Increased Femoral Anteversion Is not Associated with Internal Hip Rotation Gait in Cerebral Palsy

Christoph J Reichlin1,2, Stefan Thomas1,2, Reinald Brunner1,3 and Erich Rutz*1,3,4,5 1Pediatric Orthopaedics, University Children’s Hospital Basel, UKBB, Switzerland and University of Basel 2Department of Orthopedic Surgery and Traumatology, Kantonsspital Baselland, KSBL, Switzerland 3Laboratory for Movement Analysis, University Children’s Hospital Basel UKBB, Switzerland 4Murdoch Children’s Research Institute, The Royal Children’s Hospital Melbourne, Australia 5Department of Orthopedic Surgery and Traumatology, University Hospital Basel, USB, Switzerland


Introduction
Internal rotation gait (IRG) is a common problem in children with cerebral palsy (CP). A frequency up to 64 % has been reported [1]. It is a common doctrine that increased femoral anteversion (FAV) is one of the most important factors [2] causing IRG.
Other common factors thought to contribute are compensatory mechanisms for decreased abduction moment arm, increased muscle tone of hamstrings and/or adductors [3,4], increased muscle tone of the anterior glutei [5], increased internal rotation moment arms because of hip flexion deformity and maybe other factors as equinus of the foot [6]. But the underlying biomechanics and causes of IRG are not clearly identified. Therefore, it is not surprising that the various treatment options such as addressing soft tissue procedures and bony interventions reflect these ideas.
The femoral derotation osteotomy (FDO), proximal or distal, is the current standard treatment for IRG with the aim to correct the increased FAV. Pirpiris et al. reported excellent correction of rotation of the hip and foot progression angles in children with spactic diplegia comparing FDO at both levels, proximally or distally [7]. Besides the fact, that several outcome study reports are controversial (a recurrence rate of IRG up to 33% after FDO [8], or even higher with recurrence rate of 40% [9]) FDO is still the standard procedure for correction. Schwartz et al. reported that limbs with anteversion and significant internal hip rotation during gait benefit from an FDO, but limbs with excessive FAV and only mild internal hip rotation are at risk of developing an excessive external foot progression angle [10]. The aim of this study was to investigate if there is a correlation between FAV and IRG for the stance phase during gait in patients with CP.

Materials and Methods
Medical records and gait laboratory data were reviewed retrospectively. All children with CP who were scheduled for multilevel orthopedic surgery between February 2008 and April 2011 were included in this study. All participants had a preoperative  [12] was used and at least 6 trials were recorded. Anthropometric data were recorded for appropriate scaling. Surface EMG was recorded simultaneously. Bipolar Ag/AgCl surface electrode pairs (electrode diameter 10 mm and an inter-electrode spacing 22 mm) were placed bilaterally over the medial gastrocnemius, tibialis anterior, rectus femoris, and semitendinosus muscles. For electrode placement, the SENIAM recommendations for surface EMG were followed [14].
The ground electrode was placed over the tibial tuberosity. The EMG signals were band-pass filtered (10-700 Hz) and collected at a sampling rate of 2500 Hz. All data were expressed as a percentage of gait cycle using the Polygon software (Oxford Metrics Ltd., UK).
From the 3D gait data temporalspatial parameters (cadence, stride length, and walking speed), the Gillette Gait Index (GGI), the Gait Deviation Index (GDI), the Movement Analysis profile (MAP) and the Gait Profile Score (GPS) were calculated for all patients pre-and postoperatively for group I and II separately [15][16][17]. For statistical analysis first a Shapiro-Wilk normality test was performed to verify that the data met the assumptions of a parametric test. The Pearson and Spearman rho correlation coefficient was calculated to analyze the correlations between normally and not-normally distributed data, respectively. The level of significance for all tests was set at p ≤ 0.05.

Results
The analysis of the data showed a calculated rFAV of 37. Interestingly there was no correlation between rFAV and HIR (r = 0.02, p = 0.85), see Figure 1. The results are summarized in Table 2.  Note: Data highlighted in yellow are normally distributed. The first row shows the rho-correlation coefficient (r), the second the level of significance (p) respectively.

Discussion
Although FAV is commonly thought to be one of most important factors for IRG, our data do not show any correlation between radiologically assessed rFAV and HIR during stance phase assessed by 3-DGA in patients with CP. This result suggests that IRG may be independent from FAV. Indeed, it has been shown by modelling that FAV is a reaction on the external forces on the growing hip in CP [18]. It may even be questioned whether FAV persists after birth or whether it is a reactive shape according to the acting forces.
The doctrine that the IRG is a compensatory mechanism to restore the abduction lever arm of the gluteus medius in patients with increased FAV [19] is in our opinion still debatable. Other results, such as the high recurrence or persistence rate of IRG after FDO [8,20] and studies on biomechanical connections [6,21] also argue for the existence of other factors influencing the rotation during gait in CP.
Our results confirm the hypothesis that there is no correlation between FAV (rFAV and cFAV) and HIR in the majority of patients with CP. Even if there would be a secondary bony deformation due to pathological forces, a correlation between FAV and IRG should have been obvious. In contrast to the studies of Kim et al [20] and de Morais Filho et al [8], where the FAV was measured in clinical examination and intraoperatively, we calculated the rFAV by standardized anteroposterior pelvic radiographs and the Dunn projection and took it as relevance value for FAV. In our study the rFAV and the cFAV did not correlate, which shows a limitation of one of the procedures and support the findings of Sangeux et al. [22]. The Dunn and ap assessment were favored against CT-scan torsional studies because it permits a picture where both levels are shown simultaneously. In CT scans in contrast, CP patients are not reliable to lie steadily and not rotate the leg internally between the scans.

Conclusion
Our results do not support the common doctrine that FAV is the most important factor which causes internal hip rotation during gait in cerebral palsy. There was no correlation between hip internal rotation during gait in cerebral palsy and real femoral anteversion determined radiologically. The latter, however, correlates with maximal hip internal rotation during clinical assessment with the hips extended. Distally, external tibial torsion in contrast correlates negatively with internal hip rotation and foot progression from 3-DGA. Therefore, other factors such as indirect effects resulting from spastic equinus [6] must be considered as a cause of hip internal rotation during gait.