The effect of bilateral palmar digital nerve analgesia on the compressive force experienced by the navicular bone in horses with navicular disease

Horses with navicular disease have an increased load on the navicular bone in early stance. This has been suggested to be a response to pain in the heel region. Seven horses with clinical, radiographic and scintigraphic signs of navicular disease underwent forceplate and kinematic analysis before and after desensitisation of the heel region with a bilateral palmar digital nerve block. The compressive force exerted on the navicular bone during stance, and stride kinematics, were determined in each state. After regional analgesia of the palmar digital nerves (PDNB) the compressive force on the navicular bone was lower throughout stance. The mean +/- s.d. peak force at the beginning of stance was 7.05+/-1.10 N/kg before, and 6.46+/-1.15 N/kg after PDNB (P = 0.01) and at the end of stance the mean peak values were 5.00+/-2.05 N/kg before, and 4.39+/-1.65 N/kg after PDNB (P = 0.05). We explained this finding as indicating that the horse responds to heel pain (including pain in the navicular region) by contracting the deep digital flexor muscle to unload the heels. This increases the compressive load on the navicular bone, which may cause remodelling and, in some horses, damage to the overlying flexor cartilage, which is then painful and identified as navicular disease. This mechanism identifies navicular disease as a possible end point for a variety of heel related conditions.     

Magnetic resonance imaging changes of the navicular bursa following navicular bursoscopy in seven horses

Navicular syndrome is a multifactorial disease process in horses with multiple structures in the foot contributing to lameness. Surgical debridement is a treatment option for lesions of the navicular bursa and deep digital flexor tendon. This retrospective case series describes the magnetic resonance imaging (MRI) appearance of the navicular bursa following bursoscopy. Seven horses (three being bilaterally affected) with forelimb lameness isolated to the foot, and pre- and post-operative MRI were included. All limbs had concurrent lesions associated with the deep digital flexor tendon, navicular bone, impar ligament, collateral sesamoidean ligament and/or distal interphalangeal joint. All bursae developed or had progression of proliferative bursal tissue following surgery. At recheck MRI, following rehabilitation protocols, almost all horses had improved to resolved lameness with relatively unchanged concurrent lesions despite the navicular bursa appearance worsening. Outcomes for return to work were poor with only two horses going back to the previous level of work.     

Assessment of the ultrasonographic characteristics of the podotrochlear apparatus in clinically normal horses and horses with navicular syndrome

OBJECTIVE: To characterize the normal ultrasonographic appearance of the podotrochlear apparatus in horses by use of standardized measurements and identify soft tissue changes associated with navicular syndrome. DESIGN: Prospective study. ANIMALS: 7 clinically normal horses and 28 horses with navicular syndrome. PROCEDURE: The feasibility of identifying and measuring the soft tissue structures of the podotrochlear apparatus ultrasonographically via the transcuneal approach was assessed in 2 additional horses without navicular syndrome; both horses were euthanatized, and the structures identified ultrasonographically were confirmed at necropsy. Ultrasonographs were obtained in the study horses. Objective and subjective data were obtained to characterize ultrasonographic changes associated with navicular syndrome. RESULTS: Abnormalities of the flexor surface of the distal sesamoid (navicular) bone, the impar ligament, the distal digital annular ligament, deep digital flexor tendon (DDFT), and the podotrochlear (navicular) bursa were assessed via the transcuneal ultrasonographic approach. No significant differences were found between the measurements of the podotrochlear apparatus in normal horses and those with navicular syndrome; however, important subjective differences were detected ultrasonographically in horses with navicular syndrome. In horses with navicular syndrome, ultrasonographic findings were indicative of navicular bursitis, dystrophic mineralization of the DDFT and impar ligament, tendonitis and insertional tenopathy of the DDFT, desmitis of the impar ligament, and cortical changes in the flexor surface of the navicular bone. CONCLUSIONS AND CLINICAL RELEVANCE: Findings of ultrasonographic evaluation of the hoof appear to be useful in determining the cause of caudal heel pain and characterizing the components of navicular syndrome in horses.     

Biochemical characterisation of navicular hyaline cartilage,navicular fibrocartilage and the deep digital flexor tendon in horses with navicular disease

The study hypothesis was that navicular disease is a process analogous to degenerative joint disease, which leads to changes in navicular fibrocartilage and in deep digital flexor tendon (DDFT) matrix composition and that the process extends to the adjacent distal interphalangeal joint. The objectives were to compare the biochemical composition of the navicular articular and palmar cartilages from 18 horses with navicular disease with 49 horses with no history of front limb lameness, and to compare navicular fibrocartilage with medial meniscus of the stifle and collateral cartilage of the hoof. Cartilage oligomeric matrix protein (COMP), deoxyribonucleic acid (DNA), total glycosaminoglycan (GAG), metalloproteinases MMP-2 and MMP-9 and water content in tissues were measured. Hyaline cartilage had the highest content of COMP and COMP content in hyaline cartilage and tendon was higher in lame horses than in sound horses (p<0.05). The concentration of MMP-2 amount in hyaline cartilage was higher in lame horses than in sound horses. The MMP-2 amounts were significantly higher in tendons compared to other tissue types. Overall, 79% of the lame horses with lesions had MMP-9 in their tendons and the amount was higher than in sound horses (p<0.05). In horses with navicular disease there were matrix changes in navicular hyaline and fibrocartilage as well as the DDFT with potential implications for the pathogenesis and management of the condition.     

Scanning electron microscopic findings of the navicular bone and deep flexor tendon in podotrochlosis of horses]

In 25 adult horses the podotrochlea of 49 forelimbs was examined by means of light and electron microscopy in order to correlate clinical and morphological findings. According to the clinical diagnosis the animals were divided into three groups: lameness due to syndrome of podotrochlosis (group 1) or due to tendopathy (group 2) and horses without lameness (group 3). The most striking pathological findings of the navicular bone and the opposite surface of the deep flexor tendon were found in horses with podotrochlosis, consisting of loss of cartilage and tendon matrix with denudation of collagen fibrils, superficial degeneration and necrosis, focal occurrence of fissures and far-reaching defects, sometimes accompanied by adhesions between tendon and navicular bone surface. In radiologically only slightly altered tendons and navicular bones light and scanning electron microscopy often revealed moderate to severe pathological changes, which sometimes could also be seen in clinically healthy horses. The distribution of the lesions indicate that in course of podotrochlosis the initial alterations caused by repeated microtraumata start at the surface of the deep flexor tendon and subsequently spread to the opposite facies flexoria of the navicular bone. An involvement of the cartilage and the synovial layer of the hoof joint in cases with podotrochlosis could only be rarely observed and is to regard as a secondary manifestation.     

Endoscopic assessment and treatment of lesions of the deep digital flexor tendon in the navicular bursae of 20 lame horses

REASONS FOR PERFORMING STUDY: Clinical lesions of the deep digital flexor tendon and navicular bone are being reported with increasing frequency. However, the role of direct visualisation by navicular bursoscopy in the diagnosis and management of such injuries has not been explored. HYPOTHESIS: Navicular bursoscopy: 1) corroborates information obtained from other, noninvasive imaging modalities; 2) allows direct visualisation of lesions unidentified by other diagnostic modalities; 3) provides further information on morphology of lesions; and 4) permits minimally invasive surgical access to lesions. METHODS: The case records of all horses that underwent diagnostic navicular bursoscopy for the investigation of lameness admitted to 2 referral clinics (the Royal Veterinary College and Reynolds House Referrals) were evaluated retrospectively. Follow-up information was obtained by telephone questionnaire. RESULTS: Twenty-three bursae were examined endoscopically in 20 horses. Tears of the deep digital flexor tendon were seen in all horses (22 bursae). In 8 bursae, cartilage lesions were also present and in one bursa this was the only abnormal finding. Computed tomography and low field magnetic resonance imaging predicted tendon lesions in most cases, but failed to identify cartilage damage. Greater than 6 month follow-up information was available for 15 animals of which 11 were sound and 9 had returned to preoperative levels of performance. CONCLUSION: Lameness localised to the foot may result from tears of the deep digital flexor tendon and/or navicular fibrocartilage loss. Navicular bursoscopy allows comprehensive evaluation of these changes and also permits appropriate lesion management. POTENTIAL RELEVANCE: The diagnostic information obtained from and therapeutic options offered by bursoscopy justify its use in horses with clinical findings localising lameness to the navicular bursa.     

Relationship of foot conformation and force applied to the navicular bone of sound horses at the trot

REASONS FOR PERFORMING STUDY: Collapsed heels conformation has been implicated as causing radical biomechanical alterations, predisposing horses to navicular disease. However, the correlation between hoof conformation and the forces exerted on the navicular bone has not been documented. HYPOTHESIS: The angle of the distal phalanx in relation to the ground is correlated to the degree of heel collapse and foot conformation is correlated to the compressive force exerted by the deep digital flexor tendon on the navicular bone. METHODS: Thirty-one shod Irish Draught-cross type horses in routine work and farriery care were trotted over a forceplate, with 3-dimensional (3D) motion analysis system. A lateromedial radiograph of the right fore foot was obtained for each horse, and various measurements taken. Correlation coefficients were determined between hoof conformation measurements and between each of these and the force parameters at the beginning (15%) of stance phase, the middle of stance (50%) and at the beginning of breakover (86% of stance phase). Significance was defined as P<0.05. RESULTS: The force exerted on the navicular bone was negatively correlated (P<0.05) to the angle of the distal phalanx to the ground and to the ratio between heel and toe height. This was attributed to a smaller extending moment at the distal interphalangeal joint. There was not a significant correlation between the angle of the distal phalanx and the degree of heel collapse, and heel collapse was not significantly correlated to any of the force parameters. CONCLUSIONS: Hoof conformation has a marked correlation to the forces applied to the equine foot. Heel collapse, as defined by the change in heel angle in relation to toe angle, appears to be an inaccurate parameter. The forces applied on the foot are well correlated to the changes in the ratio of heel to toe heights and the angles of the distal phalanx. POTENTIAL RELEVANCE: Assessment of hoof conformation should be judged based on these parameters, as they may have clinical significance, whereas parallelism of the heel and toe is of less importance.     

Outcome of medical treatment for horses with foot pain: 56 cases

Reasons for performing study: Currently, there are limited data regarding the long‐term outcome of horses with foot pain treated with corrective shoeing, rest and rehabilitation, and intrasynovial anti‐inflammatory medication to target lesions detected with MRI. Objective: To report the long‐term (≥12 months) outcome of horses with foot lesions following medical therapy. Hypotheses: 1) There is no association between clinical parameters considered and a poor response to therapy. 2) Horses with a deep digital flexor tendinopathy are less likely to respond to medical therapy than horses without a deep digital flexor tendinopathy. Methods: The medical records of horses with foot pain subjected to MRI examination and medical therapy (2005–2007) were evaluated retrospectively. Data collected included history, signalment, occupation, duration and severity of lameness at the time of MRI, radiological and MRI abnormalities. Number of treatments, complications and long‐term response to treatment were obtained by detailed telephone questionnaires. Association between clinical and MRI findings and long‐term lameness were investigated. Results: Frequent abnormal structures included the navicular bone, the deep digital flexor tendon, the navicular bursa and the distal interphalangeal joint. Thirty‐four of 56 horses (60.7%) failed to return to previous level of exercise due to persistent or recurrent lameness or owners' decision to decrease the horse's athletic level; however, 11 horses (32.3%) were being used for light riding. Prognosis for horses with concurrent deep digital flexor tendon, navicular bone and navicular bursa lesions was worse than horses with individual lesions. Deep digital flexor tendinopathy was strongly associated with persistent or recurrent lameness. Conclusions: Horses with multiple foot lesions managed with conservative therapy have a guarded prognosis for long‐term soundness. Deep digital flexor tendinopathies negatively influence prognosis.     

Locomotor characteristics of horses with navicular disease

OBJECTIVE: To determine whether force-plate evaluation of horses with navicular disease would reveal an abnormal gait that persists despite loss of sensation to the palmar foot region, which may predispose such horses to navicular disease. ANIMALS: 17 clinically normal Thoroughbreds and 8 Thoroughbreds with navicular disease. PROCEDURE: Data on ground reaction forces were obtained in trotting horses, using a force plate. Force-time curve variables for clinically normal horses were derived from 4 points at the beginning and 4 points at the end of the vertical and craniocaudal horizontal plots. Principal component analysis was undertaken separately on beginning-of-stride and end-of-stride data, and the first 2 components were represented graphically. Rotation matrices were applied to equivalent data for horses with navicular disease before and after disruption of sensation by administration of a palmar digital nerve blockade. RESULTS: Prior to nerve block, horses with navicular disease differed significantly from normal horses for beginning-of-stance phase and end-of-stance phase variables. After nerve block, horses with navicular disease maintained the same significant differences from clinically normal horses only for variables at the beginning-of-stance phase. CONCLUSIONS AND CLINICAL RELEVANCE: Horses with navicular disease have abnormal limb-loading force patterns that are not altered by loss of sensation in the palmar region. These abnormal patterns were detected in a horse without navicular disease. Some horses are predisposed to navicular disease as a result of an inherent abnormal gait pattern. Analysis of gait patterns could be used for detection and appropriate management of horses susceptible to development of navicular disease.     

Deep erosions of the palmar aspect of the navicular bone diagnosed by standing magnetic resonance imaging

Reasons for performing study: Erosion of the palmar (flexor) aspect of the navicular bone is difficult to diagnose with conventional imaging techniques. Objectives: To review the clinical, magnetic resonance (MR) and pathological features of deep erosions of the palmar aspect of the navicular bone. Methods: Cases of deep erosions of the palmar aspect of the navicular bone, diagnosed by standing low field MR imaging, were selected. Clinical details, results of diagnostic procedures, MR features and pathological findings were reviewed. Results: Deep erosions of the palmar aspect of the navicular bone were diagnosed in 16 mature horses, 6 of which were bilaterally lame. Sudden onset of lameness was recorded in 63%. Radiography prior to MR imaging showed equivocal changes in 7 horses. The MR features consisted of focal areas of intermediate or high signal intensity on T1‐, T2*‐ and T2‐weighted images and STIR images affecting the dorsal aspect of the deep digital flexor tendon, the fibrocartilage of the palmar aspect, subchondral compact bone and medulla of the navicular bone. On follow‐up, 7/16 horses (44%) had been subjected to euthanasia and only one was being worked at its previous level. Erosions of the palmar aspect of the navicular bone were confirmed post mortem in 2 horses. Histologically, the lesions were characterised by localised degeneration of fibrocartilage with underlying focal osteonecrosis and fibroplasia. The adjacent deep digital flexor tendon showed fibril formation and fibrocartilaginous metaplasia. Conclusions: Deep erosions of the palmar aspect of the navicular bone are more easily diagnosed by standing low field MR imaging than by conventional radiography. The lesions involve degeneration of the palmar fibrocartilage with underlying osteonecrosis and fibroplasia affecting the subchondral compact bone and medulla, and carry a poor prognosis for return to performance. Potential relevance: Diagnosis of shallow erosive lesions of the palmar fibrocartilage may allow therapeutic intervention earlier in the disease process, thereby preventing progression to deep erosive lesions.     

Healing characteristics of deep digital flexor tenorrhaphy within the digital sheath of horses

OBJECTIVE: To describe the healing characteristics of deep digital flexor tenorrhaphy within the digital sheath. STUDY DESIGN: Experimental study. ANIMALS: Five mature horses. METHODS: Right thoracic limb, deep digital flexor tenorrhaphy was performed within the digital sheath. Limbs were cast in partial flexion using a short limb cast for 6 weeks. Next, extended heel shoes were used for limb support for 14 weeks. Healing was evaluated by sequential ultrasonographic examinations, and limb use was evaluated by force plate analysis. At 26 weeks, mechanical strength and morphologic characteristics of the repair site were evaluated. RESULTS: Gap (mean, 0.93 cm.) formation was evident in unloaded limbs at 3 weeks. This increased markedly by 6 weeks and was 5 cm at 26 weeks. Demarcation between the deep and superficial flexor tendons decreased as the transected ends adhered to the dorsal surface of the superficial flexor tendon. The intrathecal space was reduced by fibrous tissue. Mean maximum load to failure of the repair tissue was 4,616 +/- 3,556 N, with a mean stress of 12.99 +/- 2.78 MPa. The repair consistently failed at the adhesion between the transected tendon and the superficial flexor tendon. CONCLUSIONS: Intrathecal tenorrhaphy with external coaptation (in partial limb flexion) for 6 weeks resulted in gap healing, fibrous adhesion between the deep and superficial flexor tendons, fibrous tissue reduction of the intrathecal space, and a pasture-sound horse at 26 weeks. CLINICAL RELEVANCE: Without improved methods for immobilizing the deep digital flexor tendon, intrathecal tenorrhaphy is unlikely to result in first intention tendon healing.     

Ultrasound examination of distal interphalangeal joint, navicular bursa, navicular bone and deep digital tendon

Techniques were devised for real-time ultrasound examination of the coffin joint, navicular bursa, navicular bone and deep digital flexor tendon of the forelimb of the horse, including their anatomical relationships and associated fluid spaces. Correlation was made between the echogram, positive contrast arthrograms, and freeze dried gross specimens. Anatomical structures were imaged in a midsagittal plane, of a standing, clinically normal horse.     

Current concepts of navicular disease

Navicular disease is unlikely to be a single disease. The close anatomical and functional relationships between the navicular bone, collateral sesamoidean ligament, distal sesamoidean impar ligament, deep digital flexor tendon, navicular bursa and distal interphalangeal joint result in the frequent occurrence of combinations of injuries. There are a number of different pathological processes that affect the navicular bone, which probably have different aetiopathogeneses. While there is strong evidence that biomechanical forces may result in failure of functional adaptation and excessive modelling, it is likely that each disease or injury type has a multifactorial cause.     

Puncture Wounds of the Navicular Bursa in 38 Horses A Retrospective Study

The medical records of 38 horses with puncture wounds of the navicular bursa were reviewed. Only 12 horses had a satisfactory outcome (breeding or riding). Of the remaining 26 horses, 19 were euthanized, five were sold due to persistent severe lameness, one died, and one was lost to long-term follow-up. Different combinations of conservative management prior to surgical debridement and drainage of the navicular bursa were unsuccessful in resolving the condition. Horses that were treated surgically within 1 week of the injury and had a hind leg affected had the best chance of a satisfactory outcome. Additional wound debridement was necessary in 15 horses after initial surgical treatment. The most common complications encountered were navicular bone osteomyelitis and sepsis of the deep digital flexor tendon. Thirteen of 14 horses that had rupture of the deep digital flexor tendon and subluxation of the distal interphalangeal joint had an unsatisfactory outcome. One mare subsequently developed ankylosis of the distal interphalangeal joint and was a useful brood mare. Two horses that had biaxial palmar digital neurectomy because of persistent lameness were later euthanized because of navicular bone fracture and rupture of the deep digital flexor tendon. Results from limited numbers of bacterial cultures and antibiotic sensitivities suggest that penicillin and an aminoglycoside antibiotic should be used as initial antibiotic therapy. Immediate surgical debridement and appropriate antibiotic treatment are recommended as the minimum therapy for penetrating wounds of the navicular bursa in horses.     

Effect of contact stress in bones of the distal interphalangeal joint on microscopic changes in articular cartilage and ligaments

OBJECTIVE: To examine articular cartilage of the distal interphalangeal (DIP) joint and distal sesamoidean impar ligament (DSIL) as well as the deep digital flexor tendon (DDFT) for adaptive responses to contact stress. SAMPLE POPULATION: Specimens from 21 horses. PROCEDURE: Pressure-sensitive film was inserted between articular surfaces of the DIP joint. The digit was subjected to a load. Finite element models (FEM) were developed from the data. The navicular bone, distal phalanx, and distal attachments of the DSIL and DDFT were examined histologically. RESULTS: Analysis of pressure-sensitive film revealed significant increases in contact area and contact load at dorsiflexion in the joints between the distal phalanx and navicular bone and between the middle phalanx and navicular bone. The FEM results revealed compressive and shear stresses. Histologic evaluation revealed loss of proteoglycans in articular cartilage from older horses (7 to 27 years old). Tidemark advancement (up to 14 tidemarks) was observed in articular cartilage between the distal phalanx and navicular bone in older clinically normal horses. In 2 horses with navicular syndrome, more tidemarks were evident. Clinically normal horses had a progressive increase in proteoglycans in the DSIL and DDFT. CONCLUSIONS AND CLINICAL RELEVANCE: Load on the navicular bone and associated joints was highest during dorsiflexion. This increased load may be responsible for microscopic changes of tidemark advancement and proteoglycan depletion in the articular cartilage and of proteoglycan production in the DSIL and DDFT Such microscopic changes may represent adaptive responses to stresses that may progress and contribute to lameness.     

Standing MRI lesions of the distal interphalangeal joint and podotrochlear apparatus occur with a high frequency in warmblood horses

Foot pain is a common presenting complaint in Warmblood horses. The aim of this retrospective, cross‐sectional study was to determine the spectrum of foot lesions detected by magnetic resonance imaging (MRI) in Warmblood horses used for dressage, jumping, and eventing. The medical records of 550 Warmblood horses with foot pain that were scanned using standing MRI were reviewed and the following data were recorded: signalment, occupation, lameness, diagnostic analgesia, imaging results, treatments, and follow‐up assessments. Associations between standing MRI lesions and chronic lameness following treatment were tested. Abnormalities of the navicular bone (409 horses, 74%), distal interphalangeal joint (362 horses, 65%), and deep digital flexor (DDF) tendon (260 horses, 47%) occurred with the highest frequency. The following abnormalities were significantly associated (P < .05) with chronic lameness following conservative therapy: moderate to severe MRI lesions in the trabecular bone of the navicular bone, mild or severe erosions of the flexor surface of the navicular bone, moderate sagittal/parasagittal DDF tendinopathies, and moderate collateral sesamoidean desmopathies. Also, identification of concurrent lesions of the DDF tendon, navicular bone, navicular bursa, and distal sesamoidean impar ligament was associated with chronic lameness after conservative therapy. Development of effective treatment options for foot lesions that respond poorly to conservative therapy is necessary.     

Tenoscopy of the navicular bursa: Endoscopic approach and anatomy

Objectives: Our objectives were to describe an endoscopic technique of the navicular bursa, describe the endoscopic anatomy, assess its feasibility on live horses undergoing an exploratory endoscopy, and assess the usefulness of standard arthroscopic instruments introduced via a contralateral portal.Study design: This was an anatomic study on cadaver limbs and endoscopic observation on clinical cases associated with problems of the navicular bursa and/or navicular bone.Animals or sample population: The sample population was 4 cadaver forelimbs of 2 horses weighing 300 to 450 kg and 8 live horses and one pony weighing 180 to 550 kg with navicular bursa disease.Methods: One cadaver limb was left untouched; the 3 others were dissected in a different way. Dissection and endoscopy of the navicular bursa were performed on the cadaver limbs with 4-mm and 2.7-mm 30° forward oblique arthroscopes. Relative positions of the arthroscope and of various arthroscopic instruments in the bursa were observed. Then, exploratory endoscopy of the navicular bursa was performed on live horses suspected of navicular bursa disease after clinical, radiographic, and/or sonographic examination. Visualization with saline solution and carbon dioxide was compared. Standard arthroscopic instruments were introduced according to the lesions observed. Some lesions were treated and a lavage of the navicular bursa was performed in all horses. Postoperative recovery was followed until 3 months after surgery.Results: Most parts of the anatomic structures of the navicular bursa could be observed with the 4-mm or 2.7-mm arthroscope, and standard arthroscopic instruments could be introduced into the bursa. A lavage of the bursa could be performed in all horses and no iatrogenic damage or postoperative complications were noted.Conclusion: Endoscopy of the navicular bursa with standard arthroscopic instruments is a feasible technique in horses and could be a useful diagnostic modality in suspected disease of this area.Clinical application: Diagnostic endoscopy in horses suspected of navicular bursa disease can be used to complement other diagnostic means. It already is used for treatment of septic bursitis; endoscopy of the navicular bursa could have other therapeutic applications in the future.

Introduction

Arthroscopy of the dorsal aspect of the distal interphalangeal joint in horses was used for removal of extensor process fractures and for diagnosis examination of this joint.¹ Arthroscopy of the palmar (plantar) aspect of the distal interphalangeal joint was described for removal of fibrin, intra-articular lavage in septic arthritis, and to access some fractures of the distal sesamoid (navicular) bone and middle and distal phalanges.²Endoscopy of the bursa podotrochlearis (navicular bursa) was recently described for treatment of septic bursitis.³ In this procedure, the instruments were mostly introduced through the original penetrating wound at the frog and through the flexor digitorum profundus (deep digital flexor tendon). In another study,⁴ the authors observed the navicular bursa in cadaver limbs and compared the endoscopic observation with pathologic findings.Lesions of the navicular bursa and contiguous anatomic structures (deep digital flexor tendon, palmar/plantar fibrocartilaginous facies flexoria [flexor surface] of the navicular bone, ligamentum sesamoideum distale impar [impar ligament], and ligamenta sesamoidea collateralia [collateral sesamoidean ligament]) can be associated with navicular syndrome.^{5, 6 and 7}Conventional radiographs allow evaluation of osseous lesions of the navicular bone (loss of cortico-medullary definition, irregularity of the sagittal ridge of the facies flexoria, and irregularity or thickening of the flexor cortex)^{5, 8 and 9} but are less sensitive for soft tissue evaluation.Ultrasonography allows the evaluation of some soft tissue lesions.¹⁰ It can be performed at the palmar aspect of the pastern or by a transfurcal approach.Scintigraphy is more sensitive than radiography in the evaluation of navicular syndrome, and it can complete an inconclusive radiographic examination.¹¹Magnetic resonance imaging (MRI) and computed tomography (CT) scan are also valuable diagnostic means for navicular syndrome in revealing some osseous abnormalities undetectable with conventional radiographs^{8 and 12} and, for MRI, in providing a reliable evaluation of soft tissues.^{13, 14 and 15}The objectives of this study were to document an endoscopic approach to the navicular bursa, describe the endoscopic anatomy, assess the usefulness of standard surgical instruments introduced via a contralateral portal (which could have potential benefits in diagnosis or treatment of lesions in this area), and finally, to assess the feasibility of this technique in live horses undergoing an exploratory endoscopy.

Instrumentation

The procedure was performed at 2 different clinics with different sets of instruments. Equipment used included two 4-mm (Dyonics or Storz) and one 2.7-mm (Optomed) 30° forward oblique arthroscopes connected to a light cable (Optomed or Storz) and light source (Stryker or Storz). The arthroscope was connected to a camera (Stryker or Storz) and a video system, which allowed recording and printing of endoscopic views. Various surgical instruments were used: a blunt tendon knife for splitting surgery, motorized synovial resector blades (Dyonics), straight and curved curettes (Sontek), Basket type synoviectomy forceps (Acufex), and Ferris-Smith rongeurs (Sontec).

Procedure

Cadaver limbs

Four distal forelimbs from 2 French Warm Blood equine cadavers weighing 300 to 450 kg with no lameness history were examined. Radiographs of the navicular bone were previously performed to document the absence of preexisting lesions. Three views were used: Dorso (60°) proximal-palmarodistal oblique, lateromedial, and palmaro (45°) proximal-palmarodistal oblique.The first limb was partially dissected (skin and subcutaneous tissue were removed) and the navicular bursa was examined by introducing the 4-mm arthroscope lateral to the deep digital flexor tendon.Navicular bursa endoscopy was performed in a similar way on the second undissected limb. The procedure was recorded on videotape and endoscopic photographs were printed. Various instruments were introduced by a medial approach, symmetrically to the arthroscope portal.The third limb was partially dissected like the first and cut in a sagitttal way with a sharp circular saw. The 4-mm arthroscope was introduced into the bursa and its progression from the skin to the bursa was observed by a sagittal view (Figs 1 and 2).

Kinetics and kinematics of the equine hind limb: in vivo tendon loads and force plate measurements in ponies

Loads on the suspensory ligament, deep digital flexor tendon, superficial digital flexor tendon, and long digital extensor tendon of the equine hind limb were determined in ponies by use of implanted strain gauges consisting of silicone rubber tubes filled with mercury. Recordings were made simultaneously with force plate measurements and high-speed film recordings while the ponies were walking. The relationship between strain gauge signals and tendon loads was obtained from tension-strain tests performed after death of the ponies. The suspensory ligament and the 2 digital flexor tendons were loaded during the stance phase, and the extensor tendon was loaded mainly during the swing phase. The loading pattern of the suspensory ligament, with peak loads of 4.6 N/kg of body weight, correlated well with the vertical component of the ground reaction force. Maximal loading of the deep digital flexor tendon was observed during the second half of the stance phase, with peak values of 6.7 N/kg. The superficial digital flexor tendon was loaded maximally at the beginning of the stance phase, with a peak load of 4.1 N/kg, and the long digital extensor tendon was loaded maximally during the swing phase, with a peak load of 0.3 N/kg. Recordings made from this procedure for calibration of the strain gauge signals to tendon load and tendon strain, in combination with the force plate measurements, enabled verification of the results by torque analysis of the lower portion of the hind limb, using the vector of the ground reaction force, limb conformation, and limb geometric configuration. Torque analysis of the lower extremity indicated that the determined tendon loads were in agreement with the recorded ground reaction forces.     

Histopathology in horses with chronic palmar foot pain and age-matched controls. Part 2: The deep digital flexor tendon

REASONS FOR PERFORMING STUDY: Causes of palmar foot pain and the aetiopathogenesis of navicular disease remain poorly understood, despite the high incidence of foot-related lameness. HYPOTHESES: Abnormalities of the deep digital flexor tendon (DDFT) may contribute to palmar foot pain; ageing degenerative changes may be seen in horses free from lameness; and horses with lameness are likely to have a greater severity of abnormalities than age-matched horses with no history of foot pain. METHODS: Feet were selected from horses with a history of uni- or bilateral forelimb lameness of at least 2 months' duration. Histology of the DDFT from the level of the proximal interphalangeal joint to its insertion were examined and the severity of lesions for each site graded. Associations between lesions of the navicular bone, collateral sesamoidean ligaments (CSL), distal sesamoidean impar ligament, navicular bursa, distal interphalangeal (DIP) joint synovium and collateral ligaments of the DIP joint and DDFT were assessed. RESULTS: There was no relationship between age and grade of histological abnormality of the DDFT. There were significant histological differences between groups for lesions of the dorsal layers of the DDFT, but not for lesions of the palmar aspect. There were significant associations between histological grades for the superficial dorsal layer of the DDFT and flexor aspect of the navicular bone; and between the deep dorsal layer of the DDFT and the proximal border and medulla of the navicular bone. The navicular bursa grade was correlated with grades for the superficial dorsal, deep dorsal and deep palmar layers of the DDFT. The histological grades for the CSL and the superficial dorsal layer of the DDFT were also associated. CONCLUSIONS: Pathological abnormalities in lame horses often involved the DDFT in addition to the navicular bone. Vascular and matrix changes may precede changes in the fibrocartilage of the navicular bone. POTENTIAL RELEVANCE: Identification of factors leading to vascular changes within the interstitium of the DDFT and changes in matrix composition, may help in future management of palmar foot pain.     

Pathological changes in the navicular bone and associated structures of the horse.

Navicular bones from 74 horses were examined at necropsy. Animals ranged in age from eight months to 30 years. Eight horses had a clinical history of navicular disease. Degenerative lesions in the fibrocartilaginous surface of the navicular bone and of the surface of the deep flexor tendons were age related changes not necessarily related to lameness. These lesions were more extensive in horses with a history of navicular disease, and were often accompanied by adhesions and subchondral cavitation of the fibrocartilaginous surface of the navicular bone. Osteophytes, present in 12 of the 74 horses, appeared to be age-related and were uncommon in horses with a history of navicular disease. Nutrient foramina on the distal border of the navicular bone were highly variable in size and shape; in horses with a history of navicular disease they often had a small external opening that became larger as it penetrated the bone. Occlusive vascular disease (arteriosclerosis) was found in sound horses and in horses with a history of navicular disease. Thrombosis of arteries or ischemic necrosis of bone was not identified in any case.