Rupture of the Vinculum in Association with Tendon Injury within the Digital Flexor Tendon Sheath in Two Horses

Rupture of the Vinculum in Association with Tendon Injury within the Digital Flexor Tendon Sheath in Two Horses

Journal of Equine Veterinary Science 32 (2012) 851-857 Journal of Equine Veterinary Science journal homepage: www.j-evs.com Case Report Rupture of ...

578KB Sizes 0 Downloads 50 Views

Journal of Equine Veterinary Science 32 (2012) 851-857

Journal of Equine Veterinary Science journal homepage: www.j-evs.com

Case Report

Rupture of the Vinculum in Association with Tendon Injury within the Digital Flexor Tendon Sheath in Two Horses Kathryn Rose Owen BVSc, CertES(Orth), MRCVS, Guy J. Hinnigan BVSc, CertES(Orth), MRCVS, Ellen R. Singer DCM, DVSc, DipACVS/ECVS, MRCVS Musculoskeletal and Locomotion Research Group, University of Liverpool, Leahurst Campus, Neston, Wirral, UK

a r t i c l e i n f o

a b s t r a c t

Article history: Received 15 December 2011 Received in revised form 1 April 2012 Accepted 10 April 2012 Available online 3 August 2012

The following report documents an unusual anatomical finding in two cases of aseptic tenosynovitis of the digital flexor tendon sheath. Disruption of the vinculum attachment between the palmar/plantar border of the superficial digital flexor tendon and the adjacent palmar/plantar annular ligament was identified in combination with other tendon pathology within the digital flexor tendon sheath. This tenoscopic finding has not been described previously in the literature. Ó 2012 Elsevier Inc. All rights reserved.

Keywords: Vinculum Mesotendon Tendon Tenosynovitis Tenoscopy

1. Introduction A number of terms have been used to describe the synovial reflections that exist between the synovial lining of the digital flexor tendon sheath (DFTS) and the digital flexor tendons, which divide the sheath into compartments. These terms include mesotenons [1,2], mesotendons [1,3,4], and vinculae [1,2], and they are often used interchangeably in texts, which can be confusing to the reader. The synovial sheath is a sac that is folded around the tendon so that two layers can be distinguished: the inner one (visceral layer) is adherent to the tendon, whereas the outer one lines the canal in which the tendon lies (parietal layer). The two layers are continuous along a fold termed the mesotendon [1,5]. Mesotendons extend from the proximomedial and proximolateral margins of the deep digital flexor tendon (DDFT) to the adjacent synovial

Corresponding author at: Kathryn Rose Owen, BVSc, CertES(Orth), MRCVS, Oakhill Veterinary Centre, Langley lane, Goosnargh, Preston, PR3 2JQ, UK. E-mail address: [email protected] (K.R. Owen). 0737-0806/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.jevs.2012.04.006

membrane lining within the proximal recess of the DFTS [2]. The DDFT also has a mesotendon that attaches from the palmar/plantar surface at the level of the proximal interphalangeal joint to the synovial membrane lining palmar/ plantar at midline [3,6]. In areas of great mobility within the synovial sheaths, the nerve and blood supply to the tendons is through a modified mesotendon, termed a vinculum [1]. The sagittal, adhesion-like mesotendon between the superficial digital flexor tendon (SDFT) and palmar/plantar annular ligament (PAL) within the DFTS is referred to as the vinculum of the SDFT [6] (Fig. 1). 2. Case Presentation 2.1. History 2.1.1. Case 1 A 7-year-old Appaloosa gelding used for hunting presented with a history of a mild left forelimb (LF) lameness of 1-month duration. The lameness resolved with rest; however, when exercise was reintroduced, the lameness and DFTS effusion recurred. Preliminary radiography and

852

K.R. Owen et al. / Journal of Equine Veterinary Science 32 (2012) 851-857

rein on the lunge. The lameness was exacerbated by both proximal and distal limb flexions of the RH. 2.3. Diagnostic Techniques 2.3.1. Radiography 2.3.1.1. Case 1. Five standard radiographic projections of the metacarpophalangeal joint were evaluated (lateromedial, flexed lateromedial, dorsopalmar, dorsal-45 -lateralpalmaromedial, and dorsal-45 -medial-palmarolateral obliques). No significant radiographic abnormalities were detected.

Fig. 1. A line drawing of the anatomy of the palmar fetlock region (in transverse section) of a horse at the level of the proximal sesamoid bones (PSBs). This shows the location of the vinculum of the superficial digital flexor tendon (SDFT). Yellow dashed arrow, digital flexor tendon sheath; Red solid arrow, vinculum; a, deep digital flexor tendon; b, SDFT; c, manica flexoria; d, PSB; e, third metacarpal bone.

ultrasonography of the metacarpophalangeal joint region, performed by the referring veterinarian, revealed no significant abnormalities. 2.1.2. Case 2 A 13-year-old Cob gelding used for general purpose riding presented with a history of a moderate right hind limb (RH) lameness of 4 months’ duration. Intra-articular medication of the distal tarsal joints, performed by the referring veterinarian, owing to a history of distal tarsal joint osteoarthritis failed to improve the lameness. An abaxial sesamoid nerve block, performed at the level of the proximal sesamoid bones (PSBs), also failed to produce a significant improvement in the degree of lameness observed. 2.2. Clinical Findings A prominent convex swelling of the palmar/plantar fetlock region at the level of the PAL was accompanied by a moderate effusion of the DFTS in both cases. 2.2.1. Case 1 The horse showed mild resentment to firm digital palpation of the PAL and DFTS areas. The horse showed a grade 3/10 (0 ¼ sound, 10 ¼ non-weight-bearing [7]) LF lameness when trotted in a straight line on a smooth hard surface. When lunged on a soft surface, the horse showed a 3/10 LF lameness on the left rein and a 2/10 LF lameness on the right rein. When lunged on a hard surface, the degree of lameness increased to 4/10 on the LF on both reins. The lameness was exacerbated by distal limb flexion of the LF. 2.2.2. Case 2 The horse showed a 5/10 RH lameness when trotted in a straight line on a smooth hard surface, followed by a slight deterioration to a 6/10 RH lameness on the right

2.3.2. Diagnostic Anesthesia Diagnostic anesthesia was not performed in case 1 owing to the acute onset of lameness and associated DFTS effusion. In case 2, anesthesia of the medial and lateral plantar nerves of the RH was performed at a level 1 cm proximal to the level of the distal second and fourth metatarsal bones, using 3 mL of 2.0% w/v mepivacaine hydrochloride (Intra-epicaine, Arnolds Veterinary Products, Shrewsbury, UK) at each site. Within 10 minutes, the horse then showed a 1/10 RH lameness when trotted on a straight firm surface, representing a significant improvement. 2.3.3. Ultrasonography Both forelimbs in case 1 and both hind limbs in case 2 were prepared in a conventional manner for ultrasonographic evaluation. A GE Vivid-I digital ultrasound machine (GEMS Ultrasound, Tirat Carmel, Israel) with a 12-MHz linear array transducer was used to evaluate the contents of the DFTS and surrounding soft-tissue structures. Ultrasonographic examination was carried out in transverse and longitudinal planes. In both cases, a moderate degree of anechoic fluid was visible within the DFTS, consistent with the effusion palpable on clinical examination. Hypertrophy of the synovial membrane was also suspected, as tissue of variable echogenicity was visualized proximal and lateral to the PAL. Ultrasonography of the flexor tendons was largely unremarkable, except for a variable echogenicity and irregularity of the palmar border of the SDFT at the level of the vinculum attachment to the SDFT. On transverse sections at the level of the PSBs, the borders of the PAL appeared ill-defined owing to the heterogeneous echogenicity of the following structures combined: the palmar border of the SDFT, the vinculum of the SDFT, the synovial membrane of the DFTS, the PAL, and the thickened subcutaneous tissues (Fig. 2). To evaluate the thickness of the PAL, measurements were taken at the medial and lateral insertions of the PAL onto the PSBs, which were 4.4 mm and 3.9 mm, respectively, in case 1 and 6.0 mm and 4.7 mm, respectively, in case 2 (Fig. 3). The distance from the palmar/plantar surface of the SDFT to the skin surface was greater in the affected limbs when compared with the contralateral limbs (case 1: R ¼ 4.2 mm, L ¼ 8.5 mm; case 2: R ¼ 12.4 mm, L ¼ 9.1 mm). At the level of the vinculum attachment of the SDFT, there was a region of variable echogenicity located between the palmar border of the SDFT and the PAL in each lame limb. Owing to the presence of subcutaneous thickening, significant enlargement of the PAL, and the

K.R. Owen et al. / Journal of Equine Veterinary Science 32 (2012) 851-857

853

Fig. 2. Transverse ultrasonographic images of the palmar region of the (A) left forelimb (LF) and (B) right forelimb (RF) obtained at a level 27 cm distal to the accessory carpal bone in case 1. The image of the LF shows an area of variable echogenicity between the palmar border of the SDFT and the dorsal margin of the PAL, subcutaneous tissue, and skin tissue, demonstrating the difficulty in determining the boundaries of the palmar annular ligament, synovial membrane, and vinculum of the SDFT. The distance between the palmar border of the SDFT and the skin is notably increased in the LF: 6.4 mm compared with the RF: 4.2 mm (yellow broken arrows). LF, left forelimb; a, deep digital flexor tendon; RF, right forelimb; b, SDFT.

hypoechoic region between the palmar/plantar SDFT and the PAL, disruption of the vinculum attachment of the SDFT was suspected in both horses.

Fig. 3. A transverse ultrasonographic image of case 2, taken at the level of the PSBs. The probe is positioned medially to assess the thickness of the plantar annular ligament, which is considerably thickenedd7.2 mm (broken arrow). a, deep digital flexor tendon; b, SDFT.

3. Diagnosis and Surgical Procedure Owing to the recurrent nature of the lameness in both cases, the presence of DFTS effusion, PAL thickening, and the suspicion of injury to the vinculum of the SDFT, tenoscopy and PAL desmotomy were recommended. Acepromazine (ACP injection Novartis Animal Health UK Ltd., Camberley, Surrey, UK; 0.03 mg/kg/im), crystalline sodium penicillin (Crystapen, Schering-Plough Ltd., Welwyn Garden City, UK; 10 mg/kg/iv), and flunixin meglumine (Meflosyl, Fort Dodge Animal Health Ltd., Southampton, UK; 1.1 mg/kg/iv) were administered preoperatively. Romifidine hydrochloride (Sedivet, Boehringer Ingelheim Ltd., Bracknell, UK; 100 mg/kg/iv) was administered 10 minutes before induction with ketamine (Ketaset, Fort Dodge Animal Health Ltd; 2.2 mg/kg/iv) and diazepam (Diazepam injection, Hamelyn Pharmaceuticals Ltd., Gloucester, UK; 0.05 mg/kg/iv). Anesthesia was maintained with inhalational isoflurane (Isoflo, Abbott laboratories Ltd., Queensborough, Kent, UK) anesthetic. Both horses were placed in lateral recumbency, with the affected limb at uppermost position. An Esmarch bandage was applied to the distal limb to a level proximal to the surgical site. The limb was aseptically prepared from the level of the coronary band to the proximal metacarpal/metatarsal regions using dilute chlorhexidine gluconate solution (Hibiscrub, Regent Medical, Dunstable, Bedfordshire, UK) before induction. Distension of the DFTS was achieved by infiltration of 30 mL of Hartmann solution with an 18-G 1.5-inch needle directed into the DFTS, dorsal to the DDFT, between the distal margin of the PAL and the proximal margin of the proximal digital annular ligament and palmar to the neurovascular bundle on the lateral aspect of the limb. An arthroscope portal was subsequently created at this location using standard tenoscopic techniques [2]. On initial

854

K.R. Owen et al. / Journal of Equine Veterinary Science 32 (2012) 851-857

Fig. 4. A tenoscopic image of case 2, demonstrating the torn fibers of the vinculum between the plantar annular ligament (a) and the SDFT (b).

tenoscopic evaluation of the DFTS contents, it was possible to advance the scope palmar/plantar to the SDFT in both cases. The vinculum attachment of the SDFT to the sagittal midline of the PAL was absent, with an erythematous line of loose areolar tissue present on the palmar border of the SDFT (Fig. 4) along the normal line of insertion of the vinculum. The arthroscope was advanced in a proximal direction with greater ease than in a horse with an intact vinculum. 3.1. Case 1 Loose fibrous material could be seen in the lateral proximal recess of the DFTS. Birefringent tendon tissue was observed at the lateral border of the flexor tendons, which was subsequently shown to originate from the DDFT. The arthroscope was passed beneath the manica flexoria to inspect the dorsal and proximal portions of the DDFT. A 2-mm-wide strand of tendon tissue originating from the lateral margin of the DDFT indicated the presence of a DDFT tear. An instrument portal was created at the proximolateral aspect of the DFTS, approximately 6 cm proximal to the lateral PSB. The disrupted tendon tissue was grasped with arthroscopic rongeurs but remained firmly attached to the main body of the tendon. Visualization of the entire DDFT tear was not possible because of the presence of the manica flexoria within the proximal DFTS, preventing appropriate positioning of an instrument portal. The decision was made to perform an open PAL desmotomy to enable complete visualization of the tear. A 10-cm vertical skin incision was made between the palmar midline and abaxial border of the lateral sesamoid bone at the level of the PAL. Open desmotomy of the PAL enabled resection and debridement of the DDFT tear, which was approximately 2-mm wide  4.5-cm long from the lateral margin of the tendon. 3.2. Case 2 After inspection of the torn vinculum, loose connective tissue fibers were visualized within the DFTS. The medial border of the SDFT was also fibrillated in appearance from

within the fetlock canal, extending up to the proximal recess of the DFTS. An instrument portal was created in the proximomedial aspect of the DFTS after the introduction of a 19-G spinal needle to confirm the appropriate location. A motorized synovial resector (Smith & Nephew, MA) was introduced, and fibrillated tendinous tissue was removed from the SDFT. Using an identical technique to that outlined previously, the tenoscopic approach was converted to an open approach. A desmotomy of the thickened PAL was performed, and digital examination of the DFTS contents confirmed that the primary pathology was associated with desmitis of the PAL and tearing of the vinculum of the SDFT. In both cases, the DFTS was lavaged with Hartmann solution before closure. The subcutaneous tissues were closed in two layers, using a 2-metric (M) braided lactomer 9-1 (Polysorb [Tyco healthcare UK Ltd., Gosport, Portsmouth, UK]) suture material in a simple interrupted suture pattern. The edges of the skin incision were apposed using a 3-M polypropylene (Surgipro [Tyco healthcare UK Ltd.]) suture material in a horizontal mattress pattern. The arthroscopy portals were closed with interrupted cruciate sutures using 3-M polypropylene suture material. A sterile half-limb Robert Jones dressing was applied. 4. Postoperative Care Phenylbutazone (Equipalazone, Dechra Veterinary Products, Shrewsbury, Shropshire, UK; 2.2 mg/kg/iv) and crystalline sodium penicillin (10 mg/kg/iv) were administered for 72 hours postoperatively. Antibiotic therapy was continued for a further 14 days using trimethoprimsulphonamide (Trimediazine plain, Vetoquinol UK Ltd., Buckingham, UK; 30 mg/kg per os) because of a perceived increased risk of synovial sepsis using an open approach for transection of the PAL. The dressings were changed every 2-3 days, and the sutures were removed 14 days postoperatively. Bandaging was discontinued 1 week after suture removal. Case 2 was discharged from the hospital 6 days after surgery. Case 1 remained hospitalized for 10 days owing to moderate swelling and mild wound exudate at the surgical site. A 2-week period of box rest was advised in both cases, followed by commencement of an ascending hand-walking exercise program for 6 weeks before recheck at the hospital. 5. Follow-up 5.1. Case 1 In-hand walking had been increased to a total of 20 minutes daily by 6 weeks postoperatively. Clinical examination revealed a palpable thickening of the synovial membrane of the proximal DFTS of the LF. There was some thickening of the tissue in the region of the PAL, with a convex appearance to the palmar aspect of the fetlock. There was no evidence of DFTS effusion. The horse was sound at walk, with a mild (2/10) LF lameness visible at trot in a straight line and in each direction on the lunge. Ultrasonographic examination confirmed the lack of effusion within the DFTS. Moderate synovial hypertrophy was visible. There was no evidence of irregularity of the DDFT on the lateral margin at the site of the tear.

K.R. Owen et al. / Journal of Equine Veterinary Science 32 (2012) 851-857

855

6. Concluding Diagnosis 6.1. Case 1 Case 1 sustained a longitudinal tear of the lateral margin of the DDFT and desmopathy of the PAL, in conjunction with rupture of the vinculum of the SDFT. 6.2. Case 2 Case 2 had a similar diagnosis, with rupture of the vinculum of the SDFT, in combination with PAL desmopathy and fibrillation of the medial border of the SDFT. 7. Discussion

Fig. 5. Transverse ultrasonographic image of the left palmar fetlock region, 27 cm distal to the accessory carpal bone, obtained at 6 weeks postoperatively in case 1. There is an anechoic region between the palmar border of the SDFT and the subcutaneous tissues, representing the absence of the vinculum attachment of the SDFT. The tissue of mixed echogenicity palmar to the SDFT is thought to represent the torn vinculum (solid yellow arrow). a, deep digital flexor tendon; b, SDFT.

The absence of the SDFT vinculum attachment was observed with an anechoic region present between the PAL and the palmar surface of the SDFT. There appeared subjectively to be an area of tissue of mixed echogenicity thought to represent the torn vinculum at this level (Fig. 5). A continued ascending walking exercise program was recommended, with the introduction of short periods of trotting. Four months postoperatively, the horse presented for further evaluation. A complete lameness examination revealed that the LF lameness had resolved. Turnout for a period of 2 months was advised. Six months postoperatively, the horse returned successfully to its previous level of work. 5.2. Case 2 Case 2 was re-evaluated 6 weeks postoperatively. The horse was performing 20 minutes of in-hand walking daily. The affected limb remained thickened with a persistent effusion of the DFTS, and the horse showed a 4/10 RH lame when trotted on a straight line. A continued ascending walking exercise program for an additional 6 weeks was recommended. Three months postoperatively, the horse was sound at trot, with no obvious palpable differences between the affected and the contralateral limb. Four months postoperatively, the horse resumed its previous level of work.

AT-DFTS in horses is well described in the literature [8-12]. AT-DFTS is a commonly encountered condition characterized by a palpable effusion of the DFTS proximal and distal to the PAL. A number of different clinical entities have been attributed to the development of AT-DFTS, including pathology of the SDFT [4], constriction of the DFTS by a normal or an abnormal PAL [8,13,14], and idiopathic tenosynovitis [15]. More recently, tears of the manica flexoria, longitudinal tears of the DDFT [10,12], tears of the DFTS wall, the proximal mesotendon of the DDFT, and the SDFT branches [11] have all been recognized as one of the potential causes of AT-DFTS. An interesting feature encountered in the cases outlined was the presence of a torn vinculum, which in the normal horse, extends from the palmar/plantar midline of the SDFT to the PAL and proximal digital annular ligament. The etiology of this injury is unknown. As the lameness was acute in onset in both cases outlined, it may be proposed that a single overload episode creating sudden hyperextension of the fetlock may place excessive strain on the vinculum within the fetlock, leading to the rupture of the connective tissue attachment. Disruption of this structure enabled complete arthroscopic visualization of the palmar border of the SDFT both medially and laterally at the level of the PSBs, which is not usually possible with an intact vinculum without repositioning the arthroscope on the opposite side of the limb. This anatomical feature within the tendon sheath was illustrated by a radiographic contrast study as a reflection of the tendon sheath onto the SDFT [16]. Cases of tenosynovitis can be complicated by damage to the support structures of the DFTS. This includes disruption to the vinculae or mesotendon attachments [6], superimposed on the damage to the internal structures such as the DDFT, SDFT, or the manica flexoria. The mesotendons of the DDFT within the proximal DFTS are frequently visible on ultrasonographic examination. In contrast, the vinculum of the SDFT may only be seen with distension of the DFTS at the level of the PAL, when the anechoic synovial fluid outlines this structure. The role of the numerous connective tissue attachments within the DFTS is thought to be in enabling blood and lymphatic vessels and a variable nerve supply to the flexor tendons in their course through the fetlock canal [17]. It is currently unknown whether disruption to the vinculum has any effect on tendon blood supply or architecture. Injury to the vinculum may cause superficial tearing of the SDFT at its

856

K.R. Owen et al. / Journal of Equine Veterinary Science 32 (2012) 851-857

normal site of attachment. Disruption of the vinculum may also affect the blood supply residing within the connective tissue attachment. However, this is unlikely to cause a clinically significant problem, owing to the presence of multiple alternative blood and lymphatic sources, within and surrounding the DFTS. The majority of horses with injury of the flexor tendons within the DFTS will have some degree of effusion within the sheath [10-12]. Desmopathy of the PAL is also frequently associated with effusion of the DFTS; however, a convex appearance to the palmar/plantar fetlock region is a more consistent clinical finding than effusion of the DFTS in cases of primary PAL desmopathy [14]. Effusion of the DFTS was present in both horses presented in this report; however, the DFTS effusion was more marked in case 2, despite this horse having less severe pathology of the flexor tendons compared with horse 1. In case 1, the effusion was mild, which may have been because of the period of rest the horse had received before admission or because of the possibility that there is no established link between the severity of injury within the DFTS and the presence of a synovial effusion. Diagnostic analgesia was not performed in case 1 owing to the history of acute-onset effusion, ultrasonographic findings, and lack of metacarpophalangeal joint effusion. In addition, the effusion and lameness resolved with rest and returned with exercise. In case 2, only a medial and lateral plantar nerve block was performed owing to the horse’s aversion to needles. With the lack of response noted by the referring veterinary surgeon previously on performing an abaxial sesamoid nerve block, the positive response to a plantar nerve block suggested the origin of pain was related to the plantar fetlock or distal metatarsal region. In an ideal patient, intrathecal analgesia to confirm the DFTS as the origin of pain and intra-articular analgesia to exclude metacarpophalangeal joint involvement would be recommended. The identification of synovial hypertrophy, increased synovial fluid, thickening of the PAL, or the presence of echogenic material within the DFTS, in combination with lameness, can be considered as indications for tenoscopy [11,12]. In cases of longitudinal tears of the flexor tendons, disrupted collagen fibrils protruding from the tendon are the most likely cause of chronic inflammation within the DFTS. This is likely due to the continual release of inflammatory mediators in response to the exposed collagen fibrils. Because there are no intrinsic mechanisms to remove these disrupted collagen fibers within the sheath, these fibrils need to be removed surgically to promote healing and to reduce the effusion [10,12]. In both cases, the presence of lameness combined with the clinical and ultrasonographic findings lead to the requirement for further investigation by tenoscopy. In case 1, instrument access to the entire DDFT tear was difficult because of the risk of causing injury to the overlying manica flexoria. This resulted in the use of an open surgical approach to the DFTS to improve access to the DDFT lesion. A closed tenoscopic approach to longitudinal tears of the DDFT in the region of the manica flexoria has been described [11], which may be used to prevent the perceived increased risk of DFTS sepsis associated with performing transection of the PAL using an open approach.

The successful outcome of both horses reported was likely because of the mechanical removal of exposed collagen fibrils in case 1 [10] and the release of pressure within the fetlock canal by desmotomy of the PAL in case 2 [15], as the SDFT fibrillation encountered was considered mild. A rupture of the vinculum may cause an acute tenosynovitis, but in the absence of other significant tendon pathology, the prognosis for these injuries should be good. It is unlikely that injury to the vinculae is the performance-limiting factor in cases of tenosynovitis that fail to return to work. This report highlights the challenges of accurately evaluating the structures within and associated with the DFTS in cases of tenosynovitis, based on ultrasonographic examination alone. As discussed by Owen et al. [14], the presence of subcutaneous tissue thickening between the palmar border of the SDFT and the skin surface makes discerning the borders of the PAL, synovial membrane, and vinculum of the SDFT difficult (Fig. 2). The marginal longitudinal tear of the DDFT in case 1 and the fibrillation of the SDFT border in case 2 were not identified on preoperative ultrasonographic examination, but were diagnosed based on the tenoscopic examination of the DFTS. Previous studies have shown that tenoscopy remains the gold standard when compared with ultrasonography for the diagnosis of intrathecal flexor tendon pathology. In one study, the abnormalities diagnosed ultrasonographically within the DFTS were verifiable tenoscopically with a sensitivity of 90.9% and a specificity of only 53.8% [18]. Another study demonstrated that 32 of 46 (70%) marginal tears of the DDFT were recognized on ultrasonography, with the remaining tears identified only by tenoscopic evaluation of the DFTS [11]. The high percentage of falsenegatives on ultrasonography of these cases emphasizes the importance of considering tenoscopy if cases of AT-DFTS do not respond to conservative management. Magnetic resonance imaging may also offer a useful adjunctive tool to ultrasonographic evaluation to confirm the presence or absence of suspected pathology within the fetlock canal, which could aid the decision-making process in establishing appropriate surgical candidates. 8. Conclusion It is well known from previous literature that flexor tendon, manica flexoria, and PAL pathology are commonly identified in association with lameness in the horse, but the clinical importance of injury to the vinculae and mesotenons within the DFTS remains unclear. The anatomy, structural role, and clinical importance of these synovial reflections within the DFTS require further exploration through tenoscopic, diagnostic imaging, histological, and postmortem studies. Acknowledgments The authors thank The Horse Trust for generously funding the clinical scholarships of authors G.J.H. and K.R.O. References [1] Durham M, Dyson SJ, editors. Applied anatomy of the musculoskeletal system. 2nd ed. St Louis, MO: W.B. Saunders; 2011.

K.R. Owen et al. / Journal of Equine Veterinary Science 32 (2012) 851-857 [2] McIlwraith CM, Nixon AJ, Wright IM, Boening KJ, editors. Diagnostic and surgical arthroscopy in the horse. 3rd ed. Philadelphia, PA: Elsevier; 2005. [3] Denoix JM. Functional-anatomy of tendons and ligaments in the distal limbs (manus and pes). Vet Clin North Am Equine Pract 1994;10:273-322. [4] McIlwraith CW, editor. Adams’ lameness in horses. Philadelphia, PA: Lippincott Williams Wilkins; 2002. [5] Sisson S, Grossman JD, editors. Anatomy of the domestic animals. 4th ed. Philadelphia, PA: W.B. Saunders; 1953. [6] Schramme MC, Smith RK, editors. Diseases of the digital synovial sheath, palmar annular ligament, and digital annular ligaments. 2nd ed. St Louis, MO: W. B. Saunders; 2011. [7] Arkell M, Archer RM, Guitian FJ, May SA. Evidence of bias affecting the interpretation of the results of local anaesthetic nerve blocks when assessing lameness in horses. Vet Rec 2006; 159:346-9. [8] Dik KJ, Dyson SJ, Vail TB. Aseptic tenosynovitis of the digital flexor tendon sheath, fetlock and pastern annular ligament constriction. Vet Clin North Am Equine Pract 1995;11:151-62. [9] Fortier LA, Nixon AJ, Ducharme NG, Mohammed HO, Yeager A. Tenoscopic examination and proximal annular ligament desmotomy for treatment of equine "Complex" digital sheath tenosynovitis. Vet Surg 1999;28:429-35. [10] Wright IM, McMahon PJ. Tenosynovitis associated with longitudinal tears of the digital flexor tendons in horses: a report of 20 cases. Equine Vet J 1999;31:12-8.

857

[11] Smith MR, Wright IM. Noninfected tenosynovitis of the digital flexor tendon sheath: a retrospective analysis of 76 cases. Equine Vet J 2006;38:134-41. [12] Wilderjans H, Boussauw B, Madder K, Simon O. Tenosynovitis of the digital flexor tendon sheath and annular ligament constriction syndrome caused by longitudinal tears in the deep digital flexor tendon: a clinical and surgical report of 17 cases in Warmblood horses. Equine Vet J 2003;35:270-5. [13] Barr AR, Dyson SJ, Barr FJ, Obrien JK. Tendinitis of the deep digital flexor tendon in the distal metacarpal/metatarsal region associated with tenosynovitis of the digital sheath in the horse. Equine Vet J 1995;27:348-55. [14] Owen KR, Dyson SJ, Parkin TD, Singer ER, Kristoffersen M, Mair TS. Retrospective study of palmar/plantar annular ligament injury in 71 horses: 2001-2006. Equine Vet J 2008;40:237-44. [15] Gerring EL, Webbon PM. Fetlock annular ligament desmotomy: a report of 24 cases. Equine Vet J 1984;16:113-6. [16] Redding WR. Evaluation of the equine digital flexor tendon sheath using diagnostic ultrasound and contrast radiography. Pferdeheilkunde 1995;11:32. [17] Kraus BL, Kirkerhead CA, Kraus KH, Jakowski RM, Steckel RR. Vascular supply of the tendon of the equine deep digital flexor muscle within the digital sheath. Vet Surg 1995;24:102-11. [18] Edinger J, Mobius G, Ferguson J. Comparison of tenoscopic and ultrasonographic methods of examination of the digital flexor tendon sheath in horses. Vet Comp Orthop Traumatol 2005; 18:209-14.