Clinical Outcomes
The latest clinical outcomes of the DJO Surgical Reverse Shoulder Prosthesis were published by Cuff et al in the June 2008 issue of the JBJS.
Study Parameters
- Prospective, FDA study
- 112 patients (114 shoulders) were treated with a RSP between January 2004 and March 2005
- 94 patients (96 shoulders) were available for a minimum 2 years of follow-up (9 patients died and 9 were lost to follow-up)
- 63 patients (64 shoulders) were women
- 31 patients (32 shoulders) were men
- 37 primary arthroplasty for the treatment of cuff tear arthropathy
- 33 failed rotator cuff repair
- 23 failed arthroplasty
- 50/96 shoulders had glenoid bone loss
- Avg 21.9 mm remaining
- 8 shoulders with <15mm of bone
- Average age of all patients was 72 years
- Patients were prospectively evaluated clinically using ASES score, SST, and self reported satisfaction
- Patients were also prospectively evaluated radiographically for mechanical failure, loosening, and scapular notching (reviewed by an independent observer)
- In addition, all patients were videotaped while performing a standard active range of motion protocol pre-operatively and post-operatively. This video was analyzed using a digital goniometer in a blinded fashion by three independent observers that were not involved in the treatment of the patients.
Results
- Average total ASES scores improved 30.3 to 77.6
- Average ASES pain scores improved from 15.6 to 40.9
- Average SST scores improved 1.8 to 6.8
- Blinded analysis of range of motion showed:
- Average abduction improved 61° to 109.5°
- Average flexion improved from 63.4° to 118°
- Average external rotation improved from 13.4° to 28.16° (none of the patients in this study received a latissimus dorsi transfer)
- 53 patients rated their outcome as excellent (55%)
- 26 patients rated their outcome as good (27%)
- 11 patients were satisfied with their outcome (12%)
- 6 patients were unsatisfied with their outcome (6%)
- Overall 7% complication rate (9 complications in 6 patients)
- 0 instances of scapular notching
- 0 instances of mechanical baseplate failure
Optimize function while avoiding scapular notching
The DJO Surgical RSP was designed with the natural anatomy in mind.
While a reverse shoulder arthroplasty is not an anatomical reconstruction, biomechanical testing and clinical outcomes have shown the importance of maintaining anatomical relationships in the design of the components1,2,3,4,5.
Increased range of motion
In addition to the avoidance of scapular notching, placing the center of rotation of the glenoid head lateral to the face of the glenoid also provides the potential for greater range of motion. Biomechanical testing has shown that abduction is maximized in reverse shoulder arthroplasty when a lateral center of rotation is used 5. A center of rotation further from the face of the glenoid allows the humeral socket of the prosthesis more clearance in abduction before impinging against either the acromion or the superior portion of the glenoid. The testing also showed that having a humeral neck-shaft angle in the range of normal human anatomy (approximately 130 degrees) had the largest effect in avoiding scapular impingement 5. Figure 1 shows the humeral neck-shaft angle of the DJO Surgical Reverse Shoulder Prosthesis.
In addition to increased abduction, clinical and biomechanical studies have shown that a more lateral center of rotation results in increased external rotation. This occurs because a lateral center of rotation tensions the residual teres minor and infraspinatus muscles, maximizing their potentials to regain some function.
Clinical results show that while the Grammont-style prostheses with medial centers of rotation on the glenoid face show small gains or a loss of external rotation post-operatively, the DJO Surgical RSP shows significant improvements in post-operative external rotation. It is noteworthy that the improvements in external rotation in the Cuff study have been achieved without the use of a latissimus dorsi transfer.
The table below summarizes the external rotation results reported in several publications.
Table 1: External rotation results as reported in several publications.
Glenoid Baseplate Fixation
The superior design of the DJO baseplate is based on the principles of providing stable initial fixation of the baseplate to the glenoid by maximizing compression between the baseplate and the glenoid to achieve ideal conditions for bony in-growth
Previous concerns about the use of a prosthesis with a lateral center of rotation revolved around the increased stress across the glenoid-baseplate interface. These stresses were exacerbated by the highly constrained designs of these devices. An important aspect of the superior design of the DJO Surgical Reverse Shoulder Prosthesis is the secure glenoid fixation of its baseplate. The micro-motion of even the most lateral center of rotation is well below the accepted standard of 150 um needed to achieve bony in-growth. Figure 2 shows the glenoid head size, offset, and associated micro-motion.
Figure 2: Glenoid head size, offset, and associated micro-motion
The key design feature of the glenoid baseplate is the 6.5 mm cancellous type lag screw in the center of the baseplate. The central screw provides the stable fixation needed to utilize the lateral center of rotation of the glenoid head. This straightforward improvement in baseplate design comes from the understanding that compression across a fracture promotes bone healing.
Testing has shown that the compression achieved by the DJO Surgical Reverse Shoulder Prosthesis baseplate with a central screw is 10 times higher than that obtained by Grammont-style devices that depend on a central peg and peripheral screws for achieving compression4.
Bony in-growth between the baseplate and glenoid is further facilitated by DJO Surgical’s proprietary 3D Matrix porous titanium coating, which is applied to the medial surface of the baseplate. In addition, hydroxyapatite is plasma sprayed on top of the porous titanium matrix to stimulate further bony in-growth.
Versatility to manage complex anatomy
This is accomplished by offering six glenosphere sizes with different center of rotation offsets, three humeral augments, and an optional semi-contrained socket.
The DJO Surgical Reverse Shoulder Prosthesis offers six glenoid head sizes. Figure 3 shows the center of rotation offsets for each of the glenoid head sizes.
Figure 3: Center of rotation offsets for each of the glenoid head sizes.
This prosthesis also offers several different center of rotation offsets. While testing has shown that a lateral center of rotation will maximize range of motion and help to avoid scapular notching, there may be instances, such as compromised glenoid bone quality, where a surgeon would like to select a more medial center of rotation. With the DJO Surgical Reverse Shoulder Prosthesis, surgeons have the choice of being able to select either a medial or a lateral center of rotation depending on the patient’s anatomy or the surgeon’s personal preference.
The DJO Surgical Reverse Shoulder Prosthesis offers three different sizes of humeral augments (Figure 4).The purpose of the augments is to allow the surgeon to optimize the soft tissue tension without having to change the center of rotation of the device. The humeral augments are modular and can be exchanged intra-operatively or in the revision setting to help the surgeon achieve the appropriate soft tissue tension.
Incidents of dislocation in reverse shoulder arthroplasty are higher than those reported for traditional total shoulder arthroplasty. When a surgeon is concerned about an increased risk for dislocation in a particular patient, the DJO Surgical Reverse Shoulder Prosthesis offers a semi-constrained socket insert that will provide additional stability. The semi-constrained insert has 10 degrees of additional articulation surface, making it a deeper socket requiring greater distance for the head to dislocate.
References
1. Frankle M, Siegal S, Pupello D, Saleem A, Mighell M, Vasey M. The Reverse Shoulder Prosthesis for glenohumeral arthritis associated with severe rotator cuff deficiency. A minimum two-year follow-up study of sixty patients. JBJS Am. 2005 Aug; 87: 1697-1705. View on Pubmed >
2. Cuff D, Pupello D, Virani N, Levy J, Frankle M. Reverse Shoulder Arthroplasty for the Treatment of Rotator Cuff Deficiency. JBJS Am. 2008 June; 90: 1244-1251.
View on Pubmed >
3. Harman M, Vasey M, Banks S, Frankle M. Initial Glenoid Component Fixation in "Reverse" Total Shoulder Arthroplasty: A Biomechanical Evaluation. JSES. 2005; Volume 14, Number 1S: 162S-167S. View on Pubmed >
4. Frankle M, Virani N, Pupello D, Gutierrez S. The Rotator Cuff Deficient Shoulder. Chapter 8: 76-104. Order on Amazon.com >
5. Gutierrez S, Levy J, Frankle M, Cuff D, Keller T, Pupello D, Lee W. Evaluation of Abduction Range of Motion and Avoidance of Inferior Scapular Impingement in a Reverse Shoulder Model. JSES. 2008 Sept; Volume 17, Number4: 608-615. View on Pubmed >
6. Simovitch R, Zumstein M, Lohri E, Helmy N and Gerber C. Predictors of Scapular Notching in Patients Managed with the Delta III Reverse Shoulder Prosthesis. JBJS Am. 2007 March; Volume 89A, Number 3: 588-600. View on Pubmed >
*Info on file at DJO Surgical