Tibial Tubercle Anteriorization and Distalization Using the Multi-Directional Tibial Tubercle Transfer (MD3T) System

Abstract

Background:

Tibial tubercle osteotomy (TTO) is a well-established procedure that improves patella-trochlea contact area and reduces aberrant forces causing maltracking or compression of the patellofemoral joint (PFJ). Contemporary TTO surgery often involves anteriorization, medialization, distalization, or combinations like anteromedialization (AMZ). The classic Fulkerson AMZ is a time-tested standard, but the technique does not allow for isolated planar adjustments such as straight anteriorization and may not be viable for subsets of patients with medial patellofemoral cartilage lesions due to the resultant medial shift of contact forces. The Multi-Directional Tibial Tubercle Transfer (MD3T) system enhances TTO precision and modularity, enabling customizable realignments.

Indications:

Anteriorization-type TTO reduces PFJ compression and addresses pathologies such as focal chondral defects, patellofemoral pain, maltracking, and instability. Distalization-type TTO corrects patella alta in patients with a Caton-Deschamps Index ≥1.2. However, distal displacement of the tubercle can increase compressive forces in the PFJ; thus, care must be taken to avoid overcorrection and resultant overloading of the articulating surfaces. The MD3T system supports both anteriorization and distalization, ensuring controlled corrections.

Technique Description:

The MD3T employs a proprietary wedge system for precise uniplanar or multiplanar corrections during TTO. For uniplanar adjustments, a single wedge suffices; multiplanar procedures may require 2 transposable wedges. A specialized saw guide guides osteotomy cuts, and the tubercle is repositioned with bone void fillers placed under the proximal tubercle for anteriorization or superiorly for distalization. This approach maintains cortical integrity and reduces the need for extensive dissection.

Results:

The MD3T system allows for precise anteriorization and distalization while preserving both cortices and eliminating the need for extensive stripping of the anterior compartment, thereby reducing the risk of catastrophic iatrogenic neurovascular injuries.

Discussion/Conclusion:

The MD3T system simplifies TTO by providing consistent, precise corrections in multiplanar alignments. Its wedge technique preserves cortical structures, reduces neurovascular injury risk, and enhances surgical efficiency. This system effectively simplifies the intricacies associated with this complex surgery, allowing surgeons to reconstruct favorable biomechanics for their patients and establish a solid groundwork for achieving optimal clinical outcomes.

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

The following video demonstrates the surgical technique of tibial tubercle anteriorization and distalization using the novel Multi-Directional Tibial Tubercle Transfer System, known as MD3T. Our objective is to showcase how this technique simplifies and enhances the accuracy of tibial tubercle osteotomy (TTO). The surgery is performed by Dr Seth Lawrence Sherman and his team from Stanford University.

Background

TTO is a surgical procedure designed to improve patellar alignment and alleviate symptoms related to patellofemoral dysfunction, such as pain, instability, and other conditions. Specifically, anteriorization-type TTOs are frequently used to address focal chondral defects affecting the patella or trochlea, patellar instability, patellar maltracking, and patellofemoral arthritis. In contrast, distalization-type TTOs are employed to correct cases of patella alta ³ in patients with a Caton-Deschamps Index (CDI) of 1.2 or higher, with numerous authors now considering 1.4 the recommended threshold.

It is widely accepted that distalization-type TTO serves as an effective treatment for patella alta, chondrosis, and concomitant instability, with the target distalization being a CDI of 1.1 to avoid overcorrection and the risk of creating iatrogenic patellar baja. If there is a concern for overcorrection or increased distal loading with an isolated distalization TTO, a combined distalization with anteriorization can be performed to ensure that the patellar height is not overcorrected.

Indications

The primary focus of this video is to demonstrate the surgical technique and approach of tibial tubercle anteriorization and distalization using the MD3T surgical system. This technique is known for its high precision and reproducibility, with the primary goal of repositioning the patellofemoral joint (PFJ), improving patellar tracking, and minimizing pathological forces acting on the PFJ during movement.

Isolated anteriorization of the tibial tubercle was first described by Maquet ⁴ as a method to decrease the contact stresses on the PFJ. However, there have been significant complications, such as fracture, nonunion, and skin necrosis, with this procedure, causing it to be largely abandoned. Subsequently, the Fulkerson anteromedialization (AMZ) technique gained widespread acceptance as an effective treatment for PFJ pathology. This technique combines and enhances aspects of both the Maquet and Elmslie-Trillat procedures, remaining a prominent approach in contemporary TTO procedures.

The Fulkerson AMZ is a time-tested technique used for correcting a lateralized vector and unloading chondrosis, but it does not specifically allow for single plane corrections and is not viable for subsets of patients with medial patellofemoral cartilage lesions due to the resultant medial shift of contact forces. ² Studies, such as those by Rue et al, ⁴ demonstrated that straight anteriorization can produce enhanced biomechanical outcomes. Additionally, when unhinging the tibial tubercle to perform distalization following a Fulkerson AMZ or Maquet anteriorization, there is an increased risk of complications, including fracture incidence, worsened healing outcomes, and the potential occurrence of rare yet severe neurovascular injuries. ⁵

To overcome these challenges, the MD3T system was developed. This innovative system looks to further enhance these time-tested osteotomy techniques by facilitating single planar modification or combined anteriorization, medialization, and/or distalization of the tibial tubercle for improved outcomes. The following table (Figure 1), which was adapted from a review by Atzmon and colleagues, ¹ compares the techniques. The MD3T system provides a proprietary guide jig to ensure more standardized, reproducible cuts, and it avoids the need to strip the anterior compartment while preserving both cortices, reducing the risk of injury to nearby neurovascular structures.

Figure 1.

Comparison of the Fulkerson technique and MD3T system.

Technique Description

TTO with MD3T employs a standard joint surgery set along with the MD3T set, which includes the use of specified implants. Fixation is achieved using 2 bicortical screws of choice. Before the procedure, the patient is placed in a supine position on the operating table with their ipsilateral knee flexed to roughly 30°.

In this demonstration, we will use operative videos to illustrate both anteriorization and distalization types of TTO using the MD3T system on a cadaver specimen and conclude with a patient-specific case to highlight preoperative decision-making and postoperative outcomes.

This video will specifically concentrate on the left knee. The anatomic landmarks, such as the anterior aspect of the patella, the patellar tendon, and the tibial tubercle, were initially palpated and marked.

After palpating the tibial crest, an incision is made just lateral to it, providing sufficient exposure for the osteotomy. This incision can be extended up to the top of the patella, allowing ample access for common procedures such as lateral retinacular lengthening. Moreover, this approach facilitates the performance of concomitant procedures, such as medial patellofemoral ligament (MPFL) reconstruction, and allows access to the joint for cartilage restoration. If required, an additional accessory incision can be made for the femoral aspect of the MPFL. Developing the plane and meticulously dissecting the underlying tissues enables improved visibility of essential anatomic landmarks and structures, including the tibial tubercle and patella tendon.

Adequate exposure is necessary to ensure easy access beneath the patellar tendon. The goal is to create ample space to insert a finger, enabling smooth access beneath the tendon. The objective is to define and uncover both sides of the patellar tendon without harming the tendon itself and refraining from penetrating the fat pad layer by staying in the correct plane. Subsequently, a minimal peeling of the anterior compartment is carried out by detaching the muscular soft tissue directly from the bone, allowing for visualization of the lateral cortex. Unlike the Fulkerson procedure, the goal is to expose solely the anterior aspect of the lateral cortex without the need to dive deeply or infringe upon any part of the anterior compartment.

Upon completion of the dissection, we have a clear view of the tibial tubercle, patellar tendon, the patella itself, the tibial crest, and the contents of the anterior compartment. Additionally, both borders of the patellar tendon are visible, with ample exposure beneath the tendon and above the tubercle and the lateral cortex after superficial peeling of the anterior compartment.

The next step involves positioning the primary guide centrally on the tibial tubercle, which is accomplished by employing a lateral cortical finder and applying pressure toward the lateral cortical bone. The guide should be placed as high as feasible on the tibial tubercle, with the index finger positioned beneath the patellar tendon and just above the tibial tuberosity, serving as a stabilizing support and proximal buttress for the guide. Ensuring proper alignment with the tibial spine is critical. Once the guide is in position, the unicortical set screws may be inserted, starting with the proximal screw. It is crucial not to fully tighten the proximal screw until the guide is aligned with the tibial spine. Once the guide is aligned with the tibial spine, the proximal screw can be tightened, and the distal hole can be drilled.

Subsequently, the sawing guide is positioned and firmly secured with the set screws. The saw is then carefully aligned adjacent to the patellar tendon. The sawing procedure proceeds from the proximal end to the distal end, focusing on preserving the integrity of the lateral cortex and proceeding approximately 50% of the distance to the posterior cortex without violating it. Furthermore, retracting and shielding the distal portion of the patellar tendon is recommended during the proximal sawing process.

In cases where the tendon is excessively broad, as seen in this particular instance, it is advisable to remove the guide and use the outrigger to prevent any accidental removal of the medial aspect of the tendon. The outrigger should be carefully aligned with the medial border of the tendon while ensuring it does not breach the medial cortex. Following the lateral sawing, we verify that the lateral cortex remains intact and has not been breached. Finally, the cuts are completed using a sagittal saw and osteotome. For the transverse proximal cut, it is important to extend the 2 vertical cuts just above the tibial tubercle while protecting the patellar tendon. The cut can be performed either freehand or with the assistance of the designated Army-Navy retractor to accommodate the osteotome. After completing all the cuts, the bone wedge is released with careful and gentle maneuvering using the osteotome. Finally, the bone wedge can be unhinged.

For anteriorization, the distal periosteum can be preserved and left intact, while the detachment and elevation are limited to the proximal portion. Following the clearance of debris from the bone bed, bone chips or alternative bone graft materials can be added until the desired anteriorization is achieved.

We have acquired cancellous bone from the distal region and transplanted it to the proximal area, packing it as needed to achieve a slight anteriorization of 4 to 5 mm, thus eliminating the necessity for additional bone grafting. However, to reach our target correction of 8 to 10 mm, we must introduce bone graft into the defect. In this demonstration, Play-Doh serves as the bone graft material. The bone graft is positioned over the prepared bone bed to restore the desired correction of an 8-mm anteriorization. If required, a guide pin can be inserted for further reference and alignment.

To achieve distalization, the bone wedge is unhinged, and the tip is shortened with a rongeur. To fit the shortened wedge into the bone defect, the distal kerf is widened using a sagittal saw to accommodate the trimmed bone wedge. Subsequently, the bone pedicle is repositioned and pushed distally until the desired level of distalization is attained and the gap is filled using a bone graft. We can see that the desired 10-mm distalization was achieved without anteriorization or medialization. Lastly, a combined approach involving both anteriorization and distalization can be employed by integrating both techniques and positioning bone grafts as needed. The ultimate fixation is established by using 2 bicortical headless compression screws and suturing both the periosteal sleeve and the pilled anterior compartment. Notably, the patellar tendon area remains untouched to minimize the risk of contractions, enabling the fat pad to seal the gap.

The following case is of a 15-year-old healthy, active girl with aspirations of playing softball, who has a history of recurrent patellar dislocations following a failed MPFL reconstruction 1 year ago. She presents with no obvious effusion, apprehension with medial patellar deviation at 60°, a subtle J-sign, no lateral retinaculum tightening or fixed patellar tilt, and good knee range of motion. The radiographs show a good leg alignment and an increased patellar height with a CDI of 1.4. Magnetic resonance imaging shows a mild lateral patellar subluxation and tilt, and a computed tomography scan shows a tibial tubercle-trochlear groove (TT-TG) distance of 15 mm and no major rotational abnormalities. We identified the MPFL insufficiency and increased patellar height as the main contributing factors resulting in patellofemoral instability and therefore planned a TTO distalization and MPFL reconstruction.

Results

As TTO is rarely an isolated procedure, any concomitant procedures should be taken into consideration during postoperative rehabilitation. Generally, patients are permitted to bear a maximum of 10% of their body weight for 4 to 6 weeks, using crutches while also maintaining an immediate full passive range of motion as tolerated. Typically, a hinged knee brace is worn for 6 weeks, initially locked at −10° of extension, followed by gradual brace weaning with transition to a sleeve. During postoperative rehabilitation, physical therapy can begin using closed-chain kinetic movements as tolerated once the patient is weightbearing. Final approval by the surgeon should be attained before return to running or other plyometric movements.

Discussion/Conclusion

In conclusion, the MD3T system employs a unique wedge technique that enables accurate and consistent correction in multiplanar alignment during TTO. It allows for precise anteriorization and distalization while preserving both cortices and eliminating the need for extensive stripping of the anterior compartment, thereby reducing the risk of catastrophic iatrogenic neurovascular injuries, and may result in reduced postoperative pain and accelerated rehabilitation. Compared to classical anteriorization and distalization techniques, the MD3T system is a modular, precise, reproducible, and teachable technique that simplifies the intricacies associated with this complex surgery, allowing surgeons to reconstruct favorable biomechanics and establish a solid groundwork for achieving optimal clinical outcomes, thereby ensuring the best possible results for their patients.