The trochlea forms the upper part of the gliding surface in which the patella is guided during flexion and extension of the knee joint. In trochlear dysplasia, this gliding groove is too shallow or asymmetrical in shape, causing the patella to lose its stable guidance. As a result, the kneecap no longer remains centered during flexion, leading to abnormal stress on the patellar gliding track, which causes pain and a feeling of instability. The lack of bony guidance for the kneecap also increases the likelihood of patellar dislocations, in which the kneecap slips out of the patellar glide track.
Anatomically, the trochlea is formed by bony and cartilaginous structures, which enable low-friction gliding. If the shape is altered, contact between the patella and the trochlea becomes irregular, which in the long term promotes the development of cartilage damage behind the patella and in the area of the trochlea.
Surgical treatment of trochlear dysplasia: Two specialists perform a trochleoplasty on the knee joint.
The causes of trochlear dysplasia are congenital developmental abnormalities. Genetic predisposition explains why trochlear dysplasia tends to run in families. Furthermore, trochlear dysplasia is always bilateral, though the severity may vary.
It is not uncommon for affected patients to also have other congenital abnormalities, which may represent additional risk factors for patellar dislocations and must be taken into account when treating trochlear dysplasia. These include, among others, a high-set patella (patella alta) and torsional deformities of the upper and/or lower leg. Repeated patellar dislocations can cause damage to the articular cartilage and lead to an increase in symptoms of instability.
The diagnosis of trochlear dysplasia is made via an MRI scan. According to the Dejour classification, four types (A to D) are distinguished depending on the severity of the deformity. While type A shows mild flattening, type D is characterized by a severely altered and asymmetrical trochlea with a ridge. This classification helps to assess the need for surgical treatment.
As already mentioned, trochlear dysplasia is often associated with other congenital risk factors and abnormalities that exacerbate the symptoms. A comprehensive clinical and imaging analysis is therefore required, covering all factors that may contribute to patellofemoral instability. Accordingly, a careful clinical examination of gait and the function of the adjacent joints is just as necessary as an assessment of the stability of the patellar glide. Depending on the clinical findings, further imaging investigations such as leg axis or torsion measurements may be required to take into account the need to address other risk factors in the management of trochlear dysplasia.
The treatment of trochlear dysplasia depends on the severity and symptoms. Mild forms are treated conservatively, for example through targeted muscle training, physiotherapy and exercises to align the leg axis or stabilize the patella. Such coordinated functional training can improve patellar tracking and alleviate symptoms in mild cases of trochlear dysplasia or patellofemoral instability. Orthopedic aids or bandages can further support the patella’s gliding motion.
In cases of severe deformity and recurrent dislocations, surgical treatment is recommended. Trochleoplasty, in which the bony guide surface for the patella is reconstructed, is of particular importance for restoring stable patellar tracking and load-bearing capacity, as an inadequately formed bony gliding surface has a significant negative biomechanical impact on instability. Trochleoplasty is frequently performed in combination with ligament reconstruction and other bony procedures.
In a trochleoplasty, the bony patellar glide surface is remodeled during surgery so that the patella can once again be guided stably within the newly shaped glide surface.
To achieve this, during the operation the cartilage of the trochlea is detached from the rest of the femur along with a thin layer of bone (bone-cartilage lamella). This allows bone to be removed from the underlying bone and a new, anatomically adapted bony groove to be created. The detached bone-cartilage lamella is then fitted into the newly formed guide groove and fixed in place with absorbable sutures or pins. The newly created trochlea enables improved bony guidance of the patella, thereby significantly reducing the risk of recurrent dislocation.
As trochleoplasty is frequently performed in cases of patellofemoral instability and in patients with recurrent patellar dislocations, this procedure is usually combined with ligament replacement (MPFL replacement). In addition to restoring the bony guidance of the patellar glide surface, this also stabilizes the ligamentous apparatus.
The operation requires surgical expertise to ensure that the groove can be remodeled to fit the patella. The procedure can be performed either open or arthroscopically and takes one to two hours, depending on any additional procedures that may be required. A hospital stay of 1–2 days is to be expected following the operation.
Post-operatively, mobilization is carried out gradually under the guidance of a physiotherapist.
Crutches are mainly used to relieve pressure on the knee joint, prevent swelling and also to reduce pain. In addition to physiotherapy and lymphatic drainage, daily self-exercises are particularly helpful in rebuilding mobility and load-bearing capacity after surgery, so that everyday activities can gradually be resumed after approximately 6 weeks. This is followed by a rehabilitation program focusing on building muscle, strength and coordination. Regular exercise bike training, training on a rowing machine and independent training at the gym help you to recover as quickly as possible after an operation. Depending on the procedure, the healing of the bone and cartilage structures, and progress in building up muscle, strength and coordination, sporting activities can be resumed after 6–12 months. Regular follow-up appointments ensure the healing process is on track and help prevent complications.
The prognosis following trochleoplasty is very good when the procedure is performed for the correct indication.
Various high-impact clinical studies, such as those by Dejour et al. or Nelitz M., have demonstrated that trochleoplasty leads to a significant improvement in symptoms and instability. Furthermore, biomechanical studies have shown that remodeling the trochlear groove not only achieves centring of the patellar tracking but also an improved distribution of cartilage load. It can be assumed that this also reduces the risk of cartilage damage. Long-term studies have shown that patients with severe trochlear dysplasia and patellar instability, in particular, benefit sustainably from trochleoplasty combined with MPFL reconstruction. Due to the favorable clinical outcomes and the positive results of published studies, trochleoplasty is recommended by international professional societies and experts as an effective treatment method for patellofemoral instability.
How is trochlear dysplasia diagnosed?
In addition to a comprehensive clinical examination, imaging techniques are essential for assessing and classifying the severity of trochlear dysplasia. MRI scans, in particular, enable the shape of the trochlea to be assessed and asymmetries to be identified. The severity of trochlear dysplasia is classified according to Dejour (Types A–D) and is particularly relevant for determining the need for surgery.
When is surgery necessary?
The need for trochleoplasty depends, on the one hand, on the patient’s symptoms and, on the other, on the severity of the instability. As severe trochlear dysplasia in particular is significant for patellofemoral symptoms, the possibility of trochleoplasty should always be considered when treating patellofemoral instability.
However, as various other congenital risk factors, in addition to trochlear dysplasia, can also contribute to patellofemoral symptoms, a careful analysis of all factors is always required for treatment planning. These include, among others, leg axis misalignments, torsional deformities and, for example, a high-riding patella. Taking into account the symptoms, clinical findings and imaging results, an individual treatment plan can then be drawn up for each patient.
How is trochleoplasty performed?
In trochleoplasty, the missing bony patellar glide surface is remodeled during surgery so that the patella can be guided stably within a newly formed glide surface. To achieve this, the cartilage-bone lamella of the trochlea is detached from the rest of the femur. This allows an anatomical bony socket to be created, into which the previously detached bone-cartilage lamella can be repositioned and fixed.
What is a combined trochleoplasty and MPFL reconstruction?
Trochleoplasties are often combined with ligament reconstruction to stabilize the patella in cases of severe patellofemoral instability, in addition to restoring bony guidance. With a so-called replacement reconstruction of the medial patellofemoral ligament, the MPFL – the most important passive stabilizer of the patellar glide – is anatomically reconstructed using the patient’s own tendon.
What are the outcomes following trochleoplasty?
As various high-quality published clinical studies show, the outcomes following trochleoplasty are very good when the procedure is performed for the correct indication, meaning that both stability and symptoms can be improved in the long term.
What role does post-operative care play?
Particularly in the first few weeks after the operation, alongside physiotherapy and lymphatic drainage, daily self-exercises are of paramount importance in regaining mobility and load-bearing capacity. Appropriate self-exercises should be discussed with the physiotherapist. Particularly in the first few weeks, it is recommended to perform self-exercises several times a day in short intervals of 4–5 sessions of 10 minutes each, so as not to overload the recently operated knee joint. Once the ability to cope with everyday activities and full knee mobility have been regained, muscle strength and coordination must be built up before sporting activities can be resumed.
What complications can arise?
The risk of a recurrent patellar dislocation is extremely low (one to two per cent). However, it is not uncommon for there to be a restriction in full flexion or a grinding noise behind the kneecap. To counteract this, and in particular to prevent scarring, home exercises and physiotherapy are of crucial importance. Until muscle strength and coordination have been fully restored, residual symptoms and pain around the kneecap, depending on the level of activity, can be expected for up to six months after the operation. Postoperative infections, thromboses or bruising are relatively rare (one to two per cent overall) and, as with any other surgical procedure, may occur, just as temporary bruising, swelling or pain may occur.
