Criteria for preserving posterior cruciate ligament depending on intra-operative gap measurement in total knee replacement

Abstract

Objectives: Because posterior cruciate ligament (PCL) resection makes flexion gaps wider in total knee replacement (TKR), preserving or sacrificing a PCL affects the gap equivalence; however, there are no criteria for the PCL resection that consider gap situations of each knee. This study aims to investigate gap characteristics of knees and to consider the criteria for PCL resection.

Methods: The extension and flexion gaps were measured, first with the PCL preserved and subsequently with the PCL removed (in cases in which posterior substitute components were selected). The PCL preservation or sacrifice was solely determined by the gap measurement results, without considering other functions of the PCL such as 'roll back.'

Results: Wide variations were observed in the extension and flexion gaps. The flexion gaps were significantly larger than the extension gaps. Cases with 18 mm or more flexion gap and with larger flexion than extension gap were implanted with cruciate retaining component. A posterior substitute component was implanted with the other cases.

Conclusions: In order to make adequate gaps, it is important to decide whether to preserve the PCL based on the intra-operative gap measurements made with the PCL intact. Cite this article: Bone Joint Res 2014;3:95-100.

Keywords: Arthroplasty; Gap; Knee; Posterior cruciate ligament.

Fig. 1

Diagram showing the pre-cut of the femoral posterior condyle.

Fig. 2

Intra-operative photograph showing measurement of the flexion gap with the patella reduced.

Fig. 3

Graph showing measurement results of the gaps after pre-cut of the femoral posterior condyle with the posterior cruciate ligament (PCL) preserved. The mean extension gap was 16.9 mm (sd 2.9) and the corrected flexion gap by the amount of the pre-cut was 20.5 mm (sd 3.2). The flexion gap was significantly larger than the extension gap (p < 0.001). The range of both gaps were too wide to know pre-operatively in each case. Cases with 18 mm or more (minimum space to set the component) flexion gap and larger flexion gap than extension gap (Group 1) were implanted with a CR component, except for cases with PCL insufficiency. A PS component was implanted with the other cases (Group 2, 3 and 4). ○, implanted with CR component; △▲, implanted with PS component; ▲, PS implanted due to PCL insufficiency.

Figs. 4a - 4b

Figure 4a – Graph showing gap difference between the extension gap and the corrected flexion gap. The mean of the difference was 3.6 mm (sd 2.7) and the variation of the difference was wide. Figure 4b – Graph showing gap difference by group. Group A: pre-operative flexion contracture < 20°. Group B: flexion contracture ≥ 20°. The mean differences between extension and corrected flexion gaps were 3.4 mm (sd 2.5) in group A and 3.9 mm (sd 3.0) in group B, (p = 0.42). Additionally, if groups A and B are divided at flexion contracture of 15°, 25° and 30°, the p-values are 0.39, 0.38 and 0.20 respectively.

Figs. 4a - 4b

Figure 4a – Graph showing gap difference between the extension gap and the corrected flexion gap. The mean of the difference was 3.6 mm (sd 2.7) and the variation of the difference was wide. Figure 4b – Graph showing gap difference by group. Group A: pre-operative flexion contracture < 20°. Group B: flexion contracture ≥ 20°. The mean differences between extension and corrected flexion gaps were 3.4 mm (sd 2.5) in group A and 3.9 mm (sd 3.0) in group B, (p = 0.42). Additionally, if groups A and B are divided at flexion contracture of 15°, 25° and 30°, the p-values are 0.39, 0.38 and 0.20 respectively.

Fig. 5

Graph showing gaps and flexion contracture. The mean extension and corrected flexion gaps were 17.2 mm (sd 3.0) and 20.6 mm (sd 3.2) in group A and 16.3 mm (sd 2.8) and 20.2 mm (sd 3.3) in group B, respectively. There were no significant differences between the two groups.

Fig. 6

Graph showing gap increase after posterior cruciate ligament (PCL) resection. The flexion gap increase was significantly larger than extension, and the variation of the flexion gap increase was wide. The gap increases following PCL resection were 0.6 mm (sd 0.9) in extension and 2.7 mm (sd 2.0) in flexion, and the difference between the increases of both gaps was significant (p < 0.001).

Fig. 7

Graph showing the difference between implanted and measured sizes of the femoral component. Most cases were implanted with ± 1 size compared with the measured size of the femur (CR, cruciate retaining; PS posterior substitute).