ACL Injury

Lower Limb

Overview

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

Test descriptions are written with AI assistance from standard clinical texts. Where a test lists Sources, its description has been checked against them; those sources are independent and do not endorse OsteoKit. Accuracy figures and grades (A–D) appear only when checked against the published study; tests without one are marked “No accuracy study”.

Further reading: full test procedures are described in standard clinical examination texts, e.g. Magee & Manske, Orthopedic Physical Assessment (7th ed.), and Cook & Hegedus, Orthopedic Physical Examination Tests: An Evidence-Based Approach (2nd ed.).

Grade A
A+ABCDStrong clinical value: substantially changes the diagnosis (LR ≥10 or ≤0.1)
useful both to rule in and rule out.

Lachman Test

Procedure

Patient supine, relaxed, knee bent to 20–30° (support it on your thigh if needed). Stabilise the lower femur with one hand and pull the upper tibia forwards with the other. Compare the amount of movement and the end-feel with the other knee.

Positive Finding

More forward movement than on the other side, with a soft or absent end-point.

Sensitivity / Specificity

85%/94%

Reference: Benjaminse A et al., J Orthop Sports Phys Ther 2006; PMID 16715828

Interpretation

The most useful single examination test for an ACL tear, especially in acute injuries. A negative Lachman makes a tear less likely, and a positive one makes it likely. Check the tibia is not sagging backwards first, which can mimic forward movement.

Sources

Grade A
A+ABCDStrong clinical value: substantially changes the diagnosis (LR ≥10 or ≤0.1)
useful both to rule in and rule out.

Anterior Drawer Test

Procedure

Patient supine, hip bent to 45° and knee to 90°, foot flat. Sit gently on the foot, check the tibia is not sagging, then pull the upper tibia forwards with the hamstrings relaxed. Compare with the other knee.

Positive Finding

More forward movement of the tibia than on the other side.

Sensitivity / Specificity

92% (chronic)/91% (chronic)

Reference: Benjaminse A et al., J Orthop Sports Phys Ther 2006; PMID 16715828

Interpretation

Useful in chronic ACL deficiency; in acute injuries pain, swelling and hamstring guarding often make it falsely negative. Use the Lachman test first. Note: accuracy applies to chronic ACL injury; the anterior drawer test performs poorly in the acute setting (Benjaminse 2006).

Sources

Grade A
A+ABCDStrong clinical value: substantially changes the diagnosis (LR ≥10 or ≤0.1)
best for ruling IN (confirmation).

Pivot Shift Test

Procedure

Patient supine and fully relaxed. Start with the knee straight, internally rotate the tibia and apply a valgus force, then slowly bend the knee.

Positive Finding

A clunk at about 20–40° of flexion as the lateral tibial plateau, which had slipped forwards, reduces back into place.

Sensitivity / Specificity

24%/98%

Reference: Benjaminse A et al., J Orthop Sports Phys Ther 2006; PMID 16715828

Interpretation

When positive, it strongly supports an ACL tear. It is often negative in the acute, painful knee because the patient guards, so a negative test rules little out. It reproduces the 'giving way' patients describe.

Sources

Grade A
A+ABCDStrong clinical value: substantially changes the diagnosis (LR ≥10 or ≤0.1)
useful both to rule in and rule out.

KT-1000 or KT-2000 Arthrometer Test

Procedure

Performed with a knee arthrometer: the device is strapped to the leg with the knee bent to about 30°, and anterior tibial movement is measured under set forces and a maximum manual pull, compared with the other knee.

Positive Finding

More anterior movement in millimetres on the injured side than the other side.

Sensitivity / Specificity

93%/93%

Reference: van Eck CF et al., Knee Surg Sports Traumatol Arthrosc 2013; PMID 23073818

Interpretation

Gives an objective measure of laxity for diagnosis and follow-up after reconstruction. Measurements depend on the examiner and technique, so use the same protocol each time. Figures are for maximum manual force; sensitivity is lower at fixed 69–89 N (van Eck 2013).

Sources

No accuracy study

Flexion-Rotation Drawer Test

Procedure

Patient supine. Hold the lower leg with the knee nearly straight and let the thigh drop back and rotate under gravity, then bend the knee gently while pushing the tibia backwards.

Positive Finding

A reduction of the tibia (a smooth clunk) as the knee bends, similar to the pivot shift.

Interpretation

A gentler version of the pivot shift, used when the patient cannot relax. The Segond sign is a different finding: a small avulsion fracture on the outer tibia on X-ray, which strongly suggests an ACL tear. Note: the Segond sign is a radiographic avulsion finding, not a physical examination test; sensitivity/specificity of a bedside manoeuvre are not established.

Further reading

No accuracy study
Cluster

Composite Clinical Examination (Multi-test Battery)

Procedure

Combine the history (non-contact twisting injury, a pop, rapid swelling within hours, giving way) with the Lachman, anterior drawer and pivot shift tests.

Positive Finding

A typical history together with a positive Lachman or pivot shift test.

Interpretation

The history plus a positive Lachman or pivot shift makes an ACL tear very likely. Refer for orthopaedic assessment; MRI confirms the tear and shows associated meniscal and bone injuries.

Sources

Further reading

⚠ 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

Care is individual: surgery and rehabilitation alone are both options, depending on age, activity, sport and other injuries. Early care is rest, ice, compression and elevation, then physiotherapy.

Region

Knee joint capsule and surrounding tissues

Technique

Soft tissue, knee and quadricepsNo trials found

Rationale

Hands-on work to the quadriceps and the tissues around the knee to ease tension and pain.

How it's done & evidence

How it's done

Hands-on kneading, stroking and sustained pressure to the quadriceps, the patellar and quadriceps tendons, the iliotibial band near the knee and the tissues around the joint. Transverse friction massage across a tendon is one form. In trials it was given alongside exercise.

Evidence in ACL Injury

Searched 24 Oct 2026: no trials of soft tissue technique in ACL injury.

Region

Patellofemoral joint (kneecap glides)

Technique

Articulation, knee (tibiofemoral and patellofemoral)No trials found

Rationale

Gentle, rhythmic glides of the knee and kneecap within their range to ease pain and stiffness.

How it's done, cautions & evidence

How it's done

Passive, low-velocity glides of the knee within its range, with no thrust: distraction and front-to-back glides of the tibia on the femur, and glides of the kneecap in each direction, usually 2–3 oscillations a second for 1–2 minutes. A Mulligan variant holds a sustained glide of the tibia while the patient actively bends and straightens the knee.

Cautions

In knee osteoarthritis trials, no serious adverse events were reported with manual therapy.

Evidence in ACL Injury

Searched 24 Oct 2026: no trials of patellar mobilisation in ACL injury.

Region

Hip and thigh muscles

Technique

Muscle energy, hip and thigh musclesNo trials found

Rationale

Low-force, patient-powered stretch for tight hip and thigh muscles.

How it's done, cautions & evidence

How it's done

The muscle (for example the hamstrings, adductors or rectus femoris) is taken to its barrier. The patient pushes gently, at about 10–20% effort, against resistance for 5–10 seconds, relaxes for 3–5 seconds, and the new barrier is taken up.

Cautions

Not used with an acute fracture, a joint infection or a bone malignancy; take care with severe osteoporosis or after surgery that limits muscle contraction. Use the least force needed: too much can tear a muscle or pull off a tendon, especially in older patients.

Evidence in ACL Injury

Searched 24 Oct 2026: no trials of hip muscle energy technique in ACL injury.

Rehabilitation Exercises

Supine Knee Flexion-Extension Slides

Range of MotionBeginner

Prone Knee Flexion with Towel Roll

Range of MotionBeginner

Supine Hamstring Stretch with Strap

StretchingBeginner

Standing Quadriceps Stretch

StretchingBeginner

Quadriceps Sets (Isometric Contraction)

StrengtheningBeginner

Supine Glute Bridges

StrengtheningIntermediate

Standing Hamstring Curls (Early Phase)

StrengtheningIntermediate

Single-Leg Stance on Firm Surface

StrengtheningIntermediate

Single-Leg Stance on Foam Surface

BalanceIntermediate

Tandem Stance (Heel-Toe)

BalanceIntermediate

Wall Squats (Partial Range)

PosturalIntermediate

Stationary Cycling (Pain-Free Range)

CardiovascularIntermediate

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