Comprehensive guide to the medial parapatellar surgical approach for total knee arthroplasty and distal femur fractures - positioning, technique, dangers, and exam points
Reviewed by OrthoVellum Editorial Team
Orthopaedic clinicians and medical editors • Published by OrthoVellum Medical Education Team
Gold Standard for TKA | Extensile Access | Protect Patella Tendon
The skin incision is anterior midline, not medial. This preserves blood supply to skin flaps from both medial and lateral geniculate vessels. Medial skin incisions risk lateral flap necrosis.
The arthrotomy is medial parapatellar - approximately 1cm medial to the patellar border. This goes through capsule and VMO insertion. Too lateral risks patellar maltracking; too medial makes closure difficult.
Never over-evert the patella. Excessive lateral eversion can avulse the patellar tendon insertion. In stiff knees, perform quadriceps snip or tibial tubercle osteotomy rather than force eversion.
The infrapatellar branch of saphenous nerve (IPBSN) crosses the incision and is always sacrificed. Counsel patients about anterolateral knee numbness postoperatively.
The medial parapatellar approach is the gold standard for TKA and most knee arthroplasty procedures, providing excellent visualization of all compartments. Key distinction: the skin incision is anterior midline (preserving blood supply from both medial and lateral geniculate vessels), while the arthrotomy is medial parapatellar (approximately 1cm medial to the patella border through VMO and capsule). The patella is everted laterally—never over-tension or risk avulsing the patellar tendon insertion; in stiff knees, use quadriceps snip or tibial tubercle osteotomy instead. The infrapatellar branch of the saphenous nerve (IPBSN) is always sacrificed, causing anterolateral knee numbness. The inferior geniculate artery is at risk during subperiosteal tibial elevation. The approach can be extended proximally (quadriceps snip) or distally (TTO) for difficult exposures.
Memory Hook:MIDLINE reminds you the skin incision is anterior midline - NOT medial!
Memory Hook:PATELLA guides your arthrotomy - parapatellar means BESIDE the patella, not through it
Memory Hook:DANGERS lists the key structures you must protect during medial parapatellar approach
The medial parapatellar approach is the most widely used surgical approach to the knee. It provides excellent exposure of the entire knee joint including medial, lateral, and patellofemoral compartments.
Primary indications:
Why Medial Parapatellar?
The medial parapatellar approach is preferred over lateral approaches because: (1) the VMO insertion is weaker than the vastus lateralis, making medial elevation easier; (2) most patients have valgus alignment, making medial release advantageous; (3) the patella naturally everts laterally when the knee is flexed.
Advantages:
Disadvantages:
Extensor mechanism:
Blood supply:
The patella receives most of its blood supply through the inferior pole via the fat pad. Aggressive fat pad debridement during TKA can compromise patellar blood supply and lead to patellar necrosis or fracture. Preserve fat pad attachments when possible.
Nerve structures:
Key relationships:
| Structure | Proximal Attachment | Distal Attachment | Clinical Significance |
|---|---|---|---|
| Quadriceps tendon | Rectus femoris, VL, VM, VI | Superior pole patella | Preserved in medial parapatellar approach |
| Patella | Quadriceps insertion | Patellar tendon origin | Blood supply from inferior pole - preserve fat pad |
| Patellar tendon | Inferior pole patella | Tibial tubercle | NEVER over-evert - risk avulsion |
| VMO | Adductor tubercle | Medial patella/retinaculum | Incised during arthrotomy, repaired at closure |
Assessment:
Imaging review:
Consent points:
Multiple longitudinal scars: Use the most lateral scar to preserve medial blood supply. Minimum 6cm distance between parallel incisions.
Transverse scars: Can cross perpendicular scars but risk skin necrosis at intersection.
Flexion less than 70 degrees: Plan for extensile techniques (quadriceps snip, V-Y turndown, or tibial tubercle osteotomy). Do NOT force patellar eversion in a stiff knee.
Key Concept: There is NO true internervous plane in the medial parapatellar approach.
Unlike hip approaches where muscles can be separated along nerve-defined boundaries, the medial parapatellar approach works by incising through the VMO muscle directly. The VMO is innervated by the femoral nerve, and the incision through it is a trans-nervous rather than inter-nervous approach.
Definition: A surgical plane between two muscles that are supplied by different nerves. This allows separation without denervating either muscle.
Example: Posterior hip approach (between gluteus medius/maximus [superior gluteal] and short external rotators [L5/S1 plexus])
No internervous plane: The VMO is incised directly through its substance. This is necessary because the extensor mechanism is a continuous structure.
Repair required: The VMO must be repaired during closure to restore extensor mechanism function.
Why no internervous plane?
Viva Answer
When asked about internervous planes in the medial parapatellar approach, state clearly: "The medial parapatellar approach does NOT utilize a true internervous plane. The entire quadriceps mechanism is femoral nerve-innervated. The approach works by incising through the VMO insertion on the medial patella, which must be carefully repaired at closure to prevent extensor lag and patellar maltracking."
Contrast with alternative approaches:
| Approach | Internervous Plane Status | Nerve Considerations |
|---|---|---|
| Medial parapatellar | NO internervous plane | Transects VMO (femoral nerve) |
| Subvastus | NO true plane | Works deep to VMO without transecting |
| Midvastus | NO true plane | Splits VM fibers (still femoral nerve) |
| Lateral parapatellar | NO true plane | Transects VL (femoral nerve) |
Standard Patient Position:
Key Setup Considerations:
Knee Range Requirements:
Draping:
Tourniquet Considerations:
Supine, hip bump, thigh tourniquet, free drape. Foot of bed drops for flexion. Surgeon stands laterally, assistant medially. C-arm accessible from contralateral side.
Alternatives to assistant: Leg holder maintains knee position during bone cuts. Allows surgeon to work with both hands. Position can be changed during procedure.
Positioning for Special Situations:
Position:
Setup:
Patient supine, bump under hip if needed. Apply thigh tourniquet. Ensure full knee ROM available with foot of bed down or leg holder.
Prepare entire leg from mid-thigh to ankle. Include foot in field for alignment checks.
Impervious stockinette over foot, adhesive drapes to isolate leg. Ensure free mobility of knee.
Elevate leg 60 seconds OR apply Esmarch bandage. Inflate tourniquet to 300mmHg (or 100mmHg over systolic).
Mark incision, confirm full ROM, check tourniquet pressure, time-out complete.
Tourniquet Use in TKA
Tourniquet use in TKA is controversial. Benefits: Better visualization, cement pressurization. Risks: Increased pain, quadriceps dysfunction. Most surgeons use tourniquet for cementing only. Inflate after exsanguination, deflate after cement cured and closure begun.
When the patella cannot be everted safely (stiff knee, scarred knee, obese patient), use one of these extensile techniques:
| Technique | Indication | Advantage | Disadvantage |
|---|---|---|---|
| Quadriceps Snip | Mild to moderate stiffness | Simple, minimal morbidity, heals reliably | Limited additional exposure |
| V-Y Quadriceps Turndown | Severe stiffness or scarring | Excellent additional exposure | Risk of extensor lag if inadequate repair |
| Tibial Tubercle Osteotomy | Revision TKA, patella baja | Preserves extensor continuity, precise repair | Risk of nonunion (5%), fracture, requires fixation |
Quadriceps snip technique:
V-Y turndown technique:
Tibial tubercle osteotomy:
| Complication | Incidence | Prevention | Management |
|---|---|---|---|
| Patellar tendon avulsion | Less than 1% | Never force eversion, use extensile techniques if stiff | Immediate repair with transosseous sutures, protect 6 weeks |
| Patellar maltracking | 1-5% | Pants-over-vest closure, proper implant rotation | Lateral release, component revision if severe |
| Skin necrosis | 1-2% | Respect prior scars, midline incision, atraumatic handling | Wound care, VAC therapy, flap coverage if deep |
| Anterolateral numbness | 100% | None - IPBSN sacrifice unavoidable | Counsel preoperatively, usually well-tolerated |
| Quadriceps weakness | 10-20% transient | Minimize trauma to VMO, early mobilization | Physiotherapy, usually resolves by 6 weeks |
| Common peroneal palsy | Less than 1% | Avoid excessive valgus correction, protect during retraction | Observation, splint foot, recovery often incomplete |
Patellar tendon avulsion - catastrophic:
Skin necrosis:
The most important principle to prevent patellar tendon avulsion: If the patella will not evert easily with knee flexed and gentle traction, perform an extensile technique. Never apply excessive force. A quadriceps snip takes 2 minutes and heals reliably; a patellar tendon avulsion is a career-threatening complication for the patient.
Practice these scenarios to excel in your viva examination
"The examiner asks: 'Describe your surgical approach for a primary total knee arthroplasty.'"
"You are performing a TKA on a patient with severe arthritis and stiffness. Preoperative ROM is 20-90 degrees. After your arthrotomy, you attempt to evert the patella but it will not come laterally. What do you do?"
"During a revision TKA, while everting the patella, you feel a sudden give and loss of resistance. The patient's leg now falls into extension limply. What has happened and what do you do?"
Skin Incision Question
Q: Why is the skin incision for medial parapatellar approach placed in the anterior midline rather than medially? A: To preserve blood supply to skin flaps from both medial and lateral geniculate vessels. A medial skin incision creates a lateral skin flap with tenuous blood supply, risking skin necrosis.
IPBSN Question
Q: What nerve is invariably sacrificed during the medial parapatellar approach, and what is the clinical consequence? A: The infrapatellar branch of the saphenous nerve (IPBSN) is sacrificed as it crosses the anterior incision. This causes anterolateral knee numbness in 100% of patients, which is usually well-tolerated but must be discussed during consent.
Arthrotomy Location Question
Q: How far medial to the patellar border should the arthrotomy be made in the medial parapatellar approach? A: Approximately 1cm medial to the patellar border. Too lateral makes closure difficult and risks patellar maltracking; too medial makes the flap creation and exposure difficult.
Extensile Technique Question
Q: What is the first-line extensile technique when the patella cannot be everted safely during TKA? A: Quadriceps snip - a 2-4cm oblique cut at 45 degrees laterally through the vastus lateralis at the junction of medial and middle thirds of the quadriceps tendon. It is simple, provides 20-30% additional exposure, and heals reliably.
Closure Technique Question
Q: What is the pants-over-vest closure technique and why is it important? A: The pants-over-vest technique advances the medial VMO and capsular edge distally and overlaps it over the lateral capsule by 5-10mm. This recreates the normal VMO oblique vector (50-55 degrees) and prevents lateral patellar maltracking.
Patellar Blood Supply Question
Q: What is the primary blood supply to the patella and why is this clinically important? A: The patella receives most of its blood supply from the inferior pole via the infrapatellar fat pad. This is why aggressive fat pad debridement during TKA can compromise patellar blood supply, leading to patellar necrosis or fracture. Preserve fat pad attachments to the inferior pole.
Epidemiology:
Registry data (AOANJRR):
Consent considerations:
Orthopaedic Relevance
For Orthopaedic Operative Surgery station, you must be able to describe the medial parapatellar approach in detail: patient positioning, skin incision (anterior midline), arthrotomy location (1cm medial to patella), structures at risk (IPBSN, patellar tendon, inferior geniculate vessels), and closure technique (pants-over-vest). Know the extensile techniques (quadriceps snip, V-Y turndown, TTO) and when to use each.
High-Yield Exam Summary