Medial Indications other than AMOA

Anteromedial OA (AMOA) accounts for more than 90% of the knees we consider suitable for OUKA. However, there are some other pathologies for which the operation may be appropriate.

Mobility and Stability of the Intact and Replaced Knee

Having demonstrated in Chapter 2 that a fully conforming mobile bearing can minimise polyethylene wear, in this chapter we show that a mobile bearing prosthesis, unconstrained in the sagittal plane, can restore natural mobility and stability. For surgeon readers who are less interested in the theoretical background, it might be advisable to go straight to Chapter 4, Indications, or to start by reading the final section of this chapter, The Loaded Prosthetic Knee. If that proves interesting, the surgeon might attempt The Unloaded Prosthetic Knee. For the more research minded surgeon or engineer, it seems more logical to start with the Unloaded Natural Knee (the longest section of the chapter) and to read from there. The chapter may also be of interest to those surgeons embarking on the use of a bi-cruciate retaining total knee replacement.

The Lateral Side

Lateral unicompartmental OA is a relatively rare disease said to account for about one eighth of all unicompartmental arthritis 1 . However, the incidence may be higher because it is a disease of flexion and is commonly missed on standing AP radiographs. To identify lateral OA reliably, either a valgus stress radiograph in 45° flexion or a Rosenberg view is necessary. The clinical results of UKA in the lateral compartment have sometimes been worse than in the medial compartment 2 and sometimes better 3 . Some early papers reported results of series containing both medial and lateral operations as if they were essentially the same, but the normal anatomy and the pathological lesions of the two compartments are very different so the surgical techniques are different.

Appendix Mathematical models of the knee

Mathematical models make it possible to calculate the values of quantities which are difficult or impossible to measure and provide insights which are not obtained from experiment alone. They are a necessary adjunct to the experimental method, but are not a common feature of biological or clinical research. A model is based on a series of assumptions or hypotheses about the way a physical system works. It is validated by comparing its predictions with independent experimental measurement. Reasonable validation then gives confidence in the assumptions on which the model is based and in the predictions of quantities which cannot be measured. The purpose in presenting our models here is to explain the differences between unloaded and loaded motion described in Chapter 3.

Design and Biomechanics of the Oxford Knee

The description of the Oxford Knee starts with an explanation of the function of mobile bearings in knee prostheses. An obvious advantage is that the areas of contact between the joint surfaces are maximised. In this chapter, we shall show that wear at the polyethylene surfaces is thereby minimised and that optimal kinematics can be achieved with minimal risk of loosening. We will discuss the biomechanics of the cementless components and problems that may occur with the tibia.

Clinical Results

The results of UKA can be gathered from three main sources: the reports of the national registers, observational studies (both comparative and case series), and randomised controlled trials. In this chapter, we attempt an overview of the clinical results of UKA in general and OUKA in particular. It is important to note that the ‘result’ is of the whole arthroplasty which includes the indications, the technique as well as the implant.

Contraindications in Anteromedial Osteoarthritis

While it is important to ensure that all the necessary indications are met 1 , it is also important not to apply unnecessary contraindications. Some published lists of supposed contraindications have achieved wide acceptance without having much evidence to support them. We have recently argued with evidence that many of the suggested contraindications are unnecessary.

Management of Complications

In this chapter we describe the common modes of failure of the OUKA and suggest ways of dealing with them. We also discuss why they occur and how they can be prevented. Complications occur more commonly in the hands of learners than in those of the experienced surgeons whose reports are published in the literature. As a result, the incidence of complications is lower in published cohort series compared to national registers.

Introduction and Historical Overview

Osteoarthritis of the knee is one of the most common causes of painful loss of mobility in middle-aged and elderly people in many populations and is the main indication for knee replacement surgery. From the early days of arthroplasty, it was recognised that arthritis was often limited to the medial (or lateral) compartment of the knee and, in the pioneering operation of MacIntosh 1 , metal spacers could be used in one compartment or both. Gradually, however, as the advantages of bicompartmental arthroplasty were appreciated, unicompartmental (or partial) replacement was less and less practised, and in some countries almost disappeared. With the introduction of tricompartmental replacement, a large body of surgical opinion concluded that osteoarthritis of the knee was a disease of the whole joint (like osteoarthritis of the hip) and that common sense required the replacement of all the articular surfaces to provide long-term relief of symptoms.

Indications Anteromedial Osteoarthritis

Total knee arthroplasty is an effective treatment for most types of arthritis of the knee and requires little of the joint’s anatomy to be intact for a successful outcome. On the other hand, unicompartmental arthroplasty can only succeed if the rest of the knee is functionally intact before surgery. We will discuss, first, the pathology of osteoarthritis (OA) of the knee and then how to ascertain, before operating, that the ligaments are all functionally normal and the retained articular surfaces capable of resuming their weight-bearing role.