Carl W. Imhauser

Abnormal tibiofemoral contact stress and its association with altered kinematics after center-center anterior cruciate ligament reconstruction: an in vitro study.

Background: Abnormal tibiofemoral contact stress and aberrant kinematics may influence the progression of osteoarthritis in the anterior cruciate ligament (ACL)–deficient and the ACL-reconstructed knee. However, relationships between contact stress and kinematics after ACL reconstruction are poorly understood. Therefore, we posed the following research questions: (1) How do ACL deficiency and reconstruction affect the kinematics of and contact stress in the tibiofemoral joint? (2) What kinematic differences are associated with abnormal contact stress after ACL reconstruction? Hypothesis: Center-center ACL reconstruction will not restore knee kinematics and contact stress. Correlations will exist between abnormal contact stress and aberrant kinematics after ACL reconstruction. Study Design: Controlled laboratory study. Methods: Clinical tests of anterior and rotational stability were simulated on 11 cadaveric knees using an industrial robot. Tests were conducted with the ACL intact, sectioned, and after single-bundle ACL reconstruction using a quadrupled hamstring autograft with tunnels drilled through the center of the native footprints. Kinematics were recorded during the tests. Contact stress was continuously recorded from a stress transducer fixed to the tibial plateau, and mean contact stress was calculated regionally. Results: ACL deficiency resulted in increased mean contact stress in the posterior sectors of the medial and lateral compartments under anterior and rotational loads, respectively. Reconstruction reduced stress in these locations; however, contact stress abnormalities remained. On average, kinematics were overconstrained after ACL reconstruction (≤1.8 mm and ≤2.6° in all directions). However, combinations of overconstrained and underconstrained motions in abduction/adduction and medial-lateral translation in response to combined moments, and anterior-posterior translation, medial-lateral translation, and axial rotation in response to an anterior load were associated with abnormal mean contact stress. Conclusion: ACL reconstruction reduces high stresses generated in the posterior compartment of the ACL-deficient knee. Abnormal contact stress after ACL reconstruction is related to multiplanar variations in knee kinematics. Clinical Relevance: Clinical measures of multiplanar kinematics may help to better characterize the quality of ACL reconstruction. Such measures may help identify patients at increased risk of long-term joint degeneration following this surgery.

Effect of short-duration low-magnitude cyclic loading versus immobilization on tendon-bone healing after ACL reconstruction in a rat model

BACKGROUND Successful anterior cruciate ligament reconstruction with use of soft-tissue grafts requires healing between tendon and bone. Little is known about the effect of mechanical load on the cellular and molecular cascade of tendon-to-bone healing. Understanding these mechanical influences has critical implications for postoperative rehabilitation following anterior cruciate ligament reconstruction. The purpose of this study was to test the hypothesis that, compared with perioperative immobilization, short-duration low-magnitude cyclic axial loading would result in impaired tendon-to-bone healing after anterior cruciate ligament reconstruction in a rat model. METHODS Fifty-two male Sprague-Dawley rats underwent anterior cruciate ligament reconstruction with use of a flexor digitorum longus autograft. The patellar tendon, capsule, and ligamentous structures were circumferentially released, and an external fixator parallel to the anterior cruciate ligament graft was placed across the knee. Mechanical loading, consisting of cyclic displacement of the femur and tibia constrained to axial translation parallel to the graft, was applied daily. The rats were randomly assigned to immobilization or daily loading, for fourteen or twenty-eight days. Biomechanical, micro-computed tomographic, and histomorphometric analysis was performed on the bone-tendon-bone complexes. RESULTS The load measured across the knees during cyclic displacement increased over time (p < 0.05). Load-to-failure testing of the isolated femur-anterior cruciate ligament graft-tibia specimens revealed no significant differences between groups at two or four weeks. By two weeks postoperatively, a greater number of ED1+ inflammatory macrophages (phagocytic cells involved in the initial injury response) were seen at the tendon-bone interface after loading in the cyclically loaded group than in the immobilized group (p = 0.01). Compared with the baseline values, the number of trabeculae was significantly lower after loading for four weeks (p = 0.02). CONCLUSIONS Short-duration low-magnitude cyclic axial loading of the anterior cruciate ligament graft in the postoperative period is not detrimental to the strength of the healing tendon-bone interface but appears to be associated with greater inflammation and less bone formation in the tunnel in this rat model.

Autologous Osteochondral Transplantation of the Talus Partially Restores Contact Mechanics of the Ankle Joint

Background: Autologous osteochondral transplantation procedures provide hyaline cartilage to the site of cartilage repair. It remains unknown whether these procedures restore native contact mechanics of the ankle joint. Purpose: This study was undertaken to characterize the regional and local contact mechanics after autologous osteochondral transplantation of the talus. Study Design: Controlled laboratory study. Methods: Ten fresh-frozen cadaveric lower limb specimens were used for this study. Specimens were loaded using a 6 degrees of freedom robotic arm with 4.5 N·m of inversion and a 300-N axial compressive load in a neutral plantar/dorsiflexion. An osteochondral defect was created at the centromedial aspect of the talar dome and an autologous osteochondral graft from the ipsilateral knee was subsequently transplanted to the defect site. Regional contact mechanics were analyzed across the talar dome as a function of the defect and repair conditions and compared with those in the intact ankle. Local contact mechanics at the peripheral rim of the defect and at the graft site were also analyzed and compared with the intact condition. A 3-dimensional laser scanning system was used to determine the graft height differences relative to the native talus. Results: The creation of an osteochondral defect caused a significant decrease in force, mean pressure, and peak pressure on the medial region of the talus (P = .037). Implanting an osteochondral graft restored the force, mean pressure, and peak pressure on the medial region of the talus to intact levels (P = .05). The anterior portion of the graft carried less force, while mean and peak pressures were decreased relative to intact (P = .05). The mean difference in graft height relative to the surrounding host cartilage for the overall population was −0.2 ± 0.3 mm (range, −1.00 to 0.40 mm). Under these conditions, there was no correlation between height and pressure when the graft was sunken, flush, or proud. Conclusion/Clinical Relevance: Placement of the osteochondral graft in the most congruent position possible partially restored contact mechanics of the ankle joint. Persistent deficits in contact mechanics may be due to additional factors besides graft congruence, including structural differences in the donor cartilage when compared with the native tissue.

Biomechanical Assessment of the Anterolateral Ligament of the Knee: A Secondary Restraint in Simulated Tests of the Pivot Shift and of Anterior Stability.

BACKGROUND Injury to the lateral capsular tissues of the knee may accompany rupture of the anterior cruciate ligament (ACL). A distinct lateral structure, the anterolateral ligament, has been identified, and reconstruction strategies for this tissue in combination with ACL reconstruction have been proposed. However, the biomechanical function of the anterolateral ligament is not well understood. Thus, this study had two research questions: (1) What is the contribution of the anterolateral ligament to knee stability in the ACL-sectioned knee? (2) Does the anterolateral ligament bear increased load in the absence of the ACL? METHODS Twelve cadaveric knees from donors who were a mean (and standard deviation) of 43 ± 15 years old at the time of death were loaded using a robotic manipulator to simulate clinical tests of the pivot shift and anterior stability. Motions were recorded with the ACL intact, with the ACL sectioned, and with both the ACL and anterolateral ligament sectioned. In situ loads borne by the ACL and anterolateral ligament in the ACL-intact knee and borne by the anterolateral ligament in the ACL-sectioned knee were determined. RESULTS Sectioning the anterolateral ligament in the ACL-sectioned knee led to mean increases of 2 to 3 mm in anterior tibial translation in both anterior stability and simulated pivot-shift tests. In the ACL-intact knee, the load borne by the anterolateral ligament was a mean of ≤10.2 N in response to anterior loads and <17 N in response to the simulated pivot shift. In the ACL-sectioned knee, the load borne by the anterolateral ligament increased on average to <55% of the load normally borne by the ACL in the intact knee. However, in the ACL-sectioned knee, the anterolateral ligament engaged only after the tibia translated beyond the physiologic limits of motion of the ACL-intact knee. CONCLUSIONS The anterolateral ligament is a secondary stabilizer compared with the ACL for the simulated Lachman, anterior drawer, and pivot shift examinations. CLINICAL RELEVANCE Since the anterolateral ligament engages only during pathologic ranges of tibial translation, there is a limited need for anatomical reconstruction of the anterolateral ligament in a well-functioning ACL-reconstructed knee.

Abnormal Tibiofemoral Contact Stress and Its Association With Altered Kinematics After Center-Center Anterior Cruciate Ligament Reconstruction

Background: Abnormal tibiofemoral contact stress and aberrant kinematics may influence the progression of osteoarthritis in the anterior cruciate ligament (ACL)–deficient and the ACL-reconstructed knee. However, relationships between contact stress and kinematics after ACL reconstruction are poorly understood. Therefore, we posed the following research questions: (1) How do ACL deficiency and reconstruction affect the kinematics of and contact stress in the tibiofemoral joint? (2) What kinematic differences are associated with abnormal contact stress after ACL reconstruction? Hypothesis: Center-center ACL reconstruction will not restore knee kinematics and contact stress. Correlations will exist between abnormal contact stress and aberrant kinematics after ACL reconstruction. Study Design: Controlled laboratory study. Methods: Clinical tests of anterior and rotational stability were simulated on 11 cadaveric knees using an industrial robot. Tests were conducted with the ACL intact, sectioned, and after single-bundle ACL reconstruction using a quadrupled hamstring autograft with tunnels drilled through the center of the native footprints. Kinematics were recorded during the tests. Contact stress was continuously recorded from a stress transducer fixed to the tibial plateau, and mean contact stress was calculated regionally. Results: ACL deficiency resulted in increased mean contact stress in the posterior sectors of the medial and lateral compartments under anterior and rotational loads, respectively. Reconstruction reduced stress in these locations; however, contact stress abnormalities remained. On average, kinematics were overconstrained after ACL reconstruction (≤1.8 mm and ≤2.6° in all directions). However, combinations of overconstrained and underconstrained motions in abduction/adduction and medial-lateral translation in response to combined moments, and anterior-posterior translation, medial-lateral translation, and axial rotation in response to an anterior load were associated with abnormal mean contact stress. Conclusion: ACL reconstruction reduces high stresses generated in the posterior compartment of the ACL-deficient knee. Abnormal contact stress after ACL reconstruction is related to multiplanar variations in knee kinematics. Clinical Relevance: Clinical measures of multiplanar kinematics may help to better characterize the quality of ACL reconstruction. Such measures may help identify patients at increased risk of long-term joint degeneration following this surgery.

Lateral Ligament Repair and Reconstruction Restore Neither Contact Mechanics of the Ankle Joint nor Motion Patterns of the Hindfoot

BACKGROUND Ankle sprains may damage both the lateral ligaments of the hindfoot and the osteochondral tissue of the ankle joint. When nonoperative treatment fails, operative approaches are indicated to restore both native motion patterns at the hindfoot and ankle joint contact mechanics. The goal of the present study was to determine the effect of lateral ligament injury, repair, and reconstruction on ankle joint contact mechanics and hindfoot motion patterns. METHODS Eight cadaveric specimens were tested with use of robotic technology to apply combined compressive (200-N) and inversion (4.5-Nm) loads to the hindfoot at 0° and 20° of plantar flexion. Contact mechanics at the ankle joint were simultaneously measured. A repeated-measures experiment was designed with use of the intact condition as control, with the other conditions including sectioned anterior talofibular and calcaneofibular ligaments, the Broström and Broström-Gould repairs, and graft reconstruction. RESULTS Ligament sectioning decreased contact area and caused a medial and anterior shift in the center of pressure with inversion loads relative to those with the intact condition. There were no significant differences in inversion or coupled axial rotation with inversion between the Broström repair and the intact condition; however, medial translation of the center of pressure remained elevated after the Broström repair relative to the intact condition. The Gould modification of the Broström procedure provided additional support to the hindfoot relative to the Broström repair, reducing inversion and axial rotation with inversion beyond that of intact ligaments. There were no significant differences in center-of-pressure excursion patterns between the Broström-Gould repair and the intact ligament condition, but this repair increased contact area beyond that with the ligaments intact. Graft reconstruction more closely restored inversion motion than did the Broström-Gould repair at 20° of plantar flexion but limited coupled axial rotation. Graft reconstruction also increased contact areas beyond the lateral ligament-deficient conditions but altered center-of-pressure excursion patterns relative to the intact condition. CONCLUSIONS No lateral ankle ligament reconstruction completely restored native contact mechanics of the ankle joint and hindfoot motion patterns.

Development and validation of a computational model of the knee joint for the evaluation of surgical treatments for osteoarthritis

A three-dimensional (3D) knee joint computational model was developed and validated to predict knee joint contact forces and pressures for different degrees of malalignment. A 3D computational knee model was created from high-resolution radiological images to emulate passive sagittal rotation (full-extension to 65°-flexion) and weight acceptance. A cadaveric knee mounted on a six-degree-of-freedom robot was subjected to matching boundary and loading conditions. A ligament-tuning process minimised kinematic differences between the robotically loaded cadaver specimen and the finite element (FE) model. The model was validated by measured intra-articular force and pressure measurements. Percent full scale error between FE-predicted and in vitro-measured values in the medial and lateral compartments were 6.67% and 5.94%, respectively, for normalised peak pressure values, and 7.56% and 4.48%, respectively, for normalised force values. The knee model can accurately predict normalised intra-articular pressure and forces for different loading conditions and could be further developed for subject-specific surgical planning.

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.

Sensitivity of Plantar Pressure and Talonavicular Alignment to Lateral Column Lengthening in Flatfoot Reconstruction

BACKGROUND Lateral column lengthening (LCL) of the calcaneus is commonly performed as part of correction of the adult acquired flatfoot deformity. Increases in postoperative lateral plantar pressure associated with pain in the lateral aspect of the foot have been reported. The aim of this study was to investigate changes in pressures in the lateral aspect of the forefoot with increments of 6, 8, and 10 mm of LCL in a cadaveric flatfoot model. The hypothesis was that increasing the LCL incrementally by 2 mm will linearly increase the plantar pressures in the lateral aspect of the forefoot. METHODS Eight fresh-frozen cadaveric foot specimens were used. A robot compressively loaded the foot to 400 N with a 310-N tensile load applied to the Achilles tendon. A flatfoot model was created by resecting the medial and inferior soft tissues of the midfoot, followed by axial load of 800 N for 100 cycles. Kinematic and plantar pressure data were gathered after the different amounts of LCL (6, 8, and 10 mm) were achieved. RESULTS The talonavicular joint demonstrated a median abduction angle of 4.4° in the axial plane and -2.6° in the sagittal plane in the flatfoot condition as compared with the intact condition. The 6, 8, and 10-mm LCLs showed axial correction of talonavicular alignment by -1.4°, -4.9°, and -9.2° beyond that of the intact foot, and sagittal correction of -0.1°, 1.3°, and 2.9°, respectively. LCL of 6, 8, and 10 mm showed consistently increasing lateral forefoot average mean pressure, peak pressure, and contact area. CONCLUSIONS LCL in 2-mm increments consistently reduced talonavicular abduction and consistently increased plantar pressure in the lateral aspect of the forefoot. CLINICAL RELEVANCE The lateral column should be lengthened judiciously, as a 2-mm difference leads to significant difference not only in angular correction of the talonavicular joint but also with regard to pressure in the lateral aspect of the forefoot.

Effect of Immediate and Delayed High-Strain Loading on Tendon-to-Bone Healing After Anterior Cruciate Ligament Reconstruction

BACKGROUND We previously demonstrated, in a rat anterior cruciate ligament (ACL) graft reconstruction model, that the delayed application of low-magnitude-strain loading resulted in improved tendon-to-bone healing compared with that observed after immediate loading and after prolonged immobilization. The purpose of this study was to determine the effect of higher levels of strain loading on tendon-to-bone healing. METHODS ACL reconstruction was carried out in a rat model in three randomly assigned groups: high-strain daily loading beginning on either (1) postoperative day one (immediate-loading group; n = 7) or (2) postoperative day four (delayed-loading group; n = 11) or (3) after prolonged immobilization (immobilized group; n = 8). Animals were killed two weeks after surgery and micro-computed tomography (micro-CT) and biomechanical testing of the bone-tendon-bone complex were carried out. RESULTS The delayed-loading group had greater tissue mineral density than either the immediate-loading or immobilized group (mean [and standard deviation], 813.0 ± 24.9 mg/mL compared with 778.4 ± 32.6 mg/mL and 784.9 ± 26.4 mg/mL, respectively; p < 0.05). There was a trend toward greater bone volume per total volume fraction in both the immobilized and the delayed-loading group compared with the immediate-loading group (0.24 ± 0.03 and 0.23 ± 0.06 compared with 0.20 ± 0.05; p = 0.06). Trabecular thickness was greater in the immobilized group compared with the immediate-loading group (106.5 ± 23.0 μm compared with 72.6 ± 10.6 μm; p < 0.01). There were no significant differences in failure load or stiffness between the immobilized group and either high-strain cyclic-loading group. CONCLUSIONS Immediate application of high-strain loading appears to have a detrimental effect on healing in this rat model. Any beneficial effects of delayed loading on the healing tendon-bone interface (after a brief period of immobilization) may be offset by the detrimental effects of excessive strain levels or by the detrimental effects of stress deprivation on the graft. CLINICAL RELEVANCE The timing and magnitude of mechanical load on a healing rat ACL reconstruction graft may have important implications for postoperative rehabilitation. Avoidance of exercises that cause high graft strain in the early postoperative period may lead to improved tendon-to-bone healing in humans.