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Diagnosis, treatment and prognosis of some problems involving the fetlock and metacarpus
DIAGNOSIS,TREATMENTAND PROGNOSISOF SOMEPROBLEMSINVOLVING THE FETLOCKAND METACARPUS D. W. Richardson, DVM
controversial since the advent of surgical arthroscopy. The fragments can be easily and atraumatically removed and an excellent prognosis given if there are no other degenerative changes in the joint. In economically unworthy animals, a period of 3-4 months rest followed by intra-articnlar medications, as needed, also affords a favorable prognosis if the fragment is not markedly displaced. It is my opinion that superior conditioning when these horses return to work (i.e. "a good bottom'3 helps prolong their carpers.
In racehorses, the metacarpophalangeal joint, metacarpus, and carpus are probably the most frequently injured joints and provide some examples of the need for high quality radiographs and a complete series of projections. Many lesions are probably being recognized, more frequently now, simply because of the increasing quality of radiographs. Portable machines are more reliable, and screen-film combinations are much faster with superior detail compared to a decade ago. The disadvantage of superior equipment, however, can be immediately negated by poor positioning, poor film processing, or inappropriate technique. The metacarpophalangeal joint is probably the most radiographed joint in the Thoroughbred racehorse and also probably the most common site ofjoint pain. Four bones comprise tbejoint and each has specific areas that lesions are likely to be seen in the athletic horse. A minimum of five projections are recommended dorsopalmar, DPLMO, DPMLO, lateromedial and flexed lateromedial. Proximal phalanx Chip fractures of P1 of any size are not difficult to diagnose if they are displaced. Most dorsal P1 chips occurjustmedialto the median sagittal groove of P1. They are generally seen best on either the DPLMO or one of the lateral projections, depending on the obliquity of the fracture line and projection. Correct technique is especially important for small chips since a dark trim will "burn out" the lesion on the lateral and a light film will not have enough penetration on the oblique. The character and position of the fragment are helpful in determining its significance. A wellrounded chip that is keeping its distance from distal MC3 is probably not as significant as an angular, centripetally displaced fragment. These horses are rarely lame for more than a day or two after the fracture and may never show overt lameness. The observant groom or trainer may notice an effusion in the fetlock with some heat and there is usually a painful response to forced flexion. Horses presented often have histories of bearing in or out, especially in the later stages of a race. The treatment is less Author's address: New Bolted Center, University of Pennsylvania,Kennett Square, PA 19348 Presented at the 12th Annual Equine Seminar, sponsored by the Louisiana Veterinary Medical Association.
338
Palmar or plantar proximal P1 chip fractures most fiequently require oblique projections for best delineation of their margins. A flexed view helps further separate the base of the sesamoid from the P1 chips. This is useful when there is proliferative change at the distal dorsal margin of the sesamoids or if there is a small base sesamoid fracture. These fragments are nearly always well-rounded and are often asymptomatic. It appears that many of these fractvxes occur as foals, without clinical signs manifested until training or racing. These fragments may be manifestations of osteochondrosis since they are recognized in very young, untrained animals. They also may be caused by avulsion of a portion of the incompletely ossified proximal P1 and then develop as a traumatic secondary ossification center. They are more common in the hind limbs and are often bilateral. Treatment is arthroscopic removal, if the clinician is confident they are the source of lameness. They are frequently found incidentally and they almost never cause a low speed lameness. Arthroscopic removal is much less traumatic than arthrotumy for this specific lesion. The prognosis is very good if the diagnosis is correct. Sagittal fractures of proximal P1 are obvious if they extend more than a few centimeters from the joint surface. Many, however, are incomplete and appear to involve only the dorsal cortex. This type of short, incomplete fracture is very frequently missed without good quality radiographs. If the fracture is more than ten days old, there is usually a definite periosteal change on the dorsal cortex seen on lateral projection just distal to the capsular attachments. Initially the change is very indistinct, but in a few more weeks distinct periosteal new bone is obvious. Whenever proliferative change is seen in this area, the DP radiographs should be carefully evaluated for a sagittal fracture; inadequate technique (light film) will result in the lesion being missed. These fractures are more common in Standardbreds than Thoroughbreds and frequently involve more than one limb. Even though these fractures are short and indistinct, they may cause surprisingly severe lameness. Such fractures should always be in the clinicians index of suspicion since blocking and highspeed training may propagate the fracture. Although some surgeons recommend screw fixation for even very short sagittal cracks, rest for 3-4 months usually results in satisfactory healing. Frontal fractures of P1 are straightforward to diagnose
EQUINE VETERINARY SCIENCE
unless they are absolutely non-displaced. They are only seen in the hind limb and predominantly ha Thoroughbreds. These tend to either be displaced at the time of diagnosis or, if undisplaced, heal with a surprising amount of proliferative change. Internal fixation with small fragment screws has had excellent results. Very large frontal fragments are more unusual, require open reduction and internal fxation with 4.5 mm screws and have a poorer prognosis. Complete fractures of P1 always require at least four views. It is a serious error to take only DP and lateral views since a significant number of frontal (coronal) plane fractures separating one or both wings of P1 occur. Attempting to repair the sagittal fracture unaware of the other components is disastrous. Non-displaced or minimally displaced P1 fractures are repaired with 4.5 mm lag screws placed through stab incisions under radiographic control, displaced sagittal fractures require a small arthrotomy at the articular margin to assure accurate alignment of the proximal joint surface. Comminuted fractures, with one intact strut of bone extending to both joint surfaces, are reconstructed with lag screws using an aggressive open reduction exposing the proximal joint surface. Severely comminuted fractures are treated with an external skeletal fixator or cast coaptation. Prognosis is directly dependent on the degree of displacement and comminution. Degenerative changes of P1 are seen earliest with highdetail radiographs involving proximal dorsaljuxta articular bone. Normally, there is a well-defined trabeeular pattern to the bone in this region. Sclerosis of this subehondral bone occurs in association with degenerative change within the joint. A chicken-or-egg dilemma exists, but there is some experimental evidence suggesthag that the subchondral stiffening that occurs secondary to repetitive trauma in turn results in exaggerated mechanical wear and degeneration of the overlying cartilage. In either case, there is a good correlation of marked sclerosis in this region with articular damage. The later change ofsubchondral bone lysis seems to occur first at the dorsal articular margin in association with chronic soft tissue inflammation. Osteophytes of P 1 are most easily recognized on the oblique projections, both dorsally and palmarly. With more advanced disease, osteophytes become more circumferential and are seen on the DP view. Two commonly misinterpreted psuedo-lesions of Pl are seen rnore often as the radiographic detail improves. An oblique linear radiolueency in the dorsal cortex is not a fracture but a normal vascular channel. A relative radiolucency with welldefined margins in central Pl is not a cyst but a well-demarcated medullary cavity. Very "contrasty" films often result in this particular confusion. Proximal sesamold bone
Apical, mid-body and basilar fractures of the proximal sesamoid bones are usually very easy to diagnose radiographically with routine views. Abaxial fractures are more frequently missed and are best demonstrated by a proximal distal LM (or ML) oblique projection tangential to the abaxial surface of the suspect sesemoid. This projection also is useful in determining whether or not the fracture is articular. Axial fractures are usually associated with condylar fractures of MC3 or MT3. Diagnosis requires a well-penetrated DP radiograph that is truly positioned. Even slight obliquity will obscure the fracture line. Mid-body fractures frequently have wedge-shaped comminuted fragments present at their abaxial margins. They should not Volume 10, Number 5, 1990
be confused with the overlapping lines of the pallar and dorsal cortices that occurs due to displacement of the fracture and failure to radiograph directly through the fracture line. Apical fractures comprising <30% of the bone are removed either by arthrotomy or arthroscopically. The arthroscopic technique is useful and can be quick, but probably does not improve the prognosis significantly. The prognosis is dependent on the degree of concomitant suspensory desmitis and articular damage. Base sesamoid fractures are much more serious. Small wedgeshaped pieces extending <50% of the way to the palmar (plantar) margin of the bone can be removed arthroscopically with a fair prognosis. Larger fragments that include the entire base of the bone afford a poor prognosis. Large base fractures and mid-body fractures are repaired with screws or wire, a cancellous graft, and early cast coaptation. The prognosis is no better than fair. Approximately 50% have returned to race, but most at a significantly reduced level of competitiveness. Degenerative changes of the sesamoids involve four basic changes: marginal osteophytes, enthesiophytes, enlarged vascular channels and focal ostcolysis. Marginal ostcophytes occur at the proximal dorsal anddistal dorsal extremities of the sesamoids. Best seen on lateral projections, they are one of the later changes of generalized degenerative disease of the fetlockjoint. Enthesiophytes, proliferative bony change at the site of ligamentous attachment, occur along thepalmar (plantar) aspect of the proximal half of the sesamoid most frequently. Similar changes may also be seen involving the distal bone at the site of distal sesamoids ligament attachment. The latter changes frequently occur most prominently slightly abaxial and are, therefore, seen best on oblique projections. Enthesiophytes may be seen in conjunction with enlargement of the vascular channels in sesamoiditis. The latter change is poorly characterized pathologically, but clinically is distinctive and associated with a guarded prognosis. True lytic change, not associated with the normal trabecular pattern or vascular channels, frequently indicates sepsis. Hematogenous localization of infection to theproximal sesamoid bones appears to be a site of predilection in mature horses. Early recognition requires high quality films and is essential for successful treatment. The lytic change subsequently is associated with proliferation at the bone margin. Severe lameness associated with lytic change in the sesamoid and focal pain must be recognized early for successful management. Third metacarpal/metatarsal distal articular lesions are common and important lesions, especially in Thoroughbred racehorses. Dorsal chip fractures are rather uncommon as traumarie lesions, although OCD fragments are seen occurring from the median sagittal ridge. Radiodensities at the proximal capsular attachment usually represent dystrophic calcification within the soft tissue. O'Brien et al. described palmar third metacarpal lesions in detail (JAVMA 178(3):231-237,1981). The earliest change recognized in this region is flattening of the normally semispheric outline of the condyle with sclerosis of the subchondral plate. This is followed by erosion of the subehondral bone leading to a linear or crescentic radiolucency. Larger cystic lesions or "scooped-out" defects are seen as the more severe lesions. It is important to take true laterals and flexed laterals since only the largest defects will be seen on films that are oblique. Similarly, dorsopalmar views will also usually reveal only large lesions unless the fills are of exceptional quality. A special dorsupallar horizontal beam projection with the fetlock in slight palmar flexion is useful in outlining this area, especially if comminution at this site associated with a condylar fracture is 339
suspected. The ~eatment is rest and intra-articular medication and the prognosis is very poor. The typical lesion is not surgically accessible. Other degenerative changes of the third metacarpal bone are seen on its distal dorsal aspect. Small radiodensities here may represent OCD fragments, small chip fractures, or dystrophic calcification of the synovial pad. Displaced OCD fragments usually have a "scooped out" appearance on the medial sagittal ridge. Chip fractures tend to have sharper margins and less distinct sites of origin. Synovial calcifications have indistinct, more spherical outlines. Calcifications of the soft tissue in this region may be seen without a large villonodular lesion. The latter is frequently associated with an erosive lesion of the distal dorsal cannon bone and the mass may cause a bulge in the soft tissue outline that remains proximally positioned on a flexed lateral view. The clinician should also remember that erosive chronic proliferative (villonodular) synovitis lesions also may occur in the palmar/plantar pouch. Ultrasonography is useful for diagnosis and less invasive than contrast arthrography in both locations. Early lesions can usually be managed with intra-articular HA and corticosteroids and rest2 Truly chronic cases can be helped with surgical excision. Articular fractures of the distal third metacarpal or metatarsal bones are not difficult to diagnose with good quality films, although true hairline cracks can be quite difficult to diagnose, especially if films are too light. With fractures involving the lateral condyle of MC3 or MT3, upward spiraling or occult fractures are uncommon. Medial condylar fractures, however, demand a complete series of radiographs that include the entire diaphysis. MC3 medial condylar fractures tend to either be incomplete or spiral, whereas M'I3 medial condylar fractures frequently have an occult Y-shaped configuration at the mid-diaphysis. In MT3 medialcondylar fractures, spiraling fractures tend to have a more rapid divergence of the fracture lines on the dorsal and plantar surfaces compared to the fractures that are more susceptible to catastrophic mid-shaft failure which tend to ascend more parallel. Careful radiographic evaluation of these fractures is essential since treatment considerations are quite different. Most common bone fractures are best treated with lag screws. Non- or minimally displaced fractures can be repaired through stab incisions. Displaced fractures require accurate reduction of the distal articular surface. Medial condylar fractures, especially of MT3, should be operated with extreme caution since catastrophic failure in the mid-diaphysis can occur during anesthetic recovery, or even several days following repair. The most important consideration in the radiography of lateral condylar fractures, besides assessing their outline, is to evaluate the distal pallar surface for the previously mentioned lytic lesions or comminution. Wedge-shaped fragments are very common in displaced fractures and must be identified. Axial sasamoid fractures also should not be overlooked. Shin soreness in Thoroughbred racehorses is an extremely common malady with a spectrum of radiograpic lesions. Some horses that are extremely lame with bucked shins have absolutely no perceptible radiographic abnormalities, whereas other horses may be racing soundly with well-defined "saucer" fractures. It is likely that the entire bucked shin complex is associated with fatigue damage of the dorsal cortex. Stress fractures result from cyclic trauma, each cycle Of which is not enough to induce a fracture. The sum of the cyclical damage, however, eventually leads to a clinical fracture (one recognizable by clinical signs by radiography or another imaging modality). Acute bucked shins are often negative on plain films although high detail techniques,
340
such as xeroradiography or slow screens with single emulsion fill, may reveal non-linear radiolucencies in the superficial dorsal cortex. Such changes may or may not be seen with subtle periosteal proliferation. More advanced radiographic lesions are the oblique linear radiolucencies of the dorsal cortex called saucer or tongue fractures. These lines occur most commonly in a distal dorsal to proximal palmar direction at 30 ° to 35 ° angles to the dorsal cortex. They clearly involve the mid- and mid-distal diaphysis. most frequently and the left MC3 more often than the right. What is not clear, however, is when and whether these lines are or are not fractures. There is some evidence that the lines may initially represent areas of intensive osteoclastic resorption of bone. Such intensive osteoclasia may be stimulated by extreme cyclical stress. As the bone is resorbed, fatigue strength diminished and failure can ensue. This helps explain why there is not a good correlation between the radiographic evidence of a fracture and clinical signs. The line might be there before, during and well after clinical signs of a fracture (heat, pain, swelling) are manifested. Treatment for saucer fractures usually involves rest until the horse jogs sound followed by a gradual return to regular training, over a period of 10-12 weeks. If the fracture is recurrent or if an aggressive approach to the lesion is indicated, drilling of the dorsal cortex through the fracture line followed by a 90-day program of walking and jogging, generally (but not always) resolves the problem. I also usually place a cancellous graft in the drill holes. Proximal MC3 or MT3 fractures are less common, but are frequently difficult to diagnose. Vertical fractures involving proximal MC3 are frequently missed. Because the horse blocks sound.with intra-articular anesthetic in the intercarpal joint, the metacarpus may be overlooked and dorsopalmar projections might not be taken. The lesion is seen only on the DP view and appears to involve displacement at the palmar cortex more than the dorsal, since proliferative change dorsally is not seen. These lesions are usually treated with rest. A case with a particularly discrete and wide fracture line is suitable for lag screws. The prognosis is good. Avulsion fractures of the origin of the suspensory ligament are seen most frequently in Standardbreds in the forelimb. Radiographically, they are usually best diagnosed on the flexed lateral projection, but slight obliquity may be necessary to discern them clearly. On DP projections, the fragment is V-shaped with the apex proximally. These fragments can also be documented ultrasonographically. These lesions are treated with rest, usually about 10-12 weeks, the prognosis is favorable.
EQUINE VETERINARY SCIENCE
controversial since the advent of surgical arthroscopy. The fragments can be easily and atraumatically removed and an excellent prognosis given if there are no other degenerative changes in the joint. In economically unworthy animals, a period of 3-4 months rest followed by intra-articnlar medications, as needed, also affords a favorable prognosis if the fragment is not markedly displaced. It is my opinion that superior conditioning when these horses return to work (i.e. "a good bottom'3 helps prolong their carpers.
In racehorses, the metacarpophalangeal joint, metacarpus, and carpus are probably the most frequently injured joints and provide some examples of the need for high quality radiographs and a complete series of projections. Many lesions are probably being recognized, more frequently now, simply because of the increasing quality of radiographs. Portable machines are more reliable, and screen-film combinations are much faster with superior detail compared to a decade ago. The disadvantage of superior equipment, however, can be immediately negated by poor positioning, poor film processing, or inappropriate technique. The metacarpophalangeal joint is probably the most radiographed joint in the Thoroughbred racehorse and also probably the most common site ofjoint pain. Four bones comprise tbejoint and each has specific areas that lesions are likely to be seen in the athletic horse. A minimum of five projections are recommended dorsopalmar, DPLMO, DPMLO, lateromedial and flexed lateromedial. Proximal phalanx Chip fractures of P1 of any size are not difficult to diagnose if they are displaced. Most dorsal P1 chips occurjustmedialto the median sagittal groove of P1. They are generally seen best on either the DPLMO or one of the lateral projections, depending on the obliquity of the fracture line and projection. Correct technique is especially important for small chips since a dark trim will "burn out" the lesion on the lateral and a light film will not have enough penetration on the oblique. The character and position of the fragment are helpful in determining its significance. A wellrounded chip that is keeping its distance from distal MC3 is probably not as significant as an angular, centripetally displaced fragment. These horses are rarely lame for more than a day or two after the fracture and may never show overt lameness. The observant groom or trainer may notice an effusion in the fetlock with some heat and there is usually a painful response to forced flexion. Horses presented often have histories of bearing in or out, especially in the later stages of a race. The treatment is less Author's address: New Bolted Center, University of Pennsylvania,Kennett Square, PA 19348 Presented at the 12th Annual Equine Seminar, sponsored by the Louisiana Veterinary Medical Association.
338
Palmar or plantar proximal P1 chip fractures most fiequently require oblique projections for best delineation of their margins. A flexed view helps further separate the base of the sesamoid from the P1 chips. This is useful when there is proliferative change at the distal dorsal margin of the sesamoids or if there is a small base sesamoid fracture. These fragments are nearly always well-rounded and are often asymptomatic. It appears that many of these fractvxes occur as foals, without clinical signs manifested until training or racing. These fragments may be manifestations of osteochondrosis since they are recognized in very young, untrained animals. They also may be caused by avulsion of a portion of the incompletely ossified proximal P1 and then develop as a traumatic secondary ossification center. They are more common in the hind limbs and are often bilateral. Treatment is arthroscopic removal, if the clinician is confident they are the source of lameness. They are frequently found incidentally and they almost never cause a low speed lameness. Arthroscopic removal is much less traumatic than arthrotumy for this specific lesion. The prognosis is very good if the diagnosis is correct. Sagittal fractures of proximal P1 are obvious if they extend more than a few centimeters from the joint surface. Many, however, are incomplete and appear to involve only the dorsal cortex. This type of short, incomplete fracture is very frequently missed without good quality radiographs. If the fracture is more than ten days old, there is usually a definite periosteal change on the dorsal cortex seen on lateral projection just distal to the capsular attachments. Initially the change is very indistinct, but in a few more weeks distinct periosteal new bone is obvious. Whenever proliferative change is seen in this area, the DP radiographs should be carefully evaluated for a sagittal fracture; inadequate technique (light film) will result in the lesion being missed. These fractures are more common in Standardbreds than Thoroughbreds and frequently involve more than one limb. Even though these fractures are short and indistinct, they may cause surprisingly severe lameness. Such fractures should always be in the clinicians index of suspicion since blocking and highspeed training may propagate the fracture. Although some surgeons recommend screw fixation for even very short sagittal cracks, rest for 3-4 months usually results in satisfactory healing. Frontal fractures of P1 are straightforward to diagnose
EQUINE VETERINARY SCIENCE
unless they are absolutely non-displaced. They are only seen in the hind limb and predominantly ha Thoroughbreds. These tend to either be displaced at the time of diagnosis or, if undisplaced, heal with a surprising amount of proliferative change. Internal fixation with small fragment screws has had excellent results. Very large frontal fragments are more unusual, require open reduction and internal fxation with 4.5 mm screws and have a poorer prognosis. Complete fractures of P1 always require at least four views. It is a serious error to take only DP and lateral views since a significant number of frontal (coronal) plane fractures separating one or both wings of P1 occur. Attempting to repair the sagittal fracture unaware of the other components is disastrous. Non-displaced or minimally displaced P1 fractures are repaired with 4.5 mm lag screws placed through stab incisions under radiographic control, displaced sagittal fractures require a small arthrotomy at the articular margin to assure accurate alignment of the proximal joint surface. Comminuted fractures, with one intact strut of bone extending to both joint surfaces, are reconstructed with lag screws using an aggressive open reduction exposing the proximal joint surface. Severely comminuted fractures are treated with an external skeletal fixator or cast coaptation. Prognosis is directly dependent on the degree of displacement and comminution. Degenerative changes of P1 are seen earliest with highdetail radiographs involving proximal dorsaljuxta articular bone. Normally, there is a well-defined trabeeular pattern to the bone in this region. Sclerosis of this subehondral bone occurs in association with degenerative change within the joint. A chicken-or-egg dilemma exists, but there is some experimental evidence suggesthag that the subchondral stiffening that occurs secondary to repetitive trauma in turn results in exaggerated mechanical wear and degeneration of the overlying cartilage. In either case, there is a good correlation of marked sclerosis in this region with articular damage. The later change ofsubchondral bone lysis seems to occur first at the dorsal articular margin in association with chronic soft tissue inflammation. Osteophytes of P 1 are most easily recognized on the oblique projections, both dorsally and palmarly. With more advanced disease, osteophytes become more circumferential and are seen on the DP view. Two commonly misinterpreted psuedo-lesions of Pl are seen rnore often as the radiographic detail improves. An oblique linear radiolueency in the dorsal cortex is not a fracture but a normal vascular channel. A relative radiolucency with welldefined margins in central Pl is not a cyst but a well-demarcated medullary cavity. Very "contrasty" films often result in this particular confusion. Proximal sesamold bone
Apical, mid-body and basilar fractures of the proximal sesamoid bones are usually very easy to diagnose radiographically with routine views. Abaxial fractures are more frequently missed and are best demonstrated by a proximal distal LM (or ML) oblique projection tangential to the abaxial surface of the suspect sesemoid. This projection also is useful in determining whether or not the fracture is articular. Axial fractures are usually associated with condylar fractures of MC3 or MT3. Diagnosis requires a well-penetrated DP radiograph that is truly positioned. Even slight obliquity will obscure the fracture line. Mid-body fractures frequently have wedge-shaped comminuted fragments present at their abaxial margins. They should not Volume 10, Number 5, 1990
be confused with the overlapping lines of the pallar and dorsal cortices that occurs due to displacement of the fracture and failure to radiograph directly through the fracture line. Apical fractures comprising <30% of the bone are removed either by arthrotomy or arthroscopically. The arthroscopic technique is useful and can be quick, but probably does not improve the prognosis significantly. The prognosis is dependent on the degree of concomitant suspensory desmitis and articular damage. Base sesamoid fractures are much more serious. Small wedgeshaped pieces extending <50% of the way to the palmar (plantar) margin of the bone can be removed arthroscopically with a fair prognosis. Larger fragments that include the entire base of the bone afford a poor prognosis. Large base fractures and mid-body fractures are repaired with screws or wire, a cancellous graft, and early cast coaptation. The prognosis is no better than fair. Approximately 50% have returned to race, but most at a significantly reduced level of competitiveness. Degenerative changes of the sesamoids involve four basic changes: marginal osteophytes, enthesiophytes, enlarged vascular channels and focal ostcolysis. Marginal ostcophytes occur at the proximal dorsal anddistal dorsal extremities of the sesamoids. Best seen on lateral projections, they are one of the later changes of generalized degenerative disease of the fetlockjoint. Enthesiophytes, proliferative bony change at the site of ligamentous attachment, occur along thepalmar (plantar) aspect of the proximal half of the sesamoid most frequently. Similar changes may also be seen involving the distal bone at the site of distal sesamoids ligament attachment. The latter changes frequently occur most prominently slightly abaxial and are, therefore, seen best on oblique projections. Enthesiophytes may be seen in conjunction with enlargement of the vascular channels in sesamoiditis. The latter change is poorly characterized pathologically, but clinically is distinctive and associated with a guarded prognosis. True lytic change, not associated with the normal trabecular pattern or vascular channels, frequently indicates sepsis. Hematogenous localization of infection to theproximal sesamoid bones appears to be a site of predilection in mature horses. Early recognition requires high quality films and is essential for successful treatment. The lytic change subsequently is associated with proliferation at the bone margin. Severe lameness associated with lytic change in the sesamoid and focal pain must be recognized early for successful management. Third metacarpal/metatarsal distal articular lesions are common and important lesions, especially in Thoroughbred racehorses. Dorsal chip fractures are rather uncommon as traumarie lesions, although OCD fragments are seen occurring from the median sagittal ridge. Radiodensities at the proximal capsular attachment usually represent dystrophic calcification within the soft tissue. O'Brien et al. described palmar third metacarpal lesions in detail (JAVMA 178(3):231-237,1981). The earliest change recognized in this region is flattening of the normally semispheric outline of the condyle with sclerosis of the subchondral plate. This is followed by erosion of the subehondral bone leading to a linear or crescentic radiolucency. Larger cystic lesions or "scooped-out" defects are seen as the more severe lesions. It is important to take true laterals and flexed laterals since only the largest defects will be seen on films that are oblique. Similarly, dorsopalmar views will also usually reveal only large lesions unless the fills are of exceptional quality. A special dorsupallar horizontal beam projection with the fetlock in slight palmar flexion is useful in outlining this area, especially if comminution at this site associated with a condylar fracture is 339
suspected. The ~eatment is rest and intra-articular medication and the prognosis is very poor. The typical lesion is not surgically accessible. Other degenerative changes of the third metacarpal bone are seen on its distal dorsal aspect. Small radiodensities here may represent OCD fragments, small chip fractures, or dystrophic calcification of the synovial pad. Displaced OCD fragments usually have a "scooped out" appearance on the medial sagittal ridge. Chip fractures tend to have sharper margins and less distinct sites of origin. Synovial calcifications have indistinct, more spherical outlines. Calcifications of the soft tissue in this region may be seen without a large villonodular lesion. The latter is frequently associated with an erosive lesion of the distal dorsal cannon bone and the mass may cause a bulge in the soft tissue outline that remains proximally positioned on a flexed lateral view. The clinician should also remember that erosive chronic proliferative (villonodular) synovitis lesions also may occur in the palmar/plantar pouch. Ultrasonography is useful for diagnosis and less invasive than contrast arthrography in both locations. Early lesions can usually be managed with intra-articular HA and corticosteroids and rest2 Truly chronic cases can be helped with surgical excision. Articular fractures of the distal third metacarpal or metatarsal bones are not difficult to diagnose with good quality films, although true hairline cracks can be quite difficult to diagnose, especially if films are too light. With fractures involving the lateral condyle of MC3 or MT3, upward spiraling or occult fractures are uncommon. Medial condylar fractures, however, demand a complete series of radiographs that include the entire diaphysis. MC3 medial condylar fractures tend to either be incomplete or spiral, whereas M'I3 medial condylar fractures frequently have an occult Y-shaped configuration at the mid-diaphysis. In MT3 medialcondylar fractures, spiraling fractures tend to have a more rapid divergence of the fracture lines on the dorsal and plantar surfaces compared to the fractures that are more susceptible to catastrophic mid-shaft failure which tend to ascend more parallel. Careful radiographic evaluation of these fractures is essential since treatment considerations are quite different. Most common bone fractures are best treated with lag screws. Non- or minimally displaced fractures can be repaired through stab incisions. Displaced fractures require accurate reduction of the distal articular surface. Medial condylar fractures, especially of MT3, should be operated with extreme caution since catastrophic failure in the mid-diaphysis can occur during anesthetic recovery, or even several days following repair. The most important consideration in the radiography of lateral condylar fractures, besides assessing their outline, is to evaluate the distal pallar surface for the previously mentioned lytic lesions or comminution. Wedge-shaped fragments are very common in displaced fractures and must be identified. Axial sasamoid fractures also should not be overlooked. Shin soreness in Thoroughbred racehorses is an extremely common malady with a spectrum of radiograpic lesions. Some horses that are extremely lame with bucked shins have absolutely no perceptible radiographic abnormalities, whereas other horses may be racing soundly with well-defined "saucer" fractures. It is likely that the entire bucked shin complex is associated with fatigue damage of the dorsal cortex. Stress fractures result from cyclic trauma, each cycle Of which is not enough to induce a fracture. The sum of the cyclical damage, however, eventually leads to a clinical fracture (one recognizable by clinical signs by radiography or another imaging modality). Acute bucked shins are often negative on plain films although high detail techniques,
340
such as xeroradiography or slow screens with single emulsion fill, may reveal non-linear radiolucencies in the superficial dorsal cortex. Such changes may or may not be seen with subtle periosteal proliferation. More advanced radiographic lesions are the oblique linear radiolucencies of the dorsal cortex called saucer or tongue fractures. These lines occur most commonly in a distal dorsal to proximal palmar direction at 30 ° to 35 ° angles to the dorsal cortex. They clearly involve the mid- and mid-distal diaphysis. most frequently and the left MC3 more often than the right. What is not clear, however, is when and whether these lines are or are not fractures. There is some evidence that the lines may initially represent areas of intensive osteoclastic resorption of bone. Such intensive osteoclasia may be stimulated by extreme cyclical stress. As the bone is resorbed, fatigue strength diminished and failure can ensue. This helps explain why there is not a good correlation between the radiographic evidence of a fracture and clinical signs. The line might be there before, during and well after clinical signs of a fracture (heat, pain, swelling) are manifested. Treatment for saucer fractures usually involves rest until the horse jogs sound followed by a gradual return to regular training, over a period of 10-12 weeks. If the fracture is recurrent or if an aggressive approach to the lesion is indicated, drilling of the dorsal cortex through the fracture line followed by a 90-day program of walking and jogging, generally (but not always) resolves the problem. I also usually place a cancellous graft in the drill holes. Proximal MC3 or MT3 fractures are less common, but are frequently difficult to diagnose. Vertical fractures involving proximal MC3 are frequently missed. Because the horse blocks sound.with intra-articular anesthetic in the intercarpal joint, the metacarpus may be overlooked and dorsopalmar projections might not be taken. The lesion is seen only on the DP view and appears to involve displacement at the palmar cortex more than the dorsal, since proliferative change dorsally is not seen. These lesions are usually treated with rest. A case with a particularly discrete and wide fracture line is suitable for lag screws. The prognosis is good. Avulsion fractures of the origin of the suspensory ligament are seen most frequently in Standardbreds in the forelimb. Radiographically, they are usually best diagnosed on the flexed lateral projection, but slight obliquity may be necessary to discern them clearly. On DP projections, the fragment is V-shaped with the apex proximally. These fragments can also be documented ultrasonographically. These lesions are treated with rest, usually about 10-12 weeks, the prognosis is favorable.
EQUINE VETERINARY SCIENCE