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Novel prenatal sonographic scoring system lowers false positive diagnosis of clubfoot
The system gives physicians a way to be more confident about clubfoot diagnoses.
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Initial experiences with a new prenatal sonographic scoring system show improved prenatal detection of a true clubfoot and a decrease in the false positive rate, according to a recently presented study.
The findings were presented by Michael P. Glotzbecker, MD, at the 2010 Annual Meeting of the American Academy of Orthopaedic Surgeons in New Orleans.
Glotzbecker noted that improvement in obstetric ultrasound has led to an increased prenatal detection of clubfoot, but studies have not yet been able to correlate sonographic severity to clinical severity at birth.
“The literature is quite variable with regards to diagnosis, and the false positive rate is quite variable as well, ranging anywhere between 0 and 29%,” he said.
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A new classification system
“The classification system … [is based on] looking at the long axis of the tibia in an AP view, as well as the long axis of the foot,” Glotzbecker said. “In a normal foot, when you look at the AP view of the tibia you should not see the long axis of the foot. With clubfoot, as it begins to turn in, you’ will see them in the same plane.”
Glotzbecker’s group retrospectively identified fetuses scanned at their institution and diagnosed with clubfoot. Seventy-five newborns met the proper criteria for the study. Of these 75 who had a positive ultrasound, 60 had a confirmed clinical diagnosis. A novel sonographic severity scale was assigned to each study while being blinded to clinical scores.
Reducing false positive rates
Patients classified as “mild” on prenatal ultrasound for a given foot were significantly more likely to have a normal foot at birth than when a moderate or severe diagnosis was given. This decreased the false positive rate to 4/51.
“If you just expect that moderate or severe feet will actually have a true clubfoot, then our false positive rate drops below 10%,” Glotzbecker said. “Our new sonographic rating system was predictive of false positives for clubfoot. If you look at a foot that is classified as mild, then there is about a one-third chance that the patient will actually have a true clubfoot. If it is rated as moderate or severe, it has a 90% chance of being a true clubfoot.”
Glotzbecker added that being able to provide numbers like those found in the study would be a valuable tool for physicians trying to counsel expecting parents. — by Robert Press
Reference:
- Glotzbecker MP, Mahan ST, Estroff J, et al. Prenatally diagnosed clubfeet: Comparing ultrasonographic severity with objective clinical outcomes. Paper #647. Presented at the 2010 Annual Meeting of the American Academy of Orthopaedic Surgeons. March 6-9, 2010. New Orleans.
- Michael P. Glotzbecker, MD, can be reached at michael.glotzbecker@childrens.harvard.edu.
Clubfoot is a relatively common birth defect affecting 1.2 in 1,000 live births. The diagnosis is currently made in many cases during pregnancy using ultrasonography, which can generate a great deal of anxiety for the family. Unfortunately, current practices are associated with a number of false positive and negative diagnoses.
In this study, the authors evaluated a novel ultrasonographic severity scale designed to reduce inaccurate diagnosis. The investigators found that their classification improved the false positive rate, especially for mild cases, but it did not correlate with clinical severity at birth. However, the main limitation of the study is the lack of data related to the week when the ultrasonography was performed. Clubfoot is a fetal deformity that usually happens between 16 to 30 weeks, therefore, it is possible that if the ultrasound was done at earlier times, a milder case could have been diagnosed that could progress to a moderate or severe case. On the other hand, crowding at the end of the pregnancy is very common and can lead to positional foot deformities, so false positive results will be higher at this time. In conclusion, careful evaluation of foot position at every ultrasound visit is important and repeating the test at later weeks indicated in cases of concern.
– Jose A. Morcuende, MD, PhD
The Ponseti
Clubfoot Treatment Center
University of Iowa