Gorgonian corals commonly occur in great numbers and diversity inthe Caribbean, east Pacific and Indo-Pacific. Previous natural pro­duct investigations of Caribbean gorgonians have yielded a plethora of structurally and biologically unique compounds. These include diter­penes, sesquiterpenes, sterols and prostaglandins. Prior to this inves­tigation, very little was known about the natural products composition of the east Pacific Gorgonacea. This dissertation reports the isolation and structure elucidation of twenty-seven natural products from fifteen species of east Pacific gorgonians. Twenty of the compounds described are new and seven were previously known from other marine and terres­trial sources. The gorgonians studied were collected off the coast of southern California and Pacific Mexico, and in the Gulf of California. The structures of all of the compounds were elucidated by combined chem­ical and spectroscopic methods.

Examination of the extracts of four Lophogorgia species resulted in the isolation of a new neuromuscular toxin, lophotoxin, and six related furanocembrenolide compounds. Lophotoxin acts specifically and irreversibly at low concentrations to block indirect nerve stimulated muscle contraction. One of the Lophogorgia species studied, L. alba, also contained three new 1,4-diketone cembrenolides.

Eugorgia forreri, collected in the Gulf of California, possessed two cembrane-diterpenes which were previously isolated from a soft coral collected in Canton Atoll.

An investigation of the natural products composition of five Pacifigorgia species yielded seven sesquiterpene-derived metabolites. Six of the seven compounds possessed familiar germacrane, cadinane and guaiane ring systems. The remaining sesquiterpene contained a novel linear carbon skeleton.

Extracts of two Mexican Muricea species, M. fungifera and M. austera, contained three known germacrane derivatives, which had previ­ously been isolated from a terrestrial plant.

A comparative natural products investigation of two local Muri­ species yielded the known sterol, ergosterol peroxide, from both Muricea californica and Muricea fruticosa. In addition, only the less fouled Muricea fruticosa contained four new esterified aminosugar sapo­nin derivatives. These compounds inhibit the growth of the marine diatom, Phaedactylum tricornutum, at concentrations comparable to those found in the gorgonian tissue. This result may indicate possible roles for these compounds in preferentially reducing fouling on the surfaces of Muricea fruticosa.

Background: One of the primary goals of total knee replacement is to restore native knee function. Tibiofemoral kinematics provides an objective measure of knee function and have been used to characterize and compare knee function among native (i.e., healthy), replaced, osteoarthritic, and anterior cruciate ligament (ACL) deficient knees. Tibiofemoral kinematics specifically refers to the relative rigid body motions of the tibia with respect to the femur in all six degrees of freedom. Quantification of clinically meaningful tibiofemoral kinematics requires a joint coordinate system where motions are free from kinematic crosstalk errors. One common method to determine tibiofemoral kinematics is to capture single-plane fluoroscopic images of a patient activity and determine the relative position and orientation of the tibia with respect to the femur. This method involves the use of 3D model-to-2D image registration in which projections of 3D models of the native knee (or replaced knee) are fitted to the silhouette of their respective components in the image. The most common software used to perform this registration is JointTrack, of which there are two different versions (JointTrack Manual and JointTrack Auto). Because the precisions of the two different JointTrack programs are unknown, the first objective was to determine the overall precision of both programs in determining the AP positions of the femoral condyles for an example set of TKR components. The rationale behind using the AP Positions as the primary dependent variable is that it is one of the most common variables used to determine tibiofemoral kinematics in the literature and uses a method (lowest point) that has been validated by many research groups. Furthermore, the TKR knee was analyzed because JointTrack was specifically designed to perform image registration with the replaced knee. While the AP positions of the femoral condyles provide information about tibiofemoral kinematics in primarily one degree of freedom (internal tibial rotation), there are still relative motions in four degrees of freedom other than flexion that need to be determined. As previously stated, quantification of clinically meaningful tibiofemoral kinematics requires a joint coordinate system (JCS) where motions are free from kinematic crosstalk errors. For the JCS to be free of kinematic crosstalk errors, two key requirements are that the body-fixed flexion-extension (F-E) and internal-external rotation (I-E) axes must coincide with the functional axes and that the femoral and tibial Cartesian coordinate system origins must lie on the functional axes. However, the International Society of Biomechanics (ISB) recommends the joint coordinate system (JCS) described by Grood and Suntay, where the axes are not functional and is therefore subject to kinematic crosstalk errors. However, these errors are unknown. Therefore, the second objective of this study was to determine whether a JCS constructed using functional body-fixed axes (termed FUNC JCS) reduced kinematic crosstalk errors compared to the ISB JCS. As these JCSs were constructed for the native knee, this investigation was done in the native knee using JointTrack Manual per the information gathered from the first chapter of this thesis (Appendix A). Methods: For the first study on JointTrack precision, fluoroscopic images of 16 patients who performed a weighted deep knee bend following TKR were analyzed. JointTrack Manual and JointTrack Auto were used to perform 3D model-to-2D image registration and determine the absolute positions and orientations of the femoral and tibial components in each image. The AP positions of the femoral condyles were determined using the lowest point method. Precision was found by performing image registration 3 times for each patient and computing the variability in the AP positions measured for each trial. Intraclass correlation coefficients (ICCs) were also determined for both JointTrack programs. As the native knee requires the use of JointTrack Manual (due to degraded image and 3D model quality), further analysis was performed to inform the methods of the second study (Appendix A). In the second study, fluoroscopic images of native knees in 13 subjects performing a deep knee bend were analyzed. JointTrack Manual was used to perform 3D model-to-2D image registration and determine the absolute positions and orientations of the femoral and tibial components in each image. Relative rigid body motions of the tibia with respect to the femur in all six degrees of freedom were calculated for both the ISB JCS and the FUNC JCS using a Cardan angle sequence and corresponding transformation matrix. Results: Overall precision for the JointTrack Manual program was 3 times worse than the JointTrack Auto program for both medial and lateral AP positions of the femoral condyle (0.97 mm and 0.91 mm versus 0.34 mm and 0.38 mm, respectively; p < 0.0001 for both). ICC values for the Auto program indicated good to excellent agreement (range: 0.82 – 0.98); whereas ICC values for the Manual program indicated only moderate to good agreement (range: 0.58 – 0.82). Precision using JointTrack Manual was significantly improved for determining the medial and lateral AP positions when performing three trials and taking the average of the three trials (0.58 and 0.70 mm, respectively; p = 0.0001 for medial and p = 0.0288 for lateral). Results for the second study show that tibiofemoral kinematics using the FUNC JCS fell within the physiological range of motion in all five degrees of freedom excluding flexion-extension. Internal rotation of the tibia with respect to the femur averaged 13° for the FUNC JCS versus 10° for the ISB JCS and motions in the other four degrees of freedom (collectively termed off-axis motions) were minimal as expected based on biomechanical constraints. In contrast, off-axis motions for the ISB JCS were significantly greater; maximum valgus rotation was 4°, maximum anterior translation was 9 mm, and maximum distraction translation was 25 mm, which is not physiologic. Discussion: It is not surprising that JointTrack Auto has better precision and reproducibility as indicated by higher interobserver ICCs than JointTrack Manual for measuring the tibiofemoral kinematics of the TKR knee. JointTrack Manual requires considerably more operator intervention and considerably more time to perform image registration than JointTrack Auto. Therefore, the use of Auto over Manual is strongly recommended. However, if JointTrack Manual must be used, which is necessary for 3D models developed from image segmentation, then it is recommended to perform Manual image registration 3 times and take the average of the 3 trials for better precision. For the second study, the FUNC JCS achieved clinically meaningful kinematics by significantly reducing kinematic crosstalk errors compared to the ISB JCS and is the more suitable coordinate system. Moving forward, the ISB is well advised to update their recommendation, which was published 20 years ago, so that the updated recommendation reflects the latest knowledge.

Background: Restoring function to that of the native knee without ligament release is a goal of unrestricted kinematic alignment (KA) total knee arthroplasty (TKA). Focusing on the tibial component, two design variables that affect knee function are retention versus resection of the posterior cruciate ligament (PCL) and conformity of the medial and lateral articular surfaces to the respective condyles of the femoral component. Therefore, it is of interest to determine the effects of PCL retention versus resection and the degree of medial conformity of the tibial insert in restoring kinematics to that of the native knee after KA TKA in three different exercises of daily living and their effects on patient reported outcome scores. En route to this objective, it also was of interest to determine causes of posterior edge loading in the lateral compartment for one of the insert designs that had a high incidence.Methods: Four cohorts of patients were involved. One cohort had a TKA featuring a tibial insert with high medial conformity (ball-in-socket medial conformity) that resected the PCL (B-in-S MC-PCL). The second had an insert with less medial conformity (termed intermediate medial conformity) which retained the PCL (I MC+PCL). The third had an intermediate medial conformity that retained the PCL (I MC+PCL) and contralateral knee had an insert with ball-in-socket medial conformity that retained the PCL (B-in-S MC+PCL). The last cohort included patients with a healthy knee. Single-plane fluoroscopy captured tibiofemoral images while patients performed weighted deep knee bend, step-up, and chair rise exercises. 3D model-to-2D image registration followed by additional processing determined the anterior-posterior (A-P) positions of the femoral condyles, which were used to compute internal tibial rotation from extension to maximum flexion during each exercise. CT images were used to investigate the potential causes of posterior edge loading in the lateral compartment. Patient reported outcome scores also were determined for each cohort. Results: In the first comparison between the B-in-S MC-PCL and I MC+PCL inserts, the I MC+PCL insert led to marginally greater internal tibial rotation in deep knee bend and better post-operative patient reported outcome scores despite a relatively high incidence of posterior edge loading in the lateral compartment. In the I MC+PCL insert, the primary cause of posterior edge loading in the lateral compartment was the posterior position of the lateral femoral condyle at extension. The internal tibial rotation occurred naturally about a medial pivot point and moved the lateral condyle sufficiently posterior that contact occurred on the edge of the insert. In the second comparison between the I MC+PCL and B-in-S MC+PCL inserts, the greater medial conformity in the B-in-S MC+PCL led to greater internal tibial rotation in the deep knee exercise but not the other two exercises and the degree of medial conformity did not affect post-operative patient reported outcome scores. In the last comparison between the B-in-S MC+PCL and native knees, the B-in-S MC+PCL insert exhibited greater internal tibial rotation in the deep knee bend and similar rotation in the other two exercises. However, there were significant differences in patterns of AP movement in both compartments during all exercises. With the native knee, most rotation occurred in the first 30º of flexion in deep knee bend or the last 30° of extension in step up and chair rise whereas the change in tibial rotation occurred more evenly with flexion or extension in the KA TKA knees. Nevertheless, the median Oxford Knee Score was 43 out of 48 and the median Oxford Activity and Participation Score was 91 out of 100. Conclusion: While the B-in-S MC+PCL tibial insert design proved to best restore native tibiofemoral kinematics than the other insert designs, patterns of AP movement in both compartments differed from the native knee. However, the B-in-S MC+PCL tibial insert exhibited good patient reported outcome scores at a mean follow-up time of 8 months.

Background: Tibiofemoral kinematics describe the relative movement of the femur with respect to the tibia through flexion, which provides an objective assessment of joint function and can be used to determine whether an artificial knee restores natural movement following total knee arthroplasty (TKA). One way to measure tibiofemoral kinematics is by analyzing the anterior-posterior (AP) movement of the femoral condyles on the tibia. There are two common methods for identifying AP positions and hence condylar movements: 1) the flexion facet center (FFC), and 2) the lowest point (LP) methods. However, comparison of AP positions from the two methods in the native knee yielded contradictory findings. Three factors need to be considered before applying the FFC and LP methods. The first factor is the selected reference plane upon which the AP positions are measured. One useful plane is the plane perpendicular to the tibial mechanical axis, which allows the AP positions to be expressed in a direction consistent with the coordinate system of Grood and Suntay. However, to construct a reliable tibial mechanical axis and hence perpendicular plane, there is a need for a highly repeatable and reproducible method for identifying the distal point of the tibial mechanical axis (i.e. center of the talocrural joint). A second factor is the presence of cartilage on the 3D model of the femur, which may alter the shape of the femoral articular surface and hence positions of the FFCs and LPs. A third factor is the smoothness of the 3D model, which may also alter the shape of the femoral articular surface. Hence the objective of Chapter 1 was to determine the repeatability and reproducibility of a new method and two previously described methods for locating the center of the talocrural joint. After constructing the tibial mechanical axis using the most repeatable and reproducible method from Chapter 1, the objectives of Chapter 2 were to use the plane perpendicular to the tibial mechanical axis to determine how well the FFC and LP methods agree, and to determine whether the addition of articular cartilage and/or smoothing significantly affects the AP positions of the femoral condyles. Another subject of interest is tibiofemoral contact kinematics, which describe the movement of locations of contact by the femur on the tibia throughout flexion. Knowledge of the AP tibial contact locations in artificial knees is useful in assessing wear of tibial inserts and detecting posterior rim loading. However, existing methods for determining AP tibial contact locations based on analysis of images from single-plane fluoroscopy, such as the penetration method, are prone to error. Hence, the objectives of Chapter 3 were to create a new planar model that can determine AP tibial contact locations and determine whether errors of the planar model are lower than those of the penetration method. Methods: For Chapter 1, the medial-lateral (ML), AP, and proximal-distal (PD) coordinates of the center of the talocrural joint were determined in thirteen 3D bone models of the full tibia using the new method, termed the area centroid method, and the previously described diagonal intersection and biplanar methods. Intraobserver and interobserver intraclass correlation coefficients (ICCs) were computed to quantify the repeatability and reproducibility for each method. For Chapter 2, Magnetic Resonance (MR) images of the native knee were obtained from eleven subjects, who subsequently performed a deep knee bend under fluoroscopy. For each subject, four different MR models of the distal femur were created: femur bone, smoothed femur bone, femur bone with cartilage, and femur bone with smoothed cartilage. AP positions of the LPs and FFCs in each compartment were determined for each model type following 3D model-to-2D image registration. For Chapter 3, a slopes-of-sagittal profiles (SSP) model was created using mathematical functions to simulate articular surfaces of the tibial insert and femoral condyles. AP tibial contact locations were calculated using the model and the penetration method and simultaneously measured with a tibial force sensor in 10 cadaveric TKA knees for four flexion angles (0°, 30°, 60°, and 90°) in each compartment during passive motion. For each method, the overall bias, overall precision, and overall root mean square error (RMSE) were calculated from the differences between the computed AP tibial contact locations and the measured locations. Results: For Chapter 1, the area centroid method had excellent repeatability (ICC ≥ 0.97) and reproducibility (ICC ≥ 0.92). For the biplanar method, repeatability (ICC ≥ 0.86) was good and reproducibility (ICC ≥ 0.40) was fair. For the diagonal intersection method, repeatability (ICC ≥ 0.71) was moderate and reproducibility (ICC ≥ 0.46) was fair. For Chapter 2, the limits of agreement were ± 5.5 mm at 0° flexion, and bounded by ± 2.4 mm at 30°, 60°, and 90° flexion. The differences in AP positions between the four model types were minimal for both LPs and FFCs. For Chapter 3, the SSP model had an overall bias of 0.6 mm and precision of 2.8 mm which were significantly greater than the overall bias of -0.1 mm (p = 0.0369) and overall precision of 2.0 mm (p = 0.0021) of the penetration method. Conclusion: The area centroid method offered better repeatability and reproducibility than existing methods and is recommended when identifying the mechanical axis of the tibia. Meanwhile, the FFC and LP methods provided similar mean results during a deep knee bend at flexion angles of 30° and beyond but not at 0°. The lack of significant differences between model types in the AP positions of the femoral condyles indicate that addition of cartilage to 3D bone models is not required to accurately determine AP positions. Therefore, faster and less expensive imaging techniques such as CT can be used confidently to acquire the 3D bone models for the analysis of tibiofemoral kinematics. Finally, a planar model based on the analysis of single-plane radiographic images did not increase accuracy in AP tibial contact locations. Hence, the penetration method is preferred to determine AP tibial contact locations using single-plane radiography.

The main objective of a total knee arthroplasty (TKA) is to restore native (i.e. healthy) function, and a crucial step is determining the correct insert thickness for each patient. Two methods used to determine the insert thickness are by manually assessing the joint laxity and by using a trial insert with goniometric markings that measures the internal-external rotation orientation of the trial with respect to a mark on the femoral component. The former is qualitative and depends on the surgeon’s experience and ‘feel’ and while the latter is quantitative, it can be used only with an insert with medial ball-in-socket insert conformity. An unexplored method is to measure the force required to push a trial insert into position., which would require a specialized tool which can measure the push force. Hence, a new push force measuring tool was designed following the necessary design criteria to measure the push force intraoperatively accurately and safely. To determine whether this method has merit, the relationship between push force and insert thickness must be addressed through a clinical study. Using the new push force measuring tool, the push force was measured in 30 patients during unrestricted kinematically aligned TKA. The peak push forces going from an insert 1 mm thinner than the correct thickness as determined by an insert goniometer and from correct thickness to 1 mm thicker were measured. The mean peak forces for the different insert thicknesses were 127 ± 104 N, 127 ± 95 N, and 144 ± 96 N for 1 mm thinner, correct, and 1 mm thicker, respectively, and did not differ (p = 0.3210). As a result, measurement of peak force during trial positioning of a tibial insert cannot be used to identify the correct insert thickness.

BackgroundTotal knee arthroplasty (TKA) treats advanced osteoarthritis by replacing degenerated articular surfaces of the tibia and femur with implants. However, of approximately 1 million TKAs performed annually in the US, 20-25% of TKA patients are dissatisfied due to persistent pain, poor function, or implant failure which is conventionally performed using mechanical alignment (MA). MA TKA aligns the implants to establish a ‘straight’ limb (i.e. line connecting hip and ankle passes through center of knee); however, a straight limb is unnatural and requires ligament release in the majority of patients.

Unrestricted kinematic alignment (KA) TKA is an alternative alignment method which restores the native limb alignment and joint lines without ligament release. KA TKA is a viable alternative to MA TKA because multiple studies have reported that patients treated with KA TKA have significantly better pain relief, function, and a more normal feeling knee than patients treated with MA TKA. However, clinicians have not widely embraced KA TKA because of concern that KA TKA may compromise implant survivorship due to tibial baseplate loosening. This concern arises because baseplate loosening has been linked to varus alignment of the baseplate in MA and because most baseplates are aligned in varus in KA.

Furthermore, although promising clinical results have been achieved for KA TKA using conventional (i.e., low conforming) implants, such implants fail to restore native (i.e., healthy) knee kinematics. Medially-conforming (MC) implants better restore native knee kinematics but features of their design exacerbate the concern regarding tibial baseplate loosening.Assessing long-term risk of baseplate loosening can be evaluated in the short-term using model-based radiostereometric analysis (RSA) which measures in vivo tibial baseplate movement relative to the underlying tibia bone (termed migration). Baseplate migration is computed by acquiring biplanar radiographs postoperatively on the day of surgery and at follow-up time points over 2 years,followed by registering a 3D baseplate model onto the images to determine how its position and orientation relative to reference tibia markers change over time. To assess risk of loosening, the magnitude of the migration is compared to stability limits from the RSA literature. To assess this risk for a group of patients, mean maximum total point motion (MTPM) (i.e., largest displacement of any point on the baseplate) is compared to a limit of 0.5 mm at 1 year. To assess this risk in individual patients, there are two stability limits: a change in MTPM between 1 and 2 years (ΔMTPM) of 0.2 mm and anterior tilt at 2 years of 0.8°.

To address the concern that KA TKA using MC implants which retain the posterior cruciate ligament (KA+MC+PCL) increases risk of tibial baseplate loosening, aims were to: (1) set-up a clinical RSA laboratory and develop laboratory protocols which reduce error and (2) determine whether tibial baseplate migration for KA+MC+PCL is below the stability limits.

Aim 1: Error Reduction MethodsTo determine methods for error reduction, a protocol for quantifying bias and precision in clinical settings was developed and sources of registration error for model-based RSA were identified and evaluated. The first source of registration error was the orientation of the baseplate relative to the imaging planes. The primary objective was to determine the baseplate orientation which minimized mean registration error (i.e., bias error). A tibia phantom was rotated to achieve 24 different orientations with three independent pairs of radiographs acquired at each orientation. Bias error, quantified as mean artifactual (aMTPM), was plotted as a function of the rotation angles to determine the orientation with the lowest error. For the baseplate under study, the orientation with the lowest error was 10° rotation in flexion and 5° rotation in varus which decreased bias error by 85% relative to 0° rotation in flexion and varus. A consequence of baseplate reorientation during imaging is deviation between the globally-aligned baseplate coordinate system (BCS) (defined by calibration box) and cardinal body planes; therefore, computing migration using a local BCS (defined by baseplate) may be preferrable. Objectives were to (1) summarize the migration equations for the two BCSs and (2) provide a clinical example to demonstrate their differences. Differences in migration for the two BCSs ranged from about ±0.5 mm in translations and -0.4° to 0.7° in rotations, were largest for deviations in internal-external rotation, and were smallest for deviations in varus-valgus rotation. Migrations computed using the local BCS were independent of reorientation and therefore enhanced consistency.

The second source of registration error was the type of 3D baseplate model. The primary objective was to determine whether RE models reduced bias error relative to CAD models. Bias error, quantified as mean aMTPM, was computed between two pairs of independent biplanar radiographs from the same day for thirty-five patients. The biplanar radiographs were analyzed using each model type for all patients. Mean aMTPM was reduced by 24% when using RE models instead of CAD models.

Aim 2: Clinical Tibial Baseplate MigrationThirty-five patients enrolled in this prospective 2-year longitudinal study. Patients underwent cemented, unrestricted KA+MC+PCL TKA. Biplanar radiographs acquired on the day of surgery and at 1.5, 3, 6, 12, and 24 months were processed with model-based RSA software to determine migration in six degrees of freedom (6DOF) and in MTPM relative to the day of surgery.

For group assessment, objectives were to determine whether mean MTPM (1) was significantly < 0.5 mm at 1 year and (2) increased over time. At 1 year, mean MTPM of 0.35 mm was significantly < 0.5 mm (p = 0.0002). Mean MTPM did not increase from 6 weeks to 1 year (p = 0.3047).

For individual patient assessment of KA+MC+PCL, primary objectives were to determine the number of patients who exhibited ΔMTPM > 0.2 mm and the number of patients who exhibited anterior tilt > 0.8°. Because current stability limits linking baseplate migration to long-term risk of baseplate loosening only exist for ΔMTPM and anterior tilt, and because the concern of baseplate loosening for unrestricted KA TKA is pervasive particularly due to varus baseplate alignment, a final objective was to determine whether patient-specific alignment and loading variables were associated with migration in either 6DOF or MTPM. Hip knee ankle angle (HKAA), proximal medial tibial angle (PMTA), posterior slope angle (PSA), sex, and body mass index (BMI) were analyzed for an association with migration in 6DOF and MTPM. Thirty-two of the 35 patients were available for analysis at 2 years. One of 32 patients exhibited ΔMTPM > 0.2 mm and also exhibited anterior tilt > 0.8°. Varus rotation (p = 0.048, r ≤ 0.34) and medial translation (p = 0.0273, r ≤ 0.29) increased with increased varus baseplate alignment; however, the magnitudes of the migrations were minimal and did not manifest as increases in ΔMTPM and anterior tilt.

ConclusionsResults from Aim 1 inform RSA researchers on methods for reporting clinical bias in MTPM, reducing registration error (by reorienting the tibial baseplate during imaging and using RE models), and computing migration using local BCSs. Results from Aim 2 inform orthopedic surgeons that unrestricted KA+MC+PCL TKA does not increase risk of baseplate loosening on a group or individual patient level.

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