Sacroiliac Luxation in the Cat: Defining a Safe Corridor in the Dorsoventral Plane for Screw Insertion in Lag Fashion

Objective— To define a safe corridor in the dorsoventral plane within the feline sacral body for placement of screws inserted in lag fashion for repair of sacroiliac luxation.
Study Design— Anatomic study.
Sample Population— Frozen cadaveric feline sacra.
Methods— Feline sacra (n=20) were used to perform a radiographic study to define a safe corridor to a depth of 66% of the sacral body width. Two drill start points (A and B) were evaluated. Dorsal exit from the safe corridor was considered unacceptable.
Results— Forty safe corridors were measured. The mean articular surface was 100±6.4° from horizontal. Mean maximum, optimum, and minimum safe corridor drill angles from drill point A were 107±6.8°, 97±6.9°, and 87±7.2°, respectively, from the articular surface. Mean maximum, optimum, and minimum angles from drill point B were 109±7.2°, 99±7.1°, and 89.5±7.2°, respectively. Point B increased the risk of ventral exit from the sacral body.
Conclusions— Point A and a drill angle of 90±4° for drilling of the feline sacral body is recommended. This margin for error risks ventral exit from the body in 23/40 (58%) of the sacra in this study. Reduction of the margin for error to ±2° would reduce the risk of ventral exit to 14/40 (35%) of the sacra in this study.
Clinical Relevance— Drilling at 90° to the feline sacral articular surface is recommended. Findings from this study present a strong case for use of angled drill guides.     

Canine sacroiliac luxation: anatomic study of the craniocaudal articular surface angulation of the sacrum to define a safe corridor in the dorsal plane for placement of screws used for fixation in lag fashion

Objective: To define a safe corridor in the dorsal plane relative to the articular surface for placement of a single screw in lag fashion to achieve stabilization of sacroiliac luxation in the dog. Study Design: Cadaveric study. Methods: Dorsoventral radiographs of denuded canine sacra (n=49) were taken to determine the safe corridor in the craniocaudal plane, and the maximum, optimum and minimum angles were calculated that would allow a screw inserted in lag fashion to engage at least 60% of the width of the sacral body without cranial or caudal penetration through the bone. Results: The mean safe corridor in the dorsal plane is ～24° wide. Mean craniocaudal minimum, optimum and maximum drill angles from the drill start point were 88°, 100°, and 111° from the articular surface, respectively. No single angle will completely avoid risk of screw penetration beyond the safe corridor cranially and caudally. Conclusions: There is sufficient anatomic variation between different canine sacra that a single angle cannot be recommended for screw placement in the dorsal plane. Clinical Relevance: A standard angle cannot be recommended for screw placement in lag fashion within the canine sacrum in the dorsal plane. Because of the narrow width of the safe corridor, preoperative measurements on radiographs are recommended and a range of angled drill guides may be useful to decrease surgeon margin of error.     

Stabilization of Sacroiliac Luxation in 40 Cats Using Screws Inserted in Lag Fashion

Objective: To (1) identify prognostic indicators for stability after stabilization of sacroiliac luxation with screws inserted in lag fashion and (2) report dorsoventral dimensions of the sacrum in cats. Study Design: Multicenter retrospective study. Sample Population: Cats (n=40) with sacroiliac luxation. Methods: Case records and radiographs of cats presented at the Queen's Veterinary School Hospital Cambridge and the Royal Veterinary College Hatfield for screw fixation of sacroiliac luxation were reviewed. Dorsoventral dimensions of 15 feline cadaveric sacral bodies were measured to identify the appropriate implant size for use in fixation with screws inserted in lag fashion. Results: Of 40 cats, 13 had left, 14 right, and 13 bilateral sacroiliac luxations. Of 48 screws analyzed, 42 (87.5%) were placed within the sacral body or exited ventrally and 6 (12.5%) were considered malpositioned. Screw purchase within the sacrum was statistically different between unstable and stable repairs (P=.001). Using confidence intervals for screw length within the sacrum and effect on stability, the lowest screw depth that contained 95% of the screws that did not loosen was ∼60% of the sacral width. Mean dorsoventral sacral dimension at its narrowest point was 5.9±1.14 mm. There was no significant difference in the incidence of implant loosening between those luxations that were 100% reduced and those that were <100% reduced (P=.7837). Conclusions: Screw purchase within the feline sacrum of at least 60% of the sacral width significantly reduces the risk of loosening. Clinical Relevance: Screw placement to a depth of 60% of the width of the feline sacrum is recommended.     

Ventral abdominal approach for screw fixation of sacroiliac luxation in cadavers of cats and dogs

OBJECTIVE: To investigate a technique for repair of sacroiliac luxation with positional screw insertion from the ventral surface of the sacral wing via a ventral abdominal approach. SAMPLE POPULATION: Hemipelvis specimens from cadavers of 5 small- to large-breed dogs and 9 European shorthair cats. PROCEDURES: An optimal entry point and a safe drill corridor for implant placement were determined (4 hemipelvis specimens). Anatomic landmarks were identified, and the surgical technique for a ventral abdominal approach was described. Single positional screw placement was performed across the sacroiliac joint in 23 hemipelvis specimens. Screws were aimed at 25 degrees (n=2), 35 degrees (2), and 45 degrees (19) angles to the vertical axis in a transverse plane (alpha angles) and at a 90 degrees angle to the longitudinal axis in a dorsal plane (beta angle). Implant placement was assessed by radiographic evaluation of the cadavers and of the hemipelvis specimens devoid of soft tissue. RESULTS: By use of alpha angles of 35 degrees and 45 degrees, 20 of 21 implants were placed adequately; screws crossed the sacroiliac joint and penetrated the wing of the ilium without damaging adjacent nerves. The measured median alpha angle was 38 degrees , and the median beta angle was 88 degrees. One complication was recorded. CONCLUSIONS AND CLINICAL RELEVANCE: Cortical positional screw placement from the ventral aspect of the sacral wing by use of a ventral abdominal approach could be an alternative to conventional techniques. This novel technique may be useful for repair of bilateral sacroiliac luxation, treatment of concomitant soft tissue injuries of the caudal portion of the abdominal cavity or abdominal wall, and repair of pelvic floor fractures in a single approach.     

Evaluation of Closed Reduction and Screw Fixation in Lag Fashion of Sacroiliac Fracture‐Luxations

Objective— To evaluate outcome by radiographic assessment after closed reduction and percutaneous screw fixation in lag fashion of sacroiliac fracture‐luxations in dogs. Study Design— Retrospective study. Animals— Dogs (n=24) with sacroiliac fracture‐luxations. Methods— Medical records (1999–2006) and radiographs of 24 dogs (29 fracture‐luxations) that had stabilization of sacroiliac fracture‐luxation by fluoroscopic‐guided closed reduction and percutaneous screw fixation in lag fashion were reviewed. Signalment, body weight, number, and location of all concurrent injuries and implants used for repair were recorded. Radiographs were used to evaluate the accuracy of screw placement in the sacral body, screw depth/sacral width ratio, reduction of the sacroiliac joint, pelvic canal diameter, and hemipelvic canal width. Radiographic re‐examination (range, 4 to >8 weeks postoperatively) was available for evaluation. Results— Mean screw depth/sacral width ratio on immediate postoperative and re‐examination radiographs was 64% and 61%, respectively. Mean percentage reduction of the sacroiliac joint on immediate postoperative and re‐examination radiographs were 91% and 87%, respectively. Pelvic canal diameter ratio demonstrated successful restoration of the pelvic canal. Hemipelvic canal width ratio documented successful closed reduction repair independent of concurrent pelvic injuries. Conclusion— Successful repair of sacroiliac fracture‐luxations, determined by radiographic assessment, can be achieved by fluoroscopic‐guided closed reduction and percutaneous screw fixation in lag fashion. Clinical Relevance— Fluoroscopic‐guided closed reduction and percutaneous screw fixation in lag fashion of sacroiliac fracture‐luxations is a minimally invasive technique that restores and maintains pelvic canal dimensions and should be considered as an alternative to open reduction or nonsurgical management of sacroiliac fracture‐luxations.     

Closed Reduction and Lag Screw Fixation of Sacroiliac Luxations and Fractures

OBJECTIVE: To describe a technique for closed reduction and percutaneous insertion of a lag screw for fixation of sacroiliac fracture-luxations, and to report the success of this technique in stabilizing sacroiliac fracture-luxations. STUDY DESIGN: A retrospective clinical study. STUDY POPULATION: 13 consecutive client-owned dogs with sacroiliac fracture-luxations. METHODS: Sacroiliac fracture-luxations were stabilized by using a closed reduction and percutaneous lag screw fixation technique. Preoperative, postoperative, and last re-examination radiographs were used to assess the location and number of pelvic injuries, other orthopedic injuries, percent reduction of the sacroiliac joint, percent sacral width screw depth, position of the screw, pelvic canal diameter ratio, hemipelvic canal width ratio, and complications. Information on signalment, weight, weight-bearing status, neurologic status, and complications was obtained from the medical record. RESULTS: Mean percent reduction of the sacroiliac joint was 92.33%. All screws were placed within the sacral body with a mean screw depth/sacral width of 79.03%. No screw loosening occurred. Mean pelvic canal diameter ratios were 0.99, 1.20, and 1.14 preoperatively, immediately postoperatively, and at the last re-examination, respectively. Nine of 13 dogs were willing to walk on the ipsilateral rear leg the day after surgery. CONCLUSIONS: Closed reduction and percutaneous insertion of a lag screw for stabilization of fracture-luxation of the sacroiliac joint is an acceptable method of repair. CLINICAL RELEVANCE: Sacroiliac fracture-luxations can be successfully reduced and stabilized using a minimally invasive technique.     

In vitro study of the ilial anatomic landmarks for safe implant insertion in the first sacral vertebra of the intact canine sacroiliac joint

OBJECTIVE: To define landmarks on the canine ilial wing for accurate, consistent insertion of implants into the 1st sacral (S1) vertebral body when the sacroiliac joint is intact. STUDY DESIGN: Anatomic study. ANIMALS: Intact, cadaveric canine pelves and sacra (n=25). METHODS: Median sections (5 specimens) were drilled from the center of S1 in a lateral direction, exiting on the ilial wing. Landmarks on the ilial wing and shaft used to define this exit point were then used to locate this point on both wings of 20 articulated specimens, positioned and rigidly held so that the dorsal plane of the pelvis was aligned with a plumb line and the median plane of the pelvis was horizontal. A 2 mm hole was drilled from the marked point, parallel to the plumb line, until it exited the contralateral ilial wing. Distance of drill hole position from the geometric center (GC) of S1 was located on median and paramedian plane images derived from plane, computed tomographic (CT) scans. RESULTS: The entire drill hole was located within S1 in 18 specimens. Mean deviation of the hole from GC (ratio of the distance of GC from the closest S1 body border) in median section was 0.40 +/- 0.29 (craniocaudal direction) and 0.29 +/- 0.23 (dorsoventral). CONCLUSIONS: Use of ilial wing landmarks and drilling perpendicular to the median plane will improve accuracy for insertion of implants into S1 when the sacroiliac joint is intact. CLINICAL RELEVANCE: Ilial wing landmarks should be used to improve accuracy of implant insertion into S1.     

Open reduction of sacral fractures using transarticular implants at the articular facets of L7-S1: 8 consecutive canine patients (1995-1999)

OBJECTIVE: To describe and evaluate facet stabilization as an aid for open reduction and fixation of sacral fractures. STUDY DESIGN: A clinical case series. STUDY POPULATION: Eight consecutive client-owned dogs with sacral fractures. METHODS: A combination of a standard lateral approach to the ilium and a dorsal approach to the articular facets of L7-S1 was performed. The articular facets were reduced and stabilized with a Kirschner wire or a combination of a Kirschner wire and a cortical screw. Primary stabilization of the sacrum was then accomplished using a cortical screw inserted from the lateral aspect of the ilium, through the sacral fracture into the body of the sacrum. Accuracy of reduction, position of the implants, percent screw depth/sacral width, pelvic canal diameter ratio, and complications were assessed using radiographs and physical examination. RESULTS: Mean sacral fracture reduction was 91% immediately after surgery, and was 87% when measured at follow-up examinations. Mean screw depth/sacral width was 66%. Mean pelvic canal diameter ratio was 1.12 postoperatively and 1.03 at the 4- to 6-week reevaluation. Six of the 8 dogs were using the leg well 10 to 12 days after surgery; none had clinically detectable neurologic deficits. The long-term (mean, 2.7 years) outcome for these dogs was good (normal to grade I lameness). CONCLUSION: Fixation of the L7-S1 facet joints facilitates repair of sacral fractures.     

Sacroiliac Fracture-Separation in the Dog: A Study of 92 Cases

The case records of 92 consecutive dogs that suffered sacroiliac fracture-separation were examined. Seventy-seven per cent (71 of 92) had unilateral sacroiliac injury and 23% (21 of 92) had bilateral sacroiliac injury. Of the unilateral cases, 93% (66 of 71) of the dogs had associated acetabular, ilial, femoral, or tibial fractures; coxofemoral luxations; or cruciate injuries. Eighty-five per cent (78 of 92) of the dogs had either bilateral sacroiliac injury or unilateral sacroiliac injury and other orthopedic injuries of the opposite limb, thus disabling both hind limbs.
Sixty-five per cent (60 of 92) of the dogs received lag screw fixation of the sacroiliac joint. Of 29 dogs that were re-radiographed on an average of 437 days following fixation, 38% (11 of 29) showed evidence of loosening of the lag screw fixation.a
Screws that were placed in the body of the sacrum in some dogs resulted in the fewest loosened fixations (12%, 2 of 17), compared to other locations of screw placement. The fixation had loosened in 7% (1 of 14) of dogs that had a cumulative screw depth/sacral width of 60% or more, compared with 48% of dogs (10 of 21) where cumulative screw depth was less than 60%. The number of screws per fixation and whether the separation was fully reduced or not did not affect whether the fixation loosened.     

Acetabular component orientation as an indicator of implant luxation in cemented total hip arthroplasty

OBJECTIVE: To determine the sensitivity and specificity with which acetabular component angles of inclination and version could be used, alone or in combination, to predict luxation of cemented total hip arthroplasties (THA). STUDY DESIGN: Comparison of retrospectively selected cases and controls SAMPLE POPULATION: All THA performed at the University of Florida between 1991 and 1998 with the BioMedtrix system and for which at least 2 months of radiographic follow-up were available. All THA performed at the University of Georgia with the BioMedtrix system which subsequently luxated. METHODS: Acetabular component inclination angle (IA) and acetabular version angle (VA) were determined for each THA. Data were grouped according to outcome - luxation or no luxation - with the luxated cases from the 2 institutions pooled. Receiver operator characteristic (ROC) analysis was used to evaluate decision rules for using IA and VA as tests for detecting postoperative luxation. Sensitivity and specificity for luxation and 95% confidence bounds were computed with selected values of IA and VA as cut-points. RESULTS: The nonluxation group consisted of 68 THA with a median follow-up time of 5 months (range, 2-60 months). The luxation group consisted of 12 THA with a mean time to luxation of 36 days. The nonluxation group had a mean +/- standard deviation (SD) IA and VA of 40.3 degrees +/- 8.9 degrees and 71.1 +/- 13.6 degrees, respectively, whereas the luxation group had a mean +/- SD IA and VA of 34.7 degrees +/- 12.6 degrees and 72.9 degrees +/- 16.6 degrees, respectively. An IA cut-point of 37.8 degrees achieved 58.3% sensitivity and 57.4% specificity. A VA cut-point of 73 degrees achieved 75.0% sensitivity and 51.5% specificity. IA and VA considered simultaneously achieved a 50.0% sensitivity and 88.2% specificity. CONCLUSIONS AND CLINICAL RELEVANCE: ROC analysis indicated that both IA and VA considered individually or simultaneously were poor indicators of luxation. Although extreme values of IA may predict luxation with high specificity, the potential for luxation cannot be excluded based on apparently appropriate values of IA and VA. The results of this study also indicate that a successful outcome is possible with a wide range of acetabular component positions.     

Ventral abdominal approach for screw fixation of sacroiliac luxation in clinically affected cats

OBJECTIVE: To investigate sacroiliac luxation repair with positional screw insertion from the ventral surface of the sacral wing via a ventral abdominal approach in cats. ANIMALS: 18 European shorthair cats. PROCEDURES: All cats underwent clinical examination including orthopedic and neurologic examination and assessment of lameness and pain before and immediately after surgery and 6 and 16 weeks after surgery. All sacroiliac luxations were stabilized with a single positional 2.4-mm cortical titanium self-tapping screw. The pelvic floor was also repaired in selected cats. Screw entry points and angles determined in a prior study of cadavers were used. Radiographs were taken before surgery and during follow-up evaluations to assess postoperative sacroiliac luxation reduction, implant placement, and repair stability. RESULTS: All implants were placed correctly. Iatrogenic sciatic nerve injuries occurred in 2 cats. Median time to ambulation was 1.5 days for cats with sacroiliac luxation as the sole injury. Radiographic outcome of sacroiliac luxation repair was excellent in 15 of 17 repairs, good in 1 of 17 repairs, and poor in 1 of 17 repairs. Clinical outcome was excellent in 11 of 15 cats and good in 4 of 15 cats. CONCLUSIONS AND CLINICAL RELEVANCE: Insertion of a positional screw across the sacroiliac joint via a ventral abdominal approached can be an alternative to conventional techniques of sacroiliac luxation repair in cats. This novel technique allowed repair of bilateral sacroiliac luxation, repair of pelvic floor fractures, and treatment of soft tissue injuries of the abdominal cavity or abdominal organs with a single approach.     

Long-term outcome of distal femoral osteotomy for treatment of combined distal femoral varus and medial patellar luxation: 12 cases (1999-2004)

OBJECTIVE: To determine long-term outcome of distal femoral osteotomy as a component of treatment for distal femoral varus and medial patellar luxation in large-breed dogs. DESIGN:Retrospective case series. ANIMALS: 12 dogs (16 stifle joints). PROCEDURES: Medical records and radiographs were reviewed to identify large-breed dogs with medial patellar luxation (grade > or = 2) and femoral varus angle > or = 12 degrees treated with distal femoral osteotomy, with a minimum follow-up (by a veterinarian) of 18 months. Signalment, weight, medial patellar luxation and lameness grade, pre- and postoperative femoral varus angle, surgical technique, time to radiographic bone union, and complications were recorded. Follow-up with owners via questionnaire was performed > 18 months after surgery. RESULTS: 16 corrective distal femoral osteotomies were performed with ancillary medial patellar luxation procedures in 12 dogs; 4 dogs had staged bilateral procedures. Mean +/- SD preoperative and postoperative femoral varus angles were 16.3 +/- 4.3 degrees and 3.9 +/- 2.5 degrees , respectively. Mean +/- SD time to radiographic union of the distal femoral osteotomy was 52.6 +/- 13 days. One dog had Kirschner wire migration from the tibial tuberosity. Patellar luxation was not detected after surgery in any dog. Mean +/- SD follow-up by a veterinarian was 1,335 +/- 410 days and by use of an owner questionnaire was 1,497 +/- 464 days. All 10 variables of owner-observed patient comfort and function were significantly improved. CONCLUSIONS AND CLINICAL RELEVANCE: Distal femoral osteotomy in combination with traditional treatment provided predictable osteotomy healing, patellar stabilization, and long-term improvement in patient comfort and function when used to treat combined distal femoral varus and medial patellar luxation in large-breed dogs.     

Surgical treatment of tarsometatarsal joint luxation in a miniature horse foal

A 2-week-old Miniature Horse foal was referred for evaluation and treatment of a luxated right tarsometatarsal joint. Treatment consisted of closed reduction and internal fixation using two partially threaded Steinmann pins placed in normograde fashion through the tuber calcis into the proximal third metatarsus. Traumatic luxation has been reported to occur in the tarsocrural, proximal intertarsal and tarsometatarsal joints within the equine tarsus. Treatment for luxation of the distal intertarsal joint has not been documented. The treatment method most commonly suggested for tarsal luxation is closed reduction and cast immobilisation. Internal fixation using lag screws and plating has also been described. A combination of internal fixation and external coaptation is thought to achieve maximal stability and allow faster convalescence in cases of tarsal luxation. This case report describes for the first time a technique using two Steinmann pins to achieve successful internal fixation of a traumatic tarsometatarsal joint luxation in a 2-week-old Miniature Horse foal.     

Evaluation of risk factors for luxation after total hip replacement in dogs

OBJECTIVE: To identify risk factors for luxation after canine total hip replacement (THR). STUDY DESIGN: Retrospective study. SAMPLE POPULATION: 256 client-owned dogs that underwent THR. METHODS: Patient data surveyed included signalment, body weight, diagnosis, prior hip surgery, implant size, intraoperative complications, and angle of lateral opening of the acetabular component. RESULTS: Postoperative complications were recorded in 20 cases (7.8%). The most common complication was dorsal luxation which occurred in 12 dogs (4.7%). The interval between joint replacement and luxation ranged from 1 to 116 days (mean, 44 days). In 1 case, luxation was attributable to failure of the repair of an intraoperative fracture of the greater trochanter. Excluding this case, the mean angle of lateral opening in those dogs that sustained luxation was 62 degrees (range, 46 degrees - 75 degrees). The mean angle of lateral opening overall was 48 degrees (range, 18 degrees - 76 degrees). The angle of lateral opening was the only factor that had a statistically significant effect on whether luxation occurred (P = .035). Acetabular revision, performed primarily to reduce the angle of lateral opening, was performed in 8 dogs and successfully prevented subsequent luxation. CONCLUSION: Luxation of the prosthesis is substantially under the control of the surgeon. It is recommended that the acetabular cup be inserted at an angle of lateral opening of 35 degrees to 45 degrees. In those cases of THR luxation in which an inappropriate angle of lateral opening is identified, acetabular revision arthroplasty generally results in a good clinical outcome.     

Increased sacral screw purchase minimizes screw loosening in canine triple pelvic osteotomy

OBJECTIVE: To determine if screw loosening in triple pelvic osteotomies (TPO) is minimized when screws cranial to the ilial osteotomy had maximal sacral purchase. STUDY DESIGN: Prospective study. ANIMALS: Forty-six dogs with decreased acetabular coverage of the femoral head and minimal degenerative joint changes. METHODS: TPOs were performed where screws cranial to the ilial osteotomy were inserted to maximally engage sacral bone. Data collected were: use of ilial and ischial cerclage wire, screw length, ventrodorsal radiographic sacral width (most caudal aspect), pelvic canal diameter, and sacral penetration of the 3 cranial screws. On all subsequent radiographs, changes in screw position, pelvic canal diameter, and sacral purchase were noted. RESULTS: For 69 TPOs, 414 screws were used. Mean radiographic cranial screw length was 34.54 mm. Combined sacral depth of all 3 screws was 93.3% of sacral width. All osteotomies healed uneventfully. Twenty-four screws (6%) loosened with 12 being in the most cranial positions. Use of ischial or ilial cerclage wires did not statistically influence screw loosening. Pelvic diameter decreased by a mean of 7.79% from postoperative radiographs to the last radiographic recheck. CONCLUSIONS: By sufficiently engaging the sacrum with screws cranial to the ilial osteotomy, implant failures can be avoided and screw loosening minimized when a 6-hole TPO plate is used. CLINICAL RELEVANCE: To minimize screw-loosening in TPO, screws inserted cranial to the ilial osteotomy should be inserted to maximum sacral depth without penetrating the vertebral canal.     

The Surgical Anatomy of the Canine Sacrum for Lag Screw Fixation of the Sacroiliac Joint

One hundred canine sacral bone specimens were examined to identify surgical landmarks that may improve screw placement in sacroiliac repair. A lateral view of the sacral wing was studied, as this structure is most easily identified in the dorsal approach used for sacroiliac repair. The height and length of each sacral wing were measured. Four other features of the canine sacrum were identified and measured in comparison with the sacral wing height and length. The cranial overlap of the sacral wing over the intervertebral space of L₇-S₁ was found to have a mean of 14% of the length of the sacral wing. The ventral overlap of the sacral wing over the pelvic canal was found to be 21% of the height of the sacral wing. The ventral limit of the spinal canal (dorsal limit of the sacral body) was 45% of the sacral wing height. The first pelvic foramen was located at a mean distance of 64% of the sacral wing length and 20% of the sacral wing height. Using these four features, a composite view of the sacral wing is described to illustrate the area of the sacral body where screw placement is optimal.     

Treadmill study of the range of back movement at the walk in horses without back pain.

OBJECTIVE: To evaluate back movement during walking in horses. ANIMALS: 22 adult horses with no history or signs of back pain. PROCEDURE: 3-dimensional movements of markers on the hooves, head, and back were measured with a motion analysis system while the horses were walking on a treadmill. The positions of markers on the hooves, head, and the skin above the spinous processes of T5, T10, T16, L3, and 2 sacral vertebrae were recorded. From a minimum of 6 walking motion cycles/horse, marker movement and the time of occurrence of minimum and maximum marker positions within the motion cycle were determined. Angles were calculated between the markers on the head, T16, and S4 or S5 and between the markers on T5, T16, and S4 or S5. RESULTS: Lateral back movement was maximal at L3, where it reached (mean +/- SD) 3.5 +/- 0.8% of the horses' height at the withers. Maximum dorsoventral back movement was found at the sacrum, where it reached 4.7 +/- 1.3% of the height at the withers. In the horizontal plane, the angle between T5, T16, and S4 or S5 was altered by 11 +/- 2.5 degrees during the motion cycle. In the sagittal plane, the angle between the head, T16, and S4 or S5 was altered by 7 +/- 3 degrees. CONCLUSIONS AND CLINICAL RELEVANCE: Results of this study may be used as basic kinematic reference data for evaluation of back movement in horses.     

Value of tracheal bifurcation angle measurement as a radiographic sign of left atrial enlargement in dogs

An increased tracheal bifurcation angle on the dorsoventral projection is described as a sign of left atrium enlargement in dogs, with a normal range of 60-90 degrees reported. However in people, this angle is a poor indicator of left atrial size. Our purpose was to evaluate the value of the tracheal bifurcation angle for differentiating normal from enlarged left atrium in dogs. Dorsoventral radiographs and echocardiograms of 33 healthy and 73 dogs with confirmed degenerative myxomatous mitral valve disease were evaluated. Left atrial size was classified according to the echocardiographic left atrium to aorta ratio, as normal, mildly, moderately, or severely enlarged. Independent samples t-tests were used to compare the bifurcation angle between groups. A significant difference was observed between the angle of dogs with normal left atrium (68.1 +/- 8.5 degrees, range: 51.3-92.4 degrees) and dogs with enlarged left atrium (75.8 +/- 8.2 degrees, range: 57.3-91.7 degrees). A significant difference was also noted between the angle of normal dogs and those with moderate (75.5 +/- 6.8 degrees, range: 62.8-88.7 degrees) and severe (80.4 +/- 7.7 degrees, range: 64.7-91.7 degrees) left atrial enlargement, as well as between dogs with mild (70.7 +/- 7.2 degrees, range: 57.3-89.9 degrees) and severe enlargement. Using two discriminators, 85.1 degrees and 76.6 degrees, the bifurcation angle had a specificity of 92.6% and 88.9%, respectively, for identifying left atrial enlargement, and a sensitivity of 15.4% and 40.4%. Although significant differences were observed between dogs with normal and increased left atrial size, the large degree of overlap in the range of bifurcation angles and its poor sensitivity make the measurement of this angle of little value for diagnosing left atrial enlargement.     

Limited open reduction and stabilization of sacroiliac fracture-luxations using fluoroscopically assisted placement of a trans-iliosacral rod in five dogs

Objective— To describe percutaneous fluoroscopically assisted placement of a trans-iliosacral rod to stabilize sacroiliac fracture-luxations after limited open reduction.
Study Design— Retrospective clinical case series.
Animals— Dogs (n=5) with sacroiliac fracture-luxations.
Methods— Medical records and radiographs were reviewed to evaluate implant placement, fracture reduction, pelvic canal diameter ratio, maintenance of reduction, implant stability, assessment of union, and to identify any complications. Owners were contacted to obtain long-term assessment of limb function.
Results— Dogs weighed between 6 and 31 kg. Trans-iliosacral rods were placed correctly traversing the sacral body. Mean (±SD) percent reduction of the sacroiliac joint was 92.9±6.6%. Pelvic canal diameter ratio did not differ significantly between time periods. With the exception of 1 dog, which died in the early postoperative period, all sacroiliac fracture-luxations healed without appreciable complications. Three dogs were sound and 1 dog had a subtle lameness at final physical and radiographic examination (mean±SD: 217±205 days). Owners assessed their dog's limb function (mean±SD: 355±205 days) as good or excellent.
Conclusions— Trans-iliosacral rods can be accurately placed using intraoperative fluoroscopy after limited open reduction of sacroiliac fracture-luxations. Trans-iliosacral rods provided bilateral secure fixation, allowed early weight-bearing and dogs consistently had good long-term clinical results.
Clinical Relevance— Trans-iliosacral rods are suitable implants for the stabilization of sacroiliac fracture-luxations, particularly in dogs with bilateral fracture-luxations and/or concurrent musculoskeletal injuries.     

An in vitro biomechanical comparison of two interlocking-nail systems for fixation of ostectomized equine third metacarpal bones

OBJECTIVE--To compare the mechanical properties of 2 interlocking-nail systems for fixation of ostectomized equine third metacarpi (MC3): (1) a standard interlocking nail with 2 parallel screws proximal and distal to a 1-cm ostectomy; and (2) a modified interlocking nail with 2 screws proximal and distal to a 1-cm ostectomy with the screws offset by 30 degrees. ANIMAL OR SAMPLE POPULATION--Twelve pairs of adult equine forelimbs intact from the midradius distally. METHODS--Twelve pairs of equine MC3 were divided into 2 test groups (6 pairs each): torsion and caudocranial 4-point bending. Standard interlocking nails (6-hole, 13-mm diameter, 230-mm length) were placed in 1 randomly selected bone from each pair. Modified interlocking nails (6-hole, 13-mm, 230-mm length, screw holes offset by 30 degrees) were placed in the contralateral bone from each pair. All bones had 1-cm mid-diaphyseal ostectomies. Six construct pairs were tested in caudocranial 4-point bending to determine stiffness and failure properties. The remaining 6 construct pairs were tested in torsion to determine torsional stiffness and yield load. Mean values for each fixation method were compared using a paired t test within each group. Significance was set at P <.05. RESULTS--Mean (+/-SEM) values for the MC3-standard interlocking-nail composite and the MC3-modified interlocking-nail composite, respectively, in 4-point bending were: composite rigidity, 3,119 +/- 334.5 Nm/rad (newton. meter/radian) and 3,185 +/- 401.2 Nm/rad; yield bending moment, 205.0 +/- 18.46 Nm and 186.7 +/- 6.17 Nm; and failure bending moment, 366.4 +/- 21.82 Nm and 378.1 +/- 20.41 Nm. There were no significant differences in the biomechanical values for bending between the 2 fixation methods. In torsion, mean (+/-SEM) values for the MC3-standard interlocking-nail composite and the MC3-modified interlocking-nail composite were: composite rigidity, 135.5 +/- 7.128 Nm/rad and 112.5 +/- 7.432 Nm/rad; gap stiffness, 207.6 +/- 10.57 Nm/rad and 181.7 +/- 12.89 Nm/rad; and yield load, 123.3 +/- 2.563 Nm and 107.5 +/- 8.353 Nm, respectively. Composite rigidity and gap stiffness for standard interlocking-nail fixations were significantly higher than the modified interlocking-nail fixation technique in torsion. Yield load had a tendency to be higher for the standard interlocking-nail fixation (P =.15). CONCLUSIONS--No significant differences in biomechanical properties were identified between a standard interlocking nail and one with the screw holes offset by 30 degrees in caudocranial 4-point bending. The standard interlocking nail was superior to the modified interlocking nail in torsional gap stiffness and composite rigidity. The torsional yield load also tended to be higher for the standard interlocking nail. CLINICAL RELEVANCE--The standard interlocking nail with parallel screw holes is superior to a modified interlocking nail with the screw holes offset by 30 degrees in ostectomized equine MC3 bones in vitro when tested in torsion.