Biomechanical and computational evaluation of two loading transfer concepts for pancarpal arthrodesis in dogs

Mechanical assessment of two hybrid plate designs for pancarpal canine arthrodesis under cyclic loading

Pancarpal canine arthrodesis (PCA) sets immobilization of all three carpal joints via dorsal plating to result in bony fusion. Whereas the first version of the plate uses a round hole (RH) for the radiocarpal (RC) screw region, its modification into an oval hole (OH) in a later version improves versatility in surgical application. The aim of this study was to mechanically investigate the fatigue life of the PCA plate types implementing these two features-PCA-RH and PCA-OH. Ten PCA-RH and 20 PCA-OH stainless steel (316LVM) plates were assigned to three study groups (n = 10). All plates were pre-bent at 20° and fixed to a canine forelimb model with simulated radius, RC bone and third metacarpal bone. The OH plates were fixed with an RC screw inserted either most proximal (OH-P) or most distal (OH-D). All specimens were cyclically tested at 8 Hz under 320 N loading until failure. Fatigue life outcome measures were cycles to failure and failure mode. Cycles to failure were higher for RH plate fixation (695,264 ± 344,023) versus both OH-P (447,900 ± 176,208) and OH-D (391,822 ± 165,116) plate configurations, being significantly different between RH and OH-D, p = 0.03. No significant difference was detected between OH-P and OH-D configurations, p = 0.09. Despite potential surgical advantages, the shorter fatigue life of the PCA-OH plate design may mitigate its benefits compared to the plate design with a round radiocarpal screw hole. Moreover, the failure risk of plates with an oval hole is increased regardless from the screw position in this hole. Based on these findings, the PCA plate with the current oval radiocarpal screw hole configuration cannot be recommended for clinical use.

Retrospective Comparison of Titanium Hybrid Locking Plate with Stainless Steel Hybrid Dynamic Compression Plate for Pancarpal Arthrodesis: 23 dogs

OBJECTIVE

 The aim of this study was to evaluate outcomes and complications of dogs that had pancarpal arthrodesis (PCA) using a titanium hybrid advanced locking plate system (ALPS) and stainless steel hybrid dynamic compression plate (HDCP).

STUDY DESIGN

 Retrospective observational study.

METHODS

 Medical records (2007-2020) were reviewed for cases that had PCA performed using ALPS or HDCP. Implant characteristics including metacarpal coverage (MCov), metacarpal width occupied by screw diameter percentage and carpal arthrodesis angle (CAA), complications and outcomes were recorded.

RESULTS

 Pancarpal arthrodesis was performed with ALPS on 15 limbs from 12 dogs, and HDCP on 14 limbs from 11dogs. Median follow-up time was 1,157 days (range: 62-1,902 days) for ALPS group and 340 days (range: 43-1,465 days) for HDCP. Median MCov for ALPS group was 74% (range: 60-87.5%) compared with 56.5% (range: 49.7-91.3%) for HDCP (p = 0.001). There was no difference in CAA and metacarpal width to screw diameter percentage between ALPS and HDCP group. Major and minor complications and surgical site infection rates were not statistically different between the two groups. Plate fracture occurred in 2/15 ALPS PCA and screw loosening occurred in 4/14 HDCP PCA. Full function was achieved in 8/12 AND 8/11 OF ALPS AND HDCP: cases, respectively, which was not statistically different (p = 0.76).

CONCLUSION

 The use of ALPS offers comparable performance to HDCP for PCA.

Mechanical Evaluation of Two Hybrid Locking Plate Designs for Canine Pancarpal Arthrodesis

Hybrid locking pancarpal arthrodesis plates were designed with either a round (RH) or an oval (OH) radiocarpal hole, the latter allowing varied screw positioning. Due to concerns about potential decreased structural properties of the OH design, our aim was to compare the mechanical behavior of the contrasting plates using combined finite element analysis (FEA) and mechanical testing. Pancarpal arthrodesis plates with RH or OH design were assigned to three fixation techniques (n = 6), prebent at 20°, and fixed to canine forelimb models with simulated radius and radiocarpal and 3rd metacarpal bones. OH plates were instrumented with a radiocarpal screw inserted either most proximal (OH-P) or most distal (OH-D). Specimens were axially loaded to 300 N over 10 ramped cycles at 0.5 Hz. Plate strains were measured with strain gauges placed at areas of highest deformations as predicted by FEA under identical loading conditions. FEA predicted the highest strains (μm/m) adjacent to the radiocarpal hole (2,500 [RH], 2,900 [OH-P/OH-D]) and plate bending point (2,250 [RH], 1,900 [OH-P/OH-D]). Experimentally, peak radiocarpal hole strains were not influenced by the OH screw position (3,329 ± 443 [OH-P], 3,222 ± 467 [OH-D]; P = 0.550) but were significantly higher compared to the RH design (2,123 ± 154; P < 0.001). Peak strains at the bending point were significantly lower for OH-P (1,792 ± 174) and OH-D (1,806 ± 194) versus RH configurations (2,158 ± 114) (P ≤ 0.006). OH plates demonstrated highest peak strains next to the radiocarpal hole and were associated with more heterogenous plate strain distribution. Structural weakening associated with radiocarpal OH plate design could result in decreased fixation strength and increased risk of plate fatigue failure.

Patient-Specific Bone Multiscale Modelling, Fracture Simulation and Risk Analysis-A Survey

This paper provides a starting point for researchers and practitioners from biology, medicine, physics and engineering who can benefit from an up-to-date literature survey on patient-specific bone fracture modelling, simulation and risk analysis. This survey hints at a framework for devising realistic patient-specific bone fracture simulations. This paper has 18 sections: Section 1 presents the main interested parties; Section 2 explains the organzation of the text; Section 3 motivates further work on patient-specific bone fracture simulation; Section 4 motivates this survey; Section 5 concerns the collection of bibliographical references; Section 6 motivates the physico-mathematical approach to bone fracture; Section 7 presents the modelling of bone as a continuum; Section 8 categorizes the surveyed literature into a continuum mechanics framework; Section 9 concerns the computational modelling of bone geometry; Section 10 concerns the estimation of bone mechanical properties; Section 11 concerns the selection of boundary conditions representative of bone trauma; Section 12 concerns bone fracture simulation; Section 13 presents the multiscale structure of bone; Section 14 concerns the multiscale mathematical modelling of bone; Section 15 concerns the experimental validation of bone fracture simulations; Section 16 concerns bone fracture risk assessment. Lastly, glossaries for symbols, acronyms, and physico-mathematical terms are provided.

Estudo biomecânico comparando a utilização de placas bloqueadas híbridas na artrodese dorsal e medial do carpo de cães

RESUMO Objetivou-se com este trabalho comparar biomecanicamente os posicionamentos dorsal e medial da placa bloqueada na artrodese do carpo em cães. Para isso, foram utilizados sete pares de membros torácicos de cães eutanasiados por razões não relacionadas ao estudo, em que sete membros foram estabilizados com placa dorsal, e seus respectivos pares com placa em posicionamento medial. Os membros com as articulações radiocarpometacarpianas estabilizadas cirurgicamente foram submetidos a ensaio de compressão axial em máquina universal de ensaios de materiais, e os dados de limite de elasticidade, rigidez estrutural, carga máxima e carga no momento da fratura dos posicionamentos foram comparados por meio do teste de Student-Newman-Keuls, a um nível de significância de 5%. Todos os membros foram fraturados no terço distal do terceiro metacarpo; nos membros com placa dorsal, a fratura ocorreu distal ao orifício distal e, nos membros com placa medial, a fratura ocorreu no último orifício dos metacarpos dois e três. Não houve dobra ou quebra de placas e parafusos e não houve diferença significativa entre os posicionamentos dorsal e medial dos implantes quanto aos parâmetros avaliados.