Knee Surg Sports Traumatol Arthrosc DOI 10.1007/s00167-014-3236-6
Improving tibial component alignment in total knee arthroplasty G. Cinotti · P. Sessa · A. D’Arino · F. R. Ripani · G. Giannicola
Received: 5 December 2013 / Accepted: 11 August 2014 © European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2014
Abstract Purpose Tibia torsion may influence the accuracy of extramedullary instrumentations in total knee arthroplasty (TKA). This study assessed whether the effect of tibial torsion may be overcome using a surgical technique in which the extramedullary rod is aligned to reference points at the proximal tibia only. Methods A consecutive series of 94 knees that underwent TKA were analyzed. In the first 47 knees (group 1), a standard procedure for tibial component alignment was performed while in the second group of 47 knees, a modified surgical technique was used including the alignment of the extramedullary rod to the reference points at the proximal tibia only (group 2). Lower limb, femoral, and tibial component alignment were measured on postoperative long-leg radiographs. Results Femorotibial mechanical axes angles were similar in the two groups. Femoral component alignment also did not differ between the groups. A neutral alignment of the tibial component was achieved in 17 and 34 % of the knees in group 1 and group 2, respectively (p = 0.04). A malalignment of the tibial component >3° was found in 34 % of knees in group 1 compared with 4 % of those in group 2 (p = 0.0001). Conclusions Coronal alignment of the tibial component may improve by setting the extramedullary rod in line with anatomical references in the proximal tibia only. This technique appears to bypass the influence of tibial torsion
G. Cinotti (*) · P. Sessa · A. D’Arino · F. R. Ripani · G. Giannicola Department of Anatomical, Histological, Forensic Medicine and Orthopaedics Sciences, University “La Sapienza”, Rome, Italy e-mail: [email protected]
on the alignment of the extramedullary guide at the distal tibia. The clinical relevance of the study is that using this technique, the rate of malalignment of the tibial component may be reduced compared to a standard technique in which a fixed reference is used at the ankle joint. Keywords Total knee arthroplasty · Tibial cut · Tibial component alignment · Total knee alignment · Extramedullary instrumentations
Introduction Several investigations have shown that a proper TKA alignment influences knee biomechanics and long-term survival of the implants [12, 13, 16, 32]. However, current instrumentations are not entirely satisfactory in this respect since a varus–valgus malalignment of tibial component >3° has been reported in 2–40 % of cases [5, 14, 24, 33, 39]. A major issue in achieving a correct coronal alignment of tibial component is tibial torsion, i.e., the axial rotation of the tibia along its longitudinal axis, which causes a rotational mismatch between proximal and distal epiphysis [3, 10, 19, 25, 38]. It has been reported that, due to tibial torsion, the distal epiphysis is externally rotated compared to the proximal one by an average of 19°–28° [6, 10, 38]. This leads to a lateral shift of the anterior projection of the mechanical axis at the ankle joint compared to AP axes at the proximal tibia, a lateral shift which may be even greater when distal alignment is set at the intermalleolar point since the lateral malleolus exhibits a greater thickness compared to the medial one . As a result, if the extramedullary rod is not shifted medially at the ankle joint to compensate for tibial torsion and the different thickness of medial and lateral malleolus, and the extramedullary guide is aligned
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with the center of the intermalleolar distance, a varus tibial cut is likely to occur [6, 25]. In keeping with this, a varus malalignment of the tibial component is the most frequent error found when extramedullary systems are used  and even recent investigations reported a tibial malalignment in varus in 28 % of cases . As tibial torsion shows a wide variability among subjects, the extreme values ranging between 3° and 49° [3, 6, 10, 25, 38], it may be difficult to assess during surgery to what extent the extramedullary guide should be translated medially, at the level of the ankle joint, to compensate for tibial torsion. In this study, we investigated the accuracy of a new surgical technique in which the influence of tibial torsion on the alignment of the tibial component is bypassed by positioning the extramedullary guide in line with the proximal tibia only. Our hypothesis was that a more accurate and reproducible orientation of the tibial component may be achieved when the extramedullary instrumentation is aligned with anatomical landmarks of proximal tibia compared to standard techniques in which reference points in proximal and distal tibia are taken.
Materials and methods Eighty-six consecutive patients (94 knees) who underwent conventional TKA between January 2011 and July 2012 were included in the study. All patients had primary or secondary osteoarthritis of the knee. Patients with previous fractures around the knee or femoral and tibial shaft fractures and those with previous knee osteotomy were excluded. There were 49 women and 37 men with a median age of 72 years (range 53–86 years). In the first 43 patients (47 knees) treated between January and November 2011, a standard procedure was used (group 1) while in the second 43 patients (47 knees) operated on in the following year, Table 1 Patients demographic and preoperative characteristics in the two groups Alignment
Age Gender (F/M) Side (R/L) Weight (kg) BMI (kg/m2) Severity of deformitya
71.2 (56–85) 32:15 25:22 77.7 (65–108) 31.2 (24–42) −3.6° (−17 to 15)
72.3 (54–87) 34:13 23:24 79.2 (63–105) 30.7 (23–44) −4.3 (−19 to 17)
n.s. n.s. n.s. n.s. n.s. n.s.
Preoperative ROMb 102 (78–137)
Mean values are outsides parenthesis, and range is inside parentheses BMI body mass index a
Severity of deformity: varus (−)/valgus (+)
ROM range of motion, n.s. nonsignificant difference
a modified surgical technique was performed (group 2). There was no significant difference between the two groups in terms of preoperative deformity, severity of bone loss, preoperative knee motion, and body mass index (Table 1). Seventy-eight patients had a diagnosis of osteoarthritis and 8 of rheumatoid arthritis. Surgical technique All operations were performed by a single surgeon using a standard medial parapatellar approach. A cruciate retaining TKA with fixed bearing (Columbus, Aesculap, Germany) was implanted in all cases using a cementing technique. In no case, a patellar replacement was performed. The coronal femoral alignment was set, using an intramedullary guide, according to the anatomical–mechanical axis angle measured on preoperative radiographs, to achieve a 90° cut to the mechanical axis. Femoral component rotation was aligned at 3° of external rotation with respect to the posterior condylar axis. The tibial alignment was achieved using an extramedullary instrumentation, having planned a 90° cut in the coronal plane and 3° of posterior slope in the sagittal plane. In the coronal plane, the extramedullary guide was set, at the proximal tibia, in line with an anterior projection of mechanical axis (AP axis) connecting the posterior tibial notch with the medial one-third of the tibial tuberosity (TT), in both groups [21, 22] (Fig. 1). At the distal tibia, the extramedullary guide was set, in group 1, to a point located 5 mm medially to the center of the intermalleolar distance [4, 30] and, in group 2, in line with the proximal alignment on the TT, the extramedullary rod being locked in neutral alignment (varus–valgus = 0) in the malleolar clamp. Thus, at the ankle joint, the extramedullary rod was not aligned with anatomical landmarks; it was left free to rotate in the axial plane, according to the proximal tibial alignment, but not in the coronal plane (varus–valgus) (Fig. 1). With respect to the ankle joint and intermalleolar center, the positioning of the extramedullary rod changed depending on the degree of tibia torsion of the operated leg. In patients with reduced tibia torsion, the extramedullary rod was close to the intermalleolar center while, in those with marked tibia torsion, it lied close to the lateral border of the medial malleolus (Fig. 2). Once the tibial cut was performed, the rotational alignment of tibial tray was achieved combining the flexion–extension self-alignment technique, in which femoral rotation alignment drives tibial rotation tray to avoid a rotational mismatch between femoral and tibial component, with an alignment located between the medial border and medial one-third of the TT . In particular, we marked with electrocautery on the proximal tibia the medial border and medial one-third of the TT. We then performed knee flexion–extension with the trial components in place and we set the tibial tray alignment at the point which best combined the two techniques.
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Fig. 1 Alignment of extramedullary rod at the proximal tibia in line with an anterior projection of mechanical axis (AP axis) connecting the posterior tibial notch with the medial one-third of the tibial
tuberosity (TT) (arrow). The curved dotted line represents the TT (a). Adjustment of extramedullary rod alignment at the distal tibia according to proximal tibial alignment (b)
Implant alignment evaluation
Limb and components alignment was assessed on postoperative long-leg radiographs taken 3 months after surgery. To reduce a possible bias due to malrotation alignment, the rotation of the knee was assessed under fluoroscopic control before radiograph was taken; it was judged as satisfactory when a superimposition of one-third of the fibula head by the tibia was observed . The measurements included mechanical femorotibial angles and components alignment. The mechanical femorotibial (MFT) angle was calculated between femoral and tibial mechanical axes (Fig. 3). The coronal alignment of tibial and femoral component was assessed by calculating the angle between their respective mechanical axes and a line tangent to the plateau of tibial component and to the distal condyles of femoral component, respectively . The measurements were repeated in the sagittal plane. A MFT angle of 0° ± 3° of varus (−)/valgus (+) and a component alignment of 0° ± 3° varus (−)/ valgus (+) were considered within the normal range . Malalignment was diagnosed when the MFT angle and femur or tibial component alignment differed more than 3° from the mechanical axis. Measurements were taken by two orthopedic surgeons who were not involved in the operation nor were they aware of the surgical procedure used in each patient. The investigation was performed according to the institutionally approved guidelines, having received an informed consent from all the included patients.
A power analysis was conducted before the beginning of the study to determine the minimum sample size needed to detect a difference of 1° ± 2° . Type-I error was set at 0.05 (α 3°) in the coronal plane was present in 16 and in 2 knees in group 1 and group 2, respectively (p = 0.0001). A valgus malalignment of the tibial component (>3°) was found in no patients in both groups (Table 2; Fig. 5).
Discussion The most important finding of this study is that, in performing a TKA, the alignment of the tibial component may be improved using a surgical technique in which the extramedullary rod is set in line with anatomical landmarks in the proximal tibia only. This technique seems to reduce inaccurate placements of the extramedullary guide at the ankle joint, which may occur due to the effect of tibial torsion on the anterior projection of the mechanical axis at the distal tibia.
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Fig. 4 Box plots showing the distribution of tibial component alignment in the two groups. The boxes represent the median and interquartile range (IQR), and error bars represent the range of data
Table 2 Tibial component alignment Alignment Standard
No. of cases (%)vr/vg No. of cases (%)vr/vg Neutral 1° 2° 3° 4° 5°
8 (17) 6 (13) 13 (28) 4 (8) 14 (30)
0 3/3 11/2 4/0 14/0
16 (34) 6 (13) 15 (32) 8 (17) 2 (4)
0 6/0 10/5 5/3 2/0
0.04 n.s. n.s. n.s. 0.0008
vr Varus, vg valgus * Difference between the two groups (Fisher’s exact test) ** Outliers with 4° and 5° of malalignment Fig. 3 a Radiographs showing the measurements of MFT angle. b, c Coronal alignment of femoral and tibial components
Extramedullary and intramedullary systems are commonly used for the alignment of tibial component in standard TKA. They showed similar accuracy in the presence of normal tibial morphology [8, 18, 23], but extramedullary instrumentations were found more accurate when tibial bowing or posttraumatic deformities are present [5, 8, 20, 27]. The limitation of extramedullary systems is that their accuracy relies on the identification of anatomical landmarks that should guide the surgeon in positioning the extramedullary rod in line with the mechanical axis. In the proximal tibia, several reference points including tibial tuberosity, posterior cruciate ligament insertion,
intercondylar eminence, and center of tibial plateau [1, 2, 7, 21, 22, 30] have been investigated. However, at the distal tibia and ankle joint, most of the anatomical landmarks usually recommended, i.e., the intermalleolar distance or a definite point from it, the second metatarsal, and the anterior tibialis tendon, have not been validated in anatomical studies [2, 8, 17, 30, 33, 39]. Schneider et al.  found that, among palpable tendons, the extensor hallucis longus (EHL) was the most accurate landmark to identify the center of ankle joint; however, foot supination was found to affect EHL position at the ankle joint and cause a tendon displacement >1 cm. The dorsal pedis artery has been proposed as useful landmark for extramedullary instrumentations, since it lies close to the center of the talar dome and is less affected by foot position than palpable tendons . However, the dorsal pedis artery is not always palpable in
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Fig. 5 Tibial component alignment in the two groups. The cases outside the vertical dotted lines indicate outliers
elderly patients , and the accuracy with which it may be identified at surgery, particularly in obese patients, is not known. A line connecting the proximal and distal one-third of the anterior tibial border was found a reliable bony landmark in Asiatic tibiae but, in the coronal plane, its accuracy was not superior to conventional method . A further issue which may limit the accuracy of extramedullary instrumentation is tibial torsion, a wellknown anatomical feature of the tibia which is virtually present in all subjects; it shows a normal distribution with an apex of the bell curve around 35° in Caucasian tibiae . As a result of tibial torsion, the distal epiphysis is externally rotated compared with the proximal one, and the anterior projection of tibial mechanical axis at the ankle joint is shifted laterally compared with that at the proximal tibial epiphysis [6, 25]. If such a lateralization is not taken into account and the extramedullary guide is aligned with the center of the intermalleolar distance, a varus tibial cut is likely to occur [6, 25]. However, to what extent the extramedullary rod should be translated medially with respect to the intermalleolar distance has yet to be established. A medial translation of 9–11 mm from the intermalleolar distance was found to be more in line with the anterior projection of the mechanical axis at the proximal tibia than a medial translation of 5 mm . However, as investigations have also shown that tibial torsion exhibits a wide variability among patients [3, 6, 10, 25, 38], a fixed position of the extramedullary rod at the ankle joint will unlikely be in line with the anterior projection of mechanical axis in every patient. As it may be difficult to assess at surgery the amount of tibial torsion of the operated leg, we tested the accuracy of a different technique in which the extramedullary rod is aligned with a proximal projection of the tibial mechanical axis at the medial one-third of the TT, but not with reference points at the ankle joint. The extramedullary rod
was locked in neutral alignment (varus–valgus = 0) in the malleolar clamp, and its rotational alignment was in line with the proximal AP axis at the medial one-third of the TT. In the control group, the extramedullary guide was set 5 mm medially to the intermalleolar distance, since this is one of the most frequently used landmarks at the ankle joint in TKA [4, 30, 39]. We found that using this technique, the overall alignment of the operated limb was similar in the two groups but the percentage of knees with neutral alignment of tibial component was significantly higher in the proximal alignment technique group. The percentage of malalignment of femoral component was also similar in the two groups; however, malalignment of tibial component >3° was significantly reduced in group 2 compared to group 1. In the latter, a varus malalignment was observed in all cases, confirming that extramedullary instrumentations lead more likely to varus than valgus malalignment. In keeping with our hypothesis, it was found that by setting the extramedullary rod to the anterior projection of the mechanical axis at the proximal tibia and maintaining the same axial orientation of extramedullary rod at the ankle joint, the effects of tibial torsion on the distal alignment of the extramedullary systems may be neutralized. In particular, since the proximal tibial epiphysis is internally rotated with respect to the distal one, the extramedullary rod aligned with the proximal AP axis rotates internally and shifts toward the medial malleolus to such an extent as the difference between proximal and distal AP axes determined by tibia torsion. The extramedullary rod remains closely parallel to the mechanical axis being locked in neutral alignment in the malleolar clamp. A theoretical drawback of the procedure is that an erroneous alignment of the extramedullary rod at the proximal tibia may be propagated to the distal tibia; however, the low rate of malalignment found in this study would indicate that such a drawback should rarely occur.
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The study has some limitations. First, in our control group, the extramedullary rod was aligned with a point located 5 mm medially to the intermalleolar distance, and results could be different when other reference points, including palpable tendons, are used at the ankle joint. Likewise, proximal AP axis connecting the tibial notch with the medial one-third of TT was used as proximal reference; therefore, results may be different using others proximal AP axes. Second, we did not assess the relationship between the extramedullary rod and the intermalleolar center using the new technique; these data could have further demonstrated that, to achieve a correct alignment of tibial component, the extramedullary rod may not be in line, at the ankle joint, with a fixed landmark in every patient. However, this assessment is time-consuming, and its degree of accuracy may not be easily demonstrated. Third, the degree of tibial torsion differs between Caucasian and Asiatic populations [15, 28], and results may not apply to Asiatic patients. Fourth, although efforts have been made to take radiographs with proper rotational alignment of the lower limb, measurements of limb and implant alignment may be more accurate using CT scans.
Conclusion The accuracy of extramedullary instrumentation in achieving a proper coronal alignment of the tibial component may be affected by tibia torsion, which causes a lateral shift of the anterior projection of the mechanical axis at the ankle joint where the extramedullary rod should be aligned. As the range of tibia torsion is extremely wide in the general population, it may be difficult to achieve a neutral alignment of the tibial component using a fixed anatomical reference at the ankle joint in every patient. Our results showed that the effects of tibial torsion on the alignment of extramedullary instrumentation may be neutralized by setting the extramedullary rod in line with the AP axis in the proximal tibia only. This technique was found to reduce the rate of malalignment of tibial component.
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