The Slip-Fit Joint for Ease of Donning and Doffing of Orthoses that Cross the Hip Joint
Joseph Molino, MS, CPO
Michael B. Rebarber, CO
George Tanner, CPO, Cped
ABSTRACT
This article presents the rationale for designing the Slip-Fit Joint. The Slip-Fit Joint eases stress on a patient in donning and doffing an orthosis that crosses the hip joint, such as a HKAFO or a TLSO with a thigh component, especially in a bilateral situation. The Slip-Fit Joint allows a practitioner to separate the orthosis into pelvic and lower sections, and reassemble the two with initial alignment preserved. Once the two are separated, the lower section can be donned independent of the pelvic section. This feature is extremely helpful when fitting bilateral patients or patients whose risk of dislocation while in bed is high. With the Slip-Fit Joint one can also make nearly unlimited internal/external rotational adjustments.
Key Words: Slip-Fit; hip orthosis; postoperative hip management.
Hip arthroplasties are now done routinely in the United States.1 Sir John Charmley developed the technique in 1959.2 Aseptic loosening of components and dislocations are still postoperative risks, because of the difficulty of attaching components to the skeleton in hip.3 To reduce the risk of dislocation, a postoperative hip orthosis is used to provide stability to the region and limit motion.4 Postoperatively, patients are typically set with 15 degrees of abduction and allowed free flexion to 60 degrees to discourage dislocation of the hip. A study done by Lima et al.5 produced the following criteria for judging whether patients are at a high risk of dislocation:
- Poor abductors or adductor spasticity
- Only one revised component
- Compromised component position
- History of dislocation
- Anterior wall weakness and/or global instability
- Prior acetabular transplants
- Two or more surgeries on the affected side
Lima et al. advocate a team approach to hip arthroplasty patients. The team comprises nurses, physical and occupational therapists, physicians, and orthotists. Each member has defined protocols, in conjunction with orthotic protocols, for managing these types of cases. These protocols constitute the standard approach for the orthotic community in managing patients who require hip orthosis.
The Slip-Fit Joint (figure 1
) was conceived as an aid in the orthotic protocol of patients wearing bilateral or unilateral hip orthoses. Donning and doffing traditional hip orthoses requires excessive motion by the patient to get the orthosis to stay in the correct position. The pelvic section must be kept in the proper position while the lower section is manipulated into place. A "log-roll" technique is used to move the patient while the orthosis is put in place. When applied to an unstable or extremely large patient, this technique can cause difficulty during donning because often the orthosis cannot be positioned correctly. If the patient is "at risk," as defined by Lima et al.'s criteria, the misalignment could cause failure of the hip from this activity. If the patient is at high risk for dislocation, donning a traditional bilateral orthosis could cause serious complications resulting from the movement required to position the orthosis while the patient is in bed.
The Slip-Fit was designed to separate the orthosis into the pelvic component and the leg component. These components can be positioned independently then reconnected, leaving alignment intact and minimizing stress to the patient. This should reduce the risk of complications and ensure correct positioning of the orthosis on the patient.
Method
After critically evaluating hip orthosis donning and doffing procedures, the researchers determined that the procedures would be more efficient and reduce the risk of dislocation if the pelvic section were independent of the lower section for donning and doffing. Several different prototypes were tested. The design that proved most efficient and comfortable for patients was one that mounted the receiver on the pelvic section and the interlocking component above the hip joint. This design allows the orthosis to be separated into two base components while allowing adequate motion to reconnect the components.
The system design incorporates a receiver, containing a cap and locking pin, that mounts on the pelvic component. The slug receiver fits into the receiver and the hole in the slug receiver is aligned with one of two holes on the receiver. A locking pin is inserted to connect the two. Thus the original alignment chosen by the orthotist is preserved. The slug goes inside the slug receiver. The slug consists of two slug wedges connected by the slug-tightening bolt. The slug is then attached above the hip joint on the upright that connects to the leg component.
The Slip-Fit Joint functions when the slug-tightening bolt compresses the two slug wedges, which are set to expand when compressed by the orthotist during the initial fitting. This expansion is stopped by the slug receiver. The slug is effectively locked into the slug receiver. The slug is cylindrical, so it can be rotated inside the slug receiver before compression and used to set the correct amount of internal/external rotation to the leg component. The height can also be adjusted by the same method.
The slug receiver then fits into the receiver that is mounted on the pelvic section of the orthosis and is held in place by the locking pin. There are two holes on the receiver that are used for height adjustment, which is fine-tuned by adjusting the position of the slug in the slug receiver. The slug-tightening bolt can be accessed while the Slip-Fit is installed on the orthosis: The locking pin is pulled out so that only one side is engaged, and a 3/16 allen wrench is inserted through the hole in the cap. The slug-tightening bolt can then be loosened and the slugs repositioned inside the slug receiver and retightened to lock the corrected adjustments in place.
The Slip-Fit Joint increases orthosis adjustability. It has a 2.25-in. functional height adjustment range: from 6.5 in. at its longest to 4.25 in. at its shortest. The Slip Fit Joint has 50% more height adjustability than a conventional hip orthosis joint, which has only 1.5 in. of height adjustment. To make internal and external rotational adjustments with the Slip-Fit Joint, the slug is rotated in the receiver before tightening. The slug is not keyed into the slug receiver, which allows the 360-degree range of rotation. Obtaining rotation with a current orthosis requires applying torque to the uprights.
Figure 2
shows where the Slip-Fit joint is properly placed on an orthosis. For a standard hip orthosis, the Slip-Fit is designed to attach to existing hardware. On a TLSO, the hip area has to be reinforced, then the Slip-Fit is attached with a backing plate to secure it to the corresponding lateral side.
Discussion
The use of traditional postoperative hip orthosis has become standard practice in hip arthroplasty, and the JMMR Slip-Fit Joint is a device to aid in the initial fitting. It has greater adjustability than current attachments, and practitioners can internally/externally rotate to accommodate the correction without needing a torque to the upright, saving time and effort. Alignment is faster because all adjustments are made with a 3/16 Allen wrench or the locking pins. Follow-up adjustments can be completed quickly with the same methods.
Donning a hip orthosis is easier with a Slip-Fit Joint installed, patients are more comfortable, and the chance of secondary dislocation or ancillary injury is reduced. Patients in postoperative recovery are usually sore, and the Slip-Fit Joint helps avoid unnecessary movement. Donning conventional orthoses often requires gross physical movements by patients in a "log roll" motion, or pulling up on a trapeze, which can cause unnecessary pain. The Slip-Fit Joint helps keep patients comfortable, avoids further damage to the affected hip, and reduces the need for subsequent fittings.
Once the nursing staff is knowledgeable about assembling and donning the orthosis, there should be fewer callbacks to teach correct procedures. Less staffing is needed for donning and doffing because the pelvic section is separate from the leg components.
Conclusion
The Slip-Fit Joint is designed to make fitting a hip orthosis easier and quicker. The practitioner has more adjustability within the joint and it is easier to don and doff the orthosis. Patients are more comfortable because they are not being manipulated so much, and they may thus become more willing to use these devices, which may increase surgeons' success rates.
References:
- Medical Device Implants. In: U.S. National Center for Health Statistics, Vital and Health Statistics, series II. 1988;238:205.
- Harris, WH. The first 32 years of total hip arthroplasty. Clin Orthop. 1992;274:6-10.
- Schmalizried TP. et al. The mechanism of loosening of cemented acetabular components in total hip arthroplasty. Clin Orthop. 1992;274:60-64.
- Williams JF, et al. Dislocations after total hip arthroplasty. Clin Orthop. 1982:171.
- Lima D, Magnus R, Paprosky W. Team management of hip revision patients using a post-op orthosis. J Pros Orth 1994;6:1:20-24.
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