Orthodoc
Former BoneSmart staff member
This is a great topic for discussion. Here are a couple of my thoughts.
First - Jo, you have mentioned 90 degrees as being the minimum. That is the number that most orthopaedic surgeons (based on studies and clinical experience) believe will enable the patient to return to most activities. Stair climbing is usually good at 90 degrees. Descending stairs requires a bit more flexion. In general, most OS will consider MUA if the flexion does not get to 90 degrees. I have, however, experienced several patients being satisfied with even less motion (the reduction in pain and deformity trumped the lack of motion). If knee motion only gets to 90 degrees there will be some limitation in function. Some patients compensate well for this, others do not.
Second - It is important to remember (I have stated this before) that the best predictor for post-operative ROM is pre-operative ROM. This has been shown by numerous large well controlled studies. The question has come up about implants. The type of implant may have some influence on motion. There are studies that show that PS (posterior cruciate substituting) implants have slightly better motion long term than CR (cruciate retaining) implants. However, I must stress that that there are many factors that can influence this. My experience is that whether I use a CR or PS implant (I determine this in the OR depending on several factors), the final ROM is not effected by the implant, but rather soft-tissue balancing, etc.. Additionally, studies have not found that rotating platform knees (which I use as well from time to time) provide any additional ROM compared to fixed bearing devices.
Third - As far as specific manufactures are concerned. I do not feel that one manufacturer has any significant advantage over another as far as ROM is concerned. There are so many other factors that are more significant. Much of what patients see is marketing hype (but effective none the less). What I will say is that the technology that continues to advance from the manufactures will continue to make TKA one of the most successful surgeries ever done.
Fourth - (You still with me?) As far as too much flexion. This is much less of a typical problem, but can be of a concern. As the patient hyper-flexes the knee, the back of the femoral component can pinch up against the back of the polyethylene. Here is one of the instances where component design does make a difference. Some polyethylene inserts are relatively flat (non-conforming), others are more dished (more conforming). If there were to be too much "edge" loading with hyper-flexion than the poly could prematurely wear down in that spot.
Orthodoc
First - Jo, you have mentioned 90 degrees as being the minimum. That is the number that most orthopaedic surgeons (based on studies and clinical experience) believe will enable the patient to return to most activities. Stair climbing is usually good at 90 degrees. Descending stairs requires a bit more flexion. In general, most OS will consider MUA if the flexion does not get to 90 degrees. I have, however, experienced several patients being satisfied with even less motion (the reduction in pain and deformity trumped the lack of motion). If knee motion only gets to 90 degrees there will be some limitation in function. Some patients compensate well for this, others do not.
Second - It is important to remember (I have stated this before) that the best predictor for post-operative ROM is pre-operative ROM. This has been shown by numerous large well controlled studies. The question has come up about implants. The type of implant may have some influence on motion. There are studies that show that PS (posterior cruciate substituting) implants have slightly better motion long term than CR (cruciate retaining) implants. However, I must stress that that there are many factors that can influence this. My experience is that whether I use a CR or PS implant (I determine this in the OR depending on several factors), the final ROM is not effected by the implant, but rather soft-tissue balancing, etc.. Additionally, studies have not found that rotating platform knees (which I use as well from time to time) provide any additional ROM compared to fixed bearing devices.
Third - As far as specific manufactures are concerned. I do not feel that one manufacturer has any significant advantage over another as far as ROM is concerned. There are so many other factors that are more significant. Much of what patients see is marketing hype (but effective none the less). What I will say is that the technology that continues to advance from the manufactures will continue to make TKA one of the most successful surgeries ever done.
Fourth - (You still with me?) As far as too much flexion. This is much less of a typical problem, but can be of a concern. As the patient hyper-flexes the knee, the back of the femoral component can pinch up against the back of the polyethylene. Here is one of the instances where component design does make a difference. Some polyethylene inserts are relatively flat (non-conforming), others are more dished (more conforming). If there were to be too much "edge" loading with hyper-flexion than the poly could prematurely wear down in that spot.
Orthodoc
New Zealand
Tashia