Assessment of the Relationship Between Anatomic Reconstruction and Clinical Outcome Using the Equinoxe Total Shoulder Arthroplasty System

Flurin, P (Bordeaux-Merignac Sports Clinic, FR); Gregory, T (European Hospital Georges Pompidou, Paris, FR);
Wright, T (University of Florida Depart. of Ortho., Gainesville, FL); Zuckerman, J (Hosp. for Joint Diseases, NY, NY);
Angibaud, L and Roche, C (Exactech, Gainesville, FL)

Introduction

Numerous clinical studies have demonstrated that total shoulder arthroplasty can be used to reliably reduce pain and improve function in patients suffering from osteoarthritis. Additionally, numerous bench and cadaver studies have demonstrated that anatomic reconstruction using a “third generation” or anatomic shoulder system can accurately reproduce the anatomic center of rotation (theoretically improving range of motion and stability). However, no study has quantitatively demonstrated that improved anatomic reconstruction is related to improved clinical results. Therefore, the objective of this study is to evaluate the relationship between anatomic reconstruction using total shoulder arthroplasty and clinical outcome in patients suffering from osteoarthritis. If a correlation is identified, a secondary objective is to evaluate the contribution of each anatomic parameter to improved clinical outcome.

Methodology

A total of 64 Equinoxe prostheses (Generation 1; Exactech, Inc.) were implanted with cement by the lead author using a deltopectoral surgical approach to treat osteoarthritis since February 2001. Of these, 7 were excluded due to non-implant related complications and 7 were lost due to follow-up leaving a total of 50 shoulders (29 males/21 females; average age = 67 years) having a minimum one-year follow-up (average follow-up = 23.8 months). Clinical assessment was determined by the Constant score.¹ Anatomic reconstruction was determined by a comparison of pre- and post-operative radiographs for each of the following anatomic parameters:

1. Humeral Head Height (HHH, relative to the greater tuberosity)
2. Humeral Head Centering (HHC, relative to the glenoid)
3. Humeral Head Medial Offset (HHMO, distance from the center of the humeral head and the
   intramedullary axis in the Anterior/Posterior plane)
4. Humeral Head Diameter (HHD, along the anatomic neck)
5. Humeral Neck Angle (HNA, angle between the humeral head and intramedullary axis in the Anterior/Posterior plane)

The surgeon who performed the surgery compared each radiograph and assigned a rating of 0, 1, or 2 based upon the correspondence of pre- and post-operative radiographic measurements, as described in Table 1. The assigned values were summed to create an anatomic reconstruction index (ARI). The relationship between anatomic reconstruction and outcome was assessed linearly using the correlation of determination (R²).

Table 1. Quantitative Methodology for Rating the Degree of Anatomic Reconstruction

Results

The average post-operative Constant score was determined to be 79.5; average pain = 12.8; function = 18.8; mobility = 35.7; and strength = 12.0. The average increase in elevation was determined to be 54.5° (pre-op = 104.6°; post-op = 159.1°). The average increase in external rotation was determined to be 48.8° (pre-op = 2.5°; post-op = 51.3°). The average score of each anatomic parameter and its relationship to the Constant score are presented in Table 2. The relationship of each anatomic parameter to pain, total function, total mobility, and strength are presented in Table 3.

Table 2. Average Anatomic Score and its Relationship to the Constant Score

Table 3. Relationship between Anatomic Parameters and Pain, Function, Mobility, and Strength

Discussion and Conclusions

The results of this study demonstrate that improved anatomic reconstruction (as measured by HHC and ARI) does correlate with improved clinical outcomes (as measured by the Constant score). This study is significant because it introduces a functionally relevant anatomic reconstruction index and demonstrates the clinical effectiveness of the Equinoxe for treatment of osteoarthritis (based upon similarities to reported post-operative Constant score values^2,3 and increases in pre- and post-operative functional measurements). The study is limited by its two-dimensional assessment; future work should assess the relationship in three dimensions.

References

1. Constant CR, et al. A Clinical Method of Functional Assessment of the Shoulder. CORR. 1987;214:160-4.

2. Godeneche A, et al. Prosthetic Replacement in the Treatment of Osteoarthritis of the Shoulder: Early Results of 268 Cases. J Shoulder Elbow Surg. 2002;11(1):11-8.

3. Edwards T, et al. A Comparison of Hemiarthroplasty and Total Shoulder Arthroplasty in the Treatment of Primary Glenohumeral Osteoarthritis: Results of a Multicenter Study. J Shoulder Elbow Surg. 2003;12(3):207-13.