A 39-year-old male recreational basketball player presented with progressive worsening of left knee discomfort that was limiting his ability to participate in competitive sport and regular exercise. The patient had undergone reconstruction of the anterior cruciate ligament at an outside institution 18 years previously. Pain was localized to the medial compartment, and there were no reports of instability. Physical examination demonstrated a negative Lachman test, negative anterior drawer test, and a full range of motion. Plain radiographic examination revealed mild varus deformity, with preserved medial compartment joint space. MRI of the knee demonstrated an intact ACL graft and a large full-thickness chondral lesion of the medial femoral condyle. The patient wished to preserve his native knee joint and subsequently underwent a biologic arthroplasty procedure consisting of cartilage repair with concurrent high tibial osteotomy (HTO) to correct the varus malalignment.

From 0 to 6 weeks postoperatively, there is focus on maintaining/restoring range of motion and muscular strength, while minimizing effusion. Continuous passive motion typically begins on postoperative day 2, 6 h per day until 90° of knee flexion is achieved. In cases of patellofemoral compartment cartilage repair, partial weight bearing with the knee braced in full extension is allowed beginning on postoperative day 1. For cartilage repair of condylar lesions, weight bearing is restricted for the first 4 weeks. Early isometric and isotonic exercises are encouraged during the early postoperative course.

Patients begin pool-based therapy and are allowed unrestricted weight bearing by 6 weeks. Active functional training begins at 9 weeks. From 3 to 8 months postoperatively, the patient is progressed to straight-line running, and physical therapy is focused on strength and endurance training. Pain-free running at a moderate pace is expected by 8 months. From 8 to 10 months postoperatively, patients will focus on agility and sport-specific training, with expected return to sport by 10 months.

Irrespective of cartilage repair technique, particular attention should be paid to bony malalignment, even in cases of subtle deformity. Ensuring the involved compartment is sufficiently off-loaded will provide the optimal environment for cartilage repair tissue to remodel and mature. Realignment procedures that are often required in cases of extensive cartilage injury include distal femoral osteotomy, HTO, and tibial tubercle osteotomy. Depending on the deformity, these procedures may be performed independently or in combination. Care should be taken to avoid shifting the loading forces to compartments with significant cartilage injury, particularly if reliable cartilage repair treatments are not used.

Combining advanced cartilage repair techniques with corrective osteotomy has demonstrated impressive improvements in clinical outcomes compared to previously published series where little attention was paid to cartilage restoration. In cases of patellofemoral maltracking treated with tibial tubercle osteotomy alone, poor outcomes have been demonstrated in cases of associated cartilage injury [22]. In contrast to this, a number of centers, including ours, have demonstrated that successful outcomes may be achieved with tibial tubercle osteotomy in cases of extensive patellofemoral cartilage injury, if appropriate cartilage repair treatment is performed [10, 14, 19, 23]. This highlights the potential for substantial clinical improvement when the involved areas of cartilage injury are specifically addressed with tissue repair techniques, in addition to providing restoration of bony alignment and optimizing the loading forces across knee compartments. While corrective osteotomies are traditionally used with caution in cases of associated cartilage lesions affecting multiple compartments, improvements in cell-based cartilage repair techniques have the potential to enable successful treatment of articular injury in cases that may have previously been contraindicated for joint-preserving procedures, such as those considered to be early osteoarthritis.

Cartilage restoration procedures aim to provide long-term benefit by reducing the incidence of degenerative cartilage wear or by slowing the progression of degenerative change. Numerous studies have demonstrated that marrow stimulation techniques lead to the preferential formation of fibrocartilaginous tissue, with variable type II collagen content and a tendency to degenerate over time [5, 24–27]. To overcome these limitations, there has been a growing interest in alternative, cell-based methods of cartilage repair such as HA-BMAC. In addition to treating smaller and isolated cartilage lesions, our center has demonstrated promising results treating patients afflicted with knee arthropathy and early degenerative changes.

Regarding cell-based treatment options, there have been favorable preliminary results in one-stage repair using biologic scaffolds in association with bone marrow aspirate concentrate [10, 13, 19–21]. This technique relies on the presence of mesenchymal stem cells, as well as growth factors, in order to stimulate differentiation into chondrocytes, potentially leading to restoration of hyaline-like cartilage [8]. The self-renewal capacity and multi-lineage differentiation potential of MSCs may lead to more reliable methods of durable cartilage reconstruction.

The presented technique of biologic knee arthroplasty using one-stage HA-BMAC implantation, in conjunction with bony realignment procedures when indicated, has been shown to provide durable cartilage repair, with consistent improvements in clinical outcomes at our center [10, 13, 21]. There are a number of options for treating surgeons and patients to consider in cases of cartilage injury that have not responded well to non-operative management strategies. Careful assessment of lesion location and size will help guide appropriate management decisions. When considering minimally invasive treatment options, such as those that utilize an arthroscopic approach, it is important for the treating surgeon to appreciate the extent of cartilage injury, so to ensure complete visualization of cartilage injury and to properly secure the biologic repair structure [16, 28–30].

Our institution has extensive experience with both ACI and scaffold-associated mesenchymal stem cell treatment of cartilage injury [10, 13, 16, 18–20, 23, 31]. While there have been excellent outcomes achieved with the use of autologous chondrocytes, there have been similar clinical outcomes demonstrated with the use of scaffold-associated activated bone marrow aspirate concentrate. The use of single-stage cartilage repair using HA-BMAC has been a particularly attractive option, given the impressive clinical outcomes achieved and the decreased cost compared to two-stage ACI procedures.

Clinical outcome analysis for those knees treated with cartilage lesion sizes up to and greater than 20 cm² has demonstrated that HA-BMAC treatment is capable of providing pain relief and excellent functional recovery over medium-term follow-up in patients who have cartilage injury consistent with early osteoarthritis. Furthermore, in our cohort analysis, knees with multicompartment involvement that are treated with this cell-based repair procedure have had consistently good to excellent outcomes, similar to the outcomes expected with treatment of smaller, solitary lesions.

Although cartilage repair interventions are preferentially used in younger populations by many surgeons, it should be noted that some evidence suggests that the chondrogenic potential of MSCs is independent of age [32, 33]. The benefits that were demonstrated in those patients over 45 years of age treated with HA-BMAC suggest that, with the appropriate cartilage lesion, successful outcomes are not limited to a younger patient demographic [13, 21].

Considering the routine use of marrow stimulation in cartilage repair, it is important to highlight the comparative superiority of HA-BMAC with respect to more durable clinical outcomes and the similar results obtained compared to high-cost autologous chondrocyte implantation procedures. Kon et al. reported superior clinical outcomes at 5 years using an arthroscopic matrix-assisted chondrocyte implantation procedure compared to microfracture treatment [16]. Using the HA-BMAC procedure, our findings have demonstrated similar durability of cartilage repair at 5 years [13]. Furthermore, the physical properties of this graft allow it to be applied to defects in a minimally invasive fashion, as in cases of arthroscopic cartilage repair [29]. Although we are awaiting the long-term outcomes of this procedure, these results are encouraging, particularly given the reasonable cost of the procedure and the one-stage nature of the technique.