This paper presents radiological changes in femoral cortical allograft used to replace the disc in low back and leg pain syndromes. The technique originated with the use of patient’s own iliac crest but donor site pain and lack of rotational control with removal of the annulus resulted in a) femoral cortical allograft supplemented with b) posterior fixation, more recently of the trans-laminar screw variety.

Experience with over 200 patients with femoral cortical allograft indicated that the rejection rate is virtually nil. Early changes include the loss of line between donor and host bone as early as three to four weeks after surgery.

There is radiological evidence in some cases that radiological healing has taken place by four weeks. There is no radiological difference whether the patient’s own bone or allograft chips are used to pack the allograft cavity. At one year and beyond, the gap behind the allograft in the interbody space fills with host bone, thus avoiding any posterior migration of the allograft plug. There is some subsidence, over the first 12 months, into host bone. Attention to detail in surgical treatment of the end-plate is an important part of the technique.

Axial views show dramatic changes up to 10 years after surgery. Gradual erosion of allograft by host bone, both at the external and internal diameter, occurs. Finally, there is the merest shell of donor bone identified, the rest clearly replaced by host bone. Unfortunately, biopsy samples to corelate with the radiological films are not available.

Allograft bone in surgery was original with MacEwen of Glasgow (1880). Its use 30 years ago in scoliosis surgery was generally not successful. The interbody femoral cortical allograft succeeds by reason of the surgical principles involved: 1) Thorough clearance of all avascular (disc) tissue – thus, the provision of a thoroughly vascularised bed; 2) Rigid fixation (provided by the translaminar screw fixation). For reasons of cost, mechanics, biological behaviour and ease of shaping before insertion, femoral cortical allograft has provided an excellent long-term disc replacement.