Objective: Habitual patellar dislocation (HDP) in children and adolescents is divided into dislocation in flexion and dislocation in extension, but their pathogenesis remains unclear. Our purpose is to focus on investigating the anatomical difference between the extended dislocation and the flexed dislocation of HDP.
Methods: We retrospectively observed all patients diagnosed as HDP who underwent surgery at our institution from May 2016 to August 2023. Patients were categorized into two subgroups according to “J sign”: the extension group and the flexion group. We measured and compared the various anatomical parameters on CT images, including patellar dysplasia, trochlear dysplasia, alignment of the patellofemoral joint, and torsional deformity of the knee joint. Continuous data were analyzed using the t-test, while categorical data were analyzed using Fisher exact test and Mann–Whitney U test.
Results: We enrolled 20 patients (average age of 9 years old, ranging from 6 to 15; 14 patients in the extension group and 6 patients in the flexion group) with 30 knees. The extension group exhibited significantly greater Wiberg index (0.62 ± 0.09 vs. 0.56 ± 0.05, p = 0.030), lateral patellar angle (17.83 ± 4.5 vs. 12.24 ± 5.7, p = 0.009), PT/FT ratio (1.45 ± 0.1 vs. 1.31 ± 0.1, p = 0.005), and Caton–Deschamps index (1.46 ± 0.3 vs. 1.17 ± 0.1, p = 0.015) than those in the flexion group. Meanwhile, the flexion group demonstrated greater patellar lateralization distance (24.03 ± 11.5 vs. 16.26 ± 7.3, p = 0.036), patellar inclination angle (50.75 ± 13.1 vs. 29.98 ± 14.5, p = 0.001), lateral patellofemoral angle (38.49 ± 13.5 vs. 18.32 ± 8.2, p = 0.000) and congruence angle (57.57 ± 23.3 vs. 28.15 ± 16.7, p = 0.001) when knees were extending but a smaller lateral trochlear inclination angle (18.84 ± 6.9 vs. 12.49 ± 5.2, p = 0.026) than those in the extension group. Additionally, the knees in the flexion group predominated the femoral trochlea of Dejour type C and D (100%) while only half of the extension group had Dejour type C and D (51%). The duration of symptoms before surgery was significantly longer in the extension group compared to the flexion group (25.93 ± 25.8 months vs. 9.33 ± 4.18 months, p = 0.034). Parameters related to torsional abnormality of the lower extremity showed no significant difference between the two groups.
Conclusions: Patients with HDP in extension had patella alta, more severe patellar dysplasia, while those with HDP in flexion had a more inclined patella, laterally positioned patella when knees extended, and a more dysplastic femoral trochlea. These differences provide reasonable references for doctors to better understand the mechanisms of dislocation and the design of optimal surgical strategies.
Clinical Relevance: Improved understanding of anatomical features of HDP is critical to informing clinical treatment decisions.
| [1] |
S. N. Parikh and M. G. Lykissas, “Classification of Lateral Patellar Instability in Children and Adolescents,” Orthopedic Clinics of North America 47, no. 1 (2016): 145–152.
|
| [2] |
S. Batra and S. Arora, “Habitual Dislocation of Patella: A Review,” Journal of Clinical Orthopaedics and Trauma 5, no. 4 (2014): 245–251.
|
| [3] |
J. Chen, L. Sha, X. Zhang, et al., “Impact of Sex and Age on the Lateralisation of the Tibial Tubercle in Normal Paediatric and Adolescent Populations,” Knee Surgery, Sports Traumatology, Arthroscopy 32, no. 5 (2024): 1207–1215.
|
| [4] |
J. Chen, Z. Ye, C. Wu, X. Zhang, J. Zhao, and G. Xie, “Sulcus Depth, Congruence Angle, Wiberg Index, TT-TG Distance, and CDI Are Strong Predictors of Recurrent Patellar Dislocation,” Knee Surgery, Sports Traumatology, Arthroscopy 31, no. 7 (2023): 2906–2916.
|
| [5] |
A. De Leeuw, S. Abidi, L. Scarciolla, D. Petersbourg, S. Putman, and A. Cotten, “Patellar Instability: Imaging Findings,” Seminars in Musculoskeletal Radiology 28, no. 3 (2024): 257–266.
|
| [6] |
N. Pascual-Leone, H. B. Ellis, and D. W. Green, “Patellar Instability: Will My Patella Dislocate Again?,” Current Opinion in Pediatrics 34, no. 1 (2022): 76–81.
|
| [7] |
D. Wang, Z. Zhang, Y. Cao, et al., “Recurrent Patellar Dislocation Patients With High-Grade J-Sign Have Multiple Structural Bone Abnormalities in the Lower Limbs,” Knee Surgery, Sports Traumatology, Arthroscopy 32, no. 7 (2024): 1650–1659.
|
| [8] |
H. Dejour, G. Walch, L. Nove-Josserand, and C. Guier, “Factors of Patellar Instability: An Anatomic Radiographic Study,” Knee Surgery, Sports Traumatology, Arthroscopy 2, no. 1 (1994): 19–26.
|
| [9] |
T. J. Dietrich, S. F. Fucentese, and C. W. Pfirrmann, “Imaging of Individual Anatomical Risk Factors for Patellar Instability,” Seminars in Musculoskeletal Radiology 20, no. 1 (2016): 65–73.
|
| [10] |
L. Huang, Z. H. Qian, Z. Yang, X. M. Lv, and C. Feng, “Comparison of Habitual Versus Recurrent Patellar Dislocation in Children and Adolescents: Differences in Radiological Features,” Orthopaedic Journal of Sports Medicine 11, no. 7 (2023): 23259671231180574.
|
| [11] |
Y. Dai, H. Yin, C. Xu, H. Zhang, A. Guo, and N. Diao, “Association of Patellofemoral Morphology and Alignment With the Radiographic Severity of Patellofemoral Osteoarthritis,” Journal of Orthopaedic Surgery and Research 16, no. 1 (2021): 548.
|
| [12] |
A. S. Panni, S. Cerciello, N. Maffulli, M. Di Cesare, E. Servien, and P. Neyret, “Patellar Shape Can Be a Predisposing Factor in Patellar Instability,” Knee Surgery, Sports Traumatology, Arthroscopy 19, no. 4 (2011): 663–670.
|
| [13] |
J. Chen, Z. Ye, C. Wu, X. Zhang, J. Zhao, and G. Xie, “Patellar Shift Ratio (PSR) is the Optimal Measurement for Characterising Lateral Patellar Shift and a Reliable Predictor of Recurrent Patellar Dislocation,” Knee Surgery, Sports Traumatology, Arthroscopy 31, no. 7 (2023): 2818–2827.
|
| [14] |
L. Dagneaux, H. R. Bin Abd Razak, P. Laumonerie, et al., “Bony Asymmetry in Patellofemoral Morphology and Risk Factors of Instability Are Mostly Clinically Negligible,” Knee Surgery, Sports Traumatology, Arthroscopy 29, no. 11 (2021): 3793–3799.
|
| [15] |
C. C. Hasler and D. Studer, “Patella Instability in Children and Adolescents,” EFORT Open Reviews 1, no. 5 (2016): 160–166.
|
| [16] |
C. E. Franciozi, L. F. Ambra, L. J. B. Albertoni, et al., “Anteromedial Tibial Tubercle Osteotomy Improves Results of Medial Patellofemoral Ligament Reconstruction for Recurrent Patellar Instability in Patients With Tibial Tuberosity-Trochlear Groove Distance of 17 to 20 mm,” Arthroscopy 35, no. 2 (2019): 566–574.
|
| [17] |
T. O. Smith, A. Clark, S. Neda, et al., “The Intra- and Inter-Observer Reliability of the Physical Examination Methods Used to Assess Patients With Patellofemoral Joint Instability,” Knee 19, no. 4 (2012): 404–410.
|
| [18] |
L. A. Hiemstra, C. L. O'Brien, M. R. Lafave, and S. Kerslake, “Common Physical Examination Tests for Patellofemoral Instability Demonstrate Weak Inter-Rater Reliability,” Arthroscopy, Sports Medicine, and Rehabilitation 3, no. 3 (2021): e673–e677.
|
| [19] |
Z. Xue, G. Y. Song, X. Liu, et al., “Excessive Lateral Patellar Translation on Axial Computed Tomography Indicates Positive Patellar J Sign,” Knee Surgery, Sports Traumatology, Arthroscopy 26, no. 12 (2018): 3620–3625.
|
| [20] |
R. C. Manske and G. J. Davies, “Examination of the Patellofemoral Joint,” International Journal of Sports Physical Therapy 11, no. 6 (2016): 831–853.
|
| [21] |
W. R. Post, “Clinical Evaluation of Patients With Patellofemoral Disorders,” Arthroscopy 15, no. 8 (1999): 841–851.
|
| [22] |
P. P. Lee, M. Chalian, J. A. Carrino, J. Eng, and A. Chhabra, “Multimodality Correlations of Patellar Height Measurement on X-Ray, CT, and MRI,” Skeletal Radiology 41, no. 10 (2012): 1309–1314.
|
| [23] |
J. Insall and E. Salvati, “Patella Position in the Normal Knee Joint,” Radiology 101, no. 1 (1971): 101–104.
|
| [24] |
P. A. Kannus, “Long Patellar Tendon: Radiographic Sign of Patellofemoral Pain Syndrome-A Prospective Study,” Radiology 185, no. 3 (1992): 859–863.
|
| [25] |
R. C. Burgess, “A New Method of Determining Patellar Position,” Journal of Sports Medicine and Physical Fitness 29, no. 4 (1989): 389–399.
|
| [26] |
E. E. Berg, S. L. Mason, and M. J. Lucas, “Patellar Height Ratios. A Comparison of Four Measurement Methods,” American Journal of Sports Medicine 24, no. 2 (1996): 218–221.
|
| [27] |
J. S. Blackburne and T. E. Peel, “A New Method of Measuring Patellar Height,” Journal of Bone and Joint Surgery (British Volume) 59, no. 2 (1977): 241–242.
|
| [28] |
J. Caton, G. Deschamps, P. Chambat, J. L. Lerat, and H. Dejour, “Patella infera. Apropos of 128 Cases,” Revue de Chirurgie Orthopédique et Réparatrice de l'Appareil Moteur 68, no. 5 (1982): 317–325.
|
| [29] |
W. R. Hepp, “2 New Methods for Determination of the Height of Patella,” Zeitschrift für Orthopädie und Ihre Grenzgebiete 122, no. 2 (1984): 159–166.
|
| [30] |
A. de Carvalho, A. Holst Andersen, S. Topp, and A. G. Jurik, “A Method for Assessing the Height of the Patella,” International Orthopaedics 9, no. 3 (1985): 195–197.
|
| [31] |
F. V. Verhulst, J. D. P. van Sambeeck, G. S. Olthuis, J. van der Ree, and S. Koeter, “Patellar Height Measurements: Insall-Salvati Ratio Is Most Reliable Method,” Knee Surgery, Sports Traumatology, Arthroscopy 28, no. 3 (2020): 869–875.
|
| [32] |
R. A. Yue, E. A. Arendt, and M. A. Tompkins, “Patellar Height Measurements on Radiograph and Magnetic Resonance Imaging in Patellar Instability and Control Patients,” Journal of Knee Surgery 30, no. 9 (2017): 943–950.
|
| [33] |
V. Sanchis-Alfonso, “How to Deal With Chronic Patellar Instability: What Does the Literature Tell Us?,” Sports Health 8, no. 1 (2016): 86–90.
|
| [34] |
T. Koshino and K. Sugimoto, “New Measurement of Patellar Height in the Knees of Children Using the Epiphyseal Line Midpoint,” Journal of Pediatric Orthopaedics 9, no. 2 (1989): 216–218.
|
| [35] |
C. L. Phillips, D. A. Silver, P. J. Schranz, and V. Mandalia, “The Measurement of Patellar Height: A Review of the Methods of Imaging,” Journal of Bone and Joint Surgery (British Volume) 92, no. 8 (2010): 1045–1053.
|
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