Osteochondral solutions for cartilage lesions of the knee: a narrative review

Abstract

Background and Objective

Cartilage lesions of the knee occur frequently and can cause debilitating symptoms such as pain, swelling, locking, clicking, or catching. In some lesions, both the cartilage and underlying subchondral bone are affected, which may require treatment of both the osseous and cartilaginous units. The objective of this review was to assess the available evidence of advanced treatments for osteochondral lesions in the knee.

Methods

A literature search was conducted in the electronic databases of PubMed, Embase and Cochrane Library for a narrative review on studies reporting outcomes of osteochondral knee treatments. Studies were included if they reported outcomes at minimum 1-year follow-up and had minimum 5 patients, and biomechanical, translational and basic science studies were excluded.

Key Content and Findings

In addition to chondroplasty and microfracture, four major advanced osteochondral restoration procedures aimed at treating injuries to the osteochondral unit were identified in the literature, which consisted of surgical internal fixation of either acute osteochondral fragments or osteochondritis dissecans (OCD) lesions, osteochondral autograft transplantation (OAT), osteochondral allograft (OCA) transplantation and biphasic scaffold implantation. Internal fixation of acute osteochondral patellofemoral fractures has been found to have superior outcomes compared to fragment removal, but does require concomitant patellar stabilization. Fixation of OCD also leads to good outcomes without superiority for fixation method. Osteochondral autograft is an excellent treatment option for smaller defects and has a high rate of return to sport. OCA outcomes are excellent with good survival rates although reoperations can frequently occur. Finally, biphasic scaffolds are relatively recent and can be used in both more acute as well as more degenerative settings and the short-term outcomes are promising.

Conclusions

Osteochondral injury in the knee requires unique treatment options as both the underlying bone and cartilage need to be treated, due to their poor healing capacity and significant cause of morbidity. Several treatment options exist and the overall outcomes of these treatments are satisfactory in improving patient-reported outcomes, and most patients can return to activities.

Introduction

Background

Articular cartilage is a complex, biphasic biologic substance that is composed of both solid and liquid components (1). Articular cartilage is primarily made up of type II collagen, but also includes proteoglycans like aggrecan, as well as hyaluronic acid and water (1). Articular cartilage is highly organized, with four distinct layers, each with a unique structure contributing to a unique biomechanical function. Overall, this makeup provides it with the essential properties of load-distribution and joint lubrication (2). Articular cartilage has inherently poor regenerative capacity that is multifactorial in nature due to it being largely avascular, atrophic with a relatively small number of chondrocytes, and a contained intra-articular environment that can lead to localized inflammatory mediators after injury that all make healing a particular challenge (3).

Cartilage lesions of the knee are exceedingly common, with one study of 1,000 patients identifying these in 61% of patients, and a second study of 31,516 patients identifying cartilage lesions in 19,827 patients (4,5), making understanding their evaluation and management of paramount importance. These injuries can be a significant source of morbidity for patients of all ages and activity levels (6,7). While some osteochondral lesions can be asymptomatic, patients often present with pain, swelling, and mechanical symptoms (8). Further, presence of one or multiple lesions predisposes patients to increased likelihood of progression to osteoarthritis and significantly impact patient quality of life (9,10).

Rationale and knowledge gap

Due to the complex nature of cartilage lesions, their biomechanical and clinical consequences, as well as evolving treatment strategies, multiple algorithms to determine optimal treatment strategy have been presented (11,12). Techniques such as chondroplasty and microfracture have been the dominant surgical options to address these injuries. Chondroplasty aims to debride the lesion back to a stable edge with removal of the calcified layer and is typically utilized in cases of smaller lesions with variable outcomes (13-16). Microfracture involves drilling small holes within the subchondral bone to stimulate fibrocartilage formation and has been primarily used to address smaller lesions (8). While improvement in patient-reported outcomes has been demonstrated in short term studies (17), long term outcomes are generally disappointing, especially in cases of medium to large size lesions, older age, and with longer preoperative symptoms (18-21).

Beyond chondroplasty and microfracture, alternative treatment options exist for osteochondral injuries. These options include surgical fixation, which is often reserved for acute injuries, as well as osteochondral autograft transplantation (OAT), osteochondral allograft (OCA) transplantation, and non-cell-based scaffolds that promote regeneration at both the osseous and cartilage level (22,23). Although autologous chondrocyte implantation can be performed in some cases of osteochondral defects, such as osteochondritis dissecans (OCD), it remains outside the scope of this article as this mostly focuses on treatment of the entire bone-cartilage unit and is addressed in other reviews within this issue (8,24,25).

Objective

The goal of this study is to review the current literature on osteochondral injury of the knee, various modalities of treatment techniques, and their respective outcomes on patients. Additionally, we will attempt to review potential predictors of prognosis in association with each included intervention. We present this article in accordance with the Narrative Review reporting checklist (available at https://aoj.amegroups.com/article/view/10.21037/aoj-25-45/rc).

Methods

A literature search in the electronic databases of PubMed, Embase and Cochrane Library was conducted using the search terms: (‘aragonit*’ OR ‘agili-c’ OR ‘Osteochondral Implantation’ OR ‘Osteochondral Autologous Transplantation*’ OR ‘Osteochondral Autograft Transplantation*’ OR ‘OAT’ OR ‘Osteochondral Allograft Transplantation*’ OR ‘OCA’ OR ‘osteochondral fixation’ OR ‘osteochondral refixation’) AND (‘Femoral Condyle*’ OR ‘Tibial Plateau*’) on April 9, 2025 from inception to 2025. The title and abstract were independently reviewed for potential inclusion and exclusion by two reviewers (J.P.v.d.L. and E.F.). Then, the same two reviewers independently reviewed the full text of potential studies for inclusion in this narrative review.

Details of the specific search strategy are reported in Table 1. The most important osteochondral treatments for cartilage injury will be discussed, which involve acute osteochondral refixation, OAT, OCA and scaffold treatment. The procedures were assessed and reported for their common indications, surgical technique and outcomes.

Table 1. Search strategy summary for this narrative review.

Items	Specification
Date of search	April 9, 2025
Databases searched	PubMed, Embase, Cochrane Library
Search terms used	See Table S1
Timeframe	Inception–April 9, 2025
Inclusion criteria	Studies reporting outcomes on direct fixation of traumatic or osteochondritis dissecans lesions, osteochondral autograft or allograft transplantation, scaffold implantation
Exclusion criteria	Less than 1 year follow-up, less than 5 cases, autologous chondrocyte implantation, technique articles, review articles, biomechanical studies, animal studies, non-English studies
Selection process	Two assessors independently assessed title and abstract, and then independently reviewed full text. Consensus was reached by discussion and a third reviewer was consulted if needed

General considerations

In patients with cartilage injury, some overarching concepts always need to be considered. It is well-known that coronal, sagittal or axial knee malalignment can cause overload in the affected compartment that can compromise outcomes of cartilage treatments (26-33). Furthermore, ligament or meniscus deficiency (34-36) and overall joint health and systemic inflammation need to be considered in cartilage treatment (37,38), but this remains outside the scope of this study.

Chondroplasty

Indications

The most common surgical treatment for the management of cartilage injury is arthroscopic chondroplasty (39). This technique is typically used concomitantly with other procedures, or as a palliative option, as it is aimed largely at stabilizing the lesion and alleviating pain or mechanical symptoms. Still, chondroplasty can be a vital tool in the management of certain lesions. Some algorithms employ chondroplasty in cases of smaller lesions, without underlying osseous involvement, or in low demand individuals who otherwise would not be indicated for any other salvage measures (12,40). Others state that it can be used regardless of size or depth of lesion as a first line of treatment, as more advanced treatments often require an initial prior arthroscopy for planning purposes (13,14,41). Another instance in which it is frequently performed in which prolonged rehabilitation or weight bearing restriction is not feasible, such as in the case of athletes in mid-season (6).

Surgical techniques

Regardless of the device utilized in performing the chondroplasty, the technique involves debridement of the cartilage lesion, by removing diseased cartilage back to a stable border. Several methods have been described, however mechanical chondroplasty with the arthroscopic shaver and radiofrequency chondroplasty using electrocautery devices are the predominant methods.

Outcomes

Outcomes following chondroplasty alone for the management of cartilage defects have a wide range of outcomes. Studies assessing the effectiveness of chondroplasty have found that in 26% to 61% of patients, symptoms are persistent, and patients require future treatments at short- to mid-term follow-up (13,14,41). A systematic review of four studies demonstrated improvement in functional outcome measures across all included studies, though the quality of these studies was called into question by the authors (42). Specific to the use of radiofrequency chondroplasty, good outcome scores and low complication rates have been shown across studies (43). Finally, regarding the above indication for its use in athletes who wish to return to play, a study of National Football League players undergoing chondroplasty yielded a 67% rate of return to sport, however, at an average of 8.2 months (44). In terms of prognostic indicators, Anderson et al. demonstrated that sex, baseline outcome metrics, and degree of osteoarthritic changes all were factors that effected outcomes following chondroplasty (16).

Microfracture

Indications

Previously called the gold standard for management of cartilage lesions, microfracture remains a mainstay option in the treatment of cartilage lesions (45). Described initially by Steadman et al., microfracture involves causing injury to the bone beneath a cartilage lesion, stimulating the bone marrow to generate a fibrocartilage healing process (46). While historically utilized broadly, trends towards more narrow indications have emerged more recently. It is generally accepted that microfracture is indicated in middle to older aged individuals with smaller lesions (17,19,20,45).

Surgical techniques

The procedure typically begins with chondroplasty to expose the underlying osseous surface and stabilize the edges of the lesion. Similar to chondroplasty, various methods and tools have been described to complete the process of microfracture. Most often, an arthroscopic awl or pick is used to poke holes in the bone beneath the lesion. Holes should be placed 3–4 mm apart without breaking the subchondral bone plate between them. Fat emerging from the marrow cavity indicates the appropriate depth (2–4 mm) (45). Studies have reported on the high variation in specific techniques utilized in performing microfracture between patients, and how this may lead to difficult interpretation of results (47).

Outcomes

Improvements in patient reported outcomes have been reported with microfracture in both short and midterm follow up (48). Long-term studies are more mixed in results, with some reporting improvements in outcomes up to 17 years following surgery, but others noting more disappointing outcomes, especially in comparison to some of the other techniques available (20). In terms of prognostic factors, female sex, higher body mass index (BMI), and size >2 cm² have been shows to predict further cartilage loss and negative outcomes following microfracture (12). Finally, while age is typically sited as a factor in determining whether to treat with microfracture, Steadman et al. have demonstrated positive outcomes and increased activity levels following this procedure in adolescents as well (49).

Osteochondral fixation

Indications

Generally, two types of osteochondral injuries may require surgical fixation, which include acute traumatic osteochondral injuries and lesions secondary to OCD. Acute osteochondral injuries in the knee most commonly occur during patellar dislocation with a reported incidence of up to 76% in one study (Figure 1) (22). In OCD, most large unstable lesions that have failed nonoperative treatment will also require surgical refixation if feasible (11,50,51). Several treatment algorithms exist, but in general, acute surgical refixation is recommended for large (>1 cm²) unstable lesions that have minimal fragmentation with at least 3 mm of subchondral bone remaining (52).

Figure 1.

Images showing fixation of an osteochondral fracture of the lateral femoral condyle. (A) Arthroscopy shows the large defect of the lateral femoral condyle. (B) Arthroscopy confirms one large fragment for refixation. (C) The fragment is retrieved and is approximately 3.5 by 3 centimeters. (D) Lateral arthrotomy is performed and the defect is assessed and bottom of defect is debrided. (E,F) The fragment is positioned to its original position and fixated with five biocomposite screws.

Surgical techniques

Multiple techniques have been described across the literature, including bioabsorbable or metal screws and other devices. For metal screws, both headless compression screws as well as Herbert screws have been demonstrated (52,53). For the bioabsorbable devices, a mean of four nails is often utilized (54). Most of these techniques include a post-operative protocol with at least 6 weeks of non-weight bearing, though significant variability exists across described techniques as far as progression of weight bearing and return to sport protocols. Bioabsorbable screws have the disadvantage of potentially causing cyst formation or foreign-body reaction whereas metal screws often require second surgery to remove hardware (55).

Outcomes

Outcomes associated with each of these techniques have been generally positive when well-indicated. A systematic review of osteochondral fixation demonstrated improved patient-reported outcome measures (PROMs) across all techniques (51). Further, Perelli et al. conducted a study with 10-year follow-up of patients receiving OCD fixation via Herbert screws, cannulated screws and bioabsorbable screws, and found improvements in PROMs, with no significant difference based on type of fixation (56).

Various studies have also been conducted to compare osteochondral fixation to other modalities of treatment in the setting of acute patellar dislocation. Gesslein et al. compared fixation with removal of loose bodies and found significant improvements in all patient-reported outcome scores at a mean follow-up of 8.9 years (57). Similarly, Ehmann et al. showed comparable outcomes of acute fixation compared to autologous chondrocyte implantation (58).

Various complications have been reported with this treatment including hardware issues such backout and breakage, as well as hemarthrosis (56). In terms of risk factors, persistent patellar instability is independently associated with poor outcomes after acute osteochondral defect fixation in adolescents, which leads to the general recommendation to perform medial patellofemoral ligament reconstruction in the setting of primary osteochondral fixation (23,59).

Osteochondral autograft

Indications

Another option to address osteochondral injuries includes OAT, in which one or multiple osteochondral plugs are transplanted from a lesser weight-bearing region of the knee into the defect. This procedure is indicated in patients with osteochondral damage or symptomatic OCD lesions <3 cm² that involve subchondral bone loss and are unsalvageable for refixation (50). Further, multiple studies have reported it can be used to address lesions in both the patellofemoral and tibiotalar regions (60), making it a valuable technique to address more severe lesions in a multitude of locations throughout the knee. The treatment has been shown to provide a cost benefit compared to OCA but is limited by the size of lesion that can be treated, as well as donor-site morbidity (61).

Surgical techniques

Variations in surgical techniques for osteochondral autograft have been reported across the literature. OAT can be performed by obtaining a single plug (Figure 2) or in some cases, multiple plugs, typically referred to as mosaicplasty (62). Additionally, both forms of this procedure can be performed open or arthroscopically (63). It has also been studied as a useful supplement to OCD fixation (64), and alongside other augments such as platelet-rich plasma (65).

Figure 2.

Images showing treatment of osteochondral defect of the medial femoral. (A) Sagittal T1 MRI reveals pathology of both the cartilage and subchondral bone. (B) Arthroscopy confirms the lesion. (C) A medial arthrotomy is performed and the lesion is identified. (D) A 10-mm reamer is used to remove the affected cartilage and bone. (E) A 10-mm plug from the superolateral trochlea of the ipsilateral knee is placed into the prepared defect. (F) Follow-up sagittal PD with fat suppression MRI reveals incorporation of the plug at follow-up. MRI, magnetic resonance imaging; PD, proton density.

Outcomes

Outcomes following osteochondral autograft procedures have been studied extensively, both in isolation and compared to other procedures. In general, studies have noted improvements in patient-reported outcomes with good graft survival rates in short-, medium- and long-term follow-up with one study demonstrating a >60% survival rate at 15 years post-operatively, regardless of location in the knee (60,66). Similarly, a review evaluating surgical interventions for OCD management found that OAT led to improvement in all patient-reported outcomes assessed (67). Another study evaluating return to sport found patients undergoing OAT to have the fastest return to sport, with reported rates at 6.6 months post-operatively (68).

In comparison to microfractures, multiple large randomized controlled trials have demonstrated efficacy of OATs procedure. In the pediatric population, Gudas et al. conducted a randomized controlled trial revealing a 91% excellent or good healing in OATs at 4.2 years post-op compared to just 56% in the microfracture group (69). Solheim et al. conducted a similar randomized controlled trial on adults with similar results (20). Di Martino et al. compared OAT to autologous bone-cartilage paste for OCD and found significantly lower failure rates with OAT (70).

Several predictors of failure of OAT have been reported in the literature including older age, defects larger than 3 cm², obesity, and bipolar defects (62,71,72). Data on gender are conflicting with some studies reporting female gender (71) and others male gender (72) as a risk factor.

OCA

Indications

General indications for OCA include young active patients with focal full thickness osteochondral defects over 2 cm² (73). However, careful attention should be paid to patient factors that may result in a poor outcome such as BMI >35 kg/m², and current nicotine or chronic corticosteroid use (74-79). Location and defect size should also be considered and the potential need for concomitant osteotomies or meniscal transplantation (80,81). Predictors of failure of OCA also include larger defect size, prior knee surgery, older age, higher BMI, and bipolar defects (82). Traditionally, OCA of the patellofemoral joint has been considered difficult given the challenge to match the donor and recipient’s anatomy, but recent studies have shown comparable outcomes between autologous chondrocyte implantation and OCA (59,83,84).

Preservation techniques

Graft viability is imperative for a successful outcome and special attention should be paid to appropriate preservation and storage as this optimizes chondrocyte viability in the graft (85-87). Often, fresh nonfrozen grafts are available commercially in the United States through local tissue banks. However, these must be obtained in a timely fashion with the ideal harvest occurring within 24 hours and implantation within 28 days of harvest after storage in a nutritional medium at 4 to 37 ℃ (87). However, the Missouri Osteochondral Allograft Preservation System has been shown in-vitro to prolong the duration of chondrocyte viability with the benefit of storing at 25 ℃ (88-91).

Surgical techniques

Meticulous surgical technique is essential in OCA as precise placement is necessary to appropriately restore the congruity of the articular surface and maximize the integration and bone healing potential (92). Regardless of technique, an understanding of the biology of osteochondral grafts and incorporation is important to maximize successful implantation and graft incorporation.

The fragility of chondrocytes leaves them susceptible to mechanical and thermal injury during harvest or implantation that can lead to apoptosis and necrosis. This is most common around the margins of the graft at the time of harvest and the articular surface during implantation (92). Damage to the superficial zone of cartilage can negatively influence the ability of the chondrocytes to produce lubricin which aids in lowering friction in the knee (85). During implantation, impaction along the articular surface exerts a compressive force to seat the plugs and has been shown to also induce apoptosis, however, it was also found that the amplitude of force played a bigger role than the frequency of impact on this (85). Thus, it is important to take care when seating the grafts to minimize the force of impaction to preserve the viability of chondrocytes at the cartilage surface.

Equally important to the articular surface is the osseous component of the plug which works to support the cartilage surface and integrate into the host bone. However, it is known to be immunologically antigenic, which can contribute to less bone formation, slower graft incorporation and neovascularization, and increased graft resorption (93-95). Given the osseous component of the osteochondral graft functions as a scaffold, many authors have studied the influence of orthobiologic administration (i.e., platelet-rich plasma or bone marrow aspirate concentrate) to see if this increases graft incorporation and decreases graft failure. However, these studies have shown mixed results with many not finding any statistically significant influence (96-98). Although the regular administration of orthobiologic agents into the osseous scaffold has not yet been well supported by literature, irrigation of the osseous plug to clear marrow contents from the osseous scaffold should be performed (99).

The surgical technique typically involves a parapatellar arthrotomy positioned and sized to best access the lesion location. There are instrumentation guides available that aid in the preparation and insertion of the allograft. This technique is optimal for grafts up to 35 mm in diameter. Once the lesion has been exposed, a central guidewire is placed into the lesion, and the sizer is placed over this wire to determine the size of the graft necessary. The recipient site is then prepped using a core reamer to remove the articular cartilage and a minimum of 3 mm of subchondral bone. However, care should be taken to avoid a depth greater than 1 cm as these sized lesions may need to be backfilled with graft and this will increase the amount of bone healing required for the graft to take and may increase the chance of resorption. It is important to mark the donor graft to ensure proper orientation is maintained during implantation and confirm the depth of the lesion and donor. The graft should then be carefully contoured to match the dimensions of the recipient site. Once prepared, it is then irrigated with high pressure lavage to remove donor bone marrow elements prior to insertion. The recipient site should be dilated prior to implantation and to minimize the force of impact necessary to seat the donor graft (Figure 3). If necessary, bioabsorbable implants can be placed for additional fixation.

Figure 3.

Images showing treatment of osteochondral defect of the medial femoral condyle. (A) Identification of the lesion after medial arthrotomy is performed. (B) A pin is placed centrally in the defect. (C) A 22-mm reamer is used to prepare the site with 6-millimeter depth. (D) The donor site plug is harvested and the back is cleared off marrow elements using pulse lavage. (E) The plug has been prepared and the markings show the orientation of the plug (12, 4 and 8 o’clock) to match the recipient site. (F) The plug is placed with gentle finger pressure, and is confirmed to be flush with the surrounding condyle.

When appropriately sizing the graft, a technical pearl can be to place a suture tape or broad suture at the bottom of the cored recipient site prior to implantation. Thus, if the graft does not seat appropriately and requires further modification, the suture can be pulled to gently elevate the graft from the recipient site minimizing the risk of damage to the chondrocytes with a more forceful method of extraction. If there is a good donor-recipient match, the suture can be removed easily.

Outcomes

Recent systematic reviews have assessed the survival rates of OCA with an estimated 5-, 10-, 15-, 20- and 25-year survival rate of 89%, 83%, 73%, 55%, and 59% for all lesions (100). For patellar lesions, the estimated 10-year survival rate is approximately 77% (84,101) and for trochlear lesions approximately 92% (102). Several studies have shown that reoperation more frequently occurs compared to failure of OCA, and this is commonly performed for unstable chondral flaps, stiffness, or other procedures such as meniscus treatment, which occur in 20% to 45% of cases (80,82,84).

Regarding PROMS, a large systematic review and meta-analysis found a mean 31-point improvement in Lysholm score, 30-point improvement in International Knee Documentation Committee (IKDC) scores, and 1.5-point improvement in Tegner score following OCA (67). Similarly, Touhey et al. reported an improvement in IKDC scores of 33-points post-operatively (103), and Wang et al. reported an overall mean patient satisfaction of 84.7% in a large systematic review on 3,849 patients undergoing OCA (100).

Regarding return to sports, a systematic review by Touhey et al. showed that 72% of athletes returned to sports after OCA of which 84% returned to the same or higher level of sports at mean 11 months after surgery (103). Similarly, Xie et al. also found a total return to sports rate of 72% in their systematic review of 699 patients in 13 studies (104).

Off-the-shelf biocompatible osteochondral implants

Overview

Osteochondral implants or cell-free chondral and osteochondral scaffolds are off-the-shelf, bioengineered, cell-free implants aimed to treat osteochondral injuries. These implants have been utilized in the treatment of lesions secondary to OCD, osteonecrosis, and traumatic cartilage injuries and are available through a variety of proprietary entities (105,106). The goal is to create a scaffold for mesenchymal stem cell egress from the bone marrow to the cartilaginous surface promoting cartilage integration and facilitate subchondral and cartilage restoration while undergoing temporal resorption (105). These implants are generally porous, biocompatible, and biphasic composed of a cartilage segment composed of different hydrogels, synthetic polymers, or natural materials (i.e., collagen, hydroxyapatite) and a subchondral segment derived from high-strength scaffolds (i.e., tricalcium phosphate), bio-ceramics, or inorganic coral exoskeleton (calcium-carbonate) in an effort to structurally resemble the human osteochondral unit (106-109).

Indications

With the recent development of a variety of osteochondral implants, a recent consensus statement was published on the appropriate indications for the use of these off-the-shelf bioengineered scaffold implants in the treatment of cartilage injuries in the knee (110). These guidelines include indications for International Cartilage Repair Society (ICRS) grade III lesions or higher, femur location, age 18 to 75 years, total area 1 to 7 cm², less than 8° coronal malalignment, BMI <35 kg/m², and Kellgren-Lawrence osteoarthritis grade ≤2. Additional contra-indications include patients with avascular necrosis, bone or systemic infection, or a subchondral bone defect or cyst >8 mm deep (110).

Surgical pearls and pitfalls

The specific surgical technique will be dependent on the osteochondral implant selected. However, general pearls for a successful operation include confirming that there is at least 3mm of preserved bone surrounding the lesion, treating adjacent lesion with more than one implant, minimizing thermal injury when reaming the defect, and setting the depth of the defect such that implant is recessed 2 mm below the surface. Pitfalls of the procedure include not having stable cartilage surrounding the defect and implant breakage at the time of implantation as these increase the rates of failure (Figure 4) (111,112). In cases that require additional graft stability, fibrin glue can be placed over the lesion.

Figure 4.

Images showing treatment of osteochondral disease of the patellofemoral joint with aragonite-based scaffold. (A) Trochlear lesion is confirmed with arthroscopy. (B) Arthrotomy is performed (for concomitant OCA of medial femoral condyle) and lesion is drilled. (C) Lesion site is shown prior to insertion. (D) Aragonite-based scaffold is placed in the defect slightly below the surface of surrounding cartilage. (E) Radiographs directly after surgery confirm location of the scaffold. (F) Radiographs 4 months after surgery show ongoing changes and incorporation of the scaffold. OCA, osteochondral allograft transplantation.

Outcomes

To date, there are six clinical studies that have assessed outcomes of the Agili-C (106,111-116) and these designer-initiated studies all had promising results in appropriately indicated patients. They found significant improvements in PROMs, low rates of failure and need for subsequent revision surgery, and high rates of incorporation on advanced imaging at the time of follow-up with evidence of regenerated cartilage.

Altschuler et al. published a multicenter randomized controlled trial of 251 patients that were randomized between Agili-C (167 patients) and standard care consisting of microfracture or chondroplasty (84 patients) (112). At 24 months, the authors found better overall Knee Injury and Osteoarthritis Outcome Score (KOOS) score, KOOS Pain, KOOS quality of life, KOOS Activities of Daily Living, and responder rate (>30-point increase in overall KOOS score), IKDC score, and magnetic resonance imaging (MRI) articular defect fill compared to standard of care, and noted a 7% failure rate compared to 21% in the standard of care group. Reported adverse events included transient knee pain (15%) and increased swelling/effusion (5%). Two patients (1%) had wound complications required antibiotics, and one developed septic arthritis (0.6%) requiring surgical intervention (112).

Similar positive outcomes have been reported for other scaffold implants. A 2019 systematic review on available literature of the MaioRegen Osteochondral implant found significant improvement in post-operative PROMs, including IKDC, Lysholm, and KOOS scores, at 12 and 24 months in 13 of the 16 studies. Of the four studies evaluating long-term outcomes >24 months, all demonstrated significant improvement in IKDC and Tegner scores compared to their pre-operative values, with one study reporting significant improvement in post-op IKDC scores at 5 years post-operative (117). There were 52 reported minor complications across the studies including stiffness (16), fever (5), swelling and bleeding of the knee (31) and seven major complications defined as the need for repeat arthroscopy for partial scaffold detachment, a new chondral lesion, an infrapatellar ossicle, graft loosening, and graft hypertrophy. Of the studies included there was a total failure rate of 3% (117).

Cost-effectiveness analyses

Two large recent systematic reviews have reviewed the cost-effectiveness of various cartilage procedures (118,119). Schrock et al. compared microfracture, OAT and autologous chondrocyte implantation treatments on cost-effectiveness and found that microfracture was the most cost-effective procedure, followed by OAT (118). However, they did not stratify their analysis by lesion size. Everhart et al. on the other hand, assessed cost-effectiveness for the various knee cartilage defect treatments and concluded that all cartilage treatments were effective, but that microfracture was not a cost-effective treatment with lesions sizes over 3 cm² (119). Furthermore, they noted that OCA of bipolar lesions or OCA of the patellar might become less cost-effective procedures if costs or failure rates would increase.

Strengths and limitations

Strengths of this narrative review include the extent of the scope of this study and the clear indication of only including studies of osteochondral treatment. Limitations consist of not performing a formal systematic review, although two reviewers independently assessed all studies, and that studies were selected on the preference of the authors. Furthermore, no quality assessment of included studies was performed, and some studies were limited to lower evidence of data (i.e., smaller level 3 or 4 studies).

Conclusions

Osteochondral injury remains a common pathology in the knee for which there are a variety of treatment options. However, no one best treatment option exists, as studies have shown good outcomes for all treatment options when appropriately indicated. For cartilage lesions with subchondral bone involvement, treatment options depend on the chronicity of injury and degree of damage to the osteochondral unit. While chondroplasty, microfracture, and other marrow stimulating procedures can be performed, when these are not indicated based on lesion characteristics, or have failed, alternative osteochondral solutions should be considered. These include osteochondral fragment fixation for traumatic lesions, most commonly presenting in the patellofemoral joint, or OCD. For more chronic or larger osteochondral injuries with impaired subchondral bone, osteochondral autograft, OCA, or osteochondral biphasic scaffold implants can be utilized. However, further studies are required to compare these methods, optimize their techniques, and improve patient selection to ensure consistent and reproducible outcomes that mitigate the impact of cartilage injury on osteoarthritic progression.

Supplementary

The article’s supplementary files as

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All clinical procedures described in this study were performed in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patients for the publication of this article and accompanying images.