Scott M. Tucker

Contact Stress and Kinematic Analysis of All-Epiphyseal and Over-the-Top Pediatric Reconstruction Techniques for the Anterior Cruciate Ligament

Background: Adult anterior cruciate ligament (ACL) reconstruction techniques may be inappropriate to treat skeletally immature patients because of the risk of physeal complications. “Physeal-sparing” reconstruction techniques exist, but their ability to restore knee stability and contact mechanics is not well understood. Purpose: (1) To assess the ability of the all-epiphyseal (AE) and over-the-top (OT) reconstruction techniques to restore knee kinematics, (2) to assess whether these reconstruction techniques decrease the high posterior contact stresses seen with ACL deficiency, and (3) to determine whether the AE or OT technique produces abnormal tibiofemoral contact stresses. Study Design: Controlled laboratory study. Methods: Ten fresh-frozen human cadaveric knees were tested using a robotic manipulator. Tibiofemoral motions were recorded with the ACL intact, after sectioning the ACL, and after both reconstructions in each of the 10 specimens. The AE technique consisted of tunnels exclusively within the epiphysis and was fixed with suspensory cortical fixation devices. The OT procedure consisted of a central and vertical tibial tunnel with an over-the-top femoral position and was fixed with staples and posts on both ends. Anterior stability was assessed with 134-N anterior force at 0°, 15°, 30°, 60°, and 90° of knee flexion. Rotational stability was assessed with combined 8 N·m and 4 N·m of abduction and internal rotation, respectively, at 5°, 15°, and 30° of knee flexion. Results: Both reconstruction techniques off-loaded the posterior aspect of the tibial plateau compared with the ACL-deficient knee in response to both anterior loads and combined moments as demonstrated by reduced contact stresses in this region at all flexion angles. Compared with the ACL-intact condition, both the AE and OT procedures had increased posteromedial contact stresses in response to anterior load at some flexion angles, and the OT technique had increased peripheral posterolateral contact stresses at 15° in response to combined moments. Neither reconstruction technique completely restored the midjoint contact stresses. Both techniques restored anterior stability at flexion angles ≤30°; however, neither restored anterior stability at 60° and 90° of flexion. Both reconstruction techniques restored coupled anterior translation under combined moments. Additionally, the AE procedure overconstrained internal rotation in response to combined moments by 12% at 15° of flexion. Conclusion: Both reconstruction techniques provide anterior and rotational stability and decrease posterior joint contact stresses compared with the ACL-deficient knee. However, neither restored the contact mechanics and kinematics of the ACL-intact knee. Clinical Relevance: Because the AE reconstruction technique has clinical advantages over the OT procedure, the results support this technique as a potential candidate for use in the skeletally immature athlete.

ACL Fibers Near the Lateral Intercondylar Ridge Are the Most Load Bearing During Stability Examinations and Isometric Through Passive Flexion

Background: The femoral insertion of the anterior cruciate ligament (ACL) has direct and indirect fiber types located within the respective high (anterior) and low (posterior) regions of the femoral footprint. Hypothesis: The fibers in the high region of the ACL footprint carry more force and are more isometric than the fibers in the low region of the ACL footprint. Study Design: Controlled laboratory study. Methods: Ten fresh-frozen cadaveric knees were mounted to a robotic manipulator. A 134-N anterior force at 30° and 90° of flexion and combined valgus (8 N·m) and internal (4 N·m) rotation torques at 15° of flexion were applied simulating tests of anterior and rotatory stability. The ACL was sectioned at the femoral footprint by detaching either the higher band of fibers neighboring the lateral intercondylar ridge in the region of the direct insertion or the posterior, crescent-shaped fibers in the region of the indirect insertion, followed by the remainder of the ACL. The kinematics of the ACL-intact knee was replayed, and the reduction in force due to each sectioned portion of insertion fibers was measured. Isometry was assessed at anteromedial, center, and posterolateral locations within the high and low regions of the femoral footprint. Results: With an anterior tibial force at 30° of flexion, the high fibers carried 83.9% of the total anterior ACL load compared with 16.1% in the low fibers (P < .001). The high fibers also carried more anterior force than the low fibers at 90° of flexion (95.2% vs 4.8%; P < .001). Under combined torques at 15° of flexion, the high fibers carried 84.2% of the anterior ACL force compared with 15.8% in the low fibers (P < .001). Virtual ACL fibers placed at the anteromedial portion of the high region of the femoral footprint were the most isometric, with a maximum length change of 3.9 ± 1.5 mm. Conclusion: ACL fibers located high within the femoral footprint bear more force during stability testing and are more isometric during flexion than low fibers. Clinical Relevance: It may be advantageous to create a “higher” femoral tunnel during ACL reconstruction at the lateral intercondylar ridge.

Anatomy of the Radial Collateral Ligament of the Index Metacarpophalangeal Joint

PURPOSE To describe the origin and insertion of the radial collateral ligament (RCL) of the index metacarpophalangeal (MP) joint, relative to the MP joint line and other landmarks readily discernible intraoperatively. METHODS We dissected 17 fresh-frozen human cadaveric index fingers. We removed all overlying soft tissue from the MP joint except for the proper RCL. We dissected the RCL from its original insertion under loupe magnification while concurrently marking the ligamentous origin and insertion points. We measured distances of these points in relation to the bony landmarks (dorsal, articular, and volar surfaces) using digital photo analysis. The same observer recorded all measurements to reduce systematic error. RESULTS The center of the metacarpal attachment of the RCL was located 5.4 ± 1.1 mm from the dorsal border of the metacarpal, 8.0 ± 2.2mm from the volar border of the metacarpal, and 10.3 ± 3.2mm from the articular surface of the MP joint. The total width and height of the metacarpal origin site were 5.8 ± 1.6 and 6.4 ± 1.4 mm, respectively. The center of the proximal phalanx attachment of the RCL was located 6.8 ± 1.4 mm from the dorsal border of the proximal phalanx, 5.7 ± 0.9 mm from the volar border of the proximal phalanx, and 4.4 ± 0.8mm from the articular surface of the MP joint. The total width and height of the phalangeal origin site were 5.0 ± 1.1 and 5.7 ± 0.9 mm, respectively. CONCLUSIONS Our study defines the anatomic origin and insertion of the RCL of the index MP joint in relation to landmarks that are identifiable during surgery. CLINICAL RELEVANCE We believe this information will be useful to surgeons when repairing or reconstructing the RCL, allowing for recreation of normal RCL anatomy.

Accuracy of Individualized Custom Tibial Cutting Guides in UKA.

BackgroundComponent malposition is one of the major reasons for early failure of unicompartmental knee arthroplasty (UKA).Questions/PurposesIt was investigated how reproducibly patient-specific instrumentation (PSI) achieved preoperatively planned placement of the tibial component in UKA specifically assessing coronal alignment, slope and flexion of the components and axial rotation.Patients and MethodsBased on computer tomography models of ten cadaver legs, PSI jigs were generated to guide cuts perpendicular to the tibial axis in the coronal and sagittal planes and in neutral axial rotation. Deviation ≥3° from the designed orientation in a postoperative CT was defined as outside the range of acceptable alignment.ResultsMean coronal alignment was 0.4 ± 3.2° varus with two outliers. Mean slope was 2.8 ± 3.9° with six components in excessive flexion. It was noted that the implants were put in a mean of 1.7 ± 8.0° of external rotation with seven outliersConclusionsPSI helped achieve the planned coronal orientation of the component. The guides were less accurate in setting optimal tray rotation and slope.

Kinematics of passive flexion following balanced and overstuffed fixed bearing unicondylar knee arthroplasty

INTRODUCTION Progression of osteoarthritis in the unreplaced compartment following unicondylar knee arthroplasty (UKA) may be hastened if kinematics is disturbed following UKA implantation. The purpose of this study was to analyze tibiofemoral kinematics of the balanced and overstuffed UKA in comparison with the native knee during passive flexion since this is a common clinical assessment. METHODS Ten cadaveric knees were mounted to robotic manipulator and underwent passive flexion from 0 to 90°. The kinematic pathway was recorded in the native knee and in the balanced, fixed bearing UKA. The medial UKA was implanted using a measured resection technique. Additionally, a one millimeter thicker tibial insert was installed to simulate the effects of overstuffing. Tibial kinematics in relation to the femur was recorded. RESULTS Following UKA the tibia was externally rotated, and in valgus relative to the native knee near extension. In flexion, installing the UKA caused the knee to be translated medially and anteriorly. The tibia was translated distally through the entire range of flexion after UKA. Compared to the balanced UKA, overstuffing further increased valgus at full extension and distal translation of the tibia from full extension to 45° flexion. CONCLUSIONS UKA implantation altered tibiofemoral kinematics in all planes. Differences were small; nevertheless, they may affect tibiofemoral loading patterns. CLINICAL RELEVANCE Alterations in tibiofemoral kinematics following UKA might have implications for prosthesis failure and progression of osteoarthritis in the remaining compartment. Overstuffing should be avoided as it further increased valgus and did not improve the remaining kinematics.

Comparison of In Vitro Motion and Stability Between Techniques for Index Metacarpophalangeal Joint Radial Collateral Ligament Reconstruction

PURPOSE To evaluate a technique using interference screws to secure a tendon graft for reconstruction of the radial collateral ligament (RCL) of the index finger metacarpophalangeal (MCP) joint. We hypothesized that this technique would provide equivalent stability and flexion as a 4-tunnel reconstruction. METHODS We isolated the RCL in 17 cadaveric index fingers. A cyclic load was applied to the intact RCL across the MCP joint to assess flexion, ulnar deviation at neutral (UD 0), and ulnar deviation at 90° of MCP joint flexion (UD 90). The RCL was excised from its bony origin and insertion. We performed each reconstruction (4-tunnel and interference screw) sequentially on each specimen in a randomized order using a palmaris longus tendon graft. We repeated testing after each reconstruction and compared differences from the intact state between techniques using paired t-tests for all joint positions (flexion/UD 0/UD 90). RESULTS There was no statistically significant difference in UD 0 or UD 90 between the intact state and after interference screw reconstruction. Compared with the intact state, there was significantly less UD 0 and significantly more UD 90 after 4-tunnel reconstruction. There was no statistically significant difference between techniques when we compared changes in -UD 0 or UD 90. Change in flexion was statistically significantly different, which indicates that the interference screw technique better replicated intact MCP joint flexion compared with the 4-tunnel technique. CONCLUSIONS Interference screw reconstruction of the index RCL provides stability comparable to 4-tunnel reconstruction and is less technically challenging. These results substantiate our clinical experience that the interference screw technique provides an optimal combination of stability and flexion at the index MCP joint. CLINICAL RELEVANCE Using an interference screw to reconstruct the index RCL is less challenging than 4-tunnel reconstruction and provides stability and range of motion that closely resemble the native MCP joint.

Distribution of Force in the Medial Collateral Ligament Complex During Simulated Clinical Tests of Knee Stability

Background: Pivot-shift injury commonly results in combined anterior cruciate ligament (ACL)/medial collateral ligament (MCL) injury, yet the contribution of the components of the MCL complex to restraining multiplanar rotatory loads forming critical subcomponents of the pivot shift is not well understood. Purpose: To quantify the role of the MCL complex in restraining multiplanar rotatory loads. Study Design: Controlled laboratory study. Methods: A robotic manipulator was used to apply combined valgus and internal rotation torques in a simplified model of the pivot-shift examination in 12 cadaveric knees (49 ± 11 years). Tibiofemoral kinematics were recorded with the ACL intact. Loads borne by the superficial MCL (sMCL), posterior oblique ligament (POL), deep MCL (dMCL), and ACL were determined via the principle of superposition. Results: The POL bore about 50% of the load carried by the ACL in response to the combined torques at 5° and 15° of flexion. The POL bore load during the internal rotation component of the combined torques, while the sMCL carried load during the valgus and internal rotation phases of the simulated pivot. Load in the dMCL was always <10% of the ACL in response to combined valgus and internal rotation torques. Conclusion: The POL provides complementary load bearing to the ACL near extension in response to combined torques, which capture key components of the pivot-shift examination. The sMCL resists the valgus component of the maneuver alone, a loading pattern unique from those of the POL and ACL. The dMCL is not loaded during clinical tests of rotational knee stability in the ACL-competent knee. Clinical Relevance: Both the sMCL and POL work together with the ACL to resist combined moments, which form key components of the pivot-shift examination.

The Direct Insertion of the ACL Carries More Load than the Indirect Insertion An Important Consideration When Performing Anatomic ACLR

Objectives: Recent histological studies have shown that the ACL consists of two different structures: the direct and indirect insertions. The direct insertion is located along the lateral intercondylar ridge and the indirect insertion is ‘lower’ in the notch, adjacent to the posterior articular cartilage. The ‘lower’ position has become more popular for locating the femoral tunnel, as surgeons switch to the anteromedial (AM) portal drilling technique in order to place the graft in the region of the native footprint. However, a recent registry-based outcomes study has reported a 1.5 times higher graft failure rate for AM portal versus traditional transtibial techniques. The objective of this study was to investigate the load characteristics of the native ACL in the regions of the direct and indirect insertions. We hypothesized that the direct insertion would carry more load than the indirect insertion. Methods: Twelve cadaveric knees were mounted to a six degree of freedom robot equipped with a universal force-moment sensor. We simulated the Lachman and anterior drawer tests at 30oand 90o of flexion by applying a 134N anterior load, and the pivot shift test at 15o flexion by applying combined valgus (8Nm) and internal (4Nm) rotational moments. The kinematic pathway required to achieve these loading conditions was recorded for each intact knee. Using position control to repeat the loading paths, the robot recorded the loads for the ACL intact, ACL partially sectioned, and ACL completely sectioned states. Sectioning Protocol: The lateral intercondylar ridge and posterior articular margin was identified in each case. The 50% mark between this two areas was used to delineate the regions of the direct and indirect insertions (Fig. 1). Sectioning order was alternated between each cadaver. Footprint Digitization: The borders of the sectioned areas were digitized post-sectioning and mapped onto a computed tomography (CT) scan of each knee. The sectioning method was assessed under a blinded validation by experienced observers (TW, AP) who excluded two specimens that did not conform to the objective definitions of the sectioning method. Statistics: Loads were compared between direct and indirect locations at different flexion angles by conducting two-way repeated measures ANOVA models. Results: Under an anterior tibial load at 30o flexion, the direct insertion carried 83.9% (±7.2%) of the total ACL load compared to 16.1% (±7.2%) in the indirect insertion (p<0.001). The direct insertion also carried more load at 90o flexion (95.2% vs 4.8%; p<0.001). Under a combined rotatory load at 15o flexion, the direct insertion carried 84.2% (±4.2%)of the total ACL load compared to 15.8% (±4.2%) in the indirect insertion (p<0.001). Conclusion: The fibres in the direct insertion of the ACL carry more load than fibres in the indirect insertion. Previous studies have suggested that the direct insertion plays a major role in the mechanical link between the ACL and bone. With the current shift in emphasis towards anatomic ACL reconstruction, it may be beneficial to create the femoral tunnel within the direct insertion rather than ‘lower’ in the notch. Although further work is required in determining graft behaviour at the new insertions sites described in this study, our findings suggest that placing a graft in the region of the direct insertion may be an important consideration when adhering to the principles of anatomic ACL reconstruction.

ACL Fibers Inserting on the Lateral Intercondylar Ridge Carry the Greatest Loads - Are Modern Anatomic Femoral Tunnel Positions Too Low?

Objectives: Histological studies have shown that the ACL has a direct and indirect insertion on the femur [1]. The direct insertion is located along the lateral intercondylar ridge and the indirect insertion is located ‘lower’ on the lateral wall of the notch. The trend towards anatomic ACL reconstruction using the anteromedial (AM) portal technique has resulted in ‘lower’ non-isometric femoral tunnel positions and increased graft failures [2]. To our knowledge, the load transfer properties of the direct and indirect ACL insertions have not been studied. This information may help in understanding the increased failures reported with AM portal drilling. The purpose of this study was, 1) to compare the load transferred across the native ACL at the direct and indirect femoral insertions and, 2) to determine the strain behavior of ACL grafts placed at different tunnel locations within the direct and indirect insertions. Methods: Ten fresh-frozen cadaveric knees (mean age, 52.5 years; range, 29-65) were mounted to a six degree of freedom robot. A 134N anterior load at 30 and 90° flexion and a combined valgus (8Nm) and internal (4Nm) rotational moment at 15° flexion were applied. The ACL was subsequently sectioned at the femoral footprint by detaching either the direct or indirect insertion (partially sectioned state), followed by the remainder of the ACL (completely sectioned state) (Figure 1). The kinematics of the intact knee were replayed after each stage of sectioning to determine the loads transferred across the direct and indirect ACL fibers. Loads were expressed as a percentage of the total load borne by the ACL. Strain behaviour was tested by generating 3D models of the femur and tibia from CT scans of each knee. Three tunnel locations (anteromedial bundle [AM], center [C], posterolateral bundle [PL]) each were selected for the direct and indirect insertions and a virtual ACL graft was inserted. The isometry of the virtual graft was calculated through a flexion path of 0 to 90°. Results: Under an anterior tibial load at 30° flexion, the direct insertion carried 83.9% of the total ACL load compared to 16.1% in the indirect insertion (p<0.001). The direct insertion also carried more load at 90° flexion (95.2% vs 4.8%; p<0.001). Under a combined rotatory load at 15° flexion, the direct insertion carried 84.2% of the total ACL load compared to 15.8% in the indirect insertion (p<0.001). A virtual ACL graft placed at the AM position in the direct insertion demonstrated the best strain behaviour with a mean 10.9% change in length. This value was significantly lower (p<0.001) than the isometry at all 3 tunnel positions in the indirect insertion (AM = 18.5%; C = 24.9%; PL = 30.9%). Conclusion: Fibers in the direct insertion of the ACL carry more load than fibers in the indirect insertion. Virtual ACL grafts placed in the ‘higher’ direct location are more isometric than in the ‘lower’ indirect location during range of motion testing. Clinical Relevance: ‘Low’ ACL grafts in the indirect ACL insertion, resulting from AM portal drilling techniques, may experience higher loads in-vivo due to unfavorable biomechanics. With the current shift towards anatomic ACL reconstruction, it may be beneficial to create a ‘higher’ femoral tunnel within the direct insertion at the lateral intercondylar ridge. This position remains anatomical but may also be biomechanically favorable.