To determine effect of 3 half-limb casts on bone strains recorded from the proximal phalanx (P-1) and third metacarpal bone (MCIII) of equine cadaver limbs, using a mechanical testing machine.
12 equine cadaver limbs and 4 live horses.
Bone strains were recorded at middorsal P-1 and the dorsal cortical aspect of the distal third of MCIII while limbs were variably loaded with 100 to 1,000 lb of force. To determine ability of the cast to protect the distal portion of the limb from weight-bearing loads, strains were recorded with the limb in 1 of the 3 casts and with it unsupported. To determine cast-induced discomfort, weight-supporting and transfixation pin casts were evaluated on 2 live horses
All 3 casts significantly reduced bone strain at P-1. Significant differences were observed: mean 61 % reduction for the standard half-limb cast, 84% for the transfixation pin cast, and 97% for the weight-supporting cast at weight-bearing force of 500 lb. Only the weight-supporting cast significantly reduced strains recorded from MCIII. The weight-supporting cast was not well tolerated by 2 live horses.
The 3 casts significantly reduced transfer of weight-bearing forces to the distal portion of the limb. The weight-supporting cast effectively reduced strain on the P-1 to near 0, but was well tolerated by live horses. The transfixation pin cast reduced strain on the P-1 by > 80% at weight-bearing loads of 500 lb, and live horses were comfortable. Standard half-limb casts significantly reduced strains on the P- 1, but to a lesser degree than did other casts. (Am J Vet Res 1998;59:1188-1193)
Objective—–To compare transfixation and standard
full-limb casts for prevention of in vitro displacement
of a mid-diaphyseal third metacarpal osteotomy site
Sample Population—6 forelimbs from 6 horses
euthanatized for reasons not related to the musculoskeletal
Procedure—A 30° osteotomy was performed in the
mid-diaphysis of the third metacarpal bone. Two 4.5-mm cortical bone screws were placed across the
osteotomy site to maintain alignment during casting.
Two 6.35-mm Steinmann pins were placed from a lateral-to-medial direction in the distal aspect of the
radius. A full-limb cast that incorporated the pins was
applied. An extensometer was positioned in the
osteotomy site through a window placed in the dorsal
aspect of the cast, and after removal of the screws,
displacement was recorded while the limb was axially
loaded to 5,340 N (1,200 lb). Pins were removed,
and the standard full-limb cast was tested in a similar
Results—The transfixation cast significantly reduced
displacement across the osteotomy site at 445 N (100
lb), 1,112 N (250 lb), 2,224 N (500 lb), and 4,448 N
(1,000 lb), compared with the standard cast.
Conclusion and Clinical Relevance—A full-limb
transfixation cast provides significantly greater resistance
than a standard full-limb cast against axial collapse
of a mid-diaphyseal third metacarpal osteotomy
site when the bone is placed under axial compression.
Placement of full-limb transfixation casts should
be considered for the management of unstable fractures
of the third metacarpal bone in horses. (Am J
Vet Res 2000;61:1633–1635)
To determine the effect of pin hole size and number on the breaking strength of the adult equine radius when loaded in torsion to failure.
54 pairs of equine radii from adult horses.
For test one, 12 pairs of radii were used to determine the effect of pin hole size on torsional breaking strength. A 6.35-mm hole was drilled in 1 radius, and a 9.5-mm hole was drilled in the contralateral radius. For test two, 36 pairs of radii were randomly assigned to 1 of 3 treatment groups (n = 12) to determine the effect of pin hole number on the torsional breaking strength of the equine radius. One radius of each pair served as a control, and one, three, or six 6.35-mm transcortical holes were drilled in the contralateral radius. For test three, 6 pairs of radii had torsional forces applied directly to the transfixation pins, as opposed to the bone itself. One radius of a pair served as a control, and three 6.35-mm smooth Steinman pins were placed in the contralateral radius. All radii were loaded in torsion to failure, and the breaking strengths were recorded.
Compared with the 6.35-mm hole, the 9.5-mm hole significantly decreased torsional strength of the radius. There was no significant difference in mean torsional strength between the control radii and the radii with 1, 3, or 6 transcortical holes or when the transfixation pins were loaded.
Use of up to three 6.35-mm transfixation pins can be used in a full-limb transfixation pin cast to optimize stiffness without a significant decrease (12%) in bone strength. (Am J Vet Res 1998; 59:201–204)
To determine the ability of a full-limb transfixation pin cast to protect the distal portion of the equine forelimb from weight-bearing forces by measuring bone strain in vitro on cadaver limbs loaded in a mechanical testing machine.
6 forelimbs from 6 horses.
Each limb was instrumented with 3 unidirectional metal foil electrical resistant strain gauges. Gauges were placed on the dorsal aspect of the distal portion of the radius and the mid-dorsal portion of the cortex of the third metacarpal bone and the first phalanx. Each limb was tested 3 times, once supported with a transfixation pin cast, once supported by a standard full-limb cast, and finally, uncast. The limbs were tested in a mechanical testing machine under axial loads ranging from 100 to 1,000 lb, and bone strains were recorded at each load.
Compared with values for the uncast limb, the transfixation pin cast and the standard full-limb cast significantly (P < 0.001) reduced bone strain on the distal portion of the radius, third metacarpal bone, and first phalanx. Compared with the standard full-limb cast, the transfixation pin cast significantly (P < 0.001) reduced bone strain on the first phalanx.
Conclusion and Clinical Relevance
Compared with the standard full limb cast, the full-limb transfixation pin cast is more protective of the first phalanx. (Am J Vet Res 1998;59:197–200)