- Email: [email protected]
Patellar Instability
Patellar Instability
A
13-year-old boy presented to his pediatrician with knee pain after sustaining a twisting injury while playing soccer; he reported a “pop.” The patient was able to walk, and radiographs were read as negative. He was further evaluated by a pediatric orthopedist; on exam, he was able to laterally subluxate his patella (Video; available at www.jpeds. com). On flexion-extension examination, a “J” sign was present. The patient was sent for further imaging, which
revealed edema on the lateral femoral condyle (Figure 1) as well as a chondral fracture of the medial patella and edema in the lateral ligaments of the knee. The patient was diagnosed with a medial patellofemoral ligament tear secondary to traumatic patellar dislocation. Lateral instability of the patella is a common and often unrecognized cause of knee pain in an adolescent patient and involves varying degrees of lateral patellar translation relative to the femoral trochlea.1 Causes of instability include connective tissue disorders, developmental dysplasias, and trauma. Although some patients recall a specific traumatic event, others may not, which requires the diagnosis to be made on physical exam and imaging. The peak incidence of patellar dislocation occurs between the ages of 15 and 19 years old, with a rate of 11.19 per 100 000 person-years.2 The rate of acute patellar dislocations are 33% higher in females than males and the risk of recurrent injuries is three times higher in girls.3 A simple patellar tracking exam should be a part of the knee exam in all adolescents with anterior knee pain. Gently palpating the patella during flexion and extension can reveal deviations from the normal straight-line trajectory. The “Jsign” refers to a path the patella takes as it engages the femur in early flexion.4 The Q angle is the angle formed by a line drawn from the anterior superior iliac spine to central patella and then from central patella to tibial tubercle. Normal values are 14 for males and 17 for females.5 Increases in this angle are associated with an increased risk of patellar instability. The integrity of the medial patellofemoral ligament, an important stabilizer that is often injured with patellar dislocation, can be assessed by palpating along the anterior medial epicondyle (Figure 2; available at www.jpeds.com). A patellar apprehension test can also help identify abnormal mobility of the patella. Apprehension with the knee flexed to 20 as the patella is translated laterally indicates pathologic movement.4 First line management of patellar instability without fracture or loose body is conservative.6 Conservative management consists of immobilization in slight flexion for 4-6 weeks with a knee immobilizer or hinged knee brace followed by physical therapy.6 If nonoperative management fails (ie, the patient has recurrent dislocation), there are many types of surgical reconstruction options available.6 n Steven F. DeFroda, MD, ME Jonathan D. Hodax, MD, MS
Figure 1. A, Coronal MRI demonstrating edema (white star) of the lateral femoral condyle due to traumatic patellar dislocation. B, Axial MRI showing edema consistent with MPFL avulsion (white star). MPFL, medial patellofemoral ligament; MRI, magnetic resonance imaging. J Pediatr 2016;-:---. 0022-3476/$ - see front matter. Copyright ª 2016 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jpeds.2016.03.025
Department of Orthopedics
Aristides I. Cruz, Jr., MD Division of Pediatric Orthopedic Surgery Department of Orthopedics Alpert Medical School of Brown University Providence, Rhode Island
References available at www.jpeds.com 1
THE JOURNAL OF PEDIATRICS
www.jpeds.com
References 1. Khan N, Fithian D, Nomura E. Anatomy of patellar dislocation. In: Sanchis-Alfonso V, ed. Anterior Knee Pain and Patellar Instability. London: Springer; 2011 http://dx.doi.org/10.1007/978-0-85729-507-1. 2. Waterman BR, Belmont PJ, Owens BD. Patellar dislocation in the US: role of sex, age, race, and athletic participation. J Knee Surg:51-7, http://www.ncbi. nlm.nih.gov/pubmed/22624248, 2012;25. Accessed November 27, 2015.
Volume 3. Fithian DC. Epidemiology and natural history of acute patellar dislocation. Am J Sports Med 2004;32:1114-21. 4. Tanner SM, Garth WP. A modified test for patellar instability. Clin J Sport Med 2003;13:327-38. 5. Lester JD, Watson JN, Hutchinson MR. Physical examination of the patellofemoral joint. Clin Sports Med 2014;33:403-12. 6. Chotel F, Berard J, Raux S. Patellar instability in children and adolescents. Orthop Traumatol Surg Res 2014;100(1 Suppl):S125-37.
Figure 2. The location of the MPFL is marked. In thin patients, this ligament can be palpated as a thin subcutaneous cord. MPFL, medial patellofemoral ligament. 1.e1
DeFroda, Hodax, and Cruz
A
13-year-old boy presented to his pediatrician with knee pain after sustaining a twisting injury while playing soccer; he reported a “pop.” The patient was able to walk, and radiographs were read as negative. He was further evaluated by a pediatric orthopedist; on exam, he was able to laterally subluxate his patella (Video; available at www.jpeds. com). On flexion-extension examination, a “J” sign was present. The patient was sent for further imaging, which
revealed edema on the lateral femoral condyle (Figure 1) as well as a chondral fracture of the medial patella and edema in the lateral ligaments of the knee. The patient was diagnosed with a medial patellofemoral ligament tear secondary to traumatic patellar dislocation. Lateral instability of the patella is a common and often unrecognized cause of knee pain in an adolescent patient and involves varying degrees of lateral patellar translation relative to the femoral trochlea.1 Causes of instability include connective tissue disorders, developmental dysplasias, and trauma. Although some patients recall a specific traumatic event, others may not, which requires the diagnosis to be made on physical exam and imaging. The peak incidence of patellar dislocation occurs between the ages of 15 and 19 years old, with a rate of 11.19 per 100 000 person-years.2 The rate of acute patellar dislocations are 33% higher in females than males and the risk of recurrent injuries is three times higher in girls.3 A simple patellar tracking exam should be a part of the knee exam in all adolescents with anterior knee pain. Gently palpating the patella during flexion and extension can reveal deviations from the normal straight-line trajectory. The “Jsign” refers to a path the patella takes as it engages the femur in early flexion.4 The Q angle is the angle formed by a line drawn from the anterior superior iliac spine to central patella and then from central patella to tibial tubercle. Normal values are 14 for males and 17 for females.5 Increases in this angle are associated with an increased risk of patellar instability. The integrity of the medial patellofemoral ligament, an important stabilizer that is often injured with patellar dislocation, can be assessed by palpating along the anterior medial epicondyle (Figure 2; available at www.jpeds.com). A patellar apprehension test can also help identify abnormal mobility of the patella. Apprehension with the knee flexed to 20 as the patella is translated laterally indicates pathologic movement.4 First line management of patellar instability without fracture or loose body is conservative.6 Conservative management consists of immobilization in slight flexion for 4-6 weeks with a knee immobilizer or hinged knee brace followed by physical therapy.6 If nonoperative management fails (ie, the patient has recurrent dislocation), there are many types of surgical reconstruction options available.6 n Steven F. DeFroda, MD, ME Jonathan D. Hodax, MD, MS
Figure 1. A, Coronal MRI demonstrating edema (white star) of the lateral femoral condyle due to traumatic patellar dislocation. B, Axial MRI showing edema consistent with MPFL avulsion (white star). MPFL, medial patellofemoral ligament; MRI, magnetic resonance imaging. J Pediatr 2016;-:---. 0022-3476/$ - see front matter. Copyright ª 2016 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jpeds.2016.03.025
Department of Orthopedics
Aristides I. Cruz, Jr., MD Division of Pediatric Orthopedic Surgery Department of Orthopedics Alpert Medical School of Brown University Providence, Rhode Island
References available at www.jpeds.com 1
THE JOURNAL OF PEDIATRICS
www.jpeds.com
References 1. Khan N, Fithian D, Nomura E. Anatomy of patellar dislocation. In: Sanchis-Alfonso V, ed. Anterior Knee Pain and Patellar Instability. London: Springer; 2011 http://dx.doi.org/10.1007/978-0-85729-507-1. 2. Waterman BR, Belmont PJ, Owens BD. Patellar dislocation in the US: role of sex, age, race, and athletic participation. J Knee Surg:51-7, http://www.ncbi. nlm.nih.gov/pubmed/22624248, 2012;25. Accessed November 27, 2015.
Volume 3. Fithian DC. Epidemiology and natural history of acute patellar dislocation. Am J Sports Med 2004;32:1114-21. 4. Tanner SM, Garth WP. A modified test for patellar instability. Clin J Sport Med 2003;13:327-38. 5. Lester JD, Watson JN, Hutchinson MR. Physical examination of the patellofemoral joint. Clin Sports Med 2014;33:403-12. 6. Chotel F, Berard J, Raux S. Patellar instability in children and adolescents. Orthop Traumatol Surg Res 2014;100(1 Suppl):S125-37.
Figure 2. The location of the MPFL is marked. In thin patients, this ligament can be palpated as a thin subcutaneous cord. MPFL, medial patellofemoral ligament. 1.e1
DeFroda, Hodax, and Cruz