Of the 97 patients diagnosed with CMT that had hip imaging available, 12 % (12/97) were found to have hip dysplasia that required treatment. This falls within the wide range of rates previously reported in the literature, 0–20 % [1–19], but is higher than rates where only cases of DDH that required treatment were included, 0–8.5 % [3, 6, 7, 13, 19]. The wide variability in coexistence rates had been largely attributed to differences in methods, definitions, and diagnostic criteria , and this study is no exception. Additionally, this rate may be higher because we did not include patients with CMT who did not have hip imaging available in our system, which may have lowered the rate. However, one of our goals of the study was to determine whether there are patients with CMT who require hip imaging to reveal DDH requiring treatment (versus clinical exam alone); therefore, we decided to exclude those patients without imaging. Despite the wide range of coexistence rates reported in the literature, there is a growing body of evidence supporting the existence of an association between CMT and DDH, which is important for the clinician to be aware of when treating patients with either of these diagnoses.
There is general agreement that patients with CMT should be screened for DDH [6–8, 12, 15, 19]. However, there is no consensus as to whether routine screening should consist of physical exam and imaging of the hips, or physical exam alone. The most recent studies suggest that physical exam alone is sufficient screening, given that all the patients in their series with DDH had an abnormal clinical hip exam [6, 19]. Of the 12 % of patients with CMT and DDH, only 75 % (9/12) of our patients with DDH had an abnormal clinical hip exam. However, excluding the two patients who were previously treated for DDH, nine out of ten patients (90 %) with DDH had an abnormal physical exam. The argument could be made that adding imaging of the hips to routine screening is unnecessary, since the overwhelming majority present with abnormal physical exam findings. However, there was one patient in our series who had DDH that required treatment who did not have any abnormalities on clinical exam of the hip. Although patients like this may be a rarity, stating that screening hip imaging in patients with CMT is not necessary may lead to a small number of cases of DDH that go undiagnosed.
Due to the fact that there were many patients in this series who were excluded due to the lack of hip imaging, we cannot establish a true false-negative rate. Nevertheless, the presence of any false-negative exam supports the need for radiographic screening in this high-risk patient population.