Abstract
Objectives:
High-grade, symptomatic posterior cruciate ligament (PCL) tears present a treatment challenge: the PCL’s spontaneous healing potential supports conservative treatment, but excessive laxity is often encountered; PCL reconstruction, however, entails lengthy recovery, increased invasiveness, and variable long-term outcomes, with residual laxity still a liability.
Proximal and distal PCL tears are currently treated with acute arthroscopic repairs, as a minimally-invasive alternative to potentially shorten recovery and decrease morbidity compared to PCL reconstruction. For the most prevalent mid-substance PCL tear type, the deep and central tear location poses significant technical challenges for accessing and suturing the proximal and distal portions for direct repair. Instead, the more invasive PCL reconstruction remains the principal surgical treatment option for mid-substance PCL tears.
We developed a technique to repair the mid-substance PCL tear, with bi-directional ring and adjustable-length loop device (ALLD) suture constructs to capture each half of the torn PCL, maintain PCL tissue reduction and tension during healing, and minimize PCL laxity post treatment. The technique also incorporates a suture tape for internal brace (IB) reinforcement (Fig.1).
The purpose of this study was to biomechanically evaluate the new minimally-invasive mid-substance PCL repair construct in detail, with serial assessments during the stages of independent tensioning and construct formation, to examine the individual and combined stabilizing effects of the repair and the IB components. We hypothesized the novel mid-substance PCL repair construct will restore posterior stability to intact-equivalent levels, without IB over-constraint.
Methods:
Nine cadaveric knees (age 45.4 ± 11.7 yrs, 2 F/7M) were placed in 90° flexion on a mechanical testing device. Posteriorly-directed, non-destructive 134-N tibial load was applied, representative of a posterior drawer exam, and posterior tibial displacement was measured, in the following sequence of conditions: 1) Intact; 2) PCL-Deficient, with complete midpoint PCL transection; 3) IB, with a suture tape IB; 4) IB+PCLR, with IB and PCLR with bi-directional ring and adjustable-length loop device (ALLD) sutures; and 5) PCLR, with the repair construct in place but the IB is released distally (Fig 2). The order of Conditions 3 then 4, tensioning the IB first then the ligament repair second, replicates the independent tensioning sequence
After testing under non-destructive load, the complete PCL repair construct was reconstituted, by re-securing the IB distally then re-tensioning the the PCLR construct. The specimens were then loaded to failure in 90° flexion, with a posteriorly-directed excursion of the tibia at 1 mm/sec.
Displacement results through the 5 conditions were compared with repeated measures analysis of variance. Sample-size calculation based on prior studies indicated n=8 presents sufficient power.
Results:
Posterior tibial translation increased from 3.34±1.0mm Intact to 16.9±2.7mm when PCL-deficient (p< 0.001). All 3 repair conditions significantly reduced the excess PCL-deficient posterior translation (p< 0.001 for all 3). Compared to Intact, PCLR (3.14±0.4mm, p=0.32) and IB+PCLR (2.98±0.4mm, p=0.59) both restored posterior tibial translation to intact-equivalent levels, but not IB (4.66±2.0mm, p=0.01). IB+PCLR provided significantly greater stabilization than IB alone (p=0.04) and PCLR alone (p=0.02). Mean ultimate failure load of the full IB+PCLR construct was 1139±214N (Fig 3,4). All specimens failed with the IB pulling the femoral cortical button into the femoral condyle, and none at the PCLR construct.
Conclusions:
The present biomechanical study demontrates that the new minimally-invasive PCL repair technique can provide intact-level stability without reliance on IB, and that IB reinforces and protects the repair without over-constraint, confirming our hypotheses.
We sought to simplify the access, suturing, and reduction with arthroscopic techniques and implants for anterior cruciate igament repair, to make arthroscopic direct repair of mid-substance PCL tears feasible, and to address a minimally-invasive treatment gap unique to the most prevalent PCL tear type. Although the findings demonstrated the new construct’s ability to restore posterior translation to intact-PCL levels as a stand-alone construct, results favor the IB+PCLR combination, which shows the most robust stabilization and incorporates an IB for reinforcement and protection.
At non-destructive physiologic loads, IB treatment alone did not restore posterior stability to intact-equivalent levels, consistent with IB’s intended role as reinforcement, and not as a stand-alone "synthetic ligament" that can potentially over-constrain and fail over time. The uniformity of the failure mode, with IB pulling the femoral button into bone in all specimens, is partly due to cadaveric bone quality, but the nature of the failure mechanism indicates that the IB provides the main resistance to overall construct elongation at high, destructive load levels and likely protects the PCLR construct.
Suture tape-only indirect PCL repairs have been described as an arthroscopic alternative to open mid-substance PCL repair. However, based on the IB-only treatment results of the present study, if the IB is placed alone without a direct-repair component to restore PCL tension, posterior stability may not be restored to intact levels.
In conclusion, the new mid-substance PCL repair with IB reinforcement can potentially restore posterior stability to intact-equivalent levels, and may be a suitable minimally-invasive surgical alternative to PCL reconstruction.
