Outcomes Assessment of Hip Procedures

David C. Ayers

Patricia D. Franklin

Introduction

Since the first total hip replacement surgery was performed in 1962 (1), total joint replacement (TJR) utilization has emerged as the most common and costly procedure in the Medicare budget. In 2010, the number of total knee replacement (TKR) and total hip replacement (THR) procedures performed in the United States passed the one million mark (2). An aging population, growing prevalence of obesity, and an increase use in patients under 65 years of age, contribute to the recent increase in demand for TJR surgeries. Working-aged adults represent the fastest growing subgroup with more than 50% of TJR users projected to be under 65 by 2016 (3), up from 40% in 2004. In the next 20 years, THR annual use is projected to increase by 174% to a total of 572,000 (4). THR surgery is the preferred treatment for patients suffering from osteoarthritis (OA) and other degenerative conditions who experience increased pain and impaired physical function that are no longer responsive to nonsurgical care. It is therefore crucial for surgeons to be able to assess pain and function, as they are the primary symptoms prior to THR, and consequently, relief of pain and improved function are the primary patient goals following THR.

At the office visit, orthopedic surgeons assess symptoms through a thorough patient history, which is supplemented with a comprehensive physical examination of the hip (muscle strength, hip abduction and flexion, leg length differences), measures of range of motion (ROM), as well as gait assessments (with direct observation of patients walking in clinic setting). Surgeons also verify the hip pathology through examination of hip radiographs. While the physical examination and radiographic evaluation of the hip are helpful in confirming the hip pathology, neither captures or objectively assess the magnitude of the pain and disability caused by the hip pathology. Ultimately, it is the patient who is the “expert” to assess the impact that the hip arthritis or other pathology has on quality of life and daily function. Thus, the timing and need for THR are ultimately defined by the severity of the symptoms that the patient reports to the surgeon.

Ideally, surgeons will define uniform pain and disability criteria across all patients who are offered THR. The adoption of standardized measures of pain and function, or patient-reported outcome (PRO) measures, can be useful to the clinician and patient in determining progression in symptom severity. This chapter will review the evolution of standardized hip outcome measures developed for clinical research as well as the increasing adoption of PROs in orthopedic registries and clinical practice.

Patient-Reported Outcomes in Orthopedics: A Brief History

E.A. Codman and F.B. Harrington were the first to evoke the idea of following and recording the outcomes of a treatment with the goal of improving its effectiveness. In particular, they advanced the concept of the “End Result” and the need to develop a methodologic approach to evaluating clinical outcomes. The American College of Surgeons absorbed the Committee on the Standardization of Hospitals founded by Codman in 1914 (5).

Following this model, shortly after the first THR procedures were performed, measures of postoperative symptom assessments were developed. For example, the Harris Hip Score (HHS), originally developed in 1969 quickly became the gold standard in the assessment of THR outcomes. The HHS is a 10-item questionnaire where the surgeon documents the patient’s pain, function such as daily activities (putting on shoes and socks, climbing stairs, sitting, use of public transportation) and gait as well as surgeon’s physical examination of the hip and measures of ROM (6). While the surgeon completes the HHS, the patient reports many of the HHS components to the surgeon. Thus, the HHS is a first step toward PROs. A reported limitation of the HHS is that of a ceiling effect in scoring—meaning that the score does not discriminate among high levels of activity and function. This feature limits the use of the HHS for comparative effectiveness research (CER) where documentation of a full range of possible outcomes is critical.

Later, an effort to standardize the reporting of hip surgery outcomes, the Clinical and Radiographic Terminology (CART) system, arose from a combined task force of the Hip Society, the SICOT Commission on Documentation and Evaluation, and the American Academy of Orthopaedic Surgeons (AAOS). A 1990 paper reported a consensus
on a “uniform method of evaluating and reporting the results of hip-replacement surgery” through correlation of radiographic and clinical parameters (7). However, one limitation was the fact that the radiographic signs do not always correlate with the severity of the patient’s symptoms (8). Thus, the CART measure is not commonly used today.

A decade later, under the leadership of the AAOS, a national network of orthopedists tested an information system to uniformly capture clinical and patient reported outcomes. Although there was agreement on the goal to measure PROs, cumbersome office logistics prevented the system from succeeding. Despite the failed implementation, the AAOS concluded that PROs provided important information (9).

More recently, in 2010, the Agency for Healthcare Research and Quality (AHRQ) issued a large research award to the University of Massachusetts Medical School to lead a national orthopedic consortium to capture PROs to inform comparative effectiveness research on THR (and TKR) outcomes (10). Thus, it is clear that the public, patients, and surgeons see a role for PROs in the assessment of THR. This chapter will review the currently available tools and recent evidence that PROs can be effectively adopted in orthopedic practice to guide surgical decisions and outcome assessment.

PRO Measures

With the growing emphasis on evidence-based medicine, more attention has been placed on objective surgical outcome measures to assess THR success. Existing objective measures include radiographic assessment of implant alignment and evidence of implant fixation, in addition to revision rates and measures of clinical failure. However, outcome measures relevant to the patient such as the absence of pain and improved physical function are central to documenting the success, or failure, of THR. PROs have emerged as a key to capturing the patient symptoms in a uniform metric across patients and time. PROs are validated questionnaires collected directly from patients who have been tested and deemed reliable across specific patient groups. Some questionnaires are generic and can be used in patients with any medical conditions whereas others are specific to a single medical condition. PRO surveys are commonly used in clinical research and are the keystone of CER. In the last 5 to 10 years, Sweden, the United Kingdom, and New Zealand adopted PROs as a mandatory outcome for all THRs performed in their patients. The United States is now evaluating the use of these metrics in clinical practice for both THR and TKR. The AHRQ-funded Function and Outcomes Research for Comparative Effectiveness (FORCE) TJR national registry collects PROs before and after surgery on 100% of its participants across 120 surgical practices in 22 states (10). Thus, there is a strong precedence for the adoption of PROs in clinical practice to assess the impact of the THR procedure from the patient’s perspective.

Distinguishing Disease-Specific and Generic Measures

John Ware, an international leader in the development of PROs, describes a continuum of outcome measures that range from disease-specific to generic measures. Figure 33.1 explains the interrelationship of varied outcome measures and associated interpretation across the array of OA outcomes (11).

Figure 33.1, Box 1 illustrates specific OA clinical observations such as joint space narrowing on radiographs. Although these are specific measures of the OA pathology, the measures do not report the symptom severity. Figure 33.1, Box 2 illustrates that patient-reported OA symptoms such as joint pain and stiffness are needed to further characterize the severity. Beyond these symptom measures are specific measures of OA impact on the patient such as inability to climb a flight of stairs or walk a distance (Fig. 33.1, Box 3). Hip osteoarthritis outcome scale (HOOS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) are examples of surveys that collect data in Figure 33.1, Boxes 2 and 3. Finally, global or generic measures (Fig. 33.1, Box 4) capture the overall disease impact of pain and physical and emotional health on the patient’s functional health and well-being. Because these generic measures are not specific to any one condition, these measures can be used to compare health impact across diverse diseases and treatments. The measures in Figure 33.1, Boxes 3 and 4 reflect what people do (function), how they feel (ill or well), and how they evaluate those states and are called, respectively, disease-specific and generic health-related quality-of-life measures.

Figure 33.1. Continuum of clinical and generic outcomes with examples (in parentheses).

Disease-Specific Outcome Measures for THR

Disease-specific instruments are developed and validated for patients with a particular condition. Many PROs have been developed to quantify pain and functional limitations in hip OA and the perioperative hip surgery patient.

The proprietary WOMAC tool is a disease-specific instrument that has been validated for patients with knee and hip OA to measure clinical changes over time, including before and after THR surgery (12). The WOMAC measure is commonly used in OA and TJR research.

The HOOS is freely available for public use and is a brief, validated patient-administered survey with five subscales: pain, other symptoms, function in daily living, function in sports/recreation, and quality of life (13). The survey is also intended for longitudinal monitoring of hip symptoms. HOOS is described as the assessment of the patient’s “opinion regarding their hip and associated problems.” Of note, the HOOS includes the WOMAC items, and therefore allows the estimation of the WOMAC scores. In addition, the HOOS sport score assesses demanding recreational
activities to assess higher levels of postoperative function than PROs focused solely on activities of daily living.

The OXFORD hip scale, widely used in Europe and a proprietary tool, was originally developed as a 12-item questionnaire of the patient’s perception of hip symptoms before and after THR surgery. The Oxford was validated through testing for internal consistency, reproducibility, and sensitivity to change (14) and was widely adopted and subsequently updated in 2007 (15). The Oxford scale is used in many European THR registries.

Generic/Global Outcome Measures for THR

Generic measures are not disease-specific and quantify general emotional and physical health and well-being. Among the most commonly used generic measures are the short-form health surveys (SF-12/SF-36) with 12 or 36 items, respectively, to assess general physical and emotional health, vitality pain, and the effect of these issues on the patient’s social activities, roles, and daily function. Psychometric and clinical studies using the proprietary SF-36 (16,17,18,19) have spawned more than 17,000 peer-reviewed articles, including hundreds of TJR studies (20,21,22). A recent synthesis of well-controlled RCTs clearly indicates that the eight-domain and two-component (physical and mental) conceptual framework and operational definitions (functioning, subjective well-being, self-evaluations) underlying the SF-36 provide a solid foundation for comparative effectiveness evaluation and clinical assessment (23,24). Two summary scores, the mental (MCS) and physical (PCS) composite scores, and individual items (i.e., climb stairs, downhearted/blue) are commonly used in orthopedic research and clinical practice (25). With minor modifications, the veteran’s health system version (VR-12) is available free of charge.

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