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To compare in magnetic resonance imaging the anatomical risk factors for anterior cruciate ligament (ACL) injury and patellar dislocation among patients who suffered acute knee injury, 105 patients with acute knee injury resulting in 38 patellar dislocations (patella group), 35 ACL injuries (ACL group), and 32 meniscus or medial collateral ligament injuries (control group) were included. These groups were compared for risk factors for patellar dislocation (patellar height, trochlear dysplasia, and quadriceps angle of action) and for ACL injury (intercondylar width, posterior inclination of tibial plateaus, and depth of the medial plateau). Univariate analysis found statistically significant differences ( p  < 0.05) between the patella and ACL groups in patellar height (Caton-Deschamps [CD] 1.23 vs. 1.07), trochlear facet asymmetry (55 vs. 68%), PTTG (13.08 vs. 8.01 mm), and the patellar tip and trochlear groove (PTTG) angle (29.5 vs. 13.71 degrees). The patella group also differed from control in medial plateau inclination (4.8 vs. 1.87 degrees), patellar height (CD 1.23 vs 1.08), trochlear facet asymmetry (55 vs. 69%), lateral trochlear inclination (17.11 vs. 20.65 degrees), trochlear depth (4.1 vs. 6.05 mm), PTTG (13.08 vs. 9.85 mm), and the PTTG angle (29.5 vs. 17.88 degrees). The ACL and control groups were similar in all measures. Multivariate analysis found the following significant determinants between the Patella and Control groups: patellar height (CD index, odds ratio [OR]: 80.13, p  = 0.015), trochlear anatomy (asymmetry of facets M/L, OR: 1.06, p  = 0.031) and quadriceps action angle (PTTG angle, OR: 1.09, p  = 0.016); between the ACL and control groups: PTTG angle (OR: 0.936, p  = 0.04) and female gender (OR: 3.876, p  = 0.032); and between the patella and ACL groups, the CD index (OR: 67.62, p  = 0.026), asymmetry of the M/L facets (OR: 1.07, p  = 0.011) and PTTG angle (OR: 1.16, p  < 0.001). In conclusion, in patients with acute knee injury, the anatomical factors patellar height, trochlear dysplasia, and quadriceps angle of action were related to the occurrence of patellar dislocation. None of the anatomical factors studied was related to the occurrence of anterior cruciate ligament injury., Competing Interests: None declared., (Thieme. All rights reserved.)

Purpose: The purpose of this article is to review anatomical, biomechanical, and clinical data of the medial patellotibial ligament (MPTL) and medial patellomeniscal ligament (MPML), as well as studies focusing on the medial patellofemoral ligament (MPFL) but with relevant data about the MPTL and MPML., Methods: A literature search of articles specifically addressing the MPTL and/or MPML was included along with studies focusing on the MPFL but with relevant data about the MPTL and MPML., Results: The medial patellar ligaments responsible for maintaining the stability of the patellofemoral (PF) joint include the MPFL, the MPTL, and the MPML. The MPFL is considered the primary restraint to lateral patellar translation, while the latter two are considered secondary restraints. There is robust literature on the anatomical, imaging, and biomechanical characteristics of the MPFL, and also the clinical outcome of its injury and surgical reconstruction; much less is known about the MPTL and MPML. Isolated MPFL reconstruction has good clinical and functional outcomes, with a low failure rate when defined as frank re-dislocation. Complications, including continued episodes of patellar apprehension and subluxation, remain present in most series. In addition, the current literature primarily includes a homogeneous population with few excessive anatomic dysplastic factors. There is lack of knowledge on the role of MPTL and MPML in (potentially) aiding patella stabilization and improving clinical outcomes. Understanding the role of the medial-sided patellar ligaments, in particular the role of the secondary stabilizers, in PF function and injury will aid in this goal., Conclusion: MPTL and MPML have consistent basic science literature, as well as favorable clinical outcomes of surgical patellar stabilization with reconstruction of the MPTL. However, there is much heterogeneity among clinical case series and lack of comparative studies to allow clear indication for the role of isolated or combined surgical reconstruction in patellar stabilization. Therefore, this comprehensive review helps understand the current knowledge and the possible applications in the orthopedic clinical practice., Level of Evidence: V.

Background: Patellar instability is a debilitating disease. An important factor related to recurrent dislocation is patellar height. A new method of patellar height measurement, the plateau-patella angle (PPA), was proposed in 2011. However, to date, there is no study evaluating the use of this method in patients with patellar instability. The aim of this study was to evaluate the PPA in patients with recurrent patellar dislocation., Methods: This was a retrospective evaluation of the radiographs of 78 knees with patellar instability. Patellar height was measured using the Insall-Salvati (I/S), Caton-Deschamps (C/D) and Blackburne-Peel (B/P) indices and the PPA. The qualitative and quantitative correlations between the various methods and between observers were calculated., Results: The PPA had a Pearson correlation of 0.76 (P<0.001) with the I/S index, 0.78 (P<0.001) with the C/D index and 0.90 (P<0.001) with the B/P index. In the qualitative correlation using the Spearman coefficient, the PPA had a correlation of 0.52 (P<0.001) with the I/S index, 0.72 (P<0.001) with the C/D index and 0.70 (P<0.001) with the B/P index. The correlations between the conventional methods were as follows: 0.57 (P<0.001) between the I/S and C/D indices; 0.61 (P<0.001) between the I/S and B/P indices; and 0.73 (P<0.001) between the C/D and B/P indices., Conclusion: The determination of the PPA is a reproducible method that is consistent with the methods currently used to measure patellar height in patients with recurrent patellar dislocation., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Background: The location of patellar and femoral fixation of the graft in medial patellofemoral ligament reconstructions has been widely discussed. This study aimed to assess the distances between different patellar and femoral fixation points to identify the least anisometric pairs of points., Methods: Ten cadaver knees were attached to an apparatus that simulated an active range of motion of 120°, with three metallic markers fixed onto the medial side of the patella, and seven markings onto the medial epicondyle. The examined points included the proximal patella pole (1), the patellar center (3), the midpoint between points 1 and 3 (2), a point directly on the epicondyle (6), points 5mm anterior (5) and posterior (7) to the epicondyle, points 5mm anterior to point 5 (4) and 5mm posterior to point 7 (8), and points 5mm proximal (9) and distal (10) to the epicondyle. The distances between patella and femur points were measured by a photogrammetry system at 15° intervals., Findings: The pair of points that exhibited the lowest average variability in distance, and hence was the most isometric, was the patella center combined with the anterior to the medial femoral epicondyle. The pairs of points that exhibited the highest average variability in distance, and hence were the least isometric, were the ones located distal or posterior to the medial femoral epicondyle, with less influence by the patellar location., Interpretation: Surgeons should avoid positioning the graft distally or posterior to the epicondyle due to the increase in anisometry., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Replacement of the patella during total knee arthroplasty (TKA) remains controversial. Despite some attempts to establish guidelines for this procedure, there is still no consensus in the literature. When the patella is replaced, the patient is subjected to certain complications, including loosening of the component. The loosened patellar component most commonly migrates to the intra-articular region of the knee. However, there have been a few reports of migration of the component to the extra-articular region, particularly when release of the lateral retinaculum and osteonecrosis of the patella are involved. The authors report a case of patellar component loosening and extra-articular and transcutaneous migration of the component 9 years after TKA. This report is unique because, during the primary procedure, no lateral release was performed and no patellar necrosis was evident on radiographs. The component was removed in the operating room and the wound cleaned and closed. Because of the probable slow migration of the component, there was no communication between the external environment and the joint at the time of surgery. There were no further complications after the wound healed. This case emphasizes the need for periodic radiographic follow-up after TKA., (Copyright 2014, SLACK Incorporated.)