Evaluation of anatomic references for tibial sagittal alignment in total knee arthroplasty

The authors aimed to demonstrate the relationship between the sagittal mechanical axis of the tibia and other reference axes of the tibia and fibula in patients with advanced osteoarthritis of the knee joints, and then to identify a reliable landmark in order to minimize posterior tibial slope measurement errors. We evaluated 133 osteoarthritic knees with neutral or varus deformity in 64 female and 8 male patients. Axial computed tomographic images of whole tibiae including knee and ankle joints were obtained and reconstructed using 3-dimensional imaging software. Angles between the mechanical axis (MA), the tibial anatomical axis (TAA), the anterior tibial cortex (ATC) and the fibular shaft axis (FSA) were measured, and then medial and lateral tibial slope angles were measured using all axes. Mean angles between MA and the other anatomical reference lines (TAA, ATC and FSA) were 0.9, 2.2 and −2.1°, respectively. The mean values of lateral tibial slopes with respect to MA, TAA, ATC and FSA were 8.7, 10, 12 and 7.3, respectively, and their intra- and inter-observer reliabilities were higher than those of medial tibial slopes. Although posterior tibial slope change markedly according to the reference axis used, the axes used in conventional TKA showed significant correlations with each other, and thus, may be used safely if differences with the mechanical axis are considered. Moreover, the lateral tibial slope might have advantages over the medial tibial slope in terms of restoration of the natural tibial slope.     

The accuracy of the extramedullary and intramedullary femoral alignment system in total knee arthroplasty for varus osteoarthritic knee

Purpose

The intramedullary (IM) femoral alignment system does not alway guarantee accuracy of the component position in the total knee arthroplasty (TKA). In some cases, the extramedullary (EM) femoral alignment system in total knee arthroplasty (TKA) is a useful alternative surgical option to adjust femoral component alignment. In the EM technique, accuracy of the femoral head center location is mandatory. The purpose of this prospective randomized study was to compare the alignment after TKA using two different femoral alignment systems.

Methods

From January 2009 to December 2009, 91 patients (106 knees) with osteoarthritis underwent TKA. The IM femoral alignment system was used in 50 TKAs, and the EM system was used in 56 TKAs. We measured the coronal, sagittal alignment of the femoral component, and overall alignment from full-length standing. Anteroposterior radiographs were taken 1 year after surgery.

Results

The overall limb alignment was 0.2° ± 1.9° varus in the EM group and 1.1° ± 1.9° valgus in the IM group (p = 0.001). The coronal alignment of the femoral component was 90.0° ± 1.1° in the EM group and 90.3° ± 1.2° in the IM group, not statistically different (n.s.). The sagittal alignment of the femoral component was 2.3° ± 1.7° in the EM group and 2.5° ± 1.0° in the IM group (n.s.). Clinically acceptable overall limb alignment was achieved in 91.1 % of EM group and 84.0 % of IM group (n.s.).

Conclusion

The present study suggests that by applying our EM technique that uses a newly designed mechanical axis marker system, the alignment of the femoral component and overall limb alignment is reliable and at least as accurate as the standard IM technique.

Level of evidence

I.     

Conventional or navigated total knee arthroplasty affects sagittal component alignment

Purpose

Navigation systems have recently been developed to achieve highly reliable prosthetic alignment in total knee arthroplasty (TKA). However, component alignment in the sagittal plane is less reliable than that in the coronal plane even when navigation systems are used. Previous reports examining men showed differences in targeted sagittal prosthetic alignments of TKA achieved using the conventional technique and various navigation systems. However, there have been few studies examining the use of this technique in women, who are the primary candidates for TKA.

Methods

Radiographs of the entire lower extremity were obtained from 20 elder women while standing and sagittal prosthetic alignments in TKA were planned using the conventional technique as well as three navigation approaches to establish reference frames, and the observations were compared.

Results

Sagittal alignments simulated using the radiographs for the conventional technique and navigation systems differed within a mean of 3.2°?±?1.7° (mean?±?SD) to 6.3°?±?2.0°. The use of different reference points on the distal femoral condyles (insertion point of the intramedullary rod, center of the anteroposterior direction of the femoral condyles, and most distal point of the femoral condyles) for each navigation system resulted in differences in the sagittal plane up to 3.0°?±?1.5°. The use of navigation systems resulted in a more hyperextended position between the femoral and tibial components compared to that for the conventional technique.

Conclusions

Targeted sagittal prosthetic alignments of TKA achieved using the conventional technique and various navigation systems differed in elderly women. The use of different reference points on the distal femoral condyle for navigation systems resulted in different alignment in the sagittal plane. This study showed that alignment tendencies are similar in men and women.

Level of evidence

Prognostic studies, IV.     

Influence of sagittal plane component alignment on kinematics after total knee arthroplasty

Purpose

Knee kinematics is pivotal to patient satisfaction and functional ability after total knee arthroplasty (TKA). The aim of this study is to examine the influence of sagittal plane component alignment as defined by femoral component angle (FCA), tibial slope (TS) and posterior condylar offset (PCO) on knee kinematics as defined by maximum extension angle (MEA), maximum flexion angle (MFA) and range of motion (ROM) after TKA.

Methods

This is a prospective, cross-sectional study of 105 osteoarthritic knees that underwent primary cruciate retaining TKA using a single implant design at a single tertiary institution. The sagittal plane component alignment was measured on weight-bearing true lateral radiographs taken day one post-operation and knee kinematics measured using a goniometer 1 year after TKA by the primary investigator.

Results

Although the MFA was influenced by gender (P = 0.04); age, gender and pre-operative kinematics did not otherwise influence post-operative knee kinematics. The prediction model for MFA was statistically significant (P = 0.03) and accounted for 8.4 % of the variance. FCA (r = 0.3, P = 0.01) and PCO (r = 0.2, P = 0.05) demonstrated a statistically significant correlation with MFA. However, the prediction models for ROM and MEA did not achieve statistical significance. FCA (r = 0.2, P = 0.02) demonstrated a statistically significant correlation with ROM.

Conclusion

The most important findings of this study are that the FCA demonstrates weak positive correlation with MFA and ROM and that PCO demonstrates weak positive correlation with MFA. However, TS does not contribute significantly to knee kinematics after TKA. This is clinically relevant as orthopaedic surgeons can increase the PCO in cruciate retaining TKA and the FCA within therapeutic limits to improve knee kinematics.

Level of evidence

II.

     

Accuracy of manual instrumentation of tibial cutting guide in total knee arthroplasty

Purpose

The aim of this study was to evaluate the accuracy of conventional instrumentation for tibial resection in total knee arthroplasty (TKA) as assessed by a computer-based navigation system during each phase of the surgical procedure. The hypothesis is that conventional instrumentation fails to achieve optimal accuracy in final implant positioning, thus leading to surgical errors.

Methods

Forty primary TKAs were performed. The resection guide was placed using an extramedullary guide. Accurate guide positioning was assessed by the navigation system prior to the osteotomy. The alignment measurement was repeated after resection and after component implantation in order to quantify the deviation caused by the manual positioning of the prosthetic components. A deviation ≥2° was considered unsatisfactory.

Results

In the frontal plane, unsatisfactory results observed were as follows: 15 % with reference to manual positioning of the resection guide and 10 % with reference to definition of the resection plane with a tendency towards varus malalignment. In the sagittal plane, unsatisfactory results were as follows: 45 % with reference to manual positioning of the resection guide and 40 % with reference to definition of the resection plane with a trend of decreased tibial slope angle. The deviation between bone resection and subsequent implant placement was ≥2° in none of the cases.

Conclusions

The study confirms the hypothesis that conventional instrumentation fails to achieve optimal accuracy in the positioning of the tibial component. During each phase of the surgical procedure, a tendency towards varus malalignment and a decreased tibial slope angle were observed.

Levels of evidence

II.     

Evaluation of tibial rotational alignment in total knee arthroplasty: a cadaver study

Various techniques exist for establishing tibial rotational alignment during total knee arthroplasty (TKA). The purpose of this study is to establish the most precise and reproducible method to assess tibial component rotational alignment during TKA by comparing the flexion-extension technique (ROM) and the Posterior-lateral Corner Locked Technique (PLCL). Twenty posterior stabilized TKAs were performed on cadavers. The rotation angles of the tibial components obtained using the two techniques were evaluated. The tibial component rotation axis obtained using the ROM technique and the PLCL method averaged, respectively, 0.35° (±4.2°) externally rotated and 0.34° (±3°) internally rotated to the Akagi line. No significant differences between the two methods were found and a high correlation exists between the two techniques (Pearson’s coefficient = 0.88). The ROM and PLCL techniques are both precise and reproducible methods to assess tibial component rotation during TKA. However, while the ROM technique is dependent on the correct positioning of the femoral component and the soft tissue balancing, the PCLC method is easier if a complete visualization of the posterior-lateral corner of the cut tibial plateau is achieved.     

Rotation of intramedullary alignment rods affects distal femoral cutting plane in total knee arthroplasty

Purpose

Intramedullary rods are widely used to align the distal femoral cut in total knee arthroplasty. We hypothesised that both coronal (varus/valgus) and sagittal (extension/flexion) cutting plane are affected by rotational changes of intramedullary femoral alignment guides.

Methods

Distal femoral cuts using intramedullary alignment rods were simulated by means of a computer-aided engineering software in 4°, 6°, 8°, 10°, and 12° of valgus in relation to the femoral anatomical axis and 4° extension, neutral, as well as 4°, 8°, and 12° of flexion in relation to the femoral mechanical axis. This reflects the different angles between anatomical and mechanical axis in coronal and sagittal planes. To assess the influence of rotation of the alignment guide on the effective distal femoral cutting plane, all combinations were simulated with the rod gradually aligned from 40° of external to 40° of internal rotation.

Results

Rotational changes of the distal femoral alignment guides affect both the coronal and sagittal cutting planes. When alignment rods are intruded neutrally with regards to sagittal alignment, external rotation causes flexion, while internal rotation causes extension of the sagittal cutting plane. Simultaneously the coronal effect (valgus) decreases resulting in an increased varus of the cutting plane. However, when alignment rods are intruded in extension or flexion partly contradictory effects are observed. Generally the effect increases with the degree of valgus preset, rotation and flexion.

Conclusion

As incorrect rotation of intramedullary alignment guides for distal femoral cuts causes significant cutting errors, exact rotational alignment is crucial. Coronal cutting errors in the distal femoral plane might result in overall leg malalignment, asymmetric extension gaps and subsequent sagittal cutting errors.

     

Accuracy of anatomical references used for rotational alignment of tibial component in total knee arthroplasty

Purpose  

This study aimed to research which was the most reliable of the four techniques based on local anatomic markers used to determine tibial component rotation in total knee arthroplasty, and whether the markers varied in knees with varus deformity.     

The dorsal pedis artery as a new distal landmark for extramedullary tibial alignment in total knee arthroplasty

Purpose

It is better to use multiple anatomical landmarks to reduce errors in component alignment in total knee arthroplasty. Therefore, it is worthwhile to find a new landmark that can be used as an addition to conventional ones. Herein, we assessed the dorsal pedis artery as a new distal landmark for extramedullary tibial alignment.

Methods

Fifty-two ankles in patients undergoing total knee arthroplasty and 10 ankles in normal controls were included. Color Doppler ultrasonography was used to locate the dorsal pedis artery at the level of the ankle joint. Conventional landmarks, including the tibialis anterior tendon, the extensor hallucis longus tendon, the extensor digitorum longus tendon, and the malleolar centre, were also located on ultrasound images. The distances between the ankle centre and each landmark were measured and compared.

Results

The dorsal pedis artery was absent in 2 patients and impalpable but visible with ultrasonography in other 2 patients. The dorsal pedis artery was located anatomically closest to the ankle centre in patients (0.4 ± 3.4 mm lateral). Statistical analysis showed that the dorsal pedis artery, the extensor hallucis longus tendon, and the malleolar centre were located significantly closer to the ankle centre comparing with the extensor digitorum longus tendon and the tibialis anterior tendon in both patients and controls (p < 0.001).

Conclusions

As long as the dorsal pedis artery exists, it can be used as an addition to the conventional landmarks in total knee arthroplasty. Using this new landmark will help reduce errors in coronal plane alignment of tibial component.

Level of evidence

II.     

Changes in patellar alignment after total knee arthroplasty

Although the results of total knee arthroplasty continue to improve, problems related to the patellofemoral joint remain significant. This study examined the factors affecting patellar alignment after total knee arthroplasty and subsequent changes in 56 knees during a postoperative period of 5.3 years. None of the knees examined displayed any clinical complications of the patellofemoral joint; no revision surgeries were necessary, with acceptable patellar alignment on average. The patellar resection angle had a strong influence on patellar alignment. Thinning of the patellar remnant on the medial side can increase postoperative lateral tilt, which leads to a need for lateral retinacular release. Although the changes in patellar alignment were minimal, the tendency that postoperative varus alignment resulted in patellar lateral tilt was observed. As postoperative femorotibial misalignment can lead to patellofemoral problems after total knee arthroplasty, surgeons need to pay scrupulous attention to femorotibial alignment and proper patellar preparation to decrease patellofemoral complications.     

Improved accuracy of component alignment with the implementation of image-free navigation in total knee arthroplasty

Accuracy of implant positioning and reconstruction of the mechanical leg axis are major requirements for achieving good long-term results in total knee arthroplasty (TKA). The purpose of the present study was to determine whether image-free computer navigation technology has the potential to improve the accuracy of component alignment in TKA cohorts of experienced surgeons immediately and constantly. One hundred patients with primary arthritis of the knee underwent the unilateral total knee arthroplasty. The cohort of 50 TKAs implanted with conventional instrumentation was directly followed by the cohort of the very first 50 computer-assisted TKAs. All surgeries were performed by two senior surgeons. All patients received the Zimmer NexGen? total knee prosthesis (Zimmer Inc., Warsaw, IN, USA). There was no variability regarding surgeons or surgical technique, except for the use of the navigation system (StealthStation^® Treon plus^®, Medtronic Inc., Minnesota, MI, USA). Accuracy of implant positioning was measured on postoperative long-leg standing radiographs and standard lateral X-rays with regard to the valgus angle and the coronal and sagittal component angles. In addition, preoperative deformities of the mechanical leg axis, tourniquet time, age, and gender were correlated. Statistical analyses were performed using the SPSS 15.0 (SPSS Inc., Chicago, IL, USA) software package. Independent t-tests were used, with significance set at P < 0.05 (two-tailed) to compare differences in mean angular values and frontal mechanical alignment between the two cohorts. To compute the rate of optimally implanted prostheses between the two groups we used the χ² test. The average postoperative radiological frontal mechanical alignment was 1.88° of varus (range 6.1° of valgus–10.1° of varus; SD 3.68°) in the conventional cohort and 0.28° of varus (range 3.7°–6.0° of varus; SD 1.97°) in the navigated cohort. Including all criteria for optimal implant alignment, 16 cases (32%) in the conventional cohort and 31 cases (62%) in the navigated cohort have been implanted optimally. The average difference in tourniquet time was modest with additional 12.9 min in the navigated cohort compared to the conventional cohort. Our findings suggest that the experienced knee surgeons can improve immediately and constantly the accuracy of component orientation using an image-free computer-assisted navigation system in TKA. The computer-assisted technology has shown to be easy to use, safe, and efficient in routine knee replacement surgery. We believe that navigation is a key technology for various current and future surgical alignment topics and minimal-invasive lower limb surgery.     

Tibial base design and patient morphology affecting tibial coverage and rotational alignment after total knee arthroplasty

Purpose

To understand interactions between total knee arthroplasty tibial base design attributes, variations in tibial morphology, and the resulting tibial coverage and rotational alignment.

Methods

Tibial anthropometric measurements, including aspect ratio (medial–lateral width/anterior–posterior length) and tibial asymmetry, were taken for 14,791 total knee arthroplasty patients and compared with the ability of four different commercial tibial base designs to cover the resected plateau. The anthropometric measurements were also compared with the resulting tibial base rotation, which occurred when rotating the base to maximize coverage.

Results

All four tibial base designs resulted in similar coverage ranging from 80.2 (4.7) % to 83.8 (4.6) %. Mean tibial base rotation when placed to maximize coverage ranged from 3.7 (4.4)° (internal) to 3.8 (4.5)° (external) relative to the medial third of the tibial tubercle. More asymmetric tibiae and tibiae with a lower aspect ratios resulted in increased internal tibial base rotation.

Conclusions

The four tibial base designs assessed provided similar levels of tibial bone coverage across the patient population, despite different design features. Rotating the tibial base to maximize coverage did not significantly increase the tibial coverage, but induced variability in tibial base alignment. Certain tibial anthropometrics may predispose particular patients to internal tibial base mal-rotation.     

全膝关节置换术中股骨假体旋转对线的比较研究

目的 比较全膝关节置换术(TKA)中以经上髁轴和股骨后髁轴外旋3°置放股骨假体外侧支持带的松解率.方法 150例膝关节骨性关节炎患者随机分成两组,一组采用股骨上髁轴确定股骨假体的旋转对线(股骨上髁组),另一组参照股骨后髁连线外旋3°确定股骨假体旋转对线(股骨向髁组).假体安装完毕后以"无拇指"技术评价髌骨轨迹,决定是否需要做外侧支持带松解.结果 股骨上髁轴组外侧支持带松解率为6.3%,股骨后髁轴组外侧支持带松解率为15.8%(P＜0.05). 结论 TKA中股骨假体旋转对线对于髌股轨迹的优劣有着显著影响,股骨上髁轴作为旋转对线的参照可以显著改善髌股轨迹,降低外侧支持带松解率.     

The medial border of the tibial tuberosity as an auxiliary tool for tibial component rotational alignment during total knee arthroplasty (TKA)

Purpose

The objective of this study was to quantify the amount of ensuing internal rotation of the tibial component when positioned along the medial border of the tibial tubercle, thus establishing a reproducible intraoperative reference for tibial component rotational alignment during total knee arthroplasty (TKA).

Methods

The angle formed from the tibial geometric centre to the intersection of both lines from the middle of the tibial tuberosity and its medial border was measured in 50 patients. The geometric centre was determined on an axial CT slice at 10 mm below the lateral tibial plateau and transposed to a slice at the level of the most prominent part of the tibial tuberosity. Similar measurements were taken in 25 patients after TKA, in order to simulate the intraoperative appearance of the tibia after making its proximal resection.

Results

This angle was found to be similar (n.s.) in normal and post-TKA tibiae [median 20.4° (range 15°–24°) vs. 20.7° (range 16°–25°), respectively]. In 89.3 % of the patients, the angle ranged from 17° to 24°. No statistical difference (p n.s.) was found between women and men in both normal [median ?20.7° (range 16°–25°) vs. 19.9° (range 15°–24°)] and post-TKA tibiae [median 21.4° (range 19°–24°) vs. 20° (range 16°–25°)].

Conclusion

This study found that in 90 % of the patients, the medial border of the tibial tuberosity is internally rotated 17°–24° in relation to the line connecting the middle of the tuberosity to the tibial geometric centre. Since this anatomical landmark may be more easily identifiable intraoperatively than the commonly used “medial 1/3”, it can provide a better quantitative reference point and help surgeons achieve a more accurate tibial implant rotational position.

Level of evidence

Cohort and case control studies, Level III.

     

The effect of posterior tibial slope on knee flexion in posterior-stabilized total knee arthroplasty

Purpose

To evaluate and quantify the effect of the tibial slope on the postoperative maximal knee flexion and stability in the posterior-stabilized total knee arthroplasty (TKA).

Methods

Fifty-six patients (65 knees) who had undergone TKA with the posterior-stabilized prostheses were divided into the following 3 groups according to the measured tibial slopes: Group 1: ≤4°, Group 2: 4°–7° and Group 3: >7°. The preoperative range of the motion, the change in the posterior condylar offset, the elevation of the joint line, the postoperative tibiofemoral angle and the preoperative and postoperative Hospital for Special Surgery (HSS) scores were recorded. The tibial anteroposterior translation was measured using the Kneelax 3 Arthrometer at both the 30° and the 90° flexion angles.

Results

The mean values of the postoperative maximal knee flexion were 101° (SD 5), 106° (SD 5) and 113° (SD 9) in Groups 1, 2 and 3, respectively. A significant difference was found in the postoperative maximal flexion between the 3 groups (P < 0.001). However, no significant differences were found between the 3 groups in the postoperative HSS scores, the changes in the posterior condylar offset, the elevation of the joint line or the tibial anteroposterior translation at either the 30° or the 90° flexion angles. A 1° increase in the tibial slope resulted in a 1.8° flexion increment (r = 1.8, R ² = 0.463, P < 0.001).

Conclusion

An increase in the posterior tibial slope can significantly increase the postoperative maximal knee flexion. The tibial slope with an appropriate flexion and extension gap balance during the operation does not affect the joint stability.

Level of evidence

Retrospective comparative study, Level III.     

Hindfoot alignment at one year after total knee arthroplasty

Purpose

It has previously been found that valgus hindfoot alignment (HFA) improves 3 weeks following total knee arthroplasty (TKA) for varus knee osteoarthritis (OA). In the present study, HFA was evaluated prior to TKA, as well as 3 weeks and 1 year following TKA. Using these multiple evaluations, the chronological effects of TKA on HFA were investigated.

Methods

The study included 71 patients (73 legs) who underwent TKA for varus knee OA. Radiograph examinations of the entire limb and hindfoot were performed in the standing position prior to TKA, as well as 3 weeks and 1 year following TKA. The varus–valgus angle was used as an indicator of HFA in the coronal plane. Patients were divided into two groups according to the preoperative varus–valgus angle: a hindfoot varus group (varus–valgus angle <76°) and a hindfoot valgus group (varus–valgus angle ≥76°). The changes in the varus–valgus angle were evaluated and compared in both groups.

Results

In the hindfoot valgus group, the mean ± standard deviation varus–valgus angle significantly declined from 80.5 ± 3.1° prior to TKA to 78.6 ± 3.7° 3 weeks following TKA and 77.1 ± 2.7° 1 year following TKA. However, in the hindfoot varus group, the mean varus–valgus angle prior to TKA (72.7 ± 2.6°) did not differ significantly from the mean varus–valgus angles 3 weeks (72.3 ± 3.3°) or 1 year (73.5 ± 3.0°) following TKA.

Conclusions

HFA improved chronologically in legs with hindfoot valgus as a result of the alignment compensation ability of the hindfoot following TKA. However, no improvement was noted in legs with hindfoot varus because the alignment compensation ability of the hindfoot had been lost. The patients with hindfoot varus should be attended for ankle pain in the outpatient clinic after TKA.

Level of evidence

III.

     

Modular tibial plate for minimally invasive total knee arthroplasty

Purpose

Aim of the study was to evaluate the clinical and radiological results of a modular tibial plate purposely designed for minimally invasive total knee arthroplasty.

Methods

We prospectively assessed the results of 200 primary total knee replacements performed through a minimally invasive approach using a dedicated modular tibial plate, a posterior stabilized knee prosthesis, and a fixed bearing in 175 patients (139 women and 36 men), undergoing surgery between 2005 and 2009 presenting knee osteoarthritis. Median age at the time of surgery was 69?years (52–88).

Results

No patients were lost at follow-up. 3 implants underwent revision. At a mean 3?years (1–5?years) follow-up, the HHS and KSS score showed a significant improvement, increasing, respectively, from a median value of 35–95 (78–100) and from 31 points in the “knee” and 45 points in the “function” score to a median of 95 (83–100) and 94 (81–100). Using the Kaplan–Meier method, the survival rate at 5?years was 97.9% with a 95% confidence interval.

Conclusion

The implant showed good results in either clinical or radiological assessment at a short/midterm follow-up with a high survival rate.

Level of evidence

Therapeutic study, Level IV.