EFFECT OF UNIPODAL VS BIPODAL STANCE ON RADIOGRAPHIC EVALUATION OF FOREFEET IN HORSES.

Introduction/Purpose:
Lifting the contralateral forelimb is often used as a method of restraint when obtaining forefeet radiographs in horses. This experimental study was conducted to evaluate the effect of unipodal vs bipodal stance on several radiographic parameters in equine forefeet. We hypothesized that unipodal stance would influence mediolateral and sagittal balance by reducing lateral distal interphalangeal joint (DIPJ) space width and increasing flexion of the distal interphalangeal joint (DIPJ).

Methods:
Four non-lame horses with normal foot conformation were randomly selected. Lateromedial (LM) and dorsopalmar (DP) projections were obtained on both forefeet, squarely placed on blocks, using 2 x-ray generators in a fixed position laterally and dorsally to the foot. Radiographs of each foot were made in a bipodal stance, immediately followed by the same protocol in an unipodal stance (after lifting the contralateral limb) without moving neither the foot nor the x-ray generator. Several measurements were made: DIPJ space width at particular landmarks on DP and LM projections; mediolateral joint balance on DP projections; deep digital flexor tendon (DDFT) angle to solar surface of the distal phalanx (P3) and distance between P3 extensor process and dorsoproximal extent of the middle phalangeal (P2) condyle as an indication of DIPJ flexion on LM projections. A matched pairs design and student’s t-test with a 95% confidence level were used to test for statistical significance.

Results:
Compared to a bipodal stance, lateral DIPJ space width was significantly reduced on unipodal DP views (-0.75mm[I assume this is the mean?]; CI ±0,35; p<0.005), whereas medial DIPJ space width and mediolateral joint imbalance were significantly increased (+0.40mm; CI ±0.18; p<0,005 resp +1,15mm; CI ±0.42; p<0.0005). No statistical difference was observed in mean DIPJ space width on LM views between both conditions. The distance between the P3 extensor process and the dorsoproximal extent of P2 condyle, as well as the DDFT angle, were significantly increased in unipodal LM views (+1.98mm; CI ±0.83; p<0.0005 resp +10.54°; CI ±2.45; p<0,0005), indicating a higher degree of DIPJ flexion in that condition.

Discussion/Conclusion:
Unipodal stance significantly affects the mediolateral balance of the DIPJ on DP radiographs and significantly alters the phalangeal axis on LM radiographs. These findings suggest that stance should be carefully taken into consideration when radiographically evaluating equine forefeet, especially if assessing foot balance.