Reunan P. Guillou

Effect of bending direction on the mechanical behaviour of interlocking nail systems

OBJECTIVES To compare the mechanical properties of various interlocking nail constructs in medio-lateral (ML) and cranio-caudal (CC) bending. METHODS Synthetic bone models simulating a severely comminuted tibial fracture were treated with either screwed or bolted, 6 or 8 mm standard interlocking nails (ILN), or an angle-stable ILN (AS-ILN), after which they were then sequentially tested in ML and CC bending. Construct compliance, maximum angular deformation (MaxDef) and slack were statistically compared (p<0.05). RESULTS The compliance of all constructs was significantly greater in CC than in ML bending. However, due to the presence of a greater slack in the ML plane, standard ILN constructs sustained significantly more deformation in that plane. Maximum deformation of the novel AS-ILN constructs was the smallest of all constructs and consistently occurred without slack regardless of bending direction. CLINICAL SIGNIFICANCE This study suggested that standard ILN construct overall deformation and acute instability (slack) may be more critical in ML than in CC bending. Conversely, the small MaxDef and the absence of slack in both bending planes seen in novel angle-stable AS-ILN may provide optimal construct stability and in turn may be more conducive to bone healing.

In vitro evaluation of the effect of fracture configuration on the mechanical properties of standard and novel interlocking nail systems in bending.

OBJECTIVE To investigate the effect of fracture configuration on the mechanical properties of standard interlocking nails (ILNs) and a novel angle-stable ILN (ILNn) in bending. STUDY DESIGN In vitro experimental study. SAMPLE POPULATION Synthetic tibial gap fracture bone models. METHODS Bone models, featuring a 5 or 120 mm central defect, respectively, mimicking a simple diaphyseal and a comminuted fracture involving both metaphyses, were implanted with 6 or 8 mm screwed or bolted standard ILNs (ILN6s, ILN6b, ILN8s, ILN8b, respectively) or an ILNn. Specimens were tested in 4-point bending. Construct angular deformation (AD) and slack were statistically compared (P<.05). RESULTS With increasing gap size, standard ILN construct AD increased significantly by approximately 27% in ILN8b and by up to 105% in ILN6s. Similarly, standard ILN construct slack significantly increased by approximately 33% in ILN8b (from approximately 4.2 degrees to approximately 5.6 degrees) and by up to approximately 130% in ILN6s (from approximately 7 degrees to approximately 16 degrees). Conversely, there was no difference in the ILNn construct AD (approximately 4 degrees) regardless of gap size. ILNn AD was the lowest of all groups and occurred without slack. CONCLUSIONS This study demonstrated that the angle-stable ILNn provided construct stability regardless of fracture configuration, whereas the intrinsic slack of standard ILNs could jeopardize construct stability in a fracture configuration involving the metaphyses. CLINICAL RELEVANCE Use of standard ILNs may be optimal in diaphyseal fractures where circumferential nail/cortical contact could augment repair stability. Conversely, the angle-stable ILNn may represent a reliable fracture stabilization method for diaphyseal fractures as well as fractures involving the metaphyseal regions.

In Vivo Biomechanical Evaluation of a Novel Angle‐Stable Interlocking Nail Design in a Canine Tibial Fracture Model

OBJECTIVE To compare clinical outcome and callus biomechanical properties of a novel angle stable interlocking nail (AS-ILN) and a 6 mm bolted standard ILN (ILN6b) in a canine tibial fracture model. STUDY DESIGN Experimental in vivo study. ANIMALS Purpose-bred hounds (n = 11). METHODS A 5 mm mid-diaphyseal tibial ostectomy was stabilized with an AS-ILN (n = 6) or an ILN6b (n = 5). Orthopedic examinations and radiographs were performed every other week until clinical union (18 weeks). Paired tibiae were tested in torsion until failure. Callus torsional strength and toughness were statistically compared and failure mode described. Total and cortical callus volumes were computed and statistically compared from CT slices of the original ostectomy gap. Statistical significance was set at P < .05 RESULTS: From 4 to 8 weeks, lameness was less pronounced in AS-ILN than ILN6b dogs (P < .05). Clinical union was reached in all AS-ILN dogs by 10 weeks and in 3/5 ILN6b dogs at 18 weeks. Callus mechanical properties were significantly greater in AS-ILN than ILN6b specimens by 77% (failure torque) and 166% (toughness). Failure occurred by acute spiral (control and AS-ILN) or progressive transverse fractures (ILN6b). Cortical callus volume was 111% greater in AS-ILN than ILN6b specimens (P < .05). CONCLUSIONS Earlier functional recovery, callus strength and remodeling suggest that the AS-ILN provides a postoperative biomechanical environment more conducive to bone healing than a comparable standard ILN.

In vitro mechanical evaluation of a limited contact dynamic compression plate and hybrid carpal arthrodesis plate for canine pancarpal arthrodesis

OBJECTIVE To compare the mechanical properties of pancarpal arthrodesis (PCA) constructs stabilized at 20° of extension using either a 3.5 mm limited contact dynamic compression plate (LC-DCP) or a 3.5/2.7 mm hybrid plate (HP). METHODS Seven forelimb pairs were used from dogs of similar size. All soft tissues were removed except for supporting structures of the carpus and proximal metacarpal region. All plates were accurately bent to 20°, and then instrumented with two, 350Ω strain gauges applied at the level of the bend. Constructs were embedded in epoxy moulds then mounted onto a servo-hydraulic testing machine. Specimens were loaded for 10 cycles at 100N, 200N and 300N. Tenth cycle construct compliance (CC), maximum angular deformation (MAD), and peak plate strain (PPS) were compared using two-factor analysis of variance (ANOVA) and Student-Newman-Keuls post-hoc tests (p <0.05). RESULTS Regardless of load, CC was 29% to 33% smaller in the HP than the LC-DCP group (p <0.03). In each group, the CC significantly increased with increasing loads (p <0.02). Mean MAD was 19% to 22% less in HP than LC-DCP constructs, with significant differences seen at 200N and 300N loads. In both groups, MAD was significantly greater with increasing loads (p <0.02). In addition, PPS was 37% to 43% smaller for HP than LC-DCP. CLINICAL SIGNIFICANCE The mechanical advantages of the HP over the LC-DCP make it a viable alternative for PCA. Smaller CC, MAD and PSS of the HP may reduce the risk of implant failure and postoperative morbidity following PCA.

In vitro mechanical evaluation of medial plating for pantarsal arthrodesis in dogs

OBJECTIVE To compare the bending properties of pantarsal arthrodesis constructs involving either a commercially available medial arthrodesis plate (MAP1) or a specially designed second-generation plate (MAP2) implanted in cadaveric canine limbs and evaluate the effect of calcaneotibial screw (CTS) augmentation on the structural properties of both constructs. SAMPLE POPULATION 5 pairs of canine hind limbs. PROCEDURES Within pairs, specimens were stabilized with an MAP1 or MAP2 and loaded to 80% of body weight, with and without CTS augmentation. Compliance, angular deformation (AD), and plate strains were compared. RESULTS Construct compliance and AD did not differ between plates. Maximum plate strain was lower in the MAP2 than in the MAP1 (difference of approx 30%). Augmentation with a CTS reduced compliance, AD, and strains in MAP1 constructs but had no effect on those variables in MAP2 constructs. CONCLUSIONS AND CLINICAL RELEVANCE Because of lower peak strains, the MAP2 may be less susceptible to failure than the MAP1. Furthermore, CTS augmentation was unnecessary with MAP2s, which could minimize intra- and postoperative morbidity. Compared with what is known for dorsal plates, MAP2 constructs were associated with approximately 35% less AD. As a result of improved local stability, one might anticipate earlier fusion of the talocrural joint with an MAP2. In addition, plate peak strain was approximately 3.5 times lower in MAP2s than in dorsal plate constructs, which should result in greater fatigue resistance. The use of MAP2s may be a better alternative to both MAP1s and dorsal plates and could contribute to lower patient morbidity.

Effect of screw insertion torque on mechanical properties of four locking systems.

OBJECTIVE To evaluate the effect of screw insertion torque on the mechanical properties of four 3.5 mm locking systems: New Generation Devices (NGD), Securos (PAX), Synthes (SYN), and Veterinary Orthopedic Implants (VOI). STUDY DESIGN In vitro mechanical study. METHODS Screws were inserted at 1.5 Nm, 2.5 Nm, and 3.5 Nm torques, using dedicated drill guides and a calibrated torque screwdriver. Locking mechanisms were tested under shear loading conditions using a custom-design probe. Tests were conducted under displacement control until failure. Load to failure and interface stiffness were compared between and within groups using a two-factor ANOVA (P < .05). Failure modes were described. RESULTS The SYN group had significantly greater mechanical properties compared to all other groups at any given insertion torque. Insertion torque had a significant effect on the PAX group, increasing the load to failure by 126% when increasing the insertion torque from 1.5 Nm to 3.5 Nm. Insertion torque had no significant effect on the mechanical properties of the VOI group and limited effect on the NGD and SYN groups. Single failure mode, by screw head decoupling or screw shaft fracture, occurred in the SYN and VOI groups, respectively. In contrast, NGD and PAX systems failed through a combination of screw decoupling and/or bending. CONCLUSIONS Regardless of insertion torque, the SYN locking mechanism showed the highest failure loads, interfacial stiffness as well as consistent failure mode. These findings highlight the dependability of this system. When using the PAX system an insertion torque of at least 2.5 Nm should be recommended.

Comparison of open reduction versus minimally invasive surgical approaches on screw position in canine sacroiliac lag-screw fixation

OBJECTIVE To compare accuracy and consistency of sacral screw placement in canine pelves treated for sacroiliac luxation with open reduction and internal fixation (ORIF) or minimally invasive osteosynthesis (MIO) techniques. METHODS Unilateral sacroiliac luxations created experimentally in canine cadavers were stabilized with an iliosacral lag screw applied via ORIF or MIO techniques (n = 10/group). Dorsoventral and craniocaudal screw angles were measured using computed tomography multiplanar reconstructions in transverse and dorsal planes, respectively. Ratios between pilot hole length and sacral width (PL/SW-R) were obtained. Data between groups were compared statistically (p <0.05). RESULTS Mean screw angles (±SD) were greater in ORIF specimens in both transverse (p <0.001) and dorsal planes (p <0.004). Mean PL/SW-R was smaller (p <0.001) in the ORIF group, yet was greater than 60%. While pilot holes exited the first sacral end-plate in three of 10 ORIF specimens, the spinal canal was not violated in either group. CONCLUSIONS This study demonstrates that MIO fixation of canine sacroiliac luxations provides more accurate and consistent sacral screw placement than ORIF. With proper techniques, iatrogenic neurological damage can be avoided with both techniques. The PL /SW-R, which relates to safe screw fixation, also demonstrates that screw penetration of at least 60% of the sacral width is achievable regardless of surgical approach. These findings, along with the limited dissection needed for accurate sacral screw placement, suggest that MIO of sacroiliac luxations is a valid alternative to ORIF.

Minimally invasive lag screw fixation of sacroiliac luxation/fracture using a dedicated novel instrument system: Apparatus and technique description

OBJECTIVE To describe a novel Sacroiliac Luxation Instrument System (SILIS™) and its application in minimally invasive osteosynthesis (MIO) of sacroiliac luxations/fractures (SIL/F). The SILIS was designed to provide stable SIL/F reduction and accurate sacral screw placement while reducing personnel exposure to ionizing radiation during intraoperative fluoroscopy. STUDY DESIGN Descriptive, proof of concept cadaveric study. METHODS A right SIL and a left SIL/F were created on a Labrador Retriever that had died of natural causes. Bilateral sacroiliac lag screw fixation was performed under fluoroscopic guidance with the SILIS, which consists of dedicated reduction and fixation instruments rigidly linked to table-bound 6-axis arms. RESULTS Throughout surgery, the SILIS facilitated and maintained stable reduction and allowed accurate placement of a custom designed drill guide over the sacral body without the surgeons manual holding of any reduction or fixation instruments. The surgical team was therefore able to step away from the C-arm when acquiring fluoroscopic images, thus reducing exposure to radiation. Dorsoventral and craniocaudal screw deviation from an ideal trajectory ranged from 0.9° to 3.8°. Both screws were fully located within the sacral body. CONCLUSION The SILIS addresses limitations associated with MIO of SIL/F, including maintenance of reduction throughout surgery along with reliable and accurate sacral screw placement. Distance from the X-ray source is the most effective protection against radiation. Use of the SILIS allows the surgical team to move away from the C-arm during fluoroscopy, thereby reducing personnel exposure to dangerous direct and back-scattered ionizing radiation.