Lateral Opening Wedge Distal Femur Osteotomy and Medial Patellofemoral Ligament Reconstruction for Recurrent Patellar Instability

Abstract

Background:

A uniplanar, varus-producing distal femur osteotomy (DFO) may improve patellar tracking by effectively medializing the tibial tubercle, decreasing the Q-angle, and reducing the dislocation vector on the patella.

Indications:

A 17-year-old female with 8° of genu valgum presented with 18 months of symptomatic left knee patellar instability episodes that limit her function.

Technique Description:

A lateral subvastus approach to the distal femur was performed. Medial patellofemoral ligament reconstruction (MPFL-R) was conducted up to the point of femoral-sided graft fixation. A lateral opening wedge DFO was made with a sagittal saw and osteotomes, with care taken to maintain the medial cortical hinge. After distraction of the osteotomy site and femoral head allograft wedge placement, the osteotomy was secured with a lateral distal femoral locking plate. Finally, femoral-sided graft fixation for the MPFL-R was completed.

Results:

There were no immediate complications after surgery. Surgical management led to improvement of the patient's patellar instability, which allowed return to the prior baseline level of function.

Discussion/Conclusion:

The senior author's preferred technique for a lateral opening wedge DFO in association with an MPFL-R is presented. A varus-producing DFO is a surgical option for patients with genu valgum and recurrent patellar instability who have failed conservative management. This case demonstrates the efficacy of a lateral opening wedge DFO in improving patellar tracking and improving knee function by resolving recurrent patellar instability episodes.

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

In this video, we will discuss the indications, surgical technique, and outcomes for a lateral opening wedge distal femur osteotomy (DFO) for recurrent patellar instability.

Here are our disclosures.

The following topics will be covered in this video.

We will utilize a case presentation to demonstrate the indications for a lateral opening wedge DFO. Our patient is a 17-year-old female who presented with 18 months of left knee patellar instability episodes and worsening patellofemoral knee pain and apprehension, which limited her physical activities. She had attempted extensive physical therapy and brace utilization without success. On examination, she had clinically apparent valgus alignment of the bilateral lower extremities. She demonstrated patellar tenderness and marked apprehension. The patella was noted to engage the trochlea at 70° of knee flexion. She also notably had a positive “jumping J-sign.”

Radiographs were acquired, which were largely normal. She was measured to have a Caton-Deschamps index of 1.05. Radiographs demonstrated the presence of Dejour type C trochlear dysplasia.

Full-length lower extremity radiographs were also acquired, which demonstrated coronal malalignment, with the mechanical axis of the left lower extremity extending into the lateral compartment of the knee.

Left knee magnetic resonance imaging subsequently demonstrated bony edema consistent with a patellar dislocation, trochlear dysplasia, lateral patellar subluxation, a tibial tubercle to trochlear groove (TT-TG) distance of 22 mm, and a patellar tendon–lateral trochlear ridge (PT-LTR) distance of 14 mm. The PT-LTR distance reflects the vectors that pull the patella into lateral maltracking, and a value greater than 6.5 mm is abnormal. ²

Based on the patient's clinical symptoms of recurrent patellar instability and genu valgum deformity present on examination and imaging, she was determined to be a candidate for surgical intervention consisting of a left knee arthroscopy with possible shaving chondroplasty, a medial patellofemoral ligament reconstruction (MPFL-R), and a lateral opening wedge DFO. The senior author's indication for performing a lateral opening wedge DFO for a patient with recurrent patellar instability is ≥7° of excess valgus malalignment and/or a lateral distal femoral angle less than 83°. A DFO decreases the Q-angle and reduces the dislocation vector on the patella. In addition, although the TT-TG distance was greater than 20 mm, a concomitant tibial tubercle osteotomy was not felt to be indicated as a DFO effectively corrects the TT-TG by 7 to 10 mm.^5,6 Other relevant contraindications to our proposed surgical plan would have included a normal or varus mechanical axis, medial or tricompartmental osteoarthritis, or severe osteoporosis.

Based upon preoperative templating, shown here, an 8° correction was planned to shift the mechanical axis of the left lower extremity so that it falls 62.5% of the way into the medial compartment, per the senior surgeon's preference. ⁴

Requisite materials for the lateral opening wedge DFO are listed here, as well as materials for the other concomitantly planned procedures. Tranexamic acid and regional anesthesia are utilized to perform this procedure on an outpatient basis. The patient is positioned supine on a radiolucent operating room table. We use a thigh tourniquet to reduce bleeding intraoperatively.

After an examination under anesthesia and arthroscopy are performed, a lateral subvastus approach to the distal femur is made. Perforating vessels are ligated carefully and adequate exposure is obtained for eventual osteotomy and lateral plate fixation. Next, an MPFL-R is begun utilizing the technique described by Moran et al. ³ The entirety of the MPFL-R is outside the scope of this technical article, but relevant points about performing this procedure concomitantly with a DFO will be highlighted.

After the ends of the graft have been passed between layers 2 and 3 of the medial side of the knee, Schottle's point is identified fluoroscopically, a Beath pin is placed, and then subsequently overreamed. Notably, the trajectory of the Beath pin is made posterior and proximal to avoid the eventual osteotomy site and future screw trajectory. A nitinol guidewire is placed and remains in the tunnel created. This later serves as a radiographic landmark to avoid convergence with screw fixation of the DFO. In addition, a FiberLink (Arthrex Inc, Naples, Florida) suture is passed through the tunnel on the Beath pin to serve as a visual cue to screw-tunnel convergence if disturbed.

On the back table, a femoral head allograft is prepared to allow for the indicated correction. The wedge is measured to correct approximately 1 mm for 1° at its central point and then tapered with care to match the patient's anatomy.

Next, the osteotomy is planned with the knee positioned in full extension with the extremity in neutral rotation. Flexion of the knee is avoided at this time, despite the benefit of increased distance to neurovascular structures, to avoid inducing a flexion deformity upon later fixation of the osteotomy site. Two, parallel 2.0-mm Kirschner wires (K-wires) are placed under fluoroscopic guidance aiming obliquely toward the medial epicondyle. The K-wires should not intersect the nitinol wire of the MPFL tunnel. In addition, the posterior K-wire should be placed parallel or slightly distal to the anterior K-wire to avoid making a cut in flexion. With blunt Hohmann retractors placed anteriorly and posteriorly to protect the surrounding structures, a 40-mm sagittal saw is used to make the cut along the pins under fluoroscopic guidance to maintain an appropriate orientation and trajectory of the cut, and to ensure a cut depth of approximately two thirds of the width of the femur. A broad, flat, 10-mm osteotome from the Tomofix pan is then used to complete the anterior and posterior cortical cuts while care is taken to leave the medial cortical hinge intact. A Tomofix distractor (DePuy Synthes, West Chester, Pennsylvania) is introduced and opened slowly to reach the desired coronal plane correction and avoid disruption of the medial cortical hinge. With a lamina spreader placed anteriorly to hold the correction, the previously fashioned allograft wedge is inserted to match the shape of the femur in the osteotomy site at a preferentially posterior position to, again, avoid inducing a flexion deformity. Additional cancellous chips may be added, as well.

Next, a 4-hole Tomofix plate (DePuy Synthes) is applied to the distal femur, with appropriate plate placement confirmed fluoroscopically before acquiring provisional fixation. Ideally, the MPFL femoral tunnel will be posterior to the Tomofix plate. Appropriately sized locking and cortical screws are placed distally and proximally, respectively. At this point, special attention is directed to the nitinol wire radiographically, as well as the wire and FiberLink suture clinically, to ensure no visual evidence of screw-tunnel convergence exists. Any convergence at this point can be mitigated by changes to the screw length or trajectory, and will ensure a successful concomitant MPFL-R. Final fluoroscopy is then taken with anteroposterior, lateral, and notch views of the distal femur to ensure appropriate screw lengths.

Finally, the graft ends are pulled through the tunnel using the FiberLink passing stitch placed prior to the osteotomy. The graft is then fixated with a 7 × 23 mm Mitek Milagro Advance interference screw (DePuy Synthes) under approximately 0.5 pounds (2 N) of force while the knee is maintained in 40° of flexion to maintain the patella centrally within the trochlea.

A final examination is performed to ensure the osteotomy site is stable with passive range of motion and that patellar tracking is stable and normal.

Some of the more notable potential complications of a DFO are listed here, and include nonunion or malunion, fracture or disruption of the medial cortical hinge, instrumentation failure, neurovascular injury, arthrofibrosis, and symptomatic hardware.

We restrict and gradually advance patient's weight bearing status for the first 8 weeks after surgery. A hinged knee brace is used to prevent flexion beyond 90° for the first 2 weeks postoperatively, but range of motion restrictions are removed after this point. We allow patients to return to sports after 19 to 24 weeks postoperatively, after they complete a sport-specific return to play protocol.

There is a relative scarcity of reports of clinical outcomes in the literature with lateral opening wedge DFO for addressing recurrent patellar instability in patients with genu valgum. Swarup et al, ⁵ however, reported clinical and radiographic outcomes of 8 cases with a mean follow-up time of 27 months. No knees demonstrated recurrent patellar instability and the authors reported durable radiographic and functional improvement. ⁵ In another series of 11 cases published by Wilson et al, ⁷ the authors reported no recurrent instability events in 8 of the 11 knees at a mean follow-up of 4.25 years. In addition, the authors also reported overall radiographic and functional improvement in their study population. ⁷ It is notable that medial closing wedge osteotomies have also been reported for producing a relative varus alignment to address recurrent patellar instability in patients with genu valgum. ¹ Given the scarcity of reports of lateral opening wedge DFOs in the literature for this indication, further study is recommended to evaluate the outcomes of this procedure for this indication.

From the Department of Orthopaedic Surgery at the University of Virginia, we thank you for watching.

Our references are listed here.