SLS can potentially reduce cost and operative time. The impact of caring for the child with hip spica is substantial and has been quantified in the literature, and SLS has been shown to ameliorate the burden on the family [4, 5]. Hughes et al., examined the course of treatment on a 23 pediatric femoral fractures, where DLS was used, and they found a mean of 3 weeks of time off work by one of the working parents until adequate care arrangements could be made. The family’s greatest concern was transportation [11]. In a review of 45 patients who were put on SLS for pediatric femoral fractures, Epps et al., noted that 80% of the parents had missed an average of 2 weeks from work for the care of their child, and only 50% of children continued school or daycare [3].
Historically, postoperative casting protocols for DDH varied greatly in the literature. For example, Dega used DLS for 4 weeks, then the pelvic part is cut, and after a total of 6 weeks the entire cast was removed [12]. Pemberton used DLS for 2 months without any alteration during the casting period [13]. In addition, Salter recommended 6 weeks of single-leg casting followed by 4 weeks of bilateral toe-to-groin casts with an abduction bar [14]. In the present study, the redislocation rate was higher in the DLS group, but differences were not significant.
In contrast to DDH, there are a few reports on pediatric low-energy femoral fractures comparing SLS to DLS. Jaafar et al., retrospectively reviewed their experience in a cohort of pediatric femoral fractures in 59 subjects that had SLS and compared them to 35 patients in the DLS group over a period of 4 years. The SLS group had a lower rate of leg length discrepancy. Risk of loss of reduction was similar for both casting techniques [7]. In a randomised trial of pediatric femoral fractures, Leu et al., compared 24 patients in the SLS group with 28 patients in the DLS group. The authors found statistically significant more SLS adaptability to car seats and chairs as well as less time off work for the parents. For DLS the mean time off work by caregiver, was 19 and 10 days for the SLS [5]. Earlier, in a prospective cohort by Flynn et al., 19 patients were treated with SLS and 26 were treated by DLS. There was significantly less impact on the family reported score and the need for ambulance transportation with SLS [4].
Four patients (3.1%) had osteopenic fractures in this study, although this was not as common as fractures in chronically ill patients; caregivers may need to be aware of this risk. Fractures after casting for DDH are not extensively documented in the literature. Szalay and colleagues found one z score drop after 4–6 weeks of postoperative immobilisation or non-weight bearing in 15 orthopaedic patients. This was based on measurements from the distal femur, and most of the bone mineral density loss was in the cancellous bone and transitional regions [15].
Stability of the hip as defined by MP was not markedly different between the two groups. Based on the original work of Reimers, in patients with neuromotor hip disorders, MP was strongly correlated with the center edge angle of Wiberg. In the same landmark paper, 355 measurements were taken from urographic studies of children with no hip disease, and the highest recorded values were 29%. This cut-off value was used in the current study to indicated suboptimal femoral head coverage [9]. Careful longer-term follow-up is needed to ascertain satisfactory remodelling in hips showing higher values.
Five of the DDH patients required unscheduled trips to the operating room. In a study by DiFazio et al., 300 spica casts for pediatric femoral fractures were reviewed, and 24 patients required an unplanned trip to the operating room for cast change and 77 had skin complications [16]. None of the subjects in this study had wound care for skin ulcers, but our database is not sensitive to minor cast-related skin complications, mainly because a large proportion of the patients seek medical attention, and get cast trimming and padding at facilities near where they live.
This study has several limitations; it probably lacks adequate power to detect small differences in displacement rate between the two groups. It is somewhat assuring, however, that the redislocation rate was lower in the SLS group. Post hoc power analysis showed adequate power (> 80%) if a conventional margin of 10% was computed, but a 10% margin would be considered high by many. Stiffness was not studied as an outcome measure in this report for several reasons. These reasons were mostly due to the rarity of stiffness in children, the need for longer follow-up, inconsistent documentation and the poor reliability of current measurement tools [17].
Data presented here have a direct impact on DDH patients and their caregivers. Therefore, further research addressing the limitations of the current work is suggested. Moreover, the precise role of percutaneous pinning with casting in maintaining hip stability is unknown and the duration of immobilization remains empirical and could be elucidated in the future. In conclusion, SLS casting may be used after unilateral DDH open reduction procedures, without increasing the risk of early hip instability.
