Abstract
Background:
Patellar instability is a common clinical condition in skeletally immature individuals. Surgical treatment is considered when risk of recurrence is high.
Indications:
Distal femoral osteotomy is indicated in the setting of obligate flexion dislocation where femoral valgus contributes to a shortened lateral column, with concurrent quadriceps procedures considered for chronic contracture and medial patellofemoral ligament (MPFL) reconstruction for added stabilization.
Technique Description:
This procedure is performed in a stepwise manner as some components may not be necessary based on the patient’s specific anatomy. The procedure begins with a lateral iliotibial (IT) band soft tissue release or lengthening if possible. The distal femoral osteotomy is then performed utilizing a lateral opening wedge technique. Bone graft is placed in a structural fashion to maintain the correction while a locking plate is inserted. In patients with chronic lateral patellar dislocation, correction of bony alignment may not completely restore tracking. If lateral maltracking persists after further distal soft tissue release, a VY-lengthening quadricepsplasty can be considered. To perform this, the vastus lateralis (VL) is first released. In this patient, the patella was able to be stabilized centrally after VL release, and therefore, the VY-plasty was not performed. The soft tissue attachments for the final MPFL reconstruction are then prepared, including two at the superomedial and midbody of the patella and one at the adductor tendon. The whip-stitched graft is then passed through the adductor sling followed by the patellar periosteal tunnels with the knee in slight flexion to ensure centralization within the trochlear groove. Examination under anesthesia before final fixation of the reconstruction should demonstrate 1A lateral translation.
Results:
Correction of distal femoral valgus with osteotomy, in isolation or in combination with other patellar stabilizing procedures, has demonstrated significant improvement in patient-reported outcomes and reduced redislocation rates. However, large cohort studies are limited.
Discussion/Conclusion:
Both osseous and soft tissue abnormalities are important to consider in since they can contribute in varying degrees to patellar maltracking. Therefore, assessment of patellar tracking should be performed frequently to guide extent of surgical correction necessary.
This is a visual representation of the abstract.
Video Transcript
This presentation covers the surgical treatment of flexion patellar dislocation after a limb-lengthening procedure in associated valgus. The authors’ disclosures are listed here and are also available online.
In general, the risk of patellar instability is significantly higher in young active and skeletally immature patients. This risk of instability increases with soft tissue laxity, as well as osseous deformity that can increase the lateral force vector on the patella. There are different treatments for this depending on which components are contributing the most in a given case, in this setting there is significant valgus that resulted after a leg-lengthening procedure. Keeping in mind the different soft tissue reconstructions that we perform for patellar stabilization, it is important to understand the anatomy including the medial patellofemoral ligament (MPFL) which has an osseous insertion on the patella, as well as the medial quadriceps tendon-femoral ligament (MQTFL) which has a soft tissue attachment proximally.
There are different length changes here; in the MPFL, osseous insertion is the primary restraint to lateral translation. However, the MQTFL insertion does play a secondary role and can also benefit from reconstruction when you are trying to spare the osseous insertion in a young patient. If we then look at the relevant femoral anatomy, we know that the MPFL insertion sits between the medial epicondyle in the adductor tubercle, and if you are performing an adductor tubercle-based reconstruction due to sparing the open growth plates, this can be done with adductor sling looped around the adductor tendon, which is slightly proximal to the native insertion. If we look at this relative to Schöttle’s point, we can see the point cloud here in red is the MPFL insertion on average where the blue point cloud is the adductor tubercle. As we bring in the lines that are associated with Schöttle’s point, we can see that this does change the overall length relationships as well as the anisometry where you have a slightly higher risk of increasing the overall tension in flexion when you do an adductor-based reconstruction.
Therefore, these should be allowed to range fully during the surgical reconstructions so that you don’t over constrain at any single degree of knee flexion. There is also variation in the native MPFL insertion or attachment point on the femur based on age, with it being slightly more distal in patients younger than 7 years old to the physis, and sometimes proximal to the physis as patients get older, however it frequently will cross the physis.
Our specific patient is an 11-year-old girl with Maffucci syndrome. She had initially leg length discrepancy of 7 cm. She underwent a femoral osteotomy with PRECICE (NuVasive; San Diego, CA) nail placement and medial figure 8 plates on the distal medial femur. She then had worsening valgus deformity due to her native distal femoral valgus that was then accentuated as she underwent femoral lengthening. On physical examination, she ambulated on the ball of her foot and had an externally rotated tibia, she had clinically a significant amount of valgus which we will show on examination, and had difficulty fully straightening her knee after her lengthening procedure.
Here, we can see that as we try to straighten her leg and bend it, her patella has an obligate flexion dislocation that is irreducible in flexion. She gets closer to being able to be reduced in full extension when the soft tissues are relaxed. When we then look at this from a coronal plane, we can see the significant valgus that is happening about the knee with the associated lateral patellar dislocation and flexion. When we look at her examination with active extension on the left leg, we see that she can clearly straighten her leg and that her foot is neutral and has a normal thigh foot progression angle. Due to her patellar dislocation in flexion, this inactivates her quadriceps as it does not have an appropriate fulcrum and it also externally rotates her tibia as it pulls the entire extensor mechanism to the lateral side of the knee.
When looking at her imaging, she still has open growth plates, we can see the prior nail that was placed for her lengthening, we use a combination of long leg alignment films, as well as advanced imaging with computed tomography (CT) scans and reconstructions from the hip to the ankle to see that she had significant distal femoral valgus with associated compensatory proximal tibial varus. She likely has some component of dysplasia that is difficult to determine based on her baseline deformity, as well as normal patellar height. Her valgus measures at approximately 11° and has a limb length discrepancy secondary to this deformity.
When we take all of these factors into account, she has multiple concerning and not concerning factors, and the most concerning factors are her leg length discrepancy and associated valgus which then causes the flexion dislocation. With a plan to treat this with the distal femoral osteotomy, a physeal-sparing MPFL reconstruction, as well as quadriceps release, is needed. See Table 1.
Pearls and Pitfalls of Surgical Treatment for the Obligate Flexion Dislocator
DFO, distal femoral osteotomy; IT, iliotibial.
Here, we performed our lateral approach including a significant lateral release, which has still not allowed the patella to track centrally throughout flexion where it laterally still dislocates. We then planned the distal femoral osteotomy, where we place our first guide pin distally almost parallel to the joint axis, and the proximal pin is placed perpendicular to the femoral cortex. These 2 pins, then after the osteotomy is complete, should be parallel to have proper alignment.
We then use an oscillating saw to cut parallel to each of these pins for the planned partial opening and partial closing osteotomy. Before we complete the osteotomy, we place an external fixator across our guide pins so that we can use this to get the appropriate amount of correction and prevent movement in multiple planes.
Once we have a free fragment where we can close the osteotomy down, we then use this as a combination for impacting the bone as well as closing the lateral cortex. We use plate benders to modify the distal femoral lateral plates to match the anatomy of the patient, and we slide this in a submuscular technique proximally where we will use a near-near, far-far configuration for screws in a standard AO configuration.
Once we have the plate and place and we verify that our correction is adequate, we see here the bovie cord being placed through the hip and the ankle and we can see this just at the lateral tibial spine. After this has been verified and we have fixed our plate, we then check the patellar tracking, and we see that there is still significant lateral translation of the patella as seen here, where it is essentially fixed lateral.
We then release the patellar tendon and the fat pad beneath it distally to the tibia to make sure that there is no distal contracture that is limiting the motion. The patient still would not track centrally, and we planned for VY quadriceps lengthening with here our lateral lengthening prepared so that we can close the lateral retinaculum at the finish of the surgery.
First, we released the vastus lateralus which tends to be the most tense portion of the quadriceps mechanism in this setting, and we see that the patella can actually be stabilized centrally now throughout flexion and extension without any issue. Because of this, we did not have to perform the complete VY quadricepsplasty, and we only lengthened the vastus lateralus.
Here, we perform our approach for a soft tissue sling of the MPFL reconstruction without any osseous anchors. We are planning an adductor sling on the femur and periosteal sling on the patellar portion. We make 2 small soft tissue tunnels where we place passing stitches for the semitendinosus graft to be passed. We then use fluoroscopy to try to localize the area closest to Schöttle’s point, that is also over the adductor tubercle to determine an appropriate area of isometry. We then whip-stitch the graft on either end and bring this through the soft tissue sling that we created over the adductor tubercle in the adductor tendon and then subsequently bring this back up through the patellar soft tissue sleeves, where we then tie this down to itself, as well as the adjacent periosteum. This is done with the knee in slight flexion, so that it can engage in the trochlea taking care to not over medialize or over constrain the patella. Once we have temporary sutures placed, we checked lateral patellar translation, and make sure the patient has at least 1A lateral translation. Here, we can see the 2 free ends now being overlapped on each other for final fixation. Here are temporary sutures that are being placed prior to checking our final examination under anesthesia.
After this is completed, we now see that there is 1 quadrant of lateral translation with about 2 quadrants of medial translation, and the patella is easily staying central throughout flexion and extension. We then place our final nonabsorbable sutures through the periosteum on the patellar side for final fixation of the graft, as well as now closure of the vastus lateralus and the lateral lengthening that was performed. We do this in flexion to make sure that this does not tighten throughout flexion if we fix it in extension.
Here is our final examination under anesthesia after the vastus lateralus lengthening, as well as the lateral retinaculum have been repaired. We make sure that she has full easy range of motion. We then check to see if the iliotibial (IT) band needs lengthening which was done in a standard step cut configuration due to the amount of valgus correction that we performed.
Postoperative rehabilitation after the surgery is range of motion as tolerated immediately after surgery, protected weight bearing for the first 6 weeks in a brace locked out in extension at that time, and then elimination of the protected weight bearing as well as the brace after 6 weeks, pushing hard to get full range of motion with the most significant complication here being stiffness or arthrofibrosis requiring a manipulation under anesthesia.
The outcomes of patellar instability treated with distal femoral osteotomy are very limited; however, they have shown improvement of clinical outcomes as well as decreased redislocation rate even without the reconstruction of the medial soft tissues.1,2
Here are listed references that we use throughout the talk.
Thank you very much.
Footnotes
Submitted August 21, 2021; accepted November 4, 2021.
One or more of the authors has declared the following potential conflict of interest or source of funding: M.P.F. and E.H. disclose education costs from Medwest Associates. A.B.Y. discloses personal fees from CONMED Linvatec, personal fees from JRF Ortho, personal fees from Olympus, grants from Organogenesis, non-financial support and stock or stock options from Patient IQ, non-financial support from Smith & Nephew, non-financial support from Sparta Biomedical, grants from Vericel, grants from Arthrex, Inc., and Aastrom Biosciences Inc., outside the submitted work. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.
