Background: Elevated posterior tibial slope (PTS) has been identified as an important risk factor in anterior cruciate ligament (ACL) injuries and ACL graft failures. The cutoff value to recommend treatment with slope-reducing osteotomy remains unclear and is based on expert opinion and small case series. Purpose: (1) To determine whether there is a difference in PTS shown on lateral knee radiographs and magnetic resonance imaging (MRI) scans in a group of patients who experienced revision ACL graft failure versus a control group of patients who underwent successful revision ACL reconstruction, (2) to identify cutoff values of PTS measurements that predict risk of revision ACL graft failure, and (3) to examine whether there is a correlation between radiographic and MRI measurements of PTS. Study Design: Case-control study; Level of evidence, 3. Methods: A total of 38 patients who experienced revision ACL graft failure were identified from a revision ACL database. These patients were matched 1:1 by age, sex, and graft type to a group of 38 control patients who underwent revision ACL reconstruction with no evidence of graft failure at a minimum 2 years of follow-up. Medial and lateral PTS were measured by lateral knee radiographs and MRI scans of the affected limb. Demographics, surgical characteristics, and PTS were compared between the groups. The optimal cutoff values of medial and lateral PTS per radiographs and MRI scans for predicting increased risk of revision ACL graft failure were determined by receiver operating characteristic curves. Conditional multivariable logistic regression was used to assess the relative contribution of PTS cutoff values as a predictor of revision graft failure. Results: The mean PTS values in the failure group were significantly higher than those in the control group on radiographs (medial, 13.2°± 2.9° vs 10.3°± 2.9°; P < .001; lateral, 12.9°± 3.0° vs 9.8°± 2.8°; P < .001) and MRI scans (medial, 7.2°± 3.1° vs 4.8°± 2.9°; P < .001; lateral, 8.4 ± 3.1° vs 5.9 ± 3.0°; P < .001). A radiographic medial PTS ≥14° had the highest increased risk of revision ACL graft failure with sensitivity equal to 50% and specificity to 92.1% (odds ratio, 18.71; 95% CI, 2.0-174.9; P = .01). Conclusion: Elevated PTS was a significant risk factor for revision ACL graft failure. Patients with radiographic medial PTS ≥14° had 18.7-times increased risk of revision ACL failure.
Background: Anterior cruciate ligament (ACL) ruptures are among the most common injuries in young athletes and active adults. Reconstruction of the ACL most often leads to good functional outcomes and return to full activities. However, a number of patients experience ACL graft failures requiring revision surgery. The reasons for ACL graft failure are often multifactorial, though recent attention has been given to elevated posterior tibial slope (PTS) as a risk factor for recurrent ACL injuries. Indications: In patients with 2 or more ACL reconstruction failures with a PTS ≥12 degrees, anterior closing wedge proximal tibia osteotomy (ACWPTO) may be indicated to reduce the risk of recurrent ACL graft failure and allow return to full activities. Technique Description: This surgical technique video demonstrates the ACWPTO using a case example in a young athlete. Preoperative templating on lateral radiograph is used to determine the amount of correction for the closing wedge. The osteotomy is completed using K-wires and a free hand biplanar cutting technique with the tibial tubercle left in place. This is performed with a concomitant revision ACL reconstruction using quadriceps tendon autograft. Results: There are 2 small cases series published with good clinical outcomes and return to sport activities. No ACL graft failures were reported in either study with short-term follow-up. Discussion: In this surgical technique video, we review the literature indicating elevated PTS as a risk factor in ACL injuries and recurrent ACL graft failures. We highlight important technique pearls and pitfalls to avoid complications during the surgical demonstration. Finally, we review postoperative rehabilitation guidelines and clinical outcomes within the existing literature. In patients with recurrent ACL graft failures, ACWPTO provides a safe and reliable technique to correct an elevated PTS and return patients back to full activities with reduced risk of ACL graft re-tear.
Objectives: Anterior closing wedge proximal tibia osteotomy (ACWPTO) is an effective treatment for patients with elevated posterior tibial slope (PTS) and recurrent anterior cruciate ligament (ACL) injuries. However, the preoperative planning and surgical execution can be challenging, especially with limited surgeon experience and training. The purpose of this study was to evaluate the initial design of a 3D printed patient-specific cutting guide (PSG) for performing ACWPTO in an animal model. It was hypothesized that the PSG for ACWPTO will more accurately achieve the desired PTS correction compared to a traditional free-hand (FH) technique. Methods: Thirty cadaveric porcine knees underwent lateral radiographs and computed tomography (CT) scans, and were randomly assigned to ACWPTO by PSG or FH technique. Three knees within each group were then assigned to a 10°,12°,14°,16° or 18° correction. Knees assigned to the PSG group then underwent 3D modeling and a PSG was created in SolidWorks to complete the desired PTS correction (Figure 1). Knees assigned to the FH group were templated by an experienced orthopedic surgeon for performing ACWPTO by measuring a pre-determined wedge of bone to be removed from the anterior tibia. Surgeries were then performed by an experienced (attending physician), intermediate (resident physician), and novice surgeon (medical student). Each surgeon performed ACWPTO using the PSG and FH technique for each of the intended angles of correction (10°,12°,14°,16°,18°). Following ACWPTO, post-operative radiographs and CT scans were taken to measure the PTS and the accuracy was determined as the difference between the planned and actual PTS correction (Figure 2). The accuracy, surgical time, and radiation exposure were compared between surgeons using ANOVA. Further analyses to compare the variables of interest between the FH and PSG techniques were conducted using independent samples t-tests. Results: All data are summarized in Tables 1 and 2. Overall, we found the PSG to have significantly faster surgical time (6.4 +/- 2.2 minutes versus 12.0 +/- 3.9 minutes, p < 0.001) and less radiation exposure (8.7 +/- 4.9 mGy versus 58.7 +/- 28.1 mGy, p < 0.001). While the PSG trended towards increased accuracy with radiographic measurements of PTS, this did not reach statistical significance (1.6 +/- 1.6 degrees versus 2.9 +/- 2.0 degrees, p = 0.059). The highest accuracy was found for the resident (intermediate) surgeon using the PSG (0.5 +/- 0.5 degrees), which was significantly more accurate than FH technique for this surgeon (3.6 +/- 2.5 degrees, p = 0.026). Based on CT measurements of medial and lateral PTS we found the FH technique to be as accurate as the PSG (Table 2). Conclusions: One reason for the discrepancy between radiographic and CT measurements may be the lack of standardized methods for measuring PTS in porcine knees. The proximal tibia articular surface has a more complex geometry as compared to human knees, which did make measuring consistent landmarks challenging and is one of the primary limitations of this study. Other limitations of this study include the margin of error in the design of the 3D printed PSG, and accurate placement of the PSG on the proximal tibia. Guide placement was challenging if any cartilage remained around the tibial tubercle as this was not templated in the CT design. Also, PTS measurements can be highly dependent on limb rotation and observer experience. Despite these limitations, this study demonstrated the feasibility of a 3D printed PSG for performing ACWPTO in an animal model. This PSG was as accurate as the free-hand technique based on CT measurements and trended towards improved accuracy based on radiographic measurement of PTS. Future studies are planned to investigate this design in human cadaveric specimens. [Table: see text][Figure: see text][Table: see text][Figure: see text]
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