Radiological changes ten years after St. Georg Sled unicompartmental knee replacement
Introduction
The results of unicompartmental knee replacement (UKR) are equivalent to those of total knee replacement (TKR) [1].
Reasons for failure of UKR and TKR are similar. However, UKR carries the additional risk of progressive arthritis within the retained compartments.
Few studies have examined progression of arthritis after UKR. One study, 10 years after Oxford meniscal bearing UKR showed little progression of arthritis at that time [2]. A second study, by Weale et al. [3] assessed radiological changes 5 years after fixed bearing St. Georg Sled UKR and found little evidence of progression of OA at that time. The aim of this further study was to review the same cohort of patients 10 years after St. Georg Sled UKR.
Section snippets
Patients and methods
Between 1989 and 1992, 50 UKR's were performed in 45 patients as part of a prospective randomised controlled comparison of UKR and TKR [1]. There were 17 men and 28 women with a mean age of 69.6 years (53–89). In all cases the prosthesis used was the St. Georg Sled (Waldemar Link, Hamburg, Germany), which has a metal femoral component rounded in both the anteroposterior (AP) and lateral planes and a flat all polyethylene tibial component.
Inclusion criteria
All operations were carried out for tibiofemoral OA. All knees had intact anterior and posterior cruciate ligaments (ACL, PCL). All joints had full-thickness loss of articular cartilage in the affected compartment (Ahlbäck grade O–IV) [4] identified during surgery (Table 1). The presence of osteophytes and fibrillation of the cartilage in the opposite compartment were not considered contraindications if limited to the margins of the femoral condyle. The decision to include the patient in the
Operative technique
A full description of the technique has been published previously [1]. The manufacturer's guidelines regarding the use of implants and instruments were followed. A deliberate attempt was always made to avoid overcorrection of the varus or valgus deformity so that there was no overloading of the contralateral compartment [5].
Radiological assessment
All knees were assessed before operation, at 8 months and 10 years post operatively. Standard radiographs included long-leg weight-bearing AP views of the fully extended knee and skyline views of the patello-femoral joint taken with the knee flexed to 40° and the limb rotated to centralize the patella over the femur. The film was supported on the anterior aspect of thigh, at right angles to the central ray, and centered to the posterior aspect of the patella. Schuss views, which might have
Statistical analysis
Intra-observer variability for the assessment of the severity of OA in the retained compartments was assessed by means of the unweighted kappa (κ) statistic. The Wilcoxon signed-rank test was used for ordinal data and Student's t-test for continuous data.
Results
Since each film was reviewed twice by one of the observers, it was possible to estimate the intra-observer error. There was very good intra-observer reproducibility for Ahlback measurements in the lateral and patellofemoral compartments (κ=0.79 and κ=0.84, respectively). There was moderate agreement between the two Altman intra-observer measurements (κ=0.65 and κ=0.54, respectively).
On repeated examination of the same radiograph, the maximum difference recorded was one grade using the Ahlbäck
Discussion
Unicompartmental knee replacement (UKR) can produce good long-term results that are comparable to total knee replacement (TKR) [1], but patients must be carefully selected and overcorrection of the deformity should be avoided [3].
These results show that at 10 years, progressive OA in the retained compartment is uncommon, in carefully selected patients with UKR in whom overcorrection of the deformity in the coronal plane had been largely avoided and the ACL was intact [3].
Of the 45 patients with
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