Background

Periprostetic joint infections (PJI) are often difficult to diagnose, to treat and often leave the patient with severe impaired function. The presence of low virulent bacteria is frequently discovered in apparent aseptic revisions of shoulder arthroplasties and pose a challenge to diagnose preoperatively.

Dual Isotope In111 Leucocyte/ Tc99 Bone Marrow SPECT CT scan (L/BMS) is considered the radionuclide gold standard in preoperative diagnosing PJI with reported high specificity and sensitivity in hip and knee arthroplasties.

Unfortunately, it is labour-intensive and expensive to perform and documentation using L/BMS on shoulder arthroplasties lack.

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.

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.