Are Post-Reduction Changes in Femoral Head Perfusion an Indicator for the Development of Proximal Femoral Growth Disturbance in the Surgical Management of Developmental Dysplasia of the Hip?

Proximal femoral growth disturbance (PFGD) is a critical iatrogenic complication of surgical treatment for developmental dysplasia of the hip (DDH). Patients who develop PFGD are at an increased risk for developing considerable pain and functional limitations that may necessitate early hip replacement. Our understanding of PFGD in this patient population has been limited by discrepant reporting, small sample sizes, and differences in diagnostic criteria. Historically, this complication has been referred to as osteonecrosis: a vascular insult that can cause subsequent growth disturbance. Recently, discussion about the appropriateness of this terminology has initiated a shift toward using the term “PFGD.” The reported rates of osteonecrosis/PFGD vary widely, with much debate over the risks posed by the surgical approach and timing. Results from a global, prospective cohort of infants with DDH showed a 25% rate of osteonecrosis following closed reduction1 and a 44% rate following open reduction2, although longer-term follow-up is needed. Multiple factors have been associated with the development of PFGD, to varying degrees, but a clear picture of the risk profile remains elusive. It is well understood that PFGD results from a restriction of the blood supply to the femoral head; therefore, altered perfusion and/or trauma to, or compression of, the vasculature during or following surgical reduction likely play a critical role. Research using postoperative perfusion magnetic resonance imaging (MRI) has shown an association between decreased femoral head perfusion and the development of osteonecrosis/PFGD3,4. However, this pattern was only observed in half of the resultant osteonecrosis/PFGD cases3, and other studies have demonstrated conflicting results5. Thus, postoperative perfusion MRI currently has limited value in supporting clinical decision-making. The prospective study by Kebeh et al. explored the use of contrast-enhanced ultrasound (CEUS) as a tool for quantitatively assessing changes in perfusion to the femoral head from before to after surgical reduction for DDH. The study builds upon the authors’ previous proof-of-concept work with CEUS. The study included patients 4 to 18 months of age who required surgical management of DDH with either closed or open reduction. In total, 34 hips (32 patients) were included in the study, with 11 (32%) of the hips undergoing closed reduction and 23 (68%) undergoing open reduction. The mean age (and standard deviation) at the time of reduction was 9.3 ± 3.3 months. Given the relatively young cohort, it is surprising that over two-thirds of the cohort underwent open reduction. It is not clear whether closed reduction was attempted prior to open reduction, which may have influenced changes in perfusion. The authors report that 27 (79%) of the 34 hips had a decrease in CEUS-measured perfusion following reduction, with a significant 56.2% decrease in the mean perfusion index (PI). Peak enhancement (PE) and time to peak concentration (TTP) were also impacted, with the change in PE being significant (p = 0.01). Notably, the remaining 7 hips showed an 84.9% increase in mean PI. However, the absolute post-reduction mean PI in the decreased perfusion group was still greater than that in the increased perfusion group (2.3 and 1.6, respectively), although the significance of this difference is unknown, as a test was not performed for this comparison. Of the 4 regions of interest studied, the central region of the femoral head epiphysis was the most impacted by decreased perfusion (PI, p = 0.002), followed by the peripheral region (PI, p = 0.03). Although most of the patient factors reported in this study (including International Hip Dysplasia Institute grade, age, the presence of an ossific nucleus, and surgery type) were not significantly associated with perfusion changes, a larger axial abduction angle was associated with decreased perfusion (PI, p = 0.04). It would be interesting to utilize CEUS to examine whether subsequent changes in positioning resulted in a recovery of perfusion. Taken together, it appears that all hips in the cohort had changes in perfusion following surgical reduction. This suggests that perhaps it is not the immediate post-reduction perfusion changes that are critical to understanding the development of PFGD. Reperfusion and the tissue response to transient ischemia are presumably also critical factors in the development of PFGD. Therefore, follow-up CEUS examinations would be important. These were not included in the study, which limits the ability to draw meaningful conclusions from the current results. Despite almost 80% of hips showing a significant decrease in perfusion after reduction, it is likely that only a few of these hips may actually go on to develop clinically relevant PFGD. Although this study demonstrates the capacity of CEUS to quantitatively assess changes in femoral head perfusion from before to after surgical reduction for DDH, the sample size was small, and long-term follow-up will be critical to determine whether any correlation exists between changes in femoral head perfusion and the development of PFGD.