The Effects of Onychectomy (Declawing) on Forearm and Leg Myology in a Kinkajou (Potos flavus)

Abstract

Recently, onychectomy, the "declaw" surgery in which all or part of the distal phalanges are removed, has been shown to have significant effects on the forearm muscles of felids. While this surgery should clearly affect the limb muscles (especially those that insert on the removed or modified bone), these effects have not been studied beyond felids or in the hindlimb. To that end, we herein evaluated the muscle architecture of a kinkajou (Potos flavus) that was declawed on all four of its limbs and compared its anatomy to that of intact specimens and the felid findings. As expected, some of the declawed kinkajou's muscles were substantially different from those of the intact specimens, and as was seen in felids, its digital muscles appear to have been weaker. However, unlike in the felids, the declawed kinkajou had relatively larger forearm muscles. Also, contrary to expectation, the leg muscles of the declawed kinkajou were not substantially different, perhaps reflecting important differences in limb use. Future analyses should examine this anatomy in other declawed kinkajou specimens and also look at the effects of this surgery in other taxa, for instance, non-arboreal relatives of the kinkajou as well as other arboreal taxa.

Keywords: Potos flavus; Procyonidae; antebrachial muscles; crural muscles; fascicles; muscle architecture; physiological cross-sectional area.

Figure 1

Forearm muscles of the declawed Potos flavus that is the focus of this paper (a–d) in comparison to that of an intact specimen (inset; from [47] courtesy of B. Townsend). Superficial (a) and deep (b) views of the posterior (extensor) compartments, and superficial (c) and deep (d) views anterior (flexor) compartments, respectively. Yellow = digital flexors; green = wrist flexors; red = digital extensors; blue = wrist extensors; pink = pronators/supinators/other. See Table 1 for muscle name abbreviations. ECRB is not pictured due to its position deep to BR. The asterisk denotes the position of where the amputated fourth digit would be with the cyan dot marking the head of metacarpal IV.

Figure 2

Leg muscles of the declawed Potos flavus that is the focus of this paper (a–d) in comparison to that of an intact specimen (inset; from [48] courtesy of H. Smith). Superficial (a) and deep (b) views of the medial compartments, and superficial (c) and deep (d) views of the lateral compartments, respectively. Yellow = digital flexors; green= non-digital plantar flexors; red = digital extensors; blue = evertors; pink = invertors; white = bone. See Table 1 for muscle name abbreviations.

Figure 3

Relative declawed forearm muscle mass, PCSA, and FL of the kinkajou compared to that of felids. The circles represent kinkajou values and the squares felid values. Black shapes represent muscles/functional groups that most directly relate to digital function. Filled squares are statistically significantly different in declawed versus clawed felids. Likely due to sample size, no kinkajou values were statistically significantly different between the declawed and clawed specimens.

Figure 4

Relative declawed leg muscle mass, PCSA, and FL of the kinkajou. Black circles represent muscles/functional groups that most directly relate to digital function. As with the forearm comparisons, likely due to sample size, no kinkajou values were statistically significantly different between the declawed and clawed specimens.