Customised patient instrumentation for total knee replacement

Osteoarthritis of the knee is a very common problem all over the world. In US alone every year 6,00,000 knee replacement surgeries are done and are increasing at approximately three per cent annually. In Australia, last year approximately 3,80,000 knee replacement surgeries were performed (Australian National Joint Registry 2012), which was approximately 4.5 per cent more than in the previous year. In India, around 20 to 30 crore people suffer from this problem.

However, only one lakh total knee replacement surgeries were performed last year. This is proof of the fact that despite a large patient base the number of surgeries is low. High cost of surgery with implants accounting for approx. 40 to 50 per cent of the cost of the package is a deterrent. Though Indian implant is now available and is less expensive, however, it lacks survivorship (longevity) data that is available with the imported implants. The technique is very precise and hence joint replacement surgery is not practised by all orthopaedic surgeons.

Myths/ apprehensions

Myth 1: Many people believe that avoiding activities or spending life in bed will preserve their knee joint from damage, or more activities will quickly damage their knee joint

Reality: Nothing can be farther from the truth, as “saving the joint” by becoming totally sedentary will not slow down the arthritis. On the contrary, sedentary lifestyle will weaken bones and muscles thereby predisposing your joint to early deterioration. Also routine activities including walking will not make the knee joint vulnerable for arthritis earlier. If you avoid surgery to the very last, then not only will the deformity be complex and severe, however, patient will take that much more time for physiotherapy and to recover completely from surgery.

Myth 2: Is there any harm in living with the damaged joints?

Reality: Knee replacement surgery is considered only for severely damaged knees and when conservative treatment is not helping any more. Knee replacement surgery reduced pain, corrects deformity, gives independence in activities and brings change in life style for better.

However if you choose to live with your damaged joints:

1. You continue to live with pain and walk with difficulty through life – due to the deformed joints.
2. If damaged joint becomes unstable, then you may fall and sustain fracture either around your hips or develop stress fracture along the shin-bone (tibia). Your osteoporosis may also worsen as a result of inactivity thereby making your bone more prone to fractures.
3. Deformities and instability will only worsen with age or passage of time.
4. As pain will force patients for regular consumption of analgesics and anti-inflammatory drugs – very likely to damage kidneys and cause ulcers in stomach if taken for long.

Myth 3: I am afraid of getting operated in my old age and also the pain thereafter!

Reality: Please understand that knee replacement surgery is considered mainly for elderly people. However, this should not create any undue apprehensions. Majority of patients in late 60’s or early 70’s with knee osteoarthritis believe that their life span is too short, unlike the true reality that majority live on for 90 years!

Most of the patients believe that they will either have a lot of pain during operation or that after operation they will get up in severe pain. On the contrary they feel no pain during surgery and also within four to five days after surgery (during hospital stay itself), almost all of patients are comfortable enough to ambulate (with support initially), start going to the toilet and are able to climb steps.

Myth 4: I am scared that I can become worse after the surgery and are there any risks from the surgery?

Reality: Total knee replacement is a highly successful and predictable operation. It has a success rate of over 95 per cent. This means that an overwhelming number of patients reap the benefits of surgery. Most of our patients may be suffering from one or more of the followings ailments, i.e., hypertension, diabetes mellitus, coronary artery disease (MI/angina/heart surgery), asthma, and hypothyroidism. They all are thoroughly medical evaluated by an anaesthetist and intensivist before surgery. As with any major surgery, potential risks are also involved with total knee replacement surgery, however their incidence is small.

Customised patient-specific TKR procedure

The techniques in TKR have been constantly evolving although the principles remain the same. Two major ways to perform TKR today are conventional TKR and computer-assisted TKR, and of late, customised patient-specific TKR. Patients are clinically evaluated before operation and then they undergo MRI of the knee and long standing X-rays of both lower limbs. The films and knee MRI are processed through specific programmes to generate a 3-D reconstruct of the patient knee. This 3-D reconstruct is then used to create specific zigs to give precise cuts of lower end of femur and upper end of tibia. These zigs also provide accurate sizing of the implant and precise rotational alignment of the implant in patients’ deformed knees. In the end, zigs helps to provide bony cuts which eliminate the patient’s existing deformity and provide perfect longitudinal as well as rotational alignment, thereby restoring good functions.

Merits vs demerits of other techniques

1. Conventional method:

• Large number of surgical steps is required for surgery
• Medullary canal of the femur gets violated hence more blood loss
• Implant placement accuracy after surgery is not as good

2. Navigation assisted TKR: Per operation, computer is used to help surgeons achieve more accuracy during surgery. The disadvantages are

• Equipment cost is Rs 60 – 70 lakhs
• Extra time is required to map the operated area on the computer
• Upto 10 per cent outliers, more operation time
• Gives accurate axial alignment but does not give rotational alignment accurately
• Possible risk of fracture after surgery at the site of navigational pins

3. Patient specific zig

• Extra cost of approximately Rs 45000/- per knee
• Gives component sizing, rotational and axial alignment accurately
• Reduced operation steps, less blood loss, less operation time by almost 40 per cent

This technique improves alignment and sizing by using computer-generated images of the patient’s anatomy to determine precise bone cuts, and implant positioning during the surgery. It eliminates the need to violate the intra-medullary canal, thereby reducing blood loss during and after surgery and serious complications like fat emboli. As many operative steps are reduced in this technique, and excessive dissection is not required, the operative time for the knee replacement procedure is reduced by half.

Less surgery time, less bleeding, less post-operative complications and less dissections allows quick post-operative recovery. As sizing of the implant is done before surgery and many operative steps are not required, less instrumentation is needed in operative room, thereby reducing burden of inventory and autoclaving which in turn reduces burden on the institution. Customised patient-specific instrumentation technique is good for all and includes patient, surgeons and institutions as well. One major downside is the cost involved in the manufacture of this device. It is around $1000, and takes around three to four weeks to deliver.