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A three-dimensional Fourier transform magnetic resonance imaging technique is presented. This procedure can be used to selectively detect flowing material such as blood in arteries and veins. Since flow is detected in a manner in which velocity-induced phase shifts are compensated, signal loss arising from complex flow and turbulence is minimized. The flow image is sensitive to all velocity components of flow. Applications of this technique are limited, however, to relatively straight vessels having appreciable flow. Examples of application of this technique to healthy and diseased carotid arteries are shown.

PurposeThe purpose of this study was to identify the causes of failure of previous medial patellofemoral ligament reconstruction (MPFL‐R), and to furthermore report the surgical techniques available for MPFL revision surgery. MethodsFour databases [PubMed, Ovid (MEDLINE), Cochrane Database, and EMBASE] were searched until September 29, 2020 for human studies pertaining to revision MPFL. Two reviewers screened the literature independently and in duplicate. Methodological quality of the included studies was assessed using the Methodological Index for Non‐Randomized Studies (MINORS) criteria, or the CAse REport guidelines (CARE), where appropriate. ResultsFourteen studies (one level II, one level III, two level IV, ten level V) were identified. This search resulted in a total of 76 patients with a mean age (range) of 22 (14–39) years. The patients were 75% female with a mean (range) time to revision of 24.1 (1–60) months and mean (range) follow‐up of 36.2 (2–48) months. The most common indication for revision surgery was malpositioning of the femoral tunnel (38.1%), unaddressed trochlear dysplasia (18.4%), patellar fracture (11.8%). Femoral tunnel malposition was typically treated via revision MPFL‐R with quadriceps tendon or semitendinosus autograft and may retain the primary graft if fixation points were altered. Unaddressed trochlear dysplasia was treated with deepening trochleoplasty with or without revision MPFL‐R, and patella fracture according to the nature of the fracture pattern and bone quality. Though generally, outcomes in the revision scenario across all indications were inferior to those post‐primary procedure, overall, revision patients demonstrated positive improvements in pain and instability symptoms. Transverse patella fractures treated with debridement and filling with demineralized bone matrix if required with further fixation according to the fracture pattern. ConclusionThe most common causes of MPFL failure in literature published to date, in order of decreasing frequency, are: malposition of the femoral tunnel, unaddressed trochlear dysplasia, and patellar fracture. Although surgical techniques of revision MPFL‐R to manage these failures were varied, promising outcomes have been reported to date. Larger prospective comparative studies would be useful to clarify optimal surgical management of MPFL‐R failure at long‐term follow‐up. Level of evidenceIV.

A time-resolved phase contrast magnetic resonance angiography technique is described. This technique provides a series of angiograms obtained at different phases of the cardiac cycle. Such a series of angiograms can be used to evaluate blood flow dynamics. For example, turbulent flow in the regions of vessel bifurcations is easily demonstrated and followed during systole and diastole. Retrograde flow can also be observed. Dynamic angiography can be particularly useful in distinguishing transient image features, such as signal voids due to turbulent flow, from static features arising from vessel morphology.

PurposeThe purpose of this study was to examine the existing literature to determine the dimensions of the acetabular labrum, with a focus on hypotrophic labra, including the modalities and accuracy of measurement, factors associated with smaller labra, and any impacts on surgical management. MethodsFour databases (PubMed, Ovid [MEDLINE], Cochrane Database, and EMBASE) were searched from database inception to January 2020. Two reviewers screened the literature independently and in duplicate. Methodological quality of included papers was assessed using the Methodological Index for Non‐Randomized Studies (MINORS) criteria. Where possible, data on labral size were combined using a random effects model. ResultsTwenty‐one studies (5 level II, 9 level III, 7 level IV) were identified. This resulted in 6,159 patients (6,436 hips) with a mean age of 34.3 years (range 8.4–85). The patients were 67.3% female with an average follow‐up of 57.3 months. There was no consistent definition of labral size quoted throughout the literature. The mean width on MRI/MRA was 7.3 mm (95% CI 6.9–7.8 mm), on computed tomography arthrography was 8.7 mm (95% CI 8.0–9.3), and during arthroscopy was 5.0 mm (95% CI 4.9–5.2). Inter‐observer reliability was good to excellent in all modalities. Labral hypotrophy may be associated with increased acetabular coverage. Hypertrophic labra were highly associated with acetabular dysplasia (r = − 0.706, − 0.596, − 0.504, respectively; P < 0.001). ConclusionLabral width can reliably be measured utilizing imaging techniques including magnetic resonance and computed tomography. The pooled mean labral width was 6.2 mm, and height 4.6 mm. The establishment of a gold‐standard of measurement on arthroscopy and advanced imaging would aid in clinical decision‐making regarding treatment options for patients presenting with a painful hip, particularly those with hypoplastic labra, and provide radiological guidelines for standardized labrum size classifications. Level of evidenceLevel IV.