Abstract
Background
Stress radiography is a widely used diagnostic tool to assess injury to the anterior and posterior cruciate ligaments and the medial and lateral structures of the knee. However, to date, numerous techniques have been reported in the literature with no clear consensus as to which methodology is best for assessing ligament stability.
Questions/purposes
The purpose of this review was to identify which stress radiographic techniques have support in the literature for the diagnosis of acute or chronic knee ligament injuries, to define which technique is most accurate and reliable for diagnosing knee ligament injuries, and to compare the use of stress radiography with other diagnostic tests.
Methods
Two independent reviewers performed a systematic review of PubMed (MEDLINE), the EMBASE library, and the Cochrane Controlled Trials Register for English language studies published from January 1970 to August 2013 on the diagnosis of knee ligament injuries using stress radiography. Information describing the ligament(s) investigated, stress radiographic technique, magnitude of force, measures of accuracy and reliability, and comparative diagnostic tests were extracted. Risk of bias was assessed using the QUADAS-2 tool.
Results
A total of 16 stress techniques were described for stress radiography of the knee. The diagnostic accuracy of stress radiography including the sensitivity, specificity, and positive and negative predictive values varied considerably depending on the technique and choice of displacement or gapping threshold. Excellent reliability was reported for the diagnosis of anterior cruciate ligament, posterior cruciate ligament, varus, and valgus knee injuries. Inconsistencies were found across studies regarding the efficacy of stress radiography compared with other diagnostic modalities.
Conclusions
Based on the multitude of stress techniques reported, varying levels of diagnostic accuracy, and inconsistencies regarding comparative efficacy of stress radiography to other diagnostic modalities, we are not able to make specific recommendations with regard to the best stress radiography technique for the diagnosis of knee ligament injuries. Additional comparative studies using consistent methodology and appropriate blinding are necessary to further define differences in accuracy and reliability both among stress radiography techniques and between stress radiography and other diagnostic tests.
Level of Evidence
Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
Introduction
Stress radiography is a widely used diagnostic tool that provides objective quantification of knee ligament stability. Its applications include diagnosing acute and chronic injuries [1, 21, 30, 32], comparing instability preoperatively and postoperatively [20, 24, 39, 55], and monitoring stability in nonoperatively treated patients [17]. A variety of stress techniques have been described that assess ligament stability using an anteriorly, posteriorly, varus-, or valgus-directed force to the knee [10, 14, 17, 28, 29, 37, 40, 41, 43, 45]. Side-to-side differences in the amount of displacement (anterior or posterior) or gapping (varus or valgus) increase suspicion of a functional deficit in knee ligament stability. Compared with physical examination, stress radiographs provide a quantifiable and retrievable record of instability. Physical examination alone has often been reported to be inaccurate, subjective, and poorly reproducible for assessing anterior knee laxity [3, 23, 49, 53]. Clinician experience, a patient’s pain, tolerance of the examination, and concurrent ligamentous injuries may skew physical examination interpretation, detracting in certain situations from its clinical use [22, 25, 27]. Previously reported discrepancies in the reliability and reproducibility of the physical examination have created a niche for objective and quantifiable assessments of ligament stability such as stress radiography that augment diagnostic power and enhance management decision-making [33, 35, 36].
Many factors influence the results of stress radiography in a clinical setting, including the position of the patient, knee position, muscular tone, the degree of muscular relaxation, gravity, the testing procedure, and the orientation, magnitude, direction, and amplitude of the force applied [4, 47]. In addition, viscoelastic properties, functional competence, secondary ligamentous restraints, and the inherent accuracy and reproducibility of the measurement device contribute to the degree of displacement [8, 37, 47]. The ideal stress radiographic technique is inexpensive, efficient, reproducible, accurate, and examiner-independent. Techniques described in the literature attempt to control for these variables with varying degrees of success. Despite more than four decades of use in the clinical setting, no clear consensus has emerged as to which stress radiography techniques are best for diagnosing knee ligament injuries.
This systematic review of the knee stress radiography literature therefore was designed to answer the following questions: (1) What stress radiographic techniques have support in the literature for the diagnosis of acute or chronic knee ligament injuries? (2) Which technique(s) is/are most accurate and reliable for diagnosing knee ligament injuries? (3) How does the use of stress radiography compare with other diagnostic tests?
Materials and Methods
A systematic electronic literature search was conducted in PubMed (MEDLINE), the EMBASE library, and the Cochrane Controlled Trials Register for studies published from January 1970 to August 2013. The following Boolean terms were used in the title and abstract fields: Stress Radiographs Anterior Cruciate Ligament (“Stress” AND “Radiographs” AND “Anterior” AND “Cruciate” AND “Ligament”); Stress Radiographs Posterior Cruciate Ligament (“Stress” AND “Radiographs” AND “Posterior” AND “Cruciate” AND “Ligament”); Varus Stress Radiographs (“Varus” AND “Stress” AND “Radiographs”); and Valgus Stress Radiographs (“Valgus” AND “Stress” AND “Radiographs”).
Individual searches were also conducted to screen for articles published in 2013 and not yet searchable in the databases. The following journals were searched: The American Journal of Sports Medicine, The Journal of Bone & Joint Surgery, The Bone & Joint Journal, Journal of Orthopaedic Research, Clinical Orthopaedics and Related Research, and Knee Surgery, Sports Traumatology, and Arthroscopy. No restrictions were placed on study type during the initial search. Citations were exported to an Excel spreadsheet (Microsoft Corp, Redmond, WA, USA). Six hundred seventy-one studies were identified and 266 unique studies remained after duplicates were manually removed (405 studies excluded) (Fig. 1).
Fig. 1.
The flowchart illustrates study selection criteria and the results of the systematic literature search.
Two independent reviewers (EWJ, BTW) assessed the eligibility of each study based on the information presented in the title and abstract. Inclusion and exclusion criteria were developed to best answer our research questions. Non-English articles (21 articles) and articles not pertaining to the knee (74 articles) were excluded. The remaining 171 articles were manually screened by title, abstract, and, if necessary, full text to identify studies that specifically (1) described a stress technique for the diagnosis of knee ligament injury; (2) described or compared the accuracy and/or reliability of one or several stress radiography techniques; or (3) compared stress radiography with other diagnostic techniques. All Level V evidence studies (expert opinion, case reports), editorials, and letters to the editor were also excluded. Articles considered relevant or of questionable relevance were extracted in full text and reviewed. A total of 19 studies were identified for inclusion from the electronic literature search. Reference lists were systematically reviewed to include studies consistent with the inclusion criteria that did not appear in the initial database queries. An additional 19 studies were identified by reviewer consensus to arrive at a total of 38 studies included in the final review.
After the final selection of articles was agreed on, the same two reviewers independently examined study quality using the QUADAS-2 tool [50–52] (Table 1). Differences between reviewers were settled by consensus. The QUADAS-2 tool provides an objective and transparent rating of bias and applicability for diagnostic accuracy studies. Four domains are used to assess for bias: patient selection, index text, reference standard, and flow and timing. Risk of bias was classified as low, high, or unclear for each of the four domains (Fig. 2). An overall designation of low, moderate, or high risk of bias was then assigned to each study. Overall high risk of bias was defined as a score of high or unclear risk of bias in three or four of a total of four categories, overall moderate risk of bias was defined as a score of high or unclear risk of bias in two of four categories, and an overall low risk of bias was defined as a score of high or unclear risk of bias in zero or one of four categories.
Table 1.
Risk of bias assessment for stress radiography diagnostic studies using the QUADAS-2 tool
| First author | Risk of bias by domain | Overall risk of bias§ | |||
|---|---|---|---|---|---|
| Patient selection | Index test | Reference standard | Flow and timing | ||
| ACL | |||||
| Hooper [15] | High | Unclear | Unclear | Unclear | High |
| Rijke [38] | Low | Low | High | High | Moderate |
| Granberry* [11] | – | – | – | – | – |
| Franklin [7] | Low | High | Low | Unclear | Moderate |
| Rijke [37] | High | Low | High | Low | Moderate |
| Stäubli [45] | High | High | Low | Low | Moderate |
| Lerat [29] | Low | Low | High | Unclear | Moderate |
| Dejour [6] | Unclear | Low | Unclear | Unclear | High |
| Garcés [9] | Low | Low | Low | Low | Low |
| Lerat [30] | High | Low | Unclear | High | High |
| Wirz* [54] | – | – | – | – | – |
| Beldame [1] | Low | Low | Low | Unclear | Low |
| Beldame [2] | Low | Low | High | Low | Low |
| Panisset [34] | Low | Low | High | Low | Low |
| Dejour [5] | Low | Low | High | Low | Low |
| PCL | |||||
| Stäubli [44] | High | Low | High | Low | Moderate |
| Hewett [14] | High | High | High | High | High |
| Margheritini [31] | Low | High | High | High | High |
| Schulz‡ [41] | – | – | – | – | – |
| Jung [21] | Low | Low | High | Unclear | Moderate |
| Garavaglia* [8] | – | – | – | – | – |
| Schulz [42] | Low | High | Low | Low | Low |
| Jackman‡ [16] | – | – | – | – | – |
| Garofalo [10] | Low | High | Low | Low | Low |
| Valgus | |||||
| Sawant [40] | Low | High | Low | Low | Low |
| LaPrade* [25] | – | – | – | – | – |
| Varus | |||||
| LaPrade* [26] | – | – | – | – | – |
| Gwathmey [12] | Low | Unclear | Unclear | Unclear | High |
| Multiligament | |||||
| Jacobsen† [17] | – | – | – | – | – |
| Jacobsen [18] | Low | High | Low | Low | Low |
| Jacobsen [19] | Unclear | Low | High | Unclear | High |
| McPhee [32] | Unclear | Low | High | Low | Moderate |
| Tozilli [48] | High | Low | High | High | High |
| Stäubli [46] | Unclear | Low | High | Low | Moderate |
| Harilainen [13] | Low | Unclear | Unclear | High | High |
| Stäubli [47] | High | Low | High | Low | Moderate |
| Sekiya* [43] | – | – | – | – | – |
| Lee‡ [28] | – | – | – | – | – |
Studies unable to be assessed using the QUADAS-2 tool [50–52]: * cadaveric study; †descriptive of a technique using healthy controls only; ‡characterize the reliability and repeatability of a technique only; §overall risk of bias: high = score of high or unclear risk of bias in 3 or 4 of a total of 4 categories; moderate = score of high or unclear in 2 of a total of 4 categories; low = score of high or unclear in 0 or 1 of a total of 4 categories; ACL = anterior cruciate ligament; PCL = posterior cruciate ligament.
Fig. 2.
A graphical risk of bias assessment is presented using the QUADAS-2 tool to indicate the percentage of studies with low, high, or unclear risk of bias for the patient selection, index test, reference standard, and flow and timing domains [50–52].
Data extraction identified the following key elements: (1) ligament(s) investigated; (2) stress technique; (3) magnitude of force; (4) measures of accuracy and reliability including sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and intrarater and interrater intraclass correlation coefficients (ICCs); (5) comparative diagnostic techniques; and (6) results and conclusions regarding comparative diagnostic techniques.
There has been a recent increase in the frequency of stress radiography publications for the diagnosis of knee injuries with nearly half of all studies (18 of 38 studies) included in this review published in the last 10 years (Fig. 3). Fifteen studies (39%) focused solely on the diagnosis of anterior cruciate ligament (ACL) instability, nine (24%) on the posterior cruciate ligament (PCL), two (5%) on varus, two (5%) on valgus, and 10 (26%) on multiligament assessment. Of the multiligament studies, four studies described anterior, posterior, varus, and valgus stress radiography [13, 17, 19, 32]; one described anterior, posterior, and varus stress [18]; four described anterior and posterior stress only [28, 46–48]; and one described posterior and varus stress only [43]. A total of 23 studies were purely descriptive studies of a stress radiography technique, whereas 15 studies were comparative either among stress radiograph techniques or between stress radiography and other diagnostic techniques.
Fig. 3.
The number of publications assessing stress radiographs for diagnosis of knee ligament injuries has increased over the last 10 years.
Results
Stress Techniques
The stress radiography techniques and devices described in the literature varied by the plane of stress and therefore the ligament(s) isolated (Table 2). Several techniques were used for the assessment of more than one plane of stability, including the Telos device (Metax, Hungen-Obbornhofen, Germany) [1, 2, 5, 8–10, 13, 21, 28, 31, 34, 37, 38, 41–43, 47], manual force [6, 12, 13, 32, 40, 44, 46], hydraulic force [17–19], S-type load cell [25, 26], a constant-tension spring [48], and the dynamic stress test using active muscle contraction [1, 7, 21]. A total of 16 unique stress techniques were described across all studies included in this review (Table 3). Including the multiligament studies, 12 stress radiography techniques were reported for applying stress to the ACL, eight techniques for applying stress to the PCL, three techniques for valgus stress, and four techniques for varus stress. The method for applying force and the magnitude of the force also varied across studies and stress techniques. Among ACL and PCL studies, the Telos stress device was the most commonly used stress device [1, 2, 5, 8–10, 13, 21, 28, 31, 34, 37, 38, 41–43, 47].
Table 2.
Stress radiography techniquesǂ
| First author | Stress technique | Force applied |
|---|---|---|
| ACL | ||
| Hooper [15] | Sandbag | 3 kg |
| Rijke [38] | Telos | 15 kPa |
| Granberry [11] | Genucom device | 140 N |
| Franklin [7] | Quadriceps contraction | 133–178 N |
| Rijke [37] | Telos | 0, 7, 14, 21 kPa |
| Stäubli [45] | KT-1000 | 89 N |
| Lerat [29] | Free weight | 9 kg |
| Dejour [6] | Manual | – |
| Monopodal stance test | Body weight | |
| Garces [9] | Telos | 147 N |
| Lerat [30] | Free weight | 9 kg |
| Wirz [54] | Custom steel apparatus | 50 N |
| Beldame [1] | Telos/quadriceps contraction | 250 N/– |
| Beldame [2] | Telos/free weight | 250 N/9 kg |
| Panisset [34] | Telos | 15 kg |
| Dejour [5] | Telos | 15 kg |
| PCL | ||
| Stäubli [44] | Manual | 25–30 kg |
| Hewett [14] | X-stress device | 89 N |
| Margheritini [31] | Telos | 89 N |
| Schulz [41] | Telos | 15 kPa |
| Jung [21] | Telos/hamstring contraction/kneeling | 150 N/–/– |
| Garavaglia [8] | Telos/PCL Press | 150 N/150 N |
| Schulz [42] | Telos | 150 N |
| Jackman [16] | Kneeling | – |
| Garofalo [10] | Telos/kneeling | 15 kg/– |
| Valgus | ||
| Sawant [40] | Manual | – |
| LaPrade [25] | S-type load cell | 10 N-m |
| Varus | ||
| LaPrade [26] | S-type load cell/manual | 12 N-m/– |
| Gwathmey [12] | Manual | – |
| Multiligament | ||
| Jacobsen [17] | Hydraulic force*/† | 9 kg/20–30 kg |
| Jacobsen [18] | Hydraulic force*/† | 9 kg/30 kg |
| Jacobsen [19] | Hydraulic force | 196–294 N |
| McPhee [32] | Manual | – |
| Tozilli [48] | Constant-tension spring | 50 N |
| Stäubli [46] | Manual | 200–300 N |
| Harilainen [13] | Manual*/Telos† | 147 N/– |
| Stäubli [47] | Telos | 178 N |
| Sekiya [43] | Telos | 200 N |
| Lee [28] | Telos | 150 N |
* Varus/valgus; †AP; ǂrefer to Table 3 for a more detailed description of each study and stress technique; ACL = anterior cruciate ligament; PCL = posterior cruciate ligament.
Table 3.
Summary of the stress techniques described for diagnosis of knee ligament injuries
| Stress technique | Studies using the technique (first author) | Number | Stress plane | Summary of technique | Radiographic view |
|---|---|---|---|---|---|
| Constant tension spring | LaPrade [26] | 10 | Varus | A jig was used to secure the cadaveric knees at 20° of flexion and a 12-N-m stress was applied using a model SM S-type Load Cell with an attached handle (Interface, Scottsdale, AZ, USA) | AP |
| LaPrade [25] | 18 | Valgus | A jig was used to secure the cadaveric knees at 0° and 20° of flexion; a 10-N-m stress applied using an S-type load cell | AP | |
| Custom steel apparatus | Wirz [54] | 3 | Anterior | Apparatus holds a cadaveric knee in precise flexion and rotation while a drawer forces are applied; a pulley system applies force to the tibia and the xray cassette is placed in a standard location | L |
| Free weight | Lerat [29] | 100 | AP | Anterior drawer: the patient is supine on a table with the lower extremity supported in a special leg holder and the thigh free; the foot and ankle are fixed with a strap; the opposite limb is positioned on a stool at a lower level; a free hanging 9-kg weight is hung from the distal femur Posterior drawer: the leg support is turned 180° and moved closer to support the patient and a 9-kg weight is hung from a strap at the proximal tibia |
L |
| Lerat [30] | 1050 | Anterior | See Lerat [29] | L | |
| Beldame [2] | 157 | Anterior | See Lerat [29] | L | |
| Genucom device | Granberry [11] | 8 | Anterior | A cadaveric knee is fixed and an electrogoniometer with 6 degrees of freedom is used to measure displacement; force is applied with a strap | L |
| Hamstring contraction | Jung [21] | 30 | Posterior | Patient seated and relaxed with the knee in 90° of flexion and the leg fixed to a rigid stand; the patient sustains a hamstring contraction for 10 seconds while a radiograph is taken | L |
| Hydraulic force | Jacobsen [17] | Multi | A hydraulically operated machine with 9-kg forces for varus/valgus stability at 20° flexion and 5° external rotation | L | |
| Jacobsen [18] | Multi | See Jacobsen [17] | L | ||
| Jacobsen [19] | Multi | See Jacobsen [17] | L | ||
| Kneeling | Jung [21] | 30 | Posterior | The patient kneels on a padded bench with the knee in 90° of flexion; a grip is available in front of the bench for patients to steady themselves | L |
| Garofalo [10] | 20 | Posterior | The patient kneels on a padded bench with the knee in 90° of flexion supporting the tibial tubercle; the xray cassette was placed between the knees of the patient | L | |
| KT-1000 | Stäubli [45] | 16 | Anterior | KT-1000 arthrometer used to apply an 89-N anterior drawer force for stress radiography; knee in 20° of flexion, distal femoral support, foot support to control for tibial rotation | L |
| Manual force | Dejour [6] | 281 | Anterior | Lachman test performed with simultaneous radiograph | L |
| Stäubli [44] | 24 | Anterior | 25–30 kg applied downward force on the tibia with 10°–15° knee flexion using 15-cm thigh support; 2 preloading cycles | L | |
| Sawant [40] | 23 | Valgus | Supine anesthetized patients with knees firmly bound together; feet are held in slight external rotation with valgus applied force to separate feet | AP | |
| LaPrade [26] | 10 | Varus | One hand placed at medial femoral condyle and the other placed just proximal to the lateral malleolus to apply the varus moment in 20° knee flexion | AP | |
| Gwathmey [12] | 27 | Varus | Physician applied varus stress in 20° knee flexion | AP | |
| McPhee [32] | 60 | Multi | Valgus/varus taken in both extension and 20°–30° knee flexion; using lateral stress, views were taken with the patient in the lateral position with the knee adjacent to the table; knee flexed at 90° for anterior and posterior drawer | AP/L | |
| Stäubli [46] | 138 | AP | Supine anesthetized patient; 10° knee flexion held by thigh support; 2 preloading cycles followed by 200–300 N posterior directed force; support moved to proximal tibia for anterior stress radiographs | L | |
| Harilainen [13] | 85 | Varus/valgus | Varus and valgus loads applied in 20° and 90° knee flexion, respectively | AP | |
| Monopodal stance | Dejour [6] | 281 | Anterior | Patient stands on one leg in 20° knee flexion | L |
| PCL press | Garavaglia [8] | 15 | Posterior | 180-N posterior load with the knee flexed at 100° | Ax. |
| Quadriceps contraction | Franklin [7] | 70 | Anterior | 6.8-kg ankle-suspended weight while the knee is supported by a 30 wedge; the patient straightens the knee by contracting the quadriceps | L |
| Beldame [1] | 112 | Anterior | 7-kg ankle weight is placed on the patient while contracting the quadriceps in 20° knee flexion | L | |
| Sandbag | Hooper [15] | 70 | Anterior | 3-kg sandbag placed on thigh proximal to the patella; patient lie supine in 20° knee flexion | L |
| S-type load cell | LaPrade [26] | 10 | Varus | 12-N-m load applied to the cadaveric specimen 25 cm distal to the joint line in 20° knee flexion | AP |
| LaPrade [25] | 18 | Valgus | 10-N-m load applied at the medial malleolus of the cadaveric specimen at 20° knee flexion and full extension (0°) | AP | |
| Telos | Rijke [37] | 82 | Anterior | 15-kPa force while patient lies in lateral decubitus position in 15° knee flexion | L |
| Rijke [38] | 55 | Anterior | See Rijke [37] | L | |
| Garcés [9] | 116 | Anterior | 137-N anterior displacing force for 1 minute while the patient lies on the side being tested in 20° knee flexion | L | |
| Beldame [1] | 112 | Anterior | 250-N force while the patient lies on the side being tested in 20° knee flexion | L | |
| Beldame [2] | 157 | Anterior | See Beldame [1] | L | |
| Panisset [34] | 177 | Anterior | 15-kg force while the patient lies on the side being tested in 20° knee flexion | L | |
| Dejour [5] | 300 | Anterior | 15-kg force while the patient lies on the side being tested in 20° knee flexion | L | |
| Margheritini [31] | 60 | Posterior | 89-N posterior load while the patient lies on the side being tested in 90° and 25° knee flexion | L | |
| Schulz [41] | 787 | Posterior | 19 kPa applied force while the patient lies on the side being test in 90° knee flexion | L | |
| Jung [21] | 30 | Posterior | 150-N force while the patient lies on the side being tested in 90° knee flexion | L | |
| Garavaglia [8] | 15 | Posterior | 180-N posterior load on cadaveric specimen in 30° and 80° knee flexion | L | |
| Schulz [42] | 1041 | Posterior | 150-N posterior load while the patient lies on the side being tested in 90° knee flexion | L | |
| Garofalo [10] | 20 | Posterior | 15-kg force while the patient lies on the side being tested in neutral rotation and 90° knee flexion | L | |
| Harilainen [13] | 85 | AP | 15 kp in 90° knee flexion | L | |
| Stäubli [46] | 138 | AP | A/P preloading cycles (x 2) to 223-N; lateral radiographs taken under 178-N force | L | |
| Sekiya [43] | 10 | Posterior | 200-N force posterior drawer on cadaveric specimen in 90° knee flexion | L | |
| Lee [28] | 80 | AP | 150-N load while the patient lies in decubitus position in 25° (anterior stress radiograph) and 90° (posterior stress radiograph) knee flexion; 3 preloading cycles | L | |
| X-stress device | Hewett [14] | 21 | Posterior | 89-N posterior load is applied to the proximal tibia at approximately 70° of knee flexion | L |
L = lateral; Ax. = axial; Multi = multiligament; AP = anteroposterior.
Stress Radiography Diagnostic Accuracy and Reliability
There was no consensus in the literature as to the most accurate and reliable stress radiography technique for the diagnosis of ACL, posterior cruciate ligament (PCL), medial collateral ligament (valgus), and posterolateral corner (PLC) (varus) injuries. Diagnostic accuracy and/or precision were reported in 55% of studies (21 of 38 studies) (Table 4). Sensitivity, specificity, PPV, and NPV were consistently high for the diagnosis of ACL, PCL, and combined cruciate ligament and valgus knee injuries but varied considerably among studies. No diagnostic accuracy data were reported for diagnosis of isolated varus knee injuries on stress radiography. Overall, excellent intrarater and interrater ICCs were reported for the diagnosis of ACL [28, 30], PCL [28, 42], varus [12, 26], and valgus [25] injuries on stress radiography. However, only six studies included analysis of intrarater and interrater reliability [12, 25, 26, 28, 30, 42].
Table 4.
Diagnostic accuracy and precision of stress radiography
| First author | Threshold (SSD) | Sensitivity | Specificity | PPV | NPV | Reliability (ICC) | |||
|---|---|---|---|---|---|---|---|---|---|
| Intrarater | Interrater | ||||||||
| ACL | |||||||||
| Rijke [37] | – | 0.88 | 1.00 | 1.00 | 0.93 | – | – | ||
| Rijke [37] | – | 0.67* | 0.98* | – | – | – | – | ||
| 0.50† | 1.00† | ||||||||
| 1.00ǂ | 1.00ǂ | ||||||||
| Stäubli [45] | 3 mm | 0.81 | – | – | – | – | – | ||
| Lerat [29] | 5 mm | 0.84 | 0.90 | 0.89 | 0.85 | ||||
| Dejour [6] | 2 mm | 0.92 | – | – | – | – | – | ||
| Garcés [9] | – | 0.575 | 1.00 | – | – | – | – | ||
| 0.66 | 1.00 | ||||||||
| Lerat [30] | 6 mm | 0.87ǂ,§ | 0.90ǂ,§ | 0.89ǂ,§ | 0.85ǂ,§ | 0.91*,§ | 0.97*,§ | ||
| 0.95ǂ,§ | 0.98ǂ,§ | ||||||||
| 0.92*,|| | 0.93*,|| | ||||||||
| 0.92ǂ,|| | 0.95ǂ,|| | ||||||||
| Beldame [1] | – | 0.594§ | 0.906§ | – | – | – | – | ||
| Beldame [2] | |||||||||
| Telos | – | 0.648 | 0.758 | – | – | – | – | ||
| Lerat | – | 0.432 | 0.827 | – | – | – | – | ||
| Panisset [34] | 5 mm | 0.809 | 0.818 | – | – | – | – | ||
| PCL | |||||||||
| Hewett [14] | 8 mm | 1.00 | 1.00 | ||||||
| Schulz [41] | – | – | – | – | – | 0.95 | 0.91 | ||
| Garavaglia [8] | |||||||||
| Telos 30 | |||||||||
| Isolated | 3 mm | 0.933 | 0.867 | 0.955 | 0.813 | – | – | ||
| Combination | 9 mm | 0.880 | 0.771 | 0.733 | 0.900 | – | – | ||
| Telos 80 | |||||||||
| Isolated | 6 mm | 0.976 | 0.778 | 0.911 | 0.933 | – | – | ||
| Combination | 12 mm | 0.885 | 0.794 | 0.767 | 0.900 | – | – | ||
| Valgus | |||||||||
| Sawant [40] | – | 0.9375 | 0.857 | 0.937 | 0.857 | – | – | ||
| LaPrade [25] | – | – | – | – | – | 0.99 | 0.98 | ||
| Varus | |||||||||
| LaPrade [26] | – | – | – | – | – | 0.99 | 0.97 | ||
| Gwathmey [12] | – | – | – | – | – | – | 0.963 | ||
| Multiligament | |||||||||
| Jacobsen [18] | |||||||||
| Varus | 2 mm | – | – | 1.00 | 0.92 | – | – | ||
| AP | 3 mm | – | – | 0.98 | 0.96 | – | – | ||
| Jacobsen [19] | – | – | – | 1.00 | 0.81 | – | – | ||
| Harilainen [13] | – | – | 0.86 | – | 0.99 | – | – | ||
| Varus | – | 0.55 | 0.89 | 0.71 | 0.80 | – | – | ||
| Valgus | – | 0.28 | 0.93 | 0.85 | 0.49 | – | – | ||
| A (J) | – | 0.16 | 1.00 | 1.00 | 0.50 | – | – | ||
| A (L) | – | 1.00 | 0.88 | 0.33 | 1.00 | – | – | ||
| P (J) | – | 1.00 | 0.90 | 0.40 | 1.00 | – | – | ||
| P (L) | |||||||||
| Lee [28] | – | – | – | – | – | A | P | A | P |
| MM | – | – | – | – | – | 0.713 | 0.859 | 0.853 | 0.884 |
| LL | – | – | – | – | – | 0.624 | 0.814 | 0.794 | 0.773 |
| Mid-Mid | – | – | – | – | – | 0.834 | 0.914 | 0.887 | 0.859 |
| PC | – | – | – | – | – | 0.722 | 0.852 | 0.851 | 0.914 |
| BAT | 0.891 | 0.893 | 0.923 | 0.934 | |||||
* Healthy knees; †partial tear; ǂcomplete tear; §medial compartment displacement; ||lateral compartment displacement; ¶combined MCL and ACL or PCL tear; SSD = side-to-side difference between knees in displacement on stress radiography; PPV = positive predictive value; NPV = negative predictive value; ICC, intraclass correlation coefficient; ACL = anterior cruciate ligament; Combined = combined PCL and peripheral ligament injury; PCL = posterior cruciate ligament; MCL = medial collateral ligament. Radiographic measurements: BAT = Blumensaat line–anterior tibia; LL = lateral-lateral; Mid-Mid = middle-middle; MM = medial-medial; PC = peripheral-central; A = anterior; P = posterior. Jacobsen’s (J) and Leven’s (L) measuring methods. If not otherwise specified, values are for diagnosis of complete tears only. For Lee et al., lower limit reproducibility reported only.
Stress Radiography Compared With Other Diagnostic Techniques
Stress radiography techniques were compared with alternate diagnostic techniques including instrumented arthrometry, MRI, and physical examination in 12 studies (Table 5). Three of five studies comparing stress radiography with the KT-1000 or KT-2000 (MEDmetric Corporation, San Diego, CA, USA) for the diagnosis of AP instability concluded that stress radiography is superior, whereas the other two studies showed excellent but equivalent diagnostic ability [7, 14, 29, 31, 45]. For diagnosis of ACL injury, stress radiography correlated with results of the pivot shift test but not the Lachman’s test [15], was equivalent to the GNRB computerized arthrometer [2], and offered greater sensitivity but similar specificity to the Rolimeter [34]. For the assessment of multiligament injury, stress radiography was more accurate than examination under anesthesia and clinical examination [18]. Stress radiographs with > 10 mm of posterior tibial displacement and a Grade 3 posterior drawer test were equally indicative of a combined PCL and PLC injury [43]. Varus stress radiographs correlated well with the severity of injury on MRI [12] but was not compared with physical examination or any other diagnostic tests in any study. Valgus stress radiography was not compared with other diagnostic tests in any study.
Table 5.
Stress radiography compared with alternate diagnostic tests
| First author | Comparative test | Results and conclusions |
|---|---|---|
| ACL | ||
| Hooper [15] | Pivot shift test and Lachman test | Significant correlation between the mean sagittal displacement on stress radiographs and clinical pivot shift test for a mean lateral displacement of 13.5 mm; there was no correlation with the Lachman test |
| Franklin [7] | KT-1000 | No significant difference between KT-1000 and stress radiography |
| Stäubli [45] | KT-1000 | Both KT-1000 and stress radiography are diagnostic for chronic ACL-deficient knees |
| Lerat [30] | KT-1000 | Both KT-1000 and stress radiography provide excellent diagnostic value of ACL integrity with predictive values of 90%; stress radiographs provide superior precision and independent evaluation of medial and lateral compartments |
| Beldame [2] | GNRB device | No significant difference between diagnostic performance of computerized GNRB arthrometer and stress radiography; however, stress radiography was more easily implemented in a clinical setting |
| Panisset [34] | Rolimeter and pivot shift test | Telos stress radiography provides greater sensitivity relative to Rolimeter with similar specificity; however, Telos specificity was superior when used in combination with the pivot shift test |
| PCL | ||
| Hewett [14] | KT-1000 and posterior drawer | Stress radiography is superior to both the KT-1000 and the posterior drawer in assessing for presence or absence of a complete PCL tear |
| Margheritini [31] | KT-2000 | Stress radiography is superior to the KT-2000 for quantifying posterior tibial translation; the KT-2000 underestimates the degree of posterior laxity compared with stress radiography |
| Valgus | ||
| – | – | – |
| Varus | ||
| Gwathmey [12] | MRI | Stress radiography correlates with the severity of injury diagnosed on MRI and provides information regarding degree of laxity that MRI does not |
| Multiligament | ||
| Jacobsen [18] | Clinical examination and EUA | Stress radiography was more accurate than EUA, which in turn was more accurate than clinical examiantion |
| Sekiya [43] | Grade III posterior drawer | Stress radiographs with > 10 mm of posterior tibial displacement and a Grade 3 posterior drawer test are equally indicative of a combined posterolateral corner injury |
EUA = examination under anesthesia; GNRB (GeNouRoB, Laval, France); KT-1000 (MEDmetric Corporation, San Diego, CA, USA); KT-2000 (MEDmetric Corporation); Rolimeter (Aircast Incorporated, Summit, NJ, USA); Telos (Austin & Associates, Inc, METAX, Hungen, Germany); ACL = anterior cruciate ligament; PCL = posterior cruciate ligament.
Discussion
Stress radiography offers an objective, quantifiable, noninvasive, and retrievable record that can be used to augment the diagnosis of knee ligament injuries. Over the last 10 years, interest in stress radiography has grown as was evident from the recent increase in publications on this topic. However, although stress radiography is now widely used in the clinical setting, there is a current lack of consensus as to which technique is best for assessing anterior, posterior, varus, and valgus knee stability. This review was undertaken to identify the various stress techniques that have been described in the literature for the diagnosis of acute or chronic knee ligament injuries, to compare the accuracy and reliability of these techniques, and to describe the use of stress radiography compared with other diagnostic tests.
We acknowledge several limitations in this review. First, this review excluded non-English-language articles, which may have led to the omission of additional descriptive studies of stress techniques, accuracy and reliability data, and comparative studies not available in the English language literature. Second, this review did not compare landmarks and reference points for measuring displacement or gapping on stress radiographs. Only two studies in this review reported results for comparison of measurement techniques using different landmarks and reference points on stress radiographs [28, 30]. Although we recognize that the choice of landmarks may influence the accuracy and reliability of measurements in stress radiography, this was beyond the scope of the present review. Future studies should define the optimal reference points for measuring displacement and/or gapping in knee stress radiography.
In addition, this review’s conclusions rest on the quality of the studies that have been included. Overall risk of bias was high in eight studies and moderate in 10 studies (Table 1). Risk of bias was especially high in the reference standard domain attributable in large part to interpretation of reference standard results with prior knowledge of the corresponding results of stress radiography. Conversely, when physical examination was used as the reference standard, these studies introduced bias in the index test domain by interpreting the results of stress radiography with knowledge of the results of physical examination. Other notable sources of bias included the use of multiple or inconsistent reference standards. Reported reference standards included arthroscopy, physical examination, arthrometry, and MRI. Remarkably, some comparative studies did not explicitly name a reference standard. Additional bias was potentially introduced in studies that enrolled nonconsecutive or nonrandom patients or observed an inappropriately long, highly variable, or unreported time interval between stress radiography and record of the reference standard test. To address these sources of bias, future studies should include appropriate blinding at all phases of the study to ensure independence of stress radiography protocols, reference standard evaluation of ligament stability, and measurements of displacement or gapping. Moreover, a single reference standard must be used in future studies to allow for improved comparison across studies. Based on the reference standards used in the current literature, we would recommend a consistently applied surgical reference standard because it allows for direct visualization and assessment of ligament integrity and minimizes the inaccuracies inherent in other reference standards such as MRI and physical examination.
A total of 16 unique stress radiography techniques for the diagnosis of knee ligament injuries were identified in this review, indicating a high degree of heterogeneity in methodology across studies. Although no clear consensus emerged in the literature, the Telos device was the most widely used for ACL and PCL injury studies, especially in those performed within the past 10 years. The Telos device produces an adjustable, quantifiable, and reproducible anterior or posterior force on the injured knee. Currently, no analogous device has been described in the literature for standardization of varus- or valgus-directed forces used to diagnose medial or PLC knee injuries.
Measures of the diagnostic accuracy and reliability of stress radiography varied considerably from study to study and were likely influenced by stress technique, use of anesthesia, cadaveric laboratory study design, sample size, choice of reference standard, and the threshold set for the maximum acceptable side-to-side difference for normal knees. Stress radiography performed in a clinic setting may yield varying results resulting from patient guarding or muscle contraction secondary to pain, whereas testing performed under anesthesia or in a cadaveric model would eliminate this effect. In addition, the calculated diagnostic accuracy of stress radiography techniques changes depending on the side-to-side difference limit that defines a nonfunctional ligament. For the ACL, the threshold varied from 2 mm [6] to 6 mm [30] and from 3 mm [8] to 12 mm [8] for the PCL. The inconsistent threshold for side-to-side difference for ACL and PCL injuries clouds any comparison of the diagnostic accuracy among studies and techniques.
In general, diagnostic varus and valgus stress radiography has been under underinvestigated in the literature. Future studies must validate diagnostic gapping benchmarks that have been previously described in cadaveric models. For simulated posterolateral corner injuries in a cadaveric model, LaPrade et al. [26] described an average increase in side-to-side varus gapping of 2.7 mm for isolated fibular collateral ligament tears compared with 4.0 mm for combined Grade III posterolateral corner injuries. This demonstrates the potential of stress radiography to distinguish between varying degrees of instability and injuries to multiple structures. In the case of PLC injuries, it is possible to detect injuries to multiple structures with a single stress radiography technique. However, in cases of multiligament injuries, it is necessary to perform stress radiography techniques in the appropriate planes to sufficiently assess stability.
For simulated medial knee injuries in a cadaveric model, LaPrade et al. [25] described a threshold of 3.2 mm of medial compartment gapping compared with the contralateral knee for the diagnosis of Grade III medial collateral ligament tears. However, the distribution of varus and valgus gapping across a large cohort of patients with suspected medial or lateral knee injuries and its correlation with surgically verified tears has not been investigated. Once standard cutoff points are validated in vivo, these thresholds can then be used to calculate and compare the diagnostic accuracy and reliability for varus and valgus stress radiography between studies with greater confidence.
Finally, results of the comparative diagnostic studies included in this review yield no clear consensus on the use of stress radiography compared with other diagnostic tests for knee ligament injuries. The ability to draw conclusions is limited even among studies that compared stress radiography with the same alternative diagnostic technique. One reason for this is the varying stress techniques and forces used between studies. For example, although Franklin et al. [7], Stäubli and Jakob [45], and Lerat et al. [30] all compared stress radiography for the diagnosis of ACL injury to the KT-1000, stress techniques varied. Franklin et al. use the quadriceps contraction technique at 133 N to 178 N, Stäubli et al. used the KT-1000 at 89 N, and Lerat et al. used a 9-kg free weight. A greater emphasis on consistent methodology across studies will be required in the future.
In summary, this review highlights the wide array of techniques, varying degrees of diagnostic accuracy and reproducibility, and at times contradictory conclusions regarding the use of stress radiography compared with alterative techniques for diagnosing knee ligament injury. Based on the multitude of stress techniques reported, varying levels of diagnostic accuracy, and inconsistencies regarding comparative efficacy of stress radiography to other diagnostic modalities, we are not able to make specific recommendations with regard to the best stress radiography technique for the diagnosis of knee ligament injury. To date, no gold standard for a specific stress radiographic technique or the magnitude of force applied during testing has been established for assessing anterior, posterior, varus, and valgus knee stability. Additional comparative studies are needed to further define the use of stress radiography compared with other diagnostic techniques and to establish evidence-based recommendations for the most accurate, reliable, easy-to-use, and cost-effective stress radiography technique. Specifically, further studies should be designed to eliminate common sources of bias identified in this review by using consecutive patients, a consistent and reliable reference standard, and sufficient blinding between stress radiography and reference standards. Additionally, future in vivo studies are required to validate cadaveric models as in the case of varus and valgus stress radiography.
Acknowledgments
We thank Ryan Warth MD, for his feedback throughout this review and Jim Beattie MLIS, for his assistance in retrieving articles in full text for this review.
Footnotes
One of the authors (RFL) is a paid consultant for Arthrex (Naples, FL, USA). One of the authors certifies that he (EWJ, BTW, RFL) or a member of his or her immediate family, has or may receive payments or benefits, during the study period, an amount of less than USD 10,000 from Smith & Nephew Endoscopy (London, UK), less than USD 10,000 from Arthrex, Inc, less than USD 10,000 from Siemens Medical Solutions USA (Malvern, PA, USA), less than USD 10,000 from Sonoma Orthopedics, Inc (Santa Rosa, CA, USA), less than USD 10,000 from ConMed Linvatec (Largo, FL, USA), less than USD 10,000 from Össur Americas (Foothill Ranch, CA, USA), less than USD 10,000 from Small Bone Innovations, Inc (Morrisville, PA, USA), less than USD 10,000 from Opedix (Scottsdale, AZ, USA), and less than USD 10,000 from Evidence Based Apparel (Alignmed, Santa Ana, CA, USA).
All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request.
Clinical Orthopaedics and Related Research neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDA-approval status, of any drug or device prior to clinical use.
This work was performed at the Steadman Philippon Research Institute, Vail, CO, USA.
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