Squamous cell carcinoma of the hoof wall in a stallion

Squamous cell carcinoma of the hoof wall, with resultant invasion of the right hind distal phalanx, was identified in a 15-year-old Thoroughbred stallion. The clinical features included a chronic grade 2/5 right hind limb lameness and a sessile dorsal hoof wall mass that was not sensitive to palpation. Radiography revealed a well-circumscribed circular lucency within the distal phalanx, beneath the clinically noticed hoof wall mass. These features were considered to be characteristic of a hoof wall keratoma. Surgical intervention was done 10 months later. The histologic diagnosis at the time of surgery was squamous cell carcinoma. Eight months after surgery, progressive tumor invasion of the distal phalanx resulted in a pathologic articular fracture. This case highlights the need for accurate histologic diagnosis of equine hoof wall masses to differentiate between benign and malignant conditions.     

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

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

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.     

A singular case of traumatic total hoof capsule avulsion

Total, full thickness hoof wall avulsion is rare in horses. Sometimes complications such as fracture of the distal phalanx, osteomyelitis, septic arthritis and degenerative joint disease have been reported. Limiting motion at the affected site and hoof stabilisation are essential to obtain a good hoof regeneration. This case report reviews the clinical features including diagnostic techniques (radiographic examination and venography) of a Quarter Horse filly presented with a complete and full‐thickness traumatic hoof capsule avulsion complicated by an open fracture of the third phalanx. A transfixation casting technique was performed followed after one month by 2 short limb casts applied for 2 months each. Twenty‐four months after trauma the foot had completely regrown. The dorsal aspect of the hoof wall appears to be remarkably shorter compared to the heels. From a radiographic viewpoint, the lateral aspect of the left hind foot shows diffuse bone remodelling and a deformed distal phalanx.     

Congenital bilateral aplasia of the metacarpophalangeal joints in a foal

A 2‐day‐old Warmblood filly was presented for examination of an angular limb deformity of the left front limb and an upright conformation of both metacarpophalangeal joints. Radiological examination revealed bilateral absence of the metacarpophalangeal joint space with fusion of the third metacarpal bone and first phalanx (synostosis). No treatment was undertaken. The filly was readmitted to the clinic 10 weeks later for bilateral front limb lameness. On radiological examination, the synostosis of the front metacarpophalangeal joints was still present. Physitis of the distal growth plate of the right third metacarpal bone and proximal growth plate of the right proximal phalanx, and an avulsion fracture of the palmaromedial and proximal aspect of the left middle phalanx, with a cystic like lesion on the medial aspect of distal first phalanx and proximal middle phalanx were diagnosed. Given the poor prognosis, the foal was subjected to euthanasia. Post mortem examination confirmed the absence of the metacarpophalangeal joint space with a trabecular bony union between the third metacarpal bone and the first phalanx. A rudimentary joint capsule was present at the level of the absent joints as well as a small zone of articular cartilage, which invaginated over a short distance into the dorsal trabecular bone on the right front limb. On the medial aspect of the left proximal interphalangeal joint, a focal defect of articular cartilage with exposure of subchondral bone was observed. This is the first case report of a foal born with congenital aplasia of both metacarpophalangeal joints. Congenital malformations should be considered as differential diagnosis in lame foals or foals born with angular or flexural limb deformities.     

An investigation of the relationships between angles and shapes of the hoof capsule and the distal phalanx

Reasons for performing study: There is little scientific evidence to support the premise that poor foot conformation predisposes to foot pain and lameness. Objectives: To determine relationships between external characteristics of the hoof capsule and angles of the distal phalanx; to determine variability in shape of the distal phalanx; and to investigate association between distal phalanx angles and the injury causing lameness. Materials and methods: Feet were documented photographically and radiographically. Linear and angle measurements were obtained for the hoof capsule and distal phalanx and compared statistically. Horses were categorised according to injury group, and angles and linear ratios were compared between groups. Results: There was modest correlation between hoof wall and heel angles and angles of the distal phalanx. There was variation in shape of the distal phalanx. There was no significant association between injury type and angles of the distal phalanx, although there was a trend for the angle of the dorsal aspect of the distal phalanx with the horizontal to be smaller in horses with injuries of the podotrochlear apparatus or deep digital flexor tendon compared with other groups. Conclusions: There are variations in shape of the distal phalanx largely due to differences in orientation of the concave solar border and the solar border to the horizontal. Variations in shape of the distal phalanx were not accurately correlated with external characteristics of the hoof capsule. There were weak associations between injury groups and angles of the distal phalanx. Clinical relevance: Further work is required to elucidate risk factors for foot‐related lameness.     

Arthrodesis of the Distal Interphalangeal Joint in Two Horses Using Three Parallel 5.5-mm Cortical Screws

The distal interphalangeal joint was successfully arthrodesed in two horses using three parallel 5.5-mm cortical screws and an autogenous cancellous bone graft. The screws were directed from the palmar proximal border of the second phalanx dorso-distally across the joint space and into the third phalanx. The technique was first developed on a normal horse. The second horse, a clinical case, ruptured its deep digital flexor tendon with complete luxation of the distal interphalangeal joint. Bony fusion of the distal interphalangeal joint occurred in both horses, but both also had residual lameness at a walk. Twenty-one months after the arthrodesis procedure, the clinical patient died from complications related to a subsolar abscess in the operated limb.     

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.     

Effects of analgesia of the distal interphalangeal joint and navicular bursa on experimental lameness caused by solar pain in horses

It has been hypothesized that pain originating from the dorsal margin of the sole of the hoof in horses can be attenuated by analgesia of either the distal interphalangeal (DIP) joint, or of the navicular bursa (NB). To test this hypothesis, an experimental lameness was induced in the toe region of the left forelimb in six adult horses. After this, both synovial structures were blocked and the effects on the lameness were semi-quantitatively scored. Lameness was induced by creating pressure on the dorsal margin of the sole with the help of set-screws that were screwed into a nut, welded to the inside of each branch of the shoe. Gaits were recorded on a videotape before and after application of the screws, and after application of either a local anaesthetic or saline into the DIP joint or NB. The gaits were independently evaluated by two blinded clinicians and scored. Lameness scores were high after application of the screws and remained high after the administration of saline, but decreased significantly (P < 0.05) after administration of the local anaesthetic. Analgesia of the DIP joint as well as the NB appeared to be able to desensitize a portion of the sole. It was concluded that pain arising from the toe region of the sole should not be excluded as a cause of lameness when lameness is attenuated by analgesia of the DIP joint, or of the NB.     

Management of the Dorsal Hoof Wall and Its Potential Effects on the Laminitic Hoof

Appropriate management of the equine hoof during chronic laminitis varies by protocol and practitioner. Sequential removal of the dorsal hoof wall was examined in-vivo on a laminitic horse at the walk, revealing an increase in solar force under the margin of the distal phalanx as measured through the use of an in-shoe force measuring system.     

Is there an association between ossification of the cartilages of the foot and collateral desmopathy of the distal interphalangeal joint or distal phalanx injury?

Reasons for performing study: Associations between degree of ossification of the cartilages of the foot and injuries to other structures of the foot have been suggested, but have not been investigated by large scale studies. Objectives: To describe the frequency of grade >3 ossification of the cartilages of the foot (possibly significant ossification, PSO), mediolateral symmetry of ossification and left‐right symmetry between feet; and to investigate associations between PSO and injury of either the collateral ligaments (CLs) of the distal interphalangeal (DIP) joint or the distal phalanx. Hypotheses: Possibly significant ossification of the cartilages of the foot is associated with CL and distal phalanx injury. Distal phalanx injury is associated with a mediolateral difference in ossification grade of ≥2. Methods: Horses were examined for lameness localised to the foot by perineural analgesia, and underwent radiographic and magnetic resonance imaging examinations. Age, breed, occupation, duration of lameness, lame(st) limb, primary cause of lameness, and presence or absence of CL injury were recorded. Dorsopalmar (dorsoplantar) radiographs were examined and ossification of the cartilages of the foot graded using a modification of a previously published scale. Results: One foot from each of 462 horses was included for analysis. There was left‐right symmetry of ossification between feet, and significant association between grades of each foot, with lateral ≥medial cartilages. Possibly significant ossification occurred in the maximally ossified cartilage in 59 (12.8%) feet. There were significant associations between PSO of the maximally ossified cartilage of the foot and injuries of both the CLs of the DIP joint and the distal phalanx. There was no association between distal phalanx injury and marked asymmetry of the ossified cartilages of the foot. Conclusions and clinical relevance: Extensively ossified cartilages of the foot are significantly associated with CL or distal phalanx injury. Markedly asymmetric ossification did not increase the likelihood of distal phalanx injury and should be considered at a prepurchase examination.     

Unilateral white line disease and laminitis in a quarter horse mare

A 5-year-old quarter horse mare presented with unilateral, severe, chronic forelimb lameness. Radiographs revealed extensive hoof wall separation and capsular rotation of the distal phalanx. Treatment included dorsal hoof wall resection, phenylbutazone, a bar shoe, and stall rest. Whether white line disease or laminitis was the primary lesion remains unclear.     

An investigation of the shape of the hoof capsule in hindlimbs,its relationship with the orientation of the distal phalanx and comparison with forelimb hoof capsule conformation

There is limited information documenting hind foot conformation. The objectives of the study were to describe the shape of the hoof capsule of hindlimbs from the lateral aspect in horses of variable breeds, and, within horses, to compare the conformation of the hoof capsule of forelimbs and hindlimbs and determine the orientation of the distal phalanx within the hoof capsule in hindlimbs. Lateral photographs of the fore and hind feet (n = 225) and lateromedial radiographs of the hind feet (n = 29) were obtained. Differences among breed and shoeing status groups were assessed using multivariable mixed-effects linear regression models. Angular parameters and ratios of linear measurements were compared between fore and hind feet; angular radiological variables and photographic parameters of the hind feet were compared. The mean dorsal hoof wall angle for hind feet (50.9°±3.7°) was smaller than forefeet (51.8°±3.9°) (P = 0.04). The mean heel angles for hind feet (36.4°±9.6°) were smaller than forefeet (40.1°±9.3°; P < 0.001). Dorsal hoof wall (P < 0.001) and heel (P = 0.002) angles were larger in unshod than shod feet. In the hind feet, the dorsal hoof wall was parallel to the dorsal aspect of the distal phalanx. The median angle of the distal phalanx to the horizontal (angle S) was 0.6° (interquartile range: −1.4, 2.3°). There was a positive relationship between angle S and the hoof wall angle (W); each 1° increase in angle S was associated with 0.6° increase in angle W (P < 0.001). Angle S was also positively associated with photographic heel angle; each degree increase in the angle S was associated with 1.8° increase in the heel angle (P < 0.001). It was concluded that the angle of the distal phalanx to the horizontal in hindlimbs is smaller than published values for forelimbs. The orientation of the distal phalanx in hindlimbs is correlated with external characteristics of the hoof capsule.     

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.     

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.     

Evaluation using hoof wall strain gauges of a therapeutic shoe and a hoof cast with a heel wedge as potential supportive therapy for horses with laminitis

OBJECTIVE: To evaluate using strain gauges, a hoof cast with heel wedge, and a therapeutic shoe with unsupported toe for their effectiveness in redistribution of load from the dorsal hoof wall. STUDY DESIGN: In vitro biomechanical study. SAMPLE POPULATION: Twenty forelimb specimens. METHODS: Rosette strain gauges were placed on the dorsal and lateral hoof wall of 20 normal shaped hooves. Limbs were loaded vertically using a tensile testing machine with a 1 Hz sinusoidally cycling load up to 3000 N during 15 seconds. Mean values of principal strain and direction at 2500 N load were calculated for 3 experimental conditions (unshod, therapeutic shoe with unsupported toe, and hoof cast with heel elevation) and tested by ANOVA (P<.05). RESULTS: Vertical limb loading in an unshod hoof leads to a biaxial compression of the dorsal wall with high longitudinal compression (epsilon2 = -1515 microm/m). Principal strain at the dorsal wall (epsilon2) was decreased by 23% with the therapeutic shoe and by 59% with the hoof cast. On the lateral hoof wall principal strain was unchanged with the shoe, but increased by 34% with the cast. CONCLUSIONS: Strain measurements indicate unloading of the dorsal hoof wall by both methods with the cast being more effective than the shoe. CLINICAL RELEVANCE: The hoof cast with wedge offers substantial unloading of the dorsal wall, but increases load on the quarter. Therefore a hoof cast would likely be most helpful in acute laminitis when palmar structures can still bear load. The therapeutic shoe offers rehabilitation and regrowth of the dorsal wall without increased load on the quarter wall.     

Compensation for changes in hoof conformation between shoeing sessions through the adaptation of angular kinematics of the distal segments of the limbs of horses

OBJECTIVE: To determine the mechanism that enables horses to partially counteract the shift of the center of pressure under the hoof induced by changes in hoof morphology attributable to growth and wear during a shoeing interval. ANIMALS: 18 clinically sound Warmblood horses. PROCEDURES: Horses were evaluated 2 days and 8 weeks after shoeing during trotting on a track containing pressure-force measuring plates and by use of a synchronous infrared gait analysis system set at a frequency of 240 Hz. All feet were trimmed toward straight alignment of the proximal, middle, and distal phalanges and shod with standard flat shoes. Results-Temporal characteristics such as stance time and the time between heel lift and toe off (ie, breakover duration) did not change significantly as a result of shoeing interval. Protraction and retraction angles of the limbs did not change. Compensation was achieved through an increase in the dorsal angle of the metacarpohalangeal or metarsophalangeal (fetlock) joint and a concomitant decrease of the dorsal angle of the hoof wall and fetlock. There was an additional compensatory mechanism in the hind limbs during the landing phase. CONCLUSIONS AND CLINICAL RELEVANCE: Horses compensate for changes in hoof morphology that develop during an 8-week shoeing interval such that they are able to maintain their neuromuscular pattern of movement. The compensation consists of slight alterations in the angles between the distal segments of the limb. Insight into natural compensation mechanisms for hoof imbalance will aid in the understanding and treatment of pathologic conditions in horses.     

RADIOGRAPHIC APPEARANCE OF THE FEET OF MAMMOTH DONKEYS AND THE FINDING OF SUBCLINICAL LAMINITIS

All feet of 10 clinically sound mammoth donkeys (Group I) were radiographed to determine the appearance of the distal phalanx. The distal phalanges had blunted to concave-shaped dorsal solar margins which varied in appearance from slight to pronounced. The distal phalanges of the forefeet were wider than those of the hindfeet, and also were positioned a greater distance from the dorsal aspect of the hoof wall. The greater distance between the dorsal aspect of the hoof wall and the distal phalanges seemed related to the presence of a periosteal-like bony proliferation on the dorsum of the distal phalanx. This bony proliferation occurred in those distal phalanges which also had radiographic findings consistent with pedal osteitis. Next, all feet of 5 additional mammoth donkeys (Group II) that were to be necropsied for various reasons, were examined similarly to Group I, necropsied and found to have laminitis. Only 2 of these 5 donkeys had been lame; only one had rotation of the distal phalanges (in the forefeet). Radiographic data from the 4 donkeys without rotation seemed most similar to that found in those Group I donkeys which had periosteal reactions on their distal phalanges. Conclusions from this study were that: 1) feet of mammoth donkeys have some anatomic differences from those of domestic horses, 2) subclinical laminitis and pedal osteitis can occur in mammoth donkeys, 3) rotation of the distal phalanx occurs in some, but not all laminitic donkeys, 4) laminitic changes may be more pronounced in their fore than in their hindfeet, and 5) additional studies of donkeys need to be done, examining both proven normal and confirmed laminitic feet.     

Treatment of solar prolapse using the heart bar shoe and dorsal hoof wall resection technique

This paper describes the treatment of 10 horses suffering from acute laminitis using the heart bar shoe and a dorsal hoof wall resection technique. All cases had progressed to prolapse of the tip of the pedal bone covered by solar corium through the horny sole; in one case the exposed tip of the distal phalanx became visible. Nine cases of distal phalangeal rotation and one case of distal displacement of the distal phalanx (sinking) are described. Two animals were destroyed because of the degree of lameness, one remains slightly lame at the trot and the remaining seven have returned to their previous use at comparable levels of performance.