A functional comparison of two TKR designs
Research type
Research Study
Full title
The Functional Outcomes and Stability of Total Knee Replacement Design Concepts
IRAS ID
245090
Contact name
Leela Biant
Contact email
Sponsor organisation
Manchester University NHS Foundation Trust
Clinicaltrials.gov Identifier
Duration of Study in the UK
3 years, 0 months, 1 days
Research summary
Research Summary:
Total knee replacement (TKR) is an established treatment for knee osteoarthritis and leads to a satisfactory outcome in over 75% of patients. However, up to 25% of patients are not entirely satisfied with their TKR. Patient dissatisfaction has been associated with inadequate functional outcome, especially during negotiation of stairs and slopes. This phenomenon, known as mid-flexion instability, is believed to be caused by excessive anterior-posterior motion of the implant during activities of daily living. This is characterised as a perception that the replaced knee is unsteady during certain tasks.
This study will compare the functional outcome of two implants that have been designed to provide patients with a functionally stable knee throughout its range of motion. The different design roles in preventing implant-related mid-flexion instability remain unknown.Summary of Results:
Background Total knee replacements are operations that are offered to people who have severe arthritis pain that affects their daily activities. They are successful operations in most patients. However, a small minority of patients are not entirely satisfied with their knee replacement. Some patients continue to find it difficult to carry out certain activities after their operation, and in some cases, patients report that their new knee feels unstable.
This study compared the performance of two implants designed to provide better knee stability to patients. Both implants claim to provide patients with a more stable knee than traditional implants, but there is currently no evidence to support this. This study aimed to collect some evidence to support these claims.
To see whether the implants were stable, as claimed, this study looked at specific aspects of knee function, including range of motion and walking ability.
Study Details
Half of the study participants who took part in this study were given a Medacta International (GMK-Sphere) implant, and the other half were given an implant by Depuy Synthes (Attune). The implant that the participant was given depended on who their surgeon was, as half the surgeons working on this study only used the GMK-Sphere, while the other half only used the Attune.
All participants were invited to three appointments at Trafford General Hospital. The first was before their operation, the second six-weeks after the operation, and the final visit was one-year after the operation. At each appointment, the participants were asked to complete a series of questionnaires about how they felt about their knee pain and function, mobility, and quality of life. Researchers then measured how well participants could bend and straighten both knees. Finally, the participants were asked to walk on a treadmill at their own preferred speed while their walking patterns were recorded by specialised cameras. The treadmill was first set to be level (no inclination) and later to downhill to see whether any signs of instability were seen during this more demanding activity, where instability is more likely.
Once the study finished, the researchers conducted some statistical analyses on the data to see whether any of the results had changed over time and to see if there were any differences between implants.
Study Findings
Eighty-five participants completed all aspects of this study; 54 (23 Male, 31 Female) got a GMK-Sphere implant and 31 (18 Male, 16 Female) got an Attune implant. Participants in the GMK-Sphere group were 70 years old on average, while those who got an Attune implant were 66 years old on average.
Level and downhill walking tests showed that walking speed and stride length improved significantly over time. Participants in the Attune group walked faster and had longer stride lengths compared to the GMK-Sphere group at all visits for both walking tests. This may be because the Attune group was significantly taller than the GMK-Sphere group. The improvement seen in walking speed and stride length over time was the same in each group, however. This suggests that these differences in performance were not based on the implant type.
Detailed tests of how the knee bent during level walking showed no difference between groups, but both groups were able to bend their knee more when walking after the operation. This improvement is in keeping with the faster walking speeds seen. The tests also looked at how much the knee moved inwards (towards the other knee) and outwards (away from the other knee) while walking. These movement patterns changed over time in both groups. At 1-year, participants with a GMK-Sphere tended to walk with their knee slightly angled outward, while participants with an Attune walked with their knee slightly angled inwards. These differences were not significant but show that the implants perform differently in this aspect of knee movement.
Detailed tests of how the knee bent during downhill walking showed that the Attune group were bending their knee significantly more than the GMK-Sphere. This may be linked to their significantly faster walking speed. However, both groups were able to bend their knee more when walking after the operation, showing an improvement in both groups.
Knee instability after knee replacement is common during a certain part of the walking cycle, called ‘mid-flexion’. Because of this, the researchers looked at the results of this specific part of the walking cycle carefully. No differences were seen between groups, suggesting that the ways that the implants move during mid-flexion were similar. Similar patterns have also been reported in other research, suggesting that the implants are performing well and are stable.
Tests that looked at how much the knee could straighten showed significant improvements over time (the knee got straighter) in both groups. There were no differences between groups, suggesting the implants performed similarly when the knee was straight. When the researchers looked at maximum knee bend, the results showed that both groups improved over time between 6-weeks and 1-year, but that only the GMK-Sphere group improved significantly from before their operation to 6-weeks after their operation. These results suggest that people who have the GMK-Sphere implant may recover their knee bend quicker than those with the Attune implant.
Finally, to make sure that participants were happy with the results of their knee replacement, the researchers looked at the results of the questionnaires that the participants had filled in. The questionnaires looked at knee pain and function (Oxford Knee Score), quality of life (EQ-5D and Visual Analogue Score), physical function and mental health (SF-12), and awareness of the knee (Functional Joint Score). Significant improvements were seen in scores over time for both groups, suggesting that pain lessened, and function and quality of life improved. No differences were seen between the groups in any questionnaire, suggesting that the outcomes were similar for the GMK-Sphere and Attune.
Overall, these results found little differences between the GMK-Sphere and Attune implants, suggesting that they are comparable functionally and in terms of participant feedback. Some differences in walking patterns may be explained by the fact that the Attune group were taller than the GMK-Sphere group. There was no evidence of instability in the results, as the walking patterns were like those reported by previous researchers, and no participants had a second operation to treat instability. However, people with the Attune implant may take longer to recover their knee bend than the GMK-Sphere. This may impact how long it takes these individuals to return to certain daily activities after knee replacement.
REC name
North West - Liverpool Central Research Ethics Committee
REC reference
18/NW/0640
Date of REC Opinion
6 Nov 2018
REC opinion
Further Information Favourable Opinion