Bone fractures are most commonly occur after a trauma. But one wonders how bone can break or fracture without or with trivial trauma. Common sense may suggest that a fragile or weak bone can break easily, and that is true and the underlying reason or pathophysiology of pathologic fracture. Pathologic fracture, or the bone fractures without or with minimal traumas, has been known since 19th century.(1) It is caused by weakness in the bone structure, commonly occur due to osteoporosis. (2-3) But it also could be due to other pathologies such as cancers, infections such as osteomyelitis or bone infection, bone cysts, osteomalacia (soft bone) or paget’s disease, or even osteopetrosis (hard bone). (4-11) These fractures could be cause of a wide arrays of infections from venereal diseases, to tuberculosis, and even salmonella, (5-8) or cancers such as leukemia of childhood (9), or a cause of cancer treatment such as radiation. (10) It could also occur in a wide age range from infants and children to adults, and not only in elderly who are more common to have osteoporosis. (11-12) Pathologic fracture could also occur in many bones of the body from long bones of upper and lower extremities, to the hip and vertebrae and a small bone such as lower jaw or mandible. (13)  

 Osteoporosis, known commonly appearing in old age, specially in women has also been known for long that can occur at an earlier due to treatment with corticosteroids, used often for arthritic conditions. (14-15) This is while corticosteroids are paradoxically used also in the treatment and prevention of osteoporotic fractures. (16-17) Although pathologic fractures, specially occur in long bones and in elderly with osteoporosis in the hips, it can also occurs elsewhere including vertebral bones that is again paradoxically corticosteroids are reported to be used for its treatment and prevention. (18-19) Unrecognized such pathologic fractures of the vertebra have also been reported by radiologists without any such reports by the treating physicians in cancer patients, that partly could be due to the cancers and partly due to non-corticosteroid treatments of cancers. (20)

 

Pathologic fractures could also be caused by other drugs than steroids, through the process of precipitating osteoporosis, such as GnRH agonists, aromatase inhibitors, and anti-androgens used in the chemotherapy of breast and prostate cancers, anti-diabetic thiazolidinediones, even the anti-depressants SSRIs(selective serotonin reuptake inhibitors) and proton pump inhibitors used for the treatment of acid reflux, anti-epileptics, the blood thinners heparin and warfarin, and excess thyroid hormones. (21) Apart from osteoporosis that is common in elderly, osteomyelitis or infection of the bone is the principal contributor to the pathologic fracture. Medical conditions such as any vascular phenomena, e.g. diabetes or arteriosclerosis, immune-compromised states such as autoimmune disorders and cancers could lead to osteomyelitis, hence pathologic fracture, both in adults and children. (22-23)   

 Other than osteoporosis and osteomyelitis as the most common precipitating factors to the pathologic fracture, another rare hereditary condition, “Osteopetrosis” or “stone bone” or “marble bone” where bone hardens and is denser, opposite to osteoporosis, could cause pathologic fracture. (24-25)There are three clinical groups: infantile-malignant autosomal recessive, fatal within the first few years of life (in the absence of effective therapy); intermediate autosomal recessive, appears during the first decade of life but does not follow a malignant course; and autosomal dominant, with full-life expectancy but many orthopaedic problems. (25) While osteoporosis is mostly limited to the old age, osteomyelitis, osteopetrosis and osteomalacia (soft bone) are more common in children and can lead to pathologic fractures of different body bones. One of the more common such bone fractures in children is the hip fractures as the proximal femur is more vulnerable to injury in children even by minimal traumas. (26-27) 

Conclusion:

Pathologic fracture or spontaneous breaking of the bone is caused when the bone structure is weak and fragile. This occur the most commonly in elderly, suffering from osteoporosis specially women with several child bearings, that can with minimal traumas could break their bones, specially hip fractures from simple falls. But in children and adults, the pathologic fracture could occur, even without any traumas, due to inherited such as osteopetrosis, but mostly due to acquired conditions, either because of malnutrition, e.g. rickettsia and Paget’s disease that lead to osteomalacia (soft bone), or infections causing osteomyelitis again leading to pathologic fractures. As outlined above, other medical conditions such as cancers, vascular diseases and drugs such as steroids and anti-cancer medications and else could lead to fragile bones and pathologic fracture. Appreciation of all these precipitating factors could lead to prevention of many fractures that could be debilitating and even at times life-threatening or shortening. 

References:

1. Rigby JA. Mollities Ossium in the Male, with Spontaneous Fractures. Br Med J. 1886 Jul 3;2(1331):14-5.
2. Golob, AL; Laya, MB (May 2015). “Osteoporosis: Screening, Prevention, and Management.”. The Medical clinics of North America. 99 (3): 587–606.
3. Kim DH, Vaccaro AR (2006). “Osteoporotic compression fractures of the spine; current options and considerations for treatment”. The Spine Journal. 6 (5): 479–87.
4. Trillat A. Osteomyelitis and spontaneous fractures. Lyon Chir. 1952 May-Jun;47(4):476-8.
5. Olmstead EG. Gummatous osteomyelitis with pathologic fracture complicating general paresis; a report of three cases. Am J Syph Gonorrhea Vener Dis. 1948 May;32(3):243-50.
6. Porta Bosch M. Syphilitic osteomyelitis and pathological fracture. Guys Hosp Rep. 1957;106(3):178-82.
7. Zorba PA. Tuberculous osteomyelitis of rib with pathological fracture and associated with recurring surgical emphysema. Acta Paediatr Belg. 1967;21(2):113-24.
8. Knobel B, Sommer I, Menashes Z. A rare presentation of systemic salmonellosis. Infection. 1985 Mar-Apr;13(2):70-2.
9. Rogalsky RJ, Black GB, Reed MH. Orthopaedic manifestations of leukemia in children. J Bone Joint Surg Am. 1986 Apr;68(4):494-501.
10. Gun’ko RI, Krasnov AS. Radiation injuries of the bones during treatment of uterine cancer. Vopr Onkol. 1988;34(10):1188-95.
11. Allimant H, Peiffert G. Osteomyelitis in an infant with multiple spontaneous fractures. Arch Fr Pediatr. 1951;8(2):204-5.

12. Bosman J, Tondeur G. Spontaneous fractures in children. Acta Paediatr Belg. 1967;21(2):113-24. 
13. Marchetti C, Ercolani G, Gibelli R, Donati D, Catani F. Systemic and nonsystemic causes of pathological mandibular fractures. Minerva Med. 1986 Jul 14;77(28-29):1347-53.
14. Kynaston RU. Osteoporosis and pathological fractures following treatment with ACTH and cortisone. J Invest Dermatol. 1952 May;19(3):205-10.
15. Teicher R, Nelson CT. Pathological fractures in patients with rheumatoid arthritis treated with cortison. J Am Med Assoc. 1952 Jun 21;149(8):750-2.
16. Wells, GA; Cranney, A; Peterson, J; Boucher, M; Shea, B; Robinson, V; Coyle, D; Tugwell, P (23 January 2008). “Alendronate for the primary and secondary prevention of osteoporotic fractures in postmenopausal women.”. The Cochrane database of systematic reviews (1).
17. Kim DH, Vaccaro AR (2006). “Osteoporotic compression fractures of the spine; current options and considerations for treatment”. The Spine Journal. 6 (5): 479–87.
18. Demartini F, Grokoest AW, Ragan C. On osteoporosis of the spine with spontaneous fracture. Guys Hosp Gaz.1950 Jun 7;64(1615):241-2.
19. Luder J. Vertebral collapse after cortisone therapy. Great Ormond St J. 1954 Jun;7:15-21.
20. Wild M, Dankerl P, Hammon M, Uder M, Janka R. Vertebral body fractures of unknown origin in cancer patients receiving MDCT:reporting by radiologists and awareness by clinicians. Springerplus. 2016 Apr 14;5:450.

21. Okazaki R. Fracture risk associated with drugs other than glucocorticoids. Clin Calcium. 2014 Mar;24(3):357-65. 
22. McGuire MH. The pathogenesis of adult osteomyelitis. Orthop Rev. 1989 May;18(5):564-70.
23. Guerci A, Mainard D, Thiery D. Acute haematogenous osteomyelitis of the patella revealed by a pathological fracture in multiple myeloma. J Intern Med. 1992 Jan;231(1):87-8.
24. Tolar J, Teitelbaum S, Orchard PJ (2004). “Osteopetrosis”. New England Journal of Medicine. 351 (27): 2839–49.
25. Shapiro F. Osteopetrosis. Current clinical considerations. Clin Orthop Relat Res. 1993 Sep;(294):34-44.
26. Boardman MJ, Herman MJ, Buck B, Pizzutillo PD. Hip fractures in children. J Am Acad Orthop Surg. 2009 Mar;17(3):162-73.
27. Canavese F, Samba A, Rousset M. Pathological fractures in children: Diagnosis and treatment options. Orthop Traumatol Surg Res. 2016 Feb;102(1 Suppl):S149-59.