How To Address High Intermetatarsal Angles In Bunion Surgery
- Volume 25 - Issue 12 - December 2012
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The use of preoperative radiographic images can be helpful in assessing the patient’s first ray deformities. One assesses the standard weightbearing anteroposterior (AP) view for the first metatarsal talar bisection angle (Meary’s angle), the intermetatarsal angle, the distal metatarsal articulation angle and the hallux valgus angle. On a weightbearing lateral view, one is able to assess Meary’s angle and first ray dorsiflexion, which are often associated with a significant gapping at the plantar aspect of the first tarsometatarsal joint.
So what is a high intermetatarsal angle? Traditionally, this is any angle above normal or 8 to 10 degrees. However, from a clinical standpoint, intermetatarsal angles break down into mild, moderate and severe. For this article, we chose to focus our attention on the intermetatarsal angles measuring 18 degrees and higher. What is considered a “high angle” is often surgeon specific, based on one’s experience and procedure selection.
Some authors cite the unreliability of the intermetatarsal angle in choosing the appropriate procedure for hallux valgus correction.4-6 We agree and recommend a combination of radiographic and clinical exams to choose the corrective procedure. A distal metatarsal articulation angle above normal or greater than 15 degrees is often a consequence or sign of a chronic deformity, and usually necessitates an additional distal metatarsal procedure (e.g. Reverdin osteotomy).
The last angle to take into account is the hallux valgus angle, which is often greater than 30 degrees in severe deformities. This high angle is also associated with a valgus rotation of the digit with assistance from the pull of the flexor hallucis longus tendon. One can usually address this last with a proximal phalangeal osteotomy such as an Akin osteotomy.
The other aspects of preoperative planning are patient goals and expectations. The goals of surgical correction are twofold: reduction in pain and deformity correction. One should also consider cosmesis. Formally addressing how one aims to reduce the deformity, realign the hallux and maintain the correction are all important aspects of the preoperative conversation.
A Step-By-Step Guide To The Surgical Approach
We utilize a regional popliteal nerve block and sedation for pain control and patient satisfaction. The procedure occurs with the patient supine and a small bump under the patient’s ipsilateral buttock for slight internal rotation of the extremity. A thigh tourniquet is preferable to decrease the muscular contraction that sometimes happens with the use of ankle or calf tourniquets.
First, make a 3 cm incision medial at the first MPJ, taking care to avoid and protect the dorsal medial cutaneous nerve. After retracting neurovascular structures and exposing the capsule, make an inverted L capsulotomy parallel to the first metatarsal. The key here is to have the apex of the “L” at the level of the joint so one can visualize the hypertrophic medial eminence and, if necessary, later perform a linear capsulorrhaphy. Then perform an exostectomy of the medial first metatarsal head. We recommend doing this with a very shallow resection at this stage. After correcting the proximal deformity, there is often little resection of the medial head that is necessary.