The Relationship Between Tibial Tuberosity-Trochlear Groove Distance and Abnormal Patellar Tracking in Patients With Unilateral Patellar Instability

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.

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.

Trochlea dysplasia, increased TT-TG distance and patella alta are risk factors for developing first-time and recurrent patella dislocation: a systematic review

PURPOSE

The aim of the study was to perform a systematic review and best knowledge synthesis of the present literature concerning biomechanical risk factors for developing first-time and recurrent patella dislocation.

METHODS

The study was performed as a systematic review following PRISMA guidelines. PubMed and EMBASE were systematically searched. Studies investigating participants with risk factors for first-time as well as recurrent patella dislocation were included. The records were screened, and data extracted independently by two researchers supervised by a third independent assessor. The study was registered in PROSPERO.

RESULTS

A total of 6233 records were screened, and 50 studies met the inclusion criteria. The biomechanical risk factors: trochlear dysplasia, increased tibial tuberosity-trochlear groove distance (TT-TG), and patella alta were found to be statistically significantly associated with patella dislocation in several publications and were thus recognized as risk factors for patella dislocation. The soft-tissue stabilizers: longer and thinner MPFL ligament, increased number of type 2C and decreased number of type 1 muscle fibers, and joint laxity were found to be statistically significantly associated with patella dislocation in a few publications, but due to limited evidence, no conclusion was made on this matter.

CONCLUSION

There is strong evidence in the literature that abnormalities of bony stabilizers, trochlear dysplasia, increased TT-TG distance, and patella alta are risk factors for patella dislocation. There is less evidence that soft-tissue stabilizers are risk factors. The study emphasizes the importance of a thorough investigation of bony stabilizers in clinical decision-making.

LEVEL OF EVIDENCE

Level IV.

Reliability of the TT-TG Index Versus TT-TG Distance on MRI: Morphometric Analyses in Asian Children and Adolescents

Background

The tibial tuberosity-trochlear groove (TT-TG) distance measured on magnetic resonance imaging (MRI) is commonly used to decide the treatment for patellar instability; however, the patient's joint size is not considered in this measurement. The TT-TG index has been proposed as a knee size-adjusted measurement for tibial tuberosity location.

Purpose

To evaluate the reliability of the TT-TG index compared with the TT-TG distance by analyzing variations in measurement according to age and sex in a pediatric Asian population.

Study Design

Cohort study (diagnosis); Level of evidence, 3.

Methods

A total of 698 knee MRI scans were collected in patients between 4 and 18 years of age who did not have any patellofemoral problems. Patient age, sex, height, and weight were recorded. The scans were divided into 5 groups according to patient age (4-6 years, 46 scans; 7-9 years, 56 scans; 10-12 years, 122 scans; 13-15 years, 185 scans; and 16-18 years, 289 scans); MRI scans were also divided by sex (497 male, 201 female). Three independent observers measured the TT-TG distance and TT-TG index on each scan, and age- and sex-based differences in the measurements were evaluated after adjusting for body mass index (BMI). The reliability of the measurements was calculated with the intraclass correlation coefficient (ICC).

Results

Good to excellent inter- and intraobserver agreement was found for TT-TG distance (ICC, 0.74) and TT-TG index (ICC, 0.88). The TT-TG distance was significantly different among the groups and increased with age, while variations in the TT-TG index were minimal between age groups and sexes. This finding was also consistent after compensating for the effect of BMI.

Conclusion

The TT-TG distance changed with age, while the TT-TG index was relatively constant. Therefore, the TT-TG index may be more reliable and effective for diagnosing and planning treatment, especially in children and adolescents.

Comparison between conventional MRI and weight-bearing positional MRI reveals important differences in radiological measurements of the patellofemoral joint

OBJECTIVE

To compare radiological measurements of the patellofemoral joint (PFJ) morphology and measurement reproducibility across the following scanning modalities: (a) 3 T supine MRI, (b) 0.25 T supine MRI and (c) standing 0.25 T MRI.

METHODS

Forty patients referred to MRI of the knee were scanned by high field 3 T MRI in supine position and low field 0.25 T positional (pMRI) in supine and standing positions. Radiological measurements for assessment of femoral trochlear morphology, patellar tracking, patellar height and knee flexion angle were compared across scanning situations by one-way repeated-measures ANOVA. Measurement reliability and agreement were assessed by calculation of ICC, SEM and MDC.

RESULTS

Patellar tracking differed across scanning situations, particularly between 3.0 T supine and 0.25 T standing position. Mean differences are the following: patella bisect offset (PBO): 9.6%, p ≤ 0.001; patellar tilt angle (PTA): 3.1°, p ≤ 0.001; tibial tuberosity-trochlear groove distance (TT-TG): 2.7 mm, p ≤ 0.001). Measurements revealed slight knee joint flexion in supine and slight hyperextension in the standing position (MD: 9.3°, P ≤ 0.001), likely related to the observed differences in patellar tracking. Reproducibility was comparable across MRI field strengths. In general, PBO, PTA and TT-TG were the most robust measurements in terms of reproducibility and agreement across scanning situations (ICC range: 0.85-0.94).

CONCLUSION

Significant differences in important patellofemoral morphology measurements were observed between supine and standing MRI scanning positions. These were unlikely due to physiological factors such as changes in joint loading but rather induced by slight differences in knee flexion angle. This emphasises the need to standardise knee positioning during scanning, particularly for weight-bearing positional MRI before clinical use.

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.

Advances in osteoarthritis imaging

PURPOSE OF REVIEW

Imaging plays a pivotal role for diagnosis, follow-up and stratification of osteoarthritis patients in clinical trials and research. We aim to present an overview of currently available and emerging imaging techniques for osteoarthritis assessment and provide insight into relevant benefits and pitfalls of the different modalities.

RECENT FINDINGS

Although radiography is considered sufficient for a structural diagnosis of osteoarthritis and is commonly used to define eligibility of patients for participation in clinical trials, it has inherent limitations based on the projectional nature of the technique and inherent challenges regarding reproducibility in longitudinal assessment. MRI has changed our understanding of the disease from 'wear and tear' of cartilage to a whole organ disorder. MRI assessment of structural changes of osteoarthritis includes semi-quantitative, quantitative and compositional evaluation. Ultrasound is helpful in evaluating the degree of synovitis and has value in the assessment particularly of the patella-femoral joint. Recent development of computed tomography technology including weight-bearing systems has led to broader application of this technology in a research context.

SUMMARY

Advances in MRI technology have resulted in a significant improvement in understanding osteoarthritis as a multitissue disease.

The use of cardiac CT acquisition mode for dynamic musculoskeletal imaging

OBJECTIVES

To quantitatively evaluate the impact of a cardiac acquisition CT mode on motion artifacts in comparison to a conventional cine mode for dynamic musculoskeletal (MSK) imaging.

METHODS

A rotating PMMA phantom with air-filled holes drilled at varying distances from the disk center corresponding to linear hole speeds of 0.75 cm/s, 2.0 cm/s, and 3.6 cm/s was designed. Dynamic scans were obtained in cardiac and cine modes while the phantom was rotating at 48°/s in the CT scanner. An automated workflow to compute the Jaccard distance (JD) was established to quantify degree of motion artifacts in the reconstructed phantom images. JD values between the cardiac and cine scan modes were compared using a paired sample t-test. In addition, three healthy volunteers were scanned with both modes during a cyclic flexion-extension motion of the knee and analysed using the proposed metric.

RESULTS

For all hole sizes and speeds, the cardiac scan mode had significantly lower (p-value <0.001) JD values. (0.39 [0.32-0.46]) i.e less motion artifacts in comparison to the cine mode (0.72 [0.68-0.76]). For both modes, a progressive increase in JD was also observed as the linear speed of the holes increased from 0.75 cm/s to 3.6 cm/s. The dynamic images of the three healthy volunteers showed less artifacts when scanned in cardiac mode compared to cine mode, and this was quantitatively confirmed by the JD values.

CONCLUSIONS

A cardiac scan mode could be used to study dynamic musculoskeletal phenomena especially of fast-moving joints since it significantly minimized motion artifacts.

Quality of life following medial patellofemoral ligament reconstruction combined with medial tibial tubercle transfer in patients with recurrent patellar dislocation: a retrospective comparative study

Background

Because the patients undergoing medial patellofemoral ligament reconstruction (MPFLr) combined with medial tibial tubercle transfer (TTT) procedure are usually young and active, the quality of life (QoL) is also an important prognostic factor for patients with recurrent patellar dislocation. Assessing QoL can provide more useful and accurate evidence for the effects of this procedure. This study aimed to evaluate QoL following MPFLr combined with TTT, compared with isolated MPFLr (iMPFLr).

Methods

Fifty-one patients who underwent iMPFLr + TTT and 48 patients who underwent iMPFLr were included. Clinical evaluation included QoL (EQ-5D-5L and EQ-5D VAS), functional outcomes (Kujala, Lysholm and Tegner activity scores), physical examinations (patellar apprehension test and range of motion) and redislocation rates. Radiological evaluation included patellar tilt angle and bisect offset. These preoperative and postoperative results were compared between groups at baseline and the final follow-up. The paired and independent t tests were used for the data following a normal distribution. Otherwise, the Wilcoxon and Mann–Whitney U tests were used to analyze the differences. Categorical variables were compared by chi-square or Fisher’s exact test.

Results

All of the QoL (EQ-5D-5L and EQ-5D VAS), clinical results and radiological outcomes significantly improved in both groups at the final follow-up, with no significant differences between groups. There was no significant difference in five dimensions of EQ-5D at the final follow-up, although percentages of people with problems of mobility and pain/discomfort were higher in the MPFLr + TTT group. Female patients had lower EQ-5D index and EQ-5D VAS compared with male patients in both groups at the final follow-up, but there was only a significant difference in the EQ-5D VAS.

Conclusions

Both MPFLr + TTT and iMPFLr groups obtained similar and satisfactory improvements in the QoL, clinical results and radiological outcomes, indicating that MPFLr combined with TTT is a safe and effective procedure, which can significantly improve the QoL for patients with recurrent patellar dislocation in cases of pathologically lateralized TT. However, female patients obtained lower QoL than males.

Influence of Patellofemoral Anatomy on Outcomes of Isolated Medial Patellofemoral Ligament Reconstruction for Recurrent Patellar Instability

Background:

Patella alta and elevated tibial tubercle–trochlear groove (TT-TG) distance can predispose patients to lateral patellar dislocations and recurrent instability. Their influence on patient-reported outcomes (PROs) after medial patellofemoral ligament (MPFL) reconstruction is less clear.

Hypothesis:

We hypothesized that neither moderately increased TT-TG distance nor patella alta would negatively affect PROs after isolated MPFL reconstruction in patients with relatively normal patellar tracking (no large J-sign).

Study Design:

Cohort study; Level of evidence, 3.

Methods:

We identified patients who underwent isolated MPFL reconstruction at a single institution between 2008 and 2016. The decision to perform an isolated MPFL reconstruction was at the discretion of the operating surgeon but was not performed in the setting of a large J-sign. Patient characteristics and surgical details were collected, and patients completed the Norwich Patellar Instability Score, Knee injury and Osteoarthritis Outcome Score, and Marx activity score. Patellar height (Caton-Deschamps Index [CDI]) was assessed on preoperative lateral radiographs, and TT-TG distance was measured on preoperative axial magnetic resonance imaging (MRI) scans. Patients were grouped based on CDI and TT-TG distance, and outcomes were compared. Linear regression modeling was performed to determine whether patella alta or elevated TT-TG distance was associated with poorer PRO scores.

Results:

Of 165 knees in 152 patients who underwent isolated MPFL reconstruction, 115 patients (125 knees; 76%) with minimum 1-year follow-up were contacted at a mean of 5.2 years after surgery. Recurrent dislocation occurred in 5 of 125 knees (4%). Preoperative radiographs were available in 111 knees (89%), and preoperative MRI scans were available in 89 knees (71%). Mean CDI was 1.13, and 35% had a CDI ≥1.20. Mean TT-TG distance was 17.5 mm, and 26% had a TT-TG distance >20 mm. After adjusting for patient age, sex, body mass index, and graft choice, we observed that neither patella alta nor elevated TT-TG distance were associated with poorer PROs.

Conclusion:

Isolated MPFL reconstruction in the setting of moderately elevated TT-TG distance or patella alta was not associated with worse PROs in this cohort with relatively normal patellar tracking (no large J-sign).

Utility of Diagnostic Ultrasound in the Assessment of Patellar Instability

Background

The use of imaging to diagnose patellofemoral instability is often limited by the inability to dynamically load the joint during assessment. Therefore, the diagnosis is typically based on physical examination using the glide test to assess and quantify lateral patellar translation. However, precise quantification with this technique remains difficult.

Purpose

To quantify patellar position using ultrasound imaging under dynamic loading conditions to distinguish between knees with and without medial patellofemoral complex (MPFC) injury.

Study Design

Controlled laboratory study.

Methods

In 10 cadaveric knees, the medial patellofemoral distance was measured to quantify patellar position from 0° to 40° of knee flexion at 10° increments. Knees were evaluated at each flexion angle under unloaded conditions and with 20 N of laterally directed force on the patella to mimic the glide test. Patellar position measurements were made on ultrasound images obtained before and after MPFC transection and compared for significant differences. To determine the ability of medial patellofemoral measurements to differentiate between MPFC-intact and MPFC-deficient states, area under the receiver operating characteristic (ROC) curve analysis and the Delong test were used. The optimal cutoff value to distinguish between the deficient and intact states was determined using the Youden J statistic.

Results

A significant increase in medial patellofemoral distance was observed in the MPFC-deficient state as compared with the intact state at all flexion angles (P = .005 to P < .001). When compared with the intact state, MPFC deficiency increased medial patellofemoral distance by 32.8% (6 mm) at 20° of knee flexion under 20-N load. Based on ROC analysis and the J statistic, the optimal threshold for identifying MPFC injury was 19.2 mm of medial patellofemoral distance at 20° of flexion under dynamic loading conditions (area under the ROC curve = 0.93, sensitivity = 77.8%, specificity = 100%, accuracy = 88.9%).

Conclusion

Using dynamic ultrasound assessment, we found that medial patellofemoral distance significantly increases with disruption of the MPFC.

Clinical Relevance

Dynamic ultrasound measurements can be used to accurately detect the presence of complete MPFC injury.

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.

Tibial tuberosity-trochlear groove distance: does it measure up?

Recognized anatomic variations that lead to patella instability include patella alta and trochlea dysplasia. Lateralization of the extensor mechanism relative to the trochlea is often considered to be a contributing factor; however, controversy remains as to the degree this contributes to instability and how this should be measured. As the tibial tuberosity-trochlear groove (TT-TG) is one of most common imaging measurements to assess lateralization of the extensor mechanism, it is important to understand its strengths and weaknesses. Care needs to be taken while interpreting the TT-TG value as it is affected by many factors. Medializing tibial tubercle osteotomy is sometimes used to correct the TT-TG, but may not truly address the underlying anatomical problem. This review set out to determine whether the TT-TG distance sufficiently summarizes the pathoanatomy, and if this assists with planning of surgery in patellar instability.

Cite this article: Bone Jt Open 2022;3(3):268–274.

Cartilage degeneration is associated with activation of the PI3K/AKT signaling pathway in a growing rat experimental model of developmental trochlear dysplasia

•

Established a new experimental rat model of the developmental trochlear dysplasia;

•

Using the macroscopic morphological and micro-CT to assess trochlear dysplasia;

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Using Histological staining to investigate the cartilage degradation of the model;

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Investigated the relationship of the PI3K/AKT signaling pathway with trochlear dysplasia cartilage degeneration;

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Using immunohistochemistry and qPCR to investigate the PI3K/AKT and the marker of the cartilage degeneration.

Introduction

Trochlear dysplasia is a commonly encountered lower extremity deformity in humans. However, the molecular mechanism of cartilage degeneration in trochlear dysplasia is unclear thus far.

Objectives

The PI3K/AKT signaling pathway is known to be important for regulating the pathophysiology of cartilage degeneration. The aim of this study was to investigate the relationship of the PI3K/AKT signaling pathway with trochlear dysplasia cartilage degeneration.

Methods

In total, 120 female Sprague-Dawley rats (4 weeks of age) were randomly separated into control and experimental groups. Distal femurs were isolated from the experimental group at 4, 8, and 12 weeks after surgery; they were isolated from the control group at the same time points. Micro-computed tomography and histological examination were performed to investigate trochlear anatomy and changes in trochlear cartilage. Subsequently, expression patterns of PI3K/AKT, TGFβ1, and ADAMTS-4 in cartilage were investigated by immunohistochemistry and quantitative polymerase chain reaction.

Results

In the experimental group, the trochlear dysplasia model was successfully established at 8 weeks after surgery. Moreover, cartilage degeneration was observed beginning at 8 weeks after surgery, with higher protein and mRNA expression levels of PI3K/AKT, TGFβ1, and ADAMTS-4, relative to the control group.

Conclusion

Patellar instability might lead to trochlear dysplasia in growing rats. Moreover, trochlear dysplasia may cause patellofemoral osteoarthritis; cartilage degeneration in trochlear dysplasia might be associated with activation of the PI3K/AKT signaling pathway. These results provide insights regarding the high incidence of osteoarthritis in patients with trochlear dysplasia. However, more research is needed to clarify the underlying mechanisms.

Automated Motion Analysis of Bony Joint Structures from Dynamic Computer Tomography Images: A Multi-Atlas Approach

Dynamic computer tomography (CT) is an emerging modality to analyze in-vivo joint kinematics at the bone level, but it requires manual bone segmentation and, in some instances, landmark identification. The objective of this study is to present an automated workflow for the assessment of three-dimensional in vivo joint kinematics from dynamic musculoskeletal CT images. The proposed method relies on a multi-atlas, multi-label segmentation and landmark propagation framework to extract bony structures and detect anatomical landmarks on the CT dataset. The segmented structures serve as regions of interest for the subsequent motion estimation across the dynamic sequence. The landmarks are propagated across the dynamic sequence for the construction of bone embedded reference frames from which kinematic parameters are estimated. We applied our workflow on dynamic CT images obtained from 15 healthy subjects on two different joints: thumb base (n = 5) and knee (n = 10). The proposed method resulted in segmentation accuracies of 0.90 ± 0.01 for the thumb dataset and 0.94 ± 0.02 for the knee as measured by the Dice score coefficient. In terms of motion estimation, mean differences in cardan angles between the automated algorithm and manual segmentation, and landmark identification performed by an expert were below 1°. Intraclass correlation (ICC) between cardan angles from the algorithm and results from expert manual landmarks ranged from 0.72 to 0.99 for all joints across all axes. The proposed automated method resulted in reproducible and reliable measurements, enabling the assessment of joint kinematics using 4DCT in clinical routine.

Medial Patellofemoral Ligament Reconstruction With Concomitant Lateral Patellofemoral Reconstruction for Patellar Instability

Patients with bidirectional patellar instability who are unresponsive to conservative management may benefit from a medial patellofemoral ligament (MPFL) reconstruction and lateral patellofemoral ligament (LPFL) reconstruction. If an isolated MPFL reconstruction does not provide adequate stabilization intraoperatively, combined MPFL and LPFL reconstruction allows independent reconstruction, which can be performed with a facile, reproducible technique. The purpose of this report was to describe our technique for performing an MPFL reconstruction with a concurrent soft-tissue LPFL reconstruction combined with a distalizing tibial tubercle osteotomy to correct patella alta.

Evaluating lower limb kinematics and pathology with dynamic CT

Evaluating musculoskeletal conditions of the lower limb and understanding the pathophysiology of complex bone kinematics is challenging. Static images do not take into account the dynamic component of relative bone motion and muscle activation. Fluoroscopy and dynamic MRI have important limitations. Dynamic CT (4D-CT) is an emerging alternative that combines high spatial and temporal resolution, with an increased availability in clinical practice. 4D-CT allows simultaneous visualization of bone morphology and joint kinematics. This unique combination makes it an ideal tool to evaluate functional disorders of the musculoskeletal system. In the lower limb, 4D-CT has been used to diagnose femoroacetabular impingement, patellofemoral, ankle and subtalar joint instability, or reduced range of motion. 4D-CT has also been used to demonstrate the effect of surgery, mainly on patellar instability. 4D-CT will need further research and validation before it can be widely used in clinical practice. We believe, however, it is here to stay, and will become a reference in the diagnosis of lower limb conditions and the evaluation of treatment options. Cite this article: Bone Joint J 2021;103-B(5):822-827.

Measurement of tibial tuberosity-trochlear groove distance by MRI: assessment and correction of knee positioning errors

OBJECTIVE

The tibial tuberosity-trochlear groove (TTTG) distance varies with the position of the knee in the MR or CT scanner. We present and assess a simple method for adjustment of adduction or abduction of the knee.

MATERIALS AND METHODS

MRI of the knee encompassing a three-dimensional (3D) sagittal sequence including ≥ 8 cm of the proximal tibia was analyzed (29 females, 17 males; median age 45 years). Using 3D visualization software, the central longitudinal axis of the proximal tibia (TA) was constructed, and the TTTG distance was measured before and after alignment of the TA. Observer reliability was assessed with inter- and intra-class correlation coefficient (ICC) and Bland-Altman plots.

RESULTS

Adduction of the knee occurred in 26 examinations, mean 2.7° (range 0.0° to 9.4°), and abduction in 20 examinations, mean 2.6° (range 0.0° to 7.2°). Following adjustment, the mean TTTG distance increased 2.4 mm (range 0.0 to 6.7 mm) in the knees positioned in adduction and decreased 2.3 mm when in abduction (range 0.0 to 5.5 mm). The correlation coefficient (r²) between the deviation in adduction and abduction and the difference between TTTG unadjusted and adjusted was r² = 0.96. ICCs were excellent, but limits of agreement were close to ± 3 mm.

CONCLUSION

Measurement of the TTTG distance by MRI is influenced by a systematic technique-dependent error caused by knee positioning in adduction or abduction. We suggest a simple method for adjusting the positioning.

Tibial Tubercle-Midepicondyle Distance Can Be a Better Index to Predict the Outcome of Medial Patellofemoral Ligament Reconstruction Than Tibial Tubercle-Trochlear Groove Distance

Purpose

To compare the clinical utility of tibial tubercle-midepicondyle (TT-ME) and tibial tubercle-trochlear groove (TT-TG) distances in predicting the risk for recurrent instability after isolated MPFL reconstruction.

Methods

A consecutive series of patients with recurrent patellar dislocation who underwent isolated MPFL reconstruction made up the study population. The patients were followed for a minimum of 2 years. In assessment of surgical outcome, the patient was deemed to exhibit “postoperative recurrent patellar instability” when ≥1 of the following 3 conditions was identified: redislocation, positive apprehension sign, and positive J-sign (manifestation of abnormal patellar tracking). As for radiological parameters for position of the tibial tubercle, TT-ME distance (transverse distance between the tibial tubercle and midpoint of the transepicondylar line) and TT-TG distance were measured on axial computed tomography images. The clinical utility as a factor to predict the outcome of MPFL reconstruction was compared between the 2 distances using receiver operating characteristic (ROC) analysis. In addition, various radiological indices potentially influencing the surgical outcome were subjected to multivariable logistic regression analysis.

Results

We examined 38 knees in 38 patients with a mean age at surgery of 17.6 years. Postoperative recurrent patellar instability was encountered in 8 of the 38 knees. The ROC curve analysis showed the TT-ME distance to be a significantly better indicator in predicting surgical outcome than the TT-TG distance (P = .001). The univariate analysis for radiological factors demonstrated that the TT-ME distance was significantly associated with postoperative recurrent patellar instability (odds ratio 1.42, P = .012) whereas all other factors including the TT-TG distance did not correlate with recurrent instability. The multivariable logistic regression analysis revealed that only the TT-ME distance was significantly associated with recurrent instability (P = .035).

Conclusions

Analysis of our patient population undergoing isolated MPFL reconstruction showed that the TT-ME distance was a significantly better indicator than the TT-TG distance to predict the risk for recurrent instability after isolated MPFL reconstruction performed for patellar instability.

Level of Evidence

Level IV, therapeutic case series.

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.

Tibial tuberosity-tibial intercondylar midpoint distance measured on computed tomography scanner is not biased during knee rotation and could be clinically more relevant than current measurement systems

PURPOSE

The purpose of this retrospective cross-sectional case-control study was to evaluate an alternative imaging test for lateralization of the tibial tuberosity, unbiased towards knee rotation.

METHODS

On axial CT images of 129 knees, classified as cases (two or more patellar luxations) and controls (no patellar luxations), two raters gauged the standard tibial tuberosity-trochlear groove (TT-TG) distance, tibial tuberosity-femoral intercondylar midpoint (TT-FIM) distance, and new tibial tuberosity-tibial intercondylar midpoint (TT-TIM) distance singly, and knee longitudinal rotation angles (LRAs), and the presence of femoral trochlear dysplasia (FTD) jointly.

RESULTS

All imaging tests intercorrelated and discriminated between stability groups. TT-TIM had the lowest values with the highest precision. Though poorly, TT-TG and TT-FIM negatively correlated with age and LRAs regarding femur, but positively with presence of FTD, whereas TT-TIM was unbiased. The accuracy of TT-TG (> 20 mm), TT-FIM (> 20 mm), and TT-TIM (> 13 mm) was good with almost perfect reproducibility. Only TT-TIM was sex-biased (p = 0.009), with > 12 mm cut-off in females and (presumably) > 14 mm in males.

CONCLUSION

TT-TIM is an alternative imaging test for lateralization of the tibial tuberosity, unbiased towards knee rotation.

Accuracy and Reliability of the Visual Assessment of Patellar Tracking

BACKGROUND

Abnormal patellar tracking is described as a "J-sign" when the patella exhibits excessive lateral displacement during active knee extension.

PURPOSE

To determine (1) the accuracy and reliability of the visual assessment of patellar tracking when viewed by surgeons with patellofemoral expertise and (2) whether surgeon experience (in years) correlates with the ability to accurately identify the presence and severity of patellar maltracking.

STUDY DESIGN

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

METHODS

Using a web-based assessment, 32 orthopaedic surgeon members of the International Patellofemoral Study Group determined the presence or absence of maltracking (≥2 quadrants of lateral translation) in 10 single-knee videos of patients with patellar instability during active knee extension (qualitative analysis). Surgeons then graded patellar tracking in 20 single-knee videos as follows: 0 (<1 patellar quadrant of lateral translation), 1 (1 to <2 quadrants), 2 (2 to <3 quadrants), or 3 (≥3 quadrants) (quantitative analysis). Responses were compared with a previously described grading system using patellar bisect offset measured with 4-dimensional computed tomography. We evaluated the association between number of years of surgeon experience and the ability to correctly identify and grade patellar tracking. A total of 22 surgeons repeated the survey 3 months later, and their answers were matched to the first survey, allowing for assessment of intraobserver reliability.

RESULTS

In the qualitative analysis, surgeons correctly identified videos as showing patellar maltracking 68% of the time (κ = 0.45). In the quantitative analysis, 53%, 51%, 48%, and 68% of surgeons correctly identified maltracking of grades 3, 2, 1, and 0, respectively (κ = 0.42). Surgeon experience did not correlate with ability to identify the presence (P = .59) or grade (P = .35) of patellar maltracking. Respondent answers from the second survey demonstrated inadequate intraobserver reliability (κ = 0.48).

CONCLUSION

Using visual assessment alone, surgeons correctly identified patellar maltracking in approximately two-thirds of videos and correctly graded patellar maltracking in half. Inter- and intraobserver reliability were inadequate to support the use of visual assessment alone for detecting the presence or grade of patellar maltracking. Surgeon experience did not correlate with ability to identify the presence or grade of patellar maltracking.

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.

The dysplastic trochlear sulcus due to the insufficient patellar stress in growing rats

BACKGROUND

Developmental factors were assumed to be the key factors that influenced the morphology of femoral trochlea. This study investigated the effects of insufficient patellar stress after birth on the morphological development of the femoral trochlea. Effects of insufficient patellar stress on femoral trochlea were investigated using surgical induced patellectomy and patellar dislocation in growing rat model.

METHODS

In this study, two experimental groups and one sham group (SG) were established. Thirty-six Wistar rats (female, 28 days of age) were randomly assigned to three groups. The patellectomy group (PG), rats underwent the patellectomy in this group. The dislocation group (DG), rats underwent the surgery-induced patellar dislocation. Histological staining (Safranin-O and fast green), Micro-computed tomographic (Micro-CT) analysis in two experimental endpoints (3, 12 weeks postoperatively) were selected to evaluate morphological changes of the femoral trochlea.

RESULTS

Articular cartilage on the trochlear sulcus was remodeled at 3 weeks after the surgery, and degenerated at 12 weeks through the histological staining. The femoral trochlear angle (FTA) did not show a significant difference at 3 week between the experimental groups and the sham group (PG vs SG P = 0.38, DG vs SG p = 0.05), but the FTA was significantly increased in experimental groups at 12 weeks(PG vs SG P = 0.001, DG vs SG p = 0.005). The Bone volume density (BV/TV), Trabecular number (Tb.N) under the trochlea groove were significantly reduced at 3 weeks postoperatively in the experimental groups (PG vs SG p = 0.001, DG vs SG p = 0.002). No significant difference was found in BV/TV and Tb. N among the three groups at 12 weeks postoperatively.

CONCLUSION

Surgical induced patellectomy and patellar dislocation leads to the dysplastic trochlear sulcus in growing rats. Besides the bone morphology of trochlear sulcus, the articular cartilage and subchondral trabecula under the trochlear sulcus were remodeled early stage after the surgery.

Patellofemoral morphology measurements and their associations with tibiofemoral osteoarthritis-related structural damage: exploratory analysis on the osteoarthritis initiative

OBJECTIVES

Given the coexistence and possible interactions between patellofemoral and tibiofemoral compartments, roles of patellofemoral morphology measurements in tibiofemoral osteoarthritis (OA) have not been investigated extensively. We aimed to determine whether patellofemoral morphology is associated with the presence and longitudinal worsening of tibiofemoral OA in participants of the Osteoarthritis Initiative (OAI).

METHODS

Baseline knee MRIs of 600 participants were read by two independent blinded observers in consensus to determine patellofemoral morphology measurements including tibial tuberosity to trochlear groove (TT-TG) distance, trochlear groove depth (TGD), lateral patellar tilt (LPT), and Insall-Salvati ratio (ISR). Radiographic and MRI OA knee scoring (MOAKS) measurements were extracted from baseline and 2-year follow-up readings. Associations between baseline patellofemoral morphology metrics with radiographic medial tibiofemoral compartment (MTFC) joint space loss (> 0.7 mm, between baseline and 2nd-4th-year readings), and MRI-derived cartilage damage, bone marrow lesions (BMLs), and osteophytes (baseline to 2 years), were investigated using regression models adjusted for age, sex, body mass index, and knee alignment. P values were corrected using the Benjamini-Hochberg procedure.

RESULTS

Patellofemoral morphology measurements were not associated with longitudinal joint space loss in the MTFC or MOAKS determinants. Only TT-TG distance was associated with the baseline number of subregions with cartilage defects (OR (95% CI), 1.09 (1.04-1.14), corrected p value ≤ 0.01), BMLs (OR (95% CI), 1.1 (1.04-1.17), corrected p value = 0.01), and osteophytes (OR (95% CI), 1.09 (1.05-1.14), corrected p value ≤ 0.01) in the lateral tibiofemoral compartment (LTFC), and worsening of LTFC cartilage defects over 2 years (OR (95% CI), 1.09 (1.03-1.16), corrected p value = 0.02).

CONCLUSIONS

Higher TT-TG distance was associated with concurrent MRI-derived OA-related structural damages and 2-year follow-up worsening only in LTFC. No associations were detected between patellofemoral morphology measurements and MTFC OA progression.

KEY POINTS

• Of all patellofemoral morphology measurements, the only lateralization of the tibial tubercle may be considered as a risk factor for lateral (not medial) tibiofemoral osteoarthritis worsening. • Patellofemoral morphology measurements of patella alta, trochlear dysplasia, patellar tilt, and lateralization of the tibial tubercle are not associated with radiographic and MRI-based medial tibiofemoral osteoarthritis worsening over 2 years. • Using longitudinal MRI data, each millimeter increase of TT-TG distance is associated with a 9% (95% confidence interval, 3-16%) increase in odds of longitudinal cartilage defects in the lateral tibiofemoral (but not medial) compartment over 2 years.

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.

Influence of patient-related factors on clinical outcome of tibial tubercle transfer combined with medial patellofemoral ligament reconstruction

BACKGROUND

Tibial tubercle transfer is frequently used for treating patellar instability. This study aimed to analyze the clinical results following tibial tuberosity transfer with medial patellofemoral ligament (MPFL) reconstruction in the treatment of patellar instability.

METHODS

Seventy-two cases presenting a lateralized tibial tubercle were treated with tibial tuberosity transfer and MPFL reconstruction. Pre-operative and postoperative pain levels and knee function were evaluated using common scoring systems. Cartilage status was assessed at the time of surgery, and the influence of patient-related factors was analyzed. Median and interquartile ranges were used to present the results.

RESULTS

After a mean of 27.6 (12 -76) months, a re-dislocation rate of 4.2% and significant improvement in knee function from a median of 48.0 (33 -70) to 83.0 (68 -94) and a median of 44.0 (24 -62) to 85.0 (69 -93), based on Kujala (P ≤ 0.001) and Lysholm (P ≤ 0.001) scores were observed. The Tegner score significantly increased from a median of 3.0 (2 -4) to 4.0 (4 -5) (P ≤ 0.001), while the pain level decreased from a median of 5.0 (3 -8) to 2.0 (0 -3) (P ≤ 0.001). Cartilage lesions were found in 55/72 (76.4%) knees. The likelihood of finding II° cartilage lesions was six times higher in cases of ≥ two previous operations.

CONCLUSION

Tibial tuberosity transfer with MPFL reconstruction allowed reliable patellar stabilization with a low re-dislocation rate. Patient age and unsuccessful attempts at surgical stabilization posed significant risk factors for cartilage lesions and may have limited postopertive outcomes.

Computational simulation of medial versus anteromedial tibial tuberosity transfer for patellar instability

The study utilizes dynamic simulation of knee function to determine how tibial tuberosity medialization and anteromedialization influence patellar tracking and contact pressures for knees with patellar instability. Dual limb squatting was simulated with six multibody dynamic simulation models representing knees being treated for patellar instability. Each knee exhibited lateral patellar maltracking in the pre-operative condition based on the bisect offset index. The patellar tendon attachment points on the tibia were medialized by 10 mm to represent tibial tuberosity medialization, with an additional 5 mm of anteriorization applied for anteromedialization. The patellofemoral contact pressure distribution was quantified using discrete element analysis. Data were analyzed with repeated measures analysis of variance with post-hoc tests and linear regressions. Tibial tuberosity medialization and anteromedialization significantly (p < 0.05) decreased the bisect offset index for nearly all flexion angles up to 80°, with the largest changes near full extension. Both procedures significantly decreased the maximum lateral pressure at 55°, but increased the maximum medial pressure from 30 to 80°. The pre-operative to post-operative increase in the maximum contact pressure was significantly correlated with the maximum pre-operative bisect offset index for tuberosity medialization (r²  = 0.84), but not for anteromedialization. Statement of Clinical Significance: The results indicate tibial tuberosity medialization decreases patellar lateral maltracking and lateral patellofemoral contact pressures, but increases medial contact pressures. When pre-operative patellar maltracking is relatively low, tibial tuberosity medialization is likely to increase maximum contact pressures. Tibial tuberosity anteromedialization lowers the risk of elevated post-operative contact pressures compared to medialization. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3231-3238, 2018.

Evaluation of the Effect of the Sulcus Angle and Lateral to Medial Facet Ratio of the Patellar Groove on Patella Tracking in Aging Subjects with Stable Knee Joint

Purpose

To determine whether the sulcus angle and the lateral to medial facet ratio correlate with patella lateral displacement and tilt in patients without patella instability.

Methods

Computed tomography images of the lower limb of 64 patients without known arthropathy were collected. Three-dimensional models of the lower limb with a unified coordinate system were rebuilt by using Mimics software. The sulcus angle, lateral to medial facet ratio, lateral trochlear inclination of the patellar groove, tibial tuberosity-trochlear groove (TT-TG) distance, bisect offset index, and lateral tilt of the patella were measured. Pearson's correlation test was used to determine the relationship between the aforementioned parameters.

Results

Data from 51 patients were analyzed. The sulcus angle was negatively correlated with lateral tilt inclination (p < 0.001, r = 0.8406) and positively correlated with the bisect offset index (p = 0.003, r = 0.634) and patellar tilt (p = 0.03, r = 0.551); the lateral to medial facet ratio was positively correlated with TT-TG distance (p = 0.003, r = 0.643) and bisect offset index (p = 0.026, r = 0.559).

Conclusion

The sulcus angle and lateral to medial facet ratio of the patellar groove can influence patella tracking in patients with stable knee joints.

Dynamic tracking influenced by anatomy following medial patellofemoral ligament reconstruction: Computational simulation

BACKGROUND

Continued patellar instability can occur following medial patellofemoral ligament (MPFL) reconstruction. Computational simulation of function was used to investigate the influence of the lateral position of the tibial tuberosity, trochlear dysplasia and patella alta on lateral patellar tracking following MPFL reconstruction.

METHODS

Multibody dynamic simulation models were developed to represent nine knees being treated for recurrent patellar instability. Knee extension against gravity and dual limb squatting were simulated with and without simulated MPFL reconstruction. Graft resting lengths were set to allow 10mm and five millimeters of patellar lateral translation at 30° of knee flexion. The bisect offset index, lateral tibial tuberosity to posterior cruciate ligament tibial attachment (TT-PCL) distance, lateral trochlear inclination, and Caton-Deschamps index were quantified at every five degrees of knee flexion to characterize lateral tracking, lateral position of the tibial tuberosity, trochlear dysplasia, and patella alta, respectively. For the pre-operative and post-operative conditions and each type of motion, bisect offset index was correlated with the anatomical parameters using stepwise multivariate linear regression.

RESULTS

For both motions, the pre-operative and post-operative bisect offset indices were significantly correlated with lateral trochlear inclination and lateral TT-PCL distance. For both motions, the adjusted r² decreased with MPFL reconstruction, but was still approximately 0.5 for MPFL reconstruction allowing five millimeters of lateral translation.

CONCLUSION

MPFL reconstruction decreases but does not eliminate lateral maltracking related to trochlear dysplasia and a lateralized tibial tuberosity. Patients with these pathologies are likely at the highest risk for instability related to maltracking following MPFL reconstruction.

Clinical Utility of Continuous Radial Magnetic Resonance Imaging Acquisition at 3 T in Real-time Patellofemoral Kinematic Assessment: A Feasibility Study

PURPOSE

To compare patellar instability with magnetic resonance imaging analysis using continuous real-time radial gradient-echo (GRE) imaging in the assessment of symptomatic patients and asymptomatic subjects.

METHODS

Symptomatic patients with suspected patellofemoral maltracking and asymptomatic volunteers were scanned in real time by a radial 2-dimensional GRE sequence at 3 T in axial orientation at the patella level through a range of flexion-extension. The degree of lateral maltracking, as well as the associated tibial tubercle-trochlear groove distance and trochlea depth, was measured. Patellar lateralization was categorized as normal (≤2 mm), mild (>2 to ≤5 mm), moderate (>5 to ≤10 mm), or severe (>10 mm). The patellofemoral cartilage was also assessed according to the modified Outerbridge grading system.

RESULTS

The study included 20 symptomatic patients (13 women and 7 men; mean age, 36 ± 12.8 years) and 10 asymptomatic subjects (3 women and 7 men; mean age, 33.1 years). The mean time to perform the dynamic component ranged from 3 to 7 minutes. Lateralization in the symptomatic group was normal in 10 patients, mild in 1, moderate in 8, and severe in 1. There was no lateral tracking greater than 3 mm in the volunteer group. Lateral maltracking was significantly higher in symptomatic patients than in asymptomatic subjects (4.4 ± 3.7 mm vs 1.5 ± 0.71 mm, P = .007). Lateral tracking significantly correlated with tibial tubercle-trochlear groove distance (r = 0.48, P = .006). There was excellent agreement on lateral tracking between the 2 reviewers (intraclass correlation coefficient, 0.979; 95% confidence interval, 0.956-0.990).

CONCLUSIONS

The inclusion of a dynamic radial 2-dimensional GRE sequence is a rapid and easily performed addition to the standard magnetic resonance imaging protocol and allows dynamic quantitative assessment of patellar instability and lateral maltracking in symptomatic patients. With a paucity of reported data using this technique confirming that these results reach clinical significance, future work is required to determine how much lateral tracking is clinically significant.

LEVEL OF EVIDENCE

Level III, case control.

Measurement of Tibial Tuberosity-Trochlear Groove Offset Distance by Weightbearing Cone-Beam Computed Tomography Scan

BACKGROUND

Computed tomography (CT) scans are useful for objectively measuring bone alignment because they show bone detail particularly well, and these scans have been used extensively to assess patellar orientation. The tibial tubercle-trochlear groove (TT-TG) offset distance has been shown to be influenced by knee flexion and weightbearing, yet conventional CT scans are obtained with the subject relaxed, supine, and with the knee in full extension. A new cone-beam CT scanner has been designed to allow for weightbearing images, potentially providing a more physiologically relevant assessment of patellofemoral alignment.

PURPOSE/HYPOTHESIS

The purpose of this study was to measure the TT-TG offset in healthy individuals without any history of knee complaints when CT scans were obtained while fully weightbearing on a flexed knee. Our hypothesis was that the TT-TG offset measurement in these healthy knees would be reproducible and less than the historically reported normal range.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Twenty healthy volunteers without any history of knee complaint were recruited to undergo a weightbearing cone-beam CT scan of the knee flexed at 30°. The scans were reviewed by a radiologist and an orthopaedic surgeon, and TT-TG offset was measured using the digital tools of a picture archiving and communication system. Paired t tests were used to compare TT-TG offset on 2 separate occasions for both raters. Inter- and intrarater reliability were assessed using a 2-way mixed-effects model intraclass correlation coefficient with corresponding 95% confidence intervals for TT-TG offset.

RESULTS

The mean TT-TG offset was 2.7 mm. There were no statistically significant differences in TT-TG offset between raters (Prater1 = .70; Prater2 = .49) and time of read (Ptime1 = .83; Ptime2 = .19). Good to moderate interrater reliability was found at the time of both reads, and good intrarater reliability was found for both raters.

CONCLUSION

When measured by CT scan and obtained from a subject while weightbearing on a flexed knee, the TT-TG offset is reproducible and the distance is less than that obtained via a conventional CT scan.

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

BACKGROUND

The tibial tubercle to trochlear groove (TT-TG) distance is used for screening patients with a variety of patellofemoral joint disorders to determine who may benefit from patellar medialization using a tibial tubercle osteotomy. Clinically, the TT-TG distance is predominately based on static imaging with the knee in full extension; however, the predictive ability of this measure for dynamic patellar tracking patterns is unknown.

PURPOSE

To determine whether the static TT-TG distance can predict dynamic lateral displacement of the patella.

STUDY DESIGN

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

METHODS

The static TT-TG distance was measured at full extension for 70 skeletally mature subjects with (n = 32) and without (n = 38) patellofemoral pain. The dynamic patellar tracking patterns were assessed from approximately 45° to 0° of knee flexion by use of dynamic cine-phase contrast magnetic resonance imaging. For each subject, the value of dynamic lateral tracking corresponding to the exact knee angle measured in the static images for that subject was identified. Linear regression analysis determined the predictive ability of static TT-TG distance for dynamic patellar lateral displacement for each cohort.

RESULTS

The static TT-TG distance measured with the knee in full extension cannot accurately predict dynamic lateral displacement of the patella. There was weak predictive ability among subjects with patellofemoral pain ( r² = 0.18, P = .02) and no predictive capability among controls. Among subjects with patellofemoral pain and static TT-TG distances 15 mm or more, 8 of 13 subjects (62%) demonstrated neutral or medial patellar tracking patterns.

CONCLUSION

The static TT-TG distance cannot accurately predict dynamic lateral displacement of the patella. A large percentage of patients with patellofemoral pain and pathologically large TT-TG distances may have neutral to medial maltracking patterns.

Characterization of patellar maltracking using dynamic kinematic CT imaging in patients with patellar instability

PURPOSE

Little has been reported on the relationship between patellar maltracking and instability. Patellar maltracking has been subjectively described with the "J sign" but is difficult to assess objectively using traditional imaging. Dynamic kinematic computed tomography (DKCT) allows dynamic assessment of the patellofemoral joint. DKCT was used to visualize and quantify patellar maltracking patterns, and severity of maltracking was correlated with the presence or absence of patellar instability symptoms.

METHODS

Seventy-six knees in 38 patients were analysed using DKCT. Maltracking was defined as deviation of the patella from the trajectory of the trochlear groove and was characterized by patellar bisect offset, which was measured at 10° intervals of knee flexion during active flexion and extension. Bisect offset measurements were grouped by number of quadrants of maximum lateral patellar motion, with one, two, and three quadrants corresponding to 75-99, 100-125, and >125 %, respectively. Patellar instability symptoms were correlated with maltracking severity.

RESULTS

Two knees were excluded because of poor imaging quality. Fifty of 74 knees had patellar instability, and 13 patients had bilateral symptoms. Of these, four (8 %) had normal tracking patterns; 41 (82 %) had increased lateral translation in extension, which we termed the J-sign pattern; 4 (8 %) had persistent lateralization of the patella throughout range of motion; and 1 had increased lateral translation in flexion. In knees with the J-sign pattern, degree of maltracking was graded by severity: J1 (n = 24), J2 (n = 19), and J3 (n = 15). The sensitivities of J-sign grades in predicting patellar instability symptoms were 50 % (J1), 80 % (J2), and 93 % (J3) (p < 0.01). There were significant differences in sensitivity between knees with no J sign or J1 versus J2 or J3 (p = 0.02).

CONCLUSION

DKCT showed several patellar maltracking patterns in patients with patellar instability. A J-sign pattern with more than two quadrants of lateral translation correlated with the presence of patellar instability symptoms. Incorporation of this approach of objectively quantifying maltracking patterns is recommended in the evaluation of patellofemoral instability.

LEVEL OF EVIDENCE

IV.

Dynamic Simulation of the Effects of Graft Fixation Errors During Medial Patellofemoral Ligament Reconstruction

Background:

Medial patellofemoral ligament (MPFL) reconstruction is performed to prevent recurrent instability, but errors in femoral fixation can elevate graft tension.

Hypothesis:

Errors related to femoral fixation will overconstrain the patella and increase medial patellofemoral pressures.

Study Design:

Controlled laboratory study.

Methods:

Five knees with patellar instability were represented with computational models. Kinematics during knee extension were characterized from computational reconstruction of motion performed within a dynamic computed tomography (CT) scanner. Multibody dynamic simulation of knee extension, with discrete element analysis used to quantify contact pressures, was performed for the preoperative condition and after MPFL reconstruction. A standard femoral attachment and graft resting length were set for each knee. The resting length was decreased by 2 mm, and the femoral attachment was shifted 5 mm posteriorly. The simulated errors were also combined. Root-mean-square errors were quantified for the comparison of preoperative patellar lateral shift and tilt between computationally reconstructed motion and dynamic simulation. Simulation output was compared between the preoperative and MPFL reconstruction conditions with repeated-measures Friedman tests and Dunnett comparisons against a control, which was the standard MPFL condition, with statistical significance set at P < .05.

Results:

Root-mean-square errors for simulated patellar tilt and shift were 5.8° and 3.3 mm, respectively. Patellar lateral tracking for the preoperative condition was significantly larger near full extension compared with the standard MPFL reconstruction (mean differences of 8 mm and 13° for shift and tilt, respectively, at 0°), and lateral tracking was significantly smaller for a posterior femoral attachment (mean differences of 3 mm and 4° for shift and tilt, respectively, at 0°). The maximum medial pressure was also larger for the short graft with a posterior femoral attachment than for standard MPFL reconstruction, with a significant increase in the mean value of 1.6 MPa at 30°.

Conclusion:

MPFL reconstruction reduces lateral tracking, but nonanatomic femoral fixation and overtensioning the graft overcorrect patellar tracking and increase pressure applied to medial patellar cartilage.

Clinical Relevance:

Errors in femoral fixation and graft tensioning can lead to postoperative loss of flexion and overloading of medial cartilage.

Diagnosis and Longitudinal Assessment of Osteoarthritis: Review of Available Imaging Techniques

Osteoarthritis (OA) is a major chronic and global health care problem. Recent technological advances in imaging and postprocessing techniques have enhanced the understanding and characterization of the pathophysiology of this chronic and prevalent disease. Although plain radiograph remains the modality of choice for initial assessment of OA, recent studies have shown that advanced cross-sectional imaging can improve the early detection, grading, structural damage quantification, and risk stratification of OA. This article discusses the currently available evidence regarding both the conventional and novel imaging modalities that can be used for evaluation of patients with OA and its longitudinal assessment.

Dynamic tracking influenced by anatomy in patellar instability

BACKGROUND

The current study was performed to correlate anatomical parameters related to trochlear dysplasia, tibial tuberosity position, and patella alta with in vivo patellar tracking for subjects with recurrent patellar instability.

METHODS

Eight subjects with recurrent patellar instability that failed conservative treatment were evaluated using computational reconstruction of in vivo knee motion. Computational models were created from dynamic CT scans of the knee during extension against gravity. Shape matching techniques were utilized to position a single model of each bone (femur, patella and tibia) to represent multiple positions of knee extension. Patellar tracking was characterized by the bisect offset index (lateral shift) and lateral tilt. Anatomical parameters were characterized by the inclination of the lateral ridge of the trochlear groove, the lateral distance from the tibial tuberosity to the posterior cruciate ligament attachment (lateral TT-PCL distance), and the Caton-Deschamps index. Stepwise multivariable linear regression analysis was used to relate patellar tracking to the anatomical parameters at low (<20°) and high flexion angles.

RESULTS

At low flexion angles, both lateral trochlear inclination and lateral TT-PCL distance were significantly correlated with bisect offset index (p=0.02). Only lateral trochlear inclination was significantly correlated with lateral tilt (p<0.001). At high flexion angles, bisect offset index and lateral tilt were correlated with only lateral TT-PCL distance (p≤0.02).

CONCLUSION

Parameters related to trochlear dysplasia and tibial tuberosity position were both related to patellar tracking, but the relationship changed with the flexion angle.

CLINICAL RELEVANCE

The anatomical parameters related to patellar tracking can be used to evaluate the risk of continued instability and guide surgical treatment.

Value of CT scan-assessed tibial tuberosity-trochlear groove distance in identification of patellar instability

PURPOSE

Tibial tuberosity-trochlear groove (TTTG) distance is currently considered as one of the main factors in decision-making for surgical intervention in patients with patellar instability. The current study aimed to provide a valid comparison of TTTG distance in the healthy knees with those with patellar instability.

MATERIALS AND METHODS

Patients with a history of two or more episodes of patellar dislocation in the same knee who were referred to our department for the assessment of TTTG distance were included. Asymptomatic knees of patients as well as both knees of 21 healthy individuals were used as controls.

RESULTS

A total number of 42 patients, including 14 (33.3 %) male and 28 (66.7 %) female, with a mean age of 28.6 ± 12.3 years were included. Twenty-one controls with no significant difference of personal characteristics with patients were also enrolled. The mean TTTG distance in symptomatic and asymptomatic knees of patients were 18.71 ± 3.96 mm and 17.35 ± 4.39 mm with no significant difference (P = 0.298). The mean TTTG distances of both symptomatic and asymptomatic knees of patients were significantly higher than in knees of controls (P < 0.001).

CONCLUSION

The findings of the current study are not in favor of considering TTTG distance independently in decision-making for surgical interventions. However, greater TTTG in both asymptomatic and symptomatic knees of patients compared to controls indicates that this measure could still be considered as an indicator of knee instability and even the need for surgery if considered in addition to other factors.

Editorial Commentary: Elevated Tibial Tubercle-Trochlear Groove Distance and Patellar Instability

In patients with unilateral patellar instability, tibial tuberosity-trochlear groove, lateral patellar tilt, and subluxation are greater on the side of instability. Dynamic computed tomography scan may represent a more physiologic assessment of patellofemoral tracking. A laterally positioned tuberosity may be a predisposing factor for patellar instability, a role perhaps further defined by future dynamic studies of the extensor mechanism.