Healio
Healio
October 01, 2006
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Computer-assisted Dynamic Total Knee Arthroplasty Using Whiteside’s Line for Alignment

Abstract

Computer-assisted navigation enables surgeons to measure and assess knee behavior during surgery, allowing real-time monitoring of the knee ranging from extension to flexion. Documenting passive motion before and after total knee arthroplasty (TKA) enabled the authors to analyze knee kinematics. Passive knee motion cannot predict full weight bearing knee behavior, the “crucial moment of truth” for TKA. This study supports individually adapting the femoral component rotation using the Whiteside line. Clinical follow-up alone will assess the possible benefits. In a study of 71 patients who underwent computer-assisted TKA, the authors assessed the actual rotational femoral alignment and dynamic long leg track hip-knee-ankle angle from 0°, 30°, 60°, and 90° of knee flexion before and after TKA.

Despite improvements in total knee arthroplasty (TKA), mechanical instrumentation and component malposition are still important issues to the orthopedic surgeon.1 Computer-assisted surgery is shown to achieve TKA more accurately.2-8 A malrotated prosthesis leads to poor patellar tracking, asymmetric patellofemoral joint contact, incorrect varus/valgus positioning, unbalanced flexion, and anterior femoral notching.9-11 The axis on which to judge correct rotational alignment remains controversial. However, several options exist. Since Hollister et al12 determined that the transepicondylar axis approximates the optimal flexion-extension axis of the knee, the transepicondylar axis has become a popular reference axis for femoral component rotation and patellofemoral tracking.13 Other femoral component rotational references are described in the literature, including Whiteside’s line.14,15 Siston et al16 concluded that all techniques result in highly variable rotational alignment, with no technique being superior. Navigation systems that rely on direct digitization of femoral epicondyles do not provide a more reliable means of establishing femoral rotational alignment than traditional techniques. The authors used Whiteside’s line to place the femoral implant and assessed whether this rotational reference remains safe.

Computer-assisted surgical technology enables surgeons to measure and assess knee behavior during surgery, allowing real-time monitoring of a knee’s behavior from extension to flexion. The measurements reflect passive tibial rotation of the femoral condyles and also indicate patellar tracking.17-19 In addition, the systems demonstrate soft tissue balance throughout the procedure.

In a study of 71 patients who underwent computer-assisted TKA, the authors assessed the actual rotational femoral alignment and dynamic long-leg track hip-knee-ankle angle from 0°, 30°, 60° and 90° of knee flexion before and after TKA.

Materials and Methods

Seventy-one consecutive patients underwent TKA using OrthoPilot and Columbus (B. Braun Aesculap, Tuttlingen, Germany) for endstage osteoarthritis in 2005. The study included 29 right knees and 42 left knees (27 men and 44 women). Average patient age was 70.4 years. Mean body mass index was 30.8 (±4.72; range: 23.2-48.6). Mean American Society of Anesthesiologists score was 2.6 and mean Oxford Score was 43 (±7.7; range: 28-58). Fifty-seven varus, 1 aligned, and 13 valgus knees were studied. Cruciate retaining and sacrificing prostheses were used.

A standard TKA procedure was performed with a medial parapatellar approach in 69 of the 71 patients. Two trackers were secured in the femur and the tibia. During the calibration phase, kinematic and anatomic data were collected to allow computer modeling. The surgeon verified frontal and sagittal long-leg mechanical axes on screen. A distal femoral jig allowed measurement of the femoral mechanical axis.

figure 1

Figure 1: Femoral jig rotation recorded after Whiteside’s line alignment and marked with diathermy.

Before performing bone cuts, long-leg frontal axes, hip, knee, and ankle angles were collected in extension, 30°, 60°, and 90° of knee flexion. The tibial cut was performed perpendicular to the tibial mechanical axis, using navigated instrumentation. The distal femoral cut was performed before femoral rotational alignment. Femoral jig rotation was recorded after alignment to Whiteside’s line and marked with diathermy (Figure 1). Femoral component rotation was the angle between Whiteside’s line and the posterior condylar axis. The chamfer cuts and anteroposterior (AP) cuts were completed using a monobloc guide. After component cementation, the frontal long-leg axes in extension, 30°, 60°, and 90° of knee flexion were recollected. No patellae were resurfaced.

The data collected included femoral implant rotation and the frontal hip-knee-ankle before and after TKA in extension, 30°, 60°, and 90° of knee flexion.

Results

Lateral release was not required for any knees, according to clinical results. The mean hospital stay for patients was 7.4±1.9 days. The six-week postoperative Oxford Score was 27.8±7.8 (range: 16-45). The postoperative flexion was 118°±8.6, hyperextension was 3°±2.5 (–3/9) and preoperative flexion scaled with computer was 120°±–9.1. Postoperative complications included two renal impairments, one deep vein thrombosis, two superficial hematomas, and one delayed wound healing.

Computer-assisted results showed frontal long-leg angles in 0°, 30°, 60°, and 90° knee flexion before bone cuts. The knees in varus and in valgus followed similar curves. Average angle collected decreased, approaching 0° in 90 (of flexion). After TKA, varus and valgus knees had the same pattern close to 0° (Figure 2). The frontal long-leg angles in 0°, 30°, 60°, and 90° of knee flexion were similar to the femoral mechanical axis. When femurs were in valgus >0°, angles tended towards varus. Conversely, femurs in varus <0°-oriented knees tended to become valgus, implying that femoral valgus and varus influenced tibial rotation in flexion. The mean angle for femoral implant rotation was 2.06° (external rotation ±1.32° (–1° to 5°). Dividing the hip-knee-ankle curves according to their pattern gave three main curve groups. Group A (13%) included femoral components between –1° and 0° tend to valgus with an average of 2°, group B (54%) included femoral components between 1° and 2° tend to perfect alignment with an average of 1°, and group C (33%) included femoral components between 3° and 5° (average: 2°). Average curves showed TKA flexed into valgus in group A, into varus in group C, and remained uniformly balanced in group B.

figure 2

figure 2

figure 2

figure 2

Figure 2: Monitor screen shots of the knee in 0°, 30°, 60°, and 90° (before and after TKA).

Discussion

Using computer-aided surgery, the authors measured passive, dynamic TKA alignment. Rotational alignment of the femoral component followed Whiteside’s line, joining the deepest part of the patellar groove anteriorly and the center of the intercondylar notch posteriorly. The average femoral component was 2.06°, externally rotated (–1° to 5°). Apart from two lateral approaches, no patients including 13 with preoperative valgus, required patellar release. Whiteside and Arima20 compared 46 knees using posterior femoral condylar referencing with 107 TKAs using Whiteside’s line. Significantly more patellar instability was observed in the former group than in the latter. Arima20 measured the AP axis at 4° with respect to the dorsal condyles in knees of normal cadavers. Logically, the angle may be different from angles in osteoarthritic knees with both damaged posterior condyles and patellar grooves.21 The authors observed more varus than valgus knees where medial posterior condylar abrasion consequently decreases the angle. Analyses of the curves after TKA are categorized into three groups. Group A, including curves of –1° to 0°, shows that theoretic insufficient external rotation allows the TKA to flex into valgus. Group C, which included curves of 3° to 5°, shows theoretic excess of external rotation induces varus knees. Group B, with curves of 1° to 2°, displays a straight knee flexion of about 0°, suggesting ideal balancing in flexion. Anouchi et al22 showed similar behavior on fresh anatomic knees when femoral components were rotated internally. The 5° internally-rotated components flex into valgus, whereas the 5° externally-rotated components had varus-valgus stability. With a 5° externally-rotated femoral component, knees flex into varus but remain stable between 1° and 3°; similar to Miller et al23 who demonstrated that external femoral component rotation causes significant increases in lateral tilt, external rotation, and tibial varus angle.

Flexion and extension gaps remain an issue in TKA and in revision arthroplasty. Berger et al1 compared 30 patients with patellofemoral complications and 20 control subjects, which showed combined internal rotation (femur and tibia) was significantly greater in the first group and concluded that the transepicondylar axis can be used intraoperatively to align the femoral component. Olcott and Scott24 compared Whiteside’s line, transepicondylar axis, and a line in 3° of external rotation relative to the femoral posterior condyles and a rectangular gap in flexion. He found the transepicondylar axis most consistently recreated a balanced flexion space, whereas 3° external rotation relative to the posterior condyles was least consistent, especially in valgus knees. Poilvache et al13 reported the transepicondylar axis as the most reliable femoral component rotation landmark. Keblish,25 critically analyzing the different methods, reported that the transepicondylar axis showed potential errors in landmark identification. Whiteside’s line showed potential errors in vertical line definition, while posterior condylar referencing was arbitrary, especially with distorted condyles causing internal rotation of femoral components giving variation of flexion-extension gaps. Recently, Jerosh et al,26 using computer assisted surgery, demonstrated intraoperative transepicondylar axis localization and showed that interobserver discrepancy impacts rotational alignment. Jenny and Boeri27 also found a low reproducibility of the transepicondylar axis. Computer-assisted surgery assessment suggests that transepicondylar axis alone or in combination does not seem as reliable as some authors originally conceived.1,13,27

Computer-assisted surgery provides new tools to accurately and reproducibly measure alignment, which was previously not possible. The computer-aided surgery system allows two software possibilities: one with soft tissue management capability and another without. Soft tissue management allows tensioned gap measurements, theoretically optimizing femoral and tibial component placement.28 Alternatively, the preferred method does not measure gaps but aligns components to the mechanical axis.29,30 The authors did not validate measurements with postoperative computed tomography (CT) imaging, because Stockl et al31 demonstrated that optical navigation systems yielded significantly better rotational alignment than manual techniques and found reliable correlation between CT images and intraoperative computed-assisted surgical measurements. The rotational angle measurement was reliable. Siston et al16 concluded that all techniques resulted in highly variable rotational alignment, with no superior technique. Navigation systems using direct femoral epicondylar digitization do not provide a more reliable femoral rotational alignment than traditional techniques. Using Whiteside’s line to place the femoral implant, the authors measured a mean angle, setting the knee in a safe rotational range (Figure 3).32

Documenting passive motion before and after TKA enabled the authors to analyze knee behavior. Passive knee motion cannot predict full weight-bearing knee behavior, the “crucial moment of truth” for TKA. Additional research is necessary, but this study supports individually adapting the femoral component rotation using Whiteside’s line. Clinical follow-up will assess possible benefits.

figure 3

Figure 3: Mean angles after setting the knee in safe rotational range.

References

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Authors

Drs Picard, Dean, Dillon, and Ms Mennessier are from the Golden Jubilee National Hospital, Clydebank, Glasgow and Dr Gregori is from the Hairmyres Hospital, East Kilbride, Glasgow, Scotland.