Category Archives for Patellar Instability

Tibial Tubercle Transfer

By Tibial Tubercle Osteotomy (TTO) the insertion site of the ligamentum patella on the tibia is moved either inwards or down causing a more aligned traction of the patella.

If your Patella is placed to high in relation to the groove (Patella alta), the Tibia Tubercle Transposition can bring your Patella downwards into the groove. If the Tibial Tubercle is outward placed, your Patella tends to track outwards and by medialization (moving inwards), your patella will track more correctly. The surgery should only be performed if you are having either an increased TT-TG or an decreased cartilage overlap between the patella and the trochlea groove (less than 6 mm) - read more here. A little variation of this surgery is called Fulkerson osteotomy and this can be used for a special group of patients having anterior knee pain caused by osteoarthritis in the Patellofemoral joint.

As it appears from the picture at left, the Tibial Tubercle is chiseled off and moved inwards. The bone block is fixated again by 2 - 4 screws.

This demonstrate a Patella Alta - meaning a high riding kneecap

The distalisation of the tibial tubercle have brought the patella into the trochlear groove

Trochleoplasty – The arthroscopic version

This page is about the Trochleoplasty or Grooveplasty operation. This surgery deepen the groove in which the kneecap glides. Noteworthy the surgery can be done by arthroscopic technique. 


First of all sorry for this awful word trochleoplasty, however there is no simple word to better explain it. Maybe Grooveplasty would be a better term - if you have a better suggestion please do not hesitate to contact me. Trochleoplasty is a surgery for the Trochlear groove, a groove that helps the kneecap (the Patella) to stay in place. By this surgery a new and a deeper groove is created to normalize your anatomy. 

Why am I going to have a groove operation?

If you are troubled by unstable kneecap or chronic anterior knee pain, you might also have an abnormal groove. This means that the groove for your kneecap is more shallow than normal or it can be even flat or convex. In short, when your knee groove is too shallow, this tends to make you kneecap unstable. It basically means that it might either go half the way out (called subluxation) or it even dislocate. The condition of having a shallow groove is called trochlear dysplasia or dysplastic trochlea (abnormal groove). In these cases were you groove is flat, this operation called trochleoplasty, is the best option for you.

If you have a shallow groove

We know when your groove is shallow or flat, it is a result of too much bone in the center of the groove. This basically means that you have too little bony support for the kneecap. 

The Surgery 

The principle of the groove surgery is basically to deepen the groove. First is the cartilage released from the groove. Subsequently excessive bone is removed. This is followed by creation of an outer bony wall to support the patella. After that, when the groove has been deepened and re-shaped, the cartilage is re-located by means of a special blue or white bands. Those tapes or bands are later resolved. You can find picture examples by the images below. Certainly the groove operation is, from a mechanical point of view, the most anatomically correct operation to perform, if you have an abnormal groove.


After having invented the technique, I started out 12 years ago doing arthroscopic deepening trochleoplasty procedures. I used to do the groove procedure openly by the Bereiter method. I have stopped to do the open surgery. since it leaves a bigger scar, and in addition it is more painful and I believe that I can obtain better results by doing it arthroscopic in most situations.  

More about the groove surgery

By using the pinhole technique (arthroscopic), consequently the surgery becomes less traumatic for your knee , and therefore the rehabilitation is likely to become accelerated. To notice is the groove operation mostly done in combination with a reconstruction of the inner ligament for the kneecap (MPFL reconstruction).

Why go for arthroscopic trochleoplasty instead of open trochleoplasty?

By using the pinhole technique (arthroscopic), consequently the surgery becomes less traumatic for your knee , and I have had no case of excessive scar tissue (arthrofibrosis). Doing open trochleoplasty it´s a well known risk - read more here 

Why also MPFL reconstruction?

Why is the groove surgery not enough? And why should you also have reconstructed the MFPL? (mediale patellofemoral ligament = inner ligament for kneecap). That is first of all because the MPFL is always torn when the kneecap dislocate. It does not heal normally and therefore it has to be reconstructed. Moreover it also so, that the trochlear groove, do not provide stability to your kneecap, before the kneecap reach the trochlea. Importantly this first happens after your knee is bend about 20 degrees. This means that the MPFL is needed to provides stability to your kneecap from full straightened knee and until your kneecap reach the new groove at 20 degrees of bending. Read more about MPFL reconstruction here

Arthroscopic trochleoplasty and no MPFL reconstruction. 

If you problem is chronic anterior knee pain as a consequence of a too shallow groove, and your kneecap is stable, likewise you do not need to have the ligament to stabilize the kneecap reconstructed - eventually read more in the page about anterior knee pain.

After surgery 

You are allowed full weight bearing and free range of movement, immediately after your surgery. There will not be applied any brace, but you will need crutches for approximately 3 weeks. You will only stay in hospital for approx 6 hours. Some have traveled 2000 km back home just after surgery.  Normally you start physiotherapy within 3 to 10 days after surgery. Some might think this rehabilitation regime sounds a little scary, however it have proved itself for more than ten years without any problems.

I am Lars Blond pioneer on the arthroscopic trochleoplasty. Eventually go to the front page or read my CV or download scientific papers

Trochleoplasty by pinholes = Arthroscopic Trochleoplasty

Patients have been coming from abroad to undergo the surgery. In addition I travel to where you live.

Until now I have operated patients from 13 different countries:


In case you would like a second opinion regarding your MRI or just your general knee situation, I do Zoom consultations. The cost is 175 euro. E-mail [email protected]


You can eventually go to Facebook. Check out either "Lars Blond + Trochleoplasty" or just "Trochleoplasty". Here you can notice more details and recent updates

Originally the company Arthrex helped me to develop the technique have now also produced at video in 4K quality - see it here

Arthrex is also the company that help other surgeons to learn the technique. Regularly I teach other surgeons in Arthrex Lab in Munich or I am send by Arthrex abroad to help surgeon to do their first cases.


Eventually read what some patients says in the testimonial page - or see this Youtube video called trochleoplasty gathering (Danish language but English text)


What does KneeGuru say about arthroscopic trochleoplasty? - Read here


When are you too old for this? No one know, however the trochlea cartilage have to be fairly okay, without too huge defects. The oldest one I have successfully operated was 57 years.  The youngest was 12 years.

New interesting paper for ordinary people

Latest paper about arthroscopic trochleoplasty from 2021

Research Outreach article - click here

Trochleoplasty surgery cost

The price for an isolated arthroscopic deepening trochleoplasty is approximately 9.000 euro

Patient from abroad

I have operated many patients from abroad (13 different countries and as far away as Hawaii) Some patients are willing to give advices in respect to travelling, accommodation, physiotherapy and rehabilitation etc. 

Frequently asked questions:
  • The surgery typically last 1½- 2½ hours.
  • When can you fly back? This depends on the distance but this is from 1 to 10 days. A seat with the possibility to straighten the leg is needed.
  • Crutches are used for 2-4 weeks - with huge individual differences
  • No brace is needed after this type of surgery and full weight bearing is allowed
  • Some think - should I start with one type of minor surgery and if I do not work, then try another surgery - I my view only one surgery should be necessary if the right one is done from the start.
  • Only one knee is operated (in one out of three both knees are involved)
  • How long is the recovery?
    The knee will improve the first one or two years and will be fairly okay after 3 month.

More freguently asked questions:
  • When can I return to sport or job - this has very huge individual differences and if you have an sedentary job it is about 4 weeks and lighter sports is after approx. 3 month
  • Will my insurance pay? Normally they will pay for the surgery and travelling expences (still cheaper than similar surgery in US)
  • The price for a Skype consultation incl evaluation of MRI? 175 Euro.
    MRI scans can be posted by mail, by Dropbox or or similar (E-mail: [email protected])
  • The price for combined arthroscopic trochleoplasty and MPFL reconstruction is approx. 11000 euro incl implants (implant cost alone is 2000 euro)
  • For physiotherapy and exercises Physiotherapist Dorte Nielsen ( has a huge experience of training patients troubled by patellar instability, and has seen several patients after arthroscopic trochleoplasty. Dorte Nielsen has uploaded videos on YouTube.
About Aleris Hospital

Aleris Hospital is the largest private hospital in Denmark with 10 operating rooms and has very high safety. A rate of infection close to zero and with high cleanliness and has undergone accreditation after the highest international standards and use the latest technologies. All doctors are experienced doctors. All personnel speaks English.

Rehabilitation protocol after Arthroscopic Trochleoplasty and MPFL reconstruction - by Dorte Nielsen

Rehabilitation trochleoplasty
Example of an "Arthroscopic Deepening Trochleoplasty".

Before (left) and after (right). The blue band dissolves after 6 weeks and is therefore only temporary until the cartilage has healed.

MRI before (left) and after (right)
Trochlea before and and after the groove surgery 

- "It is difficult to balance a tennis ball on a football"

Second look

Two different examples of how it looks in-site the knee 3 months after a groove surgery. If you notice has the cartilage healed very nicely and blue bands/tapes are dissolved.

Second look - 3 years after

Illustration showing the tapes in place after arthroscopic trochleoplasty

Nice small scars after combined arthroscopic trochleoplasty and MFPL reconstruction

The scars after Arthroscopic Trochleoplasty and reconstruction of the medial patellofemoral ligament eight weeks postoperatively

Eight weeks after the surgery and the scars will become much more nice over time. I recommend you to use tape in the first month after surgery, since this will reduce traction in the scars. Hence you can avoid that the scars becomes wide.

Video arthroscopic trochleoplasty

Kenneth doing well one year after

Why should I also have a groove surgery and not just MPFL reconstruction?

That is a good question and some surgeon argue that it is not necessary. Maybe it is not 100% necessary if you just want stability, but if you also want a knee without anterior knee pain, trochleoplasty have to be done. Also, sometimes I see patients having trochlear dysplasia and who have had an MPFL reconstruction only. Then after some years the kneecap starts to becomes loose again because the MPFL reconstruction get loose by time. Therefore if you visit a surgeons, who do not do trochleoplasty surgery, and you do have this flatt groove. Most importantly try to get a second opinion in case this surgeon tells you that the surgery is rare, dangerous and complicated surgery since this is not correct. 

Case Study - Mikkel

Mikkel was the first patient who was operated upon with an Arthroscopic Trochleoplasty, and this was back in March 2008. Previously he had unsuccessful kneecap-stabilizing surgery and by doctor and physiotherapist he was told that he would never be able to sports again. Most noteworthy Mikkel had been troubled in both his knee since he was 8 years old and had never been able to run. Finally he underwent surgery on both his knees with the groove surgery at 29 years old. Meaning 21 years without running. 

Follow-up on Mikkel

Today is Mikkel doing well in his knees and he is running and playing soccer. He claims that the only annoyance is the sound from the knees, when he climbs stairs. Go to YouTube and listen to his and other stories during the trochleoplasty gathering in 2014. Many thanks to Asker Blønd - my son - who created this video. Click here trochleoplasty gathering.or check this video

Outcome after trochleoplasty

Generally the outcomes after groove surgery is very good, with less than 2 percent new dislocations. Consequently is the quality of life dramatically better. I have followed all my arthroscopic trochleoplasty patients for now more than 10 years and in average there as been improvements in all measured parameters and high satisfaction.  Both the technique and the results of this operation, have been published in peer reviewed journals. Today I have presented "The Arthroscopic Deepening Trochleoplasty" technique in the United States, Japan, Netherlands, UK, Sweden, Norway, Poland, Germany, Austria, Portugal and China. Moreover has the surgery been adopted by other surgeons and is now performed in ten differnet countries world wide.

Tibial Tubercle Transfer =TT?

What about having a TT osteotomy instead of a groove surgery? The fact is that no surgeon know what exactly what is best since the science has not yet given a final answer to that question. However is there many indications that the groove surgery gives better results. In addition we know that trochleoplasty surgery normalize the anatomy. Moreover does we know that patients, who have had TT surgery after a decade are having declining results. The first trochleoplasty patients I operated more than 13 years ago are still doing fine. So based on this and my clinical experience by doing both many tibial tubercle osteotomies an trochleoplasty surgeries, I prefer to do trochleoplasty if you are having severe trochlear dysplasia.

Here is the latest paper on arthroscopic deepening trochleoplasty here or simply go the page where you can find all my scientific papers

Comments on LinkedIn 2018 and more than 5000 views

Photo library with some examples of arthrocopic trochleoplasty

Patellar Instability Overview

Patellar instability overview

A lax kneecap is a common disorder, and in the following text and subpages you can learn about this problem. Naturally it is not necessary for you to know everything there is to know in order to get treatment. However if you are a person that want to take responsibility and ask the surgeon, key questions read more.
Symptoms of unstable kneecap

For some patients with kneecap laxity the kneecap will goes out once and they will experience no further problems. Others, however, may go on to experience repeated dislocations. If the kneecap has gone out more than once, it will have a tendency to out again and again. Then things may become quite disabling. The problem can occur while doing activities, like changing direction such as in sport or dancing. For others the kneecap just seems to go out without much provocation. This can happen while walking on uneven or slippery surfaces. In some of the worst cases you need to concentrate on avoiding the kneecap popping out the groove while kneeling. In some it can be a problem while jumping in and out of a car or even during sexual activity. 

Quality of life

Your quality of life can be significantly affected, since a lot of simple daily activities must be avoided. Sometimes your disorder also might cause pain during daily life. It is very important if you are going for surgery to rule out what cause your instabiliy. Your surgery should correct the identified abnormality (or abnormalities, since there may be several factors involved).

Why me?

It is very important to find out why your kneecap dislocated. This is since you can undergo so many treatments and in order for you to have the right one, this have to be examined. This is rather complicated. I have made a site only for explaining this in order for you to ask you surgeon the critical questions - click here

The many myths

Many myths exist about loose kneecap, and one is that you will grow out of it. Mostly this disorder is worse during the teenage years. Then you learn to be more cautious and reduce your level of activity. There is furthermore a tendency for the joint to get less flexible as you age and this helps the kneecap to stay in the groove. So many grownups do not actually grow out of the condition, but they just learn to avoid the activities that provoke the dislocation.

It is just going to be trained away

Another myth is that the disorder just needs to be trained away. This is only partially true. Some may perhaps be able to avoid surgery by learning to use their knee in a more correct way. This can be via physiotherapy and by strengthening the quadriceps and gluteal muscles. A special brace that supports the kneecap can stabilize the patella. There is yet no scientific documentation that say that physiotherapy can prevent further dislocations

Easy to treat - you just need a MPFL reconstruction

The next myth is that surgery can easily treat the disorder. A significant number of patients undergo surgery only to experience that the surgery did not work as intended. As previously mentioned, is of importance to explore the reason why the kneecap dislocates. I suggest that you as a minimum have an MRI can. Then your surgery can be individualized and thereby work efficiently.

It is hereditarily

The next myth is this disorder is inherited. Actually this is true in several cases, and sometimes a dislodged kneecap can be traced back several generations. Especially if you have trochlear dysplasia.

Sorry you surgery did not work

A further myth is that if you had once undergone surgery, and it did not work, that you just need to live with it. Unfortunately this is a disorder where many patient have undergone surgery using an insufficient method. This explains why it did not help or maybe even worsened the situation. Knowledge about this disorder has changed radically over recent years. If the right surgery is done, there is a very good chance for your knee to become significantly better.

What happens when the kneecap dislocate

When the kneecap jumps out it is naturally a very unpleasant experience. Often the kneecap has to be manipulated back at the emergency department. The first time the kneecap dislocates, a ligament on the inner side is torn. This is called the Medial Patellofemoral ligament or just MPFL. Such an injury causes a lot of pain and swelling. Sometimes a fragment of the knee cartilage is loosened. In some cases a loosened piece of cartilage requires surgery to fix the piece back in place or to remove it.

How much will I get troubled?

For those troubled by a continuously loose kneecap there will be a huge variability how much distress this actually causing. However questionnaires have been developed to help both patient and surgeon to elucidate the extent of the problem. Please see an example of a questionnaire here. As previously mentioned is it not always that the kneecap jumps out again. Nevertheless it can still be very troublesome since you may experience that it nearly jumps out. This is called subluxation.

The treatment of loose kneecap

The very first time the kneecap goes out, the treatment is likely to just consist of rest, ice, compression and elevation (RICE). You should be allowed full weightbearing and full range of movement. In past years a brace for support and immobilisation was generally used. Recent research has shown that it does not have any real impact. If the knee does not get the stability wanted and the kneecap continuously is feeling loose, a kneecap stabilizing brace or surgery should be considered. Physiotherapy has also been an important part of the treatment in improving muscle balance. Still we need studies that demonstrate that it has a positive effect. Please read more about surgery here; MPFL reconstruction - Tibia tubercle osteotomy - Trochleoplasty - Rotational osteotomy

The many names for unstable kneecap

The condition of a loose kneecap has many names and here you can learn more about: dislocating kneecap, kneecap out of its groove, kneecap out of its socket, kneecap malalignment, slipped kneecap, jiggly kneecap, unstable kneecap, recurrent patellar instability, episodic patellar instability, luxating patella, unstable patella...

The condition of a loose kneecap has many names and here you can learn more about: Dislocating kneecap, kneecap out of groove, kneecap out of socket, kneecap malalignment, slipped kneecap, jiggly kneecap, unstable kneecap, recurrent patellar instability, episodic patellar instability, luxating patella, unstable patella

Dislocating Patella

Unstable kneecap is a common disorder and here you can read more about why your kneecap has become unstable.

For some patients it happens once in a lifetime and after that they have no problems.

For others the kneecap continuously dislocates or subluxate. If the kneecap has been dislocated more than once, it tends to become dislocated again and again, and then of course it becomes quite troublesome. Here you can read more about why you kneecap becomes unstable
Loose kneecap

Dislocating patella is when the kneecap pops all the way out. Sometimes it just goes half the way and you the call it a subluxating kneecap. I recommend you to either before or after having read this - go to the section Patellar Instability overview.

Why does the kneecap dislocate?

There are many reasons why the kneecap becomes unstable and the four most important will be explained beneath. Some very complicated words are involved like Trochlear Dysplasia, Patella Alta, Increased TT-TG distance and increased Femoral Antetorsion, but as said this will be explained. Occasionally the kneecap is struck by a foot or something else on the inner side so hard that it pushes the kneecap out, but mostly it is a sudden twist or turn that makes the kneecap go out.

Here you can download a PDF file from a Webinar

Here you can see and listen to the Webinar - Link

Flat groove - Trochlear Dysplasia

 The most common reason for the kneecap to dislocate is that the groove (trochlea) which patella runs in when the knee is bent is either shallow, not deep enough, or dome shaped (this is called trochlear dysplasia and there is a section only for this). If the kneecap is not contained (kept in place in the groove), the patella will have a tendency to jump out, to the outside of the knee. Among those who have experienced the first kneecap dislocation and who have a shallow groove (trochlear dysplasia) two-thirds will experience another dislocation. If you have a normal groove, in contrast, the risk will only be one-third.

Why the trochlear groove is flat is that it for unknown reasons at birth it is filled with too much bone underneath the cartilage.

3D reconstructions of a normal knee to the left and a knee with a shallow groove on the right.
MRI demonstrating two different knees. On the left it is normal and on the right the groove for the kneecap is missing (Dysplastic)
Patella Alta

Patella Alta means that the patella is too high and this is an important factor for loose kneecap. If the patella is too high there is a huge risk that, at the point where it should locate itself in the groove, it will instead go to the outer side of the groove, and dislocate. Below you can see an MRI scan with a high riding kneecap.

MRI and Patella Alta

High kneecap

Distalisation of the Tibial Turbercle for normalizing anatomy

Distalisation Tibial Turbercle
Increased TT-TG distance

Increased TT-TG distance means that the Tibial Tubercle is unusually far to the outer side of the shinbone and that causes the kneecap to track outwards. This will give a tendency to pull the kneecap out of the groove and thereby dislocate or subluxate. Often the increased TT-TG distance is caused by Trochlear Dysplasia since this makes the groove go towards the inner side (yes it is right inner side and that makes the TT-TG distance increase). In those cases where the Tibial Tubercle is rotated outwards, the treatment will consist of a Tibial Tubercle Osteotomy

Increased TT-TG distance
Trochlear dysplasia

This demonstrates and axial view on CT scan or MRI scan were both the Trochlear Groove (TG) and the Tibial Tubercle (TT) are visualised. The distance between those is normally close to 9 mm - if it is above 20 mm it is far to high.

Increased Femoral Antetorsion

In some cases the patella dislocates secondary to a malrotated hip which makes the knee go inwards (increased anteversion of the femur). By clinical examination this can be suspected and in these cases a CT or MRI scan can confirm the diagnosis. The malrotation can be corrected by a femoral rotational osteotomy. Beneath you see a figure demonstrating a left femur with severe increased internal rotation, causing the patella to dislocate. The patient had previously had a failed MPFL reconstruction. She responded very well to a combined femoral rotational osteotomy and a revision MPFL, and her pain resolved completely when the internal fixation device was removed a year after.

Typically the kneecap dislocate doing activities with changing direction, such as sports or dance. In others, it feels as if the kneecap is coming out just by walking on uneven surfaces. At worst you should concentrate if not kneecap is out of joint when doing squat or getting into and out of a car. Quality of life can be significantly affected because it discourages one from many activities.


First myth

It is a myth that it is easy to deal with by doing an operation. Quite a few patients have been operated unsuccessfully, and some even several times. It is therefore important to find the true cause of the kneecap is out of joint. Always do an MRI scan and sometimes X-rays as well. Then the operation can be individualized in order to reestablish normal anatomy. Then the operation will be effective.

Second myth

Another myth is that it is hereditary and this is in fact often not a myth, but it can be true. Sometimes dislocating kneecap can be traced several generations back.

Third myth

The next myth is that you just have to live with the problem, if it is the case that you already had surgery and the surgery has not worked as intended. Knowledge about the cause of the disorder and the treatment of it has changed radically over the last few years.