Assessment of Patellar Vascularity after Patellar Cartilage Restoration via Lateral Parapatellar Approach: Analysis Using Dynamic Contrast-Enhanced Magnetic Resonance Imaging

Abstract

Objective

Patellofemoral cartilage restoration procedures, including osteochondral allograft, particulated juvenile cartilage, and matrix-induced autologous chondrocyte implantation, have been shown to be effective treatments for patellofemoral cartilage lesions. However, concerns exist regarding disruption of the patellar vascular supply and secondary stabilizers of the patellofemoral joint during medial parapatellar approaches, especially when combined with a lateral release. A lateral parapatellar approach affords the possibility of avoiding disruption of the medial blood supply to the patella, while also allowing laterally-based soft tissue stabilization procedures. The purpose of this study was to investigate in vivo changes in patellar vascularity following patellofemoral cartilage restoration procedures performed via a lateral parapatellar approach via use of dynamic contrast-enhanced magnetic resonance (MR) imaging.

Design

This study is a prospective case series of 5 adult patients undergoing patellofemoral cartilage restoration procedures via a lateral parapatellar approach with pre-operative and post-operative dynamic contrast-enhanced MR imaging to assess changes in patellar vascularity. Secondary outcomes included knee range of motion, need for revision surgery, and complications.

Results

There was no significant post-operative difference in patellar vascularity in patients undergoing patellofemoral cartilage restoration procedures via a lateral parapatellar approach, as evaluated by qualitative MR imaging.

Conclusion

Our results suggest that a lateral parapatellar approach for cartilage restoration procedures may preserve patellar vascularity, while also allowing for lateral release to be performed through the same incision.

Keywords

patellofemoral vascularity lateral parapatellar cartilage restoration

Introduction

Patellofemoral instability is a common cause of anterior knee pain in young patients and may be associated with underlying trochlear and/or patellar cartilage defects.^1
-4 In the absence of underlying cartilage defects, bony realignment procedures (i.e., tibial tubercle osteotomy [TTO]) and soft tissue stabilization procedures (i.e., medial patellofemoral ligament reconstruction [MPFLR]) are effective surgical treatments, which may be performed without the need for arthrotomy.^1,2,5 However, cartilage restoration procedures, including osteochondral allograft (OCA), matrix-induced autologous chondrocyte implantation (MACI), and particulated juvenile cartilage (DeNovo®, Zimmer Biomet; Warsaw IN) implantation, require creation of an arthrotomy to access the articular surface of the patellofemoral joint.^1
-3,6
-10 Classically, these procedures are performed via a medial parapatellar approach, which allows access to underlying cartilage lesions and placement of the MPFLR graft through the same incision.

However, several studies have raised concerns regarding disruption of patellar vascularity in the setting of medial parapatellar arthrotomy, which may affect proper healing following cartilage restoration procedures.^11
-14 The predominant patellar vascular supply enters the patella inferomedially, such that a medial parapatellar arthrotomy risks disrupting the supreme genicular, superior medial genicular, and inferior medial genicular arterial supply ( Fig. 1 ).^11
-14 This has been proposed as a major contributing factor to the development of anterior knee pain post-operatively following total knee arthroplasty (TKA).¹³ Moreover, preserving the medial blood supply becomes especially important in the setting of concomitant lateral release, as this may risk injury to the remaining lateral patellar vascular supply. In addition, primary medial stabilizers of the patellofemoral joint, including the vastus medialis muscle, quadriceps mechanism, medial patellofemoral ligament (MPFL), and medial patellar retinaculum, are often violated during the medial parapatellar approach.^15
-17

Figure 1.

Schematic demonstrating relevant patellar vascular anatomy.

In an effort to minimize these risks, a lateral parapatellar approach has been described in TKA and patellofemoral arthroplasty (PFA), as it avoids disrupting the medial stabilizers and preserves the medial blood supply to the patella.¹⁷ Several studies have compared the effect of various TKA surgical approaches on patellar vascular supply. Gelfer et al.¹⁸ compared pre-operative and post-operative bone scans in patients undergoing TKA via either midvastus or medial parapatellar approach, demonstrating similar rates of transient patellar ischemia with both approaches. Importantly, these findings were independent of the concomitant use of a lateral release. These findings were supported by a later study by Bourke et al.,^19,20 who also demonstrated no significant difference in patellar vascularity between subvastus versus medial parapatellar approaches for TKA. To our knowledge, similar studies have not been performed in patients undergoing patellofemoral cartilage restoration, and there is a paucity of data on in vivo patellar vascular changes after lateral parapatellar arthrotomy. Animal models have suggested less disruption of soft tissue perfusion and local blood flow about the knee following lateral parapatellar arthrotomy compared with a medial-based approach²¹; however, these results have not been corroborated in human samples.

The purpose of this study was to describe qualitative changes in patellar vascularity following patellofemoral cartilage restoration procedures performed via a lateral parapatellar approach using dynamic contrast-enhanced (DCE) magnetic resonance (MR) imaging. We hypothesized that there would be no significant change in pre-operative to post-operative patellar vascularity in patients undergoing patellofemoral cartilage restoration via a lateral parapatellar approach.

Methods

Participants

Before study initiation, institutional review board approval was obtained at our institution (Study 2015-671). Eligible patients were prospectively identified from a single surgeon’s clinical patient population between November 2018 and September 2020. Eligibility criteria included patients aged 18 to 50 years who were diagnosed with patellofemoral instability, with increased tibial tubercle to trochlear groove (TT-TG) distance with associated patellar cartilage defect, and indicated for a combined TTO, medial patellofemoral ligament (MPFL) reconstruction (with or without lateral release), and patellar cartilage restoration (OCA, MACI, or particulated juvenile cartilage). Patients were excluded from the study if they had undergone previous knee surgery or if the patient had reduced kidney function or kidney failure that precluded administration of intravenous contrast. Once patients were identified as eligible subjects, informed consent was obtained. A total of 5 patients were enrolled in the study. Each patient underwent pre-operative magnetic resonance angiography (MRA) prior to surgery, followed by a second MRA between 3 and 6 months post-operatively.

Imaging

Dynamic contrast-enhanced magnetic resonance imaging

DCE MR imaging is utilized for the assessment of perfusion of blood into tissues. This is performed by acquiring a series of image volumes over time as the contrast agent is administered and circulates toward, perfuses into, and subsequently washes out of the tissue of interest. To this end, a bolus of gadolinium contrast is administered several phases (image volumes or “frames” acquired at regular temporal intervals) after the pulse sequence has begun. This enables the establishment of a baseline signal intensity in the tissue of interest. Provided perfusion occurs (i.e., the blood supply to the tissue is intact), the contrast agent will cause the signal intensity of the tissue to rise. This change in signal intensity is quantified as the enhancement ratio, E,

E = \frac{S_{t} - S_{0}}{S_{0}},

where S_t and S₀ are the signal intensities of a voxel or region of interest at a given timepoint and at baseline, respectively. Qualitatively, regions that are unperfused or poorly perfused see little, if any, enhancement (i.e., low E), and regions that are well perfused become markedly enhanced (high E). In addition, the time history of the enhancement ratio throughout the MR acquisition can be evaluated to observe if perfusion occurs but venous return is insufficient—E rises and plateaus—or, when perfusion occurs and normal venous return is present—E rises, peaks, and gradually declines as the contrast agent is “washed out” of the tissue.

DCE imaging protocol

Coronal DCE imaging of the patellae was performed using a LAVA-FLEX pulse sequence (GE Healthcare, Waukesha, WI). The scan parameters were as follows: slice thickness = 1.8 to 2.6 mm; slice spacing = 0.9 to 2.0 mm; Matrix = 256 × 128 or 256 × 160; echo time (TE) = 1.608 to 2.564 ms; repetition time (TR) = 4.482 to 12.820 ms; field of view = 12 to 25 cm; slices = 30 to 84; phases (frames) per acquisition = 26 to 45. Following the first 3 phases of image acquisition, a patient-weight-based bolus (mL/kg) of gadolinium contrast (Gadavist™ (gadobutrol); Bayer, Whippany, NJ) was administered manually via venous line (at forearm or elbow) started prior to imaging, followed by 20 mL of saline to clear the line and ensure administration of the entire bolus. All imaging was performed on either GE Discovery MR750 (3.0T) or GE Optima MR450/MR450W (1.5T) MRI scanners (GE Healthcare) utilizing standard patient positioning (supine) and 8-channel knee coils.

DCE analysis

Images were imported into a proprietary DCE Analysis software tool, previously developed by colleagues at an affiliate institution using the Interactive Data Language (IDL; ITT Exelis, McLean, VA).²² Following calculation of the temporal resolution of the imagesets, regions of interest (ROIs) were placed coinciding with the superomedial, superolateral, inferolateral, and inferomedial quadrants of a slice in which the largest cross-section and time histories of the enhancement of the ROIs were generated.

Surgical Technique

A standard anterolateral arthroscopic viewing portal was created, followed by a standard anteromedial instrument portal made under direct visualization. Diagnostic arthroscopy was carried out to identify and assess the patellofemoral cartilage, medial and lateral compartment cartilage, cruciate ligaments, menisci, and any additional intra-articular pathology. Debridement was carried out when necessary.

Attention was then turned to the arthrotomy. A lateral parapatellar approach was utilized via 5-cm incision just lateral to the lateral border of the patella, extending from 1 cm superior to the proximal pole of the patella to 1 cm inferior to the distal pole ( Fig. 2A ). Sharp dissection was carried down to the level of the iliotibial band (ITB) fascia and retinaculum, which was then incised in line with the skin incision. The interval between the IT fascia and the underlying capsule was developed ( Fig. 2B ), followed by creation of capsular arthrotomy ~2 cm lateral to the ITB fascial incision, to allow for lateral lengthening or primary repair.

Figure 2.

(A) Clinical photograph demonstrating a 5-cm lateral parapatellar incision for arthrotomy and a 1.5-cm medial incision for femoral fixation of the medial patellofemoral ligament reconstruction graft. (B) Intraoperative photograph demonstrating lateral parapatellar dissection, with the interval developed between the lateral retinaculum (grasped in forceps) and the underlying capsule (*) prior to creation of the lateral arthrotomy. (C) Eversion of the patella for cartilage restoration procedures through the lateral parapatellar arthrotomy.

Next, the patella was retracted laterally and the interval between the medial capsule and medial retinaculum was identified with sharp dissection, for tunneling of MPFL graft. Care was taken to limit surgical exposure to the proximal ½ of the medial patella to avoid disruption of the primary vascular supply entering inferomedially. Electrocautery was used to remove soft tissue from the superior 50% of the medial patella to create a bony bed for the MPFL graft. Two 1.8-mm Q-fix anchors (Smith & Nephew, Andover, MA) were placed at the midpoint of the patella and 6 to 8 mm proximal to the midpoint. The midpoint of the MPFL hamstring allograft was then laid into the bony bed, and the sutures from the Q-fix anchors were tied over the midpoint of the graft. The two ends of the hamstring graft were then whipstitched together with #2 Fiberwire (Arthrex, Inc., Naples, FL) for later fixation into the femoral socket.

Next, the patella was everted via the lateral parapatellar arthrotomy, and the base of the patellar chondral defect was debrided with a scalpel and sharp curettes to a rim of normal cartilage and a healthy bony base ( Fig. 2C ). Patients received 1 of 3 different cartilage procedures: (1) MACI, (2) particulated juvenile cartilage implantation, or (3) OCA. For those patients undergoing MACI, the graft was cut to size using a foil mold and secured into the defect with fibrin glue. For those patients undergoing particulated juvenile cartilage implantation, the defect was filled and the graft was also secured into the defect with fibrin glue. For those patients undergoing OCA, the defect was sized and reamed from patellar allograft and tamped into place. Cartilage restoration procedures were performed after TTO and prior to MPFL fixation.

Next, attention was turned to the tibial tubercle osteotomy. A 5-cm anterolateral incision over the proximal tibia along the lateral border of the tibial tubercle was made. A shingle was then cut, moving the tibial tubercle anteromedially, and in some cases distally in patients with patella alta, based on pre-operative imaging. A periosteal flap was raised and left attached distally to cover the distal aspect of the osteotomy. All osteotomies were fixed with two 4.5 fully threaded screws placed via lag by technique. Fluoroscopy was used to confirm the screw length.

Next, a 1.5-cm incision was made just posterior to the medial epicondyle for femoral fixation of the MPFL hamstring graft. A guide wire was drilled under fluoroscopy at the insertion point of the MPFL, and isometry of the MPFL graft was checked through range of motion (ROM) from 0° to 60°, with appropriate loosening of the graft beyond 60° of knee flexion. The MPFL graft was fixed to the insertion point with a 7.0 × 23-mm tenodesis screw (Arthrex, Inc.). If no lateral lengthening was required, the capsular arthrotomy and ITB fascia/retinaculum were closed. If a lateral lengthening was required, the medial leaflet of the capsular arthrotomy was closed to the lateral leaflet of the ITB fascia/retinaculum.

Follow-Up

The participants underwent standard-of-care follow-up, including a 1-week virtual appointment and in-person visits at 6 and 12 weeks post-procedure. Participants underwent a follow-up MRA 3 to 6 months after the operation to assess qualitative changes in patella vascularity compared with pre-operative MRA.

Post-Operative Rehabilitation Protocol

Post-operatively, patients were placed in a hinged knee brace in the recovery unit. Use of the CyMedica Evive brace (CyMedica Orthopedics, Inc., Tempe, AZ) with integrated muscle stimulator was recommended to patients to help regain quadriceps strength immediately after surgery and throughout their recovery. For the first 4 weeks following surgery, patients maintained the brace locked in full extension while walking, but were allowed to unlock the brace for ROM exercises as tolerated, with the goal of full extension and 90° of flexion by 2 to 3 weeks post-operatively. Patients were instructed to sleep with the brace locked in extension for the first 2 weeks. Formal physical therapy began 1 week after surgery, with a focus on increasing quad and hamstring strengthening via closed chain exercises, patellar mobility, and ROM. Patients began to transition to full-weight bearing at 4 to 6 weeks following the procedure. After this point, patients were encouraged to increase their strength, stability, and ROM as tolerated under the supervision of their therapist.

If MACI or particulated juvenile cartilage implantation procedures were performed, use of a continuous passive motion device was recommended, beginning at 0° to 30° for the first week and 0° to 60° for the second week, with progression as tolerated after 2 weeks. If distalization was performed with the TTO, the patients postponed all weight-bearing timelines by 2 weeks and restricted their ROM to 0° to 90° for the first 4 weeks.

Results

A total of 5 patients underwent pre-operative and post-operative knee MRA with DCE MR imaging protocols. A summary of their surgical procedures is included in Table 1 . Average age was 30.4 years (±8.7 years; range: 27-44 years). All included patients were female and there were 3 left knees and 2 right knees. The average interval between surgery and post-operative MRA was 4.8 months (range: 3-6 months).

Table 1.

Summary of Patient Demographics and Surgical Procedures.

Subject	Age (Years)	Sex (Male/Female)	Laterality (Left/Right)	Surgical Procedure(s)	Interval From Surgery to Post-Op MRA
1	27	Female	Left	MPFLR, TTO, lateral lengthening, trochlear OCA, patellar particulated juvenile cartilage implantation	6 months
2	33	Female	Left	MPFLR, TTO, patellar MACI	3 months
3	44	Female	Right	MPFLR, TTO, patellar MACI	5 months
4	27	Female	Left	MPFLR, TTO, patellar MACI	6 months
5	21	Female	Right	MPFLR, TTO, trochlear OCA, patellar MACI	3 months

MRA = magnetic resonance angiogram; MPFLR = medial patellofemoral ligament reconstruction; TTO = tibial tubercle osteotomy; OCA = osteochondral allograft; MACI = matrix-induced autologous chondrocyte implantation.

In 1 of the 5 patients, an injection and imaging timing malfunction precluded the analysis of the pre-operative images. Qualitative comparison of the 4 quadrants of a central paracoronal slice (in anteroposterior direction) in the pre- and post-operative DCE MRI of the remaining 4 knees revealed no discernable detriment to vascularity in 3 of the 4 knees ( Fig. 3 ). Monotonic uptake and plateau were observed in these cases in all quadrants with peak enhancement ranging from 0.4 to 1.6 (signal intensity: 1.4-2.6x baseline). Of note, in the patient with the pre-operative imaging/injection error, there was typical post-operative uptake similar to the other 3 patients described above.

Figure 3.

(A) Proton density–weighted MRI of the patella with overlay of approximate patellar quadrants as used for perfusion analysis in this study. (B) Time history of enhancement and accompanying curve fits. 1.0x enhancement means intensity at time t is 2x the intensity at baseline. Baseline intensity (not shown) is established in first 5 phases of LAVA acquisition. SM = Superomedial; SL = superolateral; IM = inferomedial; IL = inferolateral.

One case demonstrated reduced perfusion in all 4 quadrants, with the inferomedial quadrant demonstrating no quantifiable uptake of the contrast agent. The superomedial quadrant saw the smallest decline in quantifiable perfusion (among quadrants in this patella).

At average clinical follow-up of 1.2 years (range: 0.5-2.2 years), all 5 patients demonstrated excellent ROM of the operative knee, with all patients achieving full extension to at least 130° of flexion. There were no post-operative complications. Three patients (60%) underwent elective hardware removal of tibial tubercle osteotomy screws at an average of 9.5 months post-operatively (range: 6-12 months). There were no other subsequent procedures performed in these patients.

Discussion

This study aimed to further clarify the in vivo effect of lateral parapatellar arthrotomy on the vascularity of the patella in the setting of patellofemoral cartilage restoration procedures. Qualitative MR imaging data from this study supports the use of a lateral parapatellar arthrotomy in the setting of patellofemoral cartilage lesions without significant compromise to patellar vascularity.

There are several limitations to this study. First, the small sample size limits the generalizability of our results, although the vast majority of patellofemoral cartilage lesions do occur in young female patients, which is representative of our sample. Second, truly quantitative analysis of these results (i.e., rate of enhancement, area under the curve (AUC)) is not possible, due to the manual administration of contrast during the MR imaging and varying scan durations tailored to each patient. However, the authors believe that qualitative comparison to pre-operative perfusion trends does provide insight into the existence of iatrogenic compromise to patellar vascularity. In addition, the noise floor of the LAVA sequence used corresponded to approximately ± 0.075 enhancement, as demonstrated in the non-enhancing region (inferomedial quadrant) of the patient exhibiting reduced perfusion. Each of the patients included in the study underwent concomitant soft tissue and bony procedures in addition to cartilage restoration via lateral parapatellar arthrotomy, which may also affect patellar vascularity. Specifically, a small incision over the medial femoral condyle is required for fixation of the femoral limb of the MPFL graft. Importantly, dissection near the patella is carefully limited to the proximal half of the patella to minimize disruption of distal vascular supply. In addition, the authors prefer use of 1.8-mm cortically based all-suture anchors, to limit risk of disrupting the intraosseous patellar blood supply. Although this is not our preferred technique, the use of a partial thickness quadriceps autograft may also minimize this risk, as it avoids use of suture anchor fixation. Finally, the post-operative MR imaging was performed between 3 and 6 months following surgery, which limits the ability to assess changes in vascularity beyond this post-operative window. However, the primary concern with performing lateral parapatellar arthrotomies is disruption of the vascular supply at the time of surgery, such that any anticipated changes in vascularity would be expected to present on MR imaging within this timeframe. However, the authors also recognize the possibility of revascularization during this post-operative window as an inherent limitation.

To our knowledge, this is the first study to attempt to describe in vivo changes in patellar vascularity using MR imaging after lateral parapatellar arthrotomy in patients undergoing patellofemoral cartilage restoration procedures. Several studies have utilized MR imaging to evaluate patellar vascularity. Lazaro et al.¹¹ utilized quantitative and qualitative MR imaging in a cadaveric model to evaluate the effect of transverse patella fractures on patellar vascularity. The authors demonstrated that the dominant blood supply to the patella entered via the inferior pole in all cadaveric specimens, with the largest arterial contribution entering from inferomedial in 80% of specimens. The authors suggest that care should be taken during standard medial parapatellar arthrotomy, which may place this dominant blood supply at risk. These findings were corroborated in a subsequent study by Lazaro et al.,¹³ in which standard medial parapatellar arthrotomy performed for total knee arthroplasty in cadaveric specimens often violated the medial arterial blood supply to the patella. This becomes especially important in patellar cartilage restoration procedures, which rely upon neovascularization of the implanted grafts (among other factors) for appropriate healing. To our knowledge, similar studies have not been performed in the setting of cartilage restoration procedures, which typically requires a smaller medial arthrotomy; however, dissection distal and proximal to the patella is often required for adequate visualization and patellar eversion for cartilage restoration, which may place these important vascular structures at risk.

Lateral parapatellar arthrotomy, although technically more demanding, provides an alternative method for accessing the patellofemoral joint, with the possible benefit of preserving the medial vascular supply to the patella. Kocak et al.²¹ utilized a rabbit model to compare the effects of medial parapatellar, midvastus, subvastus, and lateral parapatellar arthrotomies on local soft tissue perfusion about the knee. The authors demonstrated that a lateral parapatellar arthrotomy resulted in the least impaired soft tissue perfusion and lowest oxidative stress about the knee compared with the other medial-based arthrotomy techniques. To our knowledge, similar results following lateral parapatellar arthrotomy have not been reported in human samples.

Previous in vivo studies have investigated the effect of lateral release on patellar vascularity, with varying results. Several studies have utilized pre-operative and post-operative scintigraphy to evaluate the effect of lateral release on patellar vascularity following total knee arthroplasty, demonstrating that the addition of lateral release may be associated with short-term patellar hypovascularity, although the association with post-operative outcomes and complications is unclear.^23
-26 Importantly, these patients all underwent TKA via standard medial parapatellar approach in addition to lateral release, thereby risking violation of both the medial and lateral vascular supply to the patella. Nicholls et al.²⁷ compared the effects of medial and lateral parapatellar arthrotomy on patellar vascularity using intraoperative laser Doppler flowmetry, demonstrating a trend toward less disruption of patellar vascular supply with lateral parapatellar arthrotomy, although this difference was not statistically significant. The authors do suggest that lateral parapatellar arthrotomy may provide an advantage in patients requiring lateral release, as it prevents disruption of the medial blood supply. In addition, a laterally based arthrotomy may limit distal sensory loss compared to a medial incision, due to avoidance of traversing infrapatellar branches of the saphenous nerve.

A thorough understanding of the patellar vascular anatomy is essential to preserving adequate patellar blood flow during patellar cartilage restoration procedures. With the predominant blood supply to the patella entering from the medial aspect of the patella, the use of a lateral parapatellar approach affords the advantage of preserving patellar vascularity, avoiding branches of the infrapatellar branch of the saphenous nerve, and allowing for lateral release to be performed through the same incision. This study demonstrates no significant post-operative qualitative differences in patellar vascularity in patients undergoing patellofemoral cartilage restoration procedures via a lateral parapatellar approach, as evaluated by qualitative MR imaging. Further research is required to directly compare the quantitative effect of medial and lateral parapatellar approaches on patellar vascularity in the setting of cartilage restoration procedures and their effect on cartilage implant healing and clinical outcomes.

Footnotes

Authors’ Note

Investigation performed at the Hospital for Special Surgery, New York, New York.

Acknowledgments and Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Declaration of Conflicting Interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: Tyler J. Uppstrom, MD, Ryan E. Breighner, PhD, Connor Fletcher, BD, and Douglas N. Mintz, MD, declare that they have no conflict of interests. Sabrina A. Strickland MD has investment holdings in Engage & Stryker, is a paid consultant for Smith & Nephew and Vericel, and receives royalties and research funding from Vericel.

Ethical Approval

This study was approved by the Hospital for Special Surgery Institutional Review Board.

ORCID iDs

Tyler J. Uppstrom

Connor Fletcher

Sabrina Strickland

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