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12 DISTAL LIMB REGION

Distal Limb Region

Metacarpals, Metatarsals, Digits, Sesamoids, and Associated Structures
Nicolaas E. Lambrechts

Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University,
Fort Collins, CO, USA

12.1 Introduction

Although often overlooked because of the small size and complexity of their component anatomic
structures, minor clinical findings, and paucity of available information regarding disease mani-
festation and methods of clinical examination for this region, injuries and diseases of the distal
limb are a frequent and important source of lameness. This chapter describes many conditions that
may subtly or profoundly affect a dog’s normal gait and ambulatory performance. Figure 12.1 and
Table 12.1 outline common differential diagnoses and diagnostic steps for the distal limb region.

12.2 Normal Anatomy

12.2.1 Thoracic Limb
The five metacarpals, numbered from medial to lateral, have a cylindrically shaped body articulat-
ing proximally with the distal row of carpal bones at their base and distally with the similarly
numbered phalanges at their head (Figure 12.2). Metacarpal I, the smallest, only has a proximal
epiphysis, does not bear weight, and may be supernumerary in some individuals or breeds (e.g.
Saint Bernards). Metacarpals II–V all bear weight, although the longer III and IV are believed to
bear greater loads. They all have a single distal physis and diverge from each other as they course
distally. At each of the metacarpophalangeal joints II–V, there are also articulations with a single
dorsal sesamoid (Figure 12.3), which lies within the common digital extensor tendons and two
(single in metacarpal I) elongated, inwardly curved sesamoids within the ligamentous insertion of
the interosseous muscles. These palmar sesamoids are also numbered from medial to lateral; how-
ever, only the paired sesamoids are numbered (Cake and Read 1995; Figure 12.2).
The metacarpal bones are attached to the distal row of carpal bones by synovial membranes and
numerous straight and oblique ligaments. Distal to the synovial reflections, the individual bones are
held to each other by interosseous metacarpal ligaments. There is very little movement at the carpo-
metacarpal joint. At the transversely oriented metacarpophalangeal joints, movement is mainly flexion

Canine Lameness, First Edition. Edited by Felix Michael Duerr.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/duerr/lameness