Birmingham Hip Resurfacing - Literature Review

A clinical data series was used to support the safety and effectiveness of the BIRMINGHAM HIP™ Resurfacing (BHR™) System. The BHR was implanted in 2,385 hips by a single investigator, Mr. Derek J.W. McMinn, FRCS. Mr McMinn performed his surgeries at the Birmingham Nuffield and Little Aston Hospitals, Birmingham, United Kingdom from July 1997 through May 2004. Additionally, unpublished data on 3,374 hips implanted by 140 surgeons and published reports from the experience of multiple surgeons implanting over 3,800 hips supported the safety and effectiveness of the BHR System.

Study Objectives and Assessments
The objective of the clinical data series was to demonstrate the safety and effectiveness of the BIRMINGHAM HIP Resurfacing (BHR) System. The safety assessments included data on revisions, adverse events, and deaths for the entire series of 2,385 procedures, 919 of which were 5-years post-operative; and, a metal ion literature review that included unpublished and published references. Effectiveness data was collected from the first 1,626 procedures, as they were a minimum of 2-years post-op. Of the 1,626 procedures, survivorship and patient satisfaction data were available for 546 of the 601 BHR procedures expected at 5-years post-op (90.8%). Of the 124 procedures in the X-Ray Cohort, radiographic data were available for 108 of the 118 procedures expected at 5-years post-op (91.5%). Of the 1,111 unilateral procedures evaluated for clinical effectiveness, pain and function data, as evaluated by the Oswestry-modified Harris Hip (OSHIP) Score, were available for 360 of the 395 procedures expected at 5-years post-op (91.1%).

Description of Cohorts and Data Collected
The 2,385 procedures implanted with the BIRMINGHAM HIP Resurfacing (BHR) device by a single investigator from July 1997 through May 2004 were divided into the following three main cohorts for the purposes of data analysis:
• X-ray cohort: First 124 BHR cases performed from July 1997 through December 1997.
• Oswestry cohort: Next 1,502 BHR cases performed from January 1998 through March 2002.
• McMinn cohort: Next 759 BHR cases performed from April 2002 through May 2004.

Table 2 outlines the dates of implantation, number of procedures, and types of safety and effectiveness data collected for these 3 cohorts:

Note: An X in the table indicates that this data was collected for the respective cohort
* There were 5 cases in the McMinn cohort whose implantations were performed prior to 4/02. These cases should have been part of the Oswestry cohort, but for unknown reasons were not. Therefore, unlike the majority of the McMinn cohort, some of these 5 cases have longer term follow-up. ** See note in Table 3 below regarding the number of procedures contributing to the pain and function (OSHIP) effectiveness data.
*** The pain and function data for the procedures in the McMinn cohort were collected using the Oxford Hip Score evaluation method (and not the OSHIP Score assessment method). Because the 759 procedures in the McMinn Cohort were not tracked by the Oswestry Outcome Center but by the National Health Services (NHS) Center, the FDA and Smith & Nephew, Inc. did not have access to the Oxford hip score data.

As noted in the Table above (with the large bolded “X”), 124 procedures in the X-ray cohort contributed to the assessment of radiographic effectiveness in the PMA. Radiographic evaluations were not provided for the 1,502 procedures in the Oswestry cohort or the 759 procedures in the McMinn cohort. Where there were common data elements collected in the 3 cohorts outlined above, this information was pooled into the following two combined cohorts:

• X-ray/Oswestry/McMinn combined cohort or Overall McMinn cohort: Note that for the rest of this document, this cohort will be referred to as the Overall McMinn cohort.

• X-ray/Oswestry combined cohort

Table 3 outlines the dates of implantation, number of procedures, and types of safety and effectiveness data
collected for these 2 combined cohorts

Note: An X in the table indicates that this data was collected for the respective cohort
* Although data (e.g., x-ray or pain and function) was collected for one of the cohorts identified in this row, it was not collected for all procedures in the combined cohort; therefore, an X is not included in this part of the table.
** 1,111 unilateral procedures in the X-ray/Oswestry combined cohort contributed to the assessment of pain and function effectiveness data, as evaluated by the Oswestry-modified Harris Hip (OSHIP) Score assessment method.

As noted in the Table above (with large bolded “X”s), the 2,385 procedures in the Overall McMinn cohort contributed to the assessment of safety including adverse events, revisions, and deaths. The 1,626 procedures in the X-ray/Oswestry combined cohort contributed to the assessment of survivorship. Also, as noted in the Table above, 1,111 unilateral procedures in the X-ray / Oswestry combined cohort contributed to the assessment of pain and function effectiveness data, as evaluated by the Oswestry-modified Harris Hip (OSHIP) Score. Unilateral procedures were evaluated separately as it is difficult to distinguish pain and function status of each hip separately in patients with bilateral hip involvement. Finally, 1,626 procedures in the X-ray/Oswestry Combined cohort contributed to the patient satisfaction effectiveness.

Additional Data Sources
In addition to the clinical data series cohorts, less complete data was provided on 3,374 BHR cases performed by 140 surgeons worldwide (other than the single investigator). The follow-up for these cases was also contracted to the Oswestry Outcomes Centre and includes primarily the same parameters as the follow up for the X-ray / Oswestry combined cohort (adverse events, revisions, deaths, pain and function (OSHIP) scores, and patient satisfaction). The Oswestry Outcomes Centre, therefore, collected data on a total of 5,000 BHR cases. These 5,000 cases are referred to as the Oswestry Worldwide Cohort. The Oswestry Worldwide Cohort consists of 1) the 1,626 cases of the X-ray / Oswestry cohort (the single investigator), and 2) an additional 3,374 non-McMinn (“all other”) cases. The Oswestry Outcomes Centre has provided access to all available data for the BHR cases from its database. Although the data from the 3,374 “all other” cohort was of some value, Smith and Nephew, Inc. and FDA have no ability to independently verify any of the data provided to the Oswestry Outcomes Centre by sites other than the McMinn Center, and have no ability to request additional follow-up or clarifications of any kind from non-McMinn patients or physicians. For these reasons, the analysis on the Oswestry Outcomes Centre worldwide database has some limitations, and is not considered the primary data source.

Several literature references were also included which describe the use of over 3,800 BHR devices implanted by multiple surgeons in several countries around the world. One example is the literature reference by Shimmin and Back (Shimmin AJ, Back D. “Femoral neck fractures following Birmingham hip resurfacing: A national review of 50 cases.” J Bone Joint Surg [Br] 87-B:463-4, 2005) which was used in the development of the labeling.

DATA COLLECTION METHODS

Safety Data Collection Methods
The safety data including adverse events, revisions, and deaths were collected by:
• The Oswestry Outcomes Center using an annual, patient-completed, mail-in questionnaire (deaths were identified
while attempting to perform scheduled follow-up);
• The McMinn Center by recording the findings of post-operative patient visits to the McMinn Center in patient records; and
• Recording information provided to Mr. McMinn by primary care physicians.

Also, a 100% audit of all 2,385 procedures in the Overall McMinn Cohort was performed.

EFFECTIVENESS DATA COLLECTION METHODS

Survivorship Data Collection Method
The primary effectiveness measurement was the X-Ray/Oswestry combined cohort survivorship study that included 1,626 procedures performed from July 1997 through March 2002 at the Birmingham Nuffield Hospital. These procedures were a minimum of 2 years post-op. Of the 1,626 procedures, data are available for 546 of the 601 BHR procedures eligible for 5-year follow up (90.8%). The data for the survivorship study was collected using the same methods presented above for the safety data collection methods.

Radiographic Data Collection Method
The clinical data used to support this series contained the results of an independent radiographic review of the X-Ray Cohort, the first 124 procedures performed in the series from July 1997 through December 1997. Radiographic evaluations were not provided for the 1,502 procedures in the Oswestry Cohort or the 759 procedures in the McMinn Cohort.

The radiographs were interpreted by an independent radiologist. A prospective protocol was developed and used to assess the radiographs. The 5-year AP and lateral view radiographs were compared with the baseline radiographs for the medial-lateral migration, acetabular orientation (tilt angle), femoral and acetabular radiolucencies, heterotopic ossification (HO), bone resorption, acetabular protrusion, cysts, buttressing, and other abnormalities. Radiolucency was defined as a lucent area parallel to and in close proximity to the prosthesis/bone interface encompassing at least 50% of the zone and at least 1mm in width.

A radiographic success was defined as having all of the following:
• Absence of radiolucencies or a radiolucency in any one or two zones (a score of 0-6);
• Component migration <2mm; and
• Change in acetabular angle <5Þ

A radiographic failure was defined as the following:
• Presence of incomplete or complete radiolucencies or a radiolucency in all zones (a score of 7 or 8);
• A migration of the component >2mm; or
• A change in acetabular orientation of >5Þ

The individual success criterion was the absence of radiographic findings that suggest revision is necessary.

Oswestry-Modified Harris Hip (OSHIP) Score Data Collection Method
The clinical data used to support this series were collected by the Oswestry Outcomes Center (OOC) using an annual, patient-completed, mail-in questionnaire. The responses to the pain, function, and movement questions in the questionnaire were used to generate the Oswestry-modified Harris Hip (OSHIP) Score.

The main difference between the OSHIP questionnaire and the HHS is that the OSHIP allows patient assessments without direct physician or examiner evaluation. In addition, the OSHIP questionnaire does not include the three HHS questions regarding physician assessment of Range of Motion (5 pts.), Absence of Deformity (4 pts.), and the patient’s ability to put on socks/tie shoes (4 pts.) but substitutes a “movement” question (13 pts.) that is intended for the patient to estimate their ability to flex their hip.

Patient Satisfaction Data Collection Method
Patient satisfaction data was also collected using the annual, patient-completed, mail-in questionnaire. For the purpose of the BHR study, an additional question about patient satisfaction was appended to the end of the OSHIP assessment questionnaire.

Literature References
A literature search was performed to find published studies of ceramic-on-ceramic total hip replacements to provide a comparison for the BHR clinical study data. The following two articles were identified:

• D’Antonio J., et al.: New experience with alumina-on-alumina ceramic bearings for total hip arthroplasty. J. Arthroplasty, 17(4): 2002.
• Garino JP: Modern ceramic-on-ceramic total hip systems in the United States: Early results. Clin. Orthop., 379: 2000.

The data in these references have some differences as compared to the data provided for the BHR device in this clinical data series, including:
• Different evaluations, (OSHIP for BHR and HHS for literature)
• Length of follow-up, (18-36 months and 2-4 years for the controls and 2-5 years for the BHR study)
• Mean baseline pain and function scores (e.g., 60 for OSHIP in BHR Oswestry cohort, 44 for HHS Garino study, and not reported for D’Antonio study), and
• Indications for use, (including differences in the rate of dysplasia and AVN diagnostic indications)

However, the literature information provided valuable information on approved ceramic-on-ceramic total hip replacement (THR) systems for comparison purposes including patient demographics, diagnostic indications, patient accounting, adverse events, revision rates, pain, function, and radiographic results. This information is summarized in several sections below for reference purposes.
 

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2/4/2007

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