Anterior Cruciate Ligament (ACL) Injury - MSK

Overview

Snapshot

A 27-year-old woman presents to the emergency department for severe pain in the right knee. A few hours prior to presentation, an opposing soccer player strikes her leg from her right side while her foot was planted to the ground. Afterwards, she felt a "pop" sound that was followed by severe knee pain and swelling. After the swelling improved, she feels that her right knee is unstable. On physical exam, the patient has a positive Lachman test. The patient is asked to rest, place ice and compress the knee, and elevate the affected leg. Given her sport demands, a conversation is made on the necessity of surgical reconstruction of the anterior cruciate ligament.

Introduction

Clinical definition
- injury in the form of tear or rupture affecting the anterior cruciate ligament (ACL) in the knee
Epidemiology
- incidence
  - non-contact ACL injuries are more common
- demographics
  - more common in female athletes
- risk factors
  - sports (e.g., football, soccer, skiers, and basketball)
  - motor vehicle accidents
Pathoanatomy
- normal anatomy
  - the ACL course
    - originates in the posteromedial aspect of the lateral femoral condyle
    - reaches the anteromedial aspect of the tibia
  - the ACL plays an important role in knee stability
    - it controls anterior translation of the tibia
      - it also restrains against tibial rotation, varus, and valgus stress
- pathology
  - contact mechanisms
    - injury that causes hyperextension or valgus deformation of the knee
      - e.g., football injury
    - high-speed motor vehicle accident
  - non-contact mechanisms
    - changing direction, pivoting, or landing that leads to rotation or valgus stress of the knee after sudden deceleration
Associated conditions
- unhappy triad which consists of injury to the
  - ACL
  - medial collateral ligament
  - medial meniscus
Prognosis
- the majority of athletes are able to return to their sports activities with ACL reconstruction

Presentation

Symptoms
- feeling a "pop" in the knee
  - thereafter, there is acute swelling and pain
- unstable or "giving out" knee
Physical exam
- anterior drawer test
  - the proximal tibia is anteriorly pulled while the patient is supine and the knee is flexed at 90 degrees
    - if there is anterior translation then the test is positive
- Lachman test
  - the proximal tibia is anteriorly pulled with one hand, while the other hand stabilizes the distal femur while the knee is flexed at 30 degrees
- hemarthrosis

Imaging

Magnetic resonance imaging (MRI)
- indication
  - an imaging modality that can confirm the diagnosis
  - if reconstruction is a possibility or to identify concomitant knee pathology

Studies

Making the diagnosis
- can be made based on typical clinical presentation alone
- can be confirmed by MRI or knee arthroscopy

Differential

Meniscal tear
- differentiating factor
  - patients can have a positive
    - Thessaly test
    - McMurray test
    - Apley test
Posterior collateral ligament (PCL) injury
- differentiating factor
  - patients can have a positive posterior drawer test
  - trauma is typically due to
    - a motor vehicle accident leading to "dashboard injury"
    - falling on a flexed knee while the foot is plantarflexed
    - direct trauma to the proximal tibia

Treatment

Conservative
- rest, ice, compression, and elevation (RICE) therapy
  - indication
    - management to reduce pain, edema, and hemarthrosis in the acute stage of the injury
      - nonsteroidal anti-inflammatory drugs are typically added
Operative
- surgical reconstruction
  - indications
    - performed in
      - young and active patients with high demand sports or jobs
      - significant knee instability
        
        such as injuries affecting multiple knee structures (e.g., unhappy triad)

Complications

Osteoarthritis
Arthrosis
Sports disability

Blood, Plasma, Serum	Reference Range
ALT	8-20 U/L
Amylase, serum	25-125 U/L
AST	8-20 U/L
Bilirubin, serum (adult) Total // Direct	0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca²⁺)	8.4-10.2 mg/dL
Cholesterol, serum	Rec: < 200 mg/dL
Cortisol, serum	0800 h: 5-23 μg/dL //1600 h: 3-15 μg/dL 2000 h: ≤ 50% of 0800 h
Creatine kinase, serum	Male: 25-90 U/L Female: 10-70 U/L
Creatinine, serum	0.6-1.2 mg/dL
Electrolytes, serum
Sodium (Na⁺)	136-145 mEq/L
Chloride (Cl^-)	95-105 mEq/L
Potassium (K⁺)	3.5-5.0 mEq/L
Bicarbonate (HCO₃^-)	22-28 mEq/L
Magnesium (Mg²⁺)	1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)
24-28 wks // 32-36 wks	30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks	40-220 ng/mL // 80-350 ng/mL
Ferritin, serum	Male: 15-200 ng/mL Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma	Male: 4-25 mIU/mL Female: premenopause: 4-30 mIU/mL midcycle peak: 10-90 mIU/mL postmenopause: 40-250
pH	7.35-7.45
PCO₂	33-45 mmHg
PO₂	75-105 mmHg
Glucose, serum	Fasting: 70-110 mg/dL 2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation	Fasting: <5 ng/mL Provocative stimuli: > 7ng/mL
Immunoglobulins, serum
IgA	76-390 mg/dL
IgE	0-380 IU/mL
IgG	650-1500 mg/dL
IgM	40-345 mg/dL
Iron	50-170 μg/dL
Lactate dehydrogenase, serum	45-90 U/L
Luteinizing hormone, serum/plasma	Male: 6-23 mIU/mL Female: follicular phase: 5-30 mIU/mL midcycle: 75-150 mIU/mL postmenopause 30-200 mIU/mL
Osmolality, serum	275-295 mOsmol/kd H₂O
Parathyroid hormone, serume, N-terminal	230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C)	20-70 U/L
Phosphorus (inorganic), serum	3.0-4.5 mg/dL
Prolactin, serum (hPRL)	< 20 ng/mL
Proteins, serum

Hematologic	Reference Range
Bleeding time	2-7 minutes
Erythrocyte count	Male: 4.3-5.9 million/mm³ Female: 3.5-5.5 million mm³
Erythrocyte sedimentation rate (Westergren)	Male: 0-15 mm/h Female: 0-20 mm/h
Hematocrit	Male: 41%-53% Female: 36%-46%
Hemoglobin A1c	≤ 6 %
Hemoglobin, blood	Male: 13.5-17.5 g/dL Female: 12.0-16.0 g/dL
Hemoglobin, plasma	1-4 mg/dL
Leukocyte count and differential
Leukocyte count	4,500-11,000/mm³
Segmented neutrophils	54%-62%
Bands	3%-5%
Eosinophils	1%-3%
Basophils	0%-0.75%
Lymphocytes	25%-33%
Monocytes	3%-7%
Mean corpuscular hemoglobin	25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration	31%-36% Hb/cell
Mean corpuscular volume	80-100 μm³
Partial thromboplastin time (activated)	25-40 seconds
Platelet count	150,000-400,000/mm³
Prothrombin time	11-15 seconds
Reticulocyte count	0.5%-1.5% of red cells
Thrombin time	< 2 seconds deviation from control
Volume
Plasma	Male: 25-43 mL/kg Female: 28-45 mL/kg
Red cell	Male: 20-36 mL/kg Female: 19-31 mL/kg

Cerebrospinal Fluid	Reference Range
Cell count	0-5/mm³
Chloride	118-132 mEq/L
Gamma globulin	3%-12% total proteins
Glucose	40-70 mg/dL
Pressure	70-180 mm H₂O
Proteins, total	< 40 mg/dL

Sweat	Reference Range
Chloride	0-35 mmol/L
Urine
Calcium	100-300 mg/24 h
Chloride	Varies with intake
Creatinine clearance	Male: 97-137 mL/min Female: 88-128 mL/min
Estriol, total (in pregnancy)
30 wks	6-18 mg/24 h
35 wks	9-28 mg/24 h
40 wks	13-42 mg/24 h
17-Hydroxycorticosteroids	Male: 3.0-10.0 mg/24 h Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total	Male: 8-20 mg/24 h Female: 6-15 mg/24 h
Osmolality	50-1400 mOsmol/kg H₂O
Oxalate	8-40 μg/mL
Potassium	Varies with diet
Proteins, total	< 150 mg/24 h
Sodium	Varies with diet
Uric acid	Varies with diet
Body Mass Index (BMI)	Adult: 19-25 kg/m²