Discoid meniscus

Discoid meniscus

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Definition & Anatomy

A discoid meniscus is a congenital anatomical variant in which the meniscus — almost exclusively the lateral meniscus — is abnormally large, thick, and disc-shaped rather than the normal crescent (semilunar) form. It covers most or all of the lateral tibial plateau instead of just the periphery.

Epidemiology

Incidence: ~3–5% in Western populations; higher in Asian populations (up to 15%)
Predominantly affects the lateral meniscus; discoid medial meniscus is rare
Often bilateral (~20% of cases)

Classification (Watanabe)

Type	Description
Type I — Complete	Disc covers entire tibial plateau; most common type
Type II — Incomplete	Partial coverage of tibial plateau
Type III — Wrisberg variant	Normal shape but lacks normal posterior meniscotibial (coronary) ligament attachment; highly unstable and prone to subluxation

Pathophysiology

The abnormal shape leads to:

Altered biomechanics and stress distribution across the knee
Increased susceptibility to tears (horizontal cleavage tears most common)
The Wrisberg variant lacks posterior ligamentous attachment, causing the meniscus to snap or displace during motion

Clinical Presentation

Feature	Detail
Age	Children and adolescents most commonly; may present in adulthood
Classic sign	Painful clunk (audible/palpable snap) during knee extension — pathognomonic in children
Symptoms	Lateral knee pain, swelling, limited ROM, locking, giving way
Wrisberg variant	Dramatic snapping syndrome without a tear

Bailey and Love's (p. 644) describes the hallmark as "a painful clunk on knee extension."

Diagnosis

X-ray findings (indirect signs):

Widened lateral joint space
Cupping/hypoplasia of lateral tibial plateau
Elevated lateral fibular head

MRI (gold standard):

Sagittal view: ≥3 consecutive 5 mm slices showing continuity of anterior and posterior horns (the "bow-tie sign")
Coronal view: Abnormally wide transverse diameter of lateral meniscus extending beyond the tibial rim
Identifies associated tears (horizontal cleavage tears most common)

Discoid meniscus MRI and arthroscopy composite

Panels A–B: Sagittal and coronal MRI showing continuous horns and widened lateral meniscus. Panel C: Preoperative arthroscopic view of incomplete discoid meniscus. Panel D: Post-saucerization with plasma knife. Panel E: Return to sports.

Arthroscopy: Definitive visualization; used therapeutically.

Management

Asymptomatic discoid meniscus — no intervention required; observation only.

Symptomatic (pain, mechanical symptoms, tear):

Arthroscopic saucerization (meniscoplasty) — primary treatment

Resection and remodeling of the meniscus to a normal semilunar shape (~4 mm peripheral rim retained)
Preferred over total meniscectomy to preserve meniscal function

Additional procedures:

If a tear is present: repair if possible, especially in the vascularized peripheral zone
Wrisberg variant: peripheral stabilization (repair of posterior attachments) in addition to saucerization

Total meniscectomy — historical, now avoided due to high rates of subsequent lateral compartment osteoarthritis.

Complications

Untreated: progressive lateral compartment OA, especially with total meniscectomy
Post-saucerization: residual or recurrent tears, lateral compartment OA over time, stiffness
Re-tear of the residual meniscus is the most common post-operative issue

Prognosis

Outcomes after arthroscopic saucerization are generally good, with most patients (including children) returning to full activity and sports. Early intervention before articular cartilage damage occurs improves long-term outcomes. Total meniscectomy is associated with a significantly higher rate of late-onset lateral compartment arthrosis.

Posterior approach to elbow

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posterior approach to elbow surgical anatomy technique

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posterior approach elbow surgery anatomy

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Posterior Approach to the Elbow

Indications

Distal humerus fractures (intercondylar/transcondylar)
Olecranon fractures and osteotomy
Total elbow arthroplasty
Excision of loose bodies
Elbow ankylosis / contracture release
Triceps repair
Tumors of the distal humerus

Position

Lateral decubitus (arm draped over a support) or prone position
Tourniquet applied to the upper arm
The elbow is flexed to ~90° throughout

Incision

A posterior midline longitudinal incision beginning ~8–10 cm proximal to the olecranon tip, curving gently laterally around the olecranon to avoid direct pressure on the bony prominence, then continuing distally along the subcutaneous border of the ulna.

Posterior midline incision curving laterally around the olecranon. Hash marks aid precise closure. Used here for olecranon osteotomy to expose the distal humeral articular surface.

Deep Dissection — Options for Exposure

Once skin and subcutaneous tissue are elevated as full-thickness flaps, three main strategies exist to access the elbow joint:

1. Triceps-Reflecting / Triceps-Splitting (Bryan–Morrey)

The triceps aponeurosis is elevated off the olecranon as a continuous sleeve along with the periosteum, reflecting medially
Restores continuity — no bone cut required
Used in total elbow arthroplasty
Risk: triceps avulsion / weakness

2. Olecranon Osteotomy (gold standard for articular exposure)

A chevron (V-shaped) osteotomy is made at the bare area of the olecranon (~2 cm from the tip), with the apex pointing distally
The proximal fragment with triceps attached is reflected proximally, providing wide exposure of the entire distal humeral articular surface
Fixation at closure: tension band wiring or intramedullary screw + tension band
Best visualization of the articular surface — preferred for complex distal humerus fractures

3. Paratricipital (Column) Approach

The triceps is left attached; windows are developed medial and lateral to it
Suitable for extra-articular distal humerus fractures (medial/lateral columns) without articular comminution
Avoids risks of olecranon osteotomy or triceps detachment

Internervous Plane

The posterior approach does not use a true internervous plane — it relies on the midline avascular interval. However, the key nerve at risk is:

Nerve	Location	Risk
Ulnar nerve	Medial epicondyle groove → cubital tunnel	Must be identified and protected throughout; consider anterior transposition
Radial nerve	Lateral, stays proximal	At risk if dissection extends proximally along lateral column
Posterior interosseous nerve	Not directly at risk in standard posterior approach	—

The ulnar nerve must be formally identified and protected in every posterior elbow approach.

Deep Structures Exposed

Posterior capsule of elbow joint
Distal humerus: medial and lateral columns, olecranon fossa, trochlea, capitellum (via osteotomy)
Proximal ulna and olecranon
Radial head (with additional lateral mobilization)

Closure

Repair olecranon osteotomy with tension band wiring ± intramedullary screw
Reattach triceps sleeve if Bryan–Morrey was used
Transpose ulnar nerve anteriorly if mobilized
Subcutaneous and skin closure over a drain

Key Hazards & Pitfalls

Hazard	Prevention
Ulnar nerve injury	Formal identification; protect throughout; consider transposition
Triceps dehiscence	Secure reattachment; protect in early rehabilitation
Olecranon osteotomy non-union	Rigid fixation, preserve blood supply to fragment
Skin necrosis over olecranon	Gentle lateral curve in incision; avoid direct pressure on scar
Elbow stiffness	Early mobilization protocol post-fixation

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