OTA 1997 Posters - Tibia Fractures

Safe Extra-Capsular Placement of Proximal and Distal Tibia External Fixation Pins

Thomas A. DeCoster, MD, Michelle S. Stevens, MD, Brian Robinson, MD

UNMH, Albuquerque, New Mexico, USA

Purpose: To identify the anatomic pattern of joint capsular insertion on the proximal and distal tibia so as to avoid fixator pin penetration and joint infection.

Methods: Dissection of 30 cadaveric specimens was performed with specific identification of capsular insertion on the tibia relative to the joint surface. MR imaging of patients with acute hemarthrosis were reviewed to identify the site of capsular insertion. Arthroscopic probing of the subcapsular recess was performed in 10 patients. Results are expressed in millimeters from subchondral bone.

Results: The results demonstrate that the capsule insertions on the proximal tibia 4-14 mm below the articular surface in a regular pattern (fig. 1). The anterior half of the circumference of the tibia (Zone 1) is close to the joint line (within 6mm). Postero-medial (Zone 2) and postero-lateral (zone 4) there are extensions distally to 14 mm, occasionally communicating with the tibio-fibular joint. Posteriorly (Zone 3), the capsule is confluent with the PCL and insertion could not be reliably identified but pins are not placed in this zone due to risk of neurovascular injury. The ankle capsular insertion on the distal tibia is within 8mm in adults.

Discussion: Only recently has the importance of exact capsular insertion been recognized. Penetration of the capsule by a fixation pin may allow a minor pin tract problem to result in an infected joint. The anatomic detail of capsular insertion site is not accurately described in anatomy texts or external fixation technique guides. The results presented here are consistent with recent reports but further identify the specific location of capsular insertion and provide a much better guide to safe placement of peri-articular tibial fixation pins.

Conclusion: These results define a safe zone for external fixation pin placement of greater than 14 mm from subchondral bone of the proximal tibia and greater than 8 mm from the distal tibia in adults. If wire placement closer to the knee is required then pins should be placed in zone 1 anteriorly at least 6 mm distal to the joint. Buried lag screws should be placed proximal to fixation pins in the tibial plateau.