freely, but the pelvic bones are locked together into a firm, weight-bearing structure¹. Because it is so stable, weight can pass from the spine through the hip joints into one leg while the other leg is lifted¹.

Strong ligaments (tough bands of tissue that hold bones together at a joint) hold the sacrum still as it carries the body’s weight¹. These include the sacroiliac ligaments and the sacrospinous ligament (a strong band at the back of the pelvis)¹. The sacrotuberous ligament, running from the base of the spine to the sitting bone, helps too¹.

A systematic review (a study that finds and sums up the research on a question in a set, checkable way) brought together seven 3D studies³. It found that the sacroiliac joint turned 8 degrees or less and shifted 8 mm or less about any axis³. A review of pelvic anatomy describes these joints as key to passing load between the spine and the legs⁴.

Landmarks where muscles attach

The iliac crest is the curved top rim of the hip bone¹. Its rounded front end is the anterior superior iliac spine, and just below it sits the anterior inferior iliac spine¹. Both are places where thigh muscles attach¹. The ischial tuberosity (the “sitting bone”) lies at the bottom of the ischium¹. It anchors the muscles at the back of the thigh and takes the body’s weight during sitting¹.

Most muscles that attach to the femur (thigh bone) and move it start on the pelvis¹. The pelvic floor is a sheet of muscle that closes the bottom of the pelvis¹. Part of it stretches from the pubis to the coccyx¹.

How male and female pelves differ

Male pelvic bones are generally thicker and heavier¹. The female pelvis is wider, a shape suited to childbirth¹. The angle below the pubic symphysis is over 80 degrees in females and under 70 degrees in males¹.

Breakdown

Avulsion fractures in teenagers

An avulsion fracture is a break in which a muscle pulls off a piece of the bone it attaches to². In the pelvis, these mostly happen in teenage athletes, from a sudden, strong muscle pull². This happens while the growth plates (layers of cartilage where a growing bone lengthens) are still open². In teenagers, the growth plates at the pelvic apophyses (bony bumps where muscles attach) give way more easily than the muscles and tendons². So under a sudden, large pull, from a hard contraction or a forced stretch, the growth plate can fail first².

A 2017 meta-analysis (a study that pools the results of several earlier studies) lists where these pieces can come away²:

• the anterior inferior iliac spine, where the rectus femoris (a front thigh muscle that also bends the hip) attaches²;
• the ischial tuberosity, where the hamstrings (the three long muscles at the back of the thigh) attach²;
• the anterior superior iliac spine, where the sartorius attaches, a muscle that runs from there to the inner upper shinbone^1,2;
• the iliac crest, where the tensor fasciae latae (a small muscle at the upper outer thigh) attaches²;
• the upper corner of the pubic symphysis, where the rectus abdominis (a long, flat muscle down the front of the abdomen) attaches².

The most common site differed between studies^2,5,6,7:

Study	Most common site	Next sites
2017 meta-analysis, 596 teenagers2	Anterior inferior iliac spine, 33.2%2	Ischial tuberosity 29.7%; next, anterior superior iliac spine 27.9%2
2026 pooled data, 852 fractures5	Anterior superior iliac spine, 33.1%5	Anterior inferior iliac spine 30.4%, ischial tuberosity 15.5%5
One children’s hospital, 719 fractures6	Anterior inferior iliac spine, 33.4%6	Anterior superior iliac spine 30.5%, ischial tuberosity 19.4%6
198 teenage competitive athletes, 203 fractures7	Ischial tuberosity, 109 cases7	Anterior inferior iliac spine, 45 cases7

These fractures happen in a narrow window of age and bone growth, often during sport⁶. In the series of 198 teenage athletes, they were most common in soccer and gymnastics⁷.

Stress injuries in athletes and recruits

An international consensus describes bone stress injuries as overuse injuries to bone that limit activity and can end high-level careers⁸. The term covers stress reactions (early bone stress injuries, before a crack forms) and stress fractures (small cracks in a bone from repeated loading)⁸.

A case-control study (one that compares people who have a condition with similar people who do not) looked at female Navy recruits⁹. The 25 with pelvic stress fractures were shorter and lighter than the 61 without⁹. Their self-rated fitness, past activity and a history of missed periods were not linked to the fractures⁹.

A sacral fatigue fracture is a stress fracture in normal bone from too much repeated load¹⁰. Across published imaging-confirmed cases, each one had a recent rise in training intensity and a poor diet¹⁰.

Fractures in older adults

In Finland, first pelvic fractures linked to osteoporosis (thin, weak bones) in people aged 60 or older numbered 128 in 1970 and 913 in 1997¹¹. That was a rise from 20 to 92 per 100,000 people aged 60 or older¹¹. In 1997, the age-adjusted rate was 103 per 100,000 in women and 38 in men, both higher than in 1970¹¹.

A sacral insufficiency fracture is a stress fracture in bone too weak to bear normal loads¹⁰. In published imaging-confirmed cases, the most common risk factors were these¹⁰:

• osteoporosis¹⁰;
• radiation to the pelvis¹⁰;
• rheumatoid arthritis (a long-term disease in which the body’s immune system attacks the joints)¹⁰;
• long-term use of corticosteroids (drugs that copy a type of hormone the body makes)¹⁰;
• being postmenopausal (after menopause)¹⁰.

Recovery

How bone responds to load

Muscle contractions put the largest everyday forces on bone¹². Bone adapts to the loads it usually carries¹². It tunes its structure to how much it is strained, how fast and how often, and in what pattern¹².

One theory, called the mechanostat, sets out a minimum level of strain¹². Below it, bone is lost; above it, new bone forms, adding mass and thickness¹². A 2017 review of bone mechanics adds that too little and too rare a load may lead to bone loss¹². Too much and too often may lead to a stress reaction¹².

Bone can also change its size, shape and inner structure, which makes it stronger and stiffer without adding mass¹². Measures of bone mineral density (how much mineral is packed into a given amount of bone) leave out shape and inner structure¹². Yet these add greatly to bone strength and resistance to repeated loading¹².

How broken bone heals

Fracture repair rebuilds bone, repeating many of the steps by which the skeleton first forms before birth¹³. A review of fracture healing reports that repair usually returns bone to its earlier make-up, structure and function¹³. It puts the share of fractures that do not heal normally at about 10%¹³.

A meta-analysis pooled 16 studies of 560 bone stress injuries¹⁴. Injuries at sites rich in trabecular bone (light, spongy bone found inside bones), such as the pelvis, took longer to heal¹⁴. Sites rich in cortical bone (the dense, solid outer layer of a bone), such as the tibia (shinbone), healed sooner¹⁴.

Connections

Muscles of the hip and thigh

The hamstrings start from the ischial tuberosity, apart from the short head of the biceps femoris, one of the three^1,15,16. In 5 of 6 cadaver pelvises, they began from one common tendon, covered on the proximal hamstring tendon page¹⁷. The adductor group, covered on the hip adductors page, generally starts on the pelvis and attaches to the femur¹⁸. The adductor longus tendon arises from the front of the pubic bone¹⁹.

In 11 cadaver limbs, the gluteus maximus (the large buttock muscle) arose partly from the ilium, sacrum, coccyx and nearby ligaments²⁰. In 12 cadavers, the gluteus medius (a buttock muscle beneath the gluteus maximus) arose from three sites²¹. One was the back lower edge of the iliac crest²¹. In 16 cadaver hips, the gluteus minimus (a buttock muscle beneath the gluteus medius) arose from the outer surface of the ilium, among other sites²².

In the quadriceps (four muscles at the front of the thigh), the rectus femoris has one head from the anterior inferior iliac spine^1,23. Its other head comes from the ridge of the hip socket²³.

Muscles of the trunk

The rectus abdominis starts on the pubis¹. The external oblique, the internal oblique and the transversus abdominis each attach to the ilium¹. The transversus abdominis also attaches to the pubis¹.

Farther up the back, the lumbar fibres of the erector spinae (long muscles beside the spine that straighten the back) attach to the ilium²⁴. The latissimus dorsi (the broad muscle across the middle and lower back) has a broad origin that includes the iliac crest^25,26.

Muscles that steady the pelvis

The hip adductors (inner thigh muscles) pull the thigh inward and keep the pelvis balanced during walking¹⁸. Weak gluteus medius and minimus muscles let the pelvis drop toward the other side during walking²⁷. This pattern is called Trendelenburg gait²⁷.

Bones, joints and exercises

Related exercise pages: glute bridge hold, side-lying hip abduction, deadlift and back squat^28,29,30,31. In the glute bridge, the pelvis rises off the floor until the hip reaches a neutral position²⁸. A review of side-lying hip abduction linked the spread in muscle-activity results partly to pelvis position²⁹.

A narrative review (a summary of research written without a set search method) found few studies of injuries linked to the deadlift³⁰. Those it found reported a stress fracture of the hip socket and avulsions at the anterior superior iliac spine, among others³⁰.

Sources

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3. Goode A, Hegedus EJ, Sizer P, Brismee JM, Linberg A, Cook CE (2008). Three-dimensional movements of the sacroiliac joint: a systematic review of the literature and assessment of clinical utility.. The Journal of manual & manipulative therapy. doi:10.1179/106698108790818639 PMID 19119382
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5. Molina LL, Block AM, Carsen S, Crepeau AE, Stavinoha TJ, Chau MM, Nepple JJ (2026). Outcomes of Conservative Versus Surgical Treatment of Adolescent Pelvic and Hip Avulsion Fractures: A Systematic Review and Meta-Analysis.. Journal of pediatric orthopedics. doi:10.1097/BPO.0000000000003305 PMID 42084198
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9. Kelly EW, Jonson SR, Cohen ME, Shaffer R (2000). Stress fractures of the pelvis in female navy recruits: an analysis of possible mechanisms of injury.. Military medicine. PMID 10709377
10. Yoder K, Bartsokas J, Averell K, McBride E, Long C, Cook C (2013). Risk factors associated with sacral stress fractures: a systematic review.. The Journal of manual & manipulative therapy. doi:10.1179/2042618613Y.0000000055 PMID 26109829
11. Kannus P, Palvanen M, Niemi S, Parkkari J, Järvinen M (2000). Epidemiology of osteoporotic pelvic fractures in elderly people in Finland: sharp increase in 1970-1997 and alarming projections for the new millennium.. Osteoporosis international : a journal established as result of cooperation between the European Foundation for Osteoporosis and the National Osteoporosis Foundation of the USA. doi:10.1007/s001980070112 PMID 10912847
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15. Koolmees DS, Klott JD, Poppe TR, Bernholt DL (2025). Distal Hamstring Injuries and Disorders.. Journal of the American Academy of Orthopaedic Surgeons: Global Research & Reviews. doi:10.5435/JAAOSGlobal-D-25-00248 PMID 40972536
16. Miguel-Pérez M, Iglesias-Chamorro P, Ortiz-Miguel S, Ortiz-Sagristà JC, Möller I, Blasi J, Agullò J, Martinoli C, Pérez-Bellmunt A (2024). Anatomical Relationships of the Proximal Attachment of the Hamstring Muscles with Neighboring Structures: From Ultrasound, Anatomical and Histological Findings to Clinical Implications.. Diagnostics (Basel). doi:10.3390/diagnostics14161725 PMID 39202213
17. Neuschwander TB, Benke MT, Gerhardt MB (2015). Anatomic Description of the Origin of the Proximal Hamstring.. Arthroscopy. doi:10.1016/j.arthro.2015.02.025 PMID 25896274
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22. Beck M, Sledge JB, Gautier E, Dora CF, Ganz R (2000). The anatomy and function of the gluteus minimus muscle.. The Journal of Bone and Joint Surgery. British Volume. doi:10.1302/0301-620x.82b3.10356 PMID 10813169
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25. Lehane KM, Faust T, Romeo AA, Erickson BJ (2025). Approach to diagnosing and treating tears of the latissimus dorsi and teres major.. JSES Reviews, Reports, and Techniques. doi:10.1016/j.xrrt.2025.05.015 PMID 41179423
26. Hovsepian JM, Cartaya MA, Glaser J, Oehler N, Solovyov I, Abi Mansour C, Avila JC, Vogt S (2026). Surgical anatomy, biomechanics and clinical outcomes of latissimus dorsi transfer for irreparable rotator cuff tears: a review.. Journal of Orthopaedic Surgery and Research. doi:10.1186/s13018-026-07200-9 PMID 42661214
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29. Macadam P, Cronin J, Contreras B (2015). AN EXAMINATION OF THE GLUTEAL MUSCLE ACTIVITY ASSOCIATED WITH DYNAMIC HIP ABDUCTION AND HIP EXTERNAL ROTATION EXERCISE: A SYSTEMATIC REVIEW.. International Journal of Sports Physical Therapy. PMID 26491608
30. Bengtsson V, Berglund L, Aasa U (2018). Narrative review of injuries in powerlifting with special reference to their association to the squat, bench press and deadlift.. BMJ Open Sport & Exercise Medicine. doi:10.1136/bmjsem-2018-000382 PMID 30057777
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Every source the library cites

Changes

• September 30, 2026 First published.