Small Animal Surgery, School of Veterinary and Biomedical Sciences, Division of Health Sciences, Murdoch University
Murdoch, Australia
Humeral condylar fractures (HCFs) are common and account for just over half of all humeral fractures. They may occur traumatically or atraumatically during normal activity. Animals with atraumatic HCF may have incomplete ossification of the humeral condyle (IOHC). Spaniel breeds appear to be over-represented for IOHC. Bilateral IOHC is common and evaluation of the contralateral condyle is strongly advised.
How Common are 'Atraumatic' HCFs?
Evidence in the literature would support that many HCFs are pathologic fractures and occur during 'normal activity' such as running, jumping or climbing stairs. Marcellin-Little et al (1994) reported 78% (41/55) of HCFs occurred with no history of trauma. Vannini et al (1987a) reported 69% (61/88) of HCFs occurred during normal activity.
In addition to HCF, dogs with IOHC may present with occult IOHC, unilateral or bilateral lameness referable to IOHC +/- associated degenerative joint disease +/- fragmentation of the medial part of the coronoid process (FMCP)3-5.
Lateral condylar fractures are the most common form of HCF in dogs with IOHC followed by dicondylar fractures. Medial condylar fractures are least common. Why? The lateral part of the condyle (capitulum) is:
The major load-bearing part of the humeral condyle
Eccentric to the humeral shaft causing force to be directed through the lateral epicondylar ridge rather than distributed through the humeral shaft
Weaker than the medial part of the condyle
The greater load and the relative biomechanical weakness predispose the lateral part of the condyle to fracture.
Aetiopathogenesis and IOHC
It is important to distinguish between skeletally immature and mature dogs. The high incidence of condylar fractures in immature dogs as a result of minor trauma is due to the normal relative weakness of the developing humeral condyle. The humeral condyle develops as two separate centres of ossification that appear approximately 14 days after birth. The lateral and medial centres of ossification are separated by a thin cartilaginous plate and normally unite at 70 days. HCFs consistently occur along this fusion line in both immature and mature animals. In skeletally mature animals the condyle should be fused and the cartilaginous plate completely ossified. Atraumatic fracture in mature dogs during normal activity suggests underlying abnormality through the condylar fusion zone.
Marcellin-Little et al (1994) proposed IOHC exists in dogs with atraumatic HCF and that this may be inherited as a recessive gene in spaniel breeds. Histopathological examination of bone from HCF sites in mature dogs with atraumatic fracture reveals dense cancellous bone with non-specific evidence of chronic inflammatory change and previous remodelling. Fibrous tissue, increased osteoclastic activity and increased numbers of plasma cells are typically seen.
A microangiographic study of the humeral condyle in cocker spaniel and non-cocker spaniel dogs found that cocker spaniels had a decreased vascular density in the humeral condyle6.
FMCP has also been observed in association with IOHC in cocker spaniels and springer spaniels1,7. The occurrence of FMCP and IOHC together may support a related pathogenic mechanism between these two conditions. Robin and Marcellin-Little (2001) have suggested that the pathogenesis of IOHC may be related to impaired antebrachial bone growth, similar to the pathogeneses of elbow dysplasia and radius curvus.
IOHC has been compared with atraumatic fracture of the radial carpal bone in dogs, which is also commonly bilateral8. Histopathological findings in these cases revealed fibrous connective tissue on the fracture surfaces suggestive of incomplete ossification rather than a true fracture of the radial carpal bone. The pathogenesis of this condition is not unknown.
Signalment and IOHC
HCFs have been reported in many breeds and crossbreeds, however spaniel breeds appear to be predisposed to HCF and have a significantly higher incidence of bilateral HCF1. Anecdotal reports suggest different breed prevalence of atraumatic HCFs in different countries. Occult IOHC and atraumatic fracture has now been reported in a number of breeds including springer spaniels, cocker spaniels, Brittany spaniels, Labrador retrievers, Rhodesian ridgebacks, boxer dogs, Rottweiler, German wachtel, Bernese mountain dogs, English pointers and cross breed dogs. The average age of skeletally mature dogs with atraumatic HCF is six years (range 2-13 years)1,9. This may be breed dependent. Male dogs appear to be more prone to atraumatic HCF than female dogs comprising 83%, 75% and 69% of cases in three studies that considered gender.
Radiography and IOHC
IOHC cases have a moderate incidence (20-25%) of bilateral fracture and a high incidence (86%) of bilateral disease1,9. Radiographic findings in the contralateral (non-fractured) elbow joint of dogs with atraumatic HCF may include:
A vertical radiolucent line (0.5mm-1.0mm wide) between the lateral and medial parts of the condyle. Sclerosis may extend partially or completely from the articular surface to the supracondylar foramen. Special radiographic projections (15° craniomedial-caudolateral oblique) have been proposed to increase sensitivity of detection. CT is more reliable.
Degenerative joint disease.
Periosteal proliferation on the lateral epicondylar ridge presumably due to increased stress on the epicondylar ridge due to IOHC / weakness of the humeral condyle.
Fragmented medial coronoid process presumed to be due to micro motion between the lateral and medial parts of the condyle placing abnormal stress on the medial coronoid process as FMCP is uncommon in spaniels1.
Diagnosis of Occult IOHC Prior to Fracture
This is difficult as many of the affected animals show no evidence of lameness prior to fracture. An index of suspicion and thorough physical and radiographic examination of the contralateral elbow in dogs with atraumatic HCF may enable diagnosis of bilateral disease and treatment prior to fracture of the contralateral elbow. CT scan +/-arthroscopy are increasingly being used to 'rule out' the presence of a contralateral fissure in animals with an atraumatic HCF.
Similarly inclusion of IOHC on a differential diagnosis list for dogs with forelimb lameness localised to the elbow joint, particularly spaniels and other breeds that are not commonly affected with elbow dysplasia, may enable diagnosis of this condition prior to fracture.
Repair of HCFs
Unicondylar HCFs are usually repaired via a craniolateral or medial approach, whichever is appropriate. Dicondylar fractures are challenging to repair and consideration should be given to referral. Dicondylar fractures should be repaired by a combined craniolateral and medial approach (or via an olecranon osteotomy--high complication rate and should be avoided if possible, or a triceps tenotomy--only for small dogs and cats).
The condyles should be repaired with an interfragmentary lag screw and the supracondylar component of the fracture repaired with K wires, lag screws or bone plate depending on the extent, severity and cause (traumatic or atraumatic) of the fracture. Repair techniques have been well described.
Prophylactic repair of occult IOHC is recommended. Controversy exists over whether the screw should be placed as a lag screw or a positional screw. No evidence to support either claim has been published to the author's knowledge. Reinforcement of the supracondylar ridge with a bone plate of some sort should be considered in atraumatic fractures and in prophylactic repair of occult IOHC given the pathologic nature of these fractures and the increased incidence of implant failure following repair of atraumatic HCFs. Reinforcement of the medial supracondylar ridge can be achieved with standard bone plates. Reinforcement of the lateral epicondylar ridge is more difficult due to its irregular shape. Reconstruction plates, L plates and SOP plates have been used for the lateral epicondylar ridge.
Several options exist for the type of screw used. Either cortical screws, fully threaded cancellous screws or partially threaded cancellous screws can be used. Partially threaded cancellous screws are significantly weaker and may be associated with a higher incidence of screw failure. The humeral condyle in the adult dog is quite dense bone so cancellous screws are not necessary to achieve adequate purchase except in young puppies. The author uses cortical screws for HCF repair.
Fixation Failure
Atraumatic HCFs have a higher failure rate (10-23%) than traumatic HCFs (5%).
References
1. Marcellin-Little DJ, et al. Incomplete ossification of the humeral condyle in spaniels. Veterinary Surgery, 23, 475-487, 1994
2. Vannini R, Olmstead ML, Smeak DD. An epidemiological study of 151 distal humeral fractures in dogs and cats. JAAHA, 24, 531-536, 1987a
3. Butterworth SJ, Innes JF. (2001). Incomplete humeral condylar fractures in the dog. Journal of Small Animal Practice 42: 394-398
4. Robin D, Marcellin-Little DJ. (2001). Incomplete ossification of the humeral condyle in two Labrador Retrievers. JSAP 42: 231-234. 2001
5. Meyer-Lindenberg A, et al. Incomplete Ossification of the Humeral Condyle as the cause of lameness in dogs. VCOT 15(3),187-194. 2002
6. Larsen LJ, et al. Microangiography of the humeral condyle in Cocker Spaniel and non-Cocker Spaniel dogs. VCOT, 12, 134-137, 1999.
7. Glyde M, Doyle R, Connery N. Humeral condylar fracture in dogs. IVJ. 56(3): 158-165. 2003
8. Gnudi G, et al. Radial carpal bone fracture in 13 dogs. VCOT 16 (3): 178-183 2003
9. Vannini R, Olmstead ML, Smeak DD. Humeral condylar fracture caused by minor trauma in 20 adult dogs. JAAHA, 24, 355-362, 1987b.