William D. Lew

Soft tissue release in total knee arthroplasty : Cadaver study using knees without deformities

Soft tissue releases are performed to correct fixed deformities in total knee arthroplasty. The goal of this in vitro study was to investigate the relationship between the individual steps in a medial (eight anatomic specimen knees) or lateral (four anatomic specimen knees) soft tissue release sequence, the resulting change in the medial and lateral tibiofemoral gaps, and the change in coronal angulation caused by 10 Nm varus and valgus moments in extension and 90 degrees flexion. An optical encoder was used to measure the coronal angulation. The tibiofemoral gaps were measured with calipers with the knee distracted by a 53-N load. In the medial release sequence, a significant increase in coronal angulation and medial gap occurred after the release of the anteromedial sleeve 8 cm from the medial joint line. In the lateral release sequence, there was a significant increase in the coronal angle and lateral gap after the lateral collateral ligament and popliteus tendon were released from the femur. Release of the posterior cruciate ligament led to a significant increase in angle and gap in medial and lateral release sequences. These results are specific for the particular release sequences studied, with release of the posterior cruciate being the final step in each sequence.

Osteogenic protein-1 induced bone formation in an infected segmental defect in the rat femur.

The goal of this study was to use a segmental defect model in the rat femur to determine if osteogenic protein‐1 (OP‐1) is capable of inducing bone formation in the presence of bacterial contamination. A 6 mm segmental defect was surgically created and stabilized with a polyacetyl plate and Kirschner wires in one femur in each of 126 Sprague–Dawley rats. The animals were divided into eight groups in which the defect was either left untreated, or subjected to various combinations of OP‐1 (11 or 50 μg), lyophilized bovine type I collagen (carrier for the OP‐1), and 105 colony‐forming units of Staphylococcus aureus. The animals were euthanized at either 2, 4, or 9 weeks. Quantitative radiographic and histologic analyses were performed on the harvested tissue. The initial contamination progressed to infection in all animals receiving bacteria, as determined by qualitative bacteriology. There was very little, if any, bone formation in the untreated defects, and in the contaminated defects with or without collagen carrier. Bone formation was significantly greater in contaminated defects with either dose of OP‐1, compared with contaminated defects without OP‐1. The 50 μg dose of OP‐1 induced significantly more bone formation than the 11 μg dose, both with and without bacteria. This investigation has demonstrated that OP‐1 maintains its osteoinductive capability in a contaminated segmental defect. OP‐1 may potentially be used in the clinical management of contaminated fractures.

Biomechanics of Ankle Ligament Reconstruction An In Vitro Comparison of the Broström Repair, Watson-Jones Reconstruction, and a New Anatomic Reconstruction Technique

We wanted to use biomechanical testing in a cadaveric model to compare the Broström repair, the Watson- Jones reconstruction, and a new anatomic reconstruc tion method. Eight specimens were held in a specially designed testing apparatus in which the ankle position (dorsiflexion-plantar flexion and supination-pronation) could be varied in a controlled manner. Testing was done with intact ligaments and was repeated after sectioning of the anterior talofibular ligament and the calcaneofibular ligament and after a Broström repair, a Watson-Jones reconstruction, and a new anatomic re construction were performed. An anterior drawer test was performed using an anterior translating force of 10 to 50 N, and a talar tilt test was performed using a supination torque of 1.1 to 3.4 N-m. The forces in the anterior talofibular ligament and calcaneofibular liga ment were measured with buckle transducers, and tibiotalar motion and total ankle joint motion were meas ured with an instrumented spatial linkage. The in crease in ankle joint laxity observed after sectioning of both the anterior talofibular and calcaneofibular liga ments was significantly reduced by the three recon structive techniques, although not always to the level of the intact ankle. Joint motion was restricted after the Watson-Jones procedure compared with that in the intact ankle. Unlike the Watson-Jones procedure, the ligament or graft force patterns observed during load ing after the Broström repair and the new anatomic technique resembled those observed in the intact ankle.

Effect of anterior cruciate ligament graft tensioning direction, magnitude, and flexion angle on knee biomechanics

The objective of this study was to determine the bio mechanical effect of graft tensioning during reconstruc tion of the anterior cruciate ligament. We evaluated the magnitude of the tensioning force (22 or 67 N), the flexion angle at which the tension was applied (exten sion or 30° of flexion), and the direction of application of the tensioning force (proximal, distal, or distal with a posterior force simultaneously applied to the tibia) on 10 fresh cadaveric knees. The anterior cruciate liga ment was reconstructed using a bone-patellar tendon- bone graft. The graft was then temporarily fixed during the application of each of 12 combinations of tensioning variables listed above. After each fixation, graft force and joint motion were measured during anterior tibial loads. Tensioning direction and the flexion angle significantly affected graft force and joint motion, while the magni tude of the graft tensioning did not. Graft forces were greater when the tensioning was applied at 30° of flexion. Compared with distal tensioning with and with out posterior tibial force, graft forces with proximal tensioning were greater in extension and lower in flex ion. The position of the tibia relative to the femur was posterior and externally rotated, compared with normal, for all combinations of tensioning variables in both unloaded and anterior load states.

Mechanics of the anterior drawer and talar tilt tests: A cadaveric study of lateral ligament injuries of the ankle

We analyzed the changes in lateral ligament forces during anterior drawer and talar tilt testing and examined ankle joint motion during testing, following an isolated lesion of the anterior talofibular ligament (ATFL) or a combined lesion of the ATFL and calcaneofibular ligament (CFL). 8 cadaver specimens were held in a specially designed testing apparatus in which the ankle position (dorsiflexion-plantarflexion and supination-pronation) could be varied in a controlled manner. Ligament forces were measured with buckle transducers, and joint motion was measured with an instrumented spatial linkage. An anterior drawer test was performed using an 80 N anterior translating force, and a talar tilt test was performed using a 5.7 Nm supination torque with intact ligaments, after sectioning of the ATFL, and again after sectioning of the CFL. The tests were repeated at 10 degrees dorsiflexion, neutral, and 10 degrees and 20 degrees plantarflexion. In the intact ankle, the largest increases in ATFL force were observed during testing in plantarflexion, whereas the largest increases in CFL force were observed in dorsiflexion. Isolated ATFL injury caused only small laxity changes, but a pronounced increase in laxity was observed after a combined CFL and ATFL injury.

Knee Joint Motion and Ligament Forces Before and After ACL Reconstruction

The goal of this in vitro study was to investigate the initial postoperative mechanical state of the knee with various types of anterior cruciate ligament (ACL) reconstructions. An experimental knee testing system was developed for the in vitro measurement of ligament forces and three-dimensional joint motion as external loads were applied to fresh knee specimens. Two groups of knee specimens were tested. In test series #1, two intraarticular reconstructions were performed in each of five specimens using semifree and free patellar tendon grafts with bone blocks. In test series #2, a more carefully controlled intraarticular reconstruction was performed in five specimens using a semifree composite graft consisting of the semitendinosus and gracilis tendons augmented with the Ligament Augmentation Device. Ligament force and joint motion data were collected as anteriorly directed tibial loads were applied to the normal joint, the joint with a cut ACL and the reconstructed joint. These knee joint states were compared on the basis of ACL or graft forces, joint motion and load sharing by the collateral ligaments. The dominate result of the study was that the forces and motions defining the mechanical state of the knee after the ACL reconstructions in both test series were highly variable and abnormal when compared to the normal knee state. The higher level of surgical control series #2 did not decrease this variability. There was a poor correlation between motion of the reconstructed knee relative to normal, and the ACL graft force. There was little consistent difference in force and motion results between the surgical procedures tested.

Description and Error Evaluation of an In Vitro Knee Joint Testing System

An experimental system for the analysis of knee joint biomechanics is presented. The system provides for the simultaneous recording of ligament forces using buckle transducers and three-dimensional joint motion using an instrumented spatial linkage, as in vitro specimens are subjected to a variety of external loads by a pneumatic loading apparatus with associated force transducers. The system components are described, and results of an evaluation of system errors and accuracy are presented. The experimental setup has been successfully used in the analysis of normal knee ligament mechanics, as well as surgical reconstructions of the anterior cruciate ligament. The system can also be adapted to test other human or animal in vitro joints.

Recombinant Human Osteogenic Protein-1 Induces Bone Formation in a Chronically Infected, Internally Stabilized Segmental Defect in the Rat Femur

BACKGROUND Recombinant human osteogenic protein-1 (rhOP-1), combined with a collagen carrier, has been shown to induce new-bone formation in a variety of animal models. The purpose of the present investigation was to test the hypotheses that rhOP-1 would accelerate bone formation in an internally stabilized, chronically infected, critical-size defect in the rat femur and that this effect would be enhanced by the administration of systemic antibiotic. METHODS A 6-mm segmental defect was created surgically, stabilized with a polyacetyl plate and six Kirschner wires, and contaminated with 10(4) colony-forming units of Staphylococcus aureus in one femur in each of 168 Sprague-Dawley rats. After two weeks, these infected defects were débrided surgically and were assigned to one of six treatment groups. The defects in the thirty animals in the first group received lyophilized collagen carrier mixed with 200 microg of rhOP-1 dissolved in buffer, the defects in the thirty animals in the second group received carrier with 20 microg of rhOP-1 in buffer, and the defects in the twenty-four control animals in the third group received carrier mixed with buffer without rhOP-1. The last three groups were treated identically to the first three groups, except that the animals also received the antibiotic ceftriaxone for twenty-eight days after débridement. The animals were killed at two, four, eight, or twelve weeks after débridement. Newly mineralized callus within the defect, and adjacent to and bridging the outside of the defect, was assessed with use of quantitative high-resolution radiography, microcomputed tomography, torsional failure testing, and histological analysis of undecalcified sections. RESULTS Bacterial cultures confirmed the presence of a chronic infection during the study period in all animals. At the later time-points, significantly more newly mineralized callus was present within and adjacent to the débrided defects that had been treated with 200 microg of rhOP-1, whereas minimal amounts of callus were present within and adjacent to the defects that had been treated without rhOP-1 and with 20 microg of rhOP-1. At eight and twelve weeks after débridement, there was significantly more newly mineralized callus in the group that had been treated with 200 microg of rhOP-1 with antibiotic than in the group that had been treated with 200 microg of rhOP-1 without antibiotic (p < 0.05). At twelve weeks, the values for torque, energy to failure, and linear stiffness for femora that had been treated with 200 microg of rhOP-1 with antibiotic were not significantly different from the values for intact, contralateral control femora, whereas the values for femora that had been treated with 200 microg of rhOP-1 without antibiotic remained significantly lower than those for the intact, contralateral controls (p < 0.05). CONCLUSIONS Recombinant human osteogenic protein-1 maintained its osteoinductive capability in the presence of chronic infection, and this property was enhanced by antibiotic therapy. No substantial callus formed in the infected defects without a sufficiently high dose of rhOP-1. CLINICAL RELEVANCE The treatment of an infection at the site of a fracture often necessitates removal of internal fixation. However, internal fixation is needed for fracture stability. This study presents an intervention that may accelerate fracture-healing in the presence of infection and colonized hardware, thereby permitting earlier removal of the hardware and more timely and effective treatment of the infection.

Load sharing and graft forces in anterior cruciate ligament reconstructions with the Ligament Augmentation Device

Buckle transducers were used to directly measure load sharing and overall force in three segment (semitendi nosus, gracilis, Ligament Augmentation Device) and two segment (patellar tendon, LAD) composite ACL grafts during the application of anteriorly directed loads to a series of five fresh knee specimens with a pneu matic load apparatus. The total graft forces generated in the two segment and three segment composite reconstructions during this immediate postoperative state were highly variable when compared to the normal ACL in each specimen, and were irreproducible among the five specimens. Load sharing among the graft com ponents occurred and was also variable in both recon structions, with this variation being greater in the three segment graft. The LAD carried an average of 45% of the total graft force in the three segment graft and 28% in the two segment graft. Further work is required to clarify the source of the variability in the total graft force and load sharing observed in this study.

Ligament force and joint motion in the intact ankle: a cadaveric study

Abstract The aims of this study were to measure the forces in the anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL) and the motion in the tibiotalar and subtalar joints during simulated weight-bearing in eight cadaver ankle specimens. An MTS test machine was used to apply compressive loads to specimens held in a specially designed testing apparatus in which the ankle position (dorsiflexion-plantarflexion and supination-pronation) could be varied in a controlled manner. The forces in the ATFL and CFL were measured with buckle transducers. Tibiotalar motion and total ankle joint motion were measured with an instrumented spatial linkage. The specimens were positioned sequentially at 10° dorsiflexion, neutral, and 10° and 20° plantarflexion, and this sequence was repeated at 15° supination, neutral pronation/supination, and 15° pronation. Force and motion measurements were recorded in each of these positions with and without a 375 N compressive load simulating weight-bearing. From 10° dorsiflexion to 20° plantarflexion, all motion occurred in the tibiotalar joint. In contrast, the ratio of subtalar motion to tibiotalar motion was 3:1 for supination-pronation and 4:1 for internal-external rotation. Inverse loading patterns were observed for the ATFL and CFL from plantarflexion to dorsiflexion. Compressive loading did not affect CFL tension, but it magnified the pattern of increasing ATFL tension with plantarflexion. The largest increase in ATFL force was observed in supination and plantarflexion with a compressive load (76 ± 23 N), whereas CFL tension mainly increased in supination and dorsiflexion with a compressive load (109 ± 28 N). In conclusion, the results showed that the ATFL acted as a primary restraint in inversion, where injuries typically occur (combined plantarflexion, supination and internal rotation). Also, the subtalar joint was of primary importance for normal supination-pronation and internal-external rotation.