A spacer (100, 300) comprising: an elongate body having: a central longitudinal axis extending through the body; an anterior portion (110, 310) having an anterior end tapering toward the longitudinal axis; a posterior portion (120, 320), distal from the anterior portion (110, 310) having a posterior end; a superior surface (130, 330) extending between the anterior end and the posterior end (120, 320); an inferior surface (140, 340) extending between the anterior end and the posterior end (120, 320); a first sidewall (150, 350) extending between the superior surface and the inferior surface on a first side of the longitudinal axis; and a second sidewall (160, 360) extending between the superior surface (130, 330) and the inferior surface (140, 340) on a second side of the longitudinal axis, wherein an intersection of the first sidewall (150, 350) and the superior surface (130, 330) comprises a first chamfered edge and wherein an intersection of the second sidewall (160, 360) and the inferior surface (140, 340) comprises a second chamfered edge, wherein each of the first sidewall (150, 350) and the second sidewall (160, 360) comprises a longitudinal indentation (153, 163), comprising a superior sidewall surface, and inferior sidewall surface, and a side surface extending between and connecting the respective superior sidewall surface and the respective inferior sidewall surface, characterized in that, the longitudinal indentation (153, 163) extends from the anterior portion (110, 310) through the posterior portion (120, 320) and, in that the degree of taper of the first and second chamfer (180, 190) is greatest at the anterior portion and the degree of taper of first and second chamfer (180, 190) lessen towards posterior end. a central longitudinal axis extending through the body; an anterior portion (110, 310) having an anterior end tapering toward the longitudinal axis; a posterior portion (120, 320), distal from the anterior portion (110, 310) having a posterior end; a superior surface (130, 330) extending between the anterior end and the posterior end (120, 320); an inferior surface (140, 340) extending between the anterior end and the posterior end (120, 320); a first sidewall (150, 350) extending between the superior surface and the inferior surface on a first side of the longitudinal axis; and a second sidewall (160, 360) extending between the superior surface (130, 330) and the inferior surface (140, 340) on a second side of the longitudinal axis, wherein an intersection of the first sidewall (150, 350) and the superior surface (130, 330) comprises a first chamfered edge and wherein an intersection of the second sidewall (160, 360) and the inferior surface (140, 340) comprises a second chamfered edge, wherein each of the first sidewall (150, 350) and the second sidewall (160, 360) comprises a longitudinal indentation (153, 163), comprising a superior sidewall surface, and inferior sidewall surface, and a side surface extending between and connecting the respective superior sidewall surface and the respective inferior sidewall surface, characterized in that, the longitudinal indentation (153, 163) extends from the anterior portion (110, 310) through the posterior portion (120, 320) and, in that the degree of taper of the first and second chamfer (180, 190) is greatest at the anterior portion and the degree of taper of first and second chamfer (180, 190) lessen towards posterior end.