An Anatomical Approach to Lower Extremity Reconstructive Surgery

Orthopaedic surgery of the lower extremity can be approached in several ways, but many times it is divided into soft tissue and boney reconstructive modalities. Orthopaedic sports surgery subspecialists tend to focus on soft tissue reconstruction; often with the goal of restoring as much natural motion as possible. Adult reconstructive orthopaedic surgery subspecialists often focus on boney alignment and use implants to replace degenerated cartilage and bone. There is significant overlap in these subspecialties as both make use of implants to mimic the structure and function of native anatomy to drive stability and motion. This dissertation focuses on the intersection of biomechanics, anatomy, and clinical orthopaedics of these two subspecialties. These areas are addressed through investigation of anatomical variation, muscular architecture, simulator design and construction, and comparative effectiveness via in vitro simulation. Native anatomy directs all functions of the lower extremity via muscle forces, bone, and soft tissue. We demonstrate first that native anatomy is variable and is largely subject specific through a simple case report on bilateral tendinous foramina to serve as an example as one of many variations that can occur with anatomy. Many generalities are made with anatomy in assuming everything looks like a textbook, but in reality surgeons approach and consider each patient’s specific anatomy when performing surgery. This translates over to the basic science research realm where experimental input and methods should subject specific as well in attempts to simulate kinematics of in vivo subjects. Muscle forces are integral to proper kinematics and in vitro simulation. We describe the muscular architecture of the popliteus muscle with physiological cross sectional area (PCSA) and muscle trajectory data. Analysis revealed that females are capable of producing more force in their popliteus muscle in proportion to their semimembranosus muscle than males. In addition, significant differences were found between male and female PCSA. The popliteus muscle trajectory data when combined with muscle force data suggests the popliteus muscle plays a significant dynamic role in knee kinematics. The popliteus has only been studied as a static muscle in prior literature. Our data suggests that treating the popliteus muscle as a dynamic figure in the knee would allow improved simulations focused on native knee kinematics and kinetics. During cruciate retaining total knee arthroplasty (TKA) the posterior cruciate ligament (PCL) is an important structural determinant of motion. The PCL is at risk for damage during surgery as one of the tibial bone cuts is directly oriented towards the tibial PCL attachment. An effectiveness study was performed to examine prevention of iatrogenic PCL injuries using an osteotome in a simulated surgical environment using cadavers. The use of an osteotome was found to have an absolute risk reduction of 50% when compared to the control group which did not use an osteotome to protect the PCL. The use of an osteotome to preserve the PCL during CR TKA by forming a bone island was found to be an effective means of protecting the PCL over standard technique. This method is hypothesized to reduce the incidence of instability and knee joint laxity after CR TKA by maintaining the PCL and therefore kinematic quality. Simulators enable mimicry of clinically relevant maneuvers performed in vivo with expanded potential to perform research considered unethical on living subjects. The creation of 3 separate simulators enabled description of clinically relevant kinematic situations in the knee and ankle. The University of North Texas Health Science Center (UNT HSC) ankle rig was designed to mimic an external rotational stress test of the ankle by an examiner. It allows simultaneous measurement of torque about the ankle, ultrasound imaging, and 3-dimensional motion tracking as a moment is applied to the ankle. This rig was of novel design and allows for controlled static positioning of the ankle with 6 degrees of freedom of control. In addition, it can allow 6 degrees of freedom to occur unconstrained if necessary. The UNT HSC ankle rig was used to stress test syndesmosis fixation using suture-button and internal brace constructs. The other 2 simulators represent a progression of improvement from a basic passive knee rig to a more advanced muscle loading knee rig. The initial simulator loaded the quadriceps and hamstrings through 1 line of action each while allowing the knee to passively flex and extend. The second-generation design was based on the muscle loading rig from The University of Kansas. It uses 3 lines of action to load the quadriceps and 2 lines of action to load the hamstrings with anatomically correct trajectories while allowing the knee to passively flex and extend. These simulators were built to enable in vitro simulations of the knee and ankle to describe kinematic changes from lower extremity reconstructive surgery. Ankle syndesmosis injuries are common and are traditionally treated with simple cortical screw fixation. Newer implants like the suture-button and internal brace seek to restore physiological motion at the syndesmosis by mimicking native structure and function. We used the UNT HSC ankle rig to demonstrate the ability of combinational fixation constructs to restore physiological motion at the syndesmosis. The results indicate a combined suture-button and internal brace construct more closely resembles physiologic ankle syndesmosis kinematics than the suture-button alone. In addition, we described the mechanism through which this occurs. The suture-button or internal brace alone do not adequately restrain motion, but together they do. This is due to the external rotation of the fibula. As the fibula externally rotates it allows the fibula to translate posteriorly more with the suture-button only construct. The internal brace is added to the initial suture-button only construct and restricts external rotation and the resultant vector of restraint from both implants prevents posterolateral directed forces from inducing movement of the fibula. In conclusion, we have described factors effecting physiologic motion through our anatomical variation and muscle architecture data that were applied to in vitro simulations to produce clinically relevant results. These data also show that careful restoration of native anatomical structure can produce more physiological kinematics in the knee and ankle.