Fractures of the distal phalanx in the horse

Fractures of the distal phalanx are an important cause of lameness referrable to the foot. Depending on the fracture configuration and articular involvement, conservative or surgical treatment may be required. Fractures of the distal phalanx have been divided into six categories based on fracture configuration. Discussion of clinical features, management, and prognosis for horses with distal phalangeal fractures is presented for each fracture type.     

Microanatomic characteristics of the insertion of the distal sesamoidean impar ligament and deep digital flexor tendon on the distal phalanx in healthy feet obtained from horses

OBJECTIVE: To describe microanatomic characteristics of the insertion of the aistal sesamoidean impar ligament (DSIL) and deep digital flexor tendon (DDFT) on the distal phalanx in horses. SAMPLE POPULATION: Healthy feet obtained from 62 horses of various breeds. PROCEDURE: Feet from 23 horses were used to histologically examine the insertion of the DSIL and DDFT (n = 7), its vasculature (10), and neural elements (6). In 39 other horses, the insertion zone was examined for proteoglycan. RESULTS: The insertion of the DSIL and dorsal half of the DDFT contained bundles of collagen fibers with intervening loose connective tissue septa with arteriovenous complexes (AVC) and nerve fibers. Microscopic examination revealed adaptive changes in the insertion with regard to proteoglycan content. In young adult horses, little or no staining for proteoglycans was evident, whereas in middle-aged horses, moderate proteoglycan staining was seen. Six older horses had slight proteoglycan staining at the insertion. CONCLUSIONS AND CLINICAL RELEVANCE: The study revealed that this region contained a rich neurovascular complex between the collagen bundles. A gradual increase in production of proteoglycan, evident at the insertion of the DSIL and DDFT on the distal phalanx, indicates that adaptive responses to stress rather than age alone may be the primary determining factor. These observations indicate that this insertion site may be susceptible to stress during stance and impact loading, because this region appears to be strategically situated to regulate important neurovascular functions of the foot.     

Management of a transverse fracture in the distal phalanx of a horse.

A yearling horse was presented with a septic, transverse fracture in the frontal plane of the distal phalanx. The fracture fragment was surgically removed from the parent bone via the sole. The foot was managed by corrective farriery and the horse was able to be ridden for pleasure.     

Osteosarcoma of the middle phalanx in a horse

An 11‐year‐old Thoroughbred gelding was presented for lameness investigation following acute onset hindlimb lameness, which developed during a period of paddock turnout. Clinical examination revealed a swelling over the dorsolateral aspect of the pastern that was painful on digital palpation. Radiography of this area was consistent with an aggressive bone lesion involving both joint surfaces of the middle phalanx with pathological fracture and distal collapse of this bone. On this basis, the horse was subjected to euthanasia. Post mortem histopathological examination revealed presence of an osteosarcoma without involvement of the articular cartilage. This bone tumour is extremely rare in horses and has not been reported in this anatomical location.     

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.     

Fractures of the distal phalanx in horses

Summary. Nineteen cases of fracture of the distal phalanx in horses are reviewed. This represented 1.1% of the total number of horses seen at Murdoch University Veterinary Hospital (MUVH) over a 32-month period. All horses were managed conservatively. Eight horses made a complete recovery. Three are being trained again and are not lame. Four horses made a limited recovery. Two horses are still resting and one horse was killed humanely when it still showed lameness after 2 years. One horse was killed humanely after the fracture was first diagnosed.     

Development of intraosseous infusion of the distal phalanx to access the foot lamellar circulation in the standing,conscious horse

Intraosseous (IO) infusion of the distal phalanx (IOIDP) as a delivery route targeting hoof lamellar tissue of standing, conscious horses was evaluated. Following sedation and regional nerve blockade in six Standardbred horses, a microdialysis (MD) probe was implanted into the hoof lamellar tissue of one forelimb. A purpose designed cannulated bone screw was introduced into the body of the distal phalanx, approximately 6 cm from the MD probe. Gentamicin solution (25 mg/mL) was infused at 20 μL/min through the bone screw for 2 h without the application of a tourniquet. MD and blood samples were collected at regular intervals and analysed for gentamicin concentrations.Gentamicin was present in lamellar tissue at much higher concentrations than peripheral serum. The mean concentration of gentamicin was 24.4, 20.5 and 4.4 μg/mL in extracellular fluid (ECF) and 0.28, 0.5 and 0.32 μg/mL in serum samples collected 60, 120 and 150 min after IOIDP was started, respectively. A clinically safe and efficacious IO drug delivery to the hoof lamellar tissue of standing, conscious horse was developed.     

Fusion of the distal sesamoid and distal phalanx in a yearling colt

This paper describes a rare malformation of the distal portion of the left foredigit of a 15-month-old half-bred colt which was severely lame. Radiological, pathological and tomographic studies revealed hypoplasia of the metacarpophalangeal skeleton, absence of the distal sesamoid and deformation of the distal phalanx. Morphological analysis of the lesion and computerised measurement of the width of the articular surface of the distal phalanx suggested an early fusion between the distal sesamoid and distal phalanx.     

The ossification of cartilages of the distal phalanx in the horse: An anatomical, experimental, radiographic and clinical study

This paper describes some anatomical findings relatedto ossification of the distal phalanx cartilages by anatomical and computerized tomographic sections. Radiographic findings of ossification were analyzed and correlated to age and breed. Ossification was found in 10% of warmblood horses and in 80% of draft horses and was much more severe in draft horses than in warmblood horses. The expansion of the hoof was measured in the laboratory in several feet of warmblood and draft horses and was found to be minimal with no differences whether ossification was present or not. Computerized tomography was performed on a foot of a slaughtered horse before and after up to 7000N loading in the laboratory in order to study the eventual changes of the cartilages and the hoof. These structures seemed quite unaffected by the load and expansion of the horny capsule was minimal. Minor expansion seems an inevitable structural behavior of the hoof and the classical hoof mechanism is questioned. The clinical significance of ossification in its relation to lameness was individually determined during clinical examination and by comparison of groups of horses with and without ossification with groups of horses with lameness from the foot and proximal to the foot. The severity of the ossification was related to the onset of lameness and no correlation was found. It is concluded that the clinical significance of ossification is almost nil. Ossification is not painful when developing and not thereafter. There is no correlation between navicular disease and ossification of the cartilages either. Orthopedic shoeing is of no significance at all. An unfavorable advice in purchase examinations in sporting horses due to cartilage ossification is not justified in the author's opinion.     

Primary ossifying fibroma of the proximal phalanx in a horse

A primary ossifying fibroma was found at necropsy in a 5-year-old Welsh pony cross mare that was humanely subjected to euthanasia for an intractable severe left hindlimb lameness. Antemortem radiographs of the left hind pastern were characterised by articular, subchondral and cortical areas of lysis. Primary ossifying fibroma is a rare lesion of the distal limb but should be considered when there is extensive lysis extending into the medulla and proximal cortical bone.     

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.     

Fractures of the distal phalanx of the forelimb in eight foals

Fractures of the distal phalanx of the forelimb were diagnosed in 5 colts and 3 fillies ranging in age from 2 weeks to 5 1/2 months at the time of fracture. Three fractures entered the distal interphalangeal joint and 6 fractures (one foal had bilateral fractures) were nonarticular. All foals with articular fractures became sound with conservative treatment. Four of 5 foals with nonarticular fractures became sound with conservative treatment and 1 foal developed separation of the hoof at the coronary band after application of acrylic around the hoof. On the basis of our observations in these foals, sagittal articular and nonarticular distal phalangeal fractures in foals should be treated conservatively. Foals so treated would have an excellent prognosis for return to soundness.     

Preliminary study of tendon biopsy in the horse

A series of experimental tendon biopsies is described. Three biopsies were taken from the lateral digital extensor tendon (LDET) and three from the superficial flexor tendon (SFT). The LDET biopsies resulted in little discomfort whereas the SFT biopsies led to temporary lameness. The tendons were examined histologically up to 99 days after the biopsies were removed. In all of the tendons the defect filled with granulation tissue which subsequently became organised as a longitudinally orientated collagenous scar tissue. In this small series of biopsies the histological effects of the biopsy persisted longer in the SFT than in the LDET. It is concluded that tendon biopsy cannot be advocated for safe routine use in the horse.     

A review of third phalanx fractures in the horse: sixty-five cases

Sixty-five cases of third phalanx (P3) fracture were retrieved from 20,638 case records at Michigan State University's Veterinary Clinical Center between Feb 1, 1964 and July 1, 1977. The fractures were classified by anatomic location, using a numbering system. Data from case records indicated the most common P3 fracture involved the articular surface of the coffin joint (53 of 65 cases; 81.5%). The greatest occurrence of P3 fracture was in Standardbreds (31 of 65 cases). Thirty-three of the 65 fractures were in geldings of all breeds; 57 of the cases were distributed among racing horses of four breeds; and the mean ages at time of fracture for these groups were 4.9 to 5.3 years. The most common cause of P3 fracture was racing injury. Of 57 P3 fractures of the forelimb, 51 (89.5%) involved the lateral aspect of the left limb or medial aspect of the right limb--the part of each foot supporting most of the horse's weight in turns, while racing counterclockwise. Methods and response of treatment were evaluated by questionnaires obtained from 31 of the 65 owners. This questionnaire solicited information from owners and trainers as to: (1) cause, (2) treatment, (3) outcome, and (4) the use of the horse. Results were tabulated for: (1) questionnaire information obtained, (2) a classification system for P3 fractures, based on the anatomic location of the fracture, and (3) distribution of fractures between limbs and position (medial vs lateral) within limbs.     

Lag screw fixation of avulsion fractures of the second phalanx in the horse.

Avulsion fractures of the posteromedial eminence of the 2nd phalanx were repaired, using an ASIF cortex screw in 3 reining Quarter Horses. Within 9 and 11 months, respectively, 2 horses were sound and back in competition as reining horses. The other horse was sound for pleasure class showing at 7 months after surgery.