A 24-year-old man presented with painful swelling over the front and outer aspect of his right knee after an injury when doing a squat in the gym with weights. He distinctly heard a loud “Pop” when the injury occurred. 
He was able to walk but with pain and a limp. He presented to me a day after his injury. Examination showed that he was able to fully extend his right knee and he was able to perform a straight leg raise. This implied that the extensor mechanism of his right knee was still largely intact. A complete rupture of his right knee quadriceps tendon was ruled out. He had focal tenderness over the anterolateral region of his right patella upper pole. There was a suggestion of a divet at that area during palpation. I performed a bed-side ultrasound scan and it suggested an area of tendon discontinuity over the vastus lateralis insertion into the upper pole of the patella. An MRI scan of his right knee was ordered.
Ruptured vastus lateralis tendon of the right knee.
The ruptured vastus lateralis tendon was repaired surgically. 
His right knee was protected with a hinged knee brace for the following 6 weeks. He was allowed partial weight bearing ambulation with crutches for 3 weeks followed by full weight bearing ambulation thereafter. The hinged brace allowed 0 – 30 degrees of knee flexion for the initial 2 weeks and it was gradually increased to full flexion over the following first 6 weeks. 
This is his healed surgical scar. The contour of his muscle is restored. 
He was referred to the physiotherapist to strengthen his right thigh muscles. He was able to do single leg stand and lunges when the strength of his right thigh muscles improved. Isolated vastus lateralis tendon ruptures are rare but a high degree of suspicion and low tolerance to investigate with MRI or ultrasound scans will help prevent missed diagnoses of such injuries.
