How to assess a knee tendon rupture?

Assessment of Knee Tendon Rupture

A detailed physical examination with at least two specific tests is essential for diagnosing knee tendon ruptures, including assessment for palpable gaps, decreased strength, and specific functional tests depending on the tendon involved. 1

Initial Clinical Assessment

History

• Obtain information about the mechanism and timing of injury, especially noting high-risk activities such as sports or sudden forceful contractions of the quadriceps against resistance 2
• Identify risk factors including prior injuries to the extensor mechanism, systemic illnesses, or use of corticosteroids that may weaken tendons 2
• Note any inability to bear weight, which is a key clinical indicator of severe injury 1

Physical Examination for Patellar Tendon Rupture

• Look for a palpable defect or gap in the substance of the tendon 2
• Test for inability to completely extend the knee against gravity 2
• Assess for high-riding patella (patella alta), which is a hallmark diagnostic sign 3
• Evaluate for decreased knee extension strength 1

Physical Examination for Quadriceps Tendon Rupture

• Check for a palpable suprapatellar gap 4
• Test active knee extension against gravity 4
• Assess for extensor mechanism deficit by having the patient attempt to straight leg raise 4

Diagnostic Testing

Radiographic Assessment

• Initial evaluation should include anteroposterior and lateral radiographs of the affected knee 1
• On lateral view, look for patella alta (high-riding patella) in patellar tendon ruptures, which can be confirmed by calculating the Insall-Salvati ratio 3
• Radiographs should be the initial imaging modality for patients with focal tenderness and/or inability to bear weight 1

Advanced Imaging

• While the ACR Appropriateness Criteria does not routinely recommend MRI as an initial imaging study for acute knee trauma 1, it may be useful in cases where:
  • The diagnosis is uncertain despite clinical examination 1
  • There is suspicion of associated intra-articular injuries 2
  • The rupture is neglected or chronic 2
• Ultrasound can be helpful but has limited evidence supporting routine use 1

Special Considerations

Diagnostic Pitfalls

• Excessive swelling and pain can limit examination up to 48 hours after injury, potentially masking the diagnosis 1
• Partial tears may be difficult to distinguish from complete ruptures in the acute setting, making re-examination after 3-5 days important 1
• Patients with systemic conditions (diabetes, osteogenesis imperfecta) or history of Osgood-Schlatter disease may be at higher risk for tendon ruptures 3

Timing of Treatment

• Early diagnosis is critical as the prognosis after tendon rupture depends largely on the interval between injury and repair 2
• Delayed diagnosis can lead to compromised outcomes including loss of knee flexion and decreased quadriceps strength 2

Management Approach

• Acute repair is preferred for optimal functional outcomes 4
• Surgical techniques vary based on the location of rupture (midsubstance vs. insertion) 3
• Rehabilitation protocols generally allow immediate weight-bearing with the knee locked in extension, followed by progressive range of motion exercises 4

By following this systematic approach to assessment, clinicians can accurately diagnose knee tendon ruptures and facilitate timely treatment to optimize patient outcomes.