the distraction portion of the method is shown in fig1 . in the method of the present invention , a clinician places a distractor between the upper thighs of a canine patient in ventral recumbency so that the distractor contacts the inner thighs of the patient . the weight of the dog &# 39 ; s hind quarters and abdomen should rest on the device . with the device in place , the clinician can support the device with one hand ( the &# 34 ; manipulating hand &# 34 ; or &# 34 ; non - imaging hand &# 34 ;) to prevent the device from tilting relative to the legs . the device should be positioned as proximal ( toward the hip joint portion of the femurs ) as is allowed by the weight of the dog and the interposed tissues of the ventral abdomen . no additional forces need to be applied to the device to ensure that the device is appropriately positioned close to the hips . with the same hand , can apply inward pressure to the knee ( stifle ) region of both legs to achieve distraction . in clinical use , the imager usually needs a firm grasp of the device to prevent the device from tilting as force is applied to the stifles . while maintaining the inward pressure , the clinician can use the second hand ( the &# 34 ; imaging hand &# 34 ;) to position an image acquisition device to obtain non - radiographic images of the coxofemoral ( hip ) joints in distraction . the image acquisition device is preferably a non - radiographic device , and is typically an ultrasonic transducer ( such as a 7 . 5 - mhz ultrasound transducer such as si450 , siemens quantum , inc ., issaquah , wash .). a modified dorsal view provides the best sonographic plane to image the components of the coxofemoral joint and to allow measurement of the distance moved between compression and distraction . the dorsal plane of the hip is a long axis view with the transducer directed from the side ( i . e ., left to right in the left hip ). from this initial plane , the transducer can be rotated slightly ( i . e ., clockwise in the left hip ) so that the cranial aspect of the transducer is more dorsal than the caudal portion . the desired end result is an image in which the cranial - dorsal ilium appears to form a horizontal straight line and the rounded femoral head is seen well . in this position , the transducer needs only subtle adjustment to maintain the same image plane during compression and distraction maneuvers . with practice , both hips can be evaluated , and images can be collected , within ten minutes . it is not absolutely essential that the patient &# 39 ; s hair be clipped at the transducer site , especially with young ( six to eight week old ) puppies . good quality images can be obtained through the hair coat by applying copious isopropyl alcohol and acoustic gel . to compress the hip joints , the device is removed and the legs can then be gently pulled together . it is preferred that the clinician wraps the fingers of the manipulating hand around one leg at the upper thigh while the thumb of the same hand wraps around the opposite leg , whereupon the images of the coxofemoral joints in compression can be obtained in the same manner as was described above . distraction should be performed first . the movement from distraction to compression is less stressful to the patient , resulting in a lower possibility of the patient moving . the hips should be distracted , an image collected , and then the hips placed into compression . the second , and final , image is then collected in compression . in the experience of the inventors , the highest quality images of the components of the coxofemoral joint were obtained in puppies between six and sixteen weeks of age although an age range of about 4 - 26 weeks can be suitable . it is preferred that the analysis be performed before the age at which the femoral heads are surrounded by a mineralized acetabular rim . after acquiring the images of each hip in compression and distraction , preferably on split - screen images , the distracted distance is measured . in a first preferred method for determining the distracted distance , the images are digitized , and the compression and distraction images are merged (&# 34 ; blended &# 34 ;) using image analysis software capable of blending two images ( such as nih image 1 . 60 or subsequent current version ( http :// rsb . info . nih . gov / nih - image / download . html ; see fig3 a , b of o &# 39 ; brien , supra ( 1997 ) for example of such a blended image ). this analytical method has certain shortcomings in that it requires a separate computer and specialized software to perform the time consuming and technically challenging process of image blending . moreover , the ultrasound image must be converted from the proprietary data format of the device manufacturer to a conventional format such as pict or tiff . alternatively , a simply mathematical formula that corrects for differing sized fields of view using a conversion factor ( pixel per millimeter ), provides the distraction distance when four points are identified on the images . on each image , the position of the skin is known . in addition , the highest points on both the cranial dorsal acetabular rim and the femoral head are identified . from these points , the distraction distance can be determined and normalized . in this approach , four measurements are necessary from a common reference point , such as the top of the screen or image border : 3 . caudal - most point of acetabular rim ( with hip in compression ); and using these four measurements ( summarized in fig2 ), the distraction distance is determined from the formula all measurements should be drawn with a straight vertical line and the reference points should be consistent between compression and distraction images , especially on the acetabulum rim measurements . if image measurements are taken from paper images , rather than analyzed on the ultrasound machine , the calculated distraction distance must be multiplied by a proportionality factor that can be determined by comparing the known length of a line on the ultrasound image against the length of the same line on the paper image . for example , if a 3 cm line on the ultrasound image measures 2 cm on the paper image , then the proportionality factor is 0 . 667 . in a second aspect , the present invention is a distractor that , when placed between the upper thighs of the canine patient , serves as a fulcrum for laterally displacing ( distracting ) the hips . fig3 depicts a preferred distractor . in this application , inner and outer , top and bottom refer to positions relative to the center of the distractor of fig3 . a preferred distractor 10 includes a pair of end means 12 and 13 , each of which is generally rectangular in shape with an inner face and an outer face . the distractor 10 also includes a pair of generally rectangular spaced apart side bars 14 and 16 mounted perpendicularly to the end members . the end means 12 , 13 and the side bars 14 , 16 can be solid or hollow and can be made of any rigid material such as hard plastic or lucite . a portion of each of the side bars 14 and 16 along its short side edges is recessed , to receive the end members 12 and 13 . the side bars 14 and 16 should include outward facing sides that are sufficiently large to permit the apparatus to act as a fulcrum during distraction and to permit the clinician to support the distractor with one hand in the method . optional modifications to the surface of the apparatus can be provided , such as means for supporting the apparatus in use . in the preferred embodiment , side bars 14 and 16 are not strictly speaking rectangular since each includes a pair of rounded edges toward the outer face to enhance the comfort of the canine patient during distraction . the edges toward the inner face can also be rounded , although the general shape of the side bars 14 and 16 should be rectangular , as opposed to cylindrical , and the outer faces should be generally flat . the extent to which the outer edges of side bars 14 and 16 are curved is not essential to the invention , however , some curvature is preferred . the outer faces of side bars 14 and 16 can be provided with textural indicia to further discourage slippage in use . side bars 14 and 16 are in mirror image orientation relative to each other in the distractor 10 . that is , the outside edges of side bars 14 and 16 each face the outside of the apparatus while the inside edges face toward each other and toward the inside of the distractor 10 . side bar 14 can be fixedly connected to the end members . the connection can be by attachment means 18 , such as a screw , as is shown in fig3 or by adhesive connection . in an alternate construction , a single element can comprise the pair of end means 12 and side bar 14 . side bar 16 can be slidably mounted to the end members 12 and 13 . in the preferred embodiment , a slot 20 is defined through each end member 12 , 13 . the slots 20 permit the distance between side bars 14 and 16 to be adjusted . end caps 22 provided at each end of side bar 16 pass through the slots . the end caps may be loosened to permit lateral adjustment of side bar 16 relative to end members 12 and 14 , and then tightened to prevent further change in the distance between side bars 14 and 16 during use of the apparatus 10 . the distance between side bars 14 and 16 can vary with the size of the dog , as long as when the distractor 10 is in place it can act as a fulcrum on the femurs . the optimal distance between side bars 14 and 16 is between about 3 . 5 and 4 . 5 cm for puppies that are sized like a 6 - 8 week - old labrador or golden retriever . in use , the slidable side bar 16 is adjusted laterally relative to end members 12 and 13 so that side bar 16 is spaced apart from side bar 14 at a distance such that when the hips are maximally distracted , the stifles are within one to two cm of each other , but not touching . given the variation within typical litters of puppies , the device is usually adjusted only once , at the beginning of imaging . it is , of course , understood that the relationships between the end members 12 and 13 and the side bars 14 and 16 need not necessarily be exactly rectangular . however , a rectangular fit among the parts is preferred as that arrangement facilitates a stable apparatus with minimal structural requirements . other arrangements that meet these general structural requirements are intended to fall within the scope of the present invention . in a related embodiment , the spaced apart relation between the side bars 14 , 16 can be a fixed distance , if the distractor is to be used for only canines of a particular size . indeed , the entire distractor can be formed as a single part , since no movement of any element is required in use . the present invention will be better understood upon consideration of the following examples which are intended to be exemplary and not limiting on the invention . a distractor prepared in accordance with the invention was tested using the method of the present invention on 30 puppy hips . the distraction distance was also determined using existing manual methods . the data of fig6 demonstrate an association between distraction distances measured using the distractor and those obtained using manual methods . the invention is not intended to be limited to the foregoing examples , but rather to encompass all such variations and modifications as come within the scope of the appended claims .
an apparatus is employed to determine hip joint laxity in canines . the apparatus , which is adjustable for the size of the canine , is placed between the thighs of a canine patient in ventral recumbency , the pelvic limbs are manipulated to compress or distract the coxofemoral joint and the compression or distraction is imaging by non - radiographic means .