Treatment of DDH using the Pavlik harness is a widely preferred method in children younger than age 6 months. The short- or long-term success rate of Pavlik harness treatment is known to depend on some patient-related variables as well as the radiological grade of hip dysplasia [28, 29]. Nevertheless, as a result of lack of a higher number of studies with a high level of evidence, the exact effect of the some factors on the success rate of the Pavlik harness treatment seems to be controversial. We sought to assess the effect of patient-dependent variables and ultrasonographic hip type on the efficacy of Pavlik harness treatment in children younger than age 6 months.
There are some limitations of the present study. First, there might be a bias in exclusion criteria of the patients because the exact number of patients whose parents refused the treatment and who were lost to followup after the treatment was initiated could not exactly be provided. The ratio of excluded patients is approximately 15% among the entire population and we believe that it did not significantly influence our main findings. Second, the present study only focused on the instant success rate of Pavlik harness treatment and did not include midterm or long-term followup radiological and clinical outcomes. Third, defining the success of the treatment as “sonographic improvement of the dysplastic hip in a certain time period” could be against Pavlik’s own philosophy, which had encouraged individualizing the treatment of each hip and avoided time limitations during treatment . Fourth, the correlation between the success rate of Pavlik harness treatment and initial clinical findings was not assessed to avoid bias because the same physician did not perform all clinical examinations. Finally, we could not exactly determine the compliance of the parents to the treatment protocol, although all of them were initially informed in detail. It is well known that parents’ poor compliance in maintaining the harness on their children is one of the most important failure reasons of Pavlik harness treatment .
The reported overall success rate of Pavlik harness treatment in DDH ranges from 58% to 100% [1, 3, 6, 7, 9–16, 24, 25, 27]. In the present study, Pavlik harness treatment resulted in a favorable outcome in 71% of the patients. The results of the previous studies have shown that considerably higher success rates can be obtained if Pavlik harness treatment is started before the age of 2 to 3 months [3, 6, 9–11, 26, 31]. Bilateral involvement [3, 13, 26], having two or more risk factors for DDH , and male gender  are the reported patient-related variables that correlated with a higher rate of failure in Pavlik harness treatment. The results of the present study revealed that the treatment-starting age was the only patient-related variable, with older patients being much more likely to fail treatment. More than 90% of children younger than 3 months of age (37 of 40) were treated successfully, but that number dropped to approximately one-third when the patients were older than 5 months of age (nine of 24). An age of 4 months and older was found to be the threshold value that would increase the rate of failure in Pavlik harness treatment, and this cutoff had a sensitivity of 66% and a specificity of 77%.
The reported ultrasonographic predictors of failure or complications in DDH treated by the Pavlik harness are an initially lower α angle (< 43°), higher β angle, and a worse hip type (Graf Types III and IV hips) [1, 14, 31]. The reported success rate of Pavlik harness treatment in Graf Type III and IV hips is not as high as the other Graf hip types [3, 16, 21, 22, 25, 31]. The results of the present study revealed that both a lower initial α angle and a worse Graf hip type decrease the Pavlik harness treatment success rate. An initial α angle of 46° and less increases the possibility of failure and it has high specificity (86%). Pavlik harness treatment failed more than two-thirds of Graf Type III hips and two of four Graf Type IV hips in the present study. The cartilaginous acetabular roof is pushed downward by the dislocated femoral head toward the acetabulum in Graf Type IV hips, whereas it is pushed upward by the dislocated femoral in Graf Type III hips . Besides, adductor muscles adversely influence the reduction of a highly dislocated hip while the hip is in flexion and abduction in a Pavlik harness and a higher success rate of treatment should not be expected in such a hip [2, 12, 23]. These pathoanatomical differences explain the greater difficulty to succeed in dislocated hips . In a comparative study, better ultrasonographic outcome and lesser secondary treatment need were achieved by von Rosen splint treatment than by Pavlik harness treatment in Graf Types III and IV hips under the age of 4 months . Because controversy still exists on the efficacy of Pavlik harness treatment in Graf Type III and especially in Type IV hips, prospective comparative studies with larger samples seem to be needed for assessing whether primary Pavlik harness treatment is routinely indicated and for comparing the efficacy of different treatment modalities in such hips. There are few data on the success rate of Pavlik harness treatment in ultrasonographic hip types other than Graf Type III and IV hips. The reported treatment success rate with the Pavlik harness is higher in such hips [3, 9, 31]. The success rate of Pavlik harness treatment was more than 90% in Graf Type IIa- hips, approximately three-fourths in Type IIb hips, and approximately two-thirds in Types IIc and D hips in the present study. Besides, there was a considerable difference between the treatment success rates of stable and unstable hips. Approximately three-fourths of the unstable hips could not accurately be reduced within the required time by Pavlik harness treatment. In the remaining one-fourth, the deficiency in the acetabular bony roof did not heal within a certain time, although the femoral head was properly relocated into the acetabulum. Although Graf Type D hips were initially considered to be unstable, the treatment success rate in such hips was close to the one of stable hips in the present study. Because the acetabular bony roof in a Type D hip is not as deficient and the femoral head is not as displaced as in a dislocated hip, the difference between the treatment success rates of stable and unstable hips was mainly the result of Graf Types III and IV hips in the present study.
Femoral nerve palsy is one of the failure reasons of Pavlik harness treatment and has a reported incidence of 2.5% . In the present study, femoral nerve palsy was seen in two patients in whom complete recovery was observed after discontinuation of the harness.
We conclude that Pavlik harness treatment is more likely to fail in older infants, in hips having dislocation, and in hips with severely deficient acetabular bony roofs. The threshold age and α angle values associated with an increased risk of failure are 4 months and older and 46° and less, respectively. The parents of such patients should be informed about the high risk of treatment failure. We believe that, in such older patients and worse hip types, the use of an initial Pavlik harness treatment needs to be revisited. Future studies, comparing the outcomes of the Pavlik harness treatment and other types of interventions in such patients and hip types are needed.