In addition to using special tests during clinical assessment of tibiofemoral joint laxity, instrumentation may also be used as an adjunct in confirming ACL injuries. The KT-1000 arthrometer is a device that has been validated to measure the amount of anterior tibial translation relative to the femur (Pugh, Mascarenhas, Arneja, Chin, & Leith, 2008). A review by Arneja and Leith (2009) indicates that a diagnostic test indicating ACL involvement is positive when 2 to 3 millimeters’ difference in maximal tibial anterior translation between involved and uninvolved limbs is present. The authors do not recommend testing the involved limb only (Arneja & Leith, 2009). Although KT-1000 arthrometry may be useful in developing a diagnosis of ACL tear, there is only a weak correlation between knee joint laxity and knee function following ACL reconstruction (Ross, Irrgang, Denegar, McCloy, & Unangst, 2002). Clinicians should also evaluate the integrity of other knee joint structures to aid in differential diagnosis and the assessment of concomitant injury. See the ‘Differential Diagnosis and Concomi- tant Injuries’ section below. Quadriceps strength and activation Quadriceps strength deficits are common and significant follow- ing ACL injuries, often occurring rapidly after injury (Williams et al., 2005). Manual muscle testing of knee flexors and extensors can be performed to assess for possible weakness or pain sec- ondary to the external resistance applied, but has limited validity. While a manual muscle test score below 5/5 indicates significant weakness, a score of 5/5 does not guarantee full strength. As- sessing extensor lag during a straight leg raise can be an easy clinical measure of functional quadriceps strength; absence of an extensor lag leads to better postoperative outcomes (Shelbourne, Urch, Gray, & Freeman, 2012). Quadriceps (and hamstring) strength may be most accurately as- sessed using an electromechanical dynamometer. Unfortunately, many clinicians do not have access to an electromechanical dy - namometer. In the absence of an electromechanical dynamom- eter, other methods including using a 1-repetition maximum or hand-held dynamometer secured by a strap may be used. These alternative methods (i.e., 1-repetition maximum and hand-held dynamometer secured by a strap) tend to underestimate strength (Sinacore et al., 2017), so reaching an even higher threshold of symmetry (e.g., 95% or even 100% of the uninvolved limb) may be appropriate. Another technique used by clinicians to measure quadriceps strength is the burst superimposition technique during a maximal voluntary isometric contraction (MVIC; Snyder-Mackler, Delitto, Stralka, & Bailey, 1994). During testing, a burst superimposition of electrical stimulation is delivered to the quadriceps muscle while the patient is completing a quadriceps MVIC. Quadriceps muscle activation is then calculated as the ratio of force produced during MVIC to the force produced with addition of the electri- cal stimulation, which can be used as a measure of arthrogenic muscle inhibition or the inability to fully activate a muscle due to structural changes in a joint (Lynch, Logerstedt, Axe, & Sny- der- Mackler, 2012). Testing is completed on each limb until 95% quadriceps activation is achieved, activation levels plateau, or the patient fatigues. After completing testing on each limb, a quadriceps index (QI) can be calculated as the quotient of the involved limb to the unin- volved limb multiplied by 100. The QI provides information on the strength of the quadriceps of the involved limb compared to the contralateral limb. The burst superimposition technique is supe- rior to handheld dynamometry (that is properly secured) because the patient completes an MVIC into a stationary structure that re - cords quadriceps muscle force generation. Thus, the assessment is not dependent on the ability of the examiner to provide suf- ficient resistant force for testing. Also, unlike handheld dynamom- etry, the burst superimposition technique allows for measurement of quadriceps muscle activation, providing information on the pa- tient’s ability to volitionally activate the quadriceps and whether progression of activity can be recommended.
2012). Acute knee joint effusion is also present following ACL re- construction, and it may become chronic in nature despite use of an appropriate effusion management program. Knee joint effu- sion is important to assess through the nonoperative, preopera- tive, and postoperative periods. Knee joint effusion is usually based on clinical observation, and ac- curately assessing the volume of effusion can be difficult (Wright & Luhmann, 1998). The fluctuation test and patellar tap test have either positive or negative grades, but they lack a quantified scal- ing system and are unreliable (Fritz, Delitto, Erhard, & Roman, 1998). Circumferential measurements using a tape measure can assess joint swelling but may reflect increases in girth beyond those caused only by knee joint effusion. Another method used to measure knee joint effusion is the modi- fied stroke test, which has been shown to be reliable in a clinical setting (Sturgill et al., 2009). The test quantifies knee joint effu- sion using a five-point scale, and begins by the examiner stroking any fluid upward at the medial tibiofemoral joint line two or three times. If the swelling does not immediately return, the examiner then strokes downward along the distal lateral thigh and observes for any return of fluid at the medial sulcus. The test is graded as follows: ● Grade 0 : No wave was produced with the downward stroke. ● Grade Trace : A small wave of fluid returns at the medial sulcus with the downward stroke. ● Grade 1+ : A larger return wave of fluid is produced at the medial knee. ● Grade 2+ : Swelling returns without the downward stroke. ● Grade 3+ : Inability to move the effusion out of the medial sulcus is shown. Knee joint laxity Tibiofemoral joint laxity is commonly tested via anterior tibial translation when an ACL injury is suspected. Several special tests and tools can assess tibiofemoral joint laxity, including the ante- rior drawer test, Lachman test, pivot shift test, and arthrometry. The anterior drawer test is performed with the patient lying su- pine with 90° of knee flexion and 45° of hip flexion. An anterior translation force is applied to the proximal tibia while the foot is stabilized, with a soft end feel and increased anterior tibial trans- latory excursion indicating a positive test (Magee, 2002). The an- terior drawer test is considered abnormal with a 6- to 10-mm dif- ference of anterior tibial translation compared to the uninvolved tibiofemoral joint and severely abnormal with greater than 10-mm difference according to IKDC 2000 criteria (AOSSM, 2009). The Lachman test is performed while the patient lies supine with the knee flexed 20° to 30°. The examiner stabilizes the dis- tal femur with one hand while providing an anterior force to the proximal tibia with the other hand (Magee, 2002). A soft end feel compared to the contralateral side constitutes a positive test, and the same grading system used for the anterior drawer test is also applied to the Lachman test (AOSSM, 2009). The pivot shift test is performed while the patient is in the su - pine position with the knee started in an extended position. The examiner internally rotates the tibia with one hand at the ankle while providing a valgus force with the other hand at the proxi- mal tibia while simultaneously flexing the knee. A positive test is present when anterolateral tibial subluxation is reduced as the knee moves into increased flexion (Benjaminse, Gokeler, & van der Schans, 2006). The pivot shift test (AOSSM, 2009) is graded between limbs as equal, glide (+), clunk (++), or gross (+++). The Lachman test is the most accurate for detecting ACL tears, with a sensitivity of 85% and a specificity of 94% (Benjaminse et al., 2006). The pivot shift test demonstrates very high specificity at 98% but poor sensitivity at 24% (Benjaminse et al., 2006). The anterior drawer test can be useful in chronic conditions, with a sensitivity of 92% and a specificity of 91%, but it is not as accurate in acute conditions (Benjaminse et al., 2006). When acute ACL injury is suspected, Benjaminse and colleagues recommend per- forming the Lachman test along with the pivot shift test to assist in diagnosis (Benjaminse et al., 2006).
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