Dynamic Ulna Osteotomies in Canine Elbow Displasia
Aldo Vezzoni, Med Vet, Dipl ECVS
Clinica Veterinaria, via Massarotti
Elbow dysplasia (ED) is a well-recognised developmental orthopaedic disease affecting growing dogs of several large to giant breeds. Common aspect of this condition is a progressive degenerative joint disease causing forelimb lameness. As asynchronous growth of radius and ulna has been described as one of the main causes of ED, different types of ulna osteotomy in the growing dog with ED has been proposed to restore joint congruity during the remaining growth time.
Pathogenesis of Elbow Dysplasia
Three pathologic conditions are included as causes of elbow dysplasia: ununited anconeal process (UAP), fragmented coronoid process (FCP) and osteochondritis dissecans (OCD) of the medial ridge of the humeral condyle. Several authors believe that all three conditions are manifestations of osteochondrosis (OC). The pathogenesis of OC is considered multifactorial, with a combination of general and local factors being involved. OC occurs as a result of abnormal endochondral ossification. Olsson stated that slight joint incongruity caused by disproportional growth of the radius and ulna is probably the most important reason for the occurrence of OC lesions in the elbow joint. Wind suggested that joint incongruity was a common denominator in all forms of elbow OC and that this incongruity was due to an abnormality of the ulnar trochlear notch, creating major contact points in the area of the anconeal and coronoid processes. In UAP there is an increased growth of the radius relative to the ulna, which causes proximal displacement of the radius head and subsequent abnormal pressure on the anconeal process by the humeral trochlea preventing the bony union of its ossification centre.In the FCP there is a delayed growth of the radius relative to the ulna, which causes a step between the coronoid processes of ulna and the radial head, which resultant increased weight bearing by the humeral condyle on the medial coronoid process.
Elbow Incongruity (EI)
EI is widely accepted as a common aspect of the different conditions leading to elbow dysplasia. A step in the elbow joint causes an uneven load distribution, with a stress concentration on the anconeal process when the radius is too long and on the medial coronoid process when the radius is too short.
Dynamic Ulna Osteotomy (DUO)
Corrective osteotomies has been proposed to balance radius and ulna and to restore or improve the joint congruity in ED. As radius is the main (70%) weight bearing bone in the forearm, ulna is usually selected for corrective osteotomies. Dynamic proximal ulnar osteotomy described by Gilson for the treatment of humeroulnar subluxation has been used to restore joint congruity both in UAP and FCP. Dynamic distal ulnar osteotomies has been proposed in treating moderate joint incongruity both in UAP and FCP.
DUO in UAP
DUO for treatment of UAP was described by several authors; osteotomy of proximal ulna has been demonstrated to restore a better joint congruity and to relieve the pressure on the anconeal process enough to allow the process itself to unite with the ulna. Osteotomy of proximal ulna in UAP is a lengthening osteotomy, because in this condition ulna is shorter than radius. After proximal ulna osteotomy the action of the triceps brachii muscle allows a shifting of the proximal ulna and a reduction in the pressure exerted on the anconeal process by the humerus; it improves joint congruity allowing a anatomic adaptation of the articular surfaces.
DUO for treatment of UAP was developed because of the poor results following conservative treatment and surgical removal of anconeal process (AP) and because of the inconsistent results following screw fixation alone of the AP.
Dynamic and lengthening ulnar osteotomy has been shown to improve joint congruency, to promote bone fusion of the AP and to protect screw fixation of the AP.
In group 1, where the AP is still firmly attached to the ulna with fibrocartilaginous tissue, proximal ulna osteotomy, as described later, is enough to restore joint congruency, to relieve the pressure on the AP and to allow its bony fusion with proximal ulna; lag screw fixation of the AP should not be necessary, but not contraindicated, particularly in active dogs;
In group 2, where the AP is still attached to the ulna with some fibrocartilaginous tissue but it is somewhat loose, proximal ulna osteotomy is necessary to restore joint congruency and to relieve the pressure on the AP and lag screw fixation is necessary to allow its bony fusion with proximal ulna;
In group 3, where the AP is completely loose, attached to the ulna only by the caudal ligament, the AP is no more reducible in its original position because of the flattening of its bed in the ulna, proximal ulna osteotomy is necessary to restore joint congruency and the AP is usually removed because of the poor chances of fixing it in isometric position and of achieving its bony fusion.
Fixation of a completely loose process (group 3) is unlikely to be successful and failure of implants would be anticipated, both because of the bone resorption of the process and because of flattening and remodeling of the trochlear notch which causes abnormal cycling load on the process by the humeral condyle.
DUO in FCP
Osteotomy of ulna in FCP is a sliding osteotomy. Proximal ulnar osteotomy allows caudo-medial rotation of the proximal ulna, estimated to be 10 to 15° caudally and 3° to 5° medially. According to the reported studies, it is not necessary to remove an ulnar segment to get the proper realignment in the elbow joint. The reposition of the proximal ulna in an anatomic configuration in the elbow joint relieves the abnormal humeroulnar joint contact at the medial coronoid ridge. At the same time more normal humeroradial weight bearing in the elbow is restored.
Distal ulnar osteotomy, with removal of 5 to 7 mm of bone, is a sliding osteotomy which allows the weight bearing forces to stretch the interosseous ligament and the proximal ulna to slide distally until a full humeroradial contact is restored and the pressure on the medial coronoid process is relieved.
Surgical treatment of FCP consisting in the removal of the fragmented coronoid process is a common procedure, performed either with a limited medial arthrotomy or with arthroscopy. Even after a complete removal of the loose fragments, if joint incongruity is still present, the uneven weight bearing loading in the joint causes permanent pain and lameness, limiting the results of this treatment.
The association of both procedures, FCP removal and dynamic ulna osteotomy, has been shown to increase the functional and radiographic results in treating FCP with joint incongruency.After removal of the loose medial coronoid fragments, proximal or distal ulnar osteotomy is made. Proximal ulnar osteotomyis indicated in severe joint incongruity and in dogs at the end of limb growing, while distal ulnar ostectomy is indicated in mild joint incongruity and in still growing dogs (6-8 m.). Proximal ulnar osteotomy can be performed with the same procedure as it was described for UAP, preferring the oblique osteotomy to the transverse one.A long recovery time should be anticipated, because of the age of the dog; for this reason proximal DUO in FCP cases should be limited to selected cases of severe joint incongruity. Distal ulnar osteotomy is performed in young still growing dogs with a softer interosseous ligament. It is performed subperiosteally 2 to 3 cm proximal to the distal ulnar physis line, removing a bone segment 5 to7 mm wide. In young dogs distal ulnar osteotomy is easily performed with a bone rongeur, biting the bone piece by piece. It might be made with an oscillating saw too, but the risk of injuring the interosseous vein and artery is higher. Distal ulnar osteotomy has a very low morbidity and the weight bearing on the operated leg is encouraged from the day after surgery to promote the downward sliding of the proximal ulna before callus formation. Complete bony fusion of the distal ulnar osteotomy take place after several months.
In very young dogs (5 to 7 months old), showing elbow lameness caused by incongruity with short radius and overload of the coronoid process, distal sliding ulnar osteotomy as a sole procedure was performed, to promote a spontaneous anatomical joint congruity. In this preliminary study, the early restoration of joint congruity was enough to stop the stress on the medial coronoid process. When indicated, it was performed simultaneously in both arms. Preliminary studies indicate better results when distal DUO is performed early, when incongruity and subtrochlear bone sclerosis are the only radiographic signs, and osteophytes are not yet seen.
Dogs treated with dynamic proximal ulna osteotomies should be kept at strict rest for 5-6 weeks to avoid excessive traction on the proximal ulna segment by the triceps muscle, that could result in an excessive inclination of the proximal ulna segment with limb deformation and, in severe cases, cranial subluxation of radial head.
Dogs treated with dynamic distal ulna osteotomies should be encouraged to walk on a leash from the day after surgery to promote early bone adaptation in the joint before callus formation.
Aldo Vezzoni, Med Vet, Dipl ECVS