OTA 2008 Posters

Scientific Poster #112 Upper Extremity OTA-2008

Can Glenohumeral Joint Penetration Be Avoided with Proximal Humerus Fracture Fixation?

Asheesh Bedi, MD1 (n); Lisa Case-Doro, MSE1 (n); Calista Harbaugh1 (n);
Richard Hughes, PhD1 (n); Madhav A. Karunakar, MD2 (n);
1Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, Michigan, USA;
2Department of Orthopaedic Surgery, Carolinas Medical Center, Charlotte, North Carolina, USA

Background: Locked plate and screw fixation has recently emerged as the preferred method of internal fixation of proximal humerus fractures. Most implant designs aim to maximize the length and number of screws in order to optimize humeral head purchase and prevent fixation failure in frequently osteoporotic bone. Ideally, screws should be inserted to purchase subchondral bone and improve fixation strength. However, this technique correspondingly increases the risk of screw perforation into the glenohumeral joint. Recent studies using locked plate fixation have reported a substantial risk of screw perforation.

Purpose: The purpose of our study was to determine the probability of achieving the conflicting goals of subchondral screw fixation and avoiding glenohumeral joint perforation.

Methods: A computational, probabilistic model of proximal humerus fracture locking plate and screw fixation based on previously defined parameters of proximal humerus morphology was created. The computer model was validated using Sawbones specimens. A Monte Carlo simulation was used to vary parameters of head and tuberosity morphology. Two commercially available implants were evaluated. The probabilities of screw penetration into the glenohumeral joint and the probability of screw length >5mm from the subchondral bone were calculated for varying humeral head morphology. The relationship of screw trajectory to absolute risk of joint penetration as a function of humeral retroversion was calculated.

Results: Maximal screw length results in a significant rate of joint penetration (range, 27%- 30%). Reducing the screw length by 2 mm decreased the risk of joint penetration (range, 11%-13%) but did not eliminate it. Locking screw holes with an anterior-facing trajectory are at higher risk for joint penetration (P <0.05).

Conclusions: Our results suggest that it is not possible to consistently achieve maximal subchondral fixation without accepting a risk of glenohumeral joint penetration (27%-30%). This finding is most likely related to the high rate of variability in humeral version in the population and the fixed angle of the plate and screws constructs. We recommend against maximizing length in anterior-facing screws, particularly those directed towards the anterosuperior quadrant. This region affords the poorest bone quality and presents a higher risk of joint penetration. Central and posterior screw trajectories offer the combined benefit of optimal bone quality and a reduced risk of joint penetration.

If noted, the author indicates something of value received. The codes are identified as a-research or institutional support; b-miscellaneous funding; c-royalties; d-stock options; e-consultant or employee; n-no conflicts disclosed, and *disclosure not available at time of printing.

• The FDA has not cleared this drug and/or medical device for the use described in this presentation   (i.e., the drug or medical device is being discussed for an “off label” use).  ◆FDA information not available at time of printing. Δ OTA Grant.