Ligament Healing

Phase 1 — Inflammatory (Days 0–7)

• Hematoma forms, then resorbs
• PMNs and macrophages arrive
• Type III collagen is produced (weaker collagen)
• Growth factors are released

Phase 2 — Proliferative (Weeks 1–3)

• Type III collagen production peaks
• Fibroblasts proliferate; new blood vessels form
• Scar tissue bridges the torn ends — initially disorganized
• This is the weakest point in the healing timeline (macrophages break down tissue)

Phase 3 — Remodeling & Maturation (Weeks 6 → 1+ Year)

• Type III collagen is gradually replaced by stronger Type I collagen
• After a few weeks, collagen fibers begin to align with the long axis of the ligament
• At 1 year, healed ligament still has fewer mature cross-links than normal
• A partially ruptured ligament can heal spontaneously, but its remodeling continues for years, and viscoelastic and creep properties may never fully return to normal

Intraarticular ligaments (e.g., the ACL) have poor intrinsic healing due to the joint fluid environment. Extraarticular ligaments (e.g., MCL) heal much better.

Tendon Healing

Stage 1 — Inflammation (Days 0–7)

• Hematoma, then resorption
• Type III collagen produced by tenocytes (tendon fibroblasts)
• Weakest stage of repair

Stage 2 — Proliferation (Weeks 1–6)

• Maximal Type III collagen production
• Surgical repairs are weakest at 7–10 days post-operatively

Stage 3 — Remodeling (Weeks 6 → 6 Months+)

• Begins at ~6 weeks
• Cellularity decreases; Type I collagen predominates
• Maximum repair strength is reached at approximately 6 months, achieving about two-thirds of original strength
• Tendinopathies (chronic overuse conditions) can take up to 1 year for pain to subside before return to normal activity

Summary Table

Key Factors That Slow Healing

• Intraarticular location (no blood supply, joint fluid inhibits repair)
• Old age, smoking, diabetes mellitus
• NSAID use, alcohol, corticosteroid injections

Factors That Help Healing

• Early protected motion (reduces adhesions, increases repair strength)
• Extraarticular location
• Mesenchymal stem cells, PRP scaffolds (experimental)

ACL Complete Tear — Treatment

Initial Management (All Patients)

• Immobilization is avoided
• Physical therapy to restore full range of motion (ROM)
• Achieve full ROM and good quadriceps control before any surgery
• Ice, compression, elevation for acute swelling/hemarthrosis

Treatment Decision: Operative vs. Non-Operative

• Age and activity level
• Degree of instability (pivot shift severity is most predictive of outcome)
• Associated injuries (meniscus, cartilage, collateral ligaments)
• Patient goals (return to cutting/pivoting sports vs. sedentary lifestyle)

Primary repair is NOT currently recommended — myofibroblasts coat ACL stumps, making direct healing unreliable.

Surgical Treatment — ACL Reconstruction

Surgical Technique

• Single-bundle reconstruction is the most commonly performed
• Double-bundle reconstruction does not show superior patient-reported outcomes vs. single-bundle
• Anatomic ACL reconstruction — femoral tunnel placed at 10- or 2-o'clock position to center the graft in the native ACL footprint; may improve rotational stability

Graft Options

Postoperative Rehabilitation

• Early motion and weight bearing are encouraged
• Emphasis on knee extension early
• Safe exercises: hamstring-dominated, active ROM between 35–90° flexion
• Closed kinetic chain exercises preferred (foot planted) — allows physiologic co-contraction
• Open kinetic chain extension near full extension — avoid for the first 6 weeks (stresses graft)
• No difference between accelerated and non-accelerated rehab programs
• Postoperative bracing not proven beneficial (except in downhill skiers)
• Return to sport: typically 9–12 months post-reconstruction (criteria-based, not just time-based)

Complications

Partial ACL Tears

• Management is controversial; functional stability and clinical exam are the key guides
• Single-bundle tears may be addressed with reconstruction of only the injured bundle, but outcomes are equivalent to standard full reconstruction

Key Evidence

• AAOS Clinical Practice Guideline: Management of ACL Injuries (2023) — 8 recommendations and 7 options based on systematic review; highlights individualized treatment, graft selection, and rehabilitation strategies [PMID: 36727995]