The knowledge of the changes of the rotational profile of the lower extremities with increasing age is of much interest to paediatric orthopaedic surgeons. The treatment guidelines in many torsional deformities of the lower extremities is dictated by the expectation that improvement is likely if the established and documented normal pattern of changes in the rotational profile with increasing age should occur.
This study was to determine the normal values of the rotational profile of the lower extremity in children aged 3-10 years. The clinical method described by Staheli2 was used to assess the foot progression angles while the clinical method described by Cheng3 was used in assessing both the hip rotation and the thigh foot angles in 492 Nigerian children within the 3-10 years age group residing in Benin City. This method is cheap, reliable, and reproducible and avoids exposure of the children to radiation. It can also be used for practical day to day clinical practice. Ethical consideration and cost preclude a large scale radiological study of healthy children.
FOOT PROGRESSION ANGLE
In this study, the FPA varied with age. Majority of the children (89.8%) exhibited an outtoeing FPA. The mean FPA is higher among the 3 and 4 year old and this finding is consistent with similar findings by other investigators 43. The mean FPA of 11.6˚ and 12.0˚ observed for the 3 year old male and female children respectively as well as the mean of 12.4˚ and 13.0˚ which were noted
for the 4 year old male and female children respectively is in consonance with the findings of Scrutton et al43 but at variance with the slightly lower mean FPA of 10˚ recorded for both male and female children by Staheli et al2.The discrepancy in values may possibly be due to the difference in the populations sampled in these studies.
THIGH -FOOT ANGLE
The mean TFA in the 3 years old group of male and female children were 3.7˚
and 5.0˚ respectively with this value increasing to 15˚ at 10 years in both male and female alike. This observation is in keeping with similar studies by Cheng3, Staheli2, and Odatuwa-Omagbemi7 and supports the fact that lateral tibia torsion tends to occur with increasing age. The figures for Chinese children as documented by Cheng3 are higher by 15-20˚ when compared to the finding in this study. This difference can be attributed to racial differences as the methods used for the measurements were essentially the same. This study also observed that on the average females exhibited about 1˚ more outtoeing than males, a finding that supports the earlier observation by Odatuwa-Omagbemi7.However this difference in the TFA between the sexes is not statistically significant which is in line with the findings of other workers2,3,7.
MEDIAL HIP ROTATION
The mean MHRA in the 3 year old male and female children were 40˚ and 41˚
respectively with the values increasing to 46˚ in the male children and 49.6˚ in the female children. The observed increase with age is in keeping with studies by Cheng3, Staheli2 and Odatuwa-Omabgemi7.The female children in this study
exhibited 6˚ more medial rotation than males of the same age and this was similar to the 7˚value obtained by Staheli2 and Odatuwa-Omagbemi7, although Cheng3 observed only 4˚more medial rotation in female than the male children. The gender discrepancy in the MHRA values was not statistically significant in this study. This contrasts with the measurements carried out by Cheng3 and Staheli2 who noted a statistically significant difference in the male and female MHRA values. The difference in findings between the studies may be due partly to the large population sampled by Staheli et al2 and Cheng et al3 and partly to some female genetic disposition which was highlighted in their works2,3.
LATERAL HIP ROTATION
The generally observed trend of decreasing lateral hip rotation with increasing age in this study supports similar reports by other workers2, 3, 7. The mean LHRA in this study for male children was 52.1˚ which decreased to 42.0˚ at 10 years while female children had a mean of 50˚ at 3 years which decreased to 40˚ at 10 years. These findings are consistent with the mean of 55˚ lateral hip rotation at 3 years which decreased to 40˚ at 10 years for both sexes as reported by Staheli et al2 for Caucasian American children .In addition this study indicated that male children showed an average 2˚ more lateral hip rotation than the female children which is similar to the observation by Cheng in Caucasian American children. The male children exhibited an average of 3˚
more lateral hip rotation than females in the Odatuwa-Omagbemi7 study of Nigerian children in Lagos. The reasons for these variations are unclear as similar methods were used for the assessment of the children in these studies.
TOTAL ARC HIP ROTATION
The total arc hip rotation angle is a sum of the MHRA and the LHRA .It reflects the arc of hip rotation which essentially shows minimal changes as documented by other workers on this subject. An average total hip rotation angle of 88-91˚ for male children and 90-95˚ for female children was obtained in this study. The above findings are not remarkably different from the total hip rotation angles of 80˚ and 83˚ for male and female Chinese children as reported by Cheng3. This study also supports the total hip rotation angles of 95-110˚ for both sexes in Caucasian American children as recorded by Staheli et al2. The observed higher values in female than male children may be related to the influence of sex hormone induced changes as regards ligamentous laxity and the peculiar developmental changes in the female pelvis.
CONCLUSION
In this study the foot progression angle reduces as the thigh foot axis becomes more lateral with increasing age. Medial hip rotation increases while lateral hip rotation decreases, the total hip rotation however changes very minimally as the children advance in age irrespective of their gender. The recorded normal values in this study corroborate similar findings in the children from other environments although with some slight variations.
It is therefore hoped that the values documented in this study would serve as reference data to guide the assessment of rotational problems in Nigerian children residing in Benin City. Being mindful of the scope and sample size of this study, further studies are encouraged with a larger population size to validate these values.
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APPENDIX 1
LIST OF ABBREVIATIONS
FPA-FOOT PROGRESSION ANGLE TFA-THIGH- FOOT ANGLE
MHRA-MEDIAL HIP ROTATION ANGLE LHRA-LATERAL HIP ROTATION ANGLE TMA-TRANSMALLEOLAR AXIS
SD-STANDARD DEVIATION CV-COEFFICIENT OF VARIATION CT-COMPUTERIZED TOMOGRAPHY MTA-METATARSUS ADDUCTUS
IFA-INCREASED FEMORAL ANTEVERSION ITT-INTERNAL TIBIAL TORSION
TAHR-TOTAL ARC OF HIP ROTATION