1. Bone morphogenic protein (BMP) and tissue engineering
Published: September 2013
Author: Gerhard Schmidmaier
Reviewer: Martin Stoddart
Reviewed: 2018
AO Trauma Advanced Principles Course

2. Learning objectives Identify bone morphogenetic proteins (BMP)
Evaluate research and clinical data of BMP for therapy with good outcome
Explore key outcome publications
Understand the risks
Teaching points:
Make the participants aware that the use of bone substitutes is also related to reduction techniques and soft tissue handling.

3. Why this discussion Problems with healing
Open fractures/segmental defects
Dysvascular segments/chronic nonunions
Infection/osteomyelitis
Cost and intraoperative time
Functional outcome/evidence-based medicine
BMP associated complications
This summarizes the multiple issues surrounding BMP and tissue engineering.

4. Problem: future improvements
Biomechanically well-established implants...
Research in orthopedic trauma has been mostly concentrated on the development of biomechanically well-established implants.
From a biomechanical standpoint we have reached a level that may not be improved significantly in the near future, or longer.

5. Impaired fracture healing
Complications in 5–10%
Due to:
Soft-tissue trauma
Poor biomechanics
Impaired biology
Why does one out of every 10–20 patients with a fracture have problems in fracture healing?
The primary reasons are:
Soft-tissue trauma
Poor biomechanics
Impaired biology
The use of BMPs is particularly important in cases of impaired biology.

6. Autogenous bone graft complications
Minor complication: 4–20.6%
Hematoma and seroma
Nervus cutaneus femoris lateralis
Pain (15–39%, 2-year postoperative)
Major complication: 3.4–8.6%
Fracture
Bleeding
Complications from bone graft harvest have been among the forces leading to development of alternatives to autograft.
References:
1. Goulet JA, Senunas LE, DeSilva, et al. Autogenous iliac crest bone graft. Complications and functional assessment. Clin Orthop Relat Res Jun;(339):76–81.
2. Robertson PA, Wray AC. Natural history of posterior iliac crest bone graft donation for spinal surgery: a prospective analysis of morbidity. Spine Jul 1;26(13):
3. Sasso RC, Macadaeg K, Nordmann D, et al. Selective nerve root injections can predict surgical outcome for lumbar and cervical radiculopathy: comparison to magnetic resonance imaging. J Spinal Disord Tech Dec;18(6):471–478.
(Prospektive Studie, ALIF) 6

7. Diamond concept of bone healing
Mechanical stability
Vascularization
Scaffolds
Cells
Bone healing requires multiple factors, as can be seen in this diagram. Growth factors are an important part of bone healing.
References:
1. Giannoudis PV, Einhorn TA, Marsh D. Fracture healing: the diamond concept. Injury Sep;38 Suppl 4:S3–S6.
2. Giannoudis PV, Einhorn TA, Schmidmaier G, et al. The diamond concept--open questions. Injury Sep;39 Suppl 2:S5–S8.
Growth factors

8. Osteoconductive: passive Surface/structure
Scaffold
Osteoconductive: passive
Surface/structure
Promotes in and on growth of cells
Osteoinductive: active
Stimulates bone healing
Recruits and differentiates cells
Osteogenic: active
Material contains vital cells for bone formation
BMPs
Cells
Note that BMPs are part of osteoinduction.

9. Demineralized bone matrix (DBM)
Advantages
Approved material
Unlimited resources
Disadvantages
Contains BMPs only in nanograms, less than amount found in normal bone...osteoinductive?
Amount of BMPs in DBM is highly variable
Quality of donor bone/age?
To what extent is the processing of DBMs controlled?
Does it stimulate bone healing in a environment that really requires additional bone healing stimulation?
There is a lack of good clinical trial data
Demineralized bone matrix is often used as a graft material. While it is osteoconductive, it contains only trace amounts of BMP and should not be considered strongly osteoinductive.

10. Synthetics versus bone
Bone composition
Tricalcium phosphates (TCP) and HA-based synthetic bone graft substitutes resemble the composition of normal bone
TCPs and HA have good biocompatibility
Products should remodel like normal bone
65% inorganic
Hydroxyapatite (HA): calcium and phosphate
Bone stores 99% of body's calcium
35% organic
90% collagen 1
Other proteins
References:
Sandberg MM. Matrix in cartilage and bone development: current views on the function and regulation of major organic components. Ann Med Aug;23(3):207–217.

11. Reaming irrigation aspiration (RIA)
port
Aspiration
port
Irrigation and aspiration:
Reduction of pressure and heat
Clearance of medullary canal
Graft harvest
RIA versus Iliac crest
FGFa + (2.1)
FGFb - (0.5)
VEGF - (0.5)
PDGFbb + (2.9) Comparable GF concentration
IGF-I + (1.6) vital osteogenic cells
TGF-ß (3.5)
BMP-2 + (3)
Autogenous bone graft, as is taken from the femur with the RIA device, has high levels of growth factors.
References:
Schmidmaier G, Herrmann S, Green J, et al. Quantitative assessment of growth factors in reaming aspirate, iliac crest, and platelet preparation. Bone Nov;39(5):1156–1163.

12. Composition of bone 65% inorganic
Hydroxyapatite (HA): calcium and phosphate
Bone stores 99% of body's calcium
35% organic
90% collagen 1
2.5% osteonectin
1.5% osteocalcin
1.5% phosphoproteins
< 0.1% Growth factors
Bone has very low levels of growth factors, compared to other components.
References:
Sandberg MM. Matrix in cartilage and bone development: current views on the function and regulation of major organic components. Ann Med Aug;23(3):207–217.

13. Growth factors and cell differentiation
TGF-ß superfamily
BMP-2/4/7
TGF-ß1/3
IGF-I
VEGF
PDGF
FGF
......
Multiple growth factors are involved in cell differentiation. The cells must be present in order for them to be effective.

14. Modeling/remodeling of bone
Cell differentiation is essential for bone formation and remodelling, both of which play a role in fracture healing.

15. Growth factors and cell differentiation
Chondroblasts
Enchondral
ossification
Differentiation
Proliferation
Intramembranous
ossification
MSC
Work and stimulating and controlling both differentiation, proliferation, and matrix synthesis of bone-specific cells.
Osteoblasts

16. Platelet rich plasma Advantages Autogenous Easy to collect
PDGF, IGF, TGFb, VEGF…
Mostly maxillofacial
Disadvantages
Low concentration of growth factors
Lack of prospective clinical studies
Platelet rich plasma has been suggested as a source of autogenous growth factors. There is little evidence that this is an effective means of delivering effective growth factors.

17. BMPs Advantages Multiple experimental studies Level I clinical studies
As good as or even better compared to autogenous bone
Disadvantages
Costs
DRG
Complication rates higher than first reported
BMPs were first described by Marshall Urist in 1965.

18. BMP—clinical studies Authors Year Study design Indication Patients BMP
Union rate (%)
Kujala S, et al
2004
Retrospective, observational, nonrandomized
Nonunion various sites 5 7
100
Giannoudis PV, et al UK
2005
Nonunion, osteotomies etc, various sites
653 82
Dimitriou R, et al 26 92
Ronga M, et al
Bios study group
Italy
2006
105 89
Zimmermann G, et al 23
2007
Prospective, matched pairs, controlled trial
Nonunion tibial shaft
108
Sign. higher
Ristiniemi J, et al
Prospective, controlled trial
Pilon fractures 40
Sign. faster
Nonunion pelvic girdle 9
German Chapter
2008
172 79
There are multiple clinical studies of BMP’s. However, they are often poorly controlled and underpowered.
References:
Kujala S, Raatikainen T, Ryhänen J, et al. Composite implant of native bovine bone morphogenetic protein (BMP), collagen carrier and biocoral in the treatment of resistant ulnar nonunions: report of five preliminary cases. Arch Orthop Trauma Surg Jan;124(1):26–30.
Giannoudis PV, Tzioupis C. Clinical applications of BMP-7: the UK perspective. Injury Nov;36 Suppl 3:S47–S50.
Dimitriou R, Dahabreh Z, Katsoulis E, et al. Application of recombinant BMP-7 on persistent upper and lower limb non-unions. Injury Nov;36 Suppl 4:S51–S59.
Ronga M, Baldo F, Zappalà G, et al. Recombinant human bone morphogenetic protein-7 for treatment of long bone non-union: an observational, retrospective, non-randomized study of 105 patients. Injury Sep;37 Suppl 3:S51–S56.
Zimmermann G, Moghaddam A, Wagner C, et al. [Clinical experience with bone morphogenetic protein 7 (BMP 7) in nonunions of long bones]. Unfallchirurg Jul;109(7):528–537. German.
Zimmermann G, Müller U, Löffler C, et al. [Therapeutic outcome in tibial pseudarthrosis: bone morphogenetic protein 7 (BMP-7) versus autologous bone grafting for tibial fractures]. Unfallchirurg Nov;110(11):931–938.
Ristiniemi J, Flinkkilä T, Hyvönen P, et al. RhBMP-7 accelerates the healing in distal tibial fractures treated by external fixation. J Bone Joint Surg Br Feb;89(2):265–272.
Giannoudis PV, Psarakis S, Kanakaris NK, et al. Biological enhancement of bone healing with Bone Morphogenetic Protein-7 at the clinical setting of pelvic girdle non-unions. Injury Sep;38 Suppl 4:S43–S48.

19. BMP—clinical studies BMP-2:
Govender et al (J Bone Joint Surg. 2002;84:2123–2134)
BMP-7:
Friedlaender et al (J Bone Joint Surg Am. 2001;Suppl: 151– 158)
The two commercially available recombinant of BMP’s are BMP-2 and BMP-7. BMP-2 has been studied in a large trial of open tibial fractures. BMP-7 was similarly studied in the treatment of tibial nonunion.
References:
Govender S, Csimma C, Genant HK, et al. Recombinant human bone morphogenetic protein-2 for treatment of open tibial fractures: a prospective, controlled, randomized study of four hundred and fifty patients. J Bone Joint Surg Am Dec;84-A(12):2123–2134.
Friedlaender GE, Perry CR, Cole JD, et al. Osteogenic protein-1 (bone morphogenetic protein-7) in the treatment of tibial nonunions. J Bone Joint Surg Am. 2001; Suppl:S151–S158.

20. RCT—RHOP-1 versus bone autograft
Friedlaender et al (J Bone Joint Surg Am. 2001;Suppl: 151–158)
Conclusion:
No serious product-related adverse events were reported
Demonstrates the ability of OP-1 to grow bone in a difficult model
Clinically equivalent to autograft
Eliminates harvest site pain
“OP-1 in recombinant form and combined with a type-1 bovine bone-derived collagen offers the advantages of a highly inductive molecule, with an excellent safety profile and the lack of donor site morbidity.”
Patients treated with OP-1 versus autographed were very similar.
References:
Friedlaender GE, Perry CR, Cole JD, et al. Osteogenic protein-1 (bone morphogenetic protein-7) in the treatment of tibial nonunions. J Bone Joint Surg Am. 2001;Suppl:S151–S158.

21. BMP-2 in open fractures BMP-2 insertion twice at 2 weeks
Volume: 4x4x10=160 cc
Case example of BMP-2 used in treatment of bone defect in femoral fracture.
Note that this is not an FDA approved use of the device. Furthermore, there is no evidence that it is of benefit in this application.

22. 40-year-old man, infected tibial nonunion
12 months prior, open segmental tibial fracture
Day 4 with microbiological culture (+) wound  infection
Multiple debridements, salvage
Failure to thrive at week 3
Recurrent infection x 3
Antibiotics and nail x 3
Salvaged with debridement, fixation, and BMP-7

23. BMP-7
BMP-7 shows the same efficacy in osteoinduction compared to autogenous bone grafting in the first revision surgery
BMP-7 shows a significant higher efficacy in osteoinduction compared to autogenous bone grafting in multiple failed cases

24. Humanitarian device exemption
INFUSE bone graft
OP-1
Protein
rhBMP-2
rhBMP-7
Carrier
8.0 cc collage sponge
1 g collagen granules
BMP concentration
1.5 mg/mL
0.88 mg/mL
BMP delivered
12 mg
3.5 mg
Graft produced
8 cc
4 cc
Indication
Acute, open tibial fractures reduced with IM nail
Recalcitrant long-bone nonunions where autograft is unfeasible
Regulatory status
Premarket approval
Humanitarian device exemption
Price
USD 4,900
USD 5,000
Clinical success (package insert)
Secondary interventions reduced by 41%
Nonunion rate reduced by 29%
74% union tibia
80% union long bone
OP-1 has a device exemption and NOT an approval.
OP-1 could not prove to the FDA that it was effective in treating nonunions.
INFUSE bone graft has an approval for open tibial fractures because it could prove to the FDA that it was effective.
INFUSE bone graft delivers 8 cc of graft with 12 mg of rhBMP-2 for about the same cost.

25. FDA public health notification
“Life-threatening Complications Associated with Recombinant Human Bone Morphogenetic Protein in Cervical Spine Fusion”
Issued: July 1, 2008
Oncological risks
Nerve damage

26. Complications of rhBMP-2 for treating complex tibial plateau fractures
Off-label use of BMP in a periarticular fracture situation, particularly in tibial plateau fractures, might lead to higher reoperation rates as a result of the symptoms associated with heterotopic ossification
Surgeons must exercise caution and weigh the risks and benefits of these products before using them in their patients
Clin Orthop Relat Res (2009) 467:3257–3262

27. Evidence Grade of recommendation
Good evidence (Level-I studies with consistent findings) for or against recommending intervention
Fair evidence (Level-II or III studies with consistent findings) for or against recommending intervention
Poor-quality evidence (Level-IV or V studies with consistent findings) for or against recommending intervention
There is insufficient or conflicting evidence not allowing a recommendation for or against intervention
References:
De Long WG Jr, Einhorn TA, Koval K, et al. Bone grafts and bone graft substitutes in orthopaedic trauma surgery. A critical analysis. J Bone Joint Surg Am Mar;89(3):649–658.
De Long et al (J Bone Joint Surg Am. 2007;89:649–658)

28. BMP and autograft
There is some evidence that BMP-7 and autograft together can have a better effect in atrophic nonunion than either alone
There is some evidence that BMP-7 and autograft can have a better effect in atrophic nonunion than either alone.
Reference:
Giannoudis PV, Kanakaris NK, Dimitriou R, et al. The synergistic effect of autograft and BMP-7 in the treatment of atrophic nonunions. Clin Orthop Relat Res Dec;467(12):3239–3248.

29. Take-home messages
BMPs aid in cell differentiation, an essential part of bone healing
Recombinant BMP may be part of a strategy to provide osteoinduction
BMP-2 may aid in treatment of open fractures
BMP-7 may be of benefit in treating atrophic nonunions, especially those that have been operated on multiple times
Be aware of complications arising from BMP use
The problem with BMP is the expense.