Chapter 104 Fractures of the Humerus
ANATOMY
• The proximal portion of the humerus has strong, thick cortices cranially and extends to the large deltoid tuberosity. The musculospiral groove starts caudally and twists cranially over the lateral aspect of the bone. The brachialis muscle and neurovascular structures, including the clinically significant radial nerve, lie within the musculospiral groove.
• The lateral portion of the distal humeral condyle is termed the capitulum and the medial portion is termed the trochlea.
• When viewed cranially, the bone is essentially straight; however, the medullary canal runs slightly lateral to medial from proximal to distal. Distally, the trochlea is larger than the capitulum, and is in a more direct line with the medullary canal. The capitulum has a thinner epicondylar attachment to the bone and is the main weight-bearing surface for the radial head.
• Important muscles to identify laterally are the lateral head of the triceps, the brachialis, the brachiocephalicus, and the acromial head of the deltoid. The radial nerve is important to identify laterally.
DIAGNOSIS
• Rule out injuries associated with thoracic trauma. Perform a complete clinical and radiographic examination to rule out pneumothorax, hemothorax, diaphragmatic hernia, rib fractures, chylothorax, and traumatic myocarditis.
• The neurovascular integrity of the limb is of paramount importance. Fully assess the injured forelimb.
PROXIMAL HUMERAL PHYSEAL FRACTURES
Preoperative Considerations
• This type of fracture is seen infrequently in young dogs prior to physeal closure. Closure of the proximal physis occurs between 9 and 15 months of age.
• Except for incomplete fractures, closed reduction is very difficult. Open reduction of complete fractures is recommended.
Surgical Procedure
Technique
Open Reduction
1. After preparing the limb for aseptic surgery, use a cranial approach with cranial retraction of the brachiocephalicus muscle to elevate and expose the fragments.
2. Use small pointed forceps to carefully grasp the epiphysis and use the elevator to lever the fragments into reduction.
3. Achieve fixation with double Kirschner wires or Steinmann pins, beginning at the greater tubercle. To prevent compression of the physis, do not use a figure-eight tension band.
4. Cancellous lag screws have been used by some surgeons, but they can cause interfragmentary compression and premature physeal closure.
PROXIMAL DIAPHYSEAL FRACTURES
Preoperative Considerations
• Proximal fractures are the least common diaphyseal fractures owing to the comparative strength of the humerus in this area.
• Most proximal diaphyseal fractures occur just proximal to the deltoid tuberosity. The distal fragment is displaced cranially due to the pull of the deltoid muscle, and medially due to the pull of the pectoral muscle.
• Evaluate the brachial plexus and the radial nerve. Accurate reduction is important because excessive callus production can produce postoperative pressure on these neural structures.
Surgical Procedure
Technique
Open Reduction
1. For open reduction, use a cranial approach. Incise the skin along the craniolateral aspect of the humerus, beginning at the scapular tuberosity. Incise the fascial attachment of the brachiocephalicus muscle on the cranial aspect of the humerus to allow cranial retraction of the muscle. Elevate the deltoid muscle from the deltoid tuberosity and retract it caudally to gain access to the fracture site.
2. Place single or double Steinmann pins retrograde from the fracture site into the proximal fragment (Fig. 104-1), or place the pins normograde starting at the greater tubercle of the humerus.
3. Because the fractures often are transverse, a single intramedullary pin may not provide rotational stability. Use a type I external fixator (see Chapter 111) or hemicerclage wires to provide rotational stability in a transverse or short oblique fracture.
5. In very large dogs, a bone plate applied to the cranial surface of the humerus is an excellent method of fixation. The basic principle of three screws (six cortices) above and three screws below the fracture site applies.
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