Biplanar Anterior Opening Wedge Proximal Tibial Osteotomy to Correct Reverse Tibial Slope

Abstract

Background:

Anatomically, native posterior tibial slope (PTS) ranges from 6° to 10° and have significant effects on cruciate ligament stability. PTS <6° is correlated with increased posterior tibial translation (PTT) and force on the posterior cruciate ligament (PCL), predisposing individuals to PCL injuries and an increased risk of PCL graft attenuation. In rare cases, a reverse tibial slope can occur (<0°) as a result of trauma, physeal arrest, or abnormal development. This results in increased PTT and can lead to posterior tibial subluxation. Reverse tibial slopes in patients can be treated with an anterior opening wedge proximal tibial osteotomy, which increases the PTS to a more anatomic position.

Indications:

Biplanar anterior opening wedge proximal tibial osteotomies are indicated in patients with a reverse tibial slope both with the absence of PCL insufficiency or in conjunction with PCL reconstruction.

Technique Description:

Under fluoroscopic imaging, 2 guide pins were placed perpendicular to the tibial shaft. An oscillating saw and osteotomes completed the osteotomy in line with the guide pins with the posterior cortex remaining intact. The osteotomy site was slowly opened with a spreader device to 9 mm until the posterior drawer was such that the palpable step-off between the anterior aspect of the medial femoral condyle and the medial tibial plateau was comparable to the contralateral knee. Due to the patient having slight valgus coronal plane alignment, an opening-wedge posteriorly sloped plate was then placed anterolaterally and fixed while wedges held the osteotomy open.

Results:

Biplanar anterior opening wedge osteotomies correct a flattened PTS and reverse tibial slope, and coronal malalignment, and has been shown to decrease PCL laxity, preventing future PCL failure.

Discussion:

Biomechanical studies have shown that decreased tibial slope is correlated with an increased risk of PCL injury and PCL graft failure. In patients with reverse tibial slope, experienced instability can mimic PCL insufficiency despite there being no ligamentous damage. We describe a technique that corrects reverse tibial slope and with a discussion of surgical pearls and pitfalls. This technique restores anatomic position and normal function of the knee while correcting the sagittal malalignment that could lead to future injuries.

Patient Consent Disclosure Statement:

The author(s) attests that consent has been obtained from any patient(s) appearing in this publication. If the individual may be identifiable, the author(s) has included a statement of release or other written form of approval from the patient(s) with this submission for publication.

Graphical Abstract

This is a visual representation of the abstract.

Video Transcript

This is a video presentation depicting a biplanar anterior opening wedge proximal tibial osteotomy.

Shown here are the authors’ disclosures.

The anatomically native posterior tibial slope (PTS) ranges from 6° to 10°.^4,7 A PTS of less than 6° is correlated with increased posterior tibial translation (PTT) and subsequently increased force on the native posterior cruciate ligament (PCL). This can lead to instability and symptoms mimicking a PCL injury.^2,8 Despite the similarity in presentation, the instability is caused solely by osseous deformity, rather than PCL insufficiency. In addition, decreased PTS is also associated with increased risk of PCL injury and PCL graft failure. ⁵ However, in the case of a PCL injury, a double-bundle PCL reconstruction is indicated to correct instability and is not influenced by a decreased PTS. ¹ In rare cases, a reverse or anterior tibial slope can occur, which is a slope of 0° or negative degrees.^3,9 Biplanar anterior-based opening wedge osteotomy can correct a reverse tibial slope to an anatomical range and reduce symptomatic instability. ⁶

A 56-year-old male presented to our office in March 2023 after reporting left knee pain. He had initially injured his knee in 1980 which had caused him intermittent pain since the injury but received no treatment. In the past year, the pain became more persistent to the point of daily pain. Symptoms improved with rest and worsened with activity, especially walking downhill. Rest, icing, activity modification, over-the-counter (OTC) pain medications, bracing, and physical therapy provided limited relief.

Examination of the patient’s left knee revealed a range of motion of 5 cm heel height to 140° of flexion compared to 6 cm heel height to 140° on the contralateral side. He had good quad control with no co-activation of the hamstrings. Minimal quad atrophy was present. His knee was stable to Lachman’s and valgus/varus stress. The tibia was posteriorly subluxed with the medial tibial plateau located posterior to the anterior aspect of the medial femoral condyle.

Plain radiographs revealed a slight valgus weightbearing alignment on his left knee and slight varus on his right, indicating a slight windswept alignment. The tibial slope of the left knee was measured to be −3° compared with 5° in the right knee.

Bilateral PCL stress radiographs were obtained, and 9 mm of increased PTT was observed on the left knee compared to the right.

Select sagittal and axial magnetic resonance imaging (MRI) findings are displayed. The sagittal cut demonstrates an anterior tibial slope, along with an intact PCL. The axial cut demonstrates mild to moderate anterior and lateral compartment chondromalacia.

In summary, the findings on physical examination were confirmed with imaging, and the diagnosis of an anterior slope measuring −3° was confirmed in the absence of PCL insufficiency. Chondromalacia was also observed on imaging. A plan was made for the correction of his reverse tibial slope and chondromalacia involving a left knee arthroscopy and chondroplasty, followed by an anterior opening wedge proximal tibial osteotomy.

Examination under general anesthesia showed range of motion of his left knee to be 8 cm of heel height, compared to a 4-cm heel height on his right. His posterior drawer was a 3+, and it was difficult to reduce him past neutral and to be symmetric to his normal contralateral knee. The dial test, varus and valgus stress testing, and Lachman’s test were normal, which was consistent with his initial physical examination findings. Increased genu recurvatum was observed under anesthesia compared to that in the clinic.

The anterior incision was made first, extending from the mid-patella down just medial to the tibial tubercle. We then dissected down to expose the extensor mechanism. We then dissected medially along the proximal tibia in a subperiosteal fashion, exposing the entirety of the anterior face of the proximal medial tibia at the level of the planned osteotomy, and working posteromedially, deep to the MCL. We then elevated up and performed careful dissection deep to the patellar tendon, exposing the proximal border of the tibial tubercle. We then dissected subperiosteally laterally, staying about 2 to 3 mm above his anterior compartment musculature. We partially reflected the distal-most fibers of the iliotibial (IT) band at the inferior aspect of Gerdy’s tubercle proximally, and we continued our dissection laterally, but not involving the proximal tibiofibular joint.

We now proceeded with the arthroscopy. Medial and lateral arthroscopic parapatellar portals were made, and the camera was inserted into the joint and insufflated with normal saline.

He had some localized areas of grade 1 to 2 chondromalacia on the medial and distal facets of his patella, and a gentle patellar chondroplasty was performed with a shaver.

He had a small radial tear of the posteromedial aspect of his medial meniscus, and a partial medial meniscectomy was performed with a shaver.

He had a small osseous piece in the notch portion of his knee, which appeared to be a partial tear of his posteromedial bundle and thus was subsequently debrided.

His lateral compartment showed no gapping. He had some grade 3 chondromalacia on his lateral tibial plateau that required no chondroplasty. He also had small anterior and posterior horn tears of his lateral meniscus, and a partial meniscectomy was performed with a shaver in both locations. The arthroscopy was ended at this time.

Fluoroscopic imaging was brought in, and 2 guide pins were placed perpendicular to the tibial shaft, which engaged the posterior cortex of the tibia. We then used a small anterior cruciate ligament (ACL) saw and cut the anterior cortex along the guide pins and under the patellar tendon. We then used a small osteotome to complete the osteotomy posteromedially and posterolaterally, ensuring that we were through the cortex in both locations.

We then proceeded to use a larger osteotome under the patellar tendon.

We placed an opening spreader device medially. We opened the spreader device until the posterior drawer was reduced at 9 mm of opening. The tibial tine device was placed laterally, and we placed a 9-mm posterior sloped Puddu plate with the slope plate having the larger portion on the lateral aspect to ensure that we did not place him into more valgus alignment. The plate was then fixed distally with two 4.5-mm full-threaded cortical screws and proximally with two 6.5-mm full-threaded cancellous screws. All screws were predrilled and measured to obtain the screw of correct size. Fluoroscopic imaging was used during the placement of each screw.

A medium Richards staple was placed medially to ensure that the gap would not open medially to reduce his valgus alignment.

We then thoroughly packed in Opteform allograft bone graft (Exactech) into the osteotomy site.

His posterior drawer was evaluated and observed to be reduced. Fluoroscopic images were taken to verify the location of the hardware. The deep and superficial tissues were closed with sutures.

This procedure is relatively rare, and due to the complexity of the surrounding anatomy and the difficulty in performing the osteotomy, it is not without complications. The first complication to be wary of is fracture of the posterior cortex of the tibia. A true fracture of this posterior hinge could lead to destabilization of the osteotomy site and a potential progression to malunion or nonunion. Performing this osteotomy in a supratubercle region allows for optimal metaphyseal bone stock, which is most pliable and amenable to correction. Further preoperative measurements and intraoperative fluoroscopic images should ensure appropriate anteroposterior (AP) depth to avoid cortical breakage.

Second, when attempting to address correction in 2 planes, it is easy to improperly correct the malalignment and induce more deformity in 1 plane. The anterior-based osteotomy makes correcting the sagittal imbalance quite replicable; however, addressing coronal imbalance is more difficult. In cases of valgus malalignment, placement of the sloped fixation plate anterolaterally allows for slightly increased correction laterally, and when your desired correction is attained laterally, you can address mild correction of the opening medially with a staple. Furthermore, the use of a staple will prevent late opening as well.

Lastly, neurovascular injury, namely the popliteal neurovascular bundle, is always a concern with procedures around the proximal tibia. Again, ensuring preoperative planning on the AP depth of the cut and confirming with intraoperative fluoroscopy enables one to avoid bicortical breakthrough and potential injury.

Postoperative rehabilitation guidelines for this operation involve range-of-motion restriction from 0° to 90° for 2 weeks, then advancing as tolerated. The patient is nonweightbearing for 8 weeks, at which point repeat radiographs will be obtained, and if evidence of healing is observed, a progressive partial-weightbearing program is initiated. The protocol is as follows: Advancing partial weightbearing by one-fourth body weight percentage per week until full weightbearing. Radiographs will be repeated at 3 months postoperatively. If further signs of healing are observed, the patient can wean off crutches. Physical therapy is to be started on postoperative day 1 and continues 1 to 5 times a week for 12 weeks with an emphasis on range of motion.

One paper by Bernhardson et al ² published in The American Journal of Spots Medicine (AJSM) assessed the PTS of 104 patients with PCL injuries compared to uninjured age- and sex-matched controls. In patients that suffered PCL injuries, the mean PTS was significantly different with 5.7° compared to 8.6° in uninjured controls.

Another paper by Gwinner et al ⁵ published in AJSM assessed 48 patients undergoing PCL reconstruction for PTT and PTS. PCL reconstruction significantly improved preoperative PTT from 10.9 mm to 4.9 mm. There was also a correlation between reduction in postoperative PTT and tibial slope, with a correlation coefficient of −0.77 and a coefficient of determination of 0.59. They concluded that flattening tibial slope is associated with a significantly higher PTT as well as a lower reduction in PTT. They also proposed that isolated soft tissue procedures for PCL deficiency incompletely address posterior knee instability with flattened PTS.

Radiographs were obtained on postoperative day 1 in the clinic. There is no evidence of acute fractures or soft tissue abnormalities. All joint spaces appear preserved compared to prior imaging, and the hardware is intact and nondisplaced.