Effect of Medial Opening Wedge High Tibial Osteotomy on Intraarticular Knee and Ankle Contact Pressures Eduardo M. Suero,1 Yaman Sabbagh,1 Ralf Westphal,2 Nael Hawi,1 Musa Citak,1 Friedrich M. Wahl,2 Christian Krettek,1 Emmanouil Liodakis1 1

Trauma Department, Hannover Medical School, Hannover, Germany, 2Institute for Robotics and Process Control, Braunschweig University of Technology, Braunschweig, Germany Received 29 October 2013; accepted 20 November 2014 Published online 4 March 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jor.22793

ABSTRACT: High tibial osteotomy (HTO) is a commonly used surgical technique for treating moderate osteoarthritis (OA) of the medial compartment of the knee by shifting the center of force towards the lateral compartment. Previous studies have documented the effects of HTO on the biomechanics of the knee. However, the effects of the procedure on the contact pressures within the ankle joint have not been as well described. Seven cadavers underwent an HTO procedure with sequential 5˚ valgus realignment of the leg up to 15˚ of correction. An axial force of up to 550 N was applied and the intraarticular pressure was recorded. Minor valgus realignment of the proximal tibia does not significantly alter the biomechanics of the ankle. However, moderate-to-large changes in proximal tibial alignment result in significantly decreased tibiotalar contact surface area and in changes in intraarticular ankle pressures. These findings are clinically relevant, as they provide a biomechanical rationale for the diagnosis and treatment of ankle symptoms in the setting of lower limb malalignment or after alignment correction procedures. ß 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:598–604, 2015. Keywords: high tibial osteotomy; intraarticular contact pressure; osteoarthritis; ankle biomechanics

High tibial osteotomy (HTO) is a commonly used surgical technique for treating moderate osteoarthritis (OA) of the medial compartment of the knee. It is usually performed in young, active patients, as it allows for a return to high activity levels and preserves bone stock for a possible knee arthroplasty should there be progression of the OA.1 Through either a medial opening wedge or a lateral closing wedge technique, the surgeon aims to unload the diseased compartment, leading to improved pain and function. Previous studies have documented the effects of HTO on the biomechanics of the knee.2–12 Opening wedge HTO may lead to increased patellofemoral peak pressure.2,3 A moderate-to-large increase in the valgus alignment of the lower limb can result in decreased contact pressures in the medial compartment.4,13,14 Sagittal plane changes in tibial slope lead to changes in the tibiofemoral resting point, contact pressure, cruciate ligament tension, and dynamic knee stability.7–12 However, the effects of the procedure on the biomechanics of the ankle joint have not been well described. Jeong et al. reported on a patient who developed persistent ankle pain after undergoing bilateral HTO for the treatment of OA of both knees.15 A change in the ankle tilt after HTO was deemed as the most likely cause of pain due to possible changes in the contact area of the ankle joint and the patient was treated with a corrective supramalleolar osteotomy. Other studies have shown that total knee arthroplasty Eduardo M. Suero and Yaman Sabbagh contributed equally to this work. Grant sponsor: German Research Foundation; Grant sponsor: Robert Mathys Foundation. Correspondence to: Eduardo M. Suero (E-mail: [email protected]) # 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

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(TKA), in which lower limb alignment is also corrected, results in variations in hindfoot alignment.16,17 In a series of 142 TKA cases, Lee et al. showed that 22% had newly developed or progressive ankle OA. They correlated the incidence of ankle OA after TKA with increased talar tilt, which may lead to an altered contact surface area.17 Tallroth et al. detected concomitant ankle OA in 29% of patients who were surgically treated for OA of the knee, with greater ankle tilt being associated with more degenerative changes in the ankle joint surface.18 More recently, Elson et al. presented a case of a patient with ankle pain and instability in whom an HTO was performed, resulting in significant clinical improvement.19 We designed an experiment to quantify the changes in the magnitude and the distribution of the contact pressures within both the knee and the ankle joints during axial loading of the lower limb. We hypothesized that valgus realignment of the lower limb would result in changes in the magnitude of the contact pressures and contact area within the ankle joint.

METHODS This study was approved by our institution’s ethics committee. Four fresh-frozen whole-body human cadavers (eight leg specimens) were obtained. One specimen was discarded due to having an absent anterior cruciate ligament (ACL) and Grade III osteoarthritis, leaving seven specimens available for testing. Specimens were fully thawed at room temperature prior to surgery. The cadavers were placed supine on an operating table. A medial parapatellar arthrotomy was first performed on all specimens to explore the intraarticular knee space and assess for ligamental or cartilaginous damage. The superficial fibers of the medial collateral ligament were released and a medial, L-shaped opening wedge high tibial osteotomy was performed using the technique described by Lobenhoffer and Agneskirchner (Fig. 1).1,20 With the aid of fluoroscopy, two 2.5-mm Kirschner wires were inserted 5 cm distal to the

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Figure 1. An L-shaped proximal tibial osteotomy was performed in all specimens. The tibial tuberosity was left intact and the lateral tibial cortex was carefully preserved.

joint line, starting proximal to the pes anserinus and extending to the level of the tip of the fibula at the lateral cortex. An oblique osteotomy was performed in the posterior two-thirds of the medial aspect of the tibia distal to the Kirschner wires and parallel to the tibial slope, leaving an intact 10-mm lateral bone bridge. A second osteotomy was started in the anterior one-third of the tibia at an angle of 135˚, leaving the tibial tuberosity intact. Osteotomes were carefully inserted and used to open the osteotomy up to the desired angle. An external fixator was used to secure the open-wedge osteotomy during testing at each of three steps of alignment correction: 5˚, 10˚, and 15˚. A navigation system (Vector Vision, BrainLAB, Munich, Germany) was used to track and record leg alignment changes in real time. Minimally invasive reference arrays

Figure 2. The experimental setup involved placing the leg into an axial loading device, which attached proximally to the pelvis via Schanz screws. The foot was fixed onto a distal baseplate in neutral alignment. A handle located at the distal end of the device allows for one person to apply an axial load to the leg in the caudal-craneal direction. A load cell attached to the baseplate, and in line with the direction of force, measures the applied load and torque. These data are transferred to a computer and can be visualized in real time, along with the axis of the knee, using a 3D image-based computer navigation system.

were attached to the femoral and tibial shafts. An isocentric mobile C-arm with 3D imaging capability (Siremobil ISO-C 3D, Siemens, Germany) was used to scan the knee joint. The imaging dataset was transferred to the navigation system and registration was performed. The combination of the acquired 3D imaging and computer navigation data allows for real-time monitoring of the mechanical axis. Hence, we were able to follow intraoperative changes in alignment live through a computer interface.

Table 1. Intraarticular Pressures and Contact Area in the Knee after Valgus Realignment of the Proximal Tibia

Knee Lateral compartment

Alignment change Native 5˚ 10˚ 15˚

Alignment change Native 5˚ 10˚ 15˚

Mean pressure (N/mm2) 1636.6 2182.1 3016.1 3937.3 Mean contact area (mm2) 4.1 4.5 4.1 4.0

95% CI 1527.7 2015.8 2774.3 3750.7

1745.5 2348.3 3257.9 4124.0

95% CI 3.9 4.4 4.0 3.9

4.2 4.6 4.2 4.0

Medial compartment

Change

p-value

Mean pressure (N/mm2)

– 33% 84% 141%

– .480 .008 .008

2150.0 2209.8 1665.2 772.1

Change

p-value

Mean contact area (mm2)

– 11% 1% 2%

– .055 .104 .004

4.6 5.0 3.6 2.5

95% CI 2073.2 2073.7 1483.2 681.5

2226.8 2345.9 1847.2 862.7

95% CI 4.5 4.9 3.5 2.3

4.7 5.1 3.8 2.6

Change – 3% 23% 64%

Change – 9% 21% 46%

p-value – .018 .751 .017

p-value – .014 .012 .355

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Figure 3. Large valgus changes in proximal tibial alignment resulted in increased contact pressures in the lateral compartment of the knee (A) and decreased pressures in the medial compartment (B).

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lateral sides of the tibial plateau, following the manufacturer’s guidelines. An additional sensor was inserted into the ankle joint, carefully centered over the talar dome surface. The sensors were anchored to the skin covering the posterior aspect of the knee and the ankle using #0 silk sutures. Baseline measurements were taken for each leg in its native alignment. An axial loading force was applied to the leg in the caudal-craneal direction and gradually ramped up from 0 to 550 N.23 Intraarticular contact pressure (kg) and contact area (mm2) data were measured and collected in real time. Statistical analyses were performed using Stata/SE 12.1 (StataCorp LP, College Station, TX). Multiple linear regression models were constructed to estimate changes in contact pressure and contact surface area in the medial and lateral compartments of the knee and in the ankle, in response to 5˚, 10˚ and 15˚ changes in mechanical alignment. The following variables were also measured in real time during testing and were included as covariates in our models: side; force (axial, horizontal, and vertical); torque (axial, horizontal and vertical); changes in knee alignment (varus and valgus; ante- and retrocurvature; and axial angle); and native ankle joint line alignment (neutral, varus, or valgus). For all tests, a was set at 0.05. Results are presented as mean and 95% confidence interval (95% CI); as percentage change; or as regression coefficient (Coef.) and standard error (SE), wherever appropriate.

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Additionally, a lead-impregnated axis board was used to track and confirm mechanical alignment changes after each stepwise increase in medial tibial opening.21 The axis board is placed underneath the leg, with the long axis passing through both the center of the femoral head and the center of the talus. Correct positioning is confirmed using fluoroscopy. Once the board is in place, subsequent radiographic images are used to identify the location of the mechanical axis in relation to the center of the knee joint and to quantify alignment changes by measuring the angle between the mechanical axis line and the tibial plafond outline. A previously developed stainless-steel device was used to axially load the leg.22 The apparatus is attached to the pelvis using Schanz screws and the foot is secured to a distal plate. An integrated load cell connects to the computer through a cable, so as to track in real time the applied load and torque (Fig. 2). Pressure-sensitive sensors (K-Scan 4000, Tekscan, South Boston, MA) were used to measure intraarticular contact pressures. Each sensor is 0.1 mm thin and its pressuresensitive area contains 62 sensels per cm2. The opposite end is inserted into a handle designed to read the data being collected during testing and to transfer it to a computer through a USB interface. Prior to testing each specimen, a sensor was inserted into the knee joint and carefully centered over both the medial and

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Figure 4. Changes in proximal tibial alignment did not result in important variations in contact area in the lateral compartment (A). Contact area progressively decreased in the medial compartment with changes to the alignment of the leg (B). JOURNAL OF ORTHOPAEDIC RESEARCH APRIL 2015

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Figure 5. Moderate-to-large proximal tibial alignment corrections led to a significant decrease in contact pressures in the ankle joint.

Figure 6. Tibiotalar contact area progressively decreased with moderate and large proximal tibial alignment changes.

RESULTS Effect on Intraarticular Knee Pressures A summary of knee data is presented in Table 1. Small changes in mechanical alignment (5˚) resulted in a nonsignificant 33% increase in lateral compartment contact pressures compared to the intact leg (p > 0.05). However, larger changes in alignment correction resulted in an 84% increase in contact pressures at 10˚ and a 141% increase at 15˚ (p < 0.05) (Figs. 3A & 4). In the medial compartment, a 3% increase in pressure at 5˚ (p < 0.05) was followed by a 23% decrease at 10˚ (p > 0.05) and a 64% decrease at 15˚ (p< 0.05) (Figures 3B and 4). The intraarticular surface contact area did not significantly change in the lateral compartment after 5˚ and 10˚ corrections (p > 0.05) (Fig. 5A). A significant decrease of 2% was seen after a 15˚ correction (p < 0.05). In the medial compartment, a 5˚ change in alignment resulted in a 9% increase in contact area (p < 0.05). A change in alignment of 10˚ resulted in a 21% decrease in contact area (p < 0.05), while a 15˚ change in alignment resulted in a significant 46% decrease in contact area (p > 0.05) (Fig. 5B).

Effect on Intraarticular Ankle Pressures Contact Area A summary of ankle data is presented in Table 2. A 5˚ change in mechanical alignment did not significantly alter intraarticular ankle pressures (p > 0.05). However, larger corrections decreased contact pressures by 14% at 10˚ (p < 0.05) and by 17% at 15˚ (p < 0.05) (Figs. 6 and 7). Contact area did not change significantly after a 5˚ correction. Significant decreases in contact area were seen at 10˚ (19%; p < 0.05) and at 15˚ (20% ; p < 0.05) (Figure 8). Additional Findings in the Regression Model Ankle tilt was a significant predictor in our models (p < 0.05), with valgus or varus ankle joint line alignment significantly affecting the load distributions in the knee and ankle joints. A significant interaction between mechanical alignment correction and ankle tilt was also detected (p < 0.05). A summary of the linear regression models is presented in Table 3.

Table 2. Intraarticular Pressures and Contact Area in the Ankle after Valgus Realignment of the Proximal Tibia

Ankle Alignment change Native 5˚ 10˚ 15˚ Alignment change Native 5˚ 10˚ 15˚

Mean pressure (N/mm2) 2700.0 3197.0 2308.5 2249.3

95% CI 2509.5 2996.5 2100.6 2083.9

Mean contact area (mm2) 3.5 3.4 2.8 2.8

Change 2890.4 3397.4 2516.4 2414.7

95% CI 3.4 3.3 2.7 2.7

– 18% 14% 17% Change

3.5 3.5 2.9 2.8

– 1% 19% 20%

p-value – 0.061 0.007 0.015 p-value – 0.663 0.014 0.001

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R-squared

845.94 692.58

644.59 600.14 1,114.86 796.56 769.36 703.23 861.71 3.85 9.90 14.89 231.37 17.28 25.89 24.59 159.60 92.20 1,122.37

670.64 603.52

801.64 345.66 2,507.64 2,628.08* 346.98 2,550.51* 869.22 7.81 50.92* 3.03 649.91* 133.73* 210.22* 29.07 45.55 259.89* 1,832.65 0.92

479.63 462.14 343.53

SE

360.75 1,792.32* 3,416.31*

Coef.

Mean pressure (N/mm2)

0.24 0.40

0.69* 0.70

0.92

0.30 2.17* 1.04 0.01* 0.01 0.01 0.20* 0.09* 0.02 0.08* 0.19 0.14* 0.10

0.51 0.32 0.48 0.00 0.00 0.01 0.05 0.03 0.02 0.03 0.11 0.05 0.61

0.59 0.46

0.32 0.40

2.48* 1.49*

0.38 1.68*

0.33 0.35 0.20

SE

0.78 0.67 0.91*

Coef.

Mean contact area (mm2)

Lateral compartment

Knee

0.86

2,027.12 921.73 1,124.99 13.86* 18.74* 31.04 56.99 66.17 6.45 83.02 440.21* 91.14 2,026.45

91.09 899.19

911.17 1,028.98

2,592.45* 1,220.39

1,263.24* 258.31 1,351.30*

Coef.

0.81 0.33 0.86 0.56 0.28 0.00 0.01 0.01 0.10 0.05 0.02 0.02 0.10 0.08 0.80

3.75* 1.48* 4.27* 1.40* 3.55* 0.00 0.04* 0.02 0.05 0.12 0.13* 0.09* 0.53* 0.10 1.06 0.95

0.49 0.51

0.67 0.41

0.46 0.30 0.34

SE

2.00* 2.12*

2.61* 1.68*

(reference) 454.98 499.73

(reference) 486.32 515.13 (reference) 1,306.21 986.68 (reference) 978.69 578.69 779.40 4.41 3.55 12.77 131.74 36.78 32.04 43.97 171.36 79.60 1,302.02

1.60* 1.08* 0.34

Coef.

Mean contact area(mm2)

(reference) 392.73 778.80 415.26

SE

Mean pressure (N/mm2)

Medial compartment

Coef.

0.92

4,258.59* 746.52 3,219.30* 6.07 5.53 22.84* 234.03* 338.72* 87.59* 41.41 20.47 496.93* 3,413.96

3,295.45* 183.96

1,880.04* 1,487.79*

7,402.27* 3,905.02*

Ankle

433.27 521.70 527.18 3.35 9.52 2.43 89.33 38.23 32.38 56.54 90.61 63.68 1,601.57

426.53 643.78

275.85 394.63

631.10 689.90

205.51 290.11 397.26

SE

Mean pressure (N/mm2)

472.64 1,168.86* 1,339.63*

Regression Results for the Estimation of the Effect of Alignment Correction on Knee and Ankle Load Distribution

Alignment change Native 5˚ 10˚ 15˚ Ankle tilt Neutral Valgus Varus Alignment change by ankle tilt interaction 5˚ by neutral 5˚ by valgus 5˚ by varus 10˚ by neutral 10˚ by valgus 10˚ by varus 15˚ by neutral 15˚ by valgus 15˚ by varus Left side Axial force Horizontal force Vertical force Axial torque Horizontal torque Vertical torque Varus-valgus angle change Ante-retrocurvature angle change Axial angle change Constant

Table 3.

0.90

0.47 0.28 2.06* 0.00 0.00 0.00 0.07 0.08* 0.04* 0.04* 0.05 0.02 3.42*

0.06 1.06*

0.01 0.05

1.58* 0.49

0.17 0.36* 0.88*

Coef.

0.38 0.25 0.15 0.00 0.00 0.01 0.07 0.02 0.01 0.01 0.05 0.01 0.50

0.25 0.29

0.38 0.45

0.37 0.28

0.37 0.10 0.14

SE

Mean contact area (mm2)

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DISCUSSION The results of the current study are consistent with previous research showing how valgus realignment of the lower limb leads to unloading of the medial compartment of the knee. More importantly, this is the first study that has quantified the changes in contact pressure within the ankle joint following a proximal opening-wedge tibial osteotomy and with a stepwise increase in the magnitude of alignment correction. There has been limited research examining the relationship between changes in lower limb alignment and contact pressures in the ankle joint. Knupp et al. performed supramalleolar osteotomies of the tibia and found that isolated valgus tibial osteotomy with a congruent ankle joint resulted in an anteromedial shift of the center of force over the talar surface.24 Forst et al. studied the effects of HTOs on the motion of the ankle joint and demonstrated a change in the biomechanical properties of the joint, driven by a change in the rotational direction of the fibula.25 They found that maximum dorsiflexion of the ankle before an HTO resulted in external rotation of the fibula, while internal rotation was seen after an HTO was performed. In the current study, we have shown how changes in alignment in the proximal tibia can affect the loading conditions within the ankle joint. Progressive valgus realignment of the lower limb resulted in a linear reduction in tibiotalar contact area. These results compare favorably to those presented by Tarr et al., who demonstrated that large angular proximal and distal tibial deformities resulted in a significant reduction in contact area in the tibiotalar joint.23,26 This redistribution of pressure over a smaller surface of the talar dome could have long-term implications for the biomechanics of the ankle. This is especially germane considering that previous studies have linked realignment procedures about the knee (both HTO and TKA) with the development and progression of ankle OA or ankle pain.15–19 It seems likely that the subtalar joint plays an important role in maintaining adequate alignment and force distribution.27 The anatomical preservation of the fibula during a medial opening wedge HTO may also prevent more dramatic changes in contact pressures and surface area in the ankle.28 These results may also provide additional insight for the treatment of osteochondral defects of the talar dome. Bruns and Rosenbach studied the axial load in the ankle and determined that peak pressure tended to be located over the medial talar edge, which the most common location for the occurrence of osteochondral lesions.29 Additionally, they showed that the contact area within the ankle joint was dependent on the alignment of the hindfoot and the tibia, with varus or valgus alignment shifting the loads to the medial and lateral edges of the talar dome.30 In the presence of an osteochondral lesion, an ipsilateral increase in axial load can lead to impaired healing.31,32 As we

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have shown, proximal tibial alignment leads to changes in ankle pressures, which could be helpful in guiding the treatment of patients with osteochondral defects of the talus. Tibial realignment procedures could be used to offload the diseased area in the ankle joint, with the aim of improving the healing environment for talar lesions. There are several limitations to this research. We only tested the specimens in biostatic axial loading conditions. Our current setup does not allow for testing in knee flexion or to simulate dynamic in vivo joint movements. In vivo muscular forces were not simulated in this experimental setup. It is possible that musculotendinous structures, in particular the Achilles tendon, could exert some influence on the distribution of forces within the ankle joint. Additionally, we were not able to measure the forces acting on the medial and lateral gutters. It is reasonable to expect that, with valgus realignment of the proximal tibia, there will be a lateral transfer of load towards the fibula. Another possible limitation concerns the alignment of the ankle joint line before the alignment correction procedure is made. Previous studies have shown a relationship between load distribution and ankle tilt.18 We controlled for this possible confounder by measuring the ankle joint alignment in all of the specimens used and by adjusting for ankle tilt in our regression models. The results confirm that ankle tilt does significantly affect the load distribution inside the knee and the ankle and it should be taken into account when performing loading experiments of the lower limb. This is also clinically relevant, since surgical outcome could be affected by the alignment of the patient’s ankle. In summary, we conclude that small valgus realignment of the proximal tibia does not significantly alter the biomechanics of the ankle. However, moderate-tolarge changes in proximal tibial alignment result in significantly decreased tibiotalar contact surface area and in changes in intraarticular ankle pressures. These findings are clinically relevant, as they could provide guidance to surgeons in cases of angular tibial deformity or ankle joint pain.

ACKNOWLEDGMENTS None of the authors have any professional or financial affiliations that could have biased this study. Funding awarded by the German Research Foundation (DFG) was used to construct the device used for axially loading the limb and the computer interface used to monitor changes in the knee joint during the experiments. Funding awarded by the Robert Mathys Foundation (RMS) was used for all materials required for performing the surgeries and for performing ankle measurements.

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Effect of medial opening wedge high tibial osteotomy on intraarticular knee and ankle contact pressures.

High tibial osteotomy (HTO) is a commonly used surgical technique for treating moderate osteoarthritis (OA) of the medial compartment of the knee by s...
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