**5.3.2 Osteochondral allograft**

Principles of osteochondral allograft are similar to those of autograft, with the difference being the source of the osteochondral plug. Although concern for disease transmission, cell viability, and host-graft immunogenicity exist, this technique is a very useful treatment for larger chondral and osteochondral defects (usually greater than 2 to 4 cm2). There is no limitation to the size of graft used, as entire condyles may be transplanted. Given the size constraints imposed by the transplanted graft, most allografts are implanted via an arthrotomy, although some cases may allow all-arthroscopic placement, just as with OAT.

#### **5.3.2.1 Surgical technique**

Just as with OAT, the defect is prepared to stable smooth rims with vertical walls using a sharp curette or full-radius resector and then sized. The cylindrical dowel graft is then prepared to match the size of the defect. The dowel graft is then press-fit into its recipient socket via instrumented manual impaction. Supplemental fixation is generally not required. A shell graft technique is another viable option when the dowel technique is not possible because of defect location or size. The shell is prepared freehand and usually requires fixation. This technique is technically more demanding than the dowel.

#### **5.3.2.2 Outcomes**

Outcomes after osteochondral allograft demonstrate good to excellent outcomes in 72% to 94% of patients at long-term follow-up with 5 year Kaplan-Meier survivorship around 95%, 10 year survival around 80% - 85%, and 15 year survival around 65%(Garrett 1994; Shasha, Krywulak et al. 2003; Gross, Shasha et al. 2005; Emmerson, Gortz et al. 2007). Although technically demanding, osteochondral allograft has long-term proven success in patients with larger defects and bone loss that may have failed a prior cartilage surgery.

## **5.3.3 Autologous chondrocyte implantation (ACI)**

ACI is a two-stage cartilage restoration technique indicated for lesions greater than 2 cm2 on the femoral condyles, trochlea, or patella. Stage 1 involves arthroscopic assessment of the defect and a full-thickness cartilage biopsy. Stage 2 involves cell implantation via arthrotomy under a periosteal or collagen membrane patch or, more recently, outside the U.S., cell placement onto a three-dimensional scaffold that can potentially be placed allarthroscopically. The premise behind ACI is that a biopsy and growth in culture of your own cells should theoretically produce normal hyaline articular cartilage upon implantation. However, dedifferentiation of chondrocytes when grown in monolayer culture and subsequent re-differentiation upon implantation has produced "hyaline-like" cartilage. This tissue has a Type II collagen and proteoglycan composition that is close, but not identical to that of normal hyaline articular cartilage.

Management of Knee Articular Cartilage Injuries 119

Outcomes after ACI are good to excellent in approximately 90% of patients at short- and midterm follow-up(Peterson, Minas et al. 2000; Bentley, Biant et al. 2003; Mandelbaum, Browne et al. 2007). Long-term follow-up reveals 92% patient satisfaction with significant improvements in subjective and objective clinical outcome scores (224 patients at mean 13 year follow-up, range 12 to 20 years)(Peterson, Vasiliadis et al. 2010). Several recent systematic reviews have compared ACI to other cartilage surgeries and have indicated a trend toward improved clinical and tissue outcomes following ACI versus microfracture and OAT at mid- and shortterm follow-up(Harris, Siston et al. 2010; Vavken and Samartzis 2010). The quality of evidence in the literature is methodologically poor(Jakobsen, Engebretsen et al. 2005; Harris, Siston et al. 2011) and only further higher quality randomized comparative clinical trials will be able to

The mechanical axis of the lower extremity (straight line drawn from center of hip to center of ankle) normally lies just medial to the medial tibial spine. Varus malalignment brings this axis further inside the medial compartment or even medial to the joint. With axial loading, varus malalignment causes increased pressure in the medial compartment cartilage(Loening, James et al. 2000). Increased stress may negatively impact cartilage repair and restoration procedures. Without correction of the alignment to at neutral, the outcomes of cartilage procedures have been less successful in the presence of varus malalignment. This has led to increased performance of valgus-producing high tibial osteotomy (HTO) either via an opening- (OW-HTO) or closing-wedge (CW-HTO) technique. Mechanical axis correction to neutral or slight valgus is adequate in conjunction with cartilage repair or restoration procedures(Mina, Garrett et al. 2008). For medial compartment osteoarthritis, overcorrection to up to 62% of the width of the tibial plateau from the medial tibial border is warranted(Miller, Cole et al. 2008 ). A similar technique is used for lateral compartment chondral pathology in the setting of valgus malalignment via a laterally-based opening

Outcomes after combined HTO and cartilage surgery for medial compartment cartilage pathology and varus malalignment have demonstrated significant improvements in subjective and objective clinical measures. Both CW-HTO and OW-HTO techniques have seen similar success concurrent with microfracture(Sterett and Steadman 2004; Sterett, Steadman et al. 2010; Pascale, Luraghi et al. 2011), abrasion arthroplasty(Matsunaga, Akizuki et al. 2007), and ACI(Franceschi, Longo et al. 2008; Gomoll, Kang et al. 2009; Minas,

Similar to unloading osteotomy and cartilage surgery for tibiofemoral joint articular cartilage lesions with malalignment, patellofemoral joint chondral pathology in the setting of patellofemoral malalignment also warrants unloading via tibial tubercle osteotomy when combined with cartilage surgery. In the setting of lateral patellar or trochlear defects, unloading via osteotomy should include either medialization (Elmslie-Trillat) or

determine if one cartilage repair or restoration technique is superior.

**6. Role of alignment in cartilage surgery 6.1 Role of mechanical axis of lower extremity** 

**5.3.3.3 Outcomes** 

wedge technique.

**6.1.1 Outcomes** 

Gomoll et al. 2009).

**6.2 Role of patellofemoral alignment** 

Fig. 11. 11a) Arthroscopic biopsy taken from intercondylar notch; 11b) Knee arthrotomy revealing full-thickness femoral condylar defect; 11c) Defect following debridement to stable rims; 11d) Following suture of periosteal patch and implantation of cultured autologous chondrocytes. (Reproduced with permission from Alford JW and Cole BJ: Cartilage restoration, Part 2: Techniques, outcomes, and future directions, in *American Journal of Sports Medicine* 2005; 33: 443-460. Publisher Sage Publications).

#### **5.3.3.1 Surgical technique**

ACI Stage 1 involves standard diagnostic arthroscopy with debridement of the defect and a full-thickness cartilage biopsy taken from the intercondylar notch (Figure 11a), or superomedial or superolateral edge of the medial or lateral femoral condyles, respectively. An arthroscopic ring curette or notchplasty gouge may be used to obtain two or three slivers of cartilage ~ 5 mm x 8 mm (~200 – 300 mg; 200,000 – 300,000 cells). Larger defects may warrant larger amount of tissue. The biopsy should contain a small sample of bone. Currently, the biopsy remains viable for implantation for two years after harvest. It is critical to determine the complete extent and size of the lesion by removing all loose, unstable, undermined, and unhealthy cartilage to well-shouldered, vertical walls. Healthy stable cartilage is required at the time of Stage 2. Upon implantation during Stage 2, removal of all cartilage in the bed is required down to, but not into, the subchondral bone. Any inadvertent penetration into the bone will generate undesirable bleeding. Epinephrinesoaked neuropatties may be used to achieve adequate hemostasis. With stable vertical walls (Figure 11c), the patch can be sutured (using lubricated 6-0 Vicryl suture on a P1 cutting needle) (Figure 11d) in with one small opening remaining at the most superior portion of the patch to allow for cell implantation. Sutures should be spaced 3 to 4 mm apart with a 3 mm bite onto normal cartilage and the knots tied on the patch side. Inject sterile saline under patch to test watertightness prior to inserting cell solution via 18-gauge angiocatheter. Apply fibrin glue as necessary to ensure watertight closure. Once cells are implanted, suture the remaining opening and fibrin glue as needed.

#### **5.3.3.2 Variations in technique (ACI generations)**

Currently, three generations of ACI exist. First-generation techniques involve cell implantation under a periosteal or collagen membrane patch via arthrotomy. Secondgeneration techniques utilize either arthrotomy or arthroscopy to implant cells via cellseeded, three-dimensional bioabsorbable scaffolds. Third-generation technique uses either arthrotomy or arthroscopy to deliver in-vitro treated cells within chondro-inductive and chondro-conductive, three-dimensional matrices. Although clinical outcomes of first- and second-generation ACI are not significantly different, first-generation (especially with periosteal cover) has a significantly greater number of complications, failures, and unplanned re-operations than second-generation(Harris, Siston et al. 2011).

#### **5.3.3.3 Outcomes**

118 Modern Arthroscopy

Fig. 11. 11a) Arthroscopic biopsy taken from intercondylar notch; 11b) Knee arthrotomy revealing full-thickness femoral condylar defect; 11c) Defect following debridement to stable rims; 11d) Following suture of periosteal patch and implantation of cultured autologous chondrocytes. (Reproduced with permission from Alford JW and Cole BJ: Cartilage

restoration, Part 2: Techniques, outcomes, and future directions, in *American Journal of Sports* 

ACI Stage 1 involves standard diagnostic arthroscopy with debridement of the defect and a full-thickness cartilage biopsy taken from the intercondylar notch (Figure 11a), or superomedial or superolateral edge of the medial or lateral femoral condyles, respectively. An arthroscopic ring curette or notchplasty gouge may be used to obtain two or three slivers of cartilage ~ 5 mm x 8 mm (~200 – 300 mg; 200,000 – 300,000 cells). Larger defects may warrant larger amount of tissue. The biopsy should contain a small sample of bone. Currently, the biopsy remains viable for implantation for two years after harvest. It is critical to determine the complete extent and size of the lesion by removing all loose, unstable, undermined, and unhealthy cartilage to well-shouldered, vertical walls. Healthy stable cartilage is required at the time of Stage 2. Upon implantation during Stage 2, removal of all cartilage in the bed is required down to, but not into, the subchondral bone. Any inadvertent penetration into the bone will generate undesirable bleeding. Epinephrinesoaked neuropatties may be used to achieve adequate hemostasis. With stable vertical walls (Figure 11c), the patch can be sutured (using lubricated 6-0 Vicryl suture on a P1 cutting needle) (Figure 11d) in with one small opening remaining at the most superior portion of the patch to allow for cell implantation. Sutures should be spaced 3 to 4 mm apart with a 3 mm bite onto normal cartilage and the knots tied on the patch side. Inject sterile saline under patch to test watertightness prior to inserting cell solution via 18-gauge angiocatheter. Apply fibrin glue as necessary to ensure watertight closure. Once cells are implanted, suture

Currently, three generations of ACI exist. First-generation techniques involve cell implantation under a periosteal or collagen membrane patch via arthrotomy. Secondgeneration techniques utilize either arthrotomy or arthroscopy to implant cells via cellseeded, three-dimensional bioabsorbable scaffolds. Third-generation technique uses either arthrotomy or arthroscopy to deliver in-vitro treated cells within chondro-inductive and chondro-conductive, three-dimensional matrices. Although clinical outcomes of first- and second-generation ACI are not significantly different, first-generation (especially with periosteal cover) has a significantly greater number of complications, failures, and

unplanned re-operations than second-generation(Harris, Siston et al. 2011).

*Medicine* 2005; 33: 443-460. Publisher Sage Publications).

the remaining opening and fibrin glue as needed. **5.3.3.2 Variations in technique (ACI generations)** 

**5.3.3.1 Surgical technique** 

Outcomes after ACI are good to excellent in approximately 90% of patients at short- and midterm follow-up(Peterson, Minas et al. 2000; Bentley, Biant et al. 2003; Mandelbaum, Browne et al. 2007). Long-term follow-up reveals 92% patient satisfaction with significant improvements in subjective and objective clinical outcome scores (224 patients at mean 13 year follow-up, range 12 to 20 years)(Peterson, Vasiliadis et al. 2010). Several recent systematic reviews have compared ACI to other cartilage surgeries and have indicated a trend toward improved clinical and tissue outcomes following ACI versus microfracture and OAT at mid- and shortterm follow-up(Harris, Siston et al. 2010; Vavken and Samartzis 2010). The quality of evidence in the literature is methodologically poor(Jakobsen, Engebretsen et al. 2005; Harris, Siston et al. 2011) and only further higher quality randomized comparative clinical trials will be able to determine if one cartilage repair or restoration technique is superior.
