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Carlos Gonzalez, Garrett Richards and patellofemoral injuries

We discuss some of the biomechanical and anatomical factors behind the patellofemoral injuries suffered by Rockies OF Carlos Gonzalez and Angels SP Garrett Richards, as well as their long term effects on performance.

Dustin Bradford (Gonzlaez) and Mark L. Baer - USA TODAY Sports (Richards)

The knee is the most common site of injury in all of sports and accounts for the largest number of sports injury surgeries. Despite this, knee injuries account for a low percentage of baseball injuries, but still have a significant impact, with one study showing them making up roughly seven percent of all disabled list days in MLB over a span of eleven years. Knee injuries tend to be position-specific, with catchers particularly at risk for knee injuries, given the flexion-force relationships that arise from the 30,000-plus instances of squatting they endure during an average season.

While not a catcher, Carlos Gonzalez of the Rockies is no stranger to knee injuries, particularly of the patellofemoral kind. Suffering for most of the season with left knee tendinitis, his condition had worsened to the point where surgery was required, which will have him out until at least spring training. An MRI examination last week prompted shutting down CarGo for the season after a week of rest after it showed further deterioration of the joint, prompting this week's surgery. Quoting Rockies head athletic trainer Keith Dugger, the procedure involved:

...removing a whole bursa that was in there. There was a fat pad that was kind of beat up and tore up, they cleaned it out. And then the middle third of the patella tendon, where the actual diseased tissue was, they cut that out and sewed it back together.

While the MRI results did confirm a tear of Gonzalez' left patellar tendon, it wasn't until surgical exposure that the extent of the injury was truly known, which also included degeneration of a fat pad and one of the three bursa of the knee—fluid-filled sacs that provide reduced friction, allowing for free movement within a joint—as well as the patellar tendinopathy that prompted resection of the middle third of the tendon and repair of the remaining healthy tissue. Deep to the tendon is the aforementioned fat pad, which is highly vascularized and innervated (supplied with neural elements) and can often become inflamed and impinged, causing pain and a decreased range of motion.

Biomechanically, the patella bone (or kneecap) functions as a fulcrum; it increases the moment arm—amount of leverage—of the quadriceps muscles, improving the amount of torque that the muscles can generate. A sesamoid bone, the patella is encased in the patellar tendon, and assists in how much force the tendon can exert on the femur by increasing the angle at which it acts. The patella comes in contact with the trochlea of the femur between 10 to 20 degrees of knee flexion, allowing the tendon to sustain compressive forces at the knee in 90 to 100 degrees of flexion that is as much as 7.6 times body weight.

At full extension of the knee, the patella lies on top of the fat pad, with no articulation—touching—with the femur. As flexion transpires, the patella begins to articulate with the femur, with force transfer undertaken, with maximal bony stability provided at 45 degrees of flexion. With flexion comes increased stress on the quadriceps muscles and the patellar tendon, which is the continuation of their distal common tendon. Over time, these stresses can cause the wear and tear seen in Gonzalez' knee—thickening of the tendon beyond its average of five to seven millimeters is common—as well that seen in the fat pad and bursa. This type of tear is often labeled 'jumper's knee' and is one of three forms of patellar tendon tear. Orthotics, non-steroidal medication, platelet-rich plasma injections, and shock wave treatment among others are courses of action that can be pursued along with rest, stretching, and strengthening exercises of the quadriceps.

When non-surgical approaches are exhausted, surgical debridement and repair of the tendon can be pursued, with studies showing an 82-88 percent return to pre-injury levels on average and a return to play in the three to four month range common, depending upon the position played; however, six months is an oft-cited and more conservative estimate for time until return to play. With CarGo's injury arising from the middle third of the tendon, also called the midsubstance, debridement of the damaged and diseased portion of the tendon was performed with suturing of the two tendon stumps, as well as a check of the maximal flexion possible upon repair. For more severe or chronic injuries, a release of proximal tendon tissue or a placement of allograft tissue could be indicated, as is an additional augmentation procedure, where additional materials—allograft, steel wire, or other forms of reinforcement—are placed around the area to help with strengthening of the tendon.

In terms of baseball activities, the injuries CarGo sustained were felt throughout his game, which is one crowned by a smooth line drive swing that generates a lot of power; this is coupled in the field and on the basepaths with above average speed. The effects of his knee issues was most obvious in his swing, especially in his power, as this .gif of his slugging heat maps of 2013 and each month of 2014 exhibits:


Looking at the injury through the lens of the three hitting phases, the affected left knee, which is the trail leg for a lefthanded hitter like Gonzalez, could rear its ugly head immediately in the preparatory phase, with alterations in the stance—becoming more upright—possibly being seen to alleviate some of the pain arising from fat pad impingement or from inflammation of the tendon when flexing the knees. In the coiling aspect of the preparatory phase, the hitter has a brief shift of weight to the back leg, away from the pitcher, prior to rotation of the torso and pelvis for preload in preparation for acceleration. With these patellofemoral insults, the coiling phase could be interrupted, providing less bat speed and power in the process, due to poor force generation and translation.

In the acceleration phase, the back knee can quickly rotate with the hips for further energy transfer and shifting of weight from the back to front leg; again, an injury to the back knee can become a weak link in the kinetic chain, causing an improper weight shift and energy transfer through hip rotation and into lead leg extension, causing interruptions in timing and a severe drop in power even when contact is made. Follow-through phase can also be affected by patellofemoral insults, with pain arising from the knee shifting from flexion to extension as bodyweight becomes more balanced across both legs in an effort to decelerate the body, post swing.

Similar issues can also be seen while fielding and running the bases, with the importance of knee flexion in assisting hip rotation for explosive and side-to-side movements seen in these efforts; with pain and deterioration of the tendon, the ability to freely initiate sprinting and any quick lateral movements are greatly diminished, with less lower half power generated due to pain guarding and the reduction in moment arm of the quadriceps muscles.

Long term, the procedure will benefit Gonzalez and the Rockies. Already affected by a significant history of lower extremity injuries, the minimization and possible reduction in the chronic effects of his knee tendinitis arising from the repair of the joint will only help return and maintain his lower half strength, which remains a crucial cog in his overall game. While the extended recovery period will be a tough pill to swallow, the ultimate result will be a stronger CarGo, which will allow him to return to his power-hitting ways after a disappointing and light-hitting 2014.

With the diagnosis of the injury sustained by Los Angeles Angels of Anaheim pitcher Garrett Richards finally disclosed as a tear of the left patellar tendon, let's now briefly discuss where his tear differs from CarGo's. To start, there is the immediate aspect of severity delineating the two injuries; Richards' tear occurred in a more traumatic fashion, with the tendon succumbing to some very powerful forces in a moment where his knee was in a biomechanically and anatomically unfavorable position, twisted and bent in an effort to cover first base. As such, his return to action will be a lengthier one, with current estimates of between six to nine months until he returns to baseball activities.

Surgically, the procedures involved will be similar to what was discussed with Gonzalez, with one of the bigger factors determining their disparities being where exactly Richards sustained his tear. More than likely, a complete tear of the tendon was sustained, with the question being whether the avulsion was proximal or distal to the patella. Surgical approaches are essentially the same for either type, with the difference being where suture anchors are placed; in proximal avulsions, they are placed in the inferior pole of the patella and in distal avulsions, they are placed in the tibia.

Looking at the Richards injury from a pitching mechanics perspective, we again find a number of commonalities between it and CarGo's injury, given some of the similarities mechanically between swinging a bat and throwing. However, with Richards being righthanded, his left knee is his lead/non-dominant knee, which will affect his throwing in a slightly different fashion compared to Gonzalez' swing as the left side. Since the injury was both acute and traumatic, we will look at Richards' biomechanics from a postoperative perspective, highlighting the points in his delivery where his knee provides significant contributions.

Starting with the wind-up, the lead leg is important for the initiation of forward momentum in the form of a leg kick of varying amounts of flexion, adduction, and internal rotation of the hip, which entails significant contributions from the quadriceps. Richards shouldn't be affected by the surgery to return to his usual leg kick, but transition from wind-up into acceleration will probably be the most taxing and stressful. At foot contact, the lead leg will accept all of the body weight, with the knee being put to task to provide a fulcrum for pelvic rotation and translation of energy and force from the lower body into the upper extremity. From here, further momentum will be carried into additional rotation, flexion, and adduction as the body decelerates in the follow-through phase, again taxing the patellar tendon. Also to be carefully monitored is Richards' amount of closed contact at foot strike as well and how much knee flexion he will be able to provide at foot strike, allowing him to keep his pitches low in the zone.

The injury to Richards is a devastating one, especially in comparison to the one that felled Gonzalez. While the surgery and recovery involved are not trivial, it appears that the Angels pitcher has an excellent chance of returning to full function, with little to no lingering effects of the insult. His velocity shouldn't be greatly affected, but it might be some time, given the importance of knee flexion in pitching mechanics, before he is able to re-establish command of his pitches.


Data courtesy of Brooks Baseball.

Stuart Wallace is an associate managing editor and writer at Beyond The Box Score. You can follow him on Twitter at @TClippardsSpecs.


Dines, J. S. (2012). Sports medicine of baseball. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.

Miller, M.D. (2011). Operative Techniques in Sports Medicine Surgery. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.