Comparison of the mechanical characteristics of polymerized caprolactam and monofilament nylon loops constructed in parallel strands or as braided ropes versus cranial cruciate ligaments of cattle

Mechanical properties of animal ligaments: a review and comparative study for the identification of the most suitable human ligament surrogates

The interest in the properties of animal soft tissues is often related to the desire to find an animal model to replace human counterparts due to the unsteady availability of human tissues for experimental purposes. Once the most appropriate animal model is identified, it is possible to carry out ex-vivo and in-vivo studies for the repair of ligamentous tissues and performance testing of replacement and support healing devices. This work aims to present a systematic review of the mechanical properties of ligaments reported in the scientific literature by considering different anatomical regions in humans and several animal species. This study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) method. Moreover, considering the lack of a standard protocol for preconditioning of tissues, this aspect is also addressed. Ninety-six studies were selected for the systematic review and analysed. The mechanical properties of different animal species are reported and summarised in tables. Only results from studies reporting the strain rate parameter were considered for comparison with human ligaments, as they were deemed more reliable. Elastic modulus, ultimate tensile stress, and ultimate strain properties are graphically reported identifying the range of values for each animal species and to facilitate comparison between values reported in the scientific literature in animal and human ligaments. Useful similarities between the mechanical properties of swine, cow, and rat and human ligaments have been found.

Biomechanical evaluation of bovine stifles stabilized with an innovative braided superelastic nitinol prosthesis after transection of the cranial cruciate ligament

OBJECTIVE

To determine the stability bovine stifles stabilized with nylon or nitinol superelastic prostheses after transection of the cranial cruciate ligament (CCL).

STUDY DESIGN

Ex vivo study.

SAMPLE POPULATION

Stifles (n = 15) harvested from adult bovine cadavers.

METHODS

The stifles were randomly assigned pairwise to a ligament reconstruction technique (n = 5): (1) and (2) Hamilton's technique using a prosthesis made of 24 nitinol strands (0.39 mm) braided at 40°or single 600-lb test nylon implant, and (3) nitinol prosthesis placed in femoral and tibial bone tunnels (bone-to-bone). Craniocaudal tibial translation at ±2000 N was applied to the tibia, and mediolateral angular displacement via measured under torsional tibial loading at ±60 Nm on three occasions: intact CCL, transected, and stabilized. Outcomes were evaluated with a mixed effect linear model for repeated measures.

RESULTS

Bone-to-bone using nitinol was the only repair that decreased tibial translation after CCL transection (p = .001) with a 23% change magnitude compared with intact CCL. Hamilton was the only stabilization reestablishing angular displacement, similar to intact CCL (p = .109 and .134 for nitinol and nylon). Bone-to-bone nitinol stabilization decreased angular displacement after CCL-transection with an 8% change magnitude (p = .040) without returning to normal values.

CONCLUSION

CCL replacement with nylon did restore joint stability. Nitinol prostheses passed through single femoral and tibial bone tunnels (bone-to-bone) were the only techniques reducing tibial translation.

CLINICAL SIGNIFICANCE/IMPACT

Bone-to-bone stabilization with a nitinol prosthesis may be considered as an alternative to nylon for CCL replacement in cattle. These results provide evidence to justify clinical evaluation in cattle undergoing CCL replacement.

Change in Collagen Fibril Diameter Distribution of Bovine Anterior Cruciate Ligament upon Injury Can Be Mimicked in a Nanostructured Scaffold

More than 200,000 people are suffering from Anterior Cruciate Ligament (ACL) related injuries each year in the US. There is an unmet clinical demand for improving biological attachment between grafts and the host tissue in addition to providing mechanical support. For biological graft integration, it is important to provide a physiologically feasible environment for the host cells to enable them to perform their duties. However, behavior of cells during ACL healing and the mechanism of ACL healing is not fully understood partly due to the absence of appropriate environment to test cell behavior both in vitro and in vivo. This study aims at (i) investigating the change in fibril diameter of bovine ACL tissue upon injury and (ii) fabricating nanofiber-based scaffolds to represent the morphology and structure of healthy and injured ACL tissues. We hypothesized that distribution and mean diameter of ACL fibrils will be altered upon injury. Findings revealed that the collagen fibril diameter distribution of bovine ACL changed from bimodal to unimodal upon injury with subsequent decrease in mean diameter. Polycaprolactone (PCL) scaffold fiber diameter distribution exhibited similar bimodal and unimodal distribution behavior to qualitatively represent the cases of healthy and injured ACL, respectively. The native ACL tissue demonstrated comparable modulus values only with the aligned bimodal PCL scaffolds. There was significant difference between mechanical properties of aligned bimodal and unaligned unimodal PCL scaffolds. We believe that the results obtained from measurements of diameter of collagen fibrils of native bovine ACL tissue can serve as a benchmark for scaffold design.

Investigation of a novel prosthesis technique for extracapsular stabilization of cranial cruciate ligament-deficient stifle joints in adult cattle

OBJECTIVE

To evaluate a novel prosthesis technique for extracapsular stabilization of cranial cruciate ligament (CCL)-deficient stifle joints in adult cattle.

SAMPLE

13 cadaveric bovine stifle joint specimens.

PROCEDURES

In the first of 3 study phases, the most isometric points on the distal aspect of the femur (distal femur) and proximal aspect of the tibia (proximal tibia) were determined from measurements obtained from lateromedial radiographs of a stifle joint specimen maintained at angles of 135°, 90°, 65°, and 35°. During phase 2, 800-lb-test monofilament nylon leader line was cut into 73-cm-long segments. Each segment was secured in a loop by use of 2, 3, or 4 crimping sleeves such that there were 12 replicates for each construct. Each loop was distracted to failure at a constant rate of 1 mm/s. Mean force at failure and elongation and mode of failure were compared among the 3 constructs. During phase 3, bone tunnels were created in the distal femur and proximal tibia at the isometric points identified during phase 1 in each of 12 CCL-deficient stifle joint specimens. The 3-sleeve construct was applied to each specimen. Specimens were distracted to failure at a constant rate of 1 mm/s.

RESULTS

Among the 3 constructs evaluated, the 3-sleeve construct was considered optimal in terms of strength and amount of foreign material. In phase 3, all replicates failed because of suture slippage.

CONCLUSIONS AND CLINICAL RELEVANCE

Use of 800-lb-test monofilament nylon leader line as a prosthesis might be a viable alternative for extracapsular stabilization of CCL-deficient stifle joints in adult cattle. Further in vivo studies are necessary.

Quasi-static tensile properties of the Cranial Cruciate Ligament (CrCL) in adult cattle: towards the design of a prosthetic CrCL

Mechanical properties of the Cranial Cruciate Ligament (CrCL) in adult cattle are not well documented and protocols used in the literature focus on testing a full femur-CrCL-tibia complex rather than an isolated CrCL. The aim of this study was to assess a wider range of tensile properties of the CrCL along its anatomic axis with experimental measurements of the global elongation, displacement and strain fields, in order to provide guidelines for the design of CrCL prosthetic surrogates. Fourteen bovine CrCL were harvested from seven mature cows (5.1 ± 1.3 years) weighing 631 ± 90kg. The mean CrCL length was 41.4 ± 1.5mm and its mean cross-section was 103.9 ± 23.8mm². Pre-conditioning was achieved with 30 cycles of loading from 30 to 200N at a strain rate of 0.02s^-1. Specimens were then loaded to failure at the same strain rate. The following results were obtained: the mean ultimate tensile load (UTL) 4372 ± 1485N and the median [quartiles] maximal global elongation 19.3 [17.8; 21.4] %. At first physical signs of tearing, the mean load was 3315 ± 1336N and mean elongation 13.5 ± 4.9%. The mean absorbed energy at failure was 5.23 ± 2.08 MJ.mm^-3 and the mean stiffness at various levels of elongation was: 220 ± 195N.%^-1 (5%), 285 ± 162N.%^-1 (10%), 239 ± 200N.%^-1 (15%), 146 ± 59N.%^-1 (20%), 153 ± 136N.%^-1 (25%). None of these properties were related to the bovine weight, age and side of the body (p > 0.05). An ideal prosthetic surrogate should then follow these sets of properties and the experimental data suggest that the in-vivo maximal elongation is below 13.5%.

Mechanical comparison of cortical screw fixation versus locking plate fixation in first metatarsal base osteotomy

The oblique closing base wedge osteotomy has been used for surgical treatment of moderate to severe hallux valgus deformities with an intermetatarsal angle typically greater than 15°. Several postoperative complications have been identified that relate to failure of the fixation construct used to fixate the osteotomy, especially when that construct has been subjected to a vertical load. We performed a mechanical analysis comparing 2 constructs used to fixate oblique osteotomies of the first metatarsal using composite first metatarsals. An oblique base osteotomy was uniformly performed on 40 composite first metatarsals. Of the 40 specimens, 20 were fixated with a locking plate construct and 18 with a cortical screw construct, consisting of an anchor and compression screw (2 specimens from the latter group were excluded because of hinge fracture). Each specimen was loaded in a materials testing machine to measure the maximum load at construct failure when a vertical force was applied to the plantar aspect of the metatarsal head. The mean load to failure for the locking plate construct was significantly greater than the cortical screw construct (190.0 ± 70 N versus 110.3 ± 20.3 N, p < .001). Our study results have demonstrated that the locking plate construct was able to withstand a significantly greater vertical load before failure than was the 2-cortical screw construct in oblique osteotomies performed at the base of composite first metatarsals.