Shoulder Disarticulation Interface Designs
Gerald Stark, MSEM, CPO/L, FAAOP
A prosthetist creating a shoulder disarticulation interface design faces a greater number of challenges due to the proximal position of the prosthesis. These include less anatomic prominences for suspension and indexing, greater skin coverage, triaxial dynamic loading changes, amputation variability, increased weight, motion for control options, and cosmetic concerns due to shoulder placement and functional scoliosis. These challenges are compounded by the fewer numbers of shoulder disarticulation patients (only 1,341 patients from 1988-1996). 2 As a consequence the average prosthetist may not be as familiar with socket design alternatives that can be utilized to lessen these negative residual effects.
Shoulder disarticulation also faces a higher rejection rate estimated to be more than 39%-65% for acquired and congenital deficiency respectively. 1 Some of the main factors have been linked to: insecure interface, level of amputation, lack of function, discomfort, gadget tolerance, heat dissipation, and cosmetic quality. 1
The interface should provided loading comfort that provides relief for the bony prominences of the clavicle, spine of scapula, and acromium while loading the soft tissue of the suprascapular, subscapular, thoracic, and deltopectroal areas to maintain stability. This is in lieu of the fact that amputations at this level vary. It must be realized that the stability needs and loading change as the shoulder and elbow is flexed, abducted, or extended. The method of control is also affected by the loading when using body or external power especially when using myoelectric sensors. The interface can increase heat dissipation by exposing the superior shoulder and removing inferior windows using a strut system. Conversely overall rigidity of these must be increased with structural corrugations and composite lamination techniques. At times the shoulder mobility is used to operate touch sensors or cable control. In this case the tip of the acromium is allowed to move while the rigidity is provided by a proximal collar around the shoulder.
Many strut type interface variations have evolved to replace the conventional methods to answer these needs. William Sauter of Toronto was one of the first to suggest the use of aluminum frame construction in the 1970's. 1 Ring first suggested the use of a carbon composite frame in 1971. 1 In the Mid-1980's Tom Andrew of Salt Lake City applied a compact frame with his A-P compression techniques in the "mini frame" design. Craig Heckathorne and Jack Uellendahl reported on frame technique in 1992 that allowed control motion for hybrid designs. 1 Used since the mid to late 90's, John Miguelez wrote a paper in 2003 on the "micro-frame" that advocated stabilization for myoelectric control. 3 With common origins, Randy Alley developed the "X-frame" construction method that employed suprascapular compression to augment suspension. 4 In 2008 Farnsworth et al further modified the frame technique to utilize with remnant limbs or brachial plexus injury with an external cage and strut design. 1 Regardless of the interface strategy, they all seek the common interface goals and raise functionality. This is done by minimizing skin coverage by providing rigidity only where necessary. Working in conjunction with the control method to index myosites and cable attachments.
An analysis of prevalence of shoulder disarticulation concepts was conducted among 12 upper extremity specialists who responded to a written survey from a pool of 34 requests. The specialists estimated to have seen an average of 5.08 patients per year with a high of 15 and a low of 2. The specialists were asked to order their preferred methods for impression taking, modification and structural design. Using a weighted Pareto Analysis, the top three shoulder disarticulation concepts were AP compression, XFrame construction, Flexible Liner-Rigid Frame construction were identified as used for a cumulative 78.26% of the time. The remainder of concepts, Supraspinous process, Open proximal window, Corrugation, Spandex Garment, Inferior Thoracic Bar, Axilla Shoulder Mount and Visco Elastic Panel constituted only 22.84% of use.
The responses to impression technique, fitting challenges, and control types were also ordered, Eight out of 12 used multi-splinting techniques, three indicated CAD, and three used elastic compression. Various others were used in combination with the aforementioned techniques. The biggest challenge requiring adjustment was identified by nine of the 12 as the Proximal A-P dimension and clavicular relief. External power was the preferred control method with distribution estimate at 45.08% with hybrid control at 32.58%.
With these basic goals in mind, the impression technique should seek to simulate the load and suspension areas required for optimal performance. Conventional interface design replicated the simple shape of the upper torso. Successive splinting panels were simply applied and smoothed to the shape of the limb. Although the characteristic limb shape may have been captured, the increased weight of the limb and the dynamic positioning caused a large amount of interface gapping when the prosthesis was created. Splinting techniques advocated by Andrew, Uellendahl, Miguelez, and Alley seek to simulate more localized loading that establishes greater stability in dynamic loading. Andrew advocated the A-P pressure from the subscapular area to the deltopectoral area found in his transhumeral technique. Miguelez recommended volumetric cast using splints sandwiched with cellophane and ace wrap to create compression about the thoracic area. Most methods use inferior thoracic outriggers to control lateral migration. At times these may cause impingement and are removed for greater comfort. One of the common errors is to begin the splinting process superior and work inferior with successive inferior splints. This results in the proximal superior wall gapping from the upper anatomy as the thoracic section is loaded. To correct this issue the thoracic splint can be placed and loaded until the splint becomes moderately rigid. The successive splints can then be added to the proximal area where the subscapular and the deltopectoral region may be further defined.Chart: Pareto Analysis
A tracing of the upper torso is also very helpful in positioning of the shoulder joint and shaping of the shoulder to visually compensate and increase symmetry. Often the shoulder joint is mounted in the axilla to eliminate additional M-L bulk. Although this does not approximate normal anatomic shoulder positioning, it is permitted since the shoulder is only periodically used for dressing and gross positioning. Even if the patient elects to not where a functional prosthesis, a cosmetic shoulder cap should be offered to "fill out" the clothing and provide a cosmetic and symmetrical frontal plane appearance.
Using these principles, established over time by upper extremity specialists, can help the clinician to achieve a functional and comfortable outcome. Also the variety of techniques and process provide a number of fitting options to meet the individual needs of the patient.
The Fillauer Companies, Inc.; Chattanooga, Tennessee
- Farnsworth, T., Uellendahl, J., Shoulder Region Socket Considerations, Journal of Prosthetics and Orthotics, Vol. 20, Num. 3, pg. 93-106, 2008.
- Dillingham, T., Limb Amputation and Limb Deficiency: Epidemiology and Recent Trends in the United States, Southern Medical Journal, August, Vol. 95, No. 8, 2002.
- Miguelez, J., The MicroFrame: The Next Generation of Interface Design for Glenohumeral Disarticulation and Associated Levels of Limb Deficiency, Journal of Prosthetics and Orthotics, Vol. 15, Num. 2, pg. 66-71, 2003.
- Cooper, R., Shoulder Disarticulation and Forequarter Amputation: Prosthetic Principles, Chapter 10B, Atlas of Limb Prosthetics, 2nd ed. Bowker, HK, Michael, JW, 1992, American Academy of Orthopedic Surgeons, Rosemont, Illinois, 2002.
- Alley, R., Miguelez, J., Prosthetic Rehabilitation of Glenohumeral Level Deficiencies, Functional Restoration of Adults and Children with Upper Extremity Amputations, New York, Demos Medical, 2004.