Age. Certain tumors or metastases which commonly effect the proximal femur in adults such as multiple myeloma or those that commonly spread to bone (recall the common “BLT and Kosher Pickle” mnemonic for breast, lung, thyroid, kidney, and prostate) are immediately off the list. Other tumors like acute lymphoblastic leukemia or neuroblastoma, which may present with joint pain initially, primarily occur in children younger than 5 years. Among the mechanical processes, transient synovitis peaks at 2–5 years (max around 12) and Legg-Calve-Perthes (or simply Perthes) at 4–8 years. Also, it would be highly unusual for developmental dysplasia of the hip (DDH) to have its first presentation at age 12 (screening for these begin at birth using Ortolani and Barlow maneuvers and ultrasound and orthopedic follow-up for any suspected abnormality). Coupled with the absence of fever and other constitutional symptoms, only a few diagnoses remain for groin pain with a painful limp in a 12-year-old.

SCFE commonly presents at age 10–16 years old, males are more commonly affected than females (2:1), and the condition is more common among African-American and Polynesian ethnicities. Obesity is one of the strongest risk factors, presumably due to an increased load across the physis. 50 % of SCFE patients are at/or above the 90th percentile for weight; 70 % of patients are at or above the 80th percentile. Obesity creates increased mechanical loads across the proximal femoral physis, increasing the likelihood of slippage.

Children commonly present with an antalgic gait (painful limp) and occasionally an inability to weight bear because of pain. Pain associated with SCFE most commonly presents at the groin, but can also radiate and localize to the thigh or knee. On physical exam, SCFE patients present with decreased internal rotation, and the thigh is held most comfortably resting in external rotation. Internal rotation maneuvers recreate the pain. Though a painful limp can be a sign of tumor or infection, the absence of fever, malaise, and other constitutional symptoms goes against these.

External rotation of the leg is the most common resting position of children with SCFE. This is the most comfortable position because of the mechanical direction of slippage. Often, obligatory external rotation can be observed in SCFE – when the hip is brought into flexion, the leg will involuntarily externally rotate.

This, especially in conjunction with fever or signs of infection, is classic for a psoas abscess with reflexive contracture of the psoas muscle due to spasm. Attempts at passive hip extension which stretch the psoas muscle are met with significant pain much like that seen in testing for compartment syndrome. Psoas abscess is often a sign of another underlying etiology like osteomyelitis of the spine, or pelvic inflammatory disease, especially in immunocompromised patients, so it is important to search for the primary source of the abscess.

Hip pathology may cause referred pain to the knee. Legg-Calve-Perthes disease and slipped capital femoral epiphysis can both initially present as knee pain, with no complaint of hip discomfort. Therefore, it is important to perform a complete physical exam to determine if knee pain is native to the knee or referred from the hip.

Several endocrine disorders are associated with SCFE including hypothyroidism, growth hormone abnormalities, renal osteodystrophy, hypopituitarism, and hyper- or hypoparathyroidism. These conditions can physiologically weaken the physis leading to slippage. Patients who are young (<10 years old) or thin (<50th percentile for weight) should be worked up for an underlying endocrinological disorder.

In this patient, the pain originates in the groin and radiates to the thigh toward the knee. Pain originating in the groin is highly suggestive of pathology in or around the hip joint. Pain that radiates to the groin is not typical of hip disease and suggests other pathology, particularly urologic, reproductive, or spinal etiologies.

The average patient thinks hip pain is proximal and lateral thigh pain near the greater trochanter or buttock. The hip joint itself (femoral head articulation with the acetabulum) is well medial to this, and pain should be felt in the groin region, as expected from its anatomic position. If clarification reveals a lateral or buttock origin for the pain, then trochanteric bursitis, neurogenic claudication, sciatica, or sacroiliac joint pathology should be considered.

A recent history of upper respiratory tract (URI) or viral infection in the presence of hip pain would suggest a postinfectious etiology, such as transient synovitis. Transient synovitis is the most common cause of hip pain during childhood, and though most common under 5, it can be seen into late adolescence. The pain is usually worse upon awakening and improves as the day progresses. As opposed to septic arthritis, transient synovitis presents with a mild or absent fever. The treatment for transient synovitis is usually observation as this condition is self-limiting. Note that this is a diagnosis of exclusion and a full work-up for septic arthritis, including aspiration if needed, must be done if there is any doubt.

Recent travel or exposure to wildlife can raise the concern for special cases of septic arthritis. Travel outside the United States can be accompanied by an increased exposure to tuberculosis. Children are more likely than adults to present with extrapulmonary involvement. The most common site of musculoskeletal involvement is the spine, followed by large joints (hip, knee). Exposure to wildlife in the upper Midwest and New England can raise the concern for Lyme disease. Children with Lyme arthritis are usually able to bear weight, and the pain is typically less severe than with typical bacterial arthritis. The target lesion, erythema migrans, if seen or remembered, would lead to careful consideration and treatment for Lyme disease.