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Update on incomplete ossification of the humeral condyle

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01 September 2011, at 12:00am

RACHEL HATTERSLEY outlines the incidence of IOHC, the ways it can present and its diagnosis, along with a review of the various treatment options available

INCOMPLETE ossification of the humeral condyle (IOHC) has been reported as an uncommon cause of forelimb lameness in dogs but is also an important risk factor for humeral condylar fractures in predisposed breeds (Denny, 1983; Anderson and others, 1990; Marcellin-Little and others, 1994). IOHC is recognised in a number of breeds, including English springer spaniels (ESS), cocker spaniels, Labrador retrievers and Rottweilers. Both English springer spaniels and American cocker spaniels are reported to be overrepresented for this condition with a suspected polygenic mode of inheritance (Marcellin-Little and others, 1994). The incidence of this condition within the normal ESS population is unknown but a recent abstract presented at the BVOA (British Veterinary Orthopaedic Association) reported an incidence of 8% within a population of 100 clinically unaffected ESS elbows (Moores and others, 2011). Normal ossification of the humeral condyle starts at two weeks of age in the dog and is usually complete between eight and 12 weeks of age. There are three centres of ossification which develop in the humeral condyle. One ossification centre develops into the capitulum and the lateral part of the condyle, one into the trochlea and the medial part of the condyle, and a smaller ossification centre forms the medial epicondyle. It has traditionally been thought that IOHC represented a failure of endochondral ossification although there is a report of development of an IOHC fissure in a dog which had previously had no fissure present on a CT scan. Propagation of a partial fissure to a complete fissure in an adult American cocker spaniel is also reported (Witte and others, 2010). It is commonly, but not always, a bilateral condition. Dogs with IOHC can present in one of three ways: 

  • varying degrees of forelimb lameness;
  • humeral condylar fractures; and
  • as an incidental finding.

1. Forelimb lameness

Dogs with IOHC can present with unilateral or bilateral forelimb lameness which may vary from mild and intermittent to severe. The degree of lameness is often reported to be worse after exercise and there is often limited response to antiinflammatory
medication. Elbow pain is most consistently found on extension of the joint, especially if pressure is applied to lateral condyle. Unless there is concurrent joint pathology such as medial coronoid disease or osteoarthritis, there is generally no reduction in the range of motion of the joint and there is usually no palpable joint effusion (Butterworth and Innes, 2001).  Concurrent joint pathology in ESS appears to be relatively common (Moores and others, 2011). Diagnosis of IOHC is based on confirmation of an intracondylar fissure. This is often achieved using craniocaudal radiographs of the elbow (Marcellin-
Little and others, 1994; Butterworth and Innes, 2001). However, as the x-ray beam must pass along the line of the fibrous fissure for it to be observed (Figure 1a), several views are often required and failure to see a fissure on plain radiography does not rule out a diagnosis of IOHC (Marcellin-Little and others, 1994; Butterworth and Innes, 2001; Carrera and others, 2008). It is also important to take views of the contralateral elbow joint. The intracondylar fissure is easily detected using computed tomography (CT) which has significantly improved the diagnosis of this condition (Figure 1b) (Carrera and others, 2008). Reported treatment of patients with lameness secondary to IOHC has involved placement of a transcondylar cortical screw (Butterworth and Innes, 2001). A 3.5mm or 4.5mm cortical screw is preferred because it is stiffer in bending compared to a 4.0mm cancellous screw. Some surgeons have recommended a positional screw over a lag screw on the basis of improved stability but others argue that the compression provided by the lag screw is more likely to result in union of
the fissure. Certainly, the fissure remains despite surgical
intervention in a significant number of patients. The screw size should, therefore, be as large as possible for the individual patient to reduce the risk of fatigue failure. For example, a 4.5mm cortical screw is used in the majority of springer spaniels
(Figure 2). Shaft screws, which have threads in the “trans-cortex” side of the screw only, are also available and should provide an increased area moment of inertia (and therefore increased resistance to screw failure) (Figure 3). It is important to ensure that enough of the screw tip exits the trans-cortex on the medial side of the humeral condyle as in the event of screw
failure this will aid removal. Use of a cortical autograft is reported in conjunction with a headless selftracking screw to try and encourage formation of a bony bridge across the fissure line
(Fitzpatrick and others, 2009). Post-operative care includes exercise restriction over a six-week period and suitable analgesia, usually non-steroid anti-inflammatory drugs (NSAIDs). Possible post-operative complications include failure of the transcondylar screw, seroma formation and septic arthritis. Complication rates post-surgery are unusually high with up to 25% of cases developing a postoperative infection and 30% of cases developing a seroma (Hattersley and others, 2011). This is significantly higher than the 6% infection rate reported in lateral humeral condylar fracture repair (Morgan and others, 2008). Owners should be warned of the higher complication rate prior to surgery. However, the prognosis for patients undergoing prophylactic screw placement is reported to be good for those that have an uncomplicated recovery, with resolution or at least significant improvement in the degree of lameness in the majority of cases (Butterworth and Innes, 2001; Meyer- Lindenberg and others, 2002). Owners should also be warned that even if a fissure has not been identified radiographically on pre-operative radiographs of the contralateral elbow or a CT scan, clinical signs associated with IOHC may become apparent at a later date. This may be associated with fissure propagation as previously mentioned (Witte and others, 2010). 

2. Humeral condylar fractures

Patients with IOHC can also present with humeral condylar fracture. Owners will often report that the fracture occurred during normal activity with little or no history of trauma. Prodromal lameness can also be reported. Humeral condylar fractures are divided into three categories, of which lateral humeral condylar fractures are the most common: 

  • lateral humeral condylar fractures (Figure 4a);
  • medial humeral condylar fractures (Figure 4b);
  • intracondylar fractures – classified as either a Y or T fracture depending on where the fracture lines cross the epicondylar ridges (Figure 4c).

Dogs with humeral condylar fractures present with non weightbearing lameness of the affected forelimb with marked soft tissue swelling. Pain and crepitus are noted if the elbow is manipulated. A definitive diagnosis is achieved by obtaining orthogonal radiographic views (mediolateral and craniocaudal)
of the affected elbow. Again, it is important to radiograph or perform a CT scan of the contralateral elbow to assess for the presence of IOHC. The majority of patients presenting with fracture secondary to IOHC do not have a significant history of trauma; however, full patient assessment is still a vital part of the management of these animals to ensure concurrent issues are not missed. Patients must receive suitable analgesia, most commonly a combination of a NSAID and an injectable opioid.
Bandaging of the affected limb is not usually required and indeed the weight of the dressing can act as a fulcrum if the dressing does not extend far enough proximal to the fracture.
Cage confinement prior to surgical management of these fractures is also essential. Humeral condylar fractures have an
articular portion and therefore exact anatomical reduction and rigid internal fixation of these fractures is essential:

a. Lateral condylar fractures

These fractures are approached via a lateral incision passing just cranial to the point of the lateral epicondyle. A transcondylar lag screw is used to achieve interfragmentary compression across the condyle. This is most commonly placed using an inside-out approach where the condylar portion of the fragment is externally rotated to allow placement of the glide hole for the lag screw. This ensures placement of the lag screw in the centre of the condyle. It is important to try and place the transcondylar screw parallel to the epicondylar line to reduce the risk of implant failure (Morgan and others, 2008). Some surgeons use a partially threaded cancellous screw in immature animals rather than a cortical screw which provides greater purchase in soft epiphyseal and metaphyseal bone. However, cancellous screws have a much lower bending strength than their cortical equivalents so a cortical screw is often combined with a washer in these immature patients. A second point of fixation is required in the epicondylar ridge to prevent rotation of the condylar fragment around the transcondylar screw. This is usually achieved using a Kirschner wire placed from distal at the
base of the epicondylar ridge proximally across the fracture line into the diaphysis. This implant should engage the medial cortex of the humeral diaphysis to provide stability and the pin should
be bent to prevent migration (Figure 5a).

b. Medial condylar fractures

The principles of fixation for these uncommon fractures are the same as those for the management of lateral condylar fractures although the approach is medial rather than lateral. The medial condyle of the humerus is larger than its lateral equivalent and
therefore a lag screw can be used to reduce the medial epicondylar fracture in place of a Kirschner wire (Figure 5b).

c. Intracondylar fractures

Intracondylar fractures are technically challenging and should only be attempted by an experienced surgeon. More recently, a bilateral approach has been advocated for internal reduction and fixation of these fractures although a caudal approach via an olecranon osteotomy or triceps tenotomy can also be used.
The intracondylar fissure is reduced using a transcondylar lag screw which can be placed using either a lateral or medial approach. Medial and lateral bone plates are then applied (Figure 5c). The increasing popularity of locking plates has provided another avenue of repair in these challenging cases. These plates do not require the same degree of contouring as the traditional dynamic compression plate as the screw thread locks into the plate. This can improve construct stability in areas such as the distal humeral condyle where contouring can be difficult. Post-operative care for these patients is similar and includes the provision of adequate analgesia including opioids in the initial postoperative period. NSAIDs should be continued for a minimum of 2-3 weeks post-operatively depending on the individual patient and fracture type. Exercise restriction is essential for these patients in the post-operative period and this should be stressed to the owner. Confinement to a single small
room with non-slip flooring or a cage is required in the initial post-operative period with lead exercise for toileting purposes only. Early but controlled use of the joint is a vital part of post-operative management for these patients and flexion/extension range of motion exercises can easily be carried out by the owners at home. The aim of surgical management for all fractures is an early return to function but this is particularly pertinent where the fracture involves the joint surface. This ensures loading of the bone, reduces the risk of fibrosis of the soft tissue components of the joint and is protective for chondrocyte health as it helps to ensure the correct distribution of synovial fluid throughout the joint. Post-operative radiographs are repeated at four to six weeks depending on the age of the patient and the fracture type and the exercise regime altered accordingly. The prognosis for lateral and medial condylar fractures is generally good if early and adequate reduction is achieved (Denny, 1983; Morgan and others, 2008). However, complication rates of up to 30% are reported for lateral humeral condylar fractures (Morgan and others, 2008).
In addition, there is a high incidence of radiographic osteoarthritis following these fractures and this should be discussed with the owner prior to surgery (Gordon and other, 2003). The prognosis for Y and T fractures is somewhat more guarded although one study reported a good or excellent outcome in the majority of cases in the hands of an experienced surgeon (Mckee and others, 2005).

3. IOHC as an incidental finding

IOHC can be recognised in asymptomatic patients as discussed in the introduction, usually when the “normal” elbow joint is imaged. Martin and others (2010) reported IOHC in the contralateral limb in six out of 14 dogs presenting with humeral condylar fracture. Currently, opinion varies on the management of these patients as they are at higher risk of fracture but this must be balanced with the possible post-operative complications
associated with prophylactic transcondylar screw placement. This should be discussed with the individual owner when this situation arises to allow an informed decision to be made.

  • The full list of references is available on request.

Acknowledgements

I would like to thank Professor John Innes, Dr Eithne Comerford and Rob Pettitt for their help regarding the research and writing of this article and for the use of the images.