Bone Abstracts

Cases of non-vitamin D deficiency rickets have been reported in African countries including The Gambia, South Africa and Nigeria where the likely aetiology is a chronically low dietary calcium intake. Additional aetiological factors in Gambian studies are iron deficiency leading to a disruption in phosphate metabolism.

Surgical correction of pathological rickets-like lower-limb deformities is the most common operation performed at the Beit Cure Orthopaedic Hospital in Blantyre, Malawi. During 2008–2009, 81 cases were enrolled in a surgical intervention study. The aim of this present study was to identify the characteristics and aetiology of pathological bow-leg (BL, n=44) and knock-knee deformities (KK, n=37) and to identify similarities with previously described African cohorts.

Whole blood was analysed for malaria parasite (n=1, positive) and serum for 25-hydroxyvitamin D (25OHD, DiaSorin, USA), calcium (Ca), phosphate (Phos), ferritin (Ferr), C-reactive protein (CRP) and total alkaline phosphatase (TALP)(Koni Analyzer,Finland).

At first presentation, children with BL were younger (mean (S.D.) 4.5(2.1) vs 6.7(3.9) years, P=0.002), and tended to start walking 2 months earlier than KK (P=0.1). 25% of BL and 32% of KK had family members with rickets-like deformities. In the children, the mean angle of deformity did not differ between the groups (BL: 29(9) vs KK 30(9) degrees, P=0.8). Mean 25OHD was 65(21.4) nmol/l (n=0<25 nmol/l, n=18<50 nmol/l) and tended to be higher in KK (25OHD BL: 61.1(23.7) vs KK: 69.7(17.8), P=0.08). 12% of children had low iron stores (Ferr<15 μg/l) and 44% had a degree of inflammation (CRP>10 mg/l). TALP (25%>215 RU/ml), Phos (14%<1.45 mmo/l) and Ca (12%<2.20 mmol/l) did not differ between groups or by angle of deformity with the exception of Phos which was negatively associated with angle of deformity (β-coefficient (SE) −0.006(0.003) mmol/l, r²=4.1%, P=0.05. Phos was the strongest negative predictor of TALP (β(SE) −196(47) U/l, r²=21.1%, P=0.0001).

In Malawi, children with BL are younger than those presenting with KK. As in The Gambia, rickets-like deformities in Malawi are more common in boys (75%) than girls (25%) and are unlikely to be caused by vitamin D deficiency. The inverse relationship between Phos with TALP and angle of deformity may suggest a disruption in phosphate metabolism.

Funded by the UK MRC & DFID. MRC programme:U105960371.

Disclosure: The authors declared no competing interests.