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.     

Evaluation of tachykinins and their receptors to determine sensory innervation in the dorsal hoof wall and insertion of the distal sesamoidean impar ligament and deep digital flexor tendon on the distal phalanx in healthy feet of horses

OBJECTIVE: To localize substance P (SP) and neurokinin A (NKA) and their receptors in the insertion of the distal sesamoidean impar ligament (DSIL), deep digital flexor tendon (DDFT), and dorsal hoof wall of healthy feet of horses. SAMPLE POPULATION: 18 healthy feet from horses. PROCEDURE: Samples from the dorsal hoof wall and insertion of the DSIL and DDFT of 10 feet were processed for immunocytochemical analysis, using rabbit polyclonal antisera raised against SP and NKA. Tissue sections from 8 feet were incubated with 125-labeled SP to localize tachykinin receptors and their specificity and with control solutions of radioactive SP and excess nonradioactive SP to identify areas of nonspecific binding. RESULTS: Many nerves immunoreactive for SP and NKA were localized to the region of the insertion of the DSIL and DDFT and the accompanying microvasculature and arteriovenous complexes (AVC) as well as to the microvasculature of the dorsal hoof wall. Specific neurokinin 1 receptors were localized over the microvessels and AVC of the insertion zone and small microvessels of the hoof wall. CONCLUSIONS AND CLINICAL RELEVANCE: These results document that the microvasculature of the equine foot is richly innervated and has specific receptors for tachykinins. Distributions of these tachykinin receptors on the microvasculature suggest that they form an important vasodilatory mechanism for controlling blood flow through the DSILDDFT insertion and dorsal hoof wall.     

The distal sesamoidean impar ligament: Comparison between its appearance on magnetic resonance imaging and histology of the axial third of the ligament

Reasons for performing study: There is limited knowledge about the interpretation of alterations in the distal sesamoidean impar ligament (DSIL) detected using magnetic resonance imaging (MRI) and their correlation with histopathology. Hypotheses: There would be: 1) a correlation between histopathology and MRI findings; and 2) a relationship between MR abnormalities at the origin and the insertion of the DSIL, between insertion and body; and origin and body. Methods: Fifty limbs from 28 horses were examined using high‐field MRI and histopathology. MR abnormalities of the DSIL, its origin on the navicular bone and its insertion on the distal phalanx were graded. Sections of the axial third of the DSIL were examined histologically and graded according to fibre orientation, integrity of fibroblasts, collagen architecture and vascularity. Associations between MRI and histology findings were tested by Spearman rank correlation and Chi‐squared tests. Results: There were significant correlations between the presence of a cystic structure in the distal third of the navicular bone, or a distal border fragment, or increased signal intensity in fat suppressed images at the insertion of the DSIL on the distal phalanx and the histological grade of the body of the DSIL. There were significant associations between a cystic structure in the distal third of the navicular bone and the presence of either a distal border fragment or entheseous new bone at the insertion of the DSIL, swelling of the DSIL and increased signal intensity in the DSIL in fat suppressed images; between distal elongation of the flexor border of the navicular bone and the presence of one or more distal border fragments and between swelling of the body of the DSIL and irregularity of its palmar border or increased signal intensity in fat suppressed images in the DSIL. Conclusions and clinical relevance: The presence of a cystic structure in the distal third of the navicular bone detected using MRI, a distal border fragment or increased signal intensity at the insertion of the DSIL are suggestive of significant alterations in the infrastructure of the DSIL.     

Histopathology in horses with chronic palmar foot pain and age-matched controls. Part 1: Navicular bone and related structures

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 collateral sesamoidean ligaments (CSLs), distal sesamoidean impar ligament (DSIL), deep digital flexor tendon (DDFT), navicular bone, navicular bursa, distal interphalangeal (DIP) joint or collateral ligaments (CLs) of the DIP joint may contribute to palmar foot pain. METHODS: Feet were selected from horses with a history of unilateral or bilateral forelimb lameness of at least 2 months' duration that was improved by perineural analgesia of the palmar digital nerves, immediately proximal to the cartilages of the foot (Group 1, n = 32); or from age-matched control horses (Group 2, n = 19) that were humanely destroyed for other reasons and had no history of forelimb foot pain. Eight units of tissue were collected for histology: the palmar half of the articular surface of the distal phalanx, including the insertions of the DDFT and DSIL; navicular bone and insertion of the CSLs; DDFT from the level of the proximal interphalangeal (PIP) joint to 5 mm proximal to its insertion; synovial membrane from the palmar pouch of the DIP joint and the navicular bursa; CLs of the DIP joint and DSIL. The severity of histological lesions for each site were graded. Results were compared between Groups 1 and 2. RESULTS: There was no relationship between age and grade of histological abnormality. There were significant histological differences between groups for lesions of the flexor aspect, proximal and distal borders, and medulla of the navicular bone; the DSIL and its insertion and the navicular bursa; but not for lesions of the CSLs, the dorsal aspect of the navicular bone, distal phalanx and articular cartilage, synovium or CLs of the DIP joint. CONCLUSIONS: Pathological abnormalities in lame horses often involved not only the navicular bone, but also the DSIL and navicular bursa. Abnormalities of the navicular bone medulla were generally only seen dorsal to lesions of the FFC. POTENTIAL RELEVANCE: Adaptive and reactive change may be occurring in the navicular apparatus in all horses to variable degrees and determination of the pathogenesis of lesions that lead to pain and biomechanical dysfunction should assist specific preventative or treatment protocols.     

Subjective and quantitative scintigraphic assessment of the equine foot and its relationship with foot pain

It was hypothesised that in solar bone images of the front feet of clinically normal horses, or horses with lameness unrelated to the front feet, there would be less than a 10% difference in the ratio of uptake of radiopharmaceutical in either the region of the navicular bone, or the region of insertion of the deep digital flexor tendon (DDFT), compared to the peripheral regions of the distal phalanx. Nuclear scintigraphic examination of the front feet of 15 Grand Prix show jumping horses, all of which were free from detectable lameness, was performed using dorsal, lateral and solar images. The results were compared with the examinations of 53 horses with primary foot pain, 21 with foot pain accompanying another more severe cause of lameness and 49 with lameness or poor performance unrelated to foot pain. None of the horses with foot pain had radiological changes compatible with navicular disease. All the images were evaluated subjectively. The solar views were assessed quantitatively using regions of interest around the navicular bone, the region of insertion of the deep digital flexor tendon and the toe, medial and lateral aspects of the distal phalanx. In 97% of the feet of normal showjumpers, there was <10% variance of uptake of the radiopharmaceutical in the navicular bone, the region of insertion of the DDFT and the peripheral regions of the distal phalanx. There was a significant difference in uptake of radiopharmaceutical in the region of the navicular bone in horses with foot pain compared to normal horses. There was a large incidence of false positive results related to the region of insertion of the DDFT. Lateral pool phase images appeared more sensitive in identifying potentially important DDFT lesions. There was a good correlation between a positive response to intra-articular analgesia of the distal interphalangeal joint and intrathecal analgesia of the navicular bursa and increased uptake of radiopharmaceutical in the region of the navicular bone in the horses with primary foot pain. It is concluded that quantitative scintigraphic assessment of bone phase images of the foot, in combination with local analgesic techniques, can be helpful in the identification of the potential source of pain causing lameness related to the foot, but false positive results can occur, especially in horses with low heel conformation.     

Evaluation of a tenoscopic approach for desmotomy of the accessory ligament of the deep digital flexor tendon in horses

Objective: To develop a tenoscopic approach for desmotomy of the accessory ligament of the deep digital flexor tendon (AL‐DDFT) in horses. Study Design: Experimental. Animals: Cadaveric forelimbs (n=10) and 4 forelimbs from 2 horses anesthetized for terminal teaching procedures, and 12 forelimbs of 6 experimental horses. Methods: Saline distention of the carpal flexor sheath facilitated insertion of an arthroscope into the distal medial aspect of the sheath between the AL‐DDFT and deep digital flexor tendon (DDFT). Location of an instrument portal on the lateral aspect of the metacarpus was identified with a needle. The lateral aspect of the AL‐DDFT was transected and the arthroscope and instrument were switched to transect the remaining fibers on the medial aspect. Cadaveric specimens were dissected for evaluation. Experimental horses were monitored for 30 days postoperatively. Results: Minor complications including incomplete division of the AL‐DDFT and shallow incision into the suspensory ligament were observed in some cadaver specimens. The AL‐DDFT was completely transected in all experimental horses with no suspensory ligament damage. Mean±SD surgical time (incision to skin closure) was 28.3±11.8 minutes. On ultrasonographic examination, transection of the AL‐DDFT was complete in all experimental horses. Minor DDFT fiber disruption was noted in 1 limb during ultrasound examination at day 30. Conclusions: A tenoscopic approach through the carpal flexor sheath provided adequate access for desmotomy of the AL‐DDFT.     

Cutaneous adverse food reactions in dogs: Something new to chew on

It was hypothesised that there is increased blood vessel frequency and proteoglycan staining intensity within the distal aspect of the deep digital flexor tendon (DDFT) in horses with chronic foot pain. Samples of the DDFT from three standardised sites from 10 age-matched mature horses, with chronic foot pain (Group L) or with no history of forelimb lameness (Group N), were collected for this study. A histological analysis of haematoxylin and eosin-stained sections focussed on the frequency and location of blood vessels, while safranin 0 fast green staining was used for semi-quantitative assessment of matrix proteoglycan. The frequency and immunoreactivity of endothelial cell-labelled blood vessels were determined using factor VIII immunolocalisation.There was increased frequency of blood vessels (P = 0.048) and increased proteoglycan staining intensity (P = 0.028) in Group L, compared with Group N. Qualitative micro-anatomical differences in the matrix and tenocytes were noted between Groups N and L. There was reduced factor VIII staining within the vasculature of horses from Group L, compared with Group N. The results suggested that chronic foot pain may be associated with altered DDFT matrix composition, which could be a potential indicator of degenerative change. The increased vascularity may represent a reparative response to a degenerative tendonopathy.     

Anatomical, magnetic resonance imaging and histological findings in the accessory ligament of the deep digital flexor tendon of forelimbs in nonlame horses

Reasons for performing the study: Detailed magnetic resonance imaging (MRI) and histological appearances of the accessory ligament of the deep digital flexor tendon (AL‐DDFT) have not been documented previously in detail. Objectives: To: 1) describe anatomical connections between the AL‐DDFT and adjacent structures; 2) describe high‐field and low‐field MRI and histological appearances of the AL‐DDFT in the forelimb of horses with no carpal or proximal metacarpal pain; and 3) assess the relationship between age, breed, gender, height, weight and MRI findings. Methods: Ten forelimbs were dissected to determine anatomical relationships among the AL‐DDFT and adjacent structures. High‐ and low‐field MR images of the AL‐DDFT and related structures from 29 cadaver limbs of nonlame horses were analysed subjectively and objectively. The relationship between age, breed, gender, height, weight and MRI findings was assessed using a Chi‐squared test. Twelve ALs‐DDFT were examined histologically. Histological and MRI findings were compared subjectively. Results: Fibrous bundles were seen between the AL‐DDFT and the lateral aspect of the superficial digital flexor tendon (n = 9) and the DDFT (n = 2). The AL‐DDFT had low to intermediate signal intensity in most limbs in most high‐field and low‐field MRI sequences. In 69% of limbs, oblique bands of higher signal intensity than the rest of the ligament were identified in high‐field images of the AL‐DDFT. The cross‐sectional area of the AL‐DDFT in the proximal 7 cm of the metacarpal region ranged from 68.1–299 mm². There was no significant relationship between age, gender, weight or height and either the cross‐sectional area of the AL‐DDFT or the presence of oblique higher signal intensity bands. Histological examination revealed that the AL‐DDFT had thick collagen bundles arranged in large crimps and sometimes crossing in oblique directions. The cellularity was greater than in the deep digital flexor tendon in all limbs. Conclusion and potential relevance: The large variability in the MRI appearance and size of the AL‐DDFT in nonlame horses should be borne in mind when interpreting MR images of lame horses.     

High-field magnetic resonance imaging investigation of distal border fragments of the navicular bone in horses with foot pain

Reasons for performing study: Distal border fragments of the navicular bone can be seen in lame and nonlame horses and their clinical significance remains open to debate. Objectives: To describe the magnetic resonance imaging (MRI) appearance of distal border fragments and the adjacent navicular bone. To investigate the relationship between fragments and other abnormalities of the navicular bone and the distal sesamoidean impar ligament (DSIL). Methods: Horses were included if pain causing forelimb lameness was localised to the foot and high‐field MR images were acquired. The size and location of distal border fragments were recorded. Abnormalities in the adjacent navicular bone were graded to obtain a fragment grade. A total navicular bone grade was assigned. The DSIL was also graded. A Chi‐squared test was used to test for associations between the presence of a fragment and specific lesions involving the distal border of the navicular bone, the total grade of the navicular bone, and the grade of the DSIL. Results: 427 horses were included and 111 fragments observed. There was a significant association between the presence of a fragment and the total navicular bone grade, osseous cyst‐like lesions, increased number and size of the synovial invaginations of the distal border, increased signal intensity on fat suppressed images and size of distal border entheseophytes. Conclusions: There is an association between distal border fragments and other pathological MRI abnormalities of the navicular bone. Potential relevance: Distal border fragments are part of navicular disease, but their contribution to pain and lameness remains to be clarified.     

Comparisons of computed tomography, contrast enhanced computed tomography and standing low-field magnetic resonance imaging in horses with lameness localised to the foot. Part 1: anatomic visualisation scores

Reasons for performing study: To date, few reports exist comparing magnetic resonance imaging (MRI) and computed tomography (CT) for imaging of the equine distal limb, yet clinicians are required to decide which modality to use regularly. Objectives: To report and compare anatomic visualisation scores obtained for CT, contrast enhanced CT (CECT) and standing low‐field MRI (LFMRI) in the equine foot. Hypothesis: Anatomic visualisation score discrepancies would exist between CT, CECT and LFMRI. Methods: Images of 22 lame horses (31 limbs) undergoing both CT and LFMRI of the foot were reviewed. When available, CECT images were reviewed. The deep digital flexor tendon (DDFT) was categorised into proximal to distal levels (A–D), structures were assigned visualisation scores (Grades 0–3) and technique comparisons were made using the paired marginal homogeneity test. Results: Computed tomography and LFMRI had similar visibility scores for the navicular bone, middle phalanx, DDFT‐B, collateral ligaments of the distal interphalangeal joint and collateral sesamoidean ligament of the navicular bone. The proximal and distal phalanx had lower visibility scores with LFMRI. The distal DDFT (C–D), distal sesamoidean impar ligament and synovial structures had higher scores with LFMRI. Contrast enhanced CT lowered DDFT and collateral sesamoidean ligament scores and raised distal interphalangeal synovium CT visualisation scores. Conclusions and potential relevance: Visualisation scores differ depending on imaging technique and anatomic structure of interest. This information increases our understanding of the limitations of CT, CECT and LFMRI to visualise anatomy in clinical cases.     

Verification of scintigraphic imaging for injury diagnosis in 264 horses with foot pain

REASONS FOR PERFORMING STUDY: Nuclear scintigraphy is commonly used as a diagnostic aid for foot pain, but there is limited information about different patterns of radiopharmaceutical uptake (RU) and their correlation with the results of other imaging modalities. OBJECTIVES: To describe patterns of RU in horses with foot pain. MATERIALS AND METHODS: Scintigraphic images of the feet of 264 horses with front foot pain were analysed subjectively and using region of interest analysis. Magnetic resonance images of all feet were analysed prospectively; the navicular bones were reassessed retrospectively and assigned a grade. A Spearman rank correlation test was used to test for a relationship between the scintigraphic grade of the navicular bone and magnetic resonance imaging (MRI) grade. Sensitivity and specificity of scintigraphy for detection of lesions in the deep digital flexor tendon (DDFT), the collateral ligaments (CL) of the distal interphalangeal (DIP) joint and the navicular bone were determined. RESULTS: Increased radiopharmaceutical uptake (IRU) was detected in: a) the navicular bone (36.6%); b) pool phase images in the DDFT (13.0%); and c) at the insertion of the DDFT on the distal phalanx (14.3%). There was focal IRU at the insertion of the medial or lateral CL of the DIP joint in 9.4% and 1.5% of limbs, respectively. There was IRU in the medial and lateral palmar processes in 7.6% and 3.4% of limbs, respectively. There was a significant positive correlation between the scintigraphy grade and total MRI grade for the navicular bone and no difference between either focal or diffuse IRU and total MRI grade. There was high specificity, but low sensitivity of scintigraphy for detection of MR lesions of the navicular bone, the DDFT and the CLs of the DIP joint. CONCLUSIONS: Positive nuclear scintigraphic results are good predictors of injury or disease of the navicular bone, DDFT and CLs of the DIP joint. However, a negative scintigraphic result does not preclude significant injuries. CLINICAL RELEVANCE: Nuclear scintigraphy is a useful tool in the investigation of foot lameness and may help to determine the significance of MR lesions, especially if >1 lesion is identified that may be contributing to lameness.     

Use of concurrent scintigraphic and magnetic resonance imaging evaluation to improve understanding of the pathogenesis of injury of the podotrochlear apparatus

REASONS FOR PERFORMING STUDY: Use of physiological methods of diagnostic imaging could provide insight into the pathogenesis of foot pain in live horses. OBJECTIVES: To describe patterns and intensity of increased radiopharmaceutical uptake (IRU) in the navicular bone, and relate this to distribution and types of signal intensity change in the navicular bone and to the presence or absence of lesions of the related soft tissue structures detected using MRI. MATERIALS AND METHODS: Scintigraphic and MR images of 264 horses with unilateral or bilateral foot pain were analysed and graded. A Spearman rank correlation was used to test for relationships between scintigraphic grade of the navicular bone and MRI scores for each region of the bone. Chi-square tests were used to test for associations between scintigraphy grade and presence of increased signal intensities, for differences in the proportion of focal and diffuse IRU between MRI grades, and for associations between an abnormal scintigraphic grade of the navicular bone and presence or absence of a lesion. RESULTS: There were significant positive correlations between scintigraphy grade and both maximum and total MRI grades for the navicular bone and between scintigraphy grade and the MRI grades for the flexor border, the distal border and medulla. However, there was no difference in the proportions of focal and diffuse IRU between navicular bone MRI grades, although diffuse IRU was relatively under-represented in Grade 3 navicular bones. There was no association between IRU in the navicular bone and MR lesions of either the DSIL origin or the CSL insertion, however there was an association between IRU in the navicular bone and combined lesions of the CSL, DSIL and navicular bursa. In limbs with a DDFT lesion, navicular bone scintigraphic Grades 2 and 3 were over-represented. CONCLUSIONS AND CLINICAL RELEVANCE: Scintigraphy and MRI provide complementary information about the pathogenesis of lesions of the podotrochlear apparatus. Further understanding of these disease processes may eventually permit more targeted treatments.     

Collateral desmitis of the distal interphalangeal joint in 18 horses (2001-2002)

REASONS FOR PERFORMING STUDY: There have been no previously published case series of horses examined using either scintigraphy or MRI to diagnose collateral ligament injuries not detectable using ultrasonography or radiography, nor have other concurrent soft tissue lesions been described. OBJECTIVES: To describe the clinical features of horses with desmitis of the collateral ligaments of the distal interphalangeal (DIP) joint and to evaluate the results of radiographic, ultrasonographic, scintigraphic and magnetic resonance imaging (MRI) examinations. METHODS: Horses were examined between January 2001 and January 2003 and were selected for inclusion in the study if there was unequivocal evidence of collateral desmitis of the DIP joint based on ultrasonography or MRI. Subject details, case history, results of clinical examination and responses to local analgesic techniques were reviewed. The results of radiographic, ultrasonographic, scintigraphic and MRI examinations were assessed. RESULTS: Eighteen horses were identified with desmitis of a collateral ligament of the DIP joint, 3 horses (Group 1) based on ultrasonography alone, 7 (Group II) with positive ultrasonographic and magnetic resonance images and 8 (Group III) with no lesion detectable using ultrasonography, but lesions identified using MRI. Seventeen horses had forelimb injuries and one a hindlimb injury. The medial collateral ligament was injured most frequently (13 horses). In the majority of horses, no localising clinical signs were seen. Lameness was invariably worse in circles compared with straight lines. Lameness was improved by palmar digital analgesia in 16 horses (87%), but only 6 were nonlame. Intra-articular analgesia of the DIP joint produced improvement in lameness in 6/15 horses (40%). In 16 horses, no radiographic abnormality related to the DIP joint or collateral ligament attachments was identified. Eight of 14 horses (57%) had focal, moderately or intensely increased radiopharmaceutical uptake (IRU) at the site of insertion of the injured collateral ligament on the distal phalanx. Alteration in size and signal in the injured collateral ligament was identified using MRI. In addition, 5 horses had abnormal mineralisation and fluid in the distal phalanx at the insertion of the ligament. Eleven horses had concurrent soft tissue injuries involving the deep digital flexor tendon, distal sesamoidean impar ligament, navicular bursa or collateral ligament of the navicular bone. CONCLUSIONS AND POTENTIAL RELEVANCE: Collateral desmitis of the DIP joint should be considered as a cause of foot lameness. Although some injuries are detectable ultrasonographically, false negative results occur. Focal IRU at the ligament insertion on the distal phalanx may be indicative of injury in some horses. MRI is useful for both characterisation of the injury and identification of any concurrent injuries. Further follow-up information is required to determine factors influencing prognosis.     

Nonseptic osteitis of the distal phalanx and its palmar processes

There is a large spectrum of radiological variants of the distal phalanx that can be seen in both sound and lame horses. Osteitis of the distal phalanx implies active inflammation, a diagnosis that can only be made supported by nuclear scintigraphy, magnetic resonance imaging or computed tomography. Osteitis of the distal phalanx as a primary cause of lameness is relatively unusual, but may be the result of acute or chronic bone trauma or be associated with adjacent laminar disruption. Bone trauma may also be seen in association with moderate to extensive uniaxial or biaxial ossification of the cartilages of the foot. Bone lesions also occur in association with osteoarthritis of the distal interphalangeal (DIP) joint or at, or adjacent to, the insertion of one of the collateral ligaments of the DIP joint.     

Characterization of age- and location-associated variations in the composition of articular cartilage from the equine metacarpophalangeal joint

Objective: To characterize the impact of age, gender, location and individual animal variation on the composition of articular cartilage from the metacarpophalangeal joint of horses. Design: Cartilage specimens were obtained from the metacarpophalangeal joints of 28 male, female and castrated male horses ranging in age from one day to 27 years of age. Cartilage samples from the distal metacarpus, proximal first phalanx and proximal sesamoids were analyzed separately. Chondrocyte number, DNA content, proteoglycan concentration and total collagen content were determined for each animal and joint location. Results: Age and joint location had a significant effect on chondrocyte number and DNA content with higher cell counts and DNA content detected in cartilage from the youngest age groups and in cartilage from the metacarpus and proximal sesamoids. The influence of age on chondrocyte numbers was not significant in horses over two years of age. Both age and joint location also influenced total proteoglycan and collagen content. Lower proteoglycan and collagen concentrations were detected in younger horses, and cartilage from the metacarpus had lower proteoglycan and collagen concentrations than that from other joint locations. Gender did not appear to influence chondrocyte number or matrix content of equine articular cartilage. However, there was significant residual variation in cellularity, proteoglycan levels and collagen content between individual animals that could not be explained by the signalment factors considered in this study. Conclusions: Future studies examining equine articular cartilage should avoid direct morphologic comparisons between animals of different ages, and any comparisons made between individuals should be interpreted cautiously. In addition, in vitro tissue culture models should avoid the use of cartilage pooled from different animals or from different locations within the same joint.     

Lameness in 46 horses associated with deep digital flexor tendonitis in the digit: diagnosis confirmed with magnetic resonance imaging

REASONS FOR PERFORMING STUDY: The differential diagnosis of foot pain has long proved difficult and the use of magnetic resonance imaging (MRI) offers the opportunity to further the clinical understanding of the subject. OBJECTIVES: To determine the incidence of deep digital flexor tendon (DDFT) injuries in a series of 75 horses with lameness associated with pain localised to the digit, with no significant detectable radiographic or ultrasonographic abnormalities, using MRI; and to describe a variety of lesion types and relate DDF tendonitis with anamnesis, clinical features, response to local analgesic techniques and nuclear scintigraphic and ultrasonographic findings. METHODS: All horses undergoing MRI of the front feet between January 2001 and October 2002 were reviewed and those with DDFT injuries categorised according to lesion type; horses with primary tendonitis (Group I) and those with concurrent abnormalities of the navicular bone considered to be an important component of the lameness (Group II). The response to perineural analgesia of the palmar digital nerves and palmar (abaxial sesamoid) nerves, intra-articular analgesia of the distal interphalangeal (DIP) joint and analgesia of the navicular bursa were reviewed. The result of ultrasonography of the pastern and foot was recorded. Lateral, dorsal and solar pool and bone phase nuclear scintigraphic images were assessed subjectively and objectively using region of interest (ROI) analysis. RESULTS: Forty-six (61%) of 75 horses examined using MRI had lesions of the DDFT considered to be a major contributor to lameness. Thirty-two horses (43%) had primary DDFT injuries and 14 (19%) a combination of DDF tendonitis and navicular bone pathology. Lesions involved the insertional region of the tendon alone (n = 3), were proximal to the navicular bone (n = 23) or were at a combination of sites (n = 20). Lesion types included core lesions, focal and diffuse dorsal border lesions, sagittal plane splits, insertional injuries and lesions combined with other soft tissue injuries. Many horses had a combination of lesion types. Lameness was abolished by palmar digital analgesia in only 11 of 46 horses (24%). Twenty-one of 31 horses (68%) in Group I showed > 50% improvement in lameness after intra-articular analgesia of the DIP joint, whereas 11 of 12 horses (92%) in Group II had a positive response. Twelve of 18 horses (67%) in Group I had a positive response to analgesia of the navicular bursa. Nineteen horses had lesions of the DDFT extending proximal to the proximal interphalangeal joint seen using MRI, but these were identified ultrasonographically in only 2 horses. Scintigraphic abnormalities suggestive of DDFT injury were seen in 16 of 41 horses (41%), 8 in pool phase images and 8 in bone phase images. CONCLUSIONS AND POTENTIAL RELEVANCE: DDFT injuries are an important cause of lameness associated with pain arising from the digit in horses without detectable radiographic abnormalities. Lameness is not reliably improved by palmar digital analgesia, but may be improved by intra-articular analgesia of the DIP joint in at least 68% of horses. Ultrasonography is not sensitive in detecting lesions of the DDFT in the distal pastern region, but a combination of pool and bone phase scintigraphic images of the digit is helpful in some horses. Further follow-up information is required to determine the prognosis for horses with lesions of the DDFT in the digit and to establish whether this is related to lesion severity and/or location.     

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.     

ULTRASONOGRAPHY OF THE SOLAR ASPECT OF THE DISTAL PHALANX IN THE HORSE

Ultrasonographic examinations were performed on the solar aspect of the distal phalanx of 10 feet of five normal live horses (Group 1), 22 feet of seven normal cadavers (Group 2), and nine feet of five horses with pathology of the dorsal solar aspect of the distal phalanx (Group 3). Lateromedial radiographs of the distal phalanx were made in all groups, and in Group 2, digits were sagitally sectioned after imaging. The ultrasonographic and radiographic appearance of the sagittal solar aspect of the distal phalanx was described. Measurements of the distance between the sole and the distal tip of the distal phalanx (A), the solar aspect of the apex of the frog and the distal phalanx (B), and the body of the frog's surface and flexor surface of the distal sesamoid bone (C) were made ultrasonographically, radiographically, and on the sectioned cadaver specimens. There was no statistical difference between the radiographic, ultrasonographic, and direct cadaver measurements in A and C. In B, there was a statistical difference between the radiographic, ultrasonographic, and cadaver measurements-most likely as a result of the difference in trimming of the frog apex. Ultrasonographic and radiographic examination of the nine feet of the five horses in Group 3 were performed and the abnormalities described. Color flow and power Doppler ultrasonography were performed on the normal sagittal solar distal phalanx, on the impar distal sesamoidean ligament, and at the insertion of the deep digital flexor tendon on the facies flexoria of the distal phalanx. Power Doppler in these horses showed blood flow at 0.16-0.48 kHz at the tip of the distal phalanx and at 0.16 kHz at the deep digital flexor tendon insertion and in the impar distal sesamoidean ligament. Using color flow Doppler in normal horses mean blood flows ranged from 1.8 to 5.4 cm/s at the tip of the distal phalanx and 1.8-2.0 cm/s at the deep digital flexor tendon insertion and in the impar distal sesamoidean ligament.     

Deep digital flexor tendon force and digital mechanics in normal ponies and ponies with rotation of the distal phalanx as a sequel to laminitis

REASONS FOR PERFORMING STUDY: Previous studies have implicated tension in the deep digital flexor tendon (DDFT) in the rotation of the distal phalanx (DP) after the breakdown of the dorsal laminae caused by laminitis. Howeveer, once the DP has rotated, the DDFT should become shorter, reducing the force it exerts on the DP. OBJECTIVE: To compare DDFT force and ground reaction forces (GRFs) in normal ponies and ponies with rotation of the DP as a sequel to laminitis. METHODS: Six normal ponies (Group 1) and 6 sound ponies with 6-13 degrees of rotation of the DP in relation to the dorsal hoof wall (Group 2) were assessed at trot using forceplate and motion analysis. The force in the DDFT was calculated by assuming that the extending moment at the distal interphalangeal (DIP) joint resulting from the GRF was equal to the flexing moment created by the force in the DDFT during the stance phase (inverse dynamics). RESULTS: In early stance, the peak DDFT force (mean+/-s.d.) in the normal ponies was 1.92+/-1.63 N/kg. However, in Group 2, the point of zero moment was palmar to the centre of rotation of the DIP joint for the first 40% of stance and hence DDFT force was zero. Force in the DDFT reached a peak of 10.00+/-3.56 N/kg at 60.7+/-5.6% of stance in Group 1 and 6.41+/-1.37 N/kg at 79.2+/-9.6% of stance in Group 2. CONCLUSIONS: DDFT force in Group 2 laminitic ponies was much reduced until late stance, when it neared normal values. POTENTIAL RELEVANCE: Further studies of ponies with rotation of the DP as a sequel to laminitis should assist farriery aimed at reducing the force in the DDFT through the breakover phase of stance to protect damaged dorsal laminae.