Previous studies analyzing femoral components of TKAs have demonstrated the limited ability of these components to accommodate size variations seen in the patient population, particularly width and femoral offset.
The purpose of this study was to use a large data set of knee CT scans (1) to determine the variations in the distal and posterior femoral geometries and to determine whether there is a correlation between distal condylar offset and posterior femoral offset as a potential parameter for symmetry/asymmetry; and (2) to evaluate what proportion of knees would have a substantial mismatch between the implant’s size or shape and the patient’s anatomy if a femoral component of a modern standard TKA of symmetric (sTKA) or asymmetric (asTKA) designs were to be used.
A retrospective study was performed on 24,042 data sets that were generated during the design phase for a customized TKA implant. This data set was drawn from European and US-American patients. Measurements recorded for the femur included the overall AP and mediolateral (ML) widths, widths of the lateral condyle and the medial condyle, the distal condylar offset (DCO) between the lateral and medial condyles in the superoinferior direction, and the posterior femoral offset (PFO) as the difference between the medial and lateral posterior condylar offset (PCO) measured in the AP direction. A consecutively collected subset of 2367 data sets was further evaluated to determine the difference between the individual AP and ML dimensions of the femur with that of modern TKA designs using two commercially available implants from different vendors.
We observed a high degree of variability in AP and ML widths as well as in DCO and PFO. Also, we found no correlation between DCO and PCO of the knees studied. Instances of a patient having a small DCO and higher PCO were commonly seen. Analysis of the DFOs revealed that overall, 62% (14,906 of 24,042) of knees exhibited DCO > 1 mm and 83% (19,955 of 24,042) of femurs exhibited a > 2-mm difference between the lateral and medial PCO. Concerning AP and ML measurements, 23% (544 of 2367) and 25% (592 of 2367) would have a mismatch between the patient’s bony anatomy and the dimensions of the femoral component of ± 3 mm if they would have undergone a modern standard sTKA or asTKA design, respectively.
Analysis of a large number of CT scans of the knee showed that a high degree of variability exists in AP and ML widths as well as in DCO and PFO.
These findings suggest that it is possible that a greater degree of customization could result in surgeons performing fewer soft tissue releases and medial resections than now are being done to fit a fixed-geometry implant into a highly variable patient population. However, as an imaging study, it cannot support one approach to TKA over another; comparative studies that assess patient-reported outcomes and survivorship will be needed to help surgeons decide among sTKA, asTKA, and customized TKA.
M. Meier, J. Beckmann, Sportklinik Stuttgart, Stuttgart, Germany
S. Zingde, Conformis Inc, Billerica, MA, USA
A. Steinert, Krankenhaus Agatharied, Hausham, Germany
W. Kurtz, Tennessee Orthopaedic Alliance, Nashville, TN, USA
F. Koeck, MedArtes, Neutraubling, Germany
J. Beckmann, Sportklinik Stuttgart, Taubenheimstrasse 8, 70372 Stuttgart, Germany, email: Johannes.Beckmann@Sportklinik-Stuttgart.de
One of the authors (SZ) is an employee of Conformis Inc (Billerica, MA, USA). One of the authors certifies that he (AS) has received personal fees for consultant teaching, during the study period, in an amount of less than USD 10,000 from Conformis Inc, outside the submitted manuscript. One of the authors certifies that he (WK) has received or may receive research support and royalties, during the study period, in an amount of USD 10,000 to USD 100,000 from Conformis Inc, outside the submitted manuscript. One of the authors certifies that he (FK) has received personal fees and grants, during the study period, in an amount of less than USD 10,000 from Conformis Inc, outside the submitted manuscript. One of the authors certifies that he (JB) has received personal fees for consultant teaching, during the study period, in an amount of less than USD 10,000, from Smith & Nephew (Smith & Nephew GmbH, Hamburg, Germany) and personal fees for consultant teaching in an amount of less than USD 10,000 from Conformis Inc, all outside the submitted manuscript.
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Each author certifies that his or her institution waived approval for the reporting of this investigation and that all investigations were conducted in conformity with ethical principles of research.
This work was performed at Conformis Inc, Boston, MA, USA, and Sportklinik, Stuttgart, Germany.
Received July 03, 2018
Accepted November 26, 2018