John Goodfellow

Clinical results of the Oxford knee. Surface arthroplasty of the tibiofemoral joint with a meniscal bearing prosthesis.

The Oxford method of knee arthroplasty replaces the femoral condyles with convex spherical metal components and relines the tibial plateaus with flat metal components. Free meniscal bearings of polyethylene, spherically concave above and flat below, lie between the fixed metal components, held in place by their geometry and ligamentous tension. Advantages of the design include: congruity of the articulating surfaces; unconstrained tibiofemoral movement; preservation of all the ligaments with facility to tension them accurately from a range of bearing thicknesses; minimal bone excision; applicability to unicondylar use. Laboratory studies showed that combined rolling and sliding at meniscofemoral and meniscotibial interfaces mimic normal joint kinematics and mechanics. One hundred twenty-five bicompartmental implants were followed for two to six years. Pain was relieved in 90%; mean flexion limit was 99 degrees and mean flexion deformity 7 degrees. Stability and alignment were recovered in nearly all joints. Six knees failed and were successfully arthrodesed (two) or converted to another prosthesis (four). Eight knees required revision to replace a dislocated bearing (five) or to recement a loose component (three). In knees with an intact anterior cruciate ligament, there were no failures and a low revision rate (4.8%). The prosthesis is proposed as a reliable and safe alternative to more invasive prostheses in rheumatoid and osteoarthritic joints in which the disease is still limited to the articular surfaces.

THE SIGNIFICANCE OF THE FINE STRUCTURE OF ARTICULAR CARTILAGE

The collagen framework of articular cartilage is disposed, as in other connective tissues, to resist tension forces within the material. In this paper the fine structure of articular cartilage, as demonstrated by polarised light microscopy and electron microscopy, is related to the gross anatomy and to the naked eye changes of chondromalacia and fibrillation.

THE RELATIONSHIP BETWEEN DEGENERATIVE CHANGES AND LOAD-BEARING IN THE HUMAN HIP

1. A predictable pattern of degeneration occurs on both the femoral head and the acetabulum and this pattern is age dependent. 2. The degenerative areas on the femoral head are related to habitual non-use. 3. The hip is shown to be anatomically incongruent, and the dome of the acetabulum, a predictable area of degeneration, is shown also to be an area of habitual non-use. 4. The possible relationships between age-dependent degenerative changes and senile degenerative joint disease is discussed and the importance of changing geometry stressed.

THE PATTERN OF AGEING OF THE ARTICULAR CARTILAGE OF THE ELBOW JOINT

1. The age changes in the articular cartilage of the elbow joint are presented from a study of twenty-eight necropsy subjects aged eighteen to eighty-eight years. During early adult life those areas of cartilage which do not usually articulate with opposed cartilage always show some degree of chondromalacia. 2. Evidence is presented that the almost inevitable degeneration of the radio-humeral joint in old age is related to the combination of rotation and hinge movements that occur at that joint. This is in marked contrast with the relative immunity of the humero-ulnar articulation which has hinge movement only.

The anterior cruciate ligament in knee arthroplasty : a risk-factor with unconstrained meniscal prostheses

Three hundred one unconstrained meniscal arthroplasties were observed for as long as nine years, during which time 25 (8.3%) failed. Risk factors were sought by comparing the distributions of several preoperative variables in the group that failed with the group that was successful. Age, weight, the magnitude or direction of preoperative deformity, and the presence of postoperative malalignment were all without effect on the outcome of the operations. Knees with rheumatoid arthritis had a 95% survival rate at six years. Knees with osteoarthrosis had an equivalent survival rate of 83%. Knees in which the anterior cruciate ligament (ACL) was normal had a survival rate of 95% at six years; those in which the ligament was damaged or absent had an equivalent survival rate of 81%. Successful reconstruction of a knee with an unconstrained meniscal implant requires the presence and the preservation of an intact ACL.

Medial unicompartmental arthroplasty. A survival study of the Oxford meniscal knee.

One hundred twenty-one knees with medial compartment osteoarthrosis were treated by unicompartmental arthroplasty with the Oxford Knee. The strict selection criteria were (1) the presence of a functioning anterior cruciate ligament, (2) fully correctable deformity, and (3) full thickness of articular cartilage in the lateral compartment. The mean elapsed time from surgery was 44.4 months. One knee has required revision for a loose tibial component. The results at this stage are as acceptable as those of tricompartmental knee arthroplasty and better than those of high tibial osteotomy.

In vitro patellofemoral joint force determined by a non-invasive technique.

OBJECTIVE: To develop a method of measuring the magnitude, direction and point of application of the patellofemoral force (PFF), directly and non-invasively in three dimensions. DESIGN AND METHODS: The compressive PFF is replaced exactly with a tensile force applied to the front of the patella. The magnitude, direction and point of application of the tensile force are then measured. The technique was applied to six normal knees mounted in a 6 degree of freedom rig with quadriceps tendon tension force (QTF) applied to balance a flexing load and to simulate weight bearing. RESULTS: The PFF was greater than in previous more invasive in vitro studies but the results correlated well with recent theoretical analyses. At 20 degrees knee flexion the force was 75% of QTF. It increased to 100% of QTF at 60 degrees knee flexion and remained at this level at higher angles of flexion. The lateral vector of the PFF was small compared to the sagittal plane vector and became negligible beyond 60 degrees of knee flexion. The point of application of the PFF to the patella moved proximally and medially with knee flexion. CONCLUSIONS: A new and reliable method of measuring PFF non-invasively and in three dimensions has been developed. RELEVANCE: A new technique is described for measuring the PFF in vitro. The non-invasive nature of the technique makes it useful for studying the effect on the PFF of simulated pathological conditions, surgical procedures and different types of knee replacement.