CADAVERIC EVALUATION OF THE LATERAL-ANTERIOR DRAWER TEST FOR EXAMINING POSTERIOR CRUCIATE LIGAMENT INTEGRITY

Abstract

Background

Common clinical tests often fail to identify posterior cruciate ligament (PCL) ruptures, leading to undetected tears and potential degenerative changes in the knee. The lateral-anterior drawer (LAD) test has been proposed but not yet evaluated regarding its effectiveness for diagnosing PCL-ruptures.

Hypothesis

The LAD will show greater tibial translation values in lateral-anterior direction in a PCL-Cut condition compared to a PCL-Intact condition, thus serving as a useful test for clinical diagnosis of PCL integrity.

Study Design

Descriptive laboratory study.

Methods

Threaded markers were inserted into the distal femur and proximal tibia in eighteen cadaveric knees. Each femur was stabilized and the tibia translated in lateral-anterior direction for the LAD test versus in a straight posterior direction for the posterior sag sign (PSS). Each test was repeated three times with the PCL both intact and then cut, in that order. During each trial, digital images were captured at start and finish positions for the evaluation of tibial marker displacement. Tibial marker translation during each trial was digitally analyzed using photography. The PSS values served as a reference standard.

Results

The LAD tibial translation was significantly greater (U=-3.680; p<;0.002) during the PCL-Cut (10.6±5.6mm) versus PCL-Intact (7.7±5.1mm) conditions. The PSS tibial translation was significantly greater (U=-3.724; p<0.002) during the PCL-Cut (11.0±5.3mm) versus PCL-Intact (6.4±3.5mm) conditions. There was no significant difference (t=2.029; p=0.07) in mean tibial translation in respective directions after PCL dissection during the LAD test (2.9±2.1mm) versus the PSS (4.6±2.8mm).

Conclusion

The LAD test detected changes in cadaveric tibial translation corresponding with changes in PCL integrity to a degree at least as effective for assessing PCL integrity as the PSS. Further clinical study will be required to assess the utility of the LAD as a physical examination tool for diagnosing PCL injuries.

Level of Evidence

2 (laboratory study)

INTRODUCTION

Approximately two million sports injuries are registered in Germany per year, and 30% of these cases involve the knee joint,¹ making it the second most involved body region for sports injury at a national level.² A posterior cruciate ligament (PCL) rupture is considered to be one of the more severe sports-related knee injuries.³ The epidemiology of PCL injuries has not been sufficiently clarified to date.^4,5 Depending on the patient population, the reported incidence of PCL injuries ranges between 1% and 44% of all acute knee injuries.^6-10 However, the estimated number of undetected PCL ruptures is high,^11,12 thus, epidemiological data regarding actual incidence might even be greater. Moreover, detection of a PCL-rupture can be delayed or missed, often due to mild acute symptoms, poorly understood pathology, and insufficient diagnostic testing.³ A PCL-injury can be sustained during many sports including but not limited to snow skiing, martial arts, soccer, rugby, and American football.^1,3,13,14

Overlooked or misdiagnosed PCL-ruptures can lead to knee joint biomechanical changes,^15,16 ultimately lending to the development of irreversible secondary failures, and serious functional impairments.^11,12,14,17 Undetected knee instability related to PCL-rupture can produce early cartilage degeneration in response to increased compression and shearing forces in the medial and patellofemoral knee joint compartments.^12,16,17 In addition, PCL-insufficiency leads to collagen maladaptation and functional deficits similar to those seen in ACL insufficiency.^3,8,18,19 Concomitant posterolateral corner injury can lead to additional knee instability and degenerative changes.²⁰ Thus, PCL-insufficiency detection is critical, necessitating precision clinical testing.

Three clinical tests are most commonly used for examining PCL integrity, including the posterior sag sign (PSS), the posterior drawer test and the quadriceps active test.²¹ However, these often do not clearly identify PCL-ruptures.^3,22 Kopkow et al.²³ used a systematic review to report the clinical accuracy (sensitivity, specificity, positive and negative likelihood ratios) of these tests and found that the interpretation may be invalid due to poor methodology in most studies that were included.²³ The posterior drawer test examines the supine patient with the knee flexed to 80-90 degrees and the foot flat on the table. The tibia is passively translated posteriorly, parallel to the tibial plateau. However, often the patient presents with a posteriorly subluxed tibia (at rest, prior to performing the test) due to gravity, lending to minimal or unavailable posterior passive tibial movement, producing a false negative test.^3,12 Similarly, joint swelling or obesity could hinder an examiner's ability to palpate anterior tibial step-off, possibly decreasing posterior drawer test clinical accuracy.¹² Similar interpretation challenges arise with the interpretation of the PSS and/or the quadriceps active test, where test outcomes depend on consistent quadriceps muscle relaxation. Both tests are likely to be misinterpreted if the patient exhibits apprehension or increased post-traumatic muscle tone. Finally, the use of medical imaging for diagnosing PCL-ruptures should be viewed with caution.²⁴ Because the PCL can heal in an elongated position^21,25-27 it may appear intact while in fact remaining lax.

The LAD test, which is an adaption of the lateral shear test of Cyriax, has been introduced as a manually applied testing alternative that attempts to resolve the previously discussed challenges encountered while testing for PCL-rupture.²⁸ In contrast to other previously established clinical PCL tests, utilizing the LAD test does not require precise palpation of any bony landmark, any visual rating of tibial displacement, or considerable muscle relaxation, due to the testing direction that is out of any muscle's functional plane. Additionally, utilizing the LAD test might be psychologically advantageous for the patient since the manual load is not applied in the direction of instability. Any comparison of the LAD test to other well-accepted tests for identifying PCL-rupture has yet to be conducted. Therefore, the purpose of this study was to establish whether the LAD test sufficiently detects changes in in-vitro tibial translation when the PCL is disrupted. This was achieved by examining intra-specimen alterations of lateral-anterior tibial translation in specially embalmed cadaveric knees during both intact- and cut-PCL conditions. Moreover, the authors further assessed the test utility by comparing the changes in LAD translation data produced during both PCL conditions versus changes in PSS tibial translation data produced during the same PCL conditions.

METHODS

Subjects

The cadaveric specimen sample consisted of 18 previously embalmed right-sided cadaveric lower extremities (36-94 years old; mean 79 years) sectioned from pelvis to foot. The cadavers, embalmed according to the method of Thiel,²⁹ fulfilled the following criteria:

• A complete right leg with pelvis

• Undamaged muscle tissue

• No visible (surgical) scars in the knee region

• Intact cruciate ligaments*

• Undamaged posterior capsule*

(*Verified through arthroscopy performed between PCL conditions)

The Thiel cadaveric preservation method is known to sustain a high degree of suppleness, allowing near-natural passive movement of all body parts.²⁹ Utilizing these naturally preserved cadavers enabled the investigator to perform both the LAD test and PSS under conditions similar to the movement conditions found in a living person.²⁹

Pre-measurement preparation of the anatomical specimen

Threaded markers (commercially available 2cm Phillips-head screws) were inserted into the distal femur and proximal tibia in order to compare the extent of tibial translation produced with the PCL-Intact versus PCL-Cut during both the LAD and PSS testing procedures, respectively. Markers were placed in a standardized manner, positioning the knee in 90 ° flexion on a wooden wedge (37 × 50 × 32 cm³) that was fixed to the treatment table and the tibia positioned in neutral rotation (at the midpoint between maximum available tibial external and internal rotation). For the LAD test assessment, markers were inserted 3 and 5 cm distal to the knee joint line at the anterior-medial proximal tibia and 3 cm proximal to the knee joint line at the anterior-medial distal femur. For the PSS assessment, markers were inserted in the lateral proximal tibia 3 cm distal to the knee joint line, as well as in the lateral distal femur 3 cm proximal to the same joint line.

Instrumentation

To objectively record tibial translation changes produced during the PCL-Intact versus PCL-Cut conditions during both the LAD and PSS tests, digital images were captured using a commercial-quality digital reflex camera (Nikon D 70s, Nikon Corp., Japan) mounted on a commercial-grade photo tripod (Manfrotto 322RC2, Manfrotto Distribution, Cassola, Italien). All joint positions during each experimental stage were verified with an inclinometer (Baseline Bubble Inclinometer; 3B Scientific, Fabrication Enterprises INC. White Plains, NY, USA). The fluid-filled inclinometer's scale was set at zero in full knee extension prior to every usage. A hand-held dynamometer (MicroFet2−; Hoggan Health Industries, West Jordan, UT, USA) was utilized during all LAD trials in order to insure consistent force reproduction during test procedures. The device was manually calibrated prior to every usage.

Preparatory Procedures

To ensure measurement validity the camera was aligned perpendicular to each testing plane, the focal distance was established and maintained through all measurements, and an object of known dimension was placed in a consistent position in the visual field (to be later used during the digitization process for measurement calibration purposes).30 To insure compliance with these criteria, a ruler of standard length (10-20 cm) was mounted on a wooden wedge in a consistent position with respect to the cadaveric specimen and camera, while the camera was positioned as follows prior to data capture:

1. For the LAD test-the camera was positioned 1 m away from the specimen along a line that was 45 degrees anterior-medial to the tibia, allowing for data capture in an oblique plane.

2. For the PSS-the camera was positioned 1 m away from the specimen, directly lateral to the tibia at the height of the joint line, allowing for data capture in the parasagittal plane.

Data capture utilized a within-camera focal length of 55 mm in natural room illumination. The camera was manually focused during each trial prior to data capture. Digital images of marker start and finish positions were used to establish tibial marker translation for each condition during each test trial.

The cadaveric leg was repeatedly moved in flexion and extension at the knee and hip joint for five minutes to reduce tissue stiffness and minimize any residual muscle resistance. The specimen was then placed on the wooden wedge as previously described. The bony pelvis was fixated with a belt to ensure stability. The screw markers were applied to the tibia and femur as previously described.

Data Collection Procedures

The leg was adjusted to the position for PSS (90 ° hip flexion, 90 ° knee flexion, calf free-floating, and heel stabilized on a wooden block), consistent with previous reports. When used in-vivo, this position aims to maximize the influence of gravity on posterior displacement.31 For the PSS start position the tibia was manually translated to the maximum anterior position (Figure 1). For the PSS finish position the tibia was allowed to fully sag posteriorly in response to gravitational pull (Figure 2). The PSS trial was repeated three times. Digital images of start and finish positions were captured for each trial.

Figure 1.

Start position of the PSS; T = Tibia; F = Femur; L = Line coursing parallel to tibial diaphysis through lateral tibial marker; M = lateral femoral marker.

Figure 2.

Finish position of the PSS; T = Tibia; F = Femur; L = Line coursing parallel to tibial diaphysis through lateral tibial marker; M = lateral femoral marker.

Following the third PSS trial the leg was repositioned for the LAD test. The LAD test examines the knee while positioned in 90 ° flexion and the hip positioned at 45 ° flexion. While being aligned rather oblique to the tibial plateau in the extended knee, the PCL describes a circular arc of more than 60 ° during knee flexion,³² thus lending the PCL alignment to become gradually more vertical oriented with respect to the tibial plateau, attaining a near perpendicular position in the 90 degrees flexed knee.^32-35 Thus, LAD knee testing position lends the PCL to inhibiting lateral tibial movement on the femur^15,16,18,36 when the more vertically oriented intact PCL and intercondylar eminence encounter the lateral femoral condyle's medial edge.³⁷ The LAD testing force is applied from medial and slightly posterior (known as medial-posterior) to lateral and slightly anterior (known as lateral-anterior) in a direction towards the anterolateral tibial tubercle, or Gerdy's Tubercle²⁸ (Figure 3). In response, the cadaveric knee was flexed to 90 ° with the femur stabilized on the aforementioned 45 ° inclined wedge. The tibia was positioned in neutral rotation, with the foot fixed to the treatment table using a fixation strap. For the LAD start position, the proximal tibia was then gently manually positioned in the medial-posterior direction until the medial capsular structures were taut (Figure 4). For the LAD finish position, the proximal tibia was manually translated in lateral-anterior direction towards Gerdy's Tubercle (Figure 5). The proximal tibia was translated across the complete LAD test path from the start to finish positions until the first detectable manual resistance requiring a pushing force between 112 and 122 N was encountered. This force data range was based on previous in-vivo LAD pilot testing amongst eight highly experienced testers. The LAD test trial was repeated three times. Digital images of start and finish positions were captured for each trial.

Figure 3.

The LAD test performance in the clinical setting; * = medial arm pushing proximal tibia in lateral-anterior direction towards Gerdy's Tubercle; = lateral hand stabilizing the femur in a medial-posterior direction.

Figure 4.

Start position of the LAD test with PCL dissected; T = Tibia; F = Femur; L = Line coursing parallel to tibial diaphysis through anterior-medial tibial markers; M = anterior-medial femoral marker.

Figure 5.

Finish position of the LAD test with PCL dissected; T = Tibia; F = Femur; L = Line coursing parallel to tibial diaphysis through anterior-medial tibial markers; M = anterior-medial femoral marker.

After performing PSS and LAD trials with an intact PCL, an experienced anatomist examined the internal condition of the cadaveric knee through arthroscopy with the specimen positioned as previously during the LAD test. Herein the anatomist confirmed the intact status of the cruciate ligaments and posterior capsule. If the anatomist had any doubt regarding the integrity of the cruciate ligaments and/or posterior capsule, then the specimen would have been excluded from the study. However, this did not occur in any specimen. Next, the PCL was completely transected across the ligament mid-substance using an internal cutting tool guided through the arthroscope. The anatomist then re-examined the internal knee compartment to ensure that the ACL and posterior capsule remained intact.

Following isolated PCL transection, three LAD test trials were performed in the same fashion described above and digital images were captured at each start and finish position. The leg was then repositioned for the PSS as previously described and three trials were performed, capturing digital images as before.

Data Reduction and Analysis

Tibial marker displacements were digitized using a custom MATLAB Program (The Mathworks, Inc, Natwick, MA USA). The custom MATLAB program prompted the user to select a baseline image representing a resting position. In this image, a section of a standardized ruler of known distance (10-20 cm) was used to calibrate the subsequent measures. Using the coordinates of the two reference points, the total length of the selected segment was then calculated using the Pythagorean theorem. The selected distance was then converted to pixels/mm in order to proceed with further measurements. Three points on this baseline image were then chosen: two fixed points on the tibia, followed by one point on the femur. Each measurement point was established by zooming in on the intersection between the exact same four representative image pixels, reducing any error to less than a fraction of one pixel size. Lines were then extrapolated from the selected points in order to create a 90 ° angle between the points. The coordinates of a fourth point were calculated as the intersection of the two lines. The distance from this fourth point to the femoral marker was then calculated. A second image representing the end translation position was then chosen and the procedure was repeated exactly as for the baseline image. Using the two calculated distances from point four to the femoral marker, the total change in distance between the two images was then calculated in millimeters.

Several investigators have previously published studies using this standardized measurement procedure across different joint systems and tissues. Gilbert et al.^38,39 used the same measurement procedure when examining the uniplanar translation of cadaveric lumbar nerve roots during a clinical straight leg raise procedure. Similarly, Lohman et al.^40,41 used this approach to examine the uniplanar translation of cadaveric cervical nerve roots during upper extremity neural tension testing. In both cases, embedded nerve root marker translation was measured with the same process using digital fluoroscopic images. Moreover, Wilhelm et al.⁴² measured uniplanar cadaveric iliotibial band deformation mounted in a load cell during clinical-grade stretching, where markers were measured in the same fashion on digital images. Finally, the inter-tester reliability and construct validity of this uniplanar measurement approach has been previously established by Cobb et al.⁴³ who applied the approach to uniplanar tarsal bone translation during different foot postures. Their investigation tested the reliability of more than one digitizer and every single image was normalized to an object of known dimension, thus establishing the validity of this uniplanar analysis process for any image capture system at any location. In each study, significant changes in uniplanar translation were consistently observed in response to the respective study's change in conditions.

Data analyses were completed using the SPSS 22 (IBM Corp, Armonk NY, USA) software. Descriptive data, being the mean of the three trials from each test (PSS and LAD), were established for each condition. A Shapiro-Wilk test was used to establish data normality. Because the pre- versus post-cut test data violated the assumption of normality, a within-specimen Wilcoxon Signed-Rank test was used to test for significant differences in tibial translation between the intact and cut PCL conditions. The translation differences data were normally distributed, so a within-specimen t-Test was utilized to test for differences between the LAD versus PSS test conditions. The PSS values were used as a reference standard. Due to potential errors in measurement accuracy, all values were rounded to one decimal figure. Significance was set at ; < 0.05.

RESULTS

Specimen

A total of 18 cadaveric specimens were examined and no specimen was eliminated in response to exclusion criteria.

Digital Images

A total of 24 digital images were captured per specimen [3 trials × 2 positions (start position vs. end position) × 2 PCL conditions (intact vs. cut) × 2 tests (PSS vs. LAD)]. All in all, 432 images were analyzed via MATLAB as above.

LAD Testing Force Analysis

The mean (SD, 95%CI) pushing force while performing the LAD test in the PCL-Intact condition was 115.5 N (1.6; 114.6 – 116.2). The mean (SD, 95%CI) pushing force while performing the LAD test with PCL-Cut was 115.1 N (2.3; 114 – 116.2). There was no statistically significant difference in LAD force values between the PCL-Intact versus PCL-Cut conditions (u = - 0.259; p = 0.795; Figure 6)

Figure 6.

Testing Power for LAD test; PCL = Posterior Cruciate Ligament; Cut = Dissected; N = Newton; Error Bars = 95% Confidence Interval.

Figure 7.

Difference in mean tibial translation PCL-Intact versus PCL-Cut; Diff = Difference; mm = Millimeter; Cut = Dissected; PCL = Posterior Cruciate Ligament; Error Bars = 95% Confidence Interval.

Lateral-anterior drawer test

Proximal tibial lateral-anterior translation produced during the LAD (LADtrans) during the PCL-Intact condition was compared to the same during the PCL-Cut condition. The LADtrans during the PCL-Cut condition was significantly greater (u = -3.680, p = 0.002) than the LADtrans during the PCL-Intact condition (Table 1).

Table 1.

Descriptive Data; LAD = Lateral-Anterior Drawer Test; PSS = Posterior Sag Sign; PCL = Posterior Cruciate Ligament; Cut = Dissected; SD = Standard Deviation; 95%CI = 95% Confidence Interval

CONDITION	MEAN (mm)	SD (mm)	95%CI (mm)	Statistic	p-Value
LAD, PCL-Intact	7.7	5.1	5.2 - 10.3	u = -3.680	0.002
LAD, PCL-Cut	10.6	5.6	7.8 - 13.4
PSS, PCL-Intact	6.4	3.5	4.6 - 8.1	u = -3.724	0.002
PSS, PCL-Cut	11.0	5.3	8.3 - 13.6
LAD Diff	2.9	2.1	1.9 - 3.9	t = 2.029	0.070
PSS Diff	4.6	2.8	3.2 - 6.0

Posterior sag sign

Proximal tibial anterior-posterior translation produced during the PSS (PSStrans) during the PCL-Intact condition was compared to the same during the PCL-Cut condition. The PSStrans during the PCL-Cut condition was significantly greater (u = -3.724, p = 0.002) than the PSStrans during the PCL-Intact condition (Table 1).

Concurrence of the LAD and the PSS

In order to compare the LAD test outcomes to the outcomes of a widely accepted clinical PCL test, PSS values were used as a reference standard.²² Based on t-Test results, the tibial translation difference between PCL-Intact and PCL-Cut during the LAD was not significantly different (t = 2.029, p = 0.07) in magnitude from the same tibial translation difference during the PSS (Table 1). In order to rule out a Type II error, a post-hoc power analysis (Cohen's r) confirmed an effect size of r = 0.3.

DISCUSSION

The statistically significant increase in lateral-anterior tibial translation during the LAD test after isolated PCL transection supports the hypothesis that there is an objective causality between PCL integrity and amount of tibial translation detected by the LAD test. The mean increase of 2.9mm in lateral-anterior translation represents a 38% increase in this lateral-anterior movement. Thus, the results of the current study show that the LAD test can detect PCL deficient knees in this in-vitro model. Other in-vivo investigations support the current findings.^15,16 Li et al.¹⁵ and van de Velde et al.¹⁶ biomechanically demonstrated that the PCL exhibits an important control function in the medial-lateral direction. In 90 degrees of knee flexion the amount of lateral tibial translation increased approximately 1.1mm¹⁵ and 1.9mm¹⁶, respectively, in patients with PCL-deficient knees when performing a single-leg lunge. While these published lateral translational values are not large, they may be relevant in the knee. The knee exhibits such tight congruencies in the collateral directions throughout the flexion-extension range. Therefore, any increase in lateral translation outside of the normal condition could be troublesome.

A possible explanation for the higher translation values witnessed in the lateral-anterior direction during the PCL-Cut condition in the current study could be that Li et al.¹⁵ and van de Velde et al.¹⁶ conducted their tests in-vivo. This is in contrast with cadaveric testing, where no muscular knee protection or dynamic stabilization occurs and the only stability is provided by passive structures (such as patellar retinacula). Thus, the subjects' knees in Li et al.¹⁵ and van de Velde et al.¹⁶ that were actively flexed during single leg lunges were potentially constrained through active and passive structures, lending to knee joint centering and decreased joint translations.⁴⁴ Moreover, these investigators only examined pure lateral tibial translation versus the lateral-anterior test in the current investigation. In the current study, the translation force was directed in an lateral-anterior direction in order to bypass the intercondylar eminence, which can serve as a structural constraint to lateral translation within the knee joint³⁷ and may partially explain decreased translation found in the aforementioned studies.

Considering the increase in lateral translation after PCL transection that was found in the current study, the LAD test could provide the clinician with a clinical appreciation for 3-D biomechanical compromise in response to PCL-rupture. While previously reported translational values are small, this presence of lateral-anterior compromise speaks to the three-dimensional constraining capability of the PCL and the LAD test could provide the clinician with clinical insight into the knee's three-dimensional stability failure in response to a PCL injury.

In the current study, the posterior tibial translation during the PSS significantly increased after the PCL was cut, which represents a 72% displacement increase. Because the PSS is commonly judged dichotomously, objective data regarding the effect of isolated PCL transection on posterior tibial displacement during the PSS is limited, creating a challenge for making any direct comparison between the current data and other investigators' findings. In response, the authors must contrast the current PSS data with posterior drawer test data from other studies, where documented posterior tibial translation is well objectified. The current data amplitudes are found to be slightly smaller compared to other posterior drawer test displacement data^45-47 but any small translation differences could be explained by dissimilar test characteristics. In contrast to the posterior drawer test biomechanical and manual force application strategies of Bergfeld et al.⁴⁵ and Fontbote et al.⁴⁷, the present study did not apply any posteriorly directed force onto the tibia. Rather, by definition, only gravity created the free-floating posterior tibial translation during the PSS procedure. As one would expect, posterior tibial translation was less during the PSS versus previously documented posterior drawer test findings, where a posteriorly directed force was applied to the tibia.^45,47

The current findings suggest that the LAD and PSS discover similar tibial translation changes in response to isolated PCL transection, as the LAD translation data were not significantly different (1.7mm) from the PSS data. The PSS was chosen as a comparison because it is well recognized,²² and while the quadriceps active test could serve as a comparison, it was not applicable to our specimen sample because it requires an in-vivo quadriceps activation that is unavailable in cadaveric specimens.^12,14 Similarly, while the posterior drawer test could be used for comparison, the test results are difficult to judge, due to a poorly recognizable starting position for the posterior drawer test.⁴⁸ Moreover, the PSS fulfills all the criteria required of a meaningful comparison test.⁴⁹ The PSS is independent from the LAD test, meaning that investigators did not use the PSS results to determine LAD test results. Additionally, since in the PSS tibial translation is judged in straight posterior direction, the PSS does not include the LAD testing direction. Furthermore, the PSS exhibits a consistency with the examined LAD test concerning the structure to be evaluated and it presents with a standardized performance procedure. Moreover, investigators have reported respectable sensitivity (79%) and specificity (100%) for the PSS.^22,48,50 Finally, post-hoc effect size calculations minimized any suspicion for a Type II error, suggesting a sufficient sample size and trustable findings of non-significance.

Investigators have reported the value of the PSS for clinical testing PCL failures in certain circumstances. However, the PSS could be more difficult to judge when the patient has a history of Osgood-Schlatter's disease, which is the most common apophysitis in pre-pubescent athletes with a prevalence of 21% in young athletes.⁵¹ Moreover, if there is swelling or obesity, the landmarks may be more difficult to locate. In order to reliably interpret the amount of any posterior tibial sag in the PCL deficient knee, the examiner has to be able to visually measure the anterior tibial plateau as the referred landmark for PSS judgment. The bony prominence in patients presenting with a history of Osgood-Schlatter's disease would possibly reduce any visually measurable displacement of tibia on femur in the sagittal plane.

Diagnosis of PCL injuries can be difficult, therefore, additional clinical tests are needed.^23,52 Correspondingly, an in-vivo study for assessing inter-rater and intra-rater reliability, as well as the clinical accuracy and criterion validity of the LAD test with respect to MRI findings, is forthcoming. In order to increase the clinician's confidence in clinical detecting PCL disruption, the LAD could be added to the toolbox and clustered with the PSS for detecting PCL tears with greater confidence. This is complemented by the practicality of the LAD test, where the manual contact of the test provides the examiner with an appreciation of the tissue integrity associated with the tibial translation. These features can be useful to aid clinician's confidence in making the diagnosis, especially considering the lower incidence of this trauma over ACL injury.⁵³ Because of the PCL's lower injury rate, most clinicians do not have the opportunity to witness this injury on a frequent basis. Thus, more testing options could help them trust their judgment,⁵² which could lead to faster and better utilization of more confirming test procedures, such as MRI.

The value of accurate and timely PCL failure detection has been debated. Patients with isolated PCL tears appear to perform at quite high levels and are less often treated surgically in the acute phase.^54,55 Yet, other afflictions may arise over time as a consequence of missed isolated PCL tears, such as cartilage and meniscal degeneration. Hamada et al.⁵⁶ evaluated 61 patients with isolated PCL deficient knees, witnessing extensive cartilage and meniscal degeneration as early as three months after the initial PCL rupture. Geissler and Whipple⁵⁷ investigated acute and chronic isolated PCL deficient knees, reporting meniscal lesions in 36% and cartilage degeneration in 49% of their patient population presenting with chronic isolated PCL ruptures. Moreover, van de Velde et al.¹⁶ observed increased cartilage deformation during single leg lunges in patients with PCL ruptures using MRI and dual orthogonal fluoroscopic imaging. These findings add to the value of early detection of PCL deficiency and the LAD may serve to enhance the clinician's detection of that condition in order to allow for clinical decision making regarding interventions.

LIMITATIONS AND FUTURE RESEARCH

The study presents with several limitations. First, the LAD versus PSS testing order was not randomized. While this could have influenced the test outcomes, randomizing the trials would have required more frequent camera angle changes, which could have increased the risk of data collection error. Thus, the authors chose to exercise the consistent data collection in the order that was previously documented.

The second limitation to this study is found in a lack of absolute blinding, where the examiner was not completely blinded to the test outcomes. However, open eyes and no complete blinding were used because the examiner was required to observe the hand placement and limb alignment throughout the test in order to maximize test consistency. Additionally, based on the location of the markers and the orientation of the camera, the examiner was not able to visualize the marker translation in the respective movement planes for each test. Moreover, while blinding was not achieved during the test procedures, image digitization was conducted by an independent investigator at a different location and time point, without knowledge of specimens in attempt to reduce any measurement bias.

Third, when interpreting the results of a cadaver study, it is important to note that the role of muscle tension and/or joint forces has not been included. Thus, any application to an in-vivo situation is premature. However, the major goal of this investigation was to examine if the proposed LAD test was able to demonstrate an increased tibial translation in lateral-anterior direction in a PCL-insufficient knee.

The LAD test shows promising results, but before it could be recommended for routine use, it should be further evaluated. Future cadaveric research could focus on a comparison of the LAD to the posterior drawer test and include accurate biomechanical testing with more precision technology, such as a material testing system (MTS). Future in-vivo studies should establish both the inter-rater and intra-rater reliability of the LAD test with subjects who have sustained a PCL-rupture. Because the influence of other ligament injures on LAD response has not been tested, future research should include a measure of other ligament failures (such as ACL) on lateral-anterior tibial displacement to further elucidate the role of PCL failure in test outcomes. Furthermore, future research should include an in-vivo comparison of the LAD test versus PSS and posterior drawer test for diagnosing PCL-ruptures. Novice versus expert testers using the LAD test in-vivo should be compared in terms of their diagnostic decision-making. Since the meniscofemoral ligaments, if present, are assumed to be a secondary stabilizer to at least posterior tibial translation,⁵⁸ future research should investigate the effect of meniscofemoral ligaments on lateral knee stability and their influence on LAD test outcomes in the PCL-deficient knee.

CONCLUSION

In summary, the LAD and PSS both detected significantly increased laxity in this in-vitro model that examined isolated PCL disruption. These findings are complemented by the practicality of the LAD test, where the manual contact of the test provides the examiner with an appreciation of the tissue integrity associated with the tibial translation. Additionally, the LAD in this in-vitro model suggests an appreciation of 3-D biomechanical compromise in response to isolated PCL-rupture. Moreover, the LAD may provide the examiner additional test information after PCL injury when severe knee joint swelling or increased quadriceps muscle tone may hinder accurate PSS or posterior drawer test interpretation of the extent of abnormal tibial translation. Furthermore, the tibial step-off that must be visualized during the PSS and/or palpated during the posterior drawer test may be diminished in the presence of obesity, swelling, increased muscle tone or tibial tubercle hyperostosis, making a clinical interpretation of those tests difficult for the novice examiner. The results of the current study offer biomechanical support to carrying out future in-vivo studies that examine the utility of the LAD in clinically diagnosing PCL injuries. Once fully investigated, the LAD test could be clustered with other tests to assist in a clinician's examination of a patient with suspected PCL-rupture.