MIXING BONE GRAFT WITH OP-1 DOES NOT IMPROVE CUP OR STEM FIXATION IN REVISION SURGERY OF THE HIP.

Department of Orthopaedics, *Sahlgrenska Hospital, Göteborg University, SE-413 45 Göteborg, Sweden. +Princess Elizabeth Orthopaedic Centre, Exeter, Great Britain eva.fermen@vgregion.se

BMP-7 or Osteopontin (OP) belongs to the transforming growth factor – ß family. It stimulates recruitment of stem cells and vascular ingrowth resulting in bone formation. Case reports have indicated that use of BMP may be beneficial in revision surgery1. We evaluated the effect on component fixation and bone remodelling after mixing OP-1 (Osteopontin, Stryker, Biotech) with impacted allograft bone during impaction grafting in hip revision surgery in a case-control study.

In a case-control study with minimum 3 years follow up we evaluated the fixation and clinical results of cemented and uncemented sockets (10 study and 10 control hips with grade 3 2-4 defects according to Gustilo-Pasternak) and cemented stems (11 study and 30 control hips with grade 2 1-4 defects) used with impaction allografting in revision surgery of the hip.

Cup study. In both groups there was an early proximal migration (median values of 0.4/0.2 in study/control groups at 3 months) followed stabilisation of most implants. At 3 years the median migration had increased to 0.5 in the study, but remained at 0.2 in the control group (p=0.4). 2 cups in the study group revised after 5 and 6 years because of loosening. Further one cup in the study group was radiographically loose. At 2 years the Harris hip score was higher in the study group (p=0.02), but the gain value (difference preoperatively – two years) and the pain score did not differ. Stem study. At 2 years the median subsidence in the study/control groups were -0.4 -16.1 to -0.1/ -0.2 -4.3 to 0.5 (p=0.2). The stems in the study group showed increased posterior tilt (-0.4 -4.5 to 0.1/ -0.1 -2.4 to 0.7, p=0.03. Between 2 and 3 years 2 stems in the study group were revised due to loosening. After 6 months the BMD had increased more or decreased less in Gruen regions 6 and 7 in the study group (p<0.04). After 2 years this difference had disappeared. At this time the study group had lost more bone mineral in region 4 (p=0.04). The Harris hip and pain scores or the gain values 0 to 2 years did not differ.

Our data do not indicate presence of any positive effect of OP-1 with clinical relevance. Poor early fixation resulting in rerevision of 4 cases in the study group prompted us to stop this investigation.

1. Cook SD, Barrack RL, Shimmin A, Morgan D, Carvajal JP. The use of osteogenic protein-1 in reconstructive surgery of the hip. J Arthroplasty. 2001 Dec; 16(8 Suppl 1): 88-94.

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