Category Archives for Patellar Instability

Tibial Tubercle Transfer

By Tibial Tubercle Transfer osteotomy the insertion site (Tibial Tubecle) 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 increased Patellotrochlear index - 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 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

Arthroscopic Trochleoplasty

This page is about the Trochleoplasty operation. This surgery create or deepen the groove in which the kneecap glides. Noteworthy the surgery can be done by arthroscopic technique and you can read more below. Though once the Arthroscopic trochleoplasty was considered experimental surgery, it is now done routinely in nine different countries.


Trochleoplasty is a surgery for the Trochlear groove, a groove that helps the kneecap, also called the Patella to stay in place. By this surgery a new and deeper groove is created to normalize anatomy. 

Why am I going to have a trochleoplasty operation?

So if you are troubled by unstable kneecap or chronic anterior knee pain, you might also have trochlear dysplasia (flatt groove). This means that a trochleoplasty operation may be the best option for you.

If you have Trochlear Dysplasia

As mentioned in the section on "Why the kneecap dislocate?" this procedure can be relevant for you. This is if your groove for the kneecap is filled up with too much bone, also called Trochlear Dysplasia (flat or shallow groove). This basically means that you have to little bony support for the Patella, and therefore it tends to pop out. 

The Surgery 

The principle of trochleoplasty is to release the cartilage from the trochlea, and to remove the excessive bone and to create an outer wall to support the patella. So when the trochlear groove has been deepened, the cartilage is finally re-located by means of a resorbable bands. You can find examples by the images below. Certainly the trochleoplasty operation is, from a mechanical point of view, the most anatomically correct operation to perform if you have trochlear dysplasia.


Since 2008 I have done more than 100 arthroscopic deepening trochleoplasty procedures. I used to do the trochleoplasty procedure open, but I have stopped this, since it leaves a bigger scar, it is more painful and less risky. For open trochleoplasty I started out in 2005.

More about the Arthroscopic Trochleoplasty

Arthroscopic trochleoplasty technique is less traumatic for your knee , and this means that the rehabilitation is likely to be more accelerated. Just to let you know, then the Arthroscopic trochleoplasty operation is nearly always performed in combination with a MPFL reconstruction.

Why also MPFL reconstruction / MPFL-R?

Why should you also have reconstructed the MFPL (mediale patellofemoral ligament) when you do the trochleoplasty? Because first of all is the MPFL always torn when the kneecap dislocate and therefore it has to be reconstructed. Moreover it also so, that the trochlear ground , do not provide stability to your kneecap, before the kneecap reach the trochlea and 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. Hence you need to have both operations simultaneous. In contrast if you problem is chronic anterior knee pain and trochlear dysplasia, here is the patella stable, and therefore you do not need to have the ligament reconstructed - eventually read more in the page about anterior knee pain.

Read more about MPFL reconstruction here

I am Lars Blond an inventor of the arthroscopic trochleoplasty - eventually go to the front page or read my CV or download scientific papers

Trochleoplasty by pinholes = Arthroscopic Trochleoplasty

Patients are coming from abroad to undergo arthroscopic trochleoplasty - or I travel to the respective places. Until now I have operated patients from 12 different countries - Norway, USA, Qatar, Spain, Romania, United Arab Emirates, Poland, India, Austria, Germany, and the United Kingdom, but naturally most patients are from Denmark.

In case you would like a second opinion regarding your MRI or just your general knee situation, I do Skype consultations. The cost is 150 euro - email [email protected]

You can eventually go to Facebook and check out either "Lars Blond + Trochleoplasty" or just "Trochleoplasty" for more details and recent updates

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

Frequently asked questions:
  • The surgery typically last 2- 2.5 hours - less if no MFPL reconstruction is needed.
  • When can you fly back? This depends on the distance but this is from 3 - 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
  • 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? 150 Euro.
    MRI scans can be posted by mail, by Dropbox or webtransfer 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-Hamlet Parken

Aleris-Hamlet Parken 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 after 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) Arthroscopic Deepening Trochleoplasty
Trochlea before and and after the trochleoplasty 

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

Arthroscopic second look

Two different examples of how it looks after 3 months postoperatively after an Arthroscopic Deepening Trochleoplasty. You see that the cartilage has healed very nicely and blue bands/tapes are dissolved.

Arthroscopic Trochleoplasty - 3 years after

Illustration showing the tapes in place after arthroscopic deepening 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 trochleoplasty and not just MPFL reconstruction?

That is a good question and no surgeon really knows for sure. Nevertheless, 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 or they develop a painful knee. Therefore if you visit a surgeons, who do not do trochleoplasty surgery, and you do have this flatt groove, try to get a second opinion in case this surgeon tells you that the surgery is rare surgery and it´s not necessary. 

Case Study - Mikkel

Mikkel was the first patient who was operated upon with an Arthroscopic Deepening Trochleoplasty, in March 2008. Previously he had unsuccessful kneecap-stabilizing surgery. Most noteworthy Mikkel had been troubled in both his knee since he was 8 years old and had been unable to run. Finally he underwent surgery on both his knees with arthroscopic trochleoplasty at 29 years old. So 21 years without running. So today, Mikkel is doing well in his knees and is running. 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 trochleoplasty is very good, with only rarely new dislocations and the quality of life seems to rise dramatically. 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. Above all until the date of this website article I have presented "The Arthroscopic Deepening Trochleoplasty" technique in the United States, Japan, Netherlands, UK, Sweden, Norway, Poland, Germany, Austria, Portugal and China. 

Tibial Tubercle Transfer?

What about having a tibial tubercle osteotomy instead of a trochleoplasty surgery? The fact is that no surgeon know what is best since the science has not yet given the answer to that question. Nevertheless is there indications that trochleoplasty give better results on within the first years. We also know that trochleoplasty normalize the anatomy. We know that patients who had tibial tubercle osteotomy after a decade are having declining results. The first trochleoplasty patients I operated more than 10 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

Photo library with some examples of arthrocopic trochleoplasty
References for Trochleoplasty papers

1. Banke IJ, Kohn LM, Meidinger G, Otto A, Hensler D, Beitzel K, Imhoff AB, Schöttle PB (2013) Combined trochleoplasty and MPFL reconstruction for treatment of chronic patellofemoral instability: a prospective minimum 2-year follow-up study. Knee Surg Sports Traumatol Arthrosc. 2014 Nov;22(11):2591-8
2. Blønd L, Haugegaard M (2013) Combined arthroscopic deepening trochleoplasty and reconstruction of the medial patellofemoral ligament for patients with recurrent patella dislocation and trochlear dysplasia. Knee Surg Sports Traumatol Arthrosc. 2014 Oct;22(10):2484-90
3. Dejour D, Byn P, Ntagiopoulos PG (2012) The Lyon’s sulcus-deepening trochleoplasty in previous unsuccessful patellofemoral surgery. International orthopaedics. 2013 Mar;37(3):433-9
4. Donell ST, Joseph G, Hing CB, Marshall TJ (2006) Modified Dejour trochleoplasty for severe dysplasia: operative technique and early clinical results. Knee 13(4):266–73
5. Fucentese SF, Zingg PO, Schmitt J, Pfirrmann CW a, Meyer DC, Koch PP (2011) Classification of trochlear dysplasia as predictor of clinical outcome after trochleoplasty. Knee Surg Sports Traumatol Arthrosc 19(10):1655–61
6. Koch PP, Fuchs B, Meyer DC, Fucentese SF (2011) Closing wedge patellar osteotomy in combination with trochleoplasty. Acta OrthopBelg 77(1):116–121
7. Masse Y (1978) [Trochleoplasty. Restoration of the intercondylar groove in subluxations and dislocations of the patella]. RevChir Orthop Reparatrice ApparMot 64(1):3–17
8. Nelitz M, Dreyhaupt J, Lippacher S (2013) Combined Trochleoplasty and Medial Patellofemoral Ligament Reconstruction for Recurrent Patellar Dislocations in Severe Trochlear Dysplasia: A Minimum 2-Year Follow-up Study. Am J Sports Med 1–8
9. Ntagiopoulos PG, Byn P, Dejour D (2013) Midterm results of comprehensive surgical reconstruction including sulcus-deepening trochleoplasty in recurrent patellar dislocations with high-grade trochlear dysplasia. Am J Sports Med 41(5):998–1004
10. Reddy KR, Reddy NS (2012) Trochleoplasty and medial patellofemoral ligament reconstruction for recurrent patellar dislocation. Indian journal of orthopaedics 46(2):242–5
11. Schöttle PB, Fucentese SF, Pfirrmann C, Bereiter H, Romero J (2005) Trochleaplasty for patellar instability due to trochlear dysplasia: A minimum 2-year clinical and radiological follow-up of 19 knees. Acta orthop 76(5):693–8
12. Thaunat M, Bessiere C, Pujol N, Boisrenoult P, Beaufils P (2011) Recession wedge trochleoplasty as an additional procedure in the surgical treatment of patellar instability with major trochlear dysplasia: early results. Orthop Traumatol Surg Res 97(8):833–45
13. Utting MR, Mulford JS, Eldridge JDJ (2008) A prospective evaluation of trochleoplasty for the treatment of patellofemoral dislocation and instability. J Bone Joint Surg Br 90(2):180–5
14. Verdonk R, Jansegers E, Stuyts B (2005) Trochleoplasty in dysplastic knee trochlea. Knee Surg Sports Traumatol Arthrosc 13(7):529–33
15. Von Knoch F, Böhm T, Bürgi ML, von Knoch M, Bereiter H, Bohm T, Burgi ML (2006) Trochleoplasty for recurrent patellar dislocation in association with trochlear dysplasia. A 4- to 14-year follow-up study. J Bone Joint Surg Br 88(10):1331–1335

The Spanish version

La operación llamada “trocleoplastia” tiene el objetivo de crear o profundizar el surco (tróclea) de la rótula. Como se mencionó en la sección "¿Por qué se desplaza la rótula" la tróclea es el surco de la rótula que tiene exceso de hueso. La finalidad de la trocleoplastia es levantar el cartílago de la tróclea y eliminar el exceso del hueso y una vez el surco (tróclea) se profundiza, el cartílago se vuelve a fijar con la ayuda de una cinta reabsorbible, como se muestra en los siguientes imágenes. La trocleoplastia es la operación anatómicamente más correcta, desde un punto de vista mecánico de la rodilla. Los resultados de la trocleoplastia parecen prometedores a largo plazo, en comparación con otros métodos, pero todavía hay poca información. Desde 2008 he hecho cerca de 80 operaciones artroscópicas de trocleoplastia para profundizar la tróclea. Antes había hecho la operación abierta (no artroscópico), pero he dejado de hacerlo porque es demasiado doloroso, hay más riesgo de infección y cicatrices de tejido. El proceso artroscópico también es más preciso y hoy ya no encuentro ninguna razón para hacer la procedimiento abierto. Algunos otros cirujanos que hacen trocleoplastia han reconocido recientemente esto y han aprendido el procedimiento artroscópico. Para la fisioterapia colaboro estrechamente con

Ejemplo de una " trocleoplastia artroscópica” para profundizar la tróclea. Antes (izquierda) y después (derecha). La cinta azul se disuelve después de 6 semanas, por lo que es sólo temporal hasta que el cartílago se haya curado.

A veces los pacientes vienen desde el extranjero para someterse a una trocleoplastia artroscópica. Hasta ahora he operado pacientes de Estados Unidos, Qatar, Noruega, Rumanía y Polonia.

La técnica artroscópica de trocleoplastia es menos traumática para la rodilla y causa menos dolor y cicatrices más pequeñas, es más precisa, y además la rehabilitación es más acelerada. La trocleoplastia artroscópica se realiza siempre en combinación con la reconstrucción del ligamento medial patelofemoral (MPFL), cuando hay instabilidad de la rótula, sin embargo, en casos con dolor de la rodilla de la zona delantera, esto no es necesario. Tanto la técnica como los resultados de esta operación se han publicado en estudios médicos revisados por pares (médicos autorizados). Hasta ahora he presentado la técnica de "La trocleoplastia artroscópica" en los Estados Unidos, Japón, Países Bajos, Reino Unido, Suecia, Noruega, Polonia. y China. El primer paciente que operé con trocleoplastia artroscópica fue Mikkel – Se va a poder leer más sobre él más adelante.

Preguntas frecuentes:

El precio de una consulta via Skype con evaluación de los imágenes de resonancia magnética? 150 Euro

La cirugía por lo general dura 2,5 horas

¿Cuándo se puede regresar en un vuelo después de la operación? Esto depende de la distancia, pero aproximadamente a partir de 3 - 10 días. Un asiento con más espacio, con la posibilidad de enderezar la pierna es necesario.

Normalmente no se necesita rodillera / abrazadera después de este tipo de cirugía

E-mail: [email protected]

Dos ejemplos diferentes de cómo se ve 3 meses después de la operación trocleoplastia artroscópica. El cartílago se ha curado y las bandas / cintas azules quedaron disueltas.

Resonancia Magnética antes (izquierda) y después (derecha) de la trocleoplastia artroscópica.

Mikkel fue el primer paciente que fue operado con un trocleoplastia artroscópica en marzo de 2008. Él anteriormente tenía una cirurgia para estabilizar la rótula sin éxito. Había tenido problemas desde los 8 años de edad y había sido incapaz de correr. Se sometió a una cirugía en ambas rodillas con trocleoplastia artroscópica con 29 años. Después de 21 años sin correr, hoy en día, las rodillas de Mikkel funcionan bien y puede correr. La única molestia que tiene es el sonido de las rodillas cuando sube las escaleras. Él habló sobre su historia durante la reunión de trocleoplastia en 2014.

La fisioterapeuta Dorte Niesen tiene una enorme experiencia trabajando con pacientes con problemas de inestabilidad de la rótula, y ha visto varios pacientes que tenían una trocleoplastia artroscópica. Dorte Nielsen ha subido vídeos a Youtube.

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, but naturally it is not necessary for you to know everything there is to know in order to get treatment. (so warning - this is nerdy)
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, and then things may become quite disabling. The problem can occur while doing activities, like changing direction such as in sport or dancing, while for others the kneecap just seems to go out without much provocation, and 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, jumping in and out of a car or during sexual activity. Quality of life can be significantly affected, since a lot of simple daily activities must be avoided. Sometimes the disorder also causes pain during daily life. It is very important if you are going for surgery to rule out what cause your instability, since the 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, since there are so many treatments and in order for you to have the right one, this have to be examined. This is rather complicated and 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 and 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 - 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 via physiotherapy and by strengthening the quadriceps and gluteal muscles. A special brace that supports the kneecap (for example DJO Tru-Pull) can stabilise 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 - for example by MRI - so that the surgery can be individualised 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.

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 your symptoms. Unfortunately this is a disorder where many patient have undergone surgery using an insufficient method, and this explains why it did not help or maybe even worsened the situation. Knowledge about this disorder has changed radically over recent years and 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 and 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 - MPFL). Such an injury causes a lot of pain and swelling and 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, but still it can be troublesome since the person may experience that it nearly jumps out (which is called subluxation).

The treatment of loose kneecap

The first time the kneecap goes out, the treatment is likely to just consist of rest, ice, compression and elevation (RICE), while allowing full weightbearing and full range of movement. In past years a brace for support and immobilisation was generally used, but 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 stabilising brace or surgery should be considered. Physiotherapy has also been an important part of the treatment in improving muscle balance, but studies have not really demonstrated that it has a positive effect on the patellar looseness itself. Please read more about surgery here; MPFL reconstruction - Elmslie-Trillat surgery - Trochleoplasty

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 or dislocating patella 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

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.


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 by an MRI scan and X-rays. Then the operation can be individualized in order to reestablish normal anatomy and then the operation will be effective.

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

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.