45.1 Goals of Procedure

Eccentric reaming is a common technique in addressing posterior glenoid wear during total shoulder replacement. Walch et al classified the patterns of acquired glenoid retroversion, as seen in Fig. 45.1. ¹ The goals of eccentric reaming are to establish relatively normal version of the glenoid without sacrificing subchondral bone for implant placement, permitting an anatomic arthroplasty to more predictably remain centered. This is a frequent challenge as the degree of retroversion has a large impact on the success of total shoulder replacements. ²

45.2 Advantages

There are several advantages to eccentrically reaming the glenoid during total shoulder arthroplasty. Glenoid version may be corrected to a more anatomical position, permitting the utilization of a standard glenoid implant, without having to utilize graft, augmented implant, or a more constrained (reverse) implant. However, it has been shown that as the glenoid retroversion increases, asymmetric reaming becomes less feasible without compromising glenoid integrity. In a study of eight cadaveric scapulae, Gillespie et al simulated posterior glenoid wear in 5-degree increments. By eccentrically reaming glenoid specimens with greater than 15 degree of retroversion, placement of a pegged glenoid was not possible in 50% of the specimens due to inadequate bone stock, peg penetration, or both. ³

Eccentric reaming is also used to correct posterior humeral subluxation when associated with glenoid retroversion, though, on occasion, posterior capsular plication is an additional technical option. Habermeyer et al evaluated 77 patients undergoing primary total shoulder arthroplasty to determine whether eccentric reaming could correct posterior subluxation. Postoperatively, no posterior subluxation was observed and 86% of the humeral heads were centered. ⁴ Gerber et al followed 33 patients undergoing total shoulder replacement whose preoperative subluxation index averaged 71% and preoperative glenoid retroversion was 18 degrees. Eccentric reaming of the glenoid was able to restore version within 0 to 10 degrees and subluxation was corrected in 21 patients. In addition, patient constant scores, age-adjusted constant scores, and subjective shoulder values improved postoperatively. ⁵

Bone graft augmentation has been described as one approach for correcting excessive glenoid retroversion. ⁶ Eccentric reaming may be less technically demanding than bone grafting and is not associated with the same significant postoperative complications. Clinical results for glenoid bone grafting have been mixed and are associated with glenoid component failure, graft complications, and instability. ⁷

In the presence of significant posterior bone loss, failure to make corrections in an attempt to normalize version may result in a variable amount of the glenoid component remaining unsupported by bone. One additional technical tip may be the use of a glenoid component sized slightly smaller than one fitting the native glenoid exactly. A smaller sized glenoid may well result in more uniform support on subchondral bone.

45.3 Indications

Eccentric reaming of the glenoid can be used in patients who have symptomatic glenohumeral arthritis with up to 10 to 15 degrees of glenoid retroversion.

Implant selection is an important consideration when selecting a version correcting technique. Implant designs have differing fixation designs: keeled, inline peg, out-of-line peg, or even hybrid implants, combining poly peg and ingrowth central fixation devices. Keeled and inline pegs may be more amenable to use with asymmetric reaming techniques when compared with out-of-line components. Out-of-line pegs sometimes are associated with perforation of the cortex, as the anterior and posterior peg preparation is in bone where there is less depth. Using a slightly smaller size glenoid may make this less of a problem. In addition, depending on how many points of fixation the particular implant design has, perforation of an anterior or a posterior peg hole is rarely a significant problem, and implant choice should take into consideration that argument that peg fixation, either inline or out of line, may more effectively resist pullout forces.