Measuring craniocaudal instability in stifle joints of dogs using stress radiographs

Craniocaudal stifle joint laxity in dogs affected by various stifle disorde rs was determined using mediolateral X-ray projections of the stifle joint in neutral and tibial compression stress position. In all, 129 stifle joint s of 80 dogs were included in the study. Patients were classified into following groups characterised by: if total c ranial cruciate ligament (CCL) rupture, 2) total CCL rupture and medial men iscus lesion, 3) partial CCL rupture, 4) partial CCL rupture and medial men iscus lesion, 5) clinically evident CCL rupture only, 6) normal stifle join ts, 7) normal stifle joint on the contralateral joint to the one affected b y the CCL rupture, 8) radiographically abnormal and clinically stable stifl e contralateral to the joint affected by the CCL rupture, and 9) other stif le disorders. Index of laxity (IL) of the stifle joint giving the extent of cranial tibial displacement relative to the femur in the stress tibial com pression projection expressed as percents of the femur width was computed. Stifle joints with IL values over 25 can be supposed to be affected by CCL rupture, whereas joints with the IL value Less than 15 can be considered to have an intact cranial cruciate ligament. There were significantly higher IL values in stifle joints with clinically or by arthrotomy diagnosed CCL r upture as compared to the group of healthy joints (Wilcoxon's test: p < 0.0 1 and p < 0.05, respectively in these ones with partial CCL rupture and med ial meniscus damage). Contrary to published data, we found considerably higher IL values in stifl e joints with total CCL rupture as compared to those ones with partial rupt ure (p < 0.01). Significant differences in the index of laxity value were n ot found in stifles with other disorder than the CCL rupture as compared to the group of healthy joints. Measurement of the index of laxity is an unde manding and noninvasive technique supplementing the clinical examination an d could serve as an early diagnostic method for the CCL injury.