Introduction: Hip arthroplasty can present surgeons with difficult bone loss. Impacted allografting is a well-established way of initally securing implant stability. However subsequent bone integration and fusion can be prolonged. Also concerns relate on maintaining bone volume of allograft during integration.

Intermittent administration of parathyroid hormone (PTH) is bone anabolic and improves fracture healing. As adjuvant in implant surgery PTH has only recently been introduced experimentally predominantly showing improved implant integration within empty peri-implant bone defects.

Given the desire to improve the graft incorporation process, the purpose of our study is to examine whether PTH improves early implant integration by accelerating healing of peri-implant bone allograft. We test the hypothesis that systemic intermittent administration of PTH increases new bone formation in allograft inserted in a gap with impacted morselized bone allograft around an experimental orthopaedic implant. We hypothesize that parathyroid hormone will improve new bone formation in allograft and preserve allograft.

Methods: An unpaired canine study was carried out following approval of our Institutional Animal Care and Use Committee. In 20 skeletally mature dogs cylindrical titanium alloy porous coated implants (6x10mm) were inserted in a 2.5 mm circumferential gap in the extraarticular cancellous bone site of the proximal humeri. Cancellous bone was milled on fine setting and impacted in the gap. Test animal were postoperatively randomised to daily treatment of placebo or parathyroid hormon rhPTH (1–34)(teriparatide)(Bachem) 5 μg / kg s.c. After 4 weeks observation time specimen blocks were harvested, sectioned and evaluated by unbiased stereological histomor-phometry (newCast, Visiopharm, Horsholm, Denmark). The endpoints were bone-to-implant contact and tissue density in an outer gap region of 1500 μm and an inner gap region reaching the implant. Since data were not normally distributed a non-parametric analysis two-sample Wilcoxon rank-sum test was applied with p-value < 0.05 considered statistically significant. Data are accordingly presented as median and interquartile ranges.

Results: Two implants in the PTH group were excluded. In the peri-centric region new bone improved significantly (outer region: PTH 21.1 (12.9–16.3) / control 15.2 (13.9–16.2), inner region: PTH 19.8 (15.8–21.5)/control 14.0 (12.9–16.3)). There were no significant differences in the amount of allograft. At the implant interface new bone for PTH was 11.5 (8.1–14.0), as for control 10.5 (7.2–14.8). Old bone for PTH was 1.5 (0.8–2.0), and old bone 1.4 (0.8–1.7). Bone tissue showed no significant differences.

Conclusion: Parathyroid hormone shows promise in significant inducing bone formation in impacted morselized allograft around implant without resorbing it significantly retaining graft volume.

Impaction allograft is an established method of securing initial stability of an implant in arthroplasty. Subsequent bone integration can be prolonged, and the volume of allograft may not be maintained. Intermittent administration of parathyroid hormone has an anabolic effect on bone and may therefore improve integration of an implant.

Using a canine implant model we tested the hypothesis that administration of parathyroid hormone may improve osseointegration of implants surrounded by bone graft. In 20 dogs a cylindrical porous-coated titanium alloy implant was inserted into normal cancellous bone in the proximal humerus and surrounded by a circumferential gap of 2.5 mm. Morsellised allograft was impacted around the implant. Half of the animals were given daily injections of human parathyroid hormone (1–34) 5 μg/kg for four weeks and half received control injections. The two groups were compared by mechanical testing and histomorphometry. We observed a significant increase in new bone formation within the bone graft in the parathyroid hormone group. There were no significant differences in the volume of allograft, bone-implant contact or in the mechanical parameters.

These findings suggest that parathyroid hormone improves new bone formation in impacted morsellised allograft around an implant and retains the graft volume without significant resorption. Fixation of the implant was neither improved nor compromised at the final follow-up of four weeks.

Introduction: Treatment of osteoarthritis by total joint replacement generally shows a high success rate; however challenges remain. Prostheses inserted without cement are popular worldwide. Insertion of uncemented implants is intended to be pressfit. Early bone growth on the implant is critical to long-term fixation.

Parathyroid hormone (PTH) is a regulator of bone metabolism. When PTH is administered intermittently it induces strong anabolic effect by increasing osteoblastic activity. Our understanding of PTH is mainly based on research on osteoporosis, in which bone formation is known to be coupled to the bone resorption. In the orthopaedic situation of a joint replacement other conditions apply.

We therefore find it of interest to examine PTH’s role as an adjuvant in implant surgery. We examine the effect of PTH on the osseointegration of an experimental orthopaedic implant in which the implant due to insertion initiates a bone repair in the implant bed. We hypothesize that parathyroid hormone will improve the bone ongrowth at the bone-implant interface.

Methods: An unpaired canine study was carried out following approval of our Institutional Animal Care and Use Committee. In 20 skeletally mature dogs cylindrical titanium alloy porous coated implants (6×10mm) were inserted pressfit (0.1 mm under-drill) in the extraarticular cancellous bone site of the proximal tibia. Test animal were postoperatively randomised to daily treatment of placebo or parathyroid hormon rhPTH (1–34)(t eriparatide)(Bachem) 5 μg/kg s.c. After 4 weeks observation time specimen blocks were harvested, sectioned and evaluated by unbiased stereological histomorphometry (CAST-grid system (Olympus Denmark)). The endpoints were bone-to-implant contact and tissue density in a 500 μm region of interest. Since data were not normally distributed a non-parametric analysis two-sample Wilcoxon rank-sum test was applied with p-value < 0.05 considered statistically significant. Data are accordingly presented as median and interquartile ranges.

Results: Two implants in the PTH group were excluded. At the implant interface tissue density for PTH was 0,193 (0,157–0,229) for bone, 0,796 (0,764–0,821) for marrow and 0 (0–0,009) for fibrous tissue, as for control 0,163 (0,141–0,193) for bone, 0,837 (0,805–0,859) for marrow and 0 (0-0) for fibrous tissue. Bone tissue showed no significant differences.

In the peri-centric region the tissue fraction for PTH was 0,238 (0,211–0,276) for bone, 0,752 (0,724–0,785) for marrow and 0 (0–0,007) for fibrous tissue, as for control 0,223 (0,201–0,235) for bone, 0,777 (0,765–0,799) for marrow and 0 (0–0) for fibrous tissue.

Conclusion: In conclusion parathyroid hormone does not show significantly induced bone formation at a titanium alloy implant that has a porous coating of titanium alloy and inserted pressfit.

Introduction: Minimal invasive surgery (MIS) seems to be part of future orthopaedic solutions. Currently, most approaches for the Bernese periacetabular osteotomy (PAO) are characterized by relatively extensive incisions, dissection and detachment of muscles. We have developed a new MIS approach for the Bernese PAO. The purposes were to reduce patient morbidity and to improve the cosmetic result following surgery without negatively influencing the achieved reorientation of the acetabular articular surface. In this study we present the surgical technique, results and compare them to the ilioinguinal (II) approach.

Methods: The new MIS technique is a trans-sartorial approach using a three inch skin incision. Previously the II approach was used. From 1999–2006 a total of 215 patients with acetabular dysplasia were operated by the same surgeon in two successive time periods with the II (97) and the trans-sartorial (118) approaches. No supplemental surgery was performed. The two approaches are retrospectively compared regarding perioperative measures, transfusion requirements, complications and the achieved reorientation of the acetabular articular surface. Data are compared by Kruskal-Wallis Test and are presented as median and interquartile range.

Results: The trans-sartorial approach significantly reduced days of admission (8 days (7–9) vs. 10 days (8–13), p< 0.0001), duration of surgery (70 min (60–75) vs. 100 min (82.5–120), p< 0.0001), perioperative blood loss (200ml (150–350) vs. 450ml (325–700), p< 0.0001) and the percentage of patients receiving blood transfusion (18.6 % vs. 3.4%). Of severe neurovascular, infectious and technical complications none occurred in the trans-sartorial group and 3 cases of arterial thrombosis were seen in the II group. The achieved reorientation measured by the CE-angle postoperatively had median values of 31° (25–36) in the II group and 33° (29–36) in the trans-sartorial group, p=0.016. The postoperative AI-angles were 10° (2–14) and 3° (0–7) in the II and trans-sartorial groups respectively, p< 0.0001.

Discussion: Our shift to the trans-sartorial approach was rewarding as the duration of surgery, perioperative blood loss and transfusion requirements were reduced. The new MIS technique is safe and improves the cosmetic result without negative influence on the achieved reorientation of the acetabular articular surface.

Introduction: Revision hip implants have poorer clinical outcome than primary implants. The fixation of the implants is often compromised by the formation of an endosteal sclerotic bone rim during the process of aseptic loosening. The cracking procedure is a bone sparing, low energy surgical technique which produces a controlled local perforation of the sclerotic bone rim. In previous studies, we showed that fixation of revision implants significantly improved by the cracking technique for both titanium (Ti) and hydroxyapatite (HA) coated implants (1). In this study we compared the cracking technique with the common technique of reaming, which completely removes the sclerotic bone rim.

Methods: A paired animal study (n=10), in which revision cavities was created by 20 micromotion implant systems inserted in both knees. Micromotion was 0.5mm per gait cycle. After 8 weeks revision surgery was performed.

Crack revision: The splined crack tool was introduced over the implant piston with firm axial hammer blows. This producing controlled cracking and local perforation of the sclerotic endosteal rim. The tool is a 6.0 mm cylinder fitted with axially spaced 1.1 mm pointed splines (8.2 mm outer diameter).

Reaming revision: A flat bottomed reamer was inserted over the implant piston using one rotation per second. The outer diameter was 8.2 mm in order to remove the sclerotic bone rim. Stable revision Ti implants was inserted. Observation period was 4 weeks. Mechanical push-out tests were performed. Students’ paired t-test was used. Data presented as mean and SEM.

Results: Shear strength was markedly higher with the cracking procedure 1.33± 0.3MPa vs. 0.34 ± 0.2 MPa (p< 0.05). Similar results was seen for Stiffness 6.7± 2.0 vs. 1.6 ± 0.9 (p< 0.05) in favor of the cracking procedure. A non-significant increase was seen in energy absorption 170± 47 vs. 50± 29 (p=0.07).

Discussion: The cracking procedure improves the mechanical fixation of Ti revision implants compared to a reaming procedure. Shear strength and stiffness was consistently higher for all implant pairs. We have previously shown that the sclerotic bone rim is a barrier for bone ingrowth and that implants inserted with an intact sclerotic bone rim will have a poor biomechanical fixation. Additionally, revision implants inserted with the cracking technique obtained a mechanical fixation comparable to primary implants. Reaming procedures are often used in hip revision surgery. However, as loss of bone stock is a common feature of revision cavities, the reaming procedure may not always be an optimal preparation method of the bone. Excessive removal of bone by reaming may compromise the long term implant stability or increase the risk of peri-implant fractures. The cracking technique may be an alternative or supplemental procedure to reaming.

Introduction: Bone grafts should be biocompatible, mechanically stable and be replaced with new bone over time. BMP’s are known to increase bone formation around allografted implants, but have also been associated with increased graft resorption and implant instability. Bone resorption can be inhibited by bisphosphonates.

We hypothesized that topical bisphosphonate (Pamidronate, Mayne Pharma) in combination with rhBMP2 (InductOs, Wyeth) would give increased mechanical implant fixation and increased new bone formation without excessive allograft resorption. We looked at both porous-coated Ti implants and HA-coated implants.

Methods: Four 2.5 mm gap implants were inserted into the proximal humeri of each of 16 dogs. The gap around each implant was filled with fresh frozen impacted allograft with or without intervention treatment. Half the dogs received Ti-implants, the other half HA-implants. The 4 treatment groups were:

allograft alone (control)

The observation time was 4 weeks.

Results: For both the Ti and HA subgroup, the control-group had significantly better mechanical fixation than all other groups by push-out test. The fixation was twofold higher in the control group than the rhBMP2-group and more than 20-fold higher than the pamidronate group and combined group. The HA implants were twice as well fixed as the Ti implants with corresponding treatment.

The HA implants had less fibrous tissue and more new bone compared to the Ti implants. The fractions of allograft were the same.

The rhBMP2 group had more new bone and much less fibrous tissue than the mechanically superior control group. However, there was almost no allograft left in the rhBMP2 group due to extreme resorption.

The addition of pamidronate seemed to freeze bone metabolism around the implants. Neither in the pamidronate group nor in the combination group was there anything but minor new bone growth. The allograft was preserved. In the pamidronate group there was a dense, thick fibrous capsule around the implants. This was not the case in the combined rhBMP2-pamidronate group, and is most likely a positive effect of the rhBMP2.

Discussion: Topical pamidronate and rhBMP2 in combination and alone greatly weakened the mechanical fixation of the implants. The experiment confirms previous reports of mechanical instability of implants when BMPs are added to periimplanteric defects. Pamidronate alone had catastrophic effects on bone metabolism and implant fixation in this experiment.

The negative results with rhBMP2 may be due to over dosage, which warrants further preclinical testing. Despite the limitations of this animal study with non-loaded implants, the results encourage extreme caution in adjuvant therapies of arthroplastic surgery.

Aims: Early bone ingrowth is known to increase primary implant þxation and reduce the risk of early implant failure. RGD peptide (Arg-Gly-Asp) has been identi-þed as playing a key role in osteoblast attachment and proliferation on various surfaces. The aim of this study is to test whether a monolayer of RGD peptide on Ti implants will increase bone ingrowth in vivo. Methods: Controlled canine study (n=8). 6 x 10mm plasma sprayed porous coated implants (Ti6Al4V) was inserted as press-þt in the proximal tibia bilaterally. Observation period was 4 weeks. Implants was coated in a 100 μM solution of cylic (RGDfK) peptide for 24 hours (Biomet-Merck, Darmstadt, Germany). Two dogs had to be excluded due to wrong placement of the implants. Results are presented as median and range. Results: A signiþcant increase in bone/implant contact was seen for the RGD treated group (p< 0.05). Bone fraction at the interface was 0.18 (0.10–0.45) compared to 0.09 (0.05–0.14) for the control. Mechanical þxation, measured by push-out test, was increased. Shear strength was 85% higher for the RGD group; however this difference was not signiþcant. Conclusions: This study shows that implant surface treatment with RGD enhances early bone ingrowth to press-þtted implants. However, future studies will be preformed regarding coating integrity and long-term effects, as well as its performance under loaded conditions.