Joint Dislocations, Sprains and Strains

• Grading: grade I stretch without laxity, grade II partial tear with some laxity, grade III complete tear with instability.
• Shoulder dislocation — most commonly anterior (about 95%), from abduction with external rotation. The arm is held abducted and externally rotated with loss of the deltoid contour. Assess the axillary nerve before and after reduction — sensation over the deltoid ("regimental badge") and deltoid function. Associated lesions: Bankart (anteroinferior labrum) and Hill–Sachs (humeral head impaction). Posterior dislocation is rare and classically follows seizures or electrocution, with the arm held adducted and internally rotated and a "light bulb" sign on radiograph.
• Hip dislocation — usually posterior, from a dashboard injury, with the limb shortened, adducted and internally rotated; risks sciatic nerve injury and avascular necrosis, so reduction is urgent.
• Ankle sprain — the anterior talofibular ligament is the most commonly injured in inversion injuries. Apply the Ottawa ankle rules to decide on radiography.
• Knee dislocation is a limb-threatening emergency requiring assessment of the popliteal artery, even with palpable pulses.
• Management of sprains and strains follows protected weight-bearing, ice, compression, elevation and early mobilisation; prolonged immobilisation delays recovery.

Mechanism groups

• Indirect leverage/torsion: abduction with external rotation levers the humeral head out anteriorly; inversion with plantarflexion loads the anterior talofibular ligament (the ATFL is taut in plantarflexion, which is why the foot is usually plantarflexed at the moment of injury); valgus-external rotation of a planted knee loads the MCL and ACL.
• Direct high-energy impact: axial load through a flexed hip and knee (dashboard injury) drives the femoral head posteriorly; high-energy hyperextension, dashboard, or varus/valgus-rotational forces (and low-energy falls in patients with obesity) produce multiligament knee dislocation.
• Violent muscle contraction: seizure, electrocution, or electroconvulsive therapy — the internal rotators overpower the external rotators, producing posterior shoulder dislocation (and posterior hip dislocation in some series).
• Eccentric muscle-tendon overload (strain): sprinting decelerates the hamstring eccentrically; sudden push-off tears the medial gastrocnemius (tennis leg) or Achilles.

Non-modifiable risk factors

• Prior dislocation or sprain: the single strongest predictor; healed ligament is type III collagen-rich scar with reduced tensile strength and blunted proprioception.
• Young age at first shoulder dislocation: recurrence risk is highest in adolescents and young adults and falls steeply with age.
• Generalized ligamentous laxity: Ehlers-Danlos, Marfan, Down syndrome; also glenoid or acetabular dysplasia.
• Seizure disorder: the classic stem setup for bilateral posterior shoulder dislocation.
• Skeletal immaturity: the physis is weaker than the ligament, so children sustain Salter-Harris fractures where adults sprain; in the elderly the rotator cuff or greater tuberosity fails instead.

Modifiable risk factors

• Sport exposure and playing conditions: collision sports, court sports, cleated shoes on high-friction surfaces.
• Deconditioning, fatigue and proprioceptive deficit: neuromuscular training programs reduce ankle and ACL injury, a point emphasized in National Athletic Trainers' Association position statements.
• Alcohol or sedative intoxication, unrestrained driving, and falls risk.
• Fluoroquinolone or systemic corticosteroid exposure: tendinopathy predisposing to rupture rather than true strain.

Tissue failure

• Ligaments and tendons are viscoelastic type I collagen structures: load applied faster than the tissue can creep pushes it past the yield point of its stress-strain curve. Microscopic fibril failure without gross laxity is grade I; partial macroscopic disruption with a soft endpoint on stress testing is grade II; complete discontinuity with an empty endpoint is grade III.
• Bleeding drives the early findings: ligaments and joint capsule are well vascularized, so tearing produces hemarthrosis or ecchymosis, prostaglandin- and bradykinin-mediated pain, and reflex muscle spasm that guards the joint. Rapid-onset (within hours) knee hemarthrosis implies ACL tear, intra-articular fracture, or patellar dislocation rather than a simple sprain.

Why dislocations look the way they do

• Shoulder: the humeral head escapes anteroinferiorly through the weakest part of the capsule, avulsing the anteroinferior labrum and impacting its posterolateral surface on the glenoid rim. The head sits anterior to the glenoid, so the arm is locked in slight abduction and external rotation, and the empty subacromial space produces the squared-off contour.
• Axillary nerve injury: the nerve leaves the posterior cord, passes through the quadrilateral space and hugs the surgical neck, so it is stretched over the displaced head — a neurapraxia that usually recovers.
• Hip: posterior displacement tears the ligamentum teres and, more importantly, disrupts the retinacular branches of the medial femoral circumflex artery that supply the femoral head retrograde — the basis for avascular necrosis. The peroneal division of the sciatic nerve is lateral and tethered, so foot drop dominates any nerve deficit.
• Knee: the popliteal artery is fixed proximally at the adductor hiatus and distally at the soleal arch, so displacement shears the intima. An intimal flap can thrombose hours later despite an initially palpable pulse.

Universal findings

• Immediate pain, refusal to use the limb, and rapid swelling: hemarthrosis and capsular distension; a joint that fills within an hour or two suggests intra-articular bleeding, not effusion.
• Fixed deformity with springy resistance to passive motion: the hallmark distinguishing dislocation from sprain — the joint cannot be moved through range because the articular surfaces are locked.
• Ecchymosis tracking distally by gravity appears over one to three days and often misleads students about the injury's location.

Injury-specific findings

• Shoulder: patient supports the affected arm with the opposite hand; palpable fullness anteriorly below the coracoid. Test sensation over the lateral deltoid and attempted deltoid contraction before and after reduction. The arm held adducted and internally rotated, with inability to externally rotate or supinate the forearm, points to the posterior variant.
• Luxatio erecta (inferior dislocation): the arm is held fully overhead and cannot be brought down — rare, high rate of neurovascular injury.
• Hip: any attempt to move the limb is intensely painful; check active ankle dorsiflexion for peroneal-division sciatic injury.
• Knee dislocation: gross instability in multiple planes; the knee may have spontaneously reduced before arrival, so a multiligament-lax knee is a dislocation until proven otherwise.
• Ankle sprain: tenderness anterior and distal to the lateral malleolus over the ATFL, positive anterior drawer of the talus, and a negative bony exam. Tenderness proximal along the fibula suggests a Maisonneuve pattern.
• Strain: pain reproduced by resisted contraction and by passive stretch, with a palpable defect and weakness in complete tears; a positive Thompson test (absent plantarflexion on calf squeeze) indicates Achilles rupture.

Step 2 — decide whether imaging is needed

• Ottawa ankle and foot rules: obtain ankle radiographs if there is pain in the malleolar zone plus bone tenderness at the posterior edge or tip of either malleolus, or inability to bear weight both immediately and in the emergency department (four steps). Obtain foot radiographs for midfoot-zone pain plus tenderness at the navicular or the base of the fifth metatarsal, or the same weight-bearing failure. Sensitivity for clinically significant fracture approaches 100%, so a negative rule reliably excludes fracture; specificity is low, so a positive rule only mandates a film. The rules are unreliable in intoxication, distracting injury, sensory deficit, and very young children.
• Ottawa knee rules: age 55 or older, isolated patellar tenderness, fibular head tenderness, inability to flex to 90 degrees, or inability to bear weight four steps immediately and in the department.

Step 4 — vascular and soft-tissue imaging

• Knee dislocation: measure the ankle-brachial index; an ABI below 0.9 or any hard sign of vascular injury mandates CT angiography and vascular surgery involvement, an approach reflected in Western Trauma Association algorithms. A normal ABI with a normal exam still warrants serial reassessment.
• MRI (or MR arthrography) defines Bankart and labral lesions, rotator cuff tears, and ACL/meniscal injury; ultrasound is a reasonable first look at the Achilles. Neither is an emergency department test.

Immediate priorities

• Reduce urgently: prolonged displacement worsens ischemia, nerve traction and cartilage injury. A hip dislocation should be reduced as soon as the patient is safely sedated — delay is the main modifiable driver of avascular necrosis. For a knee dislocation, document pulses and an ABI if this does not delay reduction, reduce immediately at the bedside, then reassess vascular status and splint.
• Analgesia for reduction: procedural sedation with an agent such as intravenous propofol or ketamine plus an opioid, under ACEP clinical policy monitoring standards, or intra-articular lidocaine for shoulder reduction, which is comparably effective with fewer respiratory adverse events and shorter observation.
• Technique: gentle, sustained traction rather than force — traction-countertraction, scapular manipulation, or the Stimson prone-hanging method for the shoulder; the Allis maneuver for the posterior hip. Reassess the axillary nerve and obtain post-reduction films before splinting.

After reduction

• Immobilization is brief and purposeful: a sling for the shoulder for a short period followed by supervised rehabilitation. Prolonged immobilization does not reduce recurrence.
• Analgesia for sprains and strains: the ACP/AAFP guideline on acute pain from non-low-back musculoskeletal injuries recommends topical NSAIDs (for example topical diclofenac), with or without menthol gel, as first-line, with oral NSAIDs or acetaminophen as alternatives; opioids are explicitly not recommended routinely.
• Functional rehabilitation with protected weight-bearing, bracing or taping, and proprioceptive/neuromuscular training is the mainstay for ankle sprain per National Athletic Trainers' Association guidance.

Definitive/surgical

• Arthroscopic Bankart repair for recurrent instability, and Latarjet coracoid transfer when there is significant glenoid bone loss; AAOS guidance supports considering early stabilization in young, high-demand first-time dislocators.
• Open reduction for irreducible or incarcerated-fragment hip dislocations; vascular repair with fasciotomy for popliteal injury; staged ligament reconstruction for the knee.

Emergencies

• Popliteal artery injury after knee dislocation: intimal flap thrombosis can present hours later with a cool, pulseless, pale leg; missed injury carries a high amputation rate. An abnormal ABI or evolving exam mandates CT angiography and vascular surgery.
• Compartment syndrome: pain out of proportion, pain on passive stretch, and tense compartments after reperfusion or high-energy injury. Pulselessness is a late finding — do not wait for it.
• Open dislocation or fracture-dislocation: requires irrigation, antibiotics and urgent operative debridement.
• Neurovascular injury from the dislocation itself: axillary artery injury in elderly patients with anterior shoulder dislocation (atherosclerotic, tethered vessels), sciatic nerve palsy with posterior hip dislocation.

Joint-specific sequelae

• Recurrent instability: capsulolabral incompetence plus an engaging Hill-Sachs defect; highest in young patients, presenting as apprehension with abduction and external rotation.
• Avascular necrosis of the femoral head: disrupted retinacular blood supply; groin pain and progressive stiffness months later, with crescent sign then collapse on imaging. Risk rises with delayed reduction.
• Post-traumatic osteoarthritis: cartilage impaction at the time of injury and residual incongruity.
• Axillary neurapraxia: deltoid weakness and lateral shoulder numbness; usually recovers over weeks, but persistent deficit warrants electrodiagnostic study.
• Rotator cuff tear rather than instability in patients over about 40 with a dislocation — inability to abduct after reduction should not be dismissed as pain alone.
• Chronic ankle instability: loss of mechanoreceptor proprioception plus lax ATFL leads to repeated giving-way; prevented by neuromuscular rehabilitation.
• Myositis ossificans after quadriceps contusion or strain; heterotopic bone with a firm, tender mass.

Treatment-related

• Iatrogenic fracture or nerve traction from forceful reduction, especially in osteoporotic bone.
• Procedural sedation adverse events: hypoventilation, aspiration.
• Immobilization complications: stiffness, adhesive capsulitis, muscle atrophy, and venous thromboembolism after lower-limb immobilization.
• NSAID toxicity: gastropathy and renal injury, particularly relevant in older or volume-depleted patients.

• Test the axillary nerve before and after every shoulder reduction: numbness over the regimental badge area plus deltoid weakness. Documenting the deficit pre-reduction is the classic "single best next step" and protects against attributing an existing palsy to the reduction.
• Seizure or electrocution plus a shoulder held adducted and internally rotated that cannot be externally rotated = posterior dislocation. The AP film can look nearly normal, so the answer is the axillary or scapular Y view, not reassurance.
• A knee dislocation with palpable pulses is still a vascular emergency: get an ankle-brachial index, and pursue CT angiography if it is below 0.9. A grossly multiligamentous-lax knee in a patient who "felt it pop back in" is a spontaneously reduced dislocation.
• Posterior hip dislocation: shortened, adducted, internally rotated — reduce urgently to limit avascular necrosis, then image for acetabular fracture. Foot drop after the injury reflects the peroneal division of the sciatic nerve.
• Ottawa ankle rules are a rule-out tool: near-perfect sensitivity, poor specificity. Bone tenderness at the malleolar tips or the base of the fifth metatarsal, or inability to take four steps, means image; the classic distractor is ordering a film for soft-tissue swelling alone.
• Early functional mobilization beats prolonged immobilization for sprains and strains, and the ACP/AAFP guideline favors topical NSAIDs over opioids for acute musculoskeletal pain.
• Age changes the associated lesion: under about 25 expect a Bankart lesion and recurrence; over about 40 expect a rotator cuff tear or greater tuberosity fracture; in a child, suspect a Salter-Harris physeal fracture rather than a ligament tear because the physis fails first.
• The common distractor is MRI: it defines labral and ligament injury but never precedes reduction, radiographs, or the neurovascular exam.