Hip pain is a common diagnostic challenge in both PM&R and Pain Medicine. Because the hip joint is located deep within the soft tissue, pain generators can be difficult to localize. For the board-certified physician, the key is recognizing the “C-sign” presentation, mastering provocative maneuvers like the FADIR and FABER tests, and understanding the mechanical impact of FAI on joint longevity.

1. Anatomy and the “C-Sign”

The hip is a ball-and-socket joint designed for weight-bearing. Intra-articular hip pain—pain arising from the joint itself—is typically felt in the groin.

• The C-Sign: Patients often describe intra-articular pain by placing their hand above the greater trochanter with the thumb posterior and fingers reaching into the groin, forming a “C.”
• Differential Diagnosis: Pain localized strictly to the lateral hip is more likely Greater Trochanteric Pain Syndrome, while posterior hip pain often points to the sacroiliac joint or lumbar spine.

2. Femoroacetabular Impingement (FAI)

FAI is a clinical syndrome of abnormal contact between the proximal femur and the acetabular rim. It is a leading cause of labral tears and premature hip osteoarthritis in young, active adults.

Bony Morphologies

• Cam Lesion: An abnormal bony “bump” at the femoral head-neck junction. During hip flexion, this bump enters the acetabulum and shears the labrum and cartilage. It is more common in young, athletic males.
• Pincer Lesion: Over-coverage of the femoral head by the acetabulum (e.g., acetabular retroversion or profunda). This leads to the acetabular rim “pinching” the labrum against the femoral neck. It is more common in middle-aged females.
• Mixed: Many patients have elements of both Cam and Pincer morphologies.

3. Physical Examination: The Diagnostic Battery

• FADIR Test (Flexion, Adduction, Internal Rotation): The most sensitive test for FAI and anterior labral tears. Bringing the hip into this position compresses the femoral neck against the acetabular rim.
• FABER (Patrick’s) Test (Flexion, Abduction, External Rotation): Used to differentiate hip joint pathology from SI joint pathology. Pain felt anteriorly in the groin suggests hip OA; pain felt posteriorly suggests the SI joint.
• McCarthy Test: With the patient supine, both hips are flexed. The affected hip is then extended, first in internal rotation and then in external rotation. A “click” or reproduction of pain suggests a labral tear.

4. Hip Osteoarthritis (OA)

Hip OA is the progressive loss of articular cartilage within the joint.

• Clinical Presentation: Patients report gradual onset of groin pain, “morning stiffness” lasting less than 30 minutes, and loss of range of motion.
• Predictive Loss of Motion: Internal rotation is typically the first plane of motion lost in hip OA.
• Radiographic Hallmarks: Joint space narrowing (typically superior-lateral), subchondral sclerosis, osteophyte formation, and subchondral cysts.

5. Interventional Management

• Intra-articular Corticosteroid Injections (IACI): Highly effective for temporary pain relief and to confirm the joint as the primary pain generator. These should be performed under ultrasound or fluoroscopic guidance to ensure accuracy.
• Hyaluronic Acid (Viscosupplementation): While common in the knee, its efficacy in the hip is less robustly supported by evidence, though it is used in mild-to-moderate cases.
• The “Hip-Spine” Syndrome: A high-yield board concept where hip OA and lumbar spinal stenosis co-exist. Improving hip mobility can often reduce the compensatory stress on the lumbar spine.

6. The Kinetic Chain

Treating the hip requires treating the muscles that stabilize it.

• The “Trendelenburg” Gait: Weakness of the hip abductors (gluteus medius) causes the contralateral pelvis to drop during the swing phase. This increases the shear forces on the joint.
• Rehabilitation Focus: Strengthening the gluteus medius and core while improving the flexibility of the hip flexors (iliopsoas) and adductors.
• Shoe Lifts: If a leg-length discrepancy is present, it can lead to asymmetric loading of the hip joint; a lift can normalize pelvic mechanics.

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High-Yield Board “Fast Facts”

• Internal Rotation: The first range of motion lost in hip OA.
• FADIR: The best screening test for FAI/Labral tears.
• Alpha Angle: A radiographic measurement used to quantify a Cam lesion (an angle >$55$–$60^\circ$ is significant).
• Groin Pain: The most reliable indicator of intra-articular hip pathology.
• Avascular Necrosis (AVN): Always consider this in patients with sudden hip pain and a history of steroid use, alcohol abuse, or Sickle Cell Disease.