HAL DAVID MARTIN, DO
Editor’s Note: Hal Martin has been leading the way into the deepest, darkest aspects of the core—what has been regarded as the “black hole” of our anatomy, a place where many pains seem to originate and stay. It seemed appropriate to ask Hal to write this chapter on the anatomy posterior and otherwise immediately adjacent to the hip.
Pain in the front can also be a pain in the butt.
—The chapter author.
JOE THE PLUMBER (FIGURE 29-1)
Joe has his own plumbing business and comes into the clinic with aching groin pain and “fat wallet” syndrome. The latter occurs not because he makes a lot of money—Joe does okay—but because he can’t sit for more than 10 minutes on one side of his butt without pain. And when he does sit, he leans onto the unaffected side as though he has a fat wallet. Joe needs to be able to sit. Otherwise, he has to do all his plumbing work squatting, which isn’t so bad, except squatting for so long, eventually, tires him out. He grades the pain an 8 on a 10-point scale, and completes our modified Harris Hip Score form, which catalogs him as an F (with 55 out of 100 points).
To investigate the issue, we go through our evaluation routine. This begins with a comprehensive history and physical examination. We then confirm our clinical impression with several tests. The pain radiates down the backside of the affected leg and worsens with activity. We rule out the lumbar spine with a back examination and magnetic resonance imaging (MRI). We do a bunch of other physical examination maneuvers. Palpation suggests the culprit to be the piriformis muscle. The pain increases with the seated piriformis stretch test (ie, we move one straight leg over the other and rotate it inward). This maneuver stretches the piriformis muscle, which sometimes compresses the sciatic nerve and does not allow normal nerve motion.
Then we do the active piriformis test. Joe lies on his unaffected side, bends his knee, drives his heel into the table, and rotates his knee away from his body against resistance. This activity makes the piriformis contract. This, again, increases the pain. We know the sensitivity and specificity of doing both these tests together to be 0.91 and 0.80, respectively. We become convinced that the problem is entrapment of the sciatic nerve. We follow with diagnostic/therapeutic injections, MRI, and nerve conduction studies.
Joe wants nonoperative treatment, and we put him on a physical therapy program. He achieves more mobility of the piriformis muscle and hip external rotators with focused piriformis stretch exercises. Joe sits with both legs flat to the ground. He bends the affected side knee and places his foot on the lateral aspect of the opposite knee. He initiates the stretch by pulling his knee inward, as far has he can, toward his chest. This set of exercises greatly alleviates the pain for several months. After 6 months, it comes back, even more piercingly than it had ever been. Our surgical treatment options include open or endoscopic sciatic nerve decompression. He chooses the minimally invasive approach and gets piriformis partial tenotomy. The procedure restores normal sciatic nerve motion and cures him.
Now, 1 year after definitive therapy, Joe’s pain is 0 and his modified Harris Hip score A+, with a 100 out of 100 total. He is back full time to work, sitting and squatting without pain, and making a good living.
The effort invested in “getting it right” should be commensurate with the importance of the decision.
—Daniel Kahneman, 2002 Nobel Prize winner in Economics and author of the best-selling book Thinking, Fast and Slow.
GETTING IT RIGHT
Professor Daniel Kahneman’s beautiful prose tells us that we arrive on a decision by either thinking fast or thinking slowly. A huge distinction exists between fast intuitive thought and slow deliberate thought processes. Solving the mystery of a perplexing problem in this region of our body comes only by thinking slowly—piecing together a puzzle of anatomy, biomechanics, clinical diagnostics, and treatment outcomes.
The first piece of the puzzle is hip pain that does not fit the usual clinical profile. Then arrives the search for the anatomical and biomechanical pieces. We have learned to recognize those pieces from our research in the laboratory. The puzzle begins to take shape when we complete the diagnostics and make the decisions. By carefully observing the outcome, hopefully, we complete the puzzle. The final answer comes after recycling the same pieces and puzzle-solving methods over and over again, and seeing if the same methods and pieces continue to solve similar puzzles.
THE FORMERLY MYSTERIOUS REGION
The hip, the way we have defined it, is just the ball and socket. The anatomical territory behind the hip has remained a “black hole” (Figure 29-2) for too long. We are talking about the region deep to the glutes, where so much pain in so many people seems to originate. The anatomy, it turns out, is readily identifiable. Most problems that reside here can be unearthed via a comprehensive history and physical examination.
The realization that one can diagnose the problems in this region requires a thorough understanding of the anatomy and biomechanics of the hip and this surrounding territory. Close anatomic and kinematic relationships exist among the lumbar spine, pelvis, and hip, so, of course, to determine what exactly is going on entails a structured approach. Failure to identify a cause of pain in this region, especially in a timely manner, can have devastating effects. In fact, delay in diagnosis can increase the perception of pain, and thereby diminish the quality of life and take away hope.
We think of the region as having 5 different anatomic levels: osseous, capsulolabral, musculotendinous, neurovascular, and kinematic (ie, adjacent anatomy relating to motion or directly to the kinematic chain). Imaging tools and other ancillary tests are usually confirmatory. Physical therapy and guided injections may provide good initial treatment options. Open or endoscopic surgical techniques show promise in selected patients.
The bottom line is that pinpointing the involved anatomy remains essential. The skill to see this spectrum of afflictions necessitates seeing what we see now in terms of functional anatomy, and also learning the knowledge that is rapidly evolving about ways that intra-articular anatomy connect to structures outside the hip joint. Much of this important dynamic occurs behind the hip.
THE CRUCIAL CONCEPT
The number of causes and consequent treatment options for posterior core pain grow as our understanding of clinical anatomy and biomechanics in this region expand.1 Think of the hip as the center axis of the largest lever-arm of the human body. These biomechanics entail a balance of interactions between the osseous and soft tissue structures that exist there, the natural ranges of motion of the contained joints and superimposed neuromuscular activity.2 Any alteration in the balance might produce pain due to disturbances of the kinematic chain in any direction from the hip joint.
That means that deep derrière pain can occur from any number of causes that emanate from intra- or extra-articular sources. The main diagnoses are intra-articular hip pathologies, spine issues, intrapelvic abnormalities, pudendal nerve entrapment, something we call ischiofemoral impingement (IFI), hamstring origin tendinopathy, deep gluteal syndrome (DGS), and secondary lumbar spine influences (SLSI). Often, DGS and SLSI come from abnormal kinematics arising from primary hip joint pathology.
ABUTMENTS IN THE BUTT
Much of the book thus far has focused on different types of bony impingements inside the hip joint (ie, cam, pincer, or mixed). That’s not the only place where abnormal abutments may occur. Many impingements also happen outside the hip joint, and, in particular, behind it. For example, subtle abnormalities in the orientation of the femoral neck or lesser trochanter may lead to extra-articular hip impingement, and then kinematic chain disturbances and posterior pain.3
Table 29-1 lists the anatomical landmarks relevant to posterior hip pain. These include different structures at each level (bone, capsulolabral and ligamentous, musculotendinous, neurovascular, and kinematic). As we have stated, intraarticular and extra-articular sources of posterior hip pain can usually be identified through a comprehensive history and physical examination.
Version, the Trochanters, and Ischiofemoral Impingement
A recent study assessed the relationship between the femoral neck “version” and lesser trochanter “version” with IFI using a standardized MRI protocol. Femoral neck version and lesser trochanter angle were significantly increased in patients with symptomatic IFI.4 A cadaveric study by Martin et al showed that even the greater trochanter can impinge on the ischium during a combination of hip flexion, abduction, and external rotation.5 This phenomenon is also called greater trochanteric pelvic impingement. While IFI is a common problem often left unrecognized, the occurrence of such greater trochanter impingement demonstrates the importance of considering each person’s anatomy individually.
Relationships Between the Back and the Posterior
Limitations in range of motion due to femoroacetabular or any other type of impingement lead to adaptations in lumbopelvic kinematics. One provisional biomechanical study suggested that “pelvic inclination” may help increase loads on the lumbar spine.6 Another cadaveric study proved a relationship between simulated IFI and lumbar facet load changes during terminal hip extension.7 Problems such as flexor contracture, posterior acetabular overcoverage, and femoral retroversion can also limit terminal hip extension and have similar effects on the lumbar spine. Secondary pelvic rotation, hyperlordosis, and facet joint overload may explain lower back symptoms in patients with hip pathologies. Limitation of terminal hip extension can increase hyperlordosis, and also narrow foramina thereby compressing adjacent lumbar nerve roots.8 One take-away from all these analyses—Every hip exam should include a back exam and every back exam should include a hip exam.
The Sciatic Nerve
The sciatic nerve plays a huge role in many of these pains (Figure 29-3). Sciatic nerve kinematic adaptation (and irritation) occurs within a dynamic narrowing of the ischial tunnel in posterior hip impingement.5,8 The sciatic nerve enters the pelvis via the sciatic notch and moves considerably with hip movement. In fact, Coppieters et al9 found that the sciatic nerve has 28 mm of excursion during hip flexion. Sciatic motion may also be greatly affected by “penetration” of the piriformis muscle. That muscle actually pierces portions of the sciatic nerve in 16.2% of the population.10
In normal situations, the sciatic nerve glides across the posterior border of the greater trochanter as the hip moves into deep flexion, abduction, and external rotation. Greater trochanteric impingement occurs when the sciatic glide is absent. These observations about the sciatic nerve also turn out to be important with respect to understanding the principles of many types of rehabilitation. In the fully flexed, abducted, and externally rotated state, the semimembranosus muscle origin and the posterior edge of the greater trochanter can come into contact.5 During hip flexion with knee extension, a spiraling phenomenon of the sciatic nerve has been observed, and then the tension gets better with hip abduction and knee flexion.11 Study of the kinematics of the sciatic nerve within the ischial tunnel continues to bear fruit.
Chronic hamstring origin abnormalities can occur in patients with posterior impingements.12 Therefore, these mechanisms should also be considered in the evaluation of posterior pain. Most hamstring injuries are from indirect trauma (ie, overuse injuries from excessive stretching or repeated forceful contractions), which leads to muscle strains, tears, or even avulsions.13
Hamstring tears, regardless of cause, lead to sciatic nerve irritation and lower buttock pain due to inflammation and scar. We call this problem ischial tunnel syndrome or hamstring syndrome. This is an important diagnosis to consider in most patients with posterior hip pain.14
Several studies demonstrate, beyond a doubt, the close relationship among the sciatic nerve, hamstring origin, and ischium (Figure 29-4). A cadaveric study by Miller and Webb15 emphasizes the intimate anatomic relationship the sciatic nerve has with the ischium and hamstring origin. The sciatic nerve lies an average of 1.2 ± 0.2 cm from the most lateral aspect of the ischial tuberosity. The branches situated there are likely to be irritated. Branches to the long head of the biceps femoris and semitendinosus muscle emerge at a close distance to the ischial tuberosity (6.9 and 7.1 cm, respectively), although this area is highly variable.16
Deep Gluteal Syndrome
DGS describes the entrapment of the sciatic nerve in the deep gluteal space. A number of structures may entrap the sciatic nerve: fibrous bands containing blood vessels, gluteal muscles, hamstring muscles, the gemelli-obturator internus complex, bone structures, vascular abnormalities, and space-occupying lesions.1 One should also remember that abutments of the sciatic nerve may also occur in locations above or below the deep gluteal space, such as by intrapelvic vascular and gynecologic abnormalities.17
Pudendal Nerve Issues
One should also remember that the pudendal nerve may a play a role in some of the mysterious pains. Pudendal nerve entrapment and/or irritation can occur at various locations, such as the intrapelvic region, near the piriformis muscle or at the sciatic notch, or involving the sacrospinous ligament or sacrotuberous ligament.18
It’s all about location, location, location.
—Numerous real estate moguls lay claim to this declaration. The statement probably originated in Chicago in the early 1900s.
LOCATING THE PAIN (TABLE 29-2)
The exact location of the pain, plus the elicitation of that pain on examination, often leads to the right answers. As discussed in Chapter 18, the site of pain or tenderness can fool you, but don’t start out with that negative attitude. Probably, nothing is more instructive than identifying where the pain is and what causes and relieves it, and then finding the exact site of tenderness and reproducing the pain with various physical examination maneuvers. So, take off your modesty hat, get a chaperone, and ask the daring questions during your history; then track down the correct diagnosis with your physical examination.
Use the ischial tuberosity as a reference point (Figure 29-5). Hamstring tendon pathologies lie lateral or posterior to the ischial tuberosity. IFI (or ischial tunnel syndrome) also occurs lateral to the ischial tuberosity, but not so lateral. DGS pain (ie, sciatic nerve impingement) manifests superiorly and laterally; that means at the sciatic notch or beyond that along the course of the sciatic nerve. Pudendal nerve entrapment signs and symptoms occur medial to the ischial tuberosity.
Sitting aggravates pudendal-origin and other pain manifesting medial to the ischial tuberosity. A toilet seat or sitting donut usually alleviates these pains, as does standing or a good night’s rest off one’s butt. The pudendal nerve entrapment patient often awakens in the morning feeling good. Then the pain progresses and gets worse and worse during the day. Pudendal nerve entrapment generates pain often described as burning, tearing, stabbing, lightning-like, electrical, sharp, or shooting. Patients often describe foreign body sensations and changes in skin sensation.18,19
Patients with sciatic nerve entrapment often have a history of trauma and sit-pain (the inability to sit for more than 30 minutes). They also often have radicular pain emanating from the low back or “hip,” with paresthesias of the affected leg.9 Patients with hamstring syndrome or IFI present similarly, so either syndrome, or the coexistence of the two, must come to mind when you observe such descriptions in lateral (to the ischial tuberosity) locations.20
Patients with distal sciatic nerve impingement have different complaints than those with more proximal causes. Take, for example, hamstring vs IFI. The hamstring patient often exacerbates the pain by sitting (eg, driving), whereas, in general, patients with IFI are more comfortable sitting. Conversely, IFI patients have more pain during the terminal hip extension part of walking. In the driving position,10,21 the hip rests in a 30-degree flexion position. Therefore, the semimembranosus of the hamstring has a different (and worse from the standpoint of pain) force vector angle. Holding the hip in 30 degrees flexion with the hamstring activated, no matter the mechanism, can reproduce sciatic nerve complaints. The terminal hip extension of walking diminishes the space between the ischium and the lesser trochanter and squeezes the sciatic nerve in IFI.
Any sort of posterior abutment can also cause low back pain, which makes the separation of spinal and posterior core issues even trickier. Limited hip range of motion has long been known to affect spine mobility and function.22–26 Patients with IFI have those symptoms due to the limited hip extension. Gomez-Hoyos confirmed that direct relationship in a cadaveric study by artificially decreasing the ischiofemoral space and seeing lumbar intrafacet joint pressure increase.
Distinguishing between sacroiliac joint disorders and hip or other posterior core disorders can be thorny, particularly considering how often hip and sacroiliac joint problems occur together. We use the rule that pain inferior and medial to the posterior superior iliac spine points to sacroiliac joint disorders. However, we must rule out gluteus maximus tendinitis. Ask whether the pain is “on” or “in” the sacroiliac joint? Only 4% of patients with sacroiliac joint pain mark that they have pain above the L5 vertebra on pain drawings,27 so the rule does has practical applicability. Sacroiliac tenderness, combined with that location of pain, has the highest sensitivity. One must remember, still, the lack of specificity. Beware that any pathology that produces loss of hip extension can cause sacroiliac joint pain and tenderness.