Similar polyethylene wear between cemented and cementless Oxford medial UKA: a 5-year follow-up randomized controlled trial on 79 patients using radiostereometry

Figures & data

Figure 1. Consort flow chart. All available data were used in the statistical analysis. A complete dataset was collected for 48 patients in the cemented group and for 23 patients in the cementless group. Demographic data at baseline were comparable between the 2 groups (Table 2). All patients were followed with RSA, conventional radiographs, and Oxford Knee Score over the 5-year follow-up period.

Table 1. Exclusion criteria

1	Neuro- or vascular disease in the affected leg
2	Extension deficit >10°
3	Preoperative maximal flexion <100°
4	Symptomatic patellar OA ^a
5	Insufficient anterior cruciate ligament (ACL)
6	Lateral compartment OA
7	Preoperatively templated for a size XS or XL femoral component ^b
8	Osteoporosis
9	Continuous vitamin K antagonist treatment
10	Fracture sequelae in the knee
11	Previous extensive surgery
12	Metabolic bone disease
13	Rheumatoid arthritis
14	Hormonal substitution for postmenopausal symptoms
15	Steroid treatment
16	Non-Danish citizens
17	Insufficient command of the Danish language
18	Dementia
19	Misuse of drugs or alcohol
20	Serious psychiatric disease
21	Disseminated malignant disease
22	Systemic hip or back condition
23	Poor dental status
24	Participation in another study

^a All patients were screened for patellar OA with patellar radiographs

^b XS or XL femoral computer aided design (CAD) models were not available for analysis.

Exclusion criteria are given from Clinicaltrials.gov, NCT00679120 (Stilling and Søballe).

Table 2. Patient demographics at baseline

	Cemented	Cementless
	(n = 55)	(n = 25)
Men: women, n	30: 25	18: 7
Right: left, n	32: 23	11: 14
Age, years ^a	63 (9) [47–81]	65 (10) [38–81]
Weight, kg ^a	87 (13) [67–121]	88 (14) [61–110]
Surgeons involved, n	7	5

^a mean (SD) [range]

Table 3. Precision of minimal joint space width (mJSW) measurements and the femorotibial contact-point location

Item	Mean	1.96 x SD
mJSW measurements, mm	0.01	0.12
Femorotibial contact point, mm
medio-lateral	0.05	1.16
anterior-posterior	0.21	2.51

The table presents the mean and 1.96 x SD of the difference between double exposures.

Figure 3. The frontal view to the left outlines the measurement of the minimal joint space width (mJSW). The dotted line represents the sagittal cross-sectional view presented to the right. The mJSW reflects the bearing thickness and the projected dotted line on the tibial component represents the femorotibial contact point. This allows the estimation of PE wear and the position of the bearing. Overhang is seen when the bearing exceeds the outline of the tibial plateau. Impingement can be identified if the bearing slides against the vertical wall (see frontal view).

Figure 2. This figure outlines the set-up of the RSA examinations. To standardize the set-up, a rectangular foam support was applied between the leg and calibration-box. Patients were also asked to move their center of gravity over the operated leg to make sure that the prosthetic knee joint was loaded.

Table 4. Oxford Knee score. Values are mean (95% CI)

Type	Baseline OKS	5-year OKS	D OKS ^a
Cemented	26 (24–27)	38 (36–40)	13 (10–15)
Cementless	23 (21–26)	39 (37–42)	16 (13–19)

^a D OKS describes the change in clinical outcome from baseline to 5-year follow-up. There was no significant difference in D OKS between the cemented and cementless group (p = 0.1). The sample decreased from n = 54 to 46 for the cemented group and n = 25 to 24 for the cementless group for 5-year OKS and D OKS.

Figure 5. Distribution plots for the extent of bearing overhang. Medial overhang is shown to the left and posterior overhang is shown to the right.

Figure 4. The linear wear-rate of the cemented and cementless Oxford UKA with 95% CI from the linear mixed model.

Figure 6. This figure visualizes a “top view” of the PE bearing and tibial component of the Oxford Medial UKA. The figures are based on the assumption that the bearing is kept parallel with respect to the vertical wall. Extreme cases of bearing overhang are visualized in Case 1 and 2. The mean bearing position for all patients with 95% prediction interval is visualized in the right panel. Case 1 represents the patient with 5 mm medial overhang and case 2 represents the patient with 5 mm posterior bearing overhang. The graphs are computed using the femorotibial contact point and the exact ratio between the size of the bearing and tibial component.