Biomechanical Study: High-Strength Sutures Improve PCL Reconstruction Stability in Porcine Model

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Biomechanical Study: High-Strength Sutures Improve PCL Reconstruction Stability in Porcine Model

If you’ve ever torn your posterior cruciate ligament (PCL)—the key stabilizer that prevents your knee from sliding backward—you know how critical it is to rebuild it with a strong, durable graft. But for surgeons, one of the biggest challenges in PCL reconstruction is fixing that graft to the tibia (shinbone) so it stays secure over time. A new study from China’s First Affiliated Hospital of China Medical University tests three common tibial fixation methods—and the results suggest combining two techniques could be the strongest option yet.

Why Tibial Fixation Matters for PCL Reconstruction

Unlike ACL surgery, which has a well-established “gold standard,” PCL reconstruction is still evolving. Many patients end up with residual looseness because the graft fails to hold up. The problem often boils down to tibial fixation: how the graft is anchored to the shinbone. Interference screws (the most common method) press the graft against the tunnel wall, but they can lack pullout strength. That’s why researchers explored transtibial tubercle fixation (TTF), a newer approach that uses high-strength sutures to tie the graft to the tibia without implants. They wanted to see if pairing TTF with an interference screw (TTF+IS) would outperform either method alone.

How the Study Was Done

The team used 36 fresh-frozen porcine tibias (a stand-in for young human bone, since their biomechanical properties are similar) and 24 porcine digital extensor tendons (as grafts). They split the samples into three groups (12 each):

  1. Interference screw (IS) alone: A titanium screw pressed the graft against the tunnel wall.
  2. TTF alone: Three No. 2 Ultrabraid sutures (high-strength) were passed through a hole in the tibial tubercle and tied to secure the graft.
  3. TTF + IS: The graft was fixed with both a screw and sutures.

Each group underwent two key tests:

  • Cyclic loading: 1,000 cycles of 50–250 Newtons (mimicking daily knee movements) to measure graft slippage (how much the graft moved in the tunnel).
  • Load-to-failure: The graft was pulled until it broke to measure stiffness (how much force it takes to stretch the graft) and ultimate failure load (the maximum force the graft can handle before failing).

The Results: TTF+IS Is the Strongest Option

Here’s what the team found:

  • Cyclic testing: All three groups had similar graft slippage (1.37–1.98 mm)—no significant difference. This means all methods held the graft in place during repeated movements.
  • Load-to-failure: The TTF+IS group was the clear winner. Its ultimate failure load (876.34 ± 58.78 Newtons) was:
    • 57% higher than IS alone (556.49 ± 65.33 N)
    • 33% higher than TTF alone (660.92 ± 77.74 N)
  • Stiffness: TTF alone had the lowest stiffness (92.77 ± 20.16 N/mm), meaning it stretched more easily. IS (120.27 ± 15.66 N/mm) and TTF+IS (131.79 ± 17.95 N/mm) were nearly identical—both provided the “springiness” needed to mimic a healthy PCL.

What This Means for Patients and Surgeons

The biggest takeaway? Combining TTF with an interference screw gives the graft extra strength without sacrificing stiffness. That’s a game-changer for:

  • Revision surgeries: Cases where the original tunnel is widened or the graft doesn’t fit the tunnel (graft-tunnel mismatch). TTF adds security without requiring more implants.
  • Cost savings: TTF uses only sutures—no metal or bioabsorbable screws—making it cheaper than other methods (like suspension buttons or anchors).

But TTF alone isn’t enough: Its low stiffness means it can’t handle the same forces as a screw or combined method. Surgeons will likely keep using IS as a base, with TTF as a supplementary fix for high-risk cases.

Limitations to Consider

Like all biomechanical studies, this one has caveats:

  • Porcine vs. human tissue: The results are promising, but we need human studies to confirm if TTF+IS works the same way in people.
  • Time-zero only: The tests measured strength right after surgery—not long-term healing (how the graft integrates with bone over months).
  • No clinical data: The study doesn’t look at patient outcomes (e.g., pain, mobility) after surgery—only lab-based strength.

The Bottom Line

For surgeons, TTF+IS offers a stronger, more versatile option for PCL reconstruction. For patients, that means a better chance of long-term knee stability and fewer complications. While more research is needed, this study adds valuable evidence to the ongoing quest for the “best” PCL fixation method.

Original study published in the Chinese Medical Journal (2021) by Ming-Yi Duan, Rui Sun, Lei-Ting Zhuang, and Hang-Zhou Zhang from the Department of Orthopedics, Joint Surgery and Sports Medicine at the First Affiliated Hospital of China Medical University.

doi.org/10.1097/CM9.0000000000001725

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