Surgical stabilization for patellar instability—such as medial patellofemoral ligament (MPFL) reconstruction, tibial tubercle osteotomy (TTO), or trochleoplasty—demonstrates high clinical efficacy, with reported success rates of 85–95%. However, like any orthopedic procedure, potential complications range from transient, self-limiting symptoms to complex issues requiring revision intervention.
Overview of Potential Complications
| Complication | Estimated Incidence | Primary Contributing Factors |
|---|---|---|
| Recurrent Instability / Subluxation | 2–5% | Unaddressed bony malalignment (high TT-TG, severe dysplasia), technical tunnel malposition, premature return to sport |
| Arthrofibrosis / Knee Stiffness | 3–7% | Prolonged postoperative immobilization, delayed passive range-of-motion (ROM) rehabilitation |
| Anterior Knee Pain | 5–10% | Graft over-tensioning, pre-existing patellofemoral cartilage lesions, quadriceps weakness |
| Surgical Site / Joint Infection | <1–2% | Uncontrolled diabetes, compromised sterile technique, wound drainage |
| Deep Vein Thrombosis (DVT) | 1–3% | Immobility, non-compliance with chemical thromboprophylaxis |
| Patellar Fracture | <1% | Excessive drill tunnel diameter, multiple cortical perforations, direct postoperative trauma |
| Hardware or Graft Failure | 2–5% | Suboptimal biologic incorporation, early high-impact rotational trauma |
Early Postoperative Risks (Weeks 0–6)
- Excessive Hemarthrosis: Intra-articular blood accumulation can delay initial quadriceps activation.
- Hypoesthesia: Numbness around the surgical scar secondary to stretching or injury of small infrapatellar saphenous nerve branches occurs in 5–15% of cases and typically improves over time.
- Surgical Site Infection: Superficial erythema requires prompt oral antibiotics; deep joint sepsis (<0.5–1%) demands urgent arthroscopic irrigation and targeted intravenous antimicrobial therapy.
Late Complications (Months 3–12)
- Graft Over-Tensioning: Excessive tension on an MPFL graft pulls the patella medially, overloading the medial patellofemoral facet and resulting in persistent flexion pain and premature chondromalacia.
- Recurrent Dislocation: Often caused by performing isolated soft-tissue reconstruction in patients with severe unaddressed structural risk factors (such as $\text{TT-TG} > 20\text{ mm}$ or high-grade trochlear dysplasia).
- Persistent Extensor Mechanism Weakness: Inadequate vastus medialis obliquus (VMO) and gluteal strengthening leads to patellar crepitus and anterior joint loading during stair ambulation.
Prevention Protocols
- Comprehensive Preoperative Imaging: Multiplanar CT and MRI to evaluate rotational alignment, patellar height (Caton-Deschamps index), and trochlear morphology prior to surgery.
- Combined Realignment When Indicated: Pairing MPFL reconstruction with bony procedures (TTO or trochleoplasty) when significant structural malalignment is identified.
- Anatomic Tunnel Placement & Isometry: Precise anatomical graft fixation (Schöttle’s point on the femur) at 30° of knee flexion to avoid graft over-tightening.
- DVT Prophylaxis: Routine use of prescribed anticoagulants for 2 to 3 weeks alongside hourly active ankle pump exercises and compression therapy.
- Accelerated Functional Rehabilitation: Early passive patellar mobilization and ROM within the first 7–14 days to prevent arthrofibrosis, advancing to closed-chain kinetic strengthening.
When to Seek Urgent Medical Evaluation
Immediate orthopedic review is warranted if the patient experiences:
- Fever $> 38.3^\circ\text{C}$ with chills.
- Increasing localized erythema, wound breakdown, or purulent drainage.
- Sudden calf swelling, warmth, and tenderness indicative of a DVT.
- Subjective feelings of patellar slipping or a sensation of the knee giving way after initial stabilization.
Early intervention preserves outcomes: postoperative stiffness treated with manipulation under anesthesia (MUA) within the first 3 months yields 75–90% success, while revision realignment for persistent instability achieves 80–85% long-term stability.
Frequently Asked Questions About Complications of Patellar Dislocation Surgery
What is the overall complication rate associated with patellar stabilization surgery?
Medial Patellofemoral Ligament (MPFL) reconstruction and associated patellar stabilization procedures demonstrate high safety profiles and predictable outcomes. The overall complication rate is low, ranging from 2% to 5%. Major complications like recurrent instability, deep infection, or implant failure occur in less than 1% to 2% of cases when managed by experienced knee surgeons.
What are the risks and clinical signs of graft over-tightening during MPFL reconstruction?
Over-tensioning the reconstructed MPFL graft is a technical pitfall that causes:
- Medial subluxation of the patella and abnormal load shift to the medial facet.
- Elevated patellofemoral contact pressures during early knee flexion.
- Persistent medial anterior knee pain and progressive articular cartilage breakdown.
- Difficulty restoring deep knee flexion during postoperative rehabilitation.
Why does knee stiffness (arthrofibrosis) occur and how is it managed?
Postoperative joint stiffness and loss of flexion are primarily caused by intra-articular fibrous adhesions (arthrofibrosis). This condition is typically linked to prolonged joint immobilization or delayed physical therapy. Prevention involves early structured passive motion within protected arcs and gentle patellar mobilizations initiated in the early postoperative phase.
Can a patellar dislocation recur after stabilization surgery?
Recurrent instability after MPFL reconstruction is rare, occurring in fewer than 2% to 4% of patients. Recurrence is most commonly associated with:
- Non-anatomical placement of the femoral tunnel outside Schöttle's landmark.
- Failure to recognize and correct concurrent severe bony abnormalities (e.g., Dejour grade C/D trochlear dysplasia or high TT-TG distance).
- Premature return to high-risk pivoting activities before complete graft integration.
How does an iatrogenic patellar fracture occur during or after surgery?
Iatrogenic patellar fractures are rare (<1%) and generally occur during or after transverse tunnel drilling across the patella. Creating oversized tunnels or placing drill holes too close to the anterior cortex creates focal stress risers. Modern fixation methods, such as suture anchors or shallow blind sockets, significantly reduce this risk.
What are the signs and symptoms of a surgical site or intra-articular infection?
Surgical site infections are uncommon (<1%), but prompt clinical evaluation is essential if any of the following arise:
- Body temperature greater than 38.3°C accompanied by chills.
- Spreading erythema, local warmth, and tense, painful swelling around incisions.
- Persistent wound discharge or purulent drainage.
- A sudden, sharp increase in resting knee pain unresponsive to analgesics.
How is deep vein thrombosis (DVT) prevented following patellar surgery?
The risk of venous thromboembolism is reduced through standard prophylactic protocols:
- Compliance with prescribed chemical anticoagulants for 2 to 4 weeks.
- Performing hourly ankle pump exercises (20–30 reps) while awake to support venous return.
- Using graduated compression stockings on the non-operative and operative limbs.
- Initiating early, protected weight-bearing ambulation with crutches.
What causes persistent anterior knee pain after patellar stabilization?
Postoperative anterior knee pain may stem from pre-existing chondral wear on the patellar or trochlear surfaces, persistent vastus medialis obliquus (VMO) inhibition, or minor irritation of the infrapatellar branch of the saphenous nerve resulting in localized hypersensitivity or numbness.
Does graft harvesting from hamstring tendons cause permanent weakness?
Harvesting an autologous gracilis or semitendinosus tendon can cause temporary donor-site soreness and a transient drop in deep flexion strength. Long-term studies demonstrate that the remaining hamstring musculature compensates, resulting in no meaningful deficit in functional athletic performance.
What steps can patients take to minimize complication risks after surgery?
To ensure optimal outcomes and minimize complication rates, patients should:
- Choose an orthopedic surgeon specialized in patellofemoral joint procedures.
- Wear the hinged knee brace locked at 0° during all weight-bearing until quadriceps control is re-established.
- Follow the designated physical therapy progression without forcing early extreme flexion.
- Refrain from smoking, as nicotine impairs microvascular perfusion and soft-tissue tendon-to-bone healing.
References