The clinical outcomes of cementless unicompartmental knee replacement in patients with reduced bone mineral density

BACKGROUND

Osteoporosis and osteopenia are conditions characterised by reduced bone mineral density (BMD). There is concern that bone with reduced BMD may not provide sufficient fixation for cementless components which primarily rely on the quality of surrounding bone. The aim of our study was to report the midterm clinical outcomes of patients with reduced BMD undergoing cementless unicompartmental knee replacements (UKR). Our hypothesis was that there would be no difference in outcome between patients with normal bone and those with reduced BMD.

METHODS

From a prospective cohort of 70 patients undergoing cementless UKR surgery, patients were categorised into normal (n = 20), osteopenic (n = 38) and osteoporotic groups (n = 12) based on their central dual-energy X-ray absorptiometry (DEXA) scans according to the World Health Organization criteria. Patients were followed up by independent research physiotherapists and outcome scores; Oxford Knee Score (OKS), Tegner score, American Knee Society Score Functional (AKSS-F) and Objective (AKSS-O) were recorded preoperatively and at a mean of 4 years postoperatively. The prevalence of reoperations, revisions and mortality was also recorded at a mean of 5 years postoperatively.

RESULTS

There were no significant differences in the midterm postoperative OKS (P = 0.83), Tegner score (P = 0.17) and AKSS-O (P = 0.67). However, the AKSS-F was significantly higher (P = 0.04) in normal (90, IQR 37.5) compared to osteoporotic (65, IQR 35) groups. There were no significant differences (P = 0.82) between normal and osteopenic bone (80, IQR 35). The revision prevalence was 5%, 2.6% and 0% in the normal, osteopenic and osteoporotic groups respectively. The reoperation prevalence was 5%, 7.9% and 0% respectively. There were no deaths in any group related to the implant.

CONCLUSIONS

We found that patients with reduced BMD could safely undergo cementless UKR surgery and have similar clinical outcomes to those with normal BMD. However, larger studies with longer follow-up are needed to confirm our findings and ensure that cementless fixation is safe in patients with reduced BMD.

Low-Contact-Stress Knee Arthroplasty: Past History or Ahead of Time?

Low-contact-stress mobile-bearing (MB) total knee arthroplasty (TKA) can rely on a long history. Its concept comprises a combination of high condylar congruency and compensatory bearing rotation to promote load sharing. However, other MB designs have become available, and critical points have been raised about the benefit of MB in general. Although there is kinematic and kinetic support for the low-contact-stress concept, there is no tribologic or clinical proof of its superiority over fixed-bearing concepts. Further study should be controlled for differences in polyethylene quality and need to provide a measure of condylar congruency to differentiate authentic low-contact-stress variants form others. [Orthopedics. 2016; 39(3):e402-e412.].

[Evolution of total knee arthroplasty. From robotics and navigation to patient-specific instruments]

In this article the evolution beginning with the robotics of total knee arthroplasty to CT-based and kinematic navigation and patient-specific instruments is described. Thereby it is pointed out that in the early 1990s, CT imaging solely for the planning of a knee endoprosthesis was considered as obsolete radiation exposure and this led to the widespread development of kinematical systems.Also a patient specific planning tool based on CAD built acryl harz blocs existed at the time. There is an ongoing process of implanting total knee arthroplasties in a more exact position. Nowadays the new evolution of soft tissue balancing by using a kinematic alignment has put these efforts into perspective.

Metal backed fixed-bearing unicondylar knee arthroplasties using minimal invasive surgery: a promising outcome analysis of 132 cases

BACKGROUND

Unicondylar knee arthroplasty (UKA) is a well-established treatment for isolated osteoarthritis (OA) of the medial knee compartment. Aim of this retrospective study was to evaluate the early clinical and radiological outcomes of a consecutive series of patients treated with medial metal backed fixed-bearing UKA. Furthermore, the influence of the component orientation on the outcome was analyzed.

METHODS

From 09/2006 to 11/2010 106 patients (132 knees; 69 ± 9 years) were treated using a metal backed fixed-bearing UKA with a MIS approach. All patients underwent a standardized clinical and radiological follow-up at 6 weeks, 1, 2 and 5 years. Mean follow-up was 3.4 ± 1.0 years. Two patients (three UKAs) deceased and two patients (two UKAs) were lost to follow-up. Three different survival analyses were performed using three different endpoints defining failure: (a) revision with exchange of any UKA component (b) aseptic loosening and (c), a worst case scenario, where it was assumed that all progressive radiolucencies would lead to aseptic loosening and thus these were additionally counted. Clinical outcome was assessed using the American knee society score (AKS) and the Oxford knee score (OKS). Radiographic analysis was done according to the American Knee Society Evaluation and Scoring System adapted for UKA and correlated with the AKS and OKS.

RESULTS

Five UKAs (3.8 %) were revised to total knee arthroplasties (TKAs) after a median of 25 (10-33) months. Five year survival was 95.2, 97.5 and 87.7% for the aforementioned endpoints. At final follow-up the median AKS knee score was 99 (50-100) points and the median AKS function score was 100 (60-100) points. The median OKS was 43 (8-48) points. Clinical outcome was independent of the component orientation.

CONCLUSION

Fixed-bearing UKA showed excellent clinical and radiological results at up to 5 years follow-up. Outcome was independent of component orientation.

[RESEARCH PROGRESS OF GENDER-SPECIFIC PROSTHESIS]

OBJECTIVE

To summarize the research progress of the design and effectiveness of gender-specific prosthesis in total knee arthroplasty (TKA).

METHODS

The relevant literature on gender-specific prosthesis in recent years was extensively reviewed and analyzed.

RESULTS

Gender-specific prosthesis is designed according to the female knee joint anatomical characteristics. In theory, it should obtain better effectiveness. But a large number of clinical studies have shown that the knee function, pain, and satisfaction has no obvious advantage when compared with conventional prosthesis after TKA for female patient.

CONCLUSION

Comprehensive evaluation should be considered when gender-specific is selected; and the effectiveness needs further follow-up.

Designing for scale: development of the ReMotion Knee for global emerging markets

Amputees living in developing countries have a profound need for affordable and reliable lower limb prosthetic devices. The World Health Organization estimates there are approximately 30 million amputees living in low-income countries, with up to 95% lacking access to prosthetic devices. Effective prosthetics can significantly affect the lives of these amputees by increasing opportunity for employment and providing improvements to long-term health and well-being. However, current solutions are inadequate: state-of-the-art solutions from the US and Europe are cost-prohibitive, while low-cost devices have been challenged by poor quality and/or unreliable performance, and have yet to achieve large scale impact. The introduction of new devices is hampered by the lack of a cohesive prosthetics industry in low-income areas; the current network of low-cost prosthetic clinics is informal and loosely organized with significant disparities in geography, patient volume and demographics, device procurement, clinical and logistical infrastructure, and funding. At D-Rev (Design Revolution) we are creating the ReMotion Knee, which is an affordable polycentric prosthetic knee joint that performs on par with devices in more industrialized regions, like the US and Europe. As of September 2012, over 4200 amputees have been fitted with the initial version of the ReMotion Knee through a partnership with the JaipurFoot Organization, with an 79% compliance rate after 2 years. We are currently scaling production of the ReMotion Knee using centralized manufacturing and distribution to serve the existing clinics in low-income countries and increase the availability of devices for amputees without access to appropriate care. At D-Rev, we develop products that target these customers through economically-sustainable models and provide a measurable impact in the lives of the world's amputees.

New technologies in knee arthroplasty

Advances in surgical technique and implant design have increased the treatment options available to joint reconstruction surgeons. New technologies for component alignment such as custom cutting blocks and disposable cutting blocks hold the potential for more anatomic component positioning and less instrument turnover which may decrease infection rates. Improved component alignment may also be obtained with the use of computer-assisted surgery. Utilization of bone-sparing designs such as patellofemoral, unicompartmental, and bicompartmental knee arthroplasty allow for the surgeon to customize treatment based on patient symptoms by addressing each compartment individually. Gender-specific designs may be useful in the setting of populations which deviate from standard dimensions that are available in traditional unisex designs. New higher-conforming bearing designs such as rotating platform bearings allow for more natural knee kinematics, while also limiting polyethylene wear by decreasing contact stress. Newer interfaces for cementless fixation utilizing porous coated surfaces allows for biologic component fixation which has the potential to increase interface durability and implant survivorship. These new materials, designs, and techniques are challenging the traditional "gold standard" cemented total knee arthroplasty and have the potential for developing a more durable and naturally feeling prosthetic knee. Further study is required to identify which patients are most appropriate for each new technology.

New trends and early clinical outcomes with a modern knee revision system

The incidence of revision total knee arthroplasty (TKA) has grown tremendously the past decade, and all projections suggest that it will continue to increase during the next 25 years. Although primary TKA remains one of the most successful orthopedic procedures, revision TKA has not as well. Failure rates for revision TKA remain significantly higher than those for primary TKA. New revision systems should be developed with new implants and instrumentation to address the difficulties frequently experienced with revision TKA. In this article, design surgeons report on the development of a new system and the early clinical experience with its use. The researchers believe that this new system is easy to use and facilitates accurate implantation, which could improve revision TKA outcomes.

Trends in total knee arthroplasty

The success of total knee arthroplasty (TKA) over the past two decades of use has resulted in the implantation of TKA into younger patients who have increased functional requirements and demand increased implant longevity. Improved functional performance requires enhanced range of motion, increased motor performance, and creation of kinematic patterns that more closely resemble the normal knee. Increased longevity necessitates more durable implant fixation, improvements in bearing materials, and lower polyethylene stresses. Considerations to reduce polyethylene wear include increased cross-linking, improved femoral component surface finish, better modular tibial locking mechanisms, and the use of mobile-bearing TKA designs that allow increased implant conformity and reduced contact stresses without increasing loads transmitted to the fixation interface.

Novel strategies in joint replacement

As the need for hip and knee replacement continues to increase, technical and material changes have allowed a dramatic evolution in the way that degenerative, inflammatory and traumatic arthritis are managed. Advances include new bearing surfaces which should have greater longevity, minimal incision joint replacement, computer guidance and partial joint resurfacing for younger patients. These advances and their implications are discussed.

Unicompartmental Knee Arthroplasty (Alias Uni-Knee)

During the past 30 years, the unicompartmental knee arthroplasty has undergone growing pains with various implant designs, refining indications, and improving surgical techniques and instrumentation. Today, studies show survivorship results comparable to the tricompartmental total knee arthroplasty and a renewed interest has emerged. Even though the unicompartmental knee arthroplasty is recommended for only a select 10-15% who have osteoarthritis of the knee, it has many advantages over the total knee arthroplasty. Although the nursing care and rehabilitation are similar to the total knee arthroplasty, including wound care, prophylactic antibiotics, and venous thromboembolism prophylaxis, the patient frequently has less pain, increased range of motion, shorter hospitalization, and fewer complications, resulting in a quicker rehabilitation.

[Innovations in total knee arthroplasty]

The development of total knee arthroplasty started in the fifth decade last century. Modern total knee joint systems represent a high grade of modularity for a usage within the whole range of joint destruction situations, such as for rheumatoid arthritis. Innovations for improved long term survival can be seen in methods reducing aseptic loosening, such as new implant materials or mobile platforms. Moreover improved surgical techniques for precise component orientation and reconstruction of a neutral leg axis have been introduced using computer assisted surgery. So far the results using this technique are very promising. Long term results are not yet available.

Design may be counterproductive for optimizing flexion after TKR

Pain-free flexion of as much as 155 degrees with stability is the ultimate goal of total knee replacement (TKR). Achieving this amount of flexion depends on implant design, surgical technique, preoperative range of motion (ROM), and patient cooperation. Current design trends are focusing on shortening the radii of curvature; such shortening, in turn, thickens the posterior femoral condyle, and increases the height of the posterior-stabilized box, both of which require removal of more bone. The end results may be excessive wear, increased patellofemoral complications, and difficult revisions. Several studies have indicated preoperative ROM is more predictive of postoperative ROM than any other criteria, including implant design. Based on currently available information, if full or almost full preoperative ROM is required for the high flex total knee design, few patients would qualify for the high flex TKA.

Optimizing flexion after total knee arthroplasty: advances in prosthetic design

The clinical results with most modern total knee arthroplasty (TKA) designs are highly satisfactory regarding pain relief and improving walking ability. However, one problem that has not been addressed fully by most current designs is the ability to consistently achieve flexion greater than 120 degrees. Although the human knee is capable of flexion of more than 150 degrees, an analysis of the results of contemporary TKA reveals that on average, patients rarely flex beyond 120 degrees. Key factors influencing range of flexion after TKA include preoperative knee motion, surgical technique, prosthetic design, and rehabilitation. The success of any total knee system may in part be linked to its ability to optimally restore normal kinematic function. Some arthroplasty designs currently are available that incorporate modifications aimed at improving range of flexion, but limited data currently are available on their function and potential advantages. Currently, an in vitro experimental model incorporating robotics is being used to investigate the kinematics of the native knee and various TKA designs at flexion angles beyond 120 degrees. This robotic model in conjunction with clinical studies may provide an understanding of the limitations of contemporary knee designs regarding achieving higher degrees of knee flexion. This may lead to the refinement of existing designs and development of newer prostheses that may enhance the range of flexion that is achievable after TKA.

Bone cement--porous coated or hydroxylapatite coated prosthesis in total knee arthroplasty--state of the art--future trends

1. Cementation in total knees is here to stay. 2. Future improvements will lie in the area of implant interfaces--in the near term by improving our polyethylene. 3. Cementless knees, with or without HA, may be indicated in the young, more active patient and where economic concerns have no impact on prosthetic selection.

Enumeration of human knee prostheses--an overview

Very often clinicians prescribe a limited number or only one type of knee mechanism because it has been found reliable or perhaps specific information on the range and variety of all available mechanisms has not been on hand. The clinician rarely has the opportunity to see all the mechanisms in a common perspective to compare the relative merits of one mechanisms with another. An attempt has been made to enumerate the available human knee-prostheses, both implants and external prostheses, according to their motion. An historical development of knee prosthesis is discussed. A classification procedure is developed for both internal and external prostheses based on their primary functions. The two major classifications in either of these prostheses are monocentric and polycentric mechanisms. A mechanism whose center of rotation does not change through out the range of motion is considered as monocentric mechanism and a mechanism whose center of rotation changes during its operation is considered as polycentric mechanism. The implants are categorized as hinged and non-hinged knee joints. The external prostheses are further classified based on certain primary functions like control in swing phase and/or in stance phase and in extension. The hierarchical classification scheme will benefit kinematicians and designers to analyze the available mechanisms and make necessary improvements. This will also provide a ready-reference to the prosthetists in selecting the best-fit prosthesis from a large family of prostheses.

The evolution of knee arthroplasty. Results with three generations of prostheses

One hundred sixty total knee arthroplasties using the Walldius (90), geometric (31), and total condylar (39) prostheses were analyzed by standardized ratings. Patients with total condylar knees had the highest mean postoperative rating, although the patients with Walldius knees derived the greatest symptomatic relief from surgery. There were 12 failures. Varus placement of the prosthesis occurred in 11 patients; eight of these knees were symptomatic. There were six wound infections, five of which were salvaged. The unsolved problems of total knee arthroplasties are: malalignment, loosening, infection, wear, and balancing mobility with stability.

Prosthetics and orthotics in developing countries

Principles of orthoses and prostheses in developing countries are discussed. Appropriate technological adaptations to suit cultural needs in developing countries have been identified and illustrative examples have been given. In view of the importance of the problem of leprosy in many developing countries, a separate description to cover prosthetic and orthotic appliances including footwear has been attempted. The material is a summary of the excellent publication from Alert in Addis Ababa.

Replacement arthroplasty of the knee joint: trends and treatment after failure

Knee joint replacement has progressed considerably in the past 15 years, although the difficulties are greater than those of hip replacement. At first, only the constrained hinge joint and a limited variety of unconstrained joints were available. Severe deformities of diseased knees and ligamentous insufficiency forced great changes to be made in unconstrained prostheses to ensure greater stability and motion and less wear and loosening. Further changes have also been made in constrained hinge joints; this has resulted in a great proliferation of prostheses of all types. Fully constrained prostheses now have restricted indications. Poor results are greatest with the fully constrained hinge group (36%) and lowest with the semiconstrained group (13%). The unconstrained prosthesis gives results intermediate between the others. Infection rate is highest in constrained and lowest in unconstrained prostheses. The loosening rate is lowest in the semiconstrained and unconstrained types.

Arthroplasty of the knee

A stable polycentric knee mechanism which allows axial rotation as well as simulating other knee movements was introduced into clinical use in 1971. The surgical and mechanical problems that presented over the past 7 1/2 years have greatly helped in improving our understanding of knee reconstruction and design. A patient satisfaction rate of 95% compares favorably with the results achieved with hip arthroplasty but the complexity of knee reconstruction far outweights that of the hip.