Biomechanical evaluation of a 4.75-mm and a 5.5-mm bone anchor at two insertion angles using one and two strands of suture.

OBJECTIVE: To compare biomechanical strength of 4.75- and 5.5-mm suture anchors when pulled at 45° or 90° angles using 1 versus 2 strands of suture. SAMPLE: 48 synthetic bone block samples. PROCEDURES: Anchors were inserted into synthetic bone blocks and tested for pullout in 4 configurations (1 suture strand vs 2 strands and 45° vs 90° insertion angle) for a total of 8 groups with 6 samples each. A 3-way ANOVA was used to compare effect of anchor size, strand amount, and angle of pull. RESULTS: All constructs failed via anchor pullout. Anchor configurations with 2 strands of suture and 4.75-mm anchor (mean, 286 ± 24 N) or 5.5-mm anchor (mean, 300 ± 15 N) had greater pullout strength than configurations with only 1 strand of suture and 4.75-mm anchor (mean, 202 ± 12 N) or 5.5-mm anchor (mean, 286 ± 13.6 N). The 5.5-mm anchors had a higher maximum load to failure under axial pull at 45° (mean, 300 ± 15 N) and 90° (mean, 295 ± 24 N), compared with 4.75-mm anchors at 45° (mean, 202 ± 12 N) and 90° (mean, 208 ± 15 N). There was a higher maximum load to failure for the double-stranded constructs, regardless of anchor size, at both angles of insertion. Anchors inserted at 45° had a higher maximum load to failure than those inserted at 90°. Constructs with 2 strands of suture had a greater pullout strength regardless of the direction of pull. CLINICAL RELEVANCE: The strength of the anchor construct is likely increased with the use of double-loaded anchors inserted at 45°. Clinicians should consider using 2 strands in clinical cases.

One-stage revision of an infected cementless total hip replacement.

A two-year-old, 44 kg dog with a right Helica cementless total hip replacement (THR) was radiographically diagnosed with implant loosening eight months after the index total hip replacement procedure. Subsequent synoviocentesis and synovial fluid culture revealed a methicillin-resistant coagulase-negative Staphylococcus spp infection of the right THR. A one-stage revision using a hybrid BFX cementless acetabular cup and CFX cemented femoral stem was performed. Vancomycin and micro-silver antimicrobial powder impregnated cement were used in the revision. At re-evaluation 27 months following the revision procedure, the patient did not exhibit any signs of lameness. Radiographic images confirmed stable implants, with bone ingrowth into the cup and no signs of implant loosening. Our report demonstrates the success of a one-stage THR revision when faced with a multi-drug resistant periprosthetic infection, when combined with the use of micro-silver antimicrobial powder and culture-based antibiotic impregnated cement therapy.

Biomechanical evaluation of polymethyl methacrylate with the addition of various doses of cefazolin, vancomycin, gentamicin, and silver microparticles.

OBJECTIVES: Numerous studies have examined the biomechanics of polymethyl methacrylate (PMMA) with added antibiotics, but direct comparison between studies is difficult. Our purpose was to evaluate the effects of the addition of antibiotic drugs and silver on compressive and bending strength of PMMA. Our null hypothesis was that there would be no significant difference in the compressive strength or bending strength of PMMA with the addition of silver or varying amounts of antibiotic drugs. METHODS: Polymethyl methacrylate was mixed with cefazolin, gentamicin, vancomycin, or silver; the control was PMMA alone. Antibiotic groups contained 20 g PMMA and 0.5 g, 1 g, 2 g, or 3 g of antibiotic. Silver groups had 0.25 g silver powder alone added to 20 g PMMA or silver with PMMA and 0, 0.5 g or 1 g of antibiotic. Samples underwent four-point bending and compression testing in air at room temperature and prevailing humidity. Pairwise comparisons between groups and to the ASTM and ISO standards were performed. RESULTS: Compression: All antibiotic and silver groups were weaker than the control. Samples with cefazolin tended to be stronger than other antibiotic groups with equivalent doses of antibiotic. All groups were above the ASTM standard, except 3 g vancomycin. Four-point bending: The addition of antibiotics did not significantly affect bending strength in groups with lower doses of antibiotics. The silver + PMMA group was weaker than the control. No groups were significantly below the ISO standard except the 3 g vancomycin group. CLINICAL SIGNIFICANCE: The addition of antibiotic or silver decreased the biomechanical strength in all samples, but not below the ASTM or ISO standard for most groups. The addition of cefazolin appears to affect strength the least, while high doses of vancomycin alter strength the most.

Radiographic localization and isometry of the origin and insertion of the canine cranial cruciate ligament.

OBJECTIVE: To radiographically define the anatomic origin and insertion of the cranial cruciate ligament translated to the lateral radiographic projection of the stifle (CrCL-Lo and CrCL-Li, respectively), to correlate these landmarks for identification of the CrCL-Lo intraoperatively, and to compare the isometry of the CrCL-Lo to the lateral fabella. STUDY DESIGN: Experimental study. SAMPLE POPULATION: Pelvic limbs (n = 12) from dogs weighing 13-26 kg. METHODS: A radiographic quadrant method was used to localize the CrCL-Lo. Mediolateral radiographic projections of each stifle were taken through a range of motion. Maximum percent change in length between each tibial marker and femoral marker during range of motion determined isometry. RESULTS: The CrCL-Lo is located at the caudal 33% and distal 50% of the lateral femoral condyle using Blumensaat's line or a line from the origin of the long digital extensor (LDE) to the lateral fabella, with no significant difference (P = .766) between the 2 reference lines. The CrCL-Li is located at the proximal 20% of the tibial plateau. No significant difference (P < .05) in isometry was found between the CrCL-Lo and lateral fabella. CONCLUSION: The CrCL-Lo is located at the caudal 1/3 and distal ½ of the lateral femoral condyle. The CrCL-Lo and lateral fabella are not significantly different in isometry when used as a proximal anchor point in extracapsular stifle stabilization.

Effect of pilot hole diameter and tapping on insertion torque and axial pullout strength of 4.0-mm cancellous bone screws.

OBJECTIVE: To evaluate the effects of pilot hole diameter and tapping on insertion torque and axial pullout strength of 4.0-mm cancellous bone screws in a synthetic canine cancellous bone substitute. SAMPLE: 75 synthetic cancellous bone blocks (15 blocks/group). PROCEDURES: For groups 1 through 5, screw size-pilot hole diameter combinations were 3.5-2.5 mm (cortical screws), 4.0-2.5 mm, 4.0-2.5 mm, 4.0-2.0 mm, and 4.0-2.0 mm, respectively. Holes were tapped in groups 1, 2, and 4 only (tap diameter, 3.5, 4.0, and 4.0 mm, respectively). One 70-mm-long screw was inserted into each block; in a servohydraulic materials testing machine, the screw was extracted (rate, 5 mm/min) until failure. Mean group values of maximum insertion torque, axial pullout strength, yield strength, and stiffness were determined. RESULTS: Mean maximum insertion torque differed significantly among the 5 groups; the group 5 value was greatest, followed by group 3, 4, 2, and 1 values. Group 3, 4, and 5 axial pullout strengths were similar and significantly greater than the group 2 value; all values were significantly greater than that for group 1. Group 5 and 4 yield strengths were similar and significantly greater than the group 3, 2, and 1 values. Stiffness in group 3 was similar to group 4 and 2 values but significantly greater than the group 5 value; all values were significantly greater than that for group 1. CONCLUSIONS AND CLINICAL RELEVANCE: These synthetic cancellous bone model findings suggested that tapping a 2.0-mm-diameter pilot hole when placing a 4.0-mm screw is the optimal insertion technique.

Evaluation of a transcondylar toggle system for stabilization of the cranial cruciate deficient stifle in small dogs and cats.

OBJECTIVE: To evaluate use of a transcondylar toggle system (TCTS) for stabilization of the cranial cruciate ligament (CrCL) deficient stifle in small dogs and cats. STUDY DESIGN: Prospective clinical study. ANIMALS: Small dogs (<7 kg; n=14) and cats (2) with CrCL-associated lameness of <3 months duration and a tibial plateau angle <32 degrees. METHODS: Affected animals had an extracapsular CrCL repair using the TCTS. Lameness score, muscle atrophy, osteoarthritis (OA) score, and range of motion (ROM) were evaluated preoperatively, and at 6 weeks and 7-10 months postoperatively. RESULTS: Operative time was 75 +/- 16 minutes. Fifty-six percent required >1 bone tunnel attempts. One dog required revision at 2 weeks because of suture loosening. All stifles were stable at 6 weeks postoperatively. Fifteen animals were available for follow-up (7-10 months). Lameness improved significantly at 6 weeks (P<.0001), whereas muscle atrophy was worse at 6 weeks (P=.008) but improved at 7-10 months (P<.0001). OA scores were unchanged at 6 weeks (P=.08) but were significantly worse at 7-10 months (P<.0001). ROM remained unchanged at 6 weeks (P=1) and 7-10 months (P=.6). CONCLUSIONS: The medially placed toggle provides a reliable short-term proximal anchor for the extracapsular suture with outcomes similar to other extracapsular techniques. The aiming device and drill bit are not recommended in their current form. CLINICAL RELEVANCE: The TCTS appears to be a well-tolerated technique for proximal suture anchoring in extracapsular CrCL repair in small dogs and cats where instrumentation and anatomic constraints preclude other techniques.

Two techniques for supplementing interlocking nail repair of fractures of the humerus, femur, and tibia: results in 12 dogs and cats.

OBJECTIVE: To describe 2 devices for improving stabilization of inadequately stabilized interlocking nail (ILN) repairs of the humerus, tibia, and femur in dogs and cats. STUDY DESIGN: Prospective study. ANIMALS: Twelve client-owned dogs and cats. METHODS: Two devices to further stabilize ILN repair of inadequately stabilized diaphyseal fractures were developed. Device 1 was an axial extension for the ILN that was connected to a conventional type I external skeletal fixator (ESF) with a short connecting bar. Device 2 had hybrid ILN bolt/ESF pins that were used to lock the ILN and serve as the pins for a type I ESF. Devices were used at the initial surgery when the stability of ILN repair was considered inadequate based on palpable fracture segment movement, insufficient medullary canal filling of the ILN at the fracture site, or when the ILN was used in a buttress mode. Outcome was obtained by recheck examinations, radiography, and telephone interview. RESULTS: Device 1 was applicable to fractures of the humerus and femur, but was not used for fractures of the tibia because the ILN extension would have interfered with the stifle. No gross loosening of the ILN/ESF extension connection to the ILN occurred. Device 2 was easily placed and used in the humerus, femur, and tibia. Device 2 allowed removal of the ILN interlock to one or both main fracture segments non-invasively. Clinically, both devices added stability compared with ILN repair alone. Both devices facilitated controlled destabilization of the fracture repair as healing progressed. Complications of pin tract infection, and premature hybrid bolt/ESF pin loosening resulting in premature ESF removal each occurred in 1 patient. Four of 28 hybrid ILN/ESF pins were grossly loose at 4- or 6-week postoperative recheck examinations. Outcomes were excellent (9), good (1), fair (1), and poor (1). CONCLUSIONS: Inadequately stabilized ILN repair of fractures can be stabilized by use of either device, both of which also permit controlled destabilization of the repair during healing. Device 2 can be used when non-invasive removal of the ILN interlock is desired during healing. CLINICAL RELEVANCE: These 2 devices should be considered as alternative methods for stabilization of inadequately stabilized ILN repairs in dogs and cats, or when controlled destabilization of an ILN fracture repair is desired.