Total Knee Replacement Using Patient-specific Templates

August 14, 2014 | Emerging Technology Reports


Proprietary names: Signature™ Personalized Patient Care System (Signature Planner, Signature guides); iFit® image-to-implant technology; iJig® instrumentation; TruMatch® Solutions; SurgiCase preoperative planning software; Mimics® Innovation suite; 3matic computer-assisted design software; MyKnee® Cutting Blocks; ShapeMatch® Cutting Guides, Visionaire™ patient-matched instrumentation; KneePlan preoperative planning software; Prophecy® Pre‑Operative Navigation Alignment Guides; Zimmer® Patient Specific Instruments System (Zimmer Patient Specific Instruments Planner, Zimmer Patient Specific Instruments) Generic names: patient-specific instruments; custom templates; custom cutting guides; custom cutting jigs; custom-fit total knee replacement; custom-fit positioning; patient-specific positioning guides

The most common underlying condition necessitating total knee replacement (TKR, also known as total knee arthroplasty) is knee osteoarthritis.1 Knee osteoarthritis occurs when the knee's cartilage degrades, resulting in joint stiffness and pain.2 If first-line treatments (e.g., weight loss, activity modification, analgesics, injections)2-4 fail to relieve discomfort and improve function, clinicians and patients may consider surgery (e.g., arthroscopic debridement, partial knee replacement, TKR).2-4 During TKR, the surgeon typically resects the articulating surfaces and a portion of the underlying bone in the knee joint using a saw guided by templates and jigs.5 The joint surfaces, including the lower end of the femur, the upper end of the tibia, and often the back surface of the patella, are replaced with artificial knee implants.6 These implants can be made of metal alloys or plastic and are typically affixed to the bone using acrylic cement.6 Most clinicians agree that TKR improves quality of life, decreases pain, and increases function.7 Generally, TKR's success rate is high, and 90% to 97% of implants survive 10 or more years after implantation.7-9 Most clinicians believe that proper implant alignment is essential for implant longevity, appropriate articulation, and wear reduction,10-12 and some clinical studies show suboptimal alignment may be associated with shortened implant longevity and poor patient outcomes.10,12 Alignment depends on finding the anatomic landmarks that will allow the surgeon to resect the bones in the proper orientation in all planes. Surgeons evaluate implant alignment after surgery by analyzing component and anatomic positions using radiographs.13 One important outcome is the overall alignment of the leg in the coronal plane, which clinicians often assess by measuring the hip-knee-ankle (HKA) angle (the angle formed between a line connecting the center of the hip to the center of the knee and a line connecting the center of the knee to the center of the ankle). Most clinicians agree that less than a 3° deviation from a neutral (i.e., 180°) HKA angle may minimize the risk of implant collapse, wear, loosening, instability, and postoperative pain.10,11 However, some clinicians have questioned whether optimal alignment is the same for every patient.14,15 Other common alignment measures include femoral and tibial component alignment in the sagittal and axial planes and femoral and tibial component rotational alignment. Surgeons have several options to aid in properly aligning knee implants: conventional instrumentation, intraoperative computer-assisted navigation, and patient-specific templates. Conventional instrumentation used during TKR includes guides and blocks to assist with proper orientation of femoral and tibial components. According to one clinical study, use of conventional instrumentation may result in malalignment (i.e., greater than 3° deviation from neutral mechanical axis) in approximately 28% of TKRs.16 To increase the accuracy of alignment during TKR, clinicians adopted the use of intraoperative computer-assisted navigation. To use intraoperative computer-assisted navigation during TKR, the surgeon drills tracking markers into the femur and tibia, registers bony landmarks into a computer, and receives feedback from the computer regarding cutting block alignment.13 Intraoperative computer-assisted navigation has been reported to decrease the incidence of malalignment approximately threefold compared to conventional instrumentation.16 However, intraoperative computer-assisted navigation may increase operative time and cost and has a steep clinician learning curve.17 To address the disadvantages of intraoperative computer-assisted navigation, manufacturers developed patient-specific templates, which purportedly allow clinicians to achieve highly accurate alignment while decreasing cost and operative time compared with intraoperative computer-assisted navigation.18 Despite advancements in TKR, controversy exists regarding which method produces the best patient outcomes. Some clinicians have questioned whether the traditional definition of malalignment is clinically relevant for all patients. One clinical study that analyzed TKR revision rates at 15-year follow-up reported a low TKR revision rate in patients with malaligned implants and no significant difference in revision rate between the aligned and malaligned groups (15.4% versus 13%, p = 0.88).15

According to one published report that analyzed the 2007 to 2008 National Health and Nutrition Examination Survey results, the prevalence and incidence of diagnosed symptomatic knee osteoarthritis vary with age, sex, and obesity status.19 The prevalence is lowest (0.74%) in nonobese men ages 25 to 35 years and highest (32.45%) in obese women ≥85 years of age.19 The estimated incidence ranges from 0.04% per year in nonobese men ≥85 years of age to 1.02% per year in obese women ages 55 to 64 years.19 The mean estimated age at diagnosis is 53.5 ±14.4 years (mean ± standard deviation SD), and the lifetime risk of symptomatic knee osteoarthritis diagnosis from age 25 is approximately 13.83%.19

In 2010, the U.S. Centers for Disease Control and Prevention estimated 719,000 patients were discharged from the hospital after TKR.20 U.S. TKR incidence is increasing rapidly and is projected to be 1,520,000 by 2020 and 3,481,000 by 2030.21 The rapidly increasing demand for this procedure places a growing burden on lower-volume, less-experienced arthroplasty surgeons.9 Worldwide, TKR incidence varies greatly by country, from fewer than 1 per 10,000 people in Brazil to 18.6 per 10,000 people in Austria.22 Reasons for this wide variation appear to be economic rather than related to health risk (e.g., percentage of elderly people, overweight and obesity, incidence of osteoarthrosis), with wealthier countries having a greater incidence of TKR.22

Patient-specific templates are a tool used during TKR to guide the surgeon in cutting the bone and aligning the tibial and femoral implants. The templates are patient-specific because the manufacturer uses images of the patient's knee to design the guides and produce a template specific to each patient's anatomy. Creation of patient-specific templates requires the following preoperative planning steps:23-25

During surgery, the surgeon places the patient-specific templates on the patient's distal femur and proximal tibia and adjusts the position of the customized contact faces of each template until locating the exact fit to the bone.26 In some models, cutting guides within the templates specify where the surgeon should cut the bones, while other template models guide the insertion of pins, which are then used to place standard cutting guides.25 The surgeon creates the bone cuts, places the knee implants, and affixes the pieces in place. Purported benefits of using patient-specific templates during TKR include the following:23-25,27-30

ECRI Institute searches identified 12 manufacturers of patient-specific templating system components for TKR. We received distribution information for two of these manufacturers: DePuy Synthes, a Johnson & Johnson company (Warsaw, IN, USA), distributes the TruMatch Solutions worldwide,31 and Wright Medical Technology, Inc. (Arlington, TN, USA) distributes the Prophecy Pre-operative Navigation Alignment Guides in the United States, European Union, Canada, Australia, Japan, and South Africa.32 For further details, see Table 1. Most manufacturers make patient-specific knee templates to align standard implants; however, ConforMIS, Inc. (Burlington, MA, USA) manufactures a system that includes patient-specific knee templates and a patient-specific total knee implant that is made using the patient's CT.

Vanguard® Complete Knee System


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