Calcified Tissue Structure in the Distal Condyle of the Third Metacarpal Bone in Young Thoroughbred Horses

Aims: To determine improvements in third metacarpal (Mc3) condylar microanatomy attributable to preconditioning exercise. To investigate developmental causes of Mc3 condylar fracture. Methods: Twelve Thoroughbred horses were raised at pasture; six received preconditioning exercise from 10 days. Calcein labels were administered 19 and 11 days prior to euthanasia at 18 months. Six horses also received 2 seasons of race-training and were euthanised at 3 years. Slices were taken from the distal Mc3 condyle in the frontal and dorsal- and palmar-oblique frontal planes, scanned with DXA and macerated (frontal slices) or embedded in PMMA (oblique slices). Articular calcified cartilage (ACC) and subchondral bone (SCB) in oblique slices were imaged using confocal scanning light microscopy and quantitative backscattered electron scanning electron microscopy. ACC and SCB in the palmar slice lateral parasagittal grooves were imaged using µCT and nanoindentation tested. Results: Characteristic spatial variations in ACC and SCB histomorphometric parameters were present, none of which was significantly related to preconditioning exercise. Thickened, aberrantly mineralised ACC was found in 13/24 parasagittal grooves in the palmar slices and on the sagittal ridge of 4/12 dorsal slices of 18-month-old horses. Deep to thickened ACC, SCB had an open marrow structure, having not adopted the buttress morphology of the normal SCB plate. SCB in 3-year-old horses had incorporated early ACC defects as notches in parasagittal grooves and a hyaline cartilage island in a sagittal ridge. ACC was less stiff and SCB more stiff in affected than unaffected parasagittal grooves. Chondroclastic resorption in the parasagittal groove may be retarded as early as 3-6 months, possibly due to localised inhibition of ACC mineralisation. Linear defects in the Mc3 parasagittal groove may develop prior to entry to race training and are not significantly affected by preconditioning exercise. Early identification of affected individuals should aid in reducing condylar fracture risk.

Year	Entry
1994	Mente PL, Lewis JL. Elastic modulus of calcified cartilage is an order of magnitude less than that of subchondral bone. J Orthop Res. September 1994;12(5):637-647.
1998	Roschger P, Fratzl P, Eschberger J, Klaushofer K. Validation of quantitative backscattered electron imaging for the measurement of mineral density distribution in human bone biopsies. Bone. October 1998;23(4):319-326.
1974	Lanyon LE. Experimental support for the trajectorial theory of bone structure. J Bone Joint Surg. 1974;56B(1):160-166.
2006	Gibson VA, Stover SM, Gibeling JC, Hazelwood SJ, Martin RB. Osteonal effects on elastic modulus and fatigue life in equine bone. J Biomech. 2006;39(2):217-225.
1996	Martin RB, Lau ST, Mathews PV, Gibson VA, Stover SM. Collagen fiber organization is related to mechanical properties and remodeling in equine bone: a comparsion of two methods. J Biomech. December 1996;29(12):1515-1521.
1997	Burr DB, Schaffler MB. The involvement of subchondral mineralized tissues in osteoarthrosis: quantitative microscopic evidence. Microsc Res Tech. May 15, 1997;37(4):343-357.
1892	Wolff J. Das Gesetz der Transformation der Knochen. Berlin: Hirschwald; 1892.
1993	Boyde A, Elliott JC, Jones SJ. Stereology and histogram analysis of backscattered electron images: age changes in bone. Bone. May–June 1993;14(3):205-210.
2005	Boutroy S, Bouxsein ML, Munoz F, Delmas PD. In vivo assessment of trabecular bone microarchitecture by high-resolution peripheral quantitative computed tomography. J Clin Endocrinol Metab. December 2005;90(12):6508-6515.
2007	Bolotin HH. DXA in vivo BMD methodology: an erroneous and misleading research and clinical gauge of bone mineral status, bone fragility, and bone remodelling. Bone. July 2007;41(1):138-154.
1983	Bullough PG, Jagannath A. The morphology of the calcification front in articular cartilage: its significance in joint function. J Bone Joint Surg. January 1983;65B(1):72-78.
1992	Gross TS, McLeod KJ, Rubin CT. Characterizing bone strain distributions in vivo using three triple rosette strain gages. J Biomech. September 1992;25(9):1081-1087.
2002	Ohashi N, Robling AG, Burr DB, Turner CH. The effects of dynamic axial loading on the rat growth plate. J Bone Miner Res. February 2002;17(2):284-292.
2005	Mow VC, Huiskes R. A brief history of science and orthopaedic biomechanics. In: Mow VC, Huiskes R, eds. Basic Orthopaedic Biomechanics & Mechano-Biology. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005:1-27.
2005	Poole KES, Van Bezooijen RL, Loveridge N, Hamersma H, Papapoulos SE, Löwik CW, Reeve J. Sclerostin is a delayed secreted product of osteocytes that inhibits bone formation. FASEB J. August 2005;19(10):1842-1844.
2005	O'Brien FJ, Taylor D, Lee TC. The effect of bone microstructure on the initiation and growth of microcracks. J Orthop Res. March 2005;23(2):475-480.
1987	Kiviranta I, Jurvelin J, Tammi M, Säämäunen A-M, Helminen HJ. Weight bearing controls glycosaminoglycan concentration and articualr cartilage thickness in the knee joints of young beagle dogs. Arthritis Rheum. July 1987;30(7):801-809.
2006	Mohsin S, O'Brien FJ, Lee TC. Osteonal crack barriers in ovine compact bone. J Anat. January 2006;208(1):81-89.
2005	Skedros JG, Holmes JL, Vajda EG, Bloebaum AD. Cement lines of secondary osteons in human bone are not mineral‐deficient: new data in a historical perspective. Anat Rec. September 2005;286A(1):781-803.
2003	Ferguson VL, Bushby AJ, Boyde A. Nanomechanical properties and mineral concentration in articular calcified cartilage and subchondral bone. J Anat. August 2003;203(2):191-202.
2006	Peterlik H, Roschger P, Klaushofer K, Fratzl P. From brittle to ductile fracture of bone. Nat Mater. January 2006;5(1):52-55.
1987	Frost HM. Bone “mass” and the “mechanostat”: a proposal. Anat Rec. September 1987;219(1):1-9.
2005	Schriefer JL, Warden SJ, Saxon LK, Robling AG, Turner CH. Cellular accommodation and the response of bone to mechanical loading. J Biomech. September 2005;38(9):1838-1845.
1995	Gibson VA, Stover SM, Martin RB, Gibeling JC, Willits NH, Gustafson MB, Griffin LV. Fatigue behavior of the equine third metacarpus: mechanical property analysis. J Orthop Res. November 1995;13(6):861-868.
2002	Deckers MML, van Bezooijen RL, van der Horst G, Hoogendam J, van der Bent C, Papapoulos SE, Löwik CWGM. Bone morphogenetic proteins stimulate angiogenesis through osteoblast-derived vascular endothelial growth factor A. Endocrinology. April 2002;143(4):1545-1553.
2003	Boyde A. The real response of bone to exercise. J Anat. August 2003;203(2):173-189.
1987	Lanyon LE. Functional strain in bone tissue as an objective, and controlling stimulus for adaptive bone remodelling. J Biomech. 1987;20(11-12):1083-1093.
2008	Bembey AK. Micro-Mechanical Properties and Composite Behaviour of Bone [PhD thesis]. Queen Mary University of London; 2008.
1999	Boyde A, Travers R, Glorieux FH, Jones SJ. The mineralization density of iliac crest bone from children with osteogenesis imperfecta. Calcif Tiss Int. March 1999;64(3):185-190.
2004	Loveridge N, Power J, Reeve J, Boyde A. Bone mineralization density and femoral neck fragility. Bone. October 2004;35(4):929-941.
1881	Roux W. Der kampf der theile im organismus: Ein beitrag zur vervollständigung der mechanischen zweckmässigkeitslehre. Leipzig: Verlag von Wilhelm Engelmann; 1881.
1987	Reid SA, Boyde A. Changes in the mineral density distribution in human bone with age: image analysis using backscattered electrons in the SEM. J Bone Miner Res. February 1987;2(1):13-22.
2006	Franz-Odendaal TA, Hall BK, Witten PE. Buried alive: how osteoblasts become osteocytes. Dev Dyn. January 2006;235(1):176-190.
2005	Mow VC, Gu WY, Chen FH. Structure and function of articular cartilage and meniscus. In: Mow VC, Huiskes R, eds. Basic Orthopaedic Biomechanics & Mechano-Biology. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005:181-258.
1983	Biewener AA, Thomason J, Lanyon LE. Mechanics of locomotion and jumping in the forelimb of the horse (Equus): in vivo stress developed in the radius and metacarpus. J Zool. 1983;201(1):67-82.
2004	Currey JD, Brear K, Zioupos P. Notch sensitivity of mammalian mineralized tissues in impact. Proc R Soc B. March 7, 2004;271(1538):517-522.
1975	Turner AS, Mills EJ, Gabel AA. In vivo measurement of bone strain in the horse. Am J Vet Res. November 1975;36(11):1573-1579.
2003	Kronenberg HM. Developmental regulation of the growth plate. Nature. May 15, 2003;423(6937):332-336.
2003	Crawford RP, Cann CE, Keaveny TM. Finite element models predict in vitro vertebral body compressive strength better than quantitative computed tomography. Bone. 2003;33(4):744-750.
1983	Biewener AA, Thomason J, Goodship A, Lanyon LE. Bone stress in the horse forelimb during locomotion at different gaits: a comparison of two experimental methods. J Biomech. 1983;16(8):565-576.
2005	Gupta HS, Schratter S, Tesch W, Roschger P, Berzlanovich A, Schoeberl T, Klaushofer K, Fratzl P. Two different correlations between nanoindentation modulus and mineral content in the bone–cartilage interface. J Struct Biol. February 2005;149(2):138-148.
1988	Eggli PS, Hunzinker EB, Schenk RK. Quantitation of structural features characterizing weight- and less-weight-bearing regions in articular cartilage: a stereological analysis of medical femoral condyles in young adult rabbits. Anat Rec. November 1988;222(3):217-227.
2003	Frost HM. Bone's mechanostat: a 2003 update. Anat Rec. 2003;275A(2):1081-1101.
2004	Burr DB. Anatomy and physiology of the mineralized tissues: role in the pathogenesis of osteoarthrosis. Osteoarthritis Cartilage. 2004;12(suppl):S20-S30.
1985	Rubin CT, Lanyon LE. Regulation of bone mass by mechanical strain magnitude. Calcif Tiss Int. 1985;37(4):411-417.
1997	Martin RB, Gibson VA, Stover SM, Gibeling JC, Griffin LV. Residual strength of equine bone is not reduced by intense fatigue loading: implications for stress fracture. J Biomech. February 1997;30(2):109-114.
2003	Cotton JR, Zioupos P, Winwood K, Taylor M. Analysis of creep strain during tensile fatigue of cortical bone. J Biomech. July 2003;36(7):943-949.
2004	Bushby AJ, Ferguson VL, Boyde A. Nanoindentation of bone: comparison of specimens tested in liquid and embedded in polymethylmethacrylate. J Bone Miner Res. January 2004;19(1):249-259.

Year

Entry

1994

Mente PL, Lewis JL. Elastic modulus of calcified cartilage is an order of magnitude less than that of subchondral bone. J Orthop Res. September 1994;12(5):637-647.

1998

Roschger P, Fratzl P, Eschberger J, Klaushofer K. Validation of quantitative backscattered electron imaging for the measurement of mineral density distribution in human bone biopsies. Bone. October 1998;23(4):319-326.

1974

Lanyon LE. Experimental support for the trajectorial theory of bone structure. J Bone Joint Surg. 1974;56B(1):160-166.

2006

Gibson VA, Stover SM, Gibeling JC, Hazelwood SJ, Martin RB. Osteonal effects on elastic modulus and fatigue life in equine bone. J Biomech. 2006;39(2):217-225.

1996

Martin RB, Lau ST, Mathews PV, Gibson VA, Stover SM. Collagen fiber organization is related to mechanical properties and remodeling in equine bone: a comparsion of two methods. J Biomech. December 1996;29(12):1515-1521.