The effects of anterolateral tenodesis on tibiofemoral contact pressures and

kinematics

Eivind Inderhaug 1, Joanna M Stephen 2,3, Hadi El-Daou 2, Andy Williams 3, Andrew A. Amis 2,4

Work performed at Imperial College London

1 Orthopaedic Surgery Department, Haraldsplass Deaconess Hospital, Bergen, Norway.

2 Biomechanics Group, Mechanical Engineering Department, Imperial College London, London, UK

3 Fortius Clinic, Fitzhardinge Street, London, UK

4 Musculoskeletal Surgery Group, Imperial College London School of Medicine, Charing Cross Hospital, London, UK.

Corresponding author:

Prof Andrew Amis,Mechanical Engineering Department,Imperial College London,London SW7 2AZ,UK

+44 (0)20 7594 7062

a.amis@imperial.ac.uk

The effects of anterolateral tenodesis on tibiofemoral contact pressures and

kinematics

ABSTRACT:

Background: Anterolateral tenodeses are increasingly popular in combination with intra-

articular ACL reconstructions. Despite the perception of risk of over-constraint and lateral

osteoarthritis, evidence is lacking on the effect of graft tensioning on knee kinematics and

intra-articular compartmental joint pressures.

Purpose: To investigate tibiofemoral joint contact pressures and kinematics related to an

anterolateral lesion and the effectiveness of a MacIntosh tenodesis in restoring these when

varying (1) graft tension and (2) tibial rotation during graft fixation.

Study design: Controlled laboratory study.

Methods: Eight fresh frozen cadaveric knees were tested in a customised rig with femur

fixed and tibia free to move from 0-90 ° flexion. The quadriceps and iliotibial band were

loaded using a weighted pulley system. At 30° intervals of knee flexion, tibiofemoral contact

pressures were measured using a Tekscan sensor and tibiofemoral kinematics were

recorded using an optical tracking system. The knee was tested intact and then with an

anterolateral soft tissue transection. MacIntosh tenodeses were then tested in a randomized

order with 20 N or 80 N graft tension, each with the tibia held in neutral intact alignment or

free to rotate.

Results: Tibial anterior translation and internal rotation were significantly increased and

lateral contact pressures significantly reduced compared to the intact knee following

anterolateral soft tissue cutting (P<0.05). Contact pressures were restored with fixed neutral

tibial rotation combined with a 20 N or 80 N graft tension or by a free hanging tibia with 20 N

graft tension (All: P>0.5). Grafts tensioned with 80 N caused significant over-constraint both

when the tibia was fixed and free hanging (All P<0.05). Increases in the lateral tibiofemoral

contact pressures were also seen when the tibia was free hanging and 80 N was used for

graft tension (P<0.05).

Conclusions: Anterolateral soft tissue injury caused reduced lateral tibiofemoral contact

pressures and altered tibiofemoral kinematics: these were restored with a MacIntosh

procedure performed with 20 N graft tension. If 80 N graft tension was used, increased

lateral contact pressures and over-constraint in internal rotation were seen. With the tibia

free hanging intact contact biomechanics were restored when 20 N graft tension was

applied, but 80 N graft tension significantly increased lateral tibiofemoral pressures and over-

constrained internal rotation. The kinematic and contact pressure effects were significantly

correlated: changes in tibial rotation caused by increased graft tension correlated with

elevated lateral articular contact pressure.

Clinical relevance: Controlling tibial position appears important when tensioning

anterolateral tenodeses. However the identified changes were subtle and may not be

clinically significant in a fully loaded knee.

Key terms: Lateral tenodesis, joint contact pressure, ACL, anterolateral ligament, ALL

What is known about this subject: Although anterolateral tenodeses are hypothesized to

increase the risk of osteoarthritis, there is no clear evidence to support this. Furthermore no

previous studies have examined intraarticular tibiofemoral pressures when performing these

procedures.

What this study adds to existing knowledge: The current work identifies that an

anterolateral lesion results in altered tibiofemoral pressures and kinematics, and that these

can be restored using a MacIntosh anterolateral tenodesis using the appropriate graft

tension (20 N). Findings also suggest that controlling the rotation of the tibia during graft

fixation is important to avoid over-constraining the joint.

INTRODUCTION:

The current gold standard surgical treatment of anterior cruciate ligament (ACL) deficiency is

an arthroscopically assisted intraarticular ACL reconstruction using an auto- or allograft.

Historical procedures for such instability included a variety of extra-articular techniques that

were found to effectively stabilize the knee at the time of surgery 4,6,10,27,29. They were,

however, largely left behind as isolated procedures due to poor long-term outcomes 18, 34, 37.

The addition of such an extraarticular procedure has in some recent studies been found to

give better control of knee stability and improvement in patient outcomes as compared to

isolated intraarticular procedures 31,36,45,48. Further, clinical, radiological and biomechanical

clues point towards possible concomitant anterolateral injuries that occur at the time of an

ACL tear 16,24,30,44,47. It can be theorised that such lesions might be a cause of the residual

knee joint laxity found in some knees if using only an intraarticular surgical procedure when

treating an ACL tear.

Numerous historical descriptions provide technical details on how the extraarticular so-called

lateral tenodeses were performed 3,4,9,12,22,27,28,32. Although the type of graft, harvesting

technique and final fixation were thoroughly described, few studies addressed how much the

graft should be tensioned and at what rotation the leg should be held (e.g. neutral or

externally rotated) at graft tensioning and fixation. Some evidence points towards a risk of

over-constraining the knee joint if too much graft tension is applied at graft fixation 19,21,39.

Also, despite little evidence in the literature, a prevailing opinion is that the lateral procedures

might change joint pressures – and therefore effectively increase the risk of postoperative

osteoarthritis 15,17,37,38. To our knowledge, there are no studies that have investigated the

effect on intraarticular joint pressures from lateral procedures.

Despite the increasing popularity of anterolateral procedures, there is still a lack of scientific

evidence regarding critical surgical steps such as graft tensioning. Such knowledge can help

refine surgical techniques in an effort to prevent potential long-term complications such as

tibiofemoral osteoarthritis, when performing anterolateral procedures in combination with

ACL reconstruction. With the use of a modified MacIntosh tenodesis, a commonly used

procedure that has been found to have biomechanically favorable properties 25, the present

study therefore aimed to:

1. Investigate any potential changes in TFJ contact pressures (peak and mean pressures)

and kinematics following sectioning of the anterolateral structures of the knee;

2. Determine whether any potential changes in TFJ contact pressures and kinematics could

be restored using a MacIntosh tenodesis.

3. Investigate how articular contact pressure is affected by tension in the tenodesis.

4. Investigate any potential relationship between rotational position of the knee and lateral

peak and mean contact pressures.

Based on observations of TFJ biomechanics, it was hypothesized that excessive graft

tension would pull the lateral aspect of the tibia into external rotation and posterior

translation, thus causing over-constraint of tibial internal rotation, and elevated lateral

compartment contact pressures.

MATERIALS AND METHODS:

Specimen preparation

After approval from the local ethical committee, eight unpaired right-sided cadaveric knees

(mean age 61.5, range 55-65, 4 male specimens) with no history of knee injury or disease

were obtained from a tissue bank. Specimens consisted of 250mm of femur and tibia, were

kept in polyethylene bags and stored at -20° C and thawed for 24h before use. Preparation

took place on one day, the knees were then stored in a refrigerator overnight at 3 °C and the

data gathering took place the following day.

Skin and subcutaneous fat were dissected away from each knee, with care taken to

preserve the medial and lateral retinacula. The fibula was fixed to the tibia with two cortical

bone screws to control valgus laxity of the fibula after the distal part was excised. The tibia

was cut to 150 mm and the femur to 200 mm length, and an intramedullary (IM) rod

cemented into each. An arthroscopy was performed in all knees to confirm a normal ACL

and to rule out meniscal or cartilage injuries. Throughout testing specimens were kept moist

with normal water spray.

Specimen loading

The quadriceps were dissected and separated into five components: rectus femoris and

vastus intermedius, vastus medialis longus, vastus medialus obliquus, vastus lateralis

longus and vastus lateralis obliquus. The iliotibial band (ITB) was separated proximally. The

knee was mounted in a test rig using the femoral IM rod with the femoral posterior condylar

axis aligned horizontally to standardise rotation, and the patella facing upward (Figure 1).

While the femur was locked in the rig, the tibia was restrained in extension by a rod

transversely in front of the distal end of the intramedullary rod that could be moved in 30°

increments from 0° to 90° of flexion by passing the transverse rod through predrilled holes in

the side walls of the test rig, and did not inhibit secondary movements (The other five

degrees of freedom of motion were unconstrained by the test rig.). Therefore the axis of

internal rotation at the tibial plateau could shift in response to ligament damage, for example.

A clamping device, which could fix the tibia in any position, was attached to the tibial IM rod.

At the start of the experiment the neutral rotation position of each knee was marked and

used for reference during the experiment.

Using a weight and pulley-system all the quadriceps heads and ITB were tensioned

separately according to their anatomical orientations and normalized physiological cross-

sectional areas (PCSA) 14 , as used in former studies 41-43. Muscle force vectors were

mimicked by the pulley system, and two loading conditions were used during the study. (1) A

tension corresponding to an open kinetic chain knee extension motion used a total load of

175 N allocated to the quadriceps heads in concordance with their PCSA 14. Based on prior

work 33, the ITB was loaded with 30 N. (2) A resting state condition, using 10% of the knee

extension tension was used to mimic muscular tension at rest.

Figure 1 The knee was mounted in a rig that held the femur rigidly, while the tibia was free

to move. A distal transverse rod passed across the tibial intramedullary rod, to block knee

extension at 0, 30, 60 and 90 degrees of flexion. Each component of the quadriceps and ITB

were tensed in anatomic directions (only two shown for clarity). A Tekscan pressure sensor

was inserted into the knee below the quadriceps-muscle via the supra-trochlear capsule, and

pulled into the tibiofemoral joint using arthroscopically placed guide-sutures which emerged

from posteriorly. Note that the pressure sensor is shown boldy for clarity, but was only 0.1

mm thick.

Kinematic measurements

Optical trackers with passive reflective markers (BrainLAB, Feldkirchen, Germany) were

mounted rigidly on the tibia and femur with custom-made blocks. A Polaris (NDI, Waterloo,

Ontario, Canada) optical tracking system was used to collect kinematic data.

Fiducial markers attached to the bones were digitized using a stylus probe to create

coordinate systems. Zero degrees of flexion was defined as the position at which the tibial

and femoral rods were parallel as seen in the sagittal plane. Anterior-posterior translation

was calculated as the perpendicular distance from the midpoint of the femoral epicondylar

axis to the tibial coronal reference plane, whilst rotation was defined around the central tibial

axis. All motions described were tibial movements relative to the femur. The Polaris tracking

system had been reported to have a translational accuracy of 0.04 mm and a rotational

accuracy of 0.03 degrees 23.

Measurement of tibiofemoral contact pressures

A 4011 K-scan sensor (Tekscan Inc, MA, USA) was used for measuring tibiofemoral lateral

and medial contact pressures, with a new sensor for each knee to avoid cumulative

degradation of accuracy. This outcome measure was chosen because elevation of cartilage

stresses is thought to be a factor predisposing to degenerative changes in-vivo. The sensor

had a size of 68x44 mm and a saturation pressure of 3.47 kPa. Calibration and equilibration

was performed as advised by the manufacturer. During the initial arthroscopy of the knee,

four passing sutures were placed at medial and lateral positions in the posterior part of the

lateral and medial compartments. Using these sutures, the sensor could be inserted through

an incision in the supratrochlear capsule and pulled around the distal femur so that it could

be secured in the tibiofemoral compartment (Figure 1). An arthroscopic drill guide (Acufex

Director, Smith & Nephew, Andover, USA) was used to make a 2 mm drill hole anterior in

the lateral tibial compartment, at the edge of the loadbearing area, so it could not affect the

contact pressure readings. A blunt rod could then be inserted to imprint on the pressure film

to make sure there was no movement of the film during testing. Finally, to examine the

hypothesis that excessive graft tension would pull the lateral aspect of the tibia into external

rotation and posterior translation, the movement of the centre of pressure on the tibial lateral

condyle was calculated for the difference between the native state and with the tenodesis

tensed to 80 N with the tibia free to rotate (which the kinematic data showed was the largest

combined translation plus rotation movement).

Surgical procedure

The knee was mounted in the testing rig where all the surgery was performed. Each knee

was first flexed and extended 10 times to minimize error from inherent stress relaxation

properties of the soft tissues. After testing of the intact knee, a mid-substance incision was

made in a distal to proximal direction in the iliotibial band (ITB). The lateral collateral

ligament (LCL) was identified and preserved. A cut was then made in the tissues deep to the

ITB and anterior to the LCL, from the lateral epicondyle and distally to the lateral joint line to

cut the ALL and capsule 11,21. Further, proximal to LCL the retrograde, supracondylar, and

proximal insertions of the ITB were identified and carefully transected 24. The knee with the

transected soft tissues was then tested.

Figure 2 – A mid substance 15 x 150 mm strip of the ITB with the tibial attachment to Gerdy´s tubercle intact was used as for the MacIntosh tenodesis. The graft was tunnelled deep to the LCL and fixed with an interference screw in a bone-tunnel at the insertion of the intermuscular septum.

The modified MacIntosh procedure was performed using a 15 x 150 mm central strip of the

ITB 5,21,22,29 (Figure 2). The formerly placed cut was extended to demarcate this strip. The

distal end of the graft was left attached to Gerdy’s tubercle, while the rest of the graft was

carefully freed from the underlying tissue. The proximal end was whipstitched to allow graft

passage and tensioning. The graft was routed deep to the LCL and into an 8 mm

transfemoral tunnel positioned proximal to the femoral epicondyle – at the insertion of the

lateral intramuscular septum. At the medial side of the knee, the lead sutures were led out of

the bone tunnel and a free-hanging weight, applying the force used for tensioning (20 N or

80 N), was mounted to the whipstitched end. After 30 seconds pre-conditioning, an 8x25mm

interference screw (RCI, Smith & Nephew, Andover, USA) was inserted into the lateral

aperture of the bone tunnel for graft fixation at 30° of flexion; the surgeon watched to ensure

that screw insertion did not push the graft into the tunnel, which would have raised the

tension. Additional back-up fixation was obtained by tying the whipstitch-sutures over a

bone-screw on the medial femoral cortex

Testing protocol

The order of the surgical procedures was block randomized so that each of the procedures

was evenly performed early/late during testing to avoid any bias due to deterioration of the

tissue. A recently published study 21 found that 20 N tension for lateral tenodeses could

restore native knee kinematics. Additionally, piloting prior to the study suggested that a

typical maximum manual pull (e.g. used in ACL reconstructions) averaged 80 N. Thus all

lateral procedures were performed with both 20 N and 80 N tensioning. Further, to

investigate the effects of rotation of the tibia at fixation, two conditions were used: the tibia

either (1) hung unrestrained during fixation (That is: it was free to move in all degrees of

freedom except extension-flexion), or (2) was held in its initial neutral rotation (using the

clamping device formerly described).

Kinematic data and contact pressures were recorded at 0°, 30°, 60° and 90° of knee flexion,

and the following 6 states of the knee were tested: (1) Intact, (2) Anterolateral lesion, (3)

MacIntosh 20 N neutral rotation, (4) MacIntosh 20 N free hanging knee, (5) MacIntosh 80 N

neutral rotation, (6) MacIntosh 80 N free hanging knee. States (1) and (2) were in that order,

whilst states (3) through (6) were randomized for each knee.

Data analysis

Assuming a critical P value of 0.01 (the overall alpha of 0.05 had a Bonferroni-correction for

5 comparisons, since the only comparisons were for the five knee states versus the intact

state) 8 cadaveric knees were found to be sufficient to detect a change of 1.3 mm of anterior

translation (an effect size of d=1.35 with a power of 80% based on prior work for which data

were available, whereas contact pressure data were not available prospectively).

Tibiofemoral contact pressures were analysed as lateral and medial compartment data

separately. For each flexion angle, a Tekscan file was saved and exported in ASCII format to

an Excel spreadsheet. Peak and mean medial and lateral pressures were calculated.

Kinematic data were collected using NDI Toolviewer (NDI, Waterloo, Ontario, Canada)

software, and were processed using custom-made Matlab scripts (Mathworks Inc., Natick,

Ma, USA). SPSS 22.0 (IBM Corp, Armonk, New York) was used for statistical analysis.

Normality of data was examined using the Shapiro-Wilk test. An a priori value of 0.05 with

corrections for multiple contrasts was used to denote statistical significance. The dependent

variables were anterior translation, internal rotation and mean/peak contact pressures for

both lateral and medial compartments. Two-way repeated measures ANOVAs (RM

ANOVAs) compared dependent variables (medial/lateral peak and mean tibiofemoral contact

pressures, tibial rotation and translation) across the two independent variables: flexion angle

(0, 30, 60, 90) and state of the knee (Intact, anterolateral cut, 4 reconstructions) in the

following way:

1. Comparison across 0°, 30°, 60° and 90° of knee flexion for the intact and

anterolateral cut states.

2. Comparison across 0°, 30°, 60° and 90° of knee flexion in the intact and in the 4

MacIntosh reconstructions.

When differences across the test conditions were found, pairwise t tests and Bonferroni

corrections were applied to correct for multiple comparisons. Finally the relationships

between the rotational position of the knee and the peak/mean lateral and medial contact

pressures were investigated using bivariate correlations.

RESULTS:

Effect of anterolateral lesion on kinematics and contact pressures

Following the anterolateral sectioning there were significant increases, in anterior translation

(P=0.016) with a maximum magnitude of 0.8 mm and in internal rotation (P=0.032) with a

maximum magnitude of 1.6°, in the unloaded knee as compared to the intact state (Figures

3 and 4). The anterolateral lesion did not cause changes in the peak lateral pressure

(P>0.05) as compared to the intact knees (Figure 5), but a significant decrease in the mean

lateral (P<0.01) pressure of maximum 0.30 MPa (Figure 6). Both the peak and the mean

medial pressures were significantly increased, by a maximum 0.18 MPa and 0.20 MPa

respectively, following anterolateral sectioning (P=0.02, P=0.041; Figures 6 and 7).

0 30 60 90

-10

-5

0

5

10

15

20

*

*

*

*

INTACTTRANSECTED20N FIXED20N FREE80N FIXED80N FREE

Flexion Angle (degrees)

Ante

rior

Tra

nsla

tion

(m

m)

30 60 90

Figure 3 – Anterior translation of the unloaded tibia for anterolateral tissues intact,

transected and with a MacIntosh tenodesis with combinations of graft tensions (20 N and 80

N) and fixed or free hanging tibia at graft fixation (N=8). (*Significantly different from intact

knees, P<0.05).

0 30 60 90

-4

-3

-2

-1

0

1

2

** *

*

*

*

*

*

INTACTTRANSECTED20N FIXED20N FREE80N FIXED80N FREE

Flexion Angle (degrees)

Inte

rnal

Rot

atio

n (d

egre

es)

0 30 60 90

Figure 4 – Internal rotation of the unloaded tibia for anterolateral tissues intact, transected

and with a MacIntosh tenodesis with combinations of graft tensions (20 N and 80 N) and

fixed or free hanging tibia at graft fixation (N=8). (*Significantly different from intact knees,

P<0.05).

0 30 60 900.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

IntactAnterolateral Transection20N FIXED20N FREE80N FIXED80N FREE

Flexion Angle (degrees)

Peak

Pre

ssur

e (M

Pa)

Figure 5 – Peak lateral pressures for intact, anterolateral cut, 20 N and 80 N graft tension

with alternating fixed and free hanging tibia (Mean plus SD, n=8)

0 30 60 900.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

* * * *

**

*

IntactAnterolateral Transection20N FIXED20N FREE80N FIXED80N FREE

Flexion Angle (degrees)

Mea

n Pr

essu

re (

MPa

)

Figure 6 – Mean lateral pressures for intact, anterolateral cut, 20 N and 80 N graft tension

with alternating fixed and free hanging tibia (*Significantly different than intact pressures

after Bonferroni-correction; mean plus SD, n=8)

0 30 60 900.0

0.5

1.0

1.5

2.0

2.5

3.0

*

* *

* IntactAnterolateral Transection20N FIXED20N FREE80N FIXED80N FREE

Flexion Angle (degrees)

Peak

Pre

ssur

e (M

Pa)

Figure 7 – Peak medial pressures for intact, anterolateral cut, 20 N and 80 N graft tension

with alternating fixed and free hanging tibia (Mean plus SD, n=8).

0 30 60 900.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4 * * * *

IntactAnterolateral Transection20N FIXED20N FREE80N FIXED80N FREE

Flexion Angle (degrees)

Mea

n Pr

essu

re (

MPa

)

Figure 8 – Mean medial pressures for intact, anterolateral cut, 20 N and 80 N graft tension

with alternating fixed and free hanging tibia (Mean plus SD, n=8).

Effect of varying graft tension and tibial position during graft fixation in the MacIntosh

tenodesis

All four tenodeses were able to restore the anterior translation, and no significant differences

from the intact knee were identified (P>0.05) (Figure 3). Internal rotation did however differ

from the intact knee (P<0.01). These differences, of 1.6° and 1.8°, found in 0° and 60° knee

flexion for both tenodeses (with the tibia free-hanging and fixed) performed with 80 N graft

tensioning – both pulled the knee into external rotation, effectively over-constraining the

knee (Figure 4).

No significant differences from intact knee values were identified in peak or mean medial

contact pressures or peak lateral contact pressures for any of the reconstructions performed

(All: P>0.05) (Figures 5, 7 and 8). For the mean lateral pressure, however, the tenodesis

with 80 N tension and a free hanging tibia displayed a significant increase in intraarticular

contact pressure compared to the intact knee of maximum 0.40 MPa (P=0.002) (Figure 6).

Relationship between internal/external rotation and lateral contact pressures

A strong positive correlation was found between mean external rotation position of the knees

and the mean lateral contact pressures, R=0.86, P<0.05, n=24. The peak lateral contact

pressures, however, only had a moderate positive correlation with external rotation position

of the knees, R=0.63, P<0.05, n=24. The contact point of the lateral femoral condyle on the

lateral tibial plateau was found to have moved anteriorly when the tibia was pulled into

external rotation by the 80 N graft tension: 1.9 +/- 1.3 (0.1 – 5.3) mm [mean +/- SD (range)].

The medial mean and peak contact pressures had only a low positive correlation R=0.297,

P>0.05, n=24 and moderate negative correlation R=-0.61, P<0.05, n=24 respectively.

DISCUSSION:

The most important findings in the current cadaveric study were changes in knee kinematics

(internal rotation and anterior translation) and intraarticular contact pressures resulting from

an anterolateral lesion of the knee, which could be normalised by a MacIntosh tenodesis

with the correct tensioning protocol. A strong correlation between external rotation of the

tibia and increases in mean lateral compartment pressures was seen throughout the study.

When varying conditions for graft tensioning and rotational position of the leg during graft

fixation, a tendency towards over-constraint of tibial rotation with resulting increased lateral

intra-articular contact pressures was found if 80 N was used for graft fixation (as opposed to

20 N) and if the position of the leg was not controlled at the time of graft fixation – effectively

pulling the tibia into external rotation, as had been hypothesized. It is important to note that

although the current effects were fully consistent, they were small, and perhaps not of

relevance in a knee undertaking rigorous cutting sports.

A recent commentary revisited an American Orthopaedic Society for Sports Medicine

(AOSSM) consensus meeting in 1989 where an international panel of knee surgeons

thoroughly reviewed the contemporary use of anterolateral procedures 15. Recommendations

were then made to approach the combined intra- and extraarticular techniques cautiously

due to a fear of over-constraint of the lateral compartment with a resulting possible lateral

osteoarthritis (OA). As pointed out by Ferretti 15, these recommendations were expert

opinions with very little evidence to support them. On the contrary, more recent publications

have indicated good outcomes after combining extraarticular procedures with modern

intraarticular ACL reconstruction17,31,35. In a review by Hewison et al. summarizing across

studies that compared isolated ACL reconstruction and combined procedures, pooling of

results found a positive effect on pivot shift (odds ratio 0.5, 95% CI 0.32-0.78) favouring a

combined procedure 17. Also, it is important to note that today’s rehabilitation has changed

dramatically from that used in the period when a majority of studies evaluating lateral

procedures were published. Former use of a postoperative plaster cast has been replaced

by early mobilisation and a more aggressive rehabilitation – these changes could perhaps

lessen the risk of OA.

Although a handful of studies have investigated the kinematic effects of combining ACL

reconstruction and anterolateral procedures 2,8,13,35,40, there is only one other study that has

evaluated the effect of varying graft tension 39. The Muller tenodesis, used in that study,

utilised a posterior strip of the ITB that was transpositioned and fixed at the junction of the

femoral shaft and the lateral femoral condyle in the isometric point called the Krackow´s K9

26. The knee was kept at a neutral position while the tension of the tenodesis was varied

between 0 N and 22 N at graft fixation. A tendency of over-constraining the knee, most

pronounced with the higher graft tension, was found both in anterior translation and internal

rotation. The authors therefore suggested that the surgeon could affect the kinematic pattern

of the knee by adjusting the tensioning of the tenodesis. In contrast the present work found

that only a much higher 80 N graft tension would result in over-constraint (seen as both

increased external rotation and increased lateral contact pressure) of the knee. Differences

in the surgical techniques could be one reason for these findings. The current MacIntosh

procedure using a central, rather than posterior, strip of the ITB was fixed to a point more

proximal along the femoral shaft than the Muller tenodesis. This point corresponds to the so-

called Kaplan-fibres - the deep osseous insertion of ITB 24. Also, the ITB graft was tunnelled

deep to the LCL in the former procedure rather than superficial to LCL in the Muller

technique. A recent study by Kittl et al., comparing length change patterns in a series of

lateral tenodeses, found both tenodeses to have relatively isometric properties, the

MacIntosh procedure, however, was reported to be closest to isometric through the knee

range of motion 25. Another difference from the study investigating the Muller tenodesis was

the current use of a clamp that held the knee in a neutral position at the time of graft

tensioning. This prevented the tibia from being pulled into an externally rotated position by

the graft tension.

Some inherent limitations in this study should be noted. The current results are seen from a

time-zero perspective and the effects of rehabilitation and early mobilisation on knee laxity

and the tibiofemoral joint compression forces are therefore not accounted for. Loading of

some of the muscles according to their relative contribution over the knee was performed,

but these tensions were small compared to the tensions that might occur during sports

involving cutting manoeuvres; the 175 N quadriceps tension plus 30 N ITB tension

corresponds to a typical knee extension exercise, as used for clinical evaluation. Also only

some of the muscles that act on the knee joint were engaged during the current testing: Not

loading the hamstrings tendons could potentially affect the kinematics and compressive

forces seen in the current results, but their passive tensions would be small compared to the

quadriceps during knee extension. However, although these comments suggest that the

articular contact stresses may have been lower in this experiment than would be expected

during load-bearing activity, that was not found to be the case: The peak pressure on the

lateral condyle in the present study was 2.5 +/- 0.7 MPa at 30o knee flexion, while Wang et al

46 measured 2.6 +/- 0.9 MPa during simulated walking activity. The stresses during sports

activities may, of course, be expected to be higher. Therefore the small changes seen in the

current study, of approximately 0.5 MPa, might not be relevant in a clinical setting. This

study deliberately used a relatively low-load scenario in order to allow the changes of

tibiofemoral kinematics and contact pressures caused by the anterolateral construct to be

discerned clearly; it may be speculated that these changes of baseline knee conditions

would appear to be relatively small in the context of imposing the loads encountered in

sporting activities. Further, the ACL was left intact in the current study to mimic a “perfect

ACL reconstruction”. This was done to isolate the effect of the anterolateral lesion and

investigate the effect of a MacIntosh tenodesis under various controlled conditions,

eliminating variability which would have arisen from an ACL reconstruction which could have

affected the clarity of the results. Thus, this was not intended to be a study which supports

isolated anterolateral tenodeses, which are usually indicated in combination with an ACL

reconstruction.

This is the first study to examine the intra-articular contact pressures related to the use of

lateral tenodeses – and also one of few that report on tibiofemoral contact pressures 1,7,20,46.

The results show the interplay of several technical factors (e.g. graft tensioning and position

of the leg at the time of graft fixation) affect the resulting intra-articular conditions after

surgery. A strong correlation between external version of the knees and increase in lateral

compartment pressures were seen. Surgeons performing such anterolateral procedures

should therefore pay attention to these technical factors - most importantly the tibia should

be held in neutral rotation at graft fixation - when performing such a procedure. The

MacIntosh tenodesis used in the current study could restore intact knee kinematics in the

anterolateral injured knee with only 20 N graft tension. If a relatively large graft tension (80

N) was used while the tibia was allowed to rotate freely, it led to a small increase in lateral

compartment contact pressure.

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