Histology of 8 atypical femoral fractures: remodeling but no healing.
OBJECTIVE
The pathophysiology behind bisphosphonate-associated atypical femoral fractures remains unclear. Histological findings at the fracture site itself may provide clues.


METHODS
Between 2008 and 2013, we collected bone biopsies including the fracture line from 4 complete and 4 incomplete atypical femoral fractures. 7 female patients reported continuous bisphosphonate use for 10 years on average. 1 patient was a man who was not using bisphosphonates. Dual-energy X-ray absorptiometry of the hip and spine showed no osteoporosis in 6 cases. The bone biopsies were evaluated by micro-computed tomography, infrared spectroscopy, and qualitative histology.


RESULTS
Incomplete fractures involved the whole cortical thickness and showed a continuous gap with a mean width of 180 µm. The gap contained amorphous material and was devoid of living cells. In contrast, the adjacent bone contained living cells, including active osteoclasts. The fracture surfaces sometimes consisted of woven bone, which may have formed in localized defects caused by surface fragmentation or resorption.


CONCLUSIONS
Atypical femoral fractures show signs of attempted healing at the fracture site. The narrow width of the fracture gap and its necrotic contents are compatible with the idea that micromotion prevents healing because it leads to strains within the fracture gap that preclude cell survival.
Orthopedics Section, Department of Clinical and Experimental Medicine, Faculty of Health Science , Linköping University.
Jörg
J
Schilcher
Olof
O
Sandberg
Hanna
H
Isaksson
Per
P
Aspenberg
D015502:Absorptiometry, Photon; D000368:Aged; D000369:Aged, 80 and over; D001706:Biopsy; D015519:Bone Density / Q000502:physiology; D016723:Bone Remodeling / Q000502:physiology; D001862:Bone Resorption / Q000503:physiopathology; D002470:Cell Survival / Q000502:physiology; D004164:Diphosphonates / Q000009:adverse effects* / Q000627:therapeutic use*; D005260:Female; D005264:Femoral Fractures / Q000139:chemically induced* / Q000473:pathology* / Q000503:physiopathology; D005269:Femur / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D010010:Osteoclasts / Q000473:pathology / Q000502:physiology; D010024:Osteoporosis / Q000517:prevention & control*; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D014945:Wound Healing / Q000502:physiology
D004164:Diphosphonates