34th Annual Scientific Meeting proceedings

Desmotomy of the accessory ligaments of the superficial (AL-SDFT) and deep digital flexor tendons (AL-DDFT) is used for two primary indications: flexural deformities and flexor tendinopathies. A rarer indication is chronic desmopathy of the accessory ligament itself. The body of evidence for these interventions includes biomechanical evaluations and clinical outcome studies, with findings that vary depending on study populations, indications, surgical techniques, and long-term follow-up.

AL-DDFT desmotomy is most often used in the management of acquired flexural deformities of the distal interphalangeal joint, particularly in foals and young horses unresponsive to conservative treatment and in severely affected cases. AL-SDFT desmotomy with or without concurrent AL-DDFT desmotomy may also be used for treatment of flexural deformity of the fetlock joint (Kidd, 2019). Savelberg et al. (1997) provided biomechanical evidence that forelimb kinematics can recover after AL-DDFT desmotomy, although alterations in joint loading during locomotion suggest adaptive changes. Retrospective studies have reported generally favourable outcomes depending on deformity severity and chronicity (Walmsley et al., 2011; Yiannikouris et al., 2011; Carlier et al., 2016). Wismann et al. (2022), however, reported reduced career longevity and diminished athletic performance in sport horses undergoing AL-DDFT desmotomy compared to a matched control group. This contrasts with the more optimistic long-term outcomes seen in Standardbreds (Stick et al., 1992), underscoring how breed and/or discipline influence prognosis. While some studies claimed significantly better results when horses were treated at a younger age (Stick et al., 1982; Carlier et al., 2016), other studies concluded no significant effect of age at surgery (Walmsley et al., 2011; Wisman et al., 2022). This seeming contradiction illustrates that the surgery can still be performed successfully in adult horses, but surgery should not be postponed in cases requiring it at a younger age.

AL-SDFT desmotomy has been used in the management of superficial digital flexor tendinopathy, particularly in racehorses, based on the idea to lengthen the functional musculotendinous unit of the SDFT (Kümmerle et al., 2019). Hu and Bramlage (2014) reported a 228/332 (69%) return-to-racing rate in Thoroughbreds following desmotomy (medial approach through the flexor carpi radialis tendon sheath). Standardbred racehorses have a better prognosis for a return to racing after AL-SDFT desmotomy than Thoroughbred racehorses (OR 4.0 95% CI 1.2-13.3) (Murphy et al., 2022). In Warmblood sport horses, Blatter et al. (2024) reported 46/62 (75%) of cases to be sound after surgery (tenoscopic desmotomy of only sub-synovial main part of AL), with 31 (51%) of these horses performing at the same level as before surgery, although recurrent injuries or persistent lameness was observed in 15 (25%) horses.

In contrast with the aforementioned clinical studies, cadaver studies have raised biomechanical concerns as AL-SDFT desmotomy resulted in increased fetlock extension and strain on both the SDFT and the suspensory ligament, suggesting potential risk for compensatory overload or re-injury (Shoemaker et al., 1991; Alexander et al., 2001). Moreover, an in vivo prospective study on 31 Thoroughbreds with SDFT tendinopathy treated with AL-SDFT desmotomy vs. 93 cases managed non-surgically reported no significant advantage of AL-SDFT desmotomy over non-surgical treatment, and horses treated by AL-SDFT desmotomy were 5.46 times more likely to develop suspensory desmitis than those treated non-surgically (95% CI 1.13 to 26.4) (Gibson et al., 1997).

AL-DDFT desmotomy has been explored as a potential treatment for chronic DDFT tendinopathy, especially for cases refractory to conservative therapies. For example, positive outcomes were reported in three Quarter Horses treated surgically for persistent DDFT tendinopathy (Humbach & Gutierrez-Nibeyro, 2018). Schramme (2017) highlighted the mechanical rationale for this approach, explaining that reducing proximal constraint may decrease strain on the injured DDFT within the foot. These findings suggest potential value in carefully selected cases but require validation in larger cohorts.

In conclusion, desmotomy of the AL-DDFT and AL-SDFT is supported by a substantial body of evidence for treatment of flexural deformities and should be considered in cases unresponsive to conservative treatment and severe cases. While AL-SDFT desmotomy has been described for treatment of tendinopathy in sport and racehorses, many studies lack a control group and there are biomechanical concerns suggesting potential risk for compensatory overload or re-injury. In selected cases, AL-DDFT desmotomy may be applied in refractory DDFT injuries, but biomechanical trade-offs may need to be considered. Further prospective and discipline-specific studies are needed to guide clinical decision-making and optimize outcomes.

References

1. Alexander GR, Gibson KT, Day RE, et al. Effects of superior check desmotomy on flexor tendon and suspensory ligament strain in equine cadaver limbs. Vet Surg. 2001;30:522–527.
2. Blatter M, Chapman H-S, Heinzel-Gutenbrunner M, et al. Performance of Warmblood horses following tenoscopic desmotomy of the main part of the accessory ligament of the superficial digital flexor tendon for treatment of tendinopathy: 62 cases. Equine Vet J. 2024 (https://doi.org/10.1111/evj.14437).
3. Carlier S, Oosterlinck M, Martens A, et al. Treatment of acquired flexural deformity of the distal interphalangeal joint in the horse: a retrospective study on 51 cases. Vlaams Dierg Tijdschr 2016;85:9–14.
4. Gibson KT, Burbidge HM, Pfeiffer DU. Superficial digital flexor tendonitis in thoroughbred race horses: outcome following non-surgical treatment and superior check desmotomy. Aust Vet J. 1997;75:631–635.
5. Hu AJ, Bramlage LR. Racing performance of Thoroughbreds with superficial digital flexor tendonitis treated with desmotomy of the accessory ligament of the superficial digital flexor tendon: 332 cases (1989-2003). J Am Vet Med Assoc. 2014;244:1441–1448.
6. Humbach KE, Gutierrez-Nibeyro SD. Desmotomy of the accessory ligament of the deep digital flexor tendon for treatment of chronic deep digital flexor tendinopathy in three Quarter Horses. Equine Vet Educ 2018;30(10):538-544.
7. Kidd JA. Flexural limb deformities. In: Equine Surgery (5^th edition) 2019. Elsevier, St Louis, Missouri. Eds: Auer, Stick, Kümmerle and Prange. Pp. 1490-1509.
8. Kümmerle JM, Theiss F, Smith RKW. Diagnosis and management of tendon and ligament disorders. In: Equine Surgery (5^th edition) 2019. Elsevier, St Louis, Missouri. Eds: Auer, Stick, Kümmerle and Prange. Pp.1411-1445.
9. Murphy DJ, Kö-Peternelj V, Aleri JW. Intralesional bone marrow and superior check desmotomy is superior to conservative treatment of equine superficial digital flexor tendonitis. Equine Vet J. 2022;54:1047–1054.
10. Savelberg HH, Buchner HH, Becker CK. Recovery of equine forelimb function after desmotomy of the accessory ligament of the deep digital flexor tendon. Equine Vet J Suppl 1997;23:27-29.
11. Schramme M. Treatment of tendinopathy in the foot – what have we learned so far? Equine Vet Educ 2018; 30(10):545-548
12. Shoemaker RS, Bertone AL, Mohammad LN, et al. Desmotomy of the accessory ligament of the superficial digital flexor muscle in equine cadaver limbs. Vet Surg. 1991;20:245–252.
13. Stick JA, Nickels FA, Williams MA. Long-term effects of desmotomy of the accessory ligament of the deep digital flexor muscle in Standardbreds: 23 cases (1979-1989). J Am Vet Med Assoc. 1992;200:1131.
14. Walmsley EA, Anderson GA, Adkins AR. Retrospective study of outcome following desmotomy of the deep digital flexor tendon for type 1 flexural deformity in Thoroughbreds. Aust Vet J. 2011;89:265–268.
15. Wismann ES, Jacobsen S, Thøfner M, et al. Long-term athletic performance in sport horses after desmotomy of the accessory ligament of the deep digital flexor tendon. Equine Vet J. 2022;54:495-501.
16. Yiannikouris S, Schneider RK, Sampson SN, et al. Desmotomy of the accessory ligament of the deep digital flexor tendon in the forelimb of 24 horses 2 years and older. Vet Surg. 2011;40:272–276.