Reviewed by Dr Vishal Pai
A trochleoplasty reshapes the groove at the end of your thigh bone that your kneecap runs in, when that groove is too shallow or flat to hold the kneecap in place. This page explains why the groove matters, who might need the operation, what it involves, and what to expect afterwards.
At a Glance
- Trochlear dysplasia means the groove for your kneecap is shallow, flat or even rounded outwards. It is the most common shape problem in knees where the kneecap keeps dislocating.
- A trochleoplasty deepens the groove so the kneecap has a stable track to run in. It is an option for severe dysplasia when the kneecap keeps dislocating.
- It is usually done together with an MPFL reconstruction, which replaces the torn ligament on the inner side of the kneecap.
- Dr Vishal Pai waits until you have finished growing before performing it, to protect the growth plate at the end of the thigh bone.
- Very few kneecaps dislocate again afterwards, and most people return to sport. Recovery takes several months.
What is a trochleoplasty?
Your kneecap (patella) slides up and down in a groove at the end of your thigh bone called the trochlea. In most knees the groove is a V-shaped valley that guides the kneecap and stops it slipping out to the side.
In trochlear dysplasia, the groove hasn’t formed properly. It may be shallow, flat, or rounded like a dome, and there is often a bump of bone at the top of the groove. With little or no valley to sit in, the kneecap can slide out more easily. Most people whose kneecap keeps dislocating have some degree of trochlear dysplasia, while it is uncommon in other knees. [1]
A trochleoplasty lifts the cartilage surface of the groove, reshapes the bone underneath into a deeper valley and lays the cartilage back down. It is the only kneecap operation that changes the shape of the groove itself.
How is trochlear dysplasia graded?
Doctors grade trochlear dysplasia from A (mild) to D (severe) using an X-ray and an MRI or CT scan. [2]
- Type A: the groove is shallower than normal, but it is still a groove.
- Type B: the groove is flat or rounded, with a bump of bone at the top.
- Type C: the two sides of the groove are uneven and the inner side is underdeveloped, but there is no bump at the top.
- Type D: a bump at the top and uneven sides, often with a sharp step, or “cliff”, between them.
Types B to D are called high-grade dysplasia. [3] The grade is a useful guide, but Dr Vishal Pai looks at it alongside your symptoms and examination. You can read more about the other causes of an unstable kneecap on the kneecap instability page.
Who might need a trochleoplasty?
Physiotherapy comes first after a kneecap dislocation. When surgery is needed, many people are treated with an MPFL reconstruction, sometimes with a tibial tubercle osteotomy. The patella stabilisation surgery page explains how the choice is made.
A trochleoplasty may be considered if:
- Your kneecap has dislocated more than once, despite physiotherapy
- Your scans show high-grade trochlear dysplasia, often with a large bump at the top of the groove [4] [5]
- Your kneecap has dislocated again after earlier stabilising surgery [4]
When the groove is very flat, a new ligament on its own is more likely to fail. [5] Deepening the groove at the same time treats the underlying cause and makes another dislocation less likely. [6]
Dr Vishal Pai reserves a trochleoplasty for high-grade dysplasia, because mild or moderate dysplasia can usually be treated with other operations. He waits until growth has finished before performing it, to protect the growth plate in the thigh bone. He doesn’t usually recommend it if your main problem is kneecap pain rather than the kneecap slipping out, or if you already have significant arthritis behind the kneecap.
Dr Vishal Pai performs this procedure in selected cases. He will explain whether it applies to your knee after examining you and reviewing your scans.
What is involved in a trochleoplasty?
The operation is done under a general anaesthetic through a cut beside the kneecap on its outer side, and you usually stay in hospital for 1 or 2 nights. The main steps are:
1. Lifting the cartilage flap
A thin flap of cartilage and bone is lifted from the surface of the groove.
2. Reshaping the groove
The bone under the flap, including any bump at the top of the groove, is reshaped from a dome into a V-shaped valley with room for the kneecap to sit in.
3. Reattaching the flap
The cartilage flap is pressed down into the new groove and held with suture tape and small bone anchors while it heals.
4. Releasing tight tissue on the outer side
In severe dysplasia, the tissues on the outer side of the kneecap are often tight. [4] They are repaired in a lengthened position so the kneecap can sit centrally in the new groove.
5. Reconstructing the MPFL
An MPFL reconstruction is usually done in the same operation. The kneecap is more stable when both are done together than after a trochleoplasty on its own. [7]
How long does it take to recover from a trochleoplasty?
Recovery takes several months. You start bending the knee straight away, because early movement helps prevent stiffness. Some swelling and aching is common for up to 6 months. Your physiotherapist leads the rehabilitation, and you move to each stage when your knee is ready, not on a fixed date.
Dr Vishal Pai will give you a written recovery plan. As a guide:
- Days 1–2You stay in hospital for 1 or 2 nights. You walk with crutches and start bending the knee straight away.
- 2 weeksYour stitches come out. The knee should straighten fully and bend to about 90 degrees.
- 2–6 weeksYou come off crutches. Most people return to desk work, and you can drive from about 4 weeks.
- 8 weeksYou see Dr Vishal Pai for a review with an X-ray.
- 4 monthsYou see Dr Vishal Pai again, with a repeat X-ray. Impact exercise starts gradually, and most people return to manual work.
- 6 months or laterYou build up to running and pivoting sports, and return to sport once you pass return-to-play testing.
- 12 monthsFinal review with an X-ray.
What results can you expect?
A trochleoplasty is very good at stopping the kneecap from dislocating. Only about 2 in 100 knees dislocate again. [8] Over the long term, people keep a stable kneecap and are generally happy with the result. [9]
Knee function improves for most people, and most return to sport. [10] If you played sport at a high level, it may be harder to get back to the same level. [11] Results vary from person to person.
What are the risks and complications?
A trochleoplasty is a bigger operation than an MPFL reconstruction on its own, and complications are more common. [12] Overall, they are similar to other kneecap stabilising operations. [13] The main risks are:
- Stiffness. This affects about 7 in 100 people. [8] It may need extra physiotherapy, or a short anaesthetic to gently bend the knee.
- Ongoing instability. A small number of people still feel the kneecap slip at times, even though it no longer fully dislocates. [8]
- Arthritis behind the kneecap. Arthritis behind the kneecap can develop over the years, and is usually mild. [8] [9] Earlier dislocations also damage the cartilage, so it isn’t clear how much of this comes from the operation. [14]
The general risks of knee surgery, such as infection and blood clots, are explained on the patella stabilisation surgery page. Dr Vishal Pai will go through all the risks with you before you decide, and you will receive a written information sheet.
Where does Dr Vishal Pai consult and operate?
Dr Vishal Pai consults at Sandringham Orthopaedic Specialists, Suite 1, 60 Bay Road, Sandringham. He operates at Calvary Holmesglen Private Hospital, 490 South Road, Moorabbin, and The Avenue Hospital, 40 The Avenue, Windsor. Patients come from across Bayside, Glen Eira and the Mornington Peninsula, and some travel from regional Victoria. For consultation fees, see appointments and fees.
References
Show all 14 referencesHide references
- Dejour H et al. 1994. Factors of patellar instability: an anatomic radiographic study. Knee Surgery, Sports Traumatology, Arthroscopy.
- Kazley JM et al. 2019. Classifications in brief: the Dejour classification of trochlear dysplasia. Clinical Orthopaedics and Related Research.
- Lippacher S et al. 2012. Observer agreement on the Dejour trochlear dysplasia classification. The American Journal of Sports Medicine.
- Dejour D et al. 2021. Trochleoplasty: indications in patellar dislocation with high-grade dysplasia. Surgical technique. Orthopaedics & Traumatology: Surgery & Research.
- Hiemstra L et al. 2025. Thin flap trochleoplasty with medial patellofemoral ligament reconstruction for recurrent patellofemoral instability with high-grade trochlear dysplasia: a series of 63 consecutive cases. The American Journal of Sports Medicine.
- Tarchala M et al. 2023. Sulcus-deepening trochleoplasty for high-grade trochlear dysplasia: demystifying the procedure, a review of the current literature. Current Reviews in Musculoskeletal Medicine.
- Ren B et al. 2019. Isolated trochleoplasty for recurrent patellar dislocation has lower outcome and higher residual instability compared with combined MPFL and trochleoplasty: a systematic review. Archives of Orthopaedic and Trauma Surgery.
- Leclerc JT et al. 2021. Complications and outcomes of trochleoplasty for patellofemoral instability: a systematic review and meta-analysis of 1000 trochleoplasties. Orthopaedics & Traumatology: Surgery & Research.
- Dejour D et al. 2024. Sulcus-deepening trochleoplasty with medial patellofemoral ligament reconstruction: outcomes at 10 to 20 years. The American Journal of Sports Medicine.
- Davies M et al. 2020. Sulcus-deepening trochleoplasty as an isolated or combined treatment strategy for patellar instability and trochlear dysplasia: a systematic review. Arthroscopy, Sports Medicine, and Rehabilitation.
- Mengis N et al. 2022. Return to sports and patients’ rehabilitation continuum after deepening trochleoplasty and concomitant patellar-stabilizing procedures: a case series of 111 patients at 2 to 4 years of follow-up. The American Journal of Sports Medicine.
- Phillips AR et al. 2024. Isolated medial patellofemoral ligament reconstruction results in lower failure and complication rates than isolated trochleoplasty and tibial tubercle osteotomy: a systematic review. Arthroscopy.
- van Sambeeck JV et al. 2017. Trochleoplasty procedures show complication rates similar to other patellar-stabilizing procedures. Knee Surgery, Sports Traumatology, Arthroscopy.
- Chaclas N et al. 2024. Trochleoplasty in pediatric patients: a systematic review. The Iowa Orthopaedic Journal.
Frequently asked questions
How do I know if I have trochlear dysplasia?
It is diagnosed on scans. A side-on X-ray of the knee can show a flat groove, and an MRI or CT scan shows its shape in more detail. The scans are always read alongside your symptoms and an examination of your knee.
Why is an MPFL reconstruction usually done at the same time?
The ligament on the inner side of the kneecap is usually torn or stretched after repeated dislocations. Deepening the groove doesn’t repair it, so the two operations are usually combined. Each one corrects a different part of the problem.
Can my teenager have a trochleoplasty?
Not while they are still growing. To protect the growth plate at the end of the thigh bone, Dr Vishal Pai waits until growth has finished. If surgery can’t wait, other operations can be considered in the meantime.
Is a trochleoplasty done through keyhole surgery?
No. Dr Vishal Pai performs a trochleoplasty as an open operation, through a cut beside the kneecap on its outer side. This lets him reshape the groove and lengthen the tight tissue on the outer side of the kneecap through the same cut.
Will my knee be normal after a trochleoplasty?
The aim is a stable kneecap that lets you get back to your usual activities, and knee function improves for most people. Some people still have pain at the front of the knee, or return to sport at a lower level.
Next step
Talk through your options
If your kneecap keeps dislocating and you've been told the groove is shallow, Dr Vishal Pai can review your scans and explain whether a trochleoplasty is right for your knee.