Early Identification and Treatment of Developmental Trochlear Femoral Dysplasia

Joint dysplasias consist of alterations in the normal development of a joint. In these cases, the formation of the normally congruent joint surfaces is altered, producing functional abnormalities that, depending on the degree of dysplasia, can lead to a spectrum of clinical manifestations ranging from complete dislocation, subluxations, severe instabilities, and ultimately early osteoarthritis.

The most studied joint dysplasia is developmental dysplasia of the hip (CDD) where the head of the femur and the acetabulum present different degrees of malformation, giving rise to a non-congruent joint. The clinical spectrum of manifestations of this pathology varies from a complete dislocation to milder forms of dysplasia that can manifest in childhood, youth or adulthood as early osteoarthritis, sometimes requiring multiple interventions for its treatment.

Early detection methods for CDD include: the identification of prenatal risk factors (intrauterine position, family history, first-born…), exploration through specific maneuvers, and confirmation by imaging tests such as ultrasound at birth. The early treatment of CDD consists of the application of a Pavlik harness whose purpose is to keep the newborn in a full-time position (frog position) in which the head of the femur remains completely congruent with the acetabulum, allowing the dysplasia to be reversed in early ages. Thanks to these early detection methods and its early treatment (with minimal adverse effects), many of these clinical alterations that previously went unnoticed have been prevented, and whose late treatment involves surgeries with a degree of invasiveness inversely related to the time of detection of DDC.

The knee is another joint susceptible to developing dysplasia. The most frequent dysplasia of the knee joint involves the femoropatellar joint (FP) formed by the patella and the femoral trochlea. Its normal function is vital to be able to flex and extend the leg since the patella acts as a lever arm increasing the strength of the quadriceps. Therefore, it is a joint subjected to high tensile forces.

In the normal knee in extension, the concave patella is located in the most proximal part of the femur without having any contact with the convex femoral trochlea. As the knee is bent, the patella runs into the deep femoral groove (normal groove angle 135º), which acts as containment and allows it to slide distally as the knee is bent further. It is in these knee flexion positions, more than 90º, where there exist more tensional forces between both articular surfaces.

Developmental trochlear femoral dysplasia (DTFD), therefore, consists of the abnormal development of both articular surfaces resulting in a non-congruent joint. However, unlike CDD, it is not detected early since it generally manifests in adolescence in the form of recurrent dislocations with minimal trauma in severe cases. Recurrent patellar dislocations are a serious and complex problem for both the patient and the surgeon since in adolescence it is not possible to reverse DTFD and surgeries to generate a normal trochlear groove (trochleoplasty) can have catastrophic results generating disability and lameness for life in a not inconsiderable percentage of patients. Milder forms of dysplasia that do not appear in adolescence produce instabilities or subluxations and alterations in the patellar tracking that trigger recurrent knee pain and often end up producing early osteoarthritis in young patients. The treatment of this type of patient is also not very rewarding and sometimes they require surgeries at an early age with poor results.

The fact that DTFD manifests itself late during adolescence, has biased the scientific community to focus its efforts on research related to the surgical treatment of this pathology and not on its prevention at an early age, as is the case with DDC. However, more recent studies are focusing their objectives on the early detection and etiological analysis of this structural anomaly in order to prevent it. Specifically, investigators conducted a study in newborns with early ultrasound in order to identify risk factors related to PRDD. These investigators concluded that the intrauterine breech position at birth was 45 times more likely to develop DTFD than the cephalic position.

Although the etiology of DTFD is not clear, more and more studies point to the idea that the lack of a mechanical stimulus by the patella in the femoral sulcus causes both articular surfaces not to develop normally. According to a study that developed an experimental study in newborn rats resecting the patella, the morphological development of the femoral trochlea is influenced by its abnormal mechanical stress. This hypothesis has also been reinforced by the work of other investigators where, in an experimental study in growing rabbits, they observed the development of DTFD in those rabbits in which they produced a permanent patella dislocation (avoiding the contact of the patella on the femoral trochlea). These findings would also justify those previously described by where it was observed that those newborns in a breech position with their legs extended (in extension, the patella is located proximal to the femoral groove and does not exert the mechanical stimulus necessary for normal groove development) had a higher incidence of DTFD.

These investigations support the hypothesis that the absence of mechanical stimulation of the patella on the femoral trochlea leads to an alteration in its development, producing DTFD. This situation led two different researchers to carry out different studies in order to find out whether in those cases with DTFD, dysplasia could be reversed by returning the mechanical stimulus of the patella to the trochlea. A study demonstrated that dislocation and subsequent reduction of the patellofemoral joint could reverse DTFD in growing rabbits and other investigators showed that realignment surgery could remodel the dysplastic trochlea at very young ages in a human clinical study after an eleven-year follow-up.

These findings suggest that it is possible to identify DTFD early in newborns with risk factors using ultrasound and that there is the possibility of modeling the dysplastic trochlea if the necessary mechanical stimulation is achieved by the patella. However, although there is evidence that this situation can be reversed, so far no clinical study has been developed in neonates with DTFD to assess the effect of different interventions. Currently, it is more than known that keeping the knee at 90º of flexion is when there are greater contact forces between the patella and the trochlea. As in DDC, this position could be maintained in newborns with DTFD by using a harness, with the intention of achieving constant and permanent mechanical stimulation of the patella on the dysplastic trochlea that allows modeling the dysplastic groove. during the early growth phase.

That is why the investigators propose the development of a randomized, double-blind clinical trial with the aim of early identification by ultrasound of newborns with risk factors for the development of DTFD and subsequently evaluate the result of treatment with a harness that maintains the knee at 90º flexion for two months.

The hypothesis under study is based on the fact that early identification and treatment of DTFD in newborns using a harness could model the dysplastic trochlea and prevent this malformation and its consequences in the short and long term, as is the case with DDC.