The purpose of this paper was to investigate the predictability of outcome of a consecutive series of cemented unicompartmental or total knee replacements in a single surgeon series.

Between September 2006 and February 2009, ninety-nine cemented, fixed bearing TKR were performed with patellar resurfacing. 52 cemented Miller Galante (Zimmer) Tibio-femoral UKR were performed in the same time interval. The minimum follow up was 6 months. Oxford and AKSS knee scores were collected prospectively at pre-operative and at routine follow up appointments.

Pre-operative mean AKSS Knee score for TKR group was 33.9 and improved to 84.2 at 1 year. Mean scores for Tibiofemoral UKR were 40.4 improving to 84.3 at 1 year.

Pre-operative mean Oxford knee score for TKR group was 34.6 (28%) and improved to 16.6 (65%) at 1 year. Mean scores for UKR were 28.5 (41%) improving to 14.0 (71%) at 1 year. These data would suggest that unicompartmental replacement performs as well as TKR.

However, in the TKR group, 59% achieved a knee score >85 and 23% an Oxford score >80%. In the UKR group, 67% achieved knee score >85 and 45% an Oxford score >80%. Conversely, only 5% of TKR achieved knee score <50 and 20% Oxford score <50% whilst 10% of UKR had a knee score <50 and 26% and Oxford score <50%.

These data show that whilst mean outcomes for TKR and UKR look similar, TKR offers a more predictable outcome with fewer clinical failures but also fewer excellent results. UKR offers a more polarised set of outcomes with far more clinically excellent results but also more clinical failures. These data can inform the ongoing debate regarding the role of unicompartmental arthroplasty. Patient selection is clearly critical but remains an inexact process.

Anterior knee pain due to dysplasia of the extensor mechanism is common. We have studied 137 knees (103 patients) in order to identify a rapid and reproducible radiological feature which would indicate the need for further analysis.

Overall, 67 knees (49%) had at least one radiological abnormality; 70 (51%) were considered normal. There were five cases of Dejour type-3 dysplasia of the femoral trochlea, nine of type-2 and 12 of type-1. There were 49 cases of patella alta and five of patella infera. Four knees had an abnormal lateral patellofemoral angle (patellar tilt), and in 15 knees there was more than one abnormality. Classification of trochlear dysplasia was difficult and showed poor reproducibility. This was also true for the measurement of the lateral patellofemoral angle. Patellar height was more easily measured but took time. The sulcus angle is an easily and rapidly measurable feature which was reproducible and was closely related to other features of dysplasia of the extensor mechanism.

The finding of a normal sulcus angle suggested that seeking other radiological evidence of malalignment of the extensor mechanism was unlikely to reveal additional useful information. The severity of other features of dysplasia of the extensor mechanism correlated with increasing sulcus angle.

We took posteroanterior weight-bearing radiographs, both with the joint fully extended and in 30° of flexion, in a consecutive series of 50 knees in 37 patients referred for the primary assessment of pain and/or stiffness. These radiographs were reported ‘blind’ both by an orthopaedic surgeon and a radiologist. Direct measurement of the joint space, together with grading of the severity of erosion according to the Ahlback criteria, was undertaken. Any other abnormality present was also documented.

The radiographs of the knees in 30° of flexion consistently showed more advanced erosion in both the medial (p = 0.001) and the lateral (p = 0.0001) tibiofemoral compartments, when compared with those of knees in full extension. The Ahlback classification of 25 joints was altered, in some cases by several grades, by the flexed position of the joint. In every case in which another abnormality was identified on the radiograph in full extension, it was also noted on that of the knee in 30° of flexion. In a further four cases, additional pathology could only be seen in the flexed knee. Every patient was able to complete the radiological examination without difficulty. Our study supports the adoption of a weight-bearing view in 30° of flexion as the standard posteroanterior radiograph for the assessment of tibiofemoral osteoarthritis in patients over 50 years of age.