He did not have any traumatic injury, so I had a low suspicion of an injury like a patellar fracture, nor did I suspect a traumatic injury his ACL ligament or meniscus.
He was just starting his growth spurt. Youth athletes are vulnerable to a different class of injuries than adult athletes. The patellar ligament is what I call a structural complex, connecting the lower portion of the knee cap (the inferior pole of the patella) to a small bump on the shin called the tibial tuberosity.
This patellar ligament complex can be injured in different locations, depending on age:
- Age 11-12- at the inferior pole of the patella, an injury called Sinding-Larsen-Johannson syndrome
- Age 13-14- at the tibial tuberosity (where the patellar ligament attaches to the tibia)- called Osgood Schlatter syndrome.
The age ranges for SLJ and OS are approximate, but as a general rule SLJ occurs earlier in adolescence, and the more common OS occurs a few years later. Their timing is based on when the bony processes, called an apophysis, fuses to the rest of the bone.
By late adolescence, the apophyses have fully fused, so we don't see these injuries much by an athlete's late 20s. We may still see irregularities in the bone, but these are remnants of a prior injury, and rarely the cause of injury itself. Instead, in athletes who are past puberty, the most common site of injury is within the patellar ligament itself (usually closer to the patella than the tibial tuberosity), a a condition called patellar tendinopathy, or jumper's knee.
In our clinic at Lake Washington Sports & Spine, Dr. Hyman and I like to use high-resolution musculoskeletal ultrasound to image the patellar ligament complex. Ultrasound is a particularly great imaging tool for assessing tendons, for the following reasons:
1. It has the highest spatial resolution- 5-10 times higher than MRI
2. Real time assessment- it is the only imaging test that adds in actually touching the patient, so we can confirm that the area being imaged is actually painful. This is particularly valuable in rough-and-tumble athletes with a history of prior injuries, to help clarify whether the injury is new
3. Fantastic tissue differential- ultrasound is great at distinguishing between different tissue types
To give an example of an ultrasound image of a patellar-ligament complex injury, the image below is that of Sinding Larsen Johannson syndrome in an 11 year-old elite-level soccer player. The yellow box shows irregularity in the apophysis of the inferior pole of the patella (to help with orientation, left is superior, right is inferior)
Getting back to the 13 year old baseball player, based on his age and pain near the patella, I was anticipating that he may have SLJ syndrome. However, his pain was located higher (on the superolateral portion of his knee cap).
Indeed, as the image below shows, the patella looked pristine in the center, with a smooth cortex
However, when I moved the probe laterally, I could see two disruptions in his cortex
This is a case of what is called a bipartite patella. The superolateral portion of the patella never fused to the remaining part of the patella. The x-ray image below shows the non-union of the bipartite patella, along with the planes of the two images above
How did I use this information clinically:
1. Relative non-use
2. Physical therapy. Particular focus include stretching of the rectus femoris at the hip, since we wanted to limit traction of the quad distally
3. Avoiding NSAIDs. The specific mechanism can interfere with healthy collagen synthesis, essential in this growing athlete
4. Regular icing
This athlete did great, and was able to return to sport in 1 month
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