It is a huge pleasure to be participating in a book on knee reconstruction using small implants. Unlike previous publications, this book does not limit the possibility of modular replacement to a single compartment, whether tibiofemoral or patellofemoral, but offers the real possibility of articular replacement adapted to the specific type and location of the damage caused by degenerative disease. It provides surgeons with an opportunity to step back and reconsider the simplistic reasoning, all too commonly accepted, in which total knee replacement (TKR) is considered as the “gold standard” when damage to the joint is not limited to a single, isolated compartment. Since the time we spent with Leonard Marmor in 1974, we have never stopped defending, often in the face of a void of cosmic proportions, modular arthroplasty as the preferred reconstructive option, despite its frequent attack by the officially recognized theoreticians. It is perhaps worth pondering an old quotation from the eminent hand surgeon Professor Vilain: “Everything has already been written, but since we have not read everything, we may continue publishing”. This appears more apropos than ever regarding the use of small implants in knee reconstruction. Indeed, it seems to have been forgotten that in 1972 Leonard Marmor was already promoting a new concept in total knee replacement, replacing the two tibiofemoral compartments at the same time in patients with osteoarthritis of the knee. Great visionary that he was, he considered that the overriding advantage of this new concept compared to the TKR technique in use at the time lay in the conservation of the ACL, sparing the soft tissues and preserving bone stock. It was only once this new concept was established he began to consider that another, purely unicompartmental solution could be envisaged in cases where the opposite compartment was healthy.
Today, after performing over 3,000 combined or isolated modular knee replacements, we are able to assert that the functional results achieved are better than those of TKR, that revision procedures are often simpler and that, subject to correct fitting, this option should no longer be considered as a temporary solution pending an inevitable conversion to TKR.
Our commitment to the defense of these small implants over the last 40 years against the onslaught of the official naysayers would never have been possible without the precious support of European surgeons working towards the same aims. I take pleasure in thanking for their support: the Marseille school under J-M. Aubaniac and, later, J-N. Argenson; the Italian orthopedics school, whose worthy representatives are S. Romagnoli and N. Confalonieri, and the British school, specifically, J. Goodfellow and his students for their work on mobile bearings and J. Newman, one of the longest standing defenders of resurfacing fixed implants and mobile bearings.
Little streams come together to make big rivers, so let us hope that this reference work will enable the peaceful river of non-invasive surgeons to exist officially at last against the torrent of systematic proponents of TKR. With hindsight, there can be no question that modular knee surgery gives better results than TKR by maintaining knee proprioception and that it alone can re-establish physiological function without reverse roll-back during walking.
On the other hand, it must be acknowledged that it is technically a more difficult operation and that in spite of the ancillary instruments available to facilitate fitting and computer-assisted surgery, knee reconstruction with small implants is more surgeon-dependent than TKR.
This obvious fact is no justification, however, for current attempts to simplify the fitting of these implants by moving the ancillaries towards those used for TKR, in order to replace resurfacing or minimal bone resection with a “half TKR” concept, with the fitting rules that this would entail. This is a commercial move aimed at reassuring surgeons who are just beginning to perform knee reconstructions using small implants and it is totally inconsistent with any possibility of respecting the philosophy of modular knee surgery.
Under no circumstances can it replace the need to complete an on-thejob apprenticeship alongside experts in teams trained to perform this type of surgery before beginning to fit these small implants. What would you prefer, a run-of-the-mill fast food or a dish that suits your palate? It is on this choice that your choice of prosthetic option and the experience of your patients will depend.


In these last years, a new interest in less invasive reconstructive surgery has involved the entire orthopedic world. The shifting demographics of patients with localized knee arthritis, including younger, more active patients, is a major impetus for the growing interest in conservative surgical alternatives.
Minimally invasive total knee replacement is increasing in popularity because of a theoretically reduced blood loss, faster recovery, and reduced economic costs. However, less invasive surgery has been often identified both by surgeons and prosthesis manufacturers, as a shorter surgical approach to the implantation of the same total prostheses used with traditional approaches.
New, more conservative surgical approaches have been proposed, such as quad-sparing, mid-vastus, or sub-vastus. While these have the advantage that they spare skin and the quadriceps tendon, they may increase the risk of muscle and nerve damage, resulting in a biological contradiction. Giulio Bizzozero, an Italian biologist pioneer, already in the early years of the last century classified tissues and cells in three categories. He identified the “reproducible” tissues, such as epithelium (skin) and endothelium, the “stable” tissues, such as mesenchyma (tendons and ligaments) that recover very well following injury, and the “noble tissues”, such as muscles and nerves, which should not be damaged as they are “perpetual” tissues.
On this purpose it has been hypothesized that real mini-invasive surgery should not be matched only with shorter incision but also with both a new respect for all the tissues and a preserved joint kinematics using new tools and smaller implants. This has led to a redefinition of mini-invasive surgery as tissue-sparing surgery.
Unicompartmental knee replacement (UKR) and patellofemoral replacement (PFR) are well-accepted surgical procedures for the treatment of knee arthritis. Furthermore, few surgeons in the world experienced the association of different small implants, matching a philosophy of real less invasive procedures.
Indeed, small implants and a preserved joint biomechanics could represent a new development in reconstructive surgery and the approaches described in this special issue highlight the attractive aspects of this strategy. In addition, the use of computer-assisted instruments may help the surgeon in reproducing this highly demanding surgery by standardizing the techniques.
The Authors strongly believe that this “personalized on-time treatment” for each patient according to the severity of the disease and using different implant options could be one of the most interesting improvements in the coming years.

The Reason for a Choice

Before starting to read this book the reader should know what it is going to explore. Nowadays, in the orthopedic world osteoarthritis, prosthesis, mini-invasive surgery, tissue-saving surgery, small implants, etc. are “hot” topics approached from a multitude of perspectives, which ultimately run the risk of becoming repetitive.
Thus, let’s first of all try to create order in these many topics, considering that the philosophy underlying the writing of this book is to repair the degenerative arthritic knee disease of our patients. But which patients? And, what type of arthritis?
In our practice, we have come to realize that our patients have progressively changed: they are younger, smarter, more sensitive to pain, more informed, more demanding, and often have an intact or surgically reconstructed anterior cruciate ligament (ACL) [2, 3, 5]. Likewise, even the arthritic knees of our own generation have changed: we see fewer and fewer knees destroyed by an advanced primary arthritis but we increasingly have to manage compartmental diseases.
In many cases, these conditions are the results of sporting injuries, previous meniscectomies, plateau or condylar fractures, osteotomies, or prolonged overuse (Fig. 1.1).


Fig. 1.1 Bicompartmental post-traumatic arthritis in a young man with an intact anterior cruciate ligament

Nevertheless, almost 90% of surgeons worldwide still implant a total prosthesis in these knees, firstly resecting ACL and often, even the posterior cruciate ligament [6-8]. In many cases, in order to maintain the promise of a MIS (mini invasive surgery) to the patients, a small incision is performed, often with higher risks of damages of the noble tissue under skin, a sort of “key-hole” surgery.
We propose a totally different strategy: tissue sparing surgery (TSS), which does not consider the length of the incision to be more important than the size of the prosthesis. This prosthetic reconstruction, whether uni- or bi-compartmental, saves the two ligaments, which are the true fulcrum of joint biomechanics.
It involves the minimal removal of bone tissue from the tibia, femoral cartilage removal, sparing of the central pivot, and a small skin incision without damaging the extensor apparatus. It is clear that this surgical solution offers a genuinely minimally invasive surgery of the knee. Nonetheless, there are several considerations that are still matters of debate, including the indications, surgical technique and medium-term result. Yet, there is no doubt that with the most recent technological developments, the increasingly precise surgical tools, computer assistance, and more convincing experience with unilateral knee replacement (UKR), positive, sometimes exciting, the short term results are possible and have led to very intense interest in this surgical approach to knee arthritis (Fig. 1.2).


Fig. 1.2 Bicompartmental reconstruction: unicompartmental and patellofemoral computer-assisted surgery

In fact, it represents a “historical return,” because the history of knee arthroplasty starts with uni- and bi-uni condylar procedures. However, inaccurate instrumentation, incorrect indications and, consequently, less success guided the choice to a total prosthesis, which was considered easier to implant because it sacrificed everything to achieve a balanced design.
It is important to know that the three compartments of the knee joint are anatomically different and that each has its own specific biomechanics. Thus, reconstructive knee surgery requires a vision of the joint that considers not only the anatomical structures but also the biomechanics as a whole, including muscle
forces and ligament constraints. Thus, total knee replacement (TKR) is not a “biological” replacement
but instead creates a new “artificial” joint with new, albeit abnormal kinematics . Despite new and sophisticated prosthetic designs (gender-specific, one or two radius curvatures, mobile-bearing, etc.), TKR sacrifices the cruciate ligaments, changes the anatomy of the compartments, and in the majority of cases includes medial and lateral condyles of the same size. In addition, it has been widely emphasized that the results of TKR depend on the use of guides, which can lead to significant errors in reconstruction of the mechanical axis of the lower limbs based on the absence of data on proper soft-tissue balancing of the ligaments, thereby affecting both the functionality and the durability of the system.
From a surgical point of view, surgical compartmental reconstruction (UKR, UKR + PFA, bi-UKR) is considerably less invasive than total replacement: the ligamentous apparatus remains undamaged, does not require the use of intramedullary tools, and permits a three-dimensional correction of an arthritis deformity. Moreover, it preserves bone stock and, in case of failure, can be more easily revised with traditional total arthroplasty.
In addition to these “surgical” advantages, there are also several practical ones, even for the patient:
• Reduced blood loss, with less need for a blood transfusion, even in the case of simultaneous bilateral implants.
Lower risk of deep-vein thrombosis and sepsis.
• Improved indications for loco-regional anesthesia.
• Reduced incidence of lift-off of the lateral compartment compared to TKR because it is ACL-sparing.
• Option of using all-polyethylene tibial implant with lower stresses between bone and prosthesis.
• Option of using different prosthetic sizes and models for each compartment, thus respecting the knee’s natural anatomy and biomechanics.
• Absence of posterior polyethylene wear (edge-loading), since the ACL is retained, which prevents posterior subluxation of the femur.
• Integrity of joint proprioception.
• Shorter hospital stay and quicker recovery of the joint, based on the better function compared to TKR.
These advantages also play a role in treatment for special indication such as in patients with neurological problems (e.g. Parkinson’s disease), in whom a total replacement leads to a worsening of the underlying disease whereas compartmental reconstruction avoids the effect of somato-agnosy (loss of sensation of a body part). Last
but not least, there is an obvious savings in health costs, an advantage in terms of the management of economic resources.
In conclusion we must point out that these results are possible only with a rigorous selection of patients and the use of a rigorous surgical technique. These two factors will provide such patients with an almost complete recovery of the range of motion in “normal” joint biomechanics.
In this volume, the reader will become familiar with all of these aspects as well as others in this extensive discussion of TSS by leading international experts. Our hope is to encourage a consideration of compartmental knee reconstruction as a valid alternative to total knee replacement.

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