What is the ED diagnosis? The most likely diagnosis?

The ED diagnosis is “low back pain”. The most likely diagnosis is spondylolysis. The patient’s plain-films are normal and in this condition they often will be. Additional imaging, obtained in follow up, is required for definitive diagnosis but not always necessary.

• Pearl: Red flags necessitating emergent imaging in the ED include but are not limited to loss of sensation in the lower extremities, groin, and/or anogenital region; inability to stand; and inability to control bladder or bowel function.

Who is typically affected?

Spondylolysis is a fracture of the pars interarticularis that is most prevalent in adolescent athletes, up to 50% of those presenting with low back pain [1-5]. The L5 is the most commonly fractured of the vertebrae [1-3]. This condition may affect those as young as 6 years old but is most likely to occur during the adolescent growth spurt (between 10-15 years old) [4].

• Pearl: Spondylolysis should always be on your differential for activity-limiting low back pain in an adolescent athlete, especially those participating in gymnastics, weight lifting, wrestling, and football (repetitive lumbar extension sports) [3].

• Pearl: Pars interarticularis injury exists on a spectrum from stress reaction to fracture (spondylolysis) to vertebral slip (spondylolisthesis). Recognition of the diagnosis with proper management can prevent progression [1,3].

What physical exam findings are expected?

Patients may exhibit pain on palpation at the affected spinal level and with performing back extension. The Stork Test (single-legged hyperextension test) is often used to assess this diagnosis [1,2,4]. Patient’s do not typically have gross spinal deformity or neurologic findings on exam. They may have a variety of associated signs/symptoms including but not limited to paraspinal tenderness due to guarding, pain referred to the lower extremities, tight hamstrings and/or hip flexors, weak hip abductors and core musculature, and a posture of lumbar lordosis at baseline [1-4].

• Pearl: The Stork Test (single-legged hyperextension test) is performed by having the patient stand on one leg and lean back into hyperextension at the waist. Provocation of pain is considered a “positive test” and may indicate a pars interarticularis defect on the side ipsilateral to the weight bearing leg. A negative test does not rule out the diagnosis as the overall sensitivity of the test for this diagnosis is particularly low (33%-71% in one study and 52-88% in another) [5-7]. Patients should be tested bilaterally as bilateral pars interarticularis defects are not uncommon.

Which imaging modalities can be used?

In the absence of concerning signs or symptoms on exam, start with weight-bearing plain-films of the lumbar spine. You only need to obtain two views: standing AP and lateral. Lateral oblique views, described as best for viewing the pars interarticularis, are not necessary to obtain as they increase radiation without increasing sensitivity [1,2]. 

If plain-films indicate vertebral slippage or dynamic instability suggestive of spondylolisthesis additional imaging from the ED may be considered but is not always necessary. There is still debate about which imaging is the gold standard, but MRI is becoming very prevalent. CT and SPECT (previously considered gold standard) are still often used in certain cases. MRI is preferable given its ability to detect lesions with high sensitivity (under appropriate imaging protocols) and without radiation exposure in comparison to CT [1,2,4].

Figure 2. MRI of the lumbar spine demonstrating right pars interarticularis fracture of L5. Author’s own media, courtesy of Dr. Andrew Peterson, MD, MSPH.

• Pearl: The “Scottie dog sign” describes the appearance of the posterior vertebral elements on a plain-film oblique view. If the “dog” (posterior elements) appears to be wearing a “collar” (fracture line) around its “neck” (pars interarticularis) spondylolysis is suggested. This finding is rarely seen and its absence should not lower clinical suspicion [8].

Do you need to consult Ortho from the ED? What is the patient’s disposition from the ED?

No, orthopedics does not need to be consulted from the ED unless “red flags” of back pain are present. Referral to sports medicine or PCP is typically appropriate as these rarely require surgical intervention. Patient’s should be instructed to rest from sport and other pain-provocative activities until follow up. 

• Pearl: Patients do not need to be sent with a hard brace or soft corset unless preferred for immobilization such as in younger children who may be less compliant [4].