Choosing Between Absolute and Relative Stability Fixation
Whether a construct is built for absolute or relative stability determines what a healing x-ray should show, and whether a missing callus is reassuring or a red flag.
Takeaways
- Absolute stability produces primary bone healing with no visible callus. Strain under 2% lets osteons remodel directly across the fracture line, and the line fades on x-ray instead of showing new bone (Goodship et al, Clin Orthop Relat Res 1998; Inacio et al, J Orthop Res 2022).
- Relative stability heals through visible callus formation. Strain between 2% and 10% triggers secondary bone healing, progressing through hematoma, soft (cartilaginous) callus, hard (bony) callus, and remodeling, seen on serial x-rays as bridging callus (Goodship et al, Clin Orthop Relat Res 1998; Inacio et al, J Orthop Res 2022).
- Fracture pattern determines whether absolute or relative stability is chosen. This 2% to 10% strain framework has guided fixation planning since the 1970s, with absolute stability (lag screw and compression plate) for simple, two-part or articular fractures and relative stability (bridge plate, IM nail, or external fixator) for comminuted, multifragmentary fractures to preserve fragment blood supply (Inacio et al, J Orthop Res 2022).
- A locked bridging plate can be too rigid to heal. Periarticular locking-plate series report nonunion in up to 19% of cases when construct stiffness suppresses the interfragmentary motion callus formation needs (Bottlang et al, J Bone Joint Surg Am 2010;92 Suppl 2:12-22, PMID 21123589).
- This rigidity problem shows up in real clinical outcomes. A 2025 multicenter study of forearm diaphyseal fractures found nonunion in 18.5% of fractures fixed with locking plates alone versus 6.2% with dynamic compression plates, an independent predictor of nonunion (Tseng et al, J Orthop Traumatol 2025).
- Reducing construct stiffness restores callus formation. In an ovine model, a stiffness-reduced locking technique (far cortical locking) produced 36% greater callus volume and 44% higher bone mineral content than standard locked plating, confirming stiffness, not biology, was the limiting factor (Fitzpatrick et al, J Bone Joint Surg Am 2010).
- The classic strain rule is itself now contested. 2025 finite-element modeling of healed ovine osteotomies found gap-closing strains averaging 51% at the far cortex, far above the textbook ceiling, suggesting local strain tolerance is higher and more regional than the 2-10% rule implies (Tanveer et al, Bone Joint Res 2025, DOI 10.1302/2046-3758.141.BJR-2024-0191.R2).