In 1980, Morrison and O’Brien reported their experiences with the reconstruction of an amputated thumb using a wrap-around neurovascular free flap from the great toe, but its indication has been limited distal to the metacarpophalangeal joint.

We have performed 37 wrap-around free flaps from the great toe for the reconstruction of thumbs amputated at distal or proximal to the MP joint. The amputation was distal and proximal to the MP joint in 25 and 12 cases respectively.

The opposition of reconstructed thumb to the other fingers was completely possible in all cases amputated distal to the MP joint. In the 12 cases amputated proximal to the MP joint of the thumb, opposition was completely possible in 6 cases in which the lilac bone block was fixated in the position of 30° flexion and 45° internal rotation. However, in the other six cases in the fixation of 30° flexion and 30° internal rotation, the opposition of the reconstructed thumb to the ring and little fingers was impossible in five cases and only to the little finger in one case.

We concluded that amputation proximal to the MP joint is not an absolute contraindication to the wraparound free flap procedure for thumb reconstruction. However, for a better functional outcome we recommend iliac bone block fixation in the position of 30° flexion and 45° internal rotation.

Introduction: Unicomparmental knee replacements have a long clinical history of success as well as failure. Recently, in Australia some 40% of knee surgery performed consists of unicompartmental knees for the treatment of medial compartment OA. This increased use of unicompartmental knees is in part due to advances in surgical technique through a minimally invasive approach. Loading conditions at the tibia-implant interface will play an important role in the stress/strain distributions at the proximal tibia. The use of an all PE tibial insert versus a metal backed component may provide a different strain disribution to the proximal tibia. This study examined the influence of metal backed and polyethylene tibial components in unicompartmental knee replacements with and without cement fixation on the initial strain distributions under various loading conditions.

Materials and Methods: Three cadaveric tibias (mean age 47 years old) were cleaned of all soft tissue and strain gauged. Rosette strain gauges (TML Ltd., Tokyo, Japan) were placed at 2 levels on the tibial cortex. The intact tibia were embedded in a low melting point alloy at a standard height and tested using an MTS 858 Bionix testing machine (MTS Systems, Min., MI). The tibia were tested in nuetral, varus and valgus positions at zero and sixty degrees of flexion. A 1500N was applied for 15 seconds and the strains measured. A K-Scan sensor (Tekscan, Boston, MA) was used to confirm the varus and valgus loading positions and to obtain a contact footprint and pressure for the intact and reconstructed tibias under the loading conditions (Fig. 1). Following intact testing, the tibias were templated and reconstructed by a surgeon familiar with the technigue. The implants were investigated with and without cement fixation and compared to their respective all polyethylene component if it was available using the same loading regime as the intact tibias. Principal strains were calculated.

Results: Tibial cortical strain distributions were significantly different at the proximal and distal sites under the loading conditions examined. The strain distribution for metal backed components was greater than the all PE design. Increasing flexion angle shifted the peak strains posteriorly. Metal backing and all PE tibial inserts presented different strain distributions on the medial side under nuetral and varus loading. Lateral compartment strains did not differ between designs, were higher proximal and decreased dramatically at the distal gauges. Cementless fixation tended to overload compared to the intact condition. Figure 2 presents the strain distribution for a typical metal backed and all poly unicompartmental knee in the nuetral position.

Discussion: Metal backed unicompartmental components overloaded the proximal cortex of the tibia. All polyethylene tibial inserts did not overload the proximal cortex and had similar strain distribution to the intact tibia. Cemented fixation allows the transfer of load to the distal tibial cortex via the proximal cortex and subchondral bone, provided that the bone cement has inter-digitised the subchondral bone.