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

a Knowledge Summary by

Julia Dubuc DMV, DÉS, DACVS-LA, M.Sc, MRCVS ^1*

Christopher Akkari BVMedSci (Hons), BVM BVS (Hons), MRCVS²

¹University of Nottingham, Sutton Bonnington Campus, Sutton Bonnington, Leicestershire, LE12 5RD
²Ringneill Equine Clinic, 53 Ringneill Road, Comber, Newtownards, BT23 6EF
^*Corresponding Author (julia.dubuc@nottingham.ac.uk)

Clinical scenario

You are required to perform prepurchase radiographs (including both stifles, tarsi and carpi as well as all four fetlocks) on a young racing thoroughbred. All joints radiographed are unremarkable aside from the left metatarsophalangeal joint, which presents a proximo-plantar osteochondral fragment (PlOF) of the medial aspect of the proximal phalanx. While the horse’s training is well under way, it has not raced yet. No lameness has been reported by the trainer and there is no obvious joint effusion on physical examination. However, the response to full hindlimb flexion is positive. The trainer asks if surgical removal is advised at this stage.

The evidence

Based on the literature currently available, there is no definitive evidence that preventative surgical removal of PlOF from the proximal phalanx in young Thoroughbreds decrease the incidence of subsequent lameness. On the other hand, a more substantial amount of publications are focused on other breeds, namely Standardbred racehorses and Warmbloods. The literature comprises mostly small case series and retrospective studies and the evidence, as is pertains to young Thoroughbreds, is therefore of low quality.

Summary of the evidence

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).

Methodology Section

Search Strategy
Databases searched and dates covered:	CAB Abstracts 1973 to Week 18 2018 PubMed NCBI 1900 to Week 23 2018
Search terms:	CAB Abstracts (equine* or horse* or equus or equid* or mare or mares or broodmare* or 'brood mare*' or pony or ponies or filly or fillies or colt or colts or stallion* or thoroughbred* or standardbred* or racehorse* or 'race horse*').mp. or exp horses/ or exp equus/ or exp equidae/ or exp mares/ or exp colts/ or exp foals/ or exp stallions/ or exp thoroughbred/ or exp racehorses/ ((osteochond* and (fragment* or chip or chips or dissecans)) or OCF or OCD).mp. (((proximal or proximo) and plantar) or (proximal and phalanx) or P1 or proximoplantar*).mp. (arthroscop* or surger* or surgical* or operat* or excision* or excise* or dissect*).mp. or exp surgery/ or exp surgical operations/ 1 and 2 and 3 and 4   PubMed (equine* or horse* or equus or equid* or mare or mares or broodmare* or 'brood mare*' or pony or ponies or filly or fillies or colt or colts or stallion* or thoroughbred* or standardbred* or racehorse* or 'race horse*') ((osteochond* and (fragment* or chip or chips  or dissecans)) or OCF or OCD) (((proximal or proximo) and plantar) or (proximal and phalanx) or P1 or proximoplantar*) (arthroscop* or surger* or surgical* or operat* or excision* or excise* or dissect*) 1 and 2 and 3 and 4
Dates searches performed:	14/5/2018 and 3/6/2018

Exclusion / Inclusion Criteria
Exclusion:	Articles not relevant to PICO question dorsoproximal fragments other joints than fetlock other breeds than thoroughbred only Conference papers/proceedings not published Non-English language publications
Inclusion:	Relevant to PICO question thoroughbred or thoroughbred racehorse conservative and surgical treatment, proximo-plantar fragments of P1

Search Outcome
Database	Number of results	Excluded – not relevant to PICO	Excluded – duplicates	Excluded – conference papers not published	Excluded – other languages	Total relevant papers
CAB Abstracts	25	18	0	1	3	3
PubMed	45	38	7	0	0	0
Total relevant papers when duplicates removed						3

The authors declare no conflicts of interest.

1. Barclay, W., Foerner, J. and Phillips, T. 1987. Lameness attributable to osteochondral fragmentation of the plantar aspect of the proximal phalanx in horses: 19 cases (1981–1985). Journal of the American Veterinary Medical Association 191, 855–857.
2. Carmalt, J.L., Borg, H., Näslund, H. and Waldner, C. 2014. Racing performance of Swedish Standardbred trotting horses with proximal palmar/plantar first phalangeal (Birkeland) fragments compared to fragment free controls. The Veterinary Journal 202, 43–47. DOI: https://doi.org/10.1016/j.tvjl.2014.07.017
3. Carmalt, J., Borg, H., Näslund, H. and Waldner, C. 2015. Racing performance in Standardbred trotting horses with proximal palmar/plantar first phalangeal fragments relative to the timing of surgery. Equine Veterinary Journal 47, 433–437. DOI: https://doi.org/10.1111/evj.12317
4. Declercq, J., Martens, A., Bogaert, L.., Boussauw, B., Forsyth, R. and Boening, K.J. 2008. Osteochondral fragmentation in the synovial pad of the fetlock in warmblood horses. Veterinary Surgery 37, 613–618. DOI: https://doi.org/10.1111/j.1532-950x.2008.00426.x
5. Declercq, J., Martens, A., Maes, D., Boussauw, B., Forsyth, R. and Boening, K.J., 2009. Dorsoproximal proximal phalanx osteochondralfragmentation in 117 Warmblood horses. Veterinary and Comparative Orthopaedics and Traumatology 22, 1–6. DOI: https://doi.org/10.3415/vcot-08-02-0016 
6. Declercq, J., Hauspie, S., Saunders, J. and Martens, A. 2011. Osteochondral fragments in the metacarpo- and metatarsophalangeal joint and their clinical importance. (Osteochondrale fragmenten in het kogelgewricht en hun klinisch belang) Vlaams Diergeneeskundig Tijdschrift, 80, 271–280.
7. Fortier, L., Foerner, J. and Nixon, A. 1995. Arthroscopic removal of axial osteochondral fragments of the plantar/palmar proximal aspect of the proximal phalanx in horses: 119 cases (1988–1992). Journal of the American Veterinary Medical Association 206, 71–74. DOI: https://doi.org/10.1111/j.1532-950X.2004.04061.x
8. Houttu, J. 1991. Arthroscopic removal of osteochondral fragments of the palmar/plantar aspect of the metacarpo/metatarsophalangeal joints. Equine Veterinary Journal 23, 163–165. DOI: https://doi.org/10.1111/j.2042-3306.1991.tb02747.x 
9. Kane, A.J., Park, R.D., McIlwraith, C.W., Rantanen, L.W., Morehead, J.P. and Bramlage, L. R. 2003. Radiographic changes in Thoroughbreds yearlings. Part I: Prevalence at the time of yearling sales. Equine Veterinary Journal 35, 354–365. DOI: https://doi.org/10.2746/042516403776014280 
10. Walsh, R., Smith, M.R.W. and Wright, I.M. 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, 624–628. DOI: https://doi.org/10.1111/evj.12795 
11. Whitton, R. and Kannegieter, N. 1994. Osteochondral fragmentation of the plantar/palmar proximal aspect of the proximal phalanx in racing horses. Australian Veterinary Journal 71, 318–321. DOI: https://doi.org/10.1111/j.1751-0813.1994.tb00906.x

RCVS Knowledge was supported in producing this Knowledge Summary by an educational grant from Petplan Charitable Trust.