gms | German Medical Science

Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2018)

23.10. - 26.10.2018, Berlin

Tibio-femoral contact force distribution is not the only factor governing pivot location in TKA

Meeting Abstract

  • presenting/speaker Adam Trepczynski - Julius Wolff Institut, Charité - Universitätsmedizin Berlin, Berlin, Germany
  • Ines Kutzner - Julius Wolff Institut, Charité - Universitätsmedizin Berlin, Berlin, Germany
  • Pascal Schütz - Institute for Biomechanics, ETH Zürich, Zürich, Switzerland
  • Jörn Dymke - Julius Wolff Institut, Charité - Universitätsmedizin Berlin, Berlin, Germany
  • Philipp von Roth - Centrum für Muskuloskeletale Chirurgie, Charité - Universitätsmedizin Berlin, Berlin, Germany
  • Georg Bergmann - Julius Wolff Institut, Charité - Universitätsmedizin Berlin, Berlin, Germany
  • William R. Taylor - Institute for Biomechanics, ETH Zürich, Zürich, Switzerland
  • Georg N. Duda - Julius Wolff Institut, Charité - Universitätsmedizin Berlin, Berlin, Germany

Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2018). Berlin, 23.-26.10.2018. Düsseldorf: German Medical Science GMS Publishing House; 2018. DocST35-962

doi: 10.3205/18dkou206, urn:nbn:de:0183-18dkou2067

Veröffentlicht: 6. November 2018

© 2018 Trepczynski et al.
Dieser Artikel ist ein Open-Access-Artikel und steht unter den Lizenzbedingungen der Creative Commons Attribution 4.0 License (Namensnennung). Lizenz-Angaben siehe http://creativecommons.org/licenses/by/4.0/.


Gliederung

Text

Objectives: Some TKA designs show a “paradoxical” anterior translation of the femur and lateral pivoting with increasing flexion, which is not observed in native knees. Altered kinematics can lead to increased patello-femoral contact forces and problems of the extensor mechanism. TKA designs aim at restoring the natural knee kinematics by optimizing implant geometry. However, it remains unclear how the loading of the knee is related to the anterior-posterior (AP) motion and the location of the pivot point. We hypothesised that the pivot is located within the compartment showing higher axial forces.

Methods: Six TKA patients (aged 68±5y), performed 5-6 repetitions of a squat. Tibio-femoral (TF) loading was measured in vivo using an instrumented tibial component, while TF kinematics were captured using a mobile video-fluoroscope [1]. The medial force ratio (MFR) was based on the medial and lateral axial forces: MFR = Fmed/(Fmed+Flat). For each patient, splines were fitted into the MFR and AP-position of the lowest femoral points as functions of flexion, while the slope of the latter was interpreted as AP movement per flexion (AP/flex). Pivoting was quantified by the medial pivot delta (MPD) defined as: MPD = |AP/flexlat|-|AP/flexmed|. Differences in MFR and MFD between the congruent, non-congruent ranges were investigated using the Mann-Whitney-U and Wilcoxon tests. The correlation between MFR and MPD was investigated per patient by linear regression.

Results and conclusion: The femoral AP movement had two distinct phases, with an abrupt change at the end of the congruent contact range, around 23° flexion. Near extension a medial pivot and lateral roll-back were observed. Beyond the congruent range, both condyles slid anteriorly (greater translation medially). On average, both the loading and pivot position were more medial near extension, and both transferred to the lateral side beyond 23° (Figure 1A [Fig. 1]). However, when considering 20°-flexion intervals (Figure 1B [Fig. 1]), not all patients showed correlations between MFR and MPD, with R2-values ranging from 0.01 (patient K1L) to 0.82 (patient K7L), with a median of 0.21.

Given the inconsistent relationship between MFR and the MPD across patients, our hypothesis was only partially confirmed. The results demonstrate that the TF kinematics is not related to the load distribution alone, and a predominantly medial knee loading does not imply a medial pivot. While the sample population was small, it was still the biggest cohort available for direct force measurements. The employed fluoroscopic 3D analysis is ideal for verifying the goals of TKA designs, in terms of kinematics.


References

1.
Taylor WR, Schütz P, Bergmann G, List R, Postolka B, Hitz M, Dymke J, Damm P, Duda G, Gerber H, Schwachmeyer V, Hosseini Nasab SH, Trepczynski A, Kutzner I. A comprehensive assessment of the musculoskeletal system: The CAMS-Knee data set. J Biomech. 2017 Dec 8;65:32-39. DOI: 10.1016/j.jbiomech.2017.09.022 Externer Link