Syriac

burkā - knee; bowing down, genuflection; middle part of plow (LSyr. 96, SL 131)

PS
*bi/ark- - knee (SED I No. 39)
Cf. *rVk(u)b(­at)­ ‘knee’ (No. 232) and discussion in [GD 163], where separation of these two roots is also favored.