Nicholas Dunbar

Accuracy of Dynamic Tactile-Guided Unicompartmental Knee Arthroplasty

Unicompartmental knee arthroplasty (UKA) can achieve excellent clinical and functional results for patients having single-compartment osteoarthritis. However, UKA is considered to be technically challenging to perform, and malalignment of implant components significantly contributes to UKA failures. It has been shown that surgical navigation and tactile robotics could be used to provide very accurate component placement when the bones were rigidly fixed in a stereotactic frame during preparation. The purpose of this investigation was to determine the clinically realized accuracy of UKA component placement using surgical navigation and tactile robotics when the bones are free to move. A group of 20 knees receiving medial UKA with dynamically referenced tactile-robotic assistance was studied. Implant placement errors were comparable with those achieved using tactile robotics with rigid stereotactic fixation.

Haptically guided robotic technology in total hip arthroplasty: A cadaveric investigation

The longevity of total hip arthroplasty (THA) continues to improve with advancements in design and bearing materials. However, the incidence of dislocation and impingement-related failures continue to rise, with the inability of the surgeon to achieve optimal component orientation cited as a cause. Computer-assistance has been shown to increase the accuracy of component orientation and robotic-assistance has been developed to translate this advantage into precise surgical execution. We sought to validate a haptically-guided robotic arm system in performing THA with the aim of comparing the accuracy of robotic-assisted acetabular cup placement to manual placement. We implanted 12 acetabular components in 6 cadaveric pelvises comparing robotic-assistance on one side with manual implantation on the other. We measured planned and actual center of rotation (COR), cup position, leg-length equalization and offset for each THA using computed tomography and the robotic platform. The root-mean-square (RMS) error for the robotic-assisted system was within 3° for cup placement and within 1mm for leg-length equalization and offset when compared to computed tomography. The robotic-assisted system was significantly more accurate than manual implantation in reproducing the COR and cup orientation, as determined by a preoperative plan. The RMS error for manual implantation compared to robotic-assistance was 5 times higher for cup inclination and 3.4 times higher for cup anteversion (p < 0.01). Robotic-assistance is more accurate than manual implantation in achieving optimal cup orientation. It has the ability to eliminate human error from THA and should be considered in light of THA failures due to component malposition.

Effect of Tibial Tuberosity Advancement on the Contact Mechanics and the Alignment of the Patellofemoral and Femorotibial Joints

OBJECTIVE To evaluate the effect of tibial tuberosity advancement (TTA) on patellofemoral (PF) contact mechanics, and alignment of the PF and femorotibial (FT) joints in cranial cruciate ligament (CrCL)-deficient stifles of dogs. STUDY DESIGN Ex vivo biomechanical study. ANIMALS Unpaired cadaveric hind limbs (n=9). METHODS Digital pressure sensors placed in the PF joint were used to measure contact force, contact area, peak and mean contact pressure, and peak pressure location with the limb under an axial load of 30% body weight and a stifle angle of 135°. The FT and PF poses were obtained using a 2-dimensional computer digitization technique. Each specimen was tested under normal, CrCL-deficient, and TTA-treated conditions. Data was normalized and analyzed, after testing for normality by Wilk-Shapiro, using 1 sample T-test, paired T-test, and ANOVA; P≤.05 was considered significant. Bonferronis correction was used when needed. RESULTS A significant cranioproximal tibial displacement and increase in patellar tilt were found in the CrCL-deficient joints. Both FT and PF alignments were restored after TTA. Contact areas and peak pressure did not vary between conditions. Peak pressure location displaced proximally from intact to CrCL-deficient condition and returned to normal after TTA. Total force measured in the CrCL-deficient stifle and TTA conditions were significantly lower than in the control. CONCLUSION TTA restored the normal FT and PF alignment, and reduced the retropatellar force by about 20%.

Effect of tibial plateau leveling osteotomy on patellofemoral alignment: a study using canine cadavers.

Tibial plateau leveling osteotomy (TPLO) has been shown to alter the biomechanics of the femorotibial joint; however, the effect of TPLO on patellofemoral (PF) joint alignment remains unknown. The purpose of this study was to evaluate PF joint kinematics before and after cranial cruciate ligament (CrCL) transection and following TPLO in a cadaveric stifle model with set patellar tendon load, tested in passive range of motion at 90°, 105°, 120°, 135° and 150° of flexion. The PF joint poses were measured on mediolateral projection radiographs using a two-dimensional computer digitization technique. In the subluxated CrCL-deficient stifle, the PF joint had an increase in patellar tilt angle. In the reduced CrCL-deficient stifle treated by TPLO, there was distal and caudal displacement of the patella relative to the femur and a decreased patellar tilt angle. The estimated patellar moment arm following TPLO was not different from the control stifle. On the basis of these results, TPLO alters PF joint kinematics. The changes in PF joint alignment induced by TPLO may be a biomechanical factor predisposing to patellar tendonitis following TPLO.

Physiological sagittal plane patellar kinematics during dynamic deep knee flexion

PurposeLateral radiographic views can be easily taken and have reveal considerable information about the patella. The purpose of this study was to obtain sagittal plane patellar kinematics data through the entire range of knee flexion under weight-bearing conditions.MethodsPatellar flexion angles relative to the femur and tibia and anterior-posterior and proximal-distal translations of the patella relative to the femur and tibia were measured from 0 to 165° knee flexion in nine healthy knees using dynamic radiographic images.ResultsThe patella flexed relative to the femur and tibia by two thirds times and one third times the knee flexion angle, respectively. The patella translated in an arc relative to the femur and tibia as the knee flexed. In early flexion, the superior and centroid points translated anteriorly and then the patella translated posteriorly relative to the femur. All three points of the patella translated posteriorly relative to the tibia during a full range of flexion. An average of four and three millimetres proximal patellar translation relative to the tibia was demonstrated from 0 to 20° and 140 to 160° knee flexion, respectively.ConclusionsPhysiological sagittal plane patellar kinematics, including patellar flexion angles and translations relative to the femur and tibia, showed generally similar patterns for each subject. Measurements of dynamic radiographic images under weight-bearing activities may enhance the opportunity to identify patellar pathological conditions.

A Biomechanical Comparison of Three Hybrid Linear-Circular External Fixator Constructs

OBJECTIVE To evaluate the stiffness, displacement, ring deformation and bone model motion of 3 configuations of linear-circular hybrid fixator constructs loaded in axial compression, craniocaudal and mediolateral bending, and torsion. STUDY DESIGN Biomechanical evaluation. SAMPLE POPULATION Three hybrid construct configurations with 8 replicates/configuration. METHODS Construct Ia used a single, 84 mm, incomplete ring and 2 tensioned olive wires to stabilize 1 bone segment and a primary hybrid rod with 3 fixation pins to stabilize the other bone segment. Constructs Ia(d) and Ib were similar to Ia with the addition of a secondary diagonal hybrid rod. Construct Ib had a fixation pin inserted orthogonally from the diagonal rod. Constructs were loaded for 10 cycles in each mode of loading using a materials testing machine. Ring deformation was assessed by obtaining serial ring measurements. Bone model motion at the fracture gap as a result of loading was also calculated. RESULTS Axial compression: constructs Ia(d) and Ib were significantly stiffer than construct Ia. Craniocaudal bending: Construct Ib was significantly stiffer than construct Ia. Mediolateral bending: there were no significant differences between constructs. Torsion: Construct Ib was significantly stiffer than constructs Ia and Ia(d) . Permanent ring deformation did not occur. Bone model translational motion decreased in constructs Ia(d) and Ib compared to construct Ia. CONCLUSIONS Addition of a secondary hybrid rod as well as biplanar fixation pin placement improved construct stiffness in several loading modes.

Kinematics of monoblock bicompartmental knee arthroplasty during weight-bearing activities

AbstractPurpose There is an increased interest in treating arthritis of the medial and patellofemoral compartments without using a total knee arthroplasty. The purpose of this study was to measure kinematics in knees with a monoblock bicompartmental arthroplasty to see whether maintaining the cruciate ligaments and lateral compartment resulted in consistent kinematics more similar to healthy knees than those observed in replaced knees.MethodsThe kinematics of ten knees with monoblock bicompartmental arthroplasty were observed using fluoroscopy during three weight-bearing activities. Model-image registration techniques were used to quantify the three-dimensional motions of the knee joints.ResultsDuring kneeling, lunging, and stair-step activities, the medial condyle remained relatively close to the centre of the tibial plateau, while the lateral condyle typically moved posteriorly with flexion. Knees generally exhibited motion patterns consistent with retained cruciate ligament function, but individual patterns varied significantly.ConclusionsBicompartmental knee arthroplasty has the potential to retain more natural knee function. Improved tools for aligning the implants and increased implant sizing options may be required to achieve highly consistent results and realize the clinical benefit of a knee arthroplasty with intact cruciate ligaments.Level of evidenceIII.