Retrospective analysis of distal limb conformation and lameness in mature horses after desmotomy of the accessory ligament of the deep digital flexor tendon for management of a flexural deformity

Mature horses that present with flexural deformity of the distal interphalangeal joint and lameness isolated to the foot may obtain long‐term benefits from desmotomy of the accessory ligament of the deep digital flexor tendon (ALDDFT). This retrospective analysis of medical records and radiographs included 13 horses, aged ≥2 years, presented for lameness isolated to the hoof region and diagnosed with flexural deformity of the distal interphalangeal joint. Radiographic angles of the hoof and distal interphalangeal joint and lameness scores were compared before and after desmotomy of the ALDDFT. Follow‐up data including the ability to perform the intended use were obtained at least one year after surgery. There was improvement in the angle between the dorsal aspect of the third phalanx and the weightbearing surface of the hoof, improved alignment between the dorsal hoof wall and dorsal aspect of the third phalanx, and improved alignment of the distal interphalangeal joint. Lameness was decreased in 9/13 horses and 10/13 horses were performing at their level of intended use. Evidence of improved hoof conformation and lameness following desmotomy of the ALDDFT in lame horses with flexural deformity of the distal interphalangeal joint would indicate this procedure should be considered in mature horses.     

Ultrasonographic diagnosis of injuries to the deep digital flexor tendon and associated structures in the equine foot (suprasesamoidean area)

Foot pain is the most common cause of lameness in horses. In sport horses, podotrochlear syndrome (‘navicular syndrome’) is reported to be the most frequent condition affecting the front foot. Ultrasonography has the potential to detect damage to the soft tissues as well as the bone surfaces; in some clinics it has become the technique of choice for the identification and documentation of many podotrochlear injuries. The purpose of this paper is to review the main pathological conditions of the proximal part of the podotrochlear apparatus (PTA) that can be diagnosed ultrasonographically, focusing on the deep digital flexor tendon (DDFT), podotrochlear bursa (PTB) and distal digital annular ligament (DDAL). Potentially significant ultrasonographic findings of the DDFT include thickening of one or both lobes, longitudinal tears, focal or diffuse changes in echogenicity, irregularities of the dorsal border and adhesions between the DDFT and the proximal sesamoidean ligament and/or distal sesamoid bone. Deep digital flexor tendon injuries are often associated with concurrent lesions of the PTB (acute to chronic bursitis) and of the DDAL (desmopathy). Both feet should be routinely examined as lesions of the PTA are often bilateral. We currently consider that ultrasonography should be routinely employed as the primary diagnostic procedure to complement radiography of the equine foot.     

Minimally invasive desmotomy of the accessory ligament of the deep digital flexor tendon in horses

This retrospective study describes ultrasound guided desmotomy of the accessory ligament of the deep digital flexor tendon in 35 cases, and a modification of this procedure using an adapted surgical instrument. The procedure was successful in 97% of cases. Wound healing was excellent in all except 4 cases. Corrective shoeing prior to surgery contributes to success. The procedure can be performed on the standing horse and offers the advantages of minimally invasive surgery which include: reduced incision length, reduced morbidity and improved cosmetic outcome. The adapted surgical instrument can be an alternative to isolate the ligament under ultrasound guidance.     

Injection of the insertion of the deep digital flexor tendon in horses using radiographic guidance

Insertional tendinopathies of the DDFT have been reported both as the sole lesion and as part of a multifocal lesion (Dyson et al. 2003). Computed tomography (CT) and magnetic resonance imaging allow specific diagnosis of deep digital flexor tendon lesions within the hoof capsule; however, direct intralesional treatment of such lesions is difficult because of the hoof's rigid structure. A technique designed to mimic intralesional injection of insertional tendinopathies of the DDFT in the standing horse using radiographic guidance was assessed. Radiographic and contrast CT imaging and sectioning of the limbs confirmed accurate injection in all cases although inadvertant administration of injectate into adjacent structures was also evident.     

Desmotomy for treatment of chronic desmitis of the accessory ligament of the deep digital flexor tendon in a horse.

Chronic lameness was determined to be caused by desmitis of the accessory ligament of the deep digital flexor tendon and adhesions associated with these 2 structures. Desmotomy of the accessory ligament, resection of adhesions, and controlled exercise during convalescence resulted in return to normal use without apparent lameness.     

Possible role of carpal hyperextension in superficial digital flexor tendinopathy

Reasons for performing study: The specific biomechanical circumstances that induce excessive superficial digital flexor tendon (SDFT) strain in horses are unknown. Hypothesis: Carpal joint hyperextension during axial limb loading during the middle of stance disproportionately enhances SDFT strains compared to suspensory ligament (SL) strains. Methods: Superficial digital flexor tendon and SL strains were measured in 7 cadaver limbs during in vitro loading that maintained carpal extension or allowed carpal hyperextension by constraining, or allowing rotation of, the radius during loading conditions that simulated the middle of stance at the walk. The effect of carpal hyperextension on SDFT and SL strains and joint angles was assessed using repeated measures ANOVA. Results: Limb loading generally resulted in higher SL strains than SDFT strains for both carpal extension and hyperextension loading conditions. Compared to carpal extension, carpal hyperextension resulted in increased strains in both the SDFT and the SL; however, a greater increase in strain was seen in the SDFT. On average, carpal hyperextension caused approximately 3° greater carpal extension, 1° greater metacarpophalangeal joint hyperextension, 1° greater proximal interphalangeal joint flexion and <1° greater distal interphalangeal joint flexion than did carpal extension. Conclusions and clinical relevance: Carpal joint hyperextension is likely to induce disproportionately higher strain in the SDFT than in the SL. Factors that affect carpal stability are likely to affect the risk for superficial digital flexor tendinopathy.     

Short-term temporal alterations in magnetic resonance signal occur in primary lesions identified in the deep digital flexor tendon of the equine digit

Reasons for performing study: Primary lesions of the deep digital flexor tendon (DDFT) within the digit are an important cause of lameness diagnosed using magnetic resonance imaging (MRI) but appearance of these lesions over time has not been documented. Objectives: To determine whether the magnetic resonance (MR) appearance of different primary DDFT lesions alter over a 6 month period and whether lesion type is a determinant of these changes. Methods: Cases included had lameness attributable to a primary lesion involving the DDFT in the digit diagnosed on MRI. Lesions were typed into parasagittal, dorsal border and core lesions. Approximate volumes and intensities were quantified for each lesion type using T2* scan sequences. Follow‐up examinations and measurements were repeated at 3 and 6 month periods following conservative management. Results: Twenty‐three horses fitted the inclusion criteria. Lesion distribution included: parasagittal (n = 7), dorsal border (n = 11) and core lesions (n = 5). No association was found between age of horse, degree of lameness and lesion type. Only dorsal border lesions showed statistically significant reduction both in volume (initial scan: 0.18 ± 0.14 cm³) at 3 months (0.11 ± 0.10 cm³, P<0.05) and 6 months (0.05 ± 0.05 cm³, P<0.01) and ratiometric intensity (initial scan: 4.06 ± 1.54) at 6 months (2.00 ± 0.43; P<0.01). Parasagittal and core lesions showed no difference in lesion volume or ratiometric intensity. Lameness improved in all lesion types following conservative management. Conclusions: Dorsal border lesions of the DDFT show reduction in both volume and intensity whereas parasagittal and core lesions do not. Potential relevance: Lesion typing may be important in predicting lesion behaviour and short‐term outcome using MR imaging.     

Deep digital flexor tendonopathy in the foot

Tendonopathy of the distal portion of the deep digital flexor tendon is a newly recognised, important cause of foot lameness in horses. Although the pathological morphology of lesions has been well described, the aetiopathogenesis remains uncertain. A conclusive diagnosis can only be made with magnetic resonance imaging, but the results of a thorough clinical examination, including regional analgesia and other imaging modalities may lead to a strong suspicion of deep digital flexor tendonopathy in the foot. The prognosis for return to soundness is guarded but new treatment modalities are currently being investigated for an improved outcome.     

Risk factors for superficial digital flexor tendinopathy in Thoroughbred racehorses in hurdle starts in the UK (2001-2009)

Reasons for performing study: Superficial digital flexor (SDF) tendinopathy is a common injury in Thoroughbred horses racing over hurdles. Identification of risk factors may allow the introduction of measures to minimise the incidence of this injury. Objective: To identify risk factors for SDF tendinopathy in Thoroughbred horses in hurdle races in the UK. Methods: Potential risk factors for SDF tendinopathy were studied between 1 January 2001 and 31 December 2009 using a retrospective cohort study design with 1031 case starts and 168,637 control starts. Potential risk factors were screened using univariable logistic regression prior to multivariable model building. Results: In the final multivariable model, 20 statistically significant risk factors were identified. Variables found to be associated with increased odds of SDF tendinopathy included: firmer going; increased horse age at first race; having had a previous SDFT injury; and racing in the summer compared to other seasons. Variables found to be associated with decreased odds included: being trained by a more successful trainer; and having raced more frequently in the preceding 9–12 months. Conclusions: This study identified multiple risk factors associated with SDF tendinopathy, some of which are difficult to explain with the current data source. Factors resulting in increased cumulative horse and tendon fatigue (increased years in racing; carrying increased weight; and racing over longer distances), firm ground, and the presence of previous tendon injury should be considered when attempting to reduce the likelihood of sustaining SDF tendinopathy. Potential relevance: The results will facilitate the development of strategies to improve the overall safety of horses in hurdle racing in the UK.     

Implantation of bone marrow-derived mesenchymal stem cells demonstrates improved outcome in horses with overstrain injury of the superficial digital flexor tendon

Reasons for performing study: Mesenchymal stem (progenitor; stromal) cell (MSC) therapy has gained popularity for the treatment of equine tendon injuries but without reports of long‐term follow‐up. Objectives: To evaluate the safety and reinjury rate of racehorses after intralesional MSC injection in a large study of naturally occurring superficial digital flexor tendinopathy and to compare these data with those published for other treatments. Methods: Safety was assessed clinically, ultrasonographically, scintigraphically and histologically in a cohort of treated cases: 141 client‐owned treated racehorses followed‐up for a minimum of 2 years after return to full work. Reinjury percentages were compared to 2 published studies of other treatments with similar selection criteria and follow‐up. The number of race starts, discipline, age, number of MSCs injected and interval between injury and treatment were analysed. Results: There were no adverse effects of the treatment with no aberrant tissue on histological examination. The reinjury percentage of all racehorses with follow‐up (n = 113) undergoing MSC treatment was 27.4%, with the rate for flat (n = 8) and National Hunt (n = 105) racehorses being 50 and 25.7%, respectively. This was significantly less than published for National Hunt racehorses treated in other ways. No relationship between outcome and age, discipline, number of MSCs injected or injury to implantation interval was found. Conclusions: Whilst recognising the limitations of historical controls, this study has shown that MPC implantation is safe and appears to reduce the reinjury rate after superficial digital flexor tendinopathy, especially in National Hunt racehorses. Potential relevance: This study has provided evidence for the long‐term efficacy of MSC treatment for tendinopathy in racehorses and provides support for translation to human tendon injuries.     

A review of the healing processes in equine superficial digital flexor tendinopathy

Tendinopathy is a significant cause of morbidity and mortality in athletic and aged horses. These injuries require prolonged convalescence and heal by the formation of scar tissue instead of neo‐tendon, predisposing to reinjury. This article reviews the biological processes involved in tendon healing and their implications for clinical practice to improve future treatment of these injuries.     

Tenosynovitis of the carpal sheath of the digital flexor tendons associated with tears of the radial head of the deep digital flexor: observations in 11 horses

Reasons for performing study: Tears of the radial head of the deep digital flexor (DDF) have not previously been documented. Objectives: To describe the presentation, clinical, ultrasonographic and tenoscopic features associated with tears of the radial head of the DDF and to report the results of treatment. Hypotheses: Tears of the radial head of the DDF cause lameness and distension of the carpal sheath of the digital flexor tendons. Removal of disrupted tissue that is extruded into the sheath can result in clinical resolution and restoration of function. Methods: Case records and diagnostic images of horses in which tearing of the radial head of the DDF was diagnosed were reviewed retrospectively and follow‐up information obtained. Results: Eleven cases were identified. Clinical, ultrasonographic and tenoscopic commonality was recorded and treatment techniques were documented. All cases returned post operatively to pre‐injury levels of work. Conclusion: Tearing of the radial head of the DDF is a clinical entity with consistent diagnostic features. Tenoscopic removal of the torn tissue is associated with a good outcome. Potential relevance: Clinicians evaluating lame horses should include tearing of the radial head of the DDF as a differential diagnosis in animals with distended carpal sheaths. Tenoscopic surgery is a recommended treatment.     

Microdamage in the equine superficial digital flexor tendon

The forelimb superficial digital flexor tendon (SDFT) is an energy-storing tendon that is highly susceptible to injury during activities such as galloping and jumping, such that it is one of the most commonly reported causes of lameness in the performance horse. This review outlines the biomechanical and biothermal effects of strain on the SDFT and how these contribute to the accumulation of microdamage. The effect of age-related alterations on strain response and subsequent injury risk is also considered. Given that tendon is a slowly healing and poorly regenerative tissue, prompt detection of early stages of pathology in vivo and timely adaptations to training protocols are likely to have a greater outcome than advances in treatment. Early screening tools and detection protocols could subsequently be of benefit in identifying subclinical signs of degeneration during the training programme. This provides an opportunity for preventative strategies to be implemented to minimise incidences of SDFT injury and reduce recovery periods in elite performance horses. Therefore, this review will focus on the modalities available to implement early screening and prevention protocols as opposed to methods to diagnose and treat injuries.     

Desmotomy of the accessory ligament of the deep digital flexor tendon in the forelimb of 24 horses 2 years and older

Objective: To report outcome after desmotomy of the accessory ligament of the deep digital flexor tendon (ALDDFT) in adult horses (≥2 years) for treatment of desmitis of the ALDDFT or flexural deformity of the distal interphalangeal joint (FDDIJ). Study Design: Case series. Animals: Horses with desmitis of the ALDDFT (n=9) and FDDIJ (n=15). Methods: Records (April 1996–July 2008) of 24 adult horses (mean age, 6.7 years) that had ALDDFT desmotomy were reviewed. Follow‐up data was obtained 12–120 months after desmotomy. Results: Outcome was available for 22 horses; 18 (82%; 6 of 8 horses with desmitis of the ALDDFT and 12 of 14 with FDDIJ) returned to their intended use within 6–24 months (mean, 12 months). Conclusion: In mature horses, ALDDFT desmotomy resulted in successful return to intended use in most horses with ALDDFT desmitis (75%) or FDDIJ (86%).     

Deep digital flexor tendon rupture in two horses: A potential complication of comminuted second phalangeal fractures

This case report describes the history, clinical findings, treatment and outcome of 2 horses with damage and eventual rupture of the deep digital flexor tendon as a result of a comminuted second phalangeal fracture. The rupture of the deep digital flexor tendon complicated the treatment and in one horse contributed to its eventual euthanasia. The athletic outcome was limited in the second case and the lack of palmar soft tissue support likely had a significant effect on the stability and biomechanics of the repair.