Introduction
Chondral injuries are becoming an increasingly recognized cause of pain and disability in the knee. , When patients with focal symptomatic chondral defects fail nonoperative management, surgical intervention is offered. There are many options for surgical treatment of symptomatic cartilage defects, and these options can be separated into palliative, reparative, restorative, and reconstructive procedures. Palliative procedures include lesion debridement and loose body removal. Reparative procedures include microfracture and drilling where the purpose is to fill the articular defect with fibrocartilaginous tissue. Restorative procedures include autologous chondrocyte implantation (ACI) and matrix-associated autologous chondrocyte implantation (MACI), which allow creation of a hyaline-like cartilage layer to fill the defect. Finally, reconstructive procedures involve osteochondral grafting, either with autograft or allograft, where fully mature hyaline cartilage and bone are transplanted into the defect.
Results following surgical treatment of cartilage defects have a wide range of success, with several patient factors including age, sex, lesion size, lesion location, and others having an effect on surgical outcome. Complications following cartilage surgery can be separated into preoperative, intraoperative, and postoperative. This chapter will discuss the various causes of these complications and provide insight into ways to avoid and mitigate these problems before, during, and after cartilage surgery.
Preoperative Complications
Diagnosis
Reaching an accurate diagnosis and properly indicating patients for surgery is one of the most difficult aspects of treating patients with cartilage issues. It can sometimes be very difficult to determine if a cartilage defect is the sole cause of a patient’s complaints because asymptomatic cartilage defects are extremely common. , Aroen et al. performed a prospective study where the authors evaluated 993 consecutive patients who underwent knee arthroscopy for a variety of reasons and reported the arthroscopic findings as it related to cartilage defects. The authors found 66% of knees had articular cartilage defects, with 20% of knees having isolated articular cartilage defects without degenerative lesions, 11% having full-thickness cartilage defects, and 6% having full-thickness cartilage defects of more than 2 cm. It was unclear exactly what proportion of the patients’ symptoms, if any, were coming from these cartilage defects. A similar study by Curl et al. reported comparable results, with 63% of 31,516 knee arthroscopies demonstrating cartilage defects. Hence, simply because a cartilage defect is seen on magnetic resonance imaging (MRI) does not mean it is the sole cause of the patient’s complaints, or even a contributing factor. For this reason, it is imperative the surgeon take an accurate history and tease out the most likely cause of the patient’s symptoms.
Patients with symptomatic cartilage defects typically present with localized pain in the area of the knee where the defect is, with or without swelling. Instability is not a symptom commonly caused by a cartilage defect, and patients who present with instability as their main complaint should be evaluated for a different cause of pain. Furthermore, patients with diffuse chondral wear are rarely symptomatic from one particular area of cartilage loss and should not be indicated for a cartilage procedure, as the results will likely be disappointing.
Imaging
Accurately imaging a focal chondral defect in the knee can be challenging, and underestimating the size of a lesion is a preoperative factor that can lead to intraoperative and postoperative complications. All patients who present with what appears to be a symptomatic cartilage defect should have a complete set of x-rays, including weight bearing anteroposterior, flexed posteroanterior, lateral, and Merchant views of the knee. Although these plain films may show osteochondral defects, it is very difficult to accurately measure the true size of the defect from these x-rays. One of the most important preoperative pieces of information is the defect size because it is one of the crucial factors that guide treatment. Many studies have shown higher failure rates for reparative procedures in larger defects (>3.0–4.5 cm 2 ) when compared with restorative and reconstructive procedures. , , As such, it is important to accurately measure the defect size preoperatively to formulate a surgical game plan to optimize results. Advanced imaging modalities such as MRI are critical aspects of the preoperative workup.
Unfortunately, although MRI offers the most accurate insight into the cartilage defect as well as to the rest of the soft tissue structures of the knee, studies have found preoperative MRI underestimates lesion size at the time of arthroscopy. , Gomoll et al. evaluated 38 patients with symptomatic full-thickness cartilage defects who underwent knee arthroscopy and arthrotomy with ACI (patients with osteochondral autograft and allograft were excluded) within 12 months of obtaining their MRI, and compared defect size between the preoperative MRI and following debridement at the time of surgery. The authors found that MRI significantly underestimated the average total defect size of the cartilage lesions when compared with measurements taken intraoperatively (3.6 cm 2 vs. 6.0 cm 2 respectively), and that 85% of the time, the defect size was larger intraoperatively than on the MRI. Therefore although obtaining an MRI is critical to evaluate the cartilage status of the rest of the knee, involvement of subchondral bone, and so on, surgeons must understand that the defect is often larger at the time of surgery and be prepared to switch procedures at the time of surgery based on intraoperative findings ( Fig. 20.1 A-E ).
Intraoperative Complications
Cartilage procedures can be technically demanding, with surgeons working either all arthroscopically or through a small arthrotomy to minimize incision size and morbidity. However, when performing any knee, hip, ankle, and so on, arthroscopy or arthrotomy, there are several technical pearls that should be followed to minimize complications. First, the arthroscope should always be atraumatically introduced into the joint. Iatrogenic chondral injury during arthroscopy is a cause of morbidity following arthroscopy, and one that can and should be meticulously avoided throughout the procedure. Also, when creating the arthrotomy great care should be taken to avoid damage to the chondral surface, as well as the menisci in the knee or labrum in the hip. Careful dissection and attention to detail can avoid these unnecessary complications.
Microfracture
Microfracture is the least technically demanding of all the adult cartilage procedures and has the fewest possible intraoperative complications. Steadman et al. described the initial technique in 2001, and although no high-level studies have evaluated the effectiveness of the initial technique, the initial technique is still what is being used today. This technique involves creation of microfracture holes that are perpendicular to the bone and are 2 to 4 mm deep (to allow blood and fat droplet extravasation from the marrow cavity) and 3 to 4 mm apart (to avoid convergence) ( Fig. 20.2 ). An arthroscopic awl or flexible drill can be used to create these holes. , Technical errors and complications involve creating holes that are too shallow or too deep or that converge and break into one another. Although the microfracture procedure is not overly difficult to perform, there is significant variability from surgeon to surgeon when preforming this procedure. Kroell et al. conducted a study where four surgeons performed the microfracture procedure on six human cadaveric knees. The authors found that all surgeons misjudged the depth (the holes were made too deep) and interhole distance (holes were made too close together), whereas 51% of holes were angled more than 10 degrees from the perpendicular. This study illustrates the importance of attention to detail when performing microfracture to avoid these potential complications.
Matrix-associated Autologous Chondrocyte Implantation
MACI (Genzyme Biosurgery, Cambridge, MA) is a third-generation ACI product where previously harvested chondrocytes from the patient’s knee are expanded in tissue culture in the lab and then seeded onto a bilayer type I/III collagen scaffold a few days before the release date. The scaffold is then secured to the cleaned cartilage defect with fibrin glue. This modification has eliminated some of the complications seen with the first- and second-generation ACI products, including patch hypertrophy and difficulty securing the path to the native cartilage. Furthermore, because this third-generation technique eliminates the need to sew a patch into place, an all-arthroscopic approach for certain lesions and locations can be performed. However, there are several possible complications when performing a MACI.
The first stage of a MACI procedure involves harvest of 200 to 300 mg of healthy cartilage from the patient’s knee. Aside from the previously mentioned complications with all arthroscopic procedures, complications specific to this first-stage procedure include harvesting an inadequate amount of healthy cartilage (ultimately necessitating a second surgery to obtain more healthy cartilage) and overaggressive or improper cartilage harvest leading to an osteochondral lesion in a weight-bearing portion of the knee joint. The cartilage biopsy should be performed using an arthroscopic gouge, and the cartilage should be harvested from the lesser-weight-bearing portions of the intercondylar notch or the medial or lateral proximal trochlea. Taking the cartilage biopsy from a weight-bearing portion of the knee essentially creates an iatrogenic osteochondral defect, and may require treatment if it becomes symptomatic. Also, the surgeon must ensure the cartilage biopsy is placed in sterile solution before it is sent to the lab. Failure to do so can lead to problems with growing the cartilage cells on the scaffold.
The second stage of a MACI involves placement of the scaffold into the cartilage defect. There are several complications that can occur during this procedure, including perforation of the subchondral plate during overly aggressive defect preparation, over- or undersizing of the scaffold, and placing the scaffold upside down. When preparing the defect, the surgeon should be mindful not to violate the subchondral plate because this can cause bleeding bone, which makes it hard for the fibrin glue to hold the scaffold in place, or to dilute chondrocyte with bone marrow cells, which could potentially lead to a more fibrotic tissue regenerating. Avoiding overaggressive use of the curette or shaver can help avoid this complication. Likewise, when the foil template is made for the MACI scaffold, great care should be taken to slightly undersize the template so the scaffold sits within the defect and is not prominent. However, the template should not be made too small because this can leave areas of the defect uncovered when the scaffold is placed. When placing the membrane on top of the foil/Tegaderm and cutting the membrane to fit the foil scaffold, the orientation of the membrane is such that the corner with a small piece previously removed at the laboratory is in the bottom left corner. Minimal manipulation of the scaffold will decrease the risk of damage to the cartilage. The scaffold is then placed into the defect (cell layer down), and fibrin glue is used to secure this into place. Gentle digital pressure should be applied to allow the membrane to adhere to the defect while the glue is drying. Failure to hold the scaffold in place long enough may compromise secure fixation of the membrane. Finally, once the membrane is secure the knee should be taken through a range of motion (ROM) exercises to ensure the graft does not become dislodged, and to make sure the graft does not catch at any point during ROM.
Osteochondral Autograft Transfer/Osteochondral Allograft Transplantation
The most technically demanding procedure of all adult cartilage treatment is an osteochondral autograft transfer (OAT) or osteochondral allograft (OCA) transplantation. In an OAT procedure, one or several bone plug(s) are harvested from a nonweight-bearing portion of the knee and transplanted into the cartilage defect as either a single plug or multiple plugs (mosaicplasty). As before, if the donor plug is harvested from a major weight-bearing portion of the knee, an iatrogenic osteochondral defect has been created and potentially will need to be addressed. In OCA transplantation, a cadaveric osteochondral plug is harvested from a donor knee and placed into a recipient cartilage defect. Although OAT involves the patient’s own cartilage, meaning initial cartilage viability is of lesser concern, OCA transplantation is different. Survival of articular cartilage in OCA transplantation is dependent on chondrocyte viability, and studies have found 70% chondrocyte viability as a threshold for successful grafts. , Mandatory disease testing of OCA grafts requires 14 days, and because grafts typically fall below the 70% chondrocyte viability threshold after 28 days of storage, there is only a 14-day window to use an OCA. New storage methods, including the Missouri Osteochondral Allograft Preservation System, have been developed in an effort to prolong chondrocyte viability of these grafts, thereby potentially increasing the amount of time these grafts can be stored before implantation (to upwards of 50 days). , However, it is important to understand the method of storage as well as the time of storage of an OCA before it is implanted to ensure proper chondrocyte viability. Decellularized osteochondral allografts should be avoided at all cost as these grafts have an unacceptably high failure rate (39%–80.4% at 2 years). ,
In both OAT and OCA transplantation, the recipient site is prepared using a reamer. For OCA transplantation especially, care must be taken to avoid reaming too deep because the desired plug depth (the sum of the thickness of the articular cartilage and subchondral bone) should be 6 to 9 mm throughout, and the donor plug must be cut to the exact depth of the recipient site to avoid graft prominence or seating too shallow. A complication that can occur during implantation of the plug is difficulty with plug insertion. If the plug is difficult to insert by hand, the plug should be removed and contoured for easier insertion as opposed to using the mallet to seat the plug more. Forceful impaction on the cartilage surface of the plug destroys the chondrocytes, leading to earlier graft failure. ,
Postoperative Complications
Certain postoperative complications including infection, deep vein thrombosis, wound dehiscence, and hematoma formation are inherent to any surgical procedure. , The following postoperative complications are unique to each of the various cartilage procedures.
Microfracture
The most common postoperative complication following microfracture of the knee is clinical failure. Although microfracture may have a role in treating small cartilage defects, the failure rates for treatment of larger defects is unacceptable high. However, the most concerning issue following microfracture in large defects is not the high failure rate, but rather the effect that the microfracture procedure will have on future cartilage procedures in the patient’s knee. Pestka et al. reviewed 28 patients with isolated cartilage defects of the knee who were treated with ACI following a previously failed microfracture (failure was defined as continued symptoms that necessitated a revision procedure) and compared these patients with a set of matched controls who underwent ACI as their first-line treatment. At a mean follow-up of 48 months, the authors found a significantly higher failure rate in patients who were initially treated with microfracture compared with those who were initially treated with ACI (25% vs. 3.5%; P = .0241). They also found significantly higher clinical outcome scores in the group treated initially with ACI. This study is important to understand because it demonstrates that microfracture is not a benign procedure that should be performed anytime a focal chondral defect is encountered. Rather, patients should be properly worked up for their symptomatic cartilage defect and treated appropriately based on activity level, defect, size, and defect characteristics.
Matrix-associated Autologous Chondrocyte Implantation
As previously mentioned, MACI is a third-generation ACI product that was created to eliminate the complications of patch hypertrophy and failure to obtain a watertight seal before injecting the chondrocytes under the patch. However, there are still postoperative issues with MACI, including persistent pain, locking, crepitus, recurrent effusions, failure of graft integration, graft fibrillation, graft hypertrophy, and disintegration of the regenerative tissue, reported in up to 18.5% of patients. , Unfortunately, these complications often require further surgical intervention including debridement or revision with OAT, OCA transplantation, or subchondral bone grafting. Although the problem of patch hypertrophy was solved with the third-generation ACI, graft hypertrophy can still be seen with MACI. Studies have shown that graft hypertrophy more commonly occurs in the tibiofemoral joint (32.1%) than the patellofemoral joint (10.4%) ( Fig. 20.3 ). Overall failure rate for MACI has been reported to be between 4.5% and 8.6% depending on the location of the chondral defect within the knee. , Many of these complications are inherent to the surgical procedure and cannot be minimized by proper surgical technique or adequate rehabilitation.
