What could be causing a protrusion-like swelling in the anterior horn area of a 12-week postoperative patient who underwent an inside-out technique on the anterior horn and all-inside technique on the posterior horn, with symptoms exacerbated by exercise like leg press but resolving completely after cessation?

Anterior Horn Meniscus Repair Complication: Parameniscal Cyst or Incomplete Healing

The protrusion-like swelling at the anterior horn repair site that appears with loading exercises and completely resolves with rest most likely represents a parameniscal cyst formation secondary to incomplete healing of the inside-out repair, or persistent mechanical instability at the repair site. 1

Primary Differential Diagnosis

Parameniscal cyst formation is the most probable diagnosis given the clinical presentation:

• Fluid extrusion through incompletely healed meniscal tissue creates parameniscal cysts that present as localized swelling and protrusion, particularly when intra-articular pressure increases during loaded activities like leg press 1
• These cysts are more common when meniscal tears have not achieved complete healing and allow synovial fluid to track into perimeniscal tissues 1
• The anterior horn of the lateral meniscus is particularly prone to this complication when repaired with inside-out technique, especially when accompanied by local parameniscal cysts 2

Alternative consideration: Incomplete repair healing with persistent mechanical instability at 12 weeks, which is within the expected healing timeline since meniscal repairs require 9-12 months for complete healing 1

Immediate Management Protocol

Stop all provocative exercises immediately:

• Discontinue leg press and squatting exercises, as these generate excessive compressive and shear forces disrupting the healing repair 1
• Knee effusion or increased pain/swelling after exercise indicates excessive loading and requires immediate modification 1, 3

Implement aggressive swelling control:

• Apply compressive cryotherapy after all activities, which is more effective than cryotherapy alone 1, 3
• Elevate the limb above heart level when resting to facilitate fluid drainage 1, 3

Regress rehabilitation protocol:

• Return to isometric quadriceps exercises and gentle range of motion without resistance 1, 4
• Focus on non-weight-bearing or minimal-load exercises until swelling resolves 1
• Progress only when no effusion develops—the knee must demonstrate no reactive swelling before advancing exercise intensity 1, 3

Diagnostic Evaluation

Rule out infection first (though unlikely at 12 weeks with proper rehabilitation):

• Assess for fever, erythema, warmth, purulent drainage, or systemic inflammatory response 1

Obtain MRI to confirm diagnosis:

• MRI will reveal parameniscal cyst formation or incomplete healing at the anterior horn repair site 5, 2
• Evaluate for gap between meniscus and anterior capsule, which can occur after repair and predispose to cyst formation 2

Rehabilitation Modification Strategy

Criterion-based progression (not time-based):

• Continue rehabilitation for the full 9-12 months as meniscal repairs require longer healing than isolated ACL reconstruction 1
• Use minimum 12 weeks before considering return to running, but only if no reactive swelling occurs 3
• The knee must tolerate each exercise level without effusion before progressing 1, 3

Exercise progression algorithm:

1. Start with isometric quadriceps exercises if they provoke no pain or effusion 3, 4
2. Progress to concentric and eccentric exercises only when the knee does not react with effusion or increased pain 3
3. Advance to closed kinetic chain exercises (partial squats in limited range) before open kinetic chain 6, 4
4. Delay return to leg press until at least 16-20 weeks postoperatively and only if no reactive swelling occurs 6

Critical Pitfalls to Avoid

The most critical error is progressing exercises if effusion develops, as this leads to prolonged symptoms and potential repair failure 1, 3

Common mistakes:

• Advancing to loaded exercises too quickly at 12 weeks—meniscal repairs need 9-12 months for complete healing 1
• Ignoring reactive swelling as a sign of excessive loading 1, 3
• Using time-based rather than criterion-based progression 3

Surgical Consideration

If conservative management fails after 4-6 weeks of modified rehabilitation:

• Arthroscopic evaluation may be warranted to assess repair integrity and address parameniscal cyst 2
• Cyst debridement with repair revision using suture anchor technique may be necessary if large gap exists between meniscus and capsule 2