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Case Report Comparison of radiography, scintigraphy and ultrasonography in the diagnosis of patellar chondromalacia in a horse, confirmed by arthroscopy J. McLellan*, S. Plevin†, P. D. Hammock‡ and G. BonenClark§ Ferguson and Hammock Equine Hospital, 6897 NW Hwy 225A, Ocala, Florida; †Ocala Equine Hospital, Ocala, Florida; ‡Countryside Veterinary Services, Louisville, Tennessee; and §Equine Sports Practitioners, Ocala, Florida, USA.

Keywords: horse; patella; chondromalacia; cartilage; stifle

Summary 1982). In horses the disease may arise in response to abnormal cartilage stresses following partial upward Patellar chondromalacia is rarely reported in the horse. In fixation of the patella (Adams 1974), or through cartilage this study, several noninvasive diagnostic modalities were overload (May 1996), and the disease is a common combined to diagnose patellar chondromalacia in a complication of medial patellar ligament desmotomy horse, later confirmed by arthroscopy. Radiography failed (Gibson et al. 1989). One report in the literature also to demonstrate pathology; nuclear scintigraphy localised describes the gross development of patellar the disease process to the left femoropatellar region; and chondromalacia in a horse following traumatic disruption ultrasonography identified pathological changes within of the femoropatellar joint (Attenburrow and Goss 1994). the affected joint. It is possible that this disease is under- There is, however, a lack of information on patellar reported in the literature due to the difficulty in accurately chondromalacia as a primary disease process in the diagnosing the condition. horse. The scarcity of reports on this disease in horses may be due more to difficulty in the noninvasive diagnosis of Introduction patellar chondromalacia than to its actual prevalence. Radiography has a low sensitivity for diagnosing cartilage Despite the prevalence of chondromalacia patellae in defects (Schneider et al. 1997; Elias and White 2004; man (Uthamanthil et al. 2006), the disease was previously Wright et al. 2006) and there is a documented disputed as a clinical entity in the horse (Rooney 1969). It discrepancy between onset of clinical signs and has since been demonstrated as comparable to the appearance of radiographic abnormalities (Dabareiner disease in man (McIlwraith and Vachon 1988) and is et al. 1993). Scintigraphy is a sensitive but nonspecific characterised by articular cartilage softening and diagnostic modality in the horse (Lamb and Koblik 1988) fibrillation on the distal aspect of the articular surface of and ultrasonography has been documented as a the patella (Noyes et al. 1989), typically in young patients sensitive method for evaluating many stifle soft tissue (Elias and White 2004). The aetiology is largely unknown injuries (Denoix 2003; Hoegaerts and Sanders 2004) in the although femoropatellar instability (Al-Rawi 1997), trauma horse. In man, MRI (Speer et al. 1991; Heron and Calvert (Zorman et al. 1990; Zhang et al. 2003) and chronic stress 1992) is the preferred noninvasive diagnostic method (Outerbridge 1961) have all been proposed. In man, although arthroscopy remains the gold standard, but patellar chondromalacia is due to changes of the invasive, tool for diagnosis and grading of patellar deepest layers of cartilage, causing blistering of the chondromalacia (Noyes and Stabler Craig 1989; Heron surface cartilage. This pattern of cartilage damage is and Calvert 1992). distinct from that seen in arthritis and, unlike arthritis, the In this Case Report, we describe a combined, damage is thought to be repairable (Salvini and Radice noninvasive imaging approach, using radiography, scintigraphy and ultrasonography in a young *Author to whom correspondence should be addressed. Thoroughbred with severe patellar chondromalacia of the Present address: PO Box 744, Williston, Florida 32696, USA. left femoropatellar joint, later confirmed by arthroscopy. EVE 09-001 Mclellan_Layout 1 19/11/2009 14:56 Page 2

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Case details Scintigraphy

History and clinical signs Between 5 and 15 min and then 2 h after the injection of 99m 7MBq/kg bwt i.v. of Tc -methylenediphosphonate A 2-year-old Thoroughbred filly initially presented with (MDP), lateral and caudal views of the left and right stifle acute onset lameness (Grade IV/V on AAEP scale) in the were taken with a low-energy, general purpose collimator left hindlimb following training exercise. The filly had been and a 500 x 700 mm rectangular field of view γ camera1 in race training for 8 months with no prior history of hindlimb using a previously described technique (Dyson et al. 2003). lameness, and prepurchase survey radiographs had Both soft tissue and pool (bone) phase images showed demonstrated no abnormalities 4 months prior to the onset increased uptake of radiopharmaceutical in the left stifle of lameness. Lameness improved one grade over (Fig 2). involving the medial and lateral femoral trochlear the following 2 days with phenylbutazone (4.4 mg/kg bwt ridges and the articular margin of the patella. A discrete i.v.). Physical examination was unremarkable apart from a ‘hot spot’ was not identified but rather a diffuse area of mild distension of the left medial femorotibial joint and increased uptake on the articular margins of these lameness exacerbated by proximal limb flexion. Perineural structures. Region of interest (ROI) analysis objectively anaesthesia of the tibial and peroneal nerves, and intra- quantified the increased radiopharmaceutical uptake in articular anaesthesia of the medial femorotibial joint and this region compared to the right stifle. femoropatellar joint failed to improve the lameness Subsequent to scintigraphic findings, radiographic significantly. Over one week of stall rest, the lameness was views intended to highlight the patella were obtained. reduced but returned to its previous level following Flexed latero-medial and cranioproximal-craniodistal proximal limb flexion. Given the persistent clinical signs the oblique (skyline patella) views were taken from the following diagnostics were undertaken, in chronological affected and unaffected stifle for direct comparison order: (Butler et al. 2000). The flexed latero-medial radiograph showed no abnormality but the skyline view highlighted a Radiography diffuse area of mild sclerotic change on the articular surface of the left patella (Fig 3). A standard series of stifle radiographs was obtained. Standing latero-medial, caudal 60° lateral-craniomedial Ultrasonography oblique and caudocranial views were taken as previously described (Butler et al. 2000) but showed no bony Ultrasonography of the left stifle was performed following a abnormalities and failed to adequately demonstrate the standardised technique (Hoegaerts and Sanders 2004) with soft tissue in the region (Fig 1). a 10 MHz linear array transducer2. Salient results included an increase in anechoic fluid within the medial recess of the medial femorotibial joint. The normally smooth anechoic line representing hyaline cartilage overlying the smooth hyperechoic subchondral bone was absent in the medial trochlear ridge (MTR). A markedly thickened, irregular hypoechoic structure of inconsistent thickness was instead imaged in the region of hyaline cartilage. The demarcation between hyaline cartilage and underlying subchondral bone in this region was poor and the subchondral bone also appeared irregular. In other areas of the MTR, little or no anechoic cartilage line could be visualised overlying the subchondral bone. Findings were similar, although less severe, in the lateral trochlear ridge (LTR). These findings were indicative of thickening and thinning of hyaline cartilage over the medial and lateral femoral trochlear ridges, exposed irregular subchondral bone, and synovitis of the femoropatellar and medial femoropatellar joints (Fig 4). It was not possible to evaluate the articular surface of the patella due to the natural orientation of this structure even in the flexed limb.

Arthroscopy

Fig 1: Lateromedial radiograph of the left stifle failed to The owner was advised of the extent of cartilage demonstrate any pathology. degeneration based on ultrasound findings and elected EVE 09-001 Mclellan_Layout 1 19/11/2009 14:56 Page 3

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a) to perform arthroscopy to both further evaluate the degree of cartilage degeneration and attempt surgical debridement of the lesions. Prior to surgery, phenylbutazone (4.4 mg/kg bwt i.v.) was administered. Following premedication with xylazine (0.8 mg/kg bwt i.v.) and butorphanol (0.04 mg/kg bwt i.v.), anaesthesia was induced with diazepam (0.05 mg/kg bwt i.v.) and ketamine (2.2 mg/kg bwt i.v.) and maintained with isoflurane vaporised in oxygen in a circle system with assisted ventilation. The filly was positioned in dorsal recumbency for arthroscopic evaluation of the left femoropatellar joint. Exploratory arthroscopy revealed severe chondromalacia of the articular surface of the patella (Noyes grade IIb) with severe fibrillation and deep ulceration over >50% of the articular surface (Fig 5). Additionally, essentially all the hyaline cartilage on the medial trochlear ridge of the femur was either missing or ulcerated (Noyes grade III), exposing subchondral bone. The lateral trochlear ridge was similar in appearance to the articular surface of the patella. A communication between the femoropatellar sac and the medial femorotibial joint sac was evident, with free cartilage debris present in both locations. No additional structural abnormalities were noted. Subchondral microfracture was carried out on all exposed subchondral bone and severely malacic b) cartilage was debrided. The femoropatellar joint was lavaged and the portals closed, and recovery was uneventful. Given the severity of the patellar chondromalacia, the owner elected to retire the filly from future race training.

Fig 2: Area of moderately intense uptake of radiopharmaceutical in the region of the left patella and trochlear ridges of the distal Fig 3: Flexed cranioproximal-craniodistal oblique (patellar skyline femur (a). Notice the increased uptake when compared to the view) also failed to demonstrate the extent of pathological normal right stifle (b) using region of interest (ROI) analysis. changes. EVE 09-001 Mclellan_Layout 1 19/11/2009 14:56 Page 4

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a) Discussion

Standard radiographic views failed to demonstrate any lesion in this stifle. This observation is in agreement with previous findings (Dabareiner et al. 1993; Schneider et al. 1997; Elias and White 2004) in relation to the low negative predictive value of radiographs of this region even when a cartilage lesion is present. This is largely due to the inability of radiography to distinguish cartilage. Interpretation in this region may be further complicated by the use of modern digital radiography systems, which are more prone to scatter (Werpy 2007). Contrast arthrography has been shown to have some use in the case of large cartilage flaps (Nickels and Sande 1982) but would have failed to adequately quantify the severity of the patellar chondromalacia in this case due to the lack of large osteochondral flaps. Only the patellar skyline view yielded evidence of mild pathology within the subchondral bone b) of the patella but was a poor prognostic indictor to the extent of pathology present within this joint.

Fig 4: a) Increased anechoic fluid within the medial recess of the medial femorotibial joint (arrow) indicative of synovitis. b) Thickened, irregular cartilage overlying left medial trochlear Fig 5: a) Cartilage fragment in the femoropatellar joint at the distal ridge (arrowheads). MTR = medial trochlear ridge. c) Comparison end of the trochlear groove (arrow). b) Extensive cartilage to normal right medial trochlear ridge demonstrating well bonded, erosions and loss on the medial trochlear ridge of the distal femur smooth cartilage. There is a reverberation artefact in this image (arrowheads) and exposed subchondral bone (arrow). MTR = (dotted arrow) due to poor limb preparation. medial trochlear ridge. EVE 09-001 Mclellan_Layout 1 19/11/2009 14:56 Page 5

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Gamma scintigraphy has been validated as an medication or time out of training, despite having no extremely sensitive method for determining the location demonstrable lesion using standard imaging techniques. It and extent of musculoskeletal problems in horses (Lamb has been reported that the disease in man similarly and Koblik 1988) and normal parameters for scintigraphic responds to rest and/or medication (Bentley and Dowd uptake in the stifle have been reported (Dyson et al. 2007). 1984). Specific views not typically included in a standard However, results are often only positive when subchondral radiographic series of the stifle may increase the sensitivity bone changes are present (Elias and White 2004) and false of radiography but only when a subchondral component negatives are possible (Dyson et al. 2003). In addition, of disease is present. In this case, scintigraphy localised the it provides little information about the nature of the disease but ultrasonography was the only noninvasive disease process. In this case, the marked increase in imaging method to both localise and characterise the radiopharmaceutical uptake in the region of the patella pathology present. This case highlights that several indicated a marked increase in bone turnover, without noninvasive modalities may be used together to diagnose elucidating the underlying pathology. patellar chondromalacia in the horse. By comparison, ultrasonographic examination was able to both localise and characterise the nature of the disease Manufacturers’ addresses process in this horse. Ultrasonography makes it possible to 1 visualise the joint capsule, surrounding soft tissue, articular General Electric, Waukesha, Wisconsin, USA. 2Pico, Universal Ultrasound, Bedford Hills, New York, USA. cartilage and subchondral bone, and allows the qualitative assessment of joint fluid. In this case, References ultrasonography positively identified synovitis and hyperechogenic foci within the joint fluid. Cartilage Adams, O.R. (1974) Lameness in Horses, 3rd edn., Lea & Febiger, ulceration and fibrillation, along with exposed subchondral Philadelphia. bone were also identified on the trochlear ridges of the Al-Rawi, Z. and Nessan, A.H. (1997) Joint hypermobility in patients with femur. It must be noted, however, that these findings were chondromalacia patellae. Br. J. Rheumatol. 36, 1324-1327. not diagnostic of patellar chondromalacia, but of Attenburrow, D.P. and Goss, V.A. (1994) Case report: acute joint pathological changes associated with femoral cartilage destabilization in the equine demonstrating early pathology in osteoarthritis. Osteoarthritis Cartilage 2, 281-283. degeneration. As it is not possible to image the patellar Bentley, G. and Dowd, G. (1984) Current concepts of etiology and articular cartilage, it is therefore possible that less severe treatment of chondromalacia patellae. Clin. Orthop. 189, 209-228. presentations of patellar chondromalacia, without Butler, J.A., Colles, C.M. and Dyson, S. (2000) The stifle and tibia. concomitant femoral pathology, would not demonstrate In: Clinical Radiology of the Horse, Blackwells Scientific, Oxford. the dramatic ultrasonographic findings present in this case. pp 285-326. Arthroscopic examination in this case confirmed the Dabareiner, R.M., Sullins, K.E. and White, N.A. (1993) Progression of extent of the chondromalacic cartilage degeneration femoropatellar osteochondrosis in nine young horses. Clinical, radiographic and arthroscopic findings. Vet. Surg. 22, 515-523. and allowed for cartilage debridement. Arthroscopy Denoix, J.M. (2003) Ultrasonographic examination of the stifle in horses. remains the gold standard for the diagnosis and staging of In: Proceedings of the American College of Veterinary Surgeons. patellar chondromalacia but has the disadvantage of p 122. being invasive, not universally available, and has a Dyson, S.J., Pilsworth, R.C., Twardock, A.R. and Martinelli, M.J. (2003) requirement for general anaesthesia. Proximal limb MRI in Orthopaedic imaging. In: Equine Scintigraphy. Equine Veterinary horses shares these latter 2 shortcomings and imaging of Journal Ltd, Newmarket. pp 77-86. equine stifle also has practical limitations (Werpy 2007). Dyson, S., McNie, K., Weekes, J. and Murray, R. (2007) Scintigraphic evaluation of the stifle in normal horses and horses with forelimb The aetiopathogenesis of this case is not clear. There lameness. Vet. Radiol. 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