Chapter 94 - Vestigial MC and MT bones Flashcards
Figure 94-1. Important soft tissue structures surrounding the small MC/
MT bone.4 a, MC/MT interosseous ligament; b, fascia metacarpi/metatarsi
palmaris/plantaris; c, ligament-like structure originating from the distal
end of the splint bone.
Figure 94-2. Classification of small MC/MT bone fractures: The bones
can be divided into three equal parts: a, proximal; b, midbody; and c,
distal.
M
Figure 94-5. (A) DLPMO radiographic view of the right MC of a horse presented with a fracture of the proximal third of the MCIV (white arrow) and a fissure of MCIII (black arrow). (B) The fracture was fixed with a 3.5-mm 6-hole LCP, with screws engaging both MCIV and MCIII.
What are the small MC/MT bones important for in horses?
Supporting and stabilizing structures
What are common conditions affecting the small MC/MT bones?
Fractures and exostoses
What rare congenital defect can affect the small MC/MT bones?
Polydactyly
Where do the small MC/MT bones articulate in the equine limb?
With the carpal and tarsal bones
Which small MC bone carries more weight in the forelimb?
MCII
What is a common cause of small MC/MT bone fractures in horses?
Kicks from other horses
How do fractures of the small MC/MT bones typically present in horses?
Different grades of lameness
What is an important consideration for proximal small MC/MT bone fractures?
Development of osteitis or osteomyelitis
MCII articulates with which bones?
second and third carpal bone whereas MCIV only articulates with fourth caral bone
In the HL the MTIV articulates with _______ bone and forms a small articulation
In the hindlimb, MTIV
has only a small articulation with the fourth tarsal bone, providing
minimal weight transfer through this articulation.
Where is located the artery in the HL?
In the hindlimb, the location of the **lateral
dorsal metatarsal artery **between MTIII and MTIV makes it particularly vulnerable to accidental or surgical injury.
Define the classifications of splint bone fractures
Simple or comminuted
Open or closed
Proximal, middle or distal bone (Fig 94-2)
Which type of splint fracture has associated suspensory desmitis?
Distal fractures have a high incidence of associated suspensory desmitis; in these cases, enlargement of the associated branch can be palpated
Which reiongal diagnostic analgesia can help you figure out the source of pain in chronic (not acute) cases?
High palmar/plantar analgesia
Proximal small MC/MT bone fractures are the most difficult to treat what are the treatment options?
Conservative with standing wound debridement (open fx) under sedation and local anest AB + NSAID+support bandage + box stall 1 month with 2 month hand walking
Surgical = internal fixation with removal of fracture fragments
What is a common treatment approach for proximal multifragment splint bone fractures?
Conservative treatment without internal fixation
What is important in follow-up care after conservative treatment of splint bone fractures?
Follow-up radiographs
What additional pathology should always be checked in closed fractures of the distal aspect of small MC/MT bones?
Suspensory ligament pathologies
Treatment
Figure 94-3. (A) Horse presented after a kick injury on the lateral aspect of the left hindlimb at the level of the proximal small MT bone. A small wound is visible. (B) Dorsolateral-to-plantaromedial oblique (DLPMO) radiograph of the left MT of the same horse showing an acute multifragment fracture of MTIV. (C) DLPMO radiographic view after segmental ostectomy of the affected MTIV.
Which imaging technique is helpful in chronic fractures or complications like osteomyelitis?
Computed Tomography (CT)
Which bone is most commonlyinvolved in proximal fractures according to some studies?
MCIV/MTIV
What is a risk associated with proximal fractures of the small MC/MT bones?
Bone sequestra
What is indicated for open multifragment fractures of MTIV?
Conservative treatment
How effective is conservative treatment for open multifragment fractures of the small MC/MT bones?
Often results in full athletic function
How much of the small MC/MT bones is typically recommended to be removed?
The distal two-thirds
In which bone is it acceptable to remove more than two-thirds?
MTIV
What is proposed when more than two-thirds of a splint bone needs removal?
Internal fixation with a small plate specially in MCII
DLPMO radiographic view of the right MC of a horse presented with a fracture of the proximal third of the MCIV (white arrow) and a fissure of MCIII
The fracture was fixed with a 3.5-mm 6-hole LCP, with screws engaging both MCIV and MCIII
What percentage of MCII may be removed without altering the biomechanics of the carpus?
80%
What is the main risk associated with implantation of metallic implants?
Postoperative infection
For which cases should the use of metallic implants be reserved?
Cases with a high probability of luxation or subluxation
What is the preferred technique for internal fixation?
Plate application with screws engaging only the small MC/MT bone
What is a common complication associated with screw fixation through MCIII/MTIII?
Persistent lameness
What types of plates are appropriate for internal fixation?
Appropriate implants include 3.5-mm locking compression plates (LCPs) or (narrow) dynamic compression plates (DCPs), semitubular plates, or reconstruction plates.
What is the ideal location for plate application on the splint bone?
The palmar or plantar abaxial aspect
What is the postoperative care for horses after internal fixation?
Box stall confinement and gradual increase in exercise
How is a segmental ostectomy typically performed?
A) Under general anesthesia in lateral recumbency
B) Standing under sedation
What is done after segmental ostectomy to close the wound?
Suturing in two layers
What is the prognosis for horses after treatment of proximal small MC/MT bone fractures?
Varies depending on fracture type and age
What complication is associated with standing surgical intervention?
A) Excessive callus formation
B) Nonunion
C) Instability of the proximal fragment
What is the treatment postoperative for complete removal of MTIV?
Full-length hindlimb cast postoperatively
Figure 94-6. (A) DLPMO radiograph of the right MC of a horse presented with an open, multifragment fracture of the proximal MCIV (arrow). (B) Same projections after wound débridement and removal of the loose fragments (arrow). (C) Two weeks later, the same projection shows that the fracture is stable.
Figure 94-7. (A) DLPMO radiograph of the left MT showing a chronic proximal fracture of MTIV with a nonunion between the proximal fragment and MTIV. (B) The fracture was stabilized with a narrow 3.5-mm 6-hole LCP, with screws engaging only the MTIV.
Figure 94-8. (A) DLPMO radiograph of the right MC showing a proximal, closed, articular fracture of MCIV. (B) Fixation of the fracture with two 3.5-mm screws.
Figure 94-9. DLPMO radiograph of the right MT, showing a luxation of the tarsometatarsal joint, that occurred during recovery after complete removal of MTIV.
In which cases can you consider screw fixation alone?
Screw fixation alone can be useful in selected cases, such as simple fractures with minimal displacement (Figure 94-8).
What are the complications described for screw fixation?
high rate of complications such as bone failure,
implant failure, r
adiographic lucency around the screws, and proliferative new bone formation at the ostectomy site
What factors influence the treatment decision for midbody fractures in horses?
Injury severity, horse’s use, and economic constraints
Why is conservative treatment often chosen for midbody fractures?
Economic reasons
What types of midbody fractures are good candidates for conservative treatment?
Chronic fractures with minimal callus and nondisplaced fresh fractures
What is a common outcome of conservative treatment for midbody fractures?
Delayed healing and exuberant callus
What surgical method is preferred by the authors for treating midbody fractures?
Partial ostectomy
What is the rationale behind partial ostectomy for midbody fractures?
To avoid instability of the remaining proximal portion
How is surgery for midbody fractures typically performed?
Under general anesthesia in lateral recumbency
What tool is used to transect the splint bone during surgery?
Osteotome and mallet
What is crucial to avoid during surgery for midbody fractures?
Trauma to the suspensory ligament and neurovascular structures
What is the prognosis for horses after conservative treatment of midbody fractures?
Good with longer convalescence
What is the prognosis after surgical treatment of midbody small MC/MT bone fractures?
Very good
What is a possible complication after conservative treatment of midbody fractures?
Excessive callus formation leading to secondary suspensory desmitis
What might be required later for some cases treated conservatively?
Surgical removal of exuberant callus
What is an important step during surgical treatment of midbody fractures?
Flushing the surgical field
What should be placed for couple days in open fractures for midbody fractures?
Placing a drain in the wound for 2 to 3 days
What is a rare complication reported during removal of the distal small MC/MT bone?
Avulsion fracture of the plantar MTIII cortex
What happened?
(A) Avulsion fracture off the palmar MCIII cortex (arrows), which developed during a fall 1 month after partial ostectomy of an MCIV bone fracture with an oscillating saw. Note the horizontal saw cut in MCIII at the most distal arrow. (B) Intraoperative cross-sectional reconstruction (Siremobile ISO 3D) at the level of the fracture: 1, Periosteal new bone formation protecting the fracture; 2, fragment in the lateropalmar cortex of MCIII; 3, intact lateropalmar cortex of MCIII; 4, direction of screw implantation through the plate. (
describe surgical approach for mid fracture
GA - LR limb uppermost
An incision is made directly over the affected bone and extends from a few centimeters proximal to the fracture to just distal to the distal aspect or “button.”
Sharp and blunt dissection is used to expose the portion of the bone to be excised. Care is taken to avoid trauma to the suspensory ligament and neurovascular structures in the area (particularly when dealing with MTIV).
An **osteotome and mallet are used to transect the splint bone just proximal to the lesion, at a 30- to 45-degree angle with the long axis of the bone.** Alternatively, an oscillating saw can be used, taking care to avoid trauma to MCIII/MTIII. The distal part is then excised, beginning distally and working proximally. Mayo scissors can be used to cut the distal attachment as well as the heavy fibrous tissue between the splint bone and MCIII/MTIII. An osteotome or chisel and mallet are used to undermine and separate the most proximal portion from MCIII/MTIII
What is the treatment of avulsion fracture of MTIII?
9-hole narrow 3.5-mm DCP applied over the MCIV with the screws extending into MCIII
What indicates a successful outcome after surgical treatment of midbody fractures?
Return to normal activity within 8 weeks
Where do distal fractures of the small MC/MT bone most frequently occur?
At the narrowest part of the bone
Which type of horses commonly suffer from distal fractures?
Racehorses
What can exacerbate strain on the distal small MC/MT bone?
Suspensory desmitis
What percentage of distal small MC/MT bone fractures is associated with suspensory desmitis?
About 50%
What is essential to evaluate before surgery for distal fractures?
Adjacent soft tissues
Why might conservative treatment be chosen for distal fractures?
For minimal or no dislocation
What can happen to distal fractures that heal as nonunions?
They often become quiescent and non-problematic
What is the surgical recommendation for distal fractures by the authors?
Excision of the fractured fragment
How far proximal to the fracture site should dissection be continued during surgery of distal fractures?
8 to 16 mm
Transection occurs 1 cm proximal with osteotome or saw obliquely
What tool is used to sever the attachments between the distal fragment and MCIII/MTIII?
Mayo scissors
What are the landmarks for the surgery and considerations for distal fractures?
LR tourniquet
An incision is made directly over the bone, cutting down to the bone surface over the length of the fragment.
The distal tip of the fragment is grasped with towel clamps or tissue forceps and elevated.
The attachments between the distal fragment and MCIII/MTIII as well as the bandlike structure that extends distal from the distal end of the small MC/MT bone and connects to the suspensory apparatus are severed with a Mayo scissors or a with a scalpel.
As upward traction is applied on the fragment’s extremity, sharp dissection is continued proximal to approximately 8 to 16 mm proximal to the fracture site.
After the distal fragment and the fracture callus are separated from MCIII/MTIII, the small MC/MT bone with its periosteum is transected obliquely with an osteotome or oscillating saw approximately 1 cm proximal to the fracture
Flush wound
In open wound drain is placed for 2 days
Figure 94-12. DMPLO radiographic view of the right MC showing a chronic fracture of MCII and a nonunion.
What is important to achieve during surgery to reduce postoperative complications for distal fractures?
Meticulous hemostasis
Figure 94-14. (A) DMPLO radiograph of a left MC of a horse presented with a closed fracture of MCII in the distal part. (B) The distal fragment was removed.
Figure 94-15. Intraoperative image of a partial ostectomy to treat a distal small MC/MT bone fracture (distal is to the left). The distal fragment of the small MC/MT bone (a) has been dissected from the surrounding tissue and upward traction is applied on the fragment’s extremity with a towel clamp. An oblique ostectomy was performed at the distal end of the proximal main portion of MCIII (arrows).
What does the prognosis depend on for distal fractures?
Coexistence of suspensory desmitis,
sesamoiditis,
and/or joint disease
What is the prognosis after surgical removal of the distal splint bone?
Excellent
What is a potential complication of conservative treatment for distal fractures?
excessive callus formation, which could interfere with the suspensory ligament and lead to persistent lameness (Figure 94-16)
Figure 94-17. (A) Photograph of a horse with splint exostosis between MCIII and MCII about 6 to 7 cm distal to the carpometacarpal joint (arrow) and moderate lameness of the affected limb. (B) Oblique radiographic projection of MCII with soft exposure showing the size of the exostosis (arrow). The exostosis was treated locally with corticosteroid injection. (C) Eight weeks after treatment, the horse was sound at a trot, and the exostosis appears smooth on radiograph (arrow).
What are exostoses (splints) in horses?
Inflammatory reactions
Where do splints most commonly develop in relation to the carpometacarpal joint?
6 to 7 cm distal to the joint
What are possible causes for splints in horses?
Direct trauma and instability between MCIII and MCII
Which small MC/MT bone is most commonly affected by splints?
MCII
Which stage of training are younger horses most likely to develop splints due to internal trauma?
Early training
How are splints typically diagnosed in horses?
Using diagnostic analgesia and radiography
What is the usual treatment for clinically active exostosis in horses?
Rest for a period of 2 to 6 weeks confined to stall rest with limited hand walking
Local cold therapy severl times daily
Local application of dimethylsulfoxide (DMSO)
Injection with corticosteroids
What is the prognosis for young horses with splints after appropriate management?
Good
What is a common complication after conservative treatment of splints?
Excessive callus formation
What surgical approach is used for large exostoses in horses?
Partial ostectomy or surgical débridement
What is polydactyly in horses?
A congenital phalangeal malformation
Where does the supernumerary digit most frequently develop in polydactyly cases?
On the medial aspect of the forelimb
What is the etiology of polydactyly in horses?
Unknown
What does the supernumerary digit in polydactyly usually represent?
A regular small MC/MT bone
What is the primary treatment for polydactyly in horses?
Surgical removal of the supernumerary digit
What is included in the anatomy of the supernumerary digit in polydactyly?
Extensor and flexor tendons, ligaments, sesamoid bones, nerves, and vessels
What surgical technique is used to remove the supernumerary digit in polydactyly?
Osteotomy with an osteotome or oscillating saw
What is the common neolasia in the appendicular skeleton?
Ossifying fibroma
An ossifying fibroma, usually found primarily in the jaw of young animals, has been described in the distal part of MCIV of a 13-year-old horse
EVE 2019 Balducci Nolameness neither pain to palpationSurgical removal occurred without complication.
A 1ary ossifying fibroma was found at necropsy in a 5yearoldWelsh pony cross mare that was humanely subjected toeuthanasia for an intractable severe left hindlimb lameness.Antemortem radiographs of the left hind pastern werecharacterised by articular, subchondral and cortical areas of lysis.
why in exostosis the MCII is the most affected?
The MCII is the most frequently affected bone because it has the larger articulation with the carpal bones and more extensive soft tissue attachments
what nerve block helps diagnosis exostosis ?
high-4-point will reduce the lameness but it is unspecific - selective block only media/lateral provides greater specificity
how many projections are recomended for diagnosis of exostosis?
Four views of the affected small MC/MT
bones are recommended (lateral, dorsopalmar/plantar, DMPLO, DLPMO), although most information is obtained on the oblique projections of the affected bone
diagnosis
Figure 94-19. Polydactyly in a foal. (A) The rudimentary medial (second) digit shown on the limb from the side. (B) Oblique radiographic view depicting the rudimentary digit. (
treatment
