## 1 Introduction  
Patellofemoral instability is a pathological condition characterized by altered joint congruence between the patella and the femoral trochlea, which manifests as episodes of subluxation or dislocation of the patella. Dislocation may be associated with osteochondral and chondral fractures of the facets of the patella and femoral condyle or injuries to the ligaments of the medial compartment, particularly the medial patellofemoral ligament. This condition is especially frequent in young and active populations. It can lead to significant functional limitations and negatively impact quality of life [1, 2]. The negative effects include recurrent pain; difficulty in walking, climbing stairs, or sports activities; and frequent episodes of knee dislocation [2]. Women are more frequently affected than men, which probably results from anatomical and biomechanical differences, such as a greater Q-angle (the line of traction of the quadriceps muscle), greater ligamentous laxity, and the muscle strength of the quadriceps femoris, which is generally lower for women [3]. Several risk factors are known for predisposal to joint instability. These include dysplasia of the patella alta, genu valgum, patella, and trochlea; generalized hyperlaxity; increased tibial external rotation and femoral anteversion; high Q angle; ligamentous laxity; and loss of integrity of the soft tissues that function as static and dynamic constraints [4]. Patellar luxation is a traumatic event that results in a complete loss of joint relationship between the patella and the femoral trochlea. It usually involves lateral dislocation, and almost all cases involve damage to the medial patellofemoral ligament, which provides an essential medial restraint against lateral patellar dislocation during the first 30\({}^{\circ}\) of flexion [4; 5]. Clinically significant patellar instability presents with a subjective sensation of instability or locking and anterior knee pain. In true dislocation, there may be deformity, pain upon palpation, swelling, and loss of function of the knee joint. Diagnosis can be carried out using clinical tests, such as the apprehension test [6]. This test is widely used and involves a clinical maneuver in which lateral pressure is applied to the patella while the knee is gently flexed, which elicits pain or apprehension if instability is present [2]. Instrumental examinations may also be employed, such as standard radiography (X-ray) and magnetic resonance imaging (MRI), which provide crucial information about bone structure and soft tissue integrity. An important factor in evaluating patients with patellofemoral joint pain or instability is the lateral positioning of the tibial tubercle (TT). This is typically assessed by measuring the mediolateral distance between the anterior TT and the deepest point of the trochlear groove (TG), which is known as the TT-TG distance. According to computed tomography (CT) imaging, a TT-TG distance \(<\) 13 mm is generally considered normal, while a distance \(>\) 13 mm is regarded as abnormal. A TT-TG distance exceeding 20 mm is classified as pathological and is frequently recommended as an indication for surgical intervention in symptomatic patients, as outlined in various treatment protocols [7; 8]. The treatment approach for patella luxation can be conservative or surgical. In conservative treatment, the initial approach involves reducing the luxation and pharmacological management of pain and inflammation. A typical aspect of this treatment option is immobilization. A light brace can be used to reduce pain during the first week [9]. The use of crutches and partial weight bearing are suggested for the first few weeks [10]. Further therapeutic action involves a rehabilitation program. After the first patellar luxation, surgery could be required in cases of osteochondral fractures and mobile bodies, significant cartilage damage, rupture of the stabilizing structures with subluxation, or complete displacement of the patella.