Patient-Specific Custom Patellofemoral Arthroplasty

Abstract

Background:

Patellofemoral arthroplasty (PFA) can be done with a number of devices that implement both inlay and onlay designs. Recent innovations in custom instrumentation allow for a new class of PFA that can precisely match the variable trochlear morphology.

Indications:

Patients with severe patellofemoral arthritis and preserved tibiofemoral joint space who had conservative treatment that has failed may benefit from PFA.

Technique Description:

A medial parapatellar arthrotomy of roughly 10 cm is used to evert the patella for visualization of the patellofemoral cartilaginous surfaces. An oscillating saw cut is performed while carefully preserving at least 12 mm of patellar bone. Three drill holes are made for future implantation of the patellar surface. Next, attention is turned to the trochlea, where any remaining cartilage is removed with a curette, with care taken not to remove any subchondral bone. A custom drill guide is then placed on the trochlea for 3 drill holes, followed by auxiliary holes with a drill bit for cement interdigitation. The wound is copiously irrigated and dried before cement is applied to the trochlea. The custom trochlear implant is carefully malleted in place, and excess cement is removed around the edges. Cement is then applied to the patella before similar implantation of the patellar implant. The medial parapatellar arthrotomy is then closed and a lateral lengthening is performed. Full range of motion is checked for appropriate patellar tracking.

Results:

Implant survivorship is greater than 90% at 5 years and 83% at 10 years. With respect to patient-reported outcomes, Knee Society functional score improved from 49 to 89, and Knee Society objective score improved from 52 to 89. In a second study featuring 25 patients with a mean greater than 11 years of follow-up, no revisions were seen, with over 90% of patients able to return to sport.

Discussion/Conclusion:

Utilizing the patient's native anatomy with a new, custom groove allows for improved, nonpathologic patellar tracking, especially in dysplastic cases, as seen in this case. This method for PFA holds the potential for improved patient satisfaction and advancement of patient-specific care in arthroplasty.

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 Narration

Today we'll be talking about patient-specific custom patellofemoral arthroplasty (PFA).

All relevant disclosures are seen here.

Educational objectives are seen here.

PFA: how can we restore native anatomy?

Background

There are several types of PFA designs, and the first we'll mention is the onlay design. The traditional onlay comes in 4 sizes and has the advantages of replacing damaged subchondral bone. This design has the disadvantages of requiring a significant amount of bone removal and being a larger implant, thus leading to more difficult revisions.

The inlay design traditionally comes in 3 sizes and is fit for a large array of trochlear complexities. The advantages of these designs over patient-specific instrumentation are that there is no customization process, so the implant is readily available. A disadvantage is that even with the wide array of trochlear convexities, the trochlea may not match the native bony anatomy, requiring removal of bone.

Research has compared inlay to onlay component performance. In a matched-pair comparison of inlay and onlay trochlear designs for PFA, the authors evaluated postoperative outcomes and arthritis progression. The authors found no significant differences in clinical outcomes between inlay and only designs. They did, however, find that over half of the onlay cohort progressed to tibiofemoral arthritis, compared to zero patients in the inlay cohort. ¹

There are several other technical considerations when performing component positioning. When using intramedullary guides, a flexed trochlear component increases the risk of patellar catching during flexion. This is true for an extended intramedullary guide as well. Larger components have the risk of overstuffing the patellofemoral joint, causing abnormal contact forces and the sensation of having a “fuller” knee. In onlay designs that remove underlying subchondral bone, there is the risk that too much bone may be removed. ¹

In response to these issues, patient-matched implants were created. These are designed for each patient's native osseous anatomy. They have the advantage of having no bone removal, and the patient-specific anatomic matching allows for ideal patellar tracking. The specific component design process means there is a delay to the operating room, allowing for the components to be manufactured. These implants also require advanced imaging, including 3-dimensional (3D) reconstruction computed tomography (CT) scans.

Patient-specific matched trochleas come in all shapes and sizes, designed to optimize patellofemoral tracking and minimize bone loss.

Accompanying each patient-specific implant is a customized guide, with a wide array of options seen here.

These guides come with saw bone models matched to patient-specific anatomy, allowing surgeons to reproduce guide placement on the saw bones before instrumentation in the patient.

Next, we will go through several cases to show the diversity of PFA implantation.

Indications

We have 3 patients. The first is a young female with a complex surgical history with persistent pain and a history of patellofemoral symptoms. The second is a middle-aged woman with a history of recent trauma and pain during flexion. Our final patient is an older man with a remote history of patella open reduction and internal fixation and worsening pain over the past 3 months.

The imaging for each patient is seen here.

The magnetic resonance images (MRIs) for each patient are also seen here. Most clinicians advise that preoperative MRIs should be obtained in all PFA candidates to ensure that medial and lateral tibiofemoral joint spaces are well preserved.

Plain radiographs reveal distinct anatomy in all 3 patients, including various degrees of arthritis.

The 3D anatomy of the trochlea is seen here in a 3D reconstruction CT.

It is translated into the 3D physical model.

This allows surgeons to predict precisely where to place the custom guide on the trochlear anatomy before instrumentation in the live patient.

Technique Description

The steps for PFA are seen here, beginning with a medial approach, with a skin incision of roughly 10 cm. Next, a medial parapatellar arthrotomy is performed with care taken to not disrupt the underlying cartilage or meniscal surfaces. We begin with a patellar cut utilizing a wide oscillating saw. Care is taken to preserve at least 12 mm of bone following the cut. Three drill holes are made next.

The trochlear guide is then placed on the saw bones model, then secured on the live patient. A drill bit is used to precut holes in the guide, and threaded pins are placed into the trochlea.

Using indelible marker followed by a scalpel, an outline for the trochlear guide is made on the underlying cartilage. The guide is then removed. The cartilage is sliced with a fresh blade for easy removal. Remnant cartilage is removed with a curette with care taken not to injure the subchondral bone. The wound is copiously irrigated. The guide is reapplied and drilled for cementation. The guide is removed, and the wound is irrigated once more. A drill bit is used to place holes in the trochlea for cement interdigitation. The trochlea is carefully dried and is now ready for cement application. Cement is applied to the trochlea and the pegs of the implant. It is carefully malleted into place, and any extra cement is removed carefully. Cement is then applied to the patella, and extra cement is removed. The medial parapatellar arthrotomy is closed, followed by a lateral lengthening. The closed incision is taken through full range of motion (ROM) to ensure appropriate patellar tracking.

Results

Finally, we will address postoperative care and outcomes following PFA.

For the first 6 weeks of rehabilitation, the goal is to protect the incision while allowing weightbearing as tolerated without any restrictions with respect to ROM. Patients wear a brace locked in extension until they are able to perform a straight-leg raise without any extension lag.

The next 6 weeks are highlighted by discontinuation of the brace and a gradual return to activities of daily living as tolerated.

After 3 months, there is a focus on strength with increasing overall activity as tolerated.

These radiographs depict initial postoperative images following patient-specific customized PFA.

Here, you'll note that the trochlear implant sits flush against the dysplastic bony trochlea, as custom implants are designed for no bony removal. Effectively, this combined with the patellar polyethylene button can make the knee appear and feel more full.

Utilizing the patient's native anatomy with their new, custom groove allows for improved, nonpathologic patellar tracking, especially in dysplastic cases seen here.

Implant survivorship is greater than 90% at 5 years and 83% at 10 years. Patients should be counseled that implant survivorship diminishes over time. ⁴

Implant survivorship is most commonly reliant to progression of tibiofemoral arthritis. ⁴

With respect to patient-reported outcomes, Knee Society functional score improved from 49 to 89, and Knee Society objective score improved from 52 to 89. ²

In a second study featuring 25 patients with a mean greater than 11 years follow-up, no revisions were seen, with over 90% of patients able to return to sport. ³

Discussion/Conclusion

In summary, patient-matched implants are an excellent option for treating isolated patellofemoral arthritis in patients with diverse anatomy. The surgical indications are paramount in determining patient success, and patella tracking postoperatively is an extremely important clinical factor in success.