Total Knee Replacement (TKR/TKA) - Surgical Steps and Bone Cuts

PATIENT POSITIONING & SETUP

• Supine with thigh support/tourniquet applied
• Knee flexed to ~90° for incision; leg hangs freely
• Tourniquet inflated after limb exsanguination (optional)

STEP 1 - SURGICAL APPROACH

Skin Incision

• Anterior midline longitudinal incision - the standard
• Made with the knee in flexion so subcutaneous tissue falls medially and laterally, improving exposure
• Incision must be long enough to avoid excessive skin tension (risk of skin necrosis)
• If prior scars exist, use the most lateral usable scar (blood supply comes predominantly from medial side)

Deep Approach (Retinacular Incision)

1. Incise through a medial cuff of the quadriceps tendon (leave 3-4 mm cuff on vastus medialis for closure)
2. Continue around the medial border of the patella
3. Extend 3-4 cm onto the anteromedial tibial surface along the medial patellar tendon border
4. Subperiosteally elevate anteromedial capsule and deep MCL off the tibia to the posteromedial corner
5. Extend and evert the patella (or sublux laterally if obese/stiff)

Alternatives: midvastus approach (splits vastus medialis obliquus muscle), subvastus approach (preserves quadriceps entirely - better patellar tracking, harder exposure).

STEP 2 - JOINT EXPOSURE AND SOFT TISSUE PREPARATION

1. Flex knee to ~90°
2. Remove the ACL and anterior horns of medial and lateral menisci
3. Remove any osteophytes (especially posterior condylar osteophytes - they block flexion and tent posterior capsule causing flexion contracture)
4. Posterior meniscal horns are removed after bone cuts

STEP 3 - BONE CUTS (MEASURED RESECTION TECHNIQUE)

CUT 1: DISTAL FEMORAL CUT (Extension Gap Cut)

• Made using an intramedullary (IM) guide (entry point: ~1 cm anterior and medial to intercondylar notch)
• Cut angle: 5-7° of valgus relative to the femoral anatomic axis (= perpendicular to the mechanical axis)
  • This angle is measured off a long-standing radiograph (angle between mechanical and anatomic femoral axes)
• Amount of resection = thickness of distal femoral component (typically ~9-10 mm)
• Establishes the extension gap
• Key rules:
  • Avoid elevating the joint line >4 mm
  • For PS (posterior-stabilized) implants: add 2 mm extra distally to compensate for PCL sacrifice
  • If a flexion contracture exists: additional resection can help, but avoid over-resection

CUT 2: PROXIMAL TIBIAL CUT (Foundation Cut - Affects Both Gaps)

• The most important cut in TKA - it affects both the flexion and extension gap
• Made using intramedullary or extramedullary guide, cut perpendicular to the tibial mechanical axis (0° in the coronal plane)
• Posterior slope: most systems incorporate 3° into the polyethylene insert; cutting guide set accordingly
• Rotation: referenced to the medial 1/3 of the tibial tubercle proximally and slightly medial to the center of the ankle distally (cross-referenced with 2nd ray of the foot and tibial crest)
• Resection amount:
  • Referenced off the less arthritic side: ~8-10 mm (equals implant thickness)
  • Referenced off the more arthritic side: typically 2 mm or less
• Protect patellar tendon and collateral ligaments with retractors during this cut

Note: Tibial cut can be performed before or after distal femoral cuts (surgeon preference).

CUT 3: FEMORAL SIZING AND ROTATION ASSESSMENT

• Component size (AP measurement of femur)
• Rotation of femoral component - this defines the shape of the flexion gap

Rotation Reference Options:

• Internal rotation of femoral component causes lateral patellar tilt or patellofemoral instability
• Excessive external rotation widens the medial flexion gap causing flexion instability

CUT 4: 4-IN-1 FEMORAL CUTS (Flexion Gap + Finishing Cuts)

• Posterior referencing: jig feet sit flush on posterior condyles; removes fixed 9 mm posteriorly regardless of component size; smaller jigs remove more anteriorly
• Anterior referencing: boom sits on anterior cortex; consistent anterior cut depth; prevents notching/overstuffing

After these cuts, assess the flexion gap - it should equal the extension gap (symmetric rectangle). A rectangular flexion gap = correct rotation.

CUT 5: INTERCONDYLAR NOTCH CUT (PS implants only)

• Performed perpendicular to the transepicondylar axis
• Removes bone from the intercondylar box to accommodate the post-and-cam mechanism of a posterior-stabilized implant
• CR (cruciate-retaining) implants skip this cut

CUT 6: PATELLAR CUT

• Standard patellar button thickness = 9 mm
• Measure native patella thickness; resect to leave enough bone
  • Example: 20 mm patella → set guide to 11-12 mm resection (some surgeons use 14 mm to protect against thin patella)
• Maintain symmetric thickness to avoid patellar tilt
• Not universally performed - patellar resurfacing is standard in the USA but not in many other countries

STEP 4 - GAP BALANCING AND SOFT TISSUE RELEASES

1. Insert spacer blocks or a tensioning device in both flexion (90°) and extension (0°) gaps
2. Gaps should be:
   • Symmetric (equal medially and laterally)
   • Equal in flexion and extension
3. If extension gap tight medially: release posterior oblique ligament, semimembranosus, posteromedial capsule
4. If flexion gap tight medially: release anterior superficial MCL, pes anserinus insertion
5. If PCL is too tight (flexion gap tight): recess or release PCL; if PCL no longer functions - convert to PS implant

STEP 5 - TRIAL REDUCTION

1. Impact femoral and tibial trial implants
2. Insert provisional polyethylene spacer trial
3. Reduce the knee and assess:
   • Stability in full extension
   • Mid-flexion stability
   • Patellar tracking ("no thumb" test)
   • Range of motion
4. Final sizing and rotational alignment confirmed

STEP 6 - COMPONENT IMPLANTATION

1. Thorough irrigation and debridement
2. Cement tibial baseplate (and/or femoral component) - depending on system (cemented vs cementless)
3. Impact femoral component
4. Insert final polyethylene insert
5. Cement or press-fit patella button
6. Confirm final ROM, stability, patellar tracking

STEP 7 - CLOSURE

1. Thorough irrigation
2. Close retinacular layer (medial parapatellar cuff) with interrupted sutures
3. Subcutaneous layer closed
4. Skin closure (staples or suture)
5. Drain placement (optional)

SUMMARY: ORDER OF BONE CUTS

1. Distal Femoral Cut      → sets extension gap (5-7° valgus IM guide)
2. Proximal Tibial Cut     → foundation cut (perpendicular to mech. axis)
3. Size & Rotate Femur     → determine AP size + rotation reference
4. Anterior Femoral Cut    → 4-in-1 jig
5. Posterior Femoral Cuts  → 4-in-1 jig (9 mm posteriorly)
6. Anterior Chamfer Cut    → 4-in-1 jig
7. Posterior Chamfer Cut   → 4-in-1 jig
8. Box Cut (PS only)       → intercondylar notch
9. Patellar Cut            → 9 mm button resurfacing

ALIGNMENT GOALS

Pain Shock (Primary / Neurogenic Shock)

Definition

• P.C. Dikshit Textbook of Forensic Medicine and Toxicology
• Parikh's Textbook of Medical Jurisprudence, Forensic Medicine and Toxicology

Two Overlapping Mechanisms

1. Sympathetico-adrenal stimulation pathway (Classic "Pain Shock")

• Sudden pooling of blood in splanchnic and peripheral vascular beds (neurogenic vasodilation)
• Reduced venous return to the heart
• Fall in cardiac output and blood pressure
• In extreme cases: sudden rise in BP can rupture a Berry aneurysm or dissecting aortic aneurysm

2. Vagal inhibition pathway (Vasovagal / Reflex)

• Sudden reflex cardiac slowing or arrest
• Paralysis of cardiac and respiratory centres
• Instantaneous collapse - can cause sudden death

"Holding the throat in an excited person may result in his collapse and instantaneous death. Other examples are: a blow on the epigastrium, sudden joy, fear, pain." - Parikh's

Pathophysiology

Pain / Emotional Stimulus / Blow on Receptor Area
           ↓
 Afferent nerve impulse to CNS
           ↓
  ┌───────────────────────────────────────────┐
  │ Sympathetic pathway       Vagal pathway   │
  │ (adrenal stimulation)   (inhibitory vagus)│
  └───────────────────────────────────────────┘
           ↓                        ↓
 Peripheral vasodilation     Bradycardia / Cardiac arrest
 (splanchnic pooling)
           ↓
 Decreased venous return → ↓ Cardiac Output → ↓ BP
           ↓
     Tissue Hypoperfusion (SHOCK)

• Loss of vasomotor tone - vasomotor center depressed or overridden
• Increased vascular capacitance → decreased venous return
• Decreased cardiac output
• Brain ischemia from hypoperfusion → further vasomotor center depression (vicious cycle)

Trigger Zones / Receptor Areas

Clinical Features

Classic neurogenic shock (spinal-type): hypotension + bradycardia + warm flushed extremities (no reflex tachycardia due to disrupted sympathetic tone) - Schwartz's Principles of Surgery

Key Distinction: Primary vs Secondary Shock

Forensic / Medicolegal Significance

1. A minor blow to a receptor area (e.g., epigastrium, throat) can cause sudden death with minimal or no external marks
2. Autopsy findings may be negative - diagnosis by exclusion
3. Must exclude: fatal wounds, poisoning, natural disease
4. At-risk populations: emotionally labile individuals, elderly, those with existing cardiac disease, severely ill patients

1. History of sudden death from blow/injury over a receptor area
2. Person of emotional temperament, elderly, or debilitated
3. Exclusion of fatal injuries, poisoning, and natural disease

Management

Immediate Measures

1. Remove the painful stimulus if possible
2. Lay patient flat / supine - elevate legs (Trendelenburg position) to improve venous return
3. Secure airway and ensure ventilation
4. IV fluid resuscitation - first-line treatment; restores intravascular volume and preload

Pharmacological (if fluids insufficient)

Monitoring

• ICU-level monitoring for haemodynamics and cardiac function
• Vasopressor support typically lasts only 24-48 hours as neurogenic shock tends to resolve
• In spinal cord injury cases: monitor for pulmonary oedema (loss of vasomotor capacity in pulmonary circulation)
• Must exclude haemorrhage in all trauma patients before attributing hypotension to neurogenic causes

Classification of Shock (Summary Table)

Trigger Finger (Stenosing Tenosynovitis)

Definition

Anatomy & Pathophysiology

A1 → A2 → C1 → A3 → C2 → A4 → C3 → A5

• The A1 pulley sits at the level of the metacarpophalangeal (MCP) joint in the distal palm
• In trigger finger, the A1 pulley undergoes fibrosis, thickening, and narrowing
• Histology shows fibrocartilaginous metaplasia of the pulley and/or flexor digitorum superficialis (FDS) tendon
• The flexor tendon (usually with a fusiform swelling or nodule) catches on the constricted pulley
• The tendon nodule is typically located just proximal to the annulus at the MCP level
• The nodule moves with the tendon and can be palpated by the examiner
• In rheumatoid arthritis, a nodule may be distal to this point

Epidemiology

Types

Clinical Features

• Pain and tenderness over the A1 pulley in the distal palm
• Snapping or clicking during digital motion - typically worse on awakening
• Patient often reports the problem is in the PIP joint (referred pain)

• Frank catching or locking in flexion
• Digit locks and requires passive extension with the other hand
• Reduced range of motion

• Fixed flexion contracture of the PIP joint
• Cannot be actively or passively corrected

Green's Classification (Froimson Grading)

Surgical indication: Grade III-IV, or Grade II failing 3 months of conservative treatment.

Differential Diagnosis

• Intra-articular disorders (loose bodies, degenerative joint disease, fractures)
• Common extensor tendon subluxation at MCP
• Dupuytren's contracture
• De Quervain's tenosynovitis (coexisting)
• Ganglion/retinacular cyst over A1 pulley

Treatment

Conservative (Non-operative)

Corticosteroid Injection Technique

• Needle enters at the distal palmar crease at 45-60° angle in the midline of the digit
• No difference between soluble and insoluble steroid preparations
• Repeat injections can be used, especially in patients preferring non-operative management
• Short course of splinting after injection may improve longevity

Trigger finger injection technique. The solid line denotes the distal palmar crease; needle enters at 45-60°. - Firestein & Kelley's Rheumatology

• More refractory to non-operative management
• Corticosteroid injections may elevate serum glucose for ≥5 days
• Patients with unstable diabetes may be better treated without injection
• Cost-analysis shows immediate surgical release is the most cost-effective strategy in diabetic patients

Surgical Treatment

• Failure of conservative management (including steroid injection)
• Grade III-IV disease
• Fixed contracture (Grade IV)
• Patient preference for definitive treatment
• Diabetic patients (cost-effective first-line)
• RA patients (specific modifications required)

Option 1: Open Surgical Release (Gold Standard - ~97% success rate)

1. Anaesthesia: Local anaesthetic infiltration proximal to incision site; tourniquet (pneumatic or forearm Esmarch wrap) or epinephrine in local anaesthetic without tourniquet
2. Incision:
   • Transverse incision ~2 cm, placed:
     • Middle, ring, small fingers: Several mm distal to the distal palmar crease
     • Index finger: Several mm distal to the proximal palmar crease
     • Thumb: Distal or proximal to the MCP joint flexion crease
   • Alternative: oblique or longitudinal incision between MCP and distal palmar crease
3. Nerve protection: Digital nerves are identified and protected. The thumb radial digital nerve is especially vulnerable (more palmar and closer to the flexor sheath than expected)
4. Exposure: Spread subcutaneous tissues to expose the annular pulley system; confirm digital nerves are safe
5. Pulley division:
   • Open the pulley with a No. 15 blade and tenotomy scissors
   • Fingers: Divide A1 and A0 (proximal palmar) pulley
   • Thumb: Divide only the A1 pulley; avoid cutting too far distally (preserve oblique pulley)
   • Incise from proximal to distal
6. Confirm release: With a local block, ask the patient to flex and extend the finger and confirm cessation of triggering intraoperatively
7. Closure and light dressing

Note: Triggering after release may occur due to catching on palmar aponeurosis transverse fibers - usually resolves with time. Occasionally a partially lacerated flexor tendon heals with a nodule causing triggering.

Option 2: Percutaneous Release

1. Inject local anaesthetic into palmar skin proximal to the release site
2. Use an 18- or 19-gauge needle (ultrasound guidance optional)
3. Position: palm up, hand on folded towel, MCP joint in slight hyperextension
4. Insert needle onto A1 pulley; orient bevel longitudinally parallel to flexor tendons
5. Move needle proximally and distally along the pulley, pressing firmly - feel for scraping/grating sensation as sheath is incised
6. When grating is eliminated, remove needle and test finger flexion/extension
7. Optional: inject corticosteroid at end
8. Adhesive bandage; encourage immediate active use

• Risk of incomplete pulley release
• Damage to flexor tendons and digital nerves
• Especially concerning for index finger and thumb (digital nerve anatomy)

Special Situations

• Preference is to excise a slip of the FDS tendon rather than release the A1 pulley
• RA patients are at risk for ulnar drift at the MCP joint - A1 pulley release can exacerbate this drift

• If triggering persists: resection of the ulnar FDS slip when necessary

Pediatric Trigger Finger vs. Trigger Thumb

The condition is developmental, not truly congenital - not noted until the patient is several years old.

Complications of Surgical Release

Key Points Summary

• Trigger finger = A1 pulley stenosis causing flexor tendon catching/locking
• Most common in thumb > ring > long finger; women >45 years
• Histology: fibrocartilaginous metaplasia of pulley/tendon
• Graded I-IV by Green's (Froimson) classification
• 60% respond to a single corticosteroid injection
• 97% success with open A1 pulley release
• Diabetics: more refractory to injection; early surgery preferred
• RA: FDS slip resection preferred over A1 release (prevents ulnar drift)
• Always protect the radial digital nerve of the thumb during release