RESUMEN
There is little published data on the strain within the medial patellofemoral ligament (MPFL) and medial retinaculum through knee motion. This study was undertaken to evaluate the three-dimensional strain across the MPFL in the native state, using a proprietary visible-light stereophotogrammetry (VLS) system, and to compare the findings to the strain in a MPFL injury model and in two different reconstructed states. This is a controlled laboratory study. Eight cadaveric knees were marked along the MPFL and medial retinaculum, placed in an activity simulator, and taken through a range a motion. A proprietary VLS system was used to calculate the strain across the medial retinaculum and MPFL at 10 different degrees of knee flexion. This process was repeated in an MPFL injury model, as well as after standardized reconstruction of the MPFL using hamstring autograft performed in both 20 and 45 degrees of flexion. Averaged over all the measurement sites, the maximum principal strain (ε1) within the native MPFL increased rapidly from full extension to 120 degrees of flexion. The highest value of ε1 (87%) was observed at 120 degrees of knee flexion in the MPFL region. The largest change in strain occurred between 25 and 30 degrees (10% increase). The strain patterns in the knees reconstructed at 45 degrees of flexion more closely resembled the strain in the native state than did the strain in the knees reconstructed at 20 degrees. Strain within the native MPFL increases as the knee flexion angle increases, with the largest change occurring between 25 and 30 degrees. Reconstruction of the MPFL at 45 degrees is preferable to reconstruction at 20 degrees as the strain across the medial retinaculum more closely resembles the strain in the native state. Knowledge of the strain across the MPFL should allow for more accurate reconstruction of the MPFL, potentially reducing the risk of patellar maltracking or cartilage overload. The proprietary VLS system used in this study has many potential uses for experimental analysis of strain in the human body.
Asunto(s)
Ligamentos Articulares/fisiología , Articulación Patelofemoral/fisiología , Adolescente , Adulto , Anciano , Humanos , Ligamentos Articulares/cirugía , Persona de Mediana Edad , Articulación Patelofemoral/cirugía , Estrés Mecánico , Adulto JovenRESUMEN
Previous studies report conflicting results on whether loss of the medial meniscus compromises knee stability after reconstruction of the anterior cruciate ligament (ACL). The purpose of this study was to determine whether the degree of medial meniscus deficiency affects the stability of the ACL-reconstructed knee. Six cadaveric knees were arthroscopically reconstructed with bone-patellar tendon-bone autografts using an anatomic "footprint" technique. Knees tested were ACL-deficient and after reconstruction under three different meniscal states: with partial medial meniscectomy, subtotal meniscectomy, and meniscal root transection. Biomechanical testing was performed at 30 and 60 degrees of flexion under two loading conditions: (1) 134-N anterior tibial load termed anterior tibial translation (ATT) and (2) 10-Nm valgus load combined with 5 Nm of internal tibial torque termed provocative pivot maneuver (PPM). Knee kinematics was measured using a custom activity simulator, motion analysis system, and three-dimensional CT reconstructions. During both ATT and PPM loading, ACL deficiency resulted in a significant increase in anterior translation compared with knees with an intact ACL or those that had undergone ACL reconstruction (p < 0.05). Neither the addition of a partial nor subtotal medial meniscectomy led to increased instability. Only after medial meniscal root transection was increased instability of the ACL-deficient knee detected compared with intact, partial, or subtotal meniscectomy states (p < 0.01). In all states of meniscal deficiency, ACL reconstruction restored internal tibial rotation and anterior translation at 30 degrees to that of the intact knee (p > 0.05). Anatomic single bundle ACL reconstruction was able to restore knee stability in all conditions of medial meniscal deficiency.