**9. The DJK prevention strategy**

Surgeons need to know when their intraoperative corrections are adequate to align CD patients optimally [61]. We propose a strategy of several steps that can be taken to minimize the risk of DJK. First is determination of the correct alignment to be achieved during surgery by utilizing the newly developed in-construct measurements. This involves anticipating the subjacent reciprocal changes to give a final result of a C2S of under 20 degrees and a cSVA of under 4 cm [62].

Secondly, the use of softer materials at the distal junction may protect against the development of Adjacent Segment Disease (ASD) and junctional kyphosis. In a retrospective case–control study by Han et al. [63] the use of cobalt chrome multiple-rod constructs (CoCr MRCs) versus titanium alloy two-rod constructs (Ti TRCs) were evaluated with a minimum of 1-year follow-up. They suggested that increasing the number of rods and their stiffness promotes proximal junctional kyphosis (PJK) in ASD surgery. PJK prevention strategies that should be considered for preventing DJK include minimizing the destruction of soft tissue at

#### *Planning Cervical Deformity Surgery Including DJK Prevention Strategies DOI: http://dx.doi.org/10.5772/intechopen.94390*

the Upper Instrumented Vertebra (UIV) (PJK) and therefore LIV (DJK) and using transition rods with softer metals [64].

Thirdly, optimization of bone health is critical. The role of pharmacotherapy in aiding implant fixation or fusion has been studied for bisphosphonates and teriparatide (Human recombinant PTH 1–34, Forteo, Ely Lilly, Indianapolis, IN). Zolendronate was found to make no statistically significant difference. Prospective trials [65] showed a significant advantage in prescribing teriparatide over bisphosphonate to aid fusion and lower the rate of pedicle screw loosening. However, the most recent published study by Oba et al. [66] must be evaluated carefully due to the short follow-up duration as well as the cost and the potential for serious sideeffects with the use of teriparatide.

Teriparatide is very expensive, and due to the limited on-label indications it can be challenging to secure insurance coverage. However, in light of the costs associated with spinal fusion surgery and the importance of preventing osteoporosisrelated complications as defined by Bjerke et al. [67], insurers are becoming more willing to consider off-label orthopedic indications for teriparatide. In addition, in most cases the patients do qualify based on their diagnosed level of osteoporosis. This emphasizes the importance of a pre-operative workup. The most commonly described and FDA-approved dosing schedule for teriparatide is 20 mcg/day. Yet, an effective [59] weekly dosing schedule of 56.5 mcg/week has been described for vertebral compression fracture (VCF) and spine fusion. Timing of treatment before and after spinal surgery is still evolving and may vary. Several studies suggest a benefit to initiating teriparatide 3 months before surgery, which is a challenge to insurance approval. Consequently, it has been suggested [60] that patients have at least 4–6 weeks of teriparatide therapy prior to surgical intervention. Following surgery, patients stay on teriparatide for at least 10 months, for a minimum of 12 months of total therapy.

Abaloparatide is a newer parathyroid hormone 1 receptor (PTH1R) agonist indicated for the treatment of osteoporosis in postmenopausal women with a high risk for fracture [61]. Because of its recent approval, abaloparatide is not mentioned in clinical guidelines for the treatment of postmenopausal osteoporosis, but its place in therapy is likely to be similar to that of teriparatide because the two drugs share a common mechanism of action. Use of either of these agents for more than two years is not recommended.

In a multi-center, multi-national, double-blind placebo-controlled clinical trial, Leder et al. [62] observed lumbar Bone Mineral Density (BMD) increases up to 6.7% over 24 weeks with abaloparatide versus only 5.5% and 1.6% in the teriparatide and placebo groups respectively (p = <0.001). Bilezikian et al. [63], in a Phase 2 randomized control trial of postmenopausal women aged 55–85 years, demonstrated consistently greater dose-dependent improvements in lumbar trabecular bone score by 12 weeks with abaloparatide when compared to teriparatide or a placebo. Trabecular bone score might correlate with subsequent improvement in pedicle screw strength [64]. Denosumab, a RANK-L inhibitor, has been approved by the FDA (Food and Drug Administration) and established in the treatment of osteoporosis, but its role in spine fusion has yet to be evaluated.

#### **10. Conclusion**

It has been estimated that the cost of healthcare in the United States is nearly twice as much as any other developed countries [65]. Therefore the prevention of complications and revision costs are becoming increasingly recognized and recent efforts have been made to qualify and quantify new prevention measures against

failure. Passias et al. [66] have found that DJK is a significant predictor of surgical readmission after ASD operations. In Scheuerman patients DJK might be well tolerated without symptoms, loss of alignment or mechanical decompensation [67].

Our DJK prevention strategy has proved successful in providing tools for the surgeon to foresee the risks of failure and modify the treatment in order to prevent disability, complications and revision surgery in cervical deformity patients.
