The patients with significant deformities and patients with ligamentous injuries are not candidates for customized 3-D knee replacement surgery. Additional contraindications for customized knee replacements include all the contraindications for a traditional knee replacement, as example active infection in the knee joint.

I have had the following issues with customized 3-D knee replacement –

1.  Some patients do not like to wait for long periods of time after their surgery is scheduled. As of 2018, the customized 3-D knee replacements takes about 6 weeks to manufacture and to deliver to the hospital. This is the major downside of using customized implants. The wait period is the major downside of using customized implants.
2. The second issue that I have had occasionally is patients go to a radiology facility with the script which clearly mentions that the CT scan is for a customized knee implant. However, the technician just does a plain CT scan. This plain CT scan is not enough for making a computerized model and to generate the prototype of the knee and to construct the customized implant. The patient therefore has to go again has to get the correct CT scan so that the customized knee implant can be manufactured.
3. For preparation of the shin bone during a customized 3-D knee replacement, there is a jig which guides the drill into the deeper part of the shin bone. In my experience, this jig should be made stronger because on occasion (on preparation of the deep part of the shin bone) the jig sheared off prematurely.
4. Some patients like to have their customized instruments that were used to replace their knees. These customized instruments need to be washed and process before delivery to the patient. I have found that this is somewhat of logistical issue coordinating washing of implants and handing it over to the patient. I have had these custom instruments processed and then these were delivered to my office and patient received these instruments in the first postoperative visit.

The patient has to go to very specific radiology centers which follow the protocol for making a customized 3-D knee replacement. The CT scan for the knee replacement surgery is very specific and not all radiology centers are able to do that.

I recommend getting a CT scan within 4 months of the scheduled surgery. The reason for this time frame is because if the deformity in the knee increases or if there are additional defects that arise in the knee after the initial CT scan is done, then the customized implant will not be as accurate as we want it to be. If the patient is considering surgery after 6 months, it is best to get the CT scan at a later date. Most patients that I see really want the surgery at the earliest available date and therefore get the CT scan as soon as possible.

The conversion of a failed partial knee replacement surgery to a full replacement surgery is called revision knee replacement. Custom knee replacements are not a good option for revision knee replacement surgery unless there are no revision knee systems in the market that can provide off the shelf option.

The customized 3-D knee replacement surgery is designed to match the natural knee joint. The CT scan provides accurate geometry for manufacturing this customize knee. The CT scan data is used to generate a computerized model of the custom knee by the custom knee manufacturing facility. Additionally, the custom knee 3-D manufacturing facility also makes very specific instruments that are customized to the anatomy of the native knee for doing the customized knee replacement.

These instruments are made specifically for the patient and make the surgery less invasive. As an example drilling into the thigh bone and the shin bone is not needed because the instruments contour very well to the anatomy around the knee joint providing accurate alignment, rotation, offset for placement of the custom knee.

The earliest the surgery can be scheduled is 6 weeks from the time the CT scan is performed. The CT scan is performed by immediately after seeing the surgeon. Six weeks is a reasonable time frame to schedule the surgery.

Additionally, it is important to ensure that the medical clearance for the patient is obtained prior to the surgery. I also get dental clearance prior to the surgery. It is important to note that the medical clearance as well as the blood investigations have to be done four weeks before the date of the surgery. If additional test, example cardiac tests are mandated by the internist, the surgery may need to be postponed. All “I’s have to be dotted, T’s have to be crossed” before the patient is actually wheeled into the operating room.

There are numerous radiology centers that do the CT scan and appointment for a CT scan is generally available within couple of days.

The CT scan appointment generally takes less than an hour. The time varies according to the radiology facility, but generally a CT scan appointment takes up less than an hour.

A customized knee replacement surgery generally takes about one hour to one and half hour to perform. By the time the patient goes into the operating room and the nurse calls the relative to visit the patient, it is a lot longer than one and half hours. The additional time is because of the time required by the anesthesiologist to anesthetize the patient which this may or may not include spinal anesthesia. There is also time that is needed to prep and drape the patient before the final surgery starts.

The customized knee replacement is manufactured from the CT scan. This CT scan is also used for manufacturing the custom knee instrumentation. This instrumentation assists in implantation of the custom knee into the patient. The customized jigs conform very well to the anatomy around the knee joint.

The traditional knee replacement uses intramedullary guide for placement of jigs on to the thigh bone. This process involves drilling the hole into the thigh bone and placement of a rod into the bone to get an accurate alignment. When a customized instrumentation is used, there is no need for placement of this intramedullary guide and there is no need to drill the bone, because the customized implants have already accounted for the alignment and geometry of the thigh bone and for the mechanical axis of the lower extremity. The surgery is therefore less invasive.

Similarly on the side of the shin bone (lower part of the knee joint), there are two ways to place the guide that is used for making the bone resections. One way is to drill hole into the shin bone (“intramedullary” guide) and place a rod into it and attach a guide to it (similar to the thigh bone) or the surgeon may choose to use an “extramedullary” guide (which means that there is a rod on the outside of the shin bone) to accurately align the guide on the shin bone so that the knee implant on the shin side will be accurately aligned.

The custom instrumentation does not need intramedullary guide. We use custom instrumentation for placement over the shin bone and the resection of the bone is made based on this less invasive guide. In addition to using the customized instruments, I also use visual techniques to ensure that the cuts are accurate.

There are several avenues in which the current technology for customized knee can be improved.

First and foremost the manufacturing process needs to be shortened. The current six weeks period as of 2018 is very long in my opinion. The patients should have the option of having knee replacement within 6 weeks of seeing the surgeon if all other requirements like medical clearances are met.

The CT scan does involve some radiation to the patient. With improved techniques, I feel we can significantly decrease amount of radiation involved with CT scanning of the knee.

There are some steps in the process which I feel are not as accurate and could be improved. As an example, during placement of the jigs for alignment of the guides on the shin side of the bone, cartilage, if any, has to be manually scraped. I feel this could create inaccuracies if additional cartilage is scraped by the surgeon or if less cartilage is scraped by a surgeon. The inaccuracy is very small. It is in millimeters, however, for patients who are tall, a small change in millimeter at the knee joint can vary the mechanical axis to a greater extent than patients who have shorter bones.

The cutting guides on the thigh bone could be consolidated into fewer cutting guides. As example, it is possible to create one cutting guide for all the cuts that are done on the thigh bone. The advantage of single cutting guide for the femur is that the process will be faster. Additionally, the inaccuracies will be decreased. As example, one cutting guide is placed, the cut is made and then the second cutting guide is placed on top of the first bone cut. I feel that if the first cutting guide is placed inaccurately, the first bone cut will be incorrect. The second cutting guide placed on the first cut just adds additional errors to the subsequent bone cuts. The use of a single cutting guide will decrease these inaccuracies.

Additionally, it is difficult for the manufacturing process to account for the flexion deformity, which is due to the soft tissues. The computerized scan is very good at evaluation of the bony anatomy, however, the knee may be bend due to fluid in the knee joint or due to contractures which are outside the knee joint and the current protocol does not account for these contractures.

The customized knee replacements are cemented into the shin bone and thigh bone. There is plastic in between the two metal parts. The underneath of the knee cap is also cemented into position.

The underneath of the kneecap is replaced by plastic, which is off the shelf. The underneath of the kneecap is not customized.

Physical therapy is mandatory after any knee replacement surgery including customized knee replacement.

• I do not change my immediate postoperative protocol for customized knee replacement. Without physical therapy, the range of motion of the knee can suffer. Whatever range the patient has at 3 months after the surgery is what remains for life. I try to achieve as much as range as possible during the surgery. This range has to be maintained postoperatively and physical therapy is a critical part of the postoperative protocol.

After having customized knee replacement, if you have requested the surgeon may give you the mold from which your knee was manufactured. The patients implant was made from this mold. This mold is customized for you and is available for you to take home.

• One of the issues that I have had is that there is some logistics involved in getting this mold and the custom instrumentation washed and processed and handing it over to the patients or relatives. Sometimes I have had the instruments washed, then delivered to my office and these instruments are then given to the patient in the postoperative visit to my office. There are some patients who love having their own custom instruments. Doing a customized knee replacements allows them the options to have these taken home with them.

“PSI” or “patient specific instrumentation” is technology of one company and “custom knee replacement” is of another. There is a significant difference between the two. PSI involves the instrumentation being specific for the patient. For PSI, the knee undergoes an MRI and the jigs (instruments used to replace the knee) are individualized or customized for the patient. The actual knee joint is “off the shelf”.

• In customized knee replacement, instruments are customized and in addition the actual knee joint is also customized for the patient.

No, the implants that caps the thigh bone and the shin bone is only one and is customized for the patient; however, the plastic between the two implants comes in numerous sizes. This allows intraoperative flexibility in resection of the bone as deemed best-fit by the surgeon.

Custom knee replacement is relatively new procedure. We do not have long-term data on customized knee replacement surgery. The current data that is available for the past few years shows that the custom knee replacement surgery results are satisfactory. The results of the custom knee replacement are equivalent to traditional knee replacement surgery.

The routine 3D printed knee replacements manufactured as of 2018 are cleared by the FDA. On occasion if I am using a customized knee replacement for a significant defect in the knee joint or for treatment of knee joint after an infection or for revision, then I have had custom knee implants made by manufacturing companies which have not been cleared by the FDA. However, I use it in my best judgment for these patients. These non-FDA approved implants are extremely far and few. The last one I did was several years before 2018. The current manufacturing company that routinely makes custom knee implants was not in existence at that time.

• If knee implant is necessitated by the patient which is custom made and which is not FDA approved, the patient will be counseled about that custom implant in advance. This non-FDA approved custom implant will be used on patients which are not candidates to get routine off the shelf joint replacement implants and who are not candidates to get routine custom made knee implants. There is nothing in the market that can be used in these patients which is why I custom make these implants in the first place.

Custom knee implants are made of cobalt-chromium-molybdenum alloy and the plastic is medical grade plastic, which is ultra-high molecular weight polyethylene which is cross-linked and also can be vitamin D infused. This is also the standard material used in off-the-shelf implants.

Custom 3-D knee replacements do not cost more than off-the-shelf implants. There should be no additional cost to the patient.

The customized knee replacements are customized for individual patients. The custom knee implants that I use are not available separately for women and men. There are no separate sizes for the implants that cap the thigh bone and the shin bone. It is just one customized implant for one patient.

As of 2018, there is no implant company that pays me for anything! I do not get paid by any hospital nor does any pharmaceutical company pay me. I work only for my patients.

Customized knee replacements are largely divided into the following:

1. Total knee replacement which is posterior cruciate “substituting”.
2. Posterior knee replacement which is posterior cruciate “retaining”.
3. Bicondylar replacement with replacement of only one compartment of the shin bone called as the “iDuo” and then there is
4. The unicompartmental customized knee replacement prosthesis.

A CT scan of the knee is needed to make a computerized model for the manufacturing company to make a customized knee implant. In addition the patient needs blood tests which are routine before any joint replacement surgery. The patient may need additional tests like cardiac stress test that may be needed by the internist to clear the physician for surgery.

The time to recover from a customized knee replacement surgery is almost identical to traditional knee replacement surgery. The hope is that because the new prosthetic implant matches the anatomy of the native bone, the long-term satisfaction scores will be improved- this is the real advantage of customized knee replacements.

I do not know hip resurfacing for a variety of reasons.  Hip resurfacing is associated with poor long term implant survivorship and is associated with more frequent complications than a regular total hip replacement.  Several studies have shown revisions for “pseudotumors” that form in the hip after hip resurfacing. The condition called as “adverse local tissue reaction” that results from metal on metal bearing surfaces, which can eat up the bone leading to significant osteolysis. There have been numerous “single component” revisions, which imply revision of one side of the prosthesis either a cup or the femoral resurfacing component.  The revision rates have been significantly more than revisions that were done for a total hip replacement. Additionally, a hip resurfacing cannot be done in females who are child bearing because the serum metal levels can be elevated after doing resurfacing from the metal on metal articulation. There have been issues with design of total hip resurfacing in which the devices could not be completely seated on the bone.  Inability to seat the femoral component has been associated with large amount of debris between the femoral neck and femoral component leading to failure of the implant. There are two peeks of failure when we look at results of total hip resurfacing.  The first peek is in the first few months after hip resurfacing and reason for the failure is fracture of the femoral neck.  In the long-term it is development of lesions due to adverse tissue reactions and due to serum metal levels. I do not believe there is good long-term implant survivorship with resurfacing.  The patient reported outcomes in the long-term are poorer with resurfacing than a regular total hip replacement because of patient needing revisions. Proponents of hip resurfacing use it because resurfacing preserves femoral stock.  There is a feeling that resurfacing increases the stability of the hip because a larger head can be used for the hip resurfacing than the one typically used in a total hip replacement. However, I feel that these advantages outweigh the risks of hip resurfacing.  Today we have larger femoral heads in regular total hip replacements that can be used in patients who are susceptible for dislocation.  Conserving femoral bone stock at the cost of early revision is not acceptable. There is significant marketing around hip resurfacing.  However, largely because of the poor long-term results, I do not do hip resurfacings. One of the important things to consider in any surgery is to consider a surgery that lasts very long time, hopefully for the life of the patient.  At the current point of time, I do not believe that the hip resurfacing meet these requirements.  I do not do hip resurfacings.

Hip resurfacing procedure is a type of hip replacement in which the femoral head is not entirely removed.  The socket is reamed and the cup is inserted into it. The head of the femur is only roughened out and a cap is placed on the femoral head. The advantage of this kind of procedure is that the less bone is removed from the femoral head. However, the risks in my opinion are significantly more with a hip resurfacing procedure in terms of survivorship of the implants.  I do not do a hip resurfacing because the long-term outcomes are not as favorable as a traditional hip replacement.  We have good predictable outcomes with a regular total hip replacement. Another concern with the hip resurfacing is metal on metal particles. These can travel into the blood and can cause adverse tissue reactions in the bone surrounding the hip.  These adverse tissue reactions can cause significant bone loss requiring significant amount of surgical work during hip replacement. The metal particles precludes use of a hip resurfacing procedure in females who are childbearing age. I believe it is important to give a good predictable long-term outcome based on literature which traditional hip replacement surgery currently affords.  I do not do a hip resurfacing.

The largest data on hip resurfacing among the many implant companies that make these devices from the “Birmingham Hip Resurfacing” made by Smith & Nephew company.  If you decide to have a hip resurfacing surgery, it is best to leave the choice of the implant to the surgeon.  Similar to data for total hip replacement surgery, surgeon familiarity with the implant is critical for good long-term outcomes. Disclaimer – I do not do hip resurfacing. The reasons are above.

Hip resurfacing similar to hip replacement can be done as a bilateral procedures (means both hips can be replaced at the same time). However, it is important to realize that it is a much bigger procedure and the patients who undergo bilateral hip surgery should have very little or no medical issues. Disclaimer – I do not do hip resurfacing. The reasons are above.

The most investigated prostheses used in hip resurfacing are hybrid design that means the femoral component is cemented into the prepared femoral head and the cup is pressed fit into the acetabulum.

There is significant marketing that goes around hip resurfacing.  However, the amount of time to recover from a hip resurfacing is similar to that of a hip replacement.  It is not significantly more or less. Marketing involved “showing off” younger patients who have done well initially after hip resurfacing but younger patients after traditional hip replacement will do equally well. The patients undergoing hip resurfacing are typically young active males who have active lifestyle and the postoperative rehabilitation is significantly faster in these patients.

The patients who undergo hip resurfacing typically have the same postoperative recovery like a traditional hip replacement surgery.

The surgical scar of a hip resurfacing is typically larger than that of a traditional hip replacement.  This is because the entire femoral head has to be dislocated in hip resurfacing. In a traditional hip replacement, the femoral head is resected and this affords good surgical exposure into the cup decreasing the length of the surgical incision. Additionally for translation of the thigh bone to prepare and insert the cup, release of gluteus tendon is required, especially of the gluteus maximus insertion and this necessitates a larger surgical incision.

Numerous implant companies manufacture hip replacement implants.  The most common is called as the Birmingham Hip Replacement which is manufactured by Smith and Nephew.  There are numerous other companies that have developed hip replacing implants and the ones in the United States are ASR by DePuy, the Conserve Plus by Wright Medical Technology, Durom by Zimmer and ReCap by Biomet.

I do not advise any impact type of activity after any sort of hip replacement.  There is tremendous amount of marketing which shows the patients are able to remain active after hip resurfacing.  However, it is not any different than a traditional hip replacement surgery – it is still an artificial part in the patient’s body.

Hip resurfacing lasts less than a traditional hip replacement surgery and is the main reason why I do not do hip resurfacing surgery for hip arthritis.

The amount of time taken for a hip resurfacing surgery is slightly more than a traditional hip replacement.  For surgeons in their learning curve it takes significantly longer to do hip resurfacing because they are not much familiar with the procedure.  For surgeons who are competent and do a good volume of resurfacing, the amount of time taken is not significantly more than a surgeon who is competent in doing traditional hip replacement.

Hospital usually has negotiated rates which are similar to that of a traditional hip replacement surgery.  It is important to enquire with your surgeon to see if the surgeon or the hospital charges extra for a hip resurfacing procedure.

After hip resurfacing procedure you should expect exactly the same type of recuperation as you would after a traditional hip replacement.  Hip resurfacing is done only through the posterior approach and I am not aware anybody doing hip resurfacing through an anterior approach.  I believe hip resurfacing done through an anterior approach to the hip will require significant surgical releases (cutting of muscles and tendons) that would compromise the advantage of anterior hip replacement surgery.