The Relationship of Static Tibial Tubercle-Trochlear Groove Measurement and Dynamic Patellar Tracking

Three-dimensional magnetic resonance imaging-based statistical shape analysis and machine learning-based prediction of patellofemoral instability

This study performed three-dimensional (3D) magnetic resonance imaging (MRI)-based statistical shape analysis (SSA) by comparing patellofemoral instability (PFI) and normal femur models, and developed a machine learning (ML)-based prediction model. Twenty (19 patients) and 31 MRI scans (30 patients) of femurs with PFI and normal femurs, respectively, were used. Bone and cartilage segmentation of the distal femurs was performed and subsequently converted into 3D reconstructed models. The pointwise distance map showed anterior elevation of the trochlea, particularly at the central floor of the proximal trochlea, in the PFI models compared with the normal models. Principal component analysis examined shape variations in the PFI group, and several principal components exhibited shape variations in the trochlear floor and intercondylar width. Multivariate analysis showed that these shape components were significantly correlated with the PFI/non-PFI distinction after adjusting for age and sex. Our ML-based prediction model for PFI achieved a strong predictive performance with an accuracy of 0.909 ± 0.015, and an area under the curve of 0.939 ± 0.009 when using a support vector machine with a linear kernel. This study demonstrated that 3D MRI-based SSA can realistically visualize statistical results on surface models and may facilitate the understanding of complex shape features.

Differences in Patellofemoral Alignment Between Static and Dynamic Extension Positions in Patients With Patellofemoral Pain

Background

Considering that patellofemoral pain (PFP) is related to dynamic factors, dynamic extension on 4-dimensional computed tomography (4-DCT) may better reflect the influence of muscles and surrounding soft tissue than static extension.

Purpose

To compare the characteristics of patellofemoral alignment between the static and dynamic knee extension position in patients with PFP and controls via 4-DCT.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

Included were 39 knees (25 patients) with PFP and 37 control knees (24 participants). For each knee, an image of the dynamic extension position (a single frame of the knee in full extension [flexion angle of -5° to 0°] selected from 21 frames of continuous images acquired by 4-DCT during active flexion and extension) and an image of the static extension position (acquired using the same equipment with the knee fully extended and the muscles relaxed) were selected. Patellofemoral alignment was evaluated between the dynamic and static extension positions and between the PFP and control groups with the following parameters: patella-patellar tendon angle (P-PTA), Blackburne-Peel ratio, bisect-offset (BO) index, lateral patellar tilt (LPT), and tibial tuberosity-trochlear groove (TT-TG) distance.

Results

In both PFP patients and controls, the P-PTA, Blackburne-Peel ratio, and BO index in the static extension position were significantly lower (P < .001 for all), while the LPT and TT-TG distance in the static extension position were significantly higher (P ≤ .034 and P < .001, respectively) compared with values in the dynamic extension position. In the comparison between groups, only P-PTA in the static extension position was significantly different (134.97° ± 4.51° [PFP] vs 137.82° ± 5.63° [control]; P = .027). No difference was found in the rate of change from the static to the dynamic extension position of any parameter between the study groups.

Conclusion

The study results revealed significant differences in patellofemoral alignment characteristics between the static and dynamic extension positions of PFP patients and controls. Multiplanar measurements may have a role in subsequent patellofemoral alignment evaluation.

Using bilateral data in controls and patients with bilateral and unilateral pathology requires increased scrutiny

In many aspects of human research, capturing multiple measures from the same participant is common due to the symmetric nature of the human body (e.g., two eyes, ten fingers, two legs, etc.). This has established a concerning paradox in biomedical and clinical research. When the same condition exist bilaterally (controls or bilateral pathology), researchers often blindly include both (or multiple) measures into the statistical analysis. This assumes that measures between the two sides are statistically independent (uncorrelated). However, there are certain inherent factors within an individual (e.g., age, sex, physical activity, gait pattern, tissue characteristics, hormonal status, pain thresholds, etc.) that would point to a statistical dependence between bilateral measures. Conversely, in unilateral pathology, it is common practice to use the contralateral side as the comparator. This assumes the exact opposite, that sans pathology, bilateral measures are perfectly correlated without bias. Both of these assumptions can lead to errors in the study conclusions. Few studies have explored the statistical dependence between multiple measures from the same participant. Thus, the purpose of this perspective is to explore the statistical considerations associated with analyzing multiple measures from the same participant and provide recommendations for navigating the use of multiple, non-temporal, data points from the same participant. To give context for these recommendations, an example dataset involving patellofemoral kinematics is provided. Due to the prevalent use of bilateral data in the current literature and the resulting potential for invalid study conclusions, we recommend that future research use caution when using multiple measures from the same participant and apply proper statistical analysis (e.g., generalized estimating equations) when these measures are not independent. If the contralateral limb is used as a comparator in unilateral pathology, strong evidence must exist that the underlying pathology has not altered the measures of interest in this contralateral limb.

Dynamic CT scanning of the knee: Combining weight bearing with real-time motion acquisition

BACKGROUND

Imaging the lower limb during weight-bearing conditions is essential to acquire advanced functional joint information. The horizontal bed position of CT systems however hinders this process. The purpose of this study was to validate and test a device to simulate realistic knee weight-bearing motion in a horizontal position during dynamic CT acquisition and process the acquired images.

METHODS

"Orthostatic squats" was compared to "Horizontal squats" on a device with loads between 35% and 55% of the body weight (%BW) in 20 healthy volunteers. Intraclass Correlation Coefficient (ICC), and standard error of measurement (SEM), were computed as measures of the reliability of curve kinematic and surface EMG (sEMG) data. Afterwards, the device was tested during dynamic CT acquisitions on three healthy volunteers and three patients with patellofemoral pain syndrome. The respective images were processed to extract Tibial-Tuberosity Trochlear-Groove distance, Bisect Offset and Lateral Patellar Tilt metrics.

RESULTS

For sEMG, the highest average ICCs (SEM) of 0.80 (6.9), was found for the load corresponding to 42%BW. Kinematic analysis showed ICCs were the highest for loads of 42%BW during the eccentric phase (0.79-0.87) and from maximum flexion back to 20° (0.76). The device proved to be safe and reliable during the acquisition of dynamic CT images and the three metrics were computed, showing preliminary differences between healthy and pathological participants.

CONCLUSIONS

This device could simulate orthostatic squats in a horizontal position with good reliability. It also successfully provided dynamic CT scan images and kinematic parameters of healthy and pathological knees during weight-bearing movement.

Future Directions in Patellofemoral Imaging and 3D Modeling

PURPOSE OF REVIEW

Patellofemoral instability involves complex, three-dimensional pathological anatomy. However, current clinical evaluation and diagnosis relies on attempting to capture the pathology through numerous two-dimensional measurements. This current review focuses on recent advancements in patellofemoral imaging and three-dimensional modeling.

RECENT FINDINGS

Several studies have demonstrated the utility of dynamic imaging modalities. Specifically, radiographic patellar tracking correlates with symptomatic instability, and quadriceps activation and weightbearing alter patellar kinematics. Further advancements include the study of three-dimensional models. Automation of commonly utilized measurements such as tibial tubercle-trochlear groove (TT-TG) distance has the potential to resolve issues with inter-rater reliability and fluctuation with knee flexion or tibial rotation. Future directions include development of robust computational models (e.g., finite element analysis) capable of incorporating patient-specific data for surgical planning purposes. While several studies have utilized novel dynamic imaging and modeling techniques to enhance our understanding of patellofemoral joint mechanics, these methods have yet to find a definitive clinical utility. Further investigation is required to develop practical implementation into clinical workflow.

Influence of Articular Geometry and Tibial Tubercle Location on Patellofemoral Kinematics and Contact Mechanics

Trochlear groove geometry and the location of the tibial tubercle, where the patellar tendon inserts, have both been associated with patellofemoral instability and can be modified surgically. Although their effects on patellofemoral biomechanics have been investigated individually, the interaction between the two is unclear. The authors' aim was to use statistical shape modeling and musculoskeletal simulation to examine the effect of patellofemoral geometry on the relationship between tibial tubercle location and patellofemoral function. A statistical shape model was used to generate new knee geometries with trochlear grooves ranging from shallow to deep. A Monte Carlo approach was used to create 750 knee models by randomly selecting a geometry and randomly translating the tibial tubercle medially/laterally and anteriorly. Each knee model was incorporated into a musculoskeletal model, and an overground walking trial was simulated. Knees with shallow trochlear geometry were more sensitive to tubercle medialization with greater changes in lateral patella position (-3.0 mm/cm medialization shallow vs -0.6 mm/cm deep) and cartilage contact pressure (-0.51 MPa/cm medialization shallow vs 0.04 MPa/cm deep). However, knees with deep trochlear geometry experienced greater increases in medial cartilage contact pressure with medialization. This modeling framework has the potential to aid in surgical decision making.

The winking sign is an indicator for increased femorotibial rotation in patients with recurrent patellar instability

PURPOSE

Rotation of the tibia relative to the femur was recently identified as a contributing risk factor for patellar instability, and correlated with its severity. The hypothesis was that in patellofemoral dysplastic knees, an increase in femorotibial rotation can be reliably detected on anteroposterior (AP) radiographs by an overlap of the lateral femoral condyle over the lateral tibial eminence.

METHODS

Sixty patients (77 knees) received low-dose computed tomography (CT) of the lower extremity for assessment of torsional malalignment due to recurrent patellofemoral instability. Three-dimensional (3D) surface models were created to assess femorotibial rotation and its relationship to other morphologic risk factors of patellofemoral instability. On weight-bearing AP knee radiographs, a femoral condyle/lateral tibial eminence superimposition was defined as a positive winking sign. Using digitally reconstructed radiographs of the 3D models, susceptibility of the winking sign to vertical/horizontal AP knee radiograph malrotation was investigated.

RESULTS

A positive winking sign was present in 30/77 knees (39.0%) and indicated a 6.3 ± 1.4° increase in femorotibial rotation (p < 0.001). Femoral condyle/tibial eminence superimposition of 1.9 mm detected an increased femorotibial rotation (> 15°) with 43% sensitivity and 90% specificity (AUC = 0.72; p = 0.002). A positive winking sign (with 2 mm overlap) disappeared in case of a 10° horizontally or 15° vertically malrotated radiograph, whereas a 4 mm overlap did not disappear at all, regardless of the quality of the radiograph. In absence of a winking sign, on the other hand, no superimposition resulted within 20° of vertical/horizontal image malrotation. Femorotibial rotation was positively correlated to TT-TG (R₂ = 0.40, p = 0.001) and patellar tilt (R₂ = 0.30, p = 0.001).

CONCLUSIONS

The winking sign reliably indicates an increased femorotibial rotation on a weight-bearing AP knee radiograph and could prove useful for day-by-day clinical work. Future research needs to investigate whether femorotibial rotation is not only a prognostic factor but a potential surgical target in patients with patellofemoral disorders.

LEVEL OF EVIDENCE

III.

Adolescents and adults with patellofemoral pain exhibit distinct patellar maltracking patterns

BACKGROUND

Chronic idiopathic patellofemoral pain is associated with patellar maltracking in both adolescents and adults. To accurately target the underlying, patient-specific etiology, it is crucial we understand if age-of-pain-onset influences maltracking.

METHODS

Twenty adolescents (13.9 ± 1.4 years) and 20 adults (28.1 ± 4.9 years) female patients with idiopathic patellofemoral pain (age-of-pain-onset: < 14 and > 18 years of age, respectively) formed the patient cohort. Twenty adolescents and 20 adults (matched for gender, age, and body mass index) formed the control cohort. We captured three-dimensional patellofemoral kinematics during knee flexion-extension using dynamic MRI. Patellar maltracking (deviation in patient-specific patellofemoral kinematics, relative to their respective age-controlled mean values) was the primary outcome measure, which was compared between individuals with adolescent-onset and adult-onset patellofemoral pain using ANOVA and discriminant analysis.

FINDINGS

The female adolescent-onset patellofemoral pain cohort demonstrated increased lateral (P = 0.032), superior (P = 0.007), and posterior (P < 0.001) maltracking, with increased patellar flexion (P < 0.001) and medial spin (P = 0.002), relative to the adult-onset patellofemoral pain cohort. Post-hoc analyses revealed increased lateral shift [mean difference ± 95% confidence interval = -2.9 ± 2.1 mm at 10° knee angle], posterior shift [-2.8 ± 2.1 mm, -3.3 ± 2.3 mm & -3.1 ± 2.4 mm at 10°, 20°& 30°], with greater patellar flexion [3.8 ± 2.6 mm & 5.0 ± 2.8 mm, at 20°& 30°] and medial spin [-2.2 ± 1.7 mm & -3.4 ± 2.3 mm at 20°& 30°]. Axial-plane maltracking accurately differentiated the patient age-of-pain-onset (60-75%, P < 0.001).

INTERPRETATION

Age-of-pain-onset influences the maltracking patterns seen in patients with patellofemoral pain; with all, but 1, degree of freedom being unique in the adolescent-onset-patellofemoral pain cohort. Clinical awareness of this distinction is crucial for correctly diagnosing a patient's pain etiology and optimizing interventional strategies.

Radiologic Measurements in the Assessment of Patellar Instability: A Systematic Review and Meta-analysis

Background:

Numerous diagnostic imaging measurements related to patellar instability have been evaluated in the literature; however, little has been done to compare these findings across multiple studies.

Purpose:

To review the different imaging measurements used to evaluate patellar instability and to assess the prevalence of each measure and its utility in predicting instability. We focused on reliability across imaging modalities and between patients with and without patellar instability.

Study Design:

Systematic review; Level of evidence, 4.

Methods:

We performed a systematic review of the literature using the PubMed, SCOPUS, and Cochrane databases. Each database was searched for variations of the terms “patellar instability,” “patellar dislocation,” “trochlear dysplasia,” “radiographic measures,” “computed tomography,” and “magnetic resonance imaging.” Studies were included if they were published after May 1, 2009, and before May 1, 2019. A meta-analysis using a random effects model was performed on several measurements, comparing instability and control groups to generate pooled values.

Results:

A total of 813 articles were identified, and 96 articles comprising 7912 patients and 106 unique metrics were included in the analysis. The mean patient age was 23.1 years (95% CI, 21.1-24.5), and 41% were male. The tibial tubercle–trochlear groove (TT-TG) distance was the most frequently included metric (59 studies), followed by the Insall-Salvati ratio and Caton-Deschamps index (both 26 studies). The interobserver intraclass correlation coefficients were excellent or good for the TT-TG distance and Insall-Salvati ratio in 100% of studies reporting them; however, for the Caton-Deschamps index and Blackburne-Peel ratio, they were excellent or good in only 43% and 40% of studies. Pooled magnetic resonance imaging values for TT-TG distance (P < .01), Insall-Salvati ratio (P = .01), and femoral sulcus angle (P = .02) were significantly different between the instability and control groups. Values for tibial tubercle–posterior cruciate ligament distance (P = .36) and Caton-Deschamps index (P = .09) were not significantly different between groups.

Conclusion:

The most commonly reported measurements for evaluating patellar instability assessed patellar tracking and trochlear morphology. The TT-TG distance was the most common measurement and was greater in the patellar instability group as compared with the control group. In addition, the TT-TG, tibial tubercle–posterior cruciate ligament, and patellar tendon–trochlear groove distances were highly reproducible measurements for patellar tracking, and the Insall-Salvati ratio had superior reproducibility for assessing patellar height.

A Word of Caution for Future Studies in Patellofemoral Pain: A Systematic Review With Meta-analysis

BACKGROUND

Patellar maltracking is widely accepted as an underlying mechanism of patellofemoral pain. However, methodological differences in the literature hinder our ability to generate a universal quantitative definition of pathological patellofemoral kinematics (patellar maltracking) in patellofemoral pain, leaving us unable to determine the cause of patellofemoral pain.

PURPOSE

To systematically review the literature to provide evidence regarding the influence of confounding variables on patellofemoral kinematics.

STUDY DESIGN

Systematic review and random effects meta-analysis of control-case studies.

METHODS

A literature search of case-control studies that evaluated patellofemoral kinematics at or near full extension and were written in English was conducted using Embase, PubMed, Scopus, and Web of Science up to September 2019. Cases were defined as patients with patellofemoral pain. Studies were eliminated if they lacked quantitative findings; had a primary aim to assess therapy efficacy; or included participants with osteoarthritis and/or previous trauma, pathology, or surgery. A quality assessment checklist was employed to evaluate each study. Meta-analyses were conducted to determine the influence of confounding variables on measures of patellofemoral kinematics.

RESULTS

Forty studies met the selection criteria, with quality scores ranging from 13% to 81%. Patient characteristics, data acquisition, and measurement methods were the primary sources of methodological variability. Active quadriceps significantly increased lateral shift (standardized mean difference [SMD]_shift = 0.33; P = .0102) and lateral tilt (SMD_tilt = 0.43; P = .006) maltracking. Individuals with pain secondary to dislocation had greater effect sizes for lateral maltracking than had those with isolated patellofemoral pain (ΔSMD_shift = 0.71, P = .0071; ΔSMD_tilt = 1.38, P = .0055).

CONCLUSION

This review exposed large methodological variability across the literature, which not only hinders the generalization of results, but ultimately mitigates our understanding of the underlying mechanism of patellofemoral pain. Although our meta-analyses support the diagnostic value of maltracking in patellofemoral pain, the numerous distinct methods for measuring maltracking and the limited control for cofounding variables across the literature prohibit defining a single quantitative profile. Compliance with specific standards for anatomic and outcome measures must be addressed by the scientific and clinical community to establish methodological uniformity in this field.

Patellofemoral Mechanics: a Review of Pathomechanics and Research Approaches

PURPOSE OF REVIEW

The patellofemoral joint is a complicated articulation of the patella and femur that is prone to pathologies. The purpose of this review is to report on the current methods of investigating patellofemoral mechanics, factors that affect joint function, and future directions in patellofemoral joint research with emerging technologies and techniques.

RECENT FINDINGS

While previous hypotheses have suggested that the patella is only a moment arm extender, recent literature has suggested that the patella influences the control of knee moments and forces acting on the tibia as well as contributes to various aspects of patellar function with minimal neural input. With advancements in simulating a six-degrees-of-freedom patellofemoral joint, we have gained a better understanding of patella motion and have shown that geometry and muscle activations impact patella mechanics. Research into influences on patella mechanics from other joints such as the hip and foot has become more prevalent. In this review, we report current in vivo, in vitro, and in silico approaches to studying the patellofemoral joint. Kinematic and anatomical factors that affect patellofemoral joint function such as patella alta and tilt or bone morphology and ligaments are discussed. Moving forward, we suggest that advanced in vivo dynamic imaging methods coupled to musculoskeletal simulation will provide further understanding of patellofemoral pathomechanics and allow engineers and clinicians to design interventions to mitigate or prevent patellofemoral pathologies.

Tibial Tubercle-Roman Arch Distance: A New Measurement of Patellar Dislocation and Indication of Tibial Tubercle Osteotomy

Background:

The surgical indication for tibial tubercle osteotomy (TTO) has been based on a tibial tubercle–trochlear groove (TT-TG) distance of 20 mm or greater in patients with patellar dislocation. However, the measurement of this parameter is less reliable in patients with trochlear dysplasia.

Hypothesis:

The novel measurement of tibial tubercle–Roman arch (TT-RA) distance would be a reliable parameter for identifying the relative position of the tibial tubercle in patients with patellar dislocation, especially those with trochlear dysplasia.

Study Design:

Cohort study (diagnosis); Level of evidence, 2.

Methods:

A total of 56 patients with a diagnosis of patellar dislocation and 60 volunteers (60 knee joints) without a history of lower extremity pain or injury were included in our study. The TT-RA distance, TT-TG distance, and some femoral anatomic parameters were assessed by use of computed tomography. The measurements were performed by a radiologist and an orthopaedic surgeon in a blinded and randomized fashion. The difference in each parameter between the study and control groups was analyzed through use of an unpaired t test. Receiver operating characteristic curve analysis was performed to evaluate the discriminatory capacity of the included parameters. The cutoff values of the included measurements with specificity and sensitivity were calculated. In addition, the TT-TG distance and TT-RA distance were analyzed using the Dejour classification to evaluate the intraclass correlation coefficient (ICC) of each parameter in different types of femoral trochlea.

Result:

A significant difference for TT-RA distance was found between the study group (23.24 ± 4.41 mm) and control group (19.15 ± 4.24 mm) (P < .001). The TT-RA distance had an area under the curve of 0.757. At a value greater than 23.74 mm, TT-RA distance had 53.57% sensitivity and 88.33% specificity for patellar dislocation. The ICCs of TT-RA distance measurements were excellent in all Dejour classifications (>0.939), whereas the ICCs of TT-TG distance measurements were relatively lower than the ICCs of TT-RA distance measurements. According to the data from included healthy individuals, the pathological TT-RA distance threshold was 26 mm.

Conclusion:

Compared with TT-TG distance, the TT-RA distance is a more reliable parameter for identifying the relative position of the tibial tubercle in patients with trochlear dysplasia. For patients with a TT-RA distance greater than 26 mm, surgery should be considered to correct the malposition of the tibial tubercle.

Arthroscopic assessment of patella tracking correlates with recurrent patellar instability

PURPOSE

For recurrent lateral patellar instability surgical algorithm, an arthroscopic assessment of patellar tracking can aid with the decision of adding a tibial tubercle transfer procedure based on knee flexion angle at which patella centrally engages in its groove. Tibial tubercle-trochlear groove distance is variable in normal values and has discrepancies between imaging modalities. The aims of our study were to assess correlation of arthroscopic patellar tracking technique with recurrent patellar instability, and to assess the accuracy and reproducibility of this technique.

METHODS

157 patients were evaluated, 64 control patients with no patellar instability, and 93 patients with recurrent patellar instability. This included 57 consecutive knee arthroscopy procedures evaluated for accuracy and reproducibility of our technique. The technique involved low flow arthroscopy and anterolateral viewing portal. Patients' knees were extended from a flexed position of 120°, and paused when the patella disengaged from its groove. The KFA was then estimated by the primary surgeon, and compared with a goniometer measurement. The assisting surgeon, blinded to the primary surgeon measurements, repeated this process. For the primary outcome, goniometer readings for KFA from the primary surgeon were used to correlate with patellar instability diagnosis.

RESULTS

Patients with patellar instability had a mean KFA of 118° compared to 44°for patients without patellar instability (p < 0.001). The mean difference between goniometer reading and estimation of KFA by each surgeon was 5° (p < 0.001) with intra-class correlation of 0.99. The mean difference between the two surgeons' goniometer readings was 8° (p < 0.001) with intra-class correlation of 0.99.

CONCLUSION

This study confirms arthroscopic assessment of patella tracking is accurate, reproducible, and a knee flexion angle of greater than 44° correlates with patellar instability diagnosis. Patella tracking can be used as an adjunct or an alternative assessment method to tibial tubercle-trochlear groove distance to determine the need for tibial tubercle transfer in patellar stabilisation surgery.

LEVEL OF EVIDENCE

Prospective Cohort Study, Level III.

A robust and semi-automatic quantitative measurement of patellofemoral instability based on four dimensional computed tomography

Patellofemoral instability is a motion related disease, featured as the patella dislocating from the trochlear groove. Four dimensional computed tomography (4DCT) enables full assessment of the patellofemoral movement. Nevertheless, the quantitative measurements of patellofemoral instability are still under research and currently of limited practical use. The aim of this study is to develop a robust and semi-automatic workflow to quantitatively describe the patellofemoral movement in a patient group of eight suffering from patellofemoral instability. The initial results show agreement with manual observations of the tibial tubercle - trochlear groove (TT-TG) distance in routine practice, and the possibility to evaluate both TT-TG distance and patellar centre - trochlear groove (PC-TG) distance dynamically during active flexion-extension-flexion movement of the knee.

Patellofemoral Pain in Adolescents: Understanding Patellofemoral Morphology and Its Relationship to Maltracking

BACKGROUND

Developing bone is highly adaptable and, as such, is susceptible to pathological shape deformation. Thus, it is imperative to quantify if changes in patellofemoral morphology are associated with adolescent-onset patellofemoral pain, as a pathway to improve our understanding of this pain's etiology.

PURPOSE

To quantify and compare patellofemoral morphology in adolescent patients with patellofemoral pain with matched healthy adolescent controls and determine if a relationship exists between patellofemoral shape and kinematics (measured during active flexion-extension).

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Using 3-dimensional static magnetic resonance images acquired during a previous study, we measured patellar, trochlear, and lateral patellar width; trochlear and patellar depth; Wiberg index; patellar-height ratio; lateral trochlear inclination; cartilage length; and lateral femoral shaft length. Student t test was used to compare shape parameters between adolescents with patellofemoral pain and controls. Pearson correlations and stepwise linear regression models were used to explore the relationship among morphology, kinematics (medial-lateral shift/tilt), and pain.

RESULTS

Relative to controls, adolescents with patellofemoral pain had larger sulci (mean ± SD, 6.6 ± 0.7 vs 6.0 ± 1.1 mm; 95% CI, 0.6 mm; P = .043; d = 0.66), lateral patellar width (23.1 ± 2.4 vs 21.4 ± 2.6 mm; 95% CI, 1.6 mm; P = .033; d = 0.70), and patella-trochlear width ratio (1.2 ± 0.1 vs 1.1 ± 0.1; 95% CI, 0.1; P < .001; d = 1.26). Shape correlated with kinematics in both cohorts and in the entire population. In the patellofemoral pain group, lateral shaft length (r = 0.518; P = .019), Wiberg index (r = 0.477; P = .033), and patellar-height ratio (r = -0.582; P = .007) were correlated with medial shift. A moderate correlation existed between patellar-height ratio and lateral patellar tilt (r = 0.527; P = .017). Half of the variation in patellar shift in the patellofemoral pain cohort was explained by the patellar-height ratio and Wiberg index (R² = 0.487; P = .003). Linear correlations with pain were not found.

CONCLUSION

This study provides direct evidence that patellofemoral morphology is altered and influences maltracking in adolescents with patellofemoral pain, highlighting the multifactorial etiology of this pain. Neither morphology nor kinematics (measured during active flexion-extension) correlated with pain. Both increases and decreases in these parameters likely lead to pain, negating a direct linear correlation.

Dynamic Evaluation of Patellofemoral Instability: A Clinical Reality or Just a Research Field? A Literature review

Patellofemoral instability (PFI) is one of the most disabling conditions in the knee, often affecting young individuals. Despite its not uncommon presentation, the underlying biomechanical features leading to this entity are not entirely understood. The suitability of classic physical examination manoeuvres and imaging tests is a matter of discussion among treating surgeons, and so are the findings provided by these means. A potential cause for this lack of consensus is the fact that, classically, the diagnostic approach for PFI has relied on statically obtained data. Many authors advocate for the study of this entity in a dynamic scenario, closer to the actual situation in which the instability episodes occur. In this literature review, we have compiled the available data from the last decades regarding dynamic evaluation methods for PFI and related conditions. Several categories are presented, grouping the related techniques and devices: physical examination, imaging modalities (ultrasound (US), magnetic resonance imaging (MRI), computed tomography (CT) and combined methods), arthroscopic evaluation, and others. In conclusion, although a vast number of quality studies are presented, in which comprehensive data about the biomechanics of the patellofemoral joint (PFJ) are described, this evidence has not yet reached clinical practice universally. Most of the data still stays in the research field and is seldom employed to assist a better understanding of the PFI cases and their ideal treatment targets.

Identifying the optimal inlet for antegrade tibial intramedullary nailing via magnetic resonance imaging

INTRODUCTION

Tibial shaft fractures treated with antegrade rigid tibial intramedullary nailing has been supported worldwide. However, the optimal inlet for nailing is still controversial. Practically, varied inlets may significantly affect the tibial alignment. This retrospective study intended to utilize magnetic resonance imaging (MRI) to investigate the optimal inlet for antegrade tibial nailing.

METHODS

MRIs of 100 consecutive adult patients (50 men and 50 women, average 27 years) were used in this study. All patients had MRIs for meniscus or knee ligament injuries. There were no fractures or prior bony anomalies. The center of the tibial width (TW) at the level of the tibial tubercle (TT) was considered the optimal inlet and was positioned on the axial view of the MRIs. Various related anatomic landmarks were investigated concomitantly. All parameters were compared statistically.

RESULTS

The medial edge of the patellar tendon (PT) was 55% from the lateral end of the TW. The apex of the TT was 38% from the lateral end of the TW. The lateral edge of the PT was 19% from the lateral end of the TW. The TT was 2.5 cm distal to the tibial articular surface. The PT width was 2.3 cm. Except for the TW, the distance from the TT to the articular surface, and PT width between genders (p < 0.001), all other parameters showed no statistical significance (p >  0.05).

CONCLUSIONS

The optimal inlet for antegrade rigid tibial intramedullary nailing may be at a site 3 mm laterally to the medial edge of the PT. There are normally no differences for the nail inlet between men and women. The PT splitting approach for nail insertion may require modification.

Varied influence of the femoral or tibial component on quadriceps angles: Verified by imaging studies

Objective

The aim of this study was to evaluate the varied influence of femoral or tibial component on Quadriceps angles (Q-angle) measured with magnetic resonance image (MRI) and full-length standing scanogram (FLSS) techniques.

Methods

Two groups of patients were studied. The first group underwent MRI studies and the second group underwent FLSS studies. Two-step procedures were carried out. Knee MRI in 60 consecutive adult patients simply taken for meniscus or ligament injuries were utilized at the first step. The standardized patellar center (PC) and tibial tubercle (TT) on the frontal plane of MRI were positioned. At the second step, the FLSS in other 100 consecutive young adult patients taken for chronic unilateral lower extremity injuries were used for locating the two landmarks from MRI. The Q-angle was then determined on the anterior superior iliac spine, standardized PC, and TT on the FLSS.

Results

For 60 patients, the standardized PC was at the point 42% from the lateral end of the trans-epicondylar line of the femur. The TT was at the point 2 cm distal to the tibial articular surface and 37% from the lateral end of the tibial width. For 100 patients, the Q-angle was an average of 9.5° and 65.2% of the Q-angle was contributed by the upper arm (the femur). Women had a larger Q-angle (10.1° vs. 8.8°, p = 0.02) and a shorter femur (41.1 vs. 44.7 cm, p < 0.001).

Conclusion

The Q-angle is about 9.5° with 65.2% contributed by the femur. The Q-angle may mainly be influenced by the femoral component.

Level of evidence

Level IV, Diagnostic Study.

Tibial Tubercle-Trochlear Groove Distance Is a Reliable and Accurate Indicator of Patellofemoral Instability

BACKGROUND

Tibial tubercle-trochlear groove (TT-TG) distance is a measurement generally made on CT scans that is commonly used to quantify the risk of patellofemoral instability (PFI); however, its interrater reliability and accuracy as an indicator of PFI in patients is poorly characterized.

QUESTIONS/PURPOSES

The purposes of our study were (1) to primarily analyze interrater reliability of the TT-TG distance among orthopaedists with varied experience as measured by MRI, (2) to secondarily compare TT-TG distances between PFI and control groups, and (3) to determine an accurate TT-TG distance threshold indicative of PFI.

METHODS

The electronic medical records of a senior fellowship-trained orthopaedic sports medicine surgeon were surveyed between 2012 and 2016 for patients who had experienced at least one episode of patellar subluxation or dislocation, who reported no other knee-related history, and who underwent MRI due to persistent PFI signs and symptoms. The records of 48 PFI patients (23 males, 25 females; 19 ± 4 years of age) were compared with 83 controls (60 males, 23 females; 31 ± 8 years of age) having no history of PFI, presenting with an isolated meniscal lesion as determined from MRI and treated by the same orthopaedist during this time. All records meeting study criteria were consecutively included to offset selection bias of the retrospective analysis. Two sports medicine fellows, one who had just completed orthopaedic residency training, and another with a year of experience after residency, and a sports medicine subspecialist with more than 15 years of experience in practice independently recorded TT-TG distance, indicative of tibial tubercle lateralization relative to the femoral trochlea, to the nearest millimeter (mm) in a blinded and randomized fashion. Intraclass correlation coefficient computed interrater reliability accompanied by standard error of measurement (SEM); a one-tailed, two-sample t-test analyzed group differences with accompanying effect size per Cohen's d; receiver operating characteristic (ROC) curve determined accuracy and threshold for PFI risk. A p value < 0.05 denoted statistical significance.

RESULTS

Interrater reliability was excellent, at 0.93 (95% confidence interval [CI], 0.84-0.97; SEM = 0.6 mm) for PFI patients and 0.95 (95% CI, 0.91-0.97; SEM = 0.4 mm) for controls. Distance was greater (95% CI, 2-5; p < 0.001) in PFI patients (14 ± 4 mm; range = 7-24 mm) than controls (10 ± 3 mm; range = 3-19 mm) with an effect size of 1 (95% CI, 0.3-2). Area under the ROC curve was 0.75 (95% CI, 0.66-0.83) and threshold was 13 mm (sensitivity = 0.52, 1-specificity = 0.25), suggesting the measure is a fairly accurate indicator of risk and values of 13 mm or greater are better suited to rule in PFI. Respective positive and negative likelihood ratios of 2 and 0.6 at this threshold confirm that this distance yields a small increase in probability for PFI and a minimal decrease in probability for risk; specifically, a 13-mm TT-TG distance is two times more likely to be found in patients with PFI. Furthermore, this threshold is estimated to increase a correct PFI diagnosis by approximately 15%.

CONCLUSIONS

The MRI-specific TT-TG distance, based on a single measurement using cartilaginous-tendon landmarks within a standardized trochlear range, is reliable as performed by orthopaedists of varied experience. Patients with PFI display a 4-mm greater distance than controls, which may represent a difference large enough for clinicians to discern in practice using MRI. A 13-mm TT-TG distance is two times more likely seen in patients with PFI. However, this threshold increases a correct PFI diagnosis by only about 15%; therefore, clinical decision-making should not be influenced by this criterion alone and instead used in conjunction with other relevant variables.

LEVEL OF EVIDENCE

Level IV, diagnostic study.

Patellar Tendon-Lateral Trochlear Ridge Distance: A Novel Measurement of Patellofemoral Instability

BACKGROUND

Abnormalities in the trochlea-patella-tibia relationship have been shown to be risk factors for recurrent patellofemoral instability, although no current measurements quantify patellar containment in the trochlea. Standard measurements, such as tibial tubercle-trochlear groove (TT-TG) distance, do not account for the containment of the patella by the trochlea. Our goal was to develop a measurement to assess how well the trochlea contained the extensor mechanism.

HYPOTHESIS

A novel measurement describing the amount of the patellar tendon lateral to the lateral trochlear ridge (PT-LTR) would be a reliable measurement and significantly greater among patients with patellofemoral instability.

STUDY DESIGN

Cohort study (diagnosis); Level of evidence, 2.

METHODS

The authors analyzed radiology records from 2005 to 2014 for patients aged 5 to 18 years with and without patellofemoral dislocations who had knee magnetic resonance imaging (MRI). Two blinded reviewers evaluated 215 MRI studies. Standard and novel morphology measurements were calculated for each knee and compared in a case-control design. Interobserver reliability of each measure was assessed by the intraclass correlation coefficient. Predictability for patellofemoral dislocation was calculated with 2-tailed independent-samples Student t tests. Discriminative capacity was calculated with receiver operating characteristic analyses and area under the curve (AUC). An optimal measurement cutoff with resultant sensitivity and specificity was calculated.

RESULTS

Standard measurements of TT-TG distance, tangential axial width of the patella (TAWP), and tangential axial trochlear width (TATW) had excellent agreement between raters; lateral femoral condyle length had good agreement; and the novel measurement-width of the tendon beyond the lateral femoral condyle (PT-LTR)-also had excellent agreement. These underwent predictability and discriminative capacity analyses. TT-TG, TAWP, TATW, and PT-LTR were significant predictors of patellofemoral instability. In receiver operating characteristic analysis, TAWP had an AUC of 0.65, below the 0.8 threshold. TATW had an AUC of 0.814 and, when <32.5 mm, was 76% sensitive and 77% specific for dislocations. TT-TG demonstrated an AUC of 0.806. TT-TG ≥13.5 mm was 76% sensitive and 76% specific for dislocations. PT-LTR demonstrated an AUC of 0.876 and, when ≥5.55 mm, was 73% sensitive and 89% specific for patellofemoral dislocation.

CONCLUSION

PT-LTR is reliable, predictable, and discriminative for patellofemoral dislocations. This measurement had sensitivity similar to that of TT-TG but with higher specificity.

Patella tracking calculation from patellofemoral positions at finite angles of knee flexion

Patellofemoral (PF) pain is a common knee disease. Patella tracking has a significant correlation with PF pain, therefore it could be used as an index for diagnosis and treatment evaluation. Previous research has proposed a method for measuring in vivo patella tracking by means of an interpolation algorithm. The present study aimed to quantify the effect of the interpolation parameters on the accuracy of the patella tracking with a motion capture experiment. The precise patella tracking of 5 knee specimens was collected and compared with the interpolated tracking. The results showed that the total interpolation error decreased to 2 mm with the number of interpolation angles increasing to 6. The number of interpolation reference points had a slight influence on the accuracy. The findings consolidated the feasibility of using interpolation to measure the in vivo patella tracking, and can help to optimize the accuracy and efficiency of the methodology.

Effect of Loading on In Vivo Tibiofemoral and Patellofemoral Kinematics of Healthy and ACL-Reconstructed Knees

BACKGROUND

Although knees that have undergone anterior cruciate ligament reconstruction (ACLR) often exhibit normal laxity on clinical examination, abnormal kinematic patterns have been observed when the joint is dynamically loaded during whole body activity. This study investigated whether abnormal knee kinematics arise with loading under isolated dynamic movements.

HYPOTHESIS

Tibiofemoral and patellofemoral kinematics of ACLR knees will be similar to those of the contralateral uninjured control knee during passive flexion-extension, with bilateral differences emerging when an inertial load is applied.

STUDY DESIGN

Controlled laboratory study.

METHODS

The bilateral knees of 18 subjects who had undergone unilateral ACLR within the past 4 years were imaged by use of magnetic resonance imaging (MRI). Their knees were cyclically (0.5 Hz) flexed passively. Subjects then actively flexed and extended their knees against an inertial load that induced stretch-shortening quadriceps contractions, as seen during the load acceptance phase of gait. A dynamic, volumetric, MRI sequence was used to track tibiofemoral and patellofemoral kinematics through 6 degrees of freedom. A repeated-measures analysis of variance was used to compare secondary tibiofemoral and patellofemoral kinematics between ACLR and healthy contralateral knees during the passive and active extension phases of the cyclic motion.

RESULTS

Relative to the passive motion, inertial loading induced significant shifts in anterior and superior tibial translation, internal tibial rotation, and all patellofemoral degrees of freedom. As hypothesized, tibiofemoral and patellofemoral kinematics were bilaterally symmetric during the passive condition. However, inertial loading induced bilateral differences, with the ACLR knees exhibiting a significant shift toward external tibial rotation. A trend toward greater medial and anterior tibial translation was seen in the ACLR knees.

CONCLUSION

This study demonstrates that abnormal knee kinematic patterns in ACLR knees emerge during a simple, active knee flexion-extension task that can be performed in an MRI scanner.

CLINICAL RELEVANCE

It is hypothesized that abnormal knee kinematics may alter cartilage loading patterns and thereby contribute to increased risk for osteoarthritis. Recent advances in quantitative MRI can be used to detect early cartilage degeneration in ACLR knees. This study demonstrates the feasibility of identifying abnormal ACLR kinematics by use of dynamic MRI, supporting the combined use of dynamic and quantitative MRI to investigate the proposed link between knee motion, cartilage contact, and early biomarkers of cartilage degeneration.