• Patella alta
• Patellar height
• Patellar instability
• Patellotrochlear index

• Humans
• Patella/diagnostic imaging
• Patella/surgery
• Female
• Male
• Adult
• Femur/diagnostic imaging
• Femur/surgery
• Joint Instability/surgery
• Joint Instability/diagnostic imaging
• Tibia/diagnostic imaging
• Tibia/surgery
• Magnetic Resonance Imaging
• Young Adult
• Middle Aged
• Patellofemoral Pain Syndrome/diagnostic imaging
• Patellofemoral Pain Syndrome/surgery
• Patellofemoral Joint/diagnostic imaging
• Patellofemoral Joint/surgery
• Osteotomy
• Adolescent
• Retrospective Studies
• Reproducibility of Results
• Chronic Pain/etiology

• Anatomy
• Imaging
• Key Terms: Knee
• Magnetic Resonance
• Patella

• Humans
• Female
• Patella/diagnostic imaging
• Cross-Sectional Studies
• Adult
• Weight-Bearing/physiology
• Patellofemoral Joint/diagnostic imaging
• Patellofemoral Joint/physiopathology
• Patellofemoral Joint/physiology
• Magnetic Resonance Imaging
• Young Adult
• Range of Motion, Articular/physiology

• Axial patellotrochlear index
• Patella alta
• Patellar height
• Patellotrochlear index

• Humans
• Magnetic Resonance Imaging/methods
• Retrospective Studies
• Male
• Female
• Patella/diagnostic imaging
• Adult
• Middle Aged
• Patellofemoral Joint/diagnostic imaging
• Adolescent
• Aged
• Young Adult
• Reference Values
• Cartilage, Articular/diagnostic imaging
• Cartilage, Articular/pathology
• Femur/diagnostic imaging

• Caton–Deschamps
• Insall–Salvati
• Patella height
• UKA
• Unicompartmental knee arthroplasty

• Aged
• Female
• Humans
• Male
• Middle Aged
• Arthroplasty, Replacement, Knee
• Knee Joint/surgery
• Knee Prosthesis
• Osteoarthritis, Knee/surgery
• Osteoarthritis, Knee/diagnostic imaging
• Patella/diagnostic imaging
• Patella/surgery
• Postoperative Period
• Radiography

• RWTH Aachen University (3131)

• Patellar alta
• Patellar dislocation
• Patellar height index
• Patellar height measurement method

• Humans
• Patellar Dislocation
• Case-Control Studies
• Joint Dislocations
• Area Under Curve
• Patella

• Dejour classification
• patella dislocation
• trochlea dysplasia

• Humans
• Female
• Young Adult
• Adult
• Patella
• Patellar Dislocation/diagnostic imaging
• Patellar Dislocation/etiology
• Patellar Dislocation/surgery
• Patellofemoral Joint
• Femur
• Tibia/surgery
• Joint Instability/etiology
• Joint Instability/surgery

• CMRPG5K0092 Chang Gung Memorial Hospital
• MOST 111-2628-B-182A-016 - Taiwan Minister of Science and Technology

• Augmentation
• Patella infera
• Patellar tendon lengthening
• Quadriceps tendon graft
• Surgical treatment

We examine the outcomes following operative treatment of intra-articular fracture combined with medial patellofemoral ligament (MPFL) reconstruction after patella dislocation.

Patients were retrospectively identified from medical records using diagnostic and surgical procedure codes. Radiological anatomical parameters and bony abnormalities of injured knees were assessed from magnetic resonance images (MRI). Inclusion criteria were traumatic patellar dislocation with chondral or osteochondral fracture and MPFL rupture, operative treatment of a chondral or osteochondral fracture combined with MPFL reconstruction, and minimum follow-up of 2 years. Outcomes were measured using the Kujala score, Tegner activity scale, and the Knee injury and Osteoarthritis Outcome Score Quality-of-Life subscale (KOOS-QLS).

During 2012 and 2015, 322 patients were treated because of patellar dislocation. Thirty-three patients had chondral or osteochondral fracture. Eleven patients (five males and six females) with a mean [standard deviation (SD)] age of 17.0 (6.5) years at the time of surgery met the inclusion criteria and were included. Five of the 11 patients had a subchondral and six an osteochondral fracture. Eight patients had a fracture in the patella and three in the femur. All patients had bony abnormalities in the knee. Nine out of 11 patients scored over 90/100 points on the Kujala scale and had good results on the Tegner scale [before surgery 5.0 (2.7) points versus after surgery 5.3 (1.6) points] and the KOOS-QLS [4.1 (4.2) points] outcome measures.

The removal or fixation of the fracture fragment combined with MPFL reconstruction is a feasible option in the treatment of symptomatic osteochondral or subchondral fragment in traumatic patellar dislocation. The short-term outcomes are encouraging.

Level of evidence: Level IV, retrospective case series.

• IKDC
• Kujala
• Patellofemoral instability
• Quality of life
• Severe trochlear dysplasia
• Trochleoplasty

Patellofemoral instability (PI) is the disruption of the patella’s relationship with the trochlear groove as a result of abnormal movement of the patella. To identify the presence of PI, conventional radiographs (anteroposterior, lateral, and axial or skyline views), magnetic resonance imaging, and computed tomography are used. In this study, we examined four main instability factors: Trochlear dysplasia, patella alta, tibial tuberosity–trochlear groove distance, and patellar tilt. We also briefly review some of the other assessment methods used in the quantitative and qualitative assessment of the patellofemoral joint, such as patellar size and shape, lateral trochlear inclination, trochlear depth, trochlear angle, and sulcus angle, in cases of PI. In addition, we reviewed the evaluation of coronal alignment, femoral anteversion, and tibial torsion. Possible causes of error that can be made when evaluating these factors are examined. PI is a multi-factorial problem. Many problems affecting bone structure and muscles morphologically and functionally can cause this condition. It is necessary to understand normal anatomy and biomechanics to make more accurate radiological measurements and to identify causes. Knowing the possible causes of measurement errors that may occur during radiological measurements and avoiding these pitfalls can provide a more reliable road map for treatment. This determines whether the disease will be treated medically and with rehabilitation or surgery without causing further complications.

• Patellofemoral instability
• Radiological evaluation errors
• Trochlear dysplasia
• Patella alta
• Tibial tuberosity-trochlear groove distance
• Patellar tilt

• Distalization
• Osteotomies
• Patella alta
• Patellofemoral instability
• Rotational abnormalities
• Treatment
• Trochlear dysplasia

To confirm whether a novel sagittal patellar angle linear equation used for evaluating patellar height by calculating expected sagittal patellar angle (SPA) at any degree of knee flexion angle is suitable for patients older than 17 years and its reliability compared with other commonly used methods.

From September 2016 to September 2019, a total number of 202 consecutive outpatients' knee lateral X‐ray radiographs were retrospectively measured and evaluated using a recently proposed linear equation Y = 1.94 + 0.74 × knee flexion(KF) angle. Patients were divided by ages into ayounger group, whose ages were between 17–49 years, and an older group, whose ages were older than 49 years, which has not been validated in the original study. Parameters such as KF, SPA, patella and patella tendon length and so on were measured on computer with picture archiving and communication system by two independent observers at an interval of 1 month. Insall‐Salvati (IS) index, Caton‐Deschamps (CD) index and Y value, correlation coefficients were calculated and compared using SPSS 22.0 software.

In the younger group, 143 patients (165 knees) were included, ages were 17–49 (31.62 ± 11.38) years, males/females were 70 (48.95%)/73 (51.05%), left knees/right knees were 83 (50.30%)/82 (49.70%), mean value of Y was 31.50° ± 10.07°, and SPA was 34.38° ± 12.38°, mean value of IS was 1.06 ± 0.17, mean value of CD was 1.04 ± 0.18. While in older group, 59 patients (78 knees) were included, ages were 50–60 (mean 54.61 ± 2.99) years, there were 32 males (54.24%) and 27 females (45.76%), 42 knees were left (53.85%) and 36 knees were right (46.15%), mean values of Y and SPA were 25.90° ± 11.55° and 29.36° ± 14.22°, mean IS index in older group was 1.06 ± 0.18, mean CD index was 1.00 ± 0.16. Intra‐ and inter‐observer reliabilities of Y in younger and older groups were 0.999, 0.999, 1.000 and 0.999, meaning high reliability and reproducibility, but low Pearson's correlation coefficients with IS and CD index were showed as −0.213 and − 0.216 in younger group and − 0.113 and − 0.316 in older group.

In patients older than 17 years, the linear equation Y = 1.94 + 0.74 × KF is a reliable and practical method to evaluate SPA regardless of age and knee flexion angle, but has weak correlation coefficients with the IS and CD index.

• Knee flexion angle
• Linear equation
• Patellar height
• Sagittal patellar angle

• Extensor mechanism tendinopathy
• Lateral patellar maltracking
• TT-TG

• MRI
• Patella alta
• Patellar height
• Patellotrochlear index
• Reliability
• Reproducibility

• Dejour classification
• IKDC
• MRI
• Oswestry-Bristol classification
• Patellofemoral instability
• Patellotrochlear index
• Recurrent patellar instability
• Trochlear dysplasia
• Trochleoplasty
• clinical outcomes
• knees
• medial patellofemoral ligament reconstruction
• surgical treatment
• tibial tuberosity
• trochlear dysplasia

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

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

Systematic review; Level of evidence, 4.

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

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

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

• TT-TG distance
• patellar instability
• radiologic measurements

• Patella
• Patella alta
• Patellar dislocation
• Patellar height
• Patellar instability

• CT
• Inter-observer reliability
• MRI
• Patellar height
• Radiography

• anatomy
• knee
• medial patellofemoral ligament
• trochlea

• MRI
• Patella alta
• Patellofemoral joint
• Patellotrochlear index

• Assessment
• Dynamic
• MRI
• Patellar height
• Patellar instability

• anterior knee pain
• jumper's knee
• overuse injury
• patella alta
• patellofemoral pain
• tendinopathy
• trochlear dysplasia

• Knee
• MRI
• Patellar instability
• Patellofemoral indices
• Weight bearing

Patella alta and patella baja are important conditions underlying a predisposition to many joint diseases, including patellar luxation and patellar chondromalacia of the articular cartilage. The frequencies of patella alta and patella baja have not yet been determined. The objectives of this study were to determine the frequency of patella alta and to determine reference values to the position of the vertical patella according to two modified techniques of the Insall–Salvati method in a group of 65 German shepherd dogs (115 stifle joints).

The upper limits of reference values for the normal vertical position of the patella were 1.79 and 2.13, depending on the method of measurement. A high prevalence of patella alta was observed in the group of German shepherd dogs. A correlation was demonstrated between the classification of dogs’ joints in the patella alta group and the multiplied risk of canine hip dysplasia (CHD) through the estimation of odds ratios.

Dogs with patella alta were healthy dogs that did not exhibit orthopaedic problems in the stifle joints. The results revealed that the risk of CHD is twice as high in dogs with higher patellar ligament length to patella length ratio.

• Insall Salvati
• Patella alta
• Patellar instability
• Vertical position of the patella

• Knee
• Measurement
• Patellar dislocation
• Patellar height
• Plateau–patella angle
• Radiograph

Patellar instability is a common clinical problem encountered by orthopedic surgeons specializing in the knee. For patients with chronic lateral patellar instability, the standard surgical approach is to stabilize the patella through a medial patellofemoral ligament (MPFL) reconstruction. Foreseeably, an increasing number of revision surgeries of the reconstructed MPFL will be seen in upcoming years. In this paper, the causes of failed MPFL reconstruction are analyzed: (1) incorrect surgical indication or inappropriate surgical technique/patient selection; (2) a technical error; and (3) an incorrect assessment of the concomitant risk factors for instability. An understanding of the anatomy and biomechanics of the MPFL and cautiousness with the imaging techniques while favoring clinical over radiological findings and the use of common sense to determine the adequate surgical technique for each particular case, are critical to minimizing MPFL surgery failure. Additionally, our approach to dealing with failure after primary MPFL reconstruction is also presented.

• Medial patellofemoral ligament
• Failed medial patellofemoral ligament reconstruction
• Trochleoplasty
• 3D-CT in patellofemoral surgery

• Medial patellofemoral ligament
• Patella
• osteotomy
• patella alta
• patella femoral pain syndrome
• patellar dislocation
• patellar instability
• tibial tubercle osteotomy
• tibial tubercle-trochlear groove
• trochlear dysplasia
• trochleoplasty

• MRI
• knee
• patellofemoral

To analyze occurrences of trochlear dysplasia in patients with Down syndrome in the presence and absence of femoropatellar instability.

Eleven knees with stable patellae and thirteen with unstable patellae in patients with Down syndrome were compared. Radiographs were produced to evaluate patellar height, trochlear angle and femoropatellar congruence angle.

The prevalence ratio for a high patella between the unstable and the stable patients was 1.01 using the Insall–Salvati index and 0.68 using the Caton–Deschamps index. For an abnormal congruence angle, the prevalence ratio was 2.04. An increased congruence angle was only found in four cases, all presenting instability.

Trochlear dysplasia was only found in cases of instability. The trochlear groove angle and the femoropatellar congruence angle correlated with the presence of patellar instability.

• Down syndrome
• Knee
• Patellar dislocation

• Dislocation
• Injury
• Instability
• Knee
• Medial patellofemoral ligament
• Patella

• Dislocation
• Injury
• Instability
• Knee
• Medial patellofemoral ligament
• Patella

• Humans
• Joint Instability/diagnosis
• Joint Instability/therapy
• Patellar Dislocation/diagnosis
• Patellar Dislocation/therapy
• Patellofemoral Joint/anatomy & histology

• MRI
• Patellar instability
• Patellofemoral engagement

Patellofemoral instability not only involves lateral patellar dislocation, patellar mal-tracking or subluxation but can also cause a limiting disability for sports activities. Its underlying causes are known as morphological anomalies of the patellofemoral joint or the mechanical axis, femorotibial malrotation, variants of the knee extensor apparatus, and ligamentous insufficiencies often accompanied by poor proprioception. Athletes with such predisposing factors are either suffering from unspecific anterior knee pain or from slightly traumatic or recurrent lateral patellar dislocation Treatment options of patellar instability are vast, and need to be tailored individually depending on the athlete’s history, age, complaints and physical demands. Different conservative and surgical treatment options are reviewed and discussed, especially limited expectations after surgery.

• MPF
• anterior knee pain
• athlete
• osteotomy
• trochleoplasty