ELBOW Pathologies

Question 1

Olecranon Bursitis

Answer 1

Definition:

• Filling of the subcutaneous bursa of the elbow with blood or serous fluid

Aetiology:

• Trauma, Inflammation, Infection, Prolonged leaning on the elbow, Acute or chronic onset

Epidemiology:

• More common in males aged 30-60 years
• Incidence largely unknown
• 0.01%-0.1% of hospital admissions
• Post-traumatic olecranon bursitis is the most common form

Risk Factors:

• Gout – Rheumatoid arthritis – Previous or repetitive trauma – Obesity – Immuno-suppression

Clinical Symptoms:

• Swelling over the tip of the elbow persisting for several hours to days
• Pain, however the lump may be painless
• Fever in 50% of cases of septic bursitis:
  
  • An abscess and pus may form over the area
• Erythema can be present in both septic and non-septic forms of bursitis
• Residual lumps post swelling

Physical Assessment:

• Notable swelling
• Palpable mass of varying tenderness
• May contain firm nodules
• May be red, and hot upon palpation
• Measure dimensions to track progress
• Mild flexion restriction in AROM and PROM
• Pain on palpation and AROM and PROM (Flexion)
• Otherwise unremarkable

Question 2

Distal Biceps Tendinopathy

Answer 2

Occurs on a spectrum of degeneration:

• Tendinitis, tendinosis, partial tear, rupture
• Changes include:
  
  • Hypertrophic change of the radial tuberosity
  • Abrasion of the tendon
  • Bicipital bursitis

The current literature supports the concept of distal biceps tendinosis as one of the chronic enthesopathies of middle age

Mechanism of Injury:

• Repetitive flexion or supination

Aetiology:

• Acute or chronic onset
• Lifting
• Throwing:
  
  • Repetitive hyperextension and pronation
  • Forceful eccentric contraction

Clinical Presentation:

• Dull ache
• Gradual onset
• Localised tenderness:
  
  • Distal belly
  • Bicipital insertion
  • Radial tuberosity
• Pain may radiate distally or proximally
• Flexion contracture
• Weakness with flexion or supination

Differential Diagnosis:

• Biceps tendon rupture
• Cubital bursitis
• Brachioradialis Tendonitis

Question 3

Distal Biceps Avulsion/Rupture

Answer 3

Definition: Catastrophic disruption of the biceps tendon or the insertion of the biceps into the radial tuberosity

Epidemiology:

• Rare, accounting for only 3% to 12% of all biceps tendon injuries:
  
  • 1.2 per 100,000 people, the dominant arm being affected 86% of the time
  • Average age of patients is 50 years old with an age range of 18 to 72 years of age

Aetiology:

• Irregularity of the radial tuberosity
• Radial bursitis
• Hypovascularity
• Steroid use
• Body builders
• Smoking
• Loaded eccentrically from a flexed to extended position

Clinical Features:

• Sudden episode of severe pain while performing a forced eccentric contraction in the anterior elbow
• Painful ‘pop’ or ‘snap’ in the region of the elbow
• Immediate loss of elbow flexion power or even pseudo-paralysis

Physical Assessment:

• A palpable defect or emptiness of the antecubital fossa
• Ecchymosis on the medial aspect of the elbow that may extend proximally and distally:
  
  • An intact lacertus fibrosus may confine the hematoma and thus prevent ecchymosis formation
• Proximal migration of the biceps musculo-tendinous unit
• +ve Biceps Hook Test

Question 4

Distal Triceps Tendinopathy

Answer 4

Also referred to Triceps enthesopathy

Mechanism of Injury:

• Overuse and forceful elbow extension or hyperextension:
  
  • Elbow extension and supination:
    
    • e.g. Tennis backhand, serve or overhead shot
• Occurs on a spectrum of tendinopathy
• Olecranon spurring may also be present

Clinical Presentation:

• Pain localized to the triceps insertion
• Pain with activities that require elbow extension

Physical Examination:

• Pain on palpation over the triceps insertion
• ROM is typically preserved
• Pain on resisted elbow extension and passive flexion

Differential Diagnosis:

• Olecranon bursitis
• Olecranon stress fracture
• Fracture of an olecranon osteophyte
• Partial tendon tear

Question 5

Distal Triceps Rupture/Olecranon Avulsion

Answer 5

Triceps tendon can rupture from its attachment at the olecranon process or the olecranon can avulse from the ulnar

Epidemiology:

• Least common of all tendon ruptures

Aetiology:

• Most commonly FOOSH, elbow extension
• Most commonly insertional
• Observed associations:
  
  • Body building
  • Anabolic steroid use
  • Hyper-parathyroidism
  • Renal osteodystrophy
  • Olecranon bursitis
  • Osteogenesis imperfecta
  • SLE
  • Marfan’s Syndrome
  • Local corticosteriod injections

Clinical Presentation:

• Pain at insertion of the triceps
• Pain with active arm extension in cases of partial avulsion/rupture
• Swelling and bruising on the posterior arm

Physical Assessment:

• Palpable defect
• Weakness/pain with elbow extension
• Ecchymosis and swelling posterior arm
• +ve Triceps squeeze test

Differential Diagnosis:

• Triceps tendonitis
• Olecranon bursitis
• Olecranon stress fractures
• Posterior elbow impingement

Question 6

Snapping Triceps Tendon

Answer 6

A sensation caused by a portion of the triceps mechanism slipping medially or laterally:

• May be confused with subluxation of the ulnar nerve over the medial epicondyle of the humerus on flexion and extension of the elbow

Aetiology:

• Abnormal medial or lateral triceps insertion (therefore often B/L)
• An aberrant triceps tendon (fluid accumulation)
• Cubitus varus and is typically present with concurrent irritation of the ulnar nerve

Clinical Presentation:

• Usually posteromedial pain and crepitation
• Aggravating factors
  
  • Overhead activities
  • Push-ups
  • Resisted flexion and extension of the elbow

Question 7

Lateral Epicondylopathy

Answer 7

Overuse syndrome of the extensor tendons of the forearm:

• Colloquially called ‘tennis elbow’

Epidemiology:

• Common
• No gender predilection
• Incidence:
  
  • 1-3% of the general population
  • Peaking between 30 and 50 years
• Most commonly in the dominant arm
• Prone to chronicity:
  
  • Natural course 12-24 months

Aetiology:

• History of repetitive work or recreational activity:
  
  • Wrist dorsiflexion with pronation and supination
• Occupations requiring prolonged computer work or heavy loads or tools
• Inexperienced racquet- or stick-sport athlete:
  
  • Concentric forces on the tendon causing microtears and inflammation

Clinical Presentation:

• Patients complain of lateral elbow pain localized to the lateral epicondyle and the common extensor tendon or just distal to it
• Patients may complain of pain on grasping movements
• Possible referred pain down the extensors

Physical Assessment:

• Symptoms reproduced by:
  
  • Resisted wrist extension / forearm supination (Cozen’s test)
  • Passive wrist flexion and pronation (Mill’s test)
  • Resisted middle finger extension (Middle finger sign)
• Elbow ROM is typically unaffected
• Reduced grip strength due to pain

Differential Diagnosis:

• Radial n. entrapment
• OCD of the capitellum
• Radiocapitellar arthritis

Question 8

Medial Epicondylopathy

Answer 8

Commonly referred to as ‘Golfer’s elbow’

Repetitive stress of the flexor-pronator group causing degenerative changes at the common flexor tendon at the medial epicondyle

Aetiological factors:

• Direct-blow
• Eccentric overload
• Wrist pronation and flexion or repetitive valgus overload
• Common in:
  
  • Golf players
  • Throwing athletes
  • Manual work (hammer use)

Epidemiology:

• Less common than lateral epicondylopathy

Clinical Presentation:

• Localized tenderness:
  
  • Anterior tip of anteromedial epicondyle
  • Pain can be localised to 2cm distal along PT or FCR
  • Can have associated ulnar neuropathy

Physical Assessment:

• Localized pain and swelling over the tendon or site of origin
• Pain on resisted wrist flexion and pronation
• Pain on passive wrist extension and supination
• Possible pain on elbow valgus stress tests
• Postive Test for medial epicondylopathy

Question 9

Radial Nerve Entrapment

Answer 9

Radial Nerve:

• Terminal branch of the posterior cord of the brachial plexus (C5, C8, T1)
• Motor supply (elbow):
  
  • Triceps
  • Aconeus
  • Brachioradialis
  • Lateral half or brachialis
• Two branches:
  
  • Superficial sensory branch
  • Deep motor branch (Posterior interosseous n.)

Epidemiology:

• Uncommon

Aetiology:

• Tumour, humeral fracture, crutches, sleeping outstretched/hyperabducted:
  
  • Saturday night palsy

Clinical Presentation:

• Sensory loss
• Motor loss:
  
  • Wrist drop

Question 10

Radial Nerve Entrapment - Proximal Humerus

Answer 10

Epidemiology:

• Most common form of radial n. entrapment

Aetiology:

• Commonly fibrous arcade and spiral groove
• Repetitive forceful arm movements
• Forceful adduction of GH:
  
  • Gymnastics
  • Wrestling
  • Running
  • Throwing
• Fracture/dislocation of the humerus

Clinical Features:

• Motor and sensory symptoms in the radial nerve distribution

Question 11

Radial Nerve Entrapment - Radial Tunnel

Answer 11

The radial tunnel extends from the level of the radiocapitellar joint to the level of the proximal aspect of the supinator muscle

Aetiology:

• Compression by fibrous bands of brachioradialis
• Trauma to the humerus or radial head
• Inflammation associated with lateral epicondylopathy

Clinical Features:

• Pain and weakness on resisted supination
• Positive middle finger sign
• Pain on resisted wrist extension
• Possible sensory change
• Motor weakness uncommon
• Night pain
• Burning pain along the lateral aspect of the forearm that can mimic lateral epicondylopathy

Question 12

Posterior Interosseous Nerve Entrapment - Arcade of Frohse

Answer 12

The arcade of Frohse is the fibrous arcade between the deep and superficial branches of the supinator muscle

Aetiology:

• Thickened tendinous edge of the supinator muscle, most likely due to repetitive pronation and supination movements

Clinical Presentation:

• Weakness in wrist, finger, thumb extension:
  
  • Partial paralysis
• Pain about the supinator origin
• No sensory loss

Question 13

Superficial Radial Nerve Entrapment

Answer 13

Also known as Cheiralgia paresthetica or Wartenberg disease

Aetiology:

• Crush or twisting injuries of the forearm
• Compression from wrist bands, casts or even handcuffs

Clinical Features:

• Pain or burning over the anatomical snuff box and the back of the hand

Question 14

Ulnar Nerve Entrapment - Proximal Humerus

Answer 14

Subscapularis

Arcade of Struthers:

• Intermuscular septum of triceps
• Hypertrophy compression

Aetiology:

• Direct compression
• Humeral fracture

Clinical Presentation:

• Pain
• Paresthesia in the fifth and half of the fourth finger
• Motor weakness in fourth and fifth finger flexors

Question 15

Ulnar Nerve Entrapment - Cubital Tunnel

Answer 15

Aetiology:

• Occupations that involve elbow flexion
• Acute trauma
• Overuse injury
• Bony spurring
• Dynamic compression:
  
  • Ulnar nerve subluxation
• Cubitus valgus deformity
• Snapping medial triceps tendon

Clinical Presentation:

• Pain and aching at the medial elbow
• Paresthesia in the fifth and half of the fourth finger
• Motor weakness in fourth and fifth finger flexors
• Chronic compression can lead to claw deformity

Question 16

Median Nerve Entrapment – Proximal Humerus

Answer 16

Location:

• Infra-clavicular entrapment
• Subscapularis
• Ligament of Struthers

Aetiology:

• Fibrous adhesions
• Thickening of fascia and ligaments
• Vascular events
• Fractures
• Biceps hypertrophy

Question 17

Median Nerve Entrapment - Elbow

Answer 17

Location:

• Antecubital fossa:
  
  • Lacertus fibrosus
• Pronator Teres muscle:
  
  • Proximal edge of flexor digitorum superficialis

Aetiology:

• Fibrous edges of muscles
• Hypertrophy
• Masses, SOL or contusions in the forearm
• Dynamic compression by repetitive supination/pronation
• Congenital anomalies
• Conditions that lead to enlargement of tissues within various tunnels and spaces e.g. hypothyroidism

Clinical Presentation:

• Pronator Teres syndrome:
  
  • Pain and paresthesia in the median nerve distribution that may mimic carpal tunnel syndrome
  • Symptoms aggravated by overuse of pronator teres
  • Symptoms are not typically worse at night as with carpal tunnel syndrome
• Anterior Interosseous Nerve syndrome:
  
  • Neuritis of unknown origin
• Motor weakness:
  
  • Inability to pinch the thumb and index finger together (Pinch grip test):
    
    • Palsy of flexor pollicis longus and flexor digitorum profundus

Physical Examination:

• Pronator Teres Syndrome:
  
  • Sensory deficit in the median nerve distribution
  • Pain on resisted pronation of the forearm that is worsened with elbow extension
  • Tinel’s sign at the carpal tunnel is typically negative
  • Test for pronator teres
• AIN Syndrome:
  
  • Positive Pinch grip test

Question 18

Elbow Sprains

Answer 18

• The elbow is stabilized by the locking of the olecranon process in its fossa when the joint is extended
• Strain can occur when the elbow is in the flexed position
• Valgus or varus forces are dissipated through the collateral ligaments:
  
  • Valgus stresses are the most common cause of injury
• Tensile forces on one side of the joint result in compressive forces on the opposite side

Question 19

Ulnar Collateral Ligament Injury

Answer 19

History:

• Trauma:
  
  • Macro (less common)
  • Micro – Valgus loading of the humeroulnar joint
• Repetitive valgus overload
• Throwers late cocking & acceleration

Predisposing Factors:

• Internal rotation (Sh°) deficits (GIRD) in the throwing athlete
• Cubitus varus

Clinical Presentation:

• Pain on the medial aspect of the elbow
• Gradual onset in cases of micro trauma
• Worse with motion
• Radial nerve compression can cause neuropathic pain into the forearm and fingers
• Tensile forces on the ulnar nerve can cause paresthesia in the ulnar nerve distribution

Physical Examination:

• Swelling over the anteromedial and posterior aspects of the elbow
• Ecchymosis over anteromedial aspect of the elbow
• Tenderness around medial elbow (2cm inferior from the medial epicondyle)
• Crepitus may be present
• Restricted ROM due to pain and stretching of muscles and ligaments especially in flexion
• Painful active wrist flexion
• Pain on end range supination and extension
• Passive wrist extension is painful at end range
• Decreased strength of wrist flexors
• Possible muscle weakness or sensory changes (radial or ulnar neuropathy)
• Positive valgus stress test (>10-25°) – Positive moving valgus stress test

Neurological Screening:

• Ulnar sensory or motor changes
• Possible radial sensory or motor changes
• Possible +ve Tinel’s sign at the elbow:
  
  • Radial n.
  • Ulnar n.

Functional Assessment:

• Decreased velocity in throwing athletes
• Pain and discomfort during various phases of throwing

DDx:

• Pronator m. strain
• Supinator m. strain
• Ulnar neuropathy
• FCR m. strain – FCU m. Strain
• Flexor avulsions
• Medial epicondylopathy

Question 20

Valgus Extension Overload Syndrome (VEOS)

Answer 20

Impingement of the posteromedial olecranon on the medial wall of the olecranon fossa:

• Also known as posteromedial impingement syndrome

History:

• Preceded by MCL injury/insufficiency
• Common in throwing athletes, but also in swimmers, gymnasts, volleyball and racket sports
• Valgus stress, radiocapitellum compression

Clinical symptoms:

• Pain at the medial aspect of the olecranon that is usually present at the acceleration and deceleration phase of throwing
• Limited extension
• Locking, crepitus, catching from loose bodies and osteophytes or chondromalacia
• Ulnar nerve irritation

Physical Examination:

• Tenderness over MCL, joint line and the posteromedial tip of the olecranon process
• Reduced extension:
  
  • Flexor contracture
• Positive Valgus stress test (>10-25°)
• Positive Valgus extension overload test
• Positive moving valgus stress test
• Potential ulnar and/or radial neuropathy

Functional Assessment:

• The location of pain during various movement is a very important diagnostic clue
• Medial pain at the start of the acceleration phase
  
  • UCL injury
• Posterior pain at full extension
  
  • VEOS

Differential Diagnosis:

• Triceps tendinopathy
• UCL lig. Injury

Question 21

‘Little Leaguer’s Elbow’

Answer 21

Term used to describe several overuse injuries in young throwing athletes that commonly result from valgus overload

History:

• Repetitive valgus stress in skeletally immature individuals
• Inadequate intervals of rest
• Poor throwing mechanics
• Use of breaking pitches
• Common in pitchers and quarterbacks
• Stresses occur during the cocking and acceleration phases

Clinical Symptoms:

• Medial elbow pain during cocking and acceleration phases of the throw
• Possible referred pain into the flexors and pronators
• Potential ulnar neuropathy

Predisposing Factors:

• Altered shoulder or scapula biomechanics
• Poor throwing stance
• Skeletal immaturity
• High throwing frequency
• Position played
• Strength and flexibility imbalances
• Type of throwing activities

Physical Assessment:

• Pain at the medial and posteromedial elbow (tensile forces)
• Pain at the lateral elbow (compressive forces)
• Increased flexor/pronator tone
• Possible crepitus/clicking/locking
• Flexor contracture
• Reduced grip and flexor strength
• Pain on end-range wrist extension, elbow pronation and extension
• Pain with resisted pronation
• Pain with valgus stress usually without instability

Differential Diagnosis:

• Flexor/pronator m. strain/tear
• Olecranon/capitullum/epicondylar fracture
• Valgus extension overload syndrome
• Lateral epicondylopathy
• Medial epicondylopathy

Question 22

Panner’s Disease

Answer 22

Panner’s Disease is characterized by necrosis and subsequent regeneration of the capitellar ossification centre

• An osteochondrosis of the epiphyseal region of the humerus

History:

• May be directly related to trauma or to changes in the circulation to the entire capitellar growth centre
• Panner’s disease is the most common cause of lateral elbow pain in the young child and is typically seen in patients younger than 10 (6-15 years)

Aetiology:

• Thought of as the Legg-Calve Perthes’ disease equivalent of the elbow
• Thought to be secondary to valgus forces at the elbow compromising the blood flow to the capitellar ossification centre
• More commonly seen in males
• The condition tends to be self-limiting

Clinical Symptoms:

• Pain (dull ache)
• Swelling over the lateral elbow
• Limitation of range of motion in a non-capsular pattern of restriction:
• Particularly flexion
• Sometimes locking, crepitus, or clicking
• Possibly joint effusion
• Always in the dominant elbow

Differential Diagnosis:

• OCD of the capitellum
• Lateral epicondylopathy

Question 23

Radiocapitellar Overload Syndrome

Answer 23

Radiocapitellum Function:

• Secondary stabiliser to valgus stress after the MCL
• Transfers axial loads during pushing movements

Repetitive compressive forces to the radiocapitellar joint can result in excessive radial head abutment against the capitellum:

• Chronic, repetitive radiocapitellar joint force may result in chondromalacia, followed by cartilage and bony degeneration

Clinical Features:

• Lateral elbow pain in athletes or manual workers who perform repetitive overhead or pushing activities
• MCL deficiency

Question 24

Radial Head and Neck Fractures

Answer 24

The radio-capitellar articulation takes more than half of the load transmitted across the elbow joint

Greatest axial loads are placed on the radiocapitellar joint with 0-30° extension and pronation of the forearm

Mechanism of injury is usually FOOSH incidents

Epidemiology:

• Represent 1% of all childhood fractures
• Most involve the physis and/or the neck
• Most are Salter-Harris Type IV #s in children
• Radial head fracture is the most common elbow fracture in adults
• Most fracture’s are extra-articular in adults
• Women 2:1
• Age 30-40 years

Concomitant injuries occur in up to 60% of radial head and neck fractures:

• Olecranon fractures
• Medial epicondyle avulsions
• Dislocations
• Terrible triad of the elbow
  
  • Dislocation of the elbow with LUCL injury combined with radial head and coronoid fractures

Classification:

• Group 1:
  
  • Primary displacement of the radial head
• Group 2:
  
  • Primary displacement of the radial neck
• Group 3:
  
  • Stress injuries

Clinical Presentation:

• Localized pain
• Swelling
• Reduced movement at the elbow

Physical Examination:

• Joint effusion
• Antalgic position
• Possible displacement of bony structures
• Severe pain could indicate possible compartment syndrome:
  
  • Radial nerve
  • Posterior Interosseous nerve (PIN)
  • Brachial a., radial a. and ulnar a.
• Pain and tenderness over the radial head or neck
• Reduced and painful pronation and supination
• Possible crepitus or locking
• Often restricted due to haematoma
• Assess the wrist as the distal radioulnar joint is often involved

Associated findings:

• MCL, LCL, interosseous membrane disruptions
• Dislocations
• Fractures of olecranon and coranoid process

Question 25

Lateral Collateral Ligament Injury

Answer 25

Mechanism of Injury: * Repetitive varus force is uncommon * Most injuries are due to dislocation or subluxation of the radial head * Varus stress must be differentiated from: * Posterolateral rotatory instability * Fracture or dislocation * Proximal radio-ulnar disassociation (annular ligament)

Question 26

Postero-Lateral Rotary Instability (PLRI)

Answer 26

Definition: * Characterized by external rotation and posterior subluxation of the ulna relative to the trochlea that occurs due to disruption of the lateral collateral elbow complex * Typically the result of FOOSH injuries: * A valgus and axial force transmitted through a supinated and extended elbow * Proximal ulnar and radial head externally rotate relative to the humerus * This may also cause the radial head to subluxate or dislocate * Lateral collateral ligament injury * Medial collateral ligament injury may be associated * Fracture to the coronoid process Three Stages: * 1. Posterolateral subluxation * 2. Incomplete dislocation * 3. Dislocation Epidemiology: * Most common type of symptomatic chronic elbow instability Clinical Symptoms: * Lateral elbow pain: * May present with lateral epicondylopathy-like symptoms * Recurrent painful locking * Recurrent episodes of instability * Snapping and/or popping * Aggravated by pushing movements Physical Examination: * Tenderness to palpation over the lateral elbow * Positive varus stress test * Postive valgus stress test in some cases * Positive posterolateral pivot-shift apprehension test * Surgical scars?

Question 27

Subluxation of the Radial Head

Answer 27

Also referred to as ‘Nurse Maid’s elbow’ Occurs in young children before the age of 8 years, with a peak incidence between 2 and 3 years Aetiology: * Poor attachment of the annular ligament to the radial head * Relatively narrow radial head compared to the radial neck Clinical Presentation: * Sudden traction injury that has been applied to the child’s arm while held in an extended and pronated position * Pulls the radial head through the annular ligament * Pain may be poorly localized * Holds the elbow flexed at about 90° and in pronation * Painful inability to use the arm, which may be accompanied by an audible or palpable click in the elbow Physical Examination: * Pain around the radial head * Decreased elbow range of motion: * Flexion, pronation and supination * The child may not be using their affected arm as much as their non-affected arm

Question 28

Elbow Dislocation

Answer 28

Epidemiology: * Most common dislocation in children * Sports account for up to 50% * Posterior elbow dislocations comprise over 90% of elbow injuries Considerable force is required to dislocate the elbow Early recognition of this injury is required due to the need for early reduction Mechanism of Injury: * FOOSH injury * Valgus plus compressive forces, posterolateral dislocation & fracture * Sports that increase the likelihood of FOOSH injury (e.g. gymnastics, rollerblading, cycling) may theoretically increase the risk of elbow dislocation * Simple dislocations * Complex dislocations * Commonly involve a disruption to the lateral ligaments followed by the capsule Physical Examination: * Evaluate for effusion * Deformity * Posterior elbow dislocations often have a very prominent olecranon and a forearm that appears foreshortened * Touch sensation of the median and ulnar nerves can be quickly assessed by testing the distal palmar aspect of the first through fifth digit * Motor function of the median and ulnar nerve can be quickly assessed by evaluating the abduction and adduction strength of the digits (ulnar nerve) and the opposability of the thumb (median nerve)

Question 29

Elbow Arthritis

Answer 29

Aetiology: * Trauma most commonly * Primary osteoarthritis * Septic arthritis * Crystalline arthropathy * Hemophilia Epidemiology: * Common in men * Manual laborers, weight lifters, and throwing athletes Clinical Presentation: * Localized pain * Weakness * Limitations in range of motion * Pain at points through the ROM * Patients may present with instability in case of severe prolonged synovitis which can disrupt the restraining structures * Locking with loose body formation Physical Examination: * Look for evidence of scarring or previous surgery * Pain common localized to the lateral elbow and over the radial head * Pain persisting throughout the entire range of motion in the late stages of the condition * Decreased ROM due to osteophytes * End-feel appraisal * Crepitus, catching, locking?