Alternative housing systems for laying hens provide mechanical loading and help reduce bone loss. Moreover, achieving greater peak bone mass during pullet phase can be crucial to prevent fractures in the production period. The aim of this study was to determine the housing system effects on bone quality of pullets. Tibiae and humeri of White Leghorn pullets reared in conventional cages (CCs) and a cage-free aviary (AV) system were studied. At 16 wk, 120 birds at random from each housing system were euthanized. Right and left tibiae and humeri were collected and further analyzed. Cortical bone density and thickness were measured using computed tomography. Periosteal and endosteal dimensions were measured at the fracture site during mechanical testing. At 4, 8, 12, and 16 wk, serum concentrations of osteocalcin and hydroxylysyl pyridinoline were analyzed as markers of bone formation and resorption. Cortical bone density was higher (P < 0.05) in humeri of AV pullets, and tibiae were denser (P < 0.05) for AV pullets in the distal section of the bone compared to CC pullets. Ash content was higher (P < 0.05) in AV humeri with no difference in tibiae ash content. Tibiae and humeri of AV pullets had a thicker cortex than the CC pullets (P < 0.05). Additionally, the tibiae and humeri of AV pullets had greater (P < 0.05) second moment of areas than the CC pullets. While some bone material properties between groups were different (P < 0.05), the differences were so small (< 7%) that they likely have no clinical significance. Serum osteocalcin concentrations were not different between the treatments, but hydroxylsyl pyridinoline concentrations were higher in CC pullets at 12 wk compared to the AV pullets and the effect reversed at 16 wk (P < 0.05). These findings indicate that tibiae and humeri respond differently to load bearing activities during growth. The improved load bearing capability and stiffness in bones of AV pullets were related to increased cross-sectional geometry.

The role of impact interface characteristics on the biomechanics and patterns of cranial fracture has not been investigated in detail, and especially for the pediatric head. In this study, infant porcine skulls aged 2-19 days were dropped with an energy to cause fracturing onto four surfaces varying in stiffness from a rigid plate to one covered with plush carpeting. Results showed that heads dropped onto the rigid surface produced more extensive cranial fracturing than onto carpeted surfaces. Contact forces generated at fracture initiation and the overall maximum contact forces were generally lower for the rigid than carpeted impacts. While the degree of cranial fracturing from impacts onto the heavy carpeted surface was comparable to that of lower-energy rigid surface impacts, there were fewer diastatic fractures. This suggests that characteristics of the cranial fracture patterns may be used to differentiate energy level from impact interface in pediatric forensic cases.

Current literature associates bending failure with butterfly fracture, in which fracture initiates transversely at the tensile surface of a bent bone and branches as it propagates toward the impact surface. The orientation of the resulting wedge fragment is often considered diagnostic of impact direction. However, experimental studies indicate bending does not always produce complete butterfly fractures or produces wedge fragments variably in tension or compression, precluding their use in interpreting directionality. This study reports results of experimental 3-point bending tests on thirteen unembalmed human femora. Complete fracture patterns varied following bending failure, but incomplete fractures and fracture surface characteristics were observed in all impacted specimens. A flat, billowy fracture surface was observed in tension, while jagged, angular peaks were observed in compression. Impact direction was accurately reconstructed using incomplete tension wedge butterfly fractures and tension and compression fracture surface criteria in all thirteen specimens.

Fracture patterns of long bones broken under various loading conditions have been well documented [1,8]. Of particular interest in the current study was the wedge or “butterfly” type fracture that occurs as a result of bending forces on a bone. Butterfly fractures generally consist of a characteristic “Y” shape across the long axis [1,7]. While no studies were found that examine the mechanism of such a fracture, it is generally accepted and widely published that the bottom of the Y fracture is found on the tensile side and the top split portion occurs on the compressive side of the neutral axis (Figure 1). This phenomenon is explained using basic solid mechanics principles. Since the tensile strength of bone is 133 MPa compared to a compressive strength of 193 MPa [6], bending initiates a transverse fracture on the tensile side. However, across the neutral axis, compressive forces dominate and tensile failure is thought not to continue. Since the shear strength of bone is 51.6 MPa [10], less than half the compressive strength, the bone appears to fail along the planes of maximum shear stress at 45° to the transverse split [3].

Recently, attention has been brought to the welfare of laying hens and the benefits provided by progressive housing systems [3]. Conventional battery cage (CC) systems provide each bird with access to feed and water at all times with room to move. One of the new housing types being implemented, referred to as a cage-free aviary system (AV), is much larger than conventional cages and houses more birds. Aviary systems comprise multiple levels providing more opportunity for movement and exercise. Hens can forage and dust bathe in an open communal area, have access to perches, and nest boxes. However, for mature hens to fully utilize an AV, pullets (pre-egg production birds) must be reared in a similar environment.