Scott Kramer

Comparison of In Situ Forces and Knee Kinematics in Anteromedial and High Anteromedial Bundle Augmentation for Partially Ruptured Anterior Cruciate Ligament

Background: High tunnel placement is common in single- and double-bundle anterior cruciate ligament (ACL) reconstructions. Similar nonanatomic tunnel placement may also occur in ACL augmentation surgery. Purpose: In this study, in situ forces and knee kinematics were compared between nonanatomic high anteromedial (AM) and anatomic AM augmentation in a knee with isolated AM bundle injury. Study Design: Controlled laboratory study. Methods: Seven fresh-frozen cadaver knees were used (age, 48 ± 12.5 years). First, intact knee kinematics was tested with a robotic–universal force sensor testing system under 2 loading conditions. An 89-N anterior load was applied, and an anterior tibial translation was measured at knee flexion angles of 0°, 30°, 60°, and 90°. Then, combined rotatory loads of 7-N·m valgus and 5-N·m internal tibial rotation were applied at 15° and 30° of knee flexion angles, which mimic the pivot shift. Afterward, only the AM bundle of the ACL was cut arthroscopically, keeping the posterolateral bundle intact. The knee was again tested using the intact knee kinematics to measure the in situ force of the AM bundle. Then, arthroscopic anatomic AM bundle reconstruction was performed with an allograft, and the knee was tested to give the in situ force of the reconstructed AM bundle. Knee kinematics under the 3 conditions (intact, anatomic AM augmentation, and nonanatomic high AM augmentation) and the in situ force were compared and analyzed. Result: The high AM graft had significantly lower in situ force than the intact and anatomic reconstructed AM bundle at 0° of knee flexion (P < .05) and the intact AM bundle at 30° of knee flexion under anterior tibial loading. There were no differences between anatomic graft and intact AM bundle. The high AM graft also had a significantly lower in situ force than the intact and anatomic reconstructed AM with simulated pivot-shift loading at 15° and 30° of flexion (P < .05). Under anterior tibial and rotatory loading, there was a difference in tibial displacement between anatomic and high AM reconstructions and between the high AM graft and intact ACL under rotational loading with the knee at 15° of flexion. Clinical Relevance: Anatomic AM augmentation can lead to biomechanical advantages at time zero when compared with the nonanatomic (high AM) augmentation. Anatomic AM augmentation better restores the knee kinematics to the intact ACL state.

Progressive Chondrocyte Death After Impact Injury Indicates a Need for Chondroprotective Therapy

Background Impact injury to articular cartilage can lead to posttraumatic osteoarthritis. Hypotheses This study tests the hypotheses that (1) chondrocyte injury occurs after impact at energies insufficient to fracture the cartilage surface, and that (2) cartilage injury patterns vary with impact energy, time after injury, and cartilage thickness. Study Design Controlled laboratory study. Methods Fresh bovine osteochondral cores were randomly divided into 5 groups: (1) control, (2) 0.35 J, (3) 0.71 J, (4) 1.07 J, and (5) 1.43 J impact energies. Cores were subjected to computer-controlled impact loading and full-thickness sections were then prepared and incubated in Dulbecco’s Modified Eagle’s Medium/F12 at 37°C. Adjacent sections were harvested 1 and 4 days after impact for viability staining and fluorescent imaging. The area of dead and living chondrocytes was quantified using custom image analysis software and reported as a percentage of total cartilage area. Results The highest impact energy fractured the cartilage in all cores (1.43 J, n = 17). Seventy-three percent and 64% of the osteochondral cores remained intact after lower energy impacts of 0.71 J and 1.07 J, respectively. At lower energy levels, fractured cores were thinner (P <.01) than those remaining intact. In cores remaining intact after impact injury, chondrocyte death increased with increasing impact energy (P <.05) and with greater time after impact (P <.05). A progressive increase in dead cells near the bone/cartilage interface and at the articular surface was observed. Conclusion These data showing progressive chondrocyte death after impact injury at energies insufficient to fracture the cartilage surface demonstrate a potential need for early chondroprotective therapy. Clinical Relevance These data show that efforts to reduce chondrocyte morbidity after joint injury may be a useful strategy to delay or prevent the onset of posttraumatic osteoarthritis.

Optical coherence tomography detection of subclinical traumatic cartilage injury.

Objectives: Posttraumatic arthritis is a major cause of disability. Current clinical imaging modalities are unable to reliably evaluate articular cartilage damage before surface breakdown, when potentially reversible changes are occurring. Optical coherence tomography (OCT) is a nondestructive imaging technology that can detect degenerative changes in articular cartilage with an intact surface. This study tests the hypothesis that OCT detects acute articular cartilage injury after impact at energy levels resulting in chondrocyte death and microstructural changes, but insufficient to produce macroscopic surface damage. Methods: Bovine osteochondral cores underwent OCT imaging and were divided into a control with no impact or were subjected to low (0.175 J) or moderate (0.35 J) energy impact. Cores were reimaged with OCT after impact and the OCT signal intensity quantified. A ratio of the superficial to deep layer intensities was calculated and compared before and after impact. Chondrocyte viability was determined 1 day after impact followed by histology and polarized microscopy. Results: Macroscopic changes to the articular surface were not observed after low and moderate impact. The OCT signal intensity ratio demonstrated a 27% increase (P = 0.006) after low impact and a 38% increase (P = 0.001) after moderate impact. Cell death increased by 150% (P < 0.001) and 200% (P < 0.001) after low and moderate energy impacts, respectively. When compared with unimpacted controls, both Mankin histology and David-Vaudey polarized microscopy scores increased (P = 0.036 and P = 0.002, respectively) after moderate energy impact. Conclusions: This study shows that OCT detects acute cartilage changes after impact injury at levels insufficient to cause visible damage to the articular surface but sufficient to cause chondrocyte death and microscopic matrix damage. This finding supports the use of OCT to detect microstructural subsurface cartilage damage that is poorly visualized with conventional imaging.

A Biomechanical Comparison of 2 Femoral Fixation Techniques for Anterior Cruciate Ligament Reconstruction in Skeletally Immature Patients: Over-the-Top Fixation Versus Transphyseal Technique

PURPOSE The purpose of this study was to compare knee kinematics and in situ forces of the graft between 2 femoral fixation techniques of anterior cruciate ligament (ACL) reconstruction: the over-the-top (OTT) fixation and transphyseal (TP) techniques. METHODS ACL reconstruction in skeletally immature patients is a challenging procedure. Regarding the femoral fixation techniques, 2 methods are commonly used: the OTT fixation and TP techniques. Ten cadaveric knees (mean age, 57 years; range, 48 to 65 years) were tested with the robotic/universal force-moment sensor system by use of (1) an 89-N anterior tibial load at full extension and 15°, 30°, 60°, and 90° of knee flexion and (2) a combined 7-Nm valgus torque and 5-Nm internal tibial rotation torque at 15° and 30° of knee flexion. RESULTS Both OTT and TP ACL reconstruction techniques closely restored the intact knee kinematics and had a significant reduction in anterior tibial translation under an anterior tibial load and in coupled anterior tibial translation under a combined rotatory load when compared with an ACL-deficient knee. When both ACL reconstruction techniques were compared, the only difference found was that the in situ force of the ACL graft reconstructed with the OTT technique in response to a combined rotatory load at 30° of flexion was significantly lower than the ACL graft reconstructed with the TP technique (5.3 ± 3.3 N and 10.7 ± 6.0 N, respectively; P = .013). CONCLUSIONS This time 0 testing showed that both ACL reconstruction techniques, OTT and TP, can reproduce the kinematics of the intact knee in response to an anterior tibial load and a combined rotatory load. CLINICAL RELEVANCE Both femoral fixation techniques exhibited comparable time 0 kinematics when subjected to simulated clinical examination loading conditions.