Perspective

Custom TKA technology may yield better postoperative knee function

About 30% of patients could obtain a "natural" knee with a custom-made knee prosthesis.

ORLANDO, Fla. — Custom knee technology used with total knee arthroplasty may yield implants that closely reproduce the patient’s condylar anatomy and are associated with improved quality and reproducibile postoperative function, according to a presenter at the Current Concepts in Joint Replacement Winter Meeting.

“Regardless of the technology that you use, the closer that you can recapitulate that patient’s anatomy the better that you will reproduce their kinematics and their function and ultimately the happiness of that knee,” Jose A. Rodriguez, MD, of the adult reconstruction and joint replacement service at Hospital for Special Surgery, said in a presentation.

Custom vs off-the-shelf implants

Jose A. Rodriguez, MD
Jose A. Rodriguez

Off-the-shelf implants are based on a set of averages, which work for about 70% of patients, Rodriguez explained in an interview with Orthopedics Today. However, the other 30% of patients experience increasing compromises “to make it work as well as it can,” he said.

“The concept I am describing is a custom, individually made knee for each individual patient where, after correcting for further deformity, an engineer looks at every single knee and recapitulates the medial and lateral condylar surfaces, as well as the patellofemoral surface independent of each other,” Rodriguez said at the meeting.

In his presentation, Rodriguez discussed a multicenter, prospective study in which Mary I. O’Connor, MD, and colleagues used timed up and go, timed walk, and timed up and down stairs tests for an aggregated locomotor function score (ALF) for patients who underwent TKA with either a ConforMIS custom-made cruciate-retaining knee prosthesis or various brands of off-the-shelf TKA prostheses.

“Interestingly, there were about 370 patients in each group, so large cohorts, varied demographics. Their postoperative knee scores and their satisfaction scores were not different,” Rodriguez said. “These were similar populations and yet their function was objectively different in every single realm that was measured such that, when it was aggregated into the ALF score, it was highly significantly faster function in the custom group.”

Lateral rollback closer to normal

In a study of in vivo TKA kinematics that Rodriguez discussed in his presentation, Zeller and colleagues found custom knee prostheses were associated with greater weight-bearing motion than off-the-shelf implants.

“The results of the lateral rollback were also much closer to normal in the custom knees” in that study, Rodriguez said.

Despite the positive results with custom, individually made prostheses seen to date, more long-term data are needed before custom made technology is more widely used in patients undergoing TKA, Rodriguez said in the interview.

“Up til now, the research we have is the first real-time fluoroscopy demonstrating how a custom knee moves relative to most off-the-shelf knees and that shows an improvement,” Rodriguez told Orthopedics Today in the interview. “[Up] til now, we have outcome data that shows that within the first 6 months there is more rapid recovery and more complete recovery in terms of how fast and how smooth the patients move, but it is short term,” he said. – by Casey Tingle

Disclosure: Rodriguez reports he does consulting and design work for Medacta, Smith & Nephew, Exactech and ConforMIS.

ORLANDO, Fla. — Custom knee technology used with total knee arthroplasty may yield implants that closely reproduce the patient’s condylar anatomy and are associated with improved quality and reproducibile postoperative function, according to a presenter at the Current Concepts in Joint Replacement Winter Meeting.

“Regardless of the technology that you use, the closer that you can recapitulate that patient’s anatomy the better that you will reproduce their kinematics and their function and ultimately the happiness of that knee,” Jose A. Rodriguez, MD, of the adult reconstruction and joint replacement service at Hospital for Special Surgery, said in a presentation.

Custom vs off-the-shelf implants

Jose A. Rodriguez, MD
Jose A. Rodriguez

Off-the-shelf implants are based on a set of averages, which work for about 70% of patients, Rodriguez explained in an interview with Orthopedics Today. However, the other 30% of patients experience increasing compromises “to make it work as well as it can,” he said.

“The concept I am describing is a custom, individually made knee for each individual patient where, after correcting for further deformity, an engineer looks at every single knee and recapitulates the medial and lateral condylar surfaces, as well as the patellofemoral surface independent of each other,” Rodriguez said at the meeting.

In his presentation, Rodriguez discussed a multicenter, prospective study in which Mary I. O’Connor, MD, and colleagues used timed up and go, timed walk, and timed up and down stairs tests for an aggregated locomotor function score (ALF) for patients who underwent TKA with either a ConforMIS custom-made cruciate-retaining knee prosthesis or various brands of off-the-shelf TKA prostheses.

“Interestingly, there were about 370 patients in each group, so large cohorts, varied demographics. Their postoperative knee scores and their satisfaction scores were not different,” Rodriguez said. “These were similar populations and yet their function was objectively different in every single realm that was measured such that, when it was aggregated into the ALF score, it was highly significantly faster function in the custom group.”

Lateral rollback closer to normal

In a study of in vivo TKA kinematics that Rodriguez discussed in his presentation, Zeller and colleagues found custom knee prostheses were associated with greater weight-bearing motion than off-the-shelf implants.

“The results of the lateral rollback were also much closer to normal in the custom knees” in that study, Rodriguez said.

Despite the positive results with custom, individually made prostheses seen to date, more long-term data are needed before custom made technology is more widely used in patients undergoing TKA, Rodriguez said in the interview.

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“Up til now, the research we have is the first real-time fluoroscopy demonstrating how a custom knee moves relative to most off-the-shelf knees and that shows an improvement,” Rodriguez told Orthopedics Today in the interview. “[Up] til now, we have outcome data that shows that within the first 6 months there is more rapid recovery and more complete recovery in terms of how fast and how smooth the patients move, but it is short term,” he said. – by Casey Tingle

Disclosure: Rodriguez reports he does consulting and design work for Medacta, Smith & Nephew, Exactech and ConforMIS.

    Perspective
    Stephen M. Howell

    Stephen M. Howell

    While the concept of a custom, individually made implant is intriguing, the improvement in patient-reported outcomes, restoration of near-normal kinematics and normal gait depends more on accurate positioning of the implants coincident to the native joint surfaces of the pre-arthritic knee using the concept of kinematic alignment than on the subtle differences in implant design.

    Mechanical alignment, which a custom, individually made (CIM) implant uses, often positions the implant surface outside the native joint surface, tightening ligaments and binding the knee, and inside the native joint surface, slackening ligaments and destabilizing the knee. A TKA with a tight and/or slack PCL and collateral and retinacular ligaments has abnormal kinematics.

    The authors non-randomized fluoroscopy study included only subjects with Knee Society Scores (KSS) above 90. Their non-randomized locomotive study concluded that KSS were not different between CIM and off-the-shelf implant brands. Hence, the differences in contact kinematics during deep knee bend and chair rise movements, and the differences in aggregated locomotive scores between implant designs, were clinically unimportant to the patient.

    Therefore, surgeons interested in improving patient-reported outcomes with use of custom implants should consider using calipered kinematic alignment, which accurately positions the femoral and tibial components within 0° ± 30° of the native joint lines in 97% of subjects.

    References:

    Calliess T, et al. Knee Surg Sports Traumatol Arthrosc. 2017;doi:10.1007/s00167-016-4136-8.

    Dossett HG, et al. Bone Joint J. 2014;doi:10.1302/0301-620X.96B7.32812.

    Gu Y, et al. J Bone Joint Surg Am. 2014;doi:10.2106/JBJS.M.00306.

    Gu Y, et al. J Orthop Res. 2016;doi:10.1002/jor.23492.

    Matsumoto T, et al. Bone Joint J. 2017;doi:10.1302/0301-620X.99B5.BJJ-2016-0688.R2.

    Nedopil AJ, et al. J Arthroplasty. 2017;doi:10.1016/j.arth.2017.09.039.

    Niki Y, et al. Knee Surg Sports Traumatol Arthrosc. 2017;doi:10.1007/s00167-017-4459-0.

    Niki Y, et al. Knee Surg Sports Traumatol Arthrosc. 2017;doi:10.1007/s00167-017-4788-z.

    Singh AK, et al. Arch Orthop Trauma Surg. 2018;doi:10.1007/s00402-017-2824-6.

    • Stephen M. Howell, MD
    • Professor of biomedical engineering University of California, Davis Davis, California Practicing knee surgeon Sacramento, California

    Disclosures: Howell reports he is a consultant for Medacta, Zimmer Biomet and ThinkSurgical.