Vascularized Joint Flap
Anatomic considerations
Background
Vascularized joint transplantation provides a living joint. Because the tissue is vascularized, this type of joint replacement can last a lifetime, and is not prone to mechanical failure like a silicone or metal implant. Small joint arthroplasty of the metatarsophalangeal (MP) and proximal interphalangeal (PIP) joints can be challenging and is often limited to the low demand patient population. The vascularized joint can in selected cases of trauma or congenital absence offer joint replacement that is permanent and functional. Additionally, because an open epiphysis continues to develop after transplantation, reconstruction in children has the potential for growth. Stiffness can be problematic, but less so in the younger patient population. In addition, the vascularized joint can also provide soft tissue and bone where those have been lost by injury or infection. Tendon can also be included with the joint as a single unit.
Preoperative Assessment
Any traumatic injury or congenital absence requires a thorough preoperative evaluation by the microsurgeon. The hand is thoroughly assessed to determine the anatomy of the loss and the potential requirements for reconstruction. If a vascularized joint transplant is felt to be the reconstruction of choice, the surgeon must evaluate the lower extremity completely. This includes a history of previous injury or surgery, and a complete skeletal, vascular and sensorimotor examination. Particular attention should be paid to the pedal pulses. If arterial inflow is thought to be questionable whether by history or physical examination, then an angiographic study of the lower extremity is performed. We however do not routinely perform angiography of the lower extremity because we have found the vessel spasm of the foot to be particularly problematic in angiography, and this often leads to results that are of no value in determining joint vascular anatomy. In healthy individuals with no clear indication for angiography, the study does not help the surgeon either plan or execute the surgical procedure.
Anatomy
Either the PIP joint of the second toe and the MP joint of the second toe can used for small joint reconstruction. The MP joints of the foot are primarily extension joints with significantly more range of motion in extension. The opposite is true for the PIP joint. When the MP joint is used for reconstruction, it is typically placed with its extensor surface volarly and the flexor surface dorsally, thus maximizing finger flexion at the joint.
A vascularized joint can be constructed from the metatarso-phalangeal (MP) joint or the proximal interphalangeal (PIP) joint of the second toe. The MP joint is primarily an extension joint, while the PIP joint is a flexion joint.
The vascular supply to the second toe is via the first dorsal metatarsal artery, a continuation of the dorsalis pedis artery. The first dorsal metatarsal can remain entirely dorsal, or in greater than 50% of cases, dives deep between the first and second metatarsal, to provide a plantar dominant inflow to the second toe. In the first web space, the termination of the plantar or dorsal dominant system can always be found sending branches to the second toe and great toe.
Operative Procedure
The second toe is dissected in the manner described in second toe transplantation.
When the second toe is isolated, before or after the arterial inflow and draining vein are divided, the toe is trimmed of tissue that is not required. If the pip joint is being used, as in the figure below, osteotomies are made on the middle and proximal phalanx, leaving behind the vascular supply and drainage, as well as any tendons that will be used. A small cuff of soft tissue is left subcutaneously while a skin paddle optionally remains for monitoring.
The second toe can be harvested and then trimmed to contour the vascularized joint. The distal phalanx and distal aspect of the mid-phalanx are removed. The flexor and extensor tendons are optional depending on the needs of the recipient site.
Here, the second toe free flap has been trimmed of skin as well as the distal phalanx and distal mid-phalanx. The joint is harvested with the extensor or flexor tendons as an option.
Harvesting without tendons significantly quickens the harvest time. Care must be taken not to injure the arterial inflow system or the venous outflow system.
If the MP joint is to be used, the distal metatarsal is harvested with the flap. After the inflow artery and outflow vein are dissected, an osteotomy of the second metatarsal is performed with a micro-oscillating saw. The distal osteotomy is performed on the proximal phalanx. The flap is then harvested en-bloc with the joint and skin paddle. Tendons are optional depending on recipient area needs.
A skin island is harvested with the joint if needed for soft tissue or for monitoring. An osteotomy of the metatarsal and proximal phalanx are performed (blue line). The length of bone harvested is dependent on recipient area needs.
The MP joint of the toe is an extension joint that maximally bends in extension (blue arrows). The joint is rotated 180 degrees on its longitudinal axis when used to reconstruct an MP of the hand.
Post-Operative Care
The foot is kept elevated for the first week and then introduced to a progressive dangling regimen. An ace wrap can provide gentle compression during dangling. Weight bearing is not begun until the donor site is well healed, often not until four to six weeks. During this time crutch use can be difficult because use of the reconstructed hand is limited.
The donor site with the second metatarsal head harvested will typically take longer before weight bearing is achieved.