Effects of Superior Check Desmotomy on Flexor Tendon and Suspensory Ligament Strain in Equine Cadaver Limbs

OBJECTIVE: To measure the effects of transection of the accessory ligament of the superficial digital flexor (SDF) muscle (superior check desmotomy) on flexor tendon and suspensory ligament (SL) strain in vitro. STUDY DESIGN: In vitro experimental biomechanical investigation. ANIMALS USED: Ten equine cadaver forelimbs. METHODS: The effects of superior check desmotomy were determined using equine cadaver forelimbs secured in a servocontrolled hydraulic testing machine. Strain sensors were used to measure strain on the superficial and deep digital flexor tendons and SL, and a goniometer was used to measure joint angles when the limb was loaded at 890 N and 3,115 N before desmotomy, and at 3,115 N after desmotomy. RESULTS: Superior check desmotomy was associated with significantly increased strains on the SDF tendon and SL, and significant alterations in the angles of the metacarpophalangeal and carpal joints. CONCLUSIONS: The superior check ligament has an important role in maintaining joint angles and load distribution in the forelimb. Lengthening of the SDF musculotendinous unit after superior check desmotomy may be associated with increased strain on the SL. CLINICAL RELEVANCE: Transection of the accessory ligament of the SDF muscle may predispose horses to SL desmitis postoperatively.     

In Vitro Performance Testing of Two Arcuate Oscillating Saw Blades Designed for Use During Tibial Plateau Leveling Osteotomy

Objective: To test the cutting performance of 2 commercially available oscillating saws designed for use during tibial plateau leveling osteotomy (TPLO) and to evaluate the influence of saline irrigation on cutting performance. Study Design: In vitro experimental study. Sample Population: Composite polyurethane test blocks (n=40); 24 mm TPLO saw blades. Methods: Controlled force cutting tests were performed using custom‐made laminated bone substitute blocks to model the canine proximal tibia. Half of the trials were irrigated with 0.9% saline solution. Outcome measures were test block temperature (measured 1.5 mm from the cutting zone), cutting rate, and cutting surface wear. Durability was measured by recording change in performance over multiple consecutive trials. Results: The Synthes blade cut the test blocks with ～64% less heat generation and at a 63% faster cutting rate compared with the Slocum blade. Although wear of the Synthes blade was ～50% greater after 19 uses, this did not negatively impact cutting performance. Saline irrigation produced no significant effect on peak cutting temperature but significantly reduced cutting rate for both saws. Conclusions: Our results favor the Synthes blade in terms of cutting performance and the Slocum blade in terms of wear resistance.     

In vitro Comparison of Secure Aberdeen and Square Knots with Plasma‐ and Fat‐Coated Polydioxanone

Objective: To determine (1) the minimum number of throws to form secure Aberdeen (AB) and square knots to start (SS) and end (SE) continuous patterns, in fat‐ and plasma‐coated polydioxanone; and (2) compare relative knot security (RKS) and knot volumes of these secure SS, SE, and AB knots. Study Design: In vitro experimental materials testing. Sample Population: Polydioxanone suture material (3 metric). Methods: Each knot was tested 20 times, and throws incrementally added until secure SS, SE, and AB knots were found. RKS and knot volumes were calculated for SS, SE, and AB knots. Results: Secure SE knots needed 5 throws in plasma or fat. Secure SS knots needed 4 throws in plasma, but 5 in fat. The minimum AB configuration that was secure in plasma or fat was 3+1, however, the 4+1 AB knot was also secure in fat. Mean (SD) RKS of secure knots were: SE 59.69% (5.91), SS 67.92% (12.50), AB 81.08% (8.99). AB knots had significantly higher mean RKS than any SS or SE knot in plasma or fat (P<.001). Mean knot volume of 3+1 AB knot was significantly smaller than any secure SS or SE knots by 22.6–69.4% (P<.0001). Mean knot volume of 4+1 AB knots was significantly smaller than all fat secure SS and SE knots by 19.9–57.5% (P=.0001). Conclusion: The knot security of the SS knot was decreased by fat coating polydioxanone suture, requiring an additional throw to keep it secure. Secure AB knots had a higher breaking strength and smaller knot volume than secure SS and SE knots. Clinical Relevance: The AB may be preferable to square knots in continuous closures. As many body fluids contain lipid, surgeons should tie knot configurations considered secure in fat. We advise tying a 4+1 AB and placing a minimum of 5 throws to tie SS and SE knots using 3 metric polydioxanone.     

Comparison of Multistage Versus One-Stage Destabilization of a Type II External Fixator Used to Stabilize an Oblique Tibial Osteotomy in Dogs

OBJECTIVE: To compare the biomechanical effects of multistage versus one-stage destabilization of a type II external skeletal fixator (ESF) used to stabilize an oblique unstable tibial osteotomy in dogs. STUDY DESIGN: In vitro, in vivo, and ex vivo experimental study. ANIMAL POPULATION: Twelve healthy adult dogs. METHODS: The biomechanical characteristics of the type II ESF used in this study were determined. This fixator was applied to both tibiae of two groups of 6 dogs to stabilize a 2-mm-wide oblique osteotomy. One fixator on each dog remained unchanged throughout the 11-week study (control group). The fixator on the opposite limb was destabilized late and acutely in one group of dogs (single-stage) and early and progressively in the other (multistage). Clinical examination, radiographic examination, and force-plate analysis were used to evaluate the results. All dogs were euthanatized at 11 weeks. All tibiae were scanned to determine the cross-sectional area of the callus in the center of the osteotomy and subjected to biomechanical tests to determine mean pull-out strength of pins and callus strength and stiffness. RESULTS: Stiffness of the type II ESF used in this study was 578 N/mm in axial compression, 0.767 Nm/deg in torsion, 261 N/mm in medio-lateral bending, and 25 N/mm in cranio-caudal bending. Peak vertical forces of the hindlimbs were significantly lower at 2.5 and 5 weeks than before surgery. Peak vertical forces of the hindlimbs did not change before and after destabilization. No significant differences could be detected between the two destabilization sequences or between all control tibiae and pooled destabilized tibiae with regards to radiographic evaluation of the healing osteotomy, cross-sectional periosteal callus area, mean pull-out strength of transfixation pins, callus strength, and callus stiffness. CONCLUSIONS AND CLINICAL RELEVANCE: Bone healing of unstable osteotomies stabilized with a type II ESF is not significantly enhanced by staged destabilization of the fixation as performed in this study.