LEGAL UPDATE: Iowa Commissioner Rejects 60% Shoulder Impairment Multiplier

On 6/25/2026, the Iowa Workers’ Compensation Commissioner issued a decision in Puentes Lopez v. Lennox Industries, Inc. that answered a question that has been circulating among workers’ compensation attorneys for quite some time: should upper extremity impairment ratings assigned for shoulder injuries be subject to a 60% multiplier?

The argument, as propounded by Claimant’s medical expert, is that since “shoulder function is considered 60 percent of the upper extremity, therefore, there should be a multiplier applied to a shoulder joint impairment.” Puentes Lopez, File No. 25005397.01 (Arb. 6/25/2026) at 9. To the extent that this argument is rooted in the AMA Guides (5^th Ed.), it springs from Section 16.4i, which affirms that “[t]he shoulder functional unit represents 60% of the upper extremity function.” AMA Guides (5^th Ed.), pg. 474.

However, as Deputy Phillips notes in his decision in Puentes Lopez, “[w]hile the Guides makes mention of this, it does not make mention of this being a consideration in an impairment rating.” Puentes Lopez at 16. Moreover, by attempting to read a 60% multiplier into the Guides, the claimant’s argument failed to accurately use them to assign an impairment rating—and, as recently reiterated by the Supreme Court in Koeller v. Cardinal Logistics, the Guides have the force of law in Iowa for purposes of determining impairment ratings. Koeller, 35 N.W.3d 335, 342.

Due to these shortcomings in Claimant’s argument, Deputy Phillips ultimately decided against applying a 60% modifier to shoulder injuries, stating: “There is no justification for his attempt to apply a multiplier based on the shoulder representing 60 percent of the function of the upper extremity." Puentes Lopez at 16. As a result, while Claimant was assigned an impairment rating for his injury, it was only the 6% impairment that was assigned using standard ROM measurement methods outlined by the Guides—not the inflated 14% impairment that Claimant’s expert lobbied for.

The decision in Puentes Lopez may be challenged on appeal. However, the outcome of the case at the arbitration level is a reminder of the importance of adhering to the Guides’ provisions. While it may be tempting to offer a novel interpretation during a hearing, veering too far from its explicit text runs the risk of being discredited.