EVE 09-001 Mclellan_Layout 1 19/11/2009 14:56 Page 1 642 EQUINE VETERINARY EDUCATION / AE / decemBER 2009 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 EQUINE VETERINARY EDUCATION / AE / decemBER 2009 643 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 3 644 EQUINE VETERINARY EDUCATION / AE / decemBER 2009 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