The piriformis muscle is centrally located within the buttock and provides an anatomic reference for structures leaving the pelvis and entering the deep gluteal space above and below it. Its muscle belly originates from the ventrolateral surface of the S2-S4 sacral vertebrae, gluteal surface of the ileum, and sacroiliac joint capsule. It crosses the greater sciatic foramen, and its tendon inserts on the piriformis fossa at the medial aspect of the greater trochanter. Within the deep gluteal space, the piriformis and adjacent fibrous bands have been most commonly associated with sciatic nerve compression. The internal obturator-gemelli complex and the quadratus femoris muscle, both distal to the piriformis, have also been implicated in cases of persistent gluteal pain. Case reports have described associated bursae, iatrogenic injury, and space-occupying lesions within these muscles such as hematomas, myositis ossificans, arteriovascular malformations, and abscesses.

History:

Patients with deep gluteal pain will often present with long-standing symptoms with or without a traumatic event. Onset can be insidious or more acute and involve isolated deep buttock pain or associated sciatica-like radiation. A standard thorough examination of history should be performed. The acuity of the onset and mechanism of symptoms can hint at the underlying issue. Proximal hamstring strains or tears will often present after running or explosive activities involving a quick acceleration or deceleration. Acute lumbosacral discogenic entrapment needs to always be ruled out, but a new onset of radiating pain after heavy lifting increases diagnostic suspicion. Stress fracture symptoms may typically develop subacutely, often in the setting of increased high-impact activity, for example, an increase in running volume. Patients who place their hips at the extremes of motion for occupational or recreational reasons may also predispose the deep gluteal structures to impingement or irritation. Yoga practitioners, for example, may report pain in extremes of external rotation and hip flexion, indicating hip intra-articular or extra-articular pathology including posterior femoroacetabular impingement, hip arthritis, or posterior greater trochanteric pain syndrome. We have found that a subset of patients who spend substantial time in the cross legged position may develop painful contact between the posterior trochanter and ischium. Painful sitting in patients who drive or are excessively sedentary at work suggests ischial bursitis, HS, or DGS. Pain during sitting may potentially help differentiate SN entrapment disorders such as DGS and HS from IFI. Patients with DGS and HS will often report an inability to sit for extended periods with concomitant radiating pain or dysesthesias. In their systematic review, Kizaki et al found that, in general, posterior hip pain, radicular pain, and pain aggravation when sitting for more than 20 to 30 minutes were the most commonly reported symptoms in DGS. Conversely, patients with IFI tend to be more comfortable sitting. IFI patients will instead complain of symptom exacerbation with walking, especially in terminal extension when the back leg approximates the femur to the ischium. Critically, however, DGS, HS, and ISI have all been associated with radiating pain and dysesthesias. Furthermore, in our experience, these entities can coexist and are not mutually exclusive of each other. Pain medial to the ischium or in a saddle distribution along with burning, electrical or foreign body sensation exacerbated by sitting but improved by standing or sitting on a toilet seat denotes pudendal nerve entrapment. Corroboration of the diagnosis usually involves a pelvic floor manual test performed by an experienced pelvic floor physical therapist.

Physical Examination:

After a thorough history creates a short list within the gluteal pain differential, a focused systematic physical examination is essential in setting the stage for accurate diagnosis. A complete hip examination including gait analysis, palpation, active and passive range of motion, provocative tests, and neurovascular assessment should be performed. Many of these tests can be performed either seated or side lying. The examination begins with an observation of gait, using a hallway or corridor if possible. Patients with greater trochanteric conditions (ie, bursitis, gluteus medius and minimum tendinitis, or tears) may exhibit a Trendelenburg gait. Internal foot progression can hint at increased femoral anteversion, which has been shown by Gomez-Hoyos et al to be found more commonly in patients with IFI. During the gait examination, the long stride test helps differentiate between IFI and HS. HS symptoms will be exacerbated at heel strike, when the hamstrings contract eccentrically. Conversely, pain recreation in terminal extension of the back leg that is subsequently relieved by taking shorter strides suggests IFI. Specifically for IFI, Gomez-Hoyos et al demonstrated a high test sensitivity and specificity of 0.94 and 0.85, respectively, for the long stride test. Hip abductor performance can then be further assessed with the patient standing. McGovern et al have shown that the single leg squat test and the step-down test offer good reliability and validity in assessing coronal plane control of the gluteal muscle group. In the sagittal plane, abnormal anterior or posterior pelvic tilt has been shown to reflect dysfunction of the pelvic stabilizers and may be a risk factor for IFI and DGS. The patient is next asked to lay supine. At this point, passive hip range of motion can be assessed. Asymmetries, especially decreased internal or external rotation with the hip flexed to 90, suggest femoroacetabular impingement (FAI) or hip arthritis. Reproduced pain with the flexion/adduction/ internal rotation (FADDIR) or flexion/abduction/external rotation (FABER) maneuver can further elucidate anterior or posterior FAI. A straight leg raise, looking for Lasegue sign can be performed to identify a discogenic cause of pain. The sacroiliac joint can be assessed by the FABER maneuver and sacroiliac palpation. Finally, the prone examination can reveal areas of tenderness. Ischial tuberosity tenderness suggests HS. Tenderness just lateral to the ischial tuberosity may indicate sciatic neuritis from entrapment secondary to DGS and IFI. Tenderness medial to the ischial tuberosity strongly suggests pudendal nerve entrapment.

Special Tests:

Deep Gluteal Syndrome

The rationale for most tests seeking to uncover DGS involves either placing the piriformis and external rotators on stretch, thereby exacerbating SN compression or resisting active external rotation. The FAIR test, for example, elicits pain when the hip and knee are flexed to 90, and the hip is internally rotated and adducted across the patient’s other leg, effectively placing the piriformis on stretch. In the study by Martin et al., a straight leg raise had only 0.15 sensitivity but 0.95 specificity when looking at SN entrapment. In their study, they also assessed two other tests, the active piriformis and piriformis stretch tests. Martin et al concluded that the combination of these two tests gives the greatest diagnostic accuracy (sensitivity 0.91 and specificity 0.80) for identifying SN entrapment.6,20 To elicit the Pace sign, the patient is seated with the legs abducted and dangling on either side of the table. A positive test will recreate pain with resistance to abduction and external rotation. Kizaki et al found that tenderness in the deep gluteal space, a positive seated piriformis test, and a positive Pace sign were the most commonly observed tests in DGS.

Hamstring Syndrome

The physical examination for HS focuses on reproducing pain in the ischial tuberosity area with either hamstring stretch or resistance to knee flexion. Tenderness over the ischial tuberosity suggests proximal hamstring pathology. A positive Puranen-Orava test reproduces pain when the patient stands and places the affected leg on a support with the knee straight and the hip at 90. 16 The modified bent knee test involves having the patient lie supine. The knee and hip are maximally flexed, and the examiner subsequently straightens the knee quickly. Cacchio et al found good reliability with a sensitivity and specificity of the Puranen-Orava test of 0.76 and 0.82, respectively, and of the modified bent knee test of 0.89 and 0.91, respectively. In addition, with the patient prone, pain or weakness with hamstring contraction against resistance with the knee at 30 flexion can help identify HS.

Ischiofemoral Impingement

The IFI test  involves having the examiner extend the affected hip while maintaining neutral positioning or adduction. Extension reproduces the pain that gets relieved with the same maneuver performed in abduction. Gomez-Hoyos showed a sensitivity and specificity of 0.82 and 0.85, respectively, for the IFI test, which in conjunction with the long stride test suggests IFI.

Greater Trochanteric Pain Syndrome

Sciatica has been reported in patients with trochanteric bursitis, with nearly 11% of patients with sciatica in one prospective study ultimately receiving a trochanteric bursitis diagnosis.29 Greater trochanteric pain syndrome is reliably denoted by tenderness with palpation over the greater trochanter with the patient in lateral decubitus and can include bursitis and abductor tendon inflammation or tearing. In this position, abduction strength is tested as well as an Ober test to assess for iliotibial band tightness. Flexion, abduction, and external rotation, the FABER test, brings the posterior greater trochanter in contact with the ischial tuberosity and can elicit pain. The iliac crest can also be palpated as some proximal gluteal muscle strains can also refer posteriorly.

Differential Diagnosis:

Gynecological and intra-abdominal disorders can masquerade as gluteal pain and sciatica. Cysts, tumors, masses, endometriosis, or dysmenorrhea can cause intrapelvic sciatic or pudendal nerve entrapment. Pain related to menses, associated bowel or bladder symptoms, or an absence of any buttock tenderness to palpation warrants further imaging workup and referral when necessary. Several common orthopaedic entities can exhibit deep gluteal pain and need to be ruled out. Stress fractures and hip arthritis can be confirmed with radiographs and magnetic resonance imaging (MRI). FAI may present with atypical lateral and posterior pain in up to 15% to 30% of patients. Lumbosacral disorders, including herniated discs, spinal stenosis, and spondylolysis, often manifest a gluteal pain component.

Summary:

Gluteal pain presents both a diagnostic and therapeutic challenge for orthopaedic surgeons because of the region’s complex, layered anatomy. Understanding the anatomic basis of the various overlapping disorders in the deep gluteal region and reinforcing the clinician’s diagnostic armamentarium with specific physical examination tests can aid in clarifying the diagnosis. Imaging and diagnostic injections further narrow the differential. Promising nonsurgical and surgical approaches bode well for improved resolution of deep gluteal pain as clinic.