Vertical Relationship Ratio (VRR): A High Reliability and Accuracy Radiographic Measurement for Basilar Invagination in Rheumatoid Arthritis

BACKGROUND Previous radiographic measurements for diagnosis of a basilar invagination or impression (BI) in rheumatoid arthritis (RA) were used as reference values based on anatomical reference distances. Due to the obscured anatomical landmarks, our group proposed a new radiographic measurement based on anatomic ratios to identify BI. MATERIAL AND METHODS The vertical relationship ratio (VRR) was developed and evaluated. The VRR is the relationship between the distance obtained with the modified Ranawat method and the C3 vertebral body height. VRR was used to assess its ability to distinguish BI in 3 patient groups (28 RA with BI, 37 RA without BI, and 56 non-RA patients). The intra- and inter-observer reliability, the sensitivities, and specificities of all measurements were analyzed. The cutoff value of VRR measurement was calculated by using the receiver operating characteristic (ROC) curve. RESULTS The VRR measurement showed excellent intra- and inter-observer reliabilities. The VRR could significantly distinguish RA patients with BI from RA patients without BI. The mean VRR of RA patients with BI (1.82±0.20) was less than for the non-RA patients (2.26±0.19) and the RA patients without BI (2.24±0.19). The cutoff value of VRR from the ROC curve was below 2.025. Its sensitivity was 92.85%, specificity was 97.85%, positive predictive value was 92.86%, and negative predictive value was 97.84%. CONCLUSIONS VRR has excellent intra-/inter-observer reliability and can distinguished BI in RA patients. We recommend using VRR in preference to the other available methods for assessment and screening BI in rheumatoid arthritis.

Prediction of Callus Subsidence in Distraction Osteogenesis Using Callus Formation Scoring System: Preliminary Study

OBJECTIVE

To develop the scoring system which describes both quality and quantity of callus formation to predict the callus subsidence.

METHODS

Forty-seven bony segments with an average lengthening of 5.17 ± 2.83 cm were included. The score was calculated based on the amount of callus classified in five patterns and the summation with the density of the callus classified in four patterns; the total score was 9. Bony subsidence >10% or >10° angulation were considered significant. We analyzed all of the data to find the most appropriate score that would prevent callus subsidence <10% and prevented angulation of the regeneration bone <10 degrees. Data was analyzed by using the receiver operating characteristic (ROC) curve. An area under the curve of 0.9-1 indicated an excellent test, 0.8-0.9 indicated a good test, 0.7-0.8 indicated a fair test, 0.6-0.7 indicated a poor test, and 0.5-0.6 indicated a fail test. The appropriate score for Ilizarov removal was selected from the highest sensitivity and specificity.

RESULTS

Twenty-two tibia segments and 25 femur segments were included. The mean of bone lengthening was 5.17 ± 2.83 cm (range, 1.6-13.5 cm) and the mean of percentage lengthening was 16.58% ± 10.03% (range, 4.63%-56.84%). The mean distraction period was 5 months. The average months of follow-up for measurement of bony subsidence was 4.2 months. Mean subsidence was 21.06% (1.54%-57.44%). The mean of callus subsidence was 1.29 ± 1.17 cm (range, 0.03-4.72 cm). There were 32 segments (68%) with callus subsidence greater than 10% and 15 segments (32%) with subsidence less than 10%. The callus subsidence ranged from 0.3 mm to 4.72 cm, with 68% of bony fragments having significant subsidence. Type 5 callus diameter was statistically significant (P < 0.0001) in preventing callus subsidence compared to the other types. Type 4 callus density was statistically significant in preventing callus subsidence compared to the other types (P < 0.0001). The ROC curve with area under the curve 0.961 and sensitivity 0.933 showed that a callus scoring system score >7.5 was effective in preventing significant callus subsidence. When using score 8 as a result from the ROC curve, 73.3% of bony fragment subsidence was <10% with sensitivity 93.3 and specificity 83.2.

CONCLUSION

Callus diameter 81%-100% and callus density type 4 could prevent significant callus subsidence. Based on the results of the present study we suggest using callus score > 8 to determine the time of Ilizarov removal.