Babhulkar which 84%(31 out of 37) were diagnosed

Babhulkar et al in 2005 reported in his study conducted retrospectively on 113 patients diagnosed as nonunion of diaphyseal bone treated by different treatment options over the duration of 15 years. Out of 113 nonunions, there were 36 tibia, 23 femur, 21 humerus, 13 radius, 18 ulna, 2 clavicle. 84 nonunions were aseptic, 29 were infected. 61 nonunions were hypertrophic and 52 were atrophic. (21)

There are various factors studied on nonunion as risk factor or etiology. Most of the nonunion has been found to have multiple etiology.

The etiology for nonunion can be broadly categorized into biological and mechanical whereas biological can be local or systemic. Trauma-related factors such as soft-tissue detachment, interruption of blood supply, irradiation of bone, infection, bone loss are frequent local biologic etiologies. Systemic biologic etiologies comprises advanced age, co-morbidities like diabetes mellitus, chronic anemia, metabolic or endocrine abnormalities, malnutrition, medications such as steroids, anti-inflammatory, antiepileptic medications, and smoking. Mechanical factors comprise improper anatomical contacts such as malalignment, the gap between fragments, malposition, and inadequate stability at the fracture site, improper implant selection, and fixation. (22)

In a case series study conducted by Brinker et al. in 683 patients with nonunion from 1998 to 2005  31 patients were referred for metabolic and endocrine evaluation out of which 84%(31 out of 37) were diagnosed to have an abnormality. 25 of 37  were diagnosed to have vitamin D deficiency other frequent diagnoses were central hypogonadism, calcium imbalances, central hypogonadism, thyroid disorders, and parathyroid hormone disorders.(23)

Patients  with fracture of long bones treated with  NSAIDs during  postsurgery period were found to have  twice likely and smokers more than three times likely  risk to get complicated  with nonunion or infection in a retrospective study by Jeffcoach et al in 1901 patients with fracture with 12.1% under NSAIDs and 18.4% smoker.(24)

Rigid external fixator was found to be significant risk factor for non-union with incidence up to 14%.(7)

Hypertrophic nonunion results from inadequate stability between bone fragments with leads to failure of the osseous transformation of the fibrous tissue formed at the fracture site.(25)

Gross mobility at fracture site due to inadequate fracture immobilization or improper internal fixation interferes with the normal healing process with the formation of fibrocartilage which fails to mature into solid callus leading often to a stiff  hypertrophic nonunion with or without deformity and limb shortening.(26)