Assessing Femoral Trochlear Morphologic Features on Cross-Sectional Imaging Before Trochleoplasty: Dejour Classification Versus Quantitative Measurement

The role of the most cranial trochlear orientation in patellar maltracking to better characterise trochlear morphology

PURPOSE

The purpose of our study is to describe a magnetic resonance imaging quantitative parameter to assess the morphology of the trochlea that could be measurable from normal to high-grade trochlear dysplasia while evaluating the most proximal slice with trochlear cartilage.

METHODS

Two groups of patients have been compared: patients with no patellofemoral pain, no previous trauma and undergoing surgery for a suspected isolated meniscal tears (group A) and patients with objective patellar instability (group B). The cranial trochlear orientation (CTO) angle is defined as the angle between the posterior bicondylar line and the most lateral and most medial points on the subchondral bone covered by cartilage digitised on the first and most cranial image with the trochlear cartilage clearly visible.

RESULTS

The final cohort included 253 patients (109 in group A and 144 in group B). CTO was significantly higher in group B (-2.5 ± 8.4 vs. -10.8 ± 5,1; p < .001). Moreover, 75% of knees in group B had a CTO > -7°, while 75% of knees in group A had a CTO < -7°. CTO was measurable in all 253 knees, whereas the lateral trochlear inclination and the sulcus angle were measurable in only 202 knees. The entire cohort was also divided into knees with CTO ≤ 0° and CTO > 0°. All knees with a CTO > 0 were in group B, and 49% of knees with CTO < 0 were in group B. CTO was positively correlated with lateral patellar tilt.

CONCLUSIONS

CTO is the only parameter that can be measured on the most cranial slice, in every patient, even in high-grade trochlear dysplasia. According to this new system, the axial trochlear shape may be divided into two types: a positive CTO and a negative CTO, with the trochlea serving, respectively, as a medial and lateral barrier.

LEVEL OF EVIDENCE

Level III.

A novel adapted MRI-based scheme for Dejour classification of trochlear dysplasia

PURPOSE

To elaborate an optimized scheme for the Dejour classification of trochlear dysplasia based on axial and sagittal MR images and to evaluate its intra- and inter-reader reliability.

MATERIAL AND METHODS

Over a period of 20 months patients with a knee MRI and the diagnosis of trochlear dysplasia were retrospectively included. Exclusion criteria were incomplete examination, qualitatively non-diagnostic examination, post trochlear surgery, missing informed consent for research purposes. Three independent evaluations were performed by two radiologists: first using an established description of the Dejour classification (types A-D) and then two evaluations using a new adapted scheme (types A-D). The adapted scheme includes a shallow trochlea, in type A no spur/no cliff, in type B with spur/no cliff, in type C no spur/with cliff, and in type D with spur/with cliff.

RESULTS

One hundred seventy-one knee MRIs (female:65.5%; left side:52.6%) were included with a median age of 34.3 years (range:11.3-79.2). Inter-reader reliability using the established description was fair for the four-type-classification (kappa(k) = 0.23; 95%CI:0.11-0.34), fair for differentiation low-grade versus high-grade dysplasia (k = 0.28;0.13-0.43), slight for differentiation spur versus no-spur types (k = 0.20;0.05-0.34). Inter-reader reliability using the adapted scheme was substantial (k = 0.79;0.75-0.83) for the four-type-classification, substantial for differentiation low-grade versus high-grade dysplasia (k = 0.80;0.75-0.85), substantial for differentiation spur versus no-spur presence (k = 0.76;0.71-0.81). Intra-reader reliability was almost perfect for the adapted scheme (k-values: 0.88-0.95; 95%CIs: 0.84-0.98).

CONCLUSION

The novel adapted scheme for Dejour classification shows an almost perfect intra-reader reliability and a substantially higher inter-reader reliability. It may become a helpful tool in the daily diagnostic work of radiologists.

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.

Shallow trochlear groove and narrow medial trochlear width at the proximal trochlea in patients with trochlear dysplasia: A three-dimensional computed tomography analysis

PURPOSE

Although the Dejour classification is the primary classification system for evaluating trochlear dysplasia, concerns have been raised about its reliability owing to its qualitative criteria and challenges associated with obtaining accurate radiographs. This study aimed to quantify trochlear dysplasia using three-dimensional (3D) computed tomography (CT) reconstruction with novel parameters related to the transepicondylar axis (TEA).

METHODS

Sixty patients were enrolled, including 20 with trochlear dysplasia and 40 healthy controls. The 3D CT model was generated using the Materialise Interactive Medical Image Control System software. The following six parameters were measured in eight consecutive planes at 15° intervals (planes 0-105): the distance from the TEA to the most cortical point of the lateral condyle ('LP-TEA', where LP stands for lateral peak), medial condyle ('MP-TEA', MP for medial peak) and deepest point of the trochlea ('TG-TEA', TG for trochlear groove). The distances from the medial epicondyle (MEC) to the corresponding TEA points were measured ('LP-MEC', 'MP-MEC' and 'TG-MEC').

RESULTS

In the dysplasia group, TG-TEA (planes 0, 15 and 30) and MP-MEC (planes 0, 15 and 30) were significantly greater than those in the control group (all p < 0.05 for planes of TG-TEA and MP-MEC). For type A dysplasia, LP-MEC (plane 0) was greater than that in the control group. For type B dysplasia, the MP-MEC (planes 0 and 15) and TG-TEA (planes 0 and 15) were greater than those of the control group. For type D dysplasia, MP-MEC (planes 0, 15 and 30) and TG-TEA (planes 0 and 15) were elevated.

CONCLUSION

The 3D CT reconstruction analysis established a reproducible method for quantifying osseous trochlear morphology. Patients with trochlear dysplasia had a shallow TG and narrow medial trochlear width at tracking angles of 0°-30°. This finding corroborates the clinical manifestations of recurrent patellar instability that occur during early flexion.

LEVEL OF EVIDENCE

Level III.

Medial Patellofemoral Complex Reconstruction (Combined Reconstruction of Medial Patellofemoral Ligament and Medial Quadriceps Tendon-Femoral Ligament) With Semitendinosus Autograft Resulted in Similar Clinical and Radiographic Outcomes to Medial Patellofemoral Ligament Reconstruction in Treating Recurrent Patellar Dislocation

PURPOSE

To compare clinical and radiographic outcomes of medial patellofemoral ligament reconstruction (MPFL-R) and medial patellofemoral complex reconstruction (MPFC-R) for recurrent patellar dislocation. Outcome measures were compared based on the Insall-Salvati index.

METHODS

Patients who were diagnosed with recurrent patellar dislocation and underwent either MPFL-R or MPFC-R (combined reconstruction of MPFL and medial quadriceps tendon-femoral ligament) were retrospectively analyzed. Group allocation was based on surgical procedure and patient characteristics were collected. Clinical assessments included patient-reported outcome measures (PROMs) and return-to-sports rates. Minimal clinically important difference analysis was performed. A subgroup analysis of PROMs was carried out between patients with an Insall-Salvati index ≤1.2 versus >1.2. The patellar tilt angle, lateral patellar displacement, and bisect offset ratio were measured pre- and postsurgery. Functional failures and complications were assessed.

RESULTS

Overall, 70 patients (72 knees) in the MPFL-R group and 58 patients (61 knees) in the MPFC-R group were included. Patient characteristics were comparable between the groups. At a minimum follow-up of 24 (mean, 50.6 ± 22.1) months, all PROMs were substantially improved (P < .001), without significant intergroup differences. The percentages of patients reaching the minimal clinically important difference were similar after MPFL-R and MPFC-R: 98.6% versus 93.4% (International Knee Documentation Committee), 97.2% versus 98.4% (Lysholm), 98.6% versus 100% (Kujala), and 77.8% versus 72.1% (Tegner). The subgroup analysis based on patellar height and the return-to-sport rates also suggested comparable results. Radiographic evaluation demonstrated significantly smaller lateral patellar displacements (P = .004) and bisect offset ratios (P < .001) but similar patellar tilt angles after MPFC-R. Four (5.6%) patients receiving MPFL-R and 2 (3.3%) patients receiving MPFC-R reported recurrence of functional instability, without statistically significant difference.

CONCLUSIONS

MPFC-R resulted in similar overall clinical and radiographic outcomes to MPFL-R in treating recurrent patellar dislocation. MPFC-R might not provide additional benefits for patients with an Insall-Salvati index >1.2.

LEVEL OF EVIDENCE

Level IV, therapeutic, retrospective cohort study.

Inconsistent repeatability of the Dejour classification of trochlear dysplasia due to the variability of imaging modalities: a systematic review

PURPOSE

The purpose of this systematic review was to critically assess the quality of papers that report on the intra- and inter-observer repeatability of the Dejour classification for trochlear dysplasia, and to identify the possible causes for poor repeatability.

METHODS

Two authors independently conducted an electronic search (four databases) on 8 February 2023 for studies (English or French) that assessed trochlear dysplasia classifications on imaging of skeletally mature participants. Exclusion criteria were reviews of clinical studies, conference proceedings, or editorials. After title, abstract, and full-text screening, characteristics of eligible studies were tabulated (author, year, journal, study design, cohort characteristics, and intra- and/or inter-observer agreement coefficients). The methodological quality of studies was assessed using the Joanna Briggs Institute (JBI) checklist for analytical cross-sectional studies. Authors analysed three components of the included studies: (1) classifications based on true lateral radiographs and slice imaging; (2) dysplasia graded into Type A vs B vs C vs D and 3) coefficients of intra- and/or inter-observer agreement.

RESULTS

The electronic search returned 3,178 references, and after removal of duplicates and irrelevant studies, ten were eligible for data extraction. A second search (31 July 2023) yielded one additional study. Eight studies did not include lateral radiographs, two studies did not explicitly state if radiographs were true lateral views, and one used true lateral radiographs in isolation. Classification of trochlear dysplasia into A vs B vs C vs D using different imaging modalities resulted in moderate to near-perfect intra-observer agreement, and slight to near-perfect inter-observer agreement. Studies distinguished between moderate and severe dysplasia using a variety of combinations: A vs B/C/D, A/B vs C/D and A/C vs B/D.

CONCLUSION

This systematic review revealed that the Dejour classification remains the most widely used to assess trochlear dysplasia and that the majority of studies that assessed the reliability of the Dejour classification, reported moderate to near-perfect inter-observer agreement; however, pooling of results for comparison among the included studies was inappropriate due to substantial variation in imaging protocols and non-standardised criteria to distinguish severe from moderate dysplasia.

LEVEL OF EVIDENCE

Level IV.

TRIAL REGISTRY

The PROSPERO registration number is CRD42023386731.

Lateral trochlear inclination measured by the transepicondylar axis holds potential for evaluating trochlear dysplasia in patients with lateral patellar dislocation

PURPOSE

To verify that lateral trochlear inclination (LTI) measured by the transepicondylar axis can reliably be used to evaluate trochlear dysplasia (TD) on MRI and can serve as an objective indication of trochleoplasty for patients with lateral patellar dislocation (LPD).

METHODS

Eighty patients with recurrent LPD and eighty healthy subjects were included. TD, posterior condylar angle (PCA), and LTI measured by the posterior condylar reference line (LTIp), surgical transepicondylar axis (LTIs), and anatomical transepicondylar axis (LTIa) were assessed on MRI. The intraclass correlation coefficient (ICC) and Bland-Altman analysis were performed, the correlations and differences amongst the parameters were identified, and a binary logistic regression model was established.

RESULTS

Each measurement had excellent inter- and intra-observer agreement. The LTIp, LTIs and LTIa were smaller in the study group than in the control group, with mean differences of 9.0°, 7.2° and 7.0°, respectively (P < 0.001). The PCA was larger in patients with LPD than in the control group (P < 0.001). LTIp was associated with PCA in the study group (r = - 0.41, P < 0.001). The pathological values of LTIp, LTIs and LTIa were 11.7°, 15.3° and 17.4°, respectively. LTIs and LTIa were independent risk factors for LPD, with ORs of 7.33 (95% CI [1.06-52.90], P = 0.048) and 10.29 (95% CI [1.38-76.96], P = 0.023), respectively.

CONCLUSION

The LTI can be reliably measured by MRI, but LTIp could potentially decrease the recorded value from the actual inclination angle. LTIs and LTIa are more appropriate to serve as trochleoplasty indications for patients with LPD, which could help orthopedists with surgical decision-making.

LEVEL OF EVIDENCE

Level III.

Patients with trochlear dysplasia have dysplastic medial femoral epiphyseal plates

PURPOSE

To investigate the growth of the epiphyseal plate in patients with trochlea dysplasia using a 3D computed tomography (CT)-based reconstruction of the bony structure of the distal femur. The epiphysis plate was divided into a medial part and a lateral part to compare their differences in patients with trochlear dysplasia.

METHODS

This retrospective study included 50 patients with trochlea dysplasia in the study group and 50 age- and sex-matched patients in the control group. Based on the CT images, MIMICS was used to reconstruct the bony structure of the distal femur. Measurements included the surface area and volume of the growth plate (both medial and lateral), the surface area and capacity of the proximal trochlea, trochlea-physis distance (TPD) (both medial and lateral), and height of the medial and lateral condyle.

RESULTS

The surface area of the medial epiphyseal plate (1339.8 ± 202.4 mm2 vs. 1596.6 ± 171.8 mm2), medial TPD (4.9 ± 2.8 mm vs. 10.6 ± 3.0 mm), height of the medial condyle (1.1 ± 2.5 mm vs. 4.9 ± 1.3 mm), and capacity of the proximal trochlear groove (821.7 ± 230.9 mm3 vs. 1520.0 ± 498.0 mm3) was significantly smaller in the study group than in the control group. A significant positive correlation was found among the area of the medial epiphyseal plate, the medial TPD, the height of the medial condyle and the capacity of the proximal trochlear groove (r = 0.502-0.638).

CONCLUSION

The medial epiphyseal plate was dysplastic in patients with trochlea dysplasia. There is a significant positive correlation between the surface area of the medial epiphyseal plate, medial TPD, height of the medial condyle and capacity of the proximal trochlear groove, which can be used to evaluate the developmental stage of the trochlea in clinical practice and to guide targeted treatment of trochlear dysplasia.

LEVEL OF EVIDENCE

III.

Sulcus-Deepening Trochleoplasty for High-Grade Trochlear Dysplasia: Demystifying the Procedure-a Review of the Current Literature

PURPOSE OF REVIEW

The most common and biomechanically influential pathoanatomic risk factor for recurrent patellofemoral instability is trochlear dysplasia. Sulcus-deepening trochleoplasty is a procedure developed to address high-grade trochlear dysplasia in the setting of patellofemoral instability. The purpose of this paper is to outline the current classification and surgical management of trochlear dysplasia as well as to review the current literature on the clinical outcomes and complications of sulcus-deepening trochleoplasty.

RECENT FINDINGS

This review outlines the most recent literature reporting evidence behind the decision-making to perform a trochleoplasty in the setting of patellofemoral instability and high-grade trochlear dysplasia. Critical parameters include grade of trochlear dysplasia, severity of symptoms, pertinent physical examination findings, surgical techniques, modifications for skeletally immature patients, and considerations for the revision setting. Historic studies have elicited concerns regarding high reported complication rates for trochleoplasty; however, recent studies consistently report good clinical outcomes and acceptable complication rates, similar to those of other patellar stabilizing procedures. The addition of a trochleoplasty in patients with high-grade dysplasia results in a lower re-dislocation rate, significant improvements in patient-reported outcome measures (PROMs) as well as high levels of patient satisfaction and return to sport. The use of sulcus-deepening trochleoplasty for the treatment of high-grade dysplasia and recurrent patellofemoral instability is a well-established technique with good outcomes and an acceptable complication profile. In patients with high-grade dysplasia, trochleoplasty results in lower re-dislocation rates, high patient satisfaction scores, and good clinical and functional outcomes. An understanding of trochleoplasty and its indications should be in the armamentarium of surgeons treating patellofemoral instability.

Comparison of Habitual Versus Recurrent Patellar Dislocation in Children and Adolescents: Differences in Radiological Features

Background

Recurrent patellar dislocation (RPD) and habitual patellar dislocation (HPD) in flexion are frequently encountered in children and adolescents.

Purpose

To compare the radiological features of RPD and HPD in children and adolescents.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

Imaging data were collected from patients aged 9 to 15 years who received surgical treatment for HPD or RPD at a single institution between June 2015 and September 2020. The prevalence of trochlear dysplasia, tibial tubercle lateralization, and lower limb rotational deformity was assessed through hip/knee/ankle computed tomography (CT) using the following quantitative indicators: trochlear depth index, lateral trochlear inclination, sulcus angle, tibial tubercle-trochlear groove (TT-TG) distance, ratio of TT-TG distance to femoral width, TT-TG angle, femoral anteversion angle, and tibial external rotation angle. The morphology of trochlea and patella were graded on knee CT using the Dejour and Wiberg classification. The Insall-Salvati index and Caton-Deschamps index were used to evaluate the height of the patella on lateral view radiographs. To evaluate lower limbs malalignment, the mechanical lateral distal femoral angle and medial proximal tibial angle were measured on weightbearing full-length radiographs. The collected data were analyzed and compared between the HPD and RPD groups.

Results

Enrolled were 15 patients (21 knees) diagnosed with HPD and 18 patients (22 knees) diagnosed with RPD. The age of first dislocation was significantly younger in the HPD group (7.6 ± 3.4 vs 11.2 ± 1.4 years; P = 0.003). Knees in the HPD group had a significantly higher proportion of Dejour type C dysplasia (57.1% vs 4.5%; P < .005) and Wiberg type 3 patella (66.7% vs 9.1%; P < .001). There were statistically significant differences between the groups in the trochlear depth index (HPD vs RPD: 1.1 ± 1.7 vs 2.2 ± 1.5 mm; P = .039), sulcus angle (170.3° ± 13.7° vs 157.3° ± 16.0°; P = .007), Insall-Salvati index (1.1 ± 0.2 vs 1.3 ± 0.2; P = .034), and tibial external rotation angle (31.3° ± 7.8° vs 38.4° ± 8.5°; P = .009).

Conclusion

Patients in the HPD group presented with poorer trochlear and patellar development, lower patellar height, and less tibial external rotation compared with patients in the RPG group.

Sulcus Angle, Trochlear Depth, and Dejour's Classification Can Be Reliably Applied To Evaluate Trochlear Dysplasia: A Systematic Review of Radiological Measurements

PURPOSE

To summarize data on the reliability of available imaging criteria for the assessment of trochlear dysplasia and to assess the methodological quality of the included studies.

METHODS

This systematic review was conducted following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guideline. Search was performed using major electronic databases from their inception to September 2021. All studies enrolling patients of any age who underwent a radiological exam to rule out features related to trochlear dysplasia were included. After the identification of available imaging criteria, reliability studies were analyzed. Descriptive statistics were used to summarize findings. Methodological quality was assessed using the Quality Appraisal of Reliability studies checklist.

RESULTS

A total of 2391 articles were identified, and 33 articles comprising 3036 patients with a mean age of 28.6 years were included. Thirty different measurements were extracted. Magnetic resonance imaging (MRI) was the most used imaging modalities (21 studies), followed by computed tomography (10 studies), conventional radiology (8 studies) and ultrasonography (US) (1 study). Sulcus angle, trochlear depth, and Dejour's classification were the most explored measurements. Overall, sulcus angle can be reliably assessed on radiography, CT and MRI, whereas trochlear depth can be reliably measured only with CT and MRI. Reliability of Dejour's classification ranged from poor or fair to very good for all imaging modalities. Methodological quality of included studies varied from 2 to 9 positive items out of 11 possible. Twenty-four studies (72.7%) were considered at high risk of bias.

CONCLUSION

Trochlear dysplasia can be reliably evaluated at least with 3 measurements: sulcus angle, trochlear depth and Dejour's classification. Methodological quality assessment showed high risk of bias in most included studies.

LEVEL OF EVIDENCE

Level III, systematic review of Level II-III studies.

Arthroscopic Anatomical Double-Bundle Medial Patellofemoral Complex Reconstruction Improves Clinical Outcomes in Treating Recurrent Patellar Dislocation Despite Trochlear Dysplasia, Elevated Tibial Tubercle-Trochlear Groove Distance, and Patellar Alta

PURPOSE

To evaluate the clinical outcomes of arthroscopically assisted double-bundle medial patellofemoral complex reconstruction (MPFC-R).

METHODS

A retrospective review was carried out among adult patients who experienced at least 2 patellar dislocations and underwent primary arthroscopically assisted MPFC-R between January 2014 and November 2019. Dejour classification, tibial tubercle-trochlear groove (TT-TG) distance, and patellar height (with Insall-Salvati index) were measured. Pre- and postoperative patellar tilt were compared. Information on outcome scores, ability to return to sports, postoperative recurrent dislocations, and complications was recorded.

RESULTS

A total of 42 MPFC-Rs in 39 patients were included. Mean age at surgery was 22.2 ± 7.6 years; 69.2% of patients were female. Mean follow-up was 47.3 ± 20.2 months. Seventy-four percent of cases had Dejour B (19.0%), C (33.3%), and D (21.4%) trochlear dysplasia; mean TT-TG distance was 19.6 ± 3.5 mm, and mean Insall-Salvati index was 1.21 ± 0.17. Mean patellar tilt decreased from 27.6 ± 11.6° to 9.4 ± 6.5° (P < .001). All patients had statistically significant (P < .001) improvement in mean International Knee Documentation Committee (IKDC) (44.9 ± 18.2 to 87.5 ± 6.9), Lysholm (61.4 ± 16.6 to 94.1 ± 6.4), Kujala (56.0 ± 16.8 to 92.9 ± 5.3), and Tegner score (2.7 ± 1.3 to 4.6 ± 1.4). The majority of patients (96.9%) returned to sports, with 90.3% returning to the same or greater level of activity. No postoperative dislocations or subluxations were reported.

CONCLUSIONS

Arthroscopically assisted double-bundle MPFC-R is a promising procedure to treat recurrent patellar instability at 2- to 7-year mid-term follow-up, despite the presence of trochlear dysplasia, elevated TT-TG distance and patellar alta. The improvement of IKDC score exceeded the minimal clinically important difference in 95.2% patients, and 66.7% surpassed the patient acceptable symptomatic state based on postoperative IKDC score with no redislocations being reported at latest follow-up.

LEVEL OF EVIDENCE

Level IV, case series, retrospective.

Sulcus depth, congruence angle, Wiberg index, TT-TG distance, and CDI are strong predictors of recurrent patellar dislocation

PURPOSE

To characterize patellofemoral morphology, determine radiological cutoff values based on computed tomography (CT) images, and clarify predominant anatomic risk factors in young patients with recurrent patellar dislocation (RPD).

METHODS

A total of 212 knees (age 23.0 ± 5.3 years, female: male = 110:102) with CT-confirmed RPD were enrolled for analysis. The control group was matched by age and sex (2:1). Patellofemoral and trochlear morphology, patellofemoral alignment, and other parameters were assessed by CT. Standardized methods were used for measurements. Receiver operating characteristic (ROC) curves and the areas under the ROC curve (AUCs) were used to assess accuracy in diagnosing RPD. The index of union (IU) was employed to identify a cutoff value for risk. A binary logistic regression model (Forward, LR) was constructed, and standardized coefficients were calculated to compare the relative strength of different predictors. Factors included in the model were employed to calculate distributions in the studied population.

RESULTS

The majority of measurements showed a significant difference between the RPD and control groups when comparing mean values. The AUC value was favorable for sulcus depth and significantly better than that for other trochlear morphology parameters (P < 0.0001). Cutoff values were 0.58 for the Wiberg index, 153.3° for the sulcus angle, 3.6 mm for the sulcus depth, 1.94 for the trochlear width ratio, 16.2° for the lateral trochlear inclination, 17.2° for the patellar lateral tilt, 25.5° for the congruence angle, 1.2 for the patellar height [Caton-Deschamps index (CDI)], 6.1° for the knee rotation, and 16.4 mm for the tibial tubercle-trochlear groove (TT-TG) distance. A binary logistic regression model (χ² = 20.826, P = 0.008) including the Wiberg index, sulcus depth, congruence angle, patellar height (CDI), and TT-TG distance was constructed for RPD (P ≤ 0.015), which showed excellent diagnostic performance, as indicated by an AUC of 0.989 (95% CI, 0.979 to 0.998). Sulcus depth showed the strongest relationship with RPD, followed by the congruence angle and Wiberg index, as indicated by the standardized coefficients - 1.43, 1.02, and 0.97, respectively. Eighty-seven percent of the RPD population had sulcus depth ≤ 3.6 mm.

CONCLUSIONS

This study provides a systematic reference of cutoff values based on CT data. The combination of five anatomic risk factors (sulcus depth, congruence angle, Wiberg index, TT-TG distance, and CDI) may be an excellent predictor of RPD as initial risk assessment. Sulcus depth, as the most frequently observed anatomic risk factor, showed the best diagnostic performance among trochlear morphological parameters and the strongest relationship with RPD, followed by the congruence angle and Wiberg index. In clinical practice, the sulcus depth, congruence angle, Wiberg index, TT-TG distance, and CDI with the proposed cutoff values can be used in combination to evaluate RPD. When assessing trochlear morphology, sulcus depth is recommended as the best radiological parameter.

LEVEL OF EVIDENCE

Level III.

Correlation of Tibial Torsion With Lower Limb Alignment and Femoral Anteversion in Patients With Patellar Instability

BACKGROUND

Alignment and rotation of the lower extremities have been suggested to be predisposing pathologic factors for patellar instability.

PURPOSE

To elucidate the relationship between the lower limb alignment and lower extremity rotation in patients with patellar instability.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Included were 83 patients with patellar instability. Computed tomography scans and standing full-leg radiographs were used to measure the tibial tuberosity-trochlear groove (TT-TG) distance, mechanical femorotibial angle (mFTA), mechanical lateral distal femoral angle (mLDFA), mechanical medial proximal tibial angle (mMPTA), femoral torsion, and tibial torsion of the different segments. The relationships between femoral torsion, tibial torsion of the different segments, and the mFTA, mLDFA, and mMPTA were evaluated. The levels of tibial torsion and femoral torsion in patients with varus, normal, or valgus alignment were compared with 1-way analysis of variance and chi-square test.

RESULTS

The total tibial torsion was significantly associated with total femoral anteversion (r = 0.329; P = .002) and mFTA (r = -0.304; P = .005). There were no significant correlations between mFTA and TT-TG distance or femoral anteversion. Compared with patients with valgus malalignment, patients with varus malalignment tended to have higher tibial torsion.

CONCLUSION

Tibial torsion was associated with leg axis alignment and femoral anteversion in patients with patellar instability. Patients with patellar instability, especially those with concurrent leg axis deformities, should undergo further radiological imaging so that tibial torsion can be assessed and a diagnosis of torsion deformity made early in the treatment pathway and the proper surgical plan formulated.

The Influence of Surgical Realignment Procedures on Dynamic Patellar Tracking: A Dynamic Magnetic Resonance Imaging-Controlled Feasibility Study

Persisting patellar maltracking following surgical realignment often remains unseen. The aim of this study was to analyze the effects of realignment procedures on patellofemoral kinematics in patients with patellofemoral instability (PFI) and patellofemoral maltracking (PM) by using dynamic magnetic resonance imaging (MRI). Patients planned for surgical patellar realignment due to PFI and a clinically and radiologically apparent PM between December 2019 and May 2022 were included. Patients without PM, limited range of motion, joint effusion, or concomitant injuries were excluded. Dynamic mediolateral translation (dMPT) and patella tilt (dPT) were measured preoperatively and three months postoperatively. In 24 patients (7 men, 17 women; mean age 23.0 years), 10 tibial tubercle transfers, 5 soft tissue patella tendon transfers, 6 trochleoplasties, 3 lateral lengthenings, 1 varizating distal femoral osteotomy (DFO), and 1 torsional DFO were performed. At final follow-up, dMPT (from 10.95 ± 5.93 mm to 4.89 ± 0.40 mm, p < 0.001) and dPT (from 14.50° ± 10.33° to 8.44° ± 7.46°, p = 0.026) were significantly improved. All static radiological parameters were corrected to physiological values. Surgical patellar realignment contributed to the significant improvement of patellofemoral kinematics, with an approximation to normal values. The postoperative application of dynamic MRI allowed for a quantification of the performed correction, allowing for a postoperative control of success.

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.

Dynamic Mediolateral Patellar Translation Is a Sex- and Size-Independent Parameter of Adult Proximal Patellar Tracking Using Dynamic 3 Tesla Magnetic Resonance Imaging

PURPOSE

To provide normal values for physiological patellofemoral tracking in a representative group of healthy individuals, as well as sex differences, using real-time 3T-magnetic resonance imaging (MRI) and to test for the reliability of the presented technique.

METHODS

One hundred knees of healthy individuals with no history of patellofemoral symptoms were scanned with dynamic MRI sequences, during repetitive cycles of flexion (40°) and full extension. Within a 30-seconds time-frame, three simultaneous, transverse slices were acquired. Dynamic mediolateral patellar translation (dMPT) and dynamic patellar tilt (dPT) were measured on two occasions by two independent examiners. Common radiological parameters were measured using static MRI, and correlations were calculated.

RESULTS

100 knees (53 right, 47 left; age: 26.7 ± 4.4 years; BMI: 22.5 ± 3.1) of 57 individuals (27 females, 30 males) were included. Mean height was 170.1 ± 7.7 cm in women and 181.8 ± 6.4 cm in men. Average patella diameter was 37.9 ± 2.7 (95% CI 37.1-38.7) mm in women and 42.4 ± 3.2 (95% CI 41.5-43.3) mm in men. In females, the patellar diameters and intercondylar distances were significantly smaller than in males (P < .001). Radiological parameters for patellar maltracking were within the normal range. During the range of motion, mean dMPT was 1.7 ± 2.4 (95% CI .9-2.5) mm in females and 1.8 ± 2.7 (95% CI 1.1-2.6) mm in males (P = .766). Mean dPT was 1.3 ± 2.9° (95% CI .4-2.1°) in females and -0.2 ± 3.8° (95% CI -1.2-.9°) in males (P = .036). Neither dMPT nor dPT was correlated with height, BMI, or patellar diameter. Intercondylar distance correlated weakly with dPT (r = -.241; P = .041). Intra- and interrater reliability were excellent for dMPT and dPT.

CONCLUSION

Dynamic mediolateral patellar translation is a size- and sex-independent parameter for proximal patellar tracking. In healthy individuals without patellofemoral abnormalities normal dMPT proximal to the trochlea groove was 1.7 ± 2.5 (1.2-2.2) mm, independent of size or sex. Normal dPT showed a dependency on sex and was 1.3 ± 2.9 (.4-2.1)° in women and -0.2 ± 3.8 (-1.2-0.9)° in men.

LEVEL OF EVIDENCE

Level II, diagnostic study.

Radiographic clues to the unstable knee: are findings of trochlear dysplasia on lateral knee radiographs reliable and predictive of patellar dislocation?

BACKGROUND

Trochlear dysplasia (TD) is a key predisposing risk factor for patellar instability (PI) and lateral patellar dislocation (LPD) injuries. It is useful to understand the reliability of radiographic findings of TD and the accuracy of knee radiographs in diagnosing patients with recent LPD.

PURPOSE

The purposes of our study are to evaluate the inter-rater reliability of specific radiographic signs of PI and staging of TD between radiologists and orthopedic surgeons, and to identify which findings are associated with recent LPD.

METHODS

This retrospective study comprised 336 patients aged 8 to 18 who obtained knee radiographs over a 3-year period. Two radiologists and two orthopedic surgeons, blinded to patient history, examined radiographs for indicators of PI. Using data from 19 confirmed LPD cases and 317 controls, inter-observer agreement (kappa, Pearson's correlation coefficient) was assessed, as was the odds ratio for likelihood of LPD.

RESULTS

There was nearly perfect agreement between radiologists for patella-tendon ratios (Pearson's correlation coefficient 0.8377, P < 0.0001) and discrimination between normal knees and high-grade TD (kappa 0.9213, P < 0.0001). There is fair agreement between radiologists and surgeons distinguishing between normal knees and high-grade TD (kappa 0.5843, P < 0.0001). Lateral knee radiographs interpreted as high-grade TD were highly predictive of LPD (odds ratio 7.58-54.8) among all readers.

CONCLUSIONS

There is high agreement between radiologists when evaluating lateral knee radiographs for signs of TD, validating the results of prior literature. Radiographic findings TD, patella alta, and effusion are variable predictors of recent LPD, greatest among patients with TD.

Diagnostic Imaging of Patellofemoral Instability

BACKGROUND

 Throughout the literature, patellofemoral instability (PI) is defined as an increased risk of re-/luxation of the patella within the patellofemoral joint (PFJ). In most patients it is caused by traumatic patella luxation or the existence of a range of predisposing anatomic risk factors leading to an unphysiological movement sequence within the PFJ also known as patellofemoral maltracking. In order to provide an individualized therapy approach, clinical and radiological evaluation of those risk factors of variable magnitude becomes essential. Diagnostic imaging such as magnetic resonance imaging (MRI), plain radiography, and computed tomography (CT) are straightforward diagnostic tools in terms of evaluation and treatment of PI.

METHOD

 In this review we performed a precise analysis of today's literature concerning the radiological evaluation of anatomic risk factors leading to PI. The purpose of the review is to present a logical compilation of the different anatomical risk factors causing PI and provide a straight overview of valuable radiological imaging techniques.

RESULTS AND CONCLUSION

 PI is frequently based on a multifactorial disposition. The most relevant predisposing risk factors are trochlea dysplasia, rupture of the medial patellofemoral ligament (MPFL), patella alta, abnormal tibial tubercle to trochlea groove distance (TT-TG), femoral torsion deformities, and genu valgum. Although plain X-rays may provide basic diagnostic value, cross-sectional imaging (MRI, CT) is the standard radiological tool in terms of evaluation and detection of severity of predisposing anatomic variants leading to PI.

KEY POINTS

  · Based on today's literature, PI is characterized as an increased risk of patella re-/luxation within the PFJ.. · Underlying anatomic risk factors of variable magnitude mark the pathological cause of PI.. · Modern diagnostic imaging (MRI and CT) permits straightforward diagnosis of the typical features in terms of PI.. · To provide an individualized therapy approach, precise radiological evaluation and determination of the severity of predisposing anatomic anomalies are essential..

CITATION FORMAT

· Maas KJ, Warncke ML, Leiderer M et al. Diagnostic Imaging of Patellofemoral Instability. Fortschr Röntgenstr 2021; 193: 1019 - 1033.

Objective assessment of patellar maltracking with 3 T dynamic magnetic resonance imaging: feasibility of a robust and reliable measuring technique

Patellofemoral maltracking predisposes the patellofemoral joint to instability. The purpose of this study was to provide a reliable dynamic magnetic resonance imaging (MRI) measuring technique for patellofemoral maltracking, and to investigate the influence of anatomical risk factors (AF) on patellar maltracking. Ten patients (2 males,8 females, average 19 years) with clinical maltracking and 20 controls (10 males,10 females,average 28 years) were examined with a dynamic, multi-slice gradient-echo MRI sequence, during repetitive flexion(40°) and full extension, in an open-chain-active-movement. In a 30-s time frame three simultaneous transverse slices were acquired. Dynamic mediolateral translation and dynamic tilt were measured at defined positions, by two independent examiners. Reproducibility was tested in a set of five knees. Common AFs for patellar maltracking (tibial-tuberosity-to-trochlear-groove-(TT-TG)-distances, trochlea-sulcus-angle, trochlea-sulcus-depth, lateral-trochlear-inclination and Caton-Deschamps-Index) were analyzed in consensus, using standard static MRI sequences. In patients, dynamic mediolateral translation was significantly greater in patients (12.4 ± 6.9 mm vs. − 0.1 ± 2.3 mm, p < 0.001) and the patella was positioned significantly more laterally (17.5 ± 6.9 mm vs. 3.1 ± 2.4 mm, p < 0.001) compared to controls. During movement, the patella tilted 16.3 ± 13.1° laterally in patients and 1.9 ± 4.3° medially in controls (dynamic tilt) (p < 0.002). All AFs were significantly different between patients and controls. Pathological TT-TG-distances, Caton-Deschamps-Indices and trochlea-sulcus-angles strongly correlated with dynamic patellar translation and dynamic patellar tilt (p < 0.001). In the patient population, the primary pathologies for maltracking were lateralized-tibial-tubercle (n = 5), trochlea dysplasia n = 2, patella alta (n = 3). Interrater-reliability for translation and tilt-measurement was excellent (0.971/0.976, 95% CIs 0.939–0.986/0.950–0.988). Dynamic MRI reliably differentiates between abnormal and physiological patellar tracking. Dynamic tracking and tilt strongly correlate with measurable AFs, which reinforces their clinical use and validates the presented technique.