Author: Michelle Post, PA-C
Michelle Post, PA-C
, shares a case illustrating when an apparent small fracture (the Segond fracture) is indicative of a more significant underlying problem, an ACL tear.
Patient History and Exam
A 13-year-old premenarchal female presented to the clinic with a swollen, painful knee two days after an injury during a basketball game. She jumped up for a rebound and, when she landed, her knee gave out and she heard a "pop." She was unable to continue playing and shortly thereafter, noticed marked swelling of the knee. She was non-weight bearing on her right leg and presented to the emergency department, where she had X-rays of the right knee. She was told she had a small fracture of the tibia and was placed in a knee immobilizer with follow-up in the ortho clinic.
Figure 1: Lachman's test
On exam, she had an antalgic gait, a large knee effusion and limited passive range of motion. She had no tenderness to palpation of the patella and medial joint line, but mild tenderness to palpitation of the lateral joint line. Her knee was stable to varus and valgus stress at 0 and 30 degrees. There was no apprehension with lateralization of the patella. She had diffuse ligamentous laxity, with hyperextension of both elbows and the left knee and demonstrated the ability to touch her thumbs to her forearms with maximum wrist flexion.
Figure 2: Pivot shift test
She had significant guarding with attempts at Lachman's maneuver, during which the patient is supine, the knee is flexed to 30 degrees and the femur is stabilized with one hand while the other hand grasps the tibia and attempts to translate the tibia anteriorly (Figure 1). Increased translation of the tibia and/or a soft endpoint as compared to the contralateral leg is a positive test. Pivot shift, McMurray and Thessaly tests were deferred to due to discomfort. The pivot shift test assesses ACL integrity and is performed with the patient supine and the knee in extension. One hand is placed on the lower leg and the other hand is placed on the lateral aspect of the proximal tibia. The leg is internally rotated and a gentle valgus force is applied while the knee is flexed. If the patient has an ACL tear, the tibia will visibly reduce on the femur with flexion of the knee (Figure 2).
Figure 3: Thessaly test
The Thessaly test is used to detect a meniscal tear and has increased sensitivity and specificity as compared to the McMurray and Apley grind tests. The patient stands flat footed on one leg while the examiner holds the patient's hands for balance. The patient flexes the knee to 20 degrees and rotates medially and laterally three times (Figure 3). The test is positive if the patient experiences joint line pain, catching or locking.
Figure 4: Segond fracture
Anteroposterior (AP) x-ray of the knee (Figure 4) revealed closing physes, a large effusion and a Segond fracture (a small avulsion fracture of the lateral tibial plateau).
Figure 5: Normal ACL
A magnetic resonance imaging (MRI) was ordered because of a suspicion for intraarticular pathology given the significant effusion and presence of the Segond fracture (Figures 5, 6).
Figure 6: Torn ACL of this patient
The MRI revealed an ACL disruption with the typical "bony bruise" pattern over the lateral tibial plateau and lateral femoral condyle. No meniscus tears were appreciated.
The patient attended physical therapy to optimize knee range of motion and quadriceps and hamstring strength preoperatively. Two weeks later, she underwent transphyseal ACL reconstruction with hamstring tendon autograft.
Difficulty obtaining a conclusive physical exam on patients with an acute ACL tear is typical. The suspicion of an ACL tear is supported by the mechanism of injury (i.e., a noncontact, twisting injury) and the presence of a large effusion. The differential diagnosis also includes patellar dislocation, fracture and meniscus tear. Partial ACL tears may not reveal pronounced laxity with Lachman's maneuver, but will typically cause a pivot shift. X-rays of the knee are essential to rule out fracture, especially in children younger than 12, who are more likely to sustain a tibial eminence fracture with the same mechanism of injury. The Segond fracture appears innocuous but is correlated with an ACL tear in 75% to 100% of cases.
MRI is used to confirm an ACL tear, but is not necessary in cases where an isolated ACL tear is suspected on exam. Meniscus tears occur frequently with ACL tears, and bucket handle tears may not only limit range of motion, but also prohibit excursion of the tibia on the femur during Lachman's maneuver, leading to a "false-negative" test. The sensitivity and specificity of MRI for meniscus tears in adults are about 80% and 90%, respectively. For children less than 12 years, however, MRI specificity is decreased because signal changes seen in the meniscus of children may reflect their normal, more abundant vasculature rather than a tear. The gold standard for diagnosis of a meniscal tear in children is arthroscopic evaluation.
For patients who would like to return to sports that require cutting, jumping, pivoting and/or contact, ACL reconstruction is recommended. Without reconstruction, the patient is at increased risk for recurrent "giving way" episodes and further damage to the articular surface and menisci, both of which may result in premature degenerative changes. Transphyseal ACL reconstruction with hamstring tendon autograft is preferred in children approaching skeletal maturity and has been shown to have 90%+ success rates without disrupting the function of the distal femoral and proximal tibial physes. Another choice for ACL autograft is bone-patellar tendon-bone, although bony plugs are generally avoided in children with open growth plates. Allografts (cadaver tissues) may also be used for ACL reconstructions, although allograft tendons take longer to remodel (up to two years) than autografts and are associated with increased laxity and higher failure rates in this population. Many different techniques of ACL reconstruction and graft fixation have been described, with no single technique proving clearly superior. There are a few published case reports of growth disturbance and also physeal narrowing on MRI after transphyseal ACL reconstruction with hamstring autograft without any clinical implications such as leg length discrepancy or angular deformity. Laxity of joints is a risk factor for ACL tears. Patients with hyperextension at the knees are sometimes encouraged to wear a custom-fit knee brace after ACL reconstruction to help prevent reinjury.
Average return to sports time is 9 to 12 months. Some studies have shown a negative impact on academic performance when ACL reconstruction is performed during the school year, but the potential risk of further damage to the knee must be considered when deciding to delay surgery.
Figure 7: Postoperative AP knee X-ray
The patient did very well postoperatively. Her postoperative AP knee X-ray is shown in Figure 7. She wore a hinge knee brace initially, which limited her range of motion, and was permitted to weight-bear as tolerated.
She underwent a rigorous physical therapy protocol, and her range of motion and strength gradually improved. Three months postoperatively, she started jogging and at five months she was jumping. Ultimately she passed an agility test, which assesses the strength, balance and endurance of the operative leg versus the nonoperative leg. She was fitted with a custom knee brace that blocks hyperextension and returned to playing basketball at nine months.
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