Framing Patellar Instability: From Diagnosis to the Treatment of the First Episode
Abstract
:1. Introduction
2. Classification of Patellofemoral Disorders
- Objective patellar instability: Patients have experienced at least one episode of patellar dislocation and present at least one or more principal factors of instability. Patellar dislocation can occur during high-energy activities such as sports and is frequently associated with hemarthrosis.
- Potential patellar instability: Patients never experienced a true patellar dislocation, although they report a rather generic feeling of instability. It may occur daily during low-demand activities, such as walking and climbing stairs. These patients present one or more principal factors of instability.
- Patellofemoral pain syndrome: Pain is the main symptom, and it is mostly attributed to cartilage wear on either the patellar or femoral side. Imaging does not show any evident factor of instability, nor can a clinical episode of patellar dislocation be identified. In subjects suffering from patellofemoral pain (PFP) syndrome, exercise therapy should be considered the first-line treatment option as it is considered the “treatment of choice” and is supported by high-level evidence. Such therapy should include exercises for strengthening the hip and knee; these exercises can be performed through kinetic chain exercises (either weight-bearing or non-weight-bearing). Additionally, joint mobilization targeted at the knee, patellofemoral taping, and neuromuscular training have also been suggested as second-line treatment options to be used in conjunction with exercise therapy [8].
3. Principal Factors of Instability
- Trochlear dysplasia indicates whether the femoral trochlea is flat or convex (instead of concave), causing abnormal patellar tracking and a loss of joint congruence (Figure 1 and Figure 2). Dejour classified trochlear dysplasia into four groups [9]. This classification system requires an accurate lateral X-ray (congruent posterior condyles) and confirmation via axial imaging of the knee (CT scan or MRI). A certain degree of trochlear dysplasia was found in up to 96% of patients with objective or potential patellar instability [7].
- Patella alta is defined as an excessive patellar height that prevents or limits patellar engagement on the trochlea during flexion, thus predisposing the patient to patellofemoral instability. It is easily measured using the Caton–Deschamps Index (CDI) on an accurate lateral knee X-ray [10,11]. It is pathological when the CDI is greater than or equal to 1.2 (Figure 3). It is present in 30% of patellar dislocations [12].
- The tibial tuberosity-trochlear groove (TT-TG) distance [13,14] is defined as the transverse length between the most prominent point of the tibial tuberosity and the trochlear groove on the femur, calculated on axial images (CT scan or MRI), representing the axial malalignment of the extensor mechanism. The greater the distance, the greater the lateralizing force acting on the patella. It is pathological when TT-TG > 13 mm on MRI or TT-TG > 20 mm on a CT scan (Figure 4 and Figure 5).
4. Patellofemoral Instability
- Recurrent, when the patella dislocates frequently during knee flexion (two or more episodes are necessary) [17];
- Habitual, when the patella dislocates every time the knee flexes in early knee flexion (<30°) and spontaneously relocates with the extension of the knee [18].
- Permanent, when the patella is permanently dislocated through the entire knee range of motion, never facing the trochlea [19].
- Type 1: patellar dislocation after trauma, without instability and without patella maltracking.
- Type 2: patella instability without clinical or radiological signs of patella maltracking.
- Type 3: a combination of patella instability and patella maltracking. This type is divided into four subtypes, according to the main cause of the maltracking: (a) soft tissue contracture; (b) patella alta; (c) an abnormal tibial tuberosity–trochlea groove distance; (d) valgus deviations; and (e) torsional deformities.
- Type 4: instability and maltracking with a loss of patella tracking due to severe trochlear dysplasia, leading to a highly unstable ‘‘floating patella”.
- Type 5: maltracking without instability.
5. Primary Dislocation: Diagnostic Framing
- Bony avulsions: depending on the size, they may require surgery [25];
- Patella alta: the CDI must be calculated. It is often the first sign of a possible PF disorder;
- Trochlear dysplasia: the crossing sign, the supra-trochlear spur, and the double contour should be identified for classification according to Dejour [9].
- Bone bruises on the medial side of the patella and the lateral condyle, which indicate with certainty the occurrence of a recent patellar dislocation;
- Osteochondral fracture with possible loose bodies, which are important to rule out, especially in skeletally immature patients. If the osteochondral fracture has a sufficient size (5–10 mm on MRI), urgent reduction and fixation, either open or arthroscopically, must be considered [25];
- Trochlear dysplasia, for which axial images are needed to achieve a correct classification according to the Dejour classification [9];
6. Primary Dislocation: Treatment Options
6.1. Urgent Surgery
6.2. Conservative Treatment
7. Primary Dislocation: Follow-Up
8. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Age | |
---|---|
>16 | 0 |
≤16 | 1 |
Bilateral instability | |
No | 0 |
Yes | 1 |
Trochlear dysplasia | |
None | 0 |
Mild (type A) | 1 |
Severe (type B–D) | 2 |
Patellar height, IS ratio | |
≤1.2 | 0 |
>1.2 | 1 |
TT-TG distance | |
<16 mm | 0 |
≥16 mm | 1 |
Patellar tilt | |
≤20° | 0 |
>20° | 1 |
Total points | 7 |
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Maggioni, D.M.; Giorgino, R.; Messina, C.; Albano, D.; Peretti, G.M.; Mangiavini, L. Framing Patellar Instability: From Diagnosis to the Treatment of the First Episode. J. Pers. Med. 2023, 13, 1225. https://doi.org/10.3390/jpm13081225
Maggioni DM, Giorgino R, Messina C, Albano D, Peretti GM, Mangiavini L. Framing Patellar Instability: From Diagnosis to the Treatment of the First Episode. Journal of Personalized Medicine. 2023; 13(8):1225. https://doi.org/10.3390/jpm13081225
Chicago/Turabian StyleMaggioni, Davide Maria, Riccardo Giorgino, Carmelo Messina, Domenico Albano, Giuseppe Michele Peretti, and Laura Mangiavini. 2023. "Framing Patellar Instability: From Diagnosis to the Treatment of the First Episode" Journal of Personalized Medicine 13, no. 8: 1225. https://doi.org/10.3390/jpm13081225
APA StyleMaggioni, D. M., Giorgino, R., Messina, C., Albano, D., Peretti, G. M., & Mangiavini, L. (2023). Framing Patellar Instability: From Diagnosis to the Treatment of the First Episode. Journal of Personalized Medicine, 13(8), 1225. https://doi.org/10.3390/jpm13081225