What is the most likely diagnosis for a 25-year-old active duty male with gradually increasing lower back pain and shin pain after running, which improves with rest?

Most Likely Diagnosis: Medial Tibial Stress Syndrome (Shin Splints)

The most likely diagnosis is medial tibial stress syndrome (MTSS), commonly known as shin splints, with the low back pain representing a secondary musculoskeletal complaint related to the same biomechanical issues or training errors that caused the shin pain. 1

Primary Diagnosis: Medial Tibial Stress Syndrome

Clinical Presentation Matches MTSS

• MTSS presents with diffuse pain along the posteromedial tibial border that develops gradually during running and improves with rest, exactly matching this patient's shin pain pattern 1, 2
• The pain is characteristically described as a dull ache following exercise and is alleviated by rest or sitting down 1
• MTSS occurs in 4% to 20% of athletes who run, making it one of the most common lower leg injuries in this population 2
• The condition results from repetitive stress and cyclic loading during running activities 2

Key Distinguishing Features from Stress Fracture

• MTSS causes diffuse tenderness along the length of the posteromedial tibial shaft, whereas stress fractures cause focal, pinpoint tenderness 3
• MTSS lacks the focal edema typically seen with stress fractures 3
• The gradual onset over 2 miles of running followed by complete resolution with rest for months is more consistent with MTSS than stress fracture 1, 2

Secondary Finding: Concurrent Low Back Pain

Biomechanical Connection

• The low back pain is likely related to the same underlying biomechanical abnormalities causing the shin splints, as overuse injuries often result from issues in the entire kinetic chain 4
• Common contributing factors include muscle imbalances, inflexibility, weakness, and poor running technique that affect multiple body regions simultaneously 4
• Imbalances at the thoracolumbar complex are specifically recognized as contributing factors to shin splints 1

Overuse Injury Pattern

• Both symptoms developed gradually with running and improve with rest, indicating an overuse pattern rather than acute trauma 4
• The patient's recent increase in running activity (running 2 miles) followed by cessation for months fits the classic pattern of overuse injury 3, 5

Risk Factors Present in This Patient

• Young active duty military personnel have significantly elevated risk for lower extremity overuse injuries 5
• Male active duty servicemembers have a stress fracture incidence of 19 per 1,000 during basic training, indicating high susceptibility to lower extremity overuse injuries in this population 5
• Recent increase in physical activity volume is a well-documented risk factor for both MTSS and stress fractures 5, 1

Differential Diagnosis Considerations

Less Likely: Tibial Stress Fracture

• Would present with focal point tenderness rather than diffuse pain 3
• Would show focal edema on examination 3
• Pain would be more severe and less likely to completely resolve with months of rest without treatment 3

Less Likely: Chronic Exertional Compartment Syndrome

• Typically causes tightness and pressure sensation rather than the described pain pattern 4
• Would not explain the concurrent low back pain 4

Less Likely: Axial Spondyloarthritis

• Would present with inflammatory back pain features (morning stiffness >30 minutes, improvement with exercise but not rest, night pain) 6
• This patient's back pain improves with rest and sitting, opposite of inflammatory pattern 6
• Age and presentation do not suggest inflammatory arthropathy 6

Clinical Pitfalls to Avoid

• Do not assume all shin pain in runners is MTSS—always palpate for focal tenderness to rule out stress fracture 3
• Do not ignore the low back pain as unrelated—evaluate the entire kinetic chain for biomechanical abnormalities contributing to both symptoms 4
• Recognize that plain radiographs have low sensitivity early in stress fractures, so if clinical suspicion is high despite negative X-rays, consider MRI 3, 5
• Avoid misdiagnosing this as an acute inflammatory condition—this is a chronic overuse injury requiring activity modification and rehabilitation, not just anti-inflammatory treatment 7, 4