Eduardo Rodriguez on 10-day DL with right knee injury. What is a knee subluxation?

Before his start on Thursday, Red Sox lefty Eduardo Rodriguez fell warming up in the bullpen. This is reportedly video of the fall.

What looked like a minor injury has now sent Rodriguez to the 10-day DL and a consultation with Dr. James Andrews.

CSNNE’s Evan Drelich reported that Rodriguez suffered a “knee subluxation.”

According to David Dombrowski, this isn’t the first time that Rodriguez has dealt with an injury like this.

“He tweaked his knee,” Dombrowski said. “It’s the same injury that he’s had in the past basically with his knee and his kneecap movement. So we felt it was the best thing to do.”

The condition that the Red Sox president of baseball operations is referring to is patellar instability. Normally, the knee cap (patella) sits centered in a groove in a person’s femur (thigh bone). As you bend and extend the knee, the patella glides smoothly up and down that groove. Depending on an individual person’s anatomy, some people are more predisposed than others to have the patella drift away from the center of the joint as they bend and extend their knee. This could be due to many things – they may have a shallow groove (trochlea) in their femur, their knee-hip aligment may be such that the quad muscles pull the patella off-course, the tissue stabilizing the knee cap in place may be looser than most people, or the patella may sit too high in the joint.

In this photo from the AAOS patient info website you can see the difference between normal patellar tracking on the top and abnormal tracking in the bottom xrays.


The patellae on the bottom are both subluxated (drifting out of joint but not fully dislocated). In a patellar subluxation the knee cap tends to drift laterally (away from the other knee). Some people’s patellae subluxate every time they bend their knees and this does not always cause pain. In Rodriguez’s case, however, it was a more significant acute injury.

Assuming that Eduardo Rodriguez has abnormal tracking of his patella and that this condition is due to some sort of anatomical predisposition, what can be done to manage it?

In general, our first approach to patellar instability is intensive physical therapy. Athletes work on flexibility and strengthening of muscles to help stabilize the patella as much as possible – basically maximizing what they were born with. Since patellar instability is something Rodriguez has been dealing with for some time, I would assume he has been working with the trainers quite a bit already.

If the patella continues to subluxate, the thick lacquer paint-like cartilage (in light blue on my drawing) which coats both the undersurface of the patella and the surface of the trochlea (groove) begins to thin. This is called patellofemoral osteoarthritis. Patellofemoral osteoarthritis is painful. If the patella has ever dislocated completely, sometimes pieces of that articular cartilage can chip off and float around the joint causing mechanical issues like locking and buckling and this can require a knee arthroscopy where the surgeon inserts a camera and tools into the knee to remove the loose pieces.


If the patella continues to subluxate, surgery can be required to correct the anatomic reason for the patellar instability. One example is called a tibial tubercle osteotomy where the surgeon attempts to correct the angle that the patella is being pulled by the muscles of the thigh by moving the place where the patellar tendon attaches.

What concerns me is that the injury was so minimal – it took a tiny “tweak” in the knee for the knee cap to shift and cause a significant amount of pain and swelling. The injury looked so minimal, in fact, that Rodriguez went ahead and made his start anyway. He didn’t have a terrific performance, but it wasn’t awful. Impressive effort.

There is a chance that Rodriguez will be able to respond enough to conservative treatment like therapy, rest, possibly injections to make it through the rest of the season. Given his history of chronic patellar subluxations and the minimal tweak that caused his most recent injury, however, I suspect surgery to improve the patellar tracking will be necessary at some point. The biggest question for the Red Sox is….when?







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