A preclinical study of stem subsidence and graft incorporation after femoral impaction grafting using porous hydroxyapatite as a bone graft extender.

This preclinical in vivo screening study compared bone graft incorporation and stem subsidence in cemented hemiarthroplasty after femoral impaction bone grafting with either morselized allograft bone (n = 5, control group) or a 1:1 mix of allograft and porous hydroxyapatite ceramics (HA) granules (n = 5, HA group). At 14 weeks, there was excellent bone graft incorporation by bone, and the stems were well fixed in both groups. The median subsidence at the cement-bone interface, measured using radiostereometric analysis, was 0.14 and 0.93 mm in the control and HA groups, respectively. The comparable histologic results between groups and good stem fixation in this study support the conduct of a larger scale investigation of the use of porous HA in femoral impaction bone grafting at revision hip arthroplasty.

Bone morphogenetic proteins and Smad expression in ovine tendon-bone healing.

PURPOSE: Bone morphogenetic proteins (BMPs) are being developed to improve tendon-bone healing. To do this, it is essential to understand the endogenous expression of BMPs and their downstream signal transduction factors, Smads, during tendon-bone healing. METHODS: An extra-articular patellar tendon-bone healing ovine model was set up, and histologic evaluation of the healing progress at the tendon-bone interface at 1, 2, 3, and 6 weeks was performed. Immunohistochemical staining of BMP-2, BMP-7, Smad1, Smad4, and Smad5 was carried out in all sections. RESULTS: The model revealed formation of a loose granuloma tissue layer between the tendon and bone at 1 week, remodeling starting at 2 weeks, and Sharpey-like collagen fiber formation at 3 and 6 weeks. All detected factors were elevated at the tendon-bone interface during healing, and the expression peaked at 2 to 3 weeks. The cells involved were osteoblastic-like cells, osteoclastic-like cells, mesenchymal cells, and fibroblasts. BMP-7 staining was mainly at the interface close to the bony side, whereas BMP-2 expression shifted to the tendon side at 6 weeks. The expression pattern of Smad1 and Smad5 was similar to that of BMP-7. Smad1 was also found to be expressed in osteoclastic-like cells at 1 and 2 weeks. Smad4 expression was the highest among all of the factors at all time points. CONCLUSIONS: The data suggest that endogenous BMP-2 and BMP-7 participate in tendon-bone healing and their functions involve their downstream signal transduction mediators, Smad1, Smad4, and Smad5. CLINICAL RELEVANCE: The temporal expression of BMPs should be considered when setting up therapeutic strategies using BMPs.

The use of OP-1 in femoral impaction grafting in a sheep model.

The aim of this pilot study was to examine bone graft incorporation in femurs impacted with allograft bone alone (control group) or with allograft containing the bone morphogenetic protein OP-1 (BMP-7) (OP-1 group) in a sheep model of cemented hemiarthroplasty. Two sheep in each group were sacrificed at 6, 18 and 26 weeks. Successful bone graft incorporation was evident in both groups by six weeks but in the OP-1 group, there had been more extensive resorption of the graft. There was one case of excessive stem subsidence in the OP-1 group at six weeks. By 18 weeks, there was remodelling and trabeculation of the new bone in the OP-1 group, but this appeared less advanced in the control group. By 26 weeks, there was remodelling of bone in the graft bed. The results of this small study suggest that OP-1 promotes initial graft resorption, thus hastening bone graft incorporation and remodelling in femoral impaction grafting. The one case of stem subsidence may be associated with the early resorption seen in the OP-1 group and reinforces the need for further studies, examining dose response and using precise measures of stem movement, before this BMP is used in femoral impaction grafting at revision hip arthroplasty.

Midterm results using a medial pivot total knee replacement compared with the Australian National Joint Replacement Registry data.

BACKGROUND: In order to emulate normal knee kinematics more closely, and thereby potentially improve wear characteristics and implant longevity, the medial pivot-type knee replacement geometry was designed. In the current study the outcome of 50 consecutive knee replacements using a medial pivot-type knee replacement was compared with the results in the Australian Orthopaedic Association National Joint Replacement Registry. METHODS: Pre- and post-operatively at follow-up evaluation consisted of the Knee Society score system and the Western Ontario and McMaster Universities Arthritis Index Score. Patient satisfaction was documented using 5-point Likert-type scales. Standard radiographs were used to assess signs of radiographic failure. Revisions were subcategorized into major total, major partial and minor. Patient records were cross-referenced against the Australian Orthopaedic Associations National Joint Replacement Registry's and the outcome compared with the registry's subset of data on the medial pivot knee used. RESULTS: According to the patients' Knee Society score system and Western Ontario and McMaster Universities Arthritis Index scores, there was good pain relief and functional improvement; none of the implants showed radiographic signs of failure. There was one minor revision. There was no statistically significant difference in revision rate compared with the registry results. DISCUSSION: The medial pivot knee-type implant in this series provided pain relief, functional improvement and a revision rate, similar to what is reported in the literature after a longer follow-up period, which is reassuring for those who use this type of implant on a day-to-day basis.