Introduction
One of the major stabilizing ligaments of the knee, the anterior cruciate ligament (ACL) primarily functions to control anterior translation of the tibia as well as provides stabilization for rotational forces and, to a lesser degree, varus and valgus stress. Consisting of two dominant bundles, an anteromedial and a posterolateral, the ACL originates on the medial aspect of the lateral femoral condyle and inserts onto the tibial plateau, approximately 15 mm posterior to the anterior articular surface (Friedberg, 2018).
The annual incidence of ACL tears is estimated at one in 3,500, although, given lack of a standard mechanism for reporting these injuries within the general population, it is likely higher. Surgical reconstruction of ACL tears accounts for up to 200,000 procedures annually in the United States (Friedberg, 2018).
The National Collegiate Athletic Association Injury Surveillance System has tracked information on athletes participating in 15 major collegiate sports since 1988. Here, we find tears associated with football, which account for the highest reported rates of ACL tears, are typically from contact. Across all major sports, young female athletes have a higher incident of ACL tears than their male counterparts. Outside of football, the most commonly described injury, known as a pivot shift injury, is a noncontact incident involving a rapid deceleration on a planted foot with a rotational or valgus force applied to the knee (Agel, Rockwood, & Klossner, 2016; Boden, Dean, Feagin, & Garrett, 2000; Friedberg, 2018; Mountcastle, Posner, Kragh, & Taylor, 2007; Prodromos, Han, Rogowski, Joyce, & Shi, 2007).
Case Presentation
A 38-year-old man presented with a 2-day history of right knee pain, swelling, and feelings of instability after sustaining a fall. He slipped on the last couple of steps of a marble staircase, lunging forward and landing on the right foot. He described a forceful pivot shift-type injury, as the rest of his body "tumbled over" the planted right foot, ultimately landed onto his buttock. He had considerable pain at that time, requiring assistance to get up from the floor. He was able to "limp away" and noted significant knee swelling within minutes of the injury occurring. A friend took him home, and he spent remainder of the day resting, icing, and elevating the leg. He took a couple of doses of ibuprofen, which helped the aching pain. He had a knee brace from a previous injury and wore that when up and about, noting the knee felt unstable otherwise. When things had not improved after another day, he presented for evaluation.
Upon presentation was an alert, oriented, affected-appropriate male in no apparent distress. He ambulated with a significantly antalgic, straight-legged gait on the right. He was wearing a knee brace but was not using any other assistive device. There was a moderate effusion and mild warmth. No deformity, discoloration, or abrasions were present. Vague tenderness about the medial and posterior knee was noted. Range of motion was 0[degrees]-110[degrees], with painful end-range flexion. There was noted laxity with anterior drawer and Lachman's test. Pivot shift, bounce home, and McMurray's tests were all positive. His strength was 5/5 and found to be distally neurovascularly intact.
Imaging obtained at the time of evaluation included anteroposterior, lateral, and oblique radiographs of the right knee (see Figure 1). These images were unremarkable. Given findings of physical examination, most concerning a tear of the ACL, the patient was recommended to have magnetic resonance imaging (MRI) of the knee. He agreed, and findings confirmed the suspected clinical diagnosis of ACL tear (see Figure 2). Other findings of the MRI, including bone marrow edema, joint effusion, generalized muscle strains, and a small meniscus tear, were consistent with the reported pivot shift injury.
Management
Initial management includes rest, ice, compression, elevation, use of nonsteroidal anti-inflammatory drugs, brace wear, and potential need for crutches with protected weight-bearing, given the patient's pain level and ambulatory status. Although ACL tears can be managed conservatively, most young, active, and athletic individuals opt for surgical reconstruction in order to return to higher level activities such as sports. Graft selection and postoperative rehabilitation programs vary by provider and continue to be a source of debate in the literature. There is, however, sufficient evidence to support a patient's choice to delay surgery if he or she wishes to undergo attempted rehabilitation before proceeding with surgery, as the difference in 5-year outcomes has no statistical significance (Friedberg, 2018; Frobell et al., 2013).
Those opting for conservative management are typically low demand, such as older adults whose primary physical activity is community ambulation. Younger patients who elect for conservative management should be aware of the risk of further joint damage, primarily meniscal tears, which may result from joint instability. These patients also have significantly lower return-to-sports rates as those who elect for surgery (Friedberg, 2018; Frobell et al., 2013).
Referral to physical therapy, and patient compliance with the prescribed therapy treatments, is paramount in achieving optimal outcomes and returning patients to their previous level of function. Therapy regimens will vary but generally focus on quadriceps and hamstring strengthening, dynamic stabilization, gait training, and injury prevention. For those who intend to return to rigorous sports, or strenuous physical activity in general, an ACL-stabilizing brace may be appropriate. Return to sports should be done in a gradual fashion and only after the patient has achieved equal range of motion, strength, and stabilization within physical therapy (Friedberg, 2018; Frobell et al., 2013).
Discussion
An ACL tear should be primary on the list of differential diagnoses for any patient presenting with a pivot shift-type injury, especially if complaining of continued knee instability. This is confirmed by testing joint laxity on physical examination. The advanced practice provider should be aware that Lachman's testing is more sensitive than the anterior drawer test. If positive, the advanced practice provider should perform MRI for confirmation and potential surgical planning (Friedberg, 2018; Frobell et al., 2013).
At minimum, patients should have initial conservative management, followed by a course of physical therapy. Younger patients, which include most athletes, should be referred to an orthopaedic sports medicine surgeon for consultation regarding surgical options. Important conversations about the timing of surgery, graft selection, rehabilitation, and return-to-sports programs should be done at the outset of treatment so that expectations better align with patient outcomes (Friedberg, 2018; Frobell et al., 2013).
References