Differential Diagnosis
Given the patient’s history and physical exam, causes of both posterior hip and low back pain must be considered.
The differential diagnosis of hip pain is broad and can be compartmentalized into both intra-articular and extra-articular causes. Intra-articular causes include a labral tear, femoroacetabular impingement, and osteoarthritis. Extra-articular causes can be subdivided by localization of the pain as either anterior, posterior, or lateral. This patient presented with posterior hip pain. Causes of posterior hip pain include sciatic nerve impingement, sacroiliac joint pathology, tendinopathy, muscle strain, and referred pain from lumbar spinal causes. Additionally, this patient has a history of bilateral THA. Therefore, orthopaedic complications of THA, such as prothesis wear, aseptic loosening, periprosthetic fracture, and leg length discrepancy, must be considered in the differential diagnosis.
The differential diagnosis for low back pain includes lumbosacral muscle strain, lumbar disc herniation, spondylosis, spinal stenosis, fracture, and malignancy. A muscle strain presents following repetitive or excessive use. On physical exam, pain is typically worse with movement, range of motion is limited, and there is tenderness to palpation of the muscles. Lumbar disc herniation occurs when an intervertebral disc exerts pressure on a spinal nerve root causing pain and radiculopathy. This typically presents with neurologic symptoms such as paresthesia, sensory loss, decreased strength, and/or diminished reflexes. Spondylosis, or the arthritic change of the spinal discs and facet joints, presents as back pain with radiation to the buttock and/or thigh along with neurologic deficits in the L5 – S1 spinal nerve root distribution. Lumbar spinal stenosis is the narrowing of the spinal canal, which presents as low back pain relieved by rest. Neurologic exam may be normal or include decreased muscle strength or sensation. Fracture can occur with significant trauma or as a result of a vertebral compression. Physical exam may show focal tenderness on palpation and history may include risk factors such as glucocorticoid use, increased age, and osteoporosis.
Finally, non-orthopaedic causes of posterior hip and low back pain include malignancy and AAA. Due to this patient’s age, malignancy must be a consideration. Patient history may reveal previous malignancy, unexplained weight loss, and/or constitutional symptoms. On physical exam, we would expect focal tenderness to palpation. Additionally, given the patient’s significant cardiac and vascular history, AAA cannot be ruled out without imaging. Unruptured AAA can present as abdominal pain radiating to the flank, back, or groin.
Given the acute nature of the patient’s pain, the HPI, and the findings on physical exam, the leading diagnosis is posterior hip and low back pain likely due to muscle strain and resultant inflammation. Due to the patient’s history of bilateral THA, orthopaedic complications such as prosthetic wear, aseptic loosening, periprosthetic fracture, and leg length discrepancy should not be ruled out without further imaging. Both malignancy and AAA are “Do Not Miss” differentials and must also be ruled out with imaging.