Chip fracture of the proximal phalanx in Thoroughbreds
Dorsoproximal fragments of the proximal phalanx are often associated with no clinical signs but they must be suspected in young Thoroughbreds with acute swelling and heat in the MCP joint (Richardson and Dyson, 2011; Ramzan, 2014). Dorsoproximal fragments may be the result of a separated centre of ossification or the result of a traumatic event during early development and sometimes they can be seen as incidental finding only when performing presale radiographs. Usually fragments due to an early development occur equally in the forelimbs and the hindlimbs while the traumatic ones are more often observed in the forelimbs (Richardson and Dyson, 2011). Although dorsoproximal fragments are often asymptomatic they can cause arthroscopic evidence of synovitis associated or not with damage of the articular cartilage (fibrillation) (McIllwraith and Bramlage, 1996; Butler et al, 2017).
Surgical removal is considered the treatment of choice when the presence of a fragment is associated with joint effusion and lameness (McIlwraith et al., 2015; Butler et al, 2017). Conservative management with resting and intra-articular injections of corticosteroids can lead to fair results in a short term perspective, and if the horse has imminent racings, but the definitive removal of the fragment has a superior long-term prognosis. The better result with surgery is mainly due to avoid degenerative changes in the articular cartilage especially when the fragment is, as in this case, unstable (McIlwraith and Bramlage, 1996; Richardson and Dyson, 2011; McIlwraith et al., 2015). In thoroughbreds most fragments are considered to be chip fracture instead of OCD fragment (Butler et al, 2017) and they’re often the result of a repetitive or acute overextension of the fetlock with a dorsal impact of the proximal phalanx on the third metacarpal bone (Ramzan, 2014). Bilateral chip fractures are fairly common (Richardson and Dyson, 2011). Ultrasound can be a helpful tool in cases with minimally displaced fragments and when radiographs are not exhaustive (Vanderperren et al., 2009; Ramzan, 2014). A standing Needle Arthroscopy for the removal of dorsal fragmentation within the MCP joint has been described avoiding risks related to general anaesthesia (Elce and Richardson, 2002; Bonilla, 2019). In North American Thoroughbreds the left forelimb (LF) is slightly more affected than the RF, but the difference is not statistically significative. A true prevalence of the RF compared to the LF has not been proved, but dorsoproximal fragments are more common in the dorsomedial aspect of the proximal aspect of the proximal phalanx (Walsh et al., 2018; Ramzan, 2014). Colòn et al. (2000) reported that 89% of the horses raced after surgery and 82% raced at a higher level, this data was recently confirmed by Ramzan and Wylie (2019) with a 85.7% of success rate. Mean time for return to racing is 3 months after surgery (Ramzan, 2014).
· Bonilla AJ (2019) Standing Needle Arthroscopy of the Metacarpophalangeal and Metatarsophalangeal Joint for Removal of Dorsal Osteochondral Fragmentation in 21 Horses. Vet Comp Orthop Traumatol; 32, pp. 420–426
· Butler JA, Colles CM, Dyson SJ, Kold SE and Poulos PW (2017) “Clinical radiology of the Horse”, 4 edition, Ch. 5 “Metacarpophalangeal and metatarsophalangeal (fetlock) joints” pp. 175-213. WILEY Blackwell.
· Colòn JL, Bramlage LR, Hance SR and Embertson RM (2000) Qualitative and quantitative documentation of the racing performance of 461 Thoroughbred racehorses after arthroscopic removal of dorsoproximal first phalanx osteochondral fractures (1986–1995). Equine vet. J.; 32 (6) 475-481
· Elce and Richardson (2002) Arthroscopic Removal of Dorsoproximal Chip Fractures of the Proximal Phalanx in Standing Horses. Veterinary Surgery 31: pp. 195-200
· McIlwraith, C.W. and Bramlage, L.R. (1996) Surgical treatment of joint injury. In: Joint Disease in the Horse, 1st edn., Eds: C.W. McIlwraith and G.W. Trotter, Saunders, Philadelphia. pp 292–316
· McIlwraith, C.W., Nixon, A.J. and Wright, I.M. (2015) Diagnostic and surgical arthroscopy of the metacarpophalangeal and metatarsophalangeal joints. In: Diagnostic and Surgical Arthroscopy in the Horse, 4th edn. Eds: C.W. McIlwraith, A.J. Nixon and I.M. Wright, Mosby Elsevier, Philadelphia. pp 111–140.
· Ramzan P.H.L. (2014) “The Racehorse a Veterinary Manual”, Ch. 2 “Regional Muscoloskeletal conditions” pp. 70-72. CRC Press
· Ramzan and Wylie (2019) “Nonsurgical and surgical management of metacarpo/ metatarsophalangeal joint dorsal chip fracture in the Thoroughbred racehorse” Equine Veterinary Journal, 0, pp. 1–5
· Richardson and Dyson (2011) “The metacarpophalangeal joint” in Ross and Dyson “Diagnosis and management of Lameness in the horse” Ch.36 pp.39-410. 3rd edition, Elsevier.
· Vanderperren, K., Martens, A.M., Declercq, J., Duchateau, L. and Saunders, J.H. (2009) Comparison of ultrasonography versus radiography for the diagnosis of dorsal fragmentation of the metacarpophalangeal or metatarsophalangeal joint in horses. J. Am. Vet. Med. Ass. 235, pp. 70–75.
· Walsh R, Smith MRW and Wright IM (2018) Frequency distribution of osteochondral fragmentation of the dorsoproximal articular surface of the proximal phalanx in racing Thoroughbreds in the UK. Equine Veterinary Journal 50, pp. 624