Penile Trauma and Fractures (Os Penis Fracture)

Penile trauma and fractures, specifically involving the os penis (baculum), are acute or chronic injuries to the canine penis, most commonly occurring in male dogs. The os penis is a unique bone found in the canine penis, located within the corpus cavernosum urethrae, extending from the bulb of the penis to the glans. Fractures of the os penis are relatively uncommon but can result from direct trauma, such as being struck by a vehicle, kicks, or bites, or from iatrogenic causes during breeding or manual manipulation. The condition is characterized by pain, hematuria, dysuria, and penile swelling, and can lead to urethral obstruction, penile deviation, and impaired reproductive function. In cats, the os penis is absent, so penile fractures are not applicable; however, penile trauma can occur from other causes. The clinical significance lies in the potential for urethral damage, urinary obstruction, and long-term sexual dysfunction. Prompt diagnosis and appropriate management are essential to preserve urinary and reproductive function.

The primary etiology of os penis fractures is direct trauma to the penis. Common causes include: 1) Vehicular accidents, where the dog is struck by a car, causing blunt force trauma to the pelvic and perineal region. 2) Kicks or blows to the abdomen or perineum from humans or other animals. 3) Bite wounds from other dogs, particularly during fights, which can cause crushing or penetrating injuries. 4) Iatrogenic trauma during breeding, especially if the male is forcibly separated from the female during copulation, or during manual semen collection if excessive force is applied. 5) Falls from heights or jumping over obstacles, leading to impact on the perineum. 6) Pathological fractures may occur in cases of os penis osteomyelitis, neoplasia (e.g., osteosarcoma), or nutritional secondary hyperparathyroidism, where the bone is weakened. In rare cases, congenital anomalies or osteogenesis imperfecta may predispose to fractures. The fracture can be simple, comminuted, or open, and may involve the urethra, leading to urethral rupture or stricture formation.

Os penis fractures are rare in veterinary medicine, with limited epidemiological data. They are almost exclusively reported in dogs, as cats lack an os penis. The condition is most commonly seen in young to middle-aged, intact male dogs, typically between 1 and 5 years of age, due to their higher activity levels and increased risk of trauma. There is no strong breed predisposition, but larger breeds may be overrepresented due to their size and outdoor access. Working dogs, hunting dogs, and dogs allowed to roam freely are at higher risk. The incidence is higher in areas with high traffic density or where dog fights are common. There is no known sex predilection beyond the male sex, as the os penis is a male-specific structure. Reproductive status (intact vs. neutered) does not significantly influence the risk, but intact males may be more likely to engage in roaming and fighting behaviors. The condition is not associated with parity or breeding status. Overall, it is an uncommon injury, but its consequences can be severe, including urethral obstruction and infertility.

The os penis is a bone that develops from the corpus cavernosum urethrae and is composed of two lateral segments that fuse cranially. It provides structural support to the penis and protects the urethra. When trauma occurs, the force is transmitted to the os penis, leading to a fracture. The fracture can be classified as simple (single break), comminuted (multiple fragments), or open (with skin or mucosal laceration). The most common site is the mid-shaft, but fractures can occur at the base or near the glans. The pathophysiological consequences include: 1) Hemorrhage: The corpus cavernosum urethrae and surrounding vascular tissue are highly vascular, leading to significant bleeding into the penile tissue and urethra, resulting in hematuria and penile hematoma. 2) Urethral injury: The urethra runs along the ventral aspect of the os penis; fracture fragments can lacerate or compress the urethra, causing partial or complete obstruction, leading to dysuria, stranguria, and potentially urethral rupture with urine extravasation into the perineal tissues. 3) Inflammation and pain: Acute inflammation with edema and pain occurs, leading to reluctance to urinate or mate. 4) Fibrosis and callus formation: During healing, fibrous tissue and callus may form, which can cause penile deviation (angulation) or stricture of the urethra, leading to chronic urinary obstruction. 5) Infection: Open fractures or penetrating wounds can introduce bacteria, leading to osteomyelitis, abscessation, or septicemia. 6) Reproductive dysfunction: Pain and structural abnormalities can cause dyspareunia, inability to copulate, or ejaculatory failure, leading to infertility.

Several factors can predispose a dog to os penis fractures: 1) Behavioral factors: Intact male dogs that roam, fight, or are aggressive are more likely to sustain trauma. 2) Environmental factors: Dogs living in urban areas with high traffic, or those allowed to roam freely, are at increased risk. 3) Breeding management: Improper handling during breeding, such as forced separation of copulating dogs, can cause iatrogenic fractures. 4) Anatomical factors: A longer or more prominent os penis may be more susceptible to trauma. 5) Underlying bone pathology: Conditions that weaken the bone, such as osteomyelitis, neoplasia, or nutritional imbalances (e.g., calcium-phosphorus imbalance), can predispose to pathological fractures. 6) Age: Young, active dogs are more prone to accidents. 7) Lack of supervision: Dogs left unsupervised outdoors are at higher risk. 8) Previous penile trauma: Scarring or fibrosis from prior injuries may alter the biomechanics and increase fracture risk.

Clinical signs of os penis fracture vary depending on the severity and location of the fracture, and whether the urethra is involved. Common signs include: 1) Acute pain: The dog may cry out, whimper, or show signs of distress, especially when urinating or when the penis is touched. 2) Hematuria: Blood in the urine is common due to urethral or vascular injury. 3) Dysuria and stranguria: Difficulty and straining to urinate, with possible complete urethral obstruction if the urethra is compressed or lacerated. 4) Penile swelling and bruising: The penis may appear swollen, edematous, and discolored (ecchymosis). 5) Penile deviation: The penis may deviate to one side due to fracture displacement or callus formation. 6) Preputial discharge: Bloody or purulent discharge may be present. 7) Licking of the genital area: The dog may frequently lick the prepuce due to pain or irritation. 8) Reluctance to mate: Intact males may refuse to breed or show signs of pain during mating. 9) Systemic signs: In severe cases with urethral rupture or infection, the dog may show lethargy, fever, anorexia, and signs of sepsis. 10) Palpable crepitus: On palpation of the penis, a grating sensation may be felt due to fracture fragments. 11) Urinary obstruction: If the urethra is completely occluded, the dog may be unable to urinate, leading to bladder distension and potentially life-threatening azotemia.

Differential diagnoses for os penis fracture include: 1) Penile hematoma: Trauma without fracture can cause a hematoma, presenting with swelling and pain, but radiography or ultrasonography will show no fracture line. 2) Urethral rupture: Can occur independently of os penis fracture, but often concurrent; signs of urine extravasation (subcutaneous swelling, cellulitis) may be present. 3) Penile neoplasia: Tumors such as transmissible venereal tumor (TVT), squamous cell carcinoma, or mast cell tumor can cause penile swelling and bleeding, but are typically chronic and progressive. 4) Penile foreign body: A foreign body (e.g., grass awn) can cause penile irritation, discharge, and pain, but imaging may reveal the object. 5) Balanoposthitis: Inflammation of the glans and prepuce, usually due to infection, can cause discharge and pain, but no fracture on imaging. 6) Priapism: Persistent erection without sexual stimulation, which can cause penile swelling and pain, but is not associated with fracture. 7) Os penis osteomyelitis: Infection of the bone can cause pain and swelling, but radiographs may show osteolytic lesions rather than a fracture line. 8) Penile paralysis: Neurological dysfunction can cause penile protrusion and inability to retract, but no fracture. 9) Urinary calculi: Urethroliths can cause dysuria and hematuria, but radiography may show radiopaque stones, and the os penis is intact. 10) Trauma to other pelvic structures: Pelvic fractures or perineal hernias can cause similar clinical signs, but careful examination and imaging will differentiate.

The diagnostic approach for suspected os penis fracture should be systematic: 1) Signalment and history: Obtain a thorough history of trauma, breeding, or other incidents. 2) Physical examination: Perform a complete physical exam, with special attention to the perineum and penis. Gently extend the penis from the prepuce to inspect for swelling, lacerations, deviation, and crepitus. Palpate the os penis carefully to detect fractures. 3) Neurological assessment: Evaluate for signs of spinal cord injury if trauma was severe. 4) Laboratory tests: Complete blood count (CBC) and serum biochemistry to assess for infection, inflammation, or azotemia. Urinalysis to detect hematuria, pyuria, or crystalluria. 5) Diagnostic imaging: a) Radiography: Obtain lateral and ventrodorsal radiographs of the pelvis and penis. The os penis is radiopaque, and fractures can be visualized. For better detail, a contrast urethrogram may be performed to assess urethral integrity. b) Ultrasonography: Can be used to evaluate soft tissue swelling, hematoma, and urethral damage. c) Advanced imaging: CT or MRI may be indicated for complex fractures or to assess the extent of soft tissue injury. 6) Urethroscopy or cystoscopy: Can directly visualize the urethra and assess for lacerations or strictures. 7) If open fracture or infection is suspected, culture and sensitivity of any discharge or tissue samples should be performed. 8) Staging of the fracture: Classify the fracture as simple, comminuted, open, or closed, and determine if the urethra is involved. This will guide treatment decisions.

Laboratory findings in os penis fracture are non-specific but can support the diagnosis and assess complications. 1) Complete blood count (CBC): May show leukocytosis with a left shift if there is secondary infection or inflammation. Anemia may be present if significant blood loss has occurred. 2) Serum biochemistry: Azotemia (elevated BUN and creatinine) may be present if urethral obstruction has led to post-renal azotemia. Electrolyte imbalances, particularly hyperkalemia, can occur with urinary obstruction. 3) Urinalysis: Hematuria is common. Pyuria and bacteriuria may be present if infection is secondary. Crystalluria may be noted if urolithiasis is a contributing factor. 4) Coagulation profile: If there is excessive bleeding, coagulation parameters may be abnormal, but this is rare. 5) Culture and sensitivity: If there is a wound or discharge, aerobic and anaerobic bacterial culture should be performed to guide antibiotic therapy. 6) In cases of suspected underlying bone disease, serum calcium, phosphorus, and parathyroid hormone levels may be evaluated. 7) Testosterone levels are not typically measured, but may be considered if reproductive function is a concern.

Imaging is crucial for the diagnosis and management of os penis fractures. 1) Radiography: Standard radiographs of the pelvis and penis are the primary imaging modality. The os penis is visible as a mineralized structure. Fractures appear as radiolucent lines, with possible displacement of fragments. Lateral and oblique views are helpful. A contrast urethrogram (retrograde urethrography) can be performed by injecting a water-soluble contrast agent into the urethra to assess for urethral tears, strictures, or extravasation. This is particularly important if urethral injury is suspected. 2) Ultrasonography: Can be used to evaluate soft tissue swelling, hematoma formation, and the integrity of the corpus cavernosum. It can also guide aspiration of fluid collections. 3) Computed Tomography (CT): Provides detailed three-dimensional imaging of the os penis and surrounding structures, which is useful for complex fractures, surgical planning, and assessing the extent of soft tissue injury. 4) Magnetic Resonance Imaging (MRI): May be used to evaluate soft tissue and vascular structures, but is less commonly available. 5) Urethroscopy: Direct visualization of the urethra can identify lacerations, strictures, or foreign bodies. 6) In cases of chronic fracture with callus formation, radiographs may show a healed fracture with deformity.

Cytology and histopathology are not typically required for the diagnosis of os penis fracture, but may be indicated in certain situations. 1) Fine-needle aspiration (FNA) of any penile mass or swelling can be performed to rule out neoplasia or infection. Cytological examination may reveal inflammatory cells, bacteria, or neoplastic cells. 2) If an open fracture is present, wound swabs can be submitted for cytology and culture. 3) Histopathology of bone or soft tissue biopsies may be performed if there is suspicion of osteomyelitis or neoplasia. In cases of chronic fracture with non-union or malunion, biopsy of the callus may be considered. 4) If the fracture is pathological due to an underlying bone disease, histopathology of the bone may reveal the etiology. 5) In cases where surgical amputation of the penis is performed, histopathology of the excised tissue can confirm the diagnosis and rule out other conditions.

Treatment of os penis fracture depends on the severity and location of the fracture, the presence of urethral injury, and the intended use of the dog (breeding vs. pet). 1) Conservative management: For simple, non-displaced fractures without urethral involvement, conservative treatment may be attempted. This includes: a) Strict cage rest and confinement for 4-6 weeks to allow bone healing. b) Analgesics: Non-steroidal anti-inflammatory drugs (NSAIDs) such as carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) for pain and inflammation. c) Antibiotics: If there is an open wound or risk of infection, broad-spectrum antibiotics such as amoxicillin-clavulanate (13.75 mg/kg PO q12h) or enrofloxacin (5 mg/kg PO q24h) should be administered. d) Urinary catheterization: If there is urethral obstruction, a urinary catheter may be placed to bypass the obstruction and allow urine drainage. e) Cold compresses initially, then warm compresses to reduce swelling. 2) Surgical management: Indicated for displaced, comminuted, or open fractures, or when urethral injury is present. Surgical options include: a) Fracture repair: Internal fixation using small pins or wires may be attempted, but is technically challenging due to the small size of the bone. b) Urethral anastomosis: If the urethra is lacerated, surgical repair may be necessary. c) Partial penile amputation (penectomy): In severe cases with extensive damage, non-viable tissue, or chronic complications, partial amputation may be the best option to preserve urinary function. d) Orchiectomy (castration): May be recommended to reduce sexual behavior and prevent future trauma, especially if the dog is not intended for breeding. 3) Emergency management: If the dog is in urinary obstruction, immediate decompression of the bladder via cystocentesis or catheterization is necessary. 4) Supportive care: Fluid therapy, nutritional support, and wound care as needed. 5) Breeding management: If the dog is intended for breeding, surgical repair should aim to preserve penile function. However, the prognosis for return to normal breeding is guarded, and artificial insemination may be recommended.

The prognosis for os penis fracture depends on several factors: 1) Severity of fracture: Simple, non-displaced fractures have a good prognosis with conservative management. Comminuted or open fractures have a guarded prognosis. 2) Urethral involvement: If the urethra is damaged, the prognosis is worse, as there is a risk of stricture formation and chronic urinary obstruction. 3) Timeliness of treatment: Early diagnosis and treatment improve the outcome. 4) Presence of infection: Osteomyelitis or abscessation can lead to chronic pain and dysfunction. 5) Intended use: For breeding dogs, the prognosis for return to normal mating is guarded, as pain, penile deviation, or fibrosis may impair copulation. Artificial insemination may be necessary. 6) Overall, with appropriate management, many dogs can regain normal urinary function, but some may have permanent penile deviation or require penile amputation. The prognosis for life is good unless there is severe trauma or sepsis.

Follow-up care is essential to monitor healing and detect complications. 1) Recheck examinations: Schedule rechecks at 2, 4, 6, and 8 weeks after the initial treatment. 2) Radiography: Repeat radiographs at 4-6 weeks to assess bone healing and callus formation. 3) Urinalysis: Monitor for hematuria or signs of infection. 4) If a urinary catheter was placed, it should be removed as soon as the dog can urinate normally. 5) Monitor for signs of urethral stricture, such as dysuria or recurrent urinary tract infections. 6) If surgery was performed, monitor the incision site for swelling, discharge, or dehiscence. 7) For breeding dogs, assess penile function and semen quality after recovery. 8) Provide owners with instructions on activity restriction and gradual return to normal exercise. 9) If the dog is not intended for breeding, consider castration to prevent future trauma and reduce sexual frustration.

Clinical Pearls: 1) Always consider os penis fracture in any male dog with acute penile pain, hematuria, and dysuria after trauma. 2) Gentle palpation of the penis can reveal crepitus, but avoid excessive manipulation to prevent further injury. 3) Radiography is essential for diagnosis; obtain orthogonal views and consider contrast urethrography if urethral injury is suspected. 4) Conservative management can be successful for simple fractures, but strict rest is crucial. 5) If surgery is needed, consult a veterinary surgeon with experience in small bone fixation. 6) In breeding dogs, early surgical intervention may improve the chance of preserving reproductive function. 7) Always assess for concurrent injuries, such as pelvic fractures or soft tissue trauma. 8) Provide adequate analgesia to manage pain and reduce stress. 9) Monitor for urinary obstruction, which is a life-threatening emergency. 10) Client education is key: advise owners to prevent roaming and fights to reduce the risk of trauma. Pitfalls: 1) Missing the diagnosis due to lack of imaging. 2) Overlooking urethral injury, leading to stricture formation. 3) Inadequate rest, leading to non-union or malunion. 4) Using antibiotics unnecessarily, which can promote resistance. 5) Attempting surgical repair without proper equipment or expertise. 6) Failing to consider the dog's breeding status when making treatment decisions. 7) Neglecting to monitor for complications such as osteomyelitis or abscessation. 8) Allowing the dog to resume normal activity too soon. 9) Not addressing underlying behavioral issues that led to trauma. 10) Assuming that a dog with a healed fracture can immediately return to breeding without assessing penile function.

Drug protocols for os penis fracture focus on pain management, infection control, and supportive care. 1) Analgesics: a) Carprofen: 2.2 mg/kg PO q12h for 3-7 days. b) Meloxicam: 0.1 mg/kg PO q24h for 3-7 days. c) Tramadol: 2-5 mg/kg PO q8-12h for additional pain relief. d) Gabapentin: 10-20 mg/kg PO q8-12h for neuropathic pain. 2) Antibiotics: a) Amoxicillin-clavulanate: 13.75 mg/kg PO q12h for 7-14 days. b) Enrofloxacin: 5 mg/kg PO q24h for 7-14 days (use with caution in young dogs). c) Cefazolin: 22 mg/kg IV q8h for perioperative prophylaxis. 3) Anti-inflammatory: a) Dexamethasone: 0.1-0.2 mg/kg IV or IM once, if severe inflammation. 4) Urinary antiseptics: a) Methenamine: 10 mg/kg PO q8h, but not commonly used. 5) Muscle relaxants: a) Diazepam: 0.5-1 mg/kg PO q8h, if urethral spasms are present. 6) Supportive care: a) Fluid therapy with balanced electrolyte solutions (e.g., Lactated Ringer's) at maintenance rates (60-100 ml/kg/day) if dehydrated. b) Nutritional support if inappetent. 7) For breeding dogs, hormonal therapy is not indicated for fracture healing, but if castration is performed, no hormonal therapy is needed. 8) If osteomyelitis is confirmed, long-term antibiotics (4-6 weeks) based on culture and sensitivity are required.

Evidence-based literature on os penis fractures is limited, consisting mainly of case reports and small case series. Key points from the literature include: 1) Os penis fractures are rare, with most reports in dogs. 2) The most common cause is vehicular trauma, followed by kicks and bites. 3) Diagnosis is confirmed by radiography, with contrast urethrography recommended to assess urethral integrity. 4) Conservative management with rest and analgesics is successful for simple, non-displaced fractures. 5) Surgical intervention is indicated for displaced or comminuted fractures, or when urethral injury is present. 6) Complications include urethral stricture, penile deviation, and osteomyelitis. 7) Prognosis for urinary function is generally good, but reproductive function may be impaired. 8) In a case series of 10 dogs, 7 were managed conservatively with good outcomes, while 3 required surgery. 9) Another report described successful repair of a comminuted fracture using a plate and screws. 10) The use of penile amputation is reserved for severe cases. 11) There are no controlled clinical trials, and recommendations are based on expert opinion and case reports. 12) The American College of Veterinary Surgeons (ACVS) and the Society for Theriogenology (ST) provide guidelines for management, emphasizing the importance of early diagnosis and individualized treatment. 13) Future research should focus on long-term outcomes and the impact on breeding soundness.