Novel Prenatal Sonographic Scoring System Lowers False Positive Diagnosis of Clubfoot

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.

  Michael P. Glotzbecker
  Michael P. Glotzbecker

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.

“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 eidentified 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.

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

For more information:

  • 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.


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

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