E. Marlowe Goble

Minimally invasive total knee replacement: principles and technique

Recent attention toward minimally invasive approaches to joint replacement has resulted in new MIS TKA techniques for the implant of conventional TKA implant components. These proposed techniques must be evaluated thoroughly and changes approached with caution. Medial and lateral techniques that minimize interruption and dissection of neuro-vascular tissues, muscles, tendons, and ligament shave been described. Patients who have undergone these procedures have benefited short term from quicker recovery time and less pain and have benefited long term from the use of conventional prosthesis. Before MIS can become an accepted surgical technique for TKA, a clear understanding of the unique guiding principles behind MIS TKA must be understood and realized. Once these basic principles are followed and the surgeon is familiar with MIS TKA techniques, this technique should prove to be a substantial step forward in the continuum of TKA procedure development.

Positioning of the tibial tunnel for anterior cruciate ligament reconstruction

Two mechanisms of unintentional anterior tibial tunnel axis shift can occur despite accurate placement of the guide wire within the proximal tibia. The first results from using a short-block reamer head joined to a shaft of smaller diameter. If the tibial tunnel is drilled obliquely, it is possible for the reamer head to displace anteriorly in the knee joint before completion of the posterior portion of the tibial tunnel. The second mechanism of anterior shift involves using two sequential drills to create the tibial tunnel. To delineate the causes of this unwanted shift, cadaveric studies and special roentgenographic studies were undertaken. Results demonstrated that the shift is related directly to the presence of high-density bone in the tibial plateau. In an effort to minimize this effect, various drill designs were tested, and it was determined that a drill-head length of 25 mm was most effective at reducing the shift without sacrificing the freedom of movement necessary to obtain precise endosteal placement of the femoral tunnel. Along with these experimental studies, a retrospective 7-year review of anterior cruciate ligament (ACL) reconstruction failures was performed to assess the clinical significance of inadvertent anterior positioning of the tibial tunnel.

Simultaneous quantitation of knee ligament forces

An apparatus and experimental technique have been developed which allow the simultaneous quantitation of human cadaver knee ligament forces with the knee in various positions and subjected to various loads. The methodology permits all the major ligaments of the knee to be kept intact, thus preserving much of their normal relative load-bearing function. A novel measurement technique was employed for ligament force measurement. Strain gauges were placed at the ligamentous insertions and origins either on cortical bone or the cancellous/cortical transition. Gauge output was subsequently calibrated quantitatively by cutting the ligaments and subjecting them to known loads. The gauging technique was thermally stable, and the method as a whole yielded reproducible relative ligament force data when knee positions and loads were repeated for a given knee specimen. Three fresh human cadaver knee specimens have been subjected to testing thus far with gauges at six ligamentous sites. Initial evaluation of the data indicate that ligamentous loading patterns were quite different from those reported in the literature as determined by other methods.

Meniscal Allograft Transplantation

The medial and lateral menisci of the knee perform vital biomechanical functions that contribute to the maintenance of articular cartilage and provide a protective barrier against degenerative joint disease. Removal or damage to all or part of the meniscus has been generally felt to increase the likelihood of articular degeneration and the development of osteoarthritis.1 In a recent study presented at the Meniscus and Articular Cartilage Transplantation study group, Vail et al2 were able to show that articular surface damage is present as early as 12 weeks postmeniscectomy in skeletally mature mongrel dogs. This study included the finding of a decreased tensile modulous for articular cartilage following meniscectomy, and suggests that changes in collagen composition, density, and structure may be early events in the pathogenesis of cartilage degeneration. Currently, it is felt that the functions of the menisci include shock absorption, load transmission, secondary mechanical stability, and possible joint lubrication and/or nutrition.

Arthroscopic and endoscopicallograft reconstruction

Abstract Advantages for the choice of an allograft anterior cruciate ligament (ACL) reconstruction include the following:rapid and uncomplicated rehabilitation; avoidance of the need to harvest a graft from the affected individual, thus avoiding possible complications; prolonged rehabilitation; a readily available source of graft material in the case of revision ACL surgery; adequate tissue availability when the need exists for multiple ligament replacement within the knee; a shortened anesthesia in surgical time to perform the procedure and tissue alternatives for individuals with a congenital tissue laxity. Disadvantages for allograft use include expense, the possibility of disease transmission, and variables in the harvest procurement in preparation of the graft. The surgical technique for installation of an allograft, bone-patellar-bone preparation, is described. This technique is designed for endoscopic tandem tunnel, minimally invasive surgery. The described use of a right-angle set screw for a femoral fixation permits ease in installation and also ease of removal of the implant device if revision or other reasons for removal of hardware is ever necessary. Right-angle set screw femoral fixation and interference screw tibial fixation permit aggressive rehabilitation in an effort to return the athlete to sport in a minimal amount of time. Pull strengths of fixation approach the tensile strength of the ligament itself.