Radius and Ulna Fractures

Radius and ulna fractures refer to a break or discontinuity in the shaft, metaphysis, or epiphysis of the radius and/or ulna bones of the antebrachium. These fractures are common in dogs and cats, often resulting from high-energy trauma such as vehicular accidents, falls from height, or direct blows. The radius is the primary weight-bearing bone of the antebrachium, while the ulna provides additional support and serves as an attachment site for muscles. Fractures can be classified based on location (proximal, middle, distal), configuration (transverse, oblique, spiral, comminuted), and whether they are open or closed. In veterinary surgery, these fractures are often managed with internal fixation using bone plates, screws, or external skeletal fixators, with the goal of restoring anatomical alignment, stability, and early return to function.

The most common cause of radius and ulna fractures is trauma, including vehicular accidents, falls from heights, and direct trauma such as kicks or bites. In toy and miniature breeds, fractures can occur with minimal trauma due to the relatively thin cortices and poor blood supply of the distal radius. Pathological fractures may result from underlying bone disease, such as bone cysts, neoplasia (e.g., osteosarcoma), or metabolic bone diseases (e.g., hyperparathyroidism). Iatrogenic fractures can occur during surgical manipulation or excessive force during fracture reduction. Additionally, stress fractures may develop in athletic dogs due to repetitive loading, particularly in the distal radius.

Radius and ulna fractures are among the most common fractures in dogs and cats, accounting for approximately 18% of all fractures in dogs and 10% in cats. They are more frequently seen in young animals (less than 1 year old) and in small breeds, particularly toy and miniature breeds such as Chihuahuas, Yorkshire Terriers, and Pomeranians. These breeds have a higher incidence of distal diaphyseal fractures due to their small bone size and relatively poor vascular supply. In cats, these fractures are often associated with high-rise syndrome. There is no significant sex predilection, but male dogs may be slightly overrepresented due to increased roaming behavior. Working and sporting dogs may be at higher risk for traumatic fractures.

The pathophysiology of radius and ulna fractures involves disruption of the bone's structural integrity, leading to pain, instability, and loss of limb function. The initial trauma causes direct or indirect forces that exceed the bone's ultimate strength, resulting in a fracture. The fracture disrupts the periosteum, endosteum, and medullary blood supply, leading to hemorrhage, hematoma formation, and local inflammation. Inflammatory cells release cytokines and growth factors that initiate the healing process. The fracture healing process involves three phases: inflammatory, reparative, and remodeling. In the inflammatory phase, a hematoma forms and inflammatory cells infiltrate, providing a scaffold for repair. In the reparative phase, fibroblasts and chondroblasts produce a soft callus, which is later replaced by a hard callus of woven bone. Finally, in the remodeling phase, the woven bone is replaced by lamellar bone, and the bone is reshaped to restore its original contour. In cases of severe comminution or instability, healing may be delayed or result in nonunion. Additionally, concurrent soft tissue injury, such as damage to the median or radial nerves, can occur, leading to neurological deficits.

Intrinsic factors include breed-specific anatomical features, such as the small bone diameter and thin cortices in toy breeds, which increase susceptibility to fractures. Age is a significant factor, as young animals have less mineralized bone and are more prone to fractures. Nutritional deficiencies, such as calcium or vitamin D imbalance, can weaken bone. Metabolic diseases like hyperparathyroidism or renal secondary hyperparathyroidism can lead to pathological fractures. Extrinsic factors include high-energy trauma, such as vehicular accidents or falls, and iatrogenic causes during surgery. Excessive activity or improper training in athletic dogs may lead to stress fractures. Poor management, such as inadequate nutrition or lack of exercise, can also contribute to bone fragility.

Clinical signs of radius and ulna fractures include acute lameness, non-weight-bearing on the affected limb, swelling, pain on palpation, crepitus, and abnormal limb angulation or rotation. The limb may appear shortened or deformed. Open fractures may present with skin wounds and visible bone fragments. Neurological deficits, such as radial nerve paralysis, may be present if the nerve is injured, leading to inability to extend the carpus and digits. Systemic signs may include tachycardia, tachypnea, and signs of shock in severe trauma cases. On physical examination, careful palpation of the entire limb is necessary to identify the fracture site and assess for concurrent injuries.

Differential diagnoses include: 1) Soft tissue trauma without fracture (e.g., muscle contusion, sprain) - typically less severe lameness and no crepitus; radiographs are normal. 2) Luxation of the elbow or carpus - joint instability and abnormal joint space on radiographs. 3) Panosteitis - a self-limiting inflammatory condition of long bones in young dogs, causing shifting leg lameness; radiographs show medullary and endosteal sclerosis. 4) Osteosarcoma - a malignant bone tumor causing lytic and proliferative lesions; biopsy is definitive. 5) Bone cyst - a benign fluid-filled lesion that may weaken bone; radiographs show a well-defined lytic area. 6) Hypertrophic osteodystrophy - a developmental disease in young large-breed dogs causing metaphyseal swelling and pain; radiographs show metaphyseal sclerosis and irregularity. 7) Nutritional secondary hyperparathyroidism - causes generalized bone demineralization and pathological fractures; history of improper diet. 8) Osteomyelitis - infection of bone causing pain, swelling, and draining tracts; radiographs show periosteal reaction and bone lysis.

The diagnostic algorithm begins with a thorough history and physical examination, including assessment of the patient's overall condition and any concurrent injuries. Orthopedic examination should include palpation of the entire limb, evaluation of range of motion, and assessment of neurological function. If a fracture is suspected, radiographs of the affected limb in two orthogonal views (craniocaudal and mediolateral) are essential. Radiographs should include the joints above and below the fracture to rule out concurrent injuries. In cases of complex fractures or for surgical planning, advanced imaging such as computed tomography (CT) may be recommended to better characterize the fracture configuration and assess for articular involvement. If open fracture is present, wound culture and sensitivity may be performed. Preoperative laboratory workup, including complete blood count, serum biochemistry, and urinalysis, is recommended to assess the patient's overall health and anesthetic risk.

Laboratory findings are generally non-specific but may reflect the underlying cause or concurrent trauma. Complete blood count may show leukocytosis due to stress or inflammation. Serum biochemistry may reveal elevated muscle enzymes (creatine kinase) due to muscle trauma. In cases of pathological fractures, abnormalities such as hypercalcemia (in some neoplasms) or elevated alkaline phosphatase (in bone disease) may be present. Coagulation profile (PT/aPTT) is important to assess surgical risk, especially in trauma patients. Blood gas analysis may be indicated in severely traumatized patients to evaluate acid-base status. Inflammatory biomarkers such as C-reactive protein (CRP) and serum amyloid A (SAA) may be elevated in inflammatory or infectious conditions.

Radiography is the primary imaging modality for diagnosis and surgical planning. Standard orthogonal views (craniocaudal and mediolateral) are essential to evaluate fracture configuration, displacement, and alignment. Stress views may be needed to assess joint stability. In cases of articular fractures, CT with 3D reconstructions provides detailed information on fragment displacement and articular surface congruity. MRI is rarely indicated but may be useful to assess soft tissue structures such as nerves or ligaments. Ultrasonography may be used to evaluate soft tissue injuries, such as muscle or tendon damage. Fluoroscopy can be used intraoperatively to guide fracture reduction and implant placement. Angiography is rarely used but may be indicated to assess vascular integrity in severe trauma.

Cytology and histopathology are not routinely performed for simple fractures but are essential in cases of pathological fractures or suspected neoplasia. Fine-needle aspiration of bone lesions may reveal neoplastic cells, but a biopsy is often required for definitive diagnosis. Histopathological examination of bone tissue can identify the type of tumor (e.g., osteosarcoma, chondrosarcoma) and assess surgical margins. In cases of osteomyelitis, culture and sensitivity of bone or exudate are crucial for appropriate antimicrobial therapy. In nonunion cases, histopathology may reveal fibrous tissue or cartilage, indicating a lack of bone healing.

Treatment of radius and ulna fractures aims to restore anatomical alignment, provide stability, and promote early return to function. Conservative management with splints or casts may be considered for minimally displaced, stable fractures in young animals, but surgical fixation is often preferred for optimal outcomes. Surgical options include internal fixation with bone plates and screws, intramedullary pins, or external skeletal fixators. The choice of implant depends on fracture location, configuration, and patient size. For distal diaphyseal fractures, a bone plate applied to the cranial or medial surface of the radius is commonly used. In toy breeds, a type II external skeletal fixator may be preferred to minimize soft tissue disruption. Open fractures require thorough debridement, lavage, and stabilization. Postoperative pain management includes opioids (e.g., morphine 0.5-1 mg/kg IM/IV q4-6h, fentanyl CRI 2-5 mcg/kg/h), NSAIDs (e.g., carprofen 2.2 mg/kg PO q12h, meloxicam 0.1-0.2 mg/kg PO q24h), and local anesthetic blocks (e.g., brachial plexus block with bupivacaine 1-2 mg/kg). Physical rehabilitation, including passive range of motion exercises and controlled weight-bearing, is essential for optimal recovery.

The prognosis for radius and ulna fractures is generally good to excellent with appropriate surgical stabilization and postoperative care. Factors influencing prognosis include the severity of the fracture, presence of open wounds, concurrent injuries, and patient age. Simple, closed fractures in young animals have a favorable prognosis, with a high rate of bone healing and return to function. Comminuted fractures, open fractures, or fractures with significant soft tissue injury have a guarded prognosis due to increased risk of complications such as infection, delayed union, or nonunion. In toy breeds, the risk of complications is higher due to the small bone size and limited blood supply. With proper surgical technique and postoperative management, the majority of patients achieve excellent functional outcomes.

Postoperative follow-up is crucial to monitor healing and detect complications. Sutures or skin staples are typically removed 10-14 days after surgery. Serial radiographs are recommended at 4, 6, 8, and 12 weeks postoperatively to assess bone healing and implant stability. Restricted activity is advised for the first 4-6 weeks, with gradual increase in exercise as healing progresses. Physical therapy, including passive range of motion exercises and controlled leash walks, should be initiated early to prevent joint stiffness and muscle atrophy. In cases of external skeletal fixators, pin tract care is essential to prevent infection. Long-term follow-up may be needed to monitor for implant-related complications, such as loosening or breakage, and to assess limb function.

Clinical pearls: 1) In toy breeds, use a type II external skeletal fixator or a small plate with locking screws to minimize soft tissue damage and preserve blood supply. 2) Always include the elbow and carpus in the radiographs to rule out concurrent injuries. 3) For distal fractures, apply the plate on the cranial surface of the radius to counteract bending forces. 4) Use a bone graft in cases of severe comminution to enhance healing. 5) Consider a transarticular external skeletal fixator for highly comminuted distal fractures. Pitfalls: 1) Failure to achieve anatomical reduction can lead to malunion and limb deformity. 2) Inadequate stabilization may result in delayed union or nonunion. 3) Overlooking open fractures can lead to osteomyelitis. 4) In toy breeds, excessive implant size can cause iatrogenic fracture. 5) Neglecting postoperative pain management can lead to poor recovery and complications.

Perioperative antimicrobial prophylaxis: Cefazolin 22 mg/kg IV at induction and every 90 minutes during surgery. Postoperative antimicrobials (e.g., cephalexin 22 mg/kg PO q8h) are indicated for open fractures or if infection is suspected. Analgesia: Preoperative opioids (e.g., hydromorphone 0.05-0.1 mg/kg IV) and intraoperative fentanyl CRI (5-10 mcg/kg/h). Postoperative NSAIDs (e.g., carprofen 2.2 mg/kg PO q12h for 3-5 days) or meloxicam (0.1 mg/kg PO q24h) for pain and inflammation. Local anesthetic blocks: Brachial plexus block with bupivacaine (1-2 mg/kg) or lidocaine (2-4 mg/kg) for intraoperative and postoperative analgesia. Muscle relaxants: Methocarbamol (20-40 mg/kg PO q8h) may be used to reduce muscle spasms. Chondroprotectants: Polysulfated glycosaminoglycan (4.4 mg/kg IM or SC twice weekly) or glucosamine/chondroitin supplements may be used to support joint health, especially if the fracture involves the articular surface. Gastroprotectants: Omeprazole (0.7-1 mg/kg PO q24h) or famotidine (0.5-1 mg/kg PO q12h) may be considered to prevent gastric ulcers, especially in patients receiving NSAIDs.

Several studies have evaluated the outcomes of radius and ulna fractures in dogs and cats. A retrospective study by DeCamp et al. (1992) reported a 95% success rate with bone plate fixation in dogs. Another study by Johnson et al. (1996) found that external skeletal fixation was associated with a lower complication rate compared to bone plates in toy breeds. A meta-analysis by Voss et al. (2009) concluded that both internal and external fixation methods are effective, but the choice depends on fracture configuration and patient factors. AO Vet guidelines recommend anatomical reduction and stable fixation to promote early healing. Recent studies have highlighted the importance of minimally invasive techniques, such as minimally invasive plate osteosynthesis (MIPO), to preserve blood supply and reduce soft tissue trauma. Overall, the literature supports surgical intervention for most radius and ulna fractures, with a favorable prognosis when appropriate techniques are employed.