DOS 2016

DOS Kongressen 2016 ·

Oxford Unicompartmental Knees display contactloss

during step-cycle motion and bicycle motion

Kristian Horsager, Bart L. Kaptein, Peter Bo Jørgensen, Maiken Stilling

Department of Orthopedic Research, Aarhus University Hospital; Biomechanics

and Imaging Group, Department of Orthopedic Surgery, Leiden University

Medical Center; Department of Orthopedic Research, Aarhus University

Hospital; Department of Orthopedic Research, Aarhus University Hospital

Background:

The Oxford Unicompartmental Knee (UKA) is designed fully con-

gruent, with the purpose of minimizing wear and wear related revisions. No

study has investigated this design feature in-vivo.

Purpose / Aim of Study:

We aimed to evaluate if the articulating surfaces of

the Oxford UKA stayed fully connected (no contactloss) during bicycle- and

step-cycle motion.

Materials and Methods:

Fifteen patients (12 males, mean age: 69 years) with

an Oxford UKA (mean in-situ: 4.4 years) participated in this cross-sectional

study. Each patient was recorded with dynamic RSA (10 fr/sec) during bicycle-

and step-cycle motion (step-up, stand, step- down). The recordings were ana-

lyzed with Model-based RSA, which allowed the quantification of contactloss

(joint space width) between the articulating surfaces. Polyethylene (PE) wear

was measured from standing RSA examinations. Clinical outcomes were evalu-

ated with American Knee Society Score (AKSS) and Oxford Knee Score (OKS).

Findings / Results:

Contactloss was seen in all patients during both exercises

(p<0.001). Median contactloss was 0.8mm (95%PI: 0.3; 1.5) for bicycle mo-

tion and 0.3mm (95%PI: 0.24; 0.35) for step-cycle motion. Contactloss oc-

curred during the late- upstroke for bicycle motion, and during initialization,

stand and end of step-cycle motion. The linear PE wear rate of 0.06 mm/year

(95%CI: 0.04; 0.08) was not correlated with contactloss (r<0.1, p>0.8). OKS

(mean 44, range: 24; 48) and AKSS Function score (mean 94, range: 30; 100)

correlated with contactloss during step-cycle motion (r<-0.55, p<0.035).

Conclusions:

All Oxford UKA displayed contactloss during bicycle- and step-

cycle motion. The size of contactloss during step-cycle motion correlated with

poorer OKS and AKSS function scores. Contactloss did not correlate with PE

wear rate.

No conflicts of interest reported

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