Relationship of the Penn Shoulder Score with Measures of Range of Motion and Strength in Patients with Shoulder Disorders: A Preliminary Report

Several authors have advocated the use of a disablement model in clinical practice and research [1,2]. Evaluation of clinical outcome should include measures in each domain of disability[3]. The model described by Nagi includes active pathology, impairment, functional limitation, and disability [4]. Active pathology refers to an “interruption of or interference with normal processes and the simultaneous efforts of the organism to regain a normal state” [4]. Clinical measures of active pathology in orthopaedics include information defining the extent of the injury, disease, or healing as determined from the interview with the patient, the medical history, the physical examination, the laboratory and imaging studies, and the operation [3]. According to Nagi, impairment is defined as any loss or abnormality of anatomic, physiologic, mental, or emotional structure or function [4]. Clinical measures of impairment of the musculoskeletal system can include pain, range of motion, muscle force, and joint stability. Nagi defines a functional limitation as a limitation in performance at the level of the whole organism or person [4]. A disability is a limitation in performance of scially defined roles and tasks within a sociocultural and physical environment [4]. Measures of functional limitations and disability include performance-based clinical assessments and patient self-report measures. Self-report measures of outcome are becoming increasingly popular with clinicians, patients, administrators, researchers, and third party payers. Several tools have been developed and used to document outcome of treatment of shoulder pathologies. These include generic quality-of-life or health status measures, condition specific tools, and tools that are applicable to all conditions of the shoulder [5]. Gerber has stated that shoulder assessment measures should include components of pain, patient satisfaction, function, range of motion, and strength [6]. There are a number of these tools available [7–13]. However, no one tool has been widely used and accepted. In order for a measure to be utilized and accepted, it must first demonstrate acceptable levels of reliability, validity, and responsiveness [5]. This information is lacking in many of the shoulder assessment tools currently available. In addition, little is known about the relationship of self-report measures of pain, satisfaction, and function with measures of range of motion and muscle force in patients with various shoulder disorders. This information could help clinicians be more efficient with their examination of patients, provide the patient with a more accurate prognosis, and evaluate progress based on valid measures [14]. The authors have developed a self-report shoulder outcome measure which evaluates the patients report of pain, satisfaction, and function [15]. This tool has demonstrated evidence of test-retest reliability, validity, and responsiveness [15]. Validity, however is an ongoing process and should be reported in a series of investigations that build on previous knowledge [16]. The primary purpose of this report, therefore, is to further validate the Penn Shoulder Score by demonstrating its relationship to impairment measures of range of motion and muscle force. We also sought to evaluate the relationship of selected items of function with measures of range of motion and muscle force, as well as the overall Penn Shoulder Score. We hypothesized that a linear relationship would exist among measures of range of motion, strength and Penn Shoulder Score corresponding to the level of difficulty reported with selected functional measures. A secondary purpose of this paper was to establish estimates of reliability, error, and minimal detectable change of clinical measures of active range of motion and strength.