Michael J. Askew

Kinematics of posterior cruciate ligament-retaining and -sacrificing mobile bearing total knee arthroplasties

The posterior cruciate ligament (PCL)-retaining, meniscal bearing and the PCL-sacrificing rotating platform designs of the LCS prosthesis (DePuy, Warsaw, IN) were designed to minimally constrain knee kinematics while minimizing bone-cement-prosthesis interface stresses and polyethylene wear. The kinematics and stability of the knee following arthroplasty with these devices rely on adequate tensioning of the remaining soft tissues by management of the flexion/extension gaps at the time of surgery. In this in vitro study, the knee kinematics of the function of the quadriceps mechanism for 8 cadaveric knees were measured quantitatively before and after implantation of these 2 prosthesis designs. Following implantation of the PCL-retaining, meniscal bearing prosthesis, anterior translations during anterior drawer testing were significantly greater (P < .05) than those seen in the intact knee. Implantation of the PCL-retaining, meniscal bearing prosthesis resulted in an increase in the extension gap of 2 mm. Quadriceps force needed to achieve full extension was increased by 30% over that needed in the intact knee. The PCL-sacrificing, rotating platform prosthesis constrained anterior translation such that nearly normal anterior knee stability was reestablished; however, the extension gap was increased by 4 mm and the quadriceps force needed to achieve full extension was 50% greater than that needed in the intact knee. Attempts to achieve joint stability by increases in the thickness of the tibial component to widen the flexion/extension gaps results in compromises of quadriceps efficiency, particularly in the absence of a functioning PCL, as demonstrated in this in vitro model. Patients receiving the PCL-sacrificing prosthesis may experience difficulty in those activities requiring quadriceps power near full extension, such as rising from a chair or ascending or descending stairs.

Kinematics of the Posterior Cruciate Ligament/Posterolateral Corner–Injured Knee After Reconstruction by Single- and Double-Bundle Intra-articular Grafts

Background Single- and double-bundle reconstructions have been proposed for the knee after combined posterior cruciate ligament/posterolateral corner injuries. Hypothesis The double-bundle posterior cruciate ligament reconstruction is superior to the single-bundle posterior cruciate ligament reconstruction with regard to restoration of normal knee kinematics to the posterior cruciate ligament/posterolateral corner-sectioned knee. Study Design Controlled laboratory study. Methods Kinematics of 8 fresh-frozen, cadaveric human knees were determined in the following conditions: intact, sectioned posterior cruciate ligament/posterolateral corner, single anterolateral bundle posterior cruciate reconstruction, and double-bundle posterior cruciate reconstruction. Results The sectioned knee demonstrated a posterior shift of the tibial neutral position and the abnormal posterior, varus, and external rotation laxities used clinically to define a combined posterior cruciate ligament/posterolateral corner injury. Both reconstructions restored the posterior laxity to levels that were not statistically different from those seen in the intact knee, but the double-bundle reconstruction more closely mimicked the posterior laxity profile of the intact knee, having statistically lower posterior laxities than did the single-bundle reconstruction at 30°, 60°, and 90° of flexion (P < .05, analysis of variance, HSD test). The resting position of the tibia after double-bundle reconstruction trended to be anteriorly subluxated relative to its position for the intact knee at flexion angles of 30° and greater (P < .05, paired t test). Neither technique corrected the abnormal varus or external rotation laxities. Conclusion With either single- or double-bundle reconstructions, additional posterolateral reconstruction is recommended to correct the external rotation laxity. Clinical Relevance Knowledge of the kinematics of the combined posterior cruciate ligament/posterolateral corner-injured knee is important in the proper diagnosis of the injury and in the selection of the appropriate surgical reconstruction.

Potential for thermal damage to articular cartilage by PMMA reconstruction of a bone cavity following tumor excision: A finite element study

Benign, giant cell tumors are often treated by intralesional excision and reconstruction with polymethylmethacrylate (PMMA) bone cement. The exothermic reaction of the in-situ polymerizing PMMA is believed to beneficially kill remaining tumor cells. However, at issue is the extent of this necrotic effect into the surrounding normal bone and the adjacent articular cartilage. Finite element analysis (ABAQUS 6.4-1) was used to determine the extent of possible thermal necrosis around prismatically shaped, PMMA implants (8-24cc in volume), placed into a peripheral, sagittally symmetric, metaphyseal defect in the proximal tibia. Temperature/exposure time conditions indicating necrotic potential during the exotherm of the polymerizing bone cement were found in regions of the cancellous bone within 3mm of the superior surface of the PMMA implant. If less than 3mm of cancellous bone existed between the PMMA implant and the subchondral bone layer, regions of the subchondral bone were also exposed to thermally necrotic conditions. However, as long as there were at least 2mm of uniform subchondral bone above the PMMA implant, the necrotic regions did not extend into the overlying articular cartilage. This was the case even when the PMMA was in direct contact with the subchondral bone. If the subchondral bone is not of sufficient thickness, or is not continuous, then care should be taken to protect the articular cartilage from thermal damage as a result of the reconstruction of the tumor cavity with PMMA bone cement.

Growth Hormone Injections Improve Bone Quality in a Mouse Model of Osteogenesis Imperfecta

Systemic growth hormone injections increased spine and femur length in a mouse model of OI. Femur BMC, cross‐sectional area, and BMD were increased. Smaller gains were produced in vertebral BMC and cross‐sectional area. Biomechanical testing showed improvements to structural and material properties in the femur midshaft, supporting expanded testing of growth hormone therapy in children with OI.

A study in vivo of the effects of a static compressive load on the proximal tibial physis in rabbits

BACKGROUND The effect of compression on the physis is generally defined by the Hueter-Volkmann principle, in which decreased linear growth of the physis results from increased compression. This investigation examined whether mechanically induced compression of rabbit physes causes changes in gene expression, cells, and extracellular components that promote physeal resilience and strength (type-II collagen and aggrecan) and cartilage hypertrophy (type-X collagen and matrix metalloprotease-13). METHODS Static compressive loads (10 N or 30 N) were applied for two or six weeks across one hind limb proximal tibial physis of thirteen-week-old female New Zealand White rabbits (n = 18). The contralateral hind limb in all rabbits underwent sham surgery with no load to serve as an internal control. Harvested physes were divided into portions for histological, immunohistochemical, and quantitative reverse transcription-polymerase chain reaction analysis. Gene expression was statistically analyzed by means of comparisons between loaded samples and unloaded shams with use of analysis of variance and a Tukey post hoc test. RESULTS Compared with unloaded shams, physes loaded at 10 N or 30 N for two weeks and at 10 N for six weeks showed histological changes in cells and matrices. Physes loaded at 30 N for six weeks were decreased in thickness and had structurally disorganized chondrocyte columns, a decreased extracellular matrix, and less intense type-II and X collagen immunohistochemical staining. Quantitative reverse transcription-polymerase chain reaction analysis of loaded samples compared with unloaded shams yielded a significantly (p ≤ 0.05) decreased gene expression of aggrecan and type-II and X collagen and no significant (p > 0.05) changes in the matrix metalloprotease-13 gene expression with increasing load. CONCLUSIONS Compressed rabbit physes generate biochemical changes in collagens, proteoglycan, and cellular and tissue matrix architecture. Changes potentially weaken overall physeal strength, consistent with the Hueter-Volkmann principle, and lend understanding of the causes of pathological conditions of the physis.

Reconstructions of the Knee Following Combined Injury to the Posterior Cruciate Ligament and the Posterior Lateral Structures

The posterior cruciate ligament (PCL) provides primary restraint to posterior tibial translation (1). Knee injuries involving only the PCL usually result in minimal disability, and are commonly treated non-surgically (2). However, combined injuries of the PCL and the posterior lateral structures (PLS) in the knee can result in considerable abnormal posterior laxity and posterolateral rotary instability leading to rapid cartilage degeneration (3). There is consensus that, in most cases, knees with this combined injury require surgical reconstruction.Copyright

In-vitro kinematic comparison of the New Jersey LCS meniscal bearing and rotating platform prostheses

An example of a mobile meniscal bearing prosthesis design is the LCS Knee System (DePuy, Inc., Warsaw, IN). This prosthesis system provides a mobile bearing prosthesis for use when the posterior cruciate ligament (PCL) is retained and a rotating platform prosthesis for use when the PCL is sacrificed iatrogenically or has been lost to pathology. The purpose of the present study was to examine, in in-vitro models, the stability provided the knee by implantation of these two versions this mobile meniscal bearing prosthesis system. Following installation of the meniscal bearing PCL-retaining prosthesis, anterior/posterior tibial translation was significantly increased over that seen in the intact knee for the anterior drawer tests at both 90 and 30 degrees of flexion. The observations in this study of increased anterior/posterior laxity following installation of the meniscal bearing prosthesis are in qualitative agreement with those made by Schlepckow (1992). However, it would appear that the design of the rotating platform PCL-sacrificing prosthesis substitutes in some way for the roles played by the anterior and posterior cruciates in the restraint of anterior/posterior tibial motion. While the bearings of the meniscal bearing prosthesis allow unhindered anterior/posterior travel over a fairly long distance, the tibial condyle design of the rotating platform prosthesis may present anterior/posterior lips to restrain anterior/posterior motion after modest amounts of anterior/posterior tibial translation.