Avascular Necrosis of the First Metatarsal Head
Section snippets
Vascular anatomy
The sources of first metatarsal blood supply include the periosteal capillary network, the nutrient artery, and the metaphyseal capital vessels. These vessels are branches of the first dorsal metatarsal artery (originating in the dorsalis pedis artery), the first plantar metatarsal artery, and the superficial branch of the medial plantar artery (Fig. 1) [6], [7]; however, there is significant variation in the detailed pattern [8]. The metaphyseal and capital vessels emanate from extracapsular
Osteotomy
Any metatarsal osteotomy has the potential to cause AVN. Most obviously it can disrupt intraosseous blood flow and compromise metatarsal head blood supply [1], [7], [9], [10]. In the metatarsal head, this is particularly true of any osteotomy that is performed distal to the point of penetration of the nutrient vessel of the bone. In such an osteotomy, the remaining blood flow is from capsular vessels; if a subcapital osteotomy is cut in an intracapsular fashion this will be lost [7]. Similarly,
Osteotomy modifications
Because distal osteotomies disrupt the intraosseous blood supply, it was emphasized that preservation of the extraosseous or capsular vessels is vital. For this reason, extracapsular exit of the osteotomy has been advocated strongly [7], [21]. Nonetheless, modifications of the Chevron osteotomy—with varying degrees of capsular disruption—have been used without a dramatic increase in the rate of AVN. Examples include Donnelly et al's [22] report on a series with a long plantar and vertical
Osteotomy and soft tissue release
Soft tissue release and distal metatarsal osteotomy may be combined to give greater correction of deformity than can be achieved by either procedure in isolation. Lateral soft tissue release reduces valgus force; it may include adductor tenotomy, capsular release, and fibular sesamoid capsular release in some cases of transection of the transverse intermetatarsal ligament [24]. Combining a distal osteotomy and soft tissue release has caused consternation since the time of Mitchell [11], who
Symptoms and signs
The presentation of AVN varies greatly; many patients are essentially asymptomatic [1], [10], [14]. Incongruity between radiology and symptomatology is recognized widely [9], [21], [24], [26]. The typical, symptomatic patient suffers painful joint space narrowing with stiffness [5], [26], [28]. In early stages (by about 4 months), there is atypical swelling with pain [13], erythema, and warmth about the joint that is associated with increasing tenderness, irritability, and not infrequently,
Radiology
Radiographs have the disadvantage of following a circulatory phenomenon by monitoring bony morphology [14], and therefore, should be approached with some caution. Radiographic findings that are consistent with AVN include crescent-shaped subchondral lucencies, focal cyst formation, or mottling that is seen most often within 2 months of surgery (Fig. 4) [28]. More full-blown findings include subchondral bony collapse, fragmentation of the head, and joint space narrowing. Cyst formation is not
Radiologic staging
Because the AVN is rare, only an anecdotal staging system is available [1] which applies the progression seen elsewhere, particularly the hip. According to Meier and Kenzora [26] there are three radiographic stages of first metatarsal head AVN: precollapse, collapse, and osteoarthritis (Table 1). Progression through the stages is not relentless.
MRI features
MRI changes include T1-decreased signal intensity that is associated with decreased cancellous bone content and T2-increased signal intensity because of hyperemia and edema; hence, there are fluid changes on proton density when compared with the other side [9], [10]. Not infrequently, near normal radiographs can be associated with an abnormal bone scan and MRI which may display the double-line sign [30]. MRI is excellent for confirming the suspicion of AVN [13] and can indicate the extent of
Management
Many cases of AVN are asymptomatic, and therefore, can be managed nonoperatively [1]. Those who have mild symptoms may benefit from simple joint debridement or synovectomy [1], although subchondral drilling has been reported [2]. Some investigators advocate a Keller procedure. Fusion of the joint can be achieved [4] and is the author's preferred option where intervention is necessary. Probably the most expeditious approach is in situ fusion with the use of cancellous graft to fill defects.
Summary
AVN of the first metatarsal head most often follows bunion surgery. Several aspects of surgery may contribute to the condition. These include the extent of soft tissue dissection; injury to the periarticular or capsular blood vessels; disruption of the intraosseous blood flow; and local trauma, including heat injury. When osteotomy and soft tissue release are combined, there probably is a greater vascular insult and increased risk of AVN; however, this is marginal if care is taken to avoid
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