Oxford medial unicompartmental knees display contact‐loss during step‐cycle motion and bicycle motion: A dynamic radiostereometric study

Abstract

The Oxford medial unicompartmental knee is designed fully congruent, with the purpose of maintaining a large contact-area throughout motion and minimize wear. No other study has investigated this design feature in-vivo. We aimed to evaluate if contact-loss was introduced between the articulating surfaces of the Oxford medial unicompartmental knee during bicycle- and step-cycle motion, and whether this correlated with essential implant parameters, such as polyethylene (PE) wear, knee-loadings, and clinical outcome. To study contact-loss, 15 patients (12 males, mean age 69 years) with an Oxford medial unicompartmental knee (7 cemented, mean follow-up 4.4 years) were examined with use of dynamic radiostereometry (RSA) (10 frames/s). PE wear was measured from static RSA and clinical outcome was evaluated with American Knee Society Score (AKSS) and Oxford Knee Score (OKS). Data on knee-loadings were acquired from the literature. Contact-loss was deteced in all patients during both exercises, and the trend of contact-loss correlated with the knee-loadings. Median contact-loss was 0.8 mm (95%PI: 0.3; 1.5) for bicycle motion and 0.3 mm (95%PI: 0.24; 0.35) for step-cycle motion, and did not correlate with the PE wear rate of mean 0.06 mm/year. Possible in-congruency was seen in three patients. Clinical outcome scores correlated with contact-loss during step-cycle motion. In conclusion, contact-loss was seen in all patients indicating a clinical tolerance during load. Contact-loss followed the knee-loadings, which could explain why no correlation was seen with PE wear, as an increase in load was acommadated by an increase in contact-area (contact-loss reduction). The size of contact-loss may reflect clinical outcome. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:357-364, 2018.

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

“…Moreover, the fully congruent mobile bearing causes compressive loads and limits shear forces, which may help reduce debonding of the HA coating before full osseointegration (Müller and Patsalis 1997, Horsager et al. 2017, 2018). Overall, the Oxford medial UKA exhibit several features that in theory reduce the dissociation of HA particles to the joint, which thus limits the potential of third-body wear.…”

“…This could be due to the standing RSA examinations, as impingement could be induced by knee motion (Horsager et al. 2018).…”

“…2011, Horsager et al. 2018). The relative difference in the measured mJSW over the 5-year follow-up represents the combined upper- and lower-surface PE wear.…”

“…Impingement against the vertical wall was noted when the mediolateral distance between the femorotibial contact point and the vertical wall was less than half the width of the bearing (Horsager et al. 2018).…”

A review of recent advances in tribology

“…[350]. The integration of biomechanics and biotribology became important and was addressed from both computational [351] and experimental [352,353] approaches. Other interesting developments included the direct observation of the lubricant film at the articulating surfaces using optical methods [354].…”