Preoperative medial knee instability is an underestimated risk factor for failure of revision ACL reconstruction

Anterior translation of the tibia was measured clinically with the Lachman and pivot-shift tests and was objectively tested with the Rolimeter®. While the pivot-shift test was divided into grade 1 (glide), grade 2 (clunk) and grade 3 (gross), the Lachman test was measured with the 2000 IKDC Knee Examination Form (grade 1: 2–5 mm, grade 2: 6–10 mm and grade 3: > 10 mm) [20]. Medial and lateral knee instability was assessed clinically according to Hughston and the American Medical Association (AMA) [2, 18] [19]. Preoperatively, a high-grade anterior knee laxity was defined as a side-to-side difference greater than 6 mm and/or pivot-shift grade 3.

Radiographs of the knee (coronal, sagittal) were performed before revision ACLR to evaluate bony structures such as PTS. The PTS was measured on the lateral knee radiograph and calculated by defining the angle between a line drawn tangentially to the tibial plateau and the proximal anatomic axis of the tibia [40]. A normal PTS was defined as 8 ± 3° [23].

Computed tomography (CT) with 3D reconstruction defined the tunnel position and bone tunnel enlargement that might suggest the need for a bone graft. Additionally, magnetic resonance imaging (MRI) of the injured knee was used to assess further lesions of the menisci, cartilage and other ligaments of the knee. Additionally, a standing long-leg radiograph to determine the mechanical axis of the lower leg was performed when valgus or varus deformity was clinically suspected. Valgus or varus deformity was defined when the mechanical femoro-tibial angle was more than 3°. The possible reasons for failure of primary ACLR are listed in Table 3.

If the diameter of the bone tunnel was more than 12 mm or if a safe new tunnel position was not guaranteed due to the previous bone tunnel position, a two-stage revision procedure was performed. Bone tunnel filling was performed using allogeneic spongiosa. At the earliest 4 months after bone tunnel filling, revision ACLR was carried out. In the case of varus or valgus deformity with additional medial or lateral knee instability grade 2 or in the case of symptomatic unicompartmental osteoarthritis or varus or valgus deformity, the leg axis was corrected by osteotomy.

All revision ACLR procedures were performed with autografts during single-bundle ACLR using hamstring, bone–patellar–tendon–bone (BPTB) or quadriceps grafts. We attempted to preserve the meniscus. Peripheral meniscal lesions that could be repaired were sutured. When meniscal tears could not be repaired, partial meniscectomy was carried out.

Extra-articular lateral tenodesis using the modified “Lemaire” procedure was performed in 51 patients when high-grade anterior knee instability (side-to-side difference ≥ 6 mm and/or pivot-shift grade 3) and Lachman grade 3 occurred [42]. Via a 4-cm skin incision placed over the lateral epicondyle, a 6–8-cm-long and 6–8-mm-wide strip of the distal tractus was prepared with preserved connection to Gerdy’s tubercle. The free end was sewn with Vicryl suture, and a 2.4-mm K-wire was inserted into the lateral femur approximately 1 cm proximal and posterior to the lateral epicondyle. If the isometric examination showed slight tension of the tenodesis in extension, a 5–6 mm drill channel was placed over the 2.4-mm wire, and tenodesis was performed at 45°.

The Hughston technique was carried out (n = 22) when patients showed grade 2 medial knee instability in full extension or 30° flexion of the knee. Postero-medial reconstruction was performed according to the description of Jacobson et al. [21]. A 4–6 cm longitudinal incision of the skin was placed over the medial epicondyle and adductor tubercle. After splitting the sartorius fascia, the proximal superficial medial collateral ligament (sMCL) and posterior oblique ligament (POL) were demonstrated. In the interval between the sMCL and POL, the joint was opened longitudinally, and the deep MCL (dMCL) and the medial meniscus were revealed. The deep structures and dMCL were tightened with sutures, and any lesion of the postero-medial meniscus complex was reconstructed and sutured to the dMCL. Using a pants-over-vest suture technique, the POL was also sutured. Any possible damage to the semimembranosus insertion was reconstructed, and the sMCL was tensioned and closed.

When grade 3 medial knee instability was diagnosed, MCL reconstruction with an autologous graft was performed (n = 3). MCL reconstruction was performed according to the descriptions of Preiss et al. [31]. A 6-mm femoral bone tunnel was created at the intersection of an imaginary extension of the posterior edge of the tibia and the Blumensaat line via a 1–2 cm skin insertion under strict fluoroscopic control of the lateral knee. A gracilis tendon autograft sutured with Vicryl at both ends was placed in the femoral tunnel and fixed with an interference screw. Thus, one branch of the femoral tunnel was used for the sMCL and the second for the POL reconstruction. A 5-mm bone tunnel was created above the pes anserinus centrally to the sMCL insertion and above the insertion of the distal arm of the semimembranosus muscle. The sMCL and POL branches were inserted into the tibial bone tunnels below the sartorius fascia and fixed with interference screws at 30° of knee flexion.

The demographic data and preoperative clinical findings are summarized in Tables 4 and 5. There were 111 patients who were clinically evaluated after revision ACLR with a mean follow-up of 35 ± 3.4 months (24–67 months). Among them, 16 patients (14.5%) were identified with failure of revision ACLR. Based on our proportions of medial instability of 0.63/0.27 in 111 patients with 16 revision ACLR failures, a post hoc power of 0.868 was achieved at a significance level of 5%.

Preoperative medial knee instability (before revision ACLR) was significantly more frequent in the failed surgery group than in the stable revision ACLR group (63% vs. 27%; p = 0.005) (Fig. 1).

High-grade anterior knee laxity occurred significantly more often in the failed revision ACLR group (69% vs. 32%; p = 0.004) (Fig. 2). Additionally, the percentage of patients with an increased PTS was significantly larger in the failed revision ACLR group than in the other group (38% vs. 10%; p = 0.002) (Fig. 3). While patients with failed revision ACLR showed significantly higher anterior translation of the tibia preoperatively in the third grade Lachman test (25% vs. 6%; p = 0.05) and a significantly greater Rolimeter® side-to-side difference (7 mm vs. 5.9 mm; p < 0.001), they were also significantly more often obese with a BMI of greater than 30 kg/m² (75% vs. 19%; p < 0.001) (Fig. 4) and demonstrated more medial meniscus lesions (81% vs. 40%; p = 0.002). The meniscus status at the time of revision ACLR, the revision graft choice and additional procedures during revision ACLR are displayed in Tables 6 and 7. Valgus-opening high tibial osteotomy in cases of varus deformity and additional symptomatic medial osteoarthritis was performed in seven patients, and slope-reducing high tibial osteotomy combined with bone tunnel filling was performed in five patients. Leg axis correction osteotomies were not performed for medial or lateral knee instability in combination with leg axis deformity (Table 7).

The results of multivariable conditional logistic regression analysis for predictors are displayed in Table 8. Preoperative medial knee instability (odds ratio, 16.8 [95% CI, 1.7–164]; p = 0.015), preoperative high-grade anterior knee laxity (odds ratio, 4.9 [95% CI, 1.1–21.6]; p = 0.034), an abnormal PTS (odds ratio, 4.9 [95% CI, 1–36.9]; p = 0.046) and a BMI greater than 30 kg/m² (odds ratio, 8.6 [95% CI, 1.8–42.1]; p = 0.008) were determined to be independent risk factors associated with failure of revision ACLR.

The multivariable conditional logistic regression analysis showed a reduced risk for failure of revision ACLR when additional medial (odds ratio,  – 13.3 [95% CI, 1.2–146.2]; p = 0.034) and/or anterolateral (odds ratio,  – 1.5 [95% CI, 0.8–1.7]; p = 0.028) stabilization was performed at the time of revision surgery.