Computerized tomography based "patient specific blocks" improve postoperative mechanical alignment in primary total knee arthroplasty

Abstract

Aim: To compare the postoperative mechanical alignment achieved after total knee arthroplasty (TKA) using computer tomography (CT) based patient specific blocks (PSB) to conventional instruments (CI).

Methods: Total 80 knees were included in the study, with 40 knees in both the groups operated using PSB and CI. All the knees were performed by a single surgeon using the same cruciate sacrificing implants. In our study we used CT based PSB to compare with CI. Postoperative mechanical femoro-tibial angle (MFT angle) was measured on long leg x-rays using picture archiving and communication system (PACS). We compared mechanical alignment achieved using PSB and CI in TKA using statistical analysis.

Results: The PSB group (group 1) included 17 females and seven males while in CI group (group 2) there were 15 females and eight males. The mean age of patients in group 1 was 60.5 years and in group 2 it was 60.2 years. The mean postoperative MFT angle measured on long-leg radiographs in group 1 was 178.23° (SD = 2.67°, range: 171.9° to 182.5°) while in group 2, the mean MFT angle was 175.73° (SD = 3.62°, range: 166.0° to 179.8°). There was significant improvement in postoperative mechanical alignment (P value = 0.001), in PSB group compared to CI. Number of outliers were also found to be less in group operated with PSB (7 Knee) compared to those operated with CI (17 Knee).

Conclusion: PSB improve mechanical alignment after total knee arthroplasty, compared to CI. This may lead to lower rates of revision in the PSB based TKA as compared to the conventional instrumentation.

Keywords: Arthroplasty; Conventional jigs; Knee; Patient specific jigs; Replacement.

Figure 1

Patient specific blocks used in the present study (A: Femoral jig, B: Tibial jig).

Figure 2

Tibial jig conforming to the proximal tibial anatomy and fiiting well to the bone. This jig is used for insertion of the proximal tibial pins followed by use of the conventional proximal tibial jig.

Figure 3

Femoral jig matching the contour of the anterior femoral cortex.

Figure 4

Postoperative weight bearing long leg radiograph measuring the hip-knee-ankle angle axis (mechanical axis).

Figure 5

Scatter diagram depicting the distribution of the post-operative mechanical femoro-tibial angle (mechanical femoro-tibial angle) in the patient specific block group (group 1). MFT: Mechanical femoro-tibial angle.

Figure 6

Scatter diagram depicting the distribution of the post-operative mechanical femoro-tibial angle (mechanical femoro-tibial angle) in the conventional instrument group (group 2). MFT: Mechanical femoro-tibial angle.