2.1 Calcium phosphate cement

The use of a calcium phosphate bone cement in the repair of acetabular fractures or filling of bony defects during revision surgery of the acetabular component of a total hip arthroplasty has been reported in multiple publications [7–9]. Seleem et al [7] performed a cadaveric study comparing the stability of impacted acetabular fragments supported with autograft versus calcium phosphate cement in a model of posterior wall fractures. After fixation of the posterior wall fragment, the remaining defect was then filled with either cancellous autograft or calcium phosphate cement. The resulting constructs were then loaded and the displacement of the fixed posterior wall fragment measured. The constructs augmented with calcium phosphate bone cement showed a statistically significant decrease in displacement compared with autograft immediately postoperatively. Although this study shows a direct advantage of calcium phosphate cement augmentation in a cadaveric model, it is not possible to evaluate the subsequent bony ingrowth into either the autograft or bone cement to determine the long-term comparison between the two techniques.

Olson et al [8] investigated the application of calcium phosphate cement as a grout between fracture fragments to simulate the acute union of the fracture fragments. The calcium phosphate cement was applied following fixation of the fracture fragments with standard internal fixation techniques. Once the cement had cured for the recommended time, the augmented construct was placed under loads of 1,700–2,200 N in an effort to simulate normal weight bearing. The micromotion between fracture fragments was noted to be decreased relative to the construct-lacking cement augmentation. Despite this positive finding, the authors emphasize that intraarticular extravasation of the cement, osteonecrosis of the posterior wall fragment, and possible delayed union or nonunion of the posterior wall fragment were not addressed by this cadaveric study.

Significant loss of bone stock is a common difficulty during revision of the acetabular component of a total hip arthroplasty. The gold standard of treatment for lost bone stock is impaction grafting of cadaveric allograft. Blom et al [9] investigated the combination of allograft with a biphasic calcium phosphate bone cement to decrease the amount of allograft required for a given defect and to augment the strength of the graft within the defect. In this prospective clinical trial, bony defects were filled with a 50:50 mixture of allograft and biphasic calcium phosphate bone cement before placement of a revision acetabular component. All surgeries were performed for aseptic loosening of a primary total hip arthroplasty with no concern for infectious processes. Although this study did not evaluate the use of the biphasic calcium phosphate bone cement in patients with an acetabular fracture, the possible use of this technique to repair bony defects found in acetabular fractures is evident. A total of 43 consecutive patients were followed up for a mean of 24 months (range, 11–48 months) in which no migration of the acetabular component was noted. The authors noted the short follow-up and that they could not comment on the long-term outcome of this defect-filling technique compared to impaction grafting with allograft alone.

2.2 Calcium sulfate cement

Moed et al [10] evaluated the natural history of calcium sulfate pellets used as bone graft substitute to fill bony defects left behind following the elevation of impacted comminuted cortical fragments during internal fixation of acetabular fractures. A total of 31 patients were followed up with plain x-ray and computed tomographic (CT) scan for a minimum of 6 months and an average of 18 months (range, 12–34 months) to determine the final outcome of the implanted calcium sulfate pellets. The typical defect repaired in this study was described as being a fairly regular cavity left behind following the elevation and repositioning of fracture fragments. At the time of the final postoperative evaluation of the 31 patients, more than 90% of the pellets had been replaced by bone in 22; between 50% and 90% of the pellets had been replaced by bone in 4; less than 50% of the pellets had been replaced by bone in 4; and pellets had not been replaced by bone in 1. In each of the patients with minimal or no bony replacement, communication with the joint cavity and synovial fluid was seen. These findings lead the authors to recommend that for optimum results, the defect filled with calcium sulfate pellets should be fully contained within bone and have no communication with the joint cavity or synovial fluid.

3.1 Parathyroid hormone

The systemic administration of intermittent parathyroid hormone (PTH) (1−34) is currently approved by the US Food and Drug Administration (FDA) for the treatment of osteoporosis, taking advantage of the anabolic effects of the active PTH peptide on bone growth. However, few published reports evaluate the use of PTH for fracture healing, and, to our knowledge, there are no publications on the use of PTH for treatment of acetabular fractures [6, 11, 12].

Two studies [13, 14] examined the administration of PTH (1−84) to women with osteoporosis and with nonoperative fractures of the pelvis. In one study [13], women older than 70 years with unilateral pelvis fractures and osteoporosis confirmed by dual x-ray absorptiometry were randomized into either the experimental (treatment with daily subcutaneous injections of 100 µg PTH for 24 months) or the control arms of the treatment protocol. Excluded from the study were patients with any treatment for osteoporosis 6 months before fracture occurrence, a history of cancer, or treatment with chemotherapy. Fracture healing was followed up and assessed on serial CT scans with functional outcome determined by the reduction of pain and the improvement in mobility as determined by scores on Visual Analog Scale (VAS) and performance on a “Get up and go” assessment. At the primary end point of 8 weeks, the treatment group had a statistically significant increase in the rate of healing and decreased pain compared to the control group.

Aspenberg et al [11] published a prospective, randomized double-blind trial in which 102 postmenopausal women with dorsally displaced distal radius fractures treated with closed reduction were administered either teriparatide or placebo to assess the effects of teriparatide on fracture healing. The primary end point was radiographic evidence of complete cortical bridging in three of four cortices. The time to healing was shorter with the administration of 20 µg teriparatide versus placebo. In a subsequent subgroup analysis, teriparatide administration appeared to improve early callus formation; however, these results must be interpreted with caution since they are from a post hoc analysis of an end point that was not originally part of the study protocol [12].

The intermittent systemic administration of PTH (1−84) or PTH (1−34) to augment endochondral or intramembranous bone repair has also been evaluated in multiple nonhuman animal models [15–18]. Each of these animal studies used fractures of the femur that were then stabilized through external, intramedullary, or plate fixation. Two studies [16, 18] were designed to evaluate fracture healing in the setting of osteoporosis using rats or cynomolgus monkeys that were pretreated with PTH (1−34) before creation of the experimental femoral fracture. Treatment with PTH was continued following fracture fixation by either intramedullary or plate fixation, respectively. The remodeling of woven to lamellar bone was accelerated in animals that were given PTH before and during fracture healing in a rat model of femoral fracture healing [16]. In the cynomolgus monkey model of fracture healing with rigid plate fixation, the intermittent administration of PTH before and after femoral fracture resulted in a dose-dependent acceleration of fracture healing [18].

In a model of intramembranous bone formation using distraction osteogenesis of a rat femur following an osteotomy, the intermittent administration of PTH resulted in accelerated consolidation of the bone forming within the osteotomy site, as evidenced by increased bone density as well as increased trabecular density [15]. Alkhiary et al [17] also evaluated the effects of intermittent PTH on fracture healing in a closed femoral fracture model in rats that were fixed with intramedullary fixation. In this study, the authors confirmed that the animals receiving PTH did not show an increase in fracture callus volume or formation but an improvement in the quality of the fracture callus with an increase in total osseous tissue volume and a decreased void space.