TTO – Tibal Tubercle Osteotomy

In TTO (patellar tendon attachment surgery), the attachment is moved on the tibia to change the direction of pull of the kneecap. There are 2 different kinds. Typically, it is moved downwards so that a kneecap that sits too high is brought down into the groove of the kneecap. It can also be moved inwards if it is too far out. (and sometimes forward to unload) 

Relocation of patellar tendon attachment because the attachment is too far out

Tibial tubercle osteotomy (mTTO) with inward relocation (medialization). This type of surgery was once widely used for patients with loose patella or anterior knee pain. The idea was that if the kneecap attachment is too far out on the tibia, the direction of pull is wrong. It was thought that if the kneecap was moving too far, it might be a good idea to undergo this type of surgery. Unfortunately, it turned out to be as good as we thought and the surgery should rarely be performed – read more at the bottom of the page. 

Patient information leaflet TTO – tendon attachment transfer

Relocation of patellar tendon attachment because the kneecap is too high riding

If the kneecap sits too high in relation to the furrow (it’s called patella alta), then the kneecap can be pulled down into the furrow (it’s called distalization tuberositas tibia osteotomy – dTTO). This type of surgery has proven to give excellent results if performed correctly and against the right background. The surgeon can see on an MRI scan whether the overlap between the cartilage of the kneecap and the cartilage of the groove is in sufficient. If the kneecap sits too high, the overlap is too small (6 mm or less). 

When is the kneecap too high?

Unfortunately, there is no consensus on how to assess whether a kneecap is too high. This means that some people undergo surgery for an elevated kneecap who don’t have the condition and vice versa. In 1971, the Insall-Salvati index method for describing kneecap height was described and in 1982 the Caton-Dechamps Index method and many more. These methods are based on X-rays and not MRI scans, which is what we use today. Unfortunately, it has been proven that if you use the old measurement methods, some people are operated on the wrong basis and have the kneecap moved too far down and get a stiff knee (believe me, I regular see those patients from elsevier). Today we look at the overlap between the cartilage on the patella and the cartilage in the groove of the kneecap – you can read more about elevated kneecap here. It takes many years to implement a new practice. In 2006, the overlap was described, but it hasn’t caught on everywhere yet. You should therefore be critical of your surgeon and request how your protruding kneecap has been assessed. Many surgeons just read what the radiologist has described in your MRI scan report and unfortunately many radiologists are not updated on this issue.

Distalization of the tibial tuberosity (dTTO) that brings the kneecap into the furrow. The kneecaps attachment (Tibial tubercle) is moved downwards and fixed with 4 thin titanium screws. Called a tibial tubercle ostetomy – TTO This was a patient with anterior knee pain due to patella alta who was successfully operated on. The screws usually stay in place for life, but can be removed. Screw heads are so small and they become countersunk, so it’s rare to need to remove the screws again.

This illustrates the technique used to move the patellar tendon attachment downwards when there is a raised patella, also called patella alta, in patients with either anterior knee pain or loose patella. The light blue is to illustrate the cartilage.

The kneecap is loose

If the kneecap attachment is moved because the kneecap is too loose, an  MPFL reconstruction is also performed. In addition, arthroscopic knee surgery is always performed (through a scope). A slightly different version of this surgery is called Fulkerson’s surgery and it can be used in a special subset of patients with anterior knee pain.

Anterior knee pain

Sometimes the patellar tendon attachment is moved because the kneecap is misaligned in its groove. This can cause pain, which is why surgery may be a good option. This type of surgery is often performed in combination with lateral retinaculum lengthening. You can read more here. A slightly different version of the patellofemoral tendon attachment surgery is called Fulkerson’s surgery and can be used in a special subgroup of patients with incipient osteoarthritis in the joint between the kneecap and the patella and with anterior knee pain.

Relocation of the patellar tendon attachment

Disadvantages of this option are as follows. Firstly, some small nerves that run across the scar in front of the patellar tendon attachment are cut. This causes altered sensation in the area. However, this can normalize over time. On the other hand, the screws that attach the patellar tendon attachment can sometimes interfere with kneeling. In the worst case scenario, the patellar tendon attachment does not heal. However, it is rare but can be seen in smokers.

A little science on the subject

As shown in the image on the left, the patellar tendon attachment is chiseled off and moved further inwards. The bone block is screwed back into place with 2 screws. This type of surgery is rarely performed today as it has been shown not to alleviate the problems.

Complications of patellar tendon relocation

Unfortunately, not everyone that achived a good result from this type of surgery. If you have had surgery for a loose kneecap, unfortunately, some people find that the kneecap remains loose, and for those who have surgery for anterior knee pain, only 2 out of 3 are satisfied, although the results for those who have the patellar tendon attachment moved downwards due to a too high shell have a significantly higher success rate. Unfortunately, complications occur in a few percent of cases. There may be pain and numbness over the operated patellar tendon attachment, in some people the bone block does not heal and some develop infection (though I have never had the latter complication). Some people experience sensory disturbances across the patellar tendon attachment and some experience discomfort when kneeling – however, this is very rare if 4 small-headed screws are used instead of 2 large-headed screws.

Why not TTO where the patellar tendon attachment is moved inwards?

Many surgeons treat Trochlear Dysplasia with TTO (Tibial Tubercle Osteotomy). There are basically two types of TTO and the most common has been TTO medialization, where the patellar tendon attachment is moved inwards. The second type is TTO distalization, where the patellar attachment is moved downwards. When TTO medialization is performed, it is to provide a pull in the patella that is more inward. It sounds logical that it should be effective, but unfortunately it’s not. It is an anatomically incorrect operation. It doesn’t solve the underlying problem, which is that the groove is flat. Often a measure called TT-TG distance is used to assess whether TTO should be performed. Previously it was said that if TT-TG was over 15 mm you should perform TTO medialization. Then came a study that showed that it didn’t help anything. then it was said that if the TT-TG had to be over 20 mm, but now it turns out that this doesn’t make any difference either click here to view the survey. Some say that if you perform trochleoplasty there is a risk of developing osteoarthritis and therefore TTO is better. In fact, it’s the other way around because trochleoplasty does not cause osteoarthritis click here. TTO causes osteoarthritis Click here.