To evaluate the inter-observer and inter-method reliability for patellar height
measurements between conventional radiographs (CR) and magnetic resonance
imaging (MRI) using 1 or 2-slices.
Reliability study; with 60 patients divided in two groups: 30 patients with
patellar instability (patella group) and 30 patients with anterior cruciate ligament or
meniscus injury (control group). CR and MRI were evaluated by two independent
observers. Insall-Salvati index (IS) and Caton-Deschamps index (CD) were measured
using three different methods: CR, 1-slice MRI or 2-slices MRI. Intra-class correlation
coefficients (ICC) were calculated for inter-observer reliability and inter-method
reliability. Bland-Altman agreement was also calculated.
The inter-observer reliability was very good for the IS with ICCs of 0.93, 0.84
and 0.82, for the CR, 1-slice MRI and 2-slices MRI, respectively. Similarly, for the CD
the ICCs were good, 0.76, 0.80 and 0.75 for the CR, 1-slice MRI and 2-slices MRI,
respectively. No differences were found between the patella and the control group. The
inter-method analysis results were: ICCs for IS (0.83, 0.86, 0.93) and CD (0.72, 0.82,
0.83), for the comparisons of CR/1-slice MR, CR/2-slices MRI and 1-slice MRI/ 2-slices
MRI, respectively. The Bland-Altman mean differences showed an 8% and a 7%
increase on IS values with 1-slice MRI and 2-slices MRI compared to CR results, while
the increase was of 9% and 1% in CD for the respective comparisons with CR.
MRI can overestimate patellar height compared to CR, as much as an 8%
increase in Insall-Salvati values when using 1 or 2-slices MRI measurements, and up to
a 9% increase in Caton-Deschamps value when using the 1-slice MRI method. It is
recommended to use the CR as the preferred method when measuring patellar height.