In Vitro Biomechanical Properties of Linear, Circular, and Hybrid External Skeletal Fixation Devices for Use in Large Ruminants GAJ RAJ SINGH, MVSc, PhD, HARI PRASAD AITHAL, MVSc, PhD, RAJENDRA KUMAR SAXENA, MVSc, PhD, PRAKASH KINJAVDEKAR, MVSc, PhD, AMARPAL, MVSc, PhD, MOZAMMEL HOQUE, MVSc, PhD, SWAPAN KUMAR MAITI, MVSc, PhD, ABHIJIT MOTIRAM PAWDE, MVSc, PhD, and HEM CHANDRA JOSHI, BE Objective—To report the biomechanical properties of 3 external skeletal fixation (ESF) devices for use in large ruminants. Study Design—In vitro biomechanical testing of ESF constructs. Sample Population—Adult buffalo (weighing, 250–350 kg) tibiae (n ¼ 27). Methods—ESF constructs (bilateral linear fixator [BLF], 4-ring circular external fixator [CEF], and hybrid fixator [HF]) were made using mild (low carbon) steel implants plated with nickel and cadaveric buffalo tibiae. After ESF application, a 1 cm mid-diaphyseal gap was created. Constructs were loaded to failure, on a materials testing machine, in axial compression (n ¼ 5/ESF type) and craniocaudal bending (n ¼ 3/ESF type). In addition, 3 CEF constructs were tested in intact tibiae under craniocaudal bending. Result—In compression, HF was the strongest and most rigid construct; yield load was significantly higher for HF than for BLF or CEF. Under bending, both CEF and HF had similar strength and modulus of elasticity. Strength for BLF was higher than CEF and HF, whereas the reverse was true for modulus of elasticity. Conclusions—ESF made from mild steel for use in large ruminants could withstand  300 kg load applied under compression and bending moment without any substantial adverse biomechanical effects on the constructs. HF was most rigid and strong under compression, whereas BLF was strongest in craniocaudal bending. Overall, HF seemed biomechanically the most suitable ESF device. Clinical Relevance—A hybrid ESF developed using mild steel is sufficiently strong and economical and may prove useful for fixation of long bone fractures in large ruminants (weighing  300 kg). r Copyright 2007 by The American College of Veterinary Surgeons INTRODUCTION E XTERNAL SKELETAL fixation (ESF) devices have been widely used for treatment of long bone fractures and limb lengthening procedures in humans and small animals. 1–5 ESF provides a sustainable and com- fortable means of weight-bearing immediately after sur- gery, maintains normal joint mobility, and provides an optimal environment for osteosynthesis and wound-heal- ing without need for an implant at the fracture site. 6 ESF are not commonly used in large animal fracture repair because of lack of suitable devices that can sustain a heavy load and the forces exerted on angularly oriented bones. Use of ESF in ruminants has also been impeded by economic constraints and difficulties with post- operative care. For clinical acceptance, an ESF must be sufficiently rigid, well tolerated, easily applied, and inex- pensive. To address these concerns, we developed differ- ent ESF (a bilateral linear fixator [BLF], a 4-ring circular Approved and funded by the Indian Council of Agricultural Research, New Delhi. The work was approved by the Committee for the Purpose of Control and Supervision on Experimental Animals (CPCSEA), Government of India. Mechanical testing was completed at the Department of Biomedical Engineering, Indian Institute of Technology, New Delhi, India. No reprints available. Submitted September 2005; Accepted November 2005 From the Division of Surgery, Indian Veterinary Research Institute, Izatnagar, Uttar Pradesh, India. r Copyright 2007 by The American College of Veterinary Surgeons 0161-3499/07 doi:10.1111/j.1532-950X.2007.00239.x 80 Veterinary Surgery 36:80–87, 2007