Recurrent patellar dislocation is described as a loss of joint congruence between the femoral trochlea and the articular facet of the patella after a second episode. The etiology is multifactorial, including local, rotational and dynamic anatomical factors, and there is no clarity about its real influence, despite its high incidence and clinical importance. A search of Pubmed, Elsevier, Scielo, and Up to date was conducted to identify recent articles on patellofemoral instability and recurrent patella dislocation. The pathogenic origin of recurrent patellar dislocation involves structural abnormalities or muscle imbalances, its management is difficult, and multiple surgical techniques can be used. We recommend studying the possible causes and being consistent with them to carry out the definitive treatment.

Recurrent patellar dislocation is described as loss of joint congruence between the femoral trochlea and the articular facet of the patella after a second episode. It is associated with factors such as direct trauma, trochlear dysplasia, ligament laxity, patella alta, bone misalignment, anatomical malrotations, and connective tissue disorder. The presence of these factors can lead to a relapse rate or residual instability of up to 80% of cases [1]. It usually occurs in adolescents due to sports activities with direct trauma, forced valgus, or knee twisting.

The etiology is multifactorial, including local, rotational and dynamic anatomical factors, and there is no clarity about its real influence, despite its high incidence and clinical importance. This ignorance is mainly due to the complexity of the patellofemoral joint, to the different causes of pain in the anterior compartment of the knee.

It is known that the fundamental factor for the development of knee instability is trochlear dysplasia. Other influencing factors are: the high position of the patella, caused by a patellar tendon that is too long, which prevents the patella from attaching well to the femoral trochlea; Also quadriceps femoris dysplasia refers to an abnormality in the insertion of the vastusmedialis in the patella. Another important condition is the too lateral position of the tibial tuberosity, which determines the valgus of the knee extensor apparatus and therefore this results in distortion in the distance between the tibial tuberosity and the trochlear Groove [2].

The etiology of patella instability is usually multifactorial. It may be related to alterations in the alignment and rotation of the lower limb, the integrity of certain ligament structures, and excessive tension of the external aileron and hypotonia of the medial aileron. Genu valgum and genu recurvatum, excessive external knee rotation and / or excessive femoral anteversion [3].

The surgical treatment of recurrent patellar luxation is controversial, since there are many techniques developed for its treatment. No gold standard technique prevails.

With the presentation of our research, we intend to recognize the main concepts about this condition, update the predisposing anatomical conditions and analyze the main therapeutic options.

A search of Pubmed, Elsevier, Scielo, and up to date was conducted to identify recent articles on patellofemoral instability and recurrent patella dislocation. The search terms were "patellofemoral instability", "medial patellofemoral ligament", "dislocation", "subluxation", "patella". The search was carried out in the period between January 3, 2021, and May 3 of the same year.

The inclusion criteria were narrative or systematic review articles and original articles whose main topic was recurrent patellar dislocation and patellofemoral instability, evaluation and treatment. English and Spanish literature was included. From a total of 151 articles selected, 120 articles that did not meet our expectations or objectives were excluded and 31 articles that met the inclusion criteria were used.

Developing

Recurrent dislocation of the patella is a rare injury, although it immediately leads us to think of an acute traumatic entity with a history of previous, evident and intense injury, but this does not happen, external violence is generally not relevant data, they are found a series of previous anatomical and functional alterations, which facilitate dislocation.

The initial traumatic episode can be minimal and be accompanied by torsion, with intense physiological stresses on the ligaments, which produces external displacement of the patella, if this is accompanied by other pre-existing anatomical affectations, it completely dislocates the patella. All of this produces internal capsular tear and hemarthrosis.

The incidence of primary patellar dislocation is 5.8 per 100,000, and this increases to 29 per 100,000 in the age group 10-17 years. Patellar instability is estimated to affect between 5 to 7 people per 100,000 inhabitants [4, 5]. The recurrence rate ranges from 15% to 44

Anatomical Considerations

Skeletal immaturity and intense physical activity in adolescence make her more prone to knee injuries. Clinical assessment can be difficult due to the severity of pain, inflammation and joint effusion, with anterior knee pain being the most frequent symptom, which can be produced by various pathological conditions. The structures that make up the knee extensor mechanism are the muscles that make up the quadriceps, the quadriceps tendon, the patella, the medial and lateral retinacles of the patella, the patellar tendon, the anterior tuberosity of the tibia, the patellar femoral joint, the infrapatellar (Hoffa), quadriceps, and prefemoral fat pads and adjacent soft tissues.

The patella is the largest sesamoid bone in the body and is located within the quadriceps and patellar tendon complex. The functions of the ball joint are both lever and pulley. As a lever, the patella magnifies the force exerted by the quadriceps in the extension of the knee; and as a pulley, the patella redirects the force of the quadriceps as it undergoes a normal lateral displacement during flexion.

According to Dejour et al. [2] suggest that trochlear dysplasia is defined as the abnormal presence of its configuration, which can be flat, shallow or convex and is present in 96% of patients with objective dislocation of the patella. This author and his collaborators described four major anatomical factors and four minor factors of patellofemoral instability. The major instability factors are trochlear dysplasia; patella alta; the distance from the tibial tuberosity to the trochlear groove increased; and the inclination of the patella. Based on these anatomical factors, they classified the Patellofemoral pathology in two groups: Objective Patellar Instability (IPO) and Potential Patellar Instability (IPP). Patients with (IPO) have a history of at least one true patella dislocation and also an anatomical abnormality. Patients with (IPP) do not have a history of a true dislocation but do have at least one anatomical abnormality and pain [17].

In the biomechanical function of the knee, the muscles that make up the quadriceps extend the knee when the leg is raised. The quadriceps contraction stabilizes the knee when the foot is on the ground. The patella allows the knee to be extended with a small contractile force from the quadriceps. The kneecap also redirects the force exerted by the quadriceps, which results in a great compressive force on the femoro-patellar joint. The extensor mechanism stabilizes the knee joint especially during deceleration and when walking downhill [13]. Lower limb deformities influence the patella and can produce dynamic or static alterations, which alter the kinematics of the patella.

Triggering initial trauma and its incomplete treatment

Structural abnormalities (patella alta, dysplasia or aplasia of the condylar groove), or Muscle imbalances (vastusmedialis weakness, thickening or retraction of the external aileron), at first, treatment can be oriented from a conservative point of view through a selective rehabilitation program, stabilizing knee orthoses and anti-inflammatory medication.

To date, no studies have demonstrated the efficacy of physical therapy or efforts in the conservative treatment of acute patellar dislocations. However, the goal of treatment after a patellar dislocation is to decrease edema, promote the vastusmedialis oblique and gluteal activity, and increase the knee's range of motion [18].

Edema has a detrimental effect on quadriceps activity, so the faster it is reduced, the better the outcome for the patient. Treatment regimens range from immediate mobilization without a brace to cast immobilization in extension for six weeks [19]. Extension immobilization can help heal the medial structures, but stiffness can be a problem with this treatment [20].

Patients with chronic patellar instability can benefit from physical therapy, which can help them regain strength, movement, and proprioception. Patellar tape can help control excessive patellar movement during therapy. Taping has also been shown to increase quadriceps muscle torque and activate the vastusmedialis oblique earlier than the vastuslateralis during stair ascents and descents. Patients with chronic patellar instability often have weak gluteal muscles. This weakness results in adduction and internal rotation of the femur during weight-bearing activities, which can accentuate patellar instability. Strengthening the gluteal muscles or gluing the hips to promote external rotation of the femur can help solve this problem [20-22].

Definitive treatment

Patellar instability is a common and challenging condition to treat in the pediatric population, traumatic dislocations of the patella are among the most frequent knee injuries, its recurrent incidence is high. Radiology is useful for a more accurate assessment of the causes of patellofemoral instability, the simple examination is the initial complementary examination and is sufficient in most cases, reserving computed tomography for patients in whom the procedure has failed. conservative treatment and rehabilitation and are valued for surgical treatment.

Recurrence of patella injuries when dislocated and managed with physical therapy, muscle strengthening, and other techniques is high (70-90%), especially when there are difficulties in patella alignment [23].

Management of multiple large joint dislocations is often difficult, particularly if a patient has a recurrent patella dislocation. Chahla J and his collaborators [24] state that, if we do not correct the pathological misalignment, the distribution of forces in the knee, this being a load zone, will cause the injury to be perpetuated, or the appearance of new ones.

Insall J [25] reports that the most widely used surgical techniques for the correction of recurrent patellar dislocation are the Krosgius-Lecene, Cambell,Cambell-Goldthwaid, Insall, Ficat and external capsulotomy with internal application.

Osteotomy of the anterior tuberosity of the tibia is an effective and safe procedure to prevent recurrent patellar instability. By medializing, anteromedializing or distalizing the anterior tuberosity of the tibia, the force vectors acting on the patella can be redistributed, restoring normal anatomy and correct alignment of the extensor apparatus.

The main indication for medialization and distal reattachment of the patellar tendon, with reconstruction of the patello femoral ligament, refers to the patella alta. The combined treatment of soft tissues and patellar height may be insufficient in those patients with severe trochlear dysplasia. 

Patella luxation is considered the most common cause of traumatic hemarthrosis in children and the second most common cause in adolescents after anterior cruciate ligament injury. It mainly affects young and active patients between the first and second decade of life and with a slightly higher incidence in women [26]. MartínezGiménez et al. [27] state that the Insall technique is associated with medial translation of the anterior tibial tuberosity and offers a high percentage of satisfactory results, with an almost complete absence complications. They also explain that Brown, using the Emslie-Trillat technique, obtains 81% good results in 42 months of follow-up, Cox et al. they obtain somewhat better results, using the Emslie-Trillat intervention (88% of excellent results and 6% of good results) in the medium term (24 months after the intervention); However, in the long term (7 years), this same author observes a deterioration down to 66% of satisfactory results. Other authors such as Hughston obtain 71% of favorable results and 29% of unfavorable results in a ten-year follow-up.

The medial patellofemoral ligament is primarily responsible for preventing lateral displacement of the patella between full extension and 30 ° of knee flexion (60% of force). Also involved: the patello-niscal ligament in 13%, the medial retinaculum in 3%, and the medial patello-tibial ligament in 3%. After 30 °, the bone structures (femoral trochlea) take on the fundamental role in containing the patella until maximum flexion [28, 29].

The medial patellofemoral ligament is the primary restrictor to translation of the patella. Treatment for this condition continues to evolve and remains controversial [30].

Trochlear dysplasia is characterized by a shallow, flattened trochlear groove associated with patellofemoral instability. Trochleoplasty, as a corrective procedure for bone abnormalities, is intended to improve patellofemoral stability in patients with severe trochlear dysplasia. There are different surgical techniques described, either performing a resection osteotomy in the external facet preserving the articular surface and fixing it with 2 screws as described by Masse, elevating the external facet with structural bone graft following the Albee technique or deepening the trochlear groove with a Powered reamer below the articular surface as described by Dejour [31]. In any case, this technique must always be associated with other procedures, whether of soft tissues such as the release of the external retinaculum or bone (osteotomies). The main complication inpatients treated with such a procedure is residual pain, at the expense of degenerative changes of the patellofemoral joint.

For Álvarez López A et al. [32] The indications for trochleoplasty are: high-grade TD, instability of the patella with inadequate or no patellofemoral congruence, and absence of patellofemoral osteoarthritis. It is contraindicated in patients with open epiphyses. This is a demanding and aggressive surgical technique, but with great potential to improve patellar entrainment, which should be reserved for those patients with severe degrees of dysplasia.

Patellar instability is a clinical syndrome due to a morphological abnormality of the femoro-patellar joint (femoral trochlea) where the patella is prone to recurrent lateral dislocation. To assess the ratio of patellar height, the Insall-Salvati index is used. Patellar tilt and / or lateralization may be the result of rupture of the medial stabilizers of the patella, after a patellar dislocation, or present without prior evidence of dislocation. Patellar tilt is a risk factor for patellar misalignment or instability. The position of the tibial tubercle is important for the inferolateral force vector of the patella. In a normal joint, the tibial tuberosity lies vertically below the femoral sulcus.

The authors of this article declare that they have no conflict of interest with the objectives of the research.

The authors of this article participated in the diagnosis, treatment, study design, and writing of the first version, as well as the final version of the manuscript in equal parts.