When is a back-of-the-knee pain not a back-of-the-knee problem?

 A case study of an elite sprinter.

 A speed athlete gets a clicking pain in the back of the left knee. It occurs when he approaches top speed and started 2 days after State Championships, where he turned his right ankle in the high jump. He has National championships coming up in a week. 

His SFMA reveals a right ankle with 34 degrees dorsiflexion, compared to his left ankle showing 41 degrees. 
His right tibia has a mobility dysfunction into internal rotation, of 5 degrees, short of the 20 degrees he should have and short of the 20 degrees on the other side. 
His Modified Thomas Test on the right highlights a lower anterior superficial chain mobility problem. 

So far - right ankle, tibio-femoral joint and anterior thigh mobility restriction. 

Left hip flexion mobility dysfunction and posterior lower chain mobility dysfunction. 

Tender proximal calf area. 

I've previously written about why the mobility dysfunctions on one side affect the other side in sprinting - here and here.

Treatment was manual therapy to the anterior lower chain on the right side and tibial rotation. 

Right ankle dorsiflexion restored to 41 degrees. Modified Thomas Test was functional and non-painful. Tibia rotation was restored, as was left hip flexion to 120 degrees (left = right) and active straight leg raise. 

Local laser to the proximal left calf for reduced sensitivity added 10 degrees more passive straight leg raise. 

In a nutshell - a click at high speed to the posterior left knee was driven by right side issues.

For the record, the sprinter ran 0.1s off his personal best the day after this consultation and treatment.