Total Knee Replacement (TKR) - Surgical Approaches

OVERVIEW - Skin Incision (Common to All Approaches)

Key point: If multiple prior scars exist, use the most lateral usable scar - blood supply to anterior knee skin comes predominantly from the medial side.

DECISION FLOWCHART

APPROACH 1: MEDIAL PARAPATELLAR (Insall's Approach)

Standard / Most Commonly Used - Gold Standard

Step-by-Step Technique (Campbell's Technique 8.1):

• Maximum exposure of knee joint
• Suitable for primary AND revision TKA
• Usable in obese patients, stiff knees, valgus deformity
• Standard reference approach

• Disrupts quadriceps mechanism (muscle-splitting)
• Potential patellar devascularization
• Slower quadriceps recovery

APPROACH 2: SUBVASTUS APPROACH ("Southern Approach")

Muscle-Sparing - Extensor Mechanism Intact

Step-by-Step Technique:

• Extensor mechanism completely intact
• Preserves vascularity to patella (supreme genicular artery intact)
• Faster quadriceps recovery
• Less postoperative pain
• Fewer patellar complications
• Reduced need for lateral release

• Obesity
• Previous upper tibial osteotomy
• Preoperative flexion <80 degrees
• Stiff knee requiring extensile exposure
• Revision TKA

APPROACH 3: MIDVASTUS APPROACH (Engh's Approach)

Muscle-Splitting (Partial) - Moderate Option

Step-by-Step Technique:

• Preserves supreme genicular artery
• Preserves quadriceps tendon
• Better early quadriceps function than medial parapatellar
• Intermediate exposure between parapatellar and subvastus

• Obesity
• Previous upper tibial osteotomy
• Preoperative flexion <80 degrees
• Mandatory careful hemostasis - postoperative hematomas reported

APPROACH 4: LATERAL PARAPATELLAR (Keblish Approach)

For Fixed Valgus Deformity

Step-by-Step Technique:

• Achieves lateral release at time of closure
• Avoids separate lateral release procedure
• Ideal for valgus deformity correction

APPROACH 5: EXTENSILE EXPOSURES (for Revision TKA)

A. Quadriceps Snip

• Oblique extension of medial parapatellar incision across quadriceps tendon at 45°
• Does not require modification of rehabilitation
• First choice extensile option

B. V-Y Quadricepsplasty (Coonse-Adams)

• Inverted V incision through quadriceps tendon extended distally as Y
• Used for severely stiff knees
• Requires slower rehabilitation

C. Tibial Tubercle Osteotomy (TTO) (Whiteside's technique)

• Osteotomize tibial tubercle with patellar tendon attached
• Provides maximum distal exposure
• Risk of non-union; requires screw fixation at closure
• Best for complex revision with component removal required

COMPARATIVE SUMMARY TABLE

PG Exam Note: Campbell's states: "Current literature supports no difference in early or long-term outcomes when comparing medial parapatellar, midvastus, and subvastus approaches." The medial parapatellar remains the standard and is used routinely by most surgeons for primary TKA.

HIGH-YIELD PG POINTS

1. Most common approach = Medial parapatellar (Insall's) - Gold standard
2. Approach for fixed valgus = Lateral parapatellar (Keblish)
3. Muscle-sparing approaches = Subvastus (entire VMO intact) and Midvastus (VMO split in line with fibers)
4. Subvastus = "Southern approach"; VMO lifted off medial intermuscular septum
5. Midvastus safe zone = 4.5 cm from patella margin
6. Patellar tendon avulsion - most feared intraoperative complication; avoid by careful attention during flexion/retraction
7. Extensile options for revision: Quadriceps snip (easiest) → V-Y Quad → TTO (most extensive)
8. Skin incision rule: Multiple scars → use most lateral scar (medial blood supply)
9. The infrapatellar branch of the saphenous nerve is nearly always compromised → lateral knee numbness (warn patient preoperatively)

TKR Approach Selection in Special Populations: Latest Evidence (2021-2026)

KEY EVIDENCE BASE

1. OBESE PATIENTS (BMI >30 / >40)

• Functional outcomes in obese patients are similar to, or often better than, those in the average patient - but complication risk is markedly higher (infection, wound healing, DVT)
• The AAOS states BMI <40 as the generally accepted threshold for elective joint replacement; NICE does not impose a BMI cutoff
• The 2025 Cureus comprehensive review explicitly states: "the medial parapatellar approach remains the preferred choice in obese patients" - subvastus and midvastus are not recommended because:
  • Adequate surgical visualization is compromised in excess adipose tissue
  • Fat pad bulk prevents adequate lateral subluxation of the patella
  • Higher hematoma risk from muscle bleeding is compounded

• Shared decision-making with patient; avoid weight bias
• BMI alone should NOT be an absolute exclusion criterion
• Preoperative optimization (nutrition, glucose control) should be offered before surgery
• Referral to tertiary centres with medical + anaesthetic + surgical expertise for high-risk obese patients

2. FAST-TRACK / ENHANCED RECOVERY (ERAS) PROGRAMS

• Subvastus (SV) showed superior ROM on days 1, 3, 4, and 6 vs. medial parapatellar
  • Day 1: MD = +6.99° (CI: 1.08-12.89)
  • Day 4: MD = +27.01° (CI: 18.09-35.92)
• Mini-SV showed significantly lower pain on days 1, 3, and 7
  • Day 1: MD = -1.98 VAS points (CI: -2.93 to -1.03)
• Differences decrease over time; no significant advantage beyond 6 weeks
• Conclusion: Quadriceps-sparing approaches are superior for fast-track programs in appropriately selected patients

Patient selection for SV in ERAS: Normal BMI, flexible subcutaneous tissues, preoperative flexion >80°, no prior tibial osteotomy

3. GENERAL POPULATION: ALL APPROACHES COMPARED (7-Approach Network Meta-Analysis)

Bottom line: No approach is universally superior in long-term outcomes. Choice should be driven by patient-specific factors and surgeon experience.

4. MINIMALLY INVASIVE APPROACHES (MIS-TKA)

• Best for pain: Mini-Midvastus (MMV) - SUCRA 80.0, mean rank 2.2
• Best for ROM: Minimally Invasive Quadriceps-Sparing (MQS) - SUCRA 90.0, mean rank 1.6
• Best for safety (fewest adverse effects): Subvastus (SUCRA 80.0) and conventional Quadriceps-Splitting
• Conclusion: MIS approaches give better short-term pain/ROM but conventional approaches have a better safety profile
• Surgeons must weigh both when selecting approach for individual patients

• MMV superior at 3 months: KSS (+2.89), VAS (-0.22), ROM (+1.08°)
• No significant difference at 6 and 12 months
• MMV takes longer to perform (+8.98 min) but achieves straight leg raise 1.91 days sooner

5. SKIN INCISION - ANTEROLATERAL vs. MIDLINE

6. VALGUS DEFORMITY

7. ELDERLY / FALL RISK PATIENTS

• Both approaches cause postoperative loss of postural sway complexity (fall risk marker)
• At 2 weeks and 1 month: Medial parapatellar group had significantly lower postural sway complexity (more random patterns = higher fall risk) compared to healthy controls
• Midvastus group showed no such significant difference from controls
• Implication for elderly/fall-prone patients: Midvastus approach may confer a postural stability advantage in the early recovery period, particularly in women

SUMMARY: APPROACH SELECTION BY POPULATION (2025-2026 Evidence)

CONSENSUS ACROSS ALL EVIDENCE

1. No approach is superior for long-term functional outcomes - blood loss, KSS at 1 year, and complication rates are equivalent across all approaches
2. Muscle-sparing approaches (SV, MV) offer a genuine early recovery advantage - best suited for ERAS programs in non-obese, flexible patients
3. Medial parapatellar remains the default for complex knees - obesity, stiffness, valgus (combined with lateral release), revision
4. The trend is shifting - a 2025 Cureus review notes the field is moving toward muscle-sparing and infrapatellar fat-pad (IFFP)-preserving techniques, supported by short-term evidence of faster rehabilitation
5. Surgeon experience trumps approach - the 2022 Zhao network meta-analysis found no difference in safety or long-term KSS; choosing a familiar approach is still defensible