Identificador: TDX:606
Autores: Escala Arnau, Joan Salvador
Resumen:
TESI DOCTORAL (DR J.S. ESCALA ARNAU).MRI has become the non invasive method of choice for the evaluation of internal derangements of the knee and has been advocated as a useful test in the evaluation of objective patellar instability (OPI).The purpose of our study was to evaluate and compare the diagnostic utility of multiple quantitative parameters as measured on knee MR examinatios of patients suffering OPI. We chose to evaluate several of the primary predisposing factors, namely trochlear dysplasia, patella alta and increased lateral patellar tilt. Special emphasis was put on the evaluation of the patellar nose.We performed a retrospective evaluation in a large and uniform group of 59 knees with clinically proven OPI and in a control group of 71 knees. Both groups were matched by age and sex.All OPI knees had presented recurrent patellar dislocation, which was documented by reduction in the emergency department or by a convincing history associated with suggestive clinical and radiographical signs.In all control knees, anterior cruciate ligament tear, patellofemoral disabilities, fractures, prior surgery or anterior knee pain were sistematically ruled out.In the OPI group, we used axial and sagittal T-1 weighted sequences. In the control group, we used axial T1-weighted or gradient-recalled-echo T2-weighted sequences and sagittal fast dual-echo MR sequences.The knee MR examinations belonging to both groups of patients were randomly mixed for imaging review. Various categories of quantitative parameters were evaluated using rulers, scales, squads and a hand-held goniometer. Where necessary, the contour of the articular cartilage was systematically used as the reference plane. As suggested by Staubli, this may be crucial because the chondral surface of the trochlear groove and patellar facets does not coincide with the contour of the subchondral bone. In the midsagittal MR section, among other things, we measured the ventral trochlear prominence, the patellar tendon length, the Caton-Deschamps index and the Insall-Salvati index.In the midsagittal MR section, we also evaluated the patellar morphology by measuring the patellar nose and the patellar nose ratio. We also calculated the morphology ratio as described by Grelsamer.Two different MR sections were used for the measurements in the axial projection. The first was through the most cranial aspect of the trochlear groove where we identified the cartilage. The second, was through the roman arch. In the axial view, we basicaly evaluated the trochlear groove depth, the lateral trochlear inclination and the lateral patellar tilt.As previusly reported, we found that OPI knees tend to have shallower trochlear groove, higher patella and larger patellar tilt than control knees.The most sensitive measurements:-With a cut-off value over 11º, the lateral patellar tilt had a sensitivity of 93%-With a cut-off value under 5 mm, the trochlear groove depth at the roman arch had a sensitivity of 86%.-With a cut-off value over 1.2, the Insall-Salvati index had a sensitivity of 78%. The most specific parameters, were:-With a cut-off value under 1.2, the morfology ratio had a specificity of 87%-Whith a cut-off value under 9 mm, the patellar nose had a specificity of 85%-With a cut-off value over 50 mm the patellar tendon length had a specificity of 85%.In a radiological study, Grelsamer found that the sagittal patella can have three distinct morphologies: type I, type II with a long patellar nose and type III with a short patellar nose. In our study, a short patellar nose was present in 46% of OPI knees but only in 14% of control knees. In other words, those patients with a large patellar nose are unlikely to suffer OPI. On the other hand, those patients with short patellar nose -and especially those whose patellar nose ratio is under 25%-- may be considered to have a dysplastic patellar morphology. Therefore, this morphology predisposes for OPI.In conclusion: In the fist place, the trochlear depth at the roman arch is an excellent parameter for evaluating trochlear dysplasia in OPI knees.Secondly, the Insall-Salvati index is better than Caton-Deschamps index for evaluating patellar height in OPI knees.Thirdly, the patellar nose ratio is a very specific parameter for ruling out OPI.Then, the lateral patellar tilt is the most sensitive parameter.And finally, as you already know, the etiology of OPI is probably multifactorial. We believe that quantitative MRI may help to identify specific predisposing factors in each individual, which in time may help us to plan appropiate surgery.
Repositori URV