Elbow dysplasia is a common cause of forelimb lameness in juvenile medium- and large-breed dogs1–3; the most common dysplastic lesion of the elbow joint is FMCP.4 Despite a wealth of literature describing the purported mechanism of formation of this lesion, the true pathogenesis of the osteochondral changes preceding FMCP remains poorly defined. Early data5 suggested that FMCP was a result of osteochondrosis. However, findings of more recent studies6–9 have countered this theory and instead suggest that primary supraphysiologic overload of the medial aspect of the coronoid process in association with joint incongruity results in formation of an FMCP. In support of the latter theory, a histomorphometric study10 of excised coronoid processes from dogs with FMCP revealed that diffuse damage and fatigue microfracture of the subchondral bone bed both preceded overt cartilage fissuring and paralleled in severity the gross pathological findings of the fragment. As well as diffuse subchondral microfracture in dysplastic specimens, adjunctive osteocyte loss and increased bone porosity have also been described.10
Clinical diagnosis of FMCP can be challenging because evidence of overt fragmentation is rarely provided via conventional radiography.11 A recent study12 involving concurrent computed tomographic and arthroscopic assessments of elbow joints in dogs revealed that this dual approach provides the most accurate assessment of pathological changes in the coronoid process in vivo. However, because of both the accessibility and cost associated with advanced imaging procedures, conventional radiography remains the most commonly used imaging technique with which a diagnosis is achieved. Assessment of secondary adaptive and degenerative changes are useful in aiding diagnosis.13 One such change, that of ulnar trochlear notch sclerosis, has been recently quantified as a change in radiopacity affecting the craniodistal aspect of the trochlear notch in dogs with FMCP.13 Results of that study indicate that an increase in ulnar trochlear notch bone radiopacity accompanies FMCP. These findings appear to contradict aspects of the aforementioned histomorphometric study10 of the MCP and associated subchondral bone in dogs, in which osteocyte loss and increased porosity rather than an increase in bone microarchitecture were detected in this region. Although sagittal and parasagittal osteochondral regional BMDs of the elbow joint in clinically normal dogs have been quantified,14 no studies have directly compared the topographic distribution of BMD in normal and fragmented coronoid processes to our knowledge. Such information would be useful for defining whether regional differences in BMD and thus differences in loading characteristics of fragmented coronoid processes differ from those of unaffected MCPs. The purpose of the study reported here was to objectively quantify BMD in MCPs of dogs with and without FMCPs by use of DEXA and to establish how previously reported regional decreases in subchondral porosity10 relate to changes in BMD in this region.
Area of interest
Bone mineral density
Dual-energy x-ray absorptiometry
Fragmented medial coronoid process
Mean bone mineral density
Medial coronoid process
PIXImus scanner, Lunar, Madison, Wis.
GraphPad Instat, version 3.06, Graphpad Software Inc, San Diego, Calif.
Hercock CA, Young IS, Innes JF, et al. Measurement of bone mineral densities in the distal thoracic bones of racing greyhounds (abstr), in Proceedings. 51st Br Small Anim Vet Assoc Cong 2008;420.
Olsson SE. The early diagnosis of fragmented coronoid process and osteochondrosis dissecans of the canine elbow joint. J Am Anim Hosp Assoc 1983;19:616–626.
Kirberger RM, Fourie SL. Elbow dysplasia in the dog: pathophysiology, diagnosis and control. J S Afr Vet Assoc 1998;69:43–54.
Olsson SE. Lameness in the dog. A review of lesions causing osteoarthritis of the shoulder, elbow, hip, stifle and hock joints, in Proceedings. 42nd Am Anim Hosp Assoc Annu Meet 1975;42:363–370.
Wind AP, Packard MR. Elbow incongruity and developmental elbow disease in the dog: part 1. J Am Anim Hosp Assoc 1986;22:711–724.
Mason DR, Schulz KS, Fujita Y. In vitro force mapping of normal canine humeroradial and humeroulnar joints. Am J Vet Res 2005;66:132–135.
Danielson KC, Fitzpatrick N, Muir P, et al.Histomorphometry of fragmented medial coronoid process in dogs: a comparison of affected and normal coronoid processes. Vet Surg 2006;35:501–509.
Haudiquet PR, Marcellin-Little DJ, Stebbins ME. Use of the distomedial-proximolateral oblique radiographic view of the elbow joint for examination of the medial coronoid process in dogs. Am J Vet Res 2002;63:1000–1005.
Moores AP, Benigni L, Lamb CR. Computed tomography versus arthroscopy for the detection of canine elbow dysplasia lesions. Vet Surg 2008;37:390–398.
Samii VF, Les CM, Schultz KC, et al.Computed tomographic osteoabsorptiometry of the elbow joint in clinically normal dogs. Am J Vet Res 2002;63:1159–1166.
Meutstege FJ. Aims of the International Elbow Working group (IEWG), Constance, Germany. Vet Comp Orthop Traumatol 1996;9:58–71.
Carter DR, Hayes WC. Bone compressive strength: the influence of density and strain rate. Science 1976;194:1174–1176.
Carter DR, Hayes WC. The compressive behaviour of bone as a two-phase porous structure. J Bone Joint Surg 1977;59:954–962.
Burr DB, Turner CH, Naick P, et al.Does microdamage accumulation affect the mechanical properties of bone? J Biomech 1998;31:337–345.
Burton NJ, Comerford EJ, Bailey M, et al.Digital analysis of ulnar trochlear notch sclerosis in Labrador retrievers. J Small Anim Pract 2007;48:220–224.
Clarke S, Wakely C, Duddly J, et al.Dual-energy X ray absorptiometry applied to the assessment of tibial subchondral bone mineral density in osteoarthritis of the knee. Skeletal Radiol 2004;33:588–595.
Eckstein F, Steinlechner M, Mullergerbl M, et al.Mechanicalstress distribution and subchondral mineralization in the human elbow joint—assessment by CT osteoabsorptiometry. Unfallchirurg 1993;96:399–404.
Burton NJ, Toscano MJ, Barr FJ. Reliability of radiological assessment of ulnar trochlear notch sclerosis in dysplastic canine elbows. J Small Anim Pract 2008;49:572–576.
Bréban S, Benhamou CL, Chappard C. Dual-energy X-ray absorptiometry assessment of tibial mid-third bone mineral density in young athletes. J Clin Densitometry 2009;12:22–27.
Kato T, Yamashita T, Mizutani S, et al.Adolescent exercise associated with long-term superior measures of bone geometry: a cross-sectional DXA and MRI study [published ahead of print Jan 5, 2009]. Br J Sports Med doi:10.1136/bjsm.2008.052308.