FRCS Mock Exam 1: Comprehensive Review

A V-Y advancement of the gastrocnemius would be required if the gap is 6 cm. Repair of an Achilles tendon is usually undertaken with the patient prone, and an incision just medial to midline to avoid sural nerve injury. Immobilizing the foot in 20
plantarflexion allows maximum skin perfusion over the tendon, by decreasing skin tension, and protects the tendon repair. A direct repair is usually possible if the gap is less than 3 cm. A V-Y advancement of the gastrocnemius can be considered if the gap is between 3 and 5 cm, and if greater than 5 cm, a flexor hallucis longus transfer must be considered.

Ulnar shortening osteotomy. It is uncommon for younger people to present with significant radial shortening as their fractures are usually well managed. In this case there is ulna impaction syndrome. The aim is to reduce this impaction. There is no need to address the DRUJ or replace the distal ulna. The Darrach procedure should be reserved for older patients with rheumatoid disease. It is associated with ongoing discomfort in the proximal stump and certainly not the first choice in this scenario.

Cuboid. The calcaneum (anterior), talus and cuboid ossification centres are usually present at birth. The lateral cuneiform appears during the first year, the medial cuneiform appears during the second year, the intermediate cuneiform and navicular appear during the third year and the posterior calcaneal centre appears during the eighth year.

Arthroscopy, excision and microfracture. The Berndt and Harty classification refers to osteochondral lesions of the talus. It is a radiographic classification: I – compression of the subchondral bone II – a partially detached osteochondral fracture III – completely detached, non-displaced fragment IV – a detached and displaced osteochondral fragment Osteochondral lesions of the talar dome are commonly anterolateral or posteromedial; they are often traumatic in origin, particularly the anterolateral lesions, but may also have an osteonecrosis/atraumatic aetiology. Type IV lesions are best treated by excision and microfracture, with good results in up to 86% of patients. Microfracture is usually undertaken arthroscopically. If simple debridement and microfracture is ineffective in reducing symptoms, chondral or osteochondral grafting is considered. Ankle arthrodesis or arthroplasty is the definitive treatment.

Arthritis. Post-traumatic arthritis is the most common complication following Lisfranc injuries. The major determinant of a good result is anatomical reduction. Patients with purely 214 ligamentous injury tend to have outcomes, even with anatomical reduction and screw fixation.

The mechanism of injury is a primary hyperflexion of the neck. A hangman’s fracture is a traumatic spondylolisthesis of C2 on C3 as a result of bilateral fracture of C2 pars or pedicles. The mechanism of injury is an extension injury (causes pars fracture) with a secondary flexion (disrupts the posterior longitudinal ligament (PLL) and the disc) resulting in the anterolisthesis. In 30% there is a concomitant C-spine fracture. There is usually no neurological deficit except in type III. Levine and Edwards have classified this fracture as follows: Type I – minimal displacement and angulation with an intact disc. Treatment: Philadelphia-like collar. Type II – displaced fracture of the pars with >3 mm displacement and significant angulation (disc and PLL disrupted). Reduce with traction then apply halo for 2 months. 63 Type IIA – no horizontal displacement but significant angulation. Reduction with hyperextension WITHOUT TRACTION then apply halo for 2 months. Type III – is associated with bilateral facet dislocation and requires an open reduction of the dislocation with C2/C3 fusion.

Nail patella syndrome. This syndrome is a result of an abnormality on chromosome 9. Patients may have subluxed or dislocated radial heads and never realize they have a problem until they have an X-ray. The syndrome can include abnormalities of the patella and nail growth, generalized ligamentous laxity and bony exostoses.

Painful nodules are an indication for surgery. The disease is usually in its early phases. The stages, according to Luck’s classification, are proliferative, involutional and finally residual. Early surgery will certainly lead to recurrence and can stimulate the disease process. Carpal tunnel surgery must be performed at a separate occasion for a similar reason. Unfortunately in the long term recurrence rates are high (50%).

Arthroscopic or open debridement. This patient is describing patellar clunk syndrome. This occurs when a fibrous nodule of tissue forms in the undersurface of the quadriceps tendon just above the patella. It is a problem with posterior stabilized knee replacements but can also occur in cruciate retaining designs. As the knee extends the nodule impinges in box of femoral component and with continued extension it jumps out with an audible or palpable clunk. Non-operative treatment is usually not successful and debridement of the nodule is requited.

During hamstring harvesting, the connection between the semitendinosus and the medial gastrocnemius must be divided. There continues to be debate as to the exact positioning of graft tunnels during ACL reconstruction, but it is generally accepted that the femoral tunnel should be placed posteriorly on the lateral wall of the notch. Therefore, for right knees this is the 10 or 11 o’clock position and for left knees the 1 or 2 o’clock position, and the tunnel should be on 109 the posterior half of Blumensaat’s line. There is also debate as to the optimal fixation method, but there is no evidence to support interference being better than suspensory. A number of connections (vinculae) exist with the hamstrings and these must be divided to avoid insufficient harvesting. A fairly predictable vincula exists between semitendinosus and medial gastrocnemius, although anatomical studies have shown that a number of vinculae can be present between both semitendinosus and gracilis and the popliteal fascia, sartorius, gastrocnemius, pretibial and superficial fascia.

Vibration is transmitted in the anterior corticospinal tract. Vibration is also transmitted in the dorsal columns. The anterior corticospinal tract is a motor pathway.

Urine cortisol. The opening line of this case may tempt one to consider the diagnosis of Duchenne’s muscular dystrophy for which choice B would be the correct answer. This child has features of Cushing’s syndrome, which can be caused by excess adrenocorticotrophic hormone (ACTH) production or occur independent of ACTH, due to an adrenal adenoma. Obesity, hypertension, bruising and proximal myopathy are all features of Cushing’s syndrome. The first step in establishing this diagnosis is to measure the urinary free cortisol. The cause of the Cushing’s syndrome can then be determined by performing the dexamethasone suppression test, measuring plasma ACTH and obtaining an MRI of the pituitary if appropriate.

Extensor carpi radialis brevis. The patient has lateral epicondylitis (tennis elbow), which usually involves a microtear of extensor carpi radialis brevis (ECRB). Histologically the lesion that was consistently identified at surgery was immature fibroblastic and vascular infiltration (angiofibroblastic dysplasia) of the origin of ECRB.

In the prediction of malunion, the presence or absence of comminution is not an important factor. Important factors in predicting early and late instability and radiographic outcome after distal radial fractures include patient age, metaphyseal comminution of the fracture and ulnar variance. Dorsal angulation has not been shown to be significant in the prediction of radiographic outcome for displaced fractures.

Tendon pull must be synergistic. These rules must be appreciated and short cuts will only lead to disaster. Donor muscles must be expendable and have adequate power, ideally MRC grade 5. Joints must be mobile with no contracture.

The thoracodorsal nerve. The lateral pectoral nerve receives contributions from C5/6/7. The axillary nerve: C5/6. The upper subscapular nerve: C5/6. The thoracodorsal nerve: C7/8 and variably C6. The radial nerve: C5/6/7/8 and variably T1.

Medial scapular winging. The long thoracic nerve supplies serratus anterior, injury to which can result in medial translation of the scapular and the inferior angle rotated medially. Lateral scapular winging (lateral translation and the inferior angle rotated laterally) can occur as result of spinal accessory nerve palsy which supplies trapezius.

Medial circumflex vessels. The blood supply to the proximal femoral epiphysis is reported to change with age. Until age 4, the supply to the femoral head is derived equally from medial and lateral circumflex vessels as well as the ligamentum teres. The physis acts as a mechanical barrier with virtually no traversing metaphyseal vessels reaching the epiphysis. After age 4, supply from the ligamentum teres diminishes and the distribution of supply from the circumflex vessels changes; the lateral circumflex system supplies predominantly the metaphysis whilst the medial circumflex system becomes the predominant supply to the proximal femoral epiphysis via its posterosuperior branch. After age 10 years, supply by the ligamentum teres diminishes further and the femoral epiphysis relies upon the end arterial supply of the retinacular vessels. With the closure of the physis at skeletal maturity, anastamoses develop between the vessels of the ligamentum teres, epiphyseal and metaphyseal systems and there is less reliance on end arteries.

10% occur in motorcyclists. Traumatic scapulothoracic dissociation is a high-energy injury, with associated injury to the brachial plexus and subclavian artery. The mechanism of injury is probably traction caused by a blunt force to the shoulder girdle, commonly seen in motorcyclists (up to 60%). The presence of a complete brachial plexus avulsion is predictive of a poor functional outcome in a patient with scapulothoracic dissociation. Treatment may include vascular repair, plexus exploration and fixation of the commonly associated clavicle fracture to instil stability. 213

Less in ceramic than polyethylene cups. The Swedish Hip Registry reports that deep infections are slightly lower with ceramic components. The exact mechanism is unclear, but may be due to bacterial adhesion being poorer on the smoother surface of ceramic components.

patients following correction of scoliosis by a cast or instrumentation. As a result of the curve correction, the angle between the SMA and the aorta is narrowed resulting in the compression of the third part of the duodenum. Initial treatment includes oral intake restriction, nasogastric suction and intravenous fluid administration. The majority of cases settle with conservative measures. In rare cases of failed non-operative treatment, surgical intervention is indicated.

Interleukin-6 (IL-6). Multiple cytokines have been measured in serum. Elevated levels of IL-6 have been associated with the development of MODS.

5º valgus, 10º external rotation, 0º flexion, 5 mm posterior talar translation. It is extremely important to fuse the ankle in the correct position. The position affects knee function and the ability to walk on uneven ground. The ideal position of arthrodesis is neutral flexion, 0–5
valgus of hindfoot valgus, 5–10
of external rotation, and slight posterior displacement of the talus under the tibia (5 mm). Posterior displacement normalizes the gait pattern and decreases the stress on the knee.

Hip aspiration. Although a radio-labelled white cell scan is more likely to be positive in infection rather than inflammation, it cannot be used to definitively differentiate between the two. A radionuclide bone scan would appear hot in both conditions. A positive hip aspirate would both identify infection, as well as guide antibiotic treatment. Von Rothenburg et al found a Tc-99m-labelled scan had sensitivity of 93% but specificity of 65%. Therefore, a positive result (positive predictive value 63%) may not definitely mean an infection, whereas a negative result (negative predictive value 94%) is likely to help rule out infection.

Anterior cervical decompression and fusion. This patient has myelopathic changes within the cord probably as a result of an anterior degenerative disc. The presence of a fixed kyphosis of >10
is a contraindication to a 64 posterior decompression þ/ fusion. In addition, posterior procedures are ineffective in this case as the anterior compression on the cord will remain. The anterior approach provides direct access to the disc herniation and provides immediate and long-term stability to the motion segment.

Inferior glenohumeral ligament complex. The rotator cuff is a dynamic stabilizer and the capsulolabral tissues are considered static stabilizers. With the arm at 90
abduction, the anterior band of the inferior glenohumeral ligament complex is the primary static stabilizer to anterior translation.

Rupture of the extensor pollicis longus (EPL) tendon. EPL rupture is seen more commonly with undisplaced distal radial fractures, rather than displaced ones. It is thought that this is due to either a mechanical attrition of the tendon or a local area of ischaemia in the tendon. Repair is not usually possible and treatment is with tendon transfer (EIP to EPL).

There is an accepted and effective treatment. Neonatal hip instability is common; if instability persists, particularly when associated with anatomical dysplasia, true DDH develops. Clinical examination is less than 100% sensitive/specific and a missed diagnosis of DDH can lead to multiple invasive procedures and lifelong disability. Ultrasound screening in the neonatal period may therefore improve the accuracy of diagnosis leading to the provision of early treatment which is less invasive and of shorter duration with a greater likelihood of normal hip development. Although hip instability is commonly detectable in the newborn, most will resolve spontaneously without the need for treatment. However, there is no evidence proving the accuracy of ultrasound as a screening tool. Although ultrasound tends to lead to less invasive treatment of shorter duration, screening may lead to overtreatment. Not only is the evidence of the effectiveness of early non-invasive treatment lacking but non-invasive treatments such as the Pavlik harness are not without morbidity and carry a risk of AVN. Therefore, although ultrasound examination is a useful tool for assessing the infant hip prior to ossification, its use for screening remains controversial. It does not meet some of the criteria for a good screening test in that information on the natural history of the disease and the optimal treatment of DDH is lacking. Some countries provide generalized screening although this is not the case in the UK where selective screening of at-risk infants is performed.

The cortical ring sign is produced by cortex of distal pole of palmar flexed scaphoid. A scapholunate distance of more than 2–3 mm as compared to the opposite side is suggestive of scapholunate dissociation. Although Madonna, who is famous for her singing, has a gap between her teeth, it is of course the actor, Terry Thomas, who has given his name to this eponymous sign. On the lateral view, an angle >60–70
suggests scapholunate dissociation.

Radiolucent lines in Gruen zones 1, 2, 6 and 7. Gruen described seven zones around a cemented femoral stem starting with zone 1 at the greater trochanter round to zone 7 at the calcar, zone 4 being at the tip of the prosthesis. He described different modes of failure of cemented stems: 238 Mode Mechanism Cause Findings 1A Pistoning Stem subsiding within cement Radiolucent lines in zones 1 and 2 1B Pistoning Stem and cement subsiding within bone Radiolucent lines in all 7 zones Medial stem pivot Lack of supermedial and inferolateral support Medial migration proximally and lateral migration distally Calcar pivot Medial-lateral toggling of distal stem Radiolucent lines in zones 4 and 5 Cantilever bending Loss of proximal support with a well-fixed distal stem Stem fracture, radiolucent lines on zones 1, 2, 6 and 7

A posterior instrumentation should stop at the distal most tilted vertebra. Scheuermann’s kyphosis is a kyphotic deformity of >45
in the thoracic spine with >5
anterior wedging across three consecutive vertebrae. The condition is often associated with a lumbar hyperlordosis. A mild scoliosis can sometimes be present. It is differentiated from postural kyphosis by the rigidity of the curve. It is the most common cause of thoracic back pain in older children and adolescents. An MRI scan is indicated to look for disc herniation, cord abnormalities and spinal stenosis. Surgery is indicated for curves >80
in skeletally mature patients, it entails a posterior spinal fusion with dual-rod instrumentation þ/ anterior release and interbody fusion. The fusion level should stop distally at the vertebra which is parallel to the floor (usually the L3 level). A ligamentum flavum excision should be performed at the apex to prevent buckling of the ligament and therefore decrease the risk of neurological deficit.

Injury to the lateral ascending vessels of the femoral neck. Avascular necrosis and collapse of the femoral head following intramedullary nailing of the femur may be seen if a piriformis fossa entry point is used; this is due to injury to the lateral ascending cervical artery, which supplies the epiphysis. Therefore, a piriformis fossa entry point is contraindicated in patients with open physes.

Risser 3. Risser staging 1–5 depends on the amount of ossification of the iliac apophysis visible on the anteroposterior (AP) radiograph. Ossification begins anterolaterally and proceeds posteromedially. The first 25% equates to Risser 1 and grade 4 equates to 100% ossification. Grade 5 is signified by fusion of the apophysis. The relevance of Risser staging is in predicting the progression of scoliotic curves. Small curves and greater skeletal maturity according to the Risser stage predicts a smaller likelihood of curve progression compared to larger curves and skeletal immaturity.

Suprascapular-axillary. Surgical fixation of a scapular neck fracture is performed via a posterior approach to the scapular/glenoid. The internervous plane is between the infraspinatus (suprascapular nerve) and the teres minor (axillary nerve). The posterior branch of the axillary nerve has intimate association with the inferior aspects of the glenoid and shoulder joint capsule, and can be found in the interval between teres minor and teres major, which may place it at particular risk during a posterior approach to the shoulder.

Ca10 (PO4)6 (OH)2. Calcium hydroxyapatite (Ca10 (PO4)6 (OH)2) forms part of the inorganic component of the bone matrix and gives it compressive strength.

Decompression of the syrinx in patients above the age of 10 years will improve or stabilize the scoliotic curve. Syringomyelia usually results from lesions that partially obstruct cerebrospinal fluid (CSF) flow including craniocervical junction abnormalities (Chiari malformations), spinal cord trauma and tumours. It often presents with central cord syndrome. Light touch, proprioception and vibration sensation are usually preserved. In most patients over the age of ten, surgical treatment of scoliosis is most likely necessary due to a large initial scoliosis curve or curve progression even after syrinx drainage.

Isotonic. Isometric muscle contraction occurs when muscle contraction generates tension without a change in its length. Plyometric exercises are defined as a muscle stretch followed by a rapid contraction and is a very efficient method of exercising to improve power delivery. Isokinetic exercises are resistance-based exercises designed to provide a specific level of resistance while maintaining a consistent speed of limb movement. They require use of special equipment such as the Cybex machine. Closed chain exercises are where the distal portion of the involved limb is stabilized – this minimizes shear forces across the joint. They are commonly used in anterior cruciate ligament (ACL) reconstruction rehabilitation.

Decreased shoulder muscle strength and endurance. McKee found that patients who had non-operative treatment of displaced (> 2 cm) midshaft clavicle fractures had significant decrease in both strength and endurance of about 80% compared to the contralateral side. Range of motion (ROM) of the affected shoulder was unaffected.

A space available for the cord (SAC) of less than 14 mm or an ADI of more than 9–10 mm is an indication for spinal stabilization. An atlantoaxial subluxation occurs in 60–80% of cases of rheumatoid arthritis (RA) as the result of pannus formation at the synovial joints between the dens and the ring of C1. An ADI of >3.5 mm on flexion extension is a common finding in RA and indicates instability; however, it is not necessarily an indication for surgery. A SAC <14 mm or an ADI >9–10 mm is associated with an increased risk of neurological injury and usually requires surgical intervention. A Ranawat C1–C2 index is the distance from the centre of the C2 pedicle to a line connecting the anterior and posterior arches of C1. It is the most reproducible measurement of invagination. A C1–C2 index <13 mm indicates basilar invagination. Subaxial subluxation occurs in 20% of cases of RA, a subluxation >4 mm or more than 20% of the body is indicative of cord compression.

Brachioradialis and extensor carpi radialis longus (ECRL) in pronation. The superficial branch of the radial nerve is compressed as it is squeezed between the brachioradialis and ECRL in pronation. This must not be confused with intersection syndrome, pain associated with the crossing of the first and second dorsal extensor compartments associated with repetitive movements of the wrist (e.g. in rowers). 18

Symmetrical muscle weakness. Rheumatoid arthritis is defined by the presence of four or more of the following criteria according to the American Rheumatism Association: improvement, present for at least 6 weeks present for at least 6 weeks 163 for at least 6 weeks 164 developmental dysplasia of the hip (DDH) in a baby aged 6 months? a. Galeazzi test. b. Asymmetric skin folds in the thighs. c. Limited hip abduction in flexion. d. Ortolani’s test. e. Barlow’s test. hip according to Herring’s modified classification of Perthes disease? a. A very narrow lateral pillar which is <50% of the original height. b. A lateral pillar with very little ossification with at least 50% of the original height. c. A lateral pillar with increased ossification with at least 50% of the original height. d. A lateral pillar with exactly 50% of the original height that is higher than the central pillar. e. Gage’s sign. be the sole indication for subcapital osteotomy? a. Metaphyseal blanch sign. b. Southwick angle >60
. c. Avascular necrosis (AVN). d. Femoral retroversion. e. Endocrinopathy. of the following radiographic views is most likely to identify a cam lesion? a. Cross table lateral. b. False profile. c. Frog lateral. d. Billings lateral. e. Dunn lateral. 172

An injury with external tibial rotation with the knee at 90
of flexion is likely to injure the posterior cruciate and lateral collateral ligaments. Neuromuscular training indeed explains the gender difference in the incidence of anterior cruciate ligament in similar sports, but it is higher in women. Furthermore, women have a greater total valgus knee loading when landing from a jump. A grade 3 posterior cruciate ligament injury does not necessarily need reconstruction. The majority of grade 1 and 2 injuries can be treated with protected weight bearing and quadriceps rehabilitation. Grade 3 injuries require immobilization in full extension for 2 to 4 weeks to protect the posterior cruciate ligament and the other posterolateral structures presumed to be damaged. Prophylactic knee bracing has not been shown to reduce anterior cruciate ligament injuries in contact sports, but has been shown to reduce medial collateral ligament injuries. 111

Deficient anterior cruciate ligament. A high tibial, valgus-producing osteotomy, either lateral closing or medial opening, is an effective surgical option for medial compartment osteoarthritis. It suits younger patients with varus alignment, fixed flexion less than 15º and flexion greater than 90º. Contraindications include lateral compartment degeneration, loss of a significant portion of the lateral meniscus, lateral tibial subluxation of greater than 1 cm, medial compartment bone loss, symptomatic patellofemoral degeneration, inflammatory arthritis and poor patient compliance. Anterior cruciate ligament deficiency alone is not a contraindication.

Presentation at 12–16 years. Tarsal coalition is due to failure of segmentation of the tarsal bones of the hind- and midfoot and can be partial or complete, fibrous, cartilaginous or bony. It is an autosomal dominant condition with a 20% incidence of multiple coalitions. Although congenital, symptoms occur when the coalition ossifies explaining why each type of coalition presents during a particular age range. Calcaneonavicular coalitions tend to present earlier between 8 and 12 years whereas talocalcaneal coalitions present later, at 12–16 years. Ossification causes loss of subtalar motion, adaptive shortening of the peronei and flatfeet; hence the term ‘spastic peroneal flatfoot’. The typical presentation comprises recurrent ankle sprains, calf pain and flatfeet. The radiographic ‘anteater sign’ represents the elongated anterior process of the calcaneum in calcaneonavicular coalition whereas talar beaking can be seen whenever there is stiffness of the subtalar joint complex. Middle facet talocalcaneal coalition 190 produces the greatest subtalar stiffness, with a valgus hindfoot. Over time, the adaptive shortening of the peroneal tendons contributes to posterior facet arthrosis in the subtalar joint regardless of the type of coalition.

They are associated with degenerate changes and cysts when due to femoro-acetabular impingement. Labral tears are often associated with subtle abnormalities of hip anatomy causing femoro-acetabular impingement (FAI). Painful clicking, snapping and similar symptoms are often due to labral tears in association with FAI. Labral tears may present as groin pain usually in certain positions and repetitive movements such as running.

Anterior shoulder dislocation. Erb’s palsy is the most common obstetric brachial plexus injury and the one with the best prognosis. It is caused by a traction injury at Erb’s point: the union of the C5 and C6 nerve roots. The most commonly affected nerves are the axillary (supplying deltoid and teres minor), the suprascapular nerve (supplying the supraspinatus and infraspinatus muscles) and the musculocutaneous nerve (supplying biceps and brachialis muscles). Erb’s palsy gives rise to the characteristic ‘waiter’s tip’ deformity of shoulder adduction and internal rotation, elbow extension, forearm pronation and wrist flexion. Like other neuromuscular conditions in children, soft tissue contractures lead to secondary bony deformity and joint incongruence. In Erb’s palsy, internal rotation of the shoulder caused by relative overactivity of subscapularis leads to dysplasia of the posterior glenoid and posterior (rather than anterior) instability.

Infection is within 3 weeks of surgery. Phillips et al found 41% of infections were successfully treated with debridement and antibiotics. Crockarell et al. found debridement successful only if performed within 2 weeks of onset of symptoms. 84

Right L5 perineural fibrosis. Gadolinium-enhanced MRI scans are helpful post discectomy in differentiating between recurrence of disc herniation, which does not enhance with gadolinium, and perineural 61 fibrosis, which shows enhancement around the root. A schwannoma enhances with gadolinium although the root would be enlarged. Systemically the patient is well and there is no evidence of fluid collection on scanning to suggest an infective process.

Sharp’s All of these lines on the anteroposterior (AP) pelvic radiograph are used to assess the degree of hip dysplasia/incongruence. Hilgenreiner’s line is made horizontally through the superior triradiate cartilage and serves as a reference for Perkin’s line and for measuring the acetabular index. Perkin’s line is perpendicular to Hilgenreiner’s at the superior edge of the ossified acetabulum. Normally, the femoral head should sit in the inferomedial quadrant at the intersection of these lines. Shenton’s line traces the lower edge of the pubis and the inferior aspect of the femoral neck. Any disruption to this line implies joint subluxation. Wiberg’s angle, known as the centre edge angle, is formed by the intersection of a line passing vertically upwards from the centre of the femoral head and a second line again passing from the centre of the head to the superior edge of the ossified acetabulum. This calculation is most reliable after age 5 due to increased ossification. A normal Wiberg’s angle is >25
. Sharps’s line is an alternative method of measuring the acetabular angle. The more common method is to use Caffey’s line drawn from the superior ossified acetabulum which forms an angle with Hilgenreiner’s line at the superior margin of the triradiate cartilage. This method measures the superior acetabular angle that should be <30
under age 2 191 and <20
after age 2. Sharp’s angle measures the inclination of the entire acetabulum. Sharp’s angle is formed by the intersection of a horizontal line at the inferior teardrop and a line passing through it that joins the superolateral and inferomedial aspects of the bony socket. It is used after 9 months when the teardrop becomes visible radiologically. Normal infants should have a value of <50
reducing to <38
in adolescence.

Central – medial – lateral; posterior – anterior. A Tillaux fracture is a Salter–Harris III avulsion injury of the anterolateral distal tibial physis by the anterior tibiofibular ligament (ATFL). It occurs following a low energy external rotation injury mechanism between the ages of 11 and 15 more commonly in girls and during sporting activities. It is the sequence of physeal closure at the distal tibia which accounts for this pattern of injury. Physeal closure begins with the central third, followed by the medial third and lastly the lateral third. Closure also occurs in a posterior to anterior direction and therefore, with injury, the strong ATFL avulses the relatively weak anterolateral portion of the epiphysis. The fragment is usually displaced anterolaterally and there may be associated diastasis. The Tillaux fragment should be fixed if displacement is >2 mm.