2015 ISAKOS Biennial Congress ePoster #1407

Relationship Between Tibial Baseplate Design and Rotational Alignment Landmarks in Primary Total Knee Arthroplasty

Pier Indelli, MD, PhD, San Jose, CA UNITED STATES
Angelo Graceffa, MD, Enna, En ITALY
Massimiliano Marcucci, Firenze ITALY
Gennaro Pipino, Bologna, Bo ITALY

Clinica Ortopedica Universita' di Firenze, Firenze, ITALY

FDA Status Cleared

Summary: The use of an asymmetric tibial baseplate might lead to an excessive external rotation of the tibial component in primary TKA.

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Abstract:

Components rotational alignment in primary total knee arthroplasty (TKA) is fundamental to avoid mid-term postoperative complications. Recently, the industry introduced different tibial baseplate designs in primary TKA: anatomical (asymmetric) designs are substituting more traditional symmetric designs. Different tibial component designs might influence the surgical technique when defining the correct rotational alignment of the tibial baseplate. The objective owas to evaluate the influence of the tibial baseplate design when using the anterior tibial cortex as the primary anatomical rotational landmark (“curve on curve” technique) in primary TKA.
Forty patients, undergoing primary TKA, were divided in two groups. Group A included 8 males and 12 females (average age 72 years): all patients received a posterior stabilized (PS) TKA (Nex-Gen, Zimmer, USA). This implant is characterized by a symmetric tibial baseplate. Group B included 10 males and 10 females (average age 69 years): all patients received a posterior-stabilized (PS) TKA (Persona, Zimmer, USA), characterized by an anatomical (asymmetric) tibial baseplate. The “Persona” tibial baseplate is characterized by an anteromedial and posteromedial asymmetry. Knee preoperative deformity was similar in both groups. Identical surgical technique, including the use of the surgical trans-epicondylar femoral axis (sTEA) and the anterior tibial cortex (“curve-on-curve”) as rotational alignment landmarks, was used. All patients underwent CT evaluation according to the Perth-CT-Protocol (Chauhan et al, JBJS-2004). Three observers independently measured the rotational alignment of the tibial component in relation to the sTEA in all knees. The reliability of each measurement was then calculated by using the intraclass correlation coefficient for interobserver agreement.
Symmetric baseplate
The rotational alignment measurement of the symmetric tibial baseplate respect to the sTEA showed 0±3° of rotation of the tibial component in 91% of the knees; all twenty tibial components (100%) showed a 0±5° of rotation. Maximum external rotation of the tibial baseplate was 5°, while maximum internal rotation was 1°. The tibial component appeared internally rotated respect to the sTEA in 8 cases, externally rotated in 12 cases.
Anatomical baseplate
The rotational alignment measurement of the asymmetric (anatomical) tibial baseplate respect to the sTEA showed 0±3° of rotation of the tibial component in 70% of the knees (14 patients); 19 tibial components (95%) showed a 0±5° of rotation. Maximum external rotation of the tibial baseplate was 9°, while maximum internal rotation was 4 °. The tibial component appeared internally rotated respect to the sTEA in 4 cases, externally rotated in 16 cases.
This study confirms the reliability of the “curve on curve” technique as an anatomical landmark during rotational alignment of the tibial component during TKA procedure. An interesting finding was to discover that the use of an asymmetric tibial baseplate might lead to an excessive external rotation of the tibial baseplate if the “curve-on-curve” technique is used. The risk of excessive external rotation of the asymmetric tibial baseplate is superior when a smaller size is chosen in the case of a borderline measurement between two different components. The clinical value of an excessive external rotation of the tibial component has still to be proven.