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KneeFurther Opinion

Does the new generation of high-flex knee prostheses improve the post-operative range of movement?

R Mehin, RS Burnett, PMA Brasher

J Bone Joint Surg [Br] 2010;92-B:1429-1434.


This meta-analysis investigates whether  the high-flex total knee implants increase the post-operative range of movement. The authors of this paper systematically searched the literature and analysed all the available papers in an attempt to clarify if the newly introduced high-flex knee prostheses improve the range of movement as the designers claim. Also they investigated if these prostheses have better results than the conventional ones.

The eligibility criteria, the data sources, search strategy and protocol are very clear and valid. The data selection was profound according to strict inclusion and exclusion criteria.The quality of the selected studies is properly evaluated and the score of each one is outlined. It is very important that the  possible influence of the industry in the outcome of the studies is investigated and recorded. Another strong point  of the study is the consideration of the blinding measurement of range of movement.The synthesis of the data is meticulous and the whole approach is technically sound, although using the limit of the range rather than the z-value from the exact p-value results in wider confidence intervals.

In the results, a detailed analysis of the eliminated articles is given. Studies such as these which were duplicated, those with patients who had pre-operative flexion more than 120°, not comparing the high-flex with conventional prostheses and non randomised control trials were excluded.The multi-nationality of the included studies is of relative value.

It is known that pain is the main symptom of osteoarthritis of the knee. Stiffness and deformity are  present but their severity is variable. Relief of pain is the primary goal of total knee replacement, but post-operative range of movement and alignment is important for functional outcome and should be considered. Many factors influence the post-operative range of movement following replacement of the knee: pre-operative planning based on the radiograph measurement, the pre-operative range of movement, surgical technique, external rotation in order to set the femoral component parallel to transepicondylar axis, but the most important one is the soft tissue balance based  on the gap technique. Newly introduced ‘high-flex’ designs with increased posterior femoral condyle offset,increased posterior slope of the tibial polyethylene, increased and deep anterior patellar cut-out of the insert, reducing the tension of the extensor mechanism are supposed to offer a greater range of movement. This is proven in laboratory studies but in clinical practice ith as not been demonstrated.  In my opinion this is the strength of this paper which gives a clear message to the orthopaedic community, that the high flex designs do not improve the range of movement, on the evidence currently available.


Macheras G

Ist IKA Hospital Athens, Athens, Greece