How To Address High Intermetatarsal Angles In Bunion Surgery
Proceed to make a 1.5 cm incision in the first intermetatarsal space at the level of the MPJ. Carry dissection down to the level of the deep transverse metatarsal ligament. Carefully transect this ligament. Utilizing a Weitlaner for retraction allows for a slight stretch on this ligament and uncoupling of the adductor head as well. After transecting the lateral metatarsal-sesamoidal ligament and the oblique head of the hallux adductor, one is able to visualize the fibular sesamoid fully while putting an adduction and varus stress on the hallux. Having already performed the medial capsulotomy, the surgeon can appreciate the amount of sesamoid reduction that one needs to maintain. As a general rule, once the lateral release is complete, adduction pressure on the medial head should create reduction of the sesamoid malposition and alignment of the first MPJ.
Finally, make a third 3 cm incision dorsomedial to the first tarsometatarsal joint. Again, the medial dorsal cutaneous nerve lies within the subcutaneous tissue plane. Identify and retract the nerve. While staying medial to the extensor hallucis longus, identify the joint and elevate the dorsal ligaments and periosteum. Utilize a Hintermann distractor with two Steinmann pins to obtain appropriate visualization of the plantar and lateral aspects of the deep joint. We routinely use a combination of curved osteotomes, curettes and a rongeur to resect the cartilage from the metatarsal and medial cuneiform. Then fenestrate the subchondral plate and fish-scale it with a drill bit and a quarter-inch osteotome.
When there are severely widened deformities, perform a more aggressive preparation of the lateral first tarsometatarsal joint to allow reduction of the high angle deviation without causing excessive shortening from wedge resection. Also, if significant first and second ray instability are present, take care to prepare the adjacent cortex on the medial aspect of the second metatarsal with a curette and drill. This allows for scarring in and around the first and second metatarsal base, and aids in sagittal plane control and reduction. A study of 77 patients showed a 30 percent incidence of an accessory intermetatarsal facet between the first and second metatarsal bases.7 This occurred in a higher incidence in first metatarsals with an increased medial obliquity of the first tarsometatarsal joint.
Then place a tenaculum reduction clamp on the dorsomedial aspect of the first metatarsal and around the second metatarsal neck. Close the clamp while recreating the windlass mechanism and dorsiflexing the hallux on the metatarsal, thereby plantarflexing the first ray at the first tarsometatarsal joint. Placing the clamp dorsomedial on the first metatarsal will also facilitate a derotational varus force on the first metatarsal. With the tenaculum, the surgeon can “dial in” the amount of reduction and visualize this via fluoroscopy. Take care not to create a negative intermetatarsal angle.
At this point, the surgeon is ready to apply fixation to stabilize the correction and facilitate fusion of the first tarsometatarsal joint. Based on clinical experience, it is our preference to use a combination of a compression lag screw and locked plating for fixation. If it is the surgeon’s judgment that the instability is just localized at the first tarsometatarsal joint and correction has occurred, place screw fixation across just the tarsometatarsal joint and apply the plate dorsomedially.
However, in most instances, we prefer to stabilize the first tarsometatarsal joint and also reduce the first ray into the stable second cuneiform to gain additional intermetatarsal angle correction and stability of the reduction. One would intentionally angle the lag screw obliquely across the first tarsometatarsal and into the second cuneiform to facilitate this.8,9