Revista de Medicina Desportiva (English) November 2018 - Page 28

Rev. Medicina Desportiva informa, 2018; 9(6):26-28. Patellar Instability in Children and Adolescents Dra. Catarina Neto Pereira 1 , Dra. Patrícia Rodrigues 2 , Dr. Delfin Tavares 3 1 Resident doctor on Orthopedics and Traumatology at the Hospital Professor Doutor Fernando Fonseca (HFF), 2 Orthopedic and Traumatology Specialist at the Hospital Dona Estefânia (HDE), 3 Director of the Orthopedic Ward at the Hospital Dona Estefânia. Lisboa RESUMO / ABSTRACT Patellar Instability is the most common pathology of the knee during growth. After the first episode of patellar dislocation there are about 40% of recurrences. Conservative treatment is the preferred strategy for the first time, but in cases with concomitant anatomic predisposition and relapse, surgical reconstruction may be considered. In these cases, when there is skeletal immaturity, the reconstruction of the medial femoro-patellar ligament may be sufficient, associated or not with soft tissue procedures, with the aim to have permanent stabilization of the patella or, at least, a gain of time for the accomplishment of a definitive bone procedure. Recurrent dislocations of the patella lead to changes in the cartilage, hence early treatment is important. Although it is still a controversial subject, the reconstruction of the medial femoro-patellar ligament has been shown to be effective in the treatment of patellar instability, with the advantage of being able to use a surgical technique that does not damage the growth cartilage. PALAVRAS-CHAVE / KEYWORDS Patellar instability, femoropatellar ligament, children/teenagers Introduction The patelofemoral pathologies are among de most frequent causes of pain in children and adolescents and the patellar instability is the most frequent pathology in the knee dur- ing the growing process. 1 The global incidence is about 50 in 100 000 children and adolescents per year, with a peak at the age of 15 years old. 2,3 The majority of the patellar dislocations have a lateral deviation, with about 40% of recurrences after the first episode of dislocation. Two thirds of the subjects have open phy- sis, which limits the type of surgery for patellar stabilization. 2,4 The treatment of the acute dislo- cations, like in the adults, is typically conservative, except if there is an osteochondral injury. The surgical treatment is recommended on cases of recurrence. 1 Probably, the most important patellar stabilizer is the medial femoropatelar ligament (MFPL), that promotes more than 50% of the medial restriction. It has been demonstrated that in the majority of the dislocations the MFPL has suffered some degree of injury 1 , and the its avulsion usually occurs at the patellar insertion. 2,5 Anatomic vari- ations, like changes on the Q angle, 26 november 2018 distance tibial tuberosity-trochlear groove, are associated to an increase of stress over the MFPL that predis- poses to patellar dislocation. 1 Predisposing factors The identification of anatomic factors that predispose to patellar dislocation is of paramount impor- tance to decide the best treatment for the patient. The ligament laxity is a commonly found factor on the females and on subjects with col- lagen disease. On the other hand, the fibrosis of the vastus lateralis is also considered a risk factor. It is believed that the increased Q angle contributes for the lateralization of the patella, however there is a poor clinical correlation, and Q angle could be decreased. 2 Trochlear dysplasia (Figure 1) that is considered a major predisposing factor for patelofemoral instability 9 , is defined as geometric abnormal- ity in the shape and in the depth of the trochlear groove, especially on the proximal area where the patella bone fits on the trochlea. 6,7 It has been demonstrated that the trochlear cartilaginous trochlear angle is already created at birth, but the bone trochlea gains its depth during adolescence. 6,8 This fact presents an enormous relevance in the evaluation for the treatment the patients with patelofemoral instabil- ity. The type of trochlear dysplasia can be classified on the profile of the X-rays according Dejour’s principles: the presence of the crossing sign, proximal groove flattened or con- vex, step-off between the trochlea and the anterior cortex of the distal femur and flattening of the lateral femoral condyl. 2,9 The X-rays are technician depend- ent and frequently they fail to dem- onstrate the proximal trochlear dys- plasia, this is, the location where the trochlea articulates with the patella bone on the first 20-30° of knee flex- ion. 7,10 The CT scan studies can help to have a better interpretation of the trochlear dysplasia components. There is a high percentage of pate- lla alta (Figure 2) in patients with recurrent dislocations. According to Insall, on patients with closed physis the profile X-ray with the knee at 45° of flexion determines if the patella is high or low, but in the patients with open tibial proximal physis it is pref- erable the Caton-Deschamps Index (CDI), that is the relation between the length from proximal anterior border of the tibia and the most inferior point of the articular surface of the patella bone and the length of the articular surface of the patella, and a CDI bigger than 1,45 (patella alta) is an important predictive fac- tor of patella instability. 2 The distance from the tibial tuberosity-trochlear groove (TT-TG) is used to determine the degree of lateralization of the tibial tuber in relation to the deepest area of the trochlear groove. A distance bigger than 20mm measured in the CT scan, with the knee in full exten- sion, is considered pathological and it is a risk factor for instability. 6,7 The increase of the distance TT-TG is rarely present as isolated in patients with patellar instability and usually is associated with other risk factors. 7 The femoral anteversion (Fig- ure 3) and tibial rotation are other risk factors to be evaluated in the patient. The femoral torsion is calculated with the angle between a line that runs thought the center of the femoral head and the center of the femoral neck and a posterior