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On-the-Track Catastrophes in the Thoroughbred Racehorse
W. Theodore Hill , in Diagnosis and Management of Lameness in the Horse (Second Edition) , 2011
The metacarpophalangeal joint is involved in most catastrophic injuries. Horses with simple, nondisplaced condylar fractures of the McIII usually develop acute lameness at the end of a race or after the race. Lameness is noticeable at a walk by the time the horse is loaded. With minimal swelling, diagnosis is presumptive initially, and appropriate supportive measures are required. Although the lameness may be substantial, localizing the injury is often difficult when displacement and swelling are minimal. However, some condylar fractures of the McIII are diagnosed after the horse has returned to the stable to cool out, without the assistance of an ambulance. An open, comminuted McIII condylar fracture causes severe lameness. The horse is pulled up during a race or immediately after the race. The proximal aspect of the displaced fragment penetrates the skin with some mild hemorrhage, making the diagnosis readily apparent.
Because the potential for further displacement and contamination is great, considerable care must be exercised to support the fracture site. Preferably a sterile bandage should be applied to the area and then the limb supported with a heavy bandage or compression boot. Excessive movement of the horse should be avoided while the horse is loaded and transported on the ambulance. Newer ambulances are equipped with a sliding partition to support the horse firmly. The prognosis is guarded because of the compound (open) nature of this injury, and extreme care in managing these horses on the track is essential to a successful outcome.
Proximal Sesamoid Bones
The PSBs are a frequent site of racing and training injury. The PSBs of the forelimbs are primarily involved. Classically, a simple fracture of a PSB results in a progressive lameness while the horse is cooling out after successfully completing a race or workout. The official veterinarian may not see many of these horses and may learn of their injuries only after receiving information from the test barn personnel, trainers, or attending veterinarians.
A more severe sagittal or midbody fracture of one or both of the PSBs causes severe, acute lameness during a race or immediately after a race. If only one PSB is involved, the loss of support of the metacarpophalangeal joint is minimal. The limb should be held by the first attendant on the scene, to prevent weight bearing and further movement, before application of a Kimzey splint. Once supported, these horses are relatively cooperative and confident to move for loading and transport.
In horses with biaxial PSB fractures, loss of metacarpophalangeal joint support is immediate. A dramatic drop of the metacarpophalangeal joint occurs whenever the horse attempts to bear weight. The limb must be supported immediately and the horse controlled to allow prompt application of a splint. These horses may attempt to move on the injured limb and, if they are not restrained, may cause substantial secondary damage to the soft tissues of the fetlock joint (see Chapters 36 and 104).
Fractures involving the metacarpophalangeal joint frequently are complex and involve some combination of condylar fractures of the McIII and PSB fractures, thus compromising the suspensory apparatus. Horses running at race speeds that sustain a McIII condylar or PSB fracture continue to gallop several strides on the injured limb before pulling up. Often they may unseat the rider and gallop considerable distances before being stopped. Additional fractures and disruption of the suspensory ligament (SL) and distal sesamoidean ligaments may result, and the injury may become open, with subluxation and disarticulation of the metacarpophalangeal joint. Depending on the severity of the injury, some of these horses may be manageable for ambulance transport. However, many require immediate euthanasia because of the extensive damage. The metacarpophalangeal joint is involved in two thirds of all catastrophic racing injuries at the New York Racing Association tracks.5
Third Metacarpal Bone
Condylar fractures of the McIII were discussed previously. Horses with minimal displacement of the fracture have a good prognosis for return to racing after surgery. Those with substantial displacement of the fracture or skin penetration have a less favorable prognosis, but with proper on-track management, many can have a reasonable outcome in an alternative career.
The McIII diaphysis is the site of a common racing and training injury referred to as bucked shins (see Chapter 102). If not properly managed, horses with bucked shins may not stride out well, move with a choppy action, and trail the field during a race. These horses may be pulled up by the jockey, but they require little on-track care.
Dorsal cortical fracture of the McIII may result from the bucked-shin complex and is an injury that is seen most frequently in late 2-year-olds or in 3-year-olds. Lameness may be intermittent, and palpation of the affected area often provides inconsistent findings. Dorsal cortical fracture of the McIII poses a serious risk to horse and rider if not detected and properly treated. If a horse with a fracture is returned to training and racing prematurely or the fracture is undiagnosed, a complete diaphyseal fracture may develop. This catastrophic injury causes a horse to fall without warning during morning workouts or a race, risking serious injury to the rider and others in close proximity. The track veterinarian is faced with an essentially unmanageable horse. The fracture usually is comminuted and open. The limb distal to the fracture site is often attached by only tendons and remaining skin. The horse may attempt to rise or manage to rise, but it is extremely unstable and usually falls again. For the safety of all assisting at the scene and for the riders who may still be down on the track, the horse should physically be kept down by capable track personnel. Immediate euthanasia is indicated. If the trainer or owner is present and requests another opinion, the attending veterinarian can sedate or anesthetize the horse long enough for another veterinarian to be summoned. Attempts to develop an anesthetic protocol to facilitate transport of these horses for potential surgical intervention have been unsuccessful. Historically, this catastrophic injury has been the cause of spectacular horse spills in racing, causing considerable loss to the horse industry, serious jockey injury, and negative media attention. Because essentially no treatment alternatives are available, all effort must be directed toward prevention. Accurate diagnosis and the removal of horses from high-intensity training and racing are essential.
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Diagnostic and Surgical Arthroscopy of the Metacarpophalangeal and Metatarsophalangeal Joints
C. Wayne McIlwraith BVSc, PhD, DSc, Dr med vet (h.c. Vienna), DSc (h.c. Massey), Laurea Dr (h.c. Turin), D vet med (h.c. London), FRCVS, Diplomate ACVS, ECVS & ACVSMR , … Ian M. Wright MA, VetMB, DEO, Diplomate ECVS, MRCVS , in Diagnostic and Surgical Arthroscopy in the Horse (Fourth Edition) , 2015
Insertion of the Arthroscope
The metacarpophalangeal joint is distended with fluid (Fig. 5-3) before making the arthroscopic portal. In this joint, distension facilitates the recognition of the correct place for the arthroscopic portal and minimizes the risk of iatrogenic trauma to the joint on entry of the arthroscopic sleeve. There are no tendon sheaths to avoid as in the carpus, and the surgeon does not have to be concerned with exact localization of structures before distension.
Distension is achieved with approximately 35 mL of fluid after inserting a needle dorsally or into the palmar pouch adjacent to the proximal sesamoid bone (Misheff & Stover, 1991) (see Fig. 5-3). Adequate distension can be recognized easily with bulging of the joint capsule on either side of the common digital extensor tendon. The outpouching of the distended joint is more prominent lateral to the common digital extensor than it is medial to it, despite the insertion of the lateral digital extensor tendon, which ramifies over the joint capsule and is penetrated when the lateral portal is created.
The site for the laterally placed arthroscopic portal is in the proximolateral quadrant created by distending the joint maximally (see Fig. 5-3). This site reduces the risk of iatrogenic damage to the sagittal ridge of the third metacarpal bone and provides the best overall view of the joint. A No. 11 blade is used to incise the skin and stab through the joint capsule (Fig. 5-4). The arthroscopic sleeve containing a conical obturator is then inserted through the joint capsule, initially perpendicular to the skin and then parallel to the articular surface of McIII to avoid iatrogenic damage to this area (Fig. 5-5). Entry is completed by advancing the sheath proximad to avoid damage to the midsagittal ridge of McIII (see Fig. 5-5). The sheath can then be directed distad once over the sagittal ridge. When the arthroscopic sleeve is inserted so that its tip touches the medial capsule, the arthroscope is inserted and the examination can begin.
As in the carpus, creation of an instrument portal and insertion of an egress cannula or probe are the next steps. A useful measure is to insert a needle at the proposed instrument portal location to check if a site is appropriate (Figs. 5-6 and 5-7). The use of a needle to ascertain ideal positioning for instrument portals represents a departure from what was previously described in the carpus. However, the carpus is unique and the skin incisions for the instrument portal are made before joint distension and insertion of the arthroscope merely to avoid entering an extensor tendon sheath. There are no such issues in the fetlock joint, or most other joints for that matter. The practice of inserting a needle to ascertain the ideal position for instrument insertion and surgical maneuverability is common to all joints other than the carpus. By making a skin incision with a scalpel and No. 11 blade, the surgeon creates the instrument portal through the joint capsule (Fig. 5-8). The small egress cannula can then be inserted through this portal without the trocar. An arthroscopic examination can then commence. At the completion of arthroscopy, the skin incisions only are closed (Fig. 5-9).
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René van Weeren , in Equine Sports Medicine and Surgery (Second Edition) , 2014
Loading the mature joint: the balance between maintenance and morbidity
The metacarpophalangeal joint is known to be the equine joint most susceptible to damage.53 It is the MCP joint that, together with the carpal joint, has received most attention in terms of effect of exercise. This can to a large extent be explained by the high incidence of condylar fractures in the MCP joint and of third carpal bone slab fractures in the carpus in racehorses.
In mature horses the articular cartilage has lost its plasticity and cannot be conditioned further, but (subchondral) bone remains responsive to exercise according to Wolff's law54 and a certain degree of loading is necessary for maintenance. Cast immobilization for seven weeks followed by a gradually increasing rehabilitation programme for eight weeks led to substantial loss of volumetric bone mineral density of subchondral bone that was not fully recovered during the rehab period.55
Too much exercise is more common in the equine industry than too little and the effect of loading may vary from avoidance of negative effects due to disuse to the infliction of severe overload-induced damage, depending on the type and intensity of exercise. Different types of high-intensity exercise were associated with different patterns of SCB thickness in tarsal joints56, and exercise-induced micro-cracks are well-known to be the initial stages of condylar fractures of the metacarpus in racehorses.57 Exercise may, apart from its effect on subchondral bone, also affect thickness of both the calcified and hyaline cartilage layer and increase the risk of osteochondral lesions.58,59 Exercise-induced loading has been shown to decrease COMP content at intermittently highly loaded areas, whereas regular lower level loading promotes COMP synthesis and/or retention.60 A similar negative effect of too much exercise was seen in an ex vivo study in which material from the dorsal radial facet of the third carpal bone, an area subjected to high contact stresses in galloping horses, was cultured.61 The material came from horses having undergone a strenuous exercise regimen and in these animals a significant reduction in aggrecan synthesis and a concomitant increase in decorin synthesis could be determined compared to less vigorously trained controls. Based on these findings, it was suggested that this alteration in articular cartilage metabolism could be a predisposing factor for cartilage degeneration and OA at a later stage.
The overall metabolism-enhancing effect of exercise on articular cartilage has been studied indirectly in several studies focusing on a variety of potential biomarkers in serum or synovial fluid. Moderate to strenuous exercise led to increases in plasma GAG levels, and serum keratan sulphate and COMP.62–64 Higher chondroitin sulphate peak chain lengths, but shorter hyaluronic acid chain lengths were found in exercised versus rested horses.65 Another study confirmed the increase in proteoglycan markers in both serum and synovial fluid after exercise, and showed the same was true for a number of collagen markers.66 Exercise increased prostaglandin E2 content in synovial fluid67, but moderate exercise did not affect MMP-1 activity.68 There is a mutual interaction between synovial fluid and articular cartilage. The former is not just a reflection of the status of the latter, but may in itself influence cartilage metabolism. In fact, the effects of joint loading on cartilage are, at least in part, mediated by alterations in the synovial fluid. Cartilage explants cultured in post-exercise synovial fluid showed enhanced GAG synthesis and diminished release when compared to cultures using pre-exercise synovial fluid.69
An influence of exercise on articular cartilage has been demonstrated in other species than the horse as well. In young Beagle dogs, moderate loading levels tended to increase GAG production, while strenuous exercise led to GAG depletion in high-load areas.70
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The Metacarpophalangeal Joint
Dean W. Richardson , Sue J. Dyson , in Diagnosis and Management of Lameness in the Horse (Second Edition) , 2011
OA of the metacarpophalangeal joint is common, especially in racehorses, endurance horses, polo ponies, event horses, and show jumpers. There is usually a progression of disease from medial to lateral, reflecting the biomechanical loading of the joint.23 The degree of lameness varies from mild to severe depending on the stage of the disease and recent work history. There is often associated synovitis and/or capsulitis, with palpable distention and/or thickening of the joint capsule. However, the absence of joint effusion does not preclude the presence of OA. There is often resentment of passive flexion of the joint and exacerbation of lameness by flexion; however, the absence of these clinical signs also does not preclude the presence of OA. The range of passive joint motion may be reduced because of increased stiffness of the soft tissues on the dorsal aspect of the joint.
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The European and Australasian Standardbreds
In Diagnosis and Management of Lameness in the Horse (Second Edition) , 2011
Osteoarthritis of the Metacarpophalangeal Joint
OA of the metacarpophalangeal joint may be acute or chronic. Acute synovitis is seen in young horses when training is intensified or when the track surface changes. Clinical signs include mild to moderate lameness, pain on palpation, and lameness after flexion. Radiographs are usually negative in young horses, but flattening or more severe changes of the sagittal ridge of the McIII in older horses with chronic OA often are seen. Contrast radiology reveals a filling defect corresponding to a hypertrophic synovial pad of the distal, dorsal aspect of the McIII. Ultrasonographic examination reveals various degrees of dorsal joint capsule thickening and increase in echogenicity of the synovial pad. Intraarticular analgesia abolishes the lameness in most horses.
In horses with acute synovitis, training program modulation (2 to 3 weeks of light jogging), corrective shoeing (wide-based shoes and pads), and intraarticular corticosteroids (a series of three injections at 2-week intervals) may resolve the problem. In these horses, concurrent pathological conditions of the articular cartilage, subchondral bone, and the synovial pad usually are lacking or mild. Horses with hypertrophic synovial pads benefit from arthroscopic surgery to remove the thickened tissues because response to medical management is poor. This is frequently the case in older horses, in which advanced OA is often present. Prognosis after surgery is only fair to guarded, however.
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Lance H. BassageII, Mike W. Ross , in Diagnosis and Management of Lameness in the Horse (Second Edition) , 2011
Low Palmar Analgesia
Analgesia of the metacarpophalangeal joint region and distal aspect of the limb is induced using the low palmar block or low palmar analgesia (low four-point). This technique blocks the medial and lateral palmar nerves and the medial and lateral palmar metacarpal nerves. In the forelimb a subcutaneous, dorsally directed ring block and block of the dorsal branch of the ulnar nerve completely abolishes skin sensation. Disagreement exists about whether abolishing skin sensation is necessary when performing perineural techniques. Abolition of skin sensation independently from nerves contributing to deep pain sensation, as in the case of the low palmar technique, does not necessarily mean deep pain is abolished, which is particularly relevant when a nerve responsible for skin sensation is blocked. When using these techniques for diagnostic purposes, it may be best to avoid blocking nerves that contribute only skin sensation, thus minimizing the number of needle insertions For therapeutic interventions, however, these nerves need to be blocked.
The low palmar block is performed at the level of the distal end (bell or button) of the second and fourth metacarpal bones (splint bones), with the limb in a standing position or held off the ground (Figure 10-7). A 20- or 22-gauge needle is used to inject 1.5 to 5 mL of local anesthetic solution at each injection site. To block the palmar metacarpal nerves, the needle is inserted perpendicular to the skin, just distal to the end of the splint bones, to a depth of 1 to 2 cm. It is important to deposit local anesthetic solution deep in the injection site, rather than simply in a subcutaneous location. While local anesthetic solution is continuously injected, the needle is slowly withdrawn, leaving a visible bleb in the subcutaneous space. To block the medial and lateral palmar nerves, the needle is inserted subcutaneously, in the palmar aspect of the space between the suspensory ligament and DDFT at the level of or slightly more proximal to the distal end of the splint bone. To improve the accuracy of the injection, using a fan-shaped injection technique is helpful. If the digital flexor tendon sheath (DFTS) is distended, the injections must be performed more proximally. Inadvertent penetration of the DFTS is possible even if it is not distended, so careful skin preparation is mandatory. To complete this block, local anesthetic solution is placed in the subcutaneous tissues from the bleb at the distal end of the splint bone to the dorsal midline. One of the Editors (SJD) does not do this last step.
An alternative technique to abolish pain associated with maladaptive or nonadaptive bone remodeling or other causes of subchondral bone pain of the distal aspect of the McIII is to block the lateral and medial palmar metacarpal nerves separately from the lateral and medial palmar nerves. In some horses suspected of having this injury, use of abbreviated low palmar analgesia will avoid additional injections of local anesthetic solution. With this technique the lateral or medial palmar metacarpal nerve, or both, can be blocked individually or together, and the horse's gait assessed. In many horses with this cause of lameness, contralateral forelimb lameness will then be seen. If lameness does not abate, the clinician then completes low palmar analgesia using the technique described previously (see the following discussion).
Alternatively, some clinicians prefer to use a longer needle first to deposit local anesthetic solution over the palmar metacarpal (metatarsal) nerves. The needle is then pushed subcutaneously to deposit local anesthetic solution over the palmar nerves (see Figure 10-7). When this modification is performed, incompletely blocking the palmar metacarpal (metatarsal) nerves or lacerating the digital vessels is possible. The lateral and medial palmar nerves can be blocked using only the lateral injection site by advancing the needle in a medial direction, palmar to the DDFT. Although each of these modifications may theoretically decrease the number of injections needed to perform this technique, they have the disadvantages of potential hemorrhage and incomplete analgesia.
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Pathophysiology of Tendon Injury
Roger K.W. Smith , in Diagnosis and Management of Lameness in the Horse (Second Edition) , 2011
Hypothesized Mechanisms of Tendon Degeneration
Sudden overextension of the metacarpophalangeal joint may cause mechanical disruption of the digital flexor tendons. Although this may be the mechanism of certain tendon injuries, such as deep digital flexor tendonitis, direct low-grade mechanical forces, such as experienced under maximal loading, could be responsible for the cumulative fatigue microdamage of the tendon matrix. Subsequent clinical tendonitis is initiated by similar, or sudden supramaximal, loading after the accumulation of microdamage.
Physical Influences: Exercise-Induced Hyperthermia
Because of the hysteresis loop, when a tendon is loaded and unloaded, a loss of stored energy as heat results in temperature increases within the equine digital flexor tendons. Thermocouples have been placed inside the SDFT, and these have recorded temperatures of up to 45° C during periods of galloping.13 Such temperatures are used to kill neoplastic cells therapeutically, so it was hypothesized that these temperatures would interfere with tenocyte metabolism and possibly destroy the cells. However, in vitro experiments have shown that tenocytes are much more resistant to these temperature increases in comparison with other fibroblast-like cells.73 However, these experiments were performed on tenocytes in suspension culture, and more recent experiments in two-dimensional culture have suggested that such temperature rises can adversely influence gap junction communication between cells.74 It is certainly possible that although the cells remain viable with such temperature increases, hyperemia may still adversely influence tendon matrix quality. An alteration in the normal balance between synthesis and resorption activity of tenocytes or a direct denaturing effect on tendon extracellular matrix may occur.
Blood flow through tendon is a complex issue, and its relevance to clinical injury is still unsubstantiated. Under maximal loading, blood flow is limited or abolished within the tendon because of the compressive forces generated by the lengthening of the tendon, and this may give rise to relative hypoxia. Indeed, color flow Doppler ultrasonography of equine tendons shows no detectable flow when a horse is standing still, and even flow in the blood vessels of the distal aspect of the limb is sluggish until the horse moves. With injury, an increase in blood flow can be detected using Doppler ultrasonography, but only when the weight-bearing load is removed from the limb when it is raised off the ground. Some areas of equine digital flexor tendons are relatively poorly perfused (e.g., the dorsal portion of the DDFT in the metacarpophalangeal joint region), and this level (but not just the dorsal surface) is a site predisposed to deep digital flexor tendonitis. However, this area also shows histological adaptation to the relatively ischemic environment, with fewer cells and increased amounts of the compression-resisting extracellular matrix components. Furthermore, the tendon may receive some of its nutrition at this site by diffusion from the digital flexor tendon sheath synovial fluid. Similar alterations in the extracellular matrix composition are seen at the corresponding positions in the SDFT, and one could assume that the forces on this tendon would be similar to those of the DDFT at the same site. Therefore a reduced blood flow would also be expected at this level, and yet clinically this region is invariably spared injury in all but the most severe tendonitis.
Equine tendon cells do rely at least in part on oxidative metabolism, although blocking aerobic metabolism does not prevent normal cell proliferation.75 Based on studies in other species, tenocytes may be more resistant to hypoxia than other, similar fibroblast-like cells.
Laser Doppler flowmetry has suggested that a change in blood supply is not the initiating cause in human Achilles tendonitis,76 in contrast to the previously proposed hypoxic cause for tendonitis based on electron microscopic investigations of normal and diseased Achilles tendons.77
Another result of poor perfusion under loading is the generation of toxic free radicals when perfusion is restored. Such reperfusion injury also was proposed as a causative factor for tendonitis through the destruction of tenocytes or tendon matrix by the free radicals, although this at present remains a speculative mechanism.
Various stimuli, including those mentioned previously, could result in the synthesis, release, or activation of proteolytic enzymes. Relatively little information is available on the constitutive or induced expression of proteases in tendon, although activity of procollagenase and aggrecanase was described in human and bovine tendon explants in vitro.78,79 An imbalance between the matrix synthesis and degradation of various extracellular matrix proteins is a possible mechanism whereby the tendon can be weakened and predisposed to clinical tendonitis, and in vitro studies have supported this as a mechanism for the weakening of tendon by cyclical mechanical load.80 Interestingly, the influence of cyclical loading in inducing proteolytic enzyme activity appears to be exaggerated with age, possibly explaining in part the age-related increase in injury risk.80
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Veterinary aspects of training the show jumping horse
Rachel C. Murray , in Equine Sports Medicine and Surgery (Second Edition) , 2014
Synovitis and osteoarthritis of the metacarpophalangeal joint is common in the older show jumping horse. Thickening of the joint capsule may be beneficial in protecting the joint, but chronic capsulitis is associated with limited range of motion and resentment of flexion or manipulation of the joint. Radiography and diagnostic analgesia are useful in diagnosis.
Traumatic injury can occur due to interference by other limbs or impact with the jump. This may be superficial. However, bone injury can occur, including impact trauma to the dorsal aspect of the fetlock and pastern. Alternatively, bone injury in the fetlock joint can been seen in jumping horses associated with repetitive overloading and hyperextension of the joint.54,55 The distal third metacarpal bone may be affected on the dorsal aspect of the parasagittal grooves located further palmar. Alternatively, or in addition, incomplete fracture or bone trauma to the sagittal groove of the proximal phalanx may occur unilaterally or bilaterally in show jumping horses. Magnetic resonance imaging and scintigraphic imaging are likely to provide most useful diagnostic information in horses with these problems.54
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The Metatarsophalangeal Joint
Mike W. Ross , in Diagnosis and Management of Lameness in the Horse (Second Edition) , 2011
The MTP joint is nearly identical to the metacarpophalangeal joint and is composed of the distal articular surface of the third metatarsal bone (MtIII), its sagittal ridge, and the medial and lateral condyles; the medial and lateral proximal sesamoid bones (PSBs); and the proximal articular surface of the proximal phalanx, which has a prominent axially located sagittal groove (see Chapter 36). Minor differences exist in the shape and length of the proximal phalanx between the forelimbs and hindlimbs but are not clinically relevant. The MTP joint normally is more upright than the metacarpophalangeal joint and can achieve a greater degree of flexion. The lateral-to-medial width of the lateral condyle of the MtIII is less than that of the medial condyle. In racehorses, based on the results of scintigraphic examination, stress-related bone injury occurs predominantly in the lateral aspect of the hindlimb, which may be related to the smaller surface area of the lateral condyle. The joint capsule, intersesamoidean and collateral sesamoidean ligaments, suspensory ligament (SL) attachments, and digital flexor tendons all function to move and support the MTP joint. The dense collateral ligaments have short deep, and long superficial components. In the hindlimb the lateral digital extensor tendon joins with the long digital extensor tendon in the proximal dorsal metatarsal region. Therefore only the long digital extensor tendon is encountered during arthrocentesis or surgical procedures performed in the dorsal aspect of the MTP joint.
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Anton E. Fürst , Christoph J. Lischer , in Equine Surgery (Fourth Edition) , 2012
The hair is clipped circumferentially from the level of the metacarpophalangeal joint to the carpus. The horse is sedated, and local anesthesia is achieved through a high palmar ring block.
After aseptic preparation of the limb and appropriate draping, a vertical incision through the skin, subcutaneous tissue, and paratenon is made directly over the lateral aspect of the DDF tendon, centered at the junction of the proximal and middle third of the MCIII (Figure 90-62, A). With the help of curved Kelly forceps, the DDF tendon is separated from the neurovascular bundle (see Figure 90-62, B), the accessory ligament, and the superficial digital flexor (SDF) tendon. The DDF tendon is elevated out of the incision (see Figure 90-62, B). During this part of the procedure, an assistant should lift the limb off the ground to relieve the tension on the DDF tendon. Care must be taken to avoid elevating the neurovascular bundle located medially to prevent its inadvertent transection together with the tendon. The elevated tendon is subsequently transected with the scalpel blade. An immediate separation of the ends of 1 to 3 cm is usually noted after complete transection of the tendon.
An alternative tenotomy technique involves the blind transection of the DDF tendon with the help of a blunt bistoury while the animal is weight bearing.117 Concomitant transection of the medially located neurovascular bundle can occur with this technique.
The subcutaneous tissue is closed with an absorbable monofilament suture material in a simple-continuous pattern. The skin is closed with stainless steel staples.
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The palmar aspect of the hand showing the epiphyses of the hand exploded. MCP joints in red.
Metacarpophalangeal articulation and articulations of digit. Palmar aspect.
| Anatomical terminology |
[ edit on Wikidata ]
The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the digits.  These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cavities on the proximal ends of the proximal phalanges .  Being condyloid, they allow the movements of flexion, extension, abduction, adduction and circumduction at the joint. 
- 1 Structure
- 1.1 Ligaments
- 1.2 Dorsal surfaces
- 2 Function
- 3 Clinical significance
- 3.1 Other animals
- 4 References
- 5 External links
Structure[ edit ]
Ligaments[ edit ]
Metacarpophalangeal articulation and articulations of digit. Ulnar aspect.
Each joint has:
- palmar ligaments of metacarpophalangeal articulations
- collateral ligaments of metacarpophalangeal articulations
Dorsal surfaces[ edit ]
The dorsal surfaces of these joints are covered by the expansions of the Extensor tendons, together with some loose areolar tissue which connects the deep surfaces of the tendons to the bones.
Function[ edit ]
The movements which occur in these joints are flexion , extension , adduction , abduction , and circumduction ; the movements of abduction and adduction are very limited, and cannot be performed while the fingers form a fist. 
The muscles of flexion and extension are as follows:
|fingers||Flexor digitorum superficialis and profundus , lumbricales , and interossei , assisted in the case of the little finger by the flexor digiti minimi brevis||extensor digitorum communis , extensor indicis proprius , and extensor digiti minimi muscle|
|thumb||flexor pollicis longus and brevis||extensor pollicis longus and brevis|
Clinical significance[ edit ]
Arthritis of the MCP is a distinguishing feature of rheumatoid arthritis , as opposed to the distal interphalangeal joint in osteoarthritis .
Other animals[ edit ]
In many quadrupeds, particularly horses and other larger animals, the metacarpophalangeal joint is referred to as the ” fetlock .” This term is translated literally as “foot-lock.” In fact, although the term fetlock does not specifically apply to other species’ metacarpophalangeal joints (for instance, humans), the “second” or “mid-finger” knuckle of the human hand does anatomically correspond to the fetlock on larger quadrupeds. For lack of a better term, the shortened name may seem more practical.
References[ edit ]
This article incorporates text in the public domain from page 332 of the 20th edition of Gray’s Anatomy (1918)
- ^ a b c Drake, Vogl and Mitchell (2015). Grey’s Anatomy for Students, 3rd Edition. Churchill Livingstone, Elsevier. p. 796. ISBN 9780702051319 .
- ^ Gray’s Anatomy (1918), see infobox
External links[ edit ]
- Hand kinesiology at the University of Kansas Medical Center
- EatonHand joi-047
- Wikipedia articles incorporating text from the 20th edition of Gray’s Anatomy (1918)
- Wikipedia articles with TA98 identifiers
- This page was last edited on 27 November 2018, at 16:57 (UTC).
- Text is available under the Creative Commons Attribution-ShareAlike License ;
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