Undercoverage of lateral trochlear resection is correlated with the tibiofemoral alignment parameters in kinematically aligned TKA: a retrospective clinical study

Abstract

Background: A mismatch between the femoral component and trochlear resection surface is observed in kinematically aligned total knee arthroplasty (KA-TKA) when conventional prostheses are employed. This mismatch is mainly manifested in the undercoverage of the lateral trochlear resection surface. The aim of the present study was to assess the relationship between the mismatch and the alignment parameters of the tibiofemoral joint.

Methods: Forty-five patients (52 knees) who underwent KA-TKA in our hospital were included. Patient-specific instrumentation was used in 16 patients (16 knees), and conventional instruments with calipers and other special tools were employed in the other 29 patients (36 knees). The widths of the exposed resection bone surface at the middle (MIDexposure) and distal (DISexposure) levels on the lateral trochlea were measured as dependent variables, whereas the hip-knee-ankle angle (HKAA), mechanical lateral distal femoral angle (mLDFA), joint line convergence angle (JLCA), medial proximal tibial angle (MPTA) and transepicondylar axis angle (TEAA) were measured as independent variables. Correlation analysis and subsequent linear regression were conducted among the dependent variables and various alignment parameters of the tibiofemoral joint.

Results: The incidence of undercoverage of the lateral trochlear resection surface was 86.5 % with MIDexposure and DISexposure values of 2.3 (0-6 mm) and 2.0 (0-5 mm), respectively. The widths of the two levels of exposed bone resection were significantly correlated with mLDFA and HKAA but were not related to TEAA.

Conclusions: The undercoverage of the trochlear resection surface in KA-TKA is mainly correlated with the degree of valgus of the distal femoral joint line. The current study suggests that this correlation should be considered in the development of KA-specific prostheses.

Keywords: Anatomy; Kinematic alignment; Osteoarthritis; Total knee arthroplasty; Trochlea.

Fig. 1

Computer-aided design (a) and intraoperative application (b) of PSI

Fig. 2

Stacked neodymium magnets (white arrows) are used to compensate for the thickness of worn articular cartilage (2 mm) in calipered KA

Fig. 3

Schematic diagrams for the measurement of tibiofemoral joint anatomical parameters: a Hip-knee-ankle angle (HKAA), b Mechanical lateral distal femoral angle (mLDFA), c Joint line convergence angle (JCLA), and d medial proximal tibial angle (MPTA)

Fig. 4

Transepicondylar axis angles (TEAAs) were measured by preoperative superimposed CT (a) and a protractor in the operating room (b). a Determination of the recess of the medial epicondyle, the prominence of the lateral epicondyle, and the highest point of the medial and lateral posterior condyles by the MIP approach of CT. The TEAA value was automatically obtained by the in-house program. b Intraoperative measurement required electrocautery to mark the position of the medial and lateral epicondyles on the distal femoral resection surface. The arms of the protractor were parallel to the posterior pedals of instruments and the electrocautery marks

Fig. 5

Intraoperative caliper measurement of the exposed bone resection of the lateral trochlea. The white and blue arrows represent the width of the exposed resection at the distal (DISexposure) and middle (MIDexposure) levels of the trochlea, respectively

Fig. 6

The influence of the distal femoral joint line (mLDFA) (a) and the alignment of the lower extremities (HKAA) (b) on the undercoverage of lateral trochlear resection, where DISexposure and MIDexposure represent the width of the exposed bone resection at the distal and middle levels of the trochlea, respectively