Lower Limb Deformities Are Additional Important Risk Factors for Patellar Dislocation
The article by Frings et al. identifies in the context of a technically carefully conducted systematic literature search eight risk factors regarding the risk of recurrent dislocation after primary patellar dislocation (age, sex, bilateral instability, high-riding patella (patella alta), and trochlear dysplasia, a pathologically increased tibial tuberosity to trochlear groove (TT-TG) distance, and location of the rupture of the medial patellofemoral ligament (MPFL))(1).
As the recent literature shows, however, two risk factors are increasingly gaining particular relevance: Valgus deformity and increased femoral neck anteversion. Biomechanically, the powerful extensor muscles of the thigh that attach to the patella constitute a power vector that substantially facilitates patellar dislocation in valgus and torsional deformities and. Corrections of the lower limb anatomy—varus derotation osteotomy or better: varus detorsion osteotomy —are therefore gaining increasing importance in the therapeutic repertoire (2, 3).
The present study did not identify valgus deformity and increased femoral neck anteversion as risk factors for recurrent patellar dislocation and were mentioned merely as an aside.
The reason for this lies in the inclusion criteria of the literature search. The only imaging modality included was magnetic resonance imaging (MRI). However, the gold standard imaging techniques in determining the alignment of the leg and the femoral head anteversion are the two techniques: long leg bilateral standing radiographs and “low dose” torsion computed tomography (CT). Simultaneous biplanar low-dose radiography (EOS), torsion MRI, and “cone beam” CT are rarely used alternative methods (4).
Let me emphasize: In addition to the risk factors for recurrent patellar dislocation, leg deformities such as valgus deformity and increased femoral neck anteversion are to be considered and should be mentioned as potentially weighty.
Dr. med. Peter H. Thaller, MSc
Klinikum der Universität München
Klinik für Allgemeine, Unfall- und Wiederherstellungschirurgie, München
|1.||Frings J, Balcarek P, Tscholl P, Liebensteiner M, Dirisamer F, Koenen P: Conservative versus surgical treatment for primary patellar dislocation—a systematic review to guide risk stratification. Dtsch Arztebl Int 2020; 117: 279–86 VOLLTEXT|
|2.||Frosch K-H, Schmeling A: A new classification system of patellar instability and patellar maltracking. Arch Orthop Trauma Surg 2016; 136: 485–97 CrossRef MEDLINE|
|3.||Franciozi CE, Ambra LF, Albertoni LJB, et al.: Increased femoral anteversion influence over surgically treated recurrent patellar instability patients. Arthroscopy 2017; 33: 633–40 CrossRef MEDLINE|
|4.||Thaller PH, Baumgart R, Burghardt R, Knuellig S, Buerklein D, Mutschler W: Digital imaging in lower limb bone deformities–standards and new perspectives. Int Congr Ser 2005; 1281: 154–8 CrossRef|