Indications

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  The MFC corticoperisoteal bone graft has been shown to be a reliable flap for reconstruction of bony defects of the upper extremity, including the clavicle, humerus, radius, ulnar, scaphoid, lunate, metacarpal, and phalangeal bones.10–13 More recent reports have described the versatility of the flap being harvested with both skin and muscle, allowing it to be used for a variety of composite defects.13

  
  
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  The MFC flap is usually elevated in one of three major patterns:

  
  
  
  
  1. 
     

     A corticocancellous block of bone of up to 3 × 3 cm for use as a structural wedge graft in cases of collapsed scaphoid nonunions, metacarpal and phalangeal defects, and (in some cases) distal radius nonunions ( Fig. 27.1a )

     
     
  2. 
     

     An osteocartilaginous graft for management of articular defects in the scaphoid, radius, or lunate

     
     
  3. 
     

     A thin corticocancellous sheet of bone that can be wrapped around tubular bones, such as the clavicle, humerus, or ulna, for cases of recalcitrant non-union ( Fig. 27.1b )

  
  
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  General indications for this procedure include small nonunions that have failed traditional therapy or patients at high risk for contemporary nonvascularized graft failure (such as proximal pole scaphoid non-union). Other indications would include:

  
  
  
  
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    Recalcitrant bony nonunions due to infection, radiation-induced osteonecrosis, or avascular necrosis

    
    
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    A bone defect (3 × 3 cm) with composite soft-tissue loss (a skin paddle of 3 × 3 cm or larger may be taken with the flap as well as a portion of the vastus medialis if muscle coverage is required for coverage of composite bony defects)

    
    
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    Small bony defects (up to 3 × 3 cm) where harvest of a fibular or iliac crest would be excessive (the small size of the MFC flap reduces risk of donor site morbidity and serves as an ideal flap for defects that necessitate coverage with a thin and pliable flap with minimal bulk)

Contraindications

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  Bony defects in uncomplicated nonunions should be managed initially with conventional grafting or pedicled vascularized bone grafts, prior to moving to an MFC flap. In addition, the MFC flap should not be the first choice in cases where the bony defect is larger than 3 to 5 cm. LaPierre has described using MFC grafts with dimensions as large as 13 × 8 cm.14 These findings have been further validated by Iorio, who in a cadaveric study found that the genicular system may be capable of perfusing flaps of up to 13 cm in length.15 Despite these findings, we would recommend using a graft with more structural integrity if the bony defect extends beyond 3 × 3 cm.

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  Relative contraindications may include radiation to the region of flap harvest or significant peripheral vascular disease involving the adductor canal or popliteal area, as these may compromise the arterial pedicle to the flap.

  
  
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  Previous knee surgery that has injured or ligated the genicular arterial system, which feeds the MFC flap, obviously will prevent the successful use of the flap.

Other patient-specific contraindications in cases of scaphoid nonunion, Preiser disease, or Kienböck disease would be the existence of radiocarpal arthritis.

Preoperative Examination and Imaging

There are few requirements for preoperative imaging when using this flap. The anatomy (discussed below) is very reliable. Attention instead is given to the nonunion site to verify the size of the defect, the bony dimension required for reconstruction, and to rule out evidence of ongoing infection. In general, imaging is performed for the following:

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  Preoperative assessment of nonunions and carpal collapse can be assessed with a CT scan. In addition, preoperative CT scans of the nonunion site allow for templating of the required graft dimensions. An MRI with gadolinium contrast is used to rule out avascular necrosis of the involved carpal bone.

  
  
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  CT angiography or an MR angiogram can be considered in patients with previous knee surgery, significant atherosclerosis, or previous knee trauma to verify the patency of the genicular arterial system.

Anatomy

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  The anatomy of the MFC flap has been studied extensively and most recently by Yamamoto and Iorio.15,16 The bone flap is located over the medial femoral condyle and is bound by three borders: posteriorly by the border of the femur, anteriorly by the medial patellar facet, and distally by the medial collateral ligament.

  
  
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  The flap is nourished from two sources: the descending genicular artery (DGA) and the medial superior genicular artery (SGA). The DGA originates from the femoral artery just distal to the adductor hiatus. It lies just deep or lateral to the adductor magnus tendon along the posterior aspect of the medial intermuscular septum.

  
  
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  The DGA has three branches, including an articular branch, a muscular branch, and a saphenous branch. The articular branch feeds the periosteum, the muscular branch nourishes the vastus medialis muscle, and the saphenous branch supplies the overlying skin. Yamamoto and colleagues studied the arterial anatomy to the medal femoral condyle in 19 cadavers. They discovered the DGA was present in 89% of the specimens, with the artery originating on average 13.7 cm from the articular surface of the knee. At its origin, the vessel had an average internal diameter of 1.5 mm (range 1 to 2 mm). An osteoarticular branch was present in 89% of specimens, branching from the DGA ~ 11.3 cm (range 5.5 to 15 cm) from the knee joint, and this branch had an average internal diameter of 1.1 mm (range 0.63 to 1.5 mm). Seventy-nine percent of specimens had an identifiable saphenous branch perfusing the skin; this branch travels with the saphenous nerve16 ( Fig. 27.2 ).

  
  
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  The SGA originates from the proximal portion of the popliteal artery. In Yamamoto′s anatomic study, this vessel was present in 100% of the specimens, with the origin of the vessel just 5.2 cm from the articular surface. The vessel has an average internal diameter of 0.78 mm at its origin, with a range of 0.38 to 1.4 mm. The vessel crosses from behind the adductor magnus tendon to anastomose with the osteoarticular branch of the DGA contributing to the perforating vessels over the condyle. The superior medial genicular artery was the dominant vessel supplying the medial femoral condyle in two of the specimens in Yamamoto′s study16 ( Fig. 27.2 ).

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  The preferred vascular supply to the flap is the DGA, as it has a longer pedicle length (5–10 cm) and larger internal diameter than the SGA, facilitating microvascular anastomosis.

  
  
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  The SGA, while smaller in diameter than the DGA, is still a very reasonable option when longer pedicle length is not required, as in cases of Kienböck′s disease and some cases of scaphoid nonunion. In addition, the SGA has a good diameter vessel match when performing an end-to-end anastomosis to side branches of the radial artery ( Fig. 27.3a–c ).

  
  
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  An average of 30 arterial perforators to the medial femoral condyle have been reported. The perforating vessels run perpendicular to the cortex and extend to an average depth of 13 mm. The majority of perforators lie in the posterior medial quadrant of the condyle.16 Care should be taken to identify these perforators and include them within the bone flap.

  
  
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  Finally, if a skin paddle is to be taken with the flap, it is necessary to separate the saphenous nerve from the saphenous branch of the DGA. Injury to this nerve will result in paresthesia or dysesthesias over the anterior medial aspect of the parapatellar/pretibial region of the leg.