Helicase Subunit Cdc45 Targets the Checkpoint Kinase Rad53 to Both Replication Initiation and Elongation Complexes after Fork Stalling.

Across eukaryotes, disruption of DNA replication causes an S phase checkpoint response, which regulates multiple processes, including inhibition of replication initiation and fork stabilization. How these events are coordinated remains poorly understood. Here, we show that the replicative helicase component Cdc45 targets the checkpoint kinase Rad53 to distinct replication complexes in the budding yeast Saccharomyces cerevisiae. Rad53 binds to forkhead-associated (FHA) interaction motifs in an unstructured loop region of Cdc45, which is phosphorylated by Rad53 itself, and this interaction is necessary for the inhibition of origin firing through Sld3. Cdc45 also recruits Rad53 to stalled replication forks, which we demonstrate is important for the response to replication stress. Finally, we show that a Cdc45 mutation found in patients with Meier-Gorlin syndrome disrupts the functional interaction with Rad53 in yeast. Together, we present a single mechanism by which a checkpoint kinase targets replication initiation and elongation complexes, which may be relevant to human disease.

DONSON facilitates Cdc45 and GINS chromatin association and is essential for DNA replication initiation.

Faithful cell division is the basis for the propagation of life and DNA replication must be precisely regulated. DNA replication stress is a prominent endogenous source of genome instability that not only leads to ageing, but also neuropathology and cancer development in humans. Specifically, the issues of how vertebrate cells select and activate origins of replication are of importance as, for example, insufficient origin firing leads to genomic instability and mutations in replication initiation factors lead to the rare human disease Meier-Gorlin syndrome. The mechanism of origin activation has been well characterised and reconstituted in yeast, however, an equal understanding of this process in higher eukaryotes is lacking. The firing of replication origins is driven by S-phase kinases (CDKs and DDK) and results in the activation of the replicative helicase and generation of two bi-directional replication forks. Our data, generated from cell-free Xenopus laevis egg extracts, show that DONSON is required for assembly of the active replicative helicase (CMG complex) at origins during replication initiation. DONSON has previously been shown to be essential during DNA replication, both in human cells and in Drosophila, but the mechanism of DONSON's action was unknown. Here we show that DONSON's presence is essential for replication initiation as it is required for Cdc45 and GINS association with Mcm2-7 complexes and helicase activation. To fulfil this role, DONSON interacts with the initiation factor, TopBP1, in a CDK-dependent manner. Following its initiation role, DONSON also forms a part of the replisome during the elongation stage of DNA replication. Mutations in DONSON have recently been shown to lead to the Meier-Gorlin syndrome; this novel replication initiation role of DONSON therefore provides the explanation for the phenotypes caused by DONSON mutations in patients.

De novo enhancer deletion of LMX1B produces a mild nail-patella clinical phenotype.

Critical genes involved in embryonic development are often transcription factors, regulating many downstream genes. LMX1B is a homeobox gene that is involved in formation of the limbs, eyes and kidneys, heterozygous loss-of-function sequence variants and deletions cause Nail-Patella syndrome. Most of the reported variants are localised within the gene's coding sequence, however, approximately 5%-10% of affected individuals do not have a pathogenic variant identified within this region. In this study, we present a family with four affected individuals across two generations with a deletion spanning a conserved upstream LMX1B-binding sequence. This deletion is de novo in the mother of three affected children. Furthermore, in this family, the manifestations appear limited to the nails and limbs, and therefore may reflect an attenuated phenotype of the classic Nail-Patella phenotype that includes ophthalmological and renal manifestations.

Functional studies in yeast confirm the pathogenicity of a new GINS3 Meier-Gorlin syndrome variant.

Meier-Gorlin syndrome (MGORS) is an autosomal recessive disorder characterized by short stature, microtia, and patellar hypoplasia, and is caused by pathogenic variants of cellular factors involved in the initiation of DNA replication. We previously reported that biallelic variants in GINS3 leading to amino acid changes at position 24 (p.Asp24) cause MGORS. Here, we describe the phenotype of a new individual homozygous for the Asp24Asn variant. We also report the clinical characteristics of an individual harboring a novel homozygous GINS3 variant (Ile25Phe) and features suggestive of MGORS. Modification of the corresponding residue in yeast Psf3 (Val9Phe) compromised S phase progression compared to a humanized Psf3 Val9Ile variant. Expression of Psf3 Val9Phe in yeast also caused sensitivity to elevated temperature and the replicative stress-inducing drug hydroxyurea, confirming partial loss of function of this variant in vivo and allowing us to upgrade the classification of this variant. Taken together, these data validate the critical importance of the GINS DNA replication complex in the molecular etiology of MGORS.

Quadriceps muscle contraction causes medial patellofemoral ligament elongation by intermeshed fibers of vastus medialis oblique muscle.

The first aim of this study was to compare the medial patellofemoral length between contracted and relaxed quadriceps muscle and second to assess the importance of the intermeshed vastus medialis oblique fibers. After a priori power analysis (α = 0.05, power [1-ß] = 0.95), 35 healthy males aged 18-30 were prospectively examined with a 3.0-T magnetic resonance imaging (MRI) scanner in 10-15° of knee flexion. Two axial MRI sequences (25 s each) were made with relaxed and contracted quadriceps. Two blinded, independent raters measured twice medial patellofemoral ligament length (curved line) and attachment-to-attachment length (straight line). Mean medial patellofemoral ligament length and attachment-to-attachment length with relaxed quadriceps was: 65.5 mm (SD = 3.7), 59.7 mm (SD = 3.6), and after contraction, it increased to 68.7 mm (SD = 5.3), 61.2 mm (SD = 4.7); p < 0.01 and <0.001, respectively. Intraclass correlation coefficients for intra- and inter-rater reliabilities ranged from 0.55 (moderate) to 0.97 (excellent). Mean medial patellofemoral ligament length elongation after quadriceps contraction was significantly greater (3.2 mm, SD = 3.9) than mean attachment-to-attachment length elongation (1.6 mm, SD = 2.8); p < 0.001. Contraction of quadriceps muscle causes elongation of the medial patellofemoral ligament to the extent greater than the elongation of distance between its attachments. This confirms that medial patellofemoral ligament elongation after quadriceps contraction results not only from movement of its patellar attachment but also directly from intermeshed vastus medialis oblique fibers pulling medial patellofemoral ligament in a different direction creating a bow-like construct in agreement with the "pull-and-guide mechanism" proposed in the literature.

T2 Mapping of Patellar Cartilage After a Single First-Time Episode of Traumatic Lateral Patellar Dislocation.

BACKGROUND: In most cases, lateral patellar dislocation (LPD) is accompanied by chondral injury and may initiate gradual degeneration of patellar cartilage, which might be detected with a T2 mapping, a well-established method for cartilage lesions assessment. PURPOSE: To examine short-term consequences of single first-time LPD in teenagers by T2 mapping of the patellar-cartilage state. STUDY TYPE: Prospective. POPULATION: 95 patients (mean age: 15.1 ± 2.3; male/female: 46/49) with first-time, complete, traumatic LPD and 51 healthy controls (mean age: 14.7 ± 2.2, male/female: 29/22). FIELD STRENGTH/SEQUENCE: 3.0 T; axial T2 mapping acquired using a 2D turbo spin-echo sequence. ASSESSMENT: MRI examination was conducted 2-4 months after first LPD. T2 values were calculated in manually segmented cartilage area via averaging over three middle level slices in six cartilage regions: deep, intermediate, superficial layers, and medial lateral parts. STATISTICAL TESTS: ANOVA analysis with Tukey's multiple comparison test, one-vs.-rest logistic regression analysis. The threshold of significance was set at P < 0.05. RESULTS: In lateral patellar cartilage, a significant increase in T2 values was found in deep and intermediate layers in both patient groups with mild (deep: 34.7 vs. 31.3 msec, intermediate: 38.7 vs. 34.6 msec, effect size = 0.55) and severe (34.8 vs. 31.3 msec, 39.1 vs. 34.6 msec, 0.55) LPD consequences as compared to controls. In the medial facet, only severe cartilage damage showed significant prolongation of T2 times in the deep layer (34.3 vs. 30.7 msec, 0.55). No significant changes in T2 values were found in the lateral superficial layer (P = 0.99), whereas mild chondromalacia resulted in a significant decrease of T2 in the medial superficial layer (41.0 vs. 43.8 msec, 0.55). DATA CONCLUSION: The study revealed substantial difference in T2 changes after LPD between medial and lateral areas of patellar cartilage. EVIDENCE LEVEL: 2 TECHNICAL EFFICACY STAGE: 2.

Improving prediction of linear regression models by integrating external information from heterogeneous populations: James-Stein estimators.

We consider the setting where (1) an internal study builds a linear regression model for prediction based on individual-level data, (2) some external studies have fitted similar linear regression models that use only subsets of the covariates and provide coefficient estimates for the reduced models without individual-level data, and (3) there is heterogeneity across these study populations. The goal is to integrate the external model summary information into fitting the internal model to improve prediction accuracy. We adapt the James-Stein shrinkage method to propose estimators that are no worse and are oftentimes better in the prediction mean squared error after information integration, regardless of the degree of study population heterogeneity. We conduct comprehensive simulation studies to investigate the numerical performance of the proposed estimators. We also apply the method to enhance a prediction model for patella bone lead level in terms of blood lead level and other covariates by integrating summary information from published literature.

CT of Periarticular Adult Knee Fractures: Classification and Management Implications.

Periarticular knee fractures, which include fractures of the distal femur, tibial plateau, and patella, account for 5%-10% of musculoskeletal injuries encountered in trauma centers and emergency rooms. These injuries are frequently complex, with articular surface involvement. Surgical principles center on reconstruction of the articular surface as well as restoration of limb length, alignment, and rotation to reestablish functional knee biomechanics. Fixation principles are guided by fracture morphology, and thus, CT with multiplanar reformats and volume rendering is routinely used to help plan surgical intervention. Fractures involving the distal femur, tibial plateau, and patella have distinct management considerations. This comprehensive CT primer of periarticular knee fractures promotes succinct and clinically relevant reporting as well as optimized communication with orthopedic trauma surgeon colleagues by tying fracture type and key CT findings with surgical decision making. Fracture patterns are presented within commonly employed fracture classification systems, rooted in specific biomechanical principles. Fracture typing of distal femur fractures and patellar fractures is performed using Arbeitsgemeinschaft für Osteosynthesefragen/Orthopedic Trauma Association (AO/OTA) classification schemes. Tibial plateau fractures are graded using the Schatzker system, informed by a newer explicitly CT-based three-column concept. For each anatomic region, the fracture pattern helps determine the surgical access required, whether bone grafting is warranted, and the choice of hardware that achieves suitable functional outcomes while minimizing the risk of articular collapse and accelerated osteoarthritis. Emphasis is also placed on recognizing bony avulsive patterns that suggest ligament injury to help guide stress testing in the early acute period. ©RSNA, 2024 Supplemental material is available for this article.

Medial Patellar Plica Thickness as a Morphologic Predictor of the Medial Patellar Plica Syndrome.

OBJECTIVE: The aim of this study was to evaluate the association between medial patellar plica (MPP) syndrome and the morphological features of the MPP, including length, width, and thickness, on knee magnetic resonance imaging (MRI). MATERIALS AND METHODS: From 2018 to 2022, 167 patients diagnosed with isolated MPP syndrome based on both MRI and arthroscopic findings were included in the "study group" and 226 patients without knee pathology on both MRI and physical examination were included in the "control group." Finally, 393 patients (mean age, 38.9 ± 5.7 years) with 405 knee MRI examinations were included. Morphological MR features of MPP were assessed, including width, length, and thickness. Multivariate regression and receiver operating characteristic analyses were performed to identify the factors associated with MPP syndrome. RESULTS: The mean thickness of MPP was significantly higher in the study group than control group (2.3 ± 0.5 mm vs 1.0 ± 0.8 mm, P < 0.001). Moreover, on multivariate analysis, MPP thickness was the only significant factor associated with MPP syndrome (odds ratio, 6.452; 95% confidence interval, 0.816-15.073; P = 0.002). On receiver operating characteristic analysis, thickness ≥1.8 mm was estimated as the optimal cutoff for predicting MPP syndrome with sensitivity of 75.9%, specificity of 65.4%, and area under the curve of 0.727 (95% confidence interval, 0.667-0.788; P < 0.001). CONCLUSIONS: Measurement of MPP thickness on MRI could be a morphological predictor of MPP syndrome.

Patellar Instability: Imaging Findings.

Patellofemoral instability results from impaired engagement of the patella in the trochlear groove at the start of flexion and may lead to pain and lateral patellar dislocation. It occurs most frequently in adolescents and young adults during sporting activities. Trochlear dysplasia, patella alta, and excessive lateralization of the tibial tuberosity are the most common risk factors for patellar instability. The main role of imaging is to depict and assess these anatomical factors and highlight features indicating previous lateral dislocation of the patella.

Relationship between patellofemoral joint morphology and chondromalacia patella.

BACKGROUND: For the normal functioning of the patellofemoral joint (PF), the relationship between the patella and the trochlear groove must be compatible. PURPOSE: To investigate the relationship between patellofemoral joint morphology (PFM) and patellar chondromalacia. MATERIAL AND METHODS: Overall, 136 knees of patients aged 20-55 years examined between March 2020 and March 2021 were included in this study. In all patients, trochlear sulcus angle, trochlear sulcus depth, trochlear facet asymmetry, patella alta (Insall-Salvati [IS] index), and patellar facet asymmetry were measured. Of these cases, 66 knees with an abnormality detected in any of the measurements for PFM were included in the case group. Moreover, 70 knees with demonstrating normal PFM measurements were included in the control group. RESULTS: The incidence and grade of chondromalacia was higher in the case group than in the control group (P < 0.001). Between the patients with and without chondromalacia trochlear sulcus angle (mean = 138.25° ± 10.02° vs. 132.58° ± 7.24°; P = 0.001), IS index (mean = 1.25 ± 0.21 vs. 1.16 ± 0.15; P = 0.014), patellar facet asymmetry (mean = 0.77 ± 0.09 vs. 0.73 ± 0.12; P = 0.039), trochlear sulcus depth (mean = 5.39 ± 1.42 mm vs. 6.27 ± 1.04 mm; P < 0.001), and trochlear facet asymmetry (mean = 0.67 ± 0.11 vs. 0.71 ± 0.09; P = 0.023) measurements, there was a significant difference. CONCLUSION: The presence of at least one of the measures indicating pathology in PFM is associated with the presence and severity of chondromalacia.

Patellar height: an important parameter in knee MRI associated with tendinopathy, quadriceps fat pad edema (QFPE), anterior cruciate ligament mucoid degeneration (ACL-MD), and lateral cartilage damage.

BACKGROUND: Some pathologies associated with abnormal patellar height have been reported in the literature. However, its relationship with some pathologies, such as anterior cruciate ligament mucoid degeneration (ACL-MD) and focal cartilage defect, has not been investigated. PURPOSE: To investigate the relationship between patellar height with patellar-quadriceps tendinopathy, quadriceps fat pad edema, ACL-MD, and focal cartilage defect. MATERIAL AND METHODS: Magnetic resonance imaging of the knees of 261 patients were classified into three groups as normal, patella alta, and patella baja, and evaluated in terms of patellar-quadriceps tendinopathy, quadriceps fat pad edema, ACL-MD, and focal cartilage defect. RESULTS: There were 261 patients (140 men, 121 women; age range = 18-60 years; mean age = 30 ± 4.7 years). Of the 261 patients, 181 (69.3%) were normal, 56 (21.4%) were patella alta, and 24 were patella baja (9.1%). Patellar-quadriceps tendinopathy, quadriceps fat pad edema, and ACL-MD rates were significantly higher compared to the normal group (P <0.05). While a moderate positive correlation was found between patellar height shift and patellar-quadriceps tendinopathy and ACL-MD, there was a small correlation between patellar height shift and quadriceps fat pad edema. The rate of focal cartilage defect was significantly higher in the middle part of the lateral femoral condyle and lateral knee joint only in patella alta. CONCLUSION: The risk of patellar-quadriceps tendinopathy, quadriceps fat pad edema, ACL-MD, and lateral focal cartilage defect is higher in patients with alta-baja. The radiologist should evaluate these pathologies more carefully, especially subtle ones, in patients with abnormal patellar height.

Simultaneous Evaluation of Tibiofemoral and Patellofemoral Mechanics in Total Knee Arthroplasty: A Combined Experimental and Computational Approach.

Contemporary total knee arthroplasty (TKA) has not fully restored natural patellofemoral (P-F) mechanics across the patient population. Previous experimental simulations have been limited in their ability to create dynamic, unconstrained, muscle-driven P-F articulation while simultaneously controlling tibiofemoral (T-F) contact mechanics. The purpose of this study was to develop a novel experimental simulation and validate a corresponding finite element model to evaluate T-F and P-F mechanics. A commercially available wear simulator was retrofitted with custom fixturing to evaluate whole-knee TKA mechanics with varying patella heights during a simulated deep knee bend. A corresponding dynamic finite element model was developed to validate kinematic and kinetic predictions against experimental measurements. Patella alta reduced P-F reaction forces in early and midflexion, corresponding with an increase in T-F forces that indicated an increase in extensor mechanism efficiency. Due to reduced wrapping of the extensor mechanism in deeper flexion for the alta condition, peak P-F forces in flexion increased from 101% to 135% of the applied quadriceps load for the baja and alta conditions, respectively. Strong agreement was observed between the experiment and model predictions with root-mean-square errors (RMSE) for P-F kinematics ranging from 0.8 deg to 3.3 deg and 0.7 mm to 1.4 mm. RMSE for P-F forces ranged from 7.4 N to 53.6 N. By simultaneously controlling dynamic, physiological loading of the T-F and P-F joint, this novel experimental simulation and validated model will be a valuable tool for investigation of future TKA designs and surgical techniques.

Patellar osteochondritis dissecans: maturation-dependent patellofemoral joint characteristics.

BACKGROUND: The likelihood of healing of osteochondritis dissecans decreases with skeletal maturity and there are theories that abnormal biomechanical forces contribute to the development and progression of these lesions. OBJECTIVE: To characterize, according to regional skeletal maturity, the morphology and alignment indices of the patellofemoral joint on MRI in patients with patellar osteochondritis dissecans. MATERIALS AND METHODS: MRI examinations of patients with patellar osteochondritis dissecans obtained between January 2008 and May 2023 were retrospectively reviewed to determine regional skeletal maturity, osteochondritis dissecans lesion size and location, patellar and trochlear morphology (Wiberg/Dejour classifications), and to calculate trochlear sulcus angles, trochlear depth index, lateral trochlear inclination, Insall-Salvati index, Caton-Deschamps index, patellar tendon-lateral trochlear ridge, and tibial tubercle-trochlear groove distances. Values were compared between skeletally immature and mature groups. RESULTS: Sixty-eight children (22 girls, 46 boys, age: 14.0 ± 1.7 years) yielded 74 knees with patellar osteochondritis dissecans lesions, 14 (19%) of which were skeletally mature. The most common anatomic location was over the central patella [median ridge (34/74 - 46%) on the axial images and over the middle third (45/74 - 61%) on the sagittal images]. Overall, mean trochlear sulcus angle (high, 151 ± 11°), trochlear depth index (low, 2.8 ± 1.4 mm), and Insall-Salvati index (borderline, 1.3 ± 0.1) were abnormal for the entire sample. Skeletally mature knees were significantly more likely to have higher (more dysplastic) Dejour types when compared to skeletally immature knees (p < 0.01). Knees in the mature group, compared to immature, had significantly more abnormal mean lateral trochlear inclination (15 ± 8° vs. 19 ± 6°, p = 0.03) and patellar tendon-lateral trochlear ridge distance (5.55 ± 4.31 mm vs. 2.89 ± 4.69 mm, p = 0.04). Half of the knees had ≥ 4 abnormal features that predispose to patellofemoral maltracking; mature knees were significantly (p = 0.02) more likely to have a higher number of abnormal features (> 6 features, 7/14, 50.0%) versus immature knees (0-3 features, 33/60, 55.0%). CONCLUSION: In children with patellar osteochondritis dissecans, abnormal patellofemoral morphology and alignment indices were common in all patients and more severe in mature knees.

Synovial hemangioma presenting with chronic painful infrapatellar mass: a case report.

BACKGROUND: Synovial hemangiomas are rare benign vascular anomalies surrounded by a synovial lining and were first described by Bouchut in 1856. These neoplasms can develop in the intra-articular region, resulting in effusions and knee pain. However, their cause remains unknown. Prompt diagnosis and intervention are critical to prevent chondral damage. Histopathological examination is used to achieve the diagnosis, which is often delayed because of a lack of specific clinical signs. This report describes a unique case in which a painful infrapatellar mass was diagnosed as a synovial hemangioma. The absence of typical magnetic resonance imaging (MRI) findings highlights the importance of arthroscopic excision for diagnosis and symptom relief. CASE PRESENTATION: A 20-year-old woman presented with persistent anterior left knee pain that became exacerbated when she climbed stairs. Despite previous pain management and physical therapy, she developed a painful lump beneath her patella that worsened over time. She had also undergone arthrocentesis, but this did not relieve her pain. Physical examination revealed a palpable, immobile 5-cm mass along the patellar tendon with limited knee flexion and extension and normal ligament stability. T1-weighted fat-saturated MRI of the left knee with gadolinium-based contrast revealed a lobulated intra-articular mass in Hoffa's fat pad that resembled a soft tissue chondroma. A biopsy of the mass was performed to provide histopathological evidence, confirming the benign nature of the mass. The subsequent excisional arthroscopy, combined with incision enlargement for mass removal, confirmed the histopathologic diagnosis of synovial hemangioma based on the presence of numerous dilated blood vessels and venous proliferation within sections of the synovium. Recovery was complete, and no residual tumor was detected on follow-up MRI after 1 year. CONCLUSION: This case study emphasizes the importance of arthroscopic excision over open surgery for patients with synovial hemangioma. The minimally invasive nature of arthroscopy combined with the well-encapsulated nature and location of the mass facilitates complete resection.

Acute patellar dislocation: how skeletal maturity affects patterns of injury.

OBJECTIVE: The main objective of this study was to understand the role of skeletal maturity in the different patterns of osteochondral and ligamentous injuries after an acute lateral patellar dislocation. MATERIALS AND METHODS: Two radiologists independently reviewed MRIs of 212 knees performed after an acute lateral patellar dislocation to evaluate the presence of high-grade patellar osteochondral injury, femoral osteochondral injury, and medial patellofemoral ligament injury. The association of skeletal maturity (indicated by a closed distal femoral physis), age, sex, and first-time versus recurrent dislocation with each of these various lesions was analyzed using Chi-square or T test, and multivariable logistic regression with estimation of odds ratios (OR). RESULTS: Skeletal maturity was significantly associated with high-grade patellar osteochondral injury [OR=2.72 (95% CI 1.00, 7.36); p=0.049] and femoral-side MPFL tear [OR=2.34 (95% CI 1.05, 5.25); p=0.039]. Skeletal immaturity was significantly associated with patellar-side MPFL tear [OR=0.35 (95% CI 0.14, 0.90); p=0.029]. CONCLUSION: Patterns of injury to the patella and medial patellofemoral ligament vary notably between the skeletally immature and mature, and these variations may be explained by the inherent weakness of the patellar secondary physis.

MR imaging after patellar MACI and MPFL reconstruction: a comparison of isolated versus combined procedures.

OBJECTIVE: To qualitatively and quantitatively evaluate the 2.5-year MRI outcome after Matrix-associated autologous chondrocyte implantation (MACI) at the patella, reconstruction of the medial patellofemoral ligament (MPFL), and combined procedures. METHODS: In 66 consecutive patients (age 22.8 ± 6.4years) with MACI at the patella (n = 16), MPFL reconstruction (MPFL; n = 31), or combined procedures (n = 19) 3T MRI was performed 2.5 years after surgery. For morphological MRI evaluation WORMS and MOCART scores were obtained. In addition quantitative cartilage T2 and T1rho relaxation times were acquired. Several clinical scores were obtained. Statistical analyses included descriptive statistics, Mann-Whitney-U-tests and Pearson correlations. RESULTS: WORMS scores at follow-up (FU) were significantly worse after combined procedures (8.7 ± 4.9) than after isolated MACI (4.3 ± 3.6, P = 0.005) and after isolated MPFL reconstruction (5.3 ± 5.7, P = 0.004). Bone marrow edema at the patella in the combined group was the only (non-significantly) worsening WORMS parameter from pre- to postoperatively. MOCART scores were significantly worse in the combined group than in the isolated MACI group (57 ± 3 vs 88 ± 9, P < 0.001). Perfect defect filling was achieved in 26% and 69% of cases in the combined and MACI group, respectively (P = 0.031). Global and patellar T2 values were higher in the combined group (Global T2: 34.0 ± 2.8ms) and MACI group (35.5 ± 3.1ms) as compared to the MPFL group (31.1 ± 3.2ms, P < 0.05). T2 values correlated significantly with clinical scores (P < 0.005). Clinical Cincinnati scores were significantly worse in the combined group (P < 0.05). CONCLUSION: After combined surgery with patellar MACI and MPFL reconstruction inferior MRI outcomes were observed than after isolated procedures. Therefore, patients with need for combined surgery may be at particular risk for osteoarthritis.

T1rho MR properties of human patellar cartilage: correlation with indentation stiffness and biochemical contents.

OBJECTIVE: Cartilage degeneration involves structural, compositional, and biomechanical alterations that may be detected non-invasively using quantitative MRI. The goal of this study was to determine if topographical variation in T1rho values correlates with indentation stiffness and biochemical contents of human patellar cartilage. DESIGN: Cadaveric patellae from unilateral knees of 5 donors with moderate degeneration were imaged at 3-Telsa with spiral chopped magnetization preparation T1rho sequence. Indentation testing was performed, followed by biochemical analyses to determine water and sulfated glycosaminoglycan contents. T1rho values were compared to indentation stiffness, using semi-circular regions of interest (ROIs) of varying sizes at each indentation site. ROIs matching the resected tissues were analyzed, and univariate and multivariate regression analyses were performed to compare T1rho values to biochemical contents. RESULTS: Grossly, superficial degenerative change of the cartilage (i.e., roughened texture and erosion) corresponded with regions of high T1rho values. High T1rho values correlated with low indentation stiffness, and the strength of correlation varied slightly with the ROI size. Spatial variations in T1rho values correlated positively with that of the water content (R2 = 0.10, p < 0.05) and negatively with the variations in the GAG content (R2 = 0.13, p < 0.01). Multivariate correlation (R2 = 0.23, p < 0.01) was stronger than either of the univariate correlations. CONCLUSION: These results demonstrate the sensitivity of T1rho values to spatially varying function and composition of cartilage and that the strength of correlation depends on the method of data analysis and consideration of multiple variables.

MRI of patellar stabilizers: Anatomic visibility, inter-reader reliability, and intra-reader reproducibility of primary and secondary ligament anatomy.

OBJECTIVE: To compare MRI features of medial and lateral patellar stabilizers in patients with and without patellar instability. METHODS: Retrospective study of 196 patients (mean age, 33.1 ± 18.5 years; 119 women) after diagnosis of patellar instability (cohort-1, acute patellar dislocation; cohort-2, chronic patellar maltracking) or no patellar instability (cohort-3, acute ACL rupture; cohort-4, chronic medial meniscus tear). On MRI, four medial and four lateral stabilizers were evaluated for visibility and injury by three readers independently. Inter- and intra-reader agreement was determined. RESULTS: Medial and lateral patellofemoral ligaments (MPFL and LPFL) were mostly or fully visualized in all cases (100%). Of the secondary patellar stabilizers, the medial patellotibial ligament was mostly or fully visualized in 166 cases (84.7%). Other secondary stabilizers were mostly or fully visualized in only a minority of cases (range, 0.5-32.1%). Injury scores for all four medial stabilizers were higher in patients with acute patellar dislocation than the other 3 cohorts (p < .05). Visibility inter- and intra-reader agreement was good for medial stabilizers (κ 0.61-0.78) and moderate-to-good for lateral stabilizers (κ 0.40-0.72). Injury inter- and intra-reader agreement was moderate-to-excellent for medial stabilizers (κ 0.43-0.90) and poor-to-moderate for lateral stabilizers (κ 0-0.50). CONCLUSION: The MPFL and LPFL were well visualized on MRI while the secondary stabilizers were less frequently visualized. The secondary stabilizers were more frequently visualized medially than laterally, and patellotibial ligaments were more frequently visualized compared to the other secondary stabilizers. Injury to the medial stabilizers was more common with acute patellar dislocation than with chronic patellar maltracking or other knee injuries.

Editorial Commentary: Absent Extreme Bony Malalignment: Medial Patellofemoral Reconstruction Is a Sufficient Primary Surgery for Adolescents With Recurrent Patella Instability.

When planning an adolescent's primary surgery for recurrent patella instability, the surgeon must weigh the failure risk of performing medial patellofemoral reconstruction (MPFLR) versus the potential morbidity of adding a concomitant bony procedure, such as tibial tubercle osteotomy. In this age group, isolated MPFLR is an excellent operation with high clinical success, low failure rates, and favorable complication profile. Patients with high grade J-sign and severe trochlea dysplasia, apprehension into deep flexion, and extremes of bony malalignment, including elevated tibial tubercle-trochlear groove distance, may benefit from "doing more" than MPFLR alone. Other factors to be considered include patella alta, generalized ligament laxity, femoral rotation, tibial torsion, and valgus malalignment. In challenging situations, such as syndromic patients (e.g., neuromuscular disorders), congenital (habitual) patella dislocation, fixed dislocations, and failed prior to MPFLR, a combined surgical approach is likely needed. Patients who require "unloading" for symptomatic chondrosis also benefit from combined bony and soft tissue surgery. However, for the majority of patients with recurrent instability and no prior surgery, an isolated soft tissue reconstruction is a rational, safe, efficient, and evidence-based selection.