International Congress of the Italian Association of Companion Animal Veterinarians

Transcription

1 International Congress of the Italian Association of Companion Animal Veterinarians 2 - May, 201 Rimini, Italy Next Congress : SCIVAC International Congress Ma -, 201 -, Italy Reprinted in IVIS with the permission of the Congress Organizers

2 69 CONGRESSO INTERNAZIONALE MULTISALA SCIVAC RIMINI MAGGIO 2011 Advances in Elbow Dysplasia in Dogs Antonio Pozzi DMV, MS, Dipl ACVS, Florida (USA) Elbow dysplasia is the most common cause of thoracic limb lameness in dogs. Elbow dysplasia is an umbrella term grouping four developmental disease processes of the elbow joints of dogs: fragmented coronoid process (FCP), ununited anconeal process (UAP), osteochondritis dissecans of the medial aspect of the distal humeral condyle (OCD) and elbow incongruity (INC). FCP is the most frequently diagnosed form of elbow dysplasia. It is most commonly first recognized in growing, large and giant breed dogs between seven and nine months of age. Bernese Mountain dogs, Labrador retrievers and Golden retrievers are the breeds most commonly affected. 1-3 Males are more commonly affected than females, although this may be a reflection of differential rate of growth. 1 Resultant elbow osteoarthritis is the third most common orthopedic condition affecting adult dogs, after conditions affecting the coxofemoral and stifle joints. Clinical signs usually reported in dogs with FCP include stiffness or a stilted forelimb gait, most obvious when first rising or after prolonged rest or vigorous exercise. Bilateral involvement is common in which case lameness may be difficult to detect. 4 These dogs often stand with the elbow adducted and the antebrachium externally rotated (supinated) in a presumed attempt to shift weight away from the affected medial compartment to the lateral compartment of the elbow joint. Joint effusion may be present on physical examination. Pain is often elicited during maximal flexion, firm supination in moderate flexion, deep digital pressure over the insertion of biceps brachii tendon on the ulna and extension of the elbow joint. 5 These limb manipulations may increase the degree of lameness transiently after the examination. Disease of the medial coronoid process and changes associated with the articulating medial aspect of the distal humeral condyle (trochlea) are the most common pathologic changes noted surgically. 4,6 Lesions noted on the medial coronoid process at surgery include cartilage malacia, fibrillation, fissuring and erosion and on histopathology subchondral bone microfissuring and erosion are noted. 7 Erosive cartilage lesions, often referred to as kissing lesions, frequently develop on the articulating surface of the trochlea of the humeral condyle, in association with medial coronoid pathology. Kissing lesions are much more likely to occur when there are displaced fragments of the medial coronoid process rather than in dogs with non-displaced fissures, indicating that both may be due to an underlying pathologic incongruity. 4 Treatment of FCP by either conservative management, surgical removal of fragments by either arthrotomy or arthroscopy or corrective osteotomies has yielded similar outcomes. 1,8-9 Irrespective of the method of treatment elected, osteoarthritis of the elbow progresses and the prognosis for a return to normal function is guarded. A total elbow replacement procedure may be required in severe cases of elbow osteoarthritis. 5 While the etiopathogenesis of UAP and OCD are understood, there is no uniform agreement regarding the etiopathogenesis of FCP. FCP is an inherited trait, although the genes responsible have yet to be identified Abnormal endochondral ossification of the coronoid process, abnormal bone structure or abnormal biomechanics of the elbow joint have been proposed as potential mechanisms. Histopathological studies of elbows affected by FCP have demonstrated that these lesions are non-healing fractures, likely a result of repetitive excessive loading. 7 Fragmented coronoid process (FCP) was first identified in dogs by Olsson in It was initially believed that FCP, like OCD of the humeral condyle, was a manifestation of osteochondrosis or a disturbance in endochondral ossification. 1,13 However it has since been substantiated that FCP is not a manifestation of osteochondrosis, but instead is a result of supraphysiologic loading, cumulating in fatigue failure and microfracture formation in the trabecular subchondral bone of the craniodistal tip or the radial incisure of the medial coronoid process. 5,7,14 Despite extensive research over the past three decades, the exact etiopathogenesis of FCP has yet to be elucidated and remains controversial, although abnormal biomechanics of the elbow resulting in this supra-physiologic loading of the medial coronoid process are considered the most likely cause. Elbow incongruity refers to a malalignment of the articulating surfaces of the bones composing the elbow joint. There are two main types of joint incongruity; physiologic and pathologic. Physiologic incongruity in the elbow joint occurs where the trochlear notch of the elbow has a small concave incongruence that allows more equal stress distribution under high load and ensures better nutrition of the articular cartilage Such incongruence is not thought to 324

3 be involved in the development of FCP. Pathologic incongruity refers to humero-ulnar conflict resulting in increased load concentrated in the area of the medial coronoid process. The main current biomechanical theories proposed to cause humero-ulnar conflict and resultant supraphysiologic loading of the medial coronoid process include static elbow incongruity (radio-ulnar length disparity), dynamic elbow incongruity (radio-ulnar longitudinal incongruence), ulnar trochlear notch geometric incongruity, primary rotational instability of the radius and ulna relative to the distal humerus and musculo-tendinous mismatch. 5 Whether pathologic incongruity itself is the cause of forelimb pain and lameness is difficult to determine as it is usually associated with FCP. 17 Radio-ulnar step incongruity occurs due to disparate growth of the paired radius and ulna during skeletal development. In the case of a short radius, increased contact pressure has been reported in the area of the tip of the medial coronoid process in cadaveric studies of radii shortened experimentally 18 and FCP has been induced by premature closure of the distal radial physis and resultant radial shortening (Figure 1C). Radio-ulnar incongruity may be a dynamic state, only occurring at certain joint positions or during elbow loading. Diagnosis of radio-ulnar incongruity during arthroscopy has been reported to have a higher diagnostic value than radiography and computed tomography (CT), as dynamic incongruity may be observed. Dynamic elbow incongruity may be present transiently during the development of elbow dysplasia but resolved by the time of diagnosis, making identification difficult. Geometric incongruity, resulting in an elliptical ulnar trochlear notch that is too constrained to accommodate the humeral condyle, is another proposed etiology (Figure 1B). Theoretically, this anomaly would cause increased pressure to occur on both the anconeal process and the medial coronoid process and both FCP and UAP could occur in the same joint. However, the incidence of UAP and FCP occurring in the same elbow is low and following three-dimensional digitizing studies and those examining the radius of curvature of the ulnar trochlear notch in breeds typically affected compared with those unaffected with FCP, it is considered unlikely that the conformation of the ulnar trochlear notch alone is responsible for clinical disease. Primary rotational instability of the radius and ulna in relation to the humerus has been proposed as a cause of FCP. The articular circumference of the radial head is greater than the corresponding circumference of the radial notch of the ulna which allows axial rotation or pronation and supination of the antebrachium. Primary rotational instability may occur during degrees of pronation and supination of the antebrachium, resulting in lateral shear and excessive loading of the medial coronoid process between the radial head and the medial humeral condyle. The effect of pronation and supination on the contact mechanics and three-dimensional kinematics of the elbow joint has not yet been investigated. The forces transmitted by articular cartilage are the sum of ground-reaction forces and those resulting from the action of musculo-tendinous units. The elbow has a high degree of inherent congruency and during a normal range of motion, the majority of the articular cartilage is in direct contact and transmitting force. The measurement of contact areas is useful to determine the pressure experienced by articular cartilage and underlying subchondral bone. The larger the overall contact area, the greater the distribution of forces and the lower the peak pressures experienced by the articular cartilage. The development of osteoarthritis depends on the degree of disruption of physiologic load transmission across the articular cartilage surface. Minor changes in normal joint contact stresses may result in cartilage degeneration. Therefore treatment for FCP should aim to restore normal joint contact mechanics, which are currently poorly understood. Previous cadaveric forelimb models have evaluated relative articular contact areas in axially-loaded normal elbows. Polymethyl methacrylate (PMMA) was applied to elbow joint surfaces prior to loading the forelimb with N/kg at an elbow flexion angle of 135º. Following loading, water-soluble paint was applied to the joint surfaces and photographs were obtained. Computer-assisted image analysis was performed to determine the areas void of PMMA that stained with water soluble paint. Three distinct contact areas were identified, including the medial coronoid process. There was no evidence of a surface radio-ulnar incongruity. A physiologic concave incongruity was identified in the normal trochlear notch. There was no change in contact area or location with increasing axial load, although the magnitude of the load applied may have been insufficient to demonstrate a load-dependent change. Two similar studies utilizing colored PMMA were subsequently performed to evaluate the effect of radial shortening, resulting in a static radioulnar step incongruity, with treatment by corrective ulnar ostectomy and humeral osteotomies on contact patterns in normal elbows. The induction of a radio-ulnar step incongruity resulted in a decrease in the combined radio-ulnar contact area, insinuating an increase in local pressure with concentration of forces on the lateral edge of the medial coronoid process. These results lend weight to the theory of radio-ulnar incongruity as a cause of FCP. Solid casting techniques, although repeatable, produce only qualitative data and may underestimate or fail to adequately evaluate some contact regions. Trans-articular force maps of normal elbows and normal elbows following humeral osteotomies have been generated using tactile array pressure sensors. The mean force and force distribution across the proximal radius and ulnar articular surfaces were determined. In normal elbows, approximately 50% of the load transferred through the elbow joint was transmitted through the proximal ulnar contact surface. Abnormalities that increase this load may result in FCP. The exact contact force, contact area, peak and mean contact pressure and peak pressure location could not be obtained from the data supplied by these sensors. I-scan sensors have been investigated for the use in determination of contact mechanics of joints. When comparing Fujifilm pressure sensitive film (standard tool for measuring joint contact mechanics in orthopedic research) with the I-scan system, the I-scan has improved accuracy and repeatability in the measurement of contact area, pressure and force. I-scan sensors will allow us to measure contact force, contact area and peak contact pressure and calculate mean contact pressure. 325

4 In-vivo kinematic studies of the forelimb of dogs at a walk and trot have been reported in two dimensions. The simultaneous investigation of in-vitro three-dimensional kinematics and contact mechanics of normal elbows to determine the effect of elbow position on joint biomechanics has not been investigated. Following the establishment of this cadaveric model to evaluate normal elbows, the contact mechanics and three-dimensional kinematics of elbows affected by FCP and the effect of corrective surgical procedures will be evaluated. END STAGE ELBOW OSTEOARTHRITIS Commonly recognised lesions associated with medial coronoid disease are typified by cartilage malacia, fibrillation, fissuring and erosion in addition to subchondral bone micro-cracks and fragmentation. Frictional erosion of the medial humeral condyle ( kissing lesion ) is frequently associated with coronoid disease whilst osteochondrosis of the medial aspect of the humeral condyle may give rise to lesions of osteochondritis dissecans. This plethora of pathology and ensuing full thickness cartilage erosion with subchondral bone exposure in the region defined by the medial coronoid process and medial aspect of the humeral condyle has been referred to as medial compartment disease (MCD). Elbow incongruity such as radio-ulnar step defects, humeroulnar incongruence/conflict, varus deformity of the humerus or imbalance between skeletal and muscular mechanics may contribute to medial compartment syndrome of the elbow joint in dogs. Pathology of the lateral aspect of the elbow joint is far less commonly observed. Non-surgical treatment of elbow osteoarthritis should always be considered as the first treatment option. Conservative treatment of osteoarthritis is based on 4 major components: 1) weight loss/control, 2) controlled low-impact activity; 3) NSAIDS; 4) chondroprotection. More recent additions to these treatments include physical therapy (a type of controlled low-impact activity), acupuncture, and intra-articular injection of hyaluronic acid, steroids, platelets enriched plasma or autologous conditioned plasma or stem cells. While medical treatment of osteoarthritis is well accepted and has been evaluated in several clinical studies, very few data are available for the most recent treatment modalities. Surgical treatments may include radial or ulnar osteotomies to address perceived incongruity, removal of free fragments and cartilage debris, debridement of lesions and subchondral micro-picking. Osteochondral Autograft Transfer System (OATS, Arthrex, Naples FL) allows resurfacing of lesions associated with OCD. Osteotomy of the ulna may lead to varus deformity of the limb and subsequent increased load on the medial compartment (Mason, 2003). Radial osteotomy protocol is yet to be well defined and thus-far has produced variable results. None of these techniques are applicable in cases of advanced elbow arthrosis and regardless of the technique employed, arthrosis is progressive. In cases where even these newer techniques are unlikely to result in a favourable clinical outcome because of chronicity of the lesions or because of severity of cartilage disease of the medial compartment at the time of presentation, there is a rationale and a clinical need for alleviation of pain and, if possible, amelioration of disease progression. Many of these patients are young and total elbow arthroplasty or elbow arthrodesis represent suboptimal therapeutic choices either because of potential complications or potentially poor functional outcome. In vitro studies of normal canine elbows have mapped force distribution across the humero-radial and humeroulnar joints and found approximately 50:50 distribution (Mason, 2005) with three distinct contact areas in the elbow joints of normal dogs (Preston, 2000). There is a radial contact area located on the caudo-medial aspect of the proximal radial articular surface with its longest dimension orientated medio-laterally; a second located on the medial aspect of the distal articular surface of the trochlear notch and extending to the lateral edge of the medial coronoid and a third contact area is located on the cranio-lateral surface of the proximal trochlear notch (Mason, 2005). Initial studies looked at the merits of both a wedge osteotomy and a sliding humeral osteotomy for force redistribution using a mid-diaphyseal humeral osteotomy. The primary goal of osteotomies for the management of osteoarthritis is the redistribution of force through the lateralisation of contact areas and pressure. Load distribution across an articular surface is a result of force and contact area. Medial opening wedge osteotomy or lateral sliding osteotomy (lateral translocation of the proximal humeral diaphysis with respect to the elbow) had been proposed to elicit lateral shifting of the load axis. Increased lateralisation of the proximal humeral segment was achieved by shimming placing spacers either beneath the proximal end of a medially applied bone plate to force the segment laterally, or placing a wedge between the ends of a mid humeral osteotomy, widest medially. In vitro, this resulted in reduction of force on the cranio-medial edge of the radial head and an increase in contact on the lateral edge. Lateral sliding osteotomy of 4 and 8 mm was compared to wedge osteotomy of 10 and 20 degrees (Mason, 2003). Force at the proximal articular surface of the ulna decreased after lateral sliding humeral osteotomy of 8 mm by 28%. It was proposed that a similar osteotomy performed clinically may be useful in the management of coronoid disease and medial compartmental osteoarthritis by decreasing pain and increasing protential for fibrocartilage healing of the articular surfaces. It was noted that the technique would increase loading of periarticular tissues and that the results of such alteration were uncertain such that iatrogenic injury to the soft tissues surrounding the joint should be avoided. Novel osteotomies have been recently described and are under investigation. The aim of these osteotomies is to achieve similar results to the sliding humeral osteotomy (shift in compartmental pressure) but with a less invasive procedure. A proximal ulnar ostotomy has been developed by Ingo Pfeil and Slobodan Tepic with the goal of causing a valgus tilt of the distal ulna and therefore of the limb. Early clinical results are promising, with resolution of lameness in some severe cases. A similar proximal ulnar osteotomy aiming at rotating the proximal ulnar to create supination has been investigated at the University of Florida. Cadaveric 326

5 studies have shown a decrease in medial compartment pressure and an increase in lateral compartment pressure. Clinical cases have not been performed yet. Both techniques are attractive because of their minimal surgical approach and technical ease. Clinical data are needed for validating both techniques. Another options for end stage elbow osteoarthritis include uni- or bi-compartmental arthroplasty. The data available for elbow arthroplasty is still scarce compared to total hip replacement. Total elbow replacement such as the Iowa total elbow or the TATE elbow replacement (both from Biomedtrix) offer semi-constrained implants with cemented or cementless fixation. The early results of the TATE are promising, but further long-term studies are needed. The main limitation of the elbow arthroplasty is that if revision surgery following catastrophic failure is needed, arthrodesis or amputation may be the only options. A more recent surgical option for medial compartment disease consists of a resurfacing prosthesis which aims at eliminating the medial compartment collapse and bone-to-bone contact caused by advanced medial OA. This procedure is called CUE (form Arthrex Vet System). Although few cases have been performed, the initial results are promising with good to excellent return to activity and minimal morbidity. REFERENCES 1. Olsson S-E. The early diagnosis of fragmented coronoid process and osteochondritis dissecans of the canine elbow joint. J Am Anim Hosp Assoc 1983;19: Ubbink GJ, Hazewinkel HA, van de Broek J, et al. Familial clustering and risk analysis for fragmented coronoid process and elbow joint incongruity in Bernese Mountain Dogs in The Netherlands. Am J Vet Res 1999;60: Ubbink GJ, van de Broek J, Hazewinkel HA, et al. Prediction of the genetic risk for fragmented coronoid process in labrador retrievers. Vet Rec 2000;147: Fitzpatrick N, Smith TJ, Evans RB, et al. Radiographic and arthroscopic findings in the elbow joints of 263 dogs with medial coronoid disease. Vet Surg 2009;38: Fitzpatrick N, Yeadon R. Working algorithm for treatment decision making for developmental disease of the medial compartment of the elbow in dogs. Vet Surg 2009;38: Van Ryssen B, van Bree H. Arthroscopic findings in 100 dogs with elbow lameness. Vet Rec 1997;140: Danielson KC, Fitzpatrick N, Muir P, et al. Histomorphometry of fragmented medial coronoid process in dogs: a comparison of affected and normal coronoid processes. Vet Surg 2006;35: Huibregste BA, Johnson AL, Muhlbauer MC, et al. The effect of treatment of fragmented coronoid process on the development of osteoarthritis of the elbow. Journal of the American Animal Hospital Association 1994;30: Grondalen J. Arthrosis in the elbow joint of young rapidly growing dogs. III. Ununited medical coronoid process of the ulna and osteochondritis dissecans of the humeral condyle. Surgical procedure for correction and postoperative investigation. Nord Vet Med 1979;31: Guthrie S, Pidduck HG. Heritability of elbow osteochondrosis within a closed population of dogs. J Small Anim Pract 1990;31: Grondalen J, Lingaas F. Arthrosis in the elbow joint of young, rapidly growing dogs: A genetic investigation. J Small Anim Pract 1991;32: Temwichitr J, Leegwater PA, Hazewinkel HA. Fragmented coronoid process in the dog: A heritable disease. Vet J Olsson S-E. A new type of elbow dysplasia in the dog? Svensk Veterinärtidning 1974;26: Guthrie S, Plummer JM, Vaughan LC. Aetiopathogenesis of canine elbow osteochondrosis: a study of loose fragments removed at arthrotomy. Res Vet Sci 1992;52: Eckstein F, Steinlechner M, Muller-Gerbl M, et al. [Mechanical stress and subchondral mineralization of the human elbow joint. A CTosteoabsorptiometric study]. Unfallchirurg 1993;96: Preston CA, Schulz KS, Kass PH. In vitro determination of contact areas in the normal elbow joint of dogs. Am J Vet Res 2000;61: Samoy Y, Van Ryssen B, Gielen I, et al. Review of the literature: elbow incongruity in the dog. Vet Comp Orthop Traumatol 2006; 19: Preston CA, Schulz KS, Taylor KT, et al. In vitro experimental study of the effect of radial shortening and ulnar ostectomy on contact patterns in the elbow joint of dogs. Am J Vet Res 2001; 62: Mason DR, Schulz KS, Fujita Y, Kass PH, Stover SM: In vitro force mapping of the normal canine humeroradial and humeroulnar joints. AJVR, 66 (1), Address for correspondence: Antonio Pozzi University of Florida College of Veterinary Medicine Gainesville, Florida, USA 327