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The Journal of Arthroplasty
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The Effect of Rotational Fixation Error of the Tibial Cutting Guide and the DistanceBetween the Guide and the Bone on the Tibial Osteotomy in Total Knee Arthroplasty
Tadashi Tsukeoka MD, PhD, Yoshikazu Tsuneizumi MD, PhD, Tae Hyun Lee MD, PhDDepartment of Orthopaedic Surgery, Chiba Rehabilitation Center, Chiba, Japan
The Conflict of Interest statement associated with thdx.doi.org/10.1016/j.arth.2012.12.008.
Computed tomography based computer simulation studies were made on fifty consecutive patients withosteoarthritis scheduled for TKA. Proximal tibial cutting was simulated with the cutting guide placed atdifferent rotational errors (−10°, 0°, 10° and 20° of internal rotation) and different distances (4 cm and 8 cm)between the alignment rod and the bone. Only ten degrees of rotation error with 8 cm of distance resulted inover 3° of varus or valgus tibial cut. Our study demonstrated that rotational mismatch between the proximaland distal part of the tibia should be avoided and the distance between the alignment rod and the bone shouldbe as short as possible to achieve proper tibial alignment.
Total knee arthroplasty (TKA) survivorship depends upon properalignment of the limb and prosthesis. Several studies have correlatedpoor outcomes with coronal malalignment of the components [1–3].Although numerous bone and soft tissue landmarks have beenadvocated [4–6], it is not easy to align an extramedullary guide tothe mechanical axis. Some authors have reported a greater frequencyof varus malalignment when the tibia is cut with use of anextramedullary alignment guide [7,8]. Almost all previously reportedstudies have emphasized the importance of the distal point of thetibia. Approximately a 5 mm difference in the horizontal plane causesonly 1° or less of change in the coronal alignment in patients with a300 mm long tibia (300 mm×tan1°=5.25 mm). We hypothesizethat the malalignment is not simply due to the difficulty of distalcentering, but also to other factors such as proximal centering,rotational errors of the cutting guide placement and the distancebetween the alignment rod and the bone. Although positioning theproximal center of an extramedullary guide at the center of theinterspinous eminence of the plateau is recommended in mostmanufacturers' manuals, when this landmark is used rotationalmalalignment seems to occur frequently. This is because the centerof the interspinous eminence has not been used to define theanteroposterior (AP) axis of the tibia accurately.
There is an extramedullary proximal tibial cutting guide systemwhich has a slit to fix the guide with a pin provisionally on the
extended line of the rod (Fig. 1). We currently use the medial borderof the tibial tubercle as the proximal center of the tibia with thisextramedullary cutting guide system because we can determine theAP axis of the tibia at the same time and confirm it directly during thesurgery. When we insert a long pin to fix the cutting block, we candetermine the AP axis of the whole cutting guide (at the distal part aswell as at the proximal part) so that it keeps the surgeon free frommaking a rotational mismatch between the proximal part and thedistal part of the tibia.
Mizu-uchi et al [9] emphasized the importance of considering therotational mismatch between the proximal tibia and the ankle joint.We hypothesized that the rotational error may occur mainly in theproximal part of the tibia, and that it is amplified by the distancebetween the alignment rod and the bone. We therefore conductedthis study to determine (1) the effect of the rotational error and thedistance between the alignment rod and the bone on the predictedtibial cutting alignment; (2) whether the medial border of the tibialtubercle could approximate the center of the proximal tibia; and (3)the accuracy of the predicted tibial cutting when there is no rotationalmismatch between the proximal and the distal part of the tibia, andwhen the tibial cutting guide was oriented using the medial border ofthe tibial tubercle and the soft tissue center of the ankle as theproximal and distal centers respectively.
Materials and Methods
Our study investigated 50 osteoarthritic knees in 50 consecutivepatients scheduled for TKA. The population consisted of 43 femalesand 7 males. None of our patients had evidence of trauma, infection,tumour, or any congenital disorder. The mean age of all patients was
Fig. 1. A tibial cutting guide system which has a slit to fix the guide with a pin provisionally on the extended line of the rod. The anteroposterior axis of the tibia can be determinedand confirmed directly during surgery. (B) Clinical use of the cutting guide system. (C) The distance between the guide and the bone was 4 cm. (D) The distance between thealignment rod and the bone was 8 cm.
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73.0 years (range 50 years to 88 years). Mean weight, height andbody mass index of the patients were 58.0 kg (range, 40 kg to 85 kg),152.0 cm (range, 138 cm to 169 cm), and 25.0 kg/m2 (range, 18.0 kg/m2 to 36.6 kg/m2), respectively. Hip-knee-ankle angle was deter-
Fig. 2. (A) Definition of the mechanical axis (MA) of the tibia. (B) Proximal tibial center. (C)posterior cruciate ligament (PCL) attachment with the medial border of the tibial tubercle.
mined from a standing weight-bearing anteroposterior radiograph ofthe whole lower extremity. The mean preoperative hip-knee-ankleangle was 14.1°±5.4° varus (range −1° to 34° varus). For computedtomography (CT) scans, the patient was placed in the supine position
The anteroposterior axis of the tibia was defined as a straight line connecting the mid-(D) Center of the distal tibial plafond.
Fig. 3. The distance between the center of the proximal tibia and the medial border ofthe tibial tubercle (d). External errors (e.r.) of 10° or internal errors (i.r.) of 10° and 20°on concentric circles 4 cm and 8 cm diameter were measured.
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on a table and the knee was extended while the ankle wasmaintainedat 0° of flexion with a leg holder. We performed preoperative high-resolution CT scans of all the affected lower limbs, including thewhole
Fig. 4. The distal tibial center for the virtual extramedullary guide was defined by soft tissue ctrue ankle center was measured (l).
tibia and fibula with a 16-detector CT unit (Toshiba Medical, Japan) inthe helical mode in a 512×512matrix, setting slice thickness at 1 mmas a part of a routine exam for TKA. We used CT-based preoperativeTKA planning software (ZedKnee LEXI Co., Ltd., Tokyo, Japan) todetermine the tibial mechanical axis (MA) and perform measure-ments. We defined the tibial MA as a straight line from the center ofthe appropriate-size Vanguard PS (Biomet Warsaw, IN, USA) tibialcomponent without posterior slope to the center of the distal tibialplafond. The center of the distal tibial plafond was determined bycircle approximation (Fig. 2). The AP axis of the tibia was defined as astraight line connecting the mid-posterior cruciate ligament (PCL)attachment with the medial border of the tibial tubercle (Fig. 2).
We measured the projected distance in the axial plane betweenthe center of the proximal tibia and the medial border of the tibialtubercle (Fig. 3. d). The distal tibial center for the virtual extra-medullary guide was defined by the soft tissue center at the level ofthe plafond (Fig. 4) and the projected distance in the axial planebetween the soft tissue center and the true ankle center wasmeasured (Fig. 4l). To examine the effects of rotational error in theproximal tibial cutting guide placement and the distance betweenthe alignment rod and the bone on the extramedullary guide in thecoronal alignment, we assumed rotational errors of 10° of externalrotation, or 10° and 20° of internal rotation, and defined the distancesbetween the alignment rod and the bone of 4 cm and 8 cmrespectively. The distal center for the virtual extramedullary guidewas defined as the soft tissue center of the ankle with an AP axisparallel to the correct AP axis of the proximal tibia (Fig. 5A).
The predicted coronal alignment of the tibial extramedullary guidecoronal alignment was measured when the AP axis of the ankle softtissue center was parallel to the proximal tibial axis. We also testedthe predicted alignment of the guide in case of an external or internalrotational error of 10° on the assumption that errors could occur evenif guide fixation was performed carefully (Fig. 5B). In addition, wecompared differences in the predicted coronal alignment of the tibialcutting guide coronal alignment between males and females.Significance was evaluated using of the Mann-Whitney U test. Weconsidered a P value of b0.05 as significant.
This study was approved by our Institutional Review Board.
enter at the level of the plafond and the distance between the soft tissue center and the
Fig. 5. (A) Effects of rotational error of fixation of the guide and the distance between the rod and the bone on predicted postoperative tibial coronal alignment. The distal end of theextramedullary guide was placed in front of the center of the ankle soft tissue center (on the line of the extended anteroposterior axis of the proximal part of the tibia). (B) Internal orexternal rotational error of 10° was simulated without mismatch between the proximal anteroposterior axis and the distal anteroposterior axis.
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Results
Table 1 shows the effect of the rotational error and the distancebetween the alignment rod and the bone on the predicted tibialcutting alignment.
We found that the medial border of the tubercle was very close tothe proximal tibial center (Table 2). Table 3 shows the accuracy of thepredicted tibial cutting when we oriented the tibial cutting guideusing the medial border of the tibial tubercle and the center of thedistal soft tissue as the proximal and distal centers respectively.
There were no significant differences in the predicted coronalalignment between males and females (P=0.23).
Discussion
Rotational errors in the proximal tibial cutting guide fixation effecta great change on the extramedullary guide coronal alignment, andthis was amplified by the distance between the alignment rod and thebone. The medial border of the tibial tubercle was very close to thecenter of the proximal tibia. The accuracy of the predicted tibialcutting was excellent when we used the medial border of the tibialtubercle and the center of the distal soft tissue as the proximal anddistal centers respectively. Even if we orient the cutting blockwith 10°
Table 1Effects of Rotational Error in the Proximal Tibial Cutting Guide Placement and the DistanAlignment.
The values are given as the mean and the standard deviation, with the range in parentheseA positive value indicates varus alignment.
of external or internal rotational error, the coronal alignment of thecutting guide was within 3°.
Although, Dennis et al [4] had excellent results from extramedul-lary alignment and recommended that the device be centered 3 mmmedial to the mid-point of the ankle, an error of more than 15 mm inthe horizontal plane would be necessary to cause a 3° deviation inalignment from the limb's mechanical axis in Japanese subjects whohave shorter tibiae than Caucasians (Fig. 2). Therefore, the occurrenceof a malalignment of the tibial cut cannot simply be due to thedifficulty in identifying the true center of the ankle. Furthermore,although some authors have reported a greater frequency of varusmalalignment when the tibia is cut using an extramedullaryalignment guide, consolidation of the medial plateau of the proximaltibia in varus knees and the posterior slope of the tibia will lead to avalgus cut of the tibia; the cutting block tends to fix the limb ininternal rotation due to the patellar tendon. Mizu-uchi et al [9]emphasized the importance of considering the rotational mismatchbetween the proximal tibia and the ankle joint. Our resultscorroborated the effect of rotational errors on tibial cutting blockalignment and showed that the error was amplified by the distancebetween the alignment rod and the bone. To improve the accuracy ofpostoperative alignment of the tibial component, it is extremelyimportant to be careful about the AP axis of the tibia at the proximaland the distal centers. Further, the alignment rod should be placed as
ce Between the Alignment Rod and the Bone on the Extramedullary Guide Coronal
Table 3The Effect of Rotational Fixation Error of the Guide on Predicted Coronal Alignment ifthe Ankle Center Is Determined By Proximal Tibial Anteroposterior Axis.
0.3°±0.5° (−0.6° to 1.3°) 1.2°±0.5° (0.3° to 2.2°) −0.6°±0.4° (−1.4° to 0.4°)
The values are given as the mean and the standard deviation, with the range inparentheses.A positive value indicates varus alignment.
Table 2The Distance to Tibial Centers From the Proximal and Distal Landmark.
Proximal Center (from theMedial Border of the Tubercle)
Distal Center (from theAnkle Soft Tissue Center)
0.6 mm±1.5 mm laterally(4.3 mm laterally to 5.5 mm medially)
1.3 mm±1.6 mm medially(3.5 mm laterally to 4.5 mm medially)
The values are given as the mean and the standard deviation, with the range inparentheses.
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close as possible to the bone. We therefore recommend usingextramedullary proximal tibial cutting guide systems that have a slitso they can be provisionally fixed with a pin on the extended line ofthe rod. This will determine the AP axis of the whole cutting guide,keeping the surgeon free frommaking a rotational mismatch betweenthe proximal part and the distal part of the tibia. We also recommendthe use of the tibia tubercle as a proximal landmark because we candetermine the AP axis of the cutting guide as well as the proximalcenter of the tibia.
Our study has limitations. First, we did not have many obesepatients in this series and further studies are needed to prove theaccuracy of using the soft tissue center as the distal center in thesepatients. We believe the distance between the soft tissue center andthe true ankle center will have a limited effect on the coronalalignment of the cutting guide because the maximum differencebetween the soft tissue center and the true ankle center was only4.5 mm in our study. Second, we analyzed alignment only in thecoronal plane, which is known to be associated with a poor outcome.Third, we studied only the simulation without the posterior tibialslope cut to simplify the problem. When we cut the proximal tibiawith a posterior slope, the internal rotational error of fixation of theproximal tibial cutting guide leads to a valgus cut and the externalrotational error leads to a varus cut. Duffy and Kramer [10] noted thata rotational error of 30o with a 7° cutting block will produce anangulation of up to 3° measured in the coronal plane. Therefore wesuggest that a rotational error of 10° has a limited effect on thepredicted tibial cutting guide coronal alignment.
In conclusion, our study demonstrated that rotational mismatchbetween the proximal and distal part of the tibia should be avoided,and the distance between the alignment rod and the bone shouldbe as short as possible to achieve proper tibial alignment in totalknee arthroplasty.
References
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5. Rajadhyaksha AD, Mehta H, Zelicof SB. Use of tibialis anterior tendon as distallandmark for extramedullary tibial alignment in total knee arthroplasty: An anato-mical study. Am J Orthop 2009;38:E68.
6. Schneider M, Heisel C, Aldinger PR, et al. Use of palpable tendons forextramedullary tibial alignment in total knee arthroplasty. J Arthroplasty2007;22:219.
7. Reed MR, Bliss W, Sher JL, et al. Extramedullary or intramedullary tibial alignmentguides: a randomised, prospective trial of radiological alignment. J Bone Joint SurgBr 2002;84B:858.
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