an interpositional knee arthroplasty is disclosed for attachment to a knee condyle . the interpositional knee arthroplasty comprises a spacer and at least one fastener extending from the spacer . the at least one fastener is designed and dimensioned to extend into the condyle without penetrating through the subcondylar plate . the spacer may be kidney shaped to facilitate attachment to the knee condyle . the fastener comprises at least one peg with at least one deformable fin attached to the peg . the deformable fin may be cup shaped . in operation , at least one hole is formed in a patient &# 39 ; s condyle . the at least one hole is dimensioned to receive the at least one peg member and deformable fin , but the hole does not extend to the subcondylar bone . when the peg member is forced into the hole in the condyle , the deformable fin collapses and wedges the peg member in the hole .