Magnetic Resonance Imaging Findings After Acute Patellar Dislocation in Children

Prevalence and Site of Concomitant Osteochondral Injuries in Patients With Acute Lateral Patellar Dislocation: A Systematic Review and Meta-analysis

Background

Osteochondral injuries (OCIs) are common in patients with acute lateral patellar dislocation, which can produce both short- and long-;term adverse effects. However, the pattern of these injuries warrants further analysis, especially in relation to patient age.

Purpose

To determine the overall prevalence of concomitant OCIs as well as the prevalence differences based on location and age after acute lateral patellar dislocations.

Study Design

Systematic review; Level of evidence, 4.

Methods

A comprehensive search of PubMed, Embase, Web of Science, and Cochrane Library was completed from inception to July 20, 2022. All articles reporting the prevalence of OCI were included. The sample characteristics such as age, study design, magnetic resonance imaging diagnostic data, and the number of patients with OCI were extracted. The Methodological Index for Non-Randomized Studies (MINORS) was used for quality assessment. The overall and per-;site injury rates were calculated, and the prevalence was stratified by age-;group (≤16 and >16 years) and compared.

Results

The systematic review included 39 studies involving 3354 patients. MINORS scores were 11.94 ± 1.98 and 16 ± 3.46 in the noncomparative and comparative studies, respectively. The overall prevalence of bone bruises and OCI was 89.6% (95% CI, 77.4%-97.7%) and 48.8% (95% CI, 39.0%-58.7%), respectively. In both overall and >16-year-old patients, the lateral femoral condyle (LFC) was the most common site of bone bruise (90.5% [95% CI, 84.0%-95.6%] and 91.5% [95% CI, 84.3%-96.9%], respectively); however, the medial patellar bruise was more common in patients ≤16 years (89.2% [95% CI, 82.9%-94.4%]). Among the pooled sites of OCI, the medial patella accounted for the largest proportion (36.9% [95% CI, 28.0%-46.3%]). OCIs were more common in patients >16 years (52.6% [95% CI, 39.4%-65.6%]) than in patients ≤16 years (46.6% [95% CI, 33.2%-60.3%]).

Conclusion

Bone bruises on the LFC were most prevalent overall and in patients >16 years, whereas bone bruises on the medial patella were more prevalent in patients ≤16 years. OCIs were frequently seen in patients >16 years, with the most common site being the medial patella.

Chondral and Soft Tissue Injuries Associated to Acute Patellar Dislocation: A Systematic Review

INTRODUCTION

Chondral and soft tissue injuries can be associated with first time patellar dislocation, but it is unclear how common they are, and which tissues are affected. A systematic review of the literature was performed to investigate the frequency, location, and extent of chondral and medial patellofemoral ligament (MPFL) injuries in patients following first time patellar dislocation.

METHODS

This systematic review was conducted according to the PRISMA guidelines. PubMed, Google Scholar, Embase, and Web of Science databases were accessed in November 2021. All the published clinical studies reporting the frequency, location, and extent of soft tissue lesions following first time patellar dislocation were accessed. Studies reporting data on habitual, congenital, or recurrent patellofemoral instability were excluded.

RESULTS

Data from 42 articles (2254 patients, mean age 21.6 ± 7.3 years) were retrieved. Ninety-eight percent of patients who experienced first time patellar dislocation demonstrated MPFL rupture at MRI. Forty-eight percent of MPFL ruptures were located at the patellar side, 34% at the femoral insertion site, and 18% in the midportion. Eighty-five percent of patients showed signs of patellar chondral damage at MRI, and trochlear chondral injuries were evidenced in 47% of patients. Intra-articular loose bodies were observed in 11.5% of patients. At arthroscopy, the medial facet and the crest of the patella more commonly exhibited chondral lesions than the lateral facet and femoral trochlea.

CONCLUSIONS

Most patients suffer chondral damage and MPFL tears following after a first time patellar dislocation.

Comparing the Tibial Tuberosity-Trochlear Groove Distance Between CT and MRI in Skeletally Immature Patients With and Without Patellar Instability

Background:

The tibial tubercle–trochlear groove (TT-TG) distance was originally described for computed tomography (CT), but it has been measured on magnetic resonance imaging (MRI) in patients with patellar instability (PI). Whether the TT-TG measured on CT versus MRI can be considered equivalent in skeletally immature children remains unclear.

Purpose:

To investigate in skeletally immature patients (1) the effects of CT versus MRI imaging modality and cartilage versus bony landmarks on consistency of TT-TG measurement, (2) the difference between CT and MRI measurements of the TT-TG, and (3) the difference in TT-TG between patients with and without PI.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

We retrospectively identified 24 skeletally immature patients with PI and 24 patients with other knee disorders or injury but without PI. The bony and cartilaginous TT-TG distances on CT and MRI were measured by 2 researchers, and related clinical data were collected. The interrater, interperiod (bony vs cartilaginous), and intermethod (CT vs MRI) reliabilities of TT-TG measurement were assessed with intraclass correlation coefficients.

Results:

The 48 study patients (19 boys, 29 girls) had a mean age of 11.3 years (range, 7-14 years). TT-TG measurements had excellent interrater reliability and good or excellent interperiod reliability but fair or poor intermethod reliability. TT-TG distance was greater on CT versus MRI (mean difference, 4.07 mm; 95% CI, 2.6-5.5 mm), and cartilaginous distance was greater than bony distance (mean difference, 2.3 mm; 95% CI, 0.79-3.8 mm). The TT-TG measured on CT was found to increase with the femoral width. Patients in the PI group had increased TT-TG distance compared with those in the control group, regardless of landmarks or modality used (P > .05 for all).

Conclusion:

For skeletally immature patients, the TT-TG distance could be evaluated on MRI, regardless of whether cartilage or bony landmarks were used. Its value could not be interchanged with CT according to our results; however, further research on this topic is needed.

Prevalence and Site of Medial Patellofemoral Ligament Injuries in Patients With Acute Lateral Patellar Dislocations: A Systematic Review and Meta-analysis

Background

Medial patellofemoral ligament (MPFL) injuries are common in patients with acute lateral patellar dislocations, but the pattern of MPFL injuries is unclear, especially with respect to patient age.

Purpose

The primary aim was to determine the prevalence of MPFL injuries according to the site of injury in patients with acute lateral patellar dislocations. The secondary aim was to compare the site of MPFL injuries in patients aged ≤16 versus >16 years.

Study Design

Systematic review; Level of evidence, 4.

Methods

A systematic literature search was performed with PubMed, Embase, and CINAHL to identify articles published from January 1, 1999, to May 31, 2019, that examined the site of MPFL injuries in patients with acute patellar dislocations. The study design, sample size, age at injury, technique used for diagnosing MPFL injuries (magnetic resonance imaging, ultrasound, and/or surgery), and prevalence and site of MPFL injuries were extracted from each study. The pooled estimate of the proportion of MPFL injuries at each site was calculated (femur, patella, midsubstance, and combined sites of injury) as well as proportions stratified by age group (≤16 and >16 years).

Results

The literature search yielded 420 unique articles, of which 52 were screened for eligibility; of these, 17 were excluded. Thus, a total of 35 articles (2558 patients) were included in the final analysis. The overall prevalence of MPFL injuries was 94.7% (95% CI, 91.2%-96.8%). Most MPFL injuries occurred at the patella (37.1% [95% CI, 30.8%-43.9%]), followed by the femur (36.8% [95% CI, 31.0%-43.0%]), combined sites (25.1% [95% CI, 20.7%-30.1%]), and the midsubstance (15.6% [95% CI, 13.2%-18.4%]). In patients aged ≤16 years, most MPFL injuries occurred at the patella (39.3% [95% CI, 27.9%-51.9%]), and in patients aged >16 years, most MPFL injuries occurred at the femur (47.2% [95% CI, 40.6%-54.0%]).

Conclusion

The prevalence of MPFL injuries in patients with acute patellar dislocations varied by site of injury and by age. MPFL injuries at the patella were most prevalent overall and in children and adolescents, and MPFL injuries at the femur were more prevalent in adults.

Acute instability of the patella: is magnetic resonance imaging mandatory?

PURPOSE

Acute dislocations of the patella represent 2 to 3% of traumatic injuries of the knee. When patients are seen in the emergency department with a dislocated patella clinical diagnosis is often very evident. However, in cases of short-lived subluxation or dislocations that have reduced spontaneously, the diagnosis can be challenging. The aim of this study was to evaluate the utility of MRI in the evaluation of acute patellar instability.

METHODS

This was a prospective study of 39 cases of acute patellar instability. The study protocol included a clinical examination by an emergency medicine doctor, a standardised series of radiographs and an MRI scan within 15 days after injury.

RESULTS

The series included 15 female and 24 male patients aged on average 23 ± 10.5 years (11-46). Twenty-four cases were following sporting accidents and 15 cases following domestic accidents. In ten cases, a blow to the medial side of the patella led to the injury and in 29 cases, a twisting mechanism with a valgus and external rotation force was responsible. Six patients presented with a clinically dislocated patella and 31 patients were deemed to have a "swollen knee". Nineteen patients described an episode of subluxation of the patella and 14 an odd sensation within the knee without being able to specifically describe what had happened. Radiographs demonstrated trochlear dysplasia in 97.5% of cases and osteochondral lesions in 20.5% of cases. MRI scan confirmed the diagnosis of acute patellar instability in 37 cases giving a sensitivity of 95%. MRI findings included 25 MPFL lesions, 31 patella lesions of which 25 were bone oedema and six medial facet fractures, 31 lateral femoral condyle bone oedema type lesions, 11 chondral lesions of which seven were osteochondral in nature and also three acute associated ACL injuries and two MCL injuries.

CONCLUSION

MRI scan is an important tool in the diagnosis and management of acute patellar dislocation and subluxation. When symptoms are subtle, MRI facilitates a diagnosis with relative ease. MRI is particularly useful in identifying the exact nature of lesions most notably chondral lesions which are frequently of significant size and therefore often require expedited surgical treatment.

Age at Time of Surgery but Not Sex Is Related to Outcomes After Medial Patellofemoral Ligament Reconstruction

BACKGROUND

Medial patellofemoral ligament (MPFL) reconstruction has become a well-accepted procedure for recurrent patellofemoral instability. Despite a growing volume of research assessing surgical results, the relationship of age and sex to outcomes after MPFL reconstruction surgery is unclear.

PURPOSE

To investigate whether age at the time of surgery or sex influenced patient-reported quality of life and clinical outcome after MPFL reconstruction for recurrent lateral patellofemoral instability.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

Between January 2010 and May 2016, 328 patients underwent primary patellofemoral stabilization. Demographic and clinical data were collected preoperatively. Patients completed the Banff Patellofemoral Instability Instrument (BPII) at the pre- and postoperative visits and were assessed clinically at 12 and 24 months. To assess the effects of age at surgery and sex on BPII, multiple linear regression models were fit predicting BPII at 12 and 24 months. An unadjusted regression was applied with the predictors being age at the time of surgery and sex. A second regression model was applied adjusting for age at first dislocation, grade of trochlear dysplasia, knee hyperextension, and the WARPS/STAID score-a measure of the risky patellofemoral instability characteristics of the patient.

RESULTS

Of 328 patients, 298 (91%) had complete data and minimum 12-month BPII scores available for analysis. There were 11 redislocations in the cohort (3.4%), all in female patients. When stratified by sex, baseline characteristics were not statistically different except for higher age at first dislocation ( P = .022) as well as higher WARPS/STAID scores ( P = .006) for males. Age at the time of surgery was statistically significant for each postoperative follow-up, with lower BPII scores apparent for each 10-year increase in age at the time of surgery. In the adjusted model, the WARPS/STAID score was significantly associated with the preoperative BPII score. For the 24-month postoperative BPII scores, age at time of surgery and preoperative WARPS/STAID score were both significant. Lower BPII scores were apparent for each 10-year increase in age at the time of surgery, as well as for lower scores on the WARPS/STAID classification.

CONCLUSION

This study demonstrated that when adjusted for risky pathoanatomy, neither age at first dislocation nor sex influences patient-reported quality of life outcomes after MPFL reconstruction. Age at the time of surgery was correlated with outcome, with lower BPII scores apparent for each 10-year increase in age at the time of MPFL reconstruction.

What's New in Pediatric Sports Conditions of the Knee?

BACKGROUND

Sports injuries are common in pediatric and adolescent patients and the evaluation and treatment of these injuries continues to evolve. The purpose of this review is to provide a comprehensive appraisal of the literature, highlighting recent updates on sports-related knee injuries in the pediatric athlete. We specifically examined literature on tibial spine fractures, osteochondritis dissecans (OCD) of the knee, and patellar instability. Because of the volume of literature on the subject, pediatric, and adolescent anterior cruciate ligament injuries were not included in this review.

METHODS

An electronic search of the PubMed, EMBASE, and Google Scholar databases was performed for keywords related to pediatric: tibial spine fractures, patellar instability, and osteochondritis dissecans (OCD). Search results were filtered by publication date to yield articles published electronically or in print on or after January 1, 2013. Papers were selected based on expert opinion and consensus by the authors and included if deemed to have contributed important findings to the above topics.

RESULTS

A total of 31 articles were deemed to have contributed significant findings to the literature: 5 tibial spine, 17 patellar instability, and 9 OCD. The level of evidence for most studies was either level III or IV.

CONCLUSIONS

The optimal treatment for tibial spine fractures remains controversial. The evaluation of risk factors for recurrent patellar instability is important in determining the optimal treatment strategy following first-time patellar dislocation. Future multicenter studies on pediatric OCD have the potential to further understanding of this difficult problem. High-level, comparative outcomes research on a variety of pediatric sports related injuries is lacking and this review may help inform topics for future study.

LEVEL OF EVIDENCE

Level IV-literature review.

Medial patellofemoral ligament reconstruction in children: do osseous abnormalities matter?

PURPOSE

Management of post-traumatic patellar instability in children with osseous abnormalities is challenging because of the presence of an open physis. The aim of our study was to compare the rate of recurrence after isolated reconstruction of the medial patellofemoral ligament (MPFL) in children with or without osseous abnormalities.

METHODS

The medical records of 25 children (27 knees) with recurrent patellar dislocation were reviewed. Each child underwent an isolated reconstruction of the MPFL using a hamstring graft. At the last follow-up, a clinical and radiographic evaluation was performed, including assessment of functional outcomes based on the Kujala score. Patients were compared in terms of the occurrence of a pre-existing osseous abnormality.

RESULTS

The mean age at the time of the surgery was 13.8 years. Eleven patients had trochlear dysplasia (40%), three had a patella alta (11%) and seven had an increased TT-TG (26%). The recurrence rate was 3.7% (one patient), after a mean follow-up of 41.1 months. Recurrence was not more frequent in patients with preoperative anatomical predisposing factors. The mean Kujala score was 95. The mean time to return to practicing sports was 7.1 months.

CONCLUSIONS

Isolated MPFL reconstruction is an effective option for the management of post-traumatic patellofemoral instability in skeletally immature patients. The results of this technique seem to be independent on either proximal or distal misalignments such as trochlear dysplasia, patella alta, or increased TT-TG.

Radiographic Reference Points Are Inaccurate With and Without a True Lateral Radiograph: The Importance of Anatomy in Medial Patellofemoral Ligament Reconstruction

BACKGROUND

Studies have reported methods for radiographically delineating medial patellofemoral ligament (MPFL) femoral tunnel position on a true lateral knee radiograph. However, obtaining a true lateral fluoroscopic radiograph intraoperatively can be challenging, rendering radiographic methods for tunnel positioning potentially inaccurate.

PURPOSE

To quantify the magnitude of MPFL femoral tunnel malposition that occurs on true lateral and aberrant lateral knee radiographs when using a previously reported radiographic technique for MPFL femoral tunnel localization.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Ten fresh-frozen cadaveric knees were dissected to expose the MPFL femoral insertion and surrounding medial knee anatomy. True lateral and aberrant lateral knee radiographs at 2.5°, 5°, and 10° off-axis were obtained with a standard mini C-arm in 4 orientations: anterior to posterior, posterior to anterior, caudal, and cephalad. A previously reported radiographic method for MPFL femoral localization was performed on all radiographs and compared in reference to the anatomic MPFL attachment center.

RESULTS

The radiographic point, as previously described, was a mean distance of 4.1 mm from the anatomic MPFL attachment on a true lateral knee radiograph. The distance between the anatomic MPFL attachment center and the radiographic point significantly increased on aberrant lateral knee radiographs with as little as 5° of rotational error in 3 of 4 orientations of rotation when a standard mini C-arm was used. This corresponded to a malposition of 7.5, 9.2, and 8.1 mm on 5°-aberrant radiographs in the anterior-posterior, posterior-anterior, and cephalad orientations, respectively (P < .005). In the same 3 orientations of rotation, MPFL tunnel malposition on the femur exceeded 5 mm on 2.5° aberrant radiographs.

CONCLUSION

The commonly utilized radiographic point, as previously described for MPFL femoral tunnel placement, results in inaccurate tunnel localization on a true lateral radiograph, and this inaccuracy is perpetuated with aberrant radiography. Aberrant lateral knee imaging of as little as 5° off-axis from true lateral has a significant effect on placement of a commonly used radiographic point relative to the anatomic MPFL femoral attachment center and results in nonanatomic MPFL tunnel placement.

CLINICAL RELEVANCE

This study demonstrates that radiographic localization of the MPFL femoral tunnel results in inaccurate tunnel placement on a true lateral radiograph, particularly when there is deviation from a true lateral fluoroscopic image, which can be difficult to obtain intraoperatively. Assessing anatomy directly intraoperatively, rather than relying solely on radiographs, may help avoid MPFL tunnel malposition.