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Computer guided restoration of joint line and femoral offset in cruciate substituting total knee arthroplasty
The Knee 19 (2012) 611–616
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The Knee
Computer guided restoration of joint line and femoral offset in cruciate substituting total knee arthroplasty☆ Gautam M. Shetty ⁎, Arun Mullaji, Sagar Bhayde Department of Orthopaedic Surgery, Breach Candy Hospital, Mumbai, India
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Article history: Received 2 December 2010 Received in revised form 18 November 2011 Accepted 20 November 2011 Keywords: Total knee arthroplasty Joint line Femoral offset Gap balance Computer-assisted surgery
a b s t r a c t Purpose: This prospective study aimed to evaluate radiographically, change in joint line and femoral condylar offset with the optimized gap balancing technique in computer-assisted, primary, cruciate-substituting total knee arthroplasties (TKAs). Methods: One hundred and twenty-nine consecutive computer-assisted TKAs were evaluated radiographically using pre- and postoperative full-length standing hip-to-ankle, antero-posterior and lateral radiographs to assess change in knee deformity, joint line height and posterior condylar offset. Results: In 49% of knees, there was a net decrease (mean 2.2 mm, range 0.2–8.4 mm) in joint line height postoperatively whereas 46.5% of knees had a net increase in joint line height (mean 2.5 mm, range 0.2– 11.2 mm). In 93% of the knees, joint line was restored to within ± 5 mm of preoperative values. In 53% of knees, there was a net increase (mean 2.9 mm, range 0.2–12 mm) in posterior offset postoperatively whereas 40% of knees had a net decrease in posterior offset (mean 4.2 mm, range 0.6–20 mm). In 82% of knees, the posterior offset was restored within ± 5 mm of preoperative values. Conclusions: Based on radiographic evaluation in extension and at 30° flexion, the current study clearly demonstrates that joint line and posterior femoral condylar offset can be restored in the majority of computerassisted, cruciate-substituting TKAs to within 5 mm of their preoperative value. The optimized gap balancing feature of the computer software allows the surgeon to simulate the effect of simultaneously adjusting femoral component size, position and distal femoral resection level on joint line and posterior femoral offset. Level of Evidence: Level II © 2011 Elsevier B.V. All rights reserved.
1. Introduction The success of total knee arthroplasty (TKA) depends to a large extent on accurate restoration of limb alignment and optimum flexion and extension gap balancing. Optimal functioning of any TKA depends on soft tissue restraints of the knee which should allow good movement without compromising stability. This requires the prosthesis to have a similar contour and move around axes close to those of the native joint and involves accurate component sizing and alignment, restoration of the natural joint line and posterior femoral condylar offset [1–3]. Large deviation of the joint line after TKA may result in decreased knee flexion, patellofemoral pain due to altered transmission of quadriceps forces, midflexion instability, decreased functional scores, and increased incidence of revisions and manipulations [4–8]. Figgie et
☆ No benefits or funds were received in support of this study by any of the authors. This article is original and has not been published before or currently submitted to any other journal. ⁎ Corresponding author at: The Arthritis Clinic, 101, Cornelian, Kemp's Corner, Cumballa Hill, Mumbai 400036, India. Tel.: +91 22 23856161; fax: +91 22 23876110. E-mail address: [email protected] (G.M. Shetty). 0968-0160/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2011.11.004
al. [8] in an analysis of 116 total knees, found improved results when the joint line was located within 8 mm of its preoperative position; there was an increase in the number of revisions and manipulations when the joint line was altered by 8 mm or more. The posterior femoral condylar offset is an important factor which affects the flexion–extension gap balance and is a crucial determinant of the final knee range of motion [1,9]. Hence restoration of posterior femoral condylar offset allows greater degree of flexion and avoids tibiofemoral impingement [1,9]. An accurate restoration of joint line depends on accuracy of surgical technique, the instruments and design of the prosthesis. Computer navigation has been introduced to improve limb and component alignment in TKA and decrease the number of outliers. Although restoration of joint line and posterior femoral condylar offset has been studied extensively in conventional cruciate-retaining primary TKA with a possible tendency to elevate the joint line postoperatively [3–5,7,9], literature is scanty regarding this aspect of cruciate-substituting primary TKA. However, elevating the joint line and failure to restore proper offset may be abrogated with the possibility of precisely assessing ligament release, gaps, bone cuts, implant sizing, and final implant position at the outset of the procedure. As joint line elevation and femoral offset are intimately related via the gaps that are created, their assessment
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postoperatively would indicate if they were optimized to a normal anatomical position to achieve equal gaps. The hypothesis of this study was that computer navigation may improve the efficiency of gap balancing and lead to optimum joint line and femoral offset after posterior cruciate-substituting TKA. Hence, the current prospective study aimed to evaluate the restoration of joint line and posterior femoral condylar offset after computer-assisted primary cruciate-substituting TKAs using the optimum gap balancing feature of the computer software.
2. Materials and methods We prospectively studied 147 consecutive primary navigated total knee arthroplasties (TKAs) performed from January 2008 to June 2008. The study was approved by the Ethics Committee of the hospital. The inclusion criterion was patients who underwent primary, cruciatesubstituting, computer-assisted TKA. We excluded patients who had preoperative and postoperative radiographs unacceptable and unsuitable for analysis (due to malposition of limbs or poor quality and exposure), and those who required an additional osteotomy, long stem tibia or constrained prosthesis. Based on the exclusion criteria, 16 limbs were excluded due to unacceptable pre- or postoperative radiographs and two limbs were excluded due to the use of a long stem tibial component. Finally, 129 primary navigated TKAs performed in 100 patients were available for analysis. The study population included 16 males and 84 females with a mean age of 67.7 years (range, 49 to 83 years). All surgeries were performed by a single surgeon at one center and the same ligament balance technique was deployed in all cases.
2.1. Surgical technique All patients were implanted with the same cruciate-substituting design (P.F.C Sigma, DePuy International Ltd, Warsaw, In, USA). A monoblock all polyethylene tibial component design was used in 90 knees and a metal-backed tibial component design used in 39 knees. All polyethylene tibial components were used in young, active patients where the bone quality was found to be good intraoperatively and a metalbacked tibial component used in elderly patients with poor bone quality. We used the Ci navigation system with its software (BrainLab, Munich, Germany). The mechanical axis of the lower limb was determined by navigation, using the center of rotation of the femoral head, the malleoli, and the center of the intercondylar notch. Conventional cutting blocks were navigated into position to perform the appropriate bone cuts. The tibial cut was first performed and it was perpendicular to the mechanical axis of the tibia. Soft-tissue release was performed (medial release for varus knees and lateral release for valgus knees) to achieve a rectangular extension gap and complete restoration of limb alignment. The medial and lateral gaps were recorded by the computer in extension when the surgeon felt that the tension was equal medially and laterally using a tensioning device. Next, the medial and lateral gaps were recorded in 90° flexion when the surgeon felt that the tension was equal medially and laterally using a tensioning device. The flexion gap was automatically equalized to the extension gap by the optimized gap-balancing feature of the computer software by simultaneously adjusting the level of distal femoral resection and the femoral component size. Once the surgeon was satisfied with the femoral size and level of distal resection, the distal femoral resection was performed with navigation. The AP cutting blocking was navigated into position and its rotation was determined using the proximal tibial cut, Whiteside's line and the transepicondylar axis while simultaneously referencing the anterior femoral surface with a stylus to avoid notching. The anteroposterior cuts were then performed followed by the notch and chamfer cuts. The final limb alignment and the gap balance in extension and flexion were confirmed using trial components. All patients underwent patellar resurfacing.
Fig. 1. A, B: Preoperative and postoperative lateral knee radiograph in 30° flexion taken with the splint and marker stand. Joint line height — DISTANCE AB [measured as the distance between the tip of fibular head (asterix) and the midline through the joint space on preoperative radiograph and as the distance between the tip of fibular head (asterix) and a line drawn tangential to the distal most point of the prosthetic femoral condyle postoperatively]; Posterior femoral offset — DISTANCE CD.
2.2. Radiographic evaluation Standing full length (hip to ankle) weight-bearing radiographs, weight-bearing anteroposterior knee radiographs and knee lateral at 30° flexion radiographs were obtained in all patients pre- and postoperatively. For this study, postoperative radiographs taken 6 weeks after surgery were used to measure various radiographic parameters. This was done to make sure that none of the patients had a postoperative flexion deformity during radiography which would have been a
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source of error during measurements. The degree of knee deformity, i.e., the hip–knee–ankle (HKA) angle was determined on standing full-length radiographs as the angle between the mechanical axis of the femur (center of the femoral head to the center of the knee joint) and the mechanical axis of the tibia (center of the knee joint to the center of the ankle). For postoperative coronal alignment of the components, medial femoral angle (measured as the angle between the mechanical axis of the femur and the line drawn tangential to the medial femoral condyle of the prosthesis), and medial tibial angle (measured as the angle between the mechanical axis of the tibia and the line drawn along the base of the tibial component) were determined on full-length hip-to-ankle radiographs. For postoperative sagittal alignment of the components, femoral flexion angle (measured as the angle between the medullary axis of the distal femur and the line drawn perpendicular to the femoral prosthesis) and tibial slope (measured as the angle between the medullary axis of the proximal tibia and the line drawn along the base of the tibial component) were determined on knee lateral radiographs. Postoperative lateral knee radiographs were also analyzed for notching of the anterior femoral cortex by the femoral component. To determine the change in joint line and posterior femoral condylar offset, knee lateral radiographs taken at 30° flexion were used. To standardize the degree of flexion during radiography, splints to hold the knee at 30° were made using fiberglass cast material. The splints had straps to fasten it to the thigh and calf. To account for magnification during radiography, these and the full-length radiographs were taken using the scaled x-ray technique. A marker stand (OrthoRx™, DePuy Orthopaedics Inc, Warsaw, IN, USA) consisting of three metal beads fixed to a radiolucent stand was placed at the midline of the bones of the affected knee joint. The inner distance between the two farthest metal beads was known to be 90 mm (y). The distance between the beads in the radiographs was then measured (x) and any distance then measured on pre- or postoperative radiographs was multiplied by the factor x/y to correct for magnification. Preoperatively, the joint line was measured as the distance between the tip of fibular head and the midline through the joint space in the lateral radiograph (Fig. 1A). Postoperatively, the joint line in lateral radiographs was measured as the distance between the tip of fibular head to a line drawn tangential to the distal most point of the prosthetic femoral condyle (Fig. 1B). The preoperative and postoperative posterior femoral offset was measured by the method described by Bellemans et al. [9] using the lateral knee radiographs taken at 30° flexion as the maximum thickness of the posterior femoral condyle, projected posterior to the tangent of the posterior cortex of the femoral shaft (Fig. 1). 2.3. Statistical analysis To estimate intra-and interobserver error for measuring distances on radiographs, pre- and postoperative joint line height was measured in 20 randomly selected knees where the parameter was measured by the first observer again and a second independent observer. Percentage of knees which showed either increase or decrease in joint line height and posterior offset postoperatively was calculated and a distribution curve for the amount of change in these two parameters postoperatively was plotted. Similarly, the percentage of knees which had postoperative joint line height and posterior offset within ±5 mm of preoperative values was also calculated. Percentage of knees in the two subgroups, based on severity of knee deformity, was compared using Fisher's exact test. Correlation between preand postoperative joint line height, pre- and postoperative femoral offset, preoperative HKA angle and postoperative joint line height and postoperative femoral offset, postoperative joint line height and postoperative femoral offset and amount of change in joint line height and posterior offset was determined using the Passing and Bablok [10,11] method of correlation and regression analysis. A p value of b0.05 was considered statistically significant.
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Fig. 2. A: Normal distribution curve of postoperative change in joint line height in all limbs. B: Normal distribution curve of postoperative change in posterior femoral offset in all limbs.
3. Results The preoperative deformity was varus in 120 limbs (HKA angle ≤180°) and valgus in 9 limbs (HKA angle >180°). The preoperative deformity was b 15° in 100 limbs (77.5%) and ≥15° in 29 limbs (22.5%). The mean preoperative HKA angle of 171° ± 7.7° changed to 180.1° ± 1.7° postoperatively. Postoperatively, the mean coronal femoral component alignment was 90° ± 0.9°, the mean coronal tibial component alignment was 90° ± 0.7°, the mean sagittal femoral component alignment was 94.4° ± 2.6° and the mean sagittal tibial component alignment (tibial slope) was 88° ± 1.6°. Pre- and postoperative radiographic data in the study population is summarized in Table 1. None of the limbs had postoperative notching of the anterior femoral cortex. Intra- and interobserver correlation analysis for pre- and postoperative joint line height measurements revealed highly significant and close correlation between the measurements made by the initial and second observer (r= 0.81, p b 0.0001) and between those made by the initial observer at two different times (r= 0.87, p b 0.0001). 3.1. Joint line In 49% of knees, there was a net decrease (mean 2.2 mm, range 0.2–8.4 mm) in joint line height postoperatively whereas 46.5% of knees had a net increase in joint line height (mean 2.5 mm, range 0.2–11.2 mm). In 93% of the knees, joint line was restored to within ±5 mm of preoperative values. Nine knees (7%) had a postoperative joint line change of > ±5 mm compared to preoperative values. Postoperative joint line was restored to within ±5 mm of preoperative values in 95% of knees with b15° of deformity when compared to 86% in knees with ≥15° of deformity (p= 0.11, Fisher's test). A distribution curve illustrating the change in joint line height postoperatively is given in Fig. 2A. 3.2. Posterior condylar offset In 53% of knees, there was a net increase (mean 2.9 mm, range 0.2–12 mm) in posterior offset postoperatively whereas 40% of knees had a net decrease in posterior
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Table 1 Pre and postoperative radiographic data. Preoperative
All knees (n = 129 knees)
Knees with preop HKA Angle b 15° (n = 100 knees)
Knees with preop HKA angle ≥ 15° (n = 29 knees)
HKA Angle Joint line (mm) Posterior offset (mm) HKA angle Joint line (mm) Posterior offset (mm) HKA angle Joint line (mm) Posterior offset (mm)
Postoperative
Mean ± S.D
Range
95% CI
Mean ± S.D
Range
95% CI
171° ± 7.7° 15.0 ± 3.4 30.4 ± 4.1 172.7° ± 5.4° 15.2 ± 3.3 30.2 ± 4.1 165° ± 10.9° 14.5 ± 3.6 31 ± 3.8
152°–203° 6–23.5 20–41 165.5°–193° 6–23.5 20–41 152°–203° 7.2–21.4 22–37.5
169.6°–172.3° 14.4–15.6 29.6–31.1 171.6°–173.7° 14.5–15.8 29.3–31 160.8°–169.1° 13.1–15.8 29.5–32.4
180.1° ± 1.7° 15.0 ± 2.8 30.3 ± 3.4 180.2° ± 1.7° 14.9 ± 2.7 30.2 ± 3.4 179.8° ± 1.6° 15.5 ± 3.2 30.6 ± 3.8
176.5°–184° 8.8–22.5 20–40 176.5°–185° 9–22.5 20–39 177°–183.5° 8.8–21.5 23–40
179.8°–180.3° 14.6–15.5 29.7–30.8 179.8°–180.5° 14.3–15.4 29.5–30.8 179.1°–180.4° 14.2–16.7 29.1–32.0
HKA Angle — Hip–Knee–Ankle angle. SD — standard deviation. CI — confidence interval.
offset (mean 4.2 mm, range 0.6–20 mm). In 82% of knees, the posterior offset was restored within ±5 mm of preoperative values. Twenty-three knees (18%) had a postoperative offset > ±5 mm compared to preoperative values. Postoperative joint line was restored to within ±5 mm of preoperative values in 71% of knees with b 15° of deformity when compared to 76% in knees with ≥15° of deformity (p = 0.81, Fisher's test). A distribution curve illustrating the change in posterior femoral offset postoperatively is given in Fig. 2B. Analysis of the amount of postoperative change in joint line height and posterior offset in individual knees (Table.2) revealed 4 broad combinations of change — increase in both joint line height and offset, decrease in both joint line height and offset, decrease in joint line height and increase in offset and increase in joint line height and decrease in offset. Among the outliers for joint line height (nine knees), six knees had a net increase in joint line height (mean: 8.5 mm, range: 7–11.2 mm) and three knees had a net decrease in joint line height (mean: 6.5 mm, range: 5.4–8.4 mm). However, the posterior offset in eight of these knees were within the acceptable ±5 mm range and one knee had an increase in posterior offset of 6.6 mm. Similarly, among the outliers for posterior offset (23 knees), 11 knees had a net increase in posterior offset (mean: 7.1 mm, range: 5.4–12 mm) and 12 knees had a net decrease in posterior offset (mean: 6.5 mm, range: 5.4–8.4 mm). However, the joint line height in 22 of these knees was within the acceptable ±5 mm range and one knee had an increase in joint line height of 8.1 mm. Statistical analysis according to the Passing and Bablok [10] method revealed strong and significant positive correlation between pre- and postoperative joint line height (r= 0.53, p b 0.0001). This was also seen in knees with b15° deformity (r= 0.54, p b 0.0001) and with ≥15° of deformity (r= 0.48, p b 0.0001). A weak negative correlation (r= −0.22, p = 0.01) between postoperative joint line and postoperative femoral offset and a weak positive correlation (r= 0.33, p = 0.0001) between preoperative and postoperative femoral offset was found. Finally, there was no significant correlation between preoperative HKA angle and postoperative joint line (r= −0.01), between preoperative HKA angle and postoperative posterior offset (r= −0.04) and between amount of postoperative change in joint line height and change in posterior offset (r= 0.04).
4. Discussion The results of the current study involving computer-assisted, cruciate-substituting TKAs indicate that joint line height in 93% of the knees and posterior femoral offset in 82% of the knees were accurately restored to within ±5 mm of preoperative values when knees were evaluated radiographically at extension and 30° flexion. The percentage of limbs where postoperative joint line and femoral offset was restored to within ±5 mm of preoperative values was not significantly different when subgroups based on severity of preoperative knee deformity were compared. In the current study using posterior stabilized components, although the mean joint line position postoperatively showed no change compared to its preoperative values, 7% (nine knees) had a postoperative joint line change of > ±5 mm compared to preoperative values. Of these, three limbs showed reduction in the joint line height and six limbs showed joint line elevation after surgery. Cope et al. [5] in a radiologic study comparing joint line in cruciate-retaining versus cruciatesubstituting TKA reported a change of less than 0.5 mm in both the groups and no significant difference in the joint line change between the two groups. Selvarajah and Hooper [12] in a prospective study of 79 cruciate-retaining mobile bearing TKA reported an average joint line elevation of 1 mm. These results appear similar to those of this study in which the mean change in the joint line was 0 (range, −8.4 mm to 11.2 mm). However, the distribution of change in joint line height postoperatively is not available from these reports.
Table 2 Combinations of postoperative change in the amount of joint line height and posterior offset in all limbs.
All limbs (n = 129)
Outliers (n = 31)
Combinations
n
Increased joint line height and offset Decreased joint line height and offset Decreased joint line height and increased offset Increased joint line height and decreased offset Others* Increased joint line height and offset Decreased joint line height and offset Decreased joint line height and increased offset Increased joint line height and decreased offset Others*
34 30 29 22 14 8 9 6 7 1
All values given as mean (range); n — number of limbs (percentage). *Others includes: No change joint line height and increased offset — 5 knees. Increased joint line height and no change offset — 4 knees. Decreased joint line height and no change offset — 4 knees. No change joint line height and no change offset — 1 knee.
(26%) (23%) (22%) (17%) (12%) (26%) (29%) (19%) (22.5%) (3.5%)
Preoperative HKA angle (degrees)
Joint line height change (mm)
Posterior offset change (mm)
173 (158.5–203) 169.8 (153–183) 172.4 (163.5–193) 170.4 (160.5–201) 166.4 (152–176.5) 174.9 (168–180) 168.9 (155–175.5) 172.6 (163.5–180) 168.5 (165–171.5) 152
2.4 (0.2–11.2) − 2.1 (− 0.2 to − 5.4) − 2.6 (− 0.4 to − 8.4) 2.7 (0.3–9) 0 (− 4 to 4) 4.2 (0.3–11.2) − 2.3 (− 0.2 to − 5.4) − 4.2 (− 1.6 to − 8.4) 4.8 (2–9) 0
3.1 (0.2–12) − 4.2 (− 1 to − 12) 2.7 (0.4–9.4) − 4 (− 0.6 to − 20) 1.2 (0–6) 6.5 (2–12) − 7.3 (− 1.5 to − 12) 5.1 (2–9.4) − 7.7 (− 1 to − 20) 6
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The posterior femoral condylar offset is reported to be a very important factor determining the degree of knee flexion which can be possible after TKA [9,13]. This has been reported to be especially important in cruciate-retaining designs [14]. Hanratty et al. [15] in a review of 69 mobile-bearing cruciate-substituting TKAs reported a mean difference of + 1 mm between the pre- and postoperative values. In the current study the mean change in posterior offset postoperatively was −0.1 mm after surgery. However, 18% (23 knees) had a postoperative offset > ±5 mm compared to preoperative values where 12 knees had decrease in offset and 11 knees had increase in posterior offset. Although computer navigation was initially introduced to improve the accuracy of limb and component alignment, later versions of software were developed to also address gap equalization; however the accuracy of joint line and posterior femoral offset restoration has not been reported in the literature. Computer navigation helps to verify the position of the cutting blocks and also verify the accuracy of the bone cuts. However inaccuracies during bone cuts in navigated TKA may still occur due to variation of saw cuts within the jig which may lead to discrepancy between the final cut and the planned cut [16]. The optimized balancing option of the navigation software helps to adjust the size and position of the femoral component simultaneously with the distal femoral resection level in order to accurately balance and equalize extension and flexion gaps. The effect of changing the level of the distal femoral cut, the degree of femoral component flexion, and the anterior-posterior translation of the component and its size, on the flexion and extension gaps and joint line position can effectively be simulated by the surgeon on the screen with this and he can override the recommendations of the software if he so desires. This provides the surgeon the flexibility to make the necessary changes in the size and position of the femoral component and yet optimize the flexion and extension gap balance, all by simulating the changes in a “virtual” manner without actually performing the cuts. As the software determines the femoral component size (and thus the posterior offset) and distal femoral resection level (and thus the joint line), this study aimed to ascertain the accuracy with which it could do so in a consecutive large series of computerassisted TKAs done by a single surgeon using the tibia first technique. There are a few drawbacks of this study. During preoperative measurement of the joint line, in some cases with severe deformities and gross reduction in joint line space with bone loss, the joint line could at best be estimated on radiographs and this may have been a potential source of error. However, the authors have tried to minimize measurement errors by using fixed splints and the scaled x-ray technique. Besides, the authors have used the tip of the fibular head as a landmark to determine joint line height because it offers the advantage of a fixed single-point bony prominence which can be easily identified and remains fixed throughout the knee range of motion. Other landmarks which are typically used for measuring joint line height are the lower pole of the patella and the tibial tuberosity. However, the lower pole of the patella may change in position with knee flexion and extension and hence may vary the joint line height measure with knee position and the tibial tuberosity is a broad landmark where no single point can be consistently identified to measure the joint line height. The reliability of using the fibular head to measure joint line height is highlighted in the current study by the highly significant and close correlation for pre- and postoperative joint line height measurements on intra-and interobserver correlation analysis. Hauschild et al. [17] have reported that intraoperative navigation and postoperative radiographic measurements correlate well only when radiographic measurements are delayed beyond 2 weeks after surgery. In the current study, measurements were done on radiographs done at 6 weeks postoperatively which are in accordance to the findings of Hauschild et al. [17]. Similarly Yaffe et al. [18] and Oberst et al. [11] have reported poor correlation between pre- and postoperative radiographic measurements and intraoperative navigation measurements. However, the current study has
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not compared intraoperative navigation data to radiographic measurements and did not aim to determine reliability of navigation data vis-avis radiographic data and has relied on the “gold-standard” of using radiographic measurements only to determine change in joint line and offset. To clearly demonstrate that computer navigation can more accurately restore joint line and posterior offset in TKA, this study should have been conducted using conventional TKA controls. Joint line height and posterior femoral offset may be considered surrogate measures of restoration of extension gap and flexion gap respectively after TKA. Hence, excessive postoperative change in joint line height and posterior offset when compared to preoperative values may affect joint stability and function. The senior surgeon aimed for and achieved an extension and flexion gap within 2 mm of each other throughout the range of motion in all knees as recorded by navigation at the end of each procedure. However, correlating change in joint line and posterior offset with computer navigated TKA to postoperative functional outcome was not a part of the study. In conclusion, the current study clearly demonstrates that joint line and posterior femoral condylar offset can be restored in the majority of the knees to within 5 mm of their preoperative values in computer navigated, cruciate-substituting TKAs. The optimized gap balancing feature of the computer software allows the surgeon to simulate the effect of simultaneously changing the size and position of the femoral component and altering the distal femoral resection level on the joint line and gaps before performing the bone cuts. Conflict of interest statement The authors wish to state that no funds or benefits were received by any of the authors in support of this study/article from any source. Acknowledgments The authors thank Prof. Harshad Thakur, M.D, School of Health System Studies, TATA Institute of Social Sciences, Mumbai, India for his help in statistical analysis. References [1] Malviya A, Lingard EA, Weir DJ, Deehan DJ. Predicting range of movement after knee replacement: the importance of posterior condylar offset and tibial slope. Knee Surg Sports Traumatol Arthrosc 2009;17:491–8. [2] Bottros J, Gad B, Krebs V, Barsoum WK. Gap balancing in total knee arthroplasty. J Arthroplasty 2006;21(4 Suppl. 1):11–5. [3] Romero J, Stähelin T, Binkert C, Pfirrmann C, Hodler J, Kessler O. The clinical consequences of flexion gap asymmetry in total knee arthroplasty. J Arthroplasty 2007;22:235–40. [4] Wyss TF, Schuster AJ, Münger P, Pfluger D, Wehrli U. Does total knee joint replacement with the soft tissue balancing surgical technique maintain the natural joint line? Arch Orthop Trauma Surg 2006;126:480–6. [5] Cope MR, O'Brien BS, Nanu AM. The influence of the posterior cruciate ligament in the maintenance of joint line in primary total knee arthroplasty: a radiologic study. J Arthroplasty 2002;17:206–8. [6] Ryu J, Saito S, Yamamoto K, Sano S. Factors influencing the postoperative range of motion in total knee arthroplasty. Bull Hosp Jt Dis 1993;53:35–40. [7] Emodi GJ, Callaghan JJ, Pedersen DR, Brown TD. Posterior cruciate ligament function following total knee arthroplasty: the effect of joint line elevation. Iowa Orthop J 1999;19:82–92. [8] Figgie III HE, Goldberg VM, Heiple KG, Moller III HS, Gordon NH. The influence of tibial-patellofemoral location on function of the knee in patients with the posterior stabilized condylar knee prosthesis. J Bone Joint Surg Am 1986;68:1035–40. [9] Bellemans J, Banks S, Victor J, Vandenneucker H, Moemans A. Fluoroscopic analysis of the kinematics of deep flexion in total knee arthroplasty. Influence of posterior condylar offset. J Bone Joint Surg Br 2002;84:50–3. [10] Passing H, Bablok W. Comparison of several regression procedures for method comparison studies and determination of sample sizes. Application of linear regression procedures for method comparison studies in Clinical Chemistry, Part II. J Clin Chem Clin Biochem 1984;22:431–45. [11] Oberst M, Bertsch C, Lahm A, Wuerstlin S, Holz U. Regression and correlation analysis of preoperative versus intraoperative assessment of axes during navigated total knee arthroplasty. Comput Aided Surg 2006;11:87–91. [12] Selvarajah E, Hooper G. Restoration of the joint line in total knee arthroplasty. J Arthroplasty 2009;24:1099–102.
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[13] Massin P, Gournay A. Optimization of the posterior condylar offset, tibial slope, and condylar roll-back in total knee arthroplasty. J Arthroplasty 2006;21:889–96. [14] Arabori M, Matsui N, Kuroda R, Mizuno K, Doita M, Kurosaka M, et al. Posterior condylar offset and flexion in posterior cruciate-retaining and posterior stabilized TKA. J Orthop Sci 2008;13:46–50. [15] Hanratty BM, Thompson NW, Wilson RK, Beverland DE. The influence of posterior condylar offset on knee flexion after total knee replacement using a cruciate-sacrificing mobile-bearing implant. J Bone Joint Surg Br 2007;89:915–8.
[16] Biant LC, Yeoh K, Walker PM, Warwick Bruce JM, Walsh R. The accuracy of bone resections made during computer navigated total knee replacement. Do we resect what the computer plans we resect? Knee 2008;15:238–41. [17] Hauschild O, Konstantinidis L, Baumann T, Niemeyer P, Suedkamp NP, Helwig P. Correlation of radiographic and navigated measurements of TKA limb alignment: a matter of time? Knee Surg Sports Traumatol Arthrosc 2010;18:1317–22. [18] Yaffe MA, Koo SS, Stulberg SD. Radiographic and navigation measurements of TKA limb alignment do not correlate. Clin Orthop Relat Res 2008;466:2736–44.
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The Knee
Computer guided restoration of joint line and femoral offset in cruciate substituting total knee arthroplasty☆ Gautam M. Shetty ⁎, Arun Mullaji, Sagar Bhayde Department of Orthopaedic Surgery, Breach Candy Hospital, Mumbai, India
a r t i c l e
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Article history: Received 2 December 2010 Received in revised form 18 November 2011 Accepted 20 November 2011 Keywords: Total knee arthroplasty Joint line Femoral offset Gap balance Computer-assisted surgery
a b s t r a c t Purpose: This prospective study aimed to evaluate radiographically, change in joint line and femoral condylar offset with the optimized gap balancing technique in computer-assisted, primary, cruciate-substituting total knee arthroplasties (TKAs). Methods: One hundred and twenty-nine consecutive computer-assisted TKAs were evaluated radiographically using pre- and postoperative full-length standing hip-to-ankle, antero-posterior and lateral radiographs to assess change in knee deformity, joint line height and posterior condylar offset. Results: In 49% of knees, there was a net decrease (mean 2.2 mm, range 0.2–8.4 mm) in joint line height postoperatively whereas 46.5% of knees had a net increase in joint line height (mean 2.5 mm, range 0.2– 11.2 mm). In 93% of the knees, joint line was restored to within ± 5 mm of preoperative values. In 53% of knees, there was a net increase (mean 2.9 mm, range 0.2–12 mm) in posterior offset postoperatively whereas 40% of knees had a net decrease in posterior offset (mean 4.2 mm, range 0.6–20 mm). In 82% of knees, the posterior offset was restored within ± 5 mm of preoperative values. Conclusions: Based on radiographic evaluation in extension and at 30° flexion, the current study clearly demonstrates that joint line and posterior femoral condylar offset can be restored in the majority of computerassisted, cruciate-substituting TKAs to within 5 mm of their preoperative value. The optimized gap balancing feature of the computer software allows the surgeon to simulate the effect of simultaneously adjusting femoral component size, position and distal femoral resection level on joint line and posterior femoral offset. Level of Evidence: Level II © 2011 Elsevier B.V. All rights reserved.
1. Introduction The success of total knee arthroplasty (TKA) depends to a large extent on accurate restoration of limb alignment and optimum flexion and extension gap balancing. Optimal functioning of any TKA depends on soft tissue restraints of the knee which should allow good movement without compromising stability. This requires the prosthesis to have a similar contour and move around axes close to those of the native joint and involves accurate component sizing and alignment, restoration of the natural joint line and posterior femoral condylar offset [1–3]. Large deviation of the joint line after TKA may result in decreased knee flexion, patellofemoral pain due to altered transmission of quadriceps forces, midflexion instability, decreased functional scores, and increased incidence of revisions and manipulations [4–8]. Figgie et
☆ No benefits or funds were received in support of this study by any of the authors. This article is original and has not been published before or currently submitted to any other journal. ⁎ Corresponding author at: The Arthritis Clinic, 101, Cornelian, Kemp's Corner, Cumballa Hill, Mumbai 400036, India. Tel.: +91 22 23856161; fax: +91 22 23876110. E-mail address: [email protected] (G.M. Shetty). 0968-0160/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2011.11.004
al. [8] in an analysis of 116 total knees, found improved results when the joint line was located within 8 mm of its preoperative position; there was an increase in the number of revisions and manipulations when the joint line was altered by 8 mm or more. The posterior femoral condylar offset is an important factor which affects the flexion–extension gap balance and is a crucial determinant of the final knee range of motion [1,9]. Hence restoration of posterior femoral condylar offset allows greater degree of flexion and avoids tibiofemoral impingement [1,9]. An accurate restoration of joint line depends on accuracy of surgical technique, the instruments and design of the prosthesis. Computer navigation has been introduced to improve limb and component alignment in TKA and decrease the number of outliers. Although restoration of joint line and posterior femoral condylar offset has been studied extensively in conventional cruciate-retaining primary TKA with a possible tendency to elevate the joint line postoperatively [3–5,7,9], literature is scanty regarding this aspect of cruciate-substituting primary TKA. However, elevating the joint line and failure to restore proper offset may be abrogated with the possibility of precisely assessing ligament release, gaps, bone cuts, implant sizing, and final implant position at the outset of the procedure. As joint line elevation and femoral offset are intimately related via the gaps that are created, their assessment
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postoperatively would indicate if they were optimized to a normal anatomical position to achieve equal gaps. The hypothesis of this study was that computer navigation may improve the efficiency of gap balancing and lead to optimum joint line and femoral offset after posterior cruciate-substituting TKA. Hence, the current prospective study aimed to evaluate the restoration of joint line and posterior femoral condylar offset after computer-assisted primary cruciate-substituting TKAs using the optimum gap balancing feature of the computer software.
2. Materials and methods We prospectively studied 147 consecutive primary navigated total knee arthroplasties (TKAs) performed from January 2008 to June 2008. The study was approved by the Ethics Committee of the hospital. The inclusion criterion was patients who underwent primary, cruciatesubstituting, computer-assisted TKA. We excluded patients who had preoperative and postoperative radiographs unacceptable and unsuitable for analysis (due to malposition of limbs or poor quality and exposure), and those who required an additional osteotomy, long stem tibia or constrained prosthesis. Based on the exclusion criteria, 16 limbs were excluded due to unacceptable pre- or postoperative radiographs and two limbs were excluded due to the use of a long stem tibial component. Finally, 129 primary navigated TKAs performed in 100 patients were available for analysis. The study population included 16 males and 84 females with a mean age of 67.7 years (range, 49 to 83 years). All surgeries were performed by a single surgeon at one center and the same ligament balance technique was deployed in all cases.
2.1. Surgical technique All patients were implanted with the same cruciate-substituting design (P.F.C Sigma, DePuy International Ltd, Warsaw, In, USA). A monoblock all polyethylene tibial component design was used in 90 knees and a metal-backed tibial component design used in 39 knees. All polyethylene tibial components were used in young, active patients where the bone quality was found to be good intraoperatively and a metalbacked tibial component used in elderly patients with poor bone quality. We used the Ci navigation system with its software (BrainLab, Munich, Germany). The mechanical axis of the lower limb was determined by navigation, using the center of rotation of the femoral head, the malleoli, and the center of the intercondylar notch. Conventional cutting blocks were navigated into position to perform the appropriate bone cuts. The tibial cut was first performed and it was perpendicular to the mechanical axis of the tibia. Soft-tissue release was performed (medial release for varus knees and lateral release for valgus knees) to achieve a rectangular extension gap and complete restoration of limb alignment. The medial and lateral gaps were recorded by the computer in extension when the surgeon felt that the tension was equal medially and laterally using a tensioning device. Next, the medial and lateral gaps were recorded in 90° flexion when the surgeon felt that the tension was equal medially and laterally using a tensioning device. The flexion gap was automatically equalized to the extension gap by the optimized gap-balancing feature of the computer software by simultaneously adjusting the level of distal femoral resection and the femoral component size. Once the surgeon was satisfied with the femoral size and level of distal resection, the distal femoral resection was performed with navigation. The AP cutting blocking was navigated into position and its rotation was determined using the proximal tibial cut, Whiteside's line and the transepicondylar axis while simultaneously referencing the anterior femoral surface with a stylus to avoid notching. The anteroposterior cuts were then performed followed by the notch and chamfer cuts. The final limb alignment and the gap balance in extension and flexion were confirmed using trial components. All patients underwent patellar resurfacing.
Fig. 1. A, B: Preoperative and postoperative lateral knee radiograph in 30° flexion taken with the splint and marker stand. Joint line height — DISTANCE AB [measured as the distance between the tip of fibular head (asterix) and the midline through the joint space on preoperative radiograph and as the distance between the tip of fibular head (asterix) and a line drawn tangential to the distal most point of the prosthetic femoral condyle postoperatively]; Posterior femoral offset — DISTANCE CD.
2.2. Radiographic evaluation Standing full length (hip to ankle) weight-bearing radiographs, weight-bearing anteroposterior knee radiographs and knee lateral at 30° flexion radiographs were obtained in all patients pre- and postoperatively. For this study, postoperative radiographs taken 6 weeks after surgery were used to measure various radiographic parameters. This was done to make sure that none of the patients had a postoperative flexion deformity during radiography which would have been a
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source of error during measurements. The degree of knee deformity, i.e., the hip–knee–ankle (HKA) angle was determined on standing full-length radiographs as the angle between the mechanical axis of the femur (center of the femoral head to the center of the knee joint) and the mechanical axis of the tibia (center of the knee joint to the center of the ankle). For postoperative coronal alignment of the components, medial femoral angle (measured as the angle between the mechanical axis of the femur and the line drawn tangential to the medial femoral condyle of the prosthesis), and medial tibial angle (measured as the angle between the mechanical axis of the tibia and the line drawn along the base of the tibial component) were determined on full-length hip-to-ankle radiographs. For postoperative sagittal alignment of the components, femoral flexion angle (measured as the angle between the medullary axis of the distal femur and the line drawn perpendicular to the femoral prosthesis) and tibial slope (measured as the angle between the medullary axis of the proximal tibia and the line drawn along the base of the tibial component) were determined on knee lateral radiographs. Postoperative lateral knee radiographs were also analyzed for notching of the anterior femoral cortex by the femoral component. To determine the change in joint line and posterior femoral condylar offset, knee lateral radiographs taken at 30° flexion were used. To standardize the degree of flexion during radiography, splints to hold the knee at 30° were made using fiberglass cast material. The splints had straps to fasten it to the thigh and calf. To account for magnification during radiography, these and the full-length radiographs were taken using the scaled x-ray technique. A marker stand (OrthoRx™, DePuy Orthopaedics Inc, Warsaw, IN, USA) consisting of three metal beads fixed to a radiolucent stand was placed at the midline of the bones of the affected knee joint. The inner distance between the two farthest metal beads was known to be 90 mm (y). The distance between the beads in the radiographs was then measured (x) and any distance then measured on pre- or postoperative radiographs was multiplied by the factor x/y to correct for magnification. Preoperatively, the joint line was measured as the distance between the tip of fibular head and the midline through the joint space in the lateral radiograph (Fig. 1A). Postoperatively, the joint line in lateral radiographs was measured as the distance between the tip of fibular head to a line drawn tangential to the distal most point of the prosthetic femoral condyle (Fig. 1B). The preoperative and postoperative posterior femoral offset was measured by the method described by Bellemans et al. [9] using the lateral knee radiographs taken at 30° flexion as the maximum thickness of the posterior femoral condyle, projected posterior to the tangent of the posterior cortex of the femoral shaft (Fig. 1). 2.3. Statistical analysis To estimate intra-and interobserver error for measuring distances on radiographs, pre- and postoperative joint line height was measured in 20 randomly selected knees where the parameter was measured by the first observer again and a second independent observer. Percentage of knees which showed either increase or decrease in joint line height and posterior offset postoperatively was calculated and a distribution curve for the amount of change in these two parameters postoperatively was plotted. Similarly, the percentage of knees which had postoperative joint line height and posterior offset within ±5 mm of preoperative values was also calculated. Percentage of knees in the two subgroups, based on severity of knee deformity, was compared using Fisher's exact test. Correlation between preand postoperative joint line height, pre- and postoperative femoral offset, preoperative HKA angle and postoperative joint line height and postoperative femoral offset, postoperative joint line height and postoperative femoral offset and amount of change in joint line height and posterior offset was determined using the Passing and Bablok [10,11] method of correlation and regression analysis. A p value of b0.05 was considered statistically significant.
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Fig. 2. A: Normal distribution curve of postoperative change in joint line height in all limbs. B: Normal distribution curve of postoperative change in posterior femoral offset in all limbs.
3. Results The preoperative deformity was varus in 120 limbs (HKA angle ≤180°) and valgus in 9 limbs (HKA angle >180°). The preoperative deformity was b 15° in 100 limbs (77.5%) and ≥15° in 29 limbs (22.5%). The mean preoperative HKA angle of 171° ± 7.7° changed to 180.1° ± 1.7° postoperatively. Postoperatively, the mean coronal femoral component alignment was 90° ± 0.9°, the mean coronal tibial component alignment was 90° ± 0.7°, the mean sagittal femoral component alignment was 94.4° ± 2.6° and the mean sagittal tibial component alignment (tibial slope) was 88° ± 1.6°. Pre- and postoperative radiographic data in the study population is summarized in Table 1. None of the limbs had postoperative notching of the anterior femoral cortex. Intra- and interobserver correlation analysis for pre- and postoperative joint line height measurements revealed highly significant and close correlation between the measurements made by the initial and second observer (r= 0.81, p b 0.0001) and between those made by the initial observer at two different times (r= 0.87, p b 0.0001). 3.1. Joint line In 49% of knees, there was a net decrease (mean 2.2 mm, range 0.2–8.4 mm) in joint line height postoperatively whereas 46.5% of knees had a net increase in joint line height (mean 2.5 mm, range 0.2–11.2 mm). In 93% of the knees, joint line was restored to within ±5 mm of preoperative values. Nine knees (7%) had a postoperative joint line change of > ±5 mm compared to preoperative values. Postoperative joint line was restored to within ±5 mm of preoperative values in 95% of knees with b15° of deformity when compared to 86% in knees with ≥15° of deformity (p= 0.11, Fisher's test). A distribution curve illustrating the change in joint line height postoperatively is given in Fig. 2A. 3.2. Posterior condylar offset In 53% of knees, there was a net increase (mean 2.9 mm, range 0.2–12 mm) in posterior offset postoperatively whereas 40% of knees had a net decrease in posterior
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Table 1 Pre and postoperative radiographic data. Preoperative
All knees (n = 129 knees)
Knees with preop HKA Angle b 15° (n = 100 knees)
Knees with preop HKA angle ≥ 15° (n = 29 knees)
HKA Angle Joint line (mm) Posterior offset (mm) HKA angle Joint line (mm) Posterior offset (mm) HKA angle Joint line (mm) Posterior offset (mm)
Postoperative
Mean ± S.D
Range
95% CI
Mean ± S.D
Range
95% CI
171° ± 7.7° 15.0 ± 3.4 30.4 ± 4.1 172.7° ± 5.4° 15.2 ± 3.3 30.2 ± 4.1 165° ± 10.9° 14.5 ± 3.6 31 ± 3.8
152°–203° 6–23.5 20–41 165.5°–193° 6–23.5 20–41 152°–203° 7.2–21.4 22–37.5
169.6°–172.3° 14.4–15.6 29.6–31.1 171.6°–173.7° 14.5–15.8 29.3–31 160.8°–169.1° 13.1–15.8 29.5–32.4
180.1° ± 1.7° 15.0 ± 2.8 30.3 ± 3.4 180.2° ± 1.7° 14.9 ± 2.7 30.2 ± 3.4 179.8° ± 1.6° 15.5 ± 3.2 30.6 ± 3.8
176.5°–184° 8.8–22.5 20–40 176.5°–185° 9–22.5 20–39 177°–183.5° 8.8–21.5 23–40
179.8°–180.3° 14.6–15.5 29.7–30.8 179.8°–180.5° 14.3–15.4 29.5–30.8 179.1°–180.4° 14.2–16.7 29.1–32.0
HKA Angle — Hip–Knee–Ankle angle. SD — standard deviation. CI — confidence interval.
offset (mean 4.2 mm, range 0.6–20 mm). In 82% of knees, the posterior offset was restored within ±5 mm of preoperative values. Twenty-three knees (18%) had a postoperative offset > ±5 mm compared to preoperative values. Postoperative joint line was restored to within ±5 mm of preoperative values in 71% of knees with b 15° of deformity when compared to 76% in knees with ≥15° of deformity (p = 0.81, Fisher's test). A distribution curve illustrating the change in posterior femoral offset postoperatively is given in Fig. 2B. Analysis of the amount of postoperative change in joint line height and posterior offset in individual knees (Table.2) revealed 4 broad combinations of change — increase in both joint line height and offset, decrease in both joint line height and offset, decrease in joint line height and increase in offset and increase in joint line height and decrease in offset. Among the outliers for joint line height (nine knees), six knees had a net increase in joint line height (mean: 8.5 mm, range: 7–11.2 mm) and three knees had a net decrease in joint line height (mean: 6.5 mm, range: 5.4–8.4 mm). However, the posterior offset in eight of these knees were within the acceptable ±5 mm range and one knee had an increase in posterior offset of 6.6 mm. Similarly, among the outliers for posterior offset (23 knees), 11 knees had a net increase in posterior offset (mean: 7.1 mm, range: 5.4–12 mm) and 12 knees had a net decrease in posterior offset (mean: 6.5 mm, range: 5.4–8.4 mm). However, the joint line height in 22 of these knees was within the acceptable ±5 mm range and one knee had an increase in joint line height of 8.1 mm. Statistical analysis according to the Passing and Bablok [10] method revealed strong and significant positive correlation between pre- and postoperative joint line height (r= 0.53, p b 0.0001). This was also seen in knees with b15° deformity (r= 0.54, p b 0.0001) and with ≥15° of deformity (r= 0.48, p b 0.0001). A weak negative correlation (r= −0.22, p = 0.01) between postoperative joint line and postoperative femoral offset and a weak positive correlation (r= 0.33, p = 0.0001) between preoperative and postoperative femoral offset was found. Finally, there was no significant correlation between preoperative HKA angle and postoperative joint line (r= −0.01), between preoperative HKA angle and postoperative posterior offset (r= −0.04) and between amount of postoperative change in joint line height and change in posterior offset (r= 0.04).
4. Discussion The results of the current study involving computer-assisted, cruciate-substituting TKAs indicate that joint line height in 93% of the knees and posterior femoral offset in 82% of the knees were accurately restored to within ±5 mm of preoperative values when knees were evaluated radiographically at extension and 30° flexion. The percentage of limbs where postoperative joint line and femoral offset was restored to within ±5 mm of preoperative values was not significantly different when subgroups based on severity of preoperative knee deformity were compared. In the current study using posterior stabilized components, although the mean joint line position postoperatively showed no change compared to its preoperative values, 7% (nine knees) had a postoperative joint line change of > ±5 mm compared to preoperative values. Of these, three limbs showed reduction in the joint line height and six limbs showed joint line elevation after surgery. Cope et al. [5] in a radiologic study comparing joint line in cruciate-retaining versus cruciatesubstituting TKA reported a change of less than 0.5 mm in both the groups and no significant difference in the joint line change between the two groups. Selvarajah and Hooper [12] in a prospective study of 79 cruciate-retaining mobile bearing TKA reported an average joint line elevation of 1 mm. These results appear similar to those of this study in which the mean change in the joint line was 0 (range, −8.4 mm to 11.2 mm). However, the distribution of change in joint line height postoperatively is not available from these reports.
Table 2 Combinations of postoperative change in the amount of joint line height and posterior offset in all limbs.
All limbs (n = 129)
Outliers (n = 31)
Combinations
n
Increased joint line height and offset Decreased joint line height and offset Decreased joint line height and increased offset Increased joint line height and decreased offset Others* Increased joint line height and offset Decreased joint line height and offset Decreased joint line height and increased offset Increased joint line height and decreased offset Others*
34 30 29 22 14 8 9 6 7 1
All values given as mean (range); n — number of limbs (percentage). *Others includes: No change joint line height and increased offset — 5 knees. Increased joint line height and no change offset — 4 knees. Decreased joint line height and no change offset — 4 knees. No change joint line height and no change offset — 1 knee.
(26%) (23%) (22%) (17%) (12%) (26%) (29%) (19%) (22.5%) (3.5%)
Preoperative HKA angle (degrees)
Joint line height change (mm)
Posterior offset change (mm)
173 (158.5–203) 169.8 (153–183) 172.4 (163.5–193) 170.4 (160.5–201) 166.4 (152–176.5) 174.9 (168–180) 168.9 (155–175.5) 172.6 (163.5–180) 168.5 (165–171.5) 152
2.4 (0.2–11.2) − 2.1 (− 0.2 to − 5.4) − 2.6 (− 0.4 to − 8.4) 2.7 (0.3–9) 0 (− 4 to 4) 4.2 (0.3–11.2) − 2.3 (− 0.2 to − 5.4) − 4.2 (− 1.6 to − 8.4) 4.8 (2–9) 0
3.1 (0.2–12) − 4.2 (− 1 to − 12) 2.7 (0.4–9.4) − 4 (− 0.6 to − 20) 1.2 (0–6) 6.5 (2–12) − 7.3 (− 1.5 to − 12) 5.1 (2–9.4) − 7.7 (− 1 to − 20) 6
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The posterior femoral condylar offset is reported to be a very important factor determining the degree of knee flexion which can be possible after TKA [9,13]. This has been reported to be especially important in cruciate-retaining designs [14]. Hanratty et al. [15] in a review of 69 mobile-bearing cruciate-substituting TKAs reported a mean difference of + 1 mm between the pre- and postoperative values. In the current study the mean change in posterior offset postoperatively was −0.1 mm after surgery. However, 18% (23 knees) had a postoperative offset > ±5 mm compared to preoperative values where 12 knees had decrease in offset and 11 knees had increase in posterior offset. Although computer navigation was initially introduced to improve the accuracy of limb and component alignment, later versions of software were developed to also address gap equalization; however the accuracy of joint line and posterior femoral offset restoration has not been reported in the literature. Computer navigation helps to verify the position of the cutting blocks and also verify the accuracy of the bone cuts. However inaccuracies during bone cuts in navigated TKA may still occur due to variation of saw cuts within the jig which may lead to discrepancy between the final cut and the planned cut [16]. The optimized balancing option of the navigation software helps to adjust the size and position of the femoral component simultaneously with the distal femoral resection level in order to accurately balance and equalize extension and flexion gaps. The effect of changing the level of the distal femoral cut, the degree of femoral component flexion, and the anterior-posterior translation of the component and its size, on the flexion and extension gaps and joint line position can effectively be simulated by the surgeon on the screen with this and he can override the recommendations of the software if he so desires. This provides the surgeon the flexibility to make the necessary changes in the size and position of the femoral component and yet optimize the flexion and extension gap balance, all by simulating the changes in a “virtual” manner without actually performing the cuts. As the software determines the femoral component size (and thus the posterior offset) and distal femoral resection level (and thus the joint line), this study aimed to ascertain the accuracy with which it could do so in a consecutive large series of computerassisted TKAs done by a single surgeon using the tibia first technique. There are a few drawbacks of this study. During preoperative measurement of the joint line, in some cases with severe deformities and gross reduction in joint line space with bone loss, the joint line could at best be estimated on radiographs and this may have been a potential source of error. However, the authors have tried to minimize measurement errors by using fixed splints and the scaled x-ray technique. Besides, the authors have used the tip of the fibular head as a landmark to determine joint line height because it offers the advantage of a fixed single-point bony prominence which can be easily identified and remains fixed throughout the knee range of motion. Other landmarks which are typically used for measuring joint line height are the lower pole of the patella and the tibial tuberosity. However, the lower pole of the patella may change in position with knee flexion and extension and hence may vary the joint line height measure with knee position and the tibial tuberosity is a broad landmark where no single point can be consistently identified to measure the joint line height. The reliability of using the fibular head to measure joint line height is highlighted in the current study by the highly significant and close correlation for pre- and postoperative joint line height measurements on intra-and interobserver correlation analysis. Hauschild et al. [17] have reported that intraoperative navigation and postoperative radiographic measurements correlate well only when radiographic measurements are delayed beyond 2 weeks after surgery. In the current study, measurements were done on radiographs done at 6 weeks postoperatively which are in accordance to the findings of Hauschild et al. [17]. Similarly Yaffe et al. [18] and Oberst et al. [11] have reported poor correlation between pre- and postoperative radiographic measurements and intraoperative navigation measurements. However, the current study has
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not compared intraoperative navigation data to radiographic measurements and did not aim to determine reliability of navigation data vis-avis radiographic data and has relied on the “gold-standard” of using radiographic measurements only to determine change in joint line and offset. To clearly demonstrate that computer navigation can more accurately restore joint line and posterior offset in TKA, this study should have been conducted using conventional TKA controls. Joint line height and posterior femoral offset may be considered surrogate measures of restoration of extension gap and flexion gap respectively after TKA. Hence, excessive postoperative change in joint line height and posterior offset when compared to preoperative values may affect joint stability and function. The senior surgeon aimed for and achieved an extension and flexion gap within 2 mm of each other throughout the range of motion in all knees as recorded by navigation at the end of each procedure. However, correlating change in joint line and posterior offset with computer navigated TKA to postoperative functional outcome was not a part of the study. In conclusion, the current study clearly demonstrates that joint line and posterior femoral condylar offset can be restored in the majority of the knees to within 5 mm of their preoperative values in computer navigated, cruciate-substituting TKAs. The optimized gap balancing feature of the computer software allows the surgeon to simulate the effect of simultaneously changing the size and position of the femoral component and altering the distal femoral resection level on the joint line and gaps before performing the bone cuts. Conflict of interest statement The authors wish to state that no funds or benefits were received by any of the authors in support of this study/article from any source. Acknowledgments The authors thank Prof. Harshad Thakur, M.D, School of Health System Studies, TATA Institute of Social Sciences, Mumbai, India for his help in statistical analysis. References [1] Malviya A, Lingard EA, Weir DJ, Deehan DJ. Predicting range of movement after knee replacement: the importance of posterior condylar offset and tibial slope. Knee Surg Sports Traumatol Arthrosc 2009;17:491–8. [2] Bottros J, Gad B, Krebs V, Barsoum WK. Gap balancing in total knee arthroplasty. J Arthroplasty 2006;21(4 Suppl. 1):11–5. [3] Romero J, Stähelin T, Binkert C, Pfirrmann C, Hodler J, Kessler O. The clinical consequences of flexion gap asymmetry in total knee arthroplasty. J Arthroplasty 2007;22:235–40. [4] Wyss TF, Schuster AJ, Münger P, Pfluger D, Wehrli U. Does total knee joint replacement with the soft tissue balancing surgical technique maintain the natural joint line? Arch Orthop Trauma Surg 2006;126:480–6. [5] Cope MR, O'Brien BS, Nanu AM. The influence of the posterior cruciate ligament in the maintenance of joint line in primary total knee arthroplasty: a radiologic study. J Arthroplasty 2002;17:206–8. [6] Ryu J, Saito S, Yamamoto K, Sano S. Factors influencing the postoperative range of motion in total knee arthroplasty. Bull Hosp Jt Dis 1993;53:35–40. [7] Emodi GJ, Callaghan JJ, Pedersen DR, Brown TD. Posterior cruciate ligament function following total knee arthroplasty: the effect of joint line elevation. Iowa Orthop J 1999;19:82–92. [8] Figgie III HE, Goldberg VM, Heiple KG, Moller III HS, Gordon NH. The influence of tibial-patellofemoral location on function of the knee in patients with the posterior stabilized condylar knee prosthesis. J Bone Joint Surg Am 1986;68:1035–40. [9] Bellemans J, Banks S, Victor J, Vandenneucker H, Moemans A. Fluoroscopic analysis of the kinematics of deep flexion in total knee arthroplasty. Influence of posterior condylar offset. J Bone Joint Surg Br 2002;84:50–3. [10] Passing H, Bablok W. Comparison of several regression procedures for method comparison studies and determination of sample sizes. Application of linear regression procedures for method comparison studies in Clinical Chemistry, Part II. J Clin Chem Clin Biochem 1984;22:431–45. [11] Oberst M, Bertsch C, Lahm A, Wuerstlin S, Holz U. Regression and correlation analysis of preoperative versus intraoperative assessment of axes during navigated total knee arthroplasty. Comput Aided Surg 2006;11:87–91. [12] Selvarajah E, Hooper G. Restoration of the joint line in total knee arthroplasty. J Arthroplasty 2009;24:1099–102.
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[13] Massin P, Gournay A. Optimization of the posterior condylar offset, tibial slope, and condylar roll-back in total knee arthroplasty. J Arthroplasty 2006;21:889–96. [14] Arabori M, Matsui N, Kuroda R, Mizuno K, Doita M, Kurosaka M, et al. Posterior condylar offset and flexion in posterior cruciate-retaining and posterior stabilized TKA. J Orthop Sci 2008;13:46–50. [15] Hanratty BM, Thompson NW, Wilson RK, Beverland DE. The influence of posterior condylar offset on knee flexion after total knee replacement using a cruciate-sacrificing mobile-bearing implant. J Bone Joint Surg Br 2007;89:915–8.
[16] Biant LC, Yeoh K, Walker PM, Warwick Bruce JM, Walsh R. The accuracy of bone resections made during computer navigated total knee replacement. Do we resect what the computer plans we resect? Knee 2008;15:238–41. [17] Hauschild O, Konstantinidis L, Baumann T, Niemeyer P, Suedkamp NP, Helwig P. Correlation of radiographic and navigated measurements of TKA limb alignment: a matter of time? Knee Surg Sports Traumatol Arthrosc 2010;18:1317–22. [18] Yaffe MA, Koo SS, Stulberg SD. Radiographic and navigation measurements of TKA limb alignment do not correlate. Clin Orthop Relat Res 2008;466:2736–44.