Aims

We wanted to evaluate the effects of a bone anabolic agent (bone morphogenetic protein 2 (BMP-2)) on an anti-catabolic background (systemic or local zoledronate) on fixation of allografted revision implants.

Introduction

Progressive resistance training (PRT) as a mean to reduce symptoms in patients with hip dysplasia (HD) has not yet been tried out. The aim of this study was to examine if PRT is feasible in patients with HD. A secondary purpose was to report data on changes of patient reported outcomes, muscle performance and hip muscle strength following PRT.

Background

An increasing number of hip prostheses are inserted without bone cement. Experimental research has shown that hydroxyapatite (HA) coated implants are strongly fixated in the bone, which is believed to reduce the likelihood of prosthetic loosening. However, in recent years, there has been much debate about the role of HA particles in third-body polyethylene (PE) wear and formerly we have shown the revision rate to be high among older-design HA coated cups.

Background

Randomized, controlled trials (RCTs) are generally accepted as the “gold standard” for the provision of the most unbiased measures of the efficacy of interventions but are often criticized for the lack of external validity. We assessed the external validity of a RCT examining the efficacy of local infiltration analgesia (LIA) compared with continuous epidural infusion after total knee arthroplasty (TKA)

Introduction

Hip and knee arthroplasty present surgeons with difficult bone loss. In these cases the use of morselized allograft is a well established way of optimizing early implant fixation. In revisions, the surgical field is potentially infected. The use of allograft bone creates a “dead space” in which the immune system has impaired access, and even a small amount of bacteria may therefore theoretically increase the risk of infection.

In vivo studies have shown that allograft bone is suitable as a vehicle of local antibiotic delivery.

We hypothesized that the allograft bone could be used as a local antibiotic delivery vehicle without impairing the implant fixation, tested by mechanical push-out.

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.

Background: Intraoperative femoral fracture is a well-known complication to primary total hip arthroplasty (THA). Experimental studies have suggested that intraoperative fractures may affect implant survival. How-ever, available clinical data are sparse.

Methods: We used data from the Danish Hip Arthroplasty Registry to identify patients treated with a primary THA due to primary osteoarthritis in Denmark between 1995 and 2005 (n=39478). Data was linked to two national Danish databases to conduct time dependent implant survival analyses. Implant survival and relative risk estimates were calculated for patients treated conservatively and patients treated with osteosynthesis after sustaining intraoperative femoral fractures during THA surgery. The reference group was THA’s performed without sustaining intraoperative femoral fracture. Furthermore we assessed the relative risk for reoperations and readmission to an orthopaedic department 3 months postoperatively.

Results: 282 patients (0.7%) were treated conservatively due to intraoperative femoral fracture and 237 patients (0.6%) were treated with osteosynthesis. The Kaplan– Meier survival plots revealed a significant poorer THA survival after osteosynthesis of intraoperative femoral fractures. In the 0–6 months postoperative period the adjusted relative risk (RR) for revision was 1.5 (95% CI: 1.1–1.7) for patients treated conservatively. In the same period the adjusted RR for revision was 5.7 (3.3–10.0) for patients treated with osteosynthesis. In the period 6 months to 11 years postoperatively we did not find any significant differences in the RR for revision among the groups.

Interpretation: Intraoperative fractures increase the relative risk for revision the first 6 postoperative months. Therefore, patients should be informed about the risk for revision when sustaining an intraoperative femoral fracture. Further, initiatives aimed at reducing the risk of revision in the first 6 months following THA should be considered in patients with intraoperative fractures including immediate revision of the stem to a larger stem with distal fixation and restricted weight bearing.

Objective: To study the effect in health status of telephone contact 2+10 weeks after total hip replacement (THR) during the first nine months after surgery. Not all of patient have improvement in their health status and quality of life, that the surgery benefits them.

Method: A randomised clinical trial enrolled 180 patients aged 65+ focusing on patients’ health status using SF-36, 4 weeks pre–to 3 and 9 months postoperative were carried out. Patients were randomised 4 weeks preoperative either to control or intervention group. Both groups received the conventional treatment. Furthermore the intervention group had postoperative telephone monitoring two and ten weeks after surgery Patients were given counselling by using an interview-guide within eight main themes referring to patients’ actual situation after THR.

Results: All patients experienced increase in their health status after THA. The intervention significantly reduced the time for patients to reach their habitual level as patients in the intervention group reached their habitual level at three months whereas patients in the control group reached this level after nine months.

Conclusion: Support by phone contact after THR seems to benefit patients’ outcome.

The presentation is based on the results of the nursing intervention program by using telephone contact to elderly patients with hip replacement after discharge.

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.

Background and purpose. At the Ganz periacetabular osteotomy the osteotomized acetabular fragment is reoriented in an adducted, extended and rotated position. Two screws fixate the acetabular fragment and the patients are allowed 30 kg weight bearing immediately after surgery. We were interested in examining the stability of the reoriented acetabulum after the Ganz osteotomy and accordingly the migration of the acetabular fragment was assessed by radiostereometry.

Methods. Thirty two dysplastic patients (thirty two hips), twenty seven females and five males were included in the study. Median age was 39 (20–57) years. Radio-stereometric examinations were done at one week, four weeks, 8 weeks and six months. Data are presented as mean with 95% CI.

Results. Six months postoperatively, the acetabular fragment had migrated 0.7mm (0.4–1.0mm) medially, and 0.7mm (0.5–0.9 mm) cranially. Mean rotation in valgus direction was 0.5° (−0.1–1.0°). In other directions, migration was below 0.4. There was no statistical difference between migration 8 weeks and 24 weeks postoperative in translation or rotation.

Interpretation. This is the first paper dealing with radio-stereometric analysis in Ganz osteotomy. Due to the very limited migration, we find our postoperative partial weight-bearing regime safe.

Introduction: The present series of studies were performed in order to investigate the effect of hydroxyapatite coating on bone ingrowth into cementless implants when subjected to pathological and mechanical conditions mimicking the clinical situation.

Material & methods and results: Hydroxyapatite (HA) and titanium alloy (Ti) coated implants were inserted into the femoral condyles in mature dogs. The observation period ranged between 4 and 16 weeks and the results were evaluated by mechanical push-out test and histomorphometric analysis.

The HA coating yielded superior effect on bone ingrowth compared to Ti when surrounded by a gap-whereas no effect was found in the press fit situation.

Allogeneic bone graft packed around the implant enhanced the anchorage of Ti implants, but HA coating alone without bone graft offered almost the same improvement in anchorage in 2 mm defects. Only minor improvement was obtained when bone graft was used together with hydroxyapatite.

Another interesting study showed that HA coating was able to prevent polyethylene particles to migrate around the implant by creating a seal of bony ingrowth.

HA coating on a porous surface resulted in significantly stronger fixation compared with HA coating on a grit blasted surface.

A clinical study (using roentgen stereophotogrammetric analysis, RSA) on total hip arthroplasty showed that HA coated femoral components were stable 3 months after surgery whereas migration of Ti coated components continued resulting in significantly less migration of HA coated components at 60 months.