Near-complete quadriceps tendon tear

The provided images show a large full-thickness defect within the quadriceps tendon.  The patella tendon is intact and not significantly redundant.  The patient could still slightly leg raise and further imaging with MRI was arranged to further assess.  

MRI confirms a large full-thickness, near-complete quadriceps tendon tear with only a small portion of the vastus lateralis tendon fibres remaining intact.  Fluid decompresses from the knee into the subcutaneous tissues through the full-thickness tear.  

The inability to straight leg raise should raise clinical suspicion of an injury to the extensor mechanism.  Ultrasound can be a useful first investigation, and further care must be taken when scanning those who can still straight leg raise, as partial or near-complete full-thickness tears as shown can present as so. 

Large knee joint effusions can also cause an inability to straight leg raise, and large effusions or haemarthrosis in younger patients should warrant MRI to assess for internal knee injuries.  If a lipohaemarthrosis is identified, both radiographs and CT should be considered.