The Importance of Medial Patellar Shape as a Risk Factor for Recurrent Patellar Dislocation in Adults.

BACKGROUND: Research on the cause of lateral patellar dislocation (LPD) has focused on trochlear morphologic parameters, joint alignment, and patellofemoral soft tissue forces. A paucity of information is available regarding how patellar morphologic parameters influence the risk for LPD. PURPOSE/HYPOTHESIS: The purpose was to assess whether patellar morphology is a risk factor for recurrent LPD. It was hypothesized that (1) patients with recurrent LPD would have decreased patellar width and volume and (2) patellar morphologic parameters would accurately discriminate patients with recurrent LPD from controls. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 3. METHODS: A total of 21 adults with recurrent LPD (age, 29.7 ± 11.1 years; height, 170.8 ± 9.9 cm; weight, 76.1 ± 17.5 kg; 57% female) were compared with 21 sex- and height-matched controls (age, 27.2 ± 6.7 years; height, 172.0 ± 10.6 cm; weight, 71.1 ± 12.8 kg; 57% female). Three-dimensional axial fat-saturated magnetic resonance imaging scans were used to measure patellar medial, lateral, and total width; patellar volume; patellar medial and lateral facet length; the Wiberg index; and previously validated knee joint alignment and femoral shape measurements (eg, tibial tuberosity to trochlear groove distance, trochlear dysplasia). RESULTS: The LPD group demonstrated reduced medial patellar width (Δ = -3.6 mm; P < .001) and medial facet length (Δ = -3.7 mm; P < .001) but no change in lateral width or facet length. This resulted in decreased total patellar width (Δ = -3.2 mm; P = .009), decreased patellar volume (Δ = -0.3 cm3; P = .025), and an increased Wiberg index (Δ = 0.05; P < .001). No significant differences were found for all other patellar shape measures between cohorts. Medial patellar width was the strongest single discriminator (83.3% accuracy) for recurrent LPD. Combining medial patellar width, patellofemoral tilt, and trochlear groove length increased the discrimination to 92.9%. CONCLUSION: The medial patellar width was significantly smaller in patients with recurrent LPD and was the single most accurate discriminator for recurrent LPD, even compared with traditional trochlear shape and joint alignment measures (eg, trochlear dysplasia, patella alta). Therefore, medial patellar morphology should be assessed in patients with LPD as a risk factor for recurrence and a potential means to improve treatment.

Measurement of TT-TG can change with sequential MRIs due to variations in tibiofemoral rotation in patellofemoral instability patients.

PURPOSE: There are various anatomic risk factors for patellofemoral instability (PFI) that help guide surgical treatment, including the tibial tubercle to trochlear groove (TT-TG) distance. However, no study has analysed the temporal changes in TT-TG prior to surgical intervention. This study sought to understand the variations in TT-TG over time for pediatric patients suffering from PFI prior to surgical intervention. The authors hypothesised that the TT-TG would substantially change between time points. METHODS: Patients undergoing medial patellofemoral ligament (MPFL) reconstruction between 2014 and 2019 by one of two fellowship-trained orthopaedic surgeons were identified. Patients were included if they had two preoperative magnetic resonance imaging (MRI) performed on the same knee within 7.5 months of each other prior to any surgical intervention and had an initial TT-TG greater than 10 mm. RESULTS: After considering 251 patients for inclusion, 21 patients met the final inclusion criteria. The mean age was 14.5 ± 2.5 years and 61.9% were female. TT-TG was initially noted to be 15.1 ± 1.8 mm. At mean time after sequential MRIs of 5.0 ± 1.9 months, TT-TG was noted to be 16.7 ± 3.2 mm. The differences between initial and subsequent TT-TG ranged from a 21.2% decrease to a 61.1% increase, with a mean difference of an 11.3% increase. Comparison between initial and subsequent TT-TG values demonstrated a significant difference (p = 0.017). Change in tibiofemoral rotation ranged from -9.2° to 7.5°. When comparing the change in TT-TG to change in tibiofemoral rotation, a significant correlation was found (p = 0.019). CONCLUSION: Despite only a mean time between MRIs of 5 months, variations in TT-TG ranged from a decrease of 21.2% to an increase of 61.1%. The significant relationship between the changes in TT-TG and changes in tibiofemoral rotation between MRIs suggest that TT-TG measurements may vary due to variations in tibiofemoral rotation at the time of individual MRIs. LEVEL OF EVIDENCE: Level IV.

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.

Editorial Commentary: When Properly Indicated, Combined Tibial Tubercle Osteotomy Reduces Risk of Recurrent Patellofemoral Instability More Than Does Isolated Medial Patellofemoral Ligament Reconstruction.

Clinical recognition and surgical treatment of patellofemoral instability has evolved dramatically over the past 3 decades. However, few patellofemoral patients present with an isolated medial patellofemoral ligament (MPFL) tear. Rather, patients often demonstrate patella alta, increased tibial tubercle to trochlear groove (TT-TG) distance, dysplasia, coronal malalignment, or combinations thereof. Given this, concomitant procedures such as tibial tubercle osteotomy (TTO) have become increasingly popularized, given their ability to anteriorize, medialize, and even distalize the patella to correct tracking. It is generally recommended that concurrent TTO be considered with primary medial patellofemoral ligament reconstruction (MPFLR) in patients with closed physes whose TT-TG distance is larger than 17 to 20 mm. MPFLR + TTO is generally safe and may decrease risk of revision surgery when compared with isolated MPFLR in properly indicated patients. However, it important to measure both knee rotation angle and tibial tubercle lateralization on magnetic resonance imaging, as both factors influence TT-TG. In patients in whom abnormal knee rotation angle is felt to be the primary driver of TT-TG, surgeons should proceed with caution when considering concomitant TTO. The pen may be mightier than the sword, but the osteotome may be mightier yet than the scalpel.

Patellar Tilt and Patellar Tendon-Trochlear Groove Angle Present the Optimum Magnetic Resonance Imaging Diagnostic Reliability for Patients With Patellar Instability.

PURPOSE: To describe, in controls and in a population with patellar instability, magnetic resonance imaging values of measurements representing major associated factors for patellar instability (patellar height, trochlear dysplasia, and extensor mechanism alignment), as well as their cutoff values. METHODS: In total, 323 knee magnetic resonance imaging scans, 142 with patellar instability and 181 controls without patellofemoral complaints (anterior cruciate, medial collateral ligament, meniscus ruptures or normal) were evaluated. Means, normality values in the control population, ideal cutoff values through receiver operating characteristic curves analysis, and interobserver reliability (intraclass correlation coefficient) were described for a series of measurements. RESULTS: All measurements were statistically different in control and instability patients, except for the patellotrochlear index and tibial tuberosity to posterior cruciate ligament distance. The interobserver intraclass correlation coefficient was good or excellent (above 0.75) only for the patellotrochlear index, patellar tendon-trochlear groove (PTTG) angle, and patellar tilt. The optimal cutoff value for each measurement was: PTTG angle ≥25.3o with sensitivity (S) of 70% and specificity (E) of 89%, patellar tilt ≥16o (S: 69% and E: 84%), trochlear sulcus angle ≥153o (S: 75% and E: 76%), Carrillon ≤12.8o (S: 62% and E: 87%), PTTG distance ≥11mm (S: 71% and E: 78%), Caton-Deschamps index ≥1.23 (S: 72% and E: 76%) and trochlear bump ≥3.95 mm (S: 76% and E: 65%). CONCLUSIONS: Caton-Deschamps index (≥1.23), trochlear sulcus angle (≥153o), ventral prominence of the trochlea (≥3.95 mm), PTTG distance (≥11 mm), PTTG angle (≥25.3o), Carrillon angle (≤12.8o), and patellar tilt (≥16o) presented better diagnostic performance for patellar instability. Patellotrochlear index and tibial tuberosity to posterior cruciate ligament distance were not related to patellar instability. The interobserver reliability of the factors related to patellar instability was excellent only for the PTTG angle and lateral patellar tilt. LEVEL OF EVIDENCE: Level III, retrospective case-control study.

Tibial tubercle to trochlear groove distance versus tibial tubercle to posterior cruciate ligament distance for predicting patellar instability: a systematic review.

PURPOSE: To determine the reliability and diagnostic accuracy of tibial tubercle-trochlear groove (TT-TG) distance versus tibial tubercle-posterior cruciate ligament (TT-PCL) distance, and to determine cutoff values of these measurements for pathological diagnosis in the context of patellar instability. METHODS: Three databases MEDLINE, PubMed and EMBASE were searched from inception to October 5, 2022 for literature outlining comparisons between TT-TG and TT-PCL in patellar instability patients. The authors adhered to the PRISMA and R-AMSTAR guidelines as well as the Cochrane Handbook for Systematic Reviews of Interventions. Data on inter-rater and intra-rater reliability, receiver-operating characteristic (ROC) curve parameters such as area under the curve (AUC), sensitivity and specificity, as well as odds ratios, cutoff values for pathological diagnosis and correlations between TT-TG and TT-PCL were recorded. The MINORS score was used for all studies in order to perform a quality assessment of included studies. RESULTS: A total of 23 studies comprising 2839 patients (2922 knees) were included in this review. Inter-rater reliability ranged from 0.71 to 0.98 and 0.55 to 0.99 for TT-TG and TT-PCL, respectively. Intra-rater reliability ranged from 0.74 to 0.99 and 0.88 to 0.98 for TT-TG and TT-PCL, respectively. AUC measuring diagnostic accuracy of patellar instability for TT-TG ranged from 0.80 to 0.84 and 0.58 to 0.76 for TT-PCL. Five studies found TT-TG to have more discriminatory power than TT-PCL at distinguishing patients with patellar instability from patients who do not. Sensitivity and specificity ranged from 21 to 85% and 62 to 100%, respectively, for TT-TG. Sensitivity and specificity ranged from 30 to 76% and 46 to 86%, respectively, for TT-PCL. Odds ratio values ranged from 1.06 to 14.02 for TT-TG and 0.98 to 6.47 for TT-PCL. Proposed cutoff TT-TG and TT-PCL values for predicting patellar instability ranged from 15.0 to 21.4 mm and 19.8 to 28.0 mm, respectively. Eight studies reported significant positive correlations between TT-TG and TT-PCL. CONCLUSION: TT-TG resulted in overall similar reliability, sensitivity and specificity as TT-PCL; however, TT-TG has better diagnostic accuracy than TT-PCL in the context of patellar instability as per AUC and odds ratio values. LEVEL OF EVIDENCE: Level IV.

Femoral Anteversion Measured by the Surgical Transepicondylar Axis Is Correlated with the Tibial Tubercle-Roman Arch Distance in Patients with Lateral Patellar Dislocation.

Background and Objectives: Various predisposing factors for lateral patellar dislocation (LPD) have been identified, but the relation between femoral rotational deformity and the tibial tubercle-Roman arch (TT-RA) distance remains elusive. Materials and Methods: We conducted this study including 72 consecutive patients with unilateral LPD. Femoral anteversion was measured by the surgical transepicondylar axis (S-tAV), and the posterior condylar reference line (P-tAV), TT-RA distance, trochlear dysplasia, knee joint rotation, patellar height, and hip-knee-ankle angle were measured by CT images or by radiographs. The correlations among these parameters were analyzed, and the parameters were compared between patients with and without a pathological TT-RA distance. Binary regression analysis was performed, and receiver operating characteristic curves were obtained. Results: The TT-RA distance was correlated with S-tAV (r = 0.360, p = 0.002), but the correlation between P-tAV and the TT-RA distance was not significant. S-tAV had an AUC of 0.711 for predicting a pathological TT-RA, with a value of >18.6° indicating 54.8% sensitivity and 82.9% specificity. S-tAV revealed an OR of 1.13 (95% CI [1.04, 1.22], p = 0.003) with regard to the pathological TT-RA distance by an adjusted regression model. Conclusions: S-tAV was significantly correlated with the TT-RA distance, with a correlation coefficient of 0.360, and was identified as an independent risk factor for a pathological TT-RA distance. However, the TT-RA distance was found to be independent of P-tAV.

Patellar Tendon-Trochlear Groove Angle Measured on a Single Computed Tomography Slice of the Distal Femoral Trochlear Groove Is a Reliable Measurement for the Evaluation of Patellar Instability.

PURPOSE: To verify the reliability of patellar tendon-trochlear groove angle (PTTG-A) measured by computed tomography (CT) and the clinical significance in evaluation of patellar instability. METHODS: A retrospective study of hospitalized patients with knee pain or injury and had knee CT from January 2017 to June 2021 was performed. PTTG-A and tibial tuberosity-trochlear groove (TT-TG) distance were measured on CT. Spearman correlation analysis was analyzed between the 2 measurements. The intraclass correlation coefficient was determined for inter- and intraobserver reproducibility. The capacity of PTTG-A and TT-TG to predict patellar instability was evaluated by the receiver operating characteristic curve. Data from the control group were used to determine the pathologic thresholds and logistic regression analysis. RESULTS: Included were 113 patients. There were 60 patients with the history of at least 2 episodes of patellar dislocation (study group) and 53 patients without a history of patellar dislocation (control group). The respective PTTG-A and TT-TG distances in the study group (35.2 ± 8.4° and 19.6 ± 4.6 mm) were significantly greater than those of the controls (20.8 ± 5.8° and 13.3 ± 4.5 mm) (P < .001). The correlation between the 2 measurements was strong (r = 0.730, P < .001). The inter- and intraobserver reliability of the PTTG-A were better than TT-TG distance in both groups. The AUC of PTTG-A was greater than that of the TT-TG distance (0.895 vs 0.769, respectively). With the cutoff value of PTTG-A and TT-TG being 26.3° and 16.3 mm, the value of the pathologic threshold of PTTG-A was 30.0°, with a dominance ratio of 16.88 (95% confidence interval 2.88-98.89, P = .002). CONCLUSIONS: The PTTG-A measured on a single CT slice of the distal femoral trochlear groove is a more reliable measurement than TT-TG distance for the prediction of patellar instability. LEVEL OF EVIDENCE: III; A retrospective cohort study.

CT and MRI measurements of tibial tubercle lateralization in patients with patellar dislocation were not equivalent but could be interchangeable.

PURPOSE: To compare the values and the relationship of tibial tubercle lateralization measurements between computerized tomography (CT) and magnetic resonance imaging (MRI). METHODS: Sixty patients with patellar dislocation who underwent both CT and MRI of the same knee joint from November 2021 to February 2022 were included in our study. The intraclass correlation coefficient (ICC) and Bland-Altman analysis were performed to evaluate the reliability of tibial tubercle-trochlear groove (TT-TG), tibial tubercle-Roman arch (TT-RA), and tibial tubercle-posterior cruciate ligament (TT-PCL) distance measurements. The values of CT and MRI measurements using the same bony landmarks were compared for the difference. Pearson correlation analysis and linear regression analysis were performed to assess the correlation between CT and MRI measurements. Finally, the estimated values obtained from the regression equation were compared with the actual values obtained from the radiological measurement to evaluate the accuracy of the equations. RESULTS: A total of 60 patients with patellar dislocation who underwent both CT and MRI of the same knee joint were included in this study. The included measurements showed excellent agreement with ICCs > 0.9. TT-TG distance measured on CT (19.5 ± 5.1 mm) had a mean of 7.1 mm higher than that on MRI (12.4 ± 4.7 mm) (P < 0.001). The mean value of TT-RA distance was 22.5 ± 3.7 mm on CT and 16.7 ± 4.9 mm on MRI (P < 0.001), showing a mean difference of 5.8 mm. The values of TT-TG distance measured by CT and MRI were significantly correlated (R = 0.5, P < 0.001). The values of TT-RA distance between these two modalities showed a better correlation than that of TT-TG distance (R = 0.6, P < 0.001). The interchange values of TT-TG distance and TT-RA distance between CT and MRI can be obtained using regression equations (TT-TG distance: y = 0.6x + 12.3; TT-RA distance: y = 0.5x + 14.4). CONCLUSION: The values of tibial tubercle lateralization measured by MRI may be underestimated compared with those measured by CT. Although the values measured on CT and MRI are not equivalent, the value in the other modality can be estimated. Therefore, an additional CT scan for tibial tubercle lateralization evaluation may not be necessary. LEVEL OF EVIDENCE: Level II.

Anatomical Characteristics Contributing to Patellar Dislocations Following MPFL Reconstruction: A Dynamic Simulation Study.

Pathologic anatomy is a primary factor contributing to redislocation of the patella following reconstruction of the medial patellofemoral ligament (MPFL). A pivot landing was simulated following MPFL reconstruction, with the hypothesis that position of the tibial tuberosity, depth of the trochlear groove, and height of the patella are correlated with lateral patellar maltracking. Thirteen dynamic simulation models represented subjects being treated for recurrent patellar instability. Simplified Hertzian contact governed patellofemoral and tibiofemoral joint reaction forces. Pivot landing was represented with and without an MPFL graft in place. Measurements related to patellar height (Caton-Deschamps index), trochlear groove depth (lateral trochlear inclination), and position of the tibial tuberosity (lateral tibial tuberosity to posterior cruciate attachment distance, or lateral TT-PCL distance) were measured from the models and correlated with patellar lateral shift with the knee extended (5 deg of flexion) and flexed (40 deg). The patella dislocated for all models without an MPFL graft and for two models with a graft represented. With an MPFL graft represented, patellar lateral shift was correlated with Caton-Deschamps index (r2 > 0.35, p < 0.03) and lateral trochlear inclination (r2 ≥ 0.45, p < 0.02) at both 5 deg and 40 deg of flexion. For a simulated pivot landing with an MPFL graft in place, lateral patellar tracking was associated with a high patella (alta) and shallow trochlear groove. The study emphasizes the importance of simulating activities that place the patella at risk of dislocation when evaluating patellar stability.

Anatomical characteristics and potential gene mutation sites of a familial recurrent patellar dislocation.

BACKGROUND: Recurrent patellar dislocation is the result of anatomical alignment and imbalance of restraint of bone and soft tissue. We investigate the anatomical characteristics of the knee joint in a family of patients with recurrent patella dislocation, and to screen the possible pathogenic genes in this family by whole exome sequencing in 4 patients and 4 healthy subjects, so as to provide theoretical basis for the pathogenesis of this disease. METHODS: The data related to patella dislocation were measured by imaging data. The peripheral blood DNA of related family members was extracted for the whole exome sequencing, and then the sequencing results were compared with the human database. By filtering out synonymous variants and high-frequency variants in population databases, and then integrating single nucleotide non-synonymous variants of family members, disease-causing genes were found. RESULTS: All patients in this family have different degrees of abnormal knee anatomy, which is closely related to patella dislocation. The sequencing results of patients and normal persons in this patella dislocation family were compared and analyzed, and the data were filtered through multiple biological databases. Find HOXB9 (NM_024017.4:c.404A>G:p.Glu135Gly),COL1A1(NM_000088.3:c.3766G>A:p.Ala1256Thr),GNPAT(NM_014236.3:c1556A>G:p.Asp519Gly),NANS(NM_018946.3:c.204G>C:p.Glu68Asp),SLC26A2(NM_000112.3:c.2065A>T:p.Thr689Ser) are nonsynonymous variants (MISSENSE). Through Sanger sequencing, the identified mutations in HOXB9 and SLC26A2 genes were only present in samples from patients with recurrent patellar dislocation. CONCLUSIONS: The patients with recurrent patellar dislocation had markedly abnormal knee anatomy in this family. HOXB9 gene and SLC26A2 gene were found to be the possible pathogenic genes or related genes for patella dislocation.

Changes in Anatomic Risk Factors for Patellar Instability During Skeletal Growth and Maturation.

BACKGROUND: Several anatomic risk factors have been identified in the pathogenesis of patellofemoral instability. The literature is sparce regarding how these anatomic risk factors change during skeletal growth and development. HYPOTHESIS: The anatomic risk factors associated with patellar instability change significantly during skeletal growth and maturation with different patterns in male versus female patients. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: Magnetic resonance imaging data from 240 unique, asymptomatic knees (7-18 years of age; 50% female) were used to measure patellar height (Caton-Deschamps index), lateral patellar tilt angle, trochlear height, trochlear groove depth, trochlear sulcus angle, and tibial tubercle-trochlear groove (TT-TG) distance. Linear regression was used to test the associations between age and anatomic findings. Two-way analysis of variance with Holm-Sídák post hoc test was used to compare anatomic characteristics between sexes in 3 age groups: prepubertal school-aged children (7-10 years old), early adolescents (11-14 years old), and late adolescents (15-18 years old). RESULTS: Patellar height (female sex), lateral patellar tilt angle (male sex), and trochlear sulcus angle (both sexes) decreased with age (P < .001). Trochlear height, depth, and TT-TG distance increased with age in both male and female participants (P < .02). Male participants had a larger sulcus angle (by 5.3°± 1.6° at age 11-14 years) and greater trochlear height (by >5 mm across medial, central, and lateral regions at age 15-18 years) than age-matched female participants (P < .01). We found no other sex-related differences in quantified anatomic features (P > .1). CONCLUSION: The findings partially support our hypothesis indicating significant age-related changes in all quantified features, which were not different between male and female participants except for trochlear sulcus angle in early adolescence and trochlear height in late adolescence. In general, the majority of anatomic risk factors for patellar instability change with maturity in a direction that assists in reducing the risk of patellar instability and/or dislocation. The only outlier is the TT-TG distance, which increased by age, and in our oldest cohort of patients, the mean fell below the normal adult range. The current observations highlight the importance of age in the interpretation of risk for injury as well as the need for further studies to identify intrinsic and extrinsic factors that may result in abnormal development of these anatomic features during skeletal growth and maturation.

Factors associated with acute articular cartilage lesions of the patella and lateral femoral condyle in acute first-time lateral patellar dislocation: A prospective magnetic resonance imaging study.

OBJECTIVES: To identify risk factors of acute articular cartilage lesions of the patella and lateral femoral condyle in acute first-time lateral patellar dislocation (LPD). METHODS: Magnetic resonance images were prospectively analyzed in 115 patients in an acute first-time LPD. Factors included gender, skeletal maturity, trochlear dysplasia, patellar height, and tibial tuberosity-trochlear groove (TT-TG) distance. Binary logistic regression analysis was carried out to identify the independent risk factors for the incidence of acute articular cartilage lesions of the patella and lateral femoral condyle in acute first-time LPD. RESULTS: The incidence of acute articular cartilage lesion of the patella and lateral femoral condyle were 46.1% and 27% in acute first-time LPD, respectively. Univariate analysis revealed significantly higher incidence rate of acute articular cartilage lesion of the patella in male (P = 0.027), skeletally mature (P = 0.035), normal TT-TG distance (P = 0.043) and normal femoral trochlea (P = 0.031). Risk factors for the incidence of acute articular cartilage lesion of the patella were skeletally mature (odds ratio (OR): 2.324), normal TT-TG distance (OR: 2.824) and normal femoral trochlea (OR: 3.835). Univariate analysis revealed significantly higher incidence rate of acute articular cartilage lesion of the lateral femoral condyle in skeletally mature (P = 0.027) and normal femoral trochlea (P = 0.031). Risk factor for the incidence of acute articular cartilage lesion of the lateral femoral condyle was normal femoral trochlea (OR: 3.347). CONCLUSIONS: For patients in acute first-time LPD, compared with other parameters, the normal femoral trochlea, normal TT-TG distance and skeletally mature are independent risk factors for the incidence of acute articular cartilage lesion of the patella, and the normal femoral trochlea is an independent risk factor for the incidence of acute articular cartilage lesion of the lateral femoral condyle.

Higher pathologic threshold of increased tibial tuberosity-trochlear groove distance should be considered for taller patients.

PURPOSE: The aim of this study was to evaluate the correlation between tibial tuberosity-trochlear groove distance (TT-TG) and body height or knee size, and to find height-related pathologic thresholds of increased TT-TG. METHODS: One-hundred and fifty-three patients with recurrent patellar instability and 151 controls were included. The TT-TG was measured on axial computed tomography (CT) images. Femora width and tibial width were selected to represent knee size. The correlation of TT-TG and gender, body height, femora width, and tibial width was evaluated. The height-related pathologic threshold of increased TT-TG was produced according to Dejour's method. To combine TT-TG with body height and knee size, three new indexes were introduced, ratio of TT-TG to body height (RTH), ratio of TT-TG to femoral width (RTF), and ratio of TT-TG to tibial width (RTT). The ability to predict patellar instability was assessed by the receiver-operating characteristic (ROC) curve, odds ratios (ORs), sensitivity, and specificity. RESULTS: In patients with patellar instability, TT-TG showed significantly correlation with patient height, femoral width, and tibial width respectively (range r = 0.266-0.283). This correlation was not found in the control group. The pathologic threshold of TT-TG was 18 mm in patients < 169 cm (53%), and the mean TT-TG was 21 mm in patients ≥ 169 cm (54%). There was significant difference in RTH, RTF, and RTT between the two groups. RTH, RTF and RTT have similar large area under the curve (AUC) with TT-TG. CONCLUSIONS: TT-TG showed significant correlation with body height and knee size, respectively. The pathologic threshold of increased TT-TG was suggested to be 21 mm for patients [Formula: see text] 169 cm and 18 mm for patients [Formula: see text] 169 cm. Body height-related pathologic threshold provided a supplement for indications of tibial tuberosity medialization. LEVEL OF EVIDENCE: IV.

The tibial tubercle-posterior cruciate ligament (TT-PCL) distance does not truly reflect the lateralization of the tibial tubercle.

PURPOSE: The role of the tibial tubercle-posterior cruciate ligament (TT-PCL) and tibial tubercle-trochlear groove (TT-TG) in recurrent patellar instability (RPI) remains unclear. This study aims to confirm the validity of the TT-TG and TT-PCL in predicting RPI and to verify whether the TT-PCL can truly reflect the lateralization of the tibial tubercle. METHODS: A total of 50 patients with RPI and 50 controls were recruited and underwent magnetic resonance imaging examinations. The TT-TG, TT-PCL, and tibial tubercle lateralization (TTL) were measured independently by two authors in a blinded and randomized fashion. T-test was used for parametric variances and the Mann-Whitney U and Chi-square tests were used for non-parametric variances. Pearson's product moment correlation coefficients were calculated to determine correlations between the defined measurements. The intraclass correlation coefficient was used to assess the reliability of the measurements. RESULTS: All defined measurements showed excellent intra- and inter-observer reliability. The TT-TG distance, TT-PCL distance, and TTL were significantly greater in the PI group than in the control group. The AUC was highest for the TT-TG distance compared with that for the TT-PCL distance, and TTL were 0.798, 0.764, and 0.769, with the calculated cut-off value of 12.5 mm, 16.5 mm, and 66.1 percentages. There was a moderate correlation (r = 0.595) between the TT-TG distance and TTL, and a weak correlation (r = 0.430) between the TT-PCL distance and TTL. CONCLUSION: Both the TT-TG distance and TT-PCL distance can be measured with excellent reliability on magnetic resonance imaging. The TT-TG distance, rather than the TT-PCL distance, has a better performance in predicting RPI. Most interestingly, the TT-PCL distance cannot reflect the real lateralization of TT. This study provides new information to evaluate TTL in patients with RPI. LEVEL OF EVIDENCE: III.

Individualized tibial tubercle-trochlear groove distance-to-patellar length ratio (TT-TG/PL) is a more reliable measurement than TT-TG alone for evaluating patellar instability.

PURPOSE: To evaluate the intra/inter-rater and diagnostic reliability of the sagittal plane adjusted patellar instability ratios (PIRs) compared to tibial tubercle-trochlear groove (TT-TG) distance alone while employing a matched case-control analysis for age and sex to minimize a potential confounding effect. METHODS: A retrospective case-control study was performed of all knee MRI studies of patients diagnosed with patellar instability, between 2005 and 2020 at a regional tertiary medical centre. Using a 1:1 case-control matching of sex and age at the time of the diagnosis, one control subject was assigned to each case of patellar instability. Measurements of TT-TG distance, sagittal patellar length (PL), sagittal patellar tendon length (PTL), TT-TG/PL ratio, and TT-TG/PTL ratio were conducted. Two orthopaedic surgery residents and a senior musculoskeletal radiologist were assigned to assess the intra- and inter-rater reliability. Inter-class coefficients were calculated (ICC). The receiver operating characteristic (ROC) curve and area under curve (AUC) for each parameter were compared to evaluate for diagnostic reliability. Odds ratios (OR) and their 95% confidence intervals (CI) were calculated and a multivariable logistic regression model was performed to control for possible confounders. RESULTS: The study included 324 individuals (162 case-control matched pairs). In terms of intra- and inter-rater reliability, TT-TG/PL and TT-TG/PTL ratios showed an excellent correlation within and between readers (TT-TG/PL; intra-rater ICC 0.94 and inter-rater ICC 0.92, TT-TG/PTL; intra-rater ICC 0.91 and inter-rater ICC 0.88). The ROC curve showed a slightly greater AUC of the TT-TG/PL ratio compared to TT-TG distance alone (0.75 vs 0.73, p < 0.001). When applying the pathologic cutoff of TT-TG ≥ 20 mm and TT-TG/PL ≥ 0.5; the calculated odds ratios for the above cutoff were as follows; TT-TG distance alone had an OR of 14 (95% CI 1.8-106.5, p = 0.011) and OR for TT-TG/PL ratio was 23 (95% CI 3.1-170.3, p = 0.002). In the multivariable analysis, while controlling for height and weight, only the association between TT-TG/PL ratio and patellar dislocation remained statistically significant with an adjusted OR of 2.7 (CI 1.3-5.4, p = 0.006), compared to TTTG distance alone (OR = 1.9, n.s.). CONCLUSIONS: Patellar instability ratios are significantly more reliable compared to TT-TG distance alone for the evaluation of patellar instability. Patellar instability ratios present superior diagnostic reliability, sensitivity and specificity, and intra\inter rater reliability. Thus, patellar instability ratios could function as a valuable diagnostic tool for the evaluation of patellar instability. LEVEL OF EVIDENCE: III.

High Rates of Damage to the Medial Patellofemoral Ligament, Lateral Trochlea, and Patellar Crest After Acute Patellar Dislocation: Magnetic Resonance Imaging Analysis.

PURPOSE: The primary outcome of interest of this study was to determine the frequency, location, and extent of chondral injuries and medial patellofemoral ligament (MPFL) tears, along with the rate of loose bodies, in the knee after acute primary patellar dislocation. The secondary outcome of interest was to conduct a multivariate analysis to investigate whether the presence of pathoanatomic abnormalities, including structural differences in the knees of the patients, is associated with the features of the lesions. METHODS: Patients who underwent magnetic resonance imaging after primary acute patellar dislocation were identified from our institutional databases. We analyzed a total of 175 magnetic resonance imaging scans of patients aged between 14 and 25 years who were eligible for inclusion. RESULTS: Chondral damage to the medial facet of the patella was present in 36 patients; patellar crest, 78 patients; and lateral patellar facet, 28 patients. One patient presented with chondral defects in the medial trochlear facet, whereas 118 patients showed chondral defects in the lateral trochlear facet. Loose bodies were present in 142 patients. A total of 161 patients (92%) showed MPFL damage. The patellar portion was affected in 119 patients. Of the patients, 28 showed a partially damaged MPFL (<50%), 42 showed MPFL damage greater than 50%, and 49 presented with a complete tear of the MPFL. MPFL lesions were observed on the femoral side in 42 patients. Fourteen patients presented with an avulsion fracture on the patellar side; 28 patients, on the femoral side. CONCLUSIONS: The MPFL was injured in 92% of 175 patients after a first-time acute patellar dislocation. Chondral damage was most frequent at the patellar crest, followed by the lateral femoral epicondyle. No association was found between patella alta, the sulcus angle, the Q angle, the tibial tubercle-trochlear groove distance, trochlear and patellar dysplasia, and soft-tissue damage. LEVEL OF EVIDENCE: Level IV, retrospective cohort study.

The effect of native knee rotation on the tibial-tubercle-trochlear-groove distance in patients with patellar instability: an analysis of MRI and CT measurements.

BACKGROUND: This study aimed to quantify the effect of lower limb rotational parameters on the difference in the tibial-tubercle-trochlear-groove (TTTG) distance when assessed with magnetic resonance imaging (MRI) and computed tomography (CT) in patients with patellar instability. It was hypothesized that an increased native knee rotation angle significantly contributes to an underestimation of TTTG by MRI. METHODS: Forty patients with patellar instability who had undergone standard radiographs, MRI and CT scans were included in this retrospective study. A musculoskeletal radiologist assessed all imaging for TTTG, femoral and tibial rotation, knee rotation and flexion angle, and trochlear dysplasia. ΔTTTG was defined as the TTTG measured on MRI subtracted from the TTTG measured on CT. Statistical analysis determined the effect of these parameters on the calculated difference between TTTG when measured on CT and MRI. RESULTS: Equal knee flexion in MRI and CT resulted in a ΔTTTG of 0.1 ± 0.3 mm compared to 4.0 ± 3.3 mm in patients with different knee flexion angles in both imaging acquisitions (p = 0.036). The knee rotation angle measured on CT (native knee rotation angle) was negatively correlated with ΔTTTG (r = - 0.365; p = 0.002), while neither tibial nor femoral rotation showed any associations with TTTG (n.s.). Trochlear dysplasia did not show any significant correlation with ΔTTTG, regardless of classification by Dejour or Lippacher (n.s.). Both the native knee rotation angle and the MRI knee flexion angle were independent predictors of ΔTTTG, yet with an opposing effect (knee rotation: 95% Confidence Interval [CI] for ß - 0.468 to - 0.154, p < 0.001; knee flexion 95% CI for ß 0.292 to 0.587, p < 0.001). Patients with a native knee rotation angle > 20° showed a ΔTTTG of - 5.8 ± 4.0 mm (MRI rather overestimates TTTG) compared to 0.9 ± 4.1 mm Δ TTTG (MRI rather underestimates TTTG) in patients with < 20° native knee rotation angle. CONCLUSION: The native knee rotation angle is an independent, inversely correlated predictor of ΔTTTG, thus opposing the effect of knee flexion during MRI acquisition. Consequently, these results suggest that not only knee flexion but also knee rotation should be appreciated when assessing TTTG during patellar instability diagnostic evaluation as it can potentially lead to a false estimation of the TTTG distance on MRI. LEVEL OF EVIDENCE: Level III.

Patellar dislocation is associated with increased tibial but not femoral rotational asymmetry.

PURPOSE: Patellar dislocation is associated with a range of anatomical abnormalities affecting the trochlea, extensor mechanism and the tibia. The relationship between patellofemoral instability and rotational abnormalities of the posterior condyles, trochlear groove and proximal tibia has not been adequately determined. This study aimed to identify the frequency and severity of anatomical risk factors to determine their relative contribution to patellofemoral instability. METHODS: A retrospective morphological study was undertaken comparing multiple anatomical measurements with magnetic resonance imaging of 50 patients with patellofemoral instability to an age- and gender-matched Control group (n = 50). Several techniques were assessed measuring both femoral and tibial axial asymmetry. A new measurement, tibial rotational asymmetry, comparing a line between the midpoints of the collateral ligaments to the axis between the patellar tendon and posterior cruciate ligament, was assessed for its association with patellofemoral instability. RESULTS: Compared to the controls, the patellofemoral instability group demonstrated a significant difference in tibial rotational asymmetry, with a mean of 2.9° (SD 3.2°) externally rotated vs - 1.6° (SD 2.2°) in the control group. Significant differences were also demonstrated regarding the sulcus angle, tibial tubercle-trochlear groove distance, tibial tubercle-posterior cruciate ligament distance, patellar size and the Insall-Salvati ratio. There were no differences between groups regarding the lengths of the posterior condyles, the heights of the trochlear ridges or lateralisation of the trochlear groove. Further analysis of the patellofemoral instability group revealed a subgroup of males with normal anatomy (7/50) and a subgroup of females with isolated patella alta (7/50). CONCLUSION: Patellofemoral instability is associated with tibial rotational asymmetry due to lateralisation of the tibial tubercle. It is also associated with patella alta and reduced trochlear groove depth. The femoral axial shape is otherwise unchanged. LEVEL OF EVIDENCE: III.

Analysis of cartilage injury patterns and risk factors for knee joint damage in patients with primary lateral patella dislocations.

BACKGROUND: Lateral patellar dislocation (LPD) frequently causes damage to the knee. Injury patterns and risk factors contributing to such injuries have not yet been examined in detail. METHODS: We retrospectively analyzed 50 consecutive patients with primary LPD. Two reviewers evaluated the MRI images regarding risk factors for LPD (Dejours classification; Caton-Deschamps Index, CDI; distance from the tibial tuberosity to trochlear groove, TT-TG; trochlear depth, TD) as well as joint damages according to the Whole-Organ Magnetic Resonance Imaging Score (WORMS). RESULTS: 33 male and 17 female patients with a mean age of 23.2 (±9.6) years were included in this study. 52% were classified Dejours ≥ B, 34% had a CDI ≥ 1.3, 22% a TT-TG ≥ 20mm and 52% a TD < 3mm. 49 out of 50 patients (98%) showed abnormalities according to WORMS. The most frequently observed abnormalities were synovitis/effusion (49/50, 98%), bone marrow oedema (44/50, 88%) and cartilage damage (42/50, 84%). Most frequently affected subregions were medial (41/50, 82%) and lateral (31/50, 62%) patella as well as the anterior (43/50, 86%), central (42/50, 84%) and posterior (11/50, 22%) portion of the lateral femoral condyle. There was no significant correlation between any of the examined risk factors and joint damages according to WORMS. Male patients had higher scores regarding total cartilage damage (5.11 vs. 2.56, p = 0.029), total score for the lateral femorotibial joint (3.15 vs. 1.65, p = 0.026) and overall total WORMS score (12.15 vs. 8.29, p = 0.038). CONCLUSION: Risk factors for LPD do not influence the risk of damages to the knee joint after primary LPD. Although LPD is generally known to affect more female than male patients, male patients suffered more severe injuries after primary LPD, particularly of the lateral femorotibial joint. Overall, our results underline the importance of MRI imaging after primary LPD.