Is removal of proximo-plantar osteochondral fragments necessary in young Thoroughbreds?

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Appraisal, application and reflection

There are very few studies evaluating the impact of proximo-plantar osteochondral fragmentation (PlOF) in young thoroughbreds. By contrast, a larger number of publications on PlOF of the proximal phalanx (P1) focused on standardbred racehorses and warmbloods is available. Based on the three studies mentioned above and taking into consideration that the breed of the horses included in the paper from Barclay et al. (1987) is not specified, a grand total of six Thoroughbreds were included and it remains unclear if all six were destined for racing.

The reported prevalence of PlOF of P1 in racing Thoroughbreds is 5.9%, with 4.1% type I and 1.8% type II fragments (Kane et al., 2003). Both dorsal and plantar fragmentation were found to be twice as common in the hind fetlocks compared to forelimbs. The same authors (Kane et al., 2003), in their retrospective radiographic survey of yearling Thoroughbred sales, also reported twice as many type I fragmentation compared to type II and that these tended to be unilateral.

It is thought that PlOF of P1 would cause lameness at high speed, or mostly during performance (Fortier et al., 1995; Houttu, 1991; Whitton et al., 1994). As previously stated, this has been investigated mostly in another type of racehorse, the standardbred trotters. Carmalt et al. (2015) reported that standardbred racehorses which had osteochondral fragmentation of the proximo-palmar/plantar aspect of the proximal phalanx did not slow down prior to surgery, or speed up after. In a case-control study from the same group (Carmalt et al., 2014), 174 standardbred racehorses with PlOF were compared with ones radiographically normal (613 horses). No difference in race speed was found between the two groups before surgical removal. Moreover, the horses did not slow down prior to, nor sped up after surgery. The authors concluded that surgical removal of proximal palmar or plantar fragmentation was not recommended. Houttu (1991), in an older study including mainly standardbred trotters undergoing fragment removal, reported that 23/45 (51%) of the horses successfully returned to training speed in 3 months and this increased to 41/45 (91%) at 6 months postsurgery. While this information is very valuable and relates to racehorses working at high speed, extrapolation of these findings to young Thoroughbreds is questionable.

Despite the evidence stated above appearing quite dated, these are the only three studies containing a variable number of Thoroughbreds to provide any follow-up information. There is no mention of a mean time to follow-up making it difficult to draw any conclusions regarding the soundness of these horses in the long-term. Although Whitton et al. (1994) reported three horses presenting refragmentation in previously operated joints, there is generally very few details regarding recurrence of the lameness and how this was subsequently addressed. Houttu (1991) reported that 3/45 (6%) of the horses which underwent surgical removal of the fragmentation were lame 3 months after surgery when the trainer attempted working at high speed and that 2/45 (4%) stayed lame due to a lesion located in the joint. However, these lesions are not described in the publication. Fortier et al. (1995) found significant association between unsuccessful racehorses and the presence of cartilage loss or synovial proliferation. While related articular cartilage or any other intra-articular pathology could influence potential future lamenesses, the data currently available in the literature is presented in ways not amenable to comparison between the different studies: 9/155 metatarsophalangeal joints had full thickness articular cartilage defect (Fortier et al., 1995) whereas 8/21 horses (38%) had intra-articular degenerative changes in arthroscopy (Whitton et al., 1994). A clear, exhaustive description of concurrent intra-articular pathology and long-term follow-up of these specific cases is needed to determine the impact of surgical or conservative management of PlOF of P1 on subsequent lameness.

The authors failed to find studies including a separate group composed of fragment free Thoroughbred horses, to act as control group as well as a conservative and surgical group. While the papers from Barclay et al. (1987) and Whitton et al. (1994) compare surgical and conservative management of these fragments, higher quality evidence, in the form of a prospective study with an extensive long-term follow-up and more detailed description of intra-articular findings, is required to determine if pre-emptive surgical removal of PlOF of the proximal phalanx is warranted and reduces the risk of lameness.

As previously mentioned, supplemental literature concerning proximal phalanx osteochondral fragmentation is available namely in warmbloods (Declercq et al., 2011; Declercq et al., 2009; Declercq et al., 2008) and also concerning dorsal osteochondral fragmentation of the proximal phalanx in Thoroughbreds (Walsh et al., 2018).

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