Introduction to Recurrent Dislocations

Recurrent dislocations of the appendicular skeleton present a formidable challenge to the orthopedic surgeon, demanding a profound understanding of joint kinematics, osseous morphology, and soft-tissue restraints. While recurrent instability can affect the hip, sternoclavicular joint, shoulder, and elbow, the patellofemoral joint remains one of the most frequently afflicted articulations, particularly in the young, active population.

Patellofemoral malalignment and recurrent patellar subluxation or dislocation are multifactorial pathologies. They arise from a delicate interplay of osseous dysplasia, ligamentous laxity, and dynamic muscular imbalances. Successful management—whether conservative or surgical—requires a systematic, evidence-based approach to identify and correct the specific anatomic deficits driving the instability.

Functional Anatomy and Biomechanics of the Patellofemoral Joint

To comprehend the pathophysiology of recurrent patellar dislocation, the surgeon must first master the normal functional anatomy of the patellofemoral articulation. Stability is achieved through a synergistic combination of static (osseous and ligamentous) and dynamic (muscular) restraints.

Static Stabilizers

• Osseous Geometry: The patella articulates within the trochlear groove of the distal femur. The lateral femoral condyle is normally more prominent anteriorly than the medial condyle, providing a critical bony buttress against lateral patellar translation.
• Medial Patellofemoral Ligament (MPFL): The MPFL is the primary passive restraint to lateral patellar displacement, contributing 50% to 60% of the total restraining force at 0 to 20 degrees of knee flexion. It originates from the saddle region between the medial epicondyle and the adductor tubercle (Schöttle's point) and inserts onto the superomedial border of the patella.
• Lateral Retinaculum: Composed of the superficial oblique and deep transverse layers, the lateral retinaculum provides lateral stability but can become pathologically contracted in chronic maltracking scenarios.

Dynamic Stabilizers

• Quadriceps Femoris: The vastus medialis obliquus (VMO) provides dynamic medial tension, counteracting the lateral vector generated by the vastus lateralis and the rectus femoris.
• The Q-Angle: The quadriceps angle (Q-angle) represents the net lateral pull of the extensor mechanism. It is measured by drawing a line from the anterior superior iliac spine (ASIS) to the center of the patella, and a second line from the center of the patella to the tibial tubercle. Normal values are typically 10 to 14 degrees in males and 15 to 17 degrees in females.

Clinical Pearl: The Q-angle is a dynamic measurement. It can be artificially increased during athletic activities by internal rotation of the femur on a fixed tibia (e.g., during a "cutting" maneuver), which dramatically increases the lateral vector force on the patella and precipitates dislocation.

Pathophysiology of Recurrent Patellar Instability

Recurrent patellar instability is rarely caused by a single anatomic defect. It is typically the culmination of several predisposing factors that compromise the patellofemoral tracking mechanism.

Osseous Dysplasia

1. Trochlear Dysplasia: A shallow or flattened trochlear groove, or a hypoplastic lateral femoral condyle, deprives the patella of its essential bony support. Dejour's classification categorizes trochlear dysplasia into four types (A through D) based on the presence of a crossing sign, supratrochlear spur, and double contour on lateral radiographs.
2. Patella Alta: A high-riding patella (patella alta) is widely considered the most common predisposing factor for recurrent dislocation. Because the patella sits proximal to the trochlear groove in full extension, it must travel further during early flexion to engage the bony constraints of the trochlea, leaving it highly vulnerable to lateral displacement.
3. Patellar Morphology: An abnormally small or dysplastic patella (e.g., Wiberg Type III) lacks the congruent articular surface necessary for smooth gliding within the intercondylar groove.

Soft Tissue Incompetence

Acute lateral patellar dislocation almost universally results in the rupture or attenuation of the MPFL. If the MPFL heals in an elongated position, the primary medial restraint is lost, leading to recurrent subluxation or dislocation even with minimal provocative force.

Comprehensive Clinical Evaluation

A meticulous physical examination is the cornerstone of diagnosing patellofemoral malalignment and determining the appropriate surgical intervention. The examination must assess dynamic tracking, ligamentous integrity, and retinacular tension.

Assessment of Dynamic Patellar Tracking

Dynamic tracking is evaluated with the examiner standing in front of the seated patient. As the patient slowly extends the knee from a flexed position, the surgeon observes the trajectory of the patella.
* The "J" Sign: A positive J sign occurs when the patella tracks centrally during flexion but suddenly subluxates laterally as the knee approaches terminal extension (0 to 10 degrees). This indicates a loss of early trochlear engagement, often secondary to patella alta or severe trochlear dysplasia.
* Active Tracking: With the knee relaxed in full extension, the patient is asked to perform an isometric quadriceps contraction. Normally, the patella should translate superiorly with minimal lateral deviation. Excessive lateral movement indicates a severe vector imbalance.

Ligamentous and Retinacular Testing

• MPFL Insufficiency Test: With the patient supine and the knee flexed to 30 degrees (over a bolster), the patella is engaged in the trochlea. The examiner applies an inferolaterally directed stress while palpating the medial retinaculum. Increased laxity compared to the contralateral knee indicates MPFL incompetence.
• Patellar Apprehension Test (Fairbank's Test): The relaxed knee is held in 20 to 30 degrees of flexion. The examiner manually translates the patella laterally. A positive test occurs when the patient exhibits sudden apprehension, complains of pain, and reflexively contracts the quadriceps to resist further lateral motion.
• Passive Patellar Glide Test: With the knee at 0 degrees and then at 20 degrees of flexion, the examiner visually divides the patella into four longitudinal quadrants. The patella is passively translated medially and laterally. Normal glide is 1 to 2 quadrants. Excursion greater than 2.5 quadrants laterally suggests MPFL laxity; limited medial glide (<1 quadrant) indicates a contracted lateral retinaculum.
• Patellar Tilt Test: Performed with the knee in 20 degrees of flexion. The examiner places their fingers along the medial border of the patella and the thumb on the lateral border, attempting to lift the lateral facet to or past the horizontal plane. Inability to elevate the lateral facet past neutral indicates excessive lateral retinacular tightness.

Surgical Warning: A tight lateral retinaculum is a consequence, not the primary cause, of recurrent instability. Isolated lateral retinacular release is rarely indicated for recurrent dislocations and can lead to iatrogenic medial patellar instability if performed indiscriminately.

Provocative Testing for Chondral Pathology

• Patellar Grind Test (Clarke's Sign): Pressure is applied to the superior pole of the patella while the patient actively contracts the quadriceps. Alternatively, the patella is manually compressed and displaced medially, laterally, superiorly, and inferiorly within the trochlear groove. Reproduction of anterior knee pain suggests underlying chondromalacia or osteochondral defects resulting from recurrent instability.

Radiographic Evaluation

A complete radiographic series is mandatory for surgical planning.

Standard Radiographs

• Anteroposterior (AP) View: Assesses overall lower extremity alignment and the presence of bipartite patella.
• True Lateral View (30 degrees flexion): Critical for evaluating patellar height (Insall-Salvati ratio > 1.2 indicates patella alta) and trochlear dysplasia (crossing sign, supratrochlear spur).
• Merchant or Sunrise View (45 degrees flexion): Evaluates patellofemoral congruence, lateral patellar tilt, and lateral subluxation.

Advanced Imaging

• Computed Tomography (CT): The gold standard for measuring the Tibial Tubercle-Trochlear Groove (TT-TG) distance. A TT-TG distance greater than 20 mm is highly pathologic and typically necessitates a tibial tubercle osteotomy. CT is also used to assess femoral anteversion and tibial torsion.
• Magnetic Resonance Imaging (MRI): Essential for evaluating acute MPFL tears (typically at the femoral origin), assessing the severity of trochlear dysplasia, and identifying osteochondral lesions (classic "kissing contusions" on the medial patellar facet and lateral femoral condyle).

Surgical Treatment Strategies

Surgical intervention is indicated for patients with recurrent patellar dislocations who have failed a comprehensive conservative rehabilitation program (focused on VMO strengthening and core/gluteal stabilization), or in acute cases with a displaced osteochondral fracture.

The surgical algorithm is dictated by the specific anatomic abnormalities identified during the clinical and radiographic evaluation.

1. Medial Patellofemoral Ligament (MPFL) Reconstruction

MPFL reconstruction has become the standard of care for recurrent patellar instability with normal or near-normal osseous anatomy (TT-TG < 15 mm, normal patellar height).

• Graft Selection: Autografts (gracilis or semitendinosus) or allografts are commonly utilized.
• Femoral Fixation: Accurate placement of the femoral tunnel is the most critical step. The anatomic footprint (Schöttle's point) is located 1 mm anterior to the posterior cortex extension line, 2.5 mm distal to the posterior articular border of the medial femoral condyle, and proximal to the level of the posterior point of Blumensaat's line.
• Patellar Fixation: The graft is fixed to the proximal half of the medial patellar border using suture anchors or interference screws.
• Tensioning: The graft must be tensioned with the knee in 30 degrees of flexion.

Surgical Pitfall: Over-tensioning the MPFL graft is a catastrophic error. The MPFL is a check-rein, not a dynamic tractor. Over-tensioning leads to medial patellofemoral overload, severe chondromalacia, loss of knee flexion, and iatrogenic medial subluxation.

2. Tibial Tubercle Osteotomy (TTO)

Bony realignment is indicated when the lateral vector is excessively high, specifically when the TT-TG distance exceeds 20 mm, or in the presence of severe patella alta.

• Anteromedialization (Fulkerson Osteotomy): This oblique osteotomy shifts the tibial tubercle medially (to correct the TT-TG distance) and anteriorly (to decompress the patellofemoral joint). It is highly effective for patients with concurrent lateral or distal patellar chondromalacia.
• Medialization (Elmslie-Trillat Procedure): A purely medial shift of the tubercle, utilized when the TT-TG is elevated but no anterior decompression is required.
• Distalization: Indicated for severe patella alta (Caton-Deschamps index > 1.2). The tubercle is osteotomized and translated distally to allow the patella to engage the trochlea earlier in the flexion arc.

3. Lateral Retinacular Lengthening

If the patellar tilt test remains negative (unable to reach neutral) after MPFL reconstruction or TTO, a lateral retinacular lengthening (rather than a complete release) may be performed. This preserves the structural integrity of the lateral capsule while restoring normal patellar tilt, minimizing the risk of iatrogenic medial instability.

4. Trochleoplasty

In cases of severe, high-grade trochlear dysplasia (Dejour Type B or D) where a massive supratrochlear spur physically blocks patellar engagement, a deepening trochleoplasty may be considered. This is a technically demanding, salvage-level procedure involving the elevation of the trochlear articular cartilage, resection of the underlying subchondral bone to create a new groove, and rigid fixation of the cartilage flap.

Postoperative Rehabilitation Protocol

Successful surgical outcomes rely heavily on strict adherence to a phased postoperative rehabilitation protocol.

Phase I: Maximum Protection (Weeks 0-4)

• Weight-Bearing: Weight-bearing as tolerated (WBAT) in a locked hinged knee brace in full extension. If a TTO was performed, weight-bearing may be restricted to toe-touch (TTWB) for 4 to 6 weeks to protect the osteotomy.
• Range of Motion (ROM): Passive and active-assisted ROM is initiated early to prevent arthrofibrosis, typically limited to 0-90 degrees for the first 4 weeks to protect the MPFL graft.
• Strengthening: Isometric quadriceps sets, straight leg raises (in the brace), and ankle pumps.

Phase II: Moderate Protection (Weeks 4-8)

• Bracing: The brace is unlocked for ambulation as quadriceps control improves and is typically discontinued by week 6.
• ROM: Progression to full, symmetric ROM.
• Strengthening: Closed kinetic chain exercises (mini-squats, leg presses) are initiated. Open kinetic chain knee extensions are avoided to prevent excessive shear forces on the patellofemoral cartilage and the healing graft.

Phase III: Advanced Strengthening (Weeks 8-16)

• Focus on proprioception, neuromuscular control, and core/pelvic stability.
• Progression of closed-chain strengthening and initiation of light plyometrics.

Phase IV: Return to Sport (Months 4-6+)

• Return to play is permitted when the patient demonstrates full, pain-free ROM, absence of effusion, and isokinetic quadriceps strength reaching at least 85-90% of the contralateral limb.
• Functional testing (e.g., single-leg hop tests) must demonstrate symmetric dynamic stability.

Conclusion

The management of recurrent patellar dislocations requires a highly analytical approach. The orthopedic surgeon must look beyond the acute ligamentous injury to identify underlying osseous dysplasias, malalignment, and dynamic imbalances. By combining a rigorous clinical examination—highlighting the J sign, patellar tilt, and apprehension tests—with advanced radiographic imaging, the surgeon can tailor a patient-specific operative plan. Whether utilizing anatomic MPFL reconstruction, precise tibial tubercle osteotomy, or a combination thereof, the ultimate goal remains the restoration of native patellofemoral kinematics and the prevention of long-term degenerative joint disease.