Orthopedic Disorders of the Distal Extremities

Chapter 113 Orthopedic Disorders of the Distal Extremities



Steven C. Budsberg


Disorders of the extremities distal to the carpus and tarsus usually result from direct trauma. Most abnormalities involve bone fracture and/or ligament damage associated with joint instability. The majority of fractures involve the metacarpal and metatarsal bones. Animals are usually presented with acute, non–weight-bearing lameness. Regardless of the bone being managed, internal fixation, external coaptation, or a combination of both can be used. Most surgeons prefer to use external coaptation whenever possible to manage fractures in these areas. In contrast, ligamentous injuries and associated joint instability rarely respond to external coaptation and often require surgical intervention. If fractures are open, proper open wound management is required before fracture fixation. Follow the generally accepted principles of fracture repair, including adequate reduction, alignment, and stable fixation, for the successful management of these injuries.



METACARPAL AND METATARSAL FRACTURES




Anatomy


The metacarpal and metatarsal bones are numbered 2 to 5, from medial to lateral. There are usually five metacarpal and four metatarsal bones. The third and fourth bones bear most of the forces transmitted through the foot.


Each bone is divided into the proximal base, middle body, and distal head.



Body Fractures


Body fractures may involve one or more bones. Racing animals may develop stress fractures of these bones. Closed reduction and coaptation usually are effective, but internal fixation may be required in cases involving multiple limb trauma, multiple bone fractures, and comminuted, severely displaced, or unstable fractures.



Preoperative Considerations



• Rule out associated injuries with a thorough physical examination and appropriate diagnostic tests.

• Identify the bone and region involved.

• Determine the type of injury (e.g., soft tissue, open or closed fracture, degloving injury).

• The number of bones involved affects treatment.

• Indications for external coaptation include
• Single-bone fractures.

• Multiple, non-displaced fractures without other limb trauma.

• Fractures that have a combination of external coaptation with appropriate internal fixation (e.g., intramedullary pins, screws, plates).

• Indications for internal fixation include
• Multiple bone fractures with severe displacement.

• Combined fractures of the third and fourth bones.

• Additional limb injury.

• Fracture in working or show dogs.

• Open fractures.

• Articular fractures.


Surgical Procedure



Objectives



• Reduce and stabilize the fractures.

• Maintain viable soft tissues.

• Preserve joint function.


Equipment



• Standard surgical pack and suture material

• Kirschner wire (K-wire) (various sizes)

• Mini-fragment plates and screws (1.5, 2.0, and 2.7 mm)

• Small self-retaining retractors

• Small bone-holding forceps


Technique



1. Place the patient in dorsal recumbency, clip the hair, and prepare the extremity for aseptic surgery.



Key Point


Because of the central (metacarpal, metatarsal) and digital pads, surgical approach via the palmar or plantar surfaces of the metacarpal and metatarsal bones is contraindicated.



2. Make a dorsal incision directly over the affected bone or joint.
a. To approach a single bone, make a longitudinal incision directly over the bone. To expose adjacent bones, make the incision between them, if necessary.

b. To approach multiple bones, make two parallel longitudinal incisions or a curved incision incorporating the entire dorsal region (Fig. 113-1).

3. Incise the deep fascia directly over the bone.
a. In the metacarpus, identify and retract the major tendons (i.e., the tendons of the common digital extensor and lateral digital extensor muscles).

b. In the metatarsal region, take care to protect the tendon of the long digital extensor muscle (Fig. 113-2).

4. Intramedullary pinning for fracture repair:
a. Antegrade the pins from distal to proximal through a predrilled hole in the dorsal surface (Fig. 113-3). (Make the predrilled guide hole with a pin one size larger than the intended intramedullary pin.) Bend the pin ends slightly to facilitate removal and to avoid entering the metacarpo(tarso)phalangeal (MP) joint.

image

Figure 113-1 Dorsal incision lines for metacarpal fractures of a single bone (left) or multiple bones (right).


image

Figure 113-2 Important tendons of the metacarpus (left) and metatarsus (right).


image

Figure 113-3 Placement of an intramedullary pin for repair of a metacarpal fracture. The center view shows how the pin is “bounced off” the palmar cortex (arrow).

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Orthopedic Disorders of the Distal Extremities

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