Planned Redundancy
In scientific systems, systems in business, and, in fact, systems of all kinds, a single point of failure (SPOF) refers to a component or any element within a system, that has the potential to lead to a failure of the entire system if it fails (referred to as a catastrophic failure). The principle of avoiding a SPOF is not specific to surgical procedures and applies to many systems within the realm of science as well as throughout the world.
SPOFs are undesirable to systems that demand high availability and reliability, such as supply chains, software applications, networks, architectural designs, and even surgical procedures. A SPOF is essentially a flaw in the design, configuration or implementation of a system, or any component of a system, which poses a potential risk because one malfunction or fault could cause the entire system to stop working. SPOFs are similar to the weakest link in a chain, where the failure of that link can threaten the integrity of the entire chain. Systems that must be highly reliable should never rely on single components.
Failure of the structural integrity of a surgical repair during the early stages of healing following surgery would be considered a catastrophic failure. NAHAH’s MFLS surgical services safeguard the strength, durability, and structural integrity of the surgical repair through planned redundancy. Adding redundant components to the surgery at various levels by design avoids potentially catastrophic SPOF within the surgical procedure.
On a primary level, planned redundancy is accomplished through load distribution. Just as the two bands comprising the cranial cruciate ligament (CrCL) originally did, by utilizing two separate primary prostheses, which are implanted along two separate load distribution pathways, this advantageously divides the overall load being carried by the stifle joint into halves. Each prosthesis then distributes and carries its share of the load (each as one of two lesser loads), and this division and separation of load distribution avoids having an SPOF that would exist if one hundred percent of the load were carried by just one prosthesis.
On a secondary level, planned redundancy is accomplished through load sharing. More redundant components are added to the surgical procedure by utilizing multiple nylon filaments within each of the two primary prostheses. Rather than using a single larger prosthesis, using multiple nylon filaments of substantial combined material strength allows for load sharing among these secondary prosthetic filaments. By creating redundancy and sharing the load in this manner, if any one of these prosthetic filaments should slacken, loosen, or break, the other remaining prosthetic filaments are there to assume and carry the load. This once again adds redundant components to the surgical procedure, this time on a secondary level within each of the two primary prostheses (and along each primary loading pathway), and avoids any SPOF. This redundancy further safeguards the structural integrity and durability of the surgical repair.
Other extracapsular procedures utilize a single implanted prosthesis (typically a single filament) to re-establish the union or connection between the tibia and the femur and are intended to provide the stability previously furnished by the cranial cruciate ligament (CrCL). Lateral suture surgery has been used in the veterinary profession for over 60 years, and to this day is still considered to be a viable option for CrCL surgical repair in smaller dogs (typically less than 30 pounds). Tightrope surgery also requires implanting a single piece of material or filament (usually a braided material, which may be more susceptible to infection). Compared to osteotomy surgeries, both of these extracapsular surgical procedures are thought not to be strong and durable enough to hold up over time and may result in stifle instability, particularly in larger dogs.
These other extracapsular surgical procedures implant a single prosthesis (filament) along a single loading pathway, and that loading pathway then carries one hundred percent of the load (weight and force) coming to bear on the stifle joint. Resultantly, these surgical procedures lack planned redundancy and inherently have a potentially catastrophic flaw in having this single point of failure. For these other extracapsular surgical procedures, this means if the single prosthesis (filament) carrying one hundred percent of the load should slacken, loosen, or break, the stifle becomes unstable once again and the surgery will then have failed.
The most straightforward way to remove a SPOF from any system is considered to be by adding redundant components to the system. Then if one component fails, the other one(s) can take over. Generally, the more redundant components a system has, the more resilient and reliable it will ultimately be. That is why auditing for single points of failure in a system is considered essential for making the system more robust and reliable. Identifying single points of failure allows for adding redundancy at different levels where a SPOF may exist.
NAHAH’s MFLS surgical services maximize the structural integrity of the repair by using the original cranial cruciate ligament as its model or template. The cranial cruciate ligament is comprised of two bands (craniomedial and caudolateral) that attach the tibia to the femur and divide and distribute the load on the stifle joint. These two bands also biomechanically provide constant and consistent isometric tension throughout the entire range of motion of the stifle joint. In a similar fashion, MFLS surgery utilizes two prostheses (each comprised of multiple nylon filaments) which are implanted along two separate load distribution pathways (craniomedial and caudolateral pathways) which re-establish the union or connection between the tibia and the femur restoring stifle joint stability and duplicating the function previously furnished by the cranial cruciate ligament (CrCL).
By dividing the total load on the stifle joint and distributing that load between two separate prostheses, the surgery incorporates planned redundancy, thereby avoiding a SPOF and, in the process, halving and minimizing the load on each pathway. By distributing the load between the two prostheses—implanted along craniomedial (upper) and caudolateral (lower) pathways as was originally provided by the CrCL—the union or connection between the tibia and the femur is re-established in a manner that restores both natural load distribution and natural stifle biomechanics, providing constant and consistent isometric tension through the stifle joint’s entire range of motion, and effectively duplicating the role and function of the original cranial cruciate ligament.
In this way, natural, authentic, and evolved stifle biomechanics are re-established, resulting in a biomechanically normal joint. Dividing the load on the two primary prostheses implanted along these two separate load distribution pathways not only duplicates(or closely approximates) the function and load distribution of the original cranial cruciate ligament, it effectively creates and incorporates redundant components into the surgical repair that make the surgical repair more robust and reliable by requiring that multiple points of failure must occur before the surgical repair itself and as a whole can fail.
The conclusion of a 2023 research article attempting to establish a three-dimensional (3D) model to identify the isometric component of the cranial cruciate ligament (CrCL) in dogs entitled, “Determination of Isometric Points in the Stifle of a Dog Using a 3D Model” identified two key findings that support and authenticate the science behind NAHAH’s MFLS surgical services. The study’s authors stated:
“it is possible that two prostheses are required to restore normal stifle biomechanics”
“the optimal configuration of an extracapsular prosthesis, based on suture tension, was shown to be between the lateral fabella and a pair of bone tunnels located in the proximal tibial crest”
These two key findings corroborate the science and theory embodied and strategically incorporated in the surgery and validate the scientific principles behind it. These findings and conclusions not only support and directly correlate with the theory and science behind the surgery, but without knowing anything about the surgery, the authors’ statements describe the most crucial and essential technical aspects of the surgical procedure, further validating its methodology and scientific principles.
Echoing the primary stated goal of NAHAH’s MFLS surgical services, the authors state: “The objective of surgical management of ruptured cranial cruciate ligament (CrCL) is to reestablish a biomechanically normal joint with the resultant return to full function.” While the CrCL in the dog is assumed to be overall isometric, as in other species, specific isometric points within the origin and insertion of the ligament have not been identified. This study aimed to develop a three-dimensional (3D) model to identify the isometric component of the CrCL in dogs and to identify any additional isometric regions of the stifle.