31 Free Vascularized Medial Femoral Condyle Grafs for Scaphoid Nonunion
Approximately 10% of the 345,000 scaphoid fractures in the United States each year will fail to unite.1 Most scaphoid nonunions can be successfully treated with open reduction and screw fixation with or without conventional bone grafting.2 However, if there is avascular necrosis (AVN) of the proximal pole, vascularized bone grafting may be appropriate. AVN of the proximal scaphoid fragment is seen in a minority of scaphoid nonunions, with the highest incidence occurring in fractures of the proximal pole.3 In 2002, Merrell et al performed a meta-analysis on the treatment outcomes of scaphoid nonunion.2 They found that the union rates were significantly improved in patients treated with vascularized bone grafting (88% union rate) as compared with conventional (nonvascularized) bone grafting techniques (47% union rate). The high union rates of scaphoid nonunions treated with a 1,2 intercompartmental supraretinacular artery (1,2 ICSRA) vascularized bone graft from the distal radius from our institution and from other centers resulted in an initial optimism.3 – 9 This experience led us to use this in patients with a scaphoid collapse and humpback deformity. Soon thereafter, reports of less than satisfying results from the 1,2 ICSRA were reported.10 , 11 This prompted a critical review of our experience, which demonstrated an overall union rate of 71% in scaphoid nonunions treated with the 1,2 ICSRA vascularized bone graft but only a 50% incidence of union when there was AVN of the proximal pole or a humpback deformity with a dorsal intercalated segmental instability (DISI) pattern.3 We identified several reasons why the 1,2 ICSRA graft may not be suitable in these conditions. First, size of graft that can be supported by the 1,2 ICSRA pedicle is ∼1.0 cm3 and the underlying cancellous bone lacks structural integrity, which may be suboptimal. Second, and more importantly, the bone must be placed on the volar aspect of the scaphoid to adequately correct the humpback deformity. This is difficult but not impossible using a dorsal graft. Interestingly, Henry described volar placement of the 1,2 ICSRA as a wedge graft in patients with DISI deformity and AVN of the proximal pole with good results.12 In this study, a large wedge-shaped graft was used with the widest portion of the wedge oriented in a volar direction to facilitate correction of the humpback deformity. The graft was inserted from a volar/radial approach. All 15 patients in the study achieved union at a mean of 11.5 weeks.12 Trumble et al13 recently reported their experience with volar placement of this graft in 30 patients with scaphoid nonunion and AVN. Nineteen patients had nonunions of the scaphoid waist and 11 had proximal pole nonunions. They performed a radial styloidectomy in each case to improve the exposure, decrease tension on the vascular pedicle, and prevent radiocarpal impingement. Twenty-eight patients healed at an average of 5.1 ± 2.4 months. These experiences led us to explore alternative donor sites for vascularized bone grafts. Vascularized bone grafts capable of providing the necessary structural support include a free vascularized corticocancellous iliac crest graft and the free vascularized medial femoral condyle (MFC) graft. We prefer the free MFC graft because of its ease of harvest, lack of donor site morbidity, and compact cancellous bone that is of similar density to the scaphoid.14
The MFC graft was initially described as a pedicled graft by Masquelet et al.15 The use of MFC grafts for the treatment of scaphoid nonunions was first introduced by Doi et al.16 They reported a 100% union rate after using the free MFC as a corticoperiosteal inlay graft in 10 patients with a scaphoid nonunion and AVN of the proximal pole without carpal collapse.16 We have subsequently used it as a structural vascularized volar wedge graft to correct a scaphoid humpback deformity14 A retrospective comparison of patients with AVN of the proximal pole and carpal collapse who were treated with either a 1,2 ICSRA graft or an MFC graft was recently reported by Jones et al.17 Union was achieved in only 40% of the patients who were treated with 1,2 ICSRA grafts at a mean time of 19 weeks as compared with a 100% union rate at a mean time of 13 weeks in the patients who were treated with an MFC graft. Based on these findings, the medial femoral condyle vascularized bone graft is our treatment of choice for the treatment of patients with a scaphoid nonunion with AVN of the proximal pole and carpal collapse.
Preoperative radiographic evaluation includes plain x-rays and computed tomographic (CT) scans to evaluate the amount of periscaphoid arthritis and scaphoid collapse. A noncontrast magnetic resonance imaging (MRI) scan is performed to rule out AVN, which is determined by demonstrating a low signal intensity of the proximal pole on T1-weighted images.
The indications for a free vascularized MFC bone graft include a scaphoid nonunion with avascular necrosis of the proximal pole as well as volar collapse (humpback) deformity of the scaphoid with or without a DISI deformity pattern. The AVN and collapse make healing unlikely by alternative, less invasive measures such as screw fixation alone, conventional nonvascularized bone graft such as iliac crest bone graft, or pedicled vascularized bone grafting from the distal radius. The patient must be willing to accept the donor site scar and potential morbidity of the procedure.
Absolute contraindications include the absence of a patent radial artery (single vessel hand) and periscaphoid arthritis [i.e., advanced scaphoid nonunion advanced collapse (SNAC) wrist]. Patients with a SNAC wrist are likely to have pain even following a successful union and are hence better served with a salvage procedure.
Tobacco use has not been shown to affect outcome17; however, we do counsel the patients on smoking cessation preoperatively based on our recent review demonstrating the effect of tobacco on 1,2 ICSRA vascularized grafts on union.3 There are no time limits as to when the procedure can be performed. We have performed the procedure successfully more than 5 years after the original scaphoid fracture.
▪ Surgical Technique14
The procedure is performed as a two-team approach with the first team exposing and preparing the scaphoid nonunion site and the recipient vessels and the second team harvesting the MFC. The periscaphoid articular surfaces should be critically examined for arthritic changes and the integrity of the intercarpal ligaments noted, especially the scapholunate ligament. If there are significant arthritic changes or the scapholunate ligament is deficient then a salvage procedure is performed instead of the graft. These issues need to be discussed with the patient during the preoperative consultation.
Medial Femoral Condyle Graft
The medial femoral condyle has a dual blood supply from the articular branch of the descending genicular vessel and the superomedial genicular vessel ( Fig. 31.1 ). The descending genicular artery (DGA) is a branch of the superficial femoral artery (SFA). It branches from the medial side of the SFA just before it enters the adductor canal ∼13.7 cm proximal to the medial joint line ( Fig. 31.2 ). The DGA is typically longer and easier to identify than the superomedial genicular artery and therefore is the preferred pedicle for the bone graft. The saphenous artery branch of the DGA gives off perforating branches to the overlying skin, and a chimeric flap with a skin paddle can thus be harvested for monitoring purposes16 , 18 ( Fig. 31.3 ). The DGA averages 2.1 mm in diameter at its origin and is therefore of a sufficient size for a vascular anastomosis.14 , 16 The descending genicular artery is found in 89% of individuals.14 However, if it is not present, the superomedial genicular artery can be utilized, although the dissection is more tedious.14 , 16
The patient is positioned supine and a sterile pneumatic tourniquet is placed on the upper thigh. The hip is flexed and externally rotated. The knee is comfortably flexed and supported by a generous bump. The ipsilateral knee is preferred so that a cane or crutch can be used with the uninjured extremity postoperatively. The ipsilateral knee also facilitates a two-team approach because the operative surgeon can be on the opposite side of the scaphoid surgeons to harvest the vascularized bone graft. The thigh skin incision is not made until the scaphoid is exposed and it is determined that the MFC graft is deemed necessary and appropriate. The dissection is performed under thigh tourniquet control. A longitudinal incision is made along the distal medial femur in a line from the distal articular surface extending 20 cm proximally along the posterior border of the vastus medialis ( Fig. 31.4A,B ). The skin and fascia are incised and the vastus medialis is elevated and the medial femoral condyle and vessels are identified deep to the vastus medialis ( Fig. 31.5A,B ). The vessels are dissected from their origin off of the SFA to the periosteum of the MFC ( Fig. 31.6A,B ). A rectangular area of graft is designed over the posterior aspect of the MFC ( Fig. 31.7 ). The distal anterior section of the MFC has the highest concentration of perforating vessels.14 The graft is designed slightly larger than the measured scaphoid defect. The periosteum overlying the three sides of the graft that are not covered by the pedicle are incised with a knife. A small osteotome or microsagittal saw is used to divide the graft from the cortex along these three sides. A Freer periosteal elevator is used to elevate the pedicle along the fourth side of the graft. With careful retraction in each direction, the last corticotomy is completed in two stages ( Fig. 31.8A-C ). The graft is removed by approaching it distally 1 to 2 cm from the distal corticotomy at a 45 degree angle ( Fig. 31.9A ). A small triangle of bone is removed to facilitate access and osteotomy of the deep surface of the graft ( Fig. 31.9B ). The graft is lifted out and is now isolated on its pedicle. The tourniquet is deflated to observe for bleeding from the graft ( Fig. 31.10 ). The graft is left attached to its pedicle and perfused until the recipient bed and vessels are prepared. The pedicle is then divided and the graft is transferred to the arm table. After graft harvest, the bed is irrigated and closed in layers over a closed-suction drain. A knee immobilizer is placed for patient comfort. The bony defect can be filled with a bone graft substitute as per surgeon preference, such as Osteoset (Wright Medical, Arlington, TN).