The Iliopsoas—aka the Psoas—aka the “Eminem Muscle”


the iliopsoas

aka the psoas

aka the “eminem muscle”




I am sort of hip to the younger stuff…Eminem…although he curses sometimes.

—President Barack Obama.

As the 2005 season wore on, the 2 most used words by Philadelphia Eagles fans were “sports hernia.” Even though the thing doesn’t exist, there was definitely something wrong with quarterback Donovan McNabb. In quarterbacks, core problems can begin in the preseason, in the psoas muscle, with all the repetitive rotational forces incurred in throwing to their receivers. Sometimes, a steroid injection—not that kind of steroid—relieves the problem. Sometimes not.


I say what I want to say and do what I want to do. There’s no in-between. People will either love you for it or hate you for it.



People either love the iliopsoas muscle or hate it. No matter the case, everybody agrees the “Eminem muscle” is important (Figures 12-1 and 12-2).


Figure 12-1. The rapper Eminem. (A) Head shot. (B) Demonstrating the insertion of the right iliopsoas muscle onto the lesser trochanter of the hip bone.

Like Eminem, the iliopsoas is big and mysterious. It somehow links the core muscles and the hip. We know that function is vital, especially for a passer, who must twist and contort his body to deliver the ball. As McNabb’s core became more of a problem, it became obvious that for McNabb the psoas was calling the signals. Finally, a different set of pains became too much, and he had to have season-ending surgery.

Because of its relatively deep location, the psoas can lead some physicians to think a person’s pain is due to a hip problem. Take 6-time All-Star slugger José Bautista, who struggled with pain in the area until it was found that his trouble wasn’t bone but muscle related. A simple injection returned José to knocking the ball out of the park.

The psoas is a mysterious muscle (Figure 12-3). It is superficial and deep, and in part thick and in part thin. Its strong nature stabilizes things. At the same time, it may stiffen, rap, and rub you the wrong way—and generally be a pain. It’s its own thing; it imitates, it mimics the adjacent troublesome environment. It also triggers headaches. Yes, it is one and the same. It’s Eminem. We would write this chapter like the theatrical production Hamilton (ie, in rap), but we are not smart enough.


Figure 12-2. Shadowed in gray behind the anterior core musculature, the psoas and iliacus muscles join forces and form a unit. The functions may mimic actions of the harness muscles or the power muscles. The psoas protects the hip, but, when inflamed, may mimic signs of hip dysfunction. Note the shadowy “Slim Shady muscle” in this illustration. This muscular unit lurks back there. The large muscle is both mysterious and important.


Figure 12-3. Our artist Rob now reveals Slim Shady in more realistic red, lurking behind the more superficial muscles. Various anterior muscles have been cut away in order to expose it. Figures 12-3 and 12-4 underscore some of the relationships with adjacent muscles. (A) Compare the 2 sides. The right medial thigh is intact, and the left side has 2 muscles divided. Both sides accentuate the space that may exist between Slim Shady and the other muscles. Inflammation within this space may travel in various directions and mimic hip and various muscles syndromes. (B) Two more perspectives of Slim Shady. Note the ghost of the head and neck of the femur on the left side.

The psoas is meant to be loved, not necessarily understood.

—An arthroscopic hip surgeon.


The answer is easy…because physicians and scientists just have not studied it enough. Failure to recognize the core as an important part of the body accounts for this lack of study. Who would have the interest to study the psoas? Orthopedists? Certainly not…the muscle is way too close to so many “dangerous” blood vessels and organs. General surgeons? No way… wouldn’t that mean the general surgeon would have to know some biomechanics?

One instance in my past drives home why this muscle remains so mysterious. As a junior attending at Duke, I became the go-to general surgeon for J. Leonard Goldner, our famous Chairman of Orthopedics. One of the things J. Leonard was famous for was “anterior lumbar fusions.” In his hands, and with his careful selection of patients, the procedure involved bone grafting the spine and was highly successful. It often cured long-standing, disabling back pain. Dr. Goldner operated on several such patients per week.

J. Leonard chose me to help him because I was quick and efficient and because he did not understand most of the anatomy surrounding the lumbar spine (eg, the bowel, the aorta, the inferior vena cava, all those big things that might cause him trouble). By the same token, I knew nothing about the lumbar spine. I would dissect all the organs and big blood vessels away from the psoas muscle and lower vertebrae in a lickety-split fashion. Of course, I initially felt proud to have been chosen to do this for this wonderful, great orthopedic surgeon. But the number of cases kept mounting; they took way too much time, and kept me from doing many other things I had to do. From my perspective then, I was doing all the surgical dissection, J. Leonard came in for a few minutes, sprinkled in a few bone chips, and took away all the glory! Don’t get me wrong. I was never bitter. I am just exaggerating my feelings just to get the point across. I loved Dr. Goldner; he was absolutely wonderful and treated me like a son.

Thinking back on those years, I can now see what was going on. J. Leonard knew a lot about the back. He was an orthopedist who had been trained in orthopedics. He knew all about the bones and nerves. But Dr. Goldner would have gotten into big trouble dissecting away the aorta, the ureter, and everything else in this anatomic region that was so important. He might have caused sudden massive hemorrhage or poop to spill all over the spine. On the flip side, I knew all about most of those other organs back there. Because of our differences in training, I could perform all these dissections well. I had those skill sets even though I knew nothing about biomechanics. When I think about it now, neither one of us then knew much about that massive muscle staring at us in the face during those dissections—the psoas.

Bingo. In a nutshell, the above story solves the mystery. We don’t know more about the iliopsoas for 2 reasons: (1) the biomechanics experts are afraid to go into this region, and (2) the people who are not afraid to enter into this region know nothing about biomechanics. Of course, the region is also deep and hard to get to. That might have had something to do with it, too.

That is why surgeons say, “Obviously, the psoas is important but…” At that point in their sentence, their voices trail off.


What we do know about it takes just a couple of paragraphs. Make that a couple of sentences. We can describe where the muscle sits, that it is big and strong, and that it must have important roles in the function of the hip and pelvis. We also know that its function must vary according to alterations in the pelvis’s bony structure or nearby muscles. Yes, that’s all we know. Two sentences, that’s what it takes.

Most of the time, we can’t even decide whether to call it the “psoas” or the “iliopsoas” muscle.


The Eminem muscle’s location is actually tricky. One can think of there being 2 muscles—the psoas and the iliacus—in the abdomen, and then 2 muscles merge as they go deeper into the pelvis and thigh. Usually as it travels down, another smaller muscle sits on top of the psoas—the psoas minor. This muscle is likely not too important except as an augmenter to the overall function of the psoas. Now that we have mentioned the latter muscle, forget about it, we shall not mention it again. Plus, we shall not use the term psoas major. In the spirit of keeping things simple, forget “major” and “minor.” Use the term psoas without a modifier. We shall use of that term in this chapter both strictly to portray the specific abdominal muscle and lazily as a nickname for the whole iliopsoas. When we use “Eminem muscle,” sometime we are trying to get across both the muscle’s mystery and importance (Figures 12-4 through 12-7).

The psoas comes from the lateral aspects of the lowermost thoracic and most of the lumbar vertebral bodies and discs. One usually thinks in terms of it arising from T12 to L4 or L5. The iliacus comes from the anterior surface of the iliac bone, the so-called iliac fossa. For the most part, these origins don’t make much difference because both fitness experts and surgeons rarely work back there. The muscles quickly become big and fleshy as they travel south and then narrow near the lesser trochanter. Clinically, we deal both with fleshy and tendinous parts after they merge. The combined muscle has a variety of different looks as it goes more distally and ends on the lesser trochanter of the femur. It can be one or multiple thick tendons or mostly fleshy muscle or both tendinous and fleshy.1


Figure 12-4. The iliopsoas forms from 2 muscles, the psoas and the iliacus, and its union is quite variable in terms of the sites of union and relative contributions of muscle bulk and tendon.


Figure 12-5. Abduction or extension highlights the muscle’s intimacy with the hip. The closest areas of contact with the hip remain somewhat controversial.


Figure 12-6. A sagittal view exhibits how the combined muscle hugs the contour of the head of the femur before it inserts onto the lesser trochanter.


Figure 12-7. Two more perspectives on the mysterious muscle. Don’t forget other nearby muscles. The rectus femoris and iliopsoas share intimate anatomic relationships in helping with the muscular component of hip stability. Note the proximity to the adductors.

Several subtle anatomic points turn out important with respect to surgery on the iliopsoas muscle and/or hip. Many of the connections of the psoas to the iliacus muscles and to other nearby soft tissues occur at or distal to the ball-and-socket hip joint. The tendon-muscle complex lies intimately anterior to the hip capsule and anterior labrum. Debate exists whether the bony “iliopectineal eminence” of the hip socket or the ball of the femur is a principal culprit in some of the severe inflammatory “hip-snapping” conditions that occur in this region. Arthroscopic hip surgeons claim that adherence to the labrum accounts for certain (“3 o’clock”) labral tears.2 The small iliocapsularis muscle might also play a role in that type of tear. It seems best to think much more broadly and in terms of a variety of anatomic factors contributing to the numerous pains that occur in this area.

An underappreciated fact is how many more connections exist between the iliacus and psoas and other soft tissues distal to the ball-and-socket hip joint and proximal to the iliopsoas’s insertion on the lesser trochanter, compared to the number of connections superior to the hip joint. Our artist Rob’s picture of the iliopsoas displays this observation quite vividly (see Figures 12-4 and 12-5). One simply sees more muscle connectivity the more distal you go. That anatomic fact may account for why partial lengthening procedures of the muscle’s most distal aspect (ie, near the lesser trochanter) seems to carry so much less morbidity than “lengthenings” or “partial releases” at the level of the joint, where they are done during hip arthroscopy.3 From what we have seen, the latter approach carries with it the risk of dramatic total or subtotal proximal retraction of the psoas muscle. That event can be innocuous or associated with profound weakness or pain.



Functionally, think of the psoas in primarily flexion and extension and secondarily external and internal rotation. One can debate the more important function, but the more important distinction to define better is what particular part of the body the muscle is flexing or rotating. One usually thinks in terms of the psoas flexing only the hip and thigh. When one considers its long length of origin, it also serves importantly to flex and straighten the vertebral column.

Look at Rob’s pictures (see Figures 12-5 through 12-7) and appreciate that rotational direction is largely determined by the body’s orientation at the time of contraction. Usually, the psoas externally rotates the hip. Look at how we can barely see the lesser trochanter in the straight-on views; thereby, contraction would make the greater trochanter go posteriorly (ie, externally rotate). Geometrically though, if one is already maximally externally rotated, the iliopsoas then internally rotates.

Considering its main functions, guess which sports or positions within sports would place the psoas at most risk for injury. You are right—sports or positions with a lot of up-and-down action or ones that involve a lot of rotational action while the person remains relatively upright. Think further: basketball players, runners, quarterbacks, tennis players, divers…the list goes on. Also think of players with their own unique ways of doing things, such as José Bautista, who generates so much power with a stance with the front leg flexed and in the air and then steps down strongly at the initiation of his swing.


Muscular volume estimates of strength place the iliopsoas first as the strongest flexor of the trunk or core, with the pubic bone the center point. Certainly, the psoas is stronger than either the tensor fascia lata or sartorius. One may have a harder time arguing that in all cases with respect to the rectus femoris. The rectus femoris is usually but not always smaller than the psoas. Then one must add in location and leverage arguments. The rectus femoris is more purely anterior and takes no turns or bends at all. Its deep central location and the pulley/leverage dynamic resulting from its various turns and bends augment psoas strength enough for it to remain in first place in the core flexor category. Other arguments come into play when some of the back muscles get included in the discussion.

Okay, enough of that discussion. Let’s leave this subject with one of the “central” themes of the book (pun intended). The more central the location of the muscle in the core, the more critical its function is likely to be. The psoas is strong and central. It must be pretty important.


The argument about strength and central location plays well for a key role for the psoas in overall core stability. One would guess, for example, that the psoas’s strength in flexion would take some of the load away from the harness muscles (see Chapters 8 through 10) during sit-ups and protect them.

Now let’s get back the psoas’s anatomic location. Note how close it is to the hip. We just discussed that some surgeons speculate that it plays a direct role in the pathophysiology of some labral tears. Note in Rob’s diagrams also how the strong Eminem muscle bends anteriorly around the hip joint, as if to protect it. Is it possible that the psoas plays a huge role in overall hip stability? You’re darn tootin’ it does. We ought to be able to draw that conclusion just on the basis of size, strength, shape, and location of the muscle. The burden of proof lies on nay-sayers who say that this is not true. One recent paper strongly implicates arthroscopic psoas lengthening including hip instability in poor clinical outcomes in patients with a certain type of anatomical orientation of their hips called femoral anteversion.4

We need to get smarter about all this. Of course, the psoas must be important for hip stability. We see patients almost every day who have done badly after arthroscopic hip surgery and psoas lengthening. Some of those patients developed real hip instability. On the other hand, the procedure has helped some patients magnificently. For several years now, arthroscopic hip surgeons have had a rather cavalier attitude about doing psoas releases at femoroacetabular impingement surgery. I am not saying we should stop doing this altogether. We just have to get smarter.

Now also consider that we see many cases of severe psoas pain after total hip replacement. These patients usually get dramatically better after psoas release.

To release or not to release the psoas, that is a real question. Certainly, there are appropriate times to do either. And the other side of the coin is that there are many patients out there with severe psoas pain and who need something aggressive done. Are there are other surgical choices? I think there have to be. Why not shave the iliopectineal eminence or other bony or soft tissue and free up the psoas in other ways?5 That way, the psoas would stay intact. It takes 2 to tango. It takes 2 anatomical parts to impinge. If the psoas is the snapping against bone or other soft tissue, couldn’t getting rid of the “snappee” be as good a potential solution as getting rid of the “snapper”?

We have to get smarter. We need more thoughtful studies. We can make some patients so much better sometimes by loosening the muscle. We can also create unstable hips and make them miserable. We’ve got to understand better more of the basic biomechanics and underlying pathophysiology.


Get it? Rap, to hit hard, the Eminem muscle, iliopsoas problems… Okay, we are stretching the analogy a bit.

Here are several case examples of psoas injuries/problems. Keep in mind 2 really important thoughts with respect to diagnosis and treatment:

  1. Psoas problems can be subtle; they mimic a lot of other core injuries including those of the hip or muscles. They even mimic sobering internal problems. When considering the psoas as a cause, you must keep in mind infections of the gastrointestinal tract, tuberculosis, appendicitis, or other serious trouble. Many of the archetypal medical traps reside in the region of the psoas. For example, abscesses classically sit on the psoas muscle, psoas symptoms and signs arise, and one gets fooled thinking about benign musculoskeletal issues. Plus, even with severe, benign psoas issues, “typical” pain with flexion/extension does not have to be manifest.
  2. A real psoas problem may occur as either a primary, isolated issue without any other cause or in conjunction with another core problem, such as a significant hip or other core muscle concern. When the underlying problem cannot be identified, one can guess that Slim Shady will return and would say: “Guess who’s back!”

Case 1. Seemingly Straightforward Psoas Bursitis

A 17-year-old multisport high school football/ice hockey player picks up tennis and enters a top state tennis tournament and gets to the championship round. He had this intense psoas bursitis without any hip or core muscle injury. This was treated by steroid injection and oral anti-inflammatories and he returned to win the championship. He remains without symptoms 6 months later but has not returned to tennis. See Figure 12-8.

The principal message that the athlete of Case 1 sends is that psoas problems can occur in isolation. In his case, tennis seemed the precipitating factor. On his own, he chose to win the tournament but to give up tennis. Other sports were too important for him to risk recurrence of this injury.


Figure 12-8. Using Rob’s earlier drawing (see Figure 12-6) (A), one can easily see (B) the anatomy of this young football/hockey/tennis player’s psoas strain (arrow) and subsequent bursitis in on MRI. Note the proximity of the psoas and the hip. (C) The bursitis can get so bad that it looks cystic (arrow).

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Apr 2, 2020 | Posted by in SPORT MEDICINE | Comments Off on The Iliopsoas—aka the Psoas—aka the “Eminem Muscle”
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