Association between measures of patella height, morphologic features of the trochlea, and patellofemoral joint alignment: the MOST study

Patellar articular overlap is better associated with patellar alignment during weight-bearing than traditional measures of patellar height

BACKGROUND

A consequence of a high riding patella is reduced osseous stability and malalignment of the patella (i.e., lateral patellar tilt and displacement). Although quantification of patellar height is a routine part of the radiographic examination of the patellofemoral joint, it is not clear which measure of patellar height is best associated with patella alignment.

HYPOTHESIS/PURPOSE

To determine if patellar articular overlap (PAO) is better associated with lateral patellar tilt and lateral patellar displacement compared to traditional measures of patellar height.

STUDY DESIGN

Cross-sectional.

METHODS

Magnetic resonance images were obtained from 50 female participants (21 with patellofemoral pain and 29 healthy controls) under loaded conditions (25-35% bodyweight) at 15-20 degrees of knee flexion. Measurements of lateral patellar tilt and displacement as well as the PAO, Insall-Salvati ratio (ISV), Caton Deschamps-index (CD-index), or the Blacburn Peel-index (BP-index) were obtained from sagittal and axial plane images.

RESULTS

The PAO was found to significantly correlated with lateral patellar tilt (r = -0.77, p < 0.001). In contrast, the ISV, CD-index, or the BP-index were not found to be associated with lateral patellar tilt (r = 0.13, p = 0.34; r = -0.14, p = 0.33; r = -0.08, p = 0.56, respectively). Both the PAO and ISV were found to be significantly correlated with lateral patellar displacement (r = -0.52, p < 0.001; r = 0.43, p = 0.002, respectively). Conversely, the CD-index and BP-index were not found to be associated with lateral patellar displacement (r = 0.03 p = 0.83; r = 0.05 p = 0.74, respectively).

CONCLUSION

Of the measures of patellar height evaluated, the PAO was found to provide the greatest association with lateral patellar tilt and displacement.

Morphology and transverse alignment of the patella have no effect on knee gait characteristics in healthy Chinese adults over the age of 40 years

Background: The influence of patella morphology and horizontal alignment on knee joint kinematics and kinetics remains uncertain. This study aimed to assess patella morphology and transverse alignment in relation to knee kinetics and kinematics in individuals without knee conditions. A secondary objective was to investigate the impact of femur and tibia alignment and shape on knee gait within this population. Patients and methods: We conducted a prospective collection of data, including full-leg anteroposterior and skyline X-ray views and three-dimensional gait data, from a cohort comprising 54 healthy individuals aged 40 years and older. Our study involved correlation and logistic regression analyses to examine the influence of patella, femur, and tibia morphology and alignment on knee gait. Results: The patellar tilt angle or the patella index did not show any significant relationships with different aspects of gait in the knee joint, such as velocity, angle, or moment (p > 0.05, respectively). Using multivariate logistic regression analysis, we found that the tibiofemoral angle and the Q angle both had a significant effect on the adduction angle (OR = 1.330, 95%CI 1.033-1.711, p = 0.027; OR = 0.475, 95%CI 0.285-0.792, p = 0.04; respectively). The primary variable influencing the knee adduction moment was the tibiofemoral angle (OR = 1.526, 95% CI 1.125-2.069, p = 0.007). Conclusion: In healthy Chinese individuals aged over 40, patella morphology and transverse alignment do not impact knee gait. However, the femoral-tibial angle has a big impact on the knee adduction moment.

Development of patellofemoral osteoarthritis with knee joint malalignment and lateral patellar dislocation after hindlimb suspension in growing rats

Knee malalignment is a risk factor for patellar instability and patellofemoral osteoarthritis (PFOA), but etiologies remain unknown. We investigated the potential effects of decreased weight loading during growth on knee alignments and patellofemoral (PF) joint pathology. Hindlimb suspension (HS) was performed in 4-week-old female rats for 2, 4, and 8 weeks (HS groups). Age-matched rats were used as controls. Three-dimensional reconstructed images of the knee were obtained using X-ray computed tomography. Tibial tubercle-trochlear groove (TT-TG) distance, patellar tilt angle, and bisect offset were measured as indices of knee alignment. Histological analysis was also performed to evaluate the changes in cartilage and synovium in the PF joints. At Week 8, TT-TG distance, patella tilt angle, and bisect offset were significantly larger in the HS group than in the control group, respectively, indicating tibial external rotation, outward patellar tilt, and external displacement of the patella. Lateral patellar dislocation was frequently found in the HS group at Week 8 (five of eight knee joints, p < 0.05). Degenerative changes in the cartilage of the trochlear groove were observed at Week 8, and synovial changes such as hypertrophy and synovitis were observed at Weeks 4 and 8. Correlation analyses revealed significant relationships between the Mankin score and bisect offset, and between the OARSI synovitis score and all knee alignments indices. These results suggest that decreased weight loading on the lower extremities in growing rats resulted in knee malalignments characterized by external rotation of tibia and high incidence of lateral patellar dislocation with concomitant PFOA.

Association among peripatellar fat pad edema and related patellofemoral maltracking parameters: a case-control magnetic resonance imaging study

BACKGROUND

The peripatellar fat pads are critical for protective cushioning during movement, and their endocrine function has been shown to affect osteoarthritis. Magnetic resonance imaging (MRI) is frequently used to visualize edema of the peripatellar fat pads due to injury. In this study, we aimed to assess the relationship between peripatellar fat pad edema and patellofemoral maltracking MRI parameters and investigate the association among cases of peripatellar fat pad edema.

METHODS

Age- and sex-matched peripatellar fat pad edema cases were identified and divided into superolateral Hoffa, quadriceps, and prefemoral groups. Images were assessed according to tibial tuberosity lateralization, trochlear dysplasia, patellar alta, patellar tilt, and bisect offset. McNemar's test or paired t-tests and Spearman's correlation were used for statistical analysis. Interobserver agreement was assessed with the intraclass correlation coefficient.

RESULTS

Of 1210 MRI scans, 50, 68, and 42 cases were in the superolateral Hoffa, quadriceps, and prefemoral groups, respectively. Subjects with superolateral Hoffa fat pad edema had a lower lateral trochlear inclination (p = 0.028), higher Insall-Salvati (p < 0.001) and modified Insall-Salvati (p = 0.021) ratios, and lower patellotrochlear index (p < 0.001) than controls. The prefemoral group had a lower lateral trochlear inclination (p = 0.014) and higher Insall-Salvati (p < 0.001) and modified Insall-Salvati (p = 0.004) ratios compared with the control group. In contrast, the patellotrochlear index (p = 0.001) was lower. Mean patellar tilt angle (p = 0.019) and mean bisect offset (p = 0.005) were significantly different between cases and controls. The quadriceps group showed no association. Superolateral Hoffa was positively correlated with prefemoral (p < 0.001, r = 0.408) and negatively correlated with quadriceps (p < 0.001, r = -0.500) fat pad edema.

CONCLUSIONS

Superolateral Hoffa and prefemoral fat pad edemas were associated with patellar maltracking parameters. Quadriceps fat pad edema and maltracking parameters were not associated. Superolateral Hoffa fat pad edema was positively correlated with prefemoral and negatively correlated with quadriceps fat pad edema.

Computed tomographic measurements of the femoral trochlea in dogs with and without medial patellar luxation

OBJECTIVES

To determine cutoff values in small (SB) and medium/large (MLB) breed dogs with and without medial patellar luxation (MPL) for identifying abnormal femoral trochlea morphology.

STUDY DESIGN

Original research.

ANIMALS

A total of 80 computed tomographic (CT) scans from client-owned dogs METHODS: Four groups of 20 dogs were created: (1) control SB, (2) control MLB, (3) MPL-SB, and (4) MPL-MLB. Two authors measured the femoral trochlear groove angle (FTGA), femoral trochlear angle (FTA), and femoral trochlear ridge inclination angle (FTRIA) in two points with CT. ANOVA and ROC-analysis were tested to the control and MPL groups to assess sensitivity, specificity, and cutoff values. Statistical significance was set to p < .05. Intraclass correlation coefficients evaluated the inter-rater agreement.

RESULTS

FTGA (± SD) in control SB (128.8° ± 4.7°) and control MLB (119.2° ± 5.6°), was smaller (p < .0001) than in MPL-SB (139.4° ± 4.4°) and MPL-MLB (133.7° ± 5.1°). FTA and FTRIA were decreased (p = .12, p = .23) in MPL-SB (2.1° ± 6.8; -0.3° ± 3.3°) and MPL-MLB (3.8° ± 5.6°; 1.7° ± 4.5°) compared to control SB (0.2° ±4.1; -0.1° ± 2.6°) and control MLB (5.3° ± 2.8°; 3.1° ± 1.3°). Cutoff values for FTGA, FTA, and FTRIA were > 134°, < -5.9°, < -2 ° (SB), and > 128.3°, < -0.4°, < -0.4° (MLB). Sensitivity, specificity, and inter-rater agreement were superior for FTGA than FTA and FTRIA.

CONCLUSIONS

Dogs without MPL had a deeper femoral trochlear groove than MPL dogs. SB had a shallower groove than MLB. The measurement of FTA and FTRIA was not reliable.

CLINICAL RELEVANCE

A FTGA <134° (SB) and < 128° (MLB) may be considered as a cutoff for trochleoplasty decision-making.

Increased lower limb length ratio in patients with patellar instability

PURPOSE

Patellar height is a risk factor for patellar instability, correlated with the tibia length/femur length (T/F) ratio. This study aimed to explore the changes in the T/F ratio in patients with patella instability and the potential correlation with the morphology of the patellofemoral joint and extensor moment arm.

METHOD

A retrospective analysis was performed to assess the ratio of lower limb length morphological characteristics of the patellofemoral by full weight-bearing long-leg standing radiographs, magnetic resonance imaging, and computed tomography in 75 patients with patellar instability and 75 participants from a randomly selected control group from January 2020 to September 2021. A total of eight parts were measured, including mechanical tibia length/femur length (mT/F) ratio, anatomical tibia length/femur length (aT/F) ratio, hip-knee-ankle angle, femoral neck-shaft angle, femoral valgus cut angle, patellar height, Dejour classification, sulcus angle, trochlear angle, medial trochlear inclination, lateral trochlear inclination, patella tilt angle and patellar tendon moment arm to evaluate the difference of morphology between patient group and control groups.

RESULTS

The mT/F (0.840 ± 0.031 vs. 0.812 ± 0.026, p < 0.001) and aT/F (0.841 ± 0.033 vs. 0.808 ± 0.028, p < 0.001) ratios in the patient group were significantly greater than that in the control group. There was a significant correlation between patellar height and increased mT/F and aT/F ratios (p < 0.05).

CONCLUSION

Patients with patellar instability had a larger lower limb length ratio, and the change in lower limb length ratio was correlated with patellar height.

LEVEL OF EVIDENCE IV

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

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

Prevalence of chondromalacia patella according to patella type and patellofemoral geometry: a retrospective study

BACKGROUND

The relationships between the morphometric structure of the patellofemoral joint, patella type and chondromalacia patella are still a matter of debate.

OBJECTIVE

To identify the prevalence of chondromalacia patella by determining the patella type and making patellofemoral morphometric measurements.

DESIGN AND SETTING

Retrospective cohort study in an orthopedics and traumatology clinic in Turkey, conducted between June 2017 and November 2019.

METHODS

This study involved 562 knees of 522 patients with anterior knee pain (246 males and 316 females; mean age 46.59 years). The patients were grouped according to presence of chondromalacia patella (group I) or absence of chondromalacia patella (group II). The patella type, lateral trochlear inclination, medial trochlear inclination, trochlear angle, sulcus angle, patellar tilt and Insall-Salvati index were assessed. Group comparisons were made using chi-square tests or Student t tests. The r value was used to determine the magnitude of relationships between pairs of variables.

RESULTS

Among the 562 knees evaluated, 265 (50.71%) presented type I patella, 195 (36.7%) type II, 100 (12.3%) type III and 2 (0.3%) type IV. Group I consisted of 448 knees and group II consisted of 114 knees. Significant differences were found between the groups in terms of age, gender, patella type and lateral inclination angles (P &lt; 0.05).

CONCLUSION

Detecting the patella type and making lateral inclination measurements in patients with anterior knee pain are of great importance for diagnosing suspected chondromalacia patella, particularly in the early degenerative period.

Patellar height measurement in Indonesian normal adult population

Background

Patellar height is the distance formed by the patella and the length of the patellar tendon. Patellar height measurement can predispose to various abnormalities in the knee joint. Patellar height can be measured using several sizes, such as the Insall-Salvati ratio (IS), Modified Insall-Salvati ratio (MIS), Caton-Deschamps index (CD), and the Blackburne-Peel (BP) index. In Indonesia, no data on the value of patellar height is available. This study aims to determine the patellar height value in Indonesians and compare if there are differences with the standard values commonly used by other countries.

Matherials and methods

This study is descriptive with 136 research subjects aged 20–40. Data were taken from December 2021 to February 2022. The results of patellar X-ray were measured using the Insall-Salvati, Modified Insall-Salvati, Caton-Deschamps, and Blackburne-Peel methods.

Results

In the measurement of patellar height, the longest measurement was found in the MIS measurement, while the shortest patellar height was measured using the BP method. The normal value of the IS method is 0.78–1.26, the MIS method is > 1.98, the CD method is 0.79–1.23, and the BP method is 0.70–1.10 for patellar height in Indonesia. This study also shows no significant difference in the value of patellar height between male and female sex using the IS measurement method.

Conclusion

There is a difference in the standard value of patellar height, which is commonly used by other countries with the standard value of patellar height in Indonesia, but it is not significant.

•

Each country has different standard value of the patella height.

•

Patellar height can be measured using several methods.

•

Indonesian patellar height standard value different with other countries.

Comparison between Single- and Multi-Radius Prostheses Used in Modified Kinematically Aligned Cruciate-Retaining Total Knee Arthroplasty

Kinematically aligned total knee arthroplasty (TKA) has gained interest for achieving more favorable clinical outcomes than mechanically aligned TKA. The present study aimed to compare the clinical outcomes of kinematically aligned TKAs using single-radius (SR) or multi-radius (MR) prostheses. Sixty modified kinematically aligned cruciate-retaining TKAs (30 SR and 30 MR type prostheses) were performed in patients with varus-type osteoarthritis using a navigation system. Intraoperative and postoperative patellar tracking were compared between the two groups. Trochlea shape was also compared between the prostheses and preoperative native anatomy using three-dimensional simulation software. Total 2 years postoperatively, the range of motion and 2011 Knee Society Scores (KSS) were compared between the two groups. There were no differences in patellar maltracking including patellar lateral shift and tilt between the two groups; however, the ratio of intraoperative lateral retinacular release for adjusting patellar tracking was significantly higher in the MR group than in the SR group. Lateral and medial facet heights in both prostheses were understuffed compared with native knee anatomy, while the deepest point of the trochlear groove was significantly more medial in the MR group. The postoperative clinical outcomes showed no significant differences between the two groups. In conclusion, modified kinematically aligned TKAs using a SR or MR prosthesis showed no significant differences in clinical outcomes or patellar tracking when appropriate lateral retinacular release was performed.

Patellar Height Correlates Modestly With Trochlear Dysplasia: A Magnetic Resonance Imaging Analysis

Purpose

To evaluate whether there is a correlation between the position of the patella and trochlear morphology in patients with and without patellar instability using exclusively MRI measurements.

Methods

MRI scans of knees in patients with patellofemoral instability and knees of patients with an ACL (anterior cruciate ligament) tear as a control group were reviewed. Measurements of patellar position (Canton-Deschamps ratio, Patellar Trochlear Index, and lateral patellar inclination) and trochlear morphology (lateral trochlear inclination and sulcus angle) were obtained from each scan. Bivariate and multivariate analysis was performed to identify correlations between study group, demographics, and patellofemoral joint measurements.

Results

There were 70 knees in the patellofemoral instability group and 60 knees in the control group. Bivariate analysis showed a significant difference in all measurements between the patellar instability group and the control group. Multivariate analysis showed modest correlations between patellar position and trochlear morphology. The Caton-Deschamps (CD) ratio correlated with patellar trochlear index (P < .001) and lateral trochlear inclination (P < .001). The respective R-square goodness of fit was 41.1%. Patellar trochlear index correlated with CD ratio (P < .001), lateral trochlear inclination (P < .001), lateral patellar inclination (P < .001), and patellar instability group (P = .011). The R-sq goodness of fit was 37.3%. Lateral patellar inclination correlated with patellar trochlear index (P < .001), Lateral trochlear inclination (P < .001), and age at first dislocation or injury (P = .02). The R-sq goodness of fit was 68.56%.

Conclusions

Using MRI-based measurements of the patellofemoral joint, we identified modest, but significant, correlations between measures of patellar height (patellar trochlear index, CD ratio, and lateral patellar inclination) and trochlear dysplasia. This correlation is unclear and is likely multifactorial, but on the basis of this work, a causal relationship between trochlear dysplasia and patella alta cannot be established.

Clinical Relevance

Radiographic evaluation of the patella and how it relates to the surrounding boney anatomy provides important information regarding our understanding of patella instability and its treatment.

An automatic measurement system of distal femur morphological parameters using 3D slicer software

In the field of joint surgery, the computer-aided design of knee prostheses suitable for the Chinese population requires a large quantity of anatomical knee data. In this study, we propose a new method that uses 3D Slicer software to automatically measure the morphological parameters of the distal femur. First, 141 femur samples were segmented from CT data to establish the femoral shape library. Next, balanced iterative reducing and clustering using hierarchies (BIRCH) combined with iterative closest point (ICP) and generalised procrustes analysis (GPA) were used to achieve fast registration of the femur samples. The statistical model was automatically calculated from the registered femur samples, and an orthopaedic surgeon marked the points on the statistical model. Finally, we developed an automatic measurement system using 3D Slicer software, and a deformable model matching method was applied to establish the point correspondence between the statistical model and the other samples. By matching points on the statistical model to corresponding points in other samples, we measured all other samples. We marked six points and measured eight parameters. We evaluated the performance of automatic matching by comparing the points marked manually with those matched automatically and verified the accuracy of the system by comparing the manual and automatic measurement results. The results indicated that the average error of the automatic matching points was 1.03 mm, and the average length error and average angle error measured automatically by the system were 0.37 mm and 0.63°, respectively. These errors were smaller than the intra-rater and inter-rater errors measured manually by two different surgeons, which showed that the accuracy of our automatic method was high. Taken together, this study established an accurate and automatic measurement system for the distal femur based on the secondary development of 3D Slicer software to assist orthopaedic surgeons in completing the measurements of big data and further promote the improved design of Chinese-specific knee prostheses.

The relationship between patellar volume and trochlear volume in patients with patellofemoral instability

AIM

To investigate a possible relationship between both the volume and morphology of the patella and the volume of the trochlea in trochlear dysplasia (TD).

MATERIALS AND METHODS

Eighteen patients with TD and 18 controls were evaluated retrospectively in two groups using computed tomography (CT). Patellar morphology was evaluated with the standard measurement methods described in the literature. Additionally trochlear sulcus volume (TV) and patellar volume (PV) were measured quantitatively using the three-dimensional volume-rendering method. The relationship between patella dimensions and volume and trochlea volume was evaluated.

RESULTS

The length of the medial patellar facet (lMP), patellar width (PW), TV and PV were significantly lower in the patient group. When compared according to Dejour types, PW was statistically significantly lower than the control group in those with high-grade and those with low-grade dysplasia. A positive correlation was found between the TV and PV in both groups (patient group: r=0.583 p=0.011; control group: r=0.485 p=0.042). CONCLUSİONS: PV and the TV are related. Therefore, PV can be used as a determining parameter in the evaluation of TD. This technique can also be used for prosthesis construction and more accurate surgical planning.

MRI signal and morphological alterations of the suprapatellar fat pad in asymptomatic subjects: are these normal variants?

OBJECTIVE

To study the prevalence of suprapatellar fat pad (SPFP) MR alterations in asymptomatic subjects, in relation to a wide range of clinical/imaging parameters, including muscle performance tests and physical activity data.

MATERIALS AND METHODS

We prospectively included 110 asymptomatic subjects as part of a cohort study. Inclusion criteria were no knee pain in the last year. Exclusion criteria were any medical/surgical history of a knee disorder. Subjects underwent knee and low-dose posture radiographs [EOS®], 3 T MRI, clinical examination including muscle performance tests, and physical activity monitoring. The presence/absence of SPFP alterations (hyperintensity and mass effect) were assessed through consensus reading on fluid-sensitive sequences. Differences between groups of knees with SPFP alterations and controls were tested for a total of 55 categorical/continuous clinical/imaging parameters, including SPFP relative-T2-signal, trochlear/patellar/lower-limb morphologic measurements. Wilcoxon-rank-sum and chi-square tests were used to compare groups of patients. The histological correlation was obtained in a cadaveric specimen.

RESULTS

SPFP alterations were common in asymptomatic subjects: hyperintensity 57% (63/110) and mass effect 37% (41/110), with 27% (30/110) showing both. Among the 55 imaging, clinical, or activity parameters tested, only increased patellar tilt angle (p = 0.02) and TT-TG distance (p = 0.03) were statistically different between groups of SPFP alterations and controls. The histological correlation showed more abundant connective tissue in SPFP compared to the prefemoral fat pad.

CONCLUSIONS

SPFP hyperintensity and mass effect are common MRI findings in asymptomatic knees, and they are not related to most imaging, clinical, and activity parameters. Care should be taken not to overcall them pathological findings as they most likely represent normal variants.

The patellofemoral morphology and the normal predicted value of tibial tuberosity-trochlear groove distance in the Chinese population

Background

Our objective was to obtain normal patellofemoral measurements to analyse sex and individual differences. In addition, the absolute values and indices of tibial tuberosity-trochlear groove (TT-TG) distances are still controversial in clinical application. A better method to enable precise prediction is still needed.

Methods

Seventy-eight knees of 78 participants without knee pathologies were included in this cross-sectional study. A CT scan was conducted for all participants and three-dimensional knee models were constructed using Mimics and SolidWorks software. We measured and analysed 19 parameters including the TT-TG distance and dimensions and shapes of the patella, femur, tibia, and trochlea. LASSO regression was used to predict the normal TT-TG distances.

Results

The dimensional parameters, TT-TG distance, and femoral aspect ratio of the men were significantly larger than those of women (all p values < 0.05). However, after controlling for the bias from age, height, and weight, there were no significant differences in TT-TG distances and anterior-posterior dimensions between the sexes (all p values > 0.05). The Pearson correlation coefficients between the anterior femoral offset and other indexes were consistently below 0.3, indicating no relationship or a weak relationship. Similar results were observed for the sulcus angle and the Wiberg index. Using LASSO regression, we obtained four parameters to predict the TT-TG distance (R² = 0.5612, p < 0.01) to achieve the optimal accuracy and convenience.

Conclusions

Normative data of patellofemoral morphology were provided for the Chinese population. The anterior-posterior dimensions of the women were thicker than those of men for the same medial-lateral dimensions. More attention should be paid to not only sex differences but also individual differences, especially the anterior condyle and trochlea. In addition, this study provided a new method to predict TT-TG distances accurately.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04454-8.

Patellar Tracking in Revision Total Knee Arthroplasty: Does Retaining a Patella From a Different Implant System Matter?

BACKGROUND

Patellar maltracking is a potential surgical complication following total knee arthroplasty (TKA) and can result in anterior knee pain, recurrent patellar dislocation, and damage to the medial patellar soft tissue stabilizers. Data remain unclear as to whether the patellar button should be revised during a revision TKA (rTKA) if changing the component implant system. Our study examines whether retaining the original patellar button during an rTKA using a different implant system affects patellar tracking.

METHODS

A retrospective cohort study of rTKA patients between August 2011 and June 2019 was performed at an urban, tertiary referral center. Patients were divided into 2 cohorts depending on whether their retained patella from their primary TKA was of the same (SIM) or different implant manufacturer (DIM) as the revision system used. Radiographic measurements were performed on preoperative and postoperative knee radiographs and differences were compared between the 2 groups. Baseline demographic data were also collected.

RESULTS

Of the 293 consecutive, aseptic rTKA cases identified, 122 underwent revision in the SIM cohort and 171 in the DIM cohort. There were no demographic differences between the groups. No statistical significance was calculated for differences in preoperative and postoperative patellar tilt or Insall-Salvati ratio between the groups. The DIM group was found to have more lateral patellar translation (-0.01 ± 6.09 vs 2.68 ± 7.61 mm, P = .001). However, when calculating differences in the magnitude of the translation (thereby removing differences due to laterality), no difference was observed (0.06 ± 3.69 vs 0.52 ± 4.95 mm, P = .394).

CONCLUSION

No clinically significant differences in patellar tracking were observed when the original patellar component was retained and a different revision implant system was used. Given the inherent risks of bone loss and fracture with patellar component revision, surgeons performing rTKA may retain the primary patella if it is well fixed and can still expect appropriate patellar tracking regardless of the revision implant system used.

LEVEL OF EVIDENCE

III, Retrospective cohort study.

The Effect of Patellar Height by Using Insall Salvati Index on Pain, Function, Muscle Strength and Postural Stability in Patients with Primary Knee Osteoarthritis

PURPOSE

The Insall-Salvati Index (ISI) is the ratio of the patellar tendon length to the length of the patella. This ratio is the most commonly used method for evaluating patellar placement and patellofemoral imbalance. The position of the patella is important for the knee joint function and also for biomechanics. The abnormal position of the patella may lead to patellofemoral malalignment and instability. Herein, we aimed to analyze the relationship between the ISI and pain, physical function, muscle strength, fall risk, and postural stability in patients with primary knee osteoarthritis (OA).

METHODS

Sixty-two symptomatic knees of 45 patients (aged between 40 -75 years) who were suffering from the primary knee OA according to the American College of Rheumatology criteria were included retrospectively in the study. Patients with stages II and III osteoarthritis according to the Kellgren-Lawrence (K/L) radiological grading system were included. The ISI was measured on the lateral knee radiograph in a 30° flexed posture. Visual Analogue scale (VAS), Western Ontario and McMaster Universities Osteoarthritis (WOMAC) and Lequesne indexes were recorded for evaluating pain and function. Tetrax Interactive Balance System was used to assess fall risk and postural stability. Isokinetic muscle strength measurements of quadriceps and hamstrings were recorded at the constant angular velocities of 60 and 180°/sec.

RESULTS

The mean age of the study population was 58.52 ±8.01 years. The frequency of the patellar situation types was as follows; patella alta; 15 (24.2%), patella baja; n=2(3.2%), and normal patellar height; n=45(72.6%). The mean ISI was 1.19 ±0.17 on the right side and 1.18±0.16 on the left side. There was no significant correlation between the ISI and VAS, WOMAC and Lequesne indexes, postural stability scores, and isokinetic measurements (r<0.3, p>0.05).

CONCLUSION

In primary knee OA, the ISI may not have an effect on pain, physical function, fall risk, postural stability, and isokinetic muscle strength.

CLINICAL TRIAL REGISTRATION NUMBER

KA18/170.

Morphological Analysis of Bone Deformities of the Distal Femur in Toy Poodles with Medial Patellar Luxation

OBJECTIVE

 The aim of this study was to evaluate the bone deformities of the distal femur of Toy Poodles with medial patellar luxation (MPL) using computed tomography.

METHODS

 Computed tomography data from 37 stifles of Toy Poodles (16 normal, 10 grade 2 MPL and 11 grade 4 MPL) were analysed. For trochlear morphology, sulcus angle, medial or lateral trochlear inclination and trochlear angle were compared. For condylar morphology, distance between the apex of the medial or lateral trochlear ridge and the most caudal point of the medial or lateral femoral condyle (MC or LC), the length of the cranial/middle (anterior) part (MC(a) or LC(a')) and caudal (posterior) part (MC(p) or LC(p')) of distal femur and medial or lateral condyle width (MCW or LCW) were measured, and the ratios of medial-to-lateral condyles and anterior-posterior parts were compared.

RESULTS

 Sulcus angle was significantly higher, and medial trochlear inclination was significantly lower in grade 4 MPL group than other groups. Lateral trochlear inclination was not significantly different among 3 groups. Trochlear angles at proximal trochlear groove were significantly lower in grade 4 MPL group than other groups. MC/LC, MC(a)/LC(a'), MC(a)/MC(p), and LC(a')/LC(p') were significantly lower in grade 4 MPL group than other groups; however, there were no significant differences in MC(p)/LC(p') and MCW/LCW among three groups.

CONCLUSION

 Hypoplasia of the cranial and middle rather than caudal compartment of the distal femur was the primary morphological abnormality in Toy Poodles with grade 4 MPL.

First-Time Acute Lateral Patellar Dislocation in Children and Adolescents: What About Unaffected Knee Patellofemoral Joint Anatomic Abnormalities?

Background and Objectives: Acute lateral patellar dislocation (LPD) is the most common acute knee disorder in children and adolescents, and may lead to functional disability. The purpose of this study was to identify key differences and correlations of the patellofemoral joint (PFJ) morphology between intact and contralateral injured knees in a first-time traumatic LPD population aged under 18 years. Materials and Methods: The data were gathered prospectively from a cohort of 58 patients (35 girls and 23 boys). The prevalence and combined prevalence of patella alta (PA) and trochlear dysplasia (TD) in both knees of patients were evaluated using X-ray by two radiologists. Results: The PFJ of patients' intact knees had a lower rate of TD (1.72% vs. 5.2%) and a less common combination of PA with shallow femoral sulcus (SFS) (22.4% vs. 44.8%) but more frequent PA (62.1% vs. 41.4%) compared with their injured knees. We noted statistically significant positive correlations (SSPCs) between the femoral sulcus angle (FSA) and PA in patients with intact (r = 0.37; p < 0.005) and contralateral injured knees (r = 0.33; p < 0.05). Conclusion: There were SSPCs between the FSA and PA in both gender and age groups of patients with intact and contralateral injured knees. The SSPCs between the FSA and PA of intact knees were higher in the patients with a more dysplastic PFJ anatomy (PA and TD) of the injured knees as compared to patients with only PA of the injured knees.

Osteoarthritic knees have a highly variable patellofemoral alignment: a systematic review

PURPOSE

This systematic review aimed to evaluate the variability of patellofemoral (PF) alignment and trochlear morphology in osteoarthritic knees.

METHODS

PF alignment of the knee was defined by the following parameters: the sulcus angle (SA), femoral trochlear depth (FTD), patellar tilt angle (PTA), lateral patellofemoral angle (LPFA), lateral femoral trochlear inclination (LFTI) and tibial tubercle-trochlear groove distance (TT-TG). The electronic databases MEDLINE and EMBASE were searched from database inception to the search date (February 19, 2019) and were screened for relevant studies. The PRISMA guidelines were followed. Articles reporting PF alignment measurements of osteoarthritic knees in patients over 40 years old were included. Data were extracted and methodological quality was assessed using a 14-item checklist.

RESULTS

A total of 8 studies met the inclusion criteria. The studies reported mean values ± SD between 120° and 141.1° ± 7.7 for the SA; 5.8 mm ± 1.4 for the FTD; between - 0.1° ± 3.3 and 10.3° ± 5.7 for the PTA; between 5.8° ± 5.4 and 17° for the LPFA; between 23.2° ± 5.0 and 27.1° ± 4.4 for the LFTI; and 5.8 mm ± 5.4 for the TT-TG.

CONCLUSION

PF alignment in the osteoarthritic knee is more variable than expected. This finding should encourage surgeons to consider the individual preoperative PF alignment more precisely with the aim of reducing anterior knee pain (AKP) after TKA. 3D-CT imaging might be of great value to analyse the PF alignment in an appropriate way.

LEVEL OF EVIDENCE

Level III.

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.

Lateral Trochlear Inclination Angle: Measurement via a 2-Image Technique to Reliably Characterize and Quantify Trochlear Dysplasia

Background:

Trochlear dysplasia (TD) is a risk factor for patellar instability (PI). The Dejour classification categorizes TD but has suboptimal reliability. Lateral trochlear inclination (LTI) is a quantitative measurement of trochlear dysplasia on a single axial magnetic resonance imaging (MRI) scan.

Hypothesis:

A modified LTI measurement technique using 2 different axial MRI scans that reference the most proximal aspect of the trochlear cartilage on 1 image and the fully formed posterior condyles on the second image would be as reliable as and significantly different from the single-image measurement technique for LTI. Further, the 2-image LTI would adequately represent overall proximal trochlear morphologic characteristics.

Study Design:

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

Methods:

Patients aged 9 to 18 years treated for PI between 2014 and 2017 were identified. The Dejour classification was radiographically determined. Single-image LTI was measured on a single axial MRI scan at the most proximal aspect of visible trochlear cartilage. A 2-image LTI was measured from 2 separate MRI scans: 1 at the most proximal aspect of trochlear cartilage and the second at the fully formed posterior condyles. This 2-image LTI was repeated at 3 subsequent levels (the first measurement is referred to as LTI-1; repeated measurements are LTI-2, LTI-3, and LTI-4, moving distally). In total, 65 patients met the inclusion criteria, and 30 were randomly selected for reliability analysis.

Results:

Inter- and intrarater reliability trended toward more variability for single-image LTI (intraclass correlation coefficient [ICC], 0.86 and 0.88, respectively) than for 2-image LTI (ICC, 0.97 and 0.96, respectively). The Dejour classification had lower intra- and interrater reliability (ICC, 0.31 and 0.73, respectively). Average single-image LTI (9.2° ± 12.6°) was greater than average 2-image LTI-1 (4.2° SD ± 11.9°) (P = .0125). Single-image LTI classified 60% of patients with PI as having TD, whereas the 2-image LTI classified 71% as having TD. The 2-image LTI was able to capture 91% of overall proximal trochlear morphologic characteristics.

Conclusion:

LTI has higher reliability when performed using a 2-image measurement technique compared with single-image LTI and Dejour classification. The strong correlation between 2-image LTI and average LTI shows that 91% of TD is represented on the most proximal axial image. Because the single-image measurement appears to underestimate dysplasia, previously described thresholds should be reexamined using this 2-image technique to appropriately characterize TD.

Relation of Patellofemoral Joint Alignment, Morphology, and Radiographic Osteoarthritis to Frequent Anterior Knee Pain: Data from the Multicenter Osteoarthritis Study

OBJECTIVE

Patellofemoral (PF) alignment and trochlear morphology are associated with PF osteoarthritis (OA) and knee pain, but whether they are associated with localized anterior knee pain is unknown, which is believed to be a symptom specific to PF joint pathology. We therefore aimed to evaluate the relation of PF alignment and morphology, as well as PFOA and tibiofemoral OA, to anterior knee pain.

METHODS

The Multicenter Osteoarthritis Study is a cohort study of individuals with, or at risk for, knee OA. We evaluated cross-sectional associations of PF alignment, trochlear morphology, and PF and tibiofemoral radiographic OA, with localized anterior knee pain (defined with a pain map). We used 2 approaches: a within-person knee-matched evaluation of participants with unilateral anterior knee pain (conditional logistic regression), and a cohort approach comparing those with anterior knee pain to those without (binomial regression).

RESULTS

With the within-person knee-matched approach (n = 110; 64% women, mean age 70 years, body mass index [BMI] 30.9), PF alignment, morphology, and tibiofemoral OA were not associated with unilateral anterior knee pain. Radiographic PFOA was associated with pain, odds ratio 5.3 (95% confidence interval [95% CI] 1.6-18.3). Using the cohort approach (n = 1,818; 7% of knees with anterior knee pain, 59% women, mean age 68 years, BMI 30.4), results were similar: only PFOA was associated with pain, with a prevalence ratio of 2.2 (95% CI 1.4-3.4).

CONCLUSION

PF alignment and trochlear morphology were not associated with anterior knee pain in individuals with, or at risk for, knee OA. Radiographic PFOA, however, was associated with pain, suggesting that features of OA, more so than mechanical features, may contribute to localized symptoms.

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.

A study of the possible effect of abnormal patella height on meniscal tears

Objective

Patellar height is key to knee biomechanics. Variations (alta/baja) have been associated with instability/dislocations, ACL ruptures etch. The effect of abnormal patella height and meniscal lesions is not clear yet; this is a first investigation of this relation.

Methods

100 patients with meniscal tears were X-Rayed to determine patellar height using the Insall-Salvati ratio and the Caton-Deschamps Index.

Results

20% had abnormal patellar height according to the Insall-Salvati ratio and 9% based on the Caton-Deschamps index.

Conclusion

This indicates that patella height could be a parameter in the occurrence of meniscal injuries worth investigating in larger populations; yet the mechanism remains unclear.

The relationship between early-onset chondromalacia and the position of the patella

Background

There are many underlying accelerator factors for chondromalacia and one of the well-known factors is patellar malalignment.

Purpose

To evaluate the relationship between early-onset chondromalacia and patellar position; and, second, to evaluate the value of patellar malalignment criteria.

Material and Methods

Patients aged 18–40 years with advanced chondromalacia were included. For comparison, a control group was defined with the same number of individuals of the same mean age. The magnetic resonance imaging (MRI) sagittal view with the greatest patellar length was used to obtain the patellar height measurement with the Insall-Salvati index. For the remaining three indices—modified Insall-Salvati, Caton-Deschamps, and Blackburne-Pell—a sagittal view with the greatest patellar articular surface was used. Discordance was defined as contradiction with the measured index and the other three indices.

Results

Both patella alta and baja were found to be predisposing factors for chondromalacia. Modified Insall-Salvati index was the most concordant measurement to define patella alta.

Conclusion

Both patella alta and patella baja were found to predispose to chondromalacia. Patella baja is rare, which may explain why it is not often mentioned as a predisposing factor. The modified Insall-Salvati index ratio was the best patella alta indicator that showed chondral status, more than patellar placement, and was more concordant with the other indices. Blackburne-Pell had the second highest number and ratio of discordance. BP cannot be optimally calculated because deciding the location of the tibial plateau seems to be problematic since it is a three-dimensional and complicated structure.

An Updated Overview of the Anatomy and Function of the Proximal Medial Patellar Restraints (Medial Patellofemoral Ligament and the Medial Quadriceps Tendon Femoral Ligament)

The medial patellofemoral ligament (MPFL) has been widely accepted to function as "the primary static restraint to lateral patellar displacement." However, current growing evidence suggests that there is a complex of medial patellofemoral/tibial ligaments, both proximal [MPFL, and medial quadriceps tendon femoral ligament (MQTFL)], and distal (medial patellotibial ligament and the medial patellomeniscal ligament) which restrain lateral patellar translation at different degrees of knee flexion. Specifically, the MQTFL has gained popularity over the last decade because of pure soft tissue attachments into the extensor mechanism that allow for avoidance of drilling tunnels into the patella during reconstruction. The purpose of this article was to report on the current knowledge (anatomy, biomechanics, diagnosis, indications for surgery, and techniques) on the proximal medial patellar restraints, namely the MPFL and the MQTFL, collectively referred to as the proximal medial patellar restraints.

Anatomic Risk Factors for Focal Cartilage Lesions in the Patella and Trochlea: A Case-Control Study

BACKGROUND

Focal cartilage lesions in the patellofemoral (PF) joint are common. Several studies correlated PF risk factors with PF instability, anterior knee pain, and PF arthritis; however, there is a lack of evidence correlating those factors to PF focal cartilage lesions.

PURPOSE

To evaluate the influence of the anatomic PF risk factors in patients with isolated focal PF cartilage lesions.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Patients with isolated PF focal cartilage lesions were included in the cartilage lesion group, and patients with other pathologies and normal PF cartilage were included in the control group. Multiple PF risk factors were accessed on magnetic resonance imaging scans: patellar morphology (patellar width, patellar thickness, and patellar angle), trochlear morphology (trochlear sulcus angle, lateral condyle index, and trochlear sulcus depth), patellar height (Insall-Salvati ratio and Caton-Deschamps index), axial patellar positioning (patellar tilt, angle of Fulkerson), and quadriceps vector (tibial tuberosity-trochlear groove distance).

RESULTS

A total of 135 patients were included in the cartilage lesion group and 100 in the control group. As compared with the control group, the cartilage lesion group had a higher sulcus angle (P = .0007), lower trochlear sulcus depth (P < .0001), lower angle of Fulkerson (P < .0001), lower patellar width (P = .0003), and higher Insall-Salvati ratio (P < .0001). From the patients in the cartilage lesion group, 36% had trochlear dysplasia; 27.6%, patella alta; and 24.7%, abnormal patellar tilt. These parameters were more frequent in the cartilage lesion group (P < .0001). Trochlear lesions were more frequent in men, presented at an older age, and had fewer associated anatomic risk factors. Patellar lesions, conversely, were more frequent in women, presented at younger age, and were more closely associated with anatomic risk factors.

CONCLUSION

PF anatomic abnormalities are significantly more common in patients with full-thickness PF cartilage lesions. Trochlear dysplasia, patella alta, and excessive lateral patellar tilt are the most common correlated factors, especially in patellar lesions.

Patellar maltracking: an update on the diagnosis and treatment strategies

Patellar maltracking occurs as a result of an imbalance in the dynamic relationship between the patella and trochlea. This is often secondary to an underlying structural abnormality. The clinical evaluation can provide useful clues for the presence of such entity; however, the diagnosis can often be challenging especially in the absence of a documented history of patellar dislocation. Imaging, particularly MRI, can detect subtle features that could lead to the diagnosis, probably even more importantly when there is no clear history of patellar dislocation or before its development. This can provide a road map for formulating a treatment strategy that would be primarily aimed at stabilizing the patellofemoral joint to halt or slow the progression of articular cartilage loss. The purpose of this article is to discuss the clinical and radiologic evaluation of patellar maltracking providing an update on the cross-sectional imaging assessment and also a synopsis of the management options.

Research Methods and Progress of Patellofemoral Joint Kinematics: A Review

Patellofemoral pain syndrome has a high morbidity, and its pathology is closely associated with patellofemoral joint kinematics. A series of in vivo and in vitro studies have been conducted to explore patellofemoral kinematics, and the findings are relevant to the diagnosis, classification, and management of patellofemoral diseases and even the whole knee joint. However, no definite conclusion on normal patellofemoral kinematics has been established. In this study, the measurement methodologies of patellofemoral kinematics (including data collection methods, loading conditions, and coordinate system) as well as their advantages and limitations were reviewed. Motion characteristics of the patella were analyzed. During knee flexion, the patellar flexion angle lagged by 30–40% compared to the tibiofemoral joint flexion. The patella tilts, rotates, and shifts medially in the initial stage of knee flexion and subsequently tilts, rotates, and shifts laterally. The finite patellar helical axis fluctuates near the femoral transepicondylar axis or posterior condylar axis. Moreover, factors affecting kinematics, such as morphology of the trochlear groove, soft tissue balance, and tibiofemoral motion, were analyzed. At the initial period of flexion, soft tissues play a vital role in adjusting patellar tracking, and during further flexion, the status of the patella is determined by the morphology of the trochlear groove and patellar facet. Our findings could increase our understanding of patellofemoral kinematics and can help to guide the operation plan for patients with patellofemoral pain syndrome.

Does patellar alignment or trochlear morphology predict worsening of patellofemoral disease within the first 5 years after anterior cruciate ligament reconstruction?

PURPOSE

We described patellofemoral alignment and trochlear morphology at one and five years after anterior cruciate ligament reconstruction (ACLR), and evaluated the associations between alignment and trochlear morphology (at one year) and worsening patellofemoral osteoarthritis (OA) features by five years. We also evaluated the associations between alignment and morphology to self-reported pain and function (Knee injury and Osteoarthritis Outcome Score, KOOS) at five years.

MATERIALS AND METHODS

In this longitudinal observational study, we followed 73 participants (mean age 29[9] years, 40% women) from one- to five-years after ACLR. Using MRI, we measured alignment and morphology, and scored cartilage and bone marrow lesions at both time points. We used mixed effects and linear regression models to achieve our stated aims.

RESULTS

Greater lateral patella displacement increased risk of cartilage worsening (Odds Ratio [95% CI]: 1.09 [1.01, 1.16]); while less lateral tilt (0.91 [0.83, 0.99]) and greater trochlear angle (0.88 [0.77, 1.00]) were protective. Greater medial trochlear inclination increased risk of bone marrow lesion worsening (1.12 [1.04, 1.19]); while greater trochlear angle was protective (0.80 [0.67, 0.96]). Greater lateral displacement was associated with worse self-reported KOOS sport and recreation scores (β [95% CI]: -11.0 [-20.9, -1.2]) and quality of life scores (-10.5 [-20.4, -0.7]).

CONCLUSIONS

Lateral displacement, lateral tilt, and morphology at 1 year post-ACLR altered the risk of worsening patellofemoral OA features four years later. Lateral displacement was the only measure associated with worse self-reported symptoms at five years. These findings may lead to novel treatment strategies for secondary prevention after ACLR.

Are Patellofemoral Joint Alignment and Shape Associated With Structural Magnetic Resonance Imaging Abnormalities and Symptoms Among People With Patellofemoral Pain?

BACKGROUND

Patellofemoral malalignment has been observed among people with patellofemoral pain (PFP) and may be associated with the presence of imaging features of osteoarthritis, symptoms, and function.

PURPOSE

To determine whether patellofemoral joint alignment and bony shape are associated with (1) cartilage, bone, and soft tissue morphological abnormalities defined on magnetic resonance imaging (MRI) and (2) reported symptoms and function among people with PFP.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Participants (mean ± SD age, 30.2 ± 9.5 years; range, 14-50 years; 78 females, 58.6%) completed questionnaires regarding demographics, pain, symptoms, and function and underwent a 3-T MRI scan of their more symptomatic eligible knee. Structural MRI abnormalities were scored with the MOAKS (Magnetic Resonance Imaging Osteoarthritis Knee Score), and MRI alignment and shape were measured with standardized methods. Associations among MOAKS features, PFP symptoms, and alignment and shape measures were evaluated with regression analyses (α = .05).

RESULTS

Minor cartilage defects were present in 22 (16.5%) participants, patellar osteophytes in 83 (62.4%), anterior femur osteophytes in 29 (21.8%), Hoffa synovitis in 81 (60.9%), and prefemoral fat pad synovitis in 49 (36.8%). A larger Insall-Salvati ratio was significantly associated with the presence of patellar osteophytes (odds ratio [OR], 51.82; 95% CI, 4.20-640.01), Hoffa synovitis (OR, 60.37; 95% CI, 4.66-782.61), and prefemoral fat pad synovitis (OR, 43.31; 95% CI, 4.28-438.72) in the patellofemoral joint. A larger patellar tilt angle was significantly associated with the presence of minor cartilage defects (OR, 1.10; 95% CI, 1.00-1.20), the presence of patellar osteophytes (OR 1.12; 95%CI 1.02-1.22), and prefemoral fat pad synovitis (OR, 1.11; 95% CI, 1.03-1.20) in the patellofemoral joint. Finally, a larger bisect offset was significantly associated with the presence of minor cartilage defects (OR, 1.05; 95% CI, 1.00-1.11) and patellar osteophytes (OR, 1.07; 95% CI, 1.01-1.14) in the patellofemoral joint. The majority of patellofemoral alignment measures were not associated with symptoms or function.

CONCLUSION

For people with PFP, the presence of morphological abnormalities defined on MRI appears to be related to particular patellofemoral alignment measures, including higher Insall-Salvati ratio (indicating patella alta), larger patellar tilt angle (indicating greater lateral tilt), and larger bisect offset (indicating greater lateral displacement). Hardly any associations were found with symptoms or function. So there might be a distinct subgroup of PFP that is more prone to developing patellofemoral osteoarthritis later in life, as particular alignment measures seem to be associated with the presence of patellar osteophytes. Prospective studies are required to investigate the longitudinal relationship between alignment or bony shape and morphological abnormalities defined on MRI in this patient population.

Lateral displacement, sulcus angle and trochlear angle are associated with early patellofemoral osteoarthritis following anterior cruciate ligament reconstruction

PURPOSE

Patellofemoral osteoarthritis (PFOA) occurs in approximately half of anterior cruciate ligament (ACL)-injured knees within 10-15 years of trauma. Risk factors for post-traumatic PFOA are poorly understood. Patellofemoral alignment and trochlear morphology may be associated with PFOA following ACL reconstruction (ACLR), and understanding these relationships, particularly early in the post-surgical time period, may guide effective early intervention strategies. In this study, patellofemoral alignment and trochlear morphology were investigated in relation to radiographic features of early PFOA 1-year post-ACLR.

METHODS

Participants (aged 18-50 years) had undergone ACLR approximately 1 year prior to being assessed. Early PFOA was defined as presence of a definite patellofemoral osteophyte on lateral or skyline radiograph. Sagittal and axial plane alignment and trochlear morphology were estimated using MRI. Using logistic regression, the relationship between alignment or morphology and presence of osteophytes was evaluated.

RESULTS

Of 111 participants [age 30 ± 8.5; 41 (37%) women], 19 (17%) had definite osteophytes, only two of whom had had patellofemoral chondral lesions noted intra-operatively. One measure of patellar alignment (bisect offset OR 1.1 [95% confidence interval 1.0, 1.2]) and two measures of trochlear morphology (sulcus angle OR 1.1 [1.0, 1.2], trochlear angle OR 1.2 [1.0, 1.5]) were associated with patellofemoral osteophytes.

CONCLUSIONS

Patellofemoral malalignment and/or altered trochlear morphology were associated with PFOA 1 year following ACLR compared to individuals post-ACLR without these features. Clarifying the role of alignment and morphology in post-traumatic PFOA may contribute to improving early intervention strategies aimed at secondary prevention.

LEVEL OF EVIDENCE

IV.

Gender differences in knee morphology and the prospects for implant design in total knee replacement

BACKGROUND

Morphological differences between female and male knees have been reported in the literature, which led to the development of so-called gender-specific implants. However, detailed morphological descriptions covering the entire joint are rare and little is known regarding whether gender differences are real sexual dimorphisms or can be explained by overall differences in size.

METHODS

We comprehensively analysed knee morphology using 33 features of the femur and 21 features of the tibia to quantify knee shape. The landmark recognition and feature extraction based on three-dimensional surface data were fully automatically applied to 412 pathological (248 female and 164 male) knees undergoing total knee arthroplasty. Subsequently, an exploratory statistical analysis was performed and linear correlation analysis was used to investigate normalization factors and gender-specific differences.

RESULTS

Statistically significant differences between genders were observed. These were pronounced for distance measurements and negligible for angular (relative) measurements. Female knees were significantly narrower at the same depth compared to male knees. The correlation analysis showed that linear correlations were higher for distance measurements defined in the same direction. After normalizing the distance features according to overall dimensions in the direction of their definition, gender-specific differences disappeared or were smaller than the related confidence intervals.

CONCLUSIONS

Implants should not be linearly scaled according to one dimension. Instead, features in medial/lateral and anterior/posterior directions should be normalized separately (non-isotropic scaling). However, large inter-individual variations of the features remain after normalization, suggesting that patient-specific design solutions are required for an improved implant design, regardless of gender.

Patella Height Correlates With Trochlear Dysplasia: A Computed Tomography Image Analysis

PURPOSE

The aim of this study was to investigate the position of the patella relative to the trochlea for a possible correlation with radiologic parameters characterizing the form of the trochlea.

METHODS

The computed tomography scans of 36 cases with patellofemoral instability and 30 without (mean age, 24.7 ± 6.8 years) were studied. The height of the patella relative to the trochlea was evaluated as the distance between the axial slice where the patella (P) showed its widest diameter, as the patella at this level has the greatest potential to form the trochlea, and the proximal entrance of the femoral trochlea (TE). The correlations between this parameter and several radiologic parameters used to evaluate trochlear dysplasia, including trochlea height, transverse trochlea shift, trochlea depth, sulcus angle, lateral and medial trochlea slope, trochlea facet asymmetry, and the Dejour trochlea type, were calculated.

RESULTS

The P-TE distance correlated significantly with all trochlea parameters evaluated, with a more dysplastic trochlea in cases of higher position of the patella: medial, central, and lateral trochlea height (0.287 <r < 0.490, P < .019), transverse trochlea shift (r = 0.516, P < .001), trochlea depth (r = -0.299, P = .015), sulcus angle (r = 0.344, P = .005), medial and lateral trochlea slope (-0.274 <r < -0.295, P < .026), trochlea facet asymmetry (r = -0.399, P = .005), and Dejour trochlea type (r = 0.394, P = .001).

CONCLUSIONS

On the basis of our findings it was concluded that patella height was significantly related to the morphology of the femoral trochlea. The strongest correlations with patella height were observed for the parameters central trochlea height (r = 0.490, P < .001) and transverse trochlea shift (r = 0.516, P < .001). A higher positioned patella was associated with a more dysplastic trochlea.

LEVEL OF EVIDENCE

Level III, retrospective cross-sectional study.

Do hip muscle weakness and dynamic knee valgus matter for the clinical evaluation and decision-making process in patients with patellofemoral pain?

•

Hip muscle weakness in PFP patients may be consequence and not the cause of pain.

•

Pain and disability may not be associated with kinematics after treatment.

•

Hip muscle weakness may have no causal relationship with dynamic knee valgus.

•

The mechanical factors that may impair the management of PFP are likely to be overestimated.

•

PFP patients should be treated on a biopsychosocial approach.

Background

Patellofemoral pain is a very common musculoskeletal condition. In the last years, evidence regarding this disease increased exponentially. Although widely investigated, this problem still frustrates patients and clinicians for having an unfavorable prognosis. Some gaps still exist in the understanding and managing of patellofemoral pain. Numerous cross-sectional association studies show an association between gluteus muscular strength and dynamic knee valgus in patients with patellofemoral pain. In spite of this biological plausibility, many evidences challenge the direct relationship between these factors. Recent studies have concluded that women with patellofemoral pain show muscular weakness of the hip based on the cross-sectional studies, however prospective studies indicate that hip weakness cannot be considered a risk for development of patellofemoral pain. In addition, some clinical trials have demonstrated that strength training of the gluteal muscles promotes significant improvement in symptoms but not alter the kinematics of the patients with patellofemoral pain. These findings cast doubt on whether the cause of this condition is really being treated, whether all individuals suffering from patellofemoral pain present dynamic knee valgus or if this is a disturbance present in only a subgroup of patients and whether the strengthening of the hip musculature is an option to consider for prevention of patellofemoral pain.

Conclusion

Certainly, more studies should be conducted to clarify the influence of mechanical patterns on this condition, but with the existing evidence so far, the importance given to these issues in the evaluation and clinical decision on treatment of these patients seems questionable. Therefore, this masterclass explores the understanding about patellofemoral pain, highlighting mainly the importance of muscular strength and dynamic knee valgus, as well as other possible factors that must be consider during the evaluation and the decision making in these patients.

Patellofemoral morphology and alignment: reference values and dose-response patterns for the relation to MRI features of patellofemoral osteoarthritis

OBJECTIVE

We aimed to (1) determine reference values for trochlear morphology and patellofemoral (PF) alignment in adults without magnetic resonance imaging (MRI)-defined PF full thickness cartilage damage or knee pain; and (2) evaluate dose-response patterns for these measures with prevalent MRI-defined PF structural damage and/or knee pain.

DESIGN

The Framingham Community Cohort is a population-based sample of ambulatory adults aged ≥50 years. We evaluated six morphology and alignment measures using MRI (n = 985), and reported reference values (mean ± 2SD) in a subsample without MRI-defined PF full thickness cartilage damage or knee pain (n = 563). With restricted cubic spline Poisson regression, we evaluated dose-response patterns of each of the six measures with prevalent MRI-defined PF structural damage or joint pain. Our primary outcome was full thickness cartilage damage.

RESULTS

For dose-response curves, prevalence ratios (PR) increased monotonically for all measures except patellar tilt, which rose with both lateral and medial tilt. Associations were generally strongest in the lateral PF compartment. PR for the strongest predictors of full thickness cartilage damage reached clinical relevance (PR > 1.5) at sulcus angle (SA) ≥135.0°; patellar tilt angle at ≤1.0° and ≥15.0°; and bisect offset ≥57.0%. Lateral trochlear inclination (LTI) achieved PR > 1.5 at ≤23.0° for full thickness cartilage damage with pain.

CONCLUSIONS

SA, patellar tilt, and bisect offset were most strongly associated with full thickness cartilage damage. LTI, patellar tilt and bisect offset had stronger associations with the addition of pain. These findings contribute to better identifying a subset of patients who may benefit from mechanically based interventions.

How Are Obesity and Body Composition Related to Patellar Cartilage? A Systematic Review

Objective.

The aim of this review was to systematically examine the evidence for an association between measures of obesity [weight and body mass index (BMI)] and body composition (fat mass and fat-free mass) and patellar cartilage, assessed using magnetic resonance imaging.

Methods.

Three electronic databases (MEDLINE, EMBASE, and CINAHL) were searched up to April 2016 using full text and MeSH terms to identify studies examining the associations between obesity and body composition, and patellar cartilage. Two independent reviewers extracted the data and assessed the methodological quality of included studies.

Results.

Seventeen studies were included: 5 cross-sectional, 10 cohort studies measuring outcomes at 2 timepoints, and 2 longitudinal studies assessing outcome only at the timepoint. Eleven studies were of high or moderate quality. In asymptomatic middle-aged adults, elevated body weight and BMI were systematically associated with worse patellofemoral cartilage scores. There was more consistent evidence for patellar cartilage defects than patellar cartilage volume, particularly in women. Increased BMI was also consistently associated with increased cartilage loss in longitudinal studies, although not all attained statistical significance.

Conclusion.

There is a need for more high-quality research to confirm these findings and to better explain the relative contributions of metabolic and biomechanical factors to the initiation of patellofemoral osteoarthritis, to devise effective strategies to manage this common and disabling condition.

Is the effectiveness of patellofemoral bracing modified by patellofemoral alignment and trochlear morphology?

Background

This study was performed to determine if the effectiveness of patellofemoral bracing as a treatment for patellofemoral osteoarthritis is influenced by patellofemoral joint alignment and trochlear morphology. We hypothesized that those with more extreme patellar malalignment would benefit more from bracing.

Methods

Thirty-eight patients who had received bracing as part of a comprehensive treatment plan for patellofemoral osteoarthritis were selected for this study. Ten measures of patellar alignment were taken from X-rays. These alignment measures were divided into percentile groups (tertiles) for contingency table analysis. Treatment outcome was measured by Western Ontario and Macmasters Universities Osteoarthritis Index (WOMAC) scores and these were dichotomised into two groups according to “Improved” or “Not Improved” according to the minimum clinically important difference (MCID). Spearman’s rho test was performed for continuous variables and Fisher’s exact test was performed for correlation between tertile groups and MCID categories.

Results

Thirty-eight patients (9 male and 29 female) between the ages of 51 to 89 were included in this study. WOMAC scores ranged from −25 to 41.67, with a mean change of −3.97, 31.6, 44.7 and 31.6% of patients falling into the “Improved” group for Global, Pain and Function scores respectively. We found a non-significant trend shown (p = 0.058, correlation coefficient 0.31) between bisect offset and change in WOMAC global, indicating a trend for higher change in WOMAC scores with increasing bisect offset. Statistically significant correlations were found between mean MCID categories for the WOMAC global and function groups when analysed against percentile groups for bisect offset (p < 0.01) and patellar subluxation distance (p < 0.05), indicating those in higher percentile groups were more likely not to improve after six months.

Conclusion

Higher bisect offset and patellar subluxation distance measures were associated with poorer outcomes. However, due to the limited sample size, more studies are required to fully examine this relationship.

Relationship of Trochlear Morphology and Patellofemoral Joint Alignment to Superolateral Hoffa Fat Pad Edema on MR Images in Individuals with or at Risk for Osteoarthritis of the Knee: The MOST Study

Purpose To determine the relationship of patellofemoral joint alignment and trochlear morphology to superolateral Hoffa fat pad (SHFP) edema on magnetic resonance (MR) images in older adults with or at risk for osteoarthritis of the knee. Materials and Methods Institutional review board approval and written informed consent were obtained from all subjects. The Multicenter Osteoarthritis Study is a prospective cohort study of older adults with or at risk for osteoarthritis of the knee. Subjects were recruited from Birmingham, Alabama, and Iowa City, Iowa. In this cross-sectional study, patellofemoral joint alignment (bisect offset, patellar tilt angle, and Insall-Salvati ratio), trochlear morphology (sulcus angle, lateral and medial trochlear inclination, and trochlear angle) and SHFP edema were assessed on MR images of the knee. Measures of alignment and morphology were divided into quartiles, and SHFP was determined to be present or absent. Separate logistic regression models were used to determine the relationship of each measure of alignment and morphology to the presence of SHFP edema, with adjustments for age, sex, and body mass index. Results SHFP edema was present in 152 (13.4%) of the 1134 knees that were included. When compared with knees with measurements in the lowest quartile, knees with measurements in the highest quartile for trochlear angle, bisect offset, and Insall-Salvati ratios were 1.6 (95% confidence interval [CI]: 1.0, 2.6), 2.3 (95% CI: 1.3, 4.0), and 8.9 (95% CI: 4.7, 16.9) times more likely to show SHFP edema, respectively. No relationship was found between other measures and SHFP edema. Conclusion A more anterior trochlear facet, a more laterally displaced patella, and knees with patella alta were significantly associated with SHFP edema on MR images in subjects with or at risk for osteoarthritis of the knee. ^© RSNA, 2017.

Variability of Measurement of Patellofemoral Indices with Knee Flexion and Quadriceps Contraction: An MRI-Based Anatomical Study

PURPOSE

The purpose of this study was to investigate the impact of varying knee flexion and quadriceps activity on patellofemoral indices measured on magnetic resonance imaging (MRI).

MATERIALS AND METHODS

MRI of the knee was performed in 20 patients for indications other than patellar or patellofemoral pathology. Axial and sagittal sequences were performed in full extension of the knee with the quadriceps relaxed, full extension of the knee with the quadriceps contracted, 30° flexion of the knee with the quadriceps relaxed, and 30° flexion with the quadriceps contracted. Bisect offset, patella tilt angle, Insall-Salvati ratio and Caton-Deschamps index were measured.

RESULTS

With the knee flexed to 30° and quadriceps relaxed, the mean values of patellar tilt angle, bisect offset, Insall-Salvati ratio and Caton-Deschamps index were all within normal limits. With the knee extended and quadriceps contracted, the mean patellar tilt angle (normal value, <15°) was 14.6° and the bisect offset (normal value, <65%) was 65%, while the Caton-Deschamps index was 1.34 (normal range, 0.6 to 1.3). With the knee extended and quadriceps relaxed, the mean Caton-Deschamps index was 1.31.

CONCLUSIONS

MRI scanning of the knee in extension with the quadriceps contracted leads to elevated patellofemoral indices. MRI taken with the knee in 30° of flexion allows more reliable assessment of the patellofemoral joint and minimises the confounding effect of quadriceps contraction.

Comparison of Radiological Parameters between Normal and Patellar Dislocation Groups in Korean Population: A Rotational Profile CT-Based Study

Purpose

Patellofemoral instability is a common cause of anterior knee pain in adolescents and young adults. Most normal and pathological values for diagnosing patellofemoral instability are based on Western literature. We conducted this radiological study to determine normal values for different patellofemoral parameters in a Korean population and to evaluate their usefulness in diagnosis.

Materials and Methods

We retrospectively reviewed the rotational profile computerized tomography (CT) scans of the patellar dislocation and control groups. Trochlear, patellar, rotational profile, and trochleo-patellar alignment parameters were compared between the groups. Receiver operating characteristic curves were drawn for significant parameters, and sensitivity and specificity were calculated for the cut-off values.

Results

There were 48 patients in the patellar dislocation group and 87 patients in the control group. In the control group and patellar dislocation group, the mean sulcus angle was 132.5° and 143.3°, respectively, trochlear depth was 6.04 mm and 3.6 mm, bisect offset was 56.4% and 99.9%, lateral patellar tilting was 9.8° and 19.2°, patellar facet asymmetry was 63.5% and 45.16%, and the tibial tuberosity-trochlear groove (TT-TG) distance was 10.91 mm and 27.16 mm, respectively.

Conclusions

The trochlear depth, bisect offset, patella tilting, and TT-TG distance were parameters that significantly contributed to patellar instability. Rotational profile CT can be considered a good diagnostic tool to assess all these parameters that help to identify anatomical aberration resulting in patellofemoral instability, thereby helping in formulating the most effective treatment plan.

Patellofemoral Pain

Patellofemoral pain is characterized by insidious onset anterior knee pain that is exaggerated under conditions of increased patellofemoral joint stress. A variety of risk factors may contribute to the development of patellofemoral pain. It is critical that the history and physical examination elucidate those risk factors specific to an individual in order to prescribe an appropriate and customized treatment plan. This article aims to review the epidemiology, risk factors, diagnosis, and management of patellofemoral pain.

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.

Patellofemoral Joint Reconstruction for Patellar Instability: Medial Patellofemoral Ligament Reconstruction, Trochleoplasty, and Tibial Tubercle Osteotomy

Recurrent patellar instability can be very debilitating and may require surgical intervention. A thorough workup must be completed in this subset of patients. Risk factors for recurrent instability include patella alta, trochlear dysplasia, an increased tibial tubercle-trochlear groove distance, and insufficiencies in the medial retinacular structures. Necessary treatment of these risk factors, once identified, should be addressed surgically. Patellofemoral reconstruction must be individually tailored to each patient's anatomy and may necessitate medial patellofemoral ligament reconstruction, tibial tubercle osteotomy, or trochleoplasty in any combination or as a standalone procedure. This article details our technique for surgical treatment of recurrent patellar instability with a medial patellofemoral ligament reconstruction, an open trochleoplasty, and a tibial tubercle osteotomy for patients with severe trochlear dysplasia, an increased tibial tubercle-trochlear groove distance, or patella alta.

Statistical modeling to characterize relationships between knee anatomy and kinematics

The mechanics of the knee are complex and dependent on the shape of the articular surfaces and their relative alignment. Insight into how anatomy relates to kinematics can establish biomechanical norms, support the diagnosis and treatment of various pathologies (e.g., patellar maltracking) and inform implant design. Prior studies have used correlations to identify anatomical measures related to specific motions. The objective of this study was to describe relationships between knee anatomy and tibiofemoral (TF) and patellofemoral (PF) kinematics using a statistical shape and function modeling approach. A principal component (PC) analysis was performed on a 20-specimen dataset consisting of shape of the bone and cartilage for the femur, tibia and patella derived from imaging and six-degree-of-freedom TF and PF kinematics from cadaveric testing during a simulated squat. The PC modes characterized links between anatomy and kinematics; the first mode captured scaling and shape changes in the condylar radii and their influence on TF anterior-posterior translation, internal-external rotation, and the location of the femoral lowest point. Subsequent modes described relations in patella shape and alta/baja alignment impacting PF kinematics. The complex interactions described with the data-driven statistical approach provide insight into knee mechanics that is useful clinically and in implant design.