ACL Injury
Lower LimbOverview
ACL injury is a common knee ligament tear typically occurring during pivoting, deceleration, or direct contact movements in sports or trauma. The injury results in knee instability, loss of proprioception, and functional limitation. Early diagnosis and appropriate management are critical to prevent secondary injuries and long-term degenerative changes.
Pathophysiology
The ACL is the primary restraint to anterior tibial translation and provides rotational stability of the knee. Injury occurs when excessive valgus stress, internal rotation, or deceleration forces are applied to a flexed or extended knee. The ligament may be partially or completely torn, disrupting mechanoreceptor feedback and proprioceptive function. This results in proprioceptive deficit, neuromuscular control loss, and altered knee biomechanics. Secondary injuries to the menisci and collateral ligaments frequently occur, particularly in acute high-energy injuries.
Typical Presentation
Site
Anterior knee joint, diffuse knee swelling, may report pain in anterolateral knee compartment
Quality
Sharp, tearing sensation at moment of injury; subsequently dull, aching pain with instability episodes; sharp pain with pivoting or deceleration movements
Intensity
Acute: severe (8-10/10); Chronic: mild to moderate (3-6/10) during functional activities
Aggravating
Pivoting on planted foot, sudden deceleration, cutting movements, stairs (especially descent), kneeling, squatting, running on uneven surfaces, activities requiring rapid direction change
Relieving
Rest, ice application, elevation, compression, anti-inflammatory medication, avoiding pivoting/rotational activities, use of knee brace for stability
Associated
Immediate effusion and swelling (within 2-4 hours), loss of extension range, apprehension with instability, difficulty weight-bearing, functional instability ('giving way'), reduced quadriceps strength, proprioceptive deficits, possible meniscal symptoms
Orthopaedic Tests
Lachman Test
Procedure
Patient supine, knee flexed 20–30°. Examiner stabilises distal femur with one hand and applies anterior tibial translation force with the other hand at the proximal tibia.
Positive Finding
Increased anterior tibial translation (soft end-feel or excessive movement) compared to the contralateral knee.
Sensitivity / Specificity
85% / 94%
Hegedus et al., 2015, British Journal of Sports Medicine
Interpretation
Highly sensitive and specific for ACL insufficiency. Most reliable single test for acute ACL injuries. Positive result indicates probable ACL tear.
Anterior Drawer Test
Procedure
Patient supine, knee flexed 90°, hip flexed 45°. Examiner stabilises foot and applies anterior translational force to proximal tibia.
Positive Finding
Increased anterior tibial translation relative to the femur or absent end-feel.
Sensitivity / Specificity
72% / 98%
Hegedus et al., 2015, British Journal of Sports Medicine
Interpretation
Highly specific but less sensitive than Lachman; positive result strongly suggests ACL tear. Less reliable in acute settings due to hamstring guarding.
Pivot Shift Test
Procedure
Patient supine, knee extended. Examiner applies valgus stress and external rotation to tibia while flexing knee; assesses for clunk or shift of tibia back into place at 20–40° flexion.
Positive Finding
Sudden anterior subluxation of tibia or palpable shift/clunk during knee flexion.
Sensitivity / Specificity
65% / 98%
Hegedus et al., 2015, British Journal of Sports Medicine
Interpretation
Highest specificity for ACL injury but requires skill and patient relaxation. Positive result is nearly pathognomonic for ACL insufficiency; absence does not rule out ACL tear.
Segond Test (Segond Sign on imaging) / Flexion-Rotation Drawer
Procedure
Patient supine, knee in 25° flexion with foot internally rotated. Examiner applies gentle anterior tibial translation and palpates for rotation and translation.
Positive Finding
Increased anterior translation with internal tibial rotation; sensation of instability or clunking.
Sensitivity / Specificity
See current literature / See current literature
Interpretation
Assesses rotational instability associated with ACL insufficiency. May be more sensitive in chronic ACL deficiency; less established in acute settings.
KT-1000 or KT-2000 Arthrometer Test
Procedure
Quantitative measurement device applied to knee in standardised position (90° flexion). Measures anterior tibial displacement under 67 N, 89 N, and maximum manual force.
Positive Finding
Side-to-side difference in anterior tibial translation ≥3 mm (or ≥5 mm depending on protocol).
Sensitivity / Specificity
90% / 95%
Hegedus et al., 2015, British Journal of Sports Medicine
Interpretation
Objective, quantifiable assessment of ACL insufficiency. Excellent for confirming clinical suspicion and monitoring outcomes; not practical for emergency departments but valuable in rehabilitation settings.
Composite Clinical Examination (Multi-test Battery)
Procedure
Sequential use of Lachman, Anterior Drawer, and Pivot Shift tests in combination to establish overall likelihood of ACL injury.
Positive Finding
Two or more positive findings; positive Lachman or Pivot Shift test.
Sensitivity / Specificity
95–97% / See current literature
Hegedus et al., 2015, British Journal of Sports Medicine
Interpretation
Combining multiple tests increases diagnostic confidence. High sensitivity when Lachman and Pivot Shift are both positive suggests ACL tear with high pre-test probability. MRI indicated for confirmation.
⚠ Red Flags
- •Acute severe swelling within 2 hours (suggestive of haemarthrosis)
- •Inability to bear weight or complete loss of function
- •Signs of neurovascular compromise (numbness, tingling, colour changes, coolness)
- •Associated posterolateral knee instability suggesting posterolateral corner injury
- •Suspected multi-ligamentous injury (ACL + PCL + collateral ligament damage)
- •Acute locked knee with mechanical block
- •Obvious knee deformity suggesting knee dislocation
- •History of significant trauma with high-energy mechanism
⚡ Yellow Flags
- •Fear-avoidance behaviour limiting rehabilitation engagement
- •Catastrophizing about injury severity or prognosis
- •Low self-efficacy regarding return to sport/activity
- •Depression or anxiety related to activity limitation and time away from sport
- •Inadequate social support for rehabilitation demands
- •Unrealistic expectations about recovery timeline
- •History of previous knee injuries or bilateral ACL injuries
- •Overtraining or poor training load management prior to injury
Osteopathic Techniques
Region
Knee joint capsule and periarticular tissues
Technique
Soft Tissue
Rationale
Addresses muscular tension in quadriceps, hamstrings, and calf muscles to reduce protective muscle guarding, improve local circulation, and reduce pain. Soft tissue techniques help normalize muscle tone around the injured knee and improve proprioceptive input from muscle mechanoreceptors.
Region
Patellofemoral joint
Technique
Articulation
Rationale
Gentle articulation of the patellofemoral joint maintains synovial fluid nutrition, prevents stiffness, and preserves normal arthrokinematics. This is particularly important in early stages when inflammatory effusion is present and in later stages to prevent secondary patellofemoral pain syndrome.
Region
Ankle and subtalar joints
Technique
MET and Articulation
Rationale
ACL injury alters weight distribution and proprioceptive feedback, often leading to compensatory ankle inversion or eversion patterns. Restoring normal ankle biomechanics reduces abnormal stress transfer to the healing ACL and improves proprioceptive feedback from ankle mechanoreceptors.
Region
Hip and pelvis
Technique
MET and Soft Tissue
Rationale
Treats hip flexor tightness, hip external rotator weakness, and pelvic asymmetry that commonly develop post-injury. Optimal hip biomechanics are essential for reducing varus/valgus stress at the knee during rehabilitation and functional activities.
Region
Lumbar spine and sacroiliac joints
Technique
Articulation and MET
Rationale
ACL injury often results in altered gait and weight distribution, creating compensatory stress through the kinetic chain. Addressing segmental restrictions in the lumbar spine and sacroiliac joints restores normal movement patterns and reduces secondary pain referral.
Region
Lymphatic system and periarticular tissues
Technique
Lymphatic
Rationale
Lymphatic technique enhances fluid drainage from the injured knee, reduces inflammatory effusion, promotes healing, and improves local circulation. This is particularly valuable in the acute phase when swelling may impede rehabilitation progress.
Add-On Approaches
Chinese Medicine
Acupuncture to local points (EX-LE5, ST35, GB34) and distal points (ST36) to reduce pain, improve circulation, and enhance proprioceptive function. Moxibustion may support local warming and circulation. TCM assessment of underlying constitutional factors may guide dietary and lifestyle recommendations to support tissue healing.
Chiropractic
Foot orthotic assessment and prescription to address biomechanical contributors to injury (flat feet, overpronation). Knee mobilization techniques for patellofemoral and tibiofemoral joints. Assessment of lower limb alignment and posture to identify contributing factors to ACL injury mechanism.
Physiotherapy
Proprioceptive retraining using balance boards, wobble cushions, and single-leg stance exercises. Progressive closed-kinetic-chain exercises (leg press, wall squats) advancing to open-kinetic-chain hamstring strengthening. Sport-specific training including agility, plyometrics, and deceleration control. Return-to-sport testing protocols.
Remedial Massage
Deep tissue massage to quadriceps, hamstring, and calf musculature to address muscle tension and improve circulation. Myofascial release techniques for iliotibial band and lateral knee structures. Remedial massage supports muscle relaxation during early rehabilitation phases when pain may limit active exercise participation.
Rehabilitation Exercises
Supine Knee Flexion-Extension Slides
Prone Knee Flexion with Towel Roll
Supine Hamstring Stretch with Strap
Standing Quadriceps Stretch
Quadriceps Sets (Isometric Contraction)
Supine Glute Bridges
Standing Hamstring Curls (Early Phase)
Single-Leg Stance on Firm Surface
Single-Leg Stance on Foam Surface
Tandem Stance (Heel-Toe)
Wall Squats (Partial Range)
Stationary Cycling (Pain-Free Range)
Referral Criteria
- •Acute ACL injury with inability to weight-bear or complete functional loss - refer to orthopedic surgeon for urgent assessment and potential imaging (MRI)
- •Signs of haemarthrosis (immediate swelling within 2 hours) - orthopedic evaluation for possible aspiration or urgent diagnostic imaging
- •Multi-ligamentous injury pattern - orthopedic surgeon for surgical consultation
- •Posterolateral knee instability or vascular compromise signs - urgent orthopedic and vascular assessment
- •Mechanical locking or catching suggestive of meniscal injury - orthopedic evaluation and possible arthroscopy
- •ACL injury in skeletally immature patient (open growth plates) - pediatric orthopedic surgeon for specialized management
- •Chronic ACL deficiency with functional instability considering return to high-demand sport - orthopedic surgeon for surgical reconstruction consultation
- •Failure to progress in rehabilitation after 6-8 weeks despite compliance - orthopedic review and possible imaging to exclude secondary injuries
- •Development of significant patellofemoral pain syndrome during rehabilitation - physiotherapy specialist assessment
- •Persistent effusion or inflammatory response not responding to conservative management - physician evaluation for possible underlying inflammatory pathology