Combined Unicompartmental Knee Arthroplasty and Trochlear Porous Calcium Carbonate Scaffold Implantation: Surgical Technique

Abstract

Unicompartmental knee arthroplasty (UKA) has emerged as a relatively joint-preserving option for younger, active patients with advanced osteoarthritis (OA) isolated to the medial or lateral compartment. The indication for UKA is more controversial in patients with mixed multi-compartment disease, that is, advanced knee OA in a single compartment coexisting with more focal disease in a separate location, most frequently the trochlea. Whereas some surgeons advocate ignoring patellofemoral compartment disease and proceeding with UKA, others are more cautious and indicate total knee arthroplasty (TKA) because of concerns that untreated defects in another compartment may lead to suboptimal outcomes. Because surgeons often have different age and activity thresholds for indicating UKA versus TKA, some patients are limited to—often ineffective—conservative care because the extent of disease is deemed too great for UKA yet they are considered too young for TKA. CartiHeal Agili-C (Smith & Nephew, Andover, MA), a porous calcium carbonate scaffold made from coral, promotes cartilage regeneration and offers an off-the-shelf biologic solution for osteochondral repair. It has received Food and Drug Administration approval for the treatment of degenerative defects in early OA. Combining UKA with CartiHeal Agili-C implantation offers the potential to preserve more of the native joint in patients with mixed multi-compartment disease.

Symptomatic knee osteoarthritis (OA) is a growing concern in the United States, affecting an estimated 14 million individuals.¹ Although traditionally considered a degenerative condition of older adults, knee OA is becoming more prevalent in younger, active patients, with one study suggesting that nearly 2 million individuals younger than 45 years and an additional 6 million individuals aged between 45 and 64 years are affected.1, 2, 3 This demographic shift has increased total knee arthroplasty (TKA) procedures in patients younger than 60 years.

TKA remains the standard surgical intervention for end-stage tricompartmental OA.⁴ However, concerns regarding implant longevity, higher risk of revision surgery, and decreased satisfaction with functional outcomes limit its indication in younger, more active patients. Additionally, up to 20% of patients report dissatisfaction after TKA, often owing to residual pain and functional limitations.⁴ These challenges highlight the need for more joint-preserving approaches, specifically in younger, active individuals with a well-preserved contralateral compartment but with more focal cartilage disease in the trochlea, which may present at least a relative contraindication to unicompartmental knee arthroplasty (UKA).

UKA has emerged as an option for patients with medial or lateral unicompartmental OA. Compared with TKA, UKA offers improved restoration of knee function, a higher quality of life, and a faster return to sport and work, particularly in the early months after surgery.^5,6 Additionally, a patient-reported outcome measure, the Forgotten Joint Score, indicates that individuals undergoing UKA are more likely to perceive their knee as “natural” compared with those receiving TKA.⁷ Investigators have reported that a significant portion of TKA patients could potentially have been treated with UKA instead.⁸ Although the ultimate decision is up to the treating surgeon, trochlear disease may push one toward TKA instead of UKA because it may contribute to persistent pain and functional impairment (Fig 1).

Fig 1.

Preoperative magnetic resonance imaging scans of the right knee of a patient with activity-related medial knee pain, positioned supine with knee extended. (A) Sagittal view demonstrating advanced medial compartment osteoarthritis. (B) Axial view revealing focal grade IV trochlear defect. Arrow in figure 1A is pointing to advance medial compartment OA. Circle in 1B is the trochlear defect.

The standard of care frequently labels the joint as a whole to be affected by either diffuse arthritis or focal chondral disease, and treatment decisions are based on this assessment. The 2 senior authors (S.S., A.G.) have been applying a more compartment-specific approach for patients in our arthroplasty practice, who are presenting at younger ages, frequently with mixed multi-compartment disease. In such patients, one compartment may be pristine whereas another shows advanced arthritic changes. The third compartment, if intact, makes for an easy indication for UKA, whereas advanced arthritic changes require TKA. The challenges lie in cases that have more focal cartilage defects that, if found in isolation, would be indicated for cartilage repair.

Traditional cartilage restoration techniques, such as matrix-induced autologous chondrocyte implantation (MACI) and osteochondral allograft transplantation (OCA), are established for the treatment of focal chondral and osteochondral defects in otherwise intact knees.⁹ MACI is less favorable for patients with chronic defects with subchondral sclerosis and edema because they may be susceptible to delayed graft integration and diminished long-term durability.⁸ OCA, the gold standard for larger osteochondral defects, is challenging in the trochlea because of the complex trochlear shape, with significant person-to-person variability complicating graft matching and circumferential flush placement. Additionally, OCA graft integration requires successful creeping substitution, and failure of incorporation remains a concern.¹⁰ Moreover, OCAs have a limited shelf life, and grafts not used within 30 days are generally discarded. Neither MACI nor OCA is generally recommended for the treatment of arthritic joints.

The CartiHeal Agili-C implant (Smith & Nephew, Andover, MA), a porous calcium carbonate scaffold derived from coral exoskeleton, has evolved as a promising option for the treatment of focal chondral lesions. Its ability to support cartilage regeneration, even in a degenerative environment, has expanded its application beyond focal cartilage defects to knees with early arthritis, as supported by the results of the Food and Drug Administration trial that led to its approval.¹¹ CartiHeal Agili-C is indicated for the treatment of one or more full-thickness (International Cartilage Regeneration & Joint Preservation Society grade III or IV) chondral lesions, with a total treatable area of 1 to 7 cm².^12,13 The implant is available as a 7.5-mm-diameter and 10-mm-long plug and requires at least 3 mm of surrounding bone for optimal integration. Surgeons can use multiple plugs to address long and narrow defects, thus preserving adjacent cartilage.^13,14 Given the promising trial data for the treatment of degenerative lesions, the senior authors have started to use this implant in conjunction with UKA in their compartment-specific treatment of mixed multi-compartment disease in patients who are not easily indicated for TKA because of age or activity level.

This article describes a surgical technique for the treatment of medial or lateral unicompartmental OA using the MAKOplasty system (Mako SmartRobotics; Stryker, Kalamazoo, MI) for robotic-assisted UKA, as well as focal trochlear chondral disease using concurrent implantation of CartiHeal Agili-C (Fig 2).

Fig 2.

Illustration of the right knee in an anterior view, depicting medial unicompartmental OA and an isolated trochlear defect

Surgical Technique

Diagnostic arthroscopy is performed, and the trochlear lesion is visualized, in addition to diffuse grade IV medial compartment changes (Video 1). Given the involvement of the medial and patellofemoral compartments, a medial parapatellar arthrotomy is made.

Unicompartmental Knee Arthroplasty

The patella is displaced laterally, and checkpoints are registered with the MAKOplasty system (Fig 3). The medial femoral condyle and medial tibial plateau are prepared with a burr, and any remaining osteophytes and meniscal tissue are removed. Trial components (Mako SmartRobotics) are placed, and the knee is taken through a full range of motion with axial load and varus stress, showing excellent component tracking and stability. The trial components are removed, and the final UKA components (Mako SmartRobotics) are cemented. Excess cement is removed; an appropriately sized polyethylene insert (Mako SmartRobotics) is placed, and the knee is kept near full extension while the cement sets. The tourniquet is released, and hemostasis is achieved using Bovie electrocautery (Bovie Medical, Clearwater, FL).

Fig 3.

Key steps of the MAKO-assisted UKA of the right knee, with the patient positioned supine and the knee flexed to 90^▫, visualized through the anteromedial surgical approach. (A) Trackers are placed, and registration is performed. (B) Femoral and tibial surfaces are prepped. (C) Trial components are placed, and stability is checked. Once determined to be satisfactory, trials are removed, and final cemented UKA components are placed. (D The knee is taken through a final range of motion, and proper gap balancing is checked.¹⁶

CartiHeal Agili-C Implantation

A cannulated perpendicularity aligner (Smith & Nephew) is used to place a cannulated pin at the desired implant position and advanced into the bone until the indicator line reaches the proximal end of the aligner (Figs 4 and 5). The aligner is removed, leaving the K-wire in place. Next, a drill sleeve (Smith & Nephew) and cannulated reamer (Smith & Nephew) are placed over the K-wire. The reamer is advanced until it bottoms out against the drill sleeve, which acts as a depth stop. The reamer and drill sleeve are removed, and bone reamings are irrigated away; the K-wire remains in place. Then, a cannulated end reamer (Smith & Nephew) is advanced by hand until the indicator line is no longer visible from all sides, ensuring a depth of 12 mm from the articular surface.¹⁵ In locations with thick cartilage, such as the central trochlea, the end reamer can be used to slightly increase the depth so that the plug seats deeper, allowing its superficial surface to align with the subchondral plate. The end reamer is removed, and the defect is irrigated with saline solution. A cannulated shaper (Smith & Nephew) is inserted over the K-wire and manually rotated clockwise until the indicator line is no longer visible from all sides and no significant resistance remains. This reshapes the cylindrical drill hole into a conical shape to fit the implant. Finally, a cartilage cutter (Smith & Nephew) is used to debride the edges of the lesion to remove flaps that could become caught in the interface during implant introduction. The CartiHeal Agili-C implant is placed by hand in the defect, with careful attention paid to implant orientation. By use of a combination of a padded tamp and finger pressure, the implant is seated in its final position approximately 2 mm below the articular surface to allow for cartilage regeneration superficial to the implant. In the example presented, 2 CartiHeal Agili-C implants are placed into the defect, leaving a 5-mm bone bridge between the plugs.¹³

Fig 4.

The cannulated reamer is placed over the K-Wire in the right knee, with the patient positioned supine and knee flexed to 90^▫, visualized through the anteromedial portal and the end cutter is rotated clockwise until the indicator line is level with the articular surface.

Fig 5.

(A) The Cartiheal Agili-C shaper is inserted over the K-wire in the right knee, with the patient positioned supine and knee flexed to 90^▫, visualized through the anteromedial portal and manually rotated clockwise until the indicator line is level with the articular surface. The K-wire is removed. (B) The cartilage cutter is used to debride the defect to a stable rim.

The arthrotomy is closed in 30° of flexion with No. 0 Vicryl sutures (Ethicon, Somerville, NJ). The skin is closed in a layered fashion with absorbable sutures, followed by placement of a running Monocryl stitch (Ethicon) and Dermabond tape (Ethicon). A sterile compressive dressing is applied (Figs 6 and 7).

Fig 6.

The Cartiheal Agili-C implant is manually inserted into the defect of the right knee, with the patient positioned supine and knee flexed to 90^▫, visualized through the anteromedial portal, gently using finger pressure until flush with the articular cartilage. (A) A tamp is used to carefully advance the implant to its final position (B) 2 mm below the surface of the articular cartilage to allow for fibrocartilaginous overgrowth.

Fig 7.

Intraoperative arthroscopy photos of the right knee, with the patient positioned supine and knee flexed to 90^▫, visualized through the anteromedial portal, demonstrating Cartiheal Agili-C placement. (A) Unprepared grade IV trochlear defect. (B) Placement of the Cartiheal Agili-C implant into the distal aspect of the defect. (C) Final positioning of two Cartiheal Agili-C implants in the trochlear defect, demonstrating a 5 mm bone bridge between implants. Upon insertion, blood infiltrates the interconnected scaffold pores.

Postoperative Rehabilitation

The patient is allowed weight bearing as tolerated and uses an assistive device as needed for the first 2 weeks postoperatively. The patient is permitted full range of motion, with a goal of 110° of flexion during weeks 2 to 5. Balance training and stair negotiation are introduced as strength and control improve, allowing a gradual return to daily activities (Figs 8 and 9).

Fig 8.

Postoperative lateral radiograph patient positioned supine and knee extended, demonstrating excellent placement of the UKA components. The Cartiheal Agili-C implants, circled in blue, can be seen in the trochlear region.

Fig 9.

Post-operative magnetic resonance imaging scan of the right knee, with the patient positioned supine and knee extended, displaying the intervening space filled with reparative tissue. Arrow in figure 9 is pointing to cartiheal plug.

Discussion

The combination of CartiHeal Agili-C implantation and UKA offers a compartment-specific approach for younger, active patients who present with clear end-stage disease in one compartment indicated for arthroplasty and more focal chondral disease in a separate compartment that is amenable to repair. The presence of this secondary defect may make some surgeons consider TKA instead of UKA—a potentially suboptimal approach in younger patients who may require one or more revisions in the future. UKA has been shown to improve general function and health outcomes and reduce postoperative pain and complications compared with TKA.¹⁶ CartiHeal Agili-C provides a single-stage, off-the-shelf solution, bypassing the challenges associated with autograft harvest while being more cost-effective than cartilage restoration techniques, such as OCA and MACI.^17,18 However, the approach has limitations because there is limited literature on the short-, mid-, and long-term outcomes of concomitant trochlear CartiHeal Agili-C implantation, especially when used concurrently with UKA (Tables 1 and 2).

Table 1.

Pearls and Pitfalls

Pearls

Contrary to the autograft mosaicplasty technique, the implants should be spaced approximately 5 mm apart. The intervening space will fill with reparative tissue.

The UKA rehabilitation protocol does not need to be altered when combined with CartiHeal Agili-C implantation in the trochlear region.

Immediate range of motion should be encouraged.

Pitfalls

The surgeon should ensure that the CartiHeal Agili-C plugs do not converge at the base of the plug. If two plugs converage, they can break when inserted.

The surgeon should ensure adequate spacing of plugs. The implant requires intact bone to completely surround the plug on all sides to provide access to bone marrow.

UKA, unicompartmental knee arthroplasty.

Table 2.

Advantages and Disadvantages

Advantages

This technique avoids the need for TKA in a young, active patient with medial or lateral compartment OA and a concomitant focal trochlear osteochondral defect.

CartiHeal Agili-C is more cost-effective than OCA or MACI.

Disadvantages

There are no short-, mid-, or long-term studies on the combined use of CartiHeal Agili-C and UKA for the treatment of medial or lateral compartment OA and a concomitant focal trochlear osteochondral defect.

MACI, matrix-induced autologous chondrocyte implantation; OA, osteoarthritis; OCA, osteochondral allograft transplantation; TKA, total knee arthroplasty; UKA, unicompartmental knee arthroplasty.

Disclosures

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: A.H.G. reports a consulting or advisory relationship with Bioventus, JRF Ortho, Moximed, Organogenesis, Smith & Nephew, and Vericel; receives nonfinancial support from JRF Ortho, Organogenesis, Smith & Nephew, CartiHeal, Hyalex Orthopaedics, and Miach Orthopaedics; receives travel reimbursement from JRF Ortho; owns equity or stocks in Moximed; receives speaking and lecture fees from Vericel, Linvatec Europe, and Pacira Therapeutics; reports board membership with Arthroscopy Association of North America, Cartilage, International Cartilage Regeneration & Joint Preservation Society, Knee Surgery, Sports Traumatology, Arthroscopy, and Orthopedic Journal of Sports Medicine; has received royalties or licensing fees from Organogenesis; has received honoraria from Joint Restoration Foundation and Vericel; has received hospitality payments from Pacira Therapeutics, Bioventus, CartiHeal, DePuy Synthes Sales, Joint Restoration Foundation, Linvatec, Miach Orthopaedics, Organogenesis, and Smith & Nephew; and has received acquisitions from Smith & Nephew. S.M.S. reports a consulting or advisory relationship with Bioventus, Miach Orthopaedics, Moximed, Smith & Nephew, and Vericel; receives nonfinancial support from Miach Orthopaedics, Smith & Nephew, JRF Ortho, American Journal of Sports Medicine, CartiHeal, Hyalex Orthopaedics, and Organogenesis; owns equity or stocks in Moximed, Smith & Nephew, Engage, and Stryker Orthopaedics; receives speaking and lecture fees from Smith & Nephew and Vericel; receives travel reimbursement from Smith & Nephew and JRF Ortho; reports board membership with Arthroscopy Association of North America; has received honoraria from Joint Restoration Foundation and Vericel; and has received hospitality payments from Bioventus, CartiHeal, DePuy Synthes Sales, Joint Restoration Foundation, Linvatec, Miach Orthopaedics, Organogenesis, Pacira Therapeutics, Smith & Nephew, and Vericel. All other authors (H.L.T., J.S.R., A.G.N.) declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Supplementary Data

Video 1

This video shows a combined surgical technique of right knee unicompartmental knee arthroplasty and Cartiheal Agili-C implantation.