Year : 2002 | Volume
: 36 | Issue : 4 | Page : 251--252
Accessory lower limb attached to the thigh- A case report
GN Khare, SK Gupta
Department of Orthopaedics, Institute of Medical Science, Banaras Hindu University, Varanasi, India
G N Khare
N-1/69-C , Krishna Bag Apartments, Nagwa, Lanka, Varanasi - 221005
|How to cite this article:|
Khare G N, Gupta S K. Accessory lower limb attached to the thigh- A case report.Indian J Orthop 2002;36:251-252
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Khare G N, Gupta S K. Accessory lower limb attached to the thigh- A case report. Indian J Orthop [serial online] 2002 [cited 2019 Sep 23 ];36:251-252
Available from: http://www.ijoonline.com/text.asp?2002/36/4/251/35944
Early splitting of one limb bud may result in an accessory limb attached to back (lumbosacral region) with associated spinal dysraphism  . However if the limb bud splits little latter the accessory limb would be attached to thigh rather than back. We report one such case associated with spina bifida, where the accessory lower limb was attached to left thigh and not to back. It is an extremely rare congenital anomaly.
A full term baby girl, weighting 2480 gm was born by uncomplicated vaginal delivery to a gravida II para I mother. There was no history of maternal illness, drug intake during pregnancy, any congenital anomalies in the family or consanguinity. At birth an accessory limb was noted attached to the left mid thigh. It continued to grow with growth of the child but the growth of the accessory limb was less compared to the normal limb.
Clinical examination revealed that the infant had an accessory lower limb arising from the left mid thigh and normal appearing lower limbs except for mild equinovarus deformity in left foot. The accessory limb had thigh, leg, knee and ankle joint and stump resembling foot. Sensations in the limb were normal. The limb had its bony attachment with femur. The thigh circumference was 1 ½ times as compared to the right thigh. The child had normal female external genitalia [Figure 1].
Plain X-rays showed that the limb had two long bones, proximal being bifid femur at mid shaft and distal being tibia [Figure 2(a)]. The femur was bifid like the inverted limb of 'Y' Xrays of lumbar spine showed spina bifida occulta at L4 -L5.
Surgery was performed when the baby was 10 months old. An elliptical incision was made around the base of the limb. The femur was osteotomised at its bifid junction and the limb was resected en mass [Figure 2(b)]. The skin flaps from around the base were used to provide adequate wound coverage. No definite neurovascular bundle could be identified. The postoperative recovery was uneventful and the baby was discharged after a week. The equinovarus deformity of the left lower limb was treated with corrective plaster casts.
A review of the literature revealed only 10 cases of a baby with a third leg associated with spina bifida. ,, In all these cases accessory limb was attached to the back (lumbo sacral or inter scapular area).
The morphogenesis of this rare malformation is not clear. Anomaly appears to be a spontaneous aberration of morphogenesis. A primary mesodermal defect involving both the early splitting of limb bud and adjacent paraxial mesoderm may explain the association of spina bifida with this anomaly.  It has also been proposed that the growth of the accessory limb occurs from a mesodermal blastema that is a result of dedifferentiation from Schwann cells. 
Animal studies  suggest that accessory limbs are caused by splitting and migration of the limb primordia due to mechanical factors. A very early splitting of one limb bud is expected to result in tripedid anomaly. No single exogenous factor can be identified as a causal agent. There are no reports of similar cases within the families of the infants born with these anomalies, which might suggest hereditary factors.
Except for the case described by Krishna et al  in which a rudimentary phallus and hyperpigmented scrotum like skin were present at the base of accessory limb, none of the reported cases have presented anomalies of the external genitalia. Interestingly, all cases except one reported by Chadha  were females.
In three patients the accessory limb was attached to the interscapular region and in seven to lumbosacral region. All the ten appendages including ours were well differentiated skeletal and musulotendinous tissues were more or less normally distributed and some degree of articulation was present in all cases. All of the accessory limbs so far described have contained neurovascular bundles except the case described by Chadha.  We also did not observe any neurovascular bundle in our case.
Single accessory limbs are difficult to classify in one category. Different authors have used different terms to classify these malformations. Although accessory limbs are often associated with malformations of the neural tube and/or gastrointestinal tract, it is difficult to classify them as cases of caudal duplication or incomplete twinning or dipygus. The later terms refer to infants born with two pairs of lower limbs and malformations of almost all organs lying below the transverse umbilical line. The term 'heterotopic redundancy' proposed to describe abnormal location of the accessory limb seems to lack specificity and fails to make reference to any associated malformations. Simply terming 'it 'tripedus' also does not justify the abnormal location. The terms 'Teratomata' 'fetus in fetus' and heteropagus' (incomplete parasite twinning) also seem to be inappropriate. In conclusion, the clearest and most complete terminological approach to these cases is, in our opinion, to refer to an accessory limb associated with other separately specified anomalies. 
Reviewing the hypothesis of Egar  and Gardner  , it is plausible that lipomyelomeningoceles are secondary neural tube defects that occur due to rupture of the neural tube under intact ectoderm. The leakage of the proteinaceous neural tube fluid acts as an abundant source of Schwann cells, which collect under the skin and dedifferentiate. The majority of the dedifferentiated cells developed into a lipomatous mass that may extend intradurally. Sometimes cartilage bone muscles and nerves may also develop in this lypomatus mass. On rare occasions, these components may grow in an organized manner and develop into an accessory limb. The stimulus for this organized growth remains uncertain. Even more baffling is the fact that this anomaly has such a predominant female predilection.
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