2015 ISAKOS Biennial Congress ePoster #1404

The Mechanical Axis After Total Knee Arthroplasty: Comparison of Patient-Specific Instrumentation and Accelerometer-Based Portable Navigation

Tatsuya Tamaki, MD, Funabashi JAPAN
Hideaki Shiratsuchi, Funabashi, Chiba JAPAN

Funabashi Orthopedic Hospital, Funabashi, JAPAN

FDA Status Not Applicable

Summary: Varus deformity of the knee tends to be over-corrected with accelerometer-based portable navigation.




Restoration of the neutral mechanical axis is considered to result in a better outcome of total knee arthroplasty (TKA). Patient-specific instrumentation (PSI) and accelerometer-based portable navigation (ABPN) are novel techniques for TKA. In this study, we analysed the mechanical axis achieved after TKA involving either PSI or ABPN.
Patients and Methods: We analysed 59 varus knees of 41 patients (9 males, 32 females) undergoing TKA performed by a single surgeon. The mean age was 71.6± 6.6 years (mean ? SD). The same designed cruciate-retaining total-knee prostheses were implanted in all knees. PSI was used on 30 knees of 22 patients (PSI group), and ABPN was used on 29 knees of 19 patients (ABPN group). The hip–knee–ankle (HKA) angle (the mechanical axis of the leg) was measured using weight-bearing anterior–posterior radiographs of full-leg length before and 6 weeks after the surgery.


The operation duration in the PSI and ABPN groups was 46.6 ± 8.3 and 50.2 ± 10.5 min, respectively. There were no major complications such as infection, prosthetic fracture, or venous thromboembolism. The mean HKA angle was 179.8°±2.4° in the PSI group and 179.0°±2.8° in the ABPN group. The neutral mechanical axis (HKA angle within 180° ± 3°) was achieved in 26 knees (87%) of the patients in the PSI group and in 23 knees (79%) of patients in the ABPN group. Under-correction of the varus deformity (HKA angle >183°) was observed in 1 knee of the patient in the PSI group and was not observed in the knees of the patients in the ABPN group; over-correction (HKA angle <177°) was not observed in 3 knees (10%) of the patients in the PSI group and in 6 knees (21%) of patients in the ABPN group.


Using either PSI or ABPN, surgeons can attain satisfactory coronal knee alignment. Varus deformity, however, tends to be over-corrected with ABPN.