Likely Causes of Unilateral Low Back Pain with Morning Stiffness Improving with Movement 8 Months Post-Injury
This clinical presentation most likely represents mechanical low back pain, specifically from facet joint arthropathy, sacroiliac joint dysfunction, or myofascial pain syndrome, given the characteristic pattern of stiffness that improves with movement and the unilateral distribution. 1, 2
Primary Diagnostic Considerations
Mechanical Causes (Most Likely)
Facet joint pain is a common source of unilateral mechanical low back pain that characteristically worsens with inactivity and improves with movement, fitting this clinical pattern perfectly 3, 2
Sacroiliac joint dysfunction frequently presents as unilateral low back pain with morning stiffness that improves throughout the day with activity 3, 2
Myofascial pain syndrome can persist months after initial injury and typically demonstrates the pattern of stiffness improving with movement 1, 2
Clinical spinal instability may develop after injury, where loss of normal spinal motion patterns causes ongoing pain, particularly with the neutral zone hypothesis suggesting that increased segmental motion contributes to persistent symptoms 4
Less Common but Important Considerations
Inflammatory spondyloarthropathy should be considered when morning stiffness improves with movement, though this typically presents bilaterally and would be unusual 8 months after a specific injury 5
Osteoarthritis of the lumbar spine can cause unilateral symptoms with characteristic morning stiffness, particularly in older patients 5
Red Flag Assessment (Critical to Rule Out)
The American College of Physicians emphasizes screening for serious underlying conditions, though these are unlikely given the clinical timeline 6:
No evidence of cauda equina syndrome (would present with urinary retention, fecal incontinence, saddle anesthesia, or motor deficits at multiple levels) 7, 6
No signs of spinal infection (would include fever, recent infection, IV drug use, or immunocompromised status) 7, 6
No malignancy indicators (history of cancer, unexplained weight loss, failure to improve after 1 month, age >50 years) 7, 6
No progressive neurologic deficits that would warrant urgent imaging 6, 1
Clinical Reasoning
The key diagnostic feature here is pain that improves with movement, which strongly suggests a mechanical rather than inflammatory or infectious etiology 1, 2. The 8-month timeline indicates this has transitioned from acute to chronic mechanical low back pain, as most mechanical episodes resolve within 12 weeks 5.
The unilateral presentation narrows the differential significantly, as conditions like spinal stenosis or discogenic pain typically present more centrally or bilaterally 3, 2.
Diagnostic Approach
Imaging is NOT indicated at this point unless red flags are present, as routine imaging for nonspecific mechanical low back pain does not improve outcomes 6, 1
Physical examination should focus on identifying the specific pain generator through provocative maneuvers for facet joints (extension and rotation), sacroiliac joints (FABER test, Gaenslen's test), and myofascial trigger points 3, 2
Neurological examination should document knee and ankle strength/reflexes, foot dorsiflexion, and sensory distribution to rule out radiculopathy 6
Common Pitfalls
Avoid ordering imaging without red flags, as this does not improve outcomes and may lead to unnecessary interventions 6, 1
Do not assume all chronic back pain requires advanced imaging—mechanical causes are diagnosed clinically in 97% of cases 2
Recognize that psychosocial factors are stronger predictors of outcomes than physical findings, so screening for depression, job dissatisfaction, and passive coping strategies is essential 6