lateral retinaculum lateral retinaculum the lateral retinaculum is the fibrous tissue on the lateral (outer) side of the kneecap (patella). the kneecap has both a medial (on the inner aspect) and a lateral (on the outer side) retinaculum, and these help to support the kneecap in its position in relation to the femur bone underneath it. lateral retinaculumidentifiersta98a03.6.08.017ta22624fma44590 44590, 44590anatomical terminology the lateral retinaculum is an extension of the fibrous 'aponeurosis' of the vastus lateralis muscle (itself a part of the quadriceps muscles making up the 'lap').