Background: Tibial tuberosity trochlear groove distance (TT-TG) is an important radiological measurement in patellofemoral instability (PFI). Where instability is recurrent, a value ≥20 mm is considered an indication for tubercle medialisation. Trochlear dysplasia commonly accompanies PFI. It can make identification of the deepest part of the trochlea difficult, which makes the TT-TG difficult or impossible to assess. To address this, we propose a new method of identifying the deepest part of trochlea based on the femoral epicondyles. It is named the tibial tuberosity mid inter-epicondyle trochlea intersection distance (TT-MIELTI).
Methods: The TT-TG and TT-MIELTI of 30 consecutive non-dysplastic knee MRIs were compared, excluding 96 knees with dysplasia, sulcus angles ≥135°, a tibial tuberosity anterior cortex which was not fully demonstrated, artefact, fracture, or Osgood Schlatter's disease. To assess inter-observer reliability three blinded researchers measured the TT-TG and the TT-MIELTI of all 30 knees. To assess intra-observer repeatability one researcher repeated the measurements after six weeks.
Results: The intraclass correlation coefficient (ICC) test demonstrated good to excellent values for all measurements (TT-TG and TT-MIELTI correlation ICC 0.94-0.97; TT-TG inter-observer reliability ICC = 0.85, intra-observer repeatability ICC = 0.90; TT-MIELTI inter-observer reliability ICC = 0.86, intra-observer repeatability ICC = 0.89. All p values < .001.) CONCLUSIONS: In non-dysplastic knees the mid inter-epicondyle trochlea intersection (MIELTI) accurately identifies the deepest part of the trochlea, and TT-MIELTI is a reliable alternative to the TT-TG. Re-assessment in dysplastic knees would be of benefit to establish its usefulness in the clinical setting.
Keywords: Femoral epicondyles; Patellar instability; Tibial tuberosity; Tibial tuberosity trochlear groove distance; Trochlear dysplasia; Trochlear groove.
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