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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.

Approximately one-third of primary knee replacements are performed on patients with bilateral symptomatic disease. This retrospective study compared the complication rate, functional outcome and cost implications of performing bilateral total knee replacements under a single anaesthetic or as staged procedures with a control group of unilateral cases. There was no significant difference in the complications or outcome. There was a significant reduction in the mean hospital admission time of 7 days per knee replacement (P < 0.001, Student's t test) by performing bilateral knee replacements for osteoarthritis under the same anaesthetic. However, a survey of practising knee surgeons in three health regions in the United Kingdom shows that only 24% would regularly perform bilateral knee replacements under one anaesthetic.

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 tibial plateaux excised during 46 unicompartmental arthroplasties for osteoarthritis were collected and photographed. The anterior cruciate ligament was intact in all joints. In every case the cartilage and bone erosion was centred anteriorly on the plateau and the posterior cartilage was intact. The site of the lesion and the intact state of the cruciate ligaments taken together explain why varus deformity was observed only in the extended knee, and why the deformity was correctable and had not become fixed. Failure of the anterior cruciate ligament may allow the erosion to extend posteriorly, producing fixed varus deformity and leading to degeneration of the lateral compartment. Anteromedial osteoarthritis is a distinct clinicopathological entity; its radiographic features enable it to be diagnosed from lateral radiographs; its anatomical features render it suitable for treatment by unicompartmental arthroplasty.

The accurate assessment of compartmental involvement in degenerative arthritis of the knee is important when planning operative treatment. Standard radiographic techniques often fail to define the degree of involvement of the less affected tibiofemoral compartment. The use of stress radiography in the preoperative assessment of 30 knees with degenerative arthritis is described and the radiographic findings correlated with the changes found at arthrotomy.

The Oxford Knee, a resurfacing prosthesis with a meniscal bearing, can be used for either bicompartmental or unicompartmental arthritis. The first 103 unicompartmental cases are presented at a mean time since operation of 36 months (range 21 to 56 months). In those cases with surviving arthroplasties, pain was relieved in 96%. The full range of pre-operative flexion was maintained and flexion deformity was improved from a mean of 6.7 to 5.4 degrees. Stability and alignment were restored to normal in nearly all the knees. Absence of the anterior cruciate ligament was associated with a significantly greater incidence of failure. Six failures occurred in 37 knees lacking a normal anterior cruciate ligament (16.2%); three occurred in 63 knees with a normal anterior cruciate ligament (4.8%) (p less than 0.02). Criteria for the future selection of patients have been deduced from our experience. The operation is recommended for knees with severe unicompartmental osteoarthritis in which all the ligaments are still intact.

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.

Unicompartmental knee arthroplasty is an attractive concept, but some reports on its use are unfavorable. A meniscal bearing prosthesis has many advantages in this mode of arthroplasty. The authors present preliminary results of 25 unicompartmental knee replacements done with the Oxford Meniscal knee, with a follow-up period of 12-54 months (mean, 21 months). They discuss the scientific basis of unicompartmental knee arthroplasty, which they conclude may be the most appropriate treatment for selected cases of degenerative arthritis of the knee.

About one-third of osteoarthritic patients requiring knee replacement have focal lesions limited mainly to the medial compartment and can achieve excellent postoperative function after medial unicompartmental replacement. However, late failures of many unicompartmental prostheses require revision at a rate about twice that of total knee replacement. The use of a fully conforming mobile-bearing meniscal unicompartmental prosthesis in the hands of experienced surgeons can reduce revision rates to levels equivalent to the best results achieved with total knee replacement. The paper argues the case for such a prosthesis and demonstrates that the usual modes of failure of unicompartmental arthroplasty, most of them biomechanical, can thereby be avoided. [ABSTRACT FROM AUTHOR]