Are custom-made knees better than off-the-shelf?
Never judge a book by its cover, let alone just the title…
and, some of what doesn’t glitter might actually be gold!
The importance of reading articles in full, with a critical eye,
rather than relying purely on just the abstract or, even, just the title!
“No difference in patient‐reported satisfaction after 12 months between customised individually made and off‐the‐shelf total knee arthroplasty”
Wendelspiess S, Kaelin R, Vogel N, Rychen T, Arnold MP
Knee Surgery, Sports Traumatology, Arthroscopy (2022) 30:2948–2957 https://doi.org/10.1007/s00167-022-06900-z
This paper should be read, carefully, in full. When one does, then the following important issues become very apparent:
ISSUES
- The patients were not randomised, and although it is not very clear from the wording in the paper, it would appear that it was the patients themselves that chose whether to have a CIM rather than a standard OTS knee:
“CIM TKA patients chose their surgeon (MPA) accordingly because of their interest in the new technology.”
Importantly, patients who are more proactively engaged in their healthcare decision-making processes tend to have higher expectations, and it is harder to achieve a good result (high patient satisfaction post-op) in patients with higher pre-operative expectations.1 Therefore, immediately, one can see that there is selection bias in this study (which is always a drawback of non-randomised studies).
- There is further, and important, selection bias in that some patients specifically had CIM knees on the recommendation of their surgeon if they had marked joint line obliquity:
“In rare cases, the patient was made aware of the possibility of a CIM TKA because of a marked joint line obliquity (tibial mechanical angle of ≤84° on long-leg radiographs) with an obvious anatomical difference in shape between the medial and lateral femoral condyles or hypoplasia of the lateral femoral condyle.”
Unfortunately, the authors fail to specify what their definition of “rare” might be, and exactly how many of the CIM patients actually fell into this category. Again, however, this is an example of selection bias, in that it is harder to achieve a good outcome in patients with more ‘difficult’ knees, and yet these ‘more difficult’ cases were specifically allocated to the CIM group.
- Patellar resurfacing was only performed selectively. However, information is given about what percentage of the CIM knees had patellar resurfacing performed compared to the OTS group. This is another potential confounding factor.
- The two groups (CIM vs OTS) were not comparable in their demographics, either, and importantly, the CIM patients were slightly younger and there were also more males in the CIM group.
Younger patients tend to have higher functional demands and higher expectations, and it therefore tends to be harder to match expectations and achieve satisfaction in these patients. This is another important confounding factor within the study.
The results of this study echo other previous studies, and report slightly higher post-operative patient satisfaction in females. However, there were more proportionally more males in the CIM group. Another confounding factor.
- The “primary” outcome measure used in this study was simply a 5-point Likert scale. This is extremely basic, and it is hard to understand why the authors chose to use such a simplistic and, inevitably, insensitive outcome measure as their primary outcome measure. Using such a basic tool significantly decreases the likelihood of any genuine differences between the two patient groups ended up being visible and apparent in the results.
- In terms of the results, no differences were seen on the 5-point Likert scale, but the KSS score was higher for the CIM group at both 4 months and 12 months post-op. (p<0.001).
- Anatomical alignment was better in the CIM group. This is important, but it is barely mentioned by the authors.
One of the specific advantages of CIM implants is that they use 3D-printed patient-specific cutting blocks, and these have been shown to give accuracy of implant placement equivalent to computer navigated / robot-assisted surgery, but without the additional invasiveness, time or costs that these involve.2 Accurate implant placement (within 3o of ideal) has been demonstrated to affect longer-term outcomes.
- Stability was better for the CIM group.
- Adverse events were more frequent in the OTS group.
- Revision was less frequent in the CIM group (4 patients needed revision surgery in the OTS group, compared to none in the CIM group).
- And finally…
The normal accepted patient satisfaction rate for OTS TKR = about 80%…
- Patient Satisfaction after Total Knee Arthroplasty: Who is Satisfied and Who is Not? Clin Orthop Relat Res2010; 468(1): 57 – 63. doi: 10.1007/s11999-009-1119-9.
“Our data confirmed that approximately one in five (19%) primary TKA patients were not satisfied with the outcome. Satisfaction with pain relief varied from 72–86% and with function from 70–84% for specific activities of daily living.”
However, the authors of the recent KSSTA paper quote a patient satisfaction rate of 89% for their OTS knees. This is way better than average… and it represents a patient dissatisfaction rate that is about 50% lower than the published norm. So, the authors really should be congratulated on that!
If patient satisfaction is reported to be about 90% with a CIM knee (as reported in the published studies on CIM knees to-date)… and if the KSSTA paper’s authors are getting an 89% satisfaction rate already with OTS knees… then there’s absolutely no way that they could ever actually demonstrate any significantly significant difference in outcomes between CIM and OTS – not if their OTS results are so abnormally good already!!
CONCLUSIONS
So, we have a paper here whose title states:
“No difference in patient‐reported satisfaction after 12 months between customised individually made and off‐the‐shelf total knee arthroplasty”
with an abstract where just one single line hints at a possible difference of potential interest:
“The postoperative KSS, notably regarding knee stability, was higher for CIM TKA (p<0.001)”
However, if you read and critically appraise the actual full paper itself then the actual conclusions that should be drawn are:
- the study is non-randomised, and there is obvious selection bias,
- there are significant potentially confounding factors between the two study groups,
- the main outcome measure was simply just a basic 5-point satisfaction scale,
- the KSS scores were significantly better in the CIM group,
- the post-operative alignment was better in the CIM group,
- the post-operative stability was better in the CIM group,
- adverse events were less frequent in the CIM group,
- revision was less frequent in the CIM group, and
- the authors’ results for their patient satisfaction scores for their OTS knees are significantly superior to the usual published expected norm for OTS knees: therefore making it extremely unlikely that any significant difference in ‘satisfaction’ could ever be observed.
A very different-looking set of conclusions compared to the study title, which is clearly deeply simplistic and actually really quite misleading.
The discrepancies between the actual stated results and what the authors chose to write as their study title and abstract is so stark as to make one wonder whether undue outside influence or bias might have been at play? (Or maybe the reviewers were simply half-asleep?!)
Finally, any paper should never be read or considered purely in isolation, and one should only form an opinion on a subject after a full analysis of the wider evidence available across a broad range of publications and studies. So, if you want to learn more about the potential benefits of custom-made knee replacement surgery, then these papers are useful, for starters:
- “A Comparison of Clinical Outcomes and Implant Preference of Patients with Bilateral TKA. One Knee with a Patient-Specific and One Knee with an Off-the-Shelf Implant.”3
“… patients in this study cohort who underwent staged bilateral TKA with a C-TKA implant in 1 knee and an OTS prosthesis in the other knee reported better for their patient-specific knee replacement, with higher FJS and KOOS, JR values, and overall, preferred the C-TKA knee more often compared with the OTS knee replacement.”
- “Accurate implant fit and leg alignment after cruciate-retaining patient-specific total knee arthroplasty.”4
“The patient-specific iTotal™ CR G2 total knee replacement system facilitated a proper fitting and positioning of the implant components. Moreover, a good restoration of the leg axis towards neutral alignment was achieved as planned.”
- “Patient Satisfaction, Functional Outcomes, and Survivorship in Patients with a Customized Posterior-Stabilized Total Knee Replacement”5
“The satisfaction rate was found to be high, with 90% of patients being satisfied or very satisfied and 88% of patients reporting a “natural” perception of their knee either some or all of the time.”
- “Patient Satisfaction, Functional Outcomes, and Implant Survivorship in Patients Undergoing Customized Cruciate-Retaining TKA”6
“Patient satisfaction was high, with 89% of C-TKA patients being either satisfied or very satisfied.”
(But remember… you need to actually read these papers in full, not just the abstracts, and certainly not just the titles! Otherwise, I’m afraid you’ve really just not ‘got it’ w.r.t. the fundamental underlying message of this entire blog! Happy reading!)
READ THE SCIENCE.
EVALUATE THE SCIENCE.
FOLLOW THE CURRENT SCIENCE.
SCIENCE IS NEVER SET.
REFERENCES
- Patient expectations and satisfaction 6 and 12 months following total hip and knee replacement. Qual Life Res 2020 Mar; 29(3): 705-719 doi: 10.1007/s11136-019-02359-7
- Comparison of postoperative coronal leg alignment in customized individually made and conventional total Knee arthroplasty. J Pers Med 2021; 11: 549
- A Comparison of Clinical Outcomes and Implant Preference of Patients with Bilateral TKA. One Knee with a Patient-Specific and One Knee with an Off-the-Shelf Implant. JBJS Reviews 2022; 10(2) – e20.00182. doi: 10.2106/JBJS.RVW.20.00182
- Accurate implant fit and leg alignment after cruciate-retaining patient-specific total knee arthroplasty.BMC Musculoskelet Disord 2020;21(1): 699 doi: 10.1186/s12891-020-03707-2
- Patient Satisfaction, Functional Outcomes, and Survivorship in Patients with a Customized Posterior-Stabilized Total Knee Replacement. JBJS Reviews e 8 – Issue 7 – p e19.00104. doi: 10.2106/JBJS.RVW.19.00104
- Patient Satisfaction, Functional Outcomes, and Implant Survivorship in Patients Undergoing Customized Cruciate-Retaining TKA. JBJS Reviews 2021; Volume 9(Issue 9): e20.00074. doi: 10.2106/JBJS.RVW.20.00074