Open Repair of the Medial Patellofemoral Ligament and Vastus Medialis Obliquus Muscle

INTRODUCTION AND BIOMECHANICAL RATIONALE

Patellofemoral instability is a complex, multifactorial condition that demands a rigorous, anatomically based approach to surgical management. The medial patellofemoral ligament (MPFL) is the primary passive restraint to lateral patellar translation, contributing 50% to 60% of the restraining force during the first 20 to 30 degrees of knee flexion. Beyond 30 degrees, the patella engages the trochlear groove, and osseous stability predominates.

The vastus medialis obliquus (VMO) provides the critical dynamic medial restraint. Its muscle fibers interdigitate with the MPFL, creating a synergistic complex that centers the patella within the trochlea during early flexion. In the event of an acute lateral patellar dislocation, the MPFL is virtually always torn, most commonly avulsing from its femoral origin near the adductor tubercle, though midsubstance and patellar-sided tears also occur.

Open repair of the MPFL and VMO imbrication/advancement is a highly specific procedure. While the modern trend has shifted heavily toward MPFL reconstruction for chronic instability, direct open repair remains a viable, tissue-sparing option for carefully selected acute cases, particularly when an avulsion can be anatomically reduced to bone.

💡 Clinical Pearl: The "Low Risk—Low Reward" Paradigm

Direct medial repair or imbrication carries a historical failure rate of approximately 30%, which is statistically comparable to conservative treatment in unselected cohorts. Therefore, isolated repair is strictly indicated for first-time dislocations with a repairable chondral defect or an acute, MRI-confirmed femoral avulsion in a high-level athlete nearing the end of their season. In cases of chronic laxity or poor tissue quality, MPFL reconstruction is the gold standard.

PREOPERATIVE EVALUATION AND PATIENT SELECTION

Successful patellofemoral surgery requires treating the patient as an individual, prioritizing the specific pathoanatomy over a "one-size-fits-all" approach. The extent of malalignment, patient age, activity level, and the condition of the articular cartilage dictate the surgical algorithm.

Clinical Examination

• Apprehension Test: Elicited at 20 to 30 degrees of flexion.
• Lateral Glide: Greater than 2 to 3 quadrants of lateral translation indicates gross MPFL incompetence.
• J-Sign: Indicates abnormal tracking and delayed trochlear engagement, often associated with patella alta.
• Patellar Tilt: A negative patellar tilt suggests a tight lateral retinaculum (Excessive Lateral Pressure Syndrome).

Radiographic Assessment

A comprehensive imaging series (AP, lateral, Merchant/Sunrise views) and advanced imaging (MRI, CT) are mandatory to assess the following parameters:
1. Patella Alta: Measured via the Insall-Salvati index. An index > 1.2 indicates alta, which delays trochlear engagement and may necessitate tibial tubercle distalization.
2. Trochlear Dysplasia: Identified on a true lateral radiograph by the "crossing sign" or a supratrochlear bump. A sulcus angle > 140 degrees on axial views confirms dysplasia.
3. Tibial Tubercle–Trochlear Groove (TT-TG) Distance: Measured on axial CT or MRI. A TT-TG > 20 mm is distinctly abnormal and typically requires a distal realignment procedure (e.g., Fulkerson or Elmslie-Trillat osteotomy).
4. Soft Tissue Integrity: MRI is critical for identifying the exact location of the MPFL tear (femoral, midsubstance, or patellar) and evaluating for osteochondral lesions (typically on the medial patellar facet or lateral femoral condyle).

SURGICAL DECISION-MAKING ALGORITHM

The surgical approach must address all components of the instability triad: Containment, Alignment, and Soft Tissue Imbalance.

1. Containment (Osseous Stability)

• Patella Alta (Insall Index > 1.2): Requires distalization of the tibial tubercle.
• Trochlear Dysplasia (Crossing sign, bump): May require MPFL reconstruction. In severe cases, a trochleoplasty may be considered, though it is a "High Risk—High Reward" procedure with significant risks of osteonecrosis, degenerative joint disease (DJD), and arthrofibrosis.
• Patellar Dysplasia (Wiberg Type C): Managed primarily with MPFL reconstruction to restore soft-tissue tethering.

2. Alignment (Vector Mechanics)

• TT-TG > 20 mm: Requires anteromedialization of the tibial tuberosity (Fulkerson osteotomy) if accompanied by lateral facet arthritis, or a straight medialization (Elmslie-Trillat) if the cartilage is preserved.
• Severe Femoral Anteversion / Tibial Torsion: May require a rotational high tibial or femoral osteotomy. This is a high-risk procedure reserved for profound rotational deformities.

3. Soft Tissue Imbalance

• Dynamic (VMO Dysfunction): Managed with aggressive physical therapy and closed-chain rehabilitation if TT-TG < 20 mm.
• Static (Incompetent MPFL): Addressed via medial imbrication/repair (if tissues are robust and the injury is acute) or MPFL reconstruction (for chronic laxity or skeletally mature patients with poor tissue).
• Excessive Lateral Pressure Syndrome: Addressed via lateral retinacular release.

⚠️ Surgical Warning: Trochleoplasty and Rotational Osteotomies

Trochleoplasty and rotational osteotomies are classified as "High Risk—High Reward." While a grooveplasty can lower recurrence rates in severely dysplastic knees, the risk-to-benefit ratio is excessively high for the average surgeon. MPFL reconstruction combined with distal realignment often yields excellent results with significantly less morbidity.

SURGICAL TECHNIQUE: OPEN MPFL AND VMO REPAIR

Step 1: Diagnostic Arthroscopy

Before any open incision is made, a thorough diagnostic arthroscopy is mandatory.
1. Establish standard anterolateral and anteromedial portals.
2. Evacuate the hemarthrosis typically present in acute dislocations.
3. Inspect the joint for osteochondral loose bodies, which frequently shear off the medial patellar facet or the lateral femoral condyle during the dislocation or reduction event.
4. Assess patellofemoral tracking dynamically through a superolateral portal. Observe the patella as it enters the trochlea at 20 to 30 degrees of flexion.
5. Address any intra-articular pathology (e.g., loose body removal, chondral debridement, or microfracture) before proceeding to the open repair.

Step 2: Patient Positioning and Approach

1. The patient remains supine with a lateral post or in a leg holder, allowing free flexion of the knee to 120 degrees.
2. A tourniquet is applied to the proximal thigh but is ideally left uninflated unless visualization is compromised, to allow for dynamic assessment of VMO tension.
3. Make a 4-cm oblique incision centered over the adductor tubercle, oriented in line with the skin cleavage planes (Langer’s lines) to optimize cosmetic healing.

Step 3: Superficial Dissection and Nerve Protection

1. Deepen the incision through the subcutaneous tissue.
2. Incise the covering fascia in line with the skin incision.
3. Critical Anatomy: Meticulously identify and protect the infrapatellar branch of the saphenous nerve, which courses anteriorly and inferiorly across the medial aspect of the knee. Injury to this nerve results in painful neuromas and medial numbness.

Step 4: Identification of the VMO and MPFL

1. Identify the distal muscular belly of the vastus medialis obliquus.
2. Gently mobilize and retract the VMO superiorly and anteriorly using a blunt retractor (e.g., a small Richardson or Army-Navy). This maneuver exposes the underlying capsule and the femoral origin of the MPFL.
3. Inspect the MPFL. The anatomical femoral attachment is located in the saddle region between the adductor tubercle and the medial epicondyle (Schöttle's point).

Step 5: Ligament Repair and VMO Advancement

The repair technique is dictated by the nature of the tissue failure:

• Direct Soft-Tissue Repair: If a robust residual stump of soft tissue remains attached to the adductor tubercle, perform a direct end-to-end repair. Use heavy, nonabsorbable braided sutures (e.g., #2 FiberWire or Ethibond) in a Krackow or locking Mason-Allen configuration to reapproximate the torn ends.
• Suture Anchor Repair (Avulsion): If the ligament is avulsed directly off the bone, prepare the footprint at the adductor tubercle/medial epicondyle with a curette or rasp to promote a bleeding bed for healing. Insert one or two double-loaded suture anchors (4.5 mm to 5.5 mm) into the anatomical footprint. Pass the sutures through the avulsed edge of the MPFL and tie them securely.
• VMO Imbrication: Once the MPFL is secured, the VMO is advanced distally and laterally over the repair site to provide dynamic reinforcement. Suture the VMO fascia to the medial border of the patella and the medial retinaculum, ensuring appropriate tension.

🔪 Surgical Pitfall: Overtightening the Medial Structures

The most common error in medial-sided surgery is overtightening. The MPFL is a check-rein, not a continuous tension band. Proximal or anterior femoral placement of anchors, or excessive imbrication, will result in medial facet overload, severe postoperative pain, and rapid cartilage degeneration. The repair must be secured with the knee at 30 degrees of flexion, ensuring the patella is centered but can still be passively glided laterally by 1 to 2 quadrants.

ADJUNCTIVE PROCEDURES

Lateral Retinacular Release

A lateral release is rarely indicated as an isolated procedure for instability; it is primarily utilized for parapatellar pain secondary to Excessive Lateral Pressure Syndrome (ELPS). In the context of instability, it is performed only when excessive lateral tightness physically prevents the patella from centering in the trochlea after medial repair.

• Technique: Most lateral releases are now performed arthroscopically. To be effective, the release must extend from the distal third of the vastus lateralis down to the tibial tuberosity, encompassing the lateral patellofemoral and lateral patellotibial ligaments.
• Warning: Indiscriminate lateral release can destroy the lateral stabilizing structures, leading to iatrogenic medial patellar subluxation—a devastating complication that is exceedingly difficult to salvage.

Distal Realignment (Osteotomies)

If the preoperative TT-TG distance exceeds 20 mm, soft-tissue repair alone will fail due to an overwhelming lateral vector force.
* Elmslie-Trillat Procedure: Indicated for instability with a TT-TG > 20 mm and strong, repairable medial structures. It involves a straight medial translation of the tibial tubercle. Healing time and the risk of proximal tibial stress fractures are significantly lower than with anteriorizing osteotomies.
* Fulkerson Osteotomy: An anteromedialization procedure indicated when a TT-TG > 20 mm is combined with symptomatic lateral facet or distal pole arthritis. It unloads the lateral facet while correcting the vector. It is strictly contraindicated in the presence of proximal or medial facet arthritis.

POSTOPERATIVE CARE AND REHABILITATION

The postoperative protocol must balance the protection of the healing medial structures with the prevention of arthrofibrosis. An accelerated rehabilitation program is the standard of care.

Phase I: Maximum Protection (Weeks 0–2)

• Weight-Bearing: Weight-bearing as tolerated (WBAT) is permitted immediately, provided the knee is locked in full extension in a hinged knee brace.
• Range of Motion (ROM): Immediate postoperative motion is initiated. Passive and active-assisted ROM from 0 to 90 degrees is encouraged to nourish the articular cartilage and prevent capsular adhesions.
• Muscle Activation: Isometric quadriceps sets and straight-leg raises (in the brace) are begun on postoperative day one to prevent VMO atrophy.

Phase II: Moderate Protection (Weeks 2–6)

• ROM: Gradually progress to full flexion as tolerated.
• Strengthening: Early strengthening emphasizes closed-kinetic-chain exercises (e.g., mini-squats, leg presses limited to 0–45 degrees). Closed-chain exercises increase joint compressive forces, which stabilizes the patella within the trochlea and protects the healing MPFL from excessive shear stress. Open-chain knee extensions are strictly avoided, as they place maximum stress on the medial repair.

Phase III: Return to Function (Weeks 6–12+)

• Progression: The brace is discontinued once the patient demonstrates excellent quadriceps control without an extensor lag.
• Advanced Rehab: Proprioceptive training, agility drills, and sport-specific exercises are introduced. Return to competitive sports is typically permitted between 4 and 6 months, contingent upon the restoration of 90% limb symmetry index (LSI) in quadriceps strength and the absence of apprehension.

CONCLUSION

Open repair of the MPFL and VMO is a powerful, targeted procedure for acute patellar instability in carefully selected patients. By adhering to strict anatomical principles—identifying the exact site of tissue failure, avoiding over-constraint, and addressing concomitant osseous malalignment—the orthopedic surgeon can reliably restore patellofemoral stability, alleviate pain, and facilitate a successful return to high-level function.