High Femoral Antetorsion Is a Major Risk Factor for Anterior Knee Pain whereas Trochlea Dysplasia Predisposes for Patella Dislocation

PURPOSE OF THE STUDY Patellofemoral stability and congruency are influenced by different parameters. Their contribution to anterior knee pain and instability is not fully understood. We investigated, if isolated femoral antetorsion of more than 25° leads to patellofemoral instability. MATERIAL AND METHODS We analyzed 90 knees in patients with patellofemoral complaints and correlated clinical and radiological characteristics. Patients presenting at our center between January 2018 and December 2020 because of patellofemoral pain or instability were included, provided that there was no previous surgical intervention done. RESULTS The severity of trochlea dysplasia classified using the Oswestry-Bristol classification significantly correlated with events of patellofemoral dislocations. (χ=8.152, p=0.043, φ=0.288). All males with a history of patella dislocation had at least a mild trochlea dysplasia. The majority of females complaining about patellofemoral symptoms in general had a dysplastic trochlea. Patella alta is more frequently found in patients with trochlea dysplasia than in patients with a normal femoral trochlea anatomy. DISCUSSION The majority of unstable patellofemoral joints showed a dysplastic trochlea. A high femoral antetorsion was found to be an additional minor factor contributing to instability. Isolated high femoral antetorsion without trochlea dysplasia rather leads to anterior knee pain without patella dislocation. Furthermore, no direct significant correlation between patella alta and patellofemoral instability was found. Patella alta can therefore rather be seen as a result of a dysplastic trochlea than a primary major risk factor for patellofemoral instability. CONCLUSIONS Trochlea dysplasia is the major risk factor for patellofemoral instability. Patella alta can rather be seen as a result of a dysplastic trochlea than as a primary risk factor for patella instability or pain. Isolated high femoral antetorsion often leads to patellofemoral pain syndrome but not to patella dislocations. Key words: MPFL, patella instability, patellofemoral instability.

The Choroid Plexus Is Permissive for a Preactivated Antigen-Experienced Memory B-Cell Subset in Multiple Sclerosis

The role of B cells in multiple sclerosis (MS) is increasingly recognized. B cells undergo compartmentalized redistribution in blood and cerebrospinal fluid (CSF) during active MS, whereby memory B cells accumulate in the CSF. While B-cell trafficking across the blood-brain barrier has been intensely investigated, cellular diapedesis through the blood-CSF barrier (BCSFB) is incompletely understood. To investigate how B cells interact with the choroid plexus to transmigrate into the CSF we isolated circulating B cells from healthy donors (HC) and MS patients, utilized an inverted cell culture filter system of human choroid plexus papilloma (HIBCPP) cells to determine transmigration rates of B-cell subsets, immunofluorescence, and electron microscopy to analyze migration routes, and qRT-PCR to determine cytokines/chemokines mediating B-cell diapedesis. We also screened the transcriptome of intrathecal B cells from MS patients. We found, that spontaneous transmigration of HC- and MS-derived B cells was scant, yet increased significantly in response to B-cell specific chemokines CXCL-12/CXCL-13, was further boosted upon pre-activation and occurred via paracellular and transcellular pathways. Migrating cells exhibited upregulation of several genes involved in B-cell activation/migration and enhanced expression of chemokine receptors CXCR4/CXCR5, and were predominantly of isotype class switched memory phenotype. This antigen-experienced migratory subset displayed more pronounced chemotactic activities in MS than in HC and was retrieved in intrathecal B cells from patients with active MS. Trafficking of class-switched memory B cells was downscaled in a small cohort of natalizumab-exposed MS patients and the proportions of these phenotypes were reduced in peripheral blood yet were enriched intrathecally in patients who experienced recurrence of disease activity after withdrawal of natalizumab. Our findings highlight the relevance of the BCSFB as important gate for the entry of potentially harmful activated B cells into the CSF.