An Evaluation of Anatomic Referencing for Femoral Component Sizing Using Computed Tomography-Based Computer Modeling

Abstract

One of the critical steps in total knee arthroplasty is femoral component positioning and sizing. Historically, there was wider variability between femoral component sizes, necessitating the concepts of anterior referencing (AR) and posterior referencing (PR). With the introduction of smaller increments between sizes, the concept of anatomic referencing has been introduced to replace AR and PR. The intent of this study was to validate the concept of anatomic referencing and show that with 2 mm increments in femoral sizes, the femoral component can be placed flush to the anterior cortex while maintaining posterior condylar offset (PCO). Digital surface models were created using 515 femurs from an established computed tomography database. Virtual bone resections, component sizing and placement were performed assuming neutral mechanical axis and a cartilage thickness of 2 mm. The appropriately sized femoral component, which had 2 mm incremental sizes, was placed flush with the anterior cortex with restoration of the PCO. The anterior–posterior distance from the posterior surface of the component to the medial and lateral surfaces of the posterior condylar cartilage were measured. The medial condyle was the limiting condyle in the majority of cases (73%). The average medial gap after appropriate femoral component matching was 0.6 mm (0.39–1.41 mm) across all sizes. The overall average condylar gap was 1.02 mm. The most common femoral component was a size 7 (57.2 mm) and the average femoral AP width was 55.9 mm. Anatomic referencing with an implant system that has 2-mm increments in femoral component sizing provides an alternative to AR and PR without compromise. Anatomic referencing allows for perfect alignment of the anterior flange of the femoral component to the anterior cortex of the femur while restoring the native PCO to within 1 mm. This avoids having to choose between AR or PR when in between femoral sizes.

Keywords

implant - anatomic referencing - total knee arthroplasty

Publication History

Received: 12 October 2023

Accepted: 07 January 2024

Accepted Manuscript online:
08 January 2024

Article published online:
27 February 2024

• References

• 1 Chang MJ, Kang SB, Chang CB. et al. Posterior condylar offset changes and its effect on clinical outcomes after posterior-substituting, fixed-bearing total knee arthroplasty: anterior versus posterior referencing. Knee Surg Relat Res 2020; 32 (01) 10
• 2 Dai Y, Scuderi GR, Penninger C, Bischoff JE, Rosenberg A. Increased shape and size offerings of femoral components improve fit during total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2014; 22 (12) 2931-2940
• 3 Lombardi Jr AV, Berend KR, Adams JB. A single total knee arthroplasty system with broad size and constraint options improves outcomes for both men and women. Orthop Proc 2011; 93: 439-439
• 4 Stambough JB, Edwards PK, Mannen EM, Barnes CL, Mears SC. Flexion instability after total knee arthroplasty. J Am Acad Orthop Surg 2019; 27 (17) 642-651
• 5 Sharkey PF, Lichstein PM, Shen C, Tokarski AT, Parvizi J. Why are total knee arthroplasties failing today–has anything changed after 10 years?. J Arthroplasty 2014; 29 (09) 1774-1778
• 6 Dalury DF, Pomeroy DL, Gorab RS, Adams MJ. Why are total knee arthroplasties being revised?. J Arthroplasty 2013; 28 (8, Suppl): 120-121
• 7 Grayson CW, Warth LC, Ziemba-Davis MM, Michael Meneghini R. Functional improvement and expectations are diminished in total knee arthroplasty patients revised for flexion instability compared to aseptic loosening and infection. J Arthroplasty 2016; 31 (10) 2241-2246
• 8 Abdel MP, Pulido L, Severson EP, Hanssen AD. Stepwise surgical correction of instability in flexion after total knee replacement. Bone Joint J 2014; 96-B (12) 1644-1648
• 9 Kannan A, O'Connell RS, Kalore N, Curtin BM, Hull JR, Jiranek WA. Revision TKA for flexion instability improves patient reported outcomes. J Arthroplasty 2015; 30 (05) 818-821
• 10 Lee OS, Lee YS. Effect of the referencing system on the posterior condylar offset and anterior flange-bone contact in posterior cruciate-substituting total knee arthroplasty. J Arthroplasty 2018; 33 (04) 1069-1075
• 11 Stamiris D, Gkekas NK, Asteriadis K. et al. Anterior femoral notching ≥ 3 mm is associated with increased risk for supracondylar periprosthetic femoral fracture after total knee arthroplasty: a systematic review and meta-analysis. Eur J Orthop Surg Traumatol 2022; 32 (03) 383-393
• 12 Shekhar A, Chandra Krishna C, Patil S, Tapasvi S. Does increased femoral component size options reduce anterior femoral notching in total knee replacement?. J Clin Orthop Trauma 2020; 11 (Suppl. 02) S223-S227
• 13 Karvonen RL, Negendank WG, Teitge RA, Reed AH, Miller PR, Fernandez-Madrid F. Factors affecting articular cartilage thickness in osteoarthritis and aging. J Rheumatol 1994; 21 (07) 1310-1318
• 14 Yue B, Varadarajan KM, Ai S, Tang T, Rubash HE, Li G. Differences of knee anthropometry between Chinese and white men and women. J Arthroplasty 2011; 26 (01) 124-130