MRI KNEE BONE AGE: A NOVEL SHORTHAND APPROACH TO REDUCE BONE AGE RADIOGRAPHS IN CHILDREN

Abstract

Background:

Determining bone age in skeletally immature patients is critical for proper management and surgical planning. Pennock et al. recently created and validated a bone age atlas using the ossification pattern of the knee on MRI in pediatric patients, obfuscating the need for a hand radiograph and its associated cost, radiation exposure, and clinical inefficiency.

Hypothesis/Purpose:

We sought to validate and demonstrate reliability of a novel shorthand method of bone age determination using knee MRI across multiple levels of medical training.

Methods:

We identified patients who underwent knee MRI and hand bone age radiograph within a ninety-day period. In collaboration with a pediatric musculoskeletal radiologist, stepwise algorithms for predicting bone age on knee MRI were developed- one for males and one for females. Six raters at varying levels of training used the algorithm to assign a bone age for each patient. Intraclass correlation coefficient (ICC) was used to compare each rater’s predicted knee bone age to the Greulich and Pyle (G&P) hand bone age and validate the shorthand algorithm. Inter-rater reliability was also calculated using ICC.

Results:

Thirty-eight patients (44.7% female) underwent a knee MRI at a mean age of 12.8 years (range 9.3-15.7). The mean time between hand bone age x-ray and knee MRI was 20.2 days (range 0-88). The inter-rater reliability for the application of our shorthand algorithm was 0.81 (95% CI: 0.72 – 0.88), indicating good inter-observer agreement. The shorthand methos was shown to be a good predictor of G&P hand bone age, both for each individual rater (ICC range: 0.73 – 0.80) and the mean knee MRI bone age across all raters (ICC 0.81; 95% CI 0.65 – 0.90). It was also shown to be a consistent predictor of hand bone age across level of training, as medical students (ICC 0.77, 95% CI 0.60-0.88), residents (ICC 0.80, 95% CI 0.65-0.89), and attending physicians (ICC 0.80, 95% CI 0.63-0.89) all achieved strong correlation between predicted knee MRI bone age and G&P hand bone age.

Conclusions:

This novel shorthand algorithm is a reliable and valid way to determine skeletal maturity using knee MRI. It can be utilized clinically across different levels of radiographic and orthopaedic expertise and reduces the need for hand bone age radiographs and consequential radiation exposure in children.

Figure 1.

Shorthand Algorithm for Knee Bone Age Using MRI for Males

Figure 2.

Shorthand Algorithm for Knee Bone Age Using MRI for Females

Table 1.

Correlation between knee MRI bone age and hand radiograph bone age (G&P) for each rater, as determined using intraclass correlation coefficients (ICC).

Rater	ICC	95% CI
Student 1	0.75	0.57 – 0.86
Student 2	0.73	0.53 – 0.86
Resident 1	0.73	0.54 – 0.85
Resident 2	0.78	0.60 – 0.88
Attending 1	0.74	0.54 – 0.85
Attending 2	0.80	0.63 – 0.89
Mean	0.83	0.68 – 0.91