ACL Graft Harvest: Patella Tendon VS Hamstring Tendon
Let's breakdown the difference in the harvest method!
Athletes who wish to get back into sports are often recommended anterior cruciate ligament (ACL) reconstruction surgeries if they have a torn ACL. One of the most common methods is to harvest a piece of your own tissue to replace the torn ACL. The patella tendon and the hamstring tendon are the most common graft choices for such surgery. In this post, we will discuss the difference in graft harvesting methods between these two graft choices. Let’s go!
Anatomical Introduction
Let’s take a closer look at the tendons. The patella tendon is very easy to find; just find your patella (knee cap) and the tibia tubercle (the bony protrusion at the very top of your shinbone), and the space in between those is where your patella tendon lies. Great! What about the hamstring tendon? In the context of ACL reconstruction, we are referring to the tendons of two very specific muscles: the semitendinosus and the gracilis. You can find those tendons pretty easily as well; just sit where you are with your foot planted firmly on the ground, then drag your foot backward. Now, use your fingers to palpate the inner back of your knees. You should be able to feel a prominent structure that feels like a thick cable. That’s your semitendinosus tendon! If you palpate above that strand of tendon, you should be able to feel another strand, and that will be your gracilis tendon. I am sure some of my physio friends would ask this:
What about the sartorius tendon? I thought these 3 tendons insert to the pes anserinus?
An interesting find that I came to know is that the sartorius muscle is shaped like a fascia covering the semitendinosus and gracilis before inserting into the pes anserinus, so technically it doesn’t have a cable-like tendon but more of a flat membrane-like tendon that “protects” the other two tendons underneath. This is why it is not an ideal graft choice for ACL reconstruction; usually, the surgeons just make an incision through the sartorius to find the two other tendons.
Graft Harvest Process
The graft harvesting process for the patella tendon goes like this:
A longitudinal incision from the inferior pole of the patella to the tibial tubercle to expose the patella tendon
2x longitudinal incisions of the patella tendon using a scalpel
Use of an oscillating saw to cut out a piece of patellar bone & tibial bone plugs
Tubularize the harvested graft
TADA you got yourself a patella tendon graft! Such graft is often referred to as a bone-tendon-bone (BTB) graft because, well, it has two small pieces of bone connecting the tendon. The bones have a unique purpose to fulfill later on, which I will explain in the next post. Let’s move on to the hamstring tendon graft harvest!
The graft harvesting process for the hamstring tendon goes like this:
Anteromedial incision at the level of the tibial tubercle to expose the sartorius fascia and pes anserinus
Incision of the sartorius fascia to expose the semitendinosus and gracilis tendons
Trimming of accessory semitendinosus tendons. If not properly done, it may cause the tendon stripper to diverge away from the main tendon, leading to an extremely short harvest!
Harvest both tendons using a tendon stripper (a cylindrical razor). Yes, this means your semitendinosus and gracilis are forever gone :(
Folding and looping to create a thicker graft
Notice that the hamstring grafts are looped because they are way thinner in diameter as compared to the patella tendon. Surgeons can decide the thickness of the patella tendon, but the size of the hamstring tendons is dependent on the host. A study found that there is a 6.8-fold greater relative risk of having a failed ACL reconstruction with graft sizes ⩽ 8 mm in diameter. Hence, the hamstring grafts are often looped to ensure that the diameter is greater than 8mm.
Alright, now that the graft is ready, the surgeons will move on to the fixation of the graft. This part is very technical, but basically, it involves a lot of bone drilling, screwing, and tying. Depending on the type of graft used, the fixation method is different as well. I have pasted the links here if you are interested in the entire process!
Hamstring Tendon ACL Reconstruction Video
Patella Tendon ACL Reconstruction Video
That’s all for now! In the next post, we will discuss in greater detail the differences between the hamstring tendon graft and the patella tendon in terms of functional recovery. Kthxbye!
References:
Figueroa, F., Figueroa, D., & Espregueira-Mendes, J. (2018). Hamstring autograft size importance in anterior cruciate ligament repair surgery. EFORT open reviews, 3(3), 93–97. https://doi.org/10.1302/2058-5241.3.170038