August 01, 2010
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Hip and knee arthroplasty: The next decade

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Looking back over the past decade, attempts to improve the outcome of total joint arthroplasty (TJA) have included the use of computer-assisted navigation, alterations in surgical exposure, improved pain control and accelerated postoperative rehabilitation. Computer-assisted navigation was designed to improve procedure reproducibility in the face of anatomic variations and deformity, as well as the imprecision of standard surgical technique. Navigation has been further expanded to include the use of robotics for specific knee arthroplasty procedures, such as unicompartmental and patellofemoral arthroplasty. While certain U.S. centers utilize navigation routinely, it has not been widely adopted by the surgical community.

Minimally invasive surgery (MIS) techniques for hip and knee arthroplasty were introduced based on the premise of minimizing deep soft-tissue dissection and most centers have adopted these techniques to varying degrees. Perhaps of greater importance, in conjunction with navigation and MIS, has been progress in the use of multimodal analgesia and postoperative rehabilitation to improve the perioperative experience. Currently, patients undergo TJA with the overall benefit of multi-drug synergistic cocktails and so experience less pain, narcotic usage, and, on average, are ambulatory in a shorter period of time following surgery and experiencing shorter hospital stays with fewer admissions to rehabilitation facilities.

The question we address: what lies ahead for TJA?

Infection

Preoperative antibiotic prophylaxis and attention to improving the external environment in which the surgery is performed has led to a decrease in the overall rate of infection after primary arthroplasty, periprosthetic infection remains amongst the most devastating complications following elective TJA.

Current methods to diagnose and treat these infections have improved, but continue to yield equivocal scenarios and culture negative infections. New diagnostic imaging methods have been introduced to assist in the evaluation for infection. Fluorodeoxyglucose positron emission tomography and immunoglobulin labeled white blood cells (WBC) are available to address the low specificity of traditional Technetium-99 bone scans in differentiating inflammation from infection. Additional work on refining the use of WBCs obtained from infected synovial fluid aspirates is likely to become commonplace practice in the next decade. WBCs demonstrate a specific gene expression profile which differs significantly from one bacterial species to another. The future goal of an outpatient test that can diagnose infection from a synovial fluid aspirate while identifying the causative organism is likely to be achieved in the next decade.

Anthony M. DiGioia III
Anthony M. DiGioia III
Editor

Additionally a novel route of antibiotic delivery has been developed by which antibiotics are covalently bonded to the prosthesis, thus enhancing local tissue administration. Tethering of the implant surface with high-dose antibiotics provides a method by which prevention, as well as local treatment of peri-prosthetic infection, may someday obviate the need for systemic intravenous antibiotics.

Implant design

Several advances have occurred in implant design since the introduction of TJA. At the knee, kinematics have been more difficult to replicate as compared to hip biomechanics. One reason for this discrepancy is based on the need to sacrifice the ACL at the time of total knee arthroplasty (TKA) in the vast majority of implant designs. Current work is underway with several implant manufacturers to develop a bi-cruciate retaining TKA that would better reproduce normal knee kinematics, allow for better joint proprioception and improve function.

While previous attempts at implant customization have never become popular (or showed significant benefit), the development of gender-specific implants has brought with it enthusiasm for patient specific instruments (PSI) customized to the patients specific anatomy based on preoperative MRI or CT imaging. The goal is to create disposable, patient-matched customized femoral and tibial blocks to allow for efficient and accurate device implantation. There is some concern regarding cost of PSI, but cost savings may be realized by having only one tray of instruments/trials compared to the traditional requirement of multiple trays for an arthroplasty procedure. Future developments may include changes in the supply chain for delivery of implants from the current holding of large inventories to a “just-in-time” manufacture and delivery system based on more precise pre-operative planning.

Basic science

As orthopedic surgery has continued to evolve, basic science represents a significantly larger component of our understanding of both diagnosis and treatment. The genetic basis for osteoarthritis (OA) and finding a biologic-based cure has been challenging. It is certain that genetics plays a critical role in the disease process, since 80 years-old previous marathon runners may present without any lower-extremity joint arthritis. Understanding this genetic basis is the first step in discovering an effective, non-arthroplasty treatment modality – we are not there yet, but we are getting closer.

Recently, orthopedic surgeons have developed a better understanding of femoroacetabular impingement (FAI) and its potential role as a precursor to the development of hip OA. Younger, more active patients diagnosed with FAI are being considered for decompression of cam (femoral) and/or pincer (acetabular) lesions via hip arthroscopy or open, surgical dislocation. Long-term effects of early decompression and labral surgery are as yet unknown; but the ability to stave off end-stage hip arthritis via decompression remains a distinct possibility and fervent hope.

The in-vitro regeneration of articular cartilage can be done reproducibly by using the proper biologic environment and appropriate growth factors. The field of functional tissue engineering is designed to expose chondrocytes to the proper biologic cues in conjunction with the appropriate mechanical environment with the use of bioreactors, in order to have cells produce an adequate extracellular matrix to carry out their proposed function. Herein lays the challenge with replacing damaged cartilage in an arthritic knee or hip with in-vitro produced neo-cartilage; not only is the chemical environment compromised due to the presence of inflammatory cytokines and cartilage toxic mediators, the mechanical environment has been altered secondary to the arthritic process which results in joint/extremity deformity. Incorporation of the biological cartilage components with non-biologic materials is also being investigated as a bridge between purely biologic and purely mechanical reconstruction.

Education

While the effort to incorporate these basic science principles into treatment modalities, a cure for OA with biological modalities is still on the distant horizon, leaving TJA the most effective and reproducible method by which to treat lower-extremity, end-stage degenerative joint disease for the near future.

As the orthopedic body of knowledge continues to increase, so does the burden of training residents and fellows. The spectrum of procedures the trainee is expected to master increases daily. While the use of simulator training has been demonstrated to improve performance in other fields of complex human performance, and has been effectively incorporated into other medical fields, including general and urologic surgery, its use in orthopedic training remains limited. The incorporation of surgical simulators in the transmission of surgical principles and performance in the next generation will increase the acquisition of expertise by improving the way surgeons learn.

  • Anthony M. DiGioia III, MD, is the editor of Emerging Technologies & Innovation, he can be reached at Renaissance Orthopaedics, PC, and Pittsburgh, Pennsylvania Innovation Center, Magee-Womens Hospital of UPMC, Pittsburgh, Pennsylvania. He is a shareholder in Blue Belt Technologies.