Intraoperative evaluation of posterior clearance to gap and range of motion using navigation system revealed that posterior clearance increased 5° in extension angle, which was correlated to preoperative varus deformity and osteophyte area in radiograph and CT images, while prepared gap balance was not disturbed.
Objectives: Large osteophyte of the posterior femoral condyle (PFC) causes impingement with tibia insert in total knee arthroplasty (TKA). Although posterior clearance (PC) removing these osteophytes improves flexion range of motion, this procedure would enlarge prepared extension gap. Also, it has been unclear how much influence would cause in extension angle, because previous studies using tensor could not investigate detailed intraoperative range of motion objectively. The purpose of this study was to evaluate the influence of PC to gap and range of motion objectively and quantitatively using a navigation system, and reveal the relationship with osteophyte size.
A total of 20 patients (2 men and 18 women) 27 knees were included to this study, and their mean age was 74.3 ± 6.9 years old. CR type TKA was performed with the image-free navigated system (OrthoPilot TKA ver. 4.2, B. Braun Aesculap, Germany). Osteophyte of the PFC was removed using a curved/straight osteotome and curettes with much care not to damage posterior articular capsule. Before and after PC, flexion gap, extension gap, flexion angle, extension angle, and hip-knee-ankle (HKA) angle were recorded by the navigation system. Preoperative osteophyte area in radiograph were measured in lateral view of the knee. In the CT images, osteophyte area in sagittal plane was defined as osteophyte area in center of medial femoral condyle. Also, osteophyte area in axial plane was defined as osteophyte area in the slice largest osteophyte observed at posterior of medial femoral condyle. Change of gap and angle by PC were calculated, and Spearman’s correlation coefficients among these parameters were estimated. In order to predict how much extension angle increase by PC, regression analysis was performed with preoperative extension angle, HKA angle, and osteophyte size as independent variables.
Mean osteophyte area in radiograph was 262.4 ± 128.6 mm2, 146.6 ± 46.8 mm2 in CT sagittal plane, and 284.9 ± 94.2 mm2 in CT axial plane. Preoperative extension angle was -11.3°, flexion angle was 108.9 ± 16.1°, and HKA angle was measured by navigation system. Extension gap increased 0.7±0.9 mm in medial and 0.9±1.5 mm in lateral (p=0.360) by PC, also there was no significant difference between medial and lateral gap in 90° flexion (p=0.790). Extension angle increased 4.9 ± 1.6° (2 to 8°), flexion angle increased 6.5 ± 5.0° (0 to 19°), and HKA decreased 0.4°. Increase of extension angle by PC was correlated with preoperative HKA angle (r=0.594, p=0.001), radiographic osteophyte area (r=0.681, p<0.001), sagittal osteophyte area (r=0.626, p=0.002), and axial osteophyte area(r=0.631, p=0.002). Furthermore, prediction formula for increase in extension angle by PC was estimated as following: increase in extension angle by PC = 0.009 x radiographic osteophyte area + 2.48 (adjusted R2 = 0.508).
Although both extension gap and flexion gap increased less than 1mm, prepared gap balance was not disrupted. PC obtaining 5° in extension angle would be a good procedure to get extension angle selectively in varus knee with large osteophyte in PFC.