In a 28‑year‑old active woman who underwent an all‑inside posterior‑horn and outside‑in anterior‑horn bucket‑handle meniscus repair and returned to sport, what are the likely causes of sudden knee giving‑way and anterior knee pain at 14 months post‑operation, and what is the recommended evaluation and management?

Meniscus Re-tear or ACL Injury

This patient most likely has either a failed meniscus repair (re-tear) or a new/missed ACL injury, and you should immediately obtain an MRI to differentiate between these diagnoses, as both require urgent surgical evaluation to prevent further cartilage damage and preserve long-term knee function.

Most Likely Diagnoses

The sudden "giving way" combined with anterior knee pain at 14 months post-repair points to two primary possibilities:

1. Failed Meniscus Repair (Re-tear)

• Failure rates for bucket-handle repairs are substantial: approximately 33% at median 19 months in long-term studies 1
• The timing (14 months) falls within the typical failure window
• Re-tears can occur even without significant trauma after an asymptomatic period 2
• All-inside repairs (used for her posterior horn) show particularly high revision rates—up to 50% at mid-term follow-up 3
• Key risk factors present in this patient:
  • Female sex increases failure risk significantly (HR 2.60) 3
  • If this was a medial meniscus tear, failure risk is 4.8 times higher than lateral 1

2. ACL Injury (New or Previously Unrecognized)

• "Giving way" is the hallmark symptom of ACL insufficiency
• The anterior knee pain location is consistent with ACL pathology
• She may have had an unrecognized partial ACL tear at initial surgery that has now progressed
• High-level athletes returning to pivoting sports remain at risk for new ACL injuries

Immediate Evaluation Algorithm

Physical Examination - Specific Maneuvers:

1. For ACL assessment:

   • Lachman test (most sensitive)
   • Anterior drawer test
   • Pivot shift test

2. For meniscus re-tear:

   • Joint line tenderness (medial vs lateral)
   • McMurray test with knee rotation
   • Thessaly test
   • Check for mechanical locking or catching
   • Assess for effusion

Imaging:

MRI is mandatory and should be obtained urgently 4. The 2025 AAOS guidelines provide strong evidence that MRI is the preferred imaging modality for evaluating meniscal pathology 4.

Management Based on Diagnosis

If Meniscus Re-tear is Confirmed:

Surgical revision should be pursued aggressively in this young, active patient to prevent accelerated osteoarthritis. The evidence is clear:

• Failed repairs lead to significantly worse outcomes: mean Kellgren-Lawrence score of 2.09 vs 0.54 for successful repairs 1
• Successful repairs show dramatically better functional scores (KOOS 89.6 vs 77.8, IKDC 88.2 vs 79.2) 1
• Revision repair is still preferable to meniscectomy when tissue quality permits, as meniscal preservation prevents osteoarthritis 4

Surgical approach for revision:

• Inside-out technique is considered gold standard for medial meniscus 5, 6
• All-inside revision has high failure rates (50%) and should be avoided if possible 3
• Consider hybrid techniques combining inside-out and all-inside methods 7

If ACL Injury is Confirmed:

Early ACL reconstruction is strongly recommended 8. The 2023 AAOS ACL guidelines provide strong evidence that:

• Risk of additional cartilage and meniscal injury increases within 3 months of ACL tear 8
• If she has a meniscus re-tear AND ACL injury, combined surgery is indicated
• Concomitant ACLR significantly improves meniscal repair survival (HR 3.63 for failure without ACLR) 3

Critical Pitfalls to Avoid

1. Do not delay imaging or surgery: The window for preventing additional damage is narrow (3 months for ACL) 8

2. Do not assume "normal" post-operative course: Giving way at 14 months is NOT normal rehabilitation progression

3. Do not perform meniscectomy without considering repair: Even in revision cases, repair should be attempted when feasible given the chondroprotective benefits 1

4. If revision meniscus repair is performed:

   • Strongly consider concomitant ACLR if any ACL laxity exists 3
   • Avoid all-inside technique for revision (50% failure rate) 3
   • Female patients have 2.6x higher failure risk—counsel accordingly 3

5. Do not rush back to sports after revision: Return to play should be delayed 4-7 months minimum, with functional testing (hop tests) before clearance 8

Bottom Line

Order MRI immediately. If meniscus re-tear: pursue revision repair with inside-out technique. If ACL injury: reconstruct urgently. If both: combined surgery is mandatory. Time is critical—delaying beyond 3 months risks irreversible cartilage damage and meniscal injury that will compromise her long-term knee function and quality of life 8.