Evidence based medicine forms the basis of clinical based practice in modern medicine. It ensures that the best care is provided to patients based on previous evidence available in the literature. In recent years, various tools have been generated to allow critical appraisal, examination of the validity and reliability of a particular medical evidence. One such commonly used critical appraisal tool originates from the Critical Appraisal Skills Programme (CASP) which was developed by the Centre of Evidence Based Medicine at the University of Oxford((CASP), 2017).
Three broad issues should be considered when appraising a systematic review study: Are the results of the study valid statistically significant? What are the is the outcome of the results? Will the results help locally?
Whilst writing a review article, the author should not only view the topic with an unbiased mind by getting rid of pre-conceived ideas, but also analyze related available literature in a methodical manner. Having a critical attitude, while studying the available literature, is of paramount importance. If anything is incompatible with his understanding of the topic, the author should pause, mentally question, and delve deeper by conducting more research.
The author of this assignment will critically appraise the following article using CASP check list; “Mid-flexion instability after total knee arthroplasty. Bone Joint J 2016;98-B(1 Suppl A):84-8. (K. Vince. 2016)
Martin and Whiteside conducted a cadaveric study of total knee arthroplasty (TKA). They identified mid-flexion laxity in the coronal plane when the femoral component was shifted 5 mm proximally and anteriorly. Therefore, joint line position, in the presence of well-balanced flexion and extension gaps, was suggested to have a profound effect on mid-flexion instability. Elevation of the joint line alters the flexion-extension axis. They proposed a hypothesis that the laxity of the posterior capsule, collateral and posterior cruciate ligaments at 30º–60º (mid-flexion range), may contribute to mid-flexion instability (Martin and Whiteside, 1990).
Advancement in the field of joint functioning (normal and prosthetic) have opened the gate for comprehending the joint line complications after TKA. Joint line instability is a prevalent cause of failure of prosthesis post-TKA. Aggravated antero-posterior/medio-lateral laxity in flexion after surgery represents flexion instability. On the basis of degree of flexion at which the laxity is noted, it is categorized into two parts; early flexion instability, when laxity occurs at 30º – 60º, or mid-flexion instability when it is noted at between 60º – 90º (K. Vince. 2016).
Simple flexion instabilities in a cruciate-retaining TKA can often be revised using a posterior stabilized implant with favorable results. Minor collateral insufficiencies causing extension instability can be managed with soft-tissue releases on the concave side of the deformity to restore alignment, but with more severe ligamentous insufficiency, a varus-valgus constrained design is preferred. In more problematic cases of global instability or genu recurvatum, symmetrical and balanced flexion and extension gaps may not be obtainable, and more constrained implants including constrained condylar or hinged devices are advised (Petrie and Haidukewych, 2016).
König et al. hypothesized that elevation of joint line and the subsequent change in the position of the femoral collateral ligament attachment sites relative to the femoral articulating surface alters the length change patterns of the collateral ligaments during knee flexion, specifically in mid-flexion. The aim of the study was to analyze the length change patterns of the collateral ligaments during knee flexion for situations of joint line elevation after TKA in order to assess whether joint line elevation can indeed contribute to mid-flexion instability (König et al., 2011).
Restoration of the joint line while maintaining balanced flexion and extension spaces is the most important step to be considered for revision of mid-flexion instability. In difficult cases, where posterior capsular release and osteophyte removal is insufficient to open the extension space, an elevated joint line may need to be accepted and components with additional constraint be used (Del Gaizo and Della Valle, 2011).
A computerized literature search was conducted using Medline, Cochrane, OVID and EMBASE. The search terms were ”Mid-Flexion”, ”Total Knee Replacement”, “Instability”, ‘Unstable and ”Revision”. The relevant articles were identified and information gleaned from reading the articles was utilized in an appropriate manner.
After selecting the relevant articles, the author discussed all the answers as per the CASP checklist.
3. Critical Appraisal
3.1 Did the review address a clearly focused question?
Mid-flexion instability after TKA: woolly thinking or a real concern? Mid-flexion instability, a form of joint instability seen after TKA, is a new and evolving concept. Recently, numerous studies have tried to explain this complication; however, to give it the status of a distinct clinical entity, more knowledge is required (Martin and Whiteside, 1990, Vince, 2014, Abdel et al., 2014). The author has certainly picked an interesting topic: mid-flexion instability is encountered in patients post TKA. The legitimacy of the author’s concern can be better evaluated by the readers after a better understanding about the topic.
3.2 Did the author look for the right type of papers?
The author has looked into previously published articles related to mid-flexion instability, given the review question. Various studies tending to find out the cause of mid-flexion deformity and giving it a distinct identity as post TKA complication have been included and correlated.
Initial studies conducted in 1990s (Pagano et al; Martin et al) stressed on the fact that joint line elevation is the major contributor of mid-flexion instability. Pagnano et al conducted posterior cruciate ligament retaining TKA on 25 patients. Clinically the patients presented with a sense of instability without frank giving way, soft tissue tenderness involving pes anserine tendons, posterior sag sign at 90º flexion and recurrent knee joint effusion. There was no evidence of infection or loosening. All these patients were posted for revision surgery. This study concluded that a revision surgery aimed at restoring balance between flexion and extension gaps in association with placement of a posterior stabilized knee implant can serve as a reliable treatment option for flexion instability post TKA (Pagnano et al., 1998).
On the contrary, certain recent recommendations highlighting the joint line elevation as the means of surgical correction of flexion instability have also been added (Abdel et al). If the extension gap is enlarged to match the flexion gap, the flexion instability is eliminated. Abdel et al listed radiographic manifestations in cases of knee instability post arthroplasty, such as inadequate distal femoral resection, excessive posterior tibial slope and varus mal-alignment of the tibial component. They also stated a surgical algorithm for the correction of flexion instability and restoration of balance between flexion and extension gaps. It was suggested to begin with by addressing the excessive tibial slop followed by correction of the axial or rotational mal-alignment of the components. Finally, introduction of a larger femoral component to increase posterior condylar offset (Abdel et al., 2014).
Vince suggested in 2014 that ligament weakening, component size mismatch, mal-positioning or polyethylene wear may lead to dislocation of knee arthroplasties. In such cases a surgical revision is recommended. It was concluded that in a case of flexion instability, the hamstrings translate the tibia posteriorly, leading to subluxation or dislocation (Vince, 2014).
3.3 Do you think all the important, relevant studies were included?
Most of the recent and relevant data pertaining to the concern of mid-flexion instability; including its presenting complaints, kinematic causes, treatment options and its relevance as a distinct pathological status; has been looked into, studied and analyzed in detail.
However, an important study to assess the mid-flexion instability intra-operatively was conducted in Osaka, Japan by Minoda et al which could have been considered. They carried out a multi-centric study of intra-operative assessment of joint gap in 259 knees posted for posterior stabilized mobile bearing TKA. The joint gap was measured by the use of a tensor device before placing the implant. The device’s shape was identical to the total knee prosthesis. The center width and asymmetry (tilting) under the distracting force of 120N were measured with the patellofemoral joint reduced and the quadriceps sutured. This study showed that joint gap became loose in mid-flexion after implantation. To their best knowledge, they considered it to be the first reporting of objective data indicative of mid-flexion instability after arthroplasty (Minoda et al., 2014).
3.4 Did the review’s authors do enough to assess the quality of the included studies?
A well-designed review is often sought right at the beginning to update one’s knowledge about a topic and genesis of a topic guideline. Creditably, the author has produced a readable synthesis of the best available literature on the topic of mid-flexion instability after TKA. Only those studies were considered that had authentic data, with no conflict of interests, and that had been published in indexed journals. Studies relating to the topic, across the continent of publication of the current paper, were also considered.
3.5 If the results of the review have been combined, was it reasonable to do so?
The results of all the papers were compared and analyzed in light of the current question. The result of the review was in accordance with findings of other researchers, so it was reasonable to combine the results of all the studies.
The aim of different studies was to confer mid-flexion instability as a unique identity and to find out its cause after TKA. Although it is a wise decision to compile all the results so that a fine conclusion could be deduced using the wider outlook of various studies but no statistical analysis of the conclusions of the various studies has been done to find out the significance.
The methods used to analyze the mid-flexion instability are totally different in all the studies quoted in the article. Hence, a further robust review is required to narrow down the causes of mid-flexion instability. Meta-analysis of the results of different studies needs to be carried out to find out if the concern is statistically significant.
3.6 What are the overall results of the review?
It is important to visualize all four sides of the knee joint, i.e., medial, lateral, anterior and posterior when performing TKA because of the role of the posterior structures in varus-valgus stability. Most of the times the operating surgeons consider only the collateral ligaments as imagined on the anteroposterior radiograph, and the extensor and posterior capsule as seen in the lateral view. This limits the visualization to 2D only. And the inability to visualize the knee joint conceptually in 3D leads to wishful thinking on mid-flexion instability, post arthroplasty, which is a real concern.
3.7 How precise are the results?
The results have been commented upon after a comprehensive research of quality papers. So, the results are borne out by valid and extensive research carried out in reputed hospitals.
The varus–valgus instability of the knee in flexion angles between 30? and 45? is also referred to as mid-flexion instability. Even knees that have been carefully balanced in extension and at 90? flexion can exhibit mid-flexion instability. Whereas the precise mechanisms causing mid-flexion instability has not been fully assessed, elevation of the joint line after TKA has been suggested as a potential contributor to mid-flexion instability. The attachment sites relative to the knee flexion axis significantly influence the length change patterns of the cruciate ligaments during flexion. Since joint line elevation alters the knee’s flexion axis relative to the location of the collateral ligaments’ femoral attachment sites, it is likely that joint line elevation can induce altered lengthening or shortening characteristics of the collateral ligaments at different flexion angles. The function of the collateral ligaments, which is critical for providing varus–valgus stability of the knee during flexion, might thus be compromised at certain points of the flexion/extension cycle.
For both static and dynamic conditions of the knee joint, gap and ligament balancing techniques are crucial steps for creating a stable knee in TKA. Yet stability related problems are still a major reason for an arthroplasty revision. An elevated joint line as a cause of mid-flexion instability has been most commonly proposed. However, regarding effects of joint line elevation on the collateral ligaments has not been discussed in detail. The collateral ligaments serve as passive stabilizers of the knee, specifically in mid-flexion.
3.8 Can the results be applied to the local population?
Yes results can be applied to the local population provided more statistical significance can be assessed of the proposed hypothesis.
3.9 Were all important outcomes considered?
The important outcome to be considered after a TKA is a stable and pain free knee joint to improve the quality of life of the patient. The author has not thoroughly considered all the outcomes and has restricted himself to the functional outcome after TKA. Having a knowledge about mid-flexion instability and finding out ways to avoid it, will help the patients to perform better after the procedure.
In order to avoid the complications of TKA, surgeon should be aware about the different causes of instability and should be careful in performing the procedure in order to achieve the goal of providing the patient with a stable and pain free knee leading to better quality of life.
3.10 Are the benefits worth the harms and costs?
Recently, mid-flexion instability after TKA has been a major cause for concern and reason for revision surgery. Various methods have been applied for precise diagnosis, which might help to find the underlying cause and lead to the discovery of an effective treatment. In the present paper, the author has thoroughly reviewed a number of studies and has compared various important features in order to find out the most important reason of mid-flexion instability post TKA. He has highlighted the need for visualizing the knee joint as a three-dimensional entity to avoid errors while repairing the joint.
The author concluded that the mid-flexion instability should be considered as a distinct clinical entity, he seldom discussed on the amount of benefit attained and the technical advancements required to get rid of the complications. Further robust studies need to be conducted to assess the effectivity of the author’s approach. This will act as a boon for patients undergoing TKA as the increase in the cases of instabilities lead to further increase in the incidences of the need of revision surgery. Hence, if we improve our surgical practices and avoid such complications, it would help decrease the burden of revision surgeries.
(CASP), C. A. S. P. 2017. Systemic Review Checklist Online. Available: http://www.casp-uk.net/casp-tools-checklists Accessed 28 December 2017.
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