Abstract
Dear Sir,
K-wire fixation is associated with a number of complications (pin-site infection, loosening, migration, nerve, tendon or vascular injury, osteomyelitis, mal-union or non-union), some of which may be reduced by the optimal percutaneous placement of wires in areas of minimal skin excursion on movement. We aimed to quantify skin movement in the digits to try and identify areas where skin movement was minimal on full flexion and extension of the digits.
We examined all five digits on a single hand in 20 adults with normal hand function. There were nine men and 11 women with a mean age of 37 years (range 25–68). There were 11 right and nine left hands irrespective of dominance. Skin movement with finger motion was assessed at the metacarpophalangeal joint (MCPJ) and interphalangeal joint (IPJ) in each digit. A reproducible marker was placed over each joint (centre point of skin creases over the dorsal aspect of the joint) with the digit in extension. Two further markers were placed, 1 cm proximal and 1 cm distal to the first. This process was done in three different axes at each joint in each digit: dorsal (down the centre of the dorsum of each digit); mid-axial (line connecting the lateral extent of the flexor creases on flexion); and dorsal three-quarter axis (midway between the other two axes) (Fig 1). Markers were placed on one side of the digit only, after pilot studies had indicated that results were consistent whichever side of the digit was used.
The joints were then flexed to a pre-determined angle confirmed using a goniometer. The distance between the three markers was re-measured in flexion to assess the amount of skin stretch or retraction. Reproducibility of the measurements to within 1 mm was confirmed by repeating the measurements on the same hand on five separate occasions. The measurements from the 20 participants shown in Table 1 include both range and mean percentage stretch or retraction achieved across each joint in full flexion. Skin movement at the mid-axial and three-quarter axes of the MCPJs could be assessed in the thumb, index and small fingers only.
Our results demonstrated that skin excursion differed markedly along different axes. As expected, the dorsal axis revealed the greatest skin excursion on movement (mean stretch of +30%), with skin in the mid-axial axis retracting on flexion (mean retraction −20%). The dorsal three-quarter axis was consistently shown to be the most stable axis with regard to skin movement, having the least skin excursion in either stretch or retraction (mean stretch +9%).
When related to the degree of flexion, dorsal skin stretch in the fingers was found to be greatest at the PIPJ (mean stretch of +0.35% per degree flexion), followed by the MCPJ (+0.29%) and finally the DIPJ (+0.20%). In the thumb, dorsal skin stretch was greatest at the IPJ (+0.41%) and least at the MCPJ (+0.32%).
Our study confirms that the insertion point for percutaneous K-wires should continue to avoid the dorsal extensor mechanism (dorsal axis) and the neurovascular bundles (mid-axial axis). Skin puncture in the dorsal three-quarter axis minimises tethering on motion, reducing the likelihood of skin complications. The effects of K-wiring on the skin are particularly important around more mobile regions such as the PIPJs of the fingers and the IPJ of the thumb, where a longitudinal skin incision at the K-wire site may further reduce tethering.